WorldWideScience

Sample records for aftershocks

  1. Aftershock identification

    CERN Document Server

    Zaliapin, Ilya; Keilis-Borok, Vladimir; Wong, Henry

    2007-01-01

    Earthquake aftershock identification is closely related to the question ``Are aftershocks different from the rest of earthquakes?'' We give a positive answer to this question and introduce a general statistical procedure for clustering analysis of seismicity that can be used, in particular, for aftershock detection. The proposed approach expands the analysis of Baiesi and Paczuski [PRE, 69, 066106 (2004)] based on the space-time-magnitude nearest-neighbor distance $\\eta$ between earthquakes. We show that for a homogeneous Poisson marked point field with exponential marks, the distance $\\eta$ has Weibull distribution, which bridges our results with classical correlation analysis for unmarked point fields. We introduce a 2D distribution of spatial and temporal components of $\\eta$, which allows us to identify the clustered part of a point field. The proposed technique is applied to several synthetic seismicity models and to the observed seismicity of Southern California.

  2. Introduction: Aftershocked

    DEFF Research Database (Denmark)

    Warner, Cameron; Hindman, Heather; Snellinger, Amanda

    2015-01-01

    Beginning at 11:56 a.m. local time on April 25, 2015 and continuing for over two months, a series of large earthquakes and significant aftershocks, numbering more than three hundred, plagued Nepal. The earthquakes destroyed homes, historical monuments, and infrastructure, and they triggered...... an ongoing series of landslides, exacerbated by the monsoon. In the days and weeks following the initial earthquake, many experts on Nepal began to discuss the underlying issues that made these earthquakes as much a human-made disaster as a natural one. Our discussions evolved into a larger investigation...

  3. Mechanical origin of aftershocks.

    Science.gov (United States)

    Lippiello, E; Giacco, F; Marzocchi, W; Godano, C; de Arcangelis, L

    2015-10-26

    Aftershocks are the most striking evidence of earthquake interactions and the physical mechanisms at the origin of their occurrence are still intensively debated. Novel insights stem from recent results on the influence of the faulting style on the aftershock organisation in magnitude and time. Our study shows that the size of the aftershock zone depends on the fault geometry. We find that positive correlations among parameters controlling aftershock occurrence in time, energy and space are a stable feature of seismicity independently of magnitude range and geographic areas. We explain the ensemble of experimental findings by means of a description of the Earth Crust as an heterogeneous elastic medium coupled with a Maxwell viscoelastic asthenosphere. Our results show that heterogeneous stress distribution in an elastic layer combined with a coupling to a viscous flow are sufficient ingredients to describe the physics of aftershock triggering.

  4. Aftershock Sets Records

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The affecting story of Feng Xiaogang’s new movie rocks the box office and people’s heartss ince being released nationwide on July 22,Chinese film director Feng Xiaogang’s latest film Aftershock has brought in more than 500

  5. Aftershock Sets Records

    Institute of Scientific and Technical Information of China (English)

    YU LINTAO

    2010-01-01

    @@ Since being released nationwide on July 22,Chinese film director Feng Xiaogang's latest film Aftershock has brought in more than 500 million yuan($73.5 million)at the box office by August 8,a new record for a domestic movie.

  6. The global aftershock zone

    Science.gov (United States)

    Parsons, Thomas E.; Margaret Segou,; Warner Marzocchi,

    2014-01-01

    The aftershock zone of each large (M ≥ 7) earthquake extends throughout the shallows of planet Earth. Most aftershocks cluster near the mainshock rupture, but earthquakes send out shivers in the form of seismic waves, and these temporary distortions are large enough to trigger other earthquakes at global range. The aftershocks that happen at great distance from their mainshock are often superposed onto already seismically active regions, making them difficult to detect and understand. From a hazard perspective we are concerned that this dynamic process might encourage other high magnitude earthquakes, and wonder if a global alarm state is warranted after every large mainshock. From an earthquake process perspective we are curious about the physics of earthquake triggering across the magnitude spectrum. In this review we build upon past studies that examined the combined global response to mainshocks. Such compilations demonstrate significant rate increases during, and immediately after (~ 45 min) M > 7.0 mainshocks in all tectonic settings and ranges. However, it is difficult to find strong evidence for M > 5 rate increases during the passage of surface waves in combined global catalogs. On the other hand, recently published studies of individual large mainshocks associate M > 5 triggering at global range that is delayed by hours to days after surface wave arrivals. The longer the delay between mainshock and global aftershock, the more difficult it is to establish causation. To address these questions, we review the response to 260 M ≥ 7.0 shallow (Z ≤ 50 km) mainshocks in 21 global regions with local seismograph networks. In this way we can examine the detailed temporal and spatial response, or lack thereof, during passing seismic waves, and over the 24 h period after their passing. We see an array of responses that can involve immediate and widespread seismicity outbreaks, delayed and localized earthquake clusters, to no response at all. About 50% of the

  7. Spatiotemporal correlations of aftershock sequences

    CERN Document Server

    Peixoto, Tiago P; Davidsen, Jörn

    2010-01-01

    Aftershock sequences are of particular interest in seismic research since they may condition seismic activity in a given region over long time spans. While they are typically identified with periods of enhanced seismic activity after a large earthquake as characterized by the Omori law, our knowledge of the spatiotemporal correlations between events in an aftershock sequence is limited. Here, we study the spatiotemporal correlations of two aftershock sequences form California (Parkfield and Hector Mine) using the recently introduced concept of "recurrent" events. We find that both sequences have very similar properties and that most of them are captured by the space-time epidemic-type aftershock sequence (ETAS) model if one takes into account catalog incompleteness. However, the stochastic model does not capture the spatiotemporal correlations leading to the observed structure of seismicity on small spatial scales.

  8. A statistical study of aftershock sequences

    OpenAIRE

    Giorgio Ranalli

    2010-01-01

    A comprehensive statistical study of the phenomenology of aftershock sequences is made in this paper. The spatial distribution of aftershocks indicates that they are mainly crustal events; however, deeper sequences also take place. The analysis of the distribution of aftershocks in 15 sequences with respect to time and magnitude leads to the statistical confirmation of a set of phenomenological laws describing the process, namely, the time-frequency law of hyperbolic decay of aftershock activ...

  9. Larger aftershocks happen farther away: nonseparability of magnitude and spatial distributions of aftershocks

    Science.gov (United States)

    Van Der Elst, Nicholas; Shaw, Bruce E.

    2015-01-01

    Aftershocks may be driven by stress concentrations left by the main shock rupture or by elastic stress transfer to adjacent fault sections or strands. Aftershocks that occur within the initial rupture may be limited in size, because the scale of the stress concentrations should be smaller than the primary rupture itself. On the other hand, aftershocks that occur on adjacent fault segments outside the primary rupture may have no such size limitation. Here we use high-precision double-difference relocated earthquake catalogs to demonstrate that larger aftershocks occur farther away than smaller aftershocks, when measured from the centroid of early aftershock activity—a proxy for the initial rupture. Aftershocks as large as or larger than the initiating event nucleate almost exclusively in the outer regions of the aftershock zone. This observation is interpreted as a signature of elastic rebound in the earthquake catalog and can be used to improve forecasting of large aftershocks.

  10. 2010 Chile Earthquake Aftershock Response

    Science.gov (United States)

    Barientos, Sergio

    2010-05-01

    The Mw=8.8 earthquake off the coast of Chile on 27 February 2010 is the 5th largest megathrust earthquake ever to be recorded and provides an unprecedented opportunity to advance our understanding of megathrust earthquakes and associated phenomena. The 2010 Chile earthquake ruptured the Concepcion-Constitucion segment of the Nazca/South America plate boundary, south of the Central Chile region and triggered a tsunami along the coast. Following the 2010 earthquake, a very energetic aftershock sequence is being observed in an area that is 600 km along strike from Valparaiso to 150 km south of Concepcion. Within the first three weeks there were over 260 aftershocks with magnitude 5.0 or greater and 18 with magnitude 6.0 or greater (NEIC, USGS). The Concepcion-Constitucion segment lies immediately north of the rupture zone associated with the great magnitude 9.5 Chile earthquake, and south of the 1906 and the 1985 Valparaiso earthquakes. The last great subduction earthquake in the region dates back to the February 1835 event described by Darwin (1871). Since 1835, part of the region was affected in the north by the Talca earthquake in December 1928, interpreted as a shallow dipping thrust event, and by the Chillan earthquake (Mw 7.9, January 1939), a slab-pull intermediate depth earthquake. For the last 30 years, geodetic studies in this area were consistent with a fully coupled elastic loading of the subduction interface at depth; this led to identify the area as a mature seismic gap with potential for an earthquake of magnitude of the order 8.5 or several earthquakes of lesser magnitude. What was less expected was the partial rupturing of the 1985 segment toward north. Today, the 2010 earthquake raises some disturbing questions: Why and how the rupture terminated where it did at the northern end? How did the 2010 earthquake load the adjacent segment to the north and did the 1985 earthquake only partially ruptured the plate interface leaving loaded asperities since

  11. Self-similar aftershock rates

    CERN Document Server

    Davidsen, Jörn

    2016-01-01

    In many important systems exhibiting crackling noise --- intermittent avalanche-like relaxation response with power-law and, thus, self-similar distributed event sizes --- the "laws" for the rate of activity after large events are not consistent with the overall self-similar behavior expected on theoretical grounds. This is in particular true for the case of seismicity and a satisfying solution to this paradox has remained outstanding. Here, we propose a generalized description of the aftershock rates which is both self-similar and consistent with all other known self-similar features. Comparing our theoretical predictions with high resolution earthquake data from Southern California we find excellent agreement, providing in particular clear evidence for a unified description of aftershocks and foreshocks. This may offer an improved way of time-dependent seismic hazard assessment and earthquake forecasting.

  12. Self-similar aftershock rates

    Science.gov (United States)

    Davidsen, Jörn; Baiesi, Marco

    2016-08-01

    In many important systems exhibiting crackling noise—an intermittent avalanchelike relaxation response with power-law and, thus, self-similar distributed event sizes—the "laws" for the rate of activity after large events are not consistent with the overall self-similar behavior expected on theoretical grounds. This is particularly true for the case of seismicity, and a satisfying solution to this paradox has remained outstanding. Here, we propose a generalized description of the aftershock rates which is both self-similar and consistent with all other known self-similar features. Comparing our theoretical predictions with high-resolution earthquake data from Southern California we find excellent agreement, providing particularly clear evidence for a unified description of aftershocks and foreshocks. This may offer an improved framework for time-dependent seismic hazard assessment and earthquake forecasting.

  13. Are Aftershocks of Large Californian Earthquakes Diffusing?

    CERN Document Server

    Helmstetter, A; Sornette, D; Helmstetter, Agnes; Ouillon, Guy; Sornette, Didier

    2003-01-01

    We analyze 21 aftershock sequences of California to test for evidence of space-time diffusion. Aftershock diffusion may result from stress diffusion and is also predicted by any mechanism of stress weakening. Here, we test an alternative mechanism to explain aftershock diffusion, based on multiple cascades of triggering. In order to characterize aftershock diffusion, we develop two methods, one based on a suitable time and space windowing that has been calibrated on the ETAS model of triggered seismicity, the other using a wavelet transform adapted to the removal of background seismicity. Both methods confirm that diffusion of seismic activity is very weak, much weaker than reported in previous studies. A possible mechanism explaining the weakness of observed diffusion is the effect of geometry, including the localization of aftershocks on a fractal fault network and the impact of extended rupture lengths which control the typical distances of interaction between earthquakes.

  14. Aftershock Statistics explained from Geometric Reductionism

    Science.gov (United States)

    Mignan, Arnaud

    2016-04-01

    The decay of aftershocks has recently been shown to follow a stretched exponential function instead of the Omori law (Mignan, Geophys. Res. Lett., 2015). This triggers a complete re-investigation of aftershock statistics in Southern California and a new physical interpretation of these results: (1) After verifying the stretched exponential behavior of aftershocks in time, I show that aftershocks follow a pure exponential in space. I then (re)demonstrate that K(M) = exp(α(M-mmin-ΔmB)) with K the aftershock production by mainshock magnitude M, α the Gutenberg-Richter distribution slope and ΔmB Båth's parameter. Based on these observations, I propose the Recursive Aftershock Stretched Exponential (RASE) model. (2) I investigate the origin of aftershocks using geometric reductionism made possible by the Non-Critical Precursory Accelerating Seismicity Theory postulate, which states that spatial density switches from δb0 for background seismicity to δbp for activated events (such as foreshocks, induced seismicity and here aftershocks) when the static stress field σ(r) exceeds the threshold σ(rA*) ∝ Δσ* with r the distance to source. The postulate explains the exponential spatial distribution (assuming that aftershocks fill a noisy fractal network within rA*) and aftershock production (assuming a constant stress drop) with K(M) = δbp.V(M), V being the volume of a rounded cuboid centred on the fault of length l ∝ exp(αM), and with radius rA*. Finally the observed stretching factor β ≈ 0.4 is explained topologically from the fractal dimension D ≈ 1.5.

  15. Forecasting area of strong aftershock occurrence

    Science.gov (United States)

    Baranov, Sergey; Shebalin, Peter

    2016-04-01

    Forecasting an area of strong aftershock was never, at our knowledge, considered in terms of operational forecasting. Different declustering models exist to separate post-factum the aftershocks from "independent" events. Large number of studies discussed in previous years the form of the distribution of the aftershocks distances from the mainshock fault. Here we present results of our attempts to assimilate the above researches into a model that can be used in operational aftershock forecasting. Our study was based on data provided by ANSS catalog for 1980-2015. We tried more than 20 well known and suggested by ourselves models of aftershock areas to retrospective forecasting of strong aftershock areas. We tried the models based on data for 12 hours after a mainshock and estimated their forecast quality using special modification of L-test to achieve an optimal model. As a result of our study is a model that can be used in operational forecasting area of strong aftershocks. The research was supported by Russian Foundation for Basic Research (Project 16-05-00263A).

  16. Modeling Aftershocks as a Stretched Exponential Relaxation

    CERN Document Server

    Mignan, Arnaud

    2015-01-01

    The decay rate of aftershocks has been modeled as a power law since the pioneering work of Omori in the late nineteenth century. Considered the second most fundamental empirical law after the Gutenberg-Richter relationship, the power law paradigm has rarely been challenged by the seismological community. By taking a view of aftershock research not biased by prior conceptions of Omori power law decay and by applying statistical methods recommended in applied mathematics, I show that all aftershock sequences tested in three regional earthquake catalogs (Southern and Northern California, Taiwan) and with three declustering techniques (nearest-neighbor, second-order moment, window methods) follow a stretched exponential instead of a power law. These results infer that aftershocks are due to a simpler relaxation process than originally thought, in accordance with most other relaxation processes observed in Nature.

  17. A statistical study of aftershock sequences

    Directory of Open Access Journals (Sweden)

    Giorgio Ranalli

    2010-02-01

    Full Text Available A comprehensive statistical study of the phenomenology of aftershock sequences is made in this paper. The spatial distribution of aftershocks indicates that they are mainly crustal events; however, deeper sequences also take place. The analysis of the distribution of aftershocks in 15 sequences with respect to time and magnitude leads to the statistical confirmation of a set of phenomenological laws describing the process, namely, the time-frequency law of hyperbolic decay of aftershock activity with time, the magnitude stability law, and the exponential magnitude- frequency distribution. The hypotheses involved are checked. The grouping of data and the statistical methods employed are chosen according to some basic well·confirmed assumptions regarding the nature of the process.

  18. Aftershock Energy Distribution by Statistical Mechanics Approach

    Science.gov (United States)

    Daminelli, R.; Marcellini, A.

    2015-12-01

    The aim of our work is to research the most probable distribution of the energy of aftershocks. We started by applying one of the fundamental principles of statistical mechanics that, in case of aftershock sequences, it could be expressed as: the greater the number of different ways in which the energy of aftershocks can be arranged among the energy cells in phase space the more probable the distribution. We assume that each cell in phase space has the same possibility to be occupied, and that more than one cell in the phase space can have the same energy. Seeing that seismic energy is proportional to products of different parameters, a number of different combinations of parameters can produce different energies (e.g., different combination of stress drop and fault area can release the same seismic energy). Let us assume that there are gi cells in the aftershock phase space characterised by the same energy released ɛi. Therefore we can assume that the Maxwell-Boltzmann statistics can be applied to aftershock sequences with the proviso that the judgment on the validity of this hypothesis is the agreement with the data. The aftershock energy distribution can therefore be written as follow: n(ɛ)=Ag(ɛ)exp(-βɛ)where n(ɛ) is the number of aftershocks with energy, ɛ, A and β are constants. Considering the above hypothesis, we can assume g(ɛ) is proportional to ɛ. We selected and analysed different aftershock sequences (data extracted from Earthquake Catalogs of SCEC, of INGV-CNT and other institutions) with a minimum magnitude retained ML=2 (in some cases ML=2.6) and a time window of 35 days. The results of our model are in agreement with the data, except in the very low energy band, where our model resulted in a moderate overestimation.

  19. Complex networks of earthquakes and aftershocks

    Directory of Open Access Journals (Sweden)

    M. Baiesi

    2005-01-01

    Full Text Available We invoke a metric to quantify the correlation between any two earthquakes. This provides a simple and straightforward alternative to using space-time windows to detect aftershock sequences and obviates the need to distinguish main shocks from aftershocks. Directed networks of earthquakes are constructed by placing a link, directed from the past to the future, between pairs of events that are strongly correlated. Each link has a weight giving the relative strength of correlation such that the sum over the incoming links to any node equals unity for aftershocks, or zero if the event had no correlated predecessors. A correlation threshold is set to drastically reduce the size of the data set without losing significant information. Events can be aftershocks of many previous events, and also generate many aftershocks. The probability distribution for the number of incoming and outgoing links are both scale free, and the networks are highly clustered. The Omori law holds for aftershock rates up to a decorrelation time that scales with the magnitude, m, of the initiating shock as tcutoff~10β m with β~-3/4. Another scaling law relates distances between earthquakes and their aftershocks to the magnitude of the initiating shock. Our results are inconsistent with the hypothesis of finite aftershock zones. We also find evidence that seismicity is dominantly triggered by small earthquakes. Our approach, using concepts from the modern theory of complex networks, together with a metric to estimate correlations, opens up new avenues of research, as well as new tools to understand seismicity.

  20. The Aftershock Risk Index - quantification of aftershock impacts during ongoing strong-seismic sequences

    Science.gov (United States)

    Schaefer, Andreas; Daniell, James; Khazai, Bijan; Wenzel, Friedemann

    2016-04-01

    The occurrence and impact of strong earthquakes often triggers the long-lasting impact of a seismic sequence. Strong earthquakes are generally followed by many aftershocks or even strong subsequently triggered ruptures. The Nepal 2015 earthquake sequence is one of the most recent examples where aftershocks significantly contributed to human and economic losses. In addition, rumours about upcoming mega-earthquakes, false predictions and on-going cycles of aftershocks induced a psychological burden on the society, which caused panic, additional casualties and prevented people from returning to normal life. This study shows the current phase of development of an operationalised aftershock intensity index, which will contribute to the mitigation of aftershock hazard. Hereby, various methods of earthquake forecasting and seismic risk assessments are utilised and an integration of the inherent aftershock intensity is performed. A spatio-temporal analysis of past earthquake clustering provides first-hand data about the nature of aftershock occurrence. Epidemic methods can additionally provide time-dependent variation indices of the cascading effects of aftershock generation. The aftershock hazard is often combined with the potential for significant losses through the vulnerability of structural systems and population. A historical database of aftershock socioeconomic effects from CATDAT has been used in order to calibrate the index based on observed impacts of historical events and their aftershocks. In addition, analytical analysis of cyclic behaviour and fragility functions of various building typologies are explored. The integration of many different probabilistic computation methods will provide a combined index parameter which can then be transformed into an easy-to-read spatio-temporal intensity index. The index provides daily updated information about the probability of the inherent seismic risk of aftershocks by providing a scalable scheme fordifferent aftershock

  1. Complex networks of earthquakes and aftershocks

    CERN Document Server

    Baiesi, M; Baiesi, Marco; Paczuski, Maya

    2004-01-01

    We invoke a metric to quantify the correlation between any two earthquakes. This provides a simple and straightforward alternative to using space-time windows to detect aftershock sequences and obviates the need to distinguish main shocks from aftershocks. Directed networks of earthquakes are constructed by placing a link, directed from the past to the future, between pairs of events that are strongly correlated. Each link has a weight giving the relative strength of correlation such that the sum over the incoming links to any node equals unity for aftershocks, or zero if the event had no correlated predecessors. Events can be aftershocks of many previous events, and also generate many aftershocks. The probability distribution for the number of incoming and outgoing links are both scale free, and the networks are highly clustered and modular. The Omori law holds for aftershock rates with a decorrelation time that grows with the magnitude of the initiating shock. Another scaling law is found for the fat-tailed...

  2. Models of wave duration and event frequency of explosion aftershocks

    Institute of Scientific and Technical Information of China (English)

    李学政; 刘文学; 沈旭峰

    2004-01-01

    The contained underground explosion (CUE) usually generates huge number of aftershocks. This kind of aftershocks induced by three CUEs was investigated in the paper. The conclusions show that the duration of aftershock waveforms are rather short, 70 percent of them range from 2 to 7; the occurrences of the aftershocks conform to negative power function, which has the power of-1.6. The aftershock sequence attenuates a little bit faster, with power of-1.0, within two weeks of post-explosions. During the early stage of post-explosions the aftershocks show up in a cluster, however, they usually show up individually during the late stage of post-explosions. The number of aftershocks generated by the compatible explosions differs by several times because of different medium and geological structure; within one month after an explosion with Richater magnitude of 5.5, the number of aftershocks attenuates to the background. Hereafter there are still tiny numbers of aftershocks.

  3. The time distribution of aftershock magnitudes, fault geometry and aftershock prediction

    CERN Document Server

    Bhattacharya, Pathikrit; Chakrabarti, B K

    2009-01-01

    We have analyzed, for the first time, the time cumulant of magnitudes of an aftershock sequence since the mainshock. This comes out to be a remarkable straight line whose slope is characteristic of the fault zone. This will provide an useful tool in understanding the temporal distribution of aftershocks after a specific mainshock.

  4. Mechanism diversity of the loma prieta aftershocks and the mechanics of mainshock-aftershock interaction.

    Science.gov (United States)

    Beroza, G C; Zoback, M D

    1993-01-01

    The diverse aftershock sequence of the 1989 Loma Prieta earthquake is inconsistent with conventional models of mainshock-aftershock interaction because the aftershocks do not accommodate mainshock-induced stress changes. Instead, the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane. This orientation implies that (i) stress drop in the mainshock was nearly complete, (ii) mainshock-induced decreases of fault strength helped were important in controlling the occurrence of after-shocks, and (iii) mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip.

  5. Operational Earthquake Forecasting of Aftershocks for New England

    Science.gov (United States)

    Ebel, J.; Fadugba, O. I.

    2015-12-01

    Although the forecasting of mainshocks is not possible, recent research demonstrates that probabilistic forecasts of expected aftershock activity following moderate and strong earthquakes is possible. Previous work has shown that aftershock sequences in intraplate regions behave similarly to those in California, and thus the operational aftershocks forecasting methods that are currently employed in California can be adopted for use in areas of the eastern U.S. such as New England. In our application, immediately after a felt earthquake in New England, a forecast of expected aftershock activity for the next 7 days will be generated based on a generic aftershock activity model. Approximately 24 hours after the mainshock, the parameters of the aftershock model will be updated using the observed aftershock activity observed to that point in time, and a new forecast of expected aftershock activity for the next 7 days will be issued. The forecast will estimate the average number of weak, felt aftershocks and the average expected number of aftershocks based on the aftershock statistics of past New England earthquakes. The forecast also will estimate the probability that an earthquake that is stronger than the mainshock will take place during the next 7 days. The aftershock forecast will specify the expected aftershocks locations as well as the areas over which aftershocks of different magnitudes could be felt. The system will use web pages, email and text messages to distribute the aftershock forecasts. For protracted aftershock sequences, new forecasts will be issued on a regular basis, such as weekly. Initially, the distribution system of the aftershock forecasts will be limited, but later it will be expanded as experience with and confidence in the system grows.

  6. Temporal characteristics of some aftershock sequences in Bulgaria

    Directory of Open Access Journals (Sweden)

    D. Solakov

    1999-06-01

    Full Text Available We apply statistical analysis to study the temporal distribution of aftershocks in aftershock sequences of five earthquakes which occurred in Bulgaria. We use the maximum likelihood method to estimate the parameters of the modified Omori formula for aftershock sequences which is directly based on a time series. We find that: the maximum likelihood estimates of the parameter p show a regional variation, with lower values of the decay rate in North Bulgaria; the modified Omori formula provides an appropriate representation of temporal variation of the aftershock activity in North Bulgaria; the aftershock sequences in South Bulgaria are best modeled by the combination of an ordinary aftershock sequence with secondary aftershock activity. A plot of the cumulative number of events versus the frequency-linearized time t clearly demonstrates a transition from aftershock to foreshock activity prior to the second 1986 Strazhitsa (North Bulgaria earthquake.

  7. Intermediate-term forecasting of aftershocks from an early aftershock sequence: Bayesian and ensemble forecasting approaches

    Science.gov (United States)

    Omi, Takahiro; Ogata, Yosihiko; Hirata, Yoshito; Aihara, Kazuyuki

    2015-04-01

    Because aftershock occurrences can cause significant seismic risks for a considerable time after the main shock, prospective forecasting of the intermediate-term aftershock activity as soon as possible is important. The epidemic-type aftershock sequence (ETAS) model with the maximum likelihood estimate effectively reproduces general aftershock activity including secondary or higher-order aftershocks and can be employed for the forecasting. However, because we cannot always expect the accurate parameter estimation from incomplete early aftershock data where many events are missing, such forecasting using only a single estimated parameter set (plug-in forecasting) can frequently perform poorly. Therefore, we here propose Bayesian forecasting that combines the forecasts by the ETAS model with various probable parameter sets given the data. By conducting forecasting tests of 1 month period aftershocks based on the first 1 day data after the main shock as an example of the early intermediate-term forecasting, we show that the Bayesian forecasting performs better than the plug-in forecasting on average in terms of the log-likelihood score. Furthermore, to improve forecasting of large aftershocks, we apply a nonparametric (NP) model using magnitude data during the learning period and compare its forecasting performance with that of the Gutenberg-Richter (G-R) formula. We show that the NP forecast performs better than the G-R formula in some cases but worse in other cases. Therefore, robust forecasting can be obtained by employing an ensemble forecast that combines the two complementary forecasts. Our proposed method is useful for a stable unbiased intermediate-term assessment of aftershock probabilities.

  8. Loading rates in California inferred from aftershocks

    Directory of Open Access Journals (Sweden)

    C. Narteau

    2008-03-01

    Full Text Available We estimate the loading rate in southern California and the change in stress induced by a transient slip event across the San Andreas fault (SAF system in central California, using a model of static fatigue. We analyze temporal properties of aftershocks in order to determine the time delay before the onset of the power law aftershock decay rate. In creep-slip and stick-slip zones, we show that the rate of change of this delay is related to seismic and aseismic deformation across the SAF system. Furthermore, we show that this rate of change is proportional to the deficit of slip rate along the SAF. This new relationship between geodetic and seismological data is in good agreement with predictions from a Limited Power Law model in which the evolution of the duration of a linear aftershock decay rate over short time results from variations in the load of the brittle upper crust.

  9. Aftershock production rate of driven viscoelastic interfaces.

    Science.gov (United States)

    Jagla, E A

    2014-10-01

    We study analytically and by numerical simulations the statistics of the aftershocks generated after large avalanches in models of interface depinning that include viscoelastic relaxation effects. We find in all the analyzed cases that the decay law of aftershocks with time can be understood by considering the typical roughness of the interface and its evolution due to relaxation. In models where there is a single viscoelastic relaxation time there is an exponential decay of the number of aftershocks with time. In models in which viscoelastic relaxation is wave-vector dependent we typically find a power-law dependence of the decay rate that is compatible with the Omori law. The factors that determine the value of the decay exponent are analyzed.

  10. Aftershock activity of Bhuj earthquake of January 26th, 2001

    Indian Academy of Sciences (India)

    Ashwani Kumar; S C Gupta; A K Jindal; Sanjay Jain; Vandana

    2003-09-01

    Following a large-sized Bhuj earthquake ( = 7.6) of January 26th, 2001, a small aperture 4- station temporary local network was deployed, in the epicentral area, for a period of about three weeks and resulted in the recording of more than 1800 aftershocks (-0.07 ≤ < 5.0). Preliminary locations of epicenters of 297 aftershocks (2.0 ≤ < 5.0) have brought out a dense cluster of aftershock activity, the center of which falls 20km NW of Bhachau. Epicentral locations of after-shocks encompass a surface area of about 50 × 40km2 that seems to indicate the surface projection of the rupture area associated with the earthquake. The distribution of aftershock activity above magnitude 3, shows that aftershocks are nonuniformly distributed and are aligned in the north, northwest and northeast directions. The epicenter of the mainshock falls on the southern edge of the delineated zone of aftershock activity and the maximum clustering of activity occurs in close proximity of the mainshock. Well-constrained focal depths of 122 aftershocks show that 89% of the aftershocks occurred at depths ranging between 6 and 25km and only 7% and 4% aftershocks occur at depths less than 5 and more than 25km respectively. The Gutenberg-Richter (GR) relationship, log = 4.52-0.89 , is fitted to the aftershock data (1.0 ≤ < 5.0) and the -value of 0.89 has been estimated for the aftershock activity.

  11. Triggering of Aftershocks by Free Oscillations

    Science.gov (United States)

    Bufe, C. G.; Varnes, D. J.

    2001-12-01

    Periodicities observed in aftershock sequences may result from earthquake triggering by free oscillations of the Earth produced by the main shock. Using an algorithm we developed to compute spectra of inter-event times, we examine inter-event intervals of teleseismically recorded aftershock sequences from large (M>7.5) main shocks that occurred during 1980-2001. Observed periodicities may result from triggering at intervals that are multiples of normal mode periods. We have focussed our analysis of inter-event times on identification of triggering by free oscillations at periods in the range 6-60 minutes. In this paper we describe our most commonly observed aftershock inter-event times and the free oscillation modes most likely to be the triggers. Because of their separation, the longer period modes are easiest to identify in the aftershock data (0S2 at 53.9 minutes, 0S3 at 35.6 minutes, 0S4 at 25.8 minutes, and 0T2 at 43.9 minutes). Evidence of triggering by 0S2 and 0T2 was also found in the aftershocks of the 1989 Loma Prieta, CA (M 7) earthquake (Kamal and Mansinha, 1996). Because of the plethora of higher modes, shorter inter-event periods are more difficult to identify with a particular mode. Preliminary analysis of the 2001 Bhuj, India (M 7.7) earthquake sequence tentatively identifies a contribution to triggering of the first four large aftershocks by multiples of 0S12 (8.37 minutes).

  12. How Long is an Aftershock Sequence?

    Science.gov (United States)

    Godano, Cataldo; Tramelli, Anna

    2016-07-01

    The occurrence of a mainschok is always followed by aftershocks spatially distributed within the fault area. The aftershocks rate decay with time is described by the empirical Omori law which was inferred by catalogues analysis. The sequences discrimination within catalogues is not a straightforward operation, especially for low-magnitude mainshocks. Here, we describe the rate decay of the Omori law obtained using different sequence discrimination tools and we discover that, when the background seismicity is excluded, the sequences tend to last for the temporal extension of the catalogue.

  13. Aftershocks : Economic Crisis and Institutional Choice

    NARCIS (Netherlands)

    Hemerijck, Anton; Knapen, Ben; Doorne, van Ellen

    2009-01-01

    Aftershocks werd geschreven op het hoogtepunt van de grootste economische crisis sinds de grote depressie. Hoewel het voorbarig zou zijn aan te nemen dat de gevolgen van de crisis al in volle omvang duidelijk zijn, is het overduidelijk dat zij ingrijpende effecten zal hebben op politiek, economisch

  14. Aftershock Decay Rates in the Iranian Plateau

    Science.gov (United States)

    Ommi, S.; Zafarani, H.; Zare, M.

    2016-07-01

    Motivated by the desire to have more information following the occurrence of damaging events, the main purpose of this article is to study aftershock sequence parameters in the Iranian plateau. To this end, the catalogue of the Iranian earthquakes between 2002 to the end of 2013 has been collected and homogenized among which 15 earthquakes have been selected to study their aftershock decay rates. For different tectonic provinces, the completeness magnitudes ( M c) of the earthquake catalogue have been calculated in different time intervals. Also, the M c variability in spatial and temporal windows has been determined for each selected event. For major Iranian earthquakes, catalogue of aftershocks has been collected thanks to three declustering methods: first, the classical windowing method of Gardner and Knopoff (Bull Seismol Soc Am 64:1363-1367, 1974); second, a modified version of this using spatial windowing based on the Wells and Coppersmith (Bull Seismol Soc Am 84:974-1002, 1994) relations; and third, the Burkhard and Grünthal (Swiss J Geosci 102:149-188, 2009) scheme. Effects of the temporal windows also have been investigated using the time periods of 1 month, 100 days, and 1 year in the declustering method of Gardner and Knopoff (Bull Seismol Soc Am 64:1363-1367, 1974). In the next step, the modified Omori law coefficients have been calculated for the 15 selected earthquakes. The calibrated regional generic model describing the temporal and magnitude distribution of aftershocks is of interest for time-dependent seismic hazard forecasts. The regional characteristics of the aftershock decay rates have been studied for the selected Iranian earthquakes in the Alborz, Zagros and Central Iran regions considering their different seismotectonics regimes. However, due to the lack of sufficient data, no results have been reported for the Kopeh-Dagh and Makran seismotectonic regions.

  15. Adaptive forecasting of aftershock activity after the main shock

    Science.gov (United States)

    Omi, Takahiro; Ogata, Yosihiko; Hirata, Yoshito; Aihara, Kazuyuki

    2014-05-01

    Forecasting aftershock activity is useful to reduce seismic risks in the affected area after the main shock. The difficulties to forecast aftershocks are (i) a forecasting model should be tailored to each aftershock sequence because the statistical property varies greatly according to an individual aftershock sequence and (ii) the forecasting model has to be estimated from highly deficient data where a significant fraction of early small aftershocks are missing from seismic records. To overcome this difficulty, we have been developing a statistical model to deal with incompletely detected aftershocks, in which the detection rate of aftershocks is sequentially estimated in a state-space modeling approach. Our method enables us to robustly estimate the forecasting model of underlying aftershocks including not only observed aftershocks but also missing ones from the incomplete catalog. We show that the Omori-Utsu formula can be well estimated only from a few hours of the data, and then it can be revised by the epidemic type aftershock sequence (ETAS) model to adaptively forecast an aftershock sequence with the individual cascading feature as the data size increases in real-time. We demonstrate that how these estimated models can effectively forecast the aftershock activity. We also discuss how these models can be implemented in an operational system for earthquake forecasting. References: T. Omi, Y. Ogata, Y. Hirata, and K. Aihiara, "Forecasting large aftershocks within one day after the main shock", Scientific Reports, 3, 2218 (2013). T. Omi, Y. Ogata, Y. Hirata, and K. Aihiara, "Estimating the ETAS model from an early aftershock sequence", (In submission).

  16. The aftershock signature of supershear earthquakes.

    Science.gov (United States)

    Bouchon, Michel; Karabulut, Hayrullah

    2008-06-01

    Recent studies show that earthquake faults may rupture at speeds exceeding the shear wave velocity of rocks. This supershear rupture produces in the ground a seismic shock wave similar to the sonic boom produced by a supersonic airplane. This shock wave may increase the destruction caused by the earthquake. We report that supershear earthquakes are characterized by a specific pattern of aftershocks: The fault plane itself is remarkably quiet whereas aftershocks cluster off the fault, on secondary structures that are activated by the supershear rupture. The post-earthquake quiescence of the fault shows that friction is relatively uniform over supershear segments, whereas the activation of off-fault structures is explained by the shock wave radiation, which produces high stresses over a wide zone surrounding the fault.

  17. Aftershocks in a frictional earthquake model.

    Science.gov (United States)

    Braun, O M; Tosatti, Erio

    2014-09-01

    Inspired by spring-block models, we elaborate a "minimal" physical model of earthquakes which reproduces two main empirical seismological laws, the Gutenberg-Richter law and the Omori aftershock law. Our point is to demonstrate that the simultaneous incorporation of aging of contacts in the sliding interface and of elasticity of the sliding plates constitutes the minimal ingredients to account for both laws within the same frictional model.

  18. Forecasting large aftershocks within one day after the main shock.

    Science.gov (United States)

    Omi, Takahiro; Ogata, Yosihiko; Hirata, Yoshito; Aihara, Kazuyuki

    2013-01-01

    Forecasting the aftershock probability has been performed by the authorities to mitigate hazards in the disaster area after a main shock. However, despite the fact that most of large aftershocks occur within a day from the main shock, the operational forecasting has been very difficult during this time-period due to incomplete recording of early aftershocks. Here we propose a real-time method for efficiently forecasting the occurrence rates of potential aftershocks using systematically incomplete observations that are available in a few hours after the main shocks. We demonstrate the method's utility by retrospective early forecasting of the aftershock activity of the 2011 Tohoku-Oki Earthquake of M9.0 in Japan. Furthermore, we compare the results by the real-time data with the compiled preliminary data to examine robustness of the present method for the aftershocks of a recent inland earthquake in Japan.

  19. Do aftershock probabilities decay with time?

    Science.gov (United States)

    Michael, Andrew J.

    2012-01-01

    So, do aftershock probabilities decay with time? Consider a thought experiment in which we are at the time of the mainshock and ask how many aftershocks will occur a day, week, month, year, or even a century from now. First we must decide how large a window to use around each point in time. Let's assume that, as we go further into the future, we are asking a less precise question. Perhaps a day from now means 1 day 10% of a day, a week from now means 1 week 10% of a week, and so on. If we ignore c because it is a small fraction of a day (e.g., Reasenberg and Jones, 1989, hereafter RJ89), and set p = 1 because it is usually close to 1 (its value in the original Omori law), then the rate of earthquakes (K=t) decays at 1=t. If the length of the windows being considered increases proportionally to t, then the number of earthquakes at any time from now is the same because the rate decrease is canceled by the increase in the window duration. Under these conditions we should never think "It's a bit late for this to be an aftershock."

  20. Estimating stress heterogeneity from aftershock rate

    CERN Document Server

    Helmstetter, A; Helmstetter, Agnes; Shaw, Bruce E.

    2005-01-01

    We estimate the rate of aftershocks triggered by a heterogeneous stress change, using the rate-and-state model of Dieterich [1994]. We show than an exponential stress distribution P(\\tau)~ exp(-\\tau/\\tau_0) gives an Omori law decay of aftershocks with time ~1/t^p, with an exponent p=1-A\\sigma_n/\\tau_0, where A is a parameter of the rate-and-state friction law, and \\sigma_n the normal stress. Omori exponent p thus decreases if the stress "heterogeneity" \\tau_0 decreases. We also invert the stress distribution P(\\tau) from the seismicity rate R(t), assuming that the stress does not change with time. We apply this method to a synthetic stress map, using the (modified) scale invariant "k^2" slip model [Herrero and Bernard, 1994]. We generate synthetic aftershock catalogs from this stress change. The seismicity rate on the rupture area shows a huge increase at short times, even if the stress decreases on average. This stochastic slip model gives a Gaussian stress distribution, but nevertheless produces an aftersho...

  1. Model for the distribution of aftershock interoccurrence times.

    Science.gov (United States)

    Shcherbakov, Robert; Yakovlev, Gleb; Turcotte, Donald L; Rundle, John B

    2005-11-18

    In this work the distribution of interoccurrence times between earthquakes in aftershock sequences is analyzed and a model based on a nonhomogeneous Poisson (NHP) process is proposed to quantify the observed scaling. In this model the generalized Omori's law for the decay of aftershocks is used as a time-dependent rate in the NHP process. The analytically derived distribution of interoccurrence times is applied to several major aftershock sequences in California to confirm the validity of the proposed hypothesis.

  2. Bayesian Predictive Distribution for the Magnitude of the Largest Aftershock

    Science.gov (United States)

    Shcherbakov, R.

    2014-12-01

    Aftershock sequences, which follow large earthquakes, last hundreds of days and are characterized by well defined frequency-magnitude and spatio-temporal distributions. The largest aftershocks in a sequence constitute significant hazard and can inflict additional damage to infrastructure. Therefore, the estimation of the magnitude of possible largest aftershocks in a sequence is of high importance. In this work, we propose a statistical model based on Bayesian analysis and extreme value statistics to describe the distribution of magnitudes of the largest aftershocks in a sequence. We derive an analytical expression for a Bayesian predictive distribution function for the magnitude of the largest expected aftershock and compute the corresponding confidence intervals. We assume that the occurrence of aftershocks can be modeled, to a good approximation, by a non-homogeneous Poisson process with a temporal event rate given by the modified Omori law. We also assume that the frequency-magnitude statistics of aftershocks can be approximated by Gutenberg-Richter scaling. We apply our analysis to 19 prominent aftershock sequences, which occurred in the last 30 years, in order to compute the Bayesian predictive distributions and the corresponding confidence intervals. In the analysis, we use the information of the early aftershocks in the sequences (in the first 1, 10, and 30 days after the main shock) to estimate retrospectively the confidence intervals for the magnitude of the expected largest aftershocks. We demonstrate by analysing 19 past sequences that in many cases we are able to constrain the magnitudes of the largest aftershocks. For example, this includes the analysis of the Darfield (Christchurch) aftershock sequence. The proposed analysis can be used for the earthquake hazard assessment and forecasting associated with the occurrence of large aftershocks. The improvement in instrumental data associated with early aftershocks can greatly enhance the analysis and

  3. Early aftershock decay rate of the M6 Parkfield earthquake

    Science.gov (United States)

    Peng, Z.; Vidale, J. E.

    2004-12-01

    Mainshock rupture is typically followed by its aftershocks that diminish in rate approximately as the reciprocal of the elapse time. However, it is notoriously difficult to observe aftershock activity in the noisy aftermath of larger earthquakes. Many aftershocks were missed in the existing seismicity catalogs in the initial few minutes (Kagan, 2004). Yet this period holds valuable information about the transition from mainshock rupture to sporadic aftershocks, and the friction laws that control earthquakes. The Parkfield section of the San Andreas fault is one of most densely seismometered places in the world. Many near-fault, non-clipped and continuous recordings of the M6 Parkfield earthquake and its aftermath have been recovered, providing an excellent opportunity for us to study the aftershock decay rates in the first few hundred seconds after the mainshock. We have so far analyzed recordings from station PKD and 13 stations in the Parkfield High Resolution Seismic Network. By scrutinizing the high-frequency signal, we are able to distinguish mainshock coda from early aftershocks. We find up to 10 times more aftershocks in the first 1000 s than in the USGS NCSN catalog. More than 30 events are detected in the first 200 s after the mainshock. None of these events are in the USGS NCSN catalog. Preliminary results suggest a strong deficit of aftershocks in the first 100 s after the mainshock relative to a 1/t aftershock rate decay. This pattern is consistent with a lack of seismicity in the first 120 s following the 10/31/2001 M5.1 Anza earthquake (Kilb et al., 2004), and our study of early aftershock rates using data from HiNet array in Japan (Vidale et al., 2004). Our observations will allow us to test the prediction of such an interval in rate-and-state friction models prior to the onset of the 1/t aftershock decay rate (Dieterich, 1994).

  4. Aftershocks in Coherent-Noise Models

    OpenAIRE

    Wilke, C.; Altmeyer, S; Martinetz, T.

    1997-01-01

    The decay pattern of aftershocks in the so-called 'coherent-noise' models [M. E. J. Newman and K. Sneppen, Phys. Rev. E54, 6226 (1996)] is studied in detail. Analytical and numerical results show that the probability to find a large event at time $t$ after an initial major event decreases as $t^{-\\tau}$ for small $t$, with the exponent $\\tau$ ranging from 0 to values well above 1. This is in contrast to Sneppen und Newman, who stated that the exponent is about 1, independent of the microscopi...

  5. Local near instantaneously dynamically triggered aftershocks of large earthquakes

    Science.gov (United States)

    Fan, Wenyuan; Shearer, Peter M.

    2016-09-01

    Aftershocks are often triggered by static- and/or dynamic-stress changes caused by mainshocks. The relative importance of the two triggering mechanisms is controversial at near-to-intermediate distances. We detected and located 48 previously unidentified large early aftershocks triggered by earthquakes with magnitudes between ≥7 and 8 within a few fault lengths (approximately 300 kilometers), during times that high-amplitude surface waves arrive from the mainshock (less than 200 seconds). The observations indicate that near-to-intermediate-field dynamic triggering commonly exists and fundamentally promotes aftershock occurrence. The mainshocks and their nearby early aftershocks are located at major subduction zones and continental boundaries, and mainshocks with all types of faulting-mechanisms (normal, reverse, and strike-slip) can trigger early aftershocks.

  6. Aftershocks halted by static stress shadows

    Science.gov (United States)

    Toda, Shinji; Stein, Ross S.; Beroza, Gregory C.; Marsan, David

    2012-06-01

    Earthquakes impart static and dynamic stress changes to the surrounding crust. Sudden fault slip causes small but permanent--static--stress changes, and passing seismic waves cause large, but brief and oscillatory--dynamic--stress changes. Because both static and dynamic stresses can trigger earthquakes within several rupture dimensions of a mainshock, it has proven difficult to disentangle their contributions to the triggering process. However, only dynamic stress can trigger earthquakes far from the source, and only static stress can create stress shadows, where the stress and thus the seismicity rate in the shadow area drops following an earthquake. Here we calculate the stress imparted by the magnitude 6.1 Joshua Tree and nearby magnitude 7.3 Landers earthquakes that occurred in California in April and June 1992, respectively, and measure seismicity through time. We show that, where the aftershock zone of the first earthquake was subjected to a static stress increase from the second, the seismicity rate jumped. In contrast, where the aftershock zone of the first earthquake fell under the stress shadow of the second and static stress dropped, seismicity shut down. The arrest of seismicity implies that static stress is a requisite element of spatial clustering of large earthquakes and should be a constituent of hazard assessment.

  7. Implications of an inverse branching aftershock sequence model.

    Science.gov (United States)

    Turcotte, D L; Abaimov, S G; Dobson, I; Rundle, J B

    2009-01-01

    The branching aftershock sequence (BASS) model is a self-similar statistical model for earthquake aftershock sequences. A prescribed parent earthquake generates a first generation of daughter aftershocks. The magnitudes and times of occurrence of the daughters are obtained from statistical distributions. The first generation daughter aftershocks then become parent earthquakes that generate second generation aftershocks. The process is then extended to higher generations. The key parameter in the BASS model is the magnitude difference Deltam* between the parent earthquake and the largest expected daughter earthquake. In the application of the BASS model to aftershocks Deltam* is positive, the largest expected daughter event is smaller than the parent, and the sequence of events (aftershocks) usually dies out, but an exponential growth in the number of events with time is also possible. In this paper we explore this behavior of the BASS model as Deltam* varies, including when Deltam* is negative and the largest expected daughter event is larger than the parent. The applications of this self-similar branching process to biology and other fields are discussed.

  8. Properties of aftershock sequences in southern California

    Science.gov (United States)

    Kisslinger, Carl; Jones, Lucile M.

    1991-07-01

    The temporal behavior of 39 aftershock sequences in southern California, 1933-1988, was modeled by the modified Omori relation. Minimum magnitudes for completeness of each sequence catalog were determined, and the maximum likelihood estimates of the parameters K, p, and c, with the standard errors on each, were determined by the Ogata algorithm. The b value of each sequence was also calculated. Many of the active faults in the region, both strike slip and thrust, were sampled. The p values were graded in terms of the size of the standard error relative to the p value itself. Most of the sequences were modeled well by the Omori relation. Many of the sequences had p values close to the mean of the whole data set, 1.11±0.25, but values significantly different from the mean, as low as 0.7 and as high as 1.8, exist. No correlation of p with either the b value of the sequence or the mainshock magnitude was found. The results suggest a direct correlation of p values is with surface heat flow, with high values in the Salton Trough (high heat flow) and one low value in the San Bernardino Mountains and on the edge of the Ventura Basin (both low heat flow). The large fraction of the sequences with p values near the mean are at locations where the heat flow is near the regional mean, 74 mW/m2. If the hypothesis that aftershock decay rate is controlled by temperature at depth is valid, the effects of other factors such as heterogeneity of the fault zone properties are superimposed on the background rate determined by temperature. Surface heat flow is taken as an indicator of crustal temperature at hypocentral depths, but the effects on heat flow of convective heat transport and variations in near-surface thermal conductivity invalidate any simple association of local variations in heat flow with details of the subsurface temperature distribution. The interpretation is that higher temperatures in the aftershock source volume caused shortened stress relaxation times in the fault

  9. A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Previous studies show that mature faults are filled with fault gouge in the shallow part and thus cannot accumulate enough strain energy for earthquakes. Therefore most earthquakes are deeper than 5 km, except those events occurring on new faults or in intact rocks. From field observation, Wenchuan earthquake is found to rupture the free surface about 200 km, but the rupture may extend underground much further from teleseismic body waves inversion and aftershocks distribution. In the northeastern end of the rupture zone, deep rupture may induce stress increase near the free surface, and trigger shallow earthquakes. An Ms 5.7 aftershock occurred at Qingchuan, northeast end of Wenchuan earthquake fault on July 24, 2008, featuring thrust mechanism with a 3 km source centroid depth. The shallow focal depth is confirmed with the sPL phase recorded at station L0205. As Rayleigh wave is well only developed for source depth less than 1/5 of epicentral distance, the observed large amplitude of Rg at a distance of 15 km implied depth of 3 km or less. Dozens of aftershocks’ sPL waveforms are also analyzed to confirm the source depths less than 3 km. On the other hand, no surface ruptures are found by geological survey or InSAR studies. It is strongly suggested that these aftershock sequences initiate fresh rupture in intact rocks triggered by stress increase from the deep co-seismic rupture of the Wenchuan mainshock.

  10. Rheology of the Tectonosphere as Inferred from Seismic Aftershock Sequences

    Directory of Open Access Journals (Sweden)

    A. E. SCHEIDEGGER

    1969-06-01

    Full Text Available Some rheological models of the mechanism of aftershock
    occurrence, namely, Benioff's, Pshennikov's, and Mogi's models, are examined
    in the light of the established laws governing the phenomenology of the
    process. It is concluded that none of them explains fully the aftershock
    mechanism. Thus, a new creep model is proposed, according to which
    aftershocks are the discontinuous manifestation of the overall plastic creep
    by which the rock readjusts itself to the stress distribution left by the main
    shock. The creep model affords a new large-scale picture of the rheology
    of the tectonosphere.

  11. A model for the distribution of aftershock waiting times

    CERN Document Server

    Shcherbakov, R; Turcotte, D L; Yakovlev, G

    2005-01-01

    In this work the distribution of inter-occurrence times between earthquakes in aftershock sequences is analyzed and a model based on a non-homogeneous Poisson (NHP) process is proposed to quantify the observed scaling. In this model the generalized Omori's law for the decay of aftershocks is used as a time-dependent rate in the NHP process. The analytically derived distribution of inter-occurrence times is applied to several major aftershock sequences in California to confirm the validity of the proposed hypothesis.

  12. Clustering analysis of seismicity and aftershock identification.

    Science.gov (United States)

    Zaliapin, Ilya; Gabrielov, Andrei; Keilis-Borok, Vladimir; Wong, Henry

    2008-07-01

    We introduce a statistical methodology for clustering analysis of seismicity in the time-space-energy domain and use it to establish the existence of two statistically distinct populations of earthquakes: clustered and nonclustered. This result can be used, in particular, for nonparametric aftershock identification. The proposed approach expands the analysis of Baiesi and Paczuski [Phys. Rev. E 69, 066106 (2004)10.1103/PhysRevE.69.066106] based on the space-time-magnitude nearest-neighbor distance eta between earthquakes. We show that for a homogeneous Poisson marked point field with exponential marks, the distance eta has the Weibull distribution, which bridges our results with classical correlation analysis for point fields. The joint 2D distribution of spatial and temporal components of eta is used to identify the clustered part of a point field. The proposed technique is applied to several seismicity models and to the observed seismicity of southern California.

  13. Aftershocks triggered by fluid intrusion: Evidence for the aftershock sequence occurred 2014 in West Bohemia/Vogtland

    Science.gov (United States)

    Hainzl, S.; Fischer, T.; Čermáková, H.; Bachura, M.; Vlček, J.

    2016-04-01

    The West Bohemia/Vogtland region, central Europe, is well known for its repeating swarm activity. However, the latest activity in 2014, although spatially overlapping with previous swarm activity, consisted of three classical aftershock sequences triggered by ML3.5, 4.4, and 3.5 events. To decode the apparent system change from swarm-type to mainshock-aftershock characteristics, we have analyzed the details of the major ML4.4 sequence based on focal mechanisms and relocated earthquake data. Our analysis shows that the mainshock occurred with rotated mechanism in a step over region of the fault plane, unfavorably oriented to the regional stress field. Most of its intense aftershock activity occurred in-plane with classical characteristics such as (i) the maximum magnitude of the aftershocks is significantly less than the mainshock magnitude and (ii) the decay can be well fitted by the Omori-Utsu law. However, the absolute number of aftershocks and the fitted Omori-Utsu c and p parameters are much larger than for typical sequences. By means of the epidemic-type aftershock sequence model, we show that an additional aseismic source with an exponentially decaying strength triggered a large fraction of the aftershocks. Corresponding pore pressure simulations with an exponentially decreasing flow rate of the fluid source show a good agreement with the observed spatial migration front of the aftershocks extending approximately with log(t). Thus, we conclude that the mainshock opened fluid pathways from a finite fluid source into the fault plane explaining the unusual high rate of aftershocks, the migration patterns, and the exponential decrease of the aseismic signal.

  14. The aftershock processes of strong earthquakes in the Western Caucasus

    Science.gov (United States)

    Baranov, S. V.; Gabsatarova, I. P.

    2015-05-01

    The aftershock processes of the four strong earthquakes that occurred in the Western Caucasus from 1991 to June 2013 are considered. The main shocks of these earthquakes include the first Racha earthquake (April 29, 1991, Ms = 6.9); second Racha earthquake (June 15, 1991, Ms = 6.2); Oni earthquake (September 7, 2009, Ms = 5.8); and East Black Sea earthquake (December 23, 2012, Ms = 5.6). Based on the simulations with the LPL relaxation model and the ETAS model of triggered seismicity, the differences in the properties of the aftershock processes and the characteristics of the fault zones accommodating the main shocks are revealed. The nonrelaxation character of the aftershocks from the East Black Sea earthquake is established. It is hypothesized and validated that this is a result of the violation of the fluid-dynamic equilibrium in the fault zone due to the destruction of the gas hydrate layer by the main shock and strong aftershocks.

  15. On the aftershocks of the Great Sumatra-Andaman earthquake

    CERN Document Server

    Guglielmi, A V; Zavyalov, A D

    2013-01-01

    Analysis of the Sumatra-Andaman earthquake on 26.12.2004 (M = 9) has allowed us to identify two non- trivial properties of the dynamics of aftershocks. First, the strongest aftershock (M = 7.2) was likely triggered by the round-the-world seismic echo of the main shock. The idea is that the surface waves propagating outwards from the main shock return back to the vicinity of the epicenter after having made a complete revolution around the Earth and induce there the aftershock. The second property is the modulation of the aftershock sequence by the fundamental oscillation of the Earth 0S2 excited by the main shock. Both results are supported by analysis of the Tohoku earthquake (11.03.2011, M = 9), as well as by the statistical analysis of the USGS earthquake catalog.

  16. A mechanism of aftershock generation based on progressive material softening

    Science.gov (United States)

    Dyskin, Arcady; Pasternak, Elena; Bunger, Andrew; Kear, James

    2015-04-01

    Observations of aftershocks after major seismic events show that the rate of aftershock generation reduces according to the generalised Omori's law. This law reproduces itself at a variety of scales starting from the scales of the earthquakes to the laboratory scale. Furthermore, the Omori's law holds for different types of fracture event from shear fracture propagation over the faults to failure in compression to failure in tension. In particular our tests show that the Omori's law describes the aftershocks in crystalline rocks in a laboratory model of hydraulic fracture and after bending failure of beams. We propose a new universal mechanism of aftershock generation that reproduces the Omori's law. We firstly note that it is not the residual stress, as conventionally assumed, but the residual strain that is created by the preceding fracture process. The aftershocks are created by the residual stress that is related to the residual strain through elastic moduli. The accumulation of the aftershock-related microcracks reduces the elastic moduli and thus reduces the residual stress. This overall reduction of the residual stress with the number of aftershocks is the reason for the rate reduction in aftershock generation. Naturally this process might be accompanied by the reduction in wave velocities, albeit, as we show, the reduction is rather low. The effect the accumulated microcracks have on the moduli considerably depends on the microcrack distribution over both positions and orientations. We found that (a) if the microcracks have isotropic distribution over orientations the classical Omori's law is reproduced; (b) if the microcracks are shear and parallel to each other but randomly situated in space the generalised Omori's law is reproduced with the exponent p1. The main feature of the latter case is the existence of a critical value of the number of sliding zones: when it is reached a large-scale sliding zone is formed.

  17. Aftershock Hazard Magnitude, Time, and Location Probability Forecasting

    Directory of Open Access Journals (Sweden)

    Kuei-Pao Chen

    2014-01-01

    Full Text Available This study combines branching aftershock sequence (BASS and modified _ law to develop a predictive model for forecasting the magnitude, time, and location of aftershocks of magnitude Mw ≥ 5.00 in large earthquakes. The developed model is presented and applied to the 17:47 20 September 1999 Mw 7.45 Chi-Chi earthquake Taiwan, 09:32 5 November 2009 (UTC Nantou Mw 6.19, 00:18 4 March 2010 (UTC Jiashian Mw 6.49 earthquake sequences, Taiwan, and 05:46 11 March 2011 (UTC Tohoku Mw 9.00 earthquake, Japan. The estimated peak ground acceleration (PGA results are remarkably similar to calculations from the recorded magnitudes in both trend and level. This study proposes an empirical equation to improve the aftershock occurrence forecast time. The forecast time results were greatly improved. The magnitude of aftershocks generally decreases with time. It was found that the aftershock forecast probability of Mw ≥ 5.00 is high in the first six days after the main shock. The results will be of interest to seismic mitigation specialists. Spatial and temporal seismicity parameters to the aftershock sequence investigation into the 17:47 20 September 1999 (UTC Mw 7.45 Chi-Chi earthquake, Taiwan found that immediately after the earthquake the area closest to the epicenter had a lower b value. This pattern suggests that at the time of the Chi-Chi earthquake, the area closest to the epicenter remained prone to large magnitude aftershocks and strong shaking. With time, however, the b value increased, indicating a reduced likelihood for large magnitude aftershocks.

  18. Source Characteristics of Aftershocks of the India Republic Day Earthquake

    Science.gov (United States)

    Horton, S.; Bodin, P.; Johnston, A.; Withers, M.; Chiu, C.; Raphael, A.; Rabak, I.; Maio, Q.; Smalley, R.; Chiu, J.; Langston, C.

    2001-05-01

    We present a preliminary analysis of aftershocks of the Mw=7.7 Republic Day (26 January) 2001 earthquake in Gujarat, India, recorded on a network of portable digital event recorders (the MAEC/ISTAR network). During the 18 day deployment, this network recorded ground motion from nearly 2000 earthquakes; almost exclusively Mveil of ignorance over the mainshock: we know of no strong-motion recordings of the mainshock, regional broad-band and seismic network data is notoriously difficult to obtain for scientific evaluation, evidence of surface rupture or deformation is fragmentary and complex or obscured by massive liquefaction, pre-existing geodetic networks are non-existent, and satellite-based radar interferometry studies have been hobbled by poor pre-earthquake images. Aftershock occurrence may provide critical evidence to determine which fault ruptured in January, 2001, and aftershock studies may provide important observational constraints on source processes and wave propagation in the region. We focus on trying to discern the mainshock fault plane, which appears to dip to the south, and whether the aftershocks are unusually deep (down to 35 km, which might help to explain the lack of obvious surface rupture). In addition to determining first-motion focal mechanisms we will examine whether stress drops of the aftershocks are, on the whole, high. We compare the seismic sources and regional propagation of Gujarati aftershocks with those of the central and eastern US.

  19. Extreme value statistics and thermodynamics of earthquakes: aftershock sequences

    Directory of Open Access Journals (Sweden)

    B. H. Lavenda

    2000-06-01

    Full Text Available The Gutenberg-Richter magnitude-frequency law takes into account the minimum detectable magnitude, and treats aftershocks as if they were independent and identically distributed random events. A new magnitude-frequency relation is proposed which takes into account the magnitude of the main shock, and the degree to which aftershocks depend on the main shock makes them appear clustered. In certain cases, there can be two branches in the order-statistics of aftershock sequences: for energies below threshold, the Pareto law applies and the asymptotic distribution of magnitude is the double-exponential distribution, while energies above threshold follow a one-parameter beta distribution, whose exponent is the cluster dimension, and the asymptotic Gompertz distribution predicts a maximum magnitude. The 1957 Aleutian Islands aftershock sequence exemplifies such dual behavior. A thermodynamics of aftershocks is constructed on the analogy between the non-conservation of the number of aftershocks and that of the particle number in degenerate gases.

  20. A Variety of Aftershock Decays in the Rate- and State-Friction Model Due to the Effect of Secondary Aftershocks: Implications Derived from an Analysis of Real Aftershock Sequences

    Science.gov (United States)

    Iwata, Takaki

    2016-01-01

    The model based on rate- and state-dependent friction law reproduces the temporal decay of an aftershock sequence with the p value of the Omori-Utsu law equal to 1, if we simply assume a constant stress rate over time. However, because p values vary in real aftershock sequences, this model requires some modification. This study examined the effect of secondary aftershocks on the variety of the p value. A large aftershock causes a stepwise stress increase in the aftershock area, and the expected seismicity rate derived from the friction law also increases abruptly. These multiple increases in the seismicity rate during its decay following a mainshock could cause variation in the apparent p value. In this study, a model incorporating this idea is applied to two aftershock sequences observed in Japan and is shown to substantially modify the modeling of aftershock activity.

  1. On the adaptive daily forecasting of seismic aftershock hazard

    Science.gov (United States)

    Ebrahimian, Hossein; Jalayer, Fatemeh; Asprone, Domenico; Lombardi, Anna Maria; Marzocchi, Warner; Prota, Andrea; Manfredi, Gaetano

    2013-04-01

    Post-earthquake ground motion hazard assessment is a fundamental initial step towards time-dependent seismic risk assessment for buildings in a post main-shock environment. Therefore, operative forecasting of seismic aftershock hazard forms a viable support basis for decision-making regarding search and rescue, inspection, repair, and re-occupation in a post main-shock environment. Arguably, an adaptive procedure for integrating the aftershock occurrence rate together with suitable ground motion prediction relations is key to Probabilistic Seismic Aftershock Hazard Assessment (PSAHA). In the short-term, the seismic hazard may vary significantly (Jordan et al., 2011), particularly after the occurrence of a high magnitude earthquake. Hence, PSAHA requires a reliable model that is able to track the time evolution of the earthquake occurrence rates together with suitable ground motion prediction relations. This work focuses on providing adaptive daily forecasts of the mean daily rate of exceeding various spectral acceleration values (the aftershock hazard). Two well-established earthquake occurrence models suitable for daily seismicity forecasts associated with the evolution of an aftershock sequence, namely, the modified Omori's aftershock model and the Epidemic Type Aftershock Sequence (ETAS) are adopted. The parameters of the modified Omori model are updated on a daily basis using Bayesian updating and based on the data provided by the ongoing aftershock sequence based on the methodology originally proposed by Jalayer et al. (2011). The Bayesian updating is used also to provide sequence-based parameter estimates for a given ground motion prediction model, i.e. the aftershock events in an ongoing sequence are exploited in order to update in an adaptive manner the parameters of an existing ground motion prediction model. As a numerical example, the mean daily rates of exceeding specific spectral acceleration values are estimated adaptively for the L'Aquila 2009

  2. Aftershocks in Coherent-Noise Models

    CERN Document Server

    Wilke, C; Martinetz, T

    1998-01-01

    The aftershock-distribution of the so-called 'coherent-noise' models (K. Sneppen, M. E. J. Newman, Physica D, in press) is studied in detail. Analytical and numerical results show that the distribution is a power-law with an exponent ranging from 0 to values well above 1. This is in contrast to Sneppen und Newman, who stated that the exponent is about 1, independent of the microscopic details of the simulation. Numerical simulations of an extended model (C. Wilke, T. Martinetz, Phys. Rev. E, in press) show that the power-law is only a generic feature of the original dynamics and does not necessarily appear in a more general context. Moreover, a rederivation of the master-equation for the model reveals a correting term that was not present in the previous works. This term does not affect the validity of the previous results, but has a measurable effect in the limit of a large mutation rate $f$. Finally, the implications of the results to the modeling of earthquakes are discussed.

  3. Anomalous statistics of aftershock sequences generated by supershear ruptures

    Directory of Open Access Journals (Sweden)

    Pathikrit Bhattacharya

    2012-05-01

    Full Text Available Most earthquake ruptures propagate with speeds smaller than the Rayleigh wave velocity of the medium. These are called sub- Rayleigh ruptures. However, under suitable conditions, segments of otherwise sub- Rayleigh seismogenic ruptures can occasionally accelerate to speeds higher than the local shear wave velocity, giving rise to so-called supershear ruptures. The occurrence of supershear ruptures is usually associated with a locally higher value of pre-stress on the fault segment compared to the sub-Rayleigh segments of the same fault. Additionally, shear stress changes generated by the supershear rupture are radiated out unattenuated to distances comparable to the depth of rupture instead of rapidly decaying at much smaller distances from the rupture. This leads to aftershocks being distributed away from the fault on the supershear segment. This study attempts to verify whether these pre- and postseismic stress conditions and the resultant spatial aftershock distributions lead to discernible features in the statistical properties of the aftershock sequences of the earthquakes known to be associated with supershear ruptures. We analyze the Gutenberg-Richter scaling, the modified Omori law and Båth’s law for the aftershock sequences of two supershear mainshocks: the 1979 MW 6.5 Imperial Valley (California and 2002 MW 7.9 Denali (Alaska earthquakes. We observe that the b-value is always higher in the supershear zone than the rest of the sequence. We also observe that there is no systematic trend in the exponent of the modified Omori law when comparing the aftershocks in the supershear zone with the rest of the aftershocks. We argue that the b-value anomaly can be explained in terms of the off-fault distribution of aftershocks around the supershear segment of the rupture.

  4. Aftershocks following the 9 april 2013 bushehr earthquake, iran.

    Science.gov (United States)

    Ardalan, Ali; Hajiuni, Alireza; Zare, Mehdi

    2013-08-28

    On 9 April 2013 at 11:52 UTC (16:22 local time), a Mw 6.2 earthquake occurred at the depth of 20 Km in Dashti district in south-west Iran's Bushehr province. The macroseismic epicenter was located nearby the city of Shonbeh. During one month after the earthquake, a total of 282 aftershocks hit the epicentral region, mostly at the east and north sides. They ranged from 2.5 to 5.7 on the Richter scale. Seventy aftershocks (24.9%) were M4.0-4.9 and eight (2.8%) were M5.0-5.7. Aftershocks are potentially able to do additional damage. In Bushehr earthquake, a M5.4 aftershock on 10 April in Chahgah village caused at least four injuries and destruction of several buildings that had been already damaged by the main shock. Knowledge about the aftershock induced damages provides opportunities for timely risk communication with the affected people and for long term community education. This will hopefully increase the community awareness and minimize the risk of further loss of lives.

  5. Aftershock activity of the 2015 Gorkha, Nepal, earthquake determined using the Kathmandu strong motion seismographic array

    Science.gov (United States)

    Ichiyanagi, Masayoshi; Takai, Nobuo; Shigefuji, Michiko; Bijukchhen, Subeg; Sasatani, Tsutomu; Rajaure, Sudhir; Dhital, Megh Raj; Takahashi, Hiroaki

    2016-02-01

    The characteristics of aftershock activity of the 2015 Gorkha, Nepal, earthquake (Mw 7.8) were evaluated. The mainshock and aftershocks were recorded continuously by the international Kathmandu strong motion seismographic array operated by Hokkaido University and Tribhuvan University. Full waveform data without saturation for all events enabled us to clarify aftershock locations and decay characteristics. The aftershock distribution was determined using the estimated local velocity structure. The hypocenter distribution in the Kathmandu metropolitan region was well determined and indicated earthquakes located shallower than 12 km depth, suggesting that aftershocks occurred at depths shallower than the Himalayan main thrust fault. Although numerical investigation suggested less resolution for the depth component, the regional aftershock epicentral distribution of the entire focal region clearly indicated earthquakes concentrated in the eastern margin of the major slip region of the mainshock. The calculated modified Omori law's p value of 1.35 suggests rapid aftershock decay and a possible high temperature structure in the aftershock region.

  6. International Aftershock Forecasting: Lessons from the Gorkha Earthquake

    Science.gov (United States)

    Michael, A. J.; Blanpied, M. L.; Brady, S. R.; van der Elst, N.; Hardebeck, J.; Mayberry, G. C.; Page, M. T.; Smoczyk, G. M.; Wein, A. M.

    2015-12-01

    Following the M7.8 Gorhka, Nepal, earthquake of April 25, 2015 the USGS issued a series of aftershock forecasts. The initial impetus for these forecasts was a request from the USAID Office of US Foreign Disaster Assistance to support their Disaster Assistance Response Team (DART) which coordinated US Government disaster response, including search and rescue, with the Government of Nepal. Because of the possible utility of the forecasts to people in the region and other response teams, the USGS released these forecasts publicly through the USGS Earthquake Program web site. The initial forecast used the Reasenberg and Jones (Science, 1989) model with generic parameters developed for active deep continental regions based on the Garcia et al. (BSSA, 2012) tectonic regionalization. These were then updated to reflect a lower productivity and higher decay rate based on the observed aftershocks, although relying on teleseismic observations, with a high magnitude-of-completeness, limited the amount of data. After the 12 May M7.3 aftershock, the forecasts used an Epidemic Type Aftershock Sequence model to better characterize the multiple sources of earthquake clustering. This model provided better estimates of aftershock uncertainty. These forecast messages were crafted based on lessons learned from the Christchurch earthquake along with input from the U.S. Embassy staff in Kathmandu. Challenges included how to balance simple messaging with forecasts over a variety of time periods (week, month, and year), whether to characterize probabilities with words such as those suggested by the IPCC (IPCC, 2010), how to word the messages in a way that would translate accurately into Nepali and not alarm the public, and how to present the probabilities of unlikely but possible large and potentially damaging aftershocks, such as the M7.3 event, which had an estimated probability of only 1-in-200 for the week in which it occurred.

  7. Simulating Aftershocks for an On Site Inspection (OSI) Exercise

    Energy Technology Data Exchange (ETDEWEB)

    Sweeney, J. J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ford, S. R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-10-05

    The experience of IFE14 emphasizes the need for a better way to simulate aftershocks during an OSI exercise. The obvious approach is to develop a digital model of aftershocks that can be used either for a real field exercise or for a computer simulation that can be done in an office, for training for example. However, this approach involves consideration of several aspects, such as how and when to introduce waveforms in a way that maximizes the realism of the data and that will be convincing to a savvy, experienced seismic analyst. The purpose of this report is to outline a plan for how this approach can be implemented.

  8. Hypocentral Relocations of the 2008 Mt. Carmel, Illinois Aftershock Sequence

    Science.gov (United States)

    Shoemaker, K.; Hamburger, M. W.; Pavlis, G. L.; Horton, S. P.; Withers, M. M.

    2009-12-01

    On April 18, 2008, a moderate sized earthquake (Mw 5.2, hypocentral depth of 16 km) occurred near the Indiana-Illinois state border within 3 km of the Mt. Carmel-New Harmony fault at the northern termination of the Wabash Valley Fault System. A total of 257 aftershocks were recorded over the next month by a fourteen-station temporary network deployed by Indiana University and University of Memphis/Center of Earthquake Research and Information (CERI). The number of recorded aftershocks is greater than aftershocks recorded from previous earthquakes in the WVFS of similar magnitude within the last 50 years. The number and density of local stations allowed the generation of precise hypocentral relocations with the combination of waveform cross-correlation and joint hypocentral techniques. The relocated hypocenters indicate a well-defined near-vertical fault plane striking east-west. The fault orientation is consistent with the focal mechanism of the main shock and nearly orthogonal with respect to the trace of the neighboring Mt. Carmel-New Harmony fault. The interpreted ruptured fault orientation suggests the aftershock sequence occurred on a transfer structure at the fault termination. The structure may be related to the change in deformation styles suggested by the transition from the northeast-trending WVFS to the northwest-trending La Salle anticlinorium.

  9. Model comparison for aftershock sequences following the 2005 Kashmir disaster

    NARCIS (Netherlands)

    Turkyilmaz, K.; Lieshout, M.N.M. van; Stein, A.

    2011-01-01

    In an earlier study (Van Lieshout and Stein, in press) we postulated the existence of two major earthquakes in Kashmir instead of a single one, based upon the pattern of aftershocks. In this note we explore this pattern further by fitting several spatial point pattern models. In particular we di

  10. Spatial Distributions of Foreshocks and Aftershocks: Static or Dynamic Triggering

    Science.gov (United States)

    Werner, M. J.; Rubin, A. M.

    2012-04-01

    In recent years, the spatial distributions of foreshocks and aftershocks have been scrutinized for evidence supporting either triggering by static stress changes induced by the permanent deformation from prior earthquakes or triggering by the dynamic stresses from seismic waves. Felzer & Brodsky (2006) identified small (mbeyond the zone traditionally thought to be affected by static stress changes. On this basis, they argued that dynamic stresses are responsible for triggering earthquakes. Richards-Dinger et al. (2010) and other studies, however, have presented several lines of evidence that suggest otherwise. One crucial question is whether the stacked distances of pairs of earthquakes, representing either mainshock-aftershock or foreshock-mainshock pairs, are in fact correctly identified and not misattributed, unrelated earthquakes. This question is especially important in the critical distance range of several to tens of earthquake radii, over which static stresses are thought to be too small to affect seismicity. If earthquake pairs in this range are not causally related, then the histogram of foreshock-mainshock and mainshock-aftershock pairs should be identical, and the difference between the two histograms can be used to identify remote triggering. Results based on southern Californian seismicity suggest that (1) the existence of a single power-law with a particular exponent may not be a robust observation, (2) geothermal regions seem to play an important role over the relevant distances, (3) remote triggering seems to exist beyond the classical static stress influence zone (perhaps out to 15 km after mainshocks with magnitudes between 3 and 4), (4) simple ETAS model simulations cannot reproduce all observations, and (5) at most one-third of the remote aftershocks had received significant static Coulomb stress change from much earlier but nearby large (m>5) quakes, suggesting that a misattribution of aftershocks statically triggered by large quakes as

  11. Aftershocks can Significantly Alter Stress Change Patterns Produced by Their Mainshock

    Science.gov (United States)

    Felzer, K. R.; Becker, T. W.; Abercrombie, R. E.; Ekström, G.; Rice, J. R.

    2001-12-01

    Many studies over the last decade have used the static Coulomb stress change produced by a mainshock to predict the locations of triggered earthquakes. This method has shown some success, but often fails to predict the locations of 20% to 40% of the aftershocks of a given mainshock. We use statistical Monte Carlo modeling to show that this amount of failure is consistent with the perturbation to the stress field provided by the aftershocks themselves. Although most aftershocks are more than a magnitude unit smaller than their mainshocks, the ability of earthquakes of all magnitudes to produce large static stress changes at short range, and the pronounced clustering of aftershock hypocenters, implies that many aftershock hypocenters in a sequence may be primarily stressed by a previous aftershock rather than by the mainshock itself. The exact percentage stressed by previous aftershocks increases with the activity of the aftershock sequence, the magnitude of the mainshock, and the time since the mainshock. Our model predicts that two days after the average California M7 earthquake, for example, over 50% of new aftershocks are primarily in response to stress changes from previous aftershocks. This means that the majority of the new aftershocks are most likely to occur near previous aftershocks, and not necessarily within regions of Coulomb stress increase from the mainshock. The same happens three days after the average M6, and three weeks after the average M5 mainshock. Our statistical modeling uses Omori's Law for aftershock decay, the Gutenberg-Richter magnitude frequency relationship, Baath's Law, and the assumptions that earthquakes of all sizes are capable of generating aftershocks and that the timing of each aftershock is essentially determined by a single mainshock. We apply our model to the 1999 M7.1 Hector Mine earthquake, which may be classified as an aftershock of the 1992 M7.3 Landers earthquake. Our modeling shows that at the time of the Hector Mine

  12. Analysis of the 1997 Zirkuh (Ghean-Birjand) aftershock sequence in east-central Iran

    Institute of Scientific and Technical Information of China (English)

    Mohammad-Reza Gheitanchi; Mohammad Raeesi

    2004-01-01

    In this study, the 1997 Zirkuh (Ghaen-Birjand) locally recorded aftershock sequence was analyzed. On the basis of the distribution of aftershocks, a NW-SE trend vertical faulting with an extension of at least 90 km could be estimated. The fault rupture causing the Zirkuh earthquake apparently initiated in the epicentral area and propagated unilaterally to southeast. The cross-section of aftershocks along the fault suggests that the aftershocks had a depth range of 20 km, indicating that the seismic activity was taking place within the upper crust and the seismogenic layer, in this region, had a thickness not greater than 20 km. The distribution of aftershocks suggested that the western block acted as hanging wall during the source process of the main shock. The time-space distribution of aftershocks showed two distinguished gaps coincided with the observed gaps on the surface faulting. It was concluded that the first gap acted as a barrier during the main shock and aftershocks, while the deeper part of second gap was ruptured either during the main shock or the aftershocks. The time-frequency pattern of aftershocks decay followed the Modified Omori relations for the first 10 days while the Omori model was best fitted for the later stage of the aftershock sequence.

  13. Decay of aftershock density with distance indicates triggering by dynamic stress.

    Science.gov (United States)

    Felzer, K R; Brodsky, E E

    2006-06-01

    The majority of earthquakes are aftershocks, yet aftershock physics is not well understood. Many studies suggest that static stress changes trigger aftershocks, but recent work suggests that shaking (dynamic stresses) may also play a role. Here we measure the decay of aftershocks as a function of distance from magnitude 2-6 mainshocks in order to clarify the aftershock triggering process. We find that for short times after the mainshock, when low background seismicity rates allow for good aftershock detection, the decay is well fitted by a single inverse power law over distances of 0.2-50 km. The consistency of the trend indicates that the same triggering mechanism is working over the entire range. As static stress changes at the more distant aftershocks are negligible, this suggests that dynamic stresses may be triggering all of these aftershocks. We infer that the observed aftershock density is consistent with the probability of triggering aftershocks being nearly proportional to seismic wave amplitude. The data are not fitted well by models that combine static stress change with the evolution of frictionally locked faults.

  14. Triggered Swarms and Induced Aftershock Sequences in Geothermal Systems

    Science.gov (United States)

    Shcherbakov, R.; Turcotte, D. L.; Yikilmaz, M. B.; Kellogg, L. H.; Rundle, J. B.

    2015-12-01

    Natural geothermal systems, which are used for energy generation, are usually associated with high seismic activity. This can be related to the large-scale injection and extraction of fluids to enhance geothermal recovery. This results in the changes of the pore pressure and pore-elastic stress field and can stimulate the occurrence of earthquakes. These systems are also prone to triggering of seismicity by the passage of seismic waves generated by large distant main shocks. In this study, we analyze clustering and triggering of seismicity at several geothermal fields in California. Particularly, we consider the seismicity at the Geysers, Coso, and Salton Sea geothermal fields. We analyze aftershock sequences generated by local large events with magnitudes greater than 4.0 and earthquake swarms generated by several significant long distant main shocks. We show that the rate of the aftershock sequences generated by the local large events in the two days before and two days after the reference event can be modelled reasonably well by the time dependent Epidemic Type Aftershock Sequence (ETAS) model. On the other hand, the swarms of activity triggered by large distant earthquakes cannot be described by the ETAS model. To model the increase in the rate of seismicity associated with triggering by large distant main shocks we introduce an additional time-dependent triggering mechanism into the ETAS model. In almost all cases the frequency-magnitude statistics of triggered sequences follow Gutenberg-Richter scaling to a good approximation. The analysis indicates that the seismicity triggered by relatively large local events can initiate sequences similar to regular aftershock sequences. In contrast, the distant main shocks trigger swarm like activity with faster decaying rates.

  15. Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines

    Science.gov (United States)

    Gibbons, Steven J.; Kværna, Tormod; Harris, David B.; Dodge, Douglas A.

    2016-04-01

    Aftershock sequences following very large earthquakes present enormous challenges to near-realtime generation of seismic bulletins. The increase in analyst resources needed to relocate an inflated number of events is compounded by failures of phase association algorithms and a significant deterioration in the quality of underlying fully automatic event bulletins. Current processing pipelines were designed a generation ago and, due to computational limitations of the time, are usually limited to single passes over the raw data. With current processing capability, multiple passes over the data are feasible. Processing the raw data at each station currently generates parametric data streams which are then scanned by a phase association algorithm to form event hypotheses. We consider the scenario where a large earthquake has occurred and propose to define a region of likely aftershock activity in which events are detected and accurately located using a separate specially targeted semi-automatic process. This effort may focus on so-called pattern detectors, but here we demonstrate a more general grid search algorithm which may cover wider source regions without requiring waveform similarity. Given many well-located aftershocks within our source region, we may remove all associated phases from the original detection lists prior to a new iteration of the phase association algorithm. We provide a proof-of-concept example for the 2015 Gorkha sequence, Nepal, recorded on seismic arrays of the International Monitoring System. Even with very conservative conditions for defining event hypotheses within the aftershock source region, we can automatically remove over half of the original detections which could have been generated by Nepal earthquakes and reduce the likelihood of false associations and spurious event hypotheses. Further reductions in the number of detections in the parametric data streams are likely using correlation and subspace detectors and/or empirical matched

  16. Disease aftershocks - The health effects of natural disasters

    Science.gov (United States)

    Guptill, S.C.

    2001-01-01

    While the initial activity of a natural disaster event may directly injure or kill a number of people, it is possible that a significant number of individuals will be affected by disease outbreaks that occur after the first effects of the disaster have passed. Coupling the epidemiologist's knowledge of disease outbreaks with geographic information systems and remote sensing technology could help natural disaster relief workers to prevent additional victims from disease aftershocks.

  17. The strong ground motion observation for the Wenchuan aftershock

    Institute of Scientific and Technical Information of China (English)

    Ruizhi Wen; Zhenghua Zhou; Xiaojun Li; Cheng Yang; Yuhuan Wang; Quan Liu; Xiaotao Yin; Mindu Zhou; Jianwen Cui

    2009-01-01

    In this paper, the mobile strong ground motion observation for the destructive earthquake is introduced. Considering the characteristics and its spatial distributions of aftershock, 59 strong ground motion instruments were installed along the Longmenshan fault area, and more than 2 000 records have been accumulated. It shows that it is necessary to perform the mobile strong ground motion observation after the destructive earthquake, and the precious collected data could be applied for further research.

  18. Empirical Assessment of Nonlinear Seismic Demand of Mainshock-Aftershock Ground Motion Sequences for Japanese Earthquakes

    Directory of Open Access Journals (Sweden)

    Katsuichiro eGoda

    2015-06-01

    Full Text Available This study investigates the effects of earthquake types, magnitudes, and hysteretic behavior on the peak and residual ductility demands of inelastic single-degree-of-freedom systems and evaluates the effects of major aftershocks on the nonlinear structural responses. An extensive dataset of real mainshock-aftershock sequences for Japanese earthquakes is developed. The constructed dataset is large, compared with previous datasets of similar kinds, and includes numerous sequences from the 2011 Tohoku earthquake, facilitating an investigation of spatial aspects of the aftershock effects. The empirical assessment of peak and residual ductility demands of numerous inelastic systems having different vibration periods, yield strengths, and hysteretic characteristics indicates that the increase in seismic demand measures due to aftershocks occurs rarely but can be significant. For a large mega-thrust subduction earthquake, a critical factor for major aftershock damage is the spatial occurrence process of aftershocks.

  19. High-Resolution Low Power, Intergrated Aftershock and Microzonation System

    Science.gov (United States)

    Zimakov, L.; Passmore, P.

    2012-04-01

    Refraction Technology, Inc. has developed a self-contained, fully integrated Aftershock System, model 160-03, providing the customer simple and quick deployment during aftershock emergency mobilization and microzonation studies. The 160-03 has no external cables or peripheral equipment for command/control and operation in the field. The 160-03 contains three major components integrated in one case: a) 24-bit resolution state-of-the art low power ADC with CPU and Lid interconnect boards; b) power source; and c) three component 2 Hz sensors (two horizontals and one vertical), and built-in ±4g accelerometer. Optionally, the 1 Hz sensors can be built-in the 160-03 system at the customer's request. The self-contained rechargeable battery pack provides power autonomy up to 7 days during data acquisition at 200 sps on continuous three weak motion and triggered three strong motion recording channels. For longer power autonomy, the 160-03 Aftershock System battery pack can be charged from an external source (solar power system). The data in the field is recorded to a built-in swappable USB flash drive. The 160-03 configuration is fixed based on a configuration file stored on the system. The detailed specifications and performance are presented and discussed

  20. Triggering of Aftershocks of the Japan 2011 Earthquake by Earth Tides

    CERN Document Server

    Datta, Arjun

    2011-01-01

    The aftershock sequence of the devastating Japan earthquake of March 2011 is analyzed for the presence of periodicities at the Earth tide periods. We use spectral analysis as well as a time-domain method KORRECT developed earlier to detect presence of diurnal and semi-diurnal periodicities in the sequence of aftershocks (M \\geq 4). This suggests that large aftershocks in the fault zone of the Japan 2011 earthquake were strongly influenced by Earth tides.

  1. Method discussion for quick response grey prediction of stronger aftershocks of an earthquake sequence

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    In this paper, we take occurrence process of early strong aftershocks of a main-after shock type′s earthquake sequence as a complex grey system, and introduce predicting method for its stronger aftershocks by grey predicting theory. Through inspection prediction for 1998 Zhangbei MS=6.2 earthquake sequence, it shows that the grey predicting method maybe has active significance for the investigation of quick response prediction problems of stronger aftershocks of an earthquake sequence.

  2. Violation of the scaling relation and non-Markovian nature of earthquake aftershocks

    CERN Document Server

    Abe, Sumiyoshi

    2008-01-01

    The statistical properties of earthquake aftershocks are studied. The scaling relation for the exponents of the Omori law and the power-law calm time distribution (i.e., the interoccurrence time distribution), which is valid if a sequence of aftershocks is a singular Markovian process, is carefully examined. Data analysis shows significant violation of the scaling relation, implying the non-Markovian nature of aftershocks.

  3. Relocation of Early and Late Aftershocks of the 2001 Bhuj Earthquake Using Joint Hypocentral Determination (JHD) Technique: Implication toward the Continued Aftershock Activity for more than Four Years

    Science.gov (United States)

    Mandal, Prantik; Narsaiah, R.; Sairam, B.; Satyamurty, C.; Raju, I. P.

    2006-08-01

    We employed layered model joint hypocentral determination (JHD) with station corrections to improve location identification for the 26 January, 2001 Mw 7.7 Bhuj early and late aftershock sequence. We relocated 999 early aftershocks using the data from a close combined network (National Geophysical Research Institute, India and Center for Earthquake Research Institute, USA) of 8 18 digital seismographs during 12 28 February, 2001. Additionally, 350 late aftershocks were also relocated using the data from 4 10 digital seismographs/accelerographs during August 2002 to December 2004. These precisely relocated aftershocks (error in the epicentral locationBhuj earthquake. The aftershock zone is confined to a 60-km long and 40-km wide region lying between the KMF to the south and NWF to the north, extending from 2 to 45 km depth. Estimated focal depths suggest that the aftershock zone became deeper with the passage of time. The P- and S-wave station corrections determined from the JHD technique indicate that the larger values (both +ve and -ve) characterize the central aftershock zone, which is surrounded by the zones of smaller values. The station corrections vary from -0.9 to +1.1 sec for the P waves and from -0.7 to +1.4 sec for the S waves. The b-value and p-value of the whole aftershock (2001 2004) sequences of Mw ≥ 3 are estimated to be 0.77 ± 0.02 and 0.99 ± 0.02, respectively. The p-value indicates a smaller value than the global median of 1.1, suggesting a relatively slow decay of aftershocks, whereas, the relatively lower b-value (less than the average b-value of 1.0 for stable continental region earthquakes of India) suggests a relatively higher probability for larger earthquakes in Kachchh in comparison to other stable continental regions of the Indian Peninsula. Further, based on the b-value, mainshock magnitude and maximum aftershock magnitude, the Bhuj aftershock sequence is categorized as the Mogi's type II sequence, indicating the region to be of

  4. Magnitude and distance distribution of strong aftershocks in Sichuan-Yunnan region

    Institute of Scientific and Technical Information of China (English)

    Lü Xiao-jian; GAO Meng-tan; GAO Zhan-wu; MI Su-ting

    2008-01-01

    Using the earthquake sequences data with Ms≥6.5 since 1966 in Sichuan-Yunnan region, we research the charac- teristic of the magnitude difference distribution between main shocks and their strong aftershocks; and then study the spatial distribution characteristic of the strong aftershocks away from their main shocks. The result shows that the magnitude difference distribution obeys intercepted exponential distribution, while the spatial distribution of strong aftershocks obeys normal distribution and the dominated distribution area of strong shocks is 10~39 krn away from main shock. Finally the probability density function of the magnitude difference distribution and the spatial distribution of strong aftershocks is deduced.

  5. The oscillatory behaviour of the aftershocks rate of the 2001 Bhuj earthquake, India: observation and interpretation

    OpenAIRE

    E. Unnikrishnan; A. G. Venkatesh Prasad; M. M. Abdul Razak; G. Jayachandran Nair

    2004-01-01

    A damaging earthquake of Mw 7.7, which struck the Bhuj region of India on January 26, 2001, was followed by a large number of aftershocks. The aftershock data available at Gauribidanur Seismic Array Station (GBA), India, till 869 h following the main shock were compiled. The plot of the aftershocks rate with time was found to be oscillatory decay. There was a sharp decrease of the aftershocks rate in the initial 144 h from the main shock and this paper presents the analysis of the tempor...

  6. Investigations of the Aftershocks of July 4, 1968 Earthquake in Epidavros

    Directory of Open Access Journals (Sweden)

    H. N. SHRIVASTAVA

    1970-06-01

    Full Text Available The spatial and tlie time distribution of the aftershocks
    of the earthquake of July 1968 in Epidavros (Greece has been studied.
    It was found that the value of b in Gutenberg-Richter's relationship was
    nearly the same for the primary as well as the secondary or second order
    aftershocks of the sequence. The focal mechanism of the second order
    aftershocks as observed from the sense of first motion of P-waves showed
    some difference from that of the main shock or its primary aftershock.

  7. The oscillatory behaviour of the aftershocks rate of the 2001 Bhuj earthquake, India: observation and interpretation

    Directory of Open Access Journals (Sweden)

    E. Unnikrishnan

    2004-06-01

    Full Text Available A damaging earthquake of Mw 7.7, which struck the Bhuj region of India on January 26, 2001, was followed by a large number of aftershocks. The aftershock data available at Gauribidanur Seismic Array Station (GBA, India, till 869 h following the main shock were compiled. The plot of the aftershocks rate with time was found to be oscillatory decay. There was a sharp decrease of the aftershocks rate in the initial 144 h from the main shock and this paper presents the analysis of the temporal characteristics of aftershock activity during this period. Astatistical best fit for the rate of aftershocks is performed using the generalised Omori?s law and the exponential decay law. The statistical errors for the exponential fit are found to be lower than that of the generalised Omori's fit. The superimposed oscillations present in the aftershock activity are extracted by differencing the observed aftershock activity from the statistical fits. The frequencies of these oscillations are found to be 0.062 h?1, 0.078 h-1, 0.102 h-1, 0.118 h-1, 0.141 h-1, 0.164 h-1, 0.233 h-1 and 0.476 h-1. Some of the plausible causes for this kind of oscillations present in the aftershock activity are also discussed in this paper.

  8. Preliminary Double-Difference Relocations of Bhuj Aftershocks

    Science.gov (United States)

    Raphael, A. J.; Bodin, P.; Horton, S.; Gomberg, J.

    2001-12-01

    The Mw=7.7 Bhuj earthquake of 26 January, 2001 in Gujarat, India, was a scientifically important earthquake that took place in a rather poorly instrumented region. Lack of nearby mainshock recordings and lack of surface rupture preclude the calculation of a high-resolution picture of the mainshock rupture processes like those presented for other recent large, better instrumented earthquakes. This is particularly vexing because, given its history of infrequent moderate-to-large earthquakes and its setting within a continental plate interior, the Bhuj earthquake might provide important insights for other high-consequence-but-low-occurrence-rate regions such as the central US. Fortunately we do have excellent recordings of numerous aftershocks on a temporary network of 8 portable seismographs. In order to constrain rupture complexity, we are computing high-resolution relative relocations of aftershocks using HypoDD, the double-difference algorithm of Waldhauser and Ellsworth \\(BSSA, 2000\\) to look for aftershock patterns that may reflect rupture characteristics. We are currently using a subset of all of the aftershocks that have been analyzed \\(P and S phases recorded on at least 4 stations\\) which consists of nearly 1000 events. This subset is less than half of all the data, and more events are being added as they are analyzed. Our preliminary results show concentrated patches of relocated aftershocks that dip to the south between 6 and 37 km deep. Strong clusters appear to illuminate the lateral edges of a rupture, with a NE trending cluster at the eastern side and a NW trending cluster at the western side, both plunging southward. The central part of the apparent rupture, which coincides with teleseismic estimates of maximum slip, appears to be relatively quiescent. We have not up to this point used waveform cross-correlation to provide relative arrival timing, but feel this may be appropriate for subsets of the overall data set. We also note the presence of

  9. Aftershocks of the 2014 South Napa, California, Earthquake: Complex faulting on secondary faults

    Science.gov (United States)

    Hardebeck, Jeanne L.; Shelly, David R.

    2016-01-01

    We investigate the aftershock sequence of the 2014 MW6.0 South Napa, California, earthquake. Low-magnitude aftershocks missing from the network catalog are detected by applying a matched-filter approach to continuous seismic data, with the catalog earthquakes serving as the waveform templates. We measure precise differential arrival times between events, which we use for double-difference event relocation in a 3D seismic velocity model. Most aftershocks are deeper than the mainshock slip, and most occur west of the mapped surface rupture. While the mainshock coseismic and postseismic slip appears to have occurred on the near-vertical, strike-slip West Napa fault, many of the aftershocks occur in a complex zone of secondary faulting. Earthquake locations in the main aftershock zone, near the mainshock hypocenter, delineate multiple dipping secondary faults. Composite focal mechanisms indicate strike-slip and oblique-reverse faulting on the secondary features. The secondary faults were moved towards failure by Coulomb stress changes from the mainshock slip. Clusters of aftershocks north and south of the main aftershock zone exhibit vertical strike-slip faulting more consistent with the West Napa Fault. The northern aftershocks correspond to the area of largest mainshock coseismic slip, while the main aftershock zone is adjacent to the fault area that has primarily slipped postseismically. Unlike most creeping faults, the zone of postseismic slip does not appear to contain embedded stick-slip patches that would have produced on-fault aftershocks. The lack of stick-slip patches along this portion of the fault may contribute to the low productivity of the South Napa aftershock sequence.

  10. Anomalous power law distribution of total lifetimes of branching processes: application to earthquake aftershock sequences.

    Science.gov (United States)

    Saichev, A; Sornette, D

    2004-10-01

    We consider a general stochastic branching process, which is relevant to earthquakes, and study the distributions of global lifetimes of the branching processes. In the earthquake context, this amounts to the distribution of the total durations of aftershock sequences including aftershocks of arbitrary generation number. Our results extend previous results on the distribution of the total number of offspring (direct and indirect aftershocks in seismicity) and of the total number of generations before extinction. We consider a branching model of triggered seismicity, the epidemic-type aftershock sequence model, which assumes that each earthquake can trigger other earthquakes ("aftershocks"). An aftershock sequence results in this model from the cascade of aftershocks of each past earthquake. Due to the large fluctuations of the number of aftershocks triggered directly by any earthquake ("productivity" or "fertility"), there is a large variability of the total number of aftershocks from one sequence to another, for the same mainshock magnitude. We study the regime where the distribution of fertilities mu is characterized by a power law approximately 1/ mu(1+gamma) and the bare Omori law for the memory of previous triggering mothers decays slowly as approximately 1/ t(1+theta;) , with 0aftershock lifetimes scales as approximately 1/ t(1+theta;/gamma) when the average branching ratio is critical (n=1) . The coefficient 1aftershocks with mainshock magnitude m (productivity), with 0.5

  11. On certain aftershock and foreshock parameters in the area of Greece

    Directory of Open Access Journals (Sweden)

    B. C. PAPAZACHOS

    1974-06-01

    Full Text Available Published information (l2 on the aftershocks and foreshocks of many principal shallow earthquakes occurred in the area of Greece between 1911 and 1973 constitutes a more or less homogeneous and complete sample of data in respect to some properties of these seismic sequences. These data have been used to determine certain parameters of these sequences. The value of the decay parameter p, in the time distribution law of aftershocks, is independent of the magnitude range and varies between 0.7 and 1.9 in this area. The smallest value was found for the aftershock sequence of an earthquake believed to be associated with the Kremasta artificial lake, while the largest value was found for the aftershock sequence of an earthquake occurred in the volcanic part of the Hellenic arc. The probability, N, that the largest aftershock will occur Tl days after the main shock or later is given by a relation of the form N = c — k log Tl. Representative values of the parameter b, in the frequency-magnitude relation, have been found for the foreshocks as well as for the aftershocks of the same main shocks, by a proper grouping of the data. This value is equal to 0.67 for foresliocks and equal to 0.92 for the corresponding aftershocks. The difference in magnitude between the main shock and the largest aftershock is almost independent of the magnitude of the main shock. The relation M0 — = 1.1 holds on an average.

  12. The role of static stress diffusion in the spatio-temporal organization of aftershocks

    CERN Document Server

    Lippiello, E; Godano, C; 10.1103/PhysRevLett.103.038501

    2009-01-01

    We investigate the spatial distribution of aftershocks and we find that aftershock linear density exhibits a maximum, that depends on the mainshock magnitude, followed by a power law decay. The exponent controlling the asymptotic decay and the fractal dimensionality of epicenters clearly indicate triggering by static stress. The non monotonic behavior of the linear density and its dependence on the mainshock magnitude can be interpreted in terms of diffusion of static stress. This is supported by the power law growth with exponent $H\\simeq 0.5$ of the average main-aftershock distance. Implementing static stress diffusion within a stochastic model for aftershock occurrence we are able to reproduce aftershock linear density spatial decay, its dependence on the mainshock magnitude and its evolution in time.

  13. Role of static stress diffusion in the spatiotemporal organization of aftershocks.

    Science.gov (United States)

    Lippiello, E; de Arcangelis, L; Godano, C

    2009-07-17

    We investigate the spatial distribution of aftershocks, and we find that aftershock linear density exhibits a maximum that depends on the main shock magnitude, followed by a power law decay. The exponent controlling the asymptotic decay and the fractal dimensionality of epicenters clearly indicate triggering by static stress. The nonmonotonic behavior of the linear density and its dependence on the main shock magnitude can be interpreted in terms of diffusion of static stress. This is supported by the power law growth with exponent H approximately 0.5 of the average main-aftershock distance. Implementing static stress diffusion within a stochastic model for aftershock occurrence, we are able to reproduce aftershock linear density spatial decay, its dependence on the main shock magnitude, and its evolution in time.

  14. Study on displacement field generated by aftershocks in Landers earthquake fault zone and its adjacent areas

    Institute of Scientific and Technical Information of China (English)

    WAN Yong-ge; SHEN Zheng-kang; LAN Cong-xin

    2005-01-01

    The displacement field generated by aftershocks in Landers earthquake fault zone and its adjacent areas is calculated in this study. The result is compared with the displacement field of the main shock calculated by co-seismic slip model of Wald and Heaton (1994). The result shows that the direction of displacement generated by aftershocks in Landers seismic fault plane and its adjacent areas is consistent with that generated by main shock. The rupture of aftershock is generally inherited from main shock. The displacement generated by aftershocks is up to an order of centimeter and can be measured by GPS sites nearby. So when we use geodetic data measured after earthquake to study the geophysical problems such as crustal viscosity structure, afterslip distribution, etc., only the displacement field generated by aftershocks considered, can uncertainty be reduced to minimum and realistic result be obtained.

  15. Static stress triggering explains the empirical aftershock distance decay

    Science.gov (United States)

    Hainzl, Sebastian; Moradpour, Javad; Davidsen, Jörn

    2014-12-01

    The shape of the spatial aftershock decay is sensitive to the triggering mechanism and thus particularly useful for discriminating between static and dynamic stress triggering. For California seismicity, it has been recently recognized that its form is more complicated than typically assumed consisting of three different regimes with transitions at the scale of the rupture length and the thickness of the crust. The intermediate distance range is characterized by a relative small decay exponent of 1.35 previously declared to relate to dynamic stress triggering. We perform comprehensive simulations of a simple clock-advance model, in which the number of aftershocks is just proportional to the Coulomb-stress change, to test whether the empirical result can be explained by static stress triggering. Similarly to the observations, the results show three scaling regimes. For simulations adapted to the depths and focal mechanisms observed in California, we find a remarkable agreement with the observation over the whole distance range for a fault distribution with fractal dimension of 1.8, which is shown to be in good agreement with an independent analysis of California seismicity.

  16. Aftershock sequences of some large earthquakes in the region of Greece

    Directory of Open Access Journals (Sweden)

    LIAPIS N.

    1967-06-01

    Full Text Available Deformation characteristics, magnitude and time distribution
    of the aftershocks of the large earthquakes, occurred in the region
    of Greece from 1926 till 1964 are investigated. An approximate relation
    between the number of aftershocks and the magnitude and focal depth
    of the main shock has been found. Also, an approximate relation has been
    derived between the magnitude of the largest aftershock and the magnitude
    and focal depth of the main sliok. The largest aftershock occurs within
    fourteen days after the main shock. In many cases large " late aftershocks "
    occur one or more months after the main shock. One or more foreshocks
    of magnitude larger than 3.5 occurred in forty per cent of the cases. The probability for an earthquake to be preceded l>y a large foreshoek not much
    smaller than the main shock is 10%. It is shown that some properties of
    the Earth's material in the aftershock region can be derived by studying the
    magnitude distribution and deformation characteristics of the aftershocks.

  17. The Use of Explosion Aftershock Probabilities for Planning and Deployment of Seismic Aftershock Monitoring System for an On-site Inspection

    Science.gov (United States)

    Labak, P.; Ford, S. R.; Sweeney, J. J.; Smith, A. T.; Spivak, A.

    2011-12-01

    One of four elements of CTBT verification regime is On-site inspection (OSI). Since the sole purpose of an OSI shall be to clarify whether a nuclear weapon test explosion or any other nuclear explosion has been carried out, inspection activities can be conducted and techniques used in order to collect facts to support findings provided in inspection reports. Passive seismological monitoring, realized by the seismic aftershock monitoring (SAMS) is one of the treaty allowed techniques during an OSI. Effective planning and deployment of SAMS during the early stages of an OSI is required due to the nature of possible events recorded and due to the treaty related constrains on size of inspection area, size of inspection team and length of an inspection. A method, which may help in planning the SAMS deployment is presented. An estimate of aftershock activity due to a theoretical underground nuclear explosion is produced using a simple aftershock rate model (Ford and Walter, 2010). The model is developed with data from the Nevada Test Site and Semipalatinsk Test Site, which we take to represent soft- and hard-rock testing environments, respectively. Estimates of expected magnitude and number of aftershocks are calculated using the models for different testing and inspection scenarios. These estimates can help to plan the SAMS deployment for an OSI by giving a probabilistic assessment of potential aftershocks in the Inspection Area (IA). The aftershock assessment combined with an estimate of the background seismicity in the IA and an empirically-derived map of threshold magnitude for the SAMS network could aid the OSI team in reporting. We tested the hard-rock model to a scenario similar to the 2008 Integrated Field Exercise 2008 deployment in Kazakhstan and produce an estimate of possible recorded aftershock activity.

  18. Aftershocks illuninate the 2011 Mineral, Virginia, earthquake causative fault zone and nearby active faults

    Science.gov (United States)

    Horton, Jr., J. Wright; Shah, Anjana K.; McNamara, Daniel E.; Snyder, Stephen L.; Carter, Aina M

    2015-01-01

    Deployment of temporary seismic stations after the 2011 Mineral, Virginia (USA), earthquake produced a well-recorded aftershock sequence. The majority of aftershocks are in a tabular cluster that delineates the previously unknown Quail fault zone. Quail fault zone aftershocks range from ~3 to 8 km in depth and are in a 1-km-thick zone striking ~036° and dipping ~50°SE, consistent with a 028°, 50°SE main-shock nodal plane having mostly reverse slip. This cluster extends ~10 km along strike. The Quail fault zone projects to the surface in gneiss of the Ordovician Chopawamsic Formation just southeast of the Ordovician–Silurian Ellisville Granodiorite pluton tail. The following three clusters of shallow (aftershocks illuminate other faults. (1) An elongate cluster of early aftershocks, ~10 km east of the Quail fault zone, extends 8 km from Fredericks Hall, strikes ~035°–039°, and appears to be roughly vertical. The Fredericks Hall fault may be a strand or splay of the older Lakeside fault zone, which to the south spans a width of several kilometers. (2) A cluster of later aftershocks ~3 km northeast of Cuckoo delineates a fault near the eastern contact of the Ordovician Quantico Formation. (3) An elongate cluster of late aftershocks ~1 km northwest of the Quail fault zone aftershock cluster delineates the northwest fault (described herein), which is temporally distinct, dips more steeply, and has a more northeastward strike. Some aftershock-illuminated faults coincide with preexisting units or structures evident from radiometric anomalies, suggesting tectonic inheritance or reactivation.

  19. Statistical estimation of the duration of aftershock sequences

    Science.gov (United States)

    Hainzl, S.; Christophersen, A.; Rhoades, D.; Harte, D.

    2016-05-01

    It is well known that large earthquakes generally trigger aftershock sequences. However, the duration of those sequences is unclear due to the gradual power-law decay with time. The triggering time is assumed to be infinite in the epidemic type aftershock sequence (ETAS) model, a widely used statistical model to describe clustering phenomena in observed earthquake catalogues. This assumption leads to the constraint that the power-law exponent p of the Omori-Utsu decay has to be larger than one to avoid supercritical conditions with accelerating seismic activity on long timescales. In contrast, seismicity models based on rate- and state-dependent friction observed in laboratory experiments predict p ≤ 1 and a finite triggering time scaling inversely to the tectonic stressing rate. To investigate this conflict, we analyse an ETAS model with finite triggering times, which allow smaller values of p. We use synthetic earthquake sequences to show that the assumption of infinite triggering times can lead to a significant bias in the maximum likelihood estimates of the ETAS parameters. Furthermore, it is shown that the triggering time can be reasonably estimated using real earthquake catalogue data, although the uncertainties are large. The analysis of real earthquake catalogues indicates mainly finite triggering times in the order of 100 days to 10 years with a weak negative correlation to the background rate, in agreement with expectations of the rate- and state-friction model. The triggering time is not the same as the apparent duration, which is the time period in which aftershocks dominate the seismicity. The apparent duration is shown to be strongly dependent on the mainshock magnitude and the level of background activity. It can be much shorter than the triggering time. Finally, we perform forward simulations to estimate the effective forecasting period, which is the time period following a mainshock, in which ETAS simulations can improve rate estimates after the

  20. Investigations on the aftershock sequence of the great Assam earthquake of August 15, 1950

    Directory of Open Access Journals (Sweden)

    V. K. GAUR

    1974-06-01

    Full Text Available The strain release curve of the aftershock sequence of the great Assam earthquake of August 15, 1950 exhibits three linear segments. A secondary aftershock sequence has also been reported; the strain release curve in this case is also linear. The b value, using the maximum likelihood method of Utsu, for the sequence is 0.52 ± 0.095. The fault plane solution shows that the fault strikes almost cast-west and dips northward at an angle of 80°; the motion is predominently strike slip (right lateral type. The spatial distribution of aftershocks shows two main centers of activity at the two ends of the probable fault.

  1. Aftershocks in Modern Perspectives: Complex Earthquake Network, Aging, and Non-Markovianity

    CERN Document Server

    Abe, Sumiyoshi

    2012-01-01

    The phenomenon of aftershocks is studied in view of science of complexity. In particular, three different concepts are examined: (i) the complex-network representation of seismicity, (ii) the event-event correlations, and (iii) the effects of long-range memory. Regarding (i), it is shown the clustering coefficient of the complex earthquake network exhibits a peculiar behavior at and after main shocks. Regarding (ii), it is found that aftershocks experience aging, and the associated scaling holds. And regarding (iii), the scaling relation to be satisfied by a class of singular Markovian processes is violated, implying the existence of the long-range memory in processes of aftershocks.

  2. A random effects epidemic-type aftershock sequence model.

    Science.gov (United States)

    Lin, Feng-Chang

    2011-04-01

    We consider an extension of the temporal epidemic-type aftershock sequence (ETAS) model with random effects as a special case of a well-known doubly stochastic self-exciting point process. The new model arises from a deterministic function that is randomly scaled by a nonnegative random variable, which is unobservable but assumed to follow either positive stable or one-parameter gamma distribution with unit mean. Both random effects models are of interest although the one-parameter gamma random effects model is more popular when modeling associated survival times. Our estimation is based on the maximum likelihood approach with marginalized intensity. The methods are shown to perform well in simulation experiments. When applied to an earthquake sequence on the east coast of Taiwan, the extended model with positive stable random effects provides a better model fit, compared to the original ETAS model and the extended model with one-parameter gamma random effects.

  3. Aftershock seismicity of the 2010 Maule Mw=8.8 Chile, earthquake: Correlation between co-seismic slip models and aftershock distribution?

    Science.gov (United States)

    Rietbrock, A.; Ryder, I.; Hayes, G.; Haberland, C.; Comte, D.; Roecker, S.

    2012-01-01

    The 27 February 2010 Maule, Chile (Mw=8.8) earthquake is one of the best instrumentally observed subduction zone megathrust events. Here we present locations, magnitudes and cumulative equivalent moment of the first -2 months of aftershocks, recorded on a temporary network deployed within 2 weeks of the occurrence of the mainshock. Using automatically-determined onset times and a back projection approach for event association, we are able to detect over 30,000 events in the time period analyzed. To further increase the location accuracy, we systematically searched for potential S-wave arrivals and events were located in a regional 2D velocity model. Additionally, we calculated regional moment tensors to gain insight into the deformation history of the aftershock sequence. We find that the aftershock seismicity is concentrated between 40 and 140 km distance from the trench over a depth range of 10 to 35 km. Focal mechanisms indicate a predominance of thrust faulting, with occasional normal faulting events. Increased activity is seen in the outer-rise region of the Nazca plate, predominantly in the northern part of the rupture area. Further down-dip, a second band of clustered seismicity, showing mainly thrust motion, is located at depths of 40–45 km. By comparing recent published mainshock source inversions with our aftershock distribution, we discriminate slip models based on the assumption that aftershocks occur in areas of rapid transition between high and low slip, surrounding high-slip regions of the mainshock.

  4. Three Ingredients for Improved Global Aftershock Forecasts: Tectonic Region, Time-Dependent Catalog Incompleteness, and Inter-Sequence Variability

    Science.gov (United States)

    Page, M. T.; Hardebeck, J.; Felzer, K. R.; Michael, A. J.; van der Elst, N.

    2015-12-01

    Following a large earthquake, seismic hazard can be orders of magnitude higher than the long-term average as a result of aftershock triggering. Due to this heightened hazard, there is a demand from emergency managers and the public for rapid, authoritative, and reliable aftershock forecasts. In the past, USGS aftershock forecasts following large, global earthquakes have been released on an ad-hoc basis with inconsistent methods, and in some cases, aftershock parameters adapted from California. To remedy this, we are currently developing an automated aftershock product that will generate more accurate forecasts based on the Reasenberg and Jones (Science, 1989) method. To better capture spatial variations in aftershock productivity and decay, we estimate regional aftershock parameters for sequences within the Garcia et al. (BSSA, 2012) tectonic regions. We find that regional variations for mean aftershock productivity exceed a factor of 10. The Reasenberg and Jones method combines modified-Omori aftershock decay, Utsu productivity scaling, and the Gutenberg-Richter magnitude distribution. We additionally account for a time-dependent magnitude of completeness following large events in the catalog. We generalize the Helmstetter et al. (2005) equation for short-term aftershock incompleteness and solve for incompleteness levels in the global NEIC catalog following large mainshocks. In addition to estimating average sequence parameters within regions, we quantify the inter-sequence parameter variability. This allows for a more complete quantification of the forecast uncertainties and Bayesian updating of the forecast as sequence-specific information becomes available.

  5. Forecasting Aftershocks from Multiple Earthquakes: Lessons from the Mw=7.3 2015 Nepal Earthquake

    Science.gov (United States)

    Jiménez, Abigail; NicBhloscaidh, Mairéad; McCloskey, John

    2016-04-01

    The Omori decay of aftershocks is often perturbed by large secondary events which present particular, but not uncommon, challenges to aftershock forecasting. The Mw = 7.8, 25 April 2015, Gorkha, Nepal earthquake was followed on 12 May by the Mw = 7.3 Kodari earthquake, superimposed its own aftershocks on the Gorkha sequence, immediately invalidating forecasts made by single-mainshock forecasting methods. The complexity of the Gorkha rupture process, where the hypocentre and moment centroid were separated by some 75 km, provided an insurmountable challenge for other standard forecasting methods. Here, we report several modifications of existing algorithms, which were developed in response to the complexity of this sequence and which appear to provide a more general framework for the robust and dependable forecasting of aftershock probabilities. We suggest that these methods may be operationalised to provide a scientific underpinning for an evidence-based management system for post-earthquake crises.

  6. A new analysis of aftershock sequence statistics and fault geometry fingerprinting

    CERN Document Server

    Bhattacharya, Pathikrit; Kamal,

    2008-01-01

    We analyzed several aftershock sequences around the globe and calculated the cumulative integral of magnitude over time. This quantity is found to have a linear relationship with time, having a slope characteristic of the causative fault zone.

  7. Evidence for fluid-triggering underlying the year 2014 aftershock sequences in NW Bohemia

    Science.gov (United States)

    Hainzl, S.; Fischer, T.; Cermakova, H.; Bachura, M.; Vlcek, J.

    2015-12-01

    The West Bohemia/Vogtland region, central Europe, is a place of localized repeating swarm activity continuously monitored during the last two decades, allowing a detailed study of the driving mechanisms. Previous earthquake episodes where characterized by swarm-type activity with gradual onsets and decays which were not related to mainshocks. However, the latest activity in the year 2014 occurred exactly in the same location as previous swarm activity but consisted of three classical aftershock sequences triggered by a M4.4 event and two ~M3.5 events. The apparent system change from swarm-type to mainshock-aftershock characteristics can have important implications for the understanding of swarm and aftershock generation as well as for seismic hazard assessment in this region. Thus we have analyzed in detail the spatiotemporal aftershock sequence based on a relocated earthquake catalog. Our analysis shows that the largest mainshock occurred in a step-over region of the fault plane with increased Coulomb stress due to previous activity. Its rupture plane connecting both segments is significantly rotated compared to most aftershocks, which occurred in-plane. The aftershock characteristics are classical in the way that (i) the aftershocks are clearly triggered by the mainshock, (ii) the maximum magnitude of the aftershocks is approximately 1.2 units less than the mainshock magnitude (Bath law), and (iii) the decay can be well fitted by the Omori-Utsu law. However, the absolute number of aftershocks and the fitted c and p values of the Omori-Utsu decay are significantly larger than for typical sequences. The fit of the epidemic type aftershock sequence (ETAS) model reveals a time-dependent background activity which exponentially decays with time after the mainshock. Pore pressure simulations with an exponentially decreasing flow rate of the fluid source show a good agreement with the observed spatial migration front of the aftershocks extending approximately with log

  8. Aftershocks of the 2014 M6 South Napa Earthquake: Detection, Location, and Focal Mechanisms

    Science.gov (United States)

    Hardebeck, J.; Shelly, D. R.

    2014-12-01

    The aftershock sequence of the South Napa earthquake is notable both for its low productivity and for its geometric complexity. The aftershocks do not clearly define a fault plane consistent with the NNW-striking vertical plane implied by the mainshock moment tensor and the mapped surface rupture, but instead seem to delineate multiple secondary structures at depth. We investigate this unusual sequence by identifying additional aftershocks that do not appear in the network catalog, relocating the combined aftershock catalog using waveform cross-correlation arrival times and double-difference techniques, and determining focal mechanisms for individual events and event clusters. Additional aftershocks are detected by applying a matched filter approach to the continuous seismic data at nearby stations, with the catalog earthquakes serving as the waveform templates. In tandem with new event detections, we measure precise differential arrival times between events, which we then use in double-difference event location. We detect about 4 times as many well-located aftershocks as in the network catalog. We relocate the events using double-difference in both a 1D and a 3D velocity model. Most of the aftershocks occur between 8 and 11 km depth, similar depth to the mainshock hypocenter and deeper than most of the slip imaged seismically and geodetically. The aftershocks form a diffuse NNW-trending structure, primarily to the north of the mainshock hypocenter and on the west side of the main surface rupture. Within this diffuse trend there are clusters of aftershocks, some suggesting a N-S strike, and some that appear to dip to the east or west. Preliminary single-event and composite focal mechanisms also imply N-S striking strike-slip structures. The mainshock hypocenter and many of the aftershocks occur near the intersection of a sharply defined NE-dipping seismicity structure and the probable location of the West Napa fault, suggesting that stress is concentrated at a

  9. Analysis of Mw 7.2 2014 Molucca Sea earthquake and its aftershocks

    Science.gov (United States)

    Shiddiqi, Hasbi Ash; Widiyantoro, Sri; Nugraha, Andri Dian; Ramdhan, Mohamad; Wiyono, Samsul Hadi; Wandono, Wandono

    2016-05-01

    A Mw 7.2 earthquake struck an area in the Molucca Sea region on November 15, 2014, and was followed by more than 300 aftershocks until the end of December 2014. This earthquake was the second largest event in the Molucca Sea during the last decade and was well recorded by local networks. Although the seismicity rate of the aftershocks was declining at the end of 2014, several significant earthquakes with magnitude (Mw) larger than five still occurred from January to May 2015 within the vicinity of the mainshock location. In this study, we investigated the earthquake process and its relation to the increasing seismicity in the Molucca Sea within six months after the earthquake. We utilized teleseismic double-difference hypocenter relocation method using local, regional, and teleseismic direct body-wave arrival times of 514 earthquakes from the time of mainshock occurrence to May 2015. Furthermore, we analyzed the focal mechanism solutions from the National Research Institute for Earth Science and Disaster Prevention (NIED), Japan. From our results, we observed that aftershocks propagated along the NNE-SSW direction within a 100 km fault segment length of the Mayu Ridge. The highest number of the aftershocks was located in the SSW direction of the main event. The aftershocks were terminated at around 60 km depth, which may represent the location of the top of the Molucca Sea Plate (MSP). Between January and May 2015, several significant earthquakes propagated westward and were extended to the Molucca Sea slab. From focal mechanism catalog, we found that the mainshock mechanism was reverse with strike 192o and dip 55o. While most of the large aftershock mechanisms were consistent with the main event, several aftershocks had reverse, oblique mechanisms. Stress inversion result from focal mechanism data revealed that the maximum stress direction was SE and was not perpendicular with fault direction. We suggest that the non-perpendicular maximum stress caused several

  10. Analysis of the spatial distribution between successive earthquakes in aftershocks series

    Directory of Open Access Journals (Sweden)

    Elisaveta Georgieva Marekova

    2014-10-01

    Full Text Available The earthquake spatial distribution is being studied, using catalogs for different recent aftershock series. The quality of the available data, taking into account the completeness of the magnitude, is examined. Based on the analysis of the catalogs, it was determined that the probability densities of the inter-event distance distribution collapse into a single curve when the data were rescaled. The collapse of the data provides a clear illustration of aftershock-occurrence self-similarity in space.

  11. An Explosion Aftershock Model with Application to On-Site Inspection

    Science.gov (United States)

    Ford, Sean R.; Labak, Peter

    2016-01-01

    An estimate of aftershock activity due to a theoretical underground nuclear explosion is produced using an aftershock rate model. The model is developed with data from the Nevada National Security Site, formerly known as the Nevada Test Site, and the Semipalatinsk Test Site, which we take to represent soft-rock and hard-rock testing environments, respectively. Estimates of expected magnitude and number of aftershocks are calculated using the models for different testing and inspection scenarios. These estimates can help inform the Seismic Aftershock Monitoring System (SAMS) deployment in a potential Comprehensive Test Ban Treaty On-Site Inspection (OSI), by giving the OSI team a probabilistic assessment of potential aftershocks in the Inspection Area (IA). The aftershock assessment, combined with an estimate of the background seismicity in the IA and an empirically derived map of threshold magnitude for the SAMS network, could aid the OSI team in reporting. We apply the hard-rock model to a M5 event and combine it with the very sensitive detection threshold for OSI sensors to show that tens of events per day are expected up to a month after an explosion measured several kilometers away.

  12. Forecasting aftershock activity: 1. Adaptive estimates based on the Omori and Gutenberg-Richter laws

    Science.gov (United States)

    Baranov, S. V.; Shebalin, P. N.

    2016-05-01

    The method for forecasting the intensity of the aftershock processes after strong earthquakes in different magnitude intervals is considered. The method is based on the joint use of the time model of the aftershock process and the Gutenberg-Richter law. The time model serves for estimating the intensity of the aftershock flow with a magnitude larger than or equal to the magnitude of completeness. The Gutenberg-Richter law is used for magnitude scaling. The suggested approach implements successive refinement of the parameters of both components of the method, which is the main novelty distinguishing it from the previous ones. This approach, to a significant extent, takes into account the variations in the parameters of the frequency-magnitude distribution, which often show themselves by the decreasing fraction of stronger aftershocks with time. Testing the method on eight aftershock sequences in the regions with different patterns of seismicity demonstrates the high probability of successful forecasts. The suggested technique can be employed in seismological monitoring centers for forecasting the aftershock activity of a strong earthquake based on the results of operational processing.

  13. Investigations of Periodic Disturbances on Seismic Aftershock Recordings

    Science.gov (United States)

    Liebsch, Mattes; Gorschlüter, Felix; Knoop, Jan-Frederik; Altmann, Jürgen

    2013-04-01

    The Comprehensive Nuclear Test-Ban Treaty Organisation (CTBTO) runs the International Monitoring System (IMS) to detect possible violations of the treaty. The seismic sensors of the IMS are set up to detect every underground explosion with a yield of 1 kT TNT equivalent or even better everywhere on the world. Under consideration of all IMS data the hypocentre of a large underground explosion is located within an area of about 1000 sq km. To verify if it was a violation of the Test-Ban Treaty the CTBTO (after CTBT entry into force) is allowed to carry out an on-site inspection (OSI) in the area of suspicion. During an OSI the hypocentre is to be located much more precisely; for this a local seismic aftershock monitoring system (SAMS) can be installed to detect small seismic events caused as a consequence of the explosion, such as relaxation of the rock around the cavity. However the magnitude of these aftershock signals is extremely weak. Other difficulties arise from other seismic signals in the inspection area, for example caused by vehicles of the inspectors, from coupling of airborne signals to the ground, or even by intended attempts to disturb the OSI. While the aftershock signals have a pulsed shape, man-made seismic signals (primarily created by engines) usually show periodic characteristics and thus are representable as a sum of sine functions and their harmonics. A mathematical expression for the Hann-windowed discrete Fourier transform of the underlying sine is used to characterise every such disturbance by the amplitude, frequency and phase. The contributions of these sines are computed and subtracted from the complex spectrum sequentially. Synthetic sines superposed to real signals, orders of magnitude stronger than the latter, can be removed successfully. Removal of periodic content from the signals of a helicopter overflight reduces the amplitude by a factor 3.3 when the frequencies are approximately constant. To reduce or prevent disturbing seismic

  14. Aftershock Records in the Kathmandu Valley of the 2015 Gorkha, Nepal, Earthquake

    Science.gov (United States)

    Shigefuji, M.; Takai, N.; Sasatani, T.; Bijukchhen, S.; Ichiyanagi, M.; Rajaure, S.; Dhital, M. R.

    2015-12-01

    The devastating earthquake, named the Gorkha Earthquake, was followed by a series of aftershocks: more than 350 of them greater than M 4 and four aftershock greater than M 6. The rupture of main shock originating 80 km NW of capital Kathmandu propagated towards east. The ensuing aftershock activities are concentrated in the eastern part of the rupture area. The aftershock of Mw 6.6 occurred about half an hour later at epicentre near to that of the main shock. The other three large aftershocks however, were originated in the eastern extreme of the rupture zone. The aftershock of Mw 7.3 that occurred on 12th May 2015 brought about more damages to infrastructures already vulnerable due to the main shock. To understand the site effect of the Kathmandu valley structure, we installed continuous recording accelerometers in four different parts of the valley. Four stations were installed along a west-to-east profile of the valley at KTP (Kirtipur; hill top), TVU (Kirtipur; hill side), PTN (Patan) and THM (Thimi). The surface S-wave velocity of the KTP site was over 700 cm s-1, but for each of the other three sites it was less than 200 cm s-1. These velocities are consistent with the geological formations; KTP is above hard rock, and TVU, PTN and THM are over the lake sediment of the valley. It is normal for the amplitude of earthquake motion to be larger in areas lying above sedimentary soil than in areas above hard rock, and these motions can be amplified further by certain deep underground structures. To know deep underground structure using with aftershock records, we installed more four instruments in the Kathmandu basin after main shock. We analysed the strong-motion data of these five aftershocks recorded in the eight strong-motion accelerometers. The station of KTP is considered as reference site to compare the effect of sediments on the earthquake waves. The large aftershocks all have highest Peak Ground Velocity (PGV) at TVU and the station of KTP showed the least

  15. High-resolution relocation and mechanism of aftershocks of the 2007 Tocopilla (Chile) earthquake

    Science.gov (United States)

    Fuenzalida, A.; Schurr, B.; Lancieri, M.; Sobiesiak, M.; Madariaga, R.

    2013-08-01

    We study the distribution of the aftershocks of Tocopilla Mw 7.7 earthquake of 2007 November 14 in northern Chile in detail. This earthquake broke the lower part of the seismogenic zone at the southern end of the Northern Chile gap, a region that had its last megathrust earthquake in 1877. The aftershocks of Tocopilla occurred in several steps: the first day they were located along the coast inside the co-seismic rupture zone. After the second day they extended ocean-wards near the Mejillones peninsula. Finally in December they concentrated in the South near the future rupture zone of the Michilla intermediate depth earthquake of 2007 December 16. The aftershock sequence was recorded by the permanent IPOC (Integrated Plate Boundary Observatory in Chile) network and the temporary task force network installed 2 weeks after the main event. A total of 1238 events were identified and the seismic arrival times were directly read from seismograms. Initially we located these events using a single event procedure and then we relocated them using the double-difference method and a cross-correlation technique to measure time differences for clusters of aftershocks. We tested a 1-D velocity model and a 2-D one that takes into account the presence of the subducted Nazca Plate. Relocation significantly reduced the width of the aftershock distribution: in the inland area, the plate interface imaged by the aftershocks is thinner than 2 km. The two velocity models give similar results for earthquakes under the coast and a larger difference for events closer to the trench. The surface imaged by the aftershocks had a length of 160 km. It extends from 30 to 50 km depth in the northern part of the rupture zone; and between 5 and 55 km depth near the Mejillones peninsula. We observed a change in the dip angle of the subduction interface from 18° to 24° at a depth of 30 km. We propose that this change in dip is closely associated with the upper limit of the rupture zone of the main

  16. Stress history controls the spatial pattern of aftershocks: case studies from strike-slip earthquakes

    Science.gov (United States)

    Utkucu, Murat; Durmuş, Hatice; Nalbant, Süleyman

    2016-09-01

    Earthquake ruptures perturb stress within the surrounding crustal volume and as it is widely accepted now these stress perturbations strongly correlates with the following seismicity. Here we have documented five cases of the mainshock-aftershock sequences generated by the strike-slip faults from different tectonic environments of world in order to demonstrate that the stress changes resulting from large preceding earthquakes decades before effect spatial distribution of the aftershocks of the current mainshocks. The studied mainshock-aftershock sequences are the 15 October 1979 Imperial Valley earthquake (Mw = 6.4) in southern California, the 27 November 1979 Khuli-Boniabad (Mw = 7.1), the 10 May 1997 Qa'enat (Mw = 7.2) and the 31 March 2006 Silakhor (Mw = 6.1) earthquakes in Iran and the 13 March 1992 Erzincan earthquake (Mw = 6.7) in Turkey. In the literature, we have been able to find only these mainshocks that are mainly characterized by dense and strong aftershock activities along and beyond the one end of their ruptures while rare aftershock occurrences with relatively lower magnitude reported for the other end of their ruptures. It is shown that the stress changes resulted from earlier mainshock(s) that are close in both time and space might be the reason behind the observed aftershock patterns. The largest aftershocks of the mainshocks studied tend to occur inside the stress-increased lobes that were also stressed by the background earthquakes and not to occur inside the stress-increased lobes that fall into the stress shadow of the background earthquakes. We suggest that the stress shadows of the previous mainshocks may persist in the crust for decades to suppress aftershock distribution of the current mainshocks. Considering active researches about use of the Coulomb stress change maps as a practical tool to forecast spatial distribution of the upcoming aftershocks for earthquake risk mitigation purposes in near-real time, it is further suggested that

  17. Aftershock communication during the Canterbury Earthquakes, New Zealand: implications for response and recovery in the built environment

    Science.gov (United States)

    Julia Becker,; Wein, Anne; Sally Potter,; Emma Doyle,; Ratliff, Jamie L.

    2015-01-01

    On 4 September 2010, a Mw7.1 earthquake occurred in Canterbury, New Zealand. Following the initial earthquake, an aftershock sequence was initiated, with the most significant aftershock being a Mw6.3 earthquake occurring on 22 February 2011. This aftershock caused severe damage to the city of Christchurch and building failures that killed 185 people. During the aftershock sequence it became evident that effective communication of aftershock information (e.g., history and forecasts) was imperative to assist with decision making during the response and recovery phases of the disaster, as well as preparedness for future aftershock events. As a consequence, a joint JCDR-USGS research project was initiated to investigate: • How aftershock information was communicated to organisations and to the public; • How people interpreted that information; • What people did in response to receiving that information; • What information people did and did not need; and • What decision-making challenges were encountered relating to aftershocks. Research was conducted by undertaking focus group meetings and interviews with a range of information providers and users, including scientists and science advisors, emergency managers and responders, engineers, communication officers, businesses, critical infrastructure operators, elected officials, and the public. The interviews and focus group meetings were recorded and transcribed, and key themes were identified. This paper focuses on the aftershock information needs for decision-making about the built environment post-earthquake, including those involved in response (e.g., for building assessment and management), recovery/reduction (e.g., the development of new building standards), and readiness (e.g. between aftershocks). The research has found that the communication of aftershock information varies with time, is contextual, and is affected by interactions among roles, by other information, and by decision objectives. A number

  18. Statistical monitoring of aftershock sequences: a case study of the 2015 Mw7.8 Gorkha, Nepal, earthquake

    Science.gov (United States)

    Ogata, Yosihiko; Tsuruoka, Hiroshi

    2016-03-01

    Early forecasting of aftershocks has become realistic and practical because of real-time detection of hypocenters. This study illustrates a statistical procedure for monitoring aftershock sequences to detect anomalies to increase the probability gain of a significantly large aftershock or even an earthquake larger than the main shock. In particular, a significant lowering (relative quiescence) in aftershock activity below the level predicted by the Omori-Utsu formula or the epidemic-type aftershock sequence model is sometimes followed by a large earthquake in a neighboring region. As an example, we detected significant lowering relative to the modeled rate after approximately 1.7 days after the main shock in the aftershock sequence of the Mw7.8 Gorkha, Nepal, earthquake of April 25, 2015. The relative quiescence lasted until the May 12, 2015, M7.3 Kodari earthquake that occurred at the eastern end of the primary aftershock zone. Space-time plots including the transformed time can indicate the local places where aftershock activity lowers (the seismicity shadow). Thus, the relative quiescence can be hypothesized to be related to stress shadowing caused by probable slow slips. In addition, the aftershock productivity of the M7.3 Kodari earthquake is approximately twice as large as that of the M7.8 main shock.

  19. Large aftershocks triggering by Coulomb failure stress following the 2001 MS=8.1 great Kunlun earthquake

    Institute of Scientific and Technical Information of China (English)

    郝平; 傅征祥; 田勤俭; 刘杰; 刘桂萍

    2004-01-01

    The great Kunlun earthquake occurred on Nov. 14, 2001 in Qinghai Province, China. Five large aftershocks with magnitude larger than 5.0 occurred near the Kunlun fault after main shock. Calculations of the change in Coulomb failure stress reveal that 4 of 5 large aftershocks occurred in areas with △σf>0 ~10(2~10-1 MPa) and one aftershock occurred in an area with △σf =-0.56 MPa. It is concluded that the permanent fault displacement due to the main shock is the main cause of activity of large aftershocks, but not the whole cause.

  20. Aftershocks of 26th January 2001 Bhuj earthquake and seismotectonics of the Kutch region

    Indian Academy of Sciences (India)

    K S Misra; R Bhutani; R Sonp

    2003-09-01

    The 26th January 2001 Bhuj earthquake was followed by intense aftershock activity. Aftershock data from United States Geological Survey (USGS) utilized in this study encompasses three months period from 26th January to 26th April 2001. Epicenters of the aftershock are plotted on a map depicting active faults. All the aftershocks of magnitude > 5 and 70% of those ranging between magnitude 3 and 5 are confined to an area resembling a horseshoe pattern with a pointed end towards NE. The other 20% of magnitude 3 to 5 are enclosed within an almost parallel boundary. Only 10% are found to be beyond this limiting boundary. 50% of the recorded aftershocks took place within the first week of the main event and this study reveals that the basic characteristic pattern of aftershock activity can be determined on the basis of the data of only one week. Four major NW-SE trending active faults are mapped in the Kutch region. They define the western limit of Cambay structure and also mark the western limit of Dharangadhra and Wadhwan basins along the SE continuation in Saurashtra. These faults separate the Kutch region into two geologically different blocks. On the SW side the mapped horseshoe pattern gets characteristically truncated along the western most fault, which is characterized by a strike-slip movement in the south and vertical movement in the north. The present study has revealed that the epicenter of the 26th January earthquake is located in the vicinity of the Bhachau township, close to the intersection with the Kutch mainland fault. Furthermore, it has been noticed that most of the epicenters of the aftershock are confined in the intersectional area of the Kutch mainland fault and the NW-SE faults.

  1. Spectral scaling of the aftershocks of the Tocopilla 2007 earthquake in northern Chile

    Science.gov (United States)

    Lancieri, M.; Madariaga, R.; Bonilla, F.

    2012-04-01

    We study the scaling of spectral properties of a set of 68 aftershocks of the 2007 November 14 Tocopilla (M 7.8) earthquake in northern Chile. These are all subduction events with similar reverse faulting focal mechanism that were recorded by a homogenous network of continuously recording strong motion instruments. The seismic moment and the corner frequency are obtained assuming that the aftershocks satisfy an inverse omega-square spectral decay; radiated energy is computed integrating the square velocity spectrum corrected for attenuation at high frequencies and for the finite bandwidth effect. Using a graphical approach, we test the scaling of seismic spectrum, and the scale invariance of the apparent stress drop with the earthquake size. To test whether the Tocopilla aftershocks scale with a single parameter, we introduce a non-dimensional number, ?, that should be constant if earthquakes are self-similar. For the Tocopilla aftershocks, Cr varies by a factor of 2. More interestingly, Cr for the aftershocks is close to 2, the value that is expected for events that are approximately modelled by a circular crack. Thus, in spite of obvious differences in waveforms, the aftershocks of the Tocopilla earthquake are self-similar. The main shock is different because its records contain large near-field waves. Finally, we investigate the scaling of energy release rate, Gc, with the slip. We estimated Gc from our previous estimates of the source parameters, assuming a simple circular crack model. We find that Gc values scale with the slip, and are in good agreement with those found by Abercrombie and Rice for the Northridge aftershocks.

  2. IDENTIFICATION OF EARTHQUAKE AFTERSHOCK AND SWARM SEQUENCES IN THE BAIKAL RIFT ZONE

    Directory of Open Access Journals (Sweden)

    N. A. Radziminovich

    2015-09-01

    Full Text Available The catalog of earthquakes (КR³6.6 which occurred in the Baikal rift zone (BRZ was declastered, and the results are presented in the article. Aftershocks of seismic events (КR³12.5 were determined by the software developed by V.B. Smirnov (Lomonosov Moscow State University with application of the algorithm co-authored by G.M. Molchan and O.E. Dmitrieva. To ensure proper control of the software application, aftershocks were also selected manually. The results of declustering show that aftershocks of the earthquakes (КR³12.5 account for about 25 per cent of all seismic events in the regional catalog. Aftershocks accompanied 90 per cent of all the earthquakes considered as main shocks. Besides, earthquake swarms, including events with КR³11, were identified. The results of this study show that, in the BRZ, the swarms and strong events with aftershocks are not spatially separated, and this conclusion differs from the views of the previous studies that reviewed data from a shorter observation period. Moreover, it is noted that the swarms may consist of several main shocks accompanied by aftershocks. The data accumulated over the last fifty years of instrumental observations support the conclusion made earlier that the swarms in BRZ occur mainly in the north-eastward direction from Lake Baikal and also confirm the trend of a small number of aftershocks accompanying earthquakes in the south-western part of the Baikal rift zone.

  3. On the origin of diverse aftershock mechanisms following the 1989 Loma Prieta earthquake

    Science.gov (United States)

    Kilb, Debi; Ellis, M.; Gomberg, J.; Davis, S.

    1997-01-01

    We test the hypothesis that the origin of the diverse suite of aftershock mechanisms following the 1989 M 7.1 Loma Prieta, California, earthquake is related to the post-main-shock static stress field. We use a 3-D boundary-element algorithm to calculate static stresses, combined with a Coulomb failure criterion to calculate conjugate failure planes at aftershock locations. The post-main-shock static stress field is taken as the sum of a pre-existing stress field and changes in stress due to the heterogeneous slip across the Loma Prieta rupture plane. The background stress field is assumed to be either a simple shear parallel to the regional trend of the San Andreas fault or approximately fault-normal compression. A suite of synthetic aftershock mechanisms from the conjugate failure planes is generated and quantitatively compared (allowing for uncertainties in both mechanism parameters and earthquake locations) to well-constrained mechanisms reported in the US Geological Survey Northern California Seismic Network catalogue. We also compare calculated rakes with those observed by resolving the calculated stress tensor onto observed focal mechanism nodal planes, assuming either plane to be a likely rupture plane. Various permutations of the assumed background stress field, frictional coefficients of aftershock fault planes, methods of comparisons, etc. explain between 52 and 92 per cent of the aftershock mechanisms. We can explain a similar proportion of mechanisms however by comparing a randomly reordered catalogue with the various suites of synthetic aftershocks. The inability to duplicate aftershock mechanisms reliably on a one-to-one basis is probably a function of the combined uncertainties in models of main-shock slip distribution, the background stress field, and aftershock locations. In particular we show theoretically that any specific main-shock slip distribution and a reasonable background stress field are able to generate a highly variable suite of failure

  4. Main shock and aftershocks of the December 13, 1990, Eastern Sicily earthquake

    Directory of Open Access Journals (Sweden)

    M. Di Bona

    1995-06-01

    Full Text Available n this paper we describe the location and the fault plane solution of the December 13, 1990, Eastern Sicily earthquake (ML = 5.4, and of its aftershock sequence. Because the main shock location is not well constrained due to the geometry of the permanent National Seismic Network in this area, we used a "master event" algorithm to locate it in relation to a well located aftershock. The revised location is slightly offshore Eastern Sicily, 4.8 km north of the largest aftershock (ML = 4.6 that occurred on December 16, 1990. The main shock has a strike-slip mechanism, indicating SE-NW compression with either left lateral motion on a NS plane, or right lateral on an EW plane. Two days after the main event we deployed a local network of eight digital stations, that provided accurate locations of the aftershocks, and the estimate of source parameters for the strongest earthquake. We observed an unusual quiescence after the ML = 5.4 event, that lasted until December 16, when a ML = 4.6 earthquake occurred. The fault plane solution of this aftershock shows normal faulting on E-W trending planes. Between December 16 and January 6, 1991, a sequence of at least 300 aftershock" was recorded by the local network. The well located earthquakes define a small source region of approximately 5 x 2 x 5 km3, with hypocentral depths ranging between 15 and 20 km. The paucity of large aftershocks, the time gap between the main shock occurrence and the beginning of the aftershock sequence (3.5 days, their different focal mechanisms (strike-slip vs. normal, and the different stress drop between main shock and after- shock suggest that the ML = 5.4 earthquake is an isolated event. The sequence of aftershocks began with the ML = 4.6 event, which is probably linked to the main shock with a complex mechanism of stress redistribution after the main faulting episode.

  5. Generalized Omori-Utsu law for aftershock sequences in southern California

    Science.gov (United States)

    Davidsen, J.; Gu, C.; Baiesi, M.

    2015-05-01

    We investigate the validity of a proposed generalized Omori-Utsu law for the aftershock sequences for the Landers, Hector Mine, Northridge and Superstition Hills earthquakes, the four largest events in the southern California catalogue we analyse. This law unifies three of the most prominent empirical laws of statistical seismology-the Gutenberg-Richter law, the Omori-Utsu law, and a generalized version of Båth's law-in a formula casting the parameters in the Omori-Utsu law as a function of the lower magnitude cutoff mc for the aftershocks considered. By applying a recently established general procedure for identifying aftershocks, we confirm that the generalized Omori-Utsu law provides a good approximation for the observed rates overall. In particular, we provide convincing evidence that the characteristic time c is not constant but a genuine function of mc, which cannot be attributed to short-term aftershock incompleteness. However, the estimation of the specific parameters is somewhat sensitive to the aftershock selection method used. This includes c(mc), which has important implications for inferring the underlying stress field.

  6. Aftershock triggering by postseismic stresses: A study based on Coulomb rate-and-state models

    Science.gov (United States)

    Cattania, Camilla; Hainzl, Sebastian; Wang, Lifeng; Enescu, Bogdan; Roth, Frank

    2015-04-01

    The spatiotemporal clustering of earthquakes is a feature of medium- and short-term seismicity, indicating that earthquakes interact. However, controversy exists about the physical mechanism behind aftershock triggering: static stress transfer and reloading by postseismic processes have been proposed as explanations. In this work, we use a Coulomb rate-and-state model to study the role of coseismic and postseismic stress changes on aftershocks and focus on two processes: creep on the main shock fault plane (afterslip) and secondary aftershock triggering by previous aftershocks. We model the seismic response to Coulomb stress changes using the Dieterich constitutive law and focus on two events: the Parkfield, Mw = 6.0, and the Tohoku, Mw = 9.0, earthquakes. We find that modeling secondary triggering systematically improves the maximum log likelihood fit of the sequences. The effect of afterslip is more subtle and difficult to assess for near-fault events, where model errors are largest. More robust conclusions can be drawn for off-fault aftershocks: following the Tohoku earthquake, afterslip promotes shallow crustal seismicity in the Fukushima region. Simple geometrical considerations indicate that afterslip-induced stress changes may have been significant on trench parallel crustal fault systems following several of the largest recorded subduction earthquakes. Moreover, the time dependence of afterslip strongly enhances its triggering potential: seismicity triggered by an instantaneous stress change decays more quickly than seismicity triggered by gradual loading, and as a result we find afterslip to be particularly important between few weeks and few months after the main shock.

  7. Decay of aftershock density with distance does not indicate triggering by dynamic stress.

    Science.gov (United States)

    Richards-Dinger, Keith; Stein, Ross S; Toda, Shinji

    2010-09-30

    Resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard. Felzer and Brodsky examined the distance distribution of earthquakes occurring in the first five minutes after 2 ≤ M aftershocks showed a uniform power-law decay with slope -1.35 out to 50 km from the mainshocks. From this they argued that the distance decay could be explained only by dynamic triggering. Here we propose an alternative explanation for the decay, and subject their hypothesis to a series of tests, none of which it passes. At distances more than 300 m from the 2 ≤ M aftershocks, is absent at distances exceeding 10 km from the mainshocks. Finally, the distance decay is found among aftershocks that occur before the arrival of the seismic wave front from the mainshock, which violates causality. We argue that Felzer and Brodsky implicitly assume that the first of two independent aftershocks along a fault rupture triggers the second, and that the first of two shocks in a creep- or intrusion-driven swarm triggers the second, when this need not be the case.

  8. Micro-earthquakes"Justunderneath"Seismic Stations as Ground Truth Events1 Application to the 2008 Wenchuan Aftershock Sequence

    Institute of Scientific and Technical Information of China (English)

    Liu Chun; Wu Zhongliang; Jiang Changsheng

    2008-01-01

    Analyzing the aftershock sequence of the 2008 Wenchuan earthquake,we considered 26 microearthquakes"just underneath"seismic stations.Making use of such special station-event configurations to determine the depth of these micro-earthquakes provided accurate relocation of aftershocks with a reference set of"ground truth (GT) events".

  9. Scaling Analysis of Time Distribution between Successive Earthquakes in Aftershock Sequences

    Directory of Open Access Journals (Sweden)

    Marekova Elisaveta

    2016-08-01

    Full Text Available The earthquake inter-event time distribution is studied, using catalogs for different recent aftershock sequences. For aftershock sequences following the Modified Omori’s Formula (MOF it seems clear that the inter-event distribution is a power law. The parameters of this law are defined and they prove to be higher than the calculated value (2 – 1/p. Based on the analysis of the catalogs, it is determined that the probability densities of the inter-event time distribution collapse into a single master curve when the data is rescaled with instantaneous intensity, R(t; Mth, defined by MOF. The curve is approximated by a gamma distribution. The collapse of the data provides a clear view of aftershock-occurrence self-similarity.

  10. Calculation of Calibration Functions and Explosive Aftershock Magnitudes in the Near Field

    Institute of Scientific and Technical Information of China (English)

    Li Xuezheng; Wang Haijun; Lei Jun

    2003-01-01

    The current calibration function used in calculating the magnitude of natural earthquakes within 5km is a constant; a fact that causes several serious difficulties for the calculation of the magnitude of small and shallow-focus earthquakes. According to the attenuation law of explosions and the propagation theory of elastic waves, the calibration function is calculated for near field quakes from 0km to 5km. Magnitudes of two aftershock sequences are calculated.The magnitudes of most explosion earthquakes are small, ranging mainly from magnitude 0.5 to 1.0. The M-t chart of the explosive aftershocks is completely different from that of strong earthquake aftershocks. It not only shows positive columnar lines indicating large magnitudes but also short negative columnar lines indicating small magnitudes.

  11. Missing data in aftershock sequences: explaining the deviations from scaling laws.

    Science.gov (United States)

    Lennartz, Sabine; Bunde, Armin; Turcotte, Donald L

    2008-10-01

    In this paper we extend the branching aftershock sequence model to study the role of missing data at short times and small amplitudes after a mainshock. We apply this model, which contains three parameters characterizing the missing data, to the magnitude and temporal statistics of four aftershock sequences in California. We find that the observed time-dependent deviations of the frequency-magnitude scaling from the Gutenberg-Richter power law dependency can be described quantitatively by the model. We also show that, for the same set of parameters, the model is able to explain quantitatively the observed magnitude-dependent deviations of the temporal decay of aftershocks from Omori's law. In addition, we show that the same sets of data can also reproduce quite well the various functional forms of the probability density functions of the return times between consecutive events with magnitudes above a prescribed threshold, as well as the violation of scaling at short and intermediate time scales.

  12. Scaling Analysis of Time Distribution between Successive Earthquakes in Aftershock Sequences

    Science.gov (United States)

    Marekova, Elisaveta

    2016-08-01

    The earthquake inter-event time distribution is studied, using catalogs for different recent aftershock sequences. For aftershock sequences following the Modified Omori's Formula (MOF) it seems clear that the inter-event distribution is a power law. The parameters of this law are defined and they prove to be higher than the calculated value (2 - 1/p). Based on the analysis of the catalogs, it is determined that the probability densities of the inter-event time distribution collapse into a single master curve when the data is rescaled with instantaneous intensity, R(t; Mth), defined by MOF. The curve is approximated by a gamma distribution. The collapse of the data provides a clear view of aftershock-occurrence self-similarity.

  13. Strong aftershocks in the northern segment of the Wenchuan earthquake rupture zone and their seismotectonic implications

    Science.gov (United States)

    Zheng, Yong; Ni, Sidao; Xie, Zujun; Lv, Jian; Ma, Hongsheng; Sommerville, Paul

    2010-11-01

    More than 28, 000 aftershocks have occurred since the 05/12/2008 Wenchuan earthquake, with dozens of them stronger than M 5. Since July, 2008, all the M > 5 earthquakes have occurred only in the northern segment of the rupture zone, suggesting obvious seismicity segmentation. We applied the double difference method to relocate all of the M > 3 aftershocks. After relocation, the aftershocks show a compact zone of seismicity, with a length of about 300 km and average width of 30 km, supporting that the hypothesis that the Beichuan-Yingxiu and Chaping-Linjiaan faults are the faults that ruptured in the earthquake. With the Cut and Paste (CAP) waveform inversion algorithm, we determined the source mechanism and focal depth of all the > M 5 aftershocks in the northern segments. The number of thrust events is close to the number of strike-slip events, but almost all of the events with thrust mechanism are distributed over the northern segment, while the aftershocks with strike-slip mechanism only occurred at the north-easternmost end, contrasting with field observations of a substantial strike-slip component of surface rupture over the northern segment. The events with strike-slip mechanism occurred at depths up to 18 km, consistent with the lack of surface rupture in the north-easternmost section. However, since early August, very shallow events (2 km) with thrust mechanism have occurred, probably releasing the strain energy of the unruptured fault in the north-easternmost section. It seems that the seismic hazard potential of the northern segment is still quite high, and more studies are needed to resolve some of the discrepancy suggested by aftershock patterns and other observations.

  14. GIS-based 3D visualization of the Mw 7.7, 2007, Tocopilla aftershocks

    Science.gov (United States)

    Eggert, S.; Sobiesiak, M.; Altenbrunn, K.

    2009-12-01

    The November 14, 2007 Mw 7.7 earthquake nucleated on the west coast of northern Chile about 40 km east of the city of Tocopilla. It took place in the southern part of a large seismic gap, the Iquique subduction zone segment which is supposed to be at the end of its seismic cycle. The Tocopilla fault plane appears to be the northern continuation of the Mw 8.0, 1995 Antofagasta earthquake. We present a complex 3D model of the rupture area including first hypocenter localizations of aftershocks following the event. The data was recorded during a mission of the German Task Force for Earthquakes after the 2007 Tocopilla earthquake. The seismic stations were recording the aftershocks from November 2007 until May 2008. In general, subduction zones have a complex structure where most of the volumes examined are characterized by strong variations in physical and material parameters. Therefore, 3D representation of the geophysical and geological conditions to be found are of great importance to understand such a subduction environment. We start with a two-dimensional visualization of the geological and geophysical setting. In a second step, we use GIS as a three-dimensional modeling tool which gives us the possibility to visualize the complex geophysical processes. One can easily add and delete data and focus on the information one needs. This allows us to investigate the aftershock distribution along the subducting slab and identify clear structures and clusters within the data set. Furthermore we combine the 2007 Tocopilla data set with the 1995 Antofagasta aftershocks which provides a new, three-dimensional insight into the segment boundary of these two events. Analyzing the aftershock sequence with a GIS-based model will not only help to visualize the setting but also be the base for various calculations and further explorations of the complex structures. Aftershocks following the 1995 Antofagasta earthquake and the 2007 Tocopilla earthquake

  15. Study on the Triggering Effect of the October,2005 Pakistan Mw7.6 Earthquake on Its Aftershocks

    Institute of Scientific and Technical Information of China (English)

    Wan Yongge; Shen Zhengkang; Shang Dan

    2007-01-01

    The influences upon aftershocks of Coulomb failure stress change (CFSC) generated by the main-shock of the October 8,2005,Pakistan earthquake are calculated and analyzed.The following factors are included in the calculation:(1) the difference between the pore fluid pressure and the medium elastic constant in the fault plane area and those of its surrounding medium;(2) the tectonic stress direction of the seismic source area;(3) the aftershock failure mechanism of aftershocks is calculated by stacking the tectonic stress with the stress change generated by the main-shock.Our study,which includes many factors,fits fairly well with the aftershock distribution.It indicates that most of the aftershocks were triggered by the Pakistan main-shock that occurred on October 8, 2005.

  16. Spatial and temporal analysis of the Mw 7.7, 2007, Tocopilla aftershock sequence

    Science.gov (United States)

    Eggert, Silke; Sobiesiak, Monika

    2010-05-01

    On 14 November 2007, 15:40:51 UTC a large Mw 7.7 earthquake occurred in the region of Tocopilla in Northern Chile. The epicenter is located at 22.30°S, 69.89°W, ~ 35 km south east of the city of Tocopilla and 160 km north of Antofagasta (earthquake location by GEOFON network). The earthquake took place in the southern part of the Northern Chile seismic gap which is supposed to be at the end of its seismic cycle. Currently, the gap is spanning the rupture area of the Mw=9 1877 Iquique event, a region which is now unbroken for almost 150 years. Therefore, the 2007 Tocopilla earthquake is the first large event that occurred inside the Northern Chile seismic gap since 1877. We present a study of the spatial and temporal distribution of the aftershock activity following the 2007 Tocopilla event using the frequency-magnitude distribution and other parameters. Studying this aftershock sequence will provide closer insight into the fault dimension of this subduction zone earthquake and the tectonic setting of the region. The distribution of aftershocks into depth shows that the majority of the hypocenters are located along the subduction interface, reaching down to ~ 50 km depth. In the western part, the aftershock sequence splits into two branches, one heading towards the trench, the other bending into the crust in front of the Mejillones Peninsula. In the epicentral horizontal, we observe a concentration of aftershocks around the northern part of the Mejillones Peninsula and along the coast up to the Río Loa. This leads to the conclusion that the shallow part in the north west did probably not break during the event. The spatial density of aftershocks shows two offshore patches north-east of the peninsula. Analyzing the spatio-temporal distribution of our aftershock data set, we can see that the fault rupture propagated towards the south west with a fault plane of about 150 km length. These observations are consistent with first results by other studies. Our

  17. Bath's law Derived from the Gutenberg-Richter law and from Aftershock Properties

    CERN Document Server

    Helmsttetter, A; Helmsttetter, Agnes; Sornette, Didier

    2003-01-01

    The empirical Bath's law states that the average magnitude difference between a mainshock and its largest aftershock is 1.2, regardless of the mainshock magnitude. We first point out that the standard interpretation of Bath's law in terms of the two largest events of a self-similar set of independent events is incorrect, because it neglects the selection procedure entering the definition of aftershocks. We reconcile Bath's law with (i) the existence of a universal Gutenberg-Richter law for all earthquakes and (ii) with the empirical observation (productivity law) that each earthquake of magnitude m triggers other earthquakes at a rate ~10^(alpha m) with alpha~0.8.

  18. How ubiquitous are aftershock sequences driven by high pressure fluids at depth?

    Science.gov (United States)

    Miller, S. A.

    2008-12-01

    Strong evidence suggests that two earthquake-aftershock episodes, the 2004 Niigata (Japan) sequence and the 1997 Umbria-Marche (Italy) sequence, were driven by high pressure fluids at depth. Since Niigata was in a compressional environment and Umbria-Marche in extension, a question arises about whether such a mechanism is more general than just these two cases. Although it is not clear by what mechanism fluids of sufficient volume can be trapped in the lower crust, if such pockets of high pressure fluids exist, then they must necessarily be expelled when a large earthquake provides the hydraulic connection to the hydrostatically pressured free surface. In this talk, aftershock data is analyzed for a number of different earthquakes in a variety of tectonic settings, including 1992 Landers, 1994 Northridge, and the 2001 Bhuj earthquakes. Comparisons are made between model results of the evolved fluid pressure state from a high pressure source at depth, and the spatio-temporal distributions of aftershocks. The data is further analyzed and compared with model results for differences in the rate of aftershocks (p-value in Omori's Law) and their dependence on the orientation of the mainshock relative to the prevailing regional stress field.

  19. Spatial variation of the aftershock activity across the Kachchh Rift Basin and its seismotectonic implications

    Indian Academy of Sciences (India)

    A P Singh; O P Mishra; Dinesh Kumar; Santosh Kumar; R B S Yadav

    2012-04-01

    We analyzed 3365 relocated aftershocks with magnitude of completeness () ≥ 1.7 that occurred in the Kachchh Rift Basin (KRB) between August 2006 and December 2010. The analysis of the new aftershock catalogue has led to improved understanding of the subsurface structure and of the aftershock behaviour. We characterized aftershock behaviour in terms of -value, -value, spatial fractal dimension (s), and slip ratio (ratio of the slip that occurred on the primary fault and that of the total slip). The estimated -value is 1.05, which indicates that the earthquake occurred due to active tectonics in the region. The three dimensional -value mapping shows that a high -value region is sandwiched around the 2001 Bhuj mainshock hypocenter at depths of 20–25 km between two low -value zones above and below this depth range. The s-value was estimated from the double-logarithmic plot of the correlation integral and distance between hypocenters, and is found to be 2.64 ± 0.01, which indicates random spatial distribution beneath the source zone in a two-dimensional plane associated with fluid-filled fractures. A slip ratio of about 0.23 reveals that more slip occurred on secondary fault systems in and around the 2001 Bhuj earhquake (Mw 7.6) source zone in KRB.

  20. Aftershock source mechanisms from the June 9, 1994, Deep Bolivian Earthquake

    Science.gov (United States)

    Tinker, Mark Andrew; Wallace, Terry C.; Beck, Susan L.; Silver, Paul G.; Zandt, George

    The Mw 8.3 Bolivia earthquake occurred on June 9, 1994, at a depth of 636 km. This is the largest deep event in recorded history and ruptured a portion of the down-going Nazca slab unknown to have ruptured previously. We recorded the main shock and aftershocks on the BANJO and SEDA portable, broadband seismic arrays deployed in Bolivia during this event. Myers et al. (this issue) identified and located 36 aftershocks (M>2) for the 10-day period following the main shock. We use a grid search technique to determine focal mechanisms for 12 of these aftershocks ranging in magnitude from 2.7 to 5.3. We compare the observed P to SV and SH ratios to a series of synthetics that represent different fault plane orientations. We find consistent focal mechanisms with the T-axis roughly horizontal and oriented approximately east-west, and the P-axis predominantly vertical. The aftershock focal mechanisms indicate a rotation of the P-axis within the slab from down-dip compression prior to the main shock to a near-vertical direction afterwards. This observation is consistent with the release of shear stress on the near-horizontal rupture plane and the subsequent rotation of the maximum compressive stress to a fault -normal orientation.

  1. Comparing the Hawkes and Trigger process models for aftershock sequences following the 2005 Kashmir earthquake

    NARCIS (Netherlands)

    Türkyilmaz, K.; Lieshout, M.N.M.; Stein, A.

    2013-01-01

    In an earlier study (Van Lieshout and Stein in Math Gesoci 44(3):309–326, 2012) we postulated the existence of two major earthquakes in the 2005 Kashmir disaster instead of a single one, based upon the pattern of aftershocks. In this study, we explore this hypothesis further by fitting several spati

  2. Aftershock seismicity and Tectonic Setting of the 16 September 2015 Mw 8.3 Illapel earthquake

    Science.gov (United States)

    Lange, Dietrich; Geersen, Jacob; Barrientos, Sergio; Moreno, Marcos; Grevemeyer, Ingo; Contreras-Reyes, Eduardo; Kopp, Heidrun

    2016-04-01

    Powerful subduction zone earthquakes rupture thousands of square kilometers along continental margins but at certain locations earthquake rupture terminates. On 16 September 2015 the Mw. 8.3 Illapel earthquake ruptured a 200 km long stretch of the Central Chilean subduction zone, triggering a tsunami and causing significant damage. Here we analyze the spatial pattern of coseismic rupture and the temporal and spatial pattern of local seismicity for aftershocks and foreshocks in relation to the tectonic setting in the earthquake area. Aftershock seismicity surrounds the rupture area in lateral and downdip direction. For the first 24 hours following the mainshock we observe aftershock migration to both lateral directions with velocities of approximately 2.5 and 5 km/h. At the southern earthquake boundary aftershocks cluster around individual subducted seamounts located on the prolongation of the downthrusting Juan Fernández Ridge indicating stress transfer from the main rupture area. In the northern part of the rupture area a deeper band of local seismicity is observed indicating an alternation of seismic to aseismic behavior of the plate interface in downdip direction. This aseismic region at ~30 km depth that is also observed before the Illapel 2015 earthquake is likely controlled by the intersection of the continental Moho with the subducting slab.

  3. Relocation of the M8.0 Wenchuan earthquake and its aftershock sequence

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    We relocated M8.0 Wenchuan earthquake and 2706 aftershocks with M≥2.0 using double-difference algorithm and obtained relocations of 2553 events. To reduce the influence of lateral variation in crustal and upper mantle velocity structure, we used different velocity models for the east and west side of Longmenshan fault zone. In the relocation process, we added seismic data from portable seismic sta-tions close to the shocks to constrain focal depths. The precisions in E-W, N-S, and U-D directions after relocation are 0.6, 0.7, and 2.5 km respectively. The relocation results show that the aftershock epi-centers of Wenchuan earthquake were distributed in NE-SW direction, with a total length of about 330 km. The aftershocks were concentrated on the west side of the central fault of Longmenshan fault zone, excluding those on the north of Qingchuan, which obviously deviated from the surface fault and passed through Pingwu-Qingchuan fault in the north. The dominant focal depths of the aftershocks are between 5 and 20 km, the average depth is 13.3 km, and the depth of the relocated main shock is 16.0 km. The depth profile reveals that focal depth distribution in some of the areas is characterized by high-angle westward dipping. The rupture mode of the main shock features reverse faulting in the south, with a large strike-slip component in the north.

  4. Relocation of the M8.0 Wenchuan earthquake and its aftershock sequence

    Institute of Scientific and Technical Information of China (English)

    HUANG Yuan; WU JianPing; ZHANG TianZhong; ZHANG DongNing

    2008-01-01

    We relocated MB.0 Wenchuan earthquake and 2706 aftershocks with M≥2.0 using double-difference algorithm and obtained relocations of 2553 events. To reduce the influence of lateral variation in crustal and upper mantle velocity structure, we used different velocity models for the east and west side of Longmenshan fault zone. In the relocation process, we added seismic data from portable seismic stations close to the shocks to constrain focal depths. The precisions in E-W, N-S, and U-D directions after relocation are 0.6, 0.7, and 2.5 km respectively. The relocation results show that the aftershock epicenters of Wenchuan earthquake were distributed in NE-SW direction, with a total length of about 330km. The aftershocks were concentrated on the west side of the central fault of Longmenshan fault zone,excluding those on the north of Qingchuan, which obviously deviated from the surface fault and passed through Pingwu-Qingchuan fault in the north. The dominant focal depths of the aftershocks are between 5 and 20 km, the average depth is 13.3 km, and the depth of the relocated main shock is 16.0km. The depth profile reveals that focal depth distribution in some of the areas is characterized by high-angle westward dipping. The rupture mode of the main shock features reverse faulting in the south, with a large strike-slip component in the north.

  5. The Rule of Dynamic Strain to Near Source Aftershock Distribution of the 2014, Mw 6.0, Napa (California) Earthquake

    Science.gov (United States)

    Emolo, A.; De Matteis, R.; Convertito, V.

    2015-12-01

    The 2014 Napa was recognized as a right-lateral strike-slip fault. About 400 aftershocks occurred, mainly in the near-source range, in the two months after the earthquake. They mostly occurred between 8 and 11 km depth interesting an area of about 10 km2 north-northwest-trending with respect to the mainshock hypocenter. However, the aftershock distribution was not able to constrain the mainshock fault plane. Since Parsons et al. (2014) have shown that Coulomb static stress change does not completely explain near-source aftershock distribution, we explore whether dynamic strain transfer, enhanced by source directivity, contributed to trigger the aftershock sequence. Indeed, dynamic strain transfer triggering attributes enhanced failure probabilities to increased shear stresses or strains, to permeability changes and maybe to fault weakening. In this respect, we observe that a single inverse power law fits the decay of aftershock density as function of distance from the fault plane, suggesting that dynamic stress/strain might have played a role in the aftershocks triggering. To test this hypothesis, we used Peak-Ground Velocities (PGVs) as a proxy for peak-dynamic strain/stress field, accounting for both fault finiteness and source directivity. We first use a point source to retrieve the best parameters of the directivity function from the inversion of the PGVs. Next, the same PGVs are used to jointly infer the surface fault projection and the dominant horizontal rupture direction. Finally, we map the peak-dynamic strain/stress, modified by source geometry and directivity, to resolve the relationship between the aftershocks location and the areas of large dynamic strain values. Thus, we believe that dynamic strain/stress actually contributed to the Napa aftershock distribution. Our results may help to better constrain the Napa causative fault and complement Coulomb static stress change to identify areas that will be more likely affected by aftershocks.

  6. Three Dimensional P Wave Velocity Model for the Crust Containing Aftershocks of the Bhuj, India Earthquake

    Science.gov (United States)

    Powell, C. A.; Vlahovic, G.; Bodin, P.; Horton, S.

    2001-12-01

    A three-dimensional P wave velocity model has been constructed for the crust in the vicinity of the Mw=7.7 January 26th Bhuj, India earthquake using aftershock data obtained by CERI away teams. Aftershocks were recorded by 8 portable, digital K2 seismographs (the MAEC/ISTAR network) and by a continuously recording Guralp CMG40TD broad-band seismometer. Station spacing is roughly 30 km. The network was in place for 18 days and recorded ground motions from about 2000 aftershocks located within about 100 km of all stations. The 3-D velocity model is based upon an initial subset of 461 earthquakes with 2848 P wave arrivals. The initial 1-D velocity model was determined using VELEST and the 3-D model was determined using the nonlinear travel time tomography method of Benz et al. [1996]. Block size was set at 2 by 2 by 2 km. A 45% reduction in RMS travel time residuals was obtained after 10 iterations holding hypocenters fixed. We imaged velocity anomalies in the range -2 to 4%. Low velocities were found in the upper 6 km and the anomalies follow surface features such as the Rann of Kutch. High velocity features were imaged at depth and are associated with the aftershock hypocenters. High crustal velocities are present at depths exceeding 20 km with the exception of the crust below the Rann of Kutch. The imaged velocity anomaly pattern does not change when different starting models are used and when hypocenters are relocated using P wave arrivals only. The analysis will be extended to an expanded data set of 941 aftershocks.

  7. Effects of Aftershock Declustering in Risk Modeling: Case Study of a Subduction Sequence in Mexico

    Science.gov (United States)

    Kane, D. L.; Nyst, M.

    2014-12-01

    Earthquake hazard and risk models often assume that earthquake rates can be represented by a stationary Poisson process, and that aftershocks observed in historical seismicity catalogs represent a deviation from stationarity that must be corrected before earthquake rates are estimated. Algorithms for classifying individual earthquakes as independent mainshocks or as aftershocks vary widely, and analysis of a single catalog can produce considerably different earthquake rates depending on the declustering method implemented. As these rates are propagated through hazard and risk models, the modeled results will vary due to the assumptions implied by these choices. In particular, the removal of large aftershocks following a mainshock may lead to an underestimation of the rate of damaging earthquakes and potential damage due to a large aftershock may be excluded from the model. We present a case study based on the 1907 - 1911 sequence of nine 6.9 Mexico in order to illustrate the variability in risk under various declustering approaches. Previous studies have suggested that subduction zone earthquakes in Mexico tend to occur in clusters, and this particular sequence includes events that would be labeled as aftershocks in some declustering approaches yet are large enough to produce significant damage. We model the ground motion for each event, determine damage ratios using modern exposure data, and then compare the variability in the modeled damage from using the full catalog or one of several declustered catalogs containing only "independent" events. We also consider the effects of progressive damage caused by each subsequent event and how this might increase or decrease the total losses expected from this sequence.

  8. Implications of spatial and temporal development of the aftershock sequence for the Mw 8.3 June 9, 1994 Deep Bolivian Earthquake

    Science.gov (United States)

    Myers, Stephen C.; Wallace, Terry C.; Beck, Susan L.; Silver, Paul G.; Zandt, George; Vandecar, John; Minaya, Estela

    On June 9, 1994 the Mw 8.3 Bolivia earthquake (636 km depth) occurred in a region which had not experienced significant, deep seismicity for at least 30 years. The mainshock and aftershocks were recorded in Bolivia on the BANJO and SEDA broadband seismic arrays and on the San Calixto Network. We used the joint hypocenter determination method to determine the relative location of the aftershocks. We have identified no foreshocks and 89 aftershocks (m > 2.2) for the 20-day period following the mainshock. The frequency of aftershock occurrence decreased rapidly, with only one or two aftershocks per day occuring after day two. The temporal decay of aftershock activity is similar to shallow aftershock sequences, but the number of aftershocks is two orders of magnitude less. Additionally, a mb ∼6, apparently triggered earthquake occurred just 10 minutes after the mainshock about 330 km east-southeast of the mainshock at a depth of 671 km. The aftershock sequence occurred north and east of the mainshock and extends to a depth of 665 km. The aftershocks define a slab striking N68°W and dipping 45°NE. The strike, dip, and location of the aftershock zone are consistent with this seismicity being confined within the downward extension of the subducted Nazca plate. The location and orientation of the aftershock sequence indicate that the subducted Nazca plate bends between the NNW striking zone of deep seismicity in western Brazil and the N-S striking zone of seismicity in central Bolivia. A tear in the deep slab is not necessitated by the data. A subset of the aftershock hypocenters cluster along a subhorizontal plane near the depth of the mainshock, favoring a horizontal fault plane. The horizontal dimensions of the mainshock [Beck et al., this issue; Silver et al., 1995] and slab defined by the aftershocks are approximately equal, indicating that the mainshock ruptured through the slab.

  9. Aftershock Sequences Modeled with 3-D Stress Heterogeneity and Rate-State Seismicity Equations: Implications for Crustal Stress Estimation

    OpenAIRE

    Smith, Deborah Elaine; Dieterich, James H.

    2010-01-01

    In this paper, we present a model for studying aftershock sequences that integrates Coulomb static stress change analysis, seismicity equations based on rate-state friction nucleation of earthquakes, slip of geometrically complex faults, and fractal-like, spatially heterogeneous models of crustal stress. In addition to modeling instantaneous aftershock seismicity rate patterns with initial clustering on the Coulomb stress increase areas and an approximately 1/t diffusion back to the pre-mains...

  10. The Mechanisms and Spatiotemporal Behavior of the 2011 Mw7.1 Van, Eastern Turkey Earthquake Aftershocks

    Science.gov (United States)

    Ezgi Guvercin Isik, Sezim; Ozgun Konca, A.; Karabulut, Hayrullah

    2016-04-01

    We studied the mechanisms and spatiotemporal distribution of the aftershocks of the Mw7.1 Van Earthquake, in Eastern Turkey. The 2011 Van Earthquake occurred on a E-W trending blind thrust fault in Eastern Turkey which is under N-S compression due to convergence of the Arabian plate toward the Eurasia. In this study, we relocated and studied the mechanisms of the M3.5-5.5 aftershocks from regional Pnl and surface waves using the "Cut and Paste" algorithm of Zhu and Helmberger (1996). Our results reveal that the aftershocks in the first day following the mainshock are in the vicinity of the co-seismic slip and have mostly thrust mechanism consistent with the mainshock. In the following day, a second cluster of activity at the northeast termination of the fault ( North of Lake Erçek) has started. These aftershocks have approximately N-S lineation and left lateral source mechanisms. The aftershocks surrounding the mainshock rupture are deeper (>20 km) than the aftershocks triggered on the north (<15km). We also observe strike slip earthquakes on the south of the mainshock. Both of delayed activities (north of the mainshock and south of the mainshock) are consistent with the Coulomb stress increase due to slip on the mainshock. We propose that the Van Fault is truncated by two strike-slip faults at each end, which has determined the along-strike rupture extent of the 2011 mainshock.

  11. Spatial/Temporal interdependence of aftershocks following the 10/31/2001 M5.1 Anza Earthquake

    Science.gov (United States)

    Kilb, D.; Martynov, V.; Vernon, F. L.

    2004-12-01

    On 10/31/2001, a M5.1 earthquake occurred in the middle of the ANZA network (7 24-bit broadband stations were within 20 km of the epicenter) that spans the San Jacinto fault zone in southern California. A high pass filter (f > 1.0 Hz) was used to identify seismic arrival times of the aftershocks and in turn determine the aftershock locations. In this way, we cataloged 599 events (0digits in the location algorithm because these voids do not follow individual latitude or longitude lines, nor is this likely due to recording inaccuracies because the network coverage of the region is more than optimal. We are investigating other causes of these voids. (3) In the broadband data, we found only one detectable aftershock in the first 2 minutes of the continuous waveforms; yet on the short period records at one of the closest stations, TRO, we can identify an additional event at 15 seconds into the sequence. To quantify our detection capabilities, we estimate when aftershocks of different magnitudes can be identified within the mainshock coda. We are fairly confident that \\> M 1.5 events 45 seconds or longer after the mainshock should be detectable, which suggests that the lack of seismicity in the 45 second-2.0 minute range is potentially real. This non-zero lag-time between the mainshock and the first aftershock is inconsistent with the hypothesis that stress changes induced by a mainshock earthquake instantaneously trigger aftershocks.

  12. Aftershocks of the 2010 Mw 7.2 El Mayor-Cucapah earthquake revealcomplex faulting in the Yuha Desert, California

    Science.gov (United States)

    Kroll, K.; Cochran, Elizabeth S.; Richards-Dinger, K.; Sumy, Danielle

    2013-01-01

    We detect and precisely locate over 9500 aftershocks that occurred in the Yuha Desert region during a 2 month period following the 4 April 2010 Mw 7.2 El Mayor-Cucapah (EMC) earthquake. Events are relocated using a series of absolute and relative relocation procedures that include Hypoinverse, Velest, and hypoDD. Location errors are reduced to ~40 m horizontally and ~120 m vertically.Aftershock locations reveal a complex pattern of faulting with en echelon fault segments trending toward the northwest, approximately parallel to the North American-Pacific plate boundary and en echelon, conjugate features trending to the northeast. The relocated seismicity is highly correlated with published surface mapping of faults that experienced triggered surface slip in response to the EMC main shock. Aftershocks occurred between 2 km and 11 km depths, consistent with previous studies of seismogenic thickness in the region. Three-dimensional analysis reveals individual and intersecting fault planes that are limited in their along-strike length. These fault planes remain distinct structures at depth, indicative of conjugate faulting, and do not appear to coalesce onto a throughgoing fault segment. We observe a complex spatiotemporal migration of aftershocks, with seismicity that jumps between individual fault segments that are active for only a few days to weeks. Aftershock rates are roughly consistent with the expected earthquake production rates of Dieterich (1994). The conjugate pattern of faulting and nonuniform aftershock migration patterns suggest that strain in the Yuha Desert is being accommodated in a complex manner.

  13. Aftershock seismicity and tectonic setting of the 2015 September 16 Mw 8.3 Illapel earthquake, Central Chile

    Science.gov (United States)

    Lange, Dietrich; Geersen, Jacob; Barrientos, Sergio; Moreno, Marcos; Grevemeyer, Ingo; Contreras-Reyes, Eduardo; Kopp, Heidrun

    2016-08-01

    Powerful subduction zone earthquakes rupture thousands of square kilometres along continental margins but at certain locations earthquake rupture terminates. To date, detailed knowledge of the parameters that govern seismic rupture and aftershocks is still incomplete. On 2015 September 16, the Mw 8.3 Illapel earthquake ruptured a 200 km long stretch of the Central Chilean subduction zone, triggering a tsunami and causing significant damage. Here, we analyse the temporal and spatial pattern of the coseismic rupture and aftershocks in relation to the tectonic setting in the earthquake area. Aftershocks cluster around the area of maximum coseismic slip, in particular in lateral and downdip direction. During the first 24 hr after the main shock, aftershocks migrated in both lateral directions with velocities of approximately 2.5 and 5 km hr-1. At the southern rupture boundary, aftershocks cluster around individual subducted seamounts that are related to the downthrusting Juan Fernández Ridge. In the northern part of the rupture area, aftershocks separate into an upper cluster (above 25 km depth) and a lower cluster (below 35 km depth). This dual seismic-aseismic transition in downdip direction is also observed in the interseismic period suggesting that it may represent a persistent feature for the Central Chilean subduction zone.

  14. Aftershock seismicity and tectonic setting of the 16 September 2015 Mw 8.3 Illapel earthquake, Central Chile

    Science.gov (United States)

    Lange, Dietrich; Geersen, Jacob; Barrientos, Sergio; Moreno, Marcos; Grevemeyer, Ingo; Contreras-Reyes, Eduardo; Kopp, Heidrun

    2016-06-01

    Powerful subduction zone earthquakes rupture thousands of square kilometers along continental margins but at certain locations earthquake rupture terminates. To date detailed knowledge of the parameters that govern seismic rupture and aftershocks is still incomplete. On 16 September 2015 the Mw. 8.3 Illapel earthquake ruptured a 200 km long stretch of the Central Chilean subduction zone, triggering a tsunami and causing significant damage. Here we analyze the temporal and spatial pattern of the co-seismic rupture and aftershocks in relation to the tectonic setting in the earthquake area. Aftershocks cluster around the area of maximum coseismic slip, in particular in lateral and downdip direction. During the first 24 hours after the mainshock, aftershocks migrated in both lateral directions with velocities of approximately 2.5 and 5 km/h. At the southern rupture boundary aftershocks cluster around individual subducted seamounts that are related to the downthrusting Juan Fernández Ridge. In the northern part of the rupture area aftershocks separate into an upper cluster (above 25 km depth) and a lower cluster (below 35 km depth). This dual seismic-aseismic transition in downdip direction is also observed in the interseismic period suggesting that it may represent a persistent feature for the Central Chilean subduction zone.

  15. The aftershock sequence of the 2015 April 25 Gorkha-Nepal earthquake

    Science.gov (United States)

    Adhikari, L. B.; Gautam, U. P.; Koirala, B. P.; Bhattarai, M.; Kandel, T.; Gupta, R. M.; Timsina, C.; Maharjan, N.; Maharjan, K.; Dahal, T.; Hoste-Colomer, R.; Cano, Y.; Dandine, M.; Guilhem, A.; Merrer, S.; Roudil, P.; Bollinger, L.

    2015-12-01

    The M 7.8 2015 April 25 Gorkha earthquake devastated the mountainous southern rim of the High Himalayan range in central Nepal. The main shock was followed by 553 earthquakes of local magnitude greater than 4.0 within the first 45 days. In this study, we present and qualify the bulletin of the permanent National Seismological Centre network to determine the spatio-temporal distribution of the aftershocks. The Gorkha sequence defines a ˜140-km-long ESE trending structure, parallel to the mountain range, abutting on the presumed extension of the rupture plane of the 1934 M 8.4 earthquake. In addition, we observe a second seismicity belt located southward, under the Kathmandu basin and in the northern part of the Mahabarat range. Many aftershocks of the Gorkha earthquake sequence have been felt by the 3 millions inhabitants of the Kathmandu valley.

  16. No evidence of magnitude clustering in an aftershock sequence of nano- and picoseismicity.

    Science.gov (United States)

    Davidsen, Jörn; Kwiatek, Grzegorz; Dresen, Georg

    2012-01-20

    One of the hallmarks of our current understanding of seismicity as highlighted by the epidemic-type-aftershock sequence model is that the magnitudes of earthquakes are independent of one another and can be considered as randomly drawn from the Gutenberg-Richter distribution. This assumption forms the basis of many approaches for forecasting seismicity rates and hazard assessment. Recently, it has been suggested that the assumption of independent magnitudes is not valid. It was subsequently argued that this conclusion was not supported by the original earthquake data from California. One of the main challenges is the lack of completeness of earthquake catalogs. Here, we study an aftershock sequence of nano- and picoseismicity as observed at the Mponeng mine, for which the issue of incompleteness is much less pronounced. We show that this sequence does not exhibit any significant evidence of magnitude correlations.

  17. Real-time forecast of aftershocks from a single seismic station signal

    Science.gov (United States)

    Lippiello, E.; Cirillo, A.; Godano, G.; Papadimitriou, E.; Karakostas, V.

    2016-06-01

    The evaluation of seismic hazard in the hours following large earthquakes is strongly affected by biases due to difficulties in determining earthquake location. This leads to the huge incompleteness of instrumental catalogs. Here we show that if, on the one hand, the overlap of aftershock coda waves hides many small events, on the other hand, it leads to a well-determined empirical law controlling the decay of the amplitude of the seismic signal at a given site. The fitting parameters of this law can be related to those controlling the temporal decay of the aftershock number, and it is then possible to obtain short-term postseismic occurrence probability from a single recorded seismic signal. We therefore present a novel procedure which, without requiring earthquake location, produces more accurate and almost real-time forecast, in a site of interest, directly from the signal of a seismic station installed at that site.

  18. The Mw 5.8 Virginia Earthquake of August 23, 2011 and its Aftershocks: A Shallow High Stress Drop Event

    Science.gov (United States)

    Ellsworth, W. L.; Imanishi, K.; Luetgert, J. H.; Kruger, J.; Hamilton, J.

    2011-12-01

    We analyze the hypocentral distribution and source parameters of the aftershocks of the Virginia Earthquake of August 23, 2011 using a temporary array of telemetered instruments deployed within 20 km of the main shock. Our data come from four USGS NetQuakes accelerometers and seven IRIS/PASSCAL seismometers that were established within a few days of the earthquake. Aftershock seismograms at these near-source stations are characterized by impulsive, high-frequency P and S phases at most sites. In addition, we use the five closest permanent stations (60 - 310 km distance) to analyze the main shock. Hypocenters, crustal velocity model and station corrections were determined using the program VELEST (Kissling, et al, 1994). The aftershocks define a 10-km-long, N 30 degree E striking, 45 degree ESE dipping fault. This fault plane agrees well with the USGS moment tensor solutions for the main shock. Aftershock depths range from 2.5 to 8 km, placing the sequence in the Cambrian metamorphic rocks of the Eastern Piedmont thrust sheet. We relocated the main shock relative to a well-located Mw 3.5 aftershock using the P-wave arrival times at the five permanent stations. The main shock epicenter lies in the middle of the aftershock zone. Its focal depth, although not well constrained, is similar to the aftershocks. A crustal-scale seismic reflection profile was acquired by the USGS in 1981 along I-64 just 4 km southwest of the nearest aftershocks. This profile runs nearly parallel to the dip direction of the aftershock zone and has been interpreted to contain many ESE-dipping reverse faults in the allochthonous upper crust (Harris et al., 1986; Pratt, et al., 1988). When projected onto the reflection profile the aftershocks locate within a relatively non-reflective zone bounded above and below by prominent bands of more shallowly dipping reflectors reported by Pratt et al. (1988) raising the question whether or not the earthquake reactivated a pre-existing fault. Seismic

  19. A fractal model of earthquake occurrence: Theory, simulations and comparisons with the aftershock data

    International Nuclear Information System (INIS)

    Our understanding of earthquakes is based on the theory of plate tectonics. Earthquake dynamics is the study of the interactions of plates (solid disjoint parts of the lithosphere) which produce seismic activity. Over the last about fifty years many models have come up which try to simulate seismic activity by mimicking plate plate interactions. The validity of a given model is subject to the compliance of the synthetic seismic activity it produces to the well known empirical laws which describe the statistical features of observed seismic activity. Here we present a review of one such, purely geometric, model of earthquake dynamics, namely The Two Fractal Overlap Model. The model tries to emulate the stick-slip dynamics of lithospheric plates with fractal surfaces by evaluating the time-evolution of overlap lengths of two identical Cantor sets sliding over each other. As we show later in the text, some statistical aspects of natural seismicity are naturally captured by this simple model. More importantly, however, this model also reveals a new statistical feature of aftershock sequences which we have verified to be present in nature as well. We show that, both in the model as well as in nature, the cumulative integral of aftershock magnitudes over time is a remarkable straight line with a characteristic slope. This slope is closely related to the fractal geometry of the fault surface that produces most of thee aftershocks. We also go on to discuss the implications that this feature may have in possible predictions of aftershock magnitudes or times of occurrence.

  20. Identification of a major segment boundary between two megathrust subduction zone earthquakes from aftershock seismicity

    Science.gov (United States)

    Sobiesiak, M.; Victor, P.; Eggert, S.

    2009-04-01

    Aftershock seismicity is commonly used to characterize the extent of rupture planes of megathrust earthquakes. From unique datasets, covering the two adjacent fault planes of the Mw 8.0, 1995, Antofagasta and the Mw 7.7, 2007, Tocopilla earthquakes, we were able to identify a segment boundary (SB), located beneath Mejillones Peninsula. This segment boundary hosted the onset of the Antofagasta rupture and constituted the end of the Tocopilla rupture plane. The data recorded during the mission of the German Task Force for Earthquakes after the 2007 Tocopilla earthquake is supporting our observations regarding the northern part of the SB. 34 seismological stations registered the aftershocks from November 2007 until May 2008. First hypocenter determinations show that the aftershock sequences of both events meet along this E-W oriented segment boundary. The segment boundary is furthermore conformed by the historic record of megathrust events. Evidence for long term persistency of this SB comes from geological observations as differential uplift rates across the boundary and different fault patterns. Geomorpholocical analysis defines a topographic anomaly ~ 20 km wide and oriented along strike the SB..The main shock hypocenter determinations (NEIC, local network, ISC) which are related to the start of the rupture are all located in this zone. The SB is further characterized by intermediate b-values derived from a spatial b-value study of the Antofagasta fault plane and hosts several elongated clusters of aftershock seismicity. A detailed study of the focal mechanism solutions in one of these clusters showed a number of aligned strike slip events with one E-W striking nodal plane having a strike angle which is similar to the angle of subduction obliquity of the oceanic Nazca plate in this area. In further investigations we will search for detailed information on the nature and dynamics of processes along such a segment boundary, their meaning for the initiation of large

  1. Distribution of the largest event in the critical epidemic-type aftershock-sequence model

    Science.gov (United States)

    Vere-Jones, David; Zhuang, Jiancang

    2008-10-01

    This Brief Report corrects and extends the results of Zhuang and Ogata [Phys. Rev. E 73, 046134 (2006)] on the asymptotic behavior of the largest event in the epidemic-type aftershock-sequence model for earthquake occurrence. We show that, in the special case that the underlying branching process is critical, there exists a previously unnoticed mode of behavior, which occurs when the expected family size grows relatively slowly.

  2. A fractal model of earthquake occurrence: Theory, simulations and comparisons with the aftershock data

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharya, Pathikrit; Kamal [Department of Earth Sciences, Indian Institute of Technology, Roorkee, Uttarakhand, 247 667 (India); Chakrabarti, Bikas K, E-mail: pathikri@princeton.edu, E-mail: bikask.chakrabarti@saha.ac.in, E-mail: kamalfes@iitr.ernet.in [Theoretical Condensed Matter Physics Division and Centre for Applied Mathematics and Computational Science, Saha Institute of Nuclear Physics, Kolkata, West Bengal, 700064 (India)

    2011-09-15

    Our understanding of earthquakes is based on the theory of plate tectonics. Earthquake dynamics is the study of the interactions of plates (solid disjoint parts of the lithosphere) which produce seismic activity. Over the last about fifty years many models have come up which try to simulate seismic activity by mimicking plate plate interactions. The validity of a given model is subject to the compliance of the synthetic seismic activity it produces to the well known empirical laws which describe the statistical features of observed seismic activity. Here we present a review of one such, purely geometric, model of earthquake dynamics, namely The Two Fractal Overlap Model. The model tries to emulate the stick-slip dynamics of lithospheric plates with fractal surfaces by evaluating the time-evolution of overlap lengths of two identical Cantor sets sliding over each other. As we show later in the text, some statistical aspects of natural seismicity are naturally captured by this simple model. More importantly, however, this model also reveals a new statistical feature of aftershock sequences which we have verified to be present in nature as well. We show that, both in the model as well as in nature, the cumulative integral of aftershock magnitudes over time is a remarkable straight line with a characteristic slope. This slope is closely related to the fractal geometry of the fault surface that produces most of thee aftershocks. We also go on to discuss the implications that this feature may have in possible predictions of aftershock magnitudes or times of occurrence.

  3. Seismological aspects of the 27 June 2015 Gulf of Aqaba earthquake and its sequence of aftershocks

    Science.gov (United States)

    Abd el-aal, Abd el-aziz Khairy; Badreldin, Hazem

    2016-07-01

    On 27 June 2015, a moderate earthquake with magnitude Mb 5.2 struck the Gulf of Aqaba near Nuweiba City. This event was instrumentally recorded by the Egyptian National Seismic Network (ENSN) and many other international seismological centres. The event was felt in all the cities on the Gulf of Aqaba, as well as Suez City, Hurghada City, the greater Cairo Metropolitan Area, Israel, Jordan and the north-western part of Saudi Arabia. No casualties were reported, however. Approximately 95 aftershocks with magnitudes ranging from 0.7 to 4.2 were recorded by the ENSN following the mainshock. In the present study, the source characteristics of both the mainshock and the aftershocks were estimated using the near-source waveform data recorded by the very broadband stations of the ENSN, and these were validated by the P-wave polarity data from short period stations. Our analysis reveals that an estimated seismic moment of 0.762 × 1017 Nm was released, corresponding to a magnitude of Mw 5.2, a focal depth of 14 km, a fault radius of 0.72 km and a rupture area of approximately 1.65 km2. Monitoring the sequence of aftershocks reveals that they form a cluster around the mainshock and migrated downwards in focal depth towards the west. We compared the results we obtained with the published results from the international seismological centres. Our results are more realistic and accurate, in particular with respect to the epicenteral location, magnitude and fault plane solution which are in accordance with the hypocentre distribution of the aftershocks.

  4. Aftershocks and Omori's law in a modified Carlson-Langer model with nonlinear visco-elasticity

    CERN Document Server

    Sakaguchi, Hidetsugu

    2015-01-01

    A modified Carlson-Langer model for earthquakes is proposed, which includes nonlinear visco-elasticity. Several aftershocks are generated after the main shock owing to the damping of the additional visco-elastic force. Both the Gutenberg-Richter law and Omori's law are reproduced in a numerical simulation of the modified Carlson-Langer model on a critical percolation cluster of a square lattice.

  5. Distribution of the largest event in the critical epidemic-type aftershock-sequence model.

    Science.gov (United States)

    Vere-Jones, David; Zhuang, Jiancang

    2008-10-01

    This Brief Report corrects and extends the results of Zhuang and Ogata [Phys. Rev. E 73, 046134 (2006)] on the asymptotic behavior of the largest event in the epidemic-type aftershock-sequence model for earthquake occurrence. We show that, in the special case that the underlying branching process is critical, there exists a previously unnoticed mode of behavior, which occurs when the expected family size grows relatively slowly.

  6. Decay of aftershock density with distance does not indicate triggering by dynamic stress

    Science.gov (United States)

    Richards-Dinger, K.; Stein, R.S.; Toda, S.

    2010-01-01

    Resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard. Felzer and Brodsky examined the distance distribution of earthquakes occurring in the first five minutes after 2 ≤ M  M  M ≥ 2 aftershocks showed a uniform power-law decay with slope −1.35 out to 50 km from the mainshocks. From this they argued that the distance decay could be explained only by dynamic triggering. Here we propose an alternative explanation for the decay, and subject their hypothesis to a series of tests, none of which it passes. At distances more than 300 m from the 2 ≤  Mwave front from the mainshock, which violates causality. We argue that Felzer and Brodsky implicitly assume that the first of two independent aftershocks along a fault rupture triggers the second, and that the first of two shocks in a creep- or intrusion-driven swarm triggers the second, when this need not be the case.

  7. Long aftershock sequences within continents and implications for earthquake hazard assessment.

    Science.gov (United States)

    Stein, Seth; Liu, Mian

    2009-11-01

    One of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries. Plate tectonics gives no insight, however, into where and when earthquakes will occur within plates, because the interiors of ideal plates should not deform. As a result, within plate interiors, assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes. Here, however, we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago. We present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded. Aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries. These predictions are in accord with observations. So the common practice of treating continental earthquakes as steady-state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere. PMID:19890328

  8. Long aftershock sequences within continents and implications for earthquake hazard assessment.

    Science.gov (United States)

    Stein, Seth; Liu, Mian

    2009-11-01

    One of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries. Plate tectonics gives no insight, however, into where and when earthquakes will occur within plates, because the interiors of ideal plates should not deform. As a result, within plate interiors, assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes. Here, however, we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago. We present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded. Aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries. These predictions are in accord with observations. So the common practice of treating continental earthquakes as steady-state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere.

  9. High-Resolution Uitra Low Power, Intergrated Aftershock and Microzonation System

    Science.gov (United States)

    Passmore, P.; Zimakov, L. G.

    2012-12-01

    Rapid Aftershock Mobilization plays an essential role in the understanding of both focal mechanism and rupture propagation caused by strong earthquakes. A quick assessment of the data provides a unique opportunity to study the dynamics of the entire earthquake process in-situ. Aftershock study also provides practical information for local authorities regarding the post earthquake activity, which is very important in order to conduct the necessary actions for public safety in the area affected by the strong earthquake. Refraction Technology, Inc. has developed a self-contained, fully integrated Aftershock System, model 160-03, providing the customer simple and quick deployment during aftershock emergency mobilization and microzonation studies. The 160-03 has no external cables or peripheral equipment for command/control and operation in the field. The 160-03 contains three major components integrated in one case: a) 24-bit resolution state-of-the art low power ADC with CPU and Lid interconnect boards; b) power source; and c) three component 2 Hz sensors (two horizontals and one vertical), and built-in ±4g accelerometer. Optionally, the 1 Hz sensors can be built-in the 160-03 system at the customer's request. The self-contained rechargeable battery pack provides power autonomy up to 7 days during data acquisition at 200 sps on continuous three weak motion and triggered three strong motion recording channels. For longer power autonomy, the 160-03 Aftershock System battery pack can be charged from an external source (solar power system). The data in the field is recorded to a built-in swappable USB flash drive. The 160-03 configuration is fixed based on a configuration file stored on the system, so no external command/control interface is required for parameter setup in the field. For visual control of the system performance in the field, the 160-03 has a built-in LED display which indicates the systems recording status as well as a hot swappable USB drive and battery

  10. Tomographic velocity model for the aftershock region of the 2001 Gujarat, India earthquake

    Science.gov (United States)

    Negishi, H.; Kumar, S.; Mori, J. J.; Sato, T.; Bodin, P.; Rastogi, B.

    2002-12-01

    A tomographic inversion was applied to the aftershock data collected after the January 26, 2001 Bhuj earthquake (Ms 7.9, Mw 7.7), which occurred on a south dipping (~50 degrees) reverse fault in the state of Gujarat in western India. We used high quality arrivals from 8,374 P and 7,994 S waves of 1404 aftershocks recorded on 27 digital stations from temporary seismic arrays setup by the India-Japan team; NGRI, India; and CERI, Memphis Univ., USA, following the Bhuj main shock. First, we used the Joint Hypocenters Determination Method for obtaining relocated hypocenters and a one-dimensional Vp and Vs velocity model, and then the resultant hypocenters and 1-D velocity model were used as the initial parameters for a 3-D tomographic inversion. The tomography technique is based on a grid-modeling method by Zhao et al. . Vp, Vs and hypocenters are determined simultaneously. We tried to use the Cross-Validation Technique for determining an optimum model in the seismic tomography. This approach has been applied to other tomographic studies to investigate the quantitative fluctuation range of velocity perturbations . Significant variations in the velocity (up to 6%) and Poisson's ratio (up to 8%) are revealed in the aftershock area. It seems that the aftershock distribution corresponds to the boundary between high and low velocity heterogeneities. Small values of Vp/Vs are generally found at depths of 10 to 35 km, i.e. the depth range of aftershock distribution. However, the deeper region below the hypocenter of the mainshock, at depths of 35 to 45 km, is characterized by relatively high values of Vp/Vs and low values of Vs. This anomaly may be due to a weak fractured and fluid filled rock matrix, which might have contributed to triggering this earthquake. This earthquake occurred on a relatively deep and steeply dipping fault with a large stress drop . Theoretically it is difficult to slip steep faults, especially in the lower crust. Our tomographic investigation provides

  11. Focal Depth of the WenChuan Earthquake Aftershocks from modeling of Seismic Depth Phases

    Science.gov (United States)

    Luo, Y.; Zeng, X.; Chong, J.; Ni, S.; Chen, Y.

    2008-12-01

    After the 05/12/2008 great WenChuan earthquake in Sichuan Province of China, tens of thousands earthquakes occurred with hundreds of them stronger than M4. Those aftershocks provide valuable information about seismotectonics and rupture processes for the mainshock, particularly accurate spatial distribution of aftershocks is very informational for determining rupture fault planes. However focal depth can not be well resolved just with first arrivals recorded by relatively sparse network in Sichuan Province, therefore 3D seismicity distribution is difficult to obtain though horizontal location can be located with accuracy of 5km. Instead local/regional depth phases such as sPmP, sPn, sPL and teleseismic pP,sP are very sensitive to depth, and be readily modeled to determine depth with accuracy of 2km. With reference 1D velocity structure resolved from receiver functions and seismic refraction studies, local/regional depth phases such as sPmP, sPn and sPL are identified by comparing observed waveform with synthetic seismograms by generalized ray theory and reflectivity methods. For teleseismic depth phases well observed for M5.5 and stronger events, we developed an algorithm in inverting both depth and focal mechanism from P and SH waveforms. Also we employed the Cut and Paste (CAP) method developed by Zhao and Helmberger in modeling mechanism and depth with local waveforms, which constrains depth by fitting Pnl waveforms and the relative weight between surface wave and Pnl. After modeling all the depth phases for hundreds of events , we find that most of the M4 earthquakes occur between 2-18km depth, with aftershocks depth ranging 4-12km in the southern half of Longmenshan fault while aftershocks in the northern half featuring large depth range up to 18km. Therefore seismogenic zone in the northern segment is deeper as compared to the southern segment. All the aftershocks occur in upper crust, given that the Moho is deeper than 40km, or even 60km west of the

  12. Full waveform modelling using the VERCE platform - application to aftershock seismicity in the Chile subduction zone

    Science.gov (United States)

    Garth, Thomas; Rietbrock, Andreas; Hicks, Steve; Fuenzalida Velasco, Amaya; Casarotti, Emanuele; Spinuso, Alessandro

    2015-04-01

    The VERCE platform is an online portal that allows full waveform simulations to be run for any region where a suitable velocity model exists. We use this facility to simulate the waveforms from aftershock earthquakes from the 2014 Pisagua earthquake, and 2010 Maule earthquake that occurred at the subduction zone mega thrust in Northern and Central Chile respectively. Simulations are performed using focal mechanisms from both global earthquake catalogues, and regional earthquake catalogues. The VERCE platform supports specFEM Cartesian, and simulations are run using meshes produced by CUBIT. The full waveform modelling techniques supported on the VERCE platform are used to test the validity of a number of subduction zone velocity models from the Chilean subduction zone. For the Maule earthquake we use a 2D and 3D travel time tomography model of the rupture area (Hicks et al. 2011; 2014). For the Pisagua earthquake we test a 2D/3D composite velocity model based on tomographic studies of the region (e.g. Husen et al. 2000, Contreyes-Reyes et al. 2012) and slab1.0 (Hayes et al. 2012). Focal mechanisms from the cGMT catalogue and local focal mechanisms calculated using ISOLA (e.g. Agurto et al. 2012) are used in the simulations. The waveforms produced are directly compared to waveforms recorded on the temporary deployment for the Maule earthquake aftershocks, and waveforms recorded on the IPOC network for the Pisagua earthquake aftershocks. This work demonstrates how the VERCE platform allows waveforms from the full 3D simulations to be easily produced, allowing us to quantify the validity of both the velocity model and the source mechanisms. These simulations therefore provide an independent test of the velocity models produced synthetically and by travel time tomography studies. Initial results show that the waveform is reasonably well reproduced in the 0.05 - 0.25 frequency band using a refined 3D travel time tomography, and locally calculated focal mechanisms.

  13. An Autonomous System for Grouping Events in a Developing Aftershock Sequence

    Energy Technology Data Exchange (ETDEWEB)

    Harris, D. B. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Dodge, D. A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2011-03-22

    We describe a prototype detection framework that automatically clusters events in real time from a rapidly unfolding aftershock sequence. We use the fact that many aftershocks are repetitive, producing similar waveforms. By clustering events based on correlation measures of waveform similarity, the number of independent event instances that must be examined in detail by analysts may be reduced. Our system processes array data and acquires waveform templates with a short-term average (STA)/long-term average (LTA) detector operating on a beam directed at the P phases of the aftershock sequence. The templates are used to create correlation-type (subspace) detectors that sweep the subsequent data stream for occurrences of the same waveform pattern. Events are clustered by association with a particular detector. Hundreds of subspace detectors can run in this framework a hundred times faster than in real time. Nonetheless, to check the growth in the number of detectors, the framework pauses periodically and reclusters detections to reduce the number of event groups. These groups define new subspace detectors that replace the older generation of detectors. Because low-magnitude occurrences of a particular signal template may be missed by the STA/LTA detector, we advocate restarting the framework from the beginning of the sequence periodically to reprocess the entire data stream with the existing detectors. We tested the framework on 10 days of data from the Nevada Seismic Array (NVAR) covering the 2003 San Simeon earthquake. One hundred eighty-four automatically generated detectors produced 676 detections resulting in a potential reduction in analyst workload of up to 73%.

  14. Estimating seismic site response in Christchurch City (New Zealand) from dense low-cost aftershock arrays

    Science.gov (United States)

    Kaiser, Anna E.; Benites, Rafael A.; Chung, Angela I.; Haines, A. John; Cochran, Elizabeth S.; Fry, Bill

    2011-01-01

    The Mw 7.1 September 2010 Darfield earthquake, New Zealand, produced widespread damage and liquefaction ~40 km from the epicentre in Christchurch city. It was followed by the even more destructive Mw 6.2 February 2011 Christchurch aftershock directly beneath the city’s southern suburbs. Seismic data recorded during the two large events suggest that site effects contributed to the variations in ground motion observed throughout Christchurch city. We use densely-spaced aftershock recordings of the Darfield earthquake to investigate variations in local seismic site response within the Christchurch urban area. Following the Darfield main shock we deployed a temporary array of ~180 low-cost 14-bit MEMS accelerometers linked to the global Quake-Catcher Network (QCN). These instruments provided dense station coverage (spacing ~2 km) to complement existing New Zealand national network strong motion stations (GeoNet) within Christchurch city. Well-constrained standard spectral ratios were derived for GeoNet stations using a reference station on Miocene basalt rock in the south of the city. For noisier QCN stations, the method was adapted to find a maximum likelihood estimate of spectral ratio amplitude taking into account the variance of noise at the respective stations. Spectral ratios for QCN stations are similar to nearby GeoNet stations when the maximum likelihood method is used. Our study suggests dense low-cost accelerometer aftershock arrays can provide useful information on local-scale ground motion properties for use in microzonation. Preliminary results indicate higher amplifications north of the city centre and strong high-frequency amplification in the small, shallower basin of Heathcote Valley.

  15. Precise aftershock distribution of the 2011 off the Pacific coast of Tohoku Earthquake revealed by an ocean-bottom seismometer network

    Science.gov (United States)

    Shinohara, Masanao; Machida, Yuya; Yamada, Tomoaki; Nakahigashi, Kazuo; Shinbo, Takashi; Mochizuki, Kimihiro; Murai, Yoshio; Hino, Ryota; Ito, Yoshihiro; Sato, Toshinori; Shiobara, Hajime; Uehira, Kenji; Yakiwara, Hiroshi; Obana, Koichiro; Takahashi, Narumi; Kodaira, Shuichi; Hirata, Kenji; Tsushima, Hiroaki; Iwasaki, Takaya

    2012-12-01

    The 2011 off the Pacific coast of Tohoku Earthquake occurred at the plate boundary between the Pacific plate and the landward plate on March 11, 2011, and had a magnitude of 9. Many aftershocks occurred following the mainshock. Obtaining a precise aftershock distribution is important for understanding the mechanism of earthquake generation. In order to study the aftershock activity of this event, we carried out extensive sea-floor aftershock observations using more than 100 ocean-bottom seismometers just after the mainshock. A precise aftershock distribution for approximately three months over the whole source area was obtained from the observations. The aftershocks form a plane dipping landward over the whole area, nevertheless the epicenter distribution is not uniform. Comparing seismic velocity structures, there is no aftershock along the plate boundary where a large slip during the mainshock is estimated. Activity of aftershocks in the landward plate in the source region was high and normal fault-type, and strike-slip-type, mechanisms are dominant. Within the subducting oceanic plate, most earthquakes have also a normal fault-type, or strike-slip-type, mechanism. The stress fields in and around the source region change as a result of the mainshock.

  16. Radiated seismic energy of aftershocks of the 20 March 2012 earthquake, Mw7.5, Ometepec-Pinotepa Nacional, Mexico.

    Science.gov (United States)

    Plata Martinez, R. O.; Perez-Campos, X.; Singh, S. K.

    2014-12-01

    Radiated seismic energy is a valuable parameter in assessing the size and source characteristics of an earthquake. We study aftershocks of the 20 March 2012 earthquake (Mw7.5) in Ometepec-Pinotepa Nacional,located in the subduction zone of the Pacific coast of Mexico, with the purpose of examining the distribution of the scaled seismic energy (Es) with seismic moment (Mo), Es/Mo, over the main event's rupture area. We estimate Es from regional velocity and acceleration records. For some, larger, aftershocks we also estimate Es from teleseismic data. Preliminary energy estimations suggest that aftershocks closer to the trench have a smaller Es/Mo ratio. In contrast, Es/Mo is larger for events closer to the coast (near the epicenter of the mainshock).

  17. Study on the earthquake fault of the Lulong ML=6.2 earthquake by precise relocation of aftershock

    Institute of Scientific and Technical Information of China (English)

    LI Wen-jun; WANG Pei-de; LI Chun-lai; CHEN Qi-fu

    2005-01-01

    We have selected 171 near-field records from 391 aftershock records of the Lulong, Hebei Province, earthquake in October 1982 and relocated the hypocenter of 45 aftershocks using the program Hypoinverse. The distribution of aftershocks reveals a set of earthquake faults: a WNW stretching fault truncates two NNE stretching faults. The two branches of faults show the conjugate structure which is often seen in brittle fracture. The NNE stretching faults are connected together. The Luanhe river valley near Lulong developed to a rudiment rift basin surrounded by a series of faults. The fault of Lulong earthquake is a strike-slip fault with tension component. This fault type matches with the activity of Zhangjiakou-Bohai seismic belt (Zhang-Bo belt) and also shows the action of Zhang-Bo belt as a boundary of two secondary active blocks that truncates the NNE fault.

  18. Constraints on the Size of the Smallest Triggering Earthquake from the ETAS Model, Baath's Law, and Observed Aftershock Sequences

    CERN Document Server

    Sornette, D

    2004-01-01

    The physics of earthquake triggering together with simple assumptions of self-similarity impose the existence of a minimum magnitude m0 below which earthquakes do not trigger other earthquakes. Noting that the magnitude md of completeness of seismic catalogs has no reason to be the same as the magnitude m0 of the smallest triggering earthquake, we use quantitative fits and maximum likelihood inversions of observed aftershock sequences as well as Baath's law, compare with ETAS model predictions and thereby constrain the value of m0. We show that the branching ratio $n$ (average number of triggered earthquake per earthquake also equal to the fraction of aftershocks in seismic catalogs) is the key parameter controlling the minimum triggering magnitude m0. Conversely, physical upper bounds for m0 derived from state- and velocity-weakening friction indicate that at least 60 to 70 percent of all earthquakes are aftershocks.

  19. Statistical Properties of the Immediate Aftershocks of the 15 October 2013 Magnitude 7.1 Earthquake in Bohol, Philippines

    Directory of Open Access Journals (Sweden)

    Batac Rene C.

    2016-02-01

    Full Text Available The aftershock records of the magnitude 7.1 earthquake that hit the island of Bohol in central Philippines on 15 October 2013 is investigated in the light of previous results for the Philippines using historical earthquakes. Statistics of interevent distances and interevent times between successive aftershocks recorded for the whole month of October 2013 show marked differences from those of historical earthquakes from two Philippine catalogues of varying periods and completeness levels. In particular, the distributions closely follow only the regimes of the historical distributions that were previously attributed to the strong spatio-temporal correlations. The results therefore suggest that these correlated regimes which emerged naturally from the analyses are strongly dominated by the clustering of aftershock events.

  20. Large-amplitude Moho reflections (SmS) from Landers aftershocks, southern California

    OpenAIRE

    Mori, Jim; Helmberger, Donald

    1996-01-01

    Closely spaced aftershocks of the 28 June 1992 Landers earthquake (M_w 7.3) were used to make event record sections that show the transverse components of S and SmS arrivals at a distance of 70 to 170 km. For the data recorded toward the north in the Mojave desert, large SmS phases are observed with amplitudes 2 to 5 times greater than the direct S. For similar distances to the south, the SmS arrival is comparable to or smaller than the S. Comparisons to synthetic seismograms indicate that th...

  1. Matched-filter Detection of the Missing Foreshocks and Aftershocks of the 2015 Gorkha earthquake

    Science.gov (United States)

    Meng, L.; Huang, H.; Wang, Y.; Plasencia Linares, M. P.

    2015-12-01

    The 25 April 2015 Mw 7.8 Gorkha earthquake occurred at the bottom edge of the locking portion of the Main Himalayan Thrust (MHT), where the Indian plate under-thrusts the Himalayan wedge. The earthquake is followed by a number of large aftershocks but is not preceded by any foreshocks within ~3 weeks according to the NEIC, ISC and NSC catalog. However, a large portion of aftershocks could be missed due to either the contamination of the mainshock coda or small signal to noise ratio. It is also unclear whether there are foreshocks preceding the mainshock, the underlying physical processes of which are crucial for imminent seismic hazard assessment. Here, we employ the matched filter technique to recover the missing events from 22 April to 30 April. We collect 3-component broadband seismic waveforms recorded by one station in Nepal operated by Ev-K2-CNR, OGS Italy and eleven stations in Tibet operated by the China Earthquake Networks Center. We bandpass the seismograms to 1-6 Hz to retain high frequency energies. The template waveforms with high signal-to-noise ratios (> 5) are obtained at several closest stations. To detect and locate the events that occur around the templates, correlograms are shifted at each station with differential travel time as a function of source location based on the CRUST1.0 model. We find ~14 times more events than those listed in the ISC catalog. Some of the detected events are confirmed by visual inspections of the waveforms at the closest stations. The preliminary results show a streak of seismicity occurred around 2.5 days before the mainshock to the southeast of the mainshock hypocenter. The seismicity rate is elevated above the background level during this period of time and decayed subsequently following the Omori's law. The foreshocks appear to migrate towards the hypocenter with logarithmic time ahead of the mainshock, which indicates possible triggering of the mainshock by the propagating afterslip of the foreshocks. Immediately

  2. Using the USGS Seismic Risk Web Application to estimate aftershock damage

    Science.gov (United States)

    McGowan, Sean M.; Luco, Nicolas

    2014-01-01

    The U.S. Geological Survey (USGS) Engineering Risk Assessment Project has developed the Seismic Risk Web Application to combine earthquake hazard and structural fragility information in order to calculate the risk of earthquake damage to structures. Enabling users to incorporate their own hazard and fragility information into the calculations will make it possible to quantify (in near real-time) the risk of additional damage to structures caused by aftershocks following significant earthquakes. Results can quickly be shared with stakeholders to illustrate the impact of elevated ground motion hazard and earthquake-compromised structural integrity on the risk of damage during a short-term, post-earthquake time horizon.

  3. Heterogeneity and anomalous critical indices in the aftershocks distribution of L Aquila earthquake

    CERN Document Server

    Innocenti, D; Poccia, N; Ricci, A; Caputo, M; Bianconi, A

    2009-01-01

    The data analysis of aftershock events of L Aquila earthquake in Apennines following the main 6.3 Mw event of April 6, 2009 has been carried out by standard statistical geophysical tools. The results show the heterogeneity of seismic activity in five different geographical sub-regions indicated by anomalous critical indices of power law distributions: the exponents of the Omori law, the b values of Gutenberg-Richter magnitude-frequency distribution, and the distribution of waiting times. The heterogeneous distribution of dynamic stress and a different morphology in the five sub-regions has been found and two anomalous sub-regions have been identified.

  4. Geotechnical effects of the 2015 magnitude 7.8 Gorkha, Nepal, earthquake and aftershocks

    Science.gov (United States)

    Moss, Robb E S; Thompson, Eric; Kieffer, D Scott; Tiwari, Binod; Hashash, Youssef M A; Acharya, Indra; Adhikari, Basanta; Asimaki, Domniki; Clahan, Kevin B.; Collins, Brian D.; Dahal, Sachindra; Jibson, Randall W.; Khadka, Diwakar; Macdonald, Amy; Madugo, Chris L M; Mason, H Benjamin; Pehlivan, Menzer; Rayamajhi, Deepak; Uprety, Sital

    2015-01-01

    This article summarizes the geotechnical effects of the 25 April 2015 M 7.8 Gorkha, Nepal, earthquake and aftershocks, as documented by a reconnaissance team that undertook a broad engineering and scientific assessment of the damage and collected perishable data for future analysis. Brief descriptions are provided of ground shaking, surface fault rupture, landsliding, soil failure, and infrastructure performance. The goal of this reconnaissance effort, led by Geotechnical Extreme Events Reconnaissance, is to learn from earthquakes and mitigate hazards in future earthquakes.

  5. Variation of b and p values from aftershocks sequences along the Mexican subduction zone and their relation to plate characteristics

    Science.gov (United States)

    Ávila-Barrientos, L.; Zúñiga, F. R.; Rodríguez-Pérez, Q.; Guzmán-Speziale, M.

    2015-11-01

    Aftershock sequences along the Mexican subduction margin (between coordinates 110ºW and 91ºW) were analyzed by means of the p value from the Omori-Utsu relation and the b value from the Gutenberg-Richter relation. We focused on recent medium to large (Mw > 5.6) events considered susceptible of generating aftershock sequences suitable for analysis. The main goal was to try to find a possible correlation between aftershock parameters and plate characteristics, such as displacement rate, age and segmentation. The subduction regime of Mexico is one of the most active regions of the world with a high frequency of occurrence of medium to large events and plate characteristics change along the subduction margin. Previous studies have observed differences in seismic source characteristics at the subduction regime, which may indicate a difference in rheology and possible segmentation. The results of the analysis of the aftershock sequences indicate a slight tendency for p values to decrease from west to east with increasing of plate age although a statistical significance is undermined by the small number of aftershocks in the sequences, a particular feature distinctive of the region as compared to other world subduction regimes. The b values show an opposite, increasing trend towards the east even though the statistical significance is not enough to warrant the validation of such a trend. A linear regression between both parameters provides additional support for the inverse relation. Moreover, we calculated the seismic coupling coefficient, showing a direct relation with the p and b values. While we cannot undoubtedly confirm the hypothesis that aftershock generation depends on certain tectonic characteristics (age, thickness, temperature), our results do not reject it thus encouraging further study into this question.

  6. Triggering of tsunamigenic aftershocks from large strike-slip earthquakes: Analysis of the November 2000 New Ireland earthquake sequence

    Science.gov (United States)

    Geist, Eric L.; Parsons, Tom

    2005-10-01

    The November 2000 New Ireland earthquake sequence started with a Mw = 8.0 left-lateral main shock on 16 November and was followed by a series of aftershocks with primarily thrust mechanisms. The earthquake sequence was associated with a locally damaging tsunami on the islands of New Ireland and nearby New Britain, Bougainville, and Buka. Results from numerical tsunami-propagation models of the main shock and two of the largest thrust aftershocks (Mw > 7.0) indicate that the largest tsunami was caused by an aftershock located near the southeastern termination of the main shock, off the southern tip of New Ireland (Aftershock 1). Numerical modeling and tide gauge records at regional and far-field distances indicate that the main shock also generated tsunami waves. Large horizontal displacements associated with the main shock in regions of steep bathymetry accentuated tsunami generation for this event. Most of the damage on Bougainville and Buka Islands was caused by focusing and amplification of tsunami energy from a ridge wave between the source region and these islands. Modeling of changes in the Coulomb failure stress field caused by the main shock indicate that Aftershock 1 was likely triggered by static stress changes, provided the fault was on or synthetic to the New Britain interplate thrust as specified by the Harvard CMT mechanism. For other possible focal mechanisms of Aftershock 1 and the regional occurrence of thrust aftershocks in general, evidence for static stress change triggering is not as clear. Other triggering mechanisms such as changes in dynamic stress may also have been important. The 2000 New Ireland earthquake sequence provides evidence that tsunamis caused by thrust aftershocks can be triggered by large strike-slip earthquakes. Similar tectonic regimes that include offshore accommodation structures near large strike-slip faults are found in southern California, the Sea of Marmara, Turkey, along the Queen Charlotte fault in British Columbia

  7. Signature of Fault Healing in an Aftershock Sequence? The 2008 Wenchuan Earthquake

    Science.gov (United States)

    Zhang, Shengfeng; Wu, Zhongliang; Jiang, Changsheng

    2016-01-01

    We analyzed the aftershock sequence of the 2008 Wenchuan earthquake from May 12, 2008 to May 12, 2013 using the earthquake catalog of the China Earthquake Networks Center (CENC). In the analysis performed, we took under consideration the temporary variation in the completeness of the earthquake catalog just after the Wenchuan mainshock. The cutoff completeness magnitude from May 12 to June 27, 2008 was above 3.0 due to the impact of the earthquake sequence on the seismological observatory practice. It was observed that the b value has an increasing trend from June 27, 2008 to late April 2009, while since May 2009, the b value has remained stable. If these characteristics were associated with the possible signature of fault healing, the `apparent healing time' could be pinpointed by this measure as around 1 year. Due to two strong asperities present on the rupture of the Wenchuan mainshock, the aftershock zone can be divided into two segments, namely the north and the south segment. The b values of the two segments seem to show different trends of temporal variation. The main contribution of the increasing trend comes from the south segment, or the `initiation segment' of the main rupture.

  8. Computational Software for Fitting Seismic Data to Epidemic-Type Aftershock Sequence Models

    Science.gov (United States)

    Chu, A.

    2014-12-01

    Modern earthquake catalogs are often analyzed using spatial-temporal point process models such as the epidemic-type aftershock sequence (ETAS) models of Ogata (1998). My work introduces software to implement two of ETAS models described in Ogata (1998). To find the Maximum-Likelihood Estimates (MLEs), my software provides estimates of the homogeneous background rate parameter and the temporal and spatial parameters that govern triggering effects by applying the Expectation-Maximization (EM) algorithm introduced in Veen and Schoenberg (2008). Despite other computer programs exist for similar data modeling purpose, using EM-algorithm has the benefits of stability and robustness (Veen and Schoenberg, 2008). Spatial shapes that are very long and narrow cause difficulties in optimization convergence and problems with flat or multi-modal log-likelihood functions encounter similar issues. My program uses a robust method to preset a parameter to overcome the non-convergence computational issue. In addition to model fitting, the software is equipped with useful tools for examining modeling fitting results, for example, visualization of estimated conditional intensity, and estimation of expected number of triggered aftershocks. A simulation generator is also given with flexible spatial shapes that may be defined by the user. This open-source software has a very simple user interface. The user may execute it on a local computer, and the program also has potential to be hosted online. Java language is used for the software's core computing part and an optional interface to the statistical package R is provided.

  9. Including foreshocks and aftershocks in time-independent probabilistic seismic hazard analyses

    Science.gov (United States)

    Boyd, Oliver S.

    2012-01-01

    Time‐independent probabilistic seismic‐hazard analysis treats each source as being temporally and spatially independent; hence foreshocks and aftershocks, which are both spatially and temporally dependent on the mainshock, are removed from earthquake catalogs. Yet, intuitively, these earthquakes should be considered part of the seismic hazard, capable of producing damaging ground motions. In this study, I consider the mainshock and its dependents as a time‐independent cluster, each cluster being temporally and spatially independent from any other. The cluster has a recurrence time of the mainshock; and, by considering the earthquakes in the cluster as a union of events, dependent events have an opportunity to contribute to seismic ground motions and hazard. Based on the methods of the U.S. Geological Survey for a high‐hazard site, the inclusion of dependent events causes ground motions that are exceeded at probability levels of engineering interest to increase by about 10% but could be as high as 20% if variations in aftershock productivity can be accounted for reliably.

  10. SPECIFIC FEATURES OF FIELDS OF STRESSES ASSOCIATED WITH AFTERSHOCK PROCESSES IN THE ALTAI-SAYAN MOUNTAINOUS REGION

    Directory of Open Access Journals (Sweden)

    Olga A. Kuchay

    2015-09-01

    Full Text Available The cataclastic method developed by Yu.L. Rebetsky is applied to reconstruct the recent field of stresses related to aftershock sequences of earthquakes that occurred in the Altai-Sayan mountainous region, specifically the Altai earthquake of 27 September 2003 (М=7.3; φ=50.061o; λ=87.966o and the Busingol earthquake of 27 December 1991 (М=5.0; φ=51.1o; λ=98.13o. Upon reconstruction of the field of stresses from data on aftershocks of different magnitudes, it is revealed that orientations of maximum stresses are misaligned, and this may suggest a lack of similarity of fields of stresses in different scale ranks. The fields of stresses reconstructed from data on sequences of weak aftershocks of the Altai and Busingol earthquakes show changes in orientations of major stress axes at opposite sides of the shear faults under study. The orientation of the maximum deviation stress axes due to strong aftershocks is consistent with the regional field of stresses and does not change in the vicinity of the fault plane associated with the strong earthquakes the Altai and Sayan regions.

  11. Kinematic rupture process of the 2007 Tocopilla earthquake and its main aftershocks from teleseismic and strong-motion data

    Science.gov (United States)

    Peyrat, S.; Madariaga, R.; Buforn, E.; Campos, J.; Asch, G.; Vilotte, J. P.

    2010-09-01

    We study a large Mw = 7.6 earthquake that occurred on 2007 November 14 in the Northern Chile seismic gap near the city of Tocopilla. Using a variety of seismic data we show that this earthquake ruptured only the lower part of the interplate seismic zone and generated a series of plate interface aftershocks. Two large aftershocks on 2007 November 15 ruptured the interplate zone oceanwards of the Mejillones Peninsula, a major geographical feature in the Antofagasta region. On 2007 December 16, a large Mw = 6.8 aftershock, that occurred near the southern bottom of the fault plane of the main event, is shown to be a slab-push earthquake located inside the subducted Nazca Plate and triggered by along slab compression. Aftershocks of this event demonstrate that it occurred on an almost vertical fault. The Tocopilla earthquake took place just after the installation of a new seismological network by Chilean, German and French researchers. The accelerometric data combined with far field seismic data provide a quite complete and consistent view of the rupture process. The earthquake broke a long (130 km) and narrow (about 30-50 km) zone of the plate interface just above the transition zone. Using a non-linear kinematic inversion method, we determined that rupture occurred on two well-defined patches of roughly elliptical shape. We discuss the consequences of this event for models of gap filling earthquakes in Chile proposed in the 1970s.

  12. GIS-based 3D modeling and visualization of the Mw7.7, 2007, Tocopilla aftershocks

    Science.gov (United States)

    Eggert, S.; Sobiesiak, M.

    2009-04-01

    The November 14, 2007 Mw 7.7 earthquake nucleated on the west coast of northern Chile about 40 km east of the city of Tocopilla. It took place in the southern part of the of a large seismic gap namely, the Iquique subduction zone segment which is supposed to be at the end of its seismic cycle. The Tocopilla fault plane appears to be the northern continuation of the Mw 8.0, 1995 Antofagasta earthquake. We present a complex 3D model of the rupture area including first hypocenter localizations of aftershocks following the event. The data was recorded during a mission of the German Task Force for Earthquakes after the 2007 Tocopilla earthquake. 34 seismic stations were recording the aftershocks from November 2007 until May 2008. In general, subduction zones have a complex structure where most of the volumes examined are characterized by strong variations in physical and material parameters and are far away from a homogeneously layered half space. Therefore, 3D representation of the geophysical and geological conditions to be found are of great importance to understand such a subduction environment. Using ArcScene as a three-dimensional modeling tool gives us the possibility to visualize the aftershock distribution along the subducting slab and identify clear structures and clusters within the data set. Furthermore we combine the 2007 Tocopilla data set with the 1995 Antofagasta aftershocks which provides a new, three-dimensional insight into the segment boundary of these two events.

  13. Seismotectonic model of the MITIDJA basin using gravity data and aftershock sequence of the BOUMERDES (may 21, 2003; ALGERIA) earthquake

    Science.gov (United States)

    Ouyed, Merzouk; Idres, Mouloud; Salah Boughacha, Mohame; Bourmatte, Amar; Samai, Saddek

    2010-05-01

    The present study relates to the interpretation of gravity and seismological data in the Boumerdes area (Eastern part of the Mitidja Basin, Algeria), in relation to the earthquake of May 21, 2003 (Mw=6.8). The residual anomaly and the horizontal gradient maps made it possible to obtain the basement shape and gravity discontinuities. The seismological data processing of the aftershock sequence recorded by 16 tri-component seismological stations allowed the location of 1987 events during the period of May 23 to June 30, 2003. A seismotectonic model obtained from the aftershocks distribution and gravity data is proposed. This model consists of three active faults; one lying offshore and two other onshore faults highlighted in this study. The offshore fault striking NE-SW is consistent with the USGS focal mechanism of the main event; the onshore faults strike NW-SE. This configuration emphasizes the failure mode complexity during the main shock. The geometry and location of the onshore faults are obtained from the spatial distribution of seismicity and focal solutions, supported by the results of gravity, but also by the coastal uplift and the Algiers canyon close to one of these faults. The topography of the basement obtained by 3D gravity inversion shows that all the aftershocks located onshore occurred in the basement. The 3D model of the basement also shows that the area between the two onshore faults was raised by their movement. Keywords: Aftershock sequence, Algeria, Basement, Boumerdes earthquake, Gravity

  14. Determination of the Fault Plane of the 2013 Santa Cruz Earthquake, Bolivia, Through Relative Location of Aftershocks

    Science.gov (United States)

    Rivadeneyra Vera, J. C.; Assumpcao, M.

    2015-12-01

    The Central Andes of southern Bolivia is a highly seismic region due to the faults present in this area which eventually could generate earthquakes up to 8.5 Mw. Nevertheless most of them are shallow and have low magnitude. In 2013, an earthquake of 5.0 Mw ocurred in Santa Cruz de la Sierra, it was followed by five aftershocks in the two months after the mainshock. Distances between epicenters of the aftershocks and the mainshock are up to 34 km, which is greater than expected for an earthquake of this magnitude. Additionaly the uncertainty of the epicenters is around 20 km; this scenario is not suitable for studies looking to determine the seismogenic fault orientation. Using data from South American stations of the international network of the Incorporated Research Institutions dor Seismology (IRIS) and the relative location technique, that uses the surface waves (usually the clearest wave in noisy sismograms), the epicenters of five aftershocks of the Santa Cruz series were determinated in relation the mainshock. This method enabled to achieve epicentral locations with uncertainties smaller than 2 km, distances between the aftershocks and the mainshock are up to 7 km, in accordance with the magnitude of the earthquake. The result of the relative location showed a N - S trend of the epicenters in agreement with the location and orientation of the Mandeyapecua fault, the largest reverse fault in Bolivia. Key words: Relative location, Surface waves

  15. Aftershocks are well aligned with the background stress field, contradicting the hypothesis of highly-heterogeneous crustal stress

    Science.gov (United States)

    Hardebeck, Jeanne L.

    2010-01-01

    It has been proposed that the crustal stress field contains small-length-scale heterogeneity of much larger amplitude than the uniform background stress. This model predicts that earthquake focal mechanisms should reflect the loading stress rather than the uniform background stress. So, if the heterogeneous stress hypothesis is correct, focal mechanisms before and after a large earthquake should align with the tectonic loading and the earthquake-induced static stress perturbation, respectively. However, I show that the off-fault triggered aftershocks of the 1992 M7.3 Landers, California, earthquake align with the same stress field as the pre-Landers mechanisms. The aftershocks occurred on faults that were well oriented for failure in the pre-Landers stress field and then loaded by the Landers-induced static stress change. Aftershocks in regions experiencing a 0.05 to 5 MPa coseismic differential stress change align with the modeled Landers-induced static stress change, implying that they were triggered by the stress perturbation. Contrary to the heterogeneous stress hypothesis, these triggered aftershocks are also well aligned with the pre-Landers stress field obtained from inverting the pre-Landers focal mechanisms. Therefore, the inverted pre-Landers stress must represent the persistent background stress field. Earthquake focal mechanisms provide an unbiased sample of the spatially coherent background stress field, which is large relative to any small-scale stress heterogeneity. The counterexample provided by the Landers earthquake is strong evidence that the heterogeneous stress model is not widely applicable.

  16. Study on shear wave splitting in the aftershock region of the Yao'an earthquake in 2000

    Institute of Scientific and Technical Information of China (English)

    WANG Xin-ling; LIU Jie; ZHANG Guo-min; MA Hong-sheng; WANG Hui

    2006-01-01

    After Ms=6.5 Yao'an earthquake on January 15, 2000, a large amount of aftershock waveforms were recorded by the Near Source Digital Seismic Network (NSSN) installed by Earthquake Administration of Yunnan Province in the aftershock region. It provides profuse data to systematically analyze the features of Yao'an earthquake. The crustal anisotropy is realized by shear wave splitting propagating in the upper crust. Based on the accurate aftershock relocations, the shear wave splitting parameters are determined with the cross-correlation method, and the results of different stations and regions are discussed in this paper. These conclusions are obtained as follows:firstly, the average fast directions of aftershock region are controlled by the regional stress field and parallel to the maximum horizontal compressive stress direction; secondly, the average fast directions of disparate stations and regions are different and vary with the structural settings and regional stress fields; finally, delay time value is affected by all sorts of factors, which is affinitive with the shear wave propagating medium, especially.

  17. Aftershock distribution as a constraint on the geodetic model of coseismic slip for the 2004 Parkfield earthquake

    Science.gov (United States)

    Bennington, Ninfa; Thurber, Clifford; Feigl, Kurt; ,

    2011-01-01

    Several studies of the 2004 Parkfield earthquake have linked the spatial distribution of the event’s aftershocks to the mainshock slip distribution on the fault. Using geodetic data, we find a model of coseismic slip for the 2004 Parkfield earthquake with the constraint that the edges of coseismic slip patches align with aftershocks. The constraint is applied by encouraging the curvature of coseismic slip in each model cell to be equal to the negative of the curvature of seismicity density. The large patch of peak slip about 15 km northwest of the 2004 hypocenter found in the curvature-constrained model is in good agreement in location and amplitude with previous geodetic studies and the majority of strong motion studies. The curvature-constrained solution shows slip primarily between aftershock “streaks” with the continuation of moderate levels of slip to the southeast. These observations are in good agreement with strong motion studies, but inconsistent with the majority of published geodetic slip models. Southeast of the 2004 hypocenter, a patch of peak slip observed in strong motion studies is absent from our curvature-constrained model, but the available GPS data do not resolve slip in this region. We conclude that the geodetic slip model constrained by the aftershock distribution fits the geodetic data quite well and that inconsistencies between models derived from seismic and geodetic data can be attributed largely to resolution issues.

  18. Global Aftershock

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The catastrophic earthquake and ensuing tsunami in Japan have raised concerns about the economic backlash not only to Japan,but also to the world.Standard Chartered Bank’s report Japan:Assessing the Impact warned that Japan’s economy faces the short-term risk of stagnation and suggested the possible impact the rest of the world could face.Edited excerpt follows

  19. High-Resolution Locations and Focal Mechanisms of Aftershocks of the September 5, 2012 Mw=7.6 Nicoya, Costa Rica Earthquake

    Science.gov (United States)

    Laure, Duboeuf; Susan, Schwartz

    2015-04-01

    Subduction beneath the Nicoya Peninsula, Costa Rica generates the largest underthrusting earthquakes in the country with a recurrence interval of about 50 years. The most recent of these events occurred on September 5th 2012 (Mw 7.6). A vigorous aftershock sequence of more than 6400 earthquakes was recorded by a local seismic network within the first 4 months of the mainshock. We identify those aftershocks occurring on the mainshock fault plane and compare their locations to the 2012 mainshock slip distribution, the location of past interplate seismicity, and slow slip phenomena to better understand the mechanical behavior of this plate interface. Our focal mechanism determination includes all aftershocks occurring within the first nine days after the mainshock and aftershocks with magnitude greater than four occurring through the end of December 2012. We use the HASH (Hardebeck and Shearer, 2002) software package, based on first motion polarities, to obtain aftershock focal mechanisms. We are able to determine reliable focal mechanisms for 583 of the aftershocks and identify 264 of them as occurring on the plate interface. All of these are relocated using HypoDD (Waldhauser and Ellsworth, 2000) and their locations are compared with other plate boundary activity. We find no significant seismicity patterns as a function of time or magnitude, but confirm that deeper underthrusting events occur in the north compared to the south as revealed by previous studies (Newman et al., 2002). Most of the aftershocks occur in and around the updip part of the coseismic rupture zone. This suggests that the Nicoya mainshock released all of the accumulated strain in the deeper part of the plate interface, leaving none to occur as aftershocks. Previous interface seismicity in this region reveals a similar distribution to the aftershocks, however it extends to deeper depth and defines the entire seismogenic zone. The coseismic slip occurs even deeper than the background interface

  20. The earthquakes on 12 April 1998 and 12 July 2004 in Krn Mountains (NW Slovenia – time distribution of aftershocks and magnitude-frequency relation

    Directory of Open Access Journals (Sweden)

    Andrej Gosar

    2008-06-01

    Full Text Available Earthquakes on 12 April 1998 (ML=5.6 and 12. July 2004 (ML=4.9 in Krn Mountains were followed by extensive after shock sequences with several thousand of shocks which lasted for more than one year. In 400 days the first earthquake was followed by 104 and the second one by 89 aftershocks with ML≥2,0. Both strongest aftershocks had magnitudes smaller for 1.4 and 1.3 with respect to the mainshocks, which is slightly more than published values (1.2. Analysis of time distribution of aftershocks with maximum likelihood estimate has shown that the parameters of modified Omori’s law,which describes the hyperbolic decay of aftershock activity with time,arevery similar. This corresponds to the fact that both earthquakes occurred in the same hypocentral area. The value of p parameter is around 1.02. Aftershocks in 1998 clearly show secondary aftershock sequence which started with strongest aftershock on 6 May 1998 (ML=4.2, but there was no secondary sequence in 2004. Analysis of magnitude-frequency (Gutenberg-Richter’s relation with least squares and maximum likelihood estimate has given the value of b parameter for 1998 aftershock sequence between 0.77 and 0.83 and for 2004 sequence between 0.97 and 0.98. This means that the first earthquake was followed by more stronger after shocks.Obtained parameters of modified Omori’s law and Gutenberg-Richter’s relation are in good agreement with values published for similar aftershock sequences.

  1. Absolute site effects in Kachchh, India, determined from aftershocks of the 2002 Bhuj earthquake.

    Science.gov (United States)

    Malagnini, L.; Mayeda, K.; Bodin, P.; Akinci, A.

    2004-12-01

    What can be learned about absolute site effects on ground motions from recordings of aftershocks at ten temporary seismic stations, none of which could be considered a "reference" (hard rock) site, and for which no geotechnical information is available? This challenge motivated our current study of Bhuj aftershocks; and our answer, briefly put, is: quite a bit. We started by constraining the regional attenuation and geometric spreading: this was the result of an earlier study [Bodin et al., BSSA 2004], the goal of which was to be able to reproduce the general character of the observations with a constrained set of stochastic synthetic ground motions. Our present work is based on the same aftershock data we used in the prior study. We first produced stable and reliable, unbiased source moment-rate spectra using the technique described by Mayeda et al., [BSSA, 2003]. With these known "absolute" source spectra, and the propagation terms we quantified in the previous study we inverted for the site response using only the largest ~200 earthquakes (M>2.8) in each of two depth ranges (0-25 km, and 20-40 km), to yield the "absolute" site terms for horizontal and vertical ground motions. We were able to obtain stable results in the 1-14 hz frequency band. The results reveal that the site terms generally share a common character: small amplifications (near unity) at the longer-period end of the pass-band, and decreases (perhaps due to attenuation or near-site scattering) at the higher frequency end. This character is evident in a similar study of earthquake ground motions in the Alps at sites on hard rock [Malagnini et al., BSSA 2004]. In contrast to Alpine hard rock sites, however, the vertical site terms at our sediment and soft-rock sites are generally rather flat and featureless. We observe differences in site response between stations which appeared to be on similar geologic conditions, and vice versa. For sites that appear to be on deep unconsolidated soils

  2. The Seismic Aftershock Monitoring System (SAMS) for OSI - Experiences from IFE14

    Science.gov (United States)

    Gestermann, Nicolai; Sick, Benjamin; Häge, Martin; Blake, Thomas; Labak, Peter; Joswig, Manfred

    2016-04-01

    An on-site inspection (OSI) is the third of four elements of the verification regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The sole purpose of an OSI is to confirm whether a nuclear weapon test explosion or any other nuclear explosion has been carried out in violation of the treaty and to gather any facts which might assist in identifying any possible violator. It thus constitutes the final verification measure under the CTBT if all other available measures are not able to confirm the nature of a suspicious event. The Provisional Technical Secretariat (PTS) carried out the Integrated Field Exercise 2014 (IFE14) in the Dead Sea Area of Jordan from 3 November to 9. December 2014. It was a fictitious OSI whose aim was to test the inspection capabilities in an integrated manner. The technologies allowed during an OSI are listed in the Treaty. The aim of the Seismic Aftershock Monitoring System (SAMS) is to detect and localize aftershocks of low magnitudes of the triggering event or collapses of underground cavities. The locations of these events are expected in the vicinity of a possible previous explosion and help to narrow down the search area within an inspection area (IA) of an OSI. The success of SAMS depends on the main elements, hardware, software, deployment strategy, the search logic and not least the effective use of personnel. All elements of SAMS were tested and improved during the Built-Up Exercises (BUE) which took place in Austria and Hungary. IFE14 provided more realistic climatic and hazardous terrain conditions with limited resources. Significant variations in topography of the IA of IFE14 in the mountainous Dead Sea Area of Jordan led to considerable challenges which were not expected from experiences encountered during BUE. The SAMS uses mini arrays with an aperture of about 100 meters and with a total of 4 elements. The station network deployed during IFE14 and results of the data analysis will be presented. Possible aftershocks of

  3. Foreshocks and aftershocks of Pisagua 2014 earthquake: time and space evolution of megathrust event.

    Science.gov (United States)

    Fuenzalida Velasco, Amaya; Rietbrock, Andreas; Wollam, Jack; Thomas, Reece; de Lima Neto, Oscar; Tavera, Hernando; Garth, Thomas; Ruiz, Sergio

    2016-04-01

    The 2014 Pisagua earthquake of magnitude 8.2 is the first case in Chile where a foreshock sequence was clearly recorded by a local network, as well all the complete sequence including the mainshock and its aftershocks. The seismicity of the last year before the mainshock include numerous clusters close to the epicentral zone (Ruiz et al; 2014) but it was on 16th March that this activity became stronger with the Mw 6.7 precursory event taking place in front of Iquique coast at 12 km depth. The Pisagua earthquake arrived on 1st April 2015 breaking almost 120 km N-S and two days after a 7.6 aftershock occurred in the south of the rupture, enlarging the zone affected by this sequence. In this work, we analyse the foreshocks and aftershock sequence of Pisagua earthquake, from the spatial and time evolution for a total of 15.764 events that were recorded from the 1st March to 31th May 2015. This event catalogue was obtained from the automatic analyse of seismic raw data of more than 50 stations installed in the north of Chile and the south of Peru. We used the STA/LTA algorithm for the detection of P and S arrival times on the vertical components and then a method of back propagation in a 1D velocity model for the event association and preliminary location of its hypocenters following the algorithm outlined by Rietbrock et al. (2012). These results were then improved by locating with NonLinLoc software using a regional velocity model. We selected the larger events to analyse its moment tensor solution by a full waveform inversion using ISOLA software. In order to understand the process of nucleation and propagation of the Pisagua earthquake, we also analysed the evolution in time of the seismicity of the three months of data. The zone where the precursory events took place was strongly activated two weeks before the mainshock and remained very active until the end of the analysed period with an important quantity of the seismicity located in the upper plate and having

  4. The 25 March 1993 Scotts Mills, Oregon, earthquake and aftershock sequence: Spatial distribution, focal mechanisms, and the mount angel fault

    Science.gov (United States)

    Thomas, G.C.; Crosson, R.S.; Carver, D.L.; Yelin, T.S.

    1996-01-01

    The 25 March 1993 ML = 5.7 crustal earthquake near Scotts Mills, Oregon, was the largest earthquake to occur in the Pacific Northwest in over a decade. The mainshock was located at 45.033?? N, 122.586?? W and at a depth of about 15.1 km, based on arrival time data from the short-period Pacific Northwest Seismograph Network. Beginning about 12 h after the mainshock, investigators from the U.S. Geological Survey deployed 22 digital seismographs to record aftershocks. Using data from the temporary and permanent stations, we analyzed a subset of 50 after-shocks with quality locations. Hypocenters of these aftershocks lie on a northwesttrending steeply dipping plane (strike 290 ?? 10??, dipping 60 ?? 5?? to the north-northeast), in agreement with the preferred slip plane of the mainshock focal mechanism solution (strike 294??, dipping 58?? to the north-northeast). The planar structure defined by the aftershock locations may be a southeast continuation of the Mount Angel Fault, a reverse fault identified from both surface and subsurface evidence. The mapped southeast extent of the Mount Angel Fault is located less than 10 km west of the Scotts Mills epicentral region. In addition, the mainshock focal mechanism solution, with a combination of reverse motion and right-lateral strike slip, has a geometry and sense of motion consistent with the Mount Angel Fault. While aftershock focal mechanisms are varied, P axes are consistently oriented in a subhorizontal north-south direction. This earthquake sequence, together with the geological and geophysical evidence for the Mount Angel Fault, suggests a significant crustal earthquake hazard for this region of northwest Oregon.

  5. The Gorkha earthquake of April 25, 2015 in Nepal: Tectonic position, aftershock process, and possibilities of forecasting the evolution of seismic situation

    Science.gov (United States)

    Rogozhin, E. A.; Lutikov, A. I.; Sobisevich, L. E.; Shen, To; Kanonidi, K. Kh.

    2016-07-01

    The characteristics of the foci for the main shock and strongest aftershocks of the Gorkha earthquake of April 25, 2015 in Nepal are described. The macroseismic data and examples of seismic dislocations are discussed. The progression of the release of seismic energy by the aftershock process is analyzed. The data for the geophysical and seismological precursors of the main shock and the strongest aftershock of May 12, 2015 are presented. These data allowed us to formulate the short-term forecast of this event.

  6. The study of recent seismicity in the aftershock area of Neftegorsk earthquake using waveform cross correlation

    Science.gov (United States)

    Kitov, Ivan; Turuntaev, Sergey; Konovalov, Alexei; Stepnov, Andrey

    2016-04-01

    Unusually long duration of seismic activity (more than 20 years) was observed in the aftershock area of the 1995 Neftegorsk, Sakhalin, Russia catastrophic earthquake (Ms=7.6). To study the phenomena, we have processed seismic data from 130 events occurred within that area as measured between 2006 and 2015. In order to improve the accuracy of relative location and magnitude estimation of these events we have applied new techniques based on waveform cross correlation. We use 7 three-component (3-C) seismic stations which detected most of these events. Three-component waveform templates were prepared for these stations from those events which had signals with SNR>5 at vertical channels. The events with 3 and more templates are used as master-events for waveform cross correlation. Overall, the re-estimated location and magnitudes demonstrate higher precisions and are used for the statistical analysis and numerical modelling of seismo-tectonic regime within the studied zone.

  7. Exploring the limits of waveform correlation event detection as applied to three earthquake aftershock sequences.

    Energy Technology Data Exchange (ETDEWEB)

    Resor, Megan E.; Carr, Dorthe Bame; Young, Christopher John

    2010-05-01

    Swarms of earthquakes and/or aftershock sequences can dramatically increase the level of seismicity in a region for a period of time lasting from days to months, depending on the swarm or sequence. Such occurrences can provide a large amount of useful information to seismologists. For those who monitor seismic events for possible nuclear explosions, however, these swarms/sequences are a nuisance. In an explosion monitoring system, each event must be treated as a possible nuclear test until it can be proven, to a high degree of confidence, not to be. Seismic events recorded by the same station with highly correlated waveforms almost certainly have a similar location and source type, so clusters of events within a swarm can quickly be identified as earthquakes. We have developed a number of tools that can be used to exploit the high degree of waveform similarity expected to be associated with swarms/sequences. Dendro Tool measures correlations between known events. The Waveform Correlation Detector is intended to act as a detector, finding events in raw data which correlate with known events. The Self Scanner is used to find all correlated segments within a raw data steam and does not require an event library. All three techniques together provide an opportunity to study the similarities of events in an aftershock sequence in different ways. To comprehensively characterize the benefits and limits of waveform correlation techniques, we studied 3 aftershock sequences, using our 3 tools, at multiple stations. We explored the effects of station distance and event magnitudes on correlation results. Lastly, we show the reduction in detection threshold and analyst workload offered by waveform correlation techniques compared to STA/LTA based detection. We analyzed 4 days of data from each aftershock sequence using all three methods. Most known events clustered in a similar manner across the toolsets. Up to 25% of catalogued events were found to be a member of a cluster. In

  8. The aftershock sequence of the north-west Kashmir earthquake of September 3, 1972

    Directory of Open Access Journals (Sweden)

    R. K. S. CHOUHAN

    1975-05-01

    Full Text Available This paper is an attempt to study the aftershock sequence of the Northwest Kashmir earthquake of September 3, 1972. b value of the sequence is 1.59. The area of active strain zone is approximately 2.9 • ]013 sq. cm. The total average strain, average elastic energy and average stress of the rock before slip are 3.3 • 10~5, 3.2 ergs/cm3 and 19.8 kg/cm2. The strain rebound curve of the sequence has been constructed which shows a dual type of recovery where the compressional elastic creep is followed by the shear creep recovery. The relaxation time of the sequence is about 0.7 day, showing the Kelvin body like behaviour of the upper mantle.

  9. Applications of the predictability of the Coherent Noise Model to aftershock sequences

    Science.gov (United States)

    Christopoulos, Stavros-Richard; Sarlis, Nicholas

    2014-05-01

    A study [1] of the coherent noise model [2-4] in natural time [5-7] has shown that it exhibits predictability. Interestingly, one of the predictors suggested [1] for the coherent noise model can be generalized and applied to the case of (real) aftershock sequences. The results obtained [8] so far are beyond chance. Here, we apply this approach to several aftershock sequences of strong earthquakes with magnitudes Mw ≥6.9 in Indonesia, California and Greece, including the Mw9.2 earthquake that occurred on 26 December 2004 in Sumatra. References. [1] N. V. Sarlis and S.-R. G. Christopoulos, Predictability of the coherent-noise model and its applications, Physical Review E, 85, 051136, 2012. [2] M.E.J. Newman, Self-organized criticality, evolution and the fossil extinction record, Proc. R. Soc. London B, 263, 1605-1610, 1996. [3] M. E. J. Newman and K. Sneppen, Avalanches, scaling, and coherent noise, Phys. Rev. E, 54, 6226-6231, 1996. [4] K. Sneppen and M. Newman, Coherent noise, scale invariance and intermittency in large systems, Physica D, 110, 209 - 222. [5] P. Varotsos, N. Sarlis, and E. Skordas, Spatiotemporal complexity aspects on the interrelation between Seismic Electric Signals and seismicity, Practica of Athens Academy, 76, 294-321, 2001. [6] P.A. Varotsos, N.V. Sarlis, and E.S. Skordas, Long-range correlations in the electric signals that precede rupture, Phys. Rev. E, 66, 011902, 2002. [7] Varotsos P. A., Sarlis N. V. and Skordas E. S., Natural Time Analysis: The new view of time. Precursory Seismic Electric Signals, Earthquakes and other Complex Time-Series (Springer-Verlag, Berlin Heidelberg) 2011. [8] N. V. Sarlis and S.-R. G. Christopoulos, "Visualization of the significance of Receiver Operating Characteristics based on confidence ellipses", Computer Physics Communications, http://dx.doi.org/10.1016/j.cpc.2013.12.009

  10. Constraints on recent earthquake source parameters, fault geometry and aftershock characteristics in Oklahoma

    Science.gov (United States)

    McNamara, D. E.; Benz, H.; Herrmann, R. B.; Bergman, E. A.; McMahon, N. D.; Aster, R. C.

    2014-12-01

    In late 2009, the seismicity of Oklahoma increased dramatically. The largest of these earthquakes was a series of three damaging events (Mw 4.8, 5.6, 4.8) that occurred over a span of four days in November 2011 near the town of Prague in central Oklahoma. Studies suggest that these earthquakes were induced by reactivation of the Wilzetta fault due to the disposal of waste water from hydraulic fracturing ("fracking") and other oil and gas activities. The Wilzetta fault is a northeast trending vertical strike-slip fault that is a well known structural trap for oil and gas. Since the November 2011 Prague sequence, thousands of small to moderate (M2-M4) earthquakes have occurred throughout central Oklahoma. The most active regions are located near the towns of Stillwater and Medford in north-central Oklahoma, and Guthrie, Langston and Jones near Oklahoma City. The USGS, in collaboration with the Oklahoma Geological Survey and the University of Oklahoma, has responded by deploying numerous temporary seismic stations in the region in order to record the vigorous aftershock sequences. In this study we use data from the temporary seismic stations to re-locate all Oklahoma earthquakes in the USGS National Earthquake Information Center catalog using a multiple-event approach known as hypo-centroidal decomposition that locates earthquakes with decreased uncertainty relative to one another. Modeling from this study allows us to constrain the detailed geometry of the reactivated faults, as well as source parameters (focal mechanisms, stress drop, rupture length) for the larger earthquakes. Preliminary results from the November 2011 Prague sequence suggest that subsurface rupture lengths of the largest earthquakes are anomalously long with very low stress drop. We also observe very high Q (~1000 at 1 Hz) that explains the large felt areas and we find relatively low b-value and a rapid decay of aftershocks.

  11. The 11 April 2012 east Indian Ocean earthquake triggered large aftershocks worldwide

    Science.gov (United States)

    Pollitz, Fred F.; Stein, Ross S.; Sevilgen, Volkan; Burgmann, Roland

    2012-01-01

    Large earthquakes trigger very small earthquakes globally during passage of the seismic waves and during the following several hours to days1, 2, 3, 4, 5, 6, 7, 8, 9, 10, but so far remote aftershocks of moment magnitude M≥5.5 have not been identified11, with the lone exception of an M=6.9 quake remotely triggered by the surface waves from an M=6.6 quake 4,800 kilometres away12. The 2012 east Indian Ocean earthquake that had a moment magnitude of 8.6 is the largest strike-slip event ever recorded. Here we show that the rate of occurrence of remote M≥5.5 earthquakes (>1,500 kilometres from the epicentre) increased nearly fivefold for six days after the 2012 event, and extended in magnitude to M≥7. These global aftershocks were located along the four lobes of Love-wave radiation; all struck where the dynamic shear strain is calculated to exceed 10-7 for at least 100 seconds during dynamic-wave passage. The other M≥8.5 mainshocks during the past decade are thrusts; after these events, the global rate of occurrence of remote M≥5.5 events increased by about one-third the rate following the 2012 shock and lasted for only two days, a weaker but possibly real increase. We suggest that the unprecedented delayed triggering power of the 2012 earthquake may have arisen because of its strike-slip source geometry or because the event struck at a time of an unusually low global earthquake rate, perhaps increasing the number of nucleation sites that were very close to failure.

  12. Multiple event location analysis of aftershock sequences in the Pannonian basin

    Science.gov (United States)

    Bekesi, Eszter; Sule, Balint; Bondar, Istvan

    2016-04-01

    Accurate seismic event location is crucial to understand tectonic processes such as crustal faults that are most commonly investigated by studying seismic activity. Location errors can be significantly reduced using multiple event location methods. We applied the double difference method to relocate the earthquake occurred near Oroszlány and its 200 aftershocks to identify the geometry of the related fault. We used the extended ISC location algorithm, iLoc to determine the absolute single event locations for the Oroszlány aftershock sequence and applied double difference algorithm on the new hypocenters. To improve location precision, we added differential times from waveform cross-correlation to the multiple event location process to increase the accuracy of arrival time readings. We also tested the effect of various local 1-D velocity models on the results. We compared hypoDD results of bulletin and iLoc hypocenters to investigate the effect of initial hypocenter parameters on the relocation process. We show that hypoDD collapses the initial, rather diffuse locations into a smaller cluster and the vertical cross-sections show sharp images of seismicity. Unsurprisingly, the combined use of catalog and cross-correlation data sets provides the more accurate locations. Some of the relocated events in the cluster are ground truth quality with a location accuracy of 5 km or better. Having achieved accurate locations for the event cluster we are able to resolve the fault plane ambiguity in the moment tensor solutions and determine the accurate strike of the fault.

  13. Numerical simulation of dynamic Coulomb stress changes induced by M6.5 earthquake in Wuding, Yunnan and its relationship with aftershocks

    Institute of Scientific and Technical Information of China (English)

    HU Xiong-lin; WU Xiao-ping; YANG Run-hai; FU Hong; HU Jia-fu; HUANG Yong

    2008-01-01

    Based on the discrete wavenumber method, we calculate the fields of dynamic Coulomb rupture stress changes and static stress changes caused by M6.5 earthquake in Wuding, and study their relationship with the subsequent aftershocks. The results show that the spatial distribution patterns of the positive region of dynamic stress peak value and static stress peak value are similarly asymmetric, which are basically identical with distribution features of aftershock. The dynamic stress peak value and the static stress in the positive region are more than 0.1 MPa and 0.01 MPa of the triggering threshold, respectively, which indicates that the dynamic and static stresses are helpful for the occurrence of aftershock. This suggests that both influences of dynamic and static stresses should be con-sidered other than only either of them when studying aftershock triggering in near field.

  14. The Triggering Mechanism for the Largest Aftershock (Ms=6.3) of the Great Luhuo Event (Ms=7.6) in 1973

    Institute of Scientific and Technical Information of China (English)

    Liu Guiping; Fu Zhengxiang; Ma Ming

    2003-01-01

    The Great Luhno Event ( Ms= 7.6) occurred on February 6, 1973 in Sichuan Province. There were a lot of aftershocks in the source area. The largest aftershock (Ms= 6.3) occurred along a normal fault zone between the Xianshuihe Fault and the Gnnzi-Yushu fault. Based on the focal mechanism solution, surface rupture, coseismic dislocation and seismo-geological tectonics of the event, an elastic dislocation model of the Great Luhuo Event with a strike slip mechanism was designed and the Coulomb Failure Stress Change (ΔCFS) in the slip direction on normal faults along and surrounding the source zone due to the event was calculated. The results showed that the largest aftershock occurred in an area with ΔCFS>O, and that ΔCFS=4.5MPa. Therefore, the largest aftershock was probably triggered by the Coulomb Failure Stress Change.

  15. Application of Subspace Detection to the 6 November 2011 M5.6 Prague, Oklahoma Aftershock Sequence

    Science.gov (United States)

    McMahon, N. D.; Benz, H.; Johnson, C. E.; Aster, R. C.; McNamara, D. E.

    2015-12-01

    Subspace detection is a powerful tool for the identification of small seismic events. Subspace detectors improve upon single-event matched filtering techniques by using multiple orthogonal waveform templates whose linear combinations characterize a range of observed signals from previously identified earthquakes. Subspace detectors running on multiple stations can significantly increasing the number of locatable events, lowering the catalog's magnitude of completeness and thus providing extraordinary detail on the kinematics of the aftershock process. The 6 November 2011 M5.6 earthquake near Prague, Oklahoma is the largest earthquake instrumentally recorded in Oklahoma history and the largest earthquake resultant from deep wastewater injection. A M4.8 foreshock on 5 November 2011 and the M5.6 mainshock triggered tens of thousands of detectable aftershocks along a 20 km splay of the Wilzetta Fault Zone known as the Meeker-Prague fault. In response to this unprecedented earthquake, 21 temporary seismic stations were deployed surrounding the seismic activity. We utilized a catalog of 767 previously located aftershocks to construct subspace detectors for the 21 temporary and 10 closest permanent seismic stations. Subspace detection identified more than 500,000 new arrival-time observations, which associated into more than 20,000 locatable earthquakes. The associated earthquakes were relocated using the Bayesloc multiple-event locator, resulting in ~7,000 earthquakes with hypocentral uncertainties of less than 500 m. The relocated seismicity provides unique insight into the spatio-temporal evolution of the aftershock sequence along the Wilzetta Fault Zone and its associated structures. We find that the crystalline basement and overlying sedimentary Arbuckle formation accommodate the majority of aftershocks. While we observe aftershocks along the entire 20 km length of the Meeker-Prague fault, the vast majority of earthquakes were confined to a 9 km wide by 9 km deep

  16. The 3-D aftershock distribution of three recent M5~5.5 earthquakes in the Anza region,California

    Science.gov (United States)

    Zhang, Q.; Wdowinski, S.; Lin, G.

    2011-12-01

    The San Jacinto fault zone (SJFZ) exhibits the highest level of seismicity compared to other regions in southern California. On average, it produces four earthquakes per day, most of them at depth of 10-17 km. Over the past decade, an increasing seismic activity occurred in the Anza region, which included three M5~5.5 events and their aftershock sequences. These events occurred in 2001, 2005, and 2010. In this research we map the 3-D distribution of these three events to evaluate their rupture geometry and better understand the unusual deep seismic pattern along the SJFZ, which was termed "deep creep" (Wdowinski, 2009). We relocated 97,562 events from 1981 to 2011 in Anza region by applying the Source-Specific Station Term (SSST) method (Lin et al., 2006) and used an accurate 1-D velocity model derived from 3-D model of Lin et al (2007) and used In order to separate the aftershock sequence from background seismicity, we characterized each of the three aftershock sequences using Omori's law. Preliminary results show that all three sequences had a similar geometry of deep elongated aftershock distribution. Most aftershocks occurred at depth of 10-17 km and extended over a 70 km long segments of the SJFZ, centered at the mainshock hypocenters. A comparative study of other M5~5.5 mainshocks and their aftershock sequences in southern California reveals very different geometrical pattern, suggesting that the three Anza M5~5.5 events are unique and can be indicative of "deep creep" deformation processes. Reference 1.Lin, G.and Shearer,P.M.,2006, The COMPLOC earthquake location package,Seism. Res. Lett.77, pp.440-444. 2.Lin, G. and Shearer, P.M., Hauksson, E., and Thurber C.H.,2007, A three-dimensional crustal seismic velocity model for southern California from a composite event method,J. Geophys.Res.112, B12306, doi: 10.1029/ 2007JB004977. 3.Wdowinski, S. ,2009, Deep creep as a cause for the excess seismicity along the San Jacinto fault, Nat. Geosci.,doi:10.1038/NGEO684.

  17. 3D imaging of crustal structure under the Piedmont province in central Virginia, from reflection RVSP processing of aftershock recordings from the August 23, 2011 Virginia earthquake

    Science.gov (United States)

    Quiros, D. A.; Brown, L. D.; Cabolova, A.; Davenport, K. K.; Hole, J. A.; Mooney, W. D.

    2013-12-01

    Aftershocks from the magnitude Mw 5.8 August 23, 2011, central Virginia earthquake were recorded using an unusually dense array of seismometers in what has been termed an AIDA (Aftershock Imaging with Dense Arrays) deployment. Over 200 stations were deployed in the epicentral region of this event to a) more precisely determine hypocentral locations, b) more accurately define velocity structure in the aftershock zone, c) characterize propagation characteristics of the crust in the area, and d) image geologic structures in the hypocentral volume with reflection techniques using aftershocks as sources. The AIDA-Virginia experiment successfully recorded a large number of aftershocks from which local tomographic velocity estimates and accurate hypocentral locations were obtained. These results facilitated the use of aftershocks as sources for reflection imaging. In this study we demonstrate how earthquake sources recorded by surface arrays can be treated using the imaging techniques associated with Vertical Seismic Profiling (VSP), in particular a variant known as Reverse VSP (RVSP). The central VSP processing algorithms used for this study are VSP normal moveout (VSPnmo) and VSP-to-Common Reflection Point (CRP). Applying these techniques to individual aftershocks from the Virginia experiment results in 3D reflection images of structural complexity in the immediate vicinity of the aftershocks. The most prominent feature observed on these 3D images is a strong moderately east-dipping reflector at a depth of approximately 6 to 8 km that directly underlies, and is continuous beneath, the more steeply dipping aftershock zone. We interpret this reflector as part of a complex imbricate thrust sequence associated with Paleozoic convergence during the Appalachian orogeny. Its apparent continuity beneath the fault zone implied by the aftershock's hypocenters suggests that this inferred fault zone has little or no cumulative offset, supporting the speculation that this event

  18. The 2012 August 11 MW 6.5, 6.4 Ahar-Varzghan earthquakes, NW Iran: aftershock sequence analysis and evidence for activity migration

    Science.gov (United States)

    Rezapour, Mehdi

    2016-02-01

    The Ahar-Varzghan doublet earthquakes with magnitudes MW 6.5 and 6.4 occurred on 2012 August 11 in northwest Iran and were followed by many aftershocks. In this paper, we analyse ˜5 months of aftershocks of these events. The Ahar-Varzghan earthquakes occurred along complex faults and provide a new constraint on the earthquake hazard in northwest Iran. The general pattern of relocated aftershocks defines a complex seismic zone covering an area of approximately 25 × 10 km2. The Ahar-Varzghan aftershock sequence shows a secondary activity which started on November 7, approximately 3 months after the main shocks, with a significant increase in activity, regarding both number of events and their magnitude. This stage was characterized by a seismic zone that propagated to the west of the main shocks. The catalogue of aftershocks for the doublet earthquake has a magnitude completeness of Mc 2.0. A below-average b-value for the Ahar-Varzghan sequence indicates a structural heterogeneity in the fault plane and the compressive stress state of the region. Relocated aftershocks occupy a broad zone clustering east-west with near-vertical dip which we interpret as the fault plane of the first of the doublet main shocks (MW 6.5). The dominant depth range of the aftershocks is from 3 to about 20 km, and the focal depths decrease toward the western part of the fault. The aftershock activity has its highest concentration in the eastern and middle parts of the active fault, and tapers off toward the western part of the active fault segment, indicating mainly a unilateral rupture toward west.

  19. A case study of two M~5 mainshocks in Anza, California: Is the footprint of an aftershock sequence larger than we think?

    Science.gov (United States)

    Fritts, Karen R.; Kilb, Debi

    2009-01-01

    It has been traditionally held that aftershocks occur within one to two fault lengths of the mainshock. Here we demonstrate that this perception has been shaped by the sensitivity of seismic networks. The 31 October 2001 Mw 5.0 and 12 June 2005 Mw 5.2 Anza mainshocks in southern California occurred in the middle of the densely instrumented ANZA seismic network and thus were unusually well recorded. For the June 2005 event, aftershocks as small as M 0.0 could be observed stretching for at least 50 km along the San Jacinto fault even though the mainshock fault was only ∼4.5 km long. It was hypothesized that an observed aseismic slipping patch produced a spatially extended aftershock-triggering source, presumably slowing the decay of aftershock density with distance and leading to a broader aftershock zone. We find, however, the decay of aftershock density with distance for both Anza sequences to be similar to that observed elsewhere in California. This indicates there is no need for an additional triggering mechanism and suggests that given widespread dense instrumentation, aftershock sequences would routinely have footprints much larger than currently expected. Despite the large 2005 aftershock zone, we find that the probability that the 2005 Anza mainshock triggered the M 4.9 Yucaipa mainshock, which occurred 4.2 days later and 72 km away, to be only 14%±1%. This probability is a strong function of the time delay; had the earthquakes been separated by only an hour, the probability of triggering would have been 89%.

  20. Source mechanism of strong aftershocks (M_s≥5.6) of the 2008/05/12 Wenchuan earthquake and the implication for seismotectonics

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Dozens of >M5, hundreds of >M4, and much more >M3 aftershocks occurred after the 2008/05/12 Wenchuan earthquake, which were well recorded by permanent and portable seismic stations. After relocated with P arrival, the >M3 aftershocks show two trends of distribution, with most of the aftershocks located along the north-east strike consistent with Longmenshan fault system, yet there is a north-west trend around the epicenter. It seems that substantially more aftershocks occur in regions with crystalline bedrocks. Then we collected waveform data from National Digital Seismograph Network and regional seismograph network of China, and employed "Cut and Paste" method to obtain focal mechanisms and depths of the big aftershocks (M≥5.6). While most of those aftershocks show thrust mechanism, there are some strike slip earthquakes in the northern-most end of the rupture. Focal mechanisms show that the events located on the southern part of central Beichuan-Yingxiu Fault (BY) are mainly thrust earthquakes, which is consistent with initial mechanism of the main shock rupture. In the north part the aftershocks along the BY are also dominated by thrust slip, which is quite different from the right slip rupture of the main shock. Around Qingchuan-Pingwu Fault, the focal mechanisms are dominated by right-slip rupture with large depths (~18 km). So we suspected that in the north part the main shock might rupture on two faults: Beichuan Fault and Qingchuan-Pingwu Fault. The complex pattern of aftershock mechanisms argues for presence of a complicated fault system in the Longmenshan area.

  1. Source mechanism of strong aftershocks(Ms≥5.6)of the 2008/05/12 Wenchuan earthquake and the implication for seismotectonics

    Institute of Scientific and Technical Information of China (English)

    ZHENG Yong; MA HongSheng; L(U) Jian; NI SiDao; LI YingChun; WEI ShengJi

    2009-01-01

    Dozens of >M5,hundreds of >M4,and much more >M3 aftershocks occurred after the 2008/05/12 Wenchuan earthquake,which were well recorded by permanent and portable seismic stations.After relocated with P arrival,the >M3 aftershocks show two trends of distribution,with most of the after-shocks located along the north-east strike consistent with Longmenshan fault system,yet there is a north-west trend around the epicenter.It seems that substantially more aftershocks occur in regions with crystalline bedrocks.Then we collected waveform data from National Digital Seismograph Network and regional seismograph network of China,and employed "Cut and Paste" method to obtain focal mechanisms and depths of the big aftershocks (M≥5.6).While most of those aftershocks show thrust mechanism,there are some strike slip earthquakes in the northern-most end of the rupture.Focal mechanisms show that the events located on the southern part of central Beichuan-Yingxiu Fault (BY) are mainly thrust earthquakes,which is consistent with initial mechanism of the main shock rupture.In the north part the aftershocks along the BY are also dominated by thrust slip,which is quite different from the right slip rupture of the main shock.Around Qingchuan-Pingwu Fault,the focal mechanisms are dominated by right-slip rupture with large depths (~18 kin).So we suspected that in the north part the main shock might rupture on two faults:Beichuan Fault and Qingchuan-Pingwu Fault.The complex pattern of aftershock mechanisms argues for presence of a complicated fault system in the Long-menshan area.

  2. Increasing lengths of aftershock zones with depths of moderate-size earthquakes on the San Jacinto Fault suggests triggering of deep creep in the middle crust

    Science.gov (United States)

    Meng, Xiaofeng; Peng, Zhigang

    2016-01-01

    Recent geodetic studies along the San Jacinto Fault (SJF) in southern California revealed a shallower locking depth than the seismogenic depth outlined by microseismicity. This disagreement leads to speculations that creeping episodes drive seismicity in the lower part of the seismogenic zone. Whether deep creep occurs along the SJF holds key information on how fault slips during earthquake cycle and potential seismic hazard imposed to southern California. Here we apply a matched filter technique to 10 M > 4 earthquake sequences along the SJF since 2000 and obtain more complete earthquake catalogues. We then systematic investigate spatio-temporal evolutions of these aftershock sequences. We find anomalously large aftershock zones for earthquakes occurred below the geodetically inferred locking depth (i.e. 11-12 km), while aftershock zones of shallower main shocks are close to expectations from standard scaling relationships. Although we do not observe clear migration of aftershocks, most aftershock zones do expand systematically with logarithmic time since the main shock. All the evidences suggest that aftershocks near or below the locking depth are likely driven by deep creep following the main shock. The presence of a creeping zone below 11-12 km may have significant implications on the maximum sizes of events in this region.

  3. Attenuation of Aftershock of Moderate - Strong Earthquake in West Yunnan Area%滇西地区中强地震的余震衰减

    Institute of Scientific and Technical Information of China (English)

    钱晓东; 秦嘉政; 刘祖荫

    2001-01-01

    Attenuation feature of aftershocks for 8 moderate - strongearthquakes in west Yunnan has been analyzed. The results show that the frequency attenuation of aftershock is accorded with the modified 大森 Law of n (t) = k/ ( t + c)p. The speed of aftershock attenuation has positive correlation with geothermal flow. The moderate- small aftershocks before strong aftershock appear quiescence or increasing. That is frequency residual is less than (quiescence) 2 times of mean - square deviation. A strong aftershock is probably to occur afterwards.%研究了滇西地区8次中强地震余震序列的衰减特征,得出了余震序列频度衰减符合修正的大森定律:n(t)=k/(t+c)p关系;余震衰减的快慢与大地热流值成正相关关系;强余震前中、小余震活动会出现平静或增强现象,即频度残差小于(平静)或大于(增强)其二倍方差,且持续一段时间,其后发生强余震的可能性较大。

  4. Shape of the plate interface near the Mejillones Peninsula in Northern Chile inferred from high resolution relocation of Tocopilla aftershocks

    Science.gov (United States)

    Fuenzalida, A.; Schurr, B.; Lancieri, M.; Madariaga, R. I.

    2011-12-01

    The 14 November, Mw 7.8 2007 Tocopilla earthquake broke the southern part of seismic gap of northern Chile. The earthquake broke a rupture area 130 km by 30km along the deep plate interface between the Nazca and South American plates.The aftershock of this event were very well recorded by the IPOC (GFZ-IPGP-DGF) and Task Force networks (GFZ). Since the IPOC network was installed before the main Tocopilla earthquake we could locate the first two weeks of aftershocks with low accuracy.The first two weeks of aftershocks were characterised by a strong seismicity in the southern area starting with two big events of Mw 6.8 and 6.3 one day after the Tocopilla earthquake. On 29 November 2007 a Task Force (TF) Network of 20 short period instruments was installed by the GFZ team in the area of the Mejillones Peninsula. On 16 December a large Mw 6.8 slab push event took place at the center of this network. This event broke the oceanic crust of the subducted Nazca plate.(see Ruiz and Madariaga, this meeting). We have analysed in detail the TF data from its installation to 20 December. Hypocentral locations of the sequence were computed by automatic identification of the aftershocks and careful hand made readings of the arrival times of P and S phases for each seismogram. In a first study, we used the the nonlinear location software,NonLinLoc of Anthony Lomax using both a 1D model proposed by Husen from the study of earlier events in the region and the 2D model proposed by Patzwall et al from seismic profiles across the Mejillones Peninsula. We find that aftershocks were located along a thin, clearly defined zone that we interpret as the plate interface. As expected events situated off-shore of the Mejillones peninsula are less well located by Nonlinloc although our results suggest that several of these events occurred above the plate interface in the South American wedge. In a second step we relocated 850 events using the HypoDD method of Waldhauser et al with time delays

  5. Time-clustering behavior in the sequence of the aftershocks of the Al-Hoceima (Morocco 24 February 2004 earthquake

    Directory of Open Access Journals (Sweden)

    L. Telesca

    2009-12-01

    Full Text Available The time dynamics of the aftershock sequence of the Al-Hoceima (Morocco earthquake of 24 February 2004 has been investigated. The sequence of the occurrence times of the events with threshold magnitude Mth≥3.2 is characterized by a time-clustering behavior, identified using different fractal methods (Fano Factor, Allan Factor, Count-based Periodogram, well suited to reveal scaling features in point processes. The obtained results not only show the presence of memory phenomena and correlation structures in the Al-Hoceima aftershocks, but also furnish quantitatively the estimate of the magnitude of such correlation by means of the estimate of the scaling exponent α.

  6. Relocation of aftershocks of the 2001 Bhuj earthquake: A new insight into seismotectonics of the Kachchh seismic zone, Gujarat, India

    Science.gov (United States)

    Mandal, Prantik; Pandey, O. P.

    2010-05-01

    In view of an anomalous crust-mantle structure beneath the 2001 Bhuj earthquake region, double-difference relocations of 1402 aftershocks of the 2001 Bhuj earthquake were determined, using an improved 1D velocity model constructed from 3D velocity tomograms based on data from 10 to 58 three-component seismograph stations. This clearly delineated four major tectonic features: (i) south-dipping north Wagad fault (NWF), (ii and iii) south-dipping south Wagad faults 1 and 2 (SWF 1, SWF 2), and (iv) a northeast dipping transverse fault (ITF), which is a new find. The relocated aftershocks correlate satisfactorily with the geologically mapped and inferred faults in the epicentral region. The relocated focal depths delineate a marked variation to the tune of 12 km in the brittle-ductile transition depths beneath the central aftershock zone that could be attributed to a lateral variation in crustal composition (more or less mafic) or in the level of fracturing across the fault zone. A fault intersection between the NWF and ITF has been clearly mapped in the 10-20 km depth range beneath the central aftershock zone. It is inferred that large intraplate stresses associated with the fault intersection, deepening of the brittle-ductile transition to a depth of 34 km due to the presence of mafic/ultramafic material in the crust-mantle transition zone, and the presence of aqueous fluids (released during the metamorphic process of eclogitisation of lower crustal olivine-rich rocks) and volatile CO 2 at the hypocentral depths, might have resulted in generating the 2001 Bhuj earthquake sequence covering the entire lower crust.

  7. Foreshock and aftershock sequences of the Cremasta earthquake and their relation to the waterloading of the Cremasta artificial lake

    Directory of Open Access Journals (Sweden)

    B. PAPAZACHOS

    1968-06-01

    Full Text Available Investigation of the time and magnitude distribution
    of the fore- and aftershocks of the Cremasta lake earthquake which occurred
    on February 5, 1966 is made. The deformation characteristics and
    spatial distribution of these shocks is also studied. Strong evidence is presented
    that the foreshocks and the main shock have been triggered by the
    waterloading of the Cremasta artificial lake.

  8. The impact of static stress change, dynamic stress change, and the background stress on aftershock focal mechanisms

    Science.gov (United States)

    Hardebeck, Jeanne L.

    2014-01-01

    The focal mechanisms of earthquakes in Southern California before and after four M ≥ 6.7 main shocks provide insight into how fault systems respond to stress and changes in stress. The main shock static stress changes have two observed impacts on the seismicity: changing the focal mechanisms in a given location to favor those aligned with the static stress change and changing the spatial distribution of seismicity to favor locations where the static stress change aligns with the background stress. The aftershock focal mechanisms are significantly aligned with the static stress changes for absolute stress changes of ≥ 0.02 MPa, for up to ~20 years following the main shock. The dynamic stress changes have similar, although smaller, effects on the local focal mechanisms and the spatial seismicity distribution. Dynamic stress effects are best observed at long periods (30–60 s) and for metrics based on repeated stress cycling in the same direction. This implies that dynamic triggering operates, at least in part, through cyclic shear stress loading in the direction of fault slip. The background stress also strongly controls both the preshock and aftershock mechanisms. While most aftershock mechanisms are well oriented in the background stress field, 10% of aftershocks are identified as poorly oriented outliers, which may indicate limited heterogeneity in the postmain shock stress field. The fault plane orientations of the outliers are well oriented in the background stress, while their slip directions are not, implying that the background stress restricts the distribution of available fault planes.

  9. Simultaneous inversion of the aftershock data of the 1993 Killari earthquake in Peninsular India and its seismotectonic implications

    Indian Academy of Sciences (India)

    S Mukhopadhyay; J R Kayal; K N Khattri; B K Pradhan

    2002-03-01

    The aftershock sequence of the September 30th, 1993 Killari earthquake in the Latur district of Maharashtra state, India, recorded by 41 temporary seismograph stations are used for estimating 3-D velocity structure in the epicentral area. The local earthquake tomography (LET) method of Thurber (1983) is used. About 1500 and 1200 wave travel-times are inverted. The and wave velocities as well as / ratio vary more rapidly in the vertical as well as in the horizontal directions in the source region compared to the adjacent areas. The main shock hypocentre is located at the junction of a high velocity and a low velocity zone, representing a fault zone at 6 - 7 km depth. The estimated average errors of velocity and / ratio are ± 0.07 km/s and ± 0.016, respectively. The best resolution of and -wave velocities is obtained in the aftershock zone. The 3-D velocity structure and precise locations of the aftershocks suggest a `stationary concept' of the Killari earthquake sequence.

  10. The M 7.7 Tocopilla earthquake and its aftershock sequence: deployment of a Task Force local network

    Science.gov (United States)

    Sobiesiak, M.; Eggert, S.; Woith, H.; Grosser, H.; Peyrat, S.; Vilotte, J.; Medina, E.; Ruch, J.; Walter, T.; Victor, P.; Barrientos, S.; Gonzalez, G.

    2008-05-01

    After the November 14, 2007 Tocopilla earthquake in northern Chile, a local network of 20 short period seismic stations, 5 strong motion instruments, 6 GPS stations and 3 extensometers has been installed in the fault plane area between Tocopilla and Antofagasta by the German Task Force for earthquakes (GFZ Potsdam). The hydrogeology group of the TF sampled 20 thermal water sources in the area of the El Tatio geyser field, located about 170 km E of the epicentre. In collaboration with the IPG Paris, 4 broad band stations were deployed at the northern end of the fault plane between Tocopilla and Maria Elena. Major targets of the investigations of the aftershock sequence are the segment boundary between the 1995 Antofagasta earthquake and the recent Tocopilla event, stress transfer between both successively ruptured subduction zone segments, structural properties of the fault plane, possible consequences for the northern adjacent Iquique segment, and the influence of earthquake seismic waves on the El Tatio hydrothermal field. In our presentation we would like to show first results on the spatial distribution of the aftershocks and discuss these in relation to studies we have made on the Antofagasta aftershock sequence.

  11. Focal depths for moderate-sized aftershocks of the Wenchuan M_S8.0 earthquake and their implications

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Sliding-window cross-correlation method is firstly adopted to identify sPn phase, and to constrain focal depth from regional seismograms, by measuring the time separation between sPn and Pn phases. We present the focal depths of the 17 moderate-sized aftershocks (MS≥5.0) of the Wenchuan MS8.0 earth-quake, using the data recorded by the regional seismic broadband networks of Shaanxi, Qinghai, Gansu, Yunnan and Sichuan. Our results show focal depths of aftershocks range from 8 to 20 km, and tend to cluster at two average depths, separate at 32.5°N, i.e., 11 km to the south and 17 km to the north, indicating that these aftershocks are origin of upper-to-middle crust. Combined with other results, we suggest that the Longmenshan fault is not a through-going crustal fault and the Pingwu-Qingchuan fault may be not the northward extension of the Longmenshan thrust fault.

  12. Testing the ability of different seismic detections approaches to monitor aftershocks following a moderate magnitude event.

    Science.gov (United States)

    Romero, Paula; Díaz, Jordi; Ruiz, Mario; Cantavella, Juan Vicente; Gomez-García, Clara

    2016-04-01

    The detection and picking of seismic events is a permanent concern for seismic surveying, in particular when dealing with aftershocks of moderate magnitude events. Many efforts have been done to find the balance between computer efficiency and the robustness of the detection methods. In this work, data recorded by a high density seismic network deployed following a 5.2 magnitude event located close to Albacete, SE Spain, is used to test the ability of classical and recently proposed detection methodologies. Two days after the main shock, occurred the 23th February, a network formed by 11 stations from ICTJA-CSIC and 2 stations from IGN were deployed over the region, with inter-station distances ranging between 5 and 10 km. The network remained in operation until April 6th, 2015 and allowed to manually identify up to 552 events with magnitudes from 0.2 to 3.5 located in an area of just 25 km2 inside the network limits. The detection methods here studied applied are the classical STA/LTA, a power spectral method, a detector based in the Benford's law and a waveform similarity method. The STA/LTA method, based in the comparison of background noise and seismic signal amplitudes, is taken as a reference to evaluate the results arising from the other approaches. The power spectral density method is based in the inspection of the characteristic frequency pattern associated to seismic events. The Benford's Law detector analyses the distribution of the first-digit of displacement count in the histogram of a seismic waveform, considering that only the windows containing seismic wave arrivals will match the logarithmic law. Finally, the waveform similarity method is based in the analysis of the normalized waveform amplitude, detecting those events with waveform similar to a previously defined master event. The aim of this contribution is to inspect the ability of the different approaches to accurately detect the aftershocks events for this kind of seismic crisis and to

  13. Short-term forecasting of aftershock sequences, microseismicity and swarms inside the Corinth Gulf continental rift

    Science.gov (United States)

    Segou, Margarita

    2014-05-01

    Corinth Gulf (Central Greece) is the fastest continental rift in the world with extension rates 11-15 mm/yr with diverse seismic deformation including earthquakes with M greater than 6.0, several periods of increased microseismic activity, usually lasting few months and possibly related with fluid diffusion, and swarm episodes lasting few days. In this study I perform a retrospective forecast experiment between 1995-2012, focusing on the comparison between physics-based and statistical models for short term time classes. Even though Corinth gulf has been studied extensively in the past there is still today a debate whether earthquake activity is related with the existence of either a shallow dipping structure or steeply dipping normal faults. In the light of the above statement, two CRS realization are based on resolving Coulomb stress changes on specified receiver faults, expressing the aforementioned structural models, whereas the third CRS model uses optimally-oriented for failure planes. The CRS implementation accounts for stress changes following all major ruptures with M greater than 4.5 within the testing phase. I also estimate fault constitutive parameters from modeling the response to major earthquakes at the vicinity of the gulf (Aσ=0.2, stressing rate app. 0.02 bar/yr). The generic ETAS parameters are taken as the maximum likelihood estimates derived from the stochastic declustering of the modern seismicity catalog (1995-2012) with minimum triggering magnitude M2.5. I test whether the generic ETAS can efficiently describe the aftershock spatio-temporal clustering but also the evolution of swarm episodes and microseismicity. For the reason above, I implement likelihood tests to evaluate the forecasts for their spatial consistency and for the total amount of predicted versus observed events with M greater than 3.0 in 10-day time windows during three distinct evaluation phases; the first evaluation phase focuses on the Aigio 1995 aftershock sequence (15

  14. Continuity of the West Napa Fault Zone Inferred from Aftershock Recordings on Fault-Crossing Arrays

    Science.gov (United States)

    Catchings, R.; Goldman, M.; Slad, G. W.; Criley, C.; Chan, J. H.; Fay, R. P.; Fay, W.; Svitek, J. F.

    2014-12-01

    In an attempt to determine the continuity and lateral extent of the causative fault(s) of the 24 August 2014 Mw 6.0 Napa earthquake and possible interconnections with other mapped faults, we recorded aftershocks on three closely spaced (100 m) seismograph arrays that were positioned across the coseismic rupture zone and across mapped faults located north and south of coseismic rupture. Array 1 was located in northwest Napa, between Highway 29 and the intersection of Redwood and Mt. Veeder roads, array 2 was located southwest of Napa, ~1 km north of Cuttings Wharf, and array 3 was located south of San Pablo Bay, within the town of Alhambra. Our intent was to record high-amplitude guided waves that only travel within the causative fault zone and its extensions (Li and Vidale, 1996). Preliminary analysis of seismic data from an M 3.2 aftershock shows high-amplitude (up to 1 cm/s) seismic waves occurred on seismographs within 100 m of mapped surface ruptures and fault zones. Northwest of Napa, the high amplitudes along array 1 coincide with zones of structural damage and wide spread surface ground cracking, and along array 2 near Cuttings Wharf, the high amplitudes occur slightly east of surface ruptures seen along Los Amigas Road. We also observe relatively high-amplitude seismic waves across the Franklin Fault (array 3), approximately 32 km southeast of the mainshock epicenter; this observation suggests the West Napa and the Franklin faults may be continuous or connected. Existing fault maps show that the Franklin Fault extends at least 15 km southward to the Calaveras Fault zone and the West Napa Fault extends at least 25 km north of our array 1. Collectively, the mapped faults, surface ruptures, and guided waves suggest that the West Napa- Franklin Fault zone may extend more than 85 km before it merges with the Calaveras Fault. Assuming a continuous fault zone, the West Napa - Franklin Fault zone may be capable of generating a much larger magnitude earthquake that

  15. Detailed source process of the 2007 Tocopilla earthquake and its main aftershocks

    Science.gov (United States)

    Peyrat, S.; Madariaga, R.; Buforn, E.; Meneses, G.; Campos, J.; Favreau, P.; Bernard, P.; Vilotte, J.

    2008-12-01

    We investigated the detail rupture process of the Tocopilla earthquake (Mw 7.7) of the 14 November 2007 and of the main aftershocks that occurred in the southern part of the North Chile seismic gap using teleseismic broadband and strong motion data. The earthquake happen in the middle of the permanent broad band and strong motion network IPOC newly installed by GFZ and IPGP-CNRS, and of a digital strong- motion network operated by the University of Chile. The Tocopilla earthquake is the last large thrust subduction earthquake since the major Iquique 1877 earthquake which produced a destructive tsunami. The Arequipa (2001) and Antofagasta (1995) earthquakes already ruptured the northern and southern parts of the gap, and the intraplate intermediate depth Tarapaca earthquake (2005) may have changed the tectonic loading of this part of the Peru-Chile subduction zone. The Tocopilla earthquake raises some disturbing questions: why this earthquake didn't extent further north ; what has been the role of the Mejillones peninsula in the south which seems to act as a barrier? We studied the detailed source process using the strong motion data available. The strong-motion data show clearly two S-waves arrivals, allowing the localization of two sources. The main shock started north of the segment close to Tocopilla. The rupture propagated southward. The second source was identified to start about 20 seconds later and located 50 km south from the hypocenter. The earthquake ruptured the interplate seismic zone over more than 150 km and generated several large aftershocks, mainly located south of the rupture area with the same focal mechanism, except for the largest one that took place on the 16 December. This event is a down-dip compressional event (slab push) placed down dip of the main interplate coupling zone at the southern end of the main event rupture zone. Finally in order to understand whether the northern gap has actually been reduced or not by the occurrence of the

  16. Non extensive statistical physics properties of the 2003 (Mw6.2), Lefkada, Ionian island Greece, aftershock sequence

    Science.gov (United States)

    Vallianatos, F.; Karakostas, V.; Papadimitriou, E.

    2012-04-01

    On 14 August 2003, Lefkada Island (Central Ionian) was affected by an Mw=6.2 earthquake. Due to a dense temporary seismic network that operating immediately after the main shock occurrence, hundreds of aftershocks were recorded and located with high precision whereas relocation of the main shock and early strong aftershocks became also feasible. Thus, the spatio-temporal distribution of aftershocks onto the main and the neighboring fault segments was investigated in detail enabling the recognition of four distinctive seismicity clusters separated by less active patches. The aftershock spatiotemporal properties studied here using the concept of Non-Extensive Statistical Physics (NESP). The cumulative distribution functions of the inter-event times and the inter-event distances are estimated for the data set in each seismicity cluster and the analysis results to a value of the statistical thermodynamic qT and qD parameters for each cluster, where qT varies from 1.15 to 1.47 and qD from 0.5 to 0.77 for the interevent times and distances distributions respectively. These values confirm the complexity and non-additivity of the spatiotemporal evolution of seismicity and the usefulness of NESP in investigating such phenomena. The temporal structure is also discussed using the complementary to NESP approach of superstatistics, which is based on a superposition of ordinary local equilibrium statistical mechanics. The result indicates that the temporal evolution of the Lefkada aftershock sequence in clusters A, B and C governed by very low number of degrees of freedom while D is less organized seismicity structure with a much higher number of degrees of freedom. Acknowledgments. This work was supported in part by the THALES Program of the Ministry of Education of Greece and the European Union in the framework of the project entitled "Integrated understanding of Seismicity, using innovative Methodologies of Fracture mechanics along with Earthquake and non extensive

  17. Inferring Aftershock Sequence Properties and Tectonic Structure Using Empirical Signal Detectors

    Science.gov (United States)

    Junek, William N.; Kværna, Tormod; Pirli, Myrto; Schweitzer, Johannes; Harris, David B.; Dodge, Douglas A.; Woods, Mark T.

    2015-02-01

    Seismotectonic studies of the 2008 Storfjorden aftershock sequence were limited to data acquired by the permanent, but sparse, regional seismic network in the Svalbard archipelago. Storfjorden's remote location and harsh polar environment inhibited deployment of temporary seismometers that would have improved observations of sequence events. The lack of good station coverage prevented the detection and computation of hypocenter locations of many low magnitude events (mb < 2.5) in the NORSAR analyst-reviewed bulletin. As a result, the fine structure of the sequence's space-time distribution was not captured. In this study, an autonomous event detection and clustering framework is employed to build a more complete catalog of Storfjorden events using data from the Spitsbergen (SPITS) array. The new catalog allows the spatiotemporal distribution of seismicity within the fjord to be studied in greater detail. Information regarding the location of active event clusters provides a means of inferring the tectonic structure within the fault zone. The distribution of active clusters and moment tensor solutions for the Storfjorden sequence suggests there are at least two different structures within the fjord: a NE-SW trending linear feature with oblique-normal to strike-slip faulting and E-W trending normal faults.

  18. The Hellenic Seismological Network of Crete (HSNC): validation and results of the 2013 aftershock sequences

    Science.gov (United States)

    Chatzopoulos, G.; Papadopoulos, I.; Vallianatos, F.

    2016-02-01

    The last century, the global urbanization has leaded the majority of population to move into big, metropolitan areas. Small areas on the Earth's surface are being built with tall buildings in areas close to seismogenic zones. Such an area of great importance is the Hellenic arc in Greece. Among the regions with high seismicity is Crete, located on the subduction zone of the Eastern Mediterranean plate underneath the Aegean plate. The Hellenic Seismological Network of Crete (HSNC) has been built to cover the need on continuous monitoring of the regional seismicity in the vicinity of the South Aegean Sea and Crete Island. In the present work, with the use of Z-map software the spatial variability of Magnitude of Completeness (Mc) is calculated from HSNC's manual analysis catalogue of events from the beginning of 2008 till the end of September 2015, supporting the good coverage of HSNC in the area surrounding Crete Island. Furthermore, we discuss the 2013 seismicity when two large earthquakes occurred in the vicinity of Crete Island. The two main shocks and their aftershock sequences have been relocated with the use of HYPOINVERSE earthquake location software. Finally, the quality of seismological stations is addressed using the standard PQLX software.

  19. Comparison of main-shock and aftershock fragility curves developed for New Zealand and US buildings

    Science.gov (United States)

    Uma, S.R.; Ryu, H.; Luco, N.; Liel, A.B.; Raghunandan, M.

    2011-01-01

    Seismic risk assessment involves the development of fragility functions to express the relationship between ground motion intensity and damage potential. In evaluating the risk associated with the building inventory in a region, it is essential to capture 'actual' characteristics of the buildings and group them so that 'generic building types' can be generated for further analysis of their damage potential. Variations in building characteristics across regions/countries largely influence the resulting fragility functions, such that building models are unsuitable to be adopted for risk assessment in any other region where a different set of building is present. In this paper, for a given building type (represented in terms of height and structural system), typical New Zealand and US building models are considered to illustrate the differences in structural model parameters and their effects on resulting fragility functions for a set of main-shocks and aftershocks. From this study, the general conclusion is that the methodology and assumptions used to derive basic capacity curve parameters have a considerable influence on fragility curves.

  20. Explanation of temporal clustering of tsunami sources using the epidemic-type aftershock sequence model

    Science.gov (United States)

    Geist, Eric L.

    2014-01-01

    Temporal clustering of tsunami sources is examined in terms of a branching process model. It previously was observed that there are more short interevent times between consecutive tsunami sources than expected from a stationary Poisson process. The epidemic‐type aftershock sequence (ETAS) branching process model is fitted to tsunami catalog events, using the earthquake magnitude of the causative event from the Centennial and Global Centroid Moment Tensor (CMT) catalogs and tsunami sizes above a completeness level as a mark to indicate that a tsunami was generated. The ETAS parameters are estimated using the maximum‐likelihood method. The interevent distribution associated with the ETAS model provides a better fit to the data than the Poisson model or other temporal clustering models. When tsunamigenic conditions (magnitude threshold, submarine location, dip‐slip mechanism) are applied to the Global CMT catalog, ETAS parameters are obtained that are consistent with those estimated from the tsunami catalog. In particular, the dip‐slip condition appears to result in a near zero magnitude effect for triggered tsunami sources. The overall consistency between results from the tsunami catalog and that from the earthquake catalog under tsunamigenic conditions indicates that ETAS models based on seismicity can provide the structure for understanding patterns of tsunami source occurrence. The fractional rate of triggered tsunami sources on a global basis is approximately 14%.

  1. Record-breaking earthquake intervals in a global catalogue and an aftershock sequence

    Directory of Open Access Journals (Sweden)

    M. R. Yoder

    2010-03-01

    Full Text Available For the purposes of this study, an interval is the elapsed time between two earthquakes in a designated region; the minimum magnitude for the earthquakes is prescribed. A record-breaking interval is one that is longer (or shorter than preceding intervals; a starting time must be specified. We consider global earthquakes with magnitudes greater than 5.5 and show that the record-breaking intervals are well estimated by a Poissonian (random theory. We also consider the aftershocks of the 2004 Parkfield earthquake and show that the record-breaking intervals are approximated by very different statistics. In both cases, we calculate the number of record-breaking intervals (nrb and the record-breaking interval durations Δtrb as a function of "natural time", the number of elapsed events. We also calculate the ratio of record-breaking long intervals to record-breaking short intervals as a function of time, r(t, which is suggested to be sensitive to trends in noisy time series data. Our data indicate a possible precursory signal to large earthquakes that is consistent with accelerated moment release (AMR theory.

  2. Afterslip and aftershocks in the rate-and-state friction law

    CERN Document Server

    Helmstetter, A; Helmstetter, Agnes; Shaw, Bruce E.

    2007-01-01

    We study how a stress perturbation generated by a mainshock affects a population of faults obeying a rate-state friction law. Depending on the model parameters and on the initial state, the fault exhibits aftershocks, slow earthquakes, or decaying afterslip. We found several regimes with slip rate decaying as a power-law of time, with different characteristic times and exponents. The complexity of the model makes it unrealistic to invert for the friction law parameters from afterslip data. We modeled afterslip measurements for the Southern California Superstition Hills earthquake using the complete rate-and-state law, and found a huge variety of model parameters that can fit the observed data. In particular, it is impossible to distinguish the stable velocity strengthening regime (A>B) from the (potentially) unstable velocity weakening regime (B>A and stiffness k

  3. Anomalous stress diffusion, Omori's law and Continuous Time Random Walk in the 2010 Efpalion aftershock sequence (Corinth rift, Greece)

    Science.gov (United States)

    Michas, Georgios; Vallianatos, Filippos; Karakostas, Vassilios; Papadimitriou, Eleftheria; Sammonds, Peter

    2014-05-01

    Efpalion aftershock sequence occurred in January 2010, when an M=5.5 earthquake was followed four days later by another strong event (M=5.4) and numerous aftershocks (Karakostas et al., 2012). This activity interrupted a 15 years period of low to moderate earthquake occurrence in Corinth rift, where the last major event was the 1995 Aigion earthquake (M=6.2). Coulomb stress analysis performed in previous studies (Karakostas et al., 2012; Sokos et al., 2012; Ganas et al., 2013) indicated that the second major event and most of the aftershocks were triggered due to stress transfer. The aftershocks production rate decays as a power-law with time according to the modified Omori law (Utsu et al., 1995) with an exponent larger than one for the first four days, while after the occurrence of the second strong event the exponent turns to unity. We consider the earthquake sequence as a point process in time and space and study its spatiotemporal evolution considering a Continuous Time Random Walk (CTRW) model with a joint probability density function of inter-event times and jumps between the successive earthquakes (Metzler and Klafter, 2000). Jump length distribution exhibits finite variance, whereas inter-event times scale as a q-generalized gamma distribution (Michas et al., 2013) with a long power-law tail. These properties are indicative of a subdiffusive process in terms of CTRW. Additionally, the mean square displacement of aftershocks is constant with time after the occurrence of the first event, while it changes to a power-law with exponent close to 0.15 after the second major event, illustrating a slow diffusive process. During the first four days aftershocks cluster around the epicentral area of the second major event, while after that and taking as a reference the second event, the aftershock zone is migrating slowly with time to the west near the epicentral area of the first event. This process is much slower from what would be expected from normal diffusion, a

  4. A discussion on Corioli force effect and aftershock activity tendency of the M=8.1 Kunlun Mountain Pass earthquake on Nov. 14, 2001

    Institute of Scientific and Technical Information of China (English)

    吕坚; 高建华; 刘吉夫; 胡翠娥; 黄双凤

    2003-01-01

    Following the theory and definition of the Corioli force in physics, the Corioli force at the site of the M=8.1 Kunlun Mountain Pass earthquake on November 14, 2001, is examined in this paper on the basis of a statistical research on relationship between the Corioli force effect and the maximum aftershock magnitude of 20 earthquakes with M37.5 in Chinese mainland, and then the variation tendency of aftershock activity of the M=8.1 earthquake is discussed. The result shows: a) Analyzing the Corioli force effect is an effective method to predict maximum aftershock magnitude of large earthquakes in Chinese mainland. For the sinistral slip fault and the reverse fault with its hanging wall moving toward the right side of the cross-focus meridian plane, their Corioli force pulls the two fault walls apart, decreasing frictional resistance on fault plane during the fault movement and releasing elastic energy of the mainshock fully, so the maximum magnitude of aftershocks would be low. For the dextral slip fault, its Corioli force presses the two walls against each other and increases the frictional resistance on fault plane, prohibiting energy release of the mainshock, so the maximum magnitude of aftershocks would be high. b) The fault of the M=8.1 Kunlun Mountain earthquake on Nov. 14, 2001 is essentially a sinistral strike-slip fault, and the Corioli force pulled the two fault walls apart. Magnitude of the induced stress is about 0.06 MPa. After a comparison analysis, we suggest that the aftershock activity level will not be high in the late period of this earthquake sequence, and the maximum magnitude of the whole aftershocks sequence is estimated to be about 6.0.

  5. A Stochastic Estimate of Ground Motion at Oceano, California, for the M6.5 December 22, 2003, San Simeon Earthquake, Derived from Aftershock Recordings

    Science.gov (United States)

    di Alessandro, C.; Boatwright, J.

    2004-12-01

    The U.S. Geological Survey deployed a digital seismic station in Oceano, California, in February 2004, to investigate the cause of damage and liquefaction from the 22 December 2003 M6.5 San Simeon earthquake. This station recorded 11 M\\> 2.8 aftershocks in almost eight weeks. We use these recordings, together with recordings of the main shock and the same aftershocks obtained from nearby stations in Park Hill and San Luis Obispo, to estimate the mainshock ground motion in Oceano. We estimate the Fourier amplitude spectrum using a generalized spectral ratio analysis that averages the spectral ratios from both stations for all the co-recorded aftershocks. We test three aftershocks as Green's functions by comparing simulated and recorded acceleration amplitude spectra for the main shock at Park Hill and San Luis Obispo. Instead of deconvolving the aftershock recordings from the mainshock recordings to estimate a source-time function, we convolve the aftershock accelerograms with a stochastic operator to simulate the duration and phase of the mainshock accelerograms. These stochastic operators are determined as sets of delta functions whose delays are randomly generated from a gamma distribution with a shape parameter of 1. We choose the scale parameter by fitting Husid plots of the Park Hill and San Luis Obsipo mainshock accelerograms. This stochastic approach allows us to extend the range of aftershocks that can be used as Green's functions to events nearly three magnitude units smaller than the main shock. Our realizations for the mainshock accelerogram at Oceano yield PGAs distributed as 28±4% g. We interpret these realizations as upper bounds for the actual ground motion because our analysis assumes that the ground behaved linearly, while the liquefaction and lateral spreading indicates that the ground behaved non-linearly. Geotechnical analysis of the site indicates that a PGA of 25% g would have initiated the liquefaction.

  6. Analysis of rupture area of aftershocks caused by twin earthquakes (Case study: 11 April 2012 earthquakes of Aceh-North Sumatra)

    International Nuclear Information System (INIS)

    The 11 April 2012 earthquakes off-shore Aceh-North Sumatra are unique events for the history of Indonesian earthquake. It is unique because that they have similar magnitude, 8.5 Mw and 8.1 Mw; close to epicenter distance, similar strike-slip focal mechanism, and occuring in outer rise area. The purposes of this research are: (1) comparing area of earthquakes base on models and that of calculation, (2) fitting the shape and the area of earthquake rupture zones, (3) analyzing the relationship between rupture area and magnitude of the earthquakes. Rupture area of the earthquake fault are determined by using 4 different formulas, i.e. Utsu and Seki (1954), Wells and Coppersmith (1994), Ellsworth (2003), and Christophersen and Smith (2000). The earthquakes aftershock parameters are taken from PGN (PusatGempabumiNasional or National Earthquake Information Center) of BMKG (Indonesia Agency Meteorology Climatology and Geophysics). The aftershock epicenters are plotted by GMT’s software. After that, ellipse and rectangular models of aftershock spreading are made. The results show that: (1) rupture areas were calculated using magnitude relationship which are larger than the the aftershock distributions model, (2) the best fitting model for that earthquake aftershock distribution is rectangular associated with Utsu and Seki (1954) formula, (3) the larger the magnitude of the earthquake, the larger area of the fault

  7. Diversity of the 2014 Iquique's foreshocks and aftershocks: clues about the complex rupture process of a Mw 8.1 earthquake

    Science.gov (United States)

    León-Ríos, Sergio; Ruiz, Sergio; Maksymowicz, Andrei; Leyton, Felipe; Fuenzalida, Amaya; Madariaga, Raúl

    2016-03-01

    We study the foreshocks and aftershocks of the 1 April 2014 Iquique earthquake of Mw 8.1. Most of these events were recorded by a large digital seismic network that included the Northern Chile permanent network and up to 26 temporary broadband digital stations. We relocated and computed moment tensors for 151 events of magnitude Mw ≥ 4.5. Most of the foreshocks and aftershocks of the Iquique earthquake are distributed to the southwest of the rupture zone. These events are located in a band of about 50 km from the trench, an area where few earthquakes occur elsewhere in Chile. Another important group of aftershocks is located above the plate interface, similar to those observed during the foreshock sequence. The depths of these events were constrained by regional moment tensor (RMT) solutions obtained using the records of the dense broad band network. The majority of the foreshocks and aftershocks were associated to the interplate contact, with dip and strike angles in good agreement with the characteristics of horst and graben structures (>2000 m offset) typical of the oceanic Nazca Plate at the trench and in the outer rise region. We propose that the spatial distribution of foreshocks and aftershocks, and its seismological characteristics were strongly controlled by the rheological and tectonics conditions of the extreme erosive margin of Northern Chile.

  8. Analysis of rupture area of aftershocks caused by twin earthquakes (Case study: 11 April 2012 earthquakes of Aceh-North Sumatra)

    Energy Technology Data Exchange (ETDEWEB)

    Diansari, Angga Vertika, E-mail: anggav.bmkg@gmail.com; Purwana, Ibnu; Subakti, Hendri [Academy of Meteorology and Geophysics, Jalan Perhubungan I no.5 Tangerang 15221 (Indonesia)

    2015-04-24

    The 11 April 2012 earthquakes off-shore Aceh-North Sumatra are unique events for the history of Indonesian earthquake. It is unique because that they have similar magnitude, 8.5 Mw and 8.1 Mw; close to epicenter distance, similar strike-slip focal mechanism, and occuring in outer rise area. The purposes of this research are: (1) comparing area of earthquakes base on models and that of calculation, (2) fitting the shape and the area of earthquake rupture zones, (3) analyzing the relationship between rupture area and magnitude of the earthquakes. Rupture area of the earthquake fault are determined by using 4 different formulas, i.e. Utsu and Seki (1954), Wells and Coppersmith (1994), Ellsworth (2003), and Christophersen and Smith (2000). The earthquakes aftershock parameters are taken from PGN (PusatGempabumiNasional or National Earthquake Information Center) of BMKG (Indonesia Agency Meteorology Climatology and Geophysics). The aftershock epicenters are plotted by GMT’s software. After that, ellipse and rectangular models of aftershock spreading are made. The results show that: (1) rupture areas were calculated using magnitude relationship which are larger than the the aftershock distributions model, (2) the best fitting model for that earthquake aftershock distribution is rectangular associated with Utsu and Seki (1954) formula, (3) the larger the magnitude of the earthquake, the larger area of the fault.

  9. Modeling of Kashmir Aftershock Decay Based on Static Coulomb Stress Changes and Laboratory-Derived Rate-and-State Dependent Friction Law

    Science.gov (United States)

    Javed, F.; Hainzl, S.; Aoudia, A.; Qaisar, M.

    2016-05-01

    We model the spatial and temporal evolution of October 8, 2005 Kashmir earthquake's aftershock activity using the rate-and-state dependent friction model incorporating uncertainties in computed coseismic stress perturbations. We estimated the best possible value for frictional resistance " Aσ n", background seismicity rate " r" and coefficient of stress variation "CV" using maximum log-likelihood method. For the whole Kashmir earthquake sequence, we measure a frictional resistance Aσ n ~ 0.0185 MPa, r ~ 20 M3.7+ events/year and CV = 0.94 ± 0.01. The spatial and temporal forecasted seismicity rate of modeled aftershocks fits well with the spatial and temporal distribution of observed aftershocks that occurred in the regions with positive static stress changes as well as in the apparent stress shadow region. To quantify the effect of secondary aftershock triggering, we have re-run the estimations for 100 stochastically declustered catalogs showing that the effect of aftershock-induced secondary stress changes is obviously minor compared to the overall uncertainties, and that the stress variability related to uncertain slip model inversions and receiver mechanisms remains the major factor to provide a reasonable data fit.

  10. Regional features of coda attenuation of af-tershocks of Wuding, Yunnan earthquake in near field

    Institute of Scientific and Technical Information of China (English)

    秦嘉政; 李白基; 钱晓东; 苏有锦; 蔡静观; 付虹

    2001-01-01

    According to dispersion theory of coda of local events, using near-field data of aftershocks recorded by two mobile digital stations at the Tianxin and Yunlong after the Wuding, Yunnan MS=6.5 main-shock and sampling at different central frequencies (1.5~20 Hz), spatial distribution features of coda attenuation ratio b ( f ) are studied. The results show that there exists obvious non-uniformity of coda attenuation ratio b ( f ) given by the two stations in small region. When f <6.0 Hz the coda attenuation ratio b ( f ) observed on both sides of earthquake-generating fault are basically identical. Yunlong station is located on east side and Tianxin station on west side. The corresponding Qc( f ) is in the range of 66~120. However, in the range of high frequency ( f 36.0 Hz) the coda in near field going through major fault encounters a strong absorption from the fracture zone. The b ( f ) going through the fault ob-served at Yunlong station is 30% lower than that in Tianxin station in which the seismic waves do not go through the fault. The reason for the difference in space distribution of coda attenuation is discussed. The results also show that factor A0( f ) of wave source is not only related to the source strength, but also to frequency f. The mean free path L of S wave obtained using 1.5~20 Hz is respectively 30 km on east side of the fault and 40 km on west side, from which it is verified that there is a stronger dispersion body when seismic waves go through the fracture zone.

  11. Magnitude-dependent epidemic-type aftershock sequences model for earthquakes

    Science.gov (United States)

    Spassiani, Ilaria; Sebastiani, Giovanni

    2016-04-01

    We propose a version of the pure temporal epidemic type aftershock sequences (ETAS) model: the ETAS model with correlated magnitudes. As for the standard case, we assume the Gutenberg-Richter law to be the probability density for the magnitudes of the background events. Instead, the magnitude of the triggered shocks is assumed to be probabilistically dependent on that of the relative mother events. This probabilistic dependence is motivated by some recent works in the literature and by the results of a statistical analysis made on some seismic catalogs [Spassiani and Sebastiani, J. Geophys. Res. 121, 903 (2016), 10.1002/2015JB012398]. On the basis of the experimental evidences obtained in the latter paper for the real catalogs, we theoretically derive the probability density function for the magnitudes of the triggered shocks proposed in Spassiani and Sebastiani and there used for the analysis of two simulated catalogs. To this aim, we impose a fundamental condition: averaging over all the magnitudes of the mother events, we must obtain again the Gutenberg-Richter law. This ensures the validity of this law at any event's generation when ignoring past seismicity. The ETAS model with correlated magnitudes is then theoretically analyzed here. In particular, we use the tool of the probability generating function and the Palm theory, in order to derive an approximation of the probability of zero events in a small time interval and to interpret the results in terms of the interevent time between consecutive shocks, the latter being a very useful random variable in the assessment of seismic hazard.

  12. Shear Wave Splitting Intensity of the Maule, Chile Rupture Zone: Results from Teleseismic and Local Aftershock Datasets

    Science.gov (United States)

    Torpey, M. E.; Russo, R. M.; Chevrot, S.

    2015-12-01

    We calculated the shear wave splitting intensity (SI) of the Maule, Chile rupture zone (32°S-39°S) to constrain the seismic anisotropy of the region. Our data are from 80 of the temporary seismometers deployed as part of the IMAD (International Maule Aftershock Deployment) geophysical networks to capture the aftershocks of the Mw 8.8 megathrust event in 2010. We implemented the multichannel analysis method of Chevrot (2000) to measure the SI of 64 teleseismic SKS phases in addition to the fast orientations ϕ and splitting delays δt measured with the method of Silver & Chan (1991). To measure the SI of local aftershocks, we modified the method to allow for use of the upgoing S phase from local events in and above the Nazca slab after correcting for the initial event polarization. We compared our results with other measurement methods (Silver and Chan 1991, Wolfe and Silver 1998) that solve for splitting parameters to examine the robustness of the shear wave splitting intensity method, particularly for local datasets. The results we obtained using the splitting intensity method for the teleseismic data show an overall fast direction that is parallel to the absolute plate motion of the Nazca plate that is subducting beneath the South American plate. These results are consistent with the results we calculated using the Wolfe and Silver method. SI deriving from S waves that originate in the Nazca slab or deeper SA lithosphere are likely to reveal patterns of crustal fabric, and hence differ from the SI of the teleseismic shear waves.

  13. Complete Coulomb stress changes induced by the Ms7.6 earthquake in Lancang-Gengma, Yunnan and triggering of aftershocks by dynamic and static stress

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The spatiotemporal evolution patterns of complete Coulomb stress changes caused by 1988 Ms7.6 earthquake in Lancang-Gengma,Yunnan,are calculated and studied.And the triggering problems of Ms7.2 Gengma shock occurring 13 minutes after the main shock and of Ms5.0―6.9 aftershocks within 24 days after the main shock are discussed.The results show that the spatial distribution patterns of complete Coulomb stress changes of the Ms7.6 main shock are strongly asymmetric.The areas of positive dynamic and static Coulomb stress are both coincident well with the strong aftershocks' locations.The Ms7.2 Gengma shock and most of strong aftershocks are subjected to the triggering effect of dynamic and static Coulomb stresses induced by the Ms7.6 Lancang earthquake.

  14. Study of the epicentral trends and depth sections for aftershocks of the 26th January 2001, Bhuj earthquake in western India

    Indian Academy of Sciences (India)

    S G Gaonkar; B V Srirama; S R Samaddar; D V Punekar; Sagina Ram; Reena De; J R Kayal

    2003-09-01

    The Geological Survey of India (GSI) established a twelve-station temporary microearthquake (MEQ) network to monitor the aftershocks in the epicenter area of the Bhuj earthquake (w 7.5) of 26th January 2001. The main shock occurred in the Kutch rift basin with the epicenter to the north of Bhachao village, at an estimated depth of 25km (IMD). About 3000 aftershocks (d ≥ 1.0), were recorded by the GSI network over a monitoring period of about two and half months from 29th January 2001 to 15th April 2001. About 800 aftershocks (d ≥ 2.0) are located in this study. The epicenters are clustered in an area 60km × 30km, between 23.3°N and 23.6°N and 70°E and 70.6°E. The main shock epicenter is also located within this zone. Two major aftershock trends are observed; one in the NE direction and other in the NW direction. Out of these two trends, the NE trend was more pronounced with depth. The major NE-SW trend is parallel to the Anjar-Rapar lineament. The other trend along NW-SE is parallel to the Bhachao lineament. The aftershocks at a shallower depth (< 10 km) are aligned only along the NW-SE direction. The depth slice at 10km to 20km shows both the NE-SW trend and the NW-SE trend. At greater depth (20 km{38 km) the NE-SW trend becomes more predominant. This observation suggests that the major rupture of the main shock took place at a depth level more than 20 km; it propagated along the NE-SW direction, and a conjugate rupture followed the NW-SE direction. A N-S depth section of the aftershocks shows that some aftershocks are clustered at shallower depth ≤ 10km, but intense activity is observed at 15-38km depth. There is almost an aseismic layer at 10-15km depth. The activity is sparse below 38 km. The estimated depth of the main shock at 25km is consistent with the cluster of maximum number of the aftershocks at 20-38 km. A NW-SE depth section of the aftershocks, perpendicular to the major NE-SW trend, indicates a SE dipping plane and a NE-SW depth section

  15. A Study on Tidal Force Triggering of the Wenchuan Ms 8. 0 Earthquake and Its Strong Aftershocks

    Institute of Scientific and Technical Information of China (English)

    Chen Daqing; Yang Maling; Liu Jin

    2012-01-01

    By calculating the azimuth, phase angle and change rate of tidal force, and contrasting their rupture types, we find that in 6 of 11 reverse faulting earthquakes, the angles between the direction of the horizontal tidal force and compressive principal stress are within 33°, the vertical phase angles of all 8 strike-slip earthquakes are in the upward peak section and the vertical phase angles of two extensional normal faulting earthquakes are in the downward peak section. According to the above statistics, the mechanism of tidal force triggering of the Wenchnan Ms8. 0 Earthquake and its strong aftershocks is discussed.

  16. Using aftershocks to Image the Subducting Pacific Plate in a Region of Deep Slow Slip, Hikurangi Margin, New Zealand

    Science.gov (United States)

    Jacobs, K. M.; Hirschberg, H.; Louie, J. N.; Savage, M. K.; Bannister, S. C.

    2014-12-01

    We present seismic migrations using aftershocks of two M>6 earthquakes as sources. The Southern Cook Strait earthquake sequence, beginning on 19 July 2013, included the 21 July M=6.5 and 16 August M=6.6 2013 earthquakes, which were the largest shallow earthquakes to strike the Wellington region since 1942. Following the two largest earthquakes we began the Seddon Earthquake Aftershock Structural Investigation (SEASI) and deployed a line of 21 seismometers stretching approximately 400 km along the strike of the Hikurangi subduction zone in order to use aftershocks to illuminate the structure of the subducted Pacific slab. The SEASI line ties into the SAHKE line, which was an array of up to 900 seismometers that recorded air gun and explosion shots in deployments from 2009-2011. The SAHKE project characterized the structures perpendicular to the strike of the subduction zone. Our results use the SAHKE line as a starting point and look for strike-parallel variations in the depth of the Moho and other structures. Previous studies have suggested potential changes along strike in this region, and deep slow slip events (> 35 km) are also observed north of Wellington, further indicating that variation in properties exists along slab strike. We have used 246 M > 3 earthquakes that occurred from September 2013 through January 2014 to create common receiver gathers. Multicomponent prestack depth migration of these receiver gathers, with operator antialiasing control and prestack coherency filtering, produces reflectivity sections using a 1-D velocity model derived from the SAHKE project. Relocation of aftershocks of the Seddon earthquakes using the deployment of a temporary array by New Zealand GeoNet facilitates the migration. An initial P-P migration shows a north-dipping reflector at 15-25 km depth under the earthquake sequence, and suggests the Moho at 20-25 km depth. From Wellington, a reflector dips very gently south from 25-35 km depth, which is probably the slab

  17. On the spatial correlation between areas of high coseismic slip and aftershock clusters of the Maule earthquake Mw=8.8

    CERN Document Server

    Contreras-Reyes, Javier E

    2012-01-01

    We study the spatial distribution of clusters associated to the aftershocks of the megathrust Maule earthquake MW 8.8 of 27 February 2010. We used a recent clustering method which hinges on a nonparametric estimation of the underlying probability density function to detect subsets of points forming clusters associated to high density areas. In addition, we estimate the probability density function using a nonparametric kernel method for each of these clusters. This allow us to identify a set of regions where there is an association between frequency of events and pre-seismic locking. Specifically, our results suggest that high coseismic slip spatially correlates with high aftershock frequency.

  18. The Mw 5.8 Mineral, Virginia, earthquake of August 2011 and aftershock sequence: constraints on earthquake source parameters and fault geometry

    Science.gov (United States)

    McNamara, Daniel E.; Benz, H.M.; Herrmann, Robert B.; Bergman, Eric A.; Earle, Paul; Meltzer, Anne; Withers, Mitch; Chapman, Martin

    2014-01-01

    The Mw 5.8 earthquake of 23 August 2011 (17:51:04 UTC) (moment, M0 5.7×1017  N·m) occurred near Mineral, Virginia, within the central Virginia seismic zone and was felt by more people than any other earthquake in United States history. The U.S. Geological Survey (USGS) received 148,638 felt reports from 31 states and 4 Canadian provinces. The USGS PAGER system estimates as many as 120,000 people were exposed to shaking intensity levels of IV and greater, with approximately 10,000 exposed to shaking as high as intensity VIII. Both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast‐striking reverse fault that nucleated at a depth of approximately 7±2  km. The distribution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western United States (Horton and Williams, 2012). Near‐source and far‐field damage reports, which extend as far away as Washington, D.C., (135 km away) and Baltimore, Maryland, (200 km away) are consistent with an earthquake of this size and depth in the eastern United States (EUS). Within the first few days following the earthquake, several government and academic institutions installed 36 portable seismograph stations in the epicentral region, making this among the best‐recorded aftershock sequences in the EUS. Based on modeling of these data, we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry, area of rupture, and observations of the aftershock sequence magnitude–frequency and temporal distribution. The observed slope of the magnitude–frequency curve or b‐value for the aftershock sequence is consistent with previous EUS studies (b=0.75), suggesting that most of the accumulated strain was released by the mainshock. The aftershocks define a rupture that extends between approximately 2–8 km in depth and 8–10 km along

  19. Cumulative Coulomb Stress Triggering as an Explanation for the Canterbury (New Zealand) Aftershock Sequence: Initial Conditions Are Everything?

    Science.gov (United States)

    Bebbington, Mark; Harte, David; Williams, Charles

    2016-01-01

    Using 2 years of aftershock data and three fault-plane solutions for each of the initial M7.1 Darfield earthquake and the larger (M >6) aftershocks, we conduct a detailed examination of Coulomb stress transfer in the Canterbury 2010-2011 earthquake sequence. Moment tensor solutions exist for 283 of the events with M ≥ 3.6, while 713 other events of M ≥ 3.6 have only hypocentre and magnitude information available. We look at various methods for deciding between the two possible mechanisms for the 283 events with moment tensor solutions, including conformation to observed surface faulting, and maximum ΔCFF transfer from the Darfield main shock. For the remaining events, imputation methods for the mechanism including nearest-neighbour, kernel smoothing, and optimal plane methods are considered. Fault length, width, and depth are arrived at via a suite of scaling relations. A large (50-70 %) proportion of the faults considered were calculated to have initial loading in excess of the final stress drop. The majority of faults that accumulated positive ΔCFF during the sequence were `encouraged' by the main shock failure, but, on the other hand, of the faults that failed during the sequence, more than 50 % of faults appeared to have accumulated a negative ΔCFF from all preceding failures during the sequence. These results were qualitatively insensitive to any of the factors considered. We conclude that there is much unknown about how Coulomb stress triggering works in practice.

  20. Fractal structure and predictability of distances between consecutive events: an analysis of three seismic aftershock sequences in Southern California

    Science.gov (United States)

    Martinez, Maria-Dolors; Lana, Xavier; Monterrubio, Marisol; Serra, Carina

    2015-04-01

    Three series of distances between consecutive seismic events are analysed by means of mono- and multifractal techniques with the aim of quantifying the complexity of their physical mechanism and their predictability and predictive instability. These series are also simulated by means of fractional noise by taking into account their self-affine character, the dependence of their power spectra on frequency and the values of Hurst and Hausdorff exponents. The prediction of these series is also attempted by means of an autoregressive AR(p) process to estimate the p+1 distance depending on the previous p distances. The interevent distance series are derived from the aftershock sequences associated with Landers (Mw 7.3 June 28, 1992), Northridge (Mw 6.7 January 17, 1994) and Hector Mine (Mw 7.1 October 16, 1999) mainshocks. The seismic records are obtained from the Southern California Seismic Network (SCSN) catalogue. Aftershocks with Mw equalling to or exceeding 2.0 are considered in order to assure catalogue completeness.

  1. Source Properties of Repeating Small Earthquakes in the Aftershock Zones of the 1999 Izmit and Duzce Earthquakes

    Science.gov (United States)

    Ben-Zion, Y.; Peng, Z.

    2006-12-01

    We estimate the source parameters of repeating small earthquakes in the aftershock zones of the 1999 Mw7.4 Izmit and Mw7.1 Duzce earthquakes. The analysis employs 36 sets of highly repeating earthquakes, ranging in size from M 0 to M 3.0, that occurred from August 1999 to February 2000 along the Karadere-Duzce segment of the north Anatolian fault [Peng and Ben-Zion, 2006]. A local PASSCAL network consisting of 10 short-period stations recorded the data. We compute spectra from each seismogram using a multitaper technique. We measure the difference between events by dividing the spectra of the each individual record to the average spectra at that station [Vidale et al., 1994]. Stable spectra ratios are obtained by stacking the ratios calculated from moving windows starting from the P waves to the S-coda waves [Imanishi and Ellsworth, 2006]. Next, we estimate the seismic potencies and corner frequencies for events in each cluster using a simple source model. The continuing work will focus on deriving static stress drops, apparent stresses and radiated energy of these repeating earthquakes. A comparison of the source properties of the repeating small earthquakes with those of large aftershocks and the Duzce main shock would allow us to examine whether there are systematic variations with location and/or size.

  2. Changes in source parameters of foreshocks and aftershocks of the 2001 MS=6.0 Yajiang, Sichuan, earthquake

    Institute of Scientific and Technical Information of China (English)

    程万正; 陈天长; 魏娅玲; 朱航

    2003-01-01

    In this paper changes in focal mechanisms, parameters of wave spectra, and stress drops for the MS=5.0 foreshock and MS=6.0 mainshock in February 2001 in Yajiang County, Sichuan, and seismicity in epicentral region are studied. Comparison of focal mechanisms for the Yajiang earthquakes with distribution patterns of aftershocks, the nodal plane I, striking in the direction of NEN, of the Yajiang M=5.0 event is chosen as the faulting plane; the nodal plane II, striking in the direction of WNW, of the M=6.0 event as the faulting plane. The strikes of the two faulting planes are nearly perpendicular to each other. The level of stress drops in the epicentral region before the occurrence of the M=6.0 earthquake increases, which is consistent with increase of seismicity in the epicentral region. The rate decay of the Yajiang earthquake sequence, changes in wave spectra for foreshocks and aftershocks, and focal mechanisms are complex.

  3. Distribution of the Largest Aftershocks in Branching Models of Triggered Seismicity: Theory of the Universal Bath's law

    CERN Document Server

    Saichev, A

    2005-01-01

    Using the ETAS branching model of triggered seismicity, we apply the formalism of generating probability functions to calculate exactly the average difference between the magnitude of a mainshock and the magnitude of its largest aftershock over all generations. This average magnitude difference is found empirically to be independent of the mainshock magnitude and equal to 1.2, a universal behavior known as Bath's law. Our theory shows that Bath's law holds only sufficiently close to the critical regime of the ETAS branching process. Allowing for error bars +- 0.1 for Bath's constant value around 1.2, our exact analytical treatment of Bath's law provides new constraints on the productivity exponent alpha and the branching ratio n: $0.9 <= alpha <= 1$ and 0.8 <= n <= 1. We propose a novel method for measuring alpha based on the predicted renormalization of the Gutenberg-Richter distribution of the magnitudes of the largest aftershock. We also introduce the ``second Bath's law for foreshocks: the pro...

  4. Typical Scenario of Preparation, Implementation, and Aftershock Sequence of a Large Earthquake

    Science.gov (United States)

    Rodkin, Mikhail

    2016-04-01

    We have tried here to construct and examine the typical scenario of a large earthquake occurrence. The Harvard seismic moment GCMT catalog was used to construct the large earthquake generalized space-time vicinity (LEGV) and to investigate the seismicity behavior in LEGV. LEGV was composed of earthquakes falling into the zone of influence of any of the considerable number (100, 300, or 1,000) of largest earthquakes. The LEGV construction is aimed to enlarge the available statistics, diminish a strong random component, and to reveal in result the typical features of pre- and post-shock seismic activity in more detail. In result of the LEGV construction the character of fore- and aftershock cascades was examined in more detail than it was possible without of the use of the LEGV approach. It was shown also that the mean earthquake magnitude tends to increase, and the b-values, mean mb/mw ratios, apparent stress values, and mean depth tend to decrease. Amplitudes of all these anomalies increase with an approach to a moment of the generalized large earthquake (GLE) as a logarithm of time interval from GLE occurrence. Most of the discussed anomalies agree well with a common scenario of development of instability. Besides of such precursors of common character, one earthquake-specific precursor was found. The revealed decrease of mean earthquake depth during large earthquake preparation testifies probably for the deep fluid involvement in the process. The revealed in LEGV typical features of development of shear instability agree well with results obtained in laboratory acoustic emission (AE) study. Majority of the revealed anomalies appear to have a secondary character and are connected mainly with an increase in a mean earthquake magnitude in LEGV. The mean magnitude increase was shown to be connected mainly with a decrease of a portion of moderate size events (Mw 5.0 - 5.5) in a closer GLE vicinity. We believe that this deficit of moderate size events hardly can be

  5. April 25, 2015, Gorkha Earthquake, Nepal and Sequence of Aftershocks: Key Lessons

    Science.gov (United States)

    Guragain, R.; Dixit, A. M.; Shrestha, S. N.

    2015-12-01

    The Gorkha Earthquake of M7.8 hit Nepal on April 25, 2015 at 11:56 am local time. The epicenter of this earthquake was Barpak, Gorkha, 80 km northwest of Kathmandu Valley. The main shock was followed by hundreds of aftershocks including M6.6 and M6.7 within 48 hours and M7.3 on May 12, 2015. According to the Government of Nepal, a total of 8,686 people lost their lives, 16,808 people injured, over 500,000 buildings completely collapsed and more than 250,000 building partially damaged. The National Society for Earthquake Technology - Nepal (NSET), a not-for-profit civil society organization that has been focused on earthquake risk reduction in Nepal for past 21 years, conducted various activities to support people and the government in responding to the earthquake disaster. The activities included: i) assisting people and critical facility institutions to conduct rapid visual building damage assessment including the training; ii) information campaign to provide proper information regarding earthquake safety; iii) support rescue organizations on search and rescue operations; and iv) provide technical support to common people on repair, retrofit of damaged houses. NSET is also involved in carrying out studies related to earthquake damage, geotechnical problems, and causes of building damages. Additionally, NSET has done post-earthquake detail damage assessment of buildings throughout the affected areas. Prior to the earthquake, NSET has been working with several institutions to improve seismic performance of school buildings, private residential houses, and other critical structures. Such activities implemented during the past decade have shown the effectiveness of risk reduction. Retrofitted school buildings performed very well during the earthquake. Preparedness activities implemented at community levels have helped communities to respond immediately and save lives. Higher level of earthquake awareness achieved including safe behavior, better understanding of

  6. Ground Motion Scaling in Kachchh: a Preliminary Assessment from Aftershocks of the 2001 Bhuj, India, Earthquake

    Science.gov (United States)

    Bodin, P.; Malagnini, L.; Akinci, A.

    2002-12-01

    Considerable controversy surrounds the issues of how much and how systematically source and propagation characteristics of earthquakes that take place in relatively "stable" continental settings differ from those of earthquakes in more mobile crust. The 2001 Mw 7.7 Bhuj, India, earthquake may have been the largest such earthquake in more than 100 years. We are analyzing ground motions from aftershocks of the Bhuj earthquake recorded on a temporary network deployed within 100 km of the mainshock epicenter. Our goal is to determine the source and propagation characteristics in the region, taking into account site effects at our network sites, to facilitate comparison with similar studies in other tectonic environments. To date we have used data from about 1100 earthquakes ranging in magnitude from about 2 to about 5 1/2. We model peak amplitudes as a function of source-receiver distance for bandpass-filtered time series and the spectral amplitudes of time-windowed seismograms. Because the earthquakes occurred over a wide depth range, we have analyzed the data in two overlapping depth subsets-shallower than 25 km and deeper than 20 km. We find that propagation is well-modeled by a frequency-dependent quality factor Q = 680f0.48 combined with a rather simple geometric spreading function that varies only slightly between the deep and shallow data subsets. We modeled the source terms with an w2 single corner (Brune) model with a magnitude dependent stress drop. The larger earthquakes had stress drops of about 160 bars. Extrapolating our source and propagation values using Random Vibration Theory to an Mw 7.5 earthquake yields ground motion estimates that coincide closely with similar current estimates for eastern North America (ENA) earthquakes. Our preliminary assessment is that, from a ground motion perspective, the Bhuj earthquake presents an important opportunity to study an earthquake that (a) differs significantly from earthquakes in mobile crust, and (b) resembles

  7. Coulomb stress change for the normal-fault aftershocks triggered near the Japan Trench by the 2011 M w 9.0 Tohoku-Oki earthquake

    Science.gov (United States)

    Sato, Tamao; Hiratsuka, Shinya; Mori, Jim

    2012-12-01

    Coulomb stress triggering is examined using well-determined aftershock focal mechanisms and source models of the 2011 M w 9.0 off the Pacific coast of Tohoku Earthquake. We tested several slip distributions obtained by inverting onshore GPS-derived coseismic displacements under different a priori constraints on the initial fault parameters. The aftershock focal mechanisms are most consistent with the Coulomb stress change calculated for a slip distribution having a center of slip close to the trench. This demonstrates the capability of the Coulomb stress change to help constrain the slip distribution that is otherwise difficult to determine. Coulomb stress changes for normal-fault aftershocks near the Japan Trench are found to be strongly dependent on the slip on the shallow portion of the fault. This fact suggests the possibility that the slip on the shallow portion of the fault can be better constrained by combining information of the Coulomb stress change with other available data. The case of normal-fault aftershocks near some trench segment which are calculated to be negatively stressed shows such an example, suggesting that the actual slip on the shallow portion of the fault is larger than that inverted from GPS-derived coseismic displacements.

  8. Attempt to identify seismic sources in the eastern Mitidja basin using gravity data and aftershock sequence of the Boumerdes (May 21, 2003; Algeria) earthquake

    Science.gov (United States)

    Ouyed, Merzouk; Idres, Mouloud; Bourmatte, Amar; Boughacha, Mohamed Salah; Samai, Sadek; Yelles, Abdelkrim; Haned, Abderrahmene; Aidi, Chafik

    2011-04-01

    In order to try to identify the seismogenic sources in the epicentral area, we interpreted data collected from gravity and aftershocks in the eastern part of the Mitidja basin after the occurrence of the 21 May 2003 Boumerdes earthquake (Mw = 6.8). The residual gravity anomaly and the horizontal gradient maps revealed the basement shape and density discontinuities. A seismotectonic model obtained from the aftershocks distribution and gravity data is proposed. This model highlights three active faults: one offshore and two onshore. The offshore reverse fault striking NE-SW, parallel to the coast, is consistent with the USGS focal mechanism of the main event, which is assumed to have the most moment release. The two onshore dipping blind active faults are postulated at crossing angles near the SW tip of the main fault. The interpretation is based mainly on the re-location and distribution of aftershocks, and their focal solutions. It is also supported by the basin structures obtained from the inversion and interpretation of residual gravity anomalies, as well as by additional compiled information such as the pattern of coastal co-seismic uplift. This configuration puts forward the failure mode complexity during the main shock. The topography of the basement obtained from 3D gravity inversion shows that all the onshore located aftershocks occurred in the basement, and the area between the two onshore faults rose as a consequence of their sliding.

  9. The 2007 Tocopilla earthquake and its aftershock sequence - A subduction zone earthquake at the edge of the northern Chile seimic gap

    Science.gov (United States)

    Eggert, S.; Sobiesiak, M.; Shirzaei, M.

    2010-12-01

    On 14 November 2007 a large Mw 7.7 earthquake occurred in the region of Tocopilla in Northern Chile. The earthquake took place in the southern end of the Northern Chile seismic gap which is supposed to be at the end of its seismic cycle. Studying the event and its aftershock sequence will provide closer insight into the behavior of a subduction zone earthquake at the edge of a subduction zone segment. We present a comprehensive study of the rupture area combining seismic and geodetic data. The aftershock sequence following the earthquake was very well recorded by a local seismic network of 34 short period and broad band stations. The spatial distribution of the aftershock sequence shows a concentration of aftershocks around the north-western part of the Mejillones Peninsula and along the coast up to the Río Loa. The distribution into depth shows that the majority of the hypocenters are located along the subduction interface, reaching down to ~ 50 km depth. In the western part, the aftershock sequence splits into two branches, one heading towards the trench, the other bending into the crust in front of the Mejillones Peninsula. These seismic observations lead to the conclusion that the fault rupture propagated towards the south-west with a fault plane of about 150 km length leaving the shallow part in the north west probably unbroken. To better understand the behavior of the aftershock distribution we model the Coulomb stress transfer along the fault plane. The results show that stresses are increased in the southern part of the rupture area where we find a high concentration of aftershocks. This is consistent with the calculated energy release that shows two main patches along the plate interface rupturing from north to south. The 2007 Tocopilla earthquake is the first large event that occurred inside the Northern Chile seismic gap since the 1877 Iquique event. The rupture process stopped underneath the Mejillones Peninsula, a proposed segment boundary along the

  10. Aftershock Triggering and Estimation of the Coulomb Stress Changes with Approach of Optimally Oriented Fault Planes: Examples of Some Contemporary Earthquakes in Turkey

    Science.gov (United States)

    Demirci, Alper

    2013-04-01

    The Coulomb Stress changes due to the some moderate and large earthquakes are shaped according to the orientations of reciever faults or weakness zones along the corresponding seismogenic zones. In some cases, the determination of the fault plane parameters (e.g. length, width, strike, dip) of the receiver faults are more difficult due to the tectonical complexity of the region. Therefore, in order to understand the aftershock distrubition in such areas Coulomb stress changes can be calculated under the assumption of optimally oriented fault planes which increases the spatial correlation between stress changes and aftershock distribution. In the scope of the present sutdy, aftershock distrubiton of some contemporary earthquakes in Turkey (Simav (Mw 5.8), May 2011; Van (Mw 7.0), Oct 2011 and Gulf of Fethiye (Mw 6.1), June 2012) and their coulomb stress changes were correlated. Fault plane parameters of these earthquakes which suggest three different types of focal mechanism were calculated using moment tensor inversion technique and aftershock location data in a period of 30 days for each corresponding events were taken from Kandilli Observatory and Earthquake Research Institute (KOERI) catalog. The focal mechanisms of the selected earthquakes represent normal, strike slip and thrust faulting for the earthquakes of Simav, Gulf of Fethite and Van, respectively. Coulomb Stress Changes were calculated using the open source Matlab based (Coulomb 3.3) codes. The calculations were performed by assuming Poisson's ratio and apparent friction coefficient to be 0.25 and 0.4, respectively. The coulomb stress variations were calculated at fixed depths for each event and aftershocks were selected as ±4 km for corresponding depths. Keeping in mind that the increase of static stress more than 0.5 bar can cause the triggered events in an area, the accordance rates of Coulomb stress changes and aftershock distribution under different tectonic regimes were disscussed. The accordance

  11. Kinect Technology Game Play to Mimic Quake Catcher Network (QCN) Sensor Deployment During a Rapid Aftershock Mobilization Program (RAMP)

    Science.gov (United States)

    Kilb, D. L.; Yang, A.; Rohrlick, D.; Cochran, E. S.; Lawrence, J.; Chung, A. I.; Neighbors, C.; Choo, Y.

    2011-12-01

    The Kinect technology allows for hands-free game play, greatly increasing the accessibility of gaming for those uncomfortable using controllers. How it works is the Kinect camera transmits invisible near-infrared light and measures its "time of flight" to reflect off an object, allowing it to distinguish objects within 1 centimeter in depth and 3 mm in height and width. The middleware can also respond to body gestures and voice commands. Here, we use the Kinect Windows SDK software to create a game that mimics how scientists deploy seismic instruments following a large earthquake. The educational goal of the game is to allow the players to explore 3D space as they learn about the Quake Catcher Network's (QCN) Rapid Aftershock Mobilization Program (RAMP). Many of the scenarios within the game are taken from factual RAMP experiences. To date, only the PC platform (or a Mac running PC emulator software) is available for use, but we hope to move to other platforms (e.g., Xbox 360, iPad, iPhone) as they become available. The game is written in programming language C# using Microsoft XNA and Visual Studio 2010, graphic shading is added using High Level Shader Language (HLSL), and rendering is produced using XNA's graphics libraries. Key elements of the game include selecting sensor locations, adequately installing the sensor, and monitoring the incoming data. During game play aftershocks can occur unexpectedly, as can other problems that require attention (e.g., power outages, equipment failure, and theft). The player accrues points for quickly deploying the first sensor (recording as many initial aftershocks as possible), correctly installing the sensors (orientation with respect to north, properly securing, and testing), distributing the sensors adequately in the region, and troubleshooting problems. One can also net points for efficient use of game play time. Setting up for game play in your local environment requires: (1) the Kinect hardware ( $145); (2) a computer

  12. On the c-values of the off-fault aftershocks triggered by the 1995 Kobe earthquake, Japan

    Science.gov (United States)

    Sugaya, K.; Hiramatsu, Y.; Furumoto, M.; Katao, H.; Ogata, Y.

    2010-12-01

    The Omori-Utsu law is applicable not only to aftershocks in a source region but also to off-fault aftershocks triggered by the mainshock.In this study, we estimate the c-values using the maximum-likelihood method (Ogata, 1983) from the seismicity activation in the Tamba region induced by the coseismic static stress change due to the 1995 Kobe earthquake of M7.3, Japan. We use earthquakes (M≥1.8) shallower than 20 km from the JMA catalog and remove remarked clusters of the aftershock due to moderate earthquakes with the method of Reasenberg (1985). Our analyzed period is from the occurrence of the earthquake (17 January 1995) to December 1995. The obtained c-values in the divided subregions, near and far to the rupture zone, are 58.1 ± 26.1 days and 164.7 ± 98.0 days, respectively. This is consistent with the rate- and state-dependent friction law of Dieterich (1994) in that the c-values of induced off-fault seismicity are larger than those of the source region depending on the static stress change. We estimate Aσ and the stressing rate after the earthquake in the whole region with the average ΔCFS of 30 kPa (Hashimoto, 1995, 1997) using a grid search following Toda et al. (2005). The friction law’s parameters in the whole region are estimated to be 13.8 ~ 16.2 kPa/yr and 15.0 ~ 16.6 kPa at the stressing rate and Aσ, respectively. Furthermore, we estimate ΔCFSs in the two subregions using the stressing rate of 15.5 kPa/yr and Aσ of 15.5 kPa obtained above. The obtained ΔCFSs in the divided subregions, near and far to the rupture zone, are 39.9 ~ 43.4 kPa and 17.3 ~ 19.9 kPa, respectively. These are coincident with the distribution of ΔCFS drawn by using a geodetic fault model (Hashimoto et al., 1996).

  13. Imaging the high-frequency energy radiation process of a main shock and its early aftershock sequence: The case of the 2008 Iwate-Miyagi Nairiku earthquake, Japan

    Science.gov (United States)

    Sawazaki, Kaoru; Enescu, Bogdan

    2014-06-01

    To understand the energy release process that operates at the end of the main shock rupture and start of the aftershock activity, we propose an inversion method that uses continuous high-frequency seismogram envelopes of the main shock and early aftershocks (i.e., events that occur at short times after the main shock). In our approach, the aftershock sequence is regarded as a continuous energy release process, rather than a discrete time series of events. To correct for the contribution of coda wave energy excited by multiple scattering, we use the theoretical envelope synthesized on the basis of the radiative transfer theory as a Green's function. The site amplification factors are corrected considering the conservation of energy flux and using the coda normalization method. The inverted temporal energy release rate for the 2008 MW 6.9 Iwate-Miyagi Nairiku earthquake, Japan, decays following t-1.1, at the lapse time t of 40-900 s after the main shock origin time. This exponent of the decay rate is similar to the p value of the modified Omori law. The amount of estimated energy release is consistent with that calculated from the magnitude listed in the aftershock catalog. Although the uncertainty is large, the location of large energy release at the lapse times of 40-900 s approximately overlaps to that of the aftershocks, which surrounds the large energy release area during the main shock faulting. The maxima of the energy release rate normalized by the average decay rate distributes following a power law, similar to the Gutenberg-Richter law.

  14. Structure of the Aftershock Zone of the Mw 7.0 Haiti Earthquake from the USGS-BME Portable Instrument Deployment

    Science.gov (United States)

    Altidor, J.; Dieuseul, A.; Armbruster, J. G.; Benz, H.; Dietel, C.; Ellsworth, W. L.; Given, D.; Hough, S. E.; Ketchum, D.; Luetgert, J. H.; Maharrey, J. Z.; Meremonte, M. E.; McNamara, D. E.; Mildor, B. S.; Mooney, W. D.; Sell, R.

    2010-12-01

    Between mid-March and early-June 2010, the U.S. Geological Survey (USGS) in partnership with the Bureau des Mines et de l’Energie (BME) operated an 8-station network of high-gain, three-component continuously recording stations to record the aftershocks of the January 12, 2010 Mw 7.0 Haiti earthquake. The stations were deployed to complement stations installed previously by USGS/EERI, Canadian and French teams. The USGS-BME deployment was specifically designed to improve the north-south control of epicentral locations and to investigate their association with the Enriquillo-Plantain Garden Fault and blind faults inferred from coastal uplift and InSAR imagery. Three of the instruments were located north of the aftershock zone, including one on the island La Gonave, and three were located on the southern coast of Haiti. The remaining two were deployed near the middle of the aftershock zone. P- and S- arrival times were jointly inverted for hypocenters and a layered crustal model using program VELEST. The epicenters are aligned along an 80-km-long belt striking parallel to, but distinctly north of the surface trace of the Enriquillo Fault. Well-constrained focal depths extend to at least 20 km depth. Epicentral locations are 10 or more km north of locations determined using teleseismic data and suggest that previously reported locations for the main shock and large aftershocks will need to be revised. The principal internal structure of the aftershock zone that can be resolved at present is a sharp southern boundary to the zone between 3 and 20 km depth that dips 75 degrees to the north with a surface projection that approximately coincides with the mapped trace of the Enriquillo Fault.

  15. Long-term earthquake forecasts based on the epidemic-type aftershock sequence (ETAS model for short-term clustering

    Directory of Open Access Journals (Sweden)

    Jiancang Zhuang

    2012-07-01

    Full Text Available Based on the ETAS (epidemic-type aftershock sequence model, which is used for describing the features of short-term clustering of earthquake occurrence, this paper presents some theories and techniques related to evaluating the probability distribution of the maximum magnitude in a given space-time window, where the Gutenberg-Richter law for earthquake magnitude distribution cannot be directly applied. It is seen that the distribution of the maximum magnitude in a given space-time volume is determined in the longterm by the background seismicity rate and the magnitude distribution of the largest events in each earthquake cluster. The techniques introduced were applied to the seismicity in the Japan region in the period from 1926 to 2009. It was found that the regions most likely to have big earthquakes are along the Tohoku (northeastern Japan Arc and the Kuril Arc, both with much higher probabilities than the offshore Nankai and Tokai regions.

  16. Earthquake dynamics. Supershear rupture in a M(w) 6.7 aftershock of the 2013 Sea of Okhotsk earthquake.

    Science.gov (United States)

    Zhan, Zhongwen; Helmberger, Donald V; Kanamori, Hiroo; Shearer, Peter M

    2014-07-11

    Earthquake rupture speeds exceeding the shear-wave velocity have been reported for several shallow strike-slip events. Whether supershear rupture also can occur in deep earthquakes is unclear, because of their enigmatic faulting mechanism. Using empirical Green's functions in both regional and teleseismic waveforms, we observed supershear rupture during the 2013 moment magnitude (M(w)) 6.7 deep earthquake beneath the Sea of Okhotsk, an aftershock of the large deep earthquake (M(w) 8.3). The M(w) 6.7 event ruptured downward along a steeply dipping fault plane at an average speed of 8 kilometers per second, suggesting efficient seismic energy generation. Comparing it to the highly dissipative 1994 M(w) 8.3 Bolivia earthquake, the two events represent end members of deep earthquakes in terms of energy partitioning and imply that there is more than one rupture mechanism for deep earthquakes.

  17. A quantitative study of the energy release in the aftershocks of the Bhuj earthquake, 2001, India, using Lg phase

    Science.gov (United States)

    Jayachandran, G.; Abdul Razak, M. M.; Prasad, A. G. V.; Unnikrishnan, E.

    2003-07-01

    The devastating earthquake on 26 January 2001 at Bhuj, India, resulted in large-scale death and destruction of properties of several million US dollars. The moment magnitude of the earthquake was 7.7 and its maximum focal intensity exceeded X in MM scale. The rate of aftershocks of this earthquake, recorded at Gauribidanur seismic array station (GBA), shows a monotonic decay with time superposed with oscillations. For the Indian continent the Lg phase is a prominent arrival at regional distances. The estimate of Lg amplitude is obtained by optimally fitting the Lg wave train to a exponential decay curve. The logarithm of these amplitudes and logarithm of root mean square (rms) value of actual amplitudes of the Lg are calibrated with USGS mb to create a local mbLg magnitude scale. The energy released from these aftershocks is calculated from the rms value of Lg phase. The plot of cumulative energy release with time follows the power law of the form t p, superposed with oscillations. The exponent of the power law, p, is estimated both by a time-window scanning method and by an interpolation method. The value of p is 0.434 for time-window scanning method and 0.432 for the interpolation method. The predominant periods found in the oscillatory part of the cumulative energy, obtained by differencing the observed from the power law fit, are 10.6, 7.9, 5.4, 4.6 and 3.5 h for time-window scanning method. The corresponding periods for interpolation method are 13.4, 11.5, 7.4, 4.2, 3.5, 2.6 and 2.4 h.

  18. The Aftershock Sequence of the 2008 Achaia, Greece, Earthquake: Joint Analysis of Seismicity Relocation and Persistent Scatterers Interferometry

    Science.gov (United States)

    Karakostas, Vassilis; Mirek, Katarzyna; Mesimeri, Maria; Papadimitriou, Eleftheria; Mirek, Janusz

    2016-08-01

    On 8 June 2008 an earthquake of Mw6.4 took place in the northwestern part of Peloponnese, Greece. The main shock was felt in a wide area and caused appreciable damage along the main rupture area and particularly at the antipodal of the main shock epicenter fault edge, implying strongly unilateral rupture and stopping phase effects. Abundant aftershocks were recorded within an area of ~50 km in length in the period 8 June 2008-end of 2014, by a sufficient number of stations that secure location accuracy because the regional network is adequately dense in the area. All the available phases from seismological stations in epicentral distances up to 140 km until the end of 2014 were used for relocation with the double difference technique and waveform cross-correlation. A quite clear 3-D representation is obtained for the aftershock zone geometry and dimensions, revealing the main rupture and the activated adjacent fault segments. SAR data are processed using Stanford Method for Persistent Scatterers (StaMPS) and a surface deformation map constructed based on PS point displacement for the coseismic period. A variable slip model, with maximum slip of ~1.0 m located at the lower part of the rupture plane, is suggested and used for calculating the deformation field which was found in adequate agreement with geodetic measurements. With the same slip model the static stress changes were calculated evidencing possible triggering of the neighboring faults that were brought closer to failure. The data availability allowed monitoring the temporal variation of b values that after a continuous increase in the first 5 days, returned and stabilized to 1.0-1.1 in the following years. The fluctuation duration is considered as the equivalent time for fault healing, which appeared very short but in full accordance with the cessation of onto-fault seismicity.

  19. Relocations and 3-D Velocity Structure for Aftershocks of the 2000 W. Tottori (Japan) Earthquake and 2001 Gujarat (India) Earthquake, Using Waveform Cross-correlations

    Science.gov (United States)

    Enescu, B.; Mori, J.

    2004-12-01

    The newly developed double-difference tomography method (Zhang and Thurber,2003) makes use of both absolute and relative arrival times to produce an improved velocity model and highly accurate hypocenter locations. By using this technique, we relocate the aftershocks of the 2000 Western Tottori earthquake (Mw 6.7) and 2001 Gujarat (Mw 7.7) earthquake and obtain a 3D-velocity model of the aftershock region. The first data set consists of 1035 aftershocks recorded at 62 stations during a period of about a month following the mainshock (Shibutani et al.,2002). In order to get the best arrival times a cross-correlation analysis was used to align the waveforms. The epicentral distribution of the relocated events reveals clear earthquake lineations, some of them close to the mainshock, and an increased clustering. The aftershocks' depth distribution shows a mean shift of the hypocenters' centroid of about 580m; a clear upper cutoff of the seismic activity and some clustering can be also seen. The final P-wave velocity model shows higher-value anomalies in the vicinity of the mainshock's hypocenter, in good agreement with the results of Shibutani et al.(2004). The second data set consists of about 1300 earthquakes, recorded during one week of observations by a Japanese-Indian research team in the aftershock region of the Gujarat earthquake (Sato et al.,2001). Using the double-difference algorithm and waveform cross-correlations, we were able to identify a more clear alignment of hypocenters that define the mainshock's fault and an area of relatively few aftershocks in the region of the mainshock's hypocenter. Both studies demonstrate that the cross-correlation techniques applied for events with inter-event distances as large as 10km and cross correlation coefficients as low as 50% can produce more accurate locations than those determined from catalog phase data. We are going to discuss briefly the critical role of frequency filtering and of the time window used for cross

  20. April 7, 2009, Mw 5.5 aftershock of the L'Aquila earthquake: seismogenic fault geometry and its implication for the central Apennines active extensional tectonics (Italy).

    Science.gov (United States)

    Adinolfi, Guido Maria; Lavecchia, Giusy; De Matteis, Raffaella; Nardis Rita, De; Francesco, Brozzetti; Federica, Ferrarini; Zollo, Aldo

    2015-04-01

    On April 6, 2009 (at 01:32 UTC) a Mw 6.3 earthquake hit the town of L'Aquila (central Italy) and surrounding villages causing fatalities and severe damage in the area. After few days, a nearly 40-km-long extensional fault system was activated generating both northward and southward seismicity migration along the NW-SE trending sector of central Apennines. During the intense aftershocks sequence, different sesmogenic sources with a distinct geometry, size and the degree of involvement were reactivated. Among the relevant aftershocks with Mw 5.0 to 5.5, the largest one occurred on April 7 (at 17:47 UTC), 9 km SE-ward of the mainshock involving a source seated at much greater depths (~14 km). Despite the enormous number of studies of the 2009 L'Aquila earthquake, mainly focused on the various geological and seismological aspects of the main Paganica source, the April 7 strongest aftershock (Mw 5.5) has not yet been deeply investigated. Consistent geometric and kinematic correlations between the geological and seismological data about this seismogenic source are missing. There are still open questions concerning its unresolved geometry and the unknown style of the central Apennines structure activated at greater depths during the 2009 L'Aquila seismic sequence. Furthermore, some authors (Lavecchia et al., 2012) have supposed that the April 7, 2009 aftershock (Mw 5.5) occurred onto an high dip segment (~50°) of an east-dipping extensional basal detachment with a potential surface expression outcropping in the area of the eastern Sabina-Simbruini Mts. In this work we propose a seismological analysis of the April 7, 2009 aftershock (Mw 5.5) rupture process. In order to define the unresolved source geometry, we computed the focal mechanism through the time domain, moment tensor full waveform inversion (Dreger and Helmberger, 1993). Also, we estimated the apparent source time functions (ASTFs) by deconvolution of the impulse response of the medium from the recorded data

  1. The M w6.7 12 October 2013 western Hellenic Arc main shock and its aftershock sequence: implications for the slab properties

    Science.gov (United States)

    Papadimitriou, Eleftheria; Karakostas, Vassilis; Mesimeri, Maria; Vallianatos, Filippos

    2016-01-01

    The 12 October 2013 M w6.7 earthquake offshore Crete Island is one of the few strong earthquakes to have occurred in the last few decades in the southwestern part of the Hellenic subduction zone (HSZ), providing the opportunity to evaluate characteristics of the descending slab. The HSZ has experienced several strong (M ≥ 7.0) earthquakes in historical times with the largest one being the 365 AD, M w = 8.4 earthquake, the largest known ever occurred in the Mediterranean region. The 2013 main shock occurred in close proximity with the 365 event, on an interplate thrust fault at a depth of 26 km, onto the coupled part of the overriding and descending plates. GCMT solution shows a slightly oblique (rake = 130°) thrust faulting with downdip compression on a nearly horizontal (dip = 3°) northeast-dipping fault plane with strike (340°) parallel to the subduction front, with the compression axis being oriented in the direction of plate convergence. The subduction interface can be more clearly resolved with the integration of aftershock locations and CMT solution. For this scope, the aftershocks were relocated after obtaining a v p/v s ratio equal to 1.76, a one-dimensional velocity model and time delays that approximate the velocity structure of the study area, and the employment of double-difference technique for both phase pick data and cross-correlation differential times. The first-day relocated seismicity, alike aftershocks in the first 2 months, shows activation of an area at the upper part of the descending slab, with most activity being concentrated between 13 and 27 km, where the main shock is also encompassed. Aftershocks are rare near to the main shock, implying homogeneous slip on a large patch of the rupture plane. Based on the aftershock distribution, the size of the activated area estimated is about 24 km long and 17 km wide. Coulomb stress changes resolved for transpressive motion reveal negligible off-fault aftershock triggering, evidencing a

  2. The M w6.7 12 October 2013 western Hellenic Arc main shock and its aftershock sequence: implications for the slab properties

    Science.gov (United States)

    Papadimitriou, Eleftheria; Karakostas, Vassilis; Mesimeri, Maria; Vallianatos, Filippos

    2016-10-01

    The 12 October 2013 M w6.7 earthquake offshore Crete Island is one of the few strong earthquakes to have occurred in the last few decades in the southwestern part of the Hellenic subduction zone (HSZ), providing the opportunity to evaluate characteristics of the descending slab. The HSZ has experienced several strong ( M ≥ 7.0) earthquakes in historical times with the largest one being the 365 AD, M w = 8.4 earthquake, the largest known ever occurred in the Mediterranean region. The 2013 main shock occurred in close proximity with the 365 event, on an interplate thrust fault at a depth of 26 km, onto the coupled part of the overriding and descending plates. GCMT solution shows a slightly oblique (rake = 130°) thrust faulting with downdip compression on a nearly horizontal (dip = 3°) northeast-dipping fault plane with strike (340°) parallel to the subduction front, with the compression axis being oriented in the direction of plate convergence. The subduction interface can be more clearly resolved with the integration of aftershock locations and CMT solution. For this scope, the aftershocks were relocated after obtaining a v p/ v s ratio equal to 1.76, a one-dimensional velocity model and time delays that approximate the velocity structure of the study area, and the employment of double-difference technique for both phase pick data and cross-correlation differential times. The first-day relocated seismicity, alike aftershocks in the first 2 months, shows activation of an area at the upper part of the descending slab, with most activity being concentrated between 13 and 27 km, where the main shock is also encompassed. Aftershocks are rare near to the main shock, implying homogeneous slip on a large patch of the rupture plane. Based on the aftershock distribution, the size of the activated area estimated is about 24 km long and 17 km wide. Coulomb stress changes resolved for transpressive motion reveal negligible off-fault aftershock triggering, evidencing a

  3. The Focal Mechanism Solutions of the Ms 8.0 Wenchuan Earthquake in Sichuan on May 12,2008 and Some of Its Aftershocks

    Institute of Scientific and Technical Information of China (English)

    Guo Xiangyun; Chen Xuezhong; Li Yan'e

    2010-01-01

    The focal mechanism solutions of the Wenchuan earthquake(Ms8.0)of May 12,2008 and some of its aftershocks occurring up to December 10,2008 are determined with lower semisphere of equal-projection and first motion sign data of P waves from regional and distant stations.The focal mechanism solutions of the Ms8.0 Wenchuan earthquake are:Nodal plane Ⅰ:strike 5°,dip angle 48°,slip angle 39°; Nodal plane Ⅱ: strike 247°,dip angle62°,slip angle 131°; P axis azimuth 309°,plunge 8°,T axis azimuth 208°,plunge 54°,B axis azimuth 44°,plunge 35°.Combining geological tectonics and spatial distribution of aftershocks,nodal plane Ⅱ can be identified as a seismogenic fault.According to focal mechanism solutions,the fault activity that triggered the huge earthquake is reverse thrusting.The main rupture surface is S67°W,basically identical to the fault strike on which the earthquake occurred.The main compression stress P axis is N51°W,which is basically the same as the direction of the regional tectonic stress field.According to the results of focal mechanism solutions of aftershocks,the aftershocks occurring in the southern and northern sections of the Longmenshan fault zone have predominant orientations and are obviously different.For the main shock and the early aftershocks occurring on the southern section of the Longmenshan fault,the rupturing is mainly characterized by reverse-dip slip with some strike-slip,and over time,the aftershocks migrated towards the northern section.The rupturing in the source is mainly characterized by strike-slip with some reverse-dip slips.The stress field is controlled by the main shock stress field in the southern section of the Longmenshan tectonic zone,while it is controlled by the main shock stress field and regional stress field in the northern section of the Longmenshan tectonic zone.

  4. Relation between aftershock parameters and geodetic slip models: Case study of the 2010 Mw8.8 Maule (Chile) and the 2011 Mw9.0 Tohoku-oki (Japan) earthquakes

    Science.gov (United States)

    Zakharova, Olga; Hainzl, Sebastian; Lange, Dietrich; Enescu, Bogdan

    2016-04-01

    The distribution of local stresses, which represents as well crustal heterogeneity, is the main factor for aftershock triggering. Though neither local stresses nor crustal heterogeneity are known in detail, some information of their distribution is implicitly represented by slip and coupling values on the mainshock fault interface. Taking these two concepts as the main assumptions, we perform a comprehensive analysis of the relation between aftershock characteristics and geodetic measurements on the mainshock fault interface. As a case study we select two megathrust events, the 2010 Mw8.8 Maule (Chile) and the 2011 Mw9.0 Tohoku-oki (Japan), due to the availability of rich aftershock data as well as of geodetic inversion models. To investigate the dependency between these data sets we firstly estimated the aftershock parameter distribution, using a modified ETAS model, which allows to take into account the mainshock rupture extension. Secondly we calculate the correlation between aftershock parameters and coseismic/postseismic slip and interseismic coupling. We find: (1) aftershocks tend to occur in the areas of high coseismic slip gradient, afterslip and interseismic coupling; (2) aftershock seismic moment is released preferentially in regions of large coseismic slip, coseismic slip gradient and interseismically locked areas; (3) anomalous aftershock parameters occur in the areas of reactivated fault systems. Moreover, we show that modified ETAS model outperforms the classical one in the cases when the mainshock rupture extension cannot be neglected and represented as a point source. One of the main restriction in the presented analysis is related to the large uncertainties of the inversion models, which limit the significance of our results.

  5. Imaging the high-frequency energy radiation process of a mainshock and its early aftershock sequence for a crustal earthquake in Japan

    Science.gov (United States)

    Sawazaki, K.; Enescu, B.

    2013-12-01

    Waveform recordings of aftershocks occurring immediately after a mainshock are mostly hidden by the coda wave of the mainshock and overlap one with each other. Consequently, the detection of such early events is very difficult and the completeness of earthquake catalogs at short times after large events becomes poor. To overcome this difficulty, we developed an inversion scheme which measures the energy radiation process of the early aftershock sequence using continuous seismogram envelopes in the 1-16 Hz frequency range. This inversion scheme makes use of the coda wave envelope, synthesized on the basis of the radiative transfer theory as the Green's function. Here the multiple isotropic scattering and intrinsic attenuation parameters in a 3-D infinite scattering medium are estimated through the multiple lapse time window analysis. The site amplification factor is also corrected using the coda normalization method. We apply the envelope inversion technique to the 2008 Iwate-Miyagi Nairiku earthquake, Japan (Mw6.9), and its early aftershock sequence. The inverted energy release rate has two stages. At 10-30 s and 30-600 s after the mainshock origin time, the energy release rate decays following t(-4 to -8) and t(-1 to -2), respectively. The modified Omori formula cannot fit the energy release rate before 30 s. This change in the temporal decay rate suggests that the mechanism of energy release process changes; the energy release from the termination stage of the mainshock rupture dominates before 30 s, while that by the early aftershocks dominates at later times.

  6. Subduction earthquake deformation associated with 14 November 2007, Mw 7.8 Tocopilla earthquake in Chile: Results from InSAR and aftershocks

    Science.gov (United States)

    Motagh, Mahdi; Schurr, Bernd; Anderssohn, Jan; Cailleau, Beatrice; Walter, Thomas R.; Wang, Rongjiang; Villotte, Jean-Pierre

    2010-07-01

    On 14 November 2007, a subduction thrust earthquake, magnitude Mw = 7.8, occurred in the coastal region of northern Chile, causing substantial damage to the city of Tocopilla. We investigate the source fault of the earthquake, slip distribution and fault interaction by integrating aftershock locations, satellite interferometry data and stress model simulations. Aftershock measurements allow us to locate the area and geometry of the rupture plane in the coastal region between the cities of Tocopilla and Antofagasta. Combining two satellite viewing geometries, acquired in Envisat's Wide Swath and Image modes, we observe decimetre-scale coseismic deformation. The maximum line-of-sight displacement is found to be about 40 cm, located at the Mejillones Peninsula. Slip inversions using elastic half-space models with geometry constrained by aftershocks suggest rupturing of an area of ˜ 160 km by ˜50 km along the Nazca -South America convergent margin between latitudes 22°S and 23.5°S. The main slip is concentrated on two asperities, the largest being located in the southern part of the rupture area at a depth of approximately 30-50 km with a magnitude of about 2.5 m. Because aftershock distribution may also suggest a region of shallow crustal deformation activity located offshore, we investigate whether the 2007 Tocopilla earthquake also involved shallow crustal fault slip offshore. Although we find that the latter assumption is supported by Coulomb stress modelling and geologic inferences, our geodetic and seismic data provide insufficient constraints to resolve the exact geometry and kinematics of dislocation on this structure.

  7. Unbiased Moment Rate Spectra and Absolute Site Effects in the Kachchh Basin, India, from the Analysis of the Aftershocks of the 2001 Mw7.6 Bhuj Earthquake

    OpenAIRE

    Malagnini, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Bodin, P.; Center for Earthquake Research and Information University of Memphis; Mayeda, K.; Lawrence Livermore National Laboratory Ground-based Nuclear Explosion Monitoring Program; Akinci, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia

    2006-01-01

    What can be learned about absolute site effects on ground motions, with no geotechnical information available, in a very poorly instrumented region? In addition, can reliable source spectra be computed at a temporary deployment? These challenges motivated our current study of aftershocks of the 2001 Mw 7.6 Bhuj earthquake, in western India, where we decouple the ambiguity between absolute source radiation and site effects by first computing robust estimates of coda-derived m...

  8. Incorporating fault mechanics into inversions of aftershock data for the regional remote stress, with application to the 1992 Landers, California earthquake

    Science.gov (United States)

    Maerten, Frantz; Madden, Elizabeth H.; Pollard, David D.; Maerten, Laurent

    2016-04-01

    We present a new stress inversion algorithm that accounts for the physics relating the remote stress, slip along complex faults, and aftershock focal mechanisms, in a linear-elastic, heterogeneous, isotropic whole- or half-space. For each new remote stress, the solution of the simulation is obtained by the superposition of three pre-calculated solutions, leading to a constant time evaluation. Consequently, the full three-dimensional boundary element method model need not be recomputed and is independent of the structural complexity of the underlying model. Using a synthetic model, we evaluate several different measures of fit, or cost functions, between aftershocks and model results. Cost functions that account for aftershock slip direction provide good constraint on the remote stress, while functions that evaluate only nodal plane orientations do not. Inversion results are stable for values of friction ≤ 0.5 on mainshock faults. We demonstrate the technique by recovering the remote stress regime at the time of the 1992 M 7.3 Landers, California earthquake from its aftershocks and find that the algorithm performs well relative to methods that invert earthquakes occurring prior to the Landers mainshock. In the mechanical inversion, incorporating fault structures is necessary, but small differences in fault geometries do not impact these inversion results. Each inversion provides a complete solution for an earthquake as output, including fault slip and the stress and deformation fields around the fault(s). This allows for many additional datasets to be used as input, including fault surface slip, GPS data, InSAR data, and/or secondary fracture orientations.

  9. Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations

    Directory of Open Access Journals (Sweden)

    M. Bohnhoff

    2008-01-01

    Full Text Available The most recent devastating earthquakes that occurred along the North Anatolian Fault Zone (NAFZ in northwestern Turkey were the 1999 Izmit (Mw=7.4 and Düzce (Mw=7.1 events. In this study we present a catalog of Izmit aftershock hypocenters that was deduced from a network covering the entire 140 km long rupture of the mainshock. 7348 events with a location accuracy better than 5 km are analysed. Aftershocks were observed along the entire ruptured segment along a 20 km wide band of activity. Events are clustered in distinct regions and dominantly occur at 5 to 15 km depth. The eastern termination of the Izmit rupture is characterized by a sharp and steeply dipping boundary exactly where the Düzce mainshock initiated 87 days after the Izmit event. Relocation of the events using double-difference technology results in 4696 high-resolution hypocenters that allow resolving the internal structure of the seismically active areas with a resolution of 300 m (horizontal and 400m (vertical. Below the Akyazi Plain, representing a small pull-apart structure at a triple junction of the NAFZ, we identify planes of activity that can be correlated with nodal planes of EW extensional normal faulting aftershocks. Along the easternmost Karadere-Düzce segment we identify the down-dip extension of the Karadere fault that hosted about 1 m of right-lateral coseismic slip. At the easternmost rupture we correlate a cloud-type distribution of seismic activity with the largest aftershocks in this area, a subevent of the Izmit mainshock and the Düzce mainshock that all have an almost identical focal mechanism. This part of the NAFZ is interpreted as a classical example of a seismic barrier along the fault.

  10. Source time functions of the 1999, Jiji (Chi-Chi) earthquake from GDSN long period waveform data using aftershocks as empirical Green(s functions

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A large earthquake (MW=7.6) occurred in Jiji (Chi-Chi), Taiwan, China on September 20, 1999, and was followed by many moderate-size shocks in the following days. Two of the largest aftershocks with the magnitudes of MW=6.1 and MW=6.2, respectively, were used as empirical Green(s functions (EGFs) to obtain the source time functions (STFs) of the main shock from long-period waveform data of the Global Digital Seismograph Network (GDSN) including IRIS, GEOSCOPE and CDSN. For the MW=6.1 aftershock of September 22, there were 97 pairs of phases clear enough from 78 recordings of 26 stations; for the MW=6.2 aftershock of September 25, there were 81 pairs of phases clear enough from 72 recordings of 24 stations. For each station, 2 types of STFs were retrieved, which are called P-STF and S-STF due to being from P and S phases, respectively. Totally, 178 STF individuals were obtained for source-process analysis of the main shock. It was noticed that, in general, STFs from most of the stations had similarities except that those in special azimuths looked different or odd due to the mechanism difference between the main shock and the aftershocks; and in detail, the shapes of the STFs varied with azimuth. Both of them reflected the stability and reliability of the retrieved STFs. The comprehensive analysis of those STFs suggested that this event consisted of two sub-events, the total duration time was about 26 s, and on the average, the second event was about 7 s later than the first one, and the moment-rate amplitude of the first event was about 15% larger than that of the second one.

  11. Static stress transfer modeling and aftershock statistics for the 2002 Nenana Mountain-Denali Park, Alaska, sequence

    Science.gov (United States)

    Anderson, G.; Jones, L. M.; Ji, C.

    2002-12-01

    On October 23, 2002, the Mw 6.7 Nenana Mountain earthquake occurred in central Alaska. While this was a significant event, it became even more interesting as a foreshock to the Mw 7.9 Denali Park mainshock of November 3, 2002, which was the largest earthquake to occur on land in the United States since the 1857 Fort Tejon earthquake in southern California. Using a finite-fault rupture model and the theory of deformation from dislocations in an elastic half-space, we have modeled static Coulomb stress transfer from the Nenana Mountain event to the hypocentral region of the Denali Park event and find that the Nenana Mountain event transferred about 0.05--0.1 MPa (0.5--1 bar) of Coulomb stress to that area, encouraging failure of the later event. We have also computed the combined stress transferred to several large regional faults from the Nenana Mountain and Denali Park events using our Nenana Mountain and Denali Park rupture models. We find that the two main events combined transferred more than 0.05 MPa (0.5 bar) of Coulomb stress to the northern 50 km of the Cross Creek fault, a 150-km-long right-lateral strike slip fault in east-central Alaska, and up to 0.05 MPa of Coulomb stress to the Muldrow segment of the Denali fault, west of the Nenana Mountain rupture. It is worth noting, however, that these faults are nearest to the mainshock rupture and thus most prone to errors in the stress transfer modeling. Other major faults in the region, including the Tonzona, Farewell, and Boss Creek segments of the Denali fault, the Castle Mountain fault near Anchorage, and the Yakataga subduction interface, experienced insignificant static Coulomb stress changes, though dynamic stresses were probably much larger. Although the stress changes from these events are significant, the rates of aftershocks triggered by the Nenana Mountain foreshock and by the Denali Park mainshock are extremely low. We describe the rate of aftershocks with the Reasenberg and Jones formulation for

  12. Anisotropic upper crust above the aftershock zone of the 2013 Ms 7.0 Lushan earthquake from the shear wave splitting analysis

    Science.gov (United States)

    Liu, Ying; Zhang, Haijiang; Zhang, Xin; Pei, Shunping; An, Meijian; Dong, Shuwen

    2015-10-01

    We have conducted a systematic shear wave splitting analysis using 1000 selected aftershocks with M > 2 from the 2013 Ms 7.0 Lushan earthquake along the Longmenshan fault system in southwest China. Polarization directions of fast shear waves show a bimodal distribution with one dominant direction approximately parallel to the fault strike and the other close to the regional maximum horizontal compressive stress direction. This indicates that in this area mechanisms causing crustal seismic anisotropy are both stress induced and fault zone structure controlled. Delay times between fast and slow shear waves do not show a clear trend of increase for deeper events, suggesting the anisotropic zone is mostly above the aftershocks, which are generally located below 8 km. We further applied a shear wave splitting tomography method to measured delay times to characterize the spatial distribution of seismic anisotropy. The three-dimensional anisotropic percentage model shows strong anisotropy above 8 km but low anisotropy below it. The mainshock slip zone and its aftershocks are associated with very low or negligible anisotropy and high velocity, indicating that the zones with high anisotropy and low velocity above 8 km are mechanically weak and it is difficult for stress to accumulate there. The main and back reverse fault zones are associated with high anisotropic anomalies above ˜8 km, likely caused by shear fabric or microfractures aligned parallel to the fault zone.

  13. Rupture processes of the 2015 Mw 7.9 Gorkha earthquake and its Mw 7.3 aftershock and their implications on the seismic risk

    Science.gov (United States)

    Liu, Chengli; Zheng, Yong; Wang, Rongjiang; Shan, Bin; Xie, Zujun; Xiong, Xiong; Ge, Can

    2016-07-01

    The rupture processes of the 2015 April 25 Gorkha earthquake and its strongest aftershock occurred on May 12 in Nepal are investigated by joint inversion of seismological and geodetic data. Synthetic test shows that the sedimentary layers in the source region play an important role in the rupture process inversion. Our optimized model of the mainshock shows that the rupture has a unilateral propagation pattern. The dominant mechanism is pure thrust with maximum slip of 5.8 m, the rupture scale extends ~ 60 km along dip and ~ 150 km along strike, and the largest static stress change is ~ 7.6 MPa. The total seismic moment is 7.87 × 1020 N m, equivalent to Mw 7.9. Most seismic moment was released within 80 s and the majority seismic moment was released at the first 40 s. The rupture propagated in main slip asperity with a velocity of ~ 3.0 km/s. The strong aftershock magnitude is about Mw 7.3, and the peak slip is about 5.0 m, close to the peak slip of the mainshock. Moreover, the slips of the mainshock and the aftershocks are in good complementary, suggesting a triggering relationship between them. Considering the strain accumulation, the Gorkha earthquake ruptured only part of the seismic gap alone, thus still poses high earthquake risk, especially in the west side of the mainshock rupture zone.

  14. A Study on Shear Wave Splitting for the Sequence of the Aftershocks of the Yao'an Ms6.5 Earthquake in Yunnan Province

    Institute of Scientific and Technical Information of China (English)

    Qian Xiaodong; Li Baiji; Qin Jiazheng

    2003-01-01

    The shear wave splitting study is based on data of the 3-component digital seismograms. This was recorded at 3 sets of stations, which were set up after the Yao'an M_s6.5 earthquake, near its epicenter. The results indicate the following: ①Shear wave splitting has been observed through analyzing 236 aftershock recordings within the shear wave window. ②The time delay was mostly in the range of 3.5~10.5ms/km and the average was 7.0ms/km.③The polarization direction of the fast split S-wave was mostly in the range of N140°E~N164°E and the average was N152.4°E. ④The preferred polarization direction for the fast shear wave was different from the direction of the seismogenic structure of the mainshock (Maweijing fault) and the direction of the rupture of the aftershocks, but similar to the principal compressional amis of the regional stress field. ⑤Shear wave splitting for sequence of the aftershocks of the Yao'an earthuake was the result of anisotropy of EDA cracks controlled by stress field.

  15. On Spatial Narrative Arts in Aftershocks%论《余震》的空间叙事艺术

    Institute of Scientific and Technical Information of China (English)

    谭孟双

    2015-01-01

    Aftershocks broke the traditional time linear narrative mode and turned to spatial narrative. On the one hand, the text regulates the ups and downs of the plot with jumping and juxtaposition of physical space; on the other hand, the text constructs the mental space of Xiaodeng by adopting two techniques of montage and dreams description, and reveals the complicated true feelings inside the character from the surface memories deep into the subconsciousness, thus pushing the story plot to the climax. In Aftershocks, time, a component of narrative text, is weakened and replaced by space which demonstrates unique advantage-synchronicity. Therefore, the overall sense and spatiality brought by spatial narrative manifests new internal mechanism of modern fiction transcending the tradition.%《余震》打破一贯传统的时间线性的叙事模式,转而以空间叙事为主. 一方面,文本以物理空间的跳跃和并置调控故事情节的跌宕起伏;另一方面,通过运用蒙太奇和梦境描写两种技巧构建主人公小灯的心理空间,由表层的回忆深入至其潜意识,使人物内心深处盘根错节的真情实感呈现出来,从而将故事情节推至高潮.《余震》这部小说中,时间性作为叙事文本的构成要素被弱化,取而代之的空间则彰显出其特有的优势——"同时性". 因此,由空间叙事带来的作品的整体感、空间性展示了现代小说超越传统的新的内部机制.

  16. Foreshocks and aftershocks locations of the 2014 Pisagua, N. Chile earthquake: history of a megathrust earthquake nucleation

    Science.gov (United States)

    Fuenzalida Velasco, Amaya; Rietbrock, Andreas; Tavera, Hernando; Ryder, Isabelle; Ruiz, Sergio; Thomas, Reece; De Angelis, Silvio; Bondoux, Francis

    2015-04-01

    The April 2014 Mw 8.1 Pisagua earthquake occurred in the Northern Chile seismic gap: a region of the South American subduction zone lying between Arica city and the Mejillones Peninsula. It is believed that this part of the subduction zone has not experienced a large earthquake since 1877. Thanks to the identification of this seismic gap, the north of Chile was well instrumented before the Pisagua earthquake, including the Integrated Plate boundary Observatory Chile (IPOC) network and the Chilean local network installed by the Centro Sismologico Nacional (CSN). These instruments were able to record the full foreshock and aftershock sequences, allowing a unique opportunity to study the nucleation process of large megathrust earthquakes. To improve azimuthal coverage of the Pisagua seismic sequence, after the earthquake, in collaboration with the Instituto Geofisico del Peru (IGP) we installed a temporary seismic network in south of Peru. The network comprised 12 short-period stations located in the coastal area between Moquegua and Tacna and they were operative from 1st May 2014. We also installed three stations on the slopes of the Ticsiani volcano to monitor any possible change in volcanic activity following the Pisagua earthquake. In this work we analysed the continuous seismic data recorded by CSN and IPOC networks from 1 March to 30 June to obtain the catalogue of the sequence, including foreshocks and aftershocks. Using an automatic algorithm based in STA/LTA we obtained the picks for P and S waves. Association in time and space defined the events and computed an initial location using Hypo71 and the 1D local velocity model. More than 11,000 events were identified with this method for the whole period, but we selected the best resolved events that include more than 7 observed arrivals with at least 2 S picks of them, to relocate these events using NonLinLoc software. For the main events of the sequence we carefully estimate event locations and we obtained

  17. Corresponding relation between the result of real-time fluid analysis and estimated energy value of aftershock during drilling in WFSD

    Science.gov (United States)

    Tang, L.; Luo, L.; Lao, C.; Zeng, Y.; Liu, J.

    2014-12-01

    The real-time fluid analysis has been applied in some important drilling engineering. Recently the fluid analysis has just been completed in WFSD-1, WFSD- 2 and WFSD-4 holes, the accumulated analytical period of which is about 1200 days and the completed drilling depth is probable 8000 meters. We could see from the real-time analysis results in May 19, 2009, that the multi components of drilling mud gas change significantly, especially the abnormal changes of methane, oxygen and helium. And the high abnormal value of methane reaches 8.37% (v/v), which has exceeded the explosion concentration value of methane. Due to a few actual reasons, such as no mud circulation, the period of real-time fluid analysis would shorter than that of drilling process. The actual period of fluid analysis in WFSD-2 hole is from October 14, 2009 to April 5, 2012, so the statistical analysis of the aftershock information and the magnitude effort were both considered during this period. According to the relationship between magnitude and seismic energy of earthquake, the monthly earthquake energy values were estimated. Estimation approach is based on the formula proposed by the seismologist Richter in 1953, in which the energy value of aftershock between Ms. 3.0 and Ms. 4.0 is defined as 1, that of aftershocks between Ms. 4.0 and Ms. 5.0 is multiplied by 31.6, and that of between Ms. 5.0 and Ms. 6.0 is multiplied by 1000. Then the monthly curve of estimated energy values is showed in Fig. (Monthly curve of estimated energy value of aftershock more than 3.0 during drilling WFSD-2. X-axis represents the month, Y-axis represents the estimated energy value). We could find that some special corresponding periods through the comparison of fluid change and the energy estimated values of aftershocks from the Fig. and the poster (Fall Meeting AGU 2013, San Francisco, T23E-2645), which had showed the ratio curves of the minimum and mean value, the maximum and mean value over time. We can see that the

  18. Insights into induced earthquakes and aftershock activity with in-situ measurements of seismic velocity variations in an active underground mine

    Science.gov (United States)

    Brenguier, F.; Olivier, G.; Campillo, M.; Roux, P.; Shapiro, N.; Lynch, R.

    2015-12-01

    The behaviour of the crust shortly after large earthquakes has been the subject of numerous studies, but many co- and post-seismic processes remain poorly understood. Damage and healing of the bulk rock mass, post-seismic deformation and the mechanisms of earthquake triggering are still not well understood. These processes are important to properly model and understand the behaviour of faults and earthquake cycles.In this presentation, we will show how in-situ measurements of seismic velocity variations have given new insights into these co- and post-seismic processes. An experiment was performed where a blast was detonated in a tunnel in an underground mine, while seismic velocity variations were accurately (0.005 %) measured with ambient seismic noise correlations. Additionally, aftershock activity was examined and the influence of the removal of a piece of solid rock was estimated with elastic static stress modelling. The majority of the aftershocks were delayed with respect to the passing of the dynamic waves from the blast, while the locations of the aftershocks appeared clustered and not homogeneously spread around the blast location. A significant velocity drop is visible during the time of the blast, which is interpreted as co-seismic damage and plastic deformation. These non-elastic effects are healed by the confining stresses over a period of 5 days until the seismic velocity converges to a new baseline level. The instantaneous weakening and gradual healing observed from the velocity variations are qualitatively similar to results reported in laboratory studies. The change in the baseline level of the seismic velocity before and after the blast indicate a change in the static stress that is comparable to the results of elastic static stress modelling. The differences between the elastic model predictions and the seismic velocity variations could be due to zones of fractured rock, indicated by the spatial clustering of the aftershocks, that are not

  19. 科里奥利力对断层作用的统计研究%Statistical Study on the Effect of Coriolis Force in Aftershocks

    Institute of Scientific and Technical Information of China (English)

    盛书中; 万永革; 田力

    2009-01-01

    首先给出了分解到已知断层面法向和切向上的断层错动科里奥利应力(简称为科里奥利法向应力和切向应力)表达式,然后从哈佛大学矩心矩张量目录中选取主余震资料进行分析,按断层分类研究了科里奥利法向应力和主震震级与其最大余震震级差及主震地震矩与余震地震矩总和之差的折合矩震级间的关系.研究结果显示:地震断层错动过程中虽然产生了使断层两盘相互拉离(或挤压)的科里奥利法向应力,它降低(或增加)了断层错动时断层面上的摩擦阻力,但是应力量值太小(科里奥利法向应力估计最大不到0.1MPa,即不到一个大气压),不足以对断层错动及主震能量释放产生影响,从而影响余震的最大震级和总体水平.%The study first gives the expression for the normal component of fault movement Coriolis stress (normal Coriolis stress for short) to a certain fault plane, and then select the data of mainshock and aftershock from Harvard CMT catalog. Classification study on the normal Coriolis stress is carried out according to the fault types, and the relations between the normal Coriolis stress and the magnitude difference of mainshock and its maximum aftershock, and the converting moment magnitude of the difference of mainshock's moment tensor and the sum of total aftershocks' moment tensor are studied respectively. The results show that tensile (or compression) normal Coriolis stress is generated during the fault slip, which decreases (or increases) the frictional resistance of fault movement. However, the normal Coriolis stress was too small ( maximum normal Coriolis stress is not exceeding 0.1 MPa, namely not exceed one atmospheric pressure) to affect the fault slip and the energy release of mainshock, and affects the aftershock activity and maximum magnitude of aftershocks.

  20. Aftershocks series monitoring of the September 18, 2004 M = 4.6 earthquake at the western Pyrenees: A case of reservoir-triggered seismicity?

    Science.gov (United States)

    Ruiz, M.; Gaspà, O.; Gallart, J.; Díaz, J.; Pulgar, J. A.; García-Sansegundo, J.; López-Fernández, C.; González-Cortina, J. M.

    2006-10-01

    On September 18, 2004, a 4.6 mbLg earthquake was widely felt in the region around Pamplona, at the western Pyrenees. Preliminary locations reported an epicenter less than 20 km ESE of Pamplona and close to the Itoiz reservoir, which started impounding in January 2004. The area apparently lacks of significant seismic activity in recent times. After the main shock, which was preceded by series of foreshocks reaching magnitudes of 3.3 mbLg, a dense temporal network of 13 seismic stations was deployed there to monitor the aftershocks series and to constrain the hypocentral pattern. Aftershock determinations obtained with a double-difference algorithm define a narrow epicentral zone of less than 10 km 2, ESE-WNW oriented. The events are mainly concentrated between 3 and 9 km depth. Focal solutions were computed for the main event and 12 aftershocks including the highest secondary one of 3.8 mbLg. They show mainly normal faulting with some strike-slip component and one of the nodal planes oriented NW-SE and dipping to the NE. Cross-correlation techniques applied to detect and associate events with similar waveforms, provided up to 33 families relating the 67% of the 326 relocated aftershocks. Families show event clusters grouped by periods and migrating from NW to SE. Interestingly, the narrow epicentral zone inferred here is located less than 4 km away from the 111-m high Itoiz dam. These hypocentral results, and the correlation observed between fluctuations of the reservoir water level and the seismic activity, favour the explanation of this foreshock-aftershock series as a rapid response case of reservoir-triggered seismicity, burst by the first impoundment of the Itoiz reservoir. The region is folded and affected by shallow dipping thrusts, and the Itoiz reservoir is located on the hangingwall of a low angle southward verging thrust, which might be a case sensible to water level fluctuations. However, continued seismic monitoring in the coming years is mandatory in

  1. Investigation of the high-frequency attenuation parameter, κ (kappa), from aftershocks of the 2010 Mw 8.8 Maule, Chile earthquake

    Science.gov (United States)

    Neighbors, Corrie; Liao, E. J.; Cochran, Elizabeth S.; Funning, G. J.; Chung, A. I.; Lawrence, J. F.; Christensen, C. M.; Miller, M.; Belmonte, A.; Sepulveda, H. H. Andrés

    2014-01-01

    The Bío Bío region of Chile experienced a vigorous aftershock sequence following the 2010 February 27 Mw 8.8 Maule earthquake. The immediate aftershock sequence was captured by two temporary seismic deployments: the Quake Catcher Network Rapid Aftershock Mobilization Program (QCN RAMP) and the Incorporated Research Institutions for Seismology CHile Aftershock Mobilization Program (IRIS CHAMP). Here, we use moderate to large aftershocks (ML ≥ 4.0) occurring between 2010 March 1 and June 30 recorded by QCN RAMP and IRIS CHAMP stations to determine the spectral decay parameter, kappa (κ). First, we compare waveforms and κ estimates from the lower-resolution QCN stations to the IRIS CHAMP stations to ensure the QCN data are of sufficient quality. We find that QCN stations provide reasonable estimates of κ in comparison to traditional seismic sensors and provide valuable additional observations of local ground motion variation. Using data from both deployments, we investigate the variation in κ for the region to determine if κ is influenced primarily by local geological structure, path attenuation, or source properties (e.g. magnitude, mechanism and depth). Estimates of κ for the Bío Bío region range from 0.0022 to 0.0704 s with a mean of 0.0295 s and are in good agreement with κ values previously reported for similar tectonic environments. κ correlates with epicentral distance and, to a lesser degree, with source magnitude. We find little to no correlation between the site kappa, κ0, and mapped geology, although we were only able to compare the data to a low-resolution map of surficial geology. These results support an increasing number of studies that suggest κobservations can be attributed to a combination of source, path and site properties; additionally, measured κ are often highly scattered making it difficult to separate the contribution from each of these factors. Thus, our results suggest that contributions from the site

  2. Analysis of strong ground motions and site effects at Kantipath, Kathmandu, from 2015 Mw 7.8 Gorkha, Nepal, earthquake and its aftershocks

    Science.gov (United States)

    Dhakal, Yadab P.; Kubo, Hisahiko; Suzuki, Wataru; Kunugi, Takashi; Aoi, Shin; Fujiwara, Hiroyuki

    2016-04-01

    Strong ground motions from the 2015 Mw 7.8 Gorkha, Nepal, earthquake and its eight aftershocks recorded by a strong-motion seismograph at Kantipath (KATNP), Kathmandu, were analyzed to assess the ground-motion characteristics and site effects at this location. Remarkably large elastic pseudo-velocity responses exceeding 300 cm/s at 5 % critical damping were calculated for the horizontal components of the mainshock recordings at peak periods of 4-5 s. Conversely, the short-period ground motions of the mainshock were relatively weak despite the proximity of the site to the source fault. The horizontal components of all large-magnitude (Mw ≥ 6.3) aftershock recordings showed peak pseudo-velocity responses at periods of 3-4 s. Ground-motion prediction equations (GMPEs) describing the Nepal Himalaya region have not yet been developed. A comparison of the observational data with GMPEs for Japan showed that with the exception of the peak ground acceleration (PGA) of the mainshock, the observed PGAs and peak ground velocities at the KATNP site are generally well described by the GMPEs for crustal and plate interface events. A comparison of the horizontal-to-vertical ( H/ V) spectral ratios for the S-waves of the mainshock and aftershock recordings suggested that the KATNP site experienced a considerable nonlinear site response, which resulted in the reduced amplitudes of short-period ground motions. The GMPEs were found to underestimate the response values at the peak periods (approximately 4-5 s) of the large-magnitude events. The deep subsurface velocity model of the Kathmandu basin has not been well investigated. Therefore, a one-dimensional velocity model was constructed for the deep sediments beneath the recording station based on an analysis of the H/ V spectral ratios for S-wave coda from aftershock recordings, and it was revealed that the basin sediments strongly amplified the long-period components of the ground motions of the mainshock and large

  3. Long-period ground motion characteristic of the 1999 Jiji (Chi-Chi), Taiwan, mainshock and aftershocks

    Institute of Scientific and Technical Information of China (English)

    LI Chun-feng; ZHANG Yang; ZHAO Jin-bao; TANG Hui

    2006-01-01

    This paper investigates long-period ground motion characteristic of the 1999 Jiji (Chi-Chi), Taiwan, mainshock and aftershocks on the basis of lots of high quality digital strong motion records. The study attaches the importance to the variation of strength of the long-period ground motion with the magnitude, distance, and site condition. In the meantime, the near-fault long-period ground motion characteristic is analyzed. The result shows that the shape of the long-period response spectrum is mainly controlled by site condition and magnitude (the spectrum of class D+E is wider than that of class B+C, and the spectrum of larger magnitude is wider than that of smaller magnitude), and the effect of fault distance on the shape is not evident. And near-fault long-period ground motion characteristic depends on fault activity apparently, that is to say, the long-term ground motion in the hanger is stronger than that in the footwall, and the long-term ground motion in the north is stronger than that in the south.

  4. Coda Q in the Kachchh Basin, Western India Using Aftershocks of the Bhuj Earthquake of January 26, 2001

    Science.gov (United States)

    Gupta, S. C.; Kumar, Ashwani; Shukla, A. K.; Suresh, G.; Baidya, P. R.

    2006-08-01

    Q C -estimates of Kachchh Basin in western India have been obtained in a high frequency range from 1.5 to 24.0 Hz using the aftershock data of Bhuj earthquake of January 26, 2001 recorded within an epicentral distance of 80 km. The decay of coda waves of 30 sec window from 186 seismograms has been analysed in four lapse time windows, adopting the single backscattering model. The study shows that Q c is a function of frequency and increases as frequency increases. The frequency dependent Q c relations obtained for four lapse-time windows are: Q c =82 f 1.17 (20 50 sec), Q c =106 f 1.11 (30 60 sec), Q c =126f 1.03 (40 70 sec) and Q c =122f 1.02 (50 80 sec). These empirical relations represent the average attenuation properties of a zone covering the surface area of about 11,000, 20,000, 28,000 and 38,000 square km and a depth extent of about 60, 80, 95, 110 km, respectively. With increasing window length, the degree of frequency dependence, n, decreases marginally from 1.17 to 1.02, whereas Q 0 increases significantly from 82 to 122. At lower frequencies up to 6 Hz, Q c -1 of Kachchh Basin is in agreement with other regions of the world, whereas at higher frequencies from 12 to 24 Hz it is found to be low.

  5. Correlation between the parameters of the rate equation for simple aftershock sequences: implications for the forecasting of rates and probabilities

    CERN Document Server

    Gasperini, P; Gasperini, Paolo; Lolli, Barbara

    2005-01-01

    We analyzed the correlations among the parameters of the Reasenberg and Jones (1989) formula describing the aftershock rate after a mainshock as a function of time and magnitude, on the basis of parameter estimates made in previous works for New Zealand, Italy and California. For all of three datasets we found that the magnitude-independent productivity a is significantly correlated with the b-value of the Gutenberg-Richter law and, in some cases, with parameters p and c of the modified Omori's law. We argued that the correlation between a and b can be ascribed to an inappropriate definition of the coefficient of mainshock magnitude as the correlation becomes insignificant if the latter is assumed to be $\\alpha\\simeq$ 2/3b rather than b. This interpretation well agrees with the results of direct a estimates we made, by an epidemic type model (ETAS), from the data of some large Italian sequences. We also verified that assuming $\\alpha$ about 2/3 of the average b value estimated from Italian sequences occurred ...

  6. Comparing different models of aftershock rate decay: the role of catalog incompleteness in the first times after main shock

    CERN Document Server

    Lolli, B; Gasperini, Paolo; Lolli, Barbara

    2005-01-01

    We evaluated the efficiency of various models in describing the time decay of aftershock rate of 47 simple sequences occurred in California (37) from 1933 to 2004 and in Italy (10) from 1976 to 2004. We compared the models by the corrected Akaike Information Criterion (AICc) and the Bayesian Information Criterion (BIC), both based on the log-likelihood function but also including a penalty term that takes into account the number of independent observations and of free parameters of each model. We compared the performance of different models by varying the starting time Ts and the minimum magnitude threshold Mmin for each sequence. We found that Omori-type models including parameter c are preferable to those not including it, only for short Ts and low Mmin while the latters generally perform better than the formers for Ts longer than a few hours and Mmin larger than the main shock magnitude Mm minus 3 units. This clearly indicates that a value of parameter c different from zero does not represent a general pro...

  7. Seismic source study of the Racha-Dzhava (Georgia) earthquake from aftershocks and broad-band teleseismic body-wave records: An example of active nappe tectonics

    Science.gov (United States)

    Fuenzalida, H.; Rivera, L.; Haessler, H.; Legrand, D.; Philip, H.; Dorbath, L.; McCormack, D.; Arefiev, S.; Langer, C.; Cisternas, A.

    1997-01-01

    The Racha-Dzhava earthquake (Ms = 7.0) that occurred on 1991 April 29 at 09:12:48.1 GMT in the southern border of the Great Caucasus is the biggest event ever recorded in the region, stronger than the Spitak earthquake (Ms = 6.9) of 1988. A field expedition to the epicentral area was organised and a temporary seismic network of 37 stations was deployed to record the aftershock activity. A very precise image of the aftershock distribution is obtained, showing an elongated cloud oriented N105??, with one branch trending N310?? in the western part. The southernmost part extends over 80 km, with the depth ranging from 0 to 15 km, and dips north. The northern branch, which is about 30 km long, shows activity that ranges in depth from 5 to 15 km. The complex thrust dips northwards. A stress-tensor inversion from P-wave first-motion polarities shows a state of triaxial compression, with the major principal axis oriented roughly N-S, the minor principal axis being vertical. Body-waveform inversion of teleseismic seismograms was performed for the main shock, which can be divided into four subevents with a total rupture-time duration of 22 s. The most important part of the seismic moment was released by a gentle northerly dipping thrust. The model is consistent with the compressive tectonics of the region and is in agreement with the aftershock distribution and the stress tensor deduced from the aftershocks. The focal mechanisms of the three largest aftershocks were also inverted from body-wave records. The April 29th (Ms = 6.1) and May 5th (Ms = 5.4) aftershocks have thrust mechanisms on roughly E-W-oriented planes, similar to the main shock. Surprisingly, the June 15th (Ms = 6.2) aftershock shows a thrust fault striking N-S. This mechanism is explained by the structural control of the rupture along the east-dipping geometry of the Dzirula Massif close to the Borzhomi-Kazbeg strike-slip fault. In fact, the orientation and shape of the stress tensor produce a thrust on a N

  8. Multi-Array Back-Projections of The 2015 Gorkha Earthquake With Physics-Based Aftershock Calibrations

    Science.gov (United States)

    Meng, L.; Zhang, A.; Yagi, Y.

    2015-12-01

    The 2015 Mw 7.8 Nepal-Gorkha earthquake with casualties of over 9,000 people is the most devastating disaster to strike Nepal since the 1934 Nepal-Bihar earthquake. Its rupture process is well imaged by the teleseismic MUSIC back-projections (BP). Here, we perform independent back-projections of high-frequency recordings (0.5-2 Hz) from the Australian seismic network (AU), the North America network (NA) and the European seismic network (EU), located in complementary orientations. Our results of all three arrays show unilateral linear rupture path to the east of the hypocenter. But the propagating directions and the inferred rupture speeds differ significantly among different arrays. To understand the spatial uncertainties of the BP analysis, we image four moderate-size (M5~6) aftershocks based on the timing correction derived from the alignment of the initial P-wave of the mainshock. We find that the apparent source locations inferred from BP are systematically biased along the source-array orientation, which can be explained by the uncertainty of the 3D velocity structure deviated from the 1D reference model (e.g. IASP91). We introduced a slowness error term in travel time as a first-order calibration that successfully mitigates the source location discrepancies of different arrays. The calibrated BP results of three arrays are mutually consistent and reveal a unilateral rupture propagating eastward at a speed of 2.7 km/s along the down-dip edge of the locked Himalaya thrust zone over ~ 150 km, in agreement with a narrow slip distribution inferred from finite source inversions.

  9. The great 1933 Sanriku-oki earthquake: reappraisal of the main shock and its aftershocks and implications for its tsunami using regional tsunami and seismic data

    Science.gov (United States)

    Uchida, Naoki; Kirby, Stephen H.; Umino, Norihito; Hino, Ryota; Kazakami, Tomoe

    2016-09-01

    The aftershock distribution of the 1933 Sanriku-oki outer trench earthquake is estimated by using modern relocation methods and a newly developed velocity structure to examine the spatial extent of the source-fault and the possibility of a triggered interplate seismicity. In this study, we first examined the regional data quality of the 1933 earthquake based on smoked-paper records and then relocated the earthquakes by using the 3-D velocity structure and double-difference method. The improvements of hypocentre locations using these methods were confirmed by the examination of recent earthquakes that are accurately located based on ocean bottom seismometer data. The results show that the 1933 aftershocks occurred under both the outer- and inner-trench-slope regions. In the outer-trench-slope region, aftershocks are distributed in a ˜280-km-long area and their depths are shallower than 50 km. Although we could not constrain the fault geometry from the hypocentre distribution, the depth distribution suggests the whole lithosphere is probably not under deviatoric tension at the time of the 1933 earthquake. The occurrence of aftershocks under the inner trench slope was also confirmed by an investigation of waveform frequency difference between outer and inner trench earthquakes as recorded at Mizusawa. The earthquakes under the inner trench slope were shallow (depth ≦30 km) and the waveforms show a low-frequency character similar to the waveforms of recent, precisely located earthquakes in the same area. They are also located where recent activity of interplate thrust earthquakes is high. These suggest that the 1933 outer-trench-slope main shock triggered interplate earthquakes, which is an unusual case in the order of occurrence in contrast with the more common pairing of a large initial interplate shock with subsequent outer-slope earthquakes. The off-trench earthquakes are distributed about 80 km width in the trench perpendicular direction. This wide width cannot

  10. Joint inversion of teleseismic body-waves and geodetic data for the Mw6.8 aftershock of the Balochistan earthquake with refined epicenter location

    Science.gov (United States)

    Wei, S.; Wang, T.; Jonsson, S.; Avouac, J. P.; Helmberger, D. V.

    2014-12-01

    Aftershocks of the 2013 Balochistan earthquake are mainly concentrated along the northeastern end of the mainshock rupture despite of much larger coseismic slip to the southwest. The largest event among them is an Mw6.8 earthquake which occurred three days after the mainshock. A kinematic slip model of the mainshock was obtained by joint inversion of the teleseismic body-waves and horizontal static deformation field derived from remote sensing optical and SAR data, which is composed of seven fault segments with gradually changing strikes and dips [Avouac et al., 2014]. The remote sensing data provide well constraints on the fault geometry and spatial distribution of slip but no timing information. Meanwhile, the initiation of the teleseismic waveform is very sensitive to fault geometry of the epicenter segment (strike and dip) and spatial slip distribution but much less sensitive to the absolute location of the epicenter. The combination of the two data sets allows a much better determination of the absolute epicenter location, which is about 25km to the southwest of the NEIC epicenter location. The well located mainshock epicenter is used to establish path calibrations for teleseismic P-waves, which are essential for relocating the Mw6.8 aftershock. Our grid search shows that the refined epicenter is located right at the northeastern end of the mainshock rupture. This is confirmed by the SAR offsets calculated from images acquired after the mainshock. The azimuth and range offsets display a discontinuity across the rupture trace of the mainshock. Teleseismic only and static only, as well as joint inversions all indicate that the aftershock ruptured an asperity with 25km along strike and range from 8km to 20km in depth. The earthquake was originated in a positive Coulomb stress change regime due to the mainshock and has complementary slip distribution to the mainshock rupture at the northeastern end, suggesting that the entire seismic generic zone in the crust was

  11. Stress-based aftershock forecasts made within 24 h postmain shock: Expected north San Francisco Bay area seismicity changes after the 2014 M = 6.0 West Napa earthquake

    Science.gov (United States)

    Parsons, Tom; Segou, Margaret; Sevilgen, Volkan; Milner, Kevin; Field, Edward; Toda, Shinji; Stein, Ross S.

    2014-12-01

    We calculate stress changes resulting from the M = 6.0 West Napa earthquake on north San Francisco Bay area faults. The earthquake ruptured within a series of long faults that pose significant hazard to the Bay area, and we are thus concerned with potential increases in the probability of a large earthquake through stress transfer. We conduct this exercise as a prospective test because the skill of stress-based aftershock forecasting methodology is inconclusive. We apply three methods: (1) generalized mapping of regional Coulomb stress change, (2) stress changes resolved on Uniform California Earthquake Rupture Forecast faults, and (3) a mapped rate/state aftershock forecast. All calculations were completed within 24 h after the main shock and were made without benefit of known aftershocks, which will be used to evaluative the prospective forecast. All methods suggest that we should expect heightened seismicity on parts of the southern Rodgers Creek, northern Hayward, and Green Valley faults.

  12. Stress-based aftershock forecasts made within 24h post mainshock: Expected north San Francisco Bay area seismicity changes after the 2014M=6.0 West Napa earthquake

    Science.gov (United States)

    Parsons, Thomas E.; Segou, Margaret; Sevilgen, Volkan; Milner, Kevin; Field, Ned; Toda, Shinji; Stein, Ross S.

    2014-01-01

    We calculate stress changes resulting from the M= 6.0 West Napa earthquake on north San Francisco Bay area faults. The earthquake ruptured within a series of long faults that pose significant hazard to the Bay area, and we are thus concerned with potential increases in the probability of a large earthquake through stress transfer. We conduct this exercise as a prospective test because the skill of stress-based aftershock forecasting methodology is inconclusive. We apply three methods: (1) generalized mapping of regional Coulomb stress change, (2) stress changes resolved on Uniform California Earthquake Rupture Forecast faults, and (3) a mapped rate/state aftershock forecast. All calculations were completed within 24 h after the main shock and were made without benefit of known aftershocks, which will be used to evaluative the prospective forecast. All methods suggest that we should expect heightened seismicity on parts of the southern Rodgers Creek, northern Hayward, and Green Valley faults.

  13. Aftershock Activity Triggered By the 2014 Earthquake (Mw=6.5), and Its Implications for the Future Seismic Risk in the Marmara Sea, Turkey

    Science.gov (United States)

    Polat, O.; Kilic, T.; Turkoglu, M.; Kaplan, M.; Kilicarslan, O.; Özer, Ç.; Gok, E.

    2014-12-01

    We have performed aftershocks analysis triggered by 24.05.2014 (Mw=6.5) Gokceada Island (GI) earthquake where occurred at the W of North Anatolian Fault zone. Mainshock was widely felt in Aegean and Marmara regions of Turkey. Major damage in 228 homes was reported. Other 49 residences suffered moderate or light damage. We have well located 699 events over 1041 by at least 5 stations for one month period after the mainshock. Double difference relocation algorithm allowed us to minimize rms values less than 0.39. Initial results show clear unilateral rupture towards Gallipoli Peninsula at the W of Marmara Sea region. Aftershocks show linearity with an extension of ~110 km length, ~25 km width. Largest aftershock (Mw=5.3) was at the NE end of activation zone. Depths are mainly confined from 5 to 25 km ranges. Two locking depths are detected beneath 8 km in Lemnos Basin and Saros Trough. We also constructed focal mechanisms from regional moment tensor solutions. Digital waveform data obtained from AFAD (Turkey) and HT-AUTH (Greece). Focal mechanisms reflect complex tectonic settings. Nevertheless numerous mechanisms show dominant dextral strike-slip motions aligned NE-SW direction with minor reverse component. State of stress before the mainshock was pure shear regime. But two principal stress axes are observed as oblique for the aftershocks showing ambiguity between compression and shear. It is likely that the mean stress regime has changed after the GI earthquake. If this is so, we may expect that the strike-slip component would slowly increase later in order to recover the conditions existing before. Coulomb stress values rise at the edges of the fault segment due to accumulation of slip. We observed strong spatial correlation between the static stress change after 2014 GI earthquake and the segment that ruptured during the 1912 Murefte-Ganos (Mw=7.4) earthquake. The analysis showed that the areas of positive static stress changes reach to seismic gap in the Marmara

  14. The 16 April 2015 M w 6.0 offshore eastern Crete earthquake and its aftershock sequence: implications for local/regional seismotectonics

    Science.gov (United States)

    Görgün, Ethem; Kekovalı, Kıvanç; Kalafat, Doğan

    2016-08-01

    We examine the 16 April 2015 M w 6.0 offshore eastern Crete earthquake and its aftershock sequence in southern Aegean Sea. Centroid moment tensors for 45 earthquakes with moment magnitudes (M w) between 3.3 and 6.0 are determined by applying a waveform inversion method. The mainshock is shallow focus thrust event with a strike-slip component at a depth of 30 km. The seismic moment (M o) of the mainshock is estimated as 1.33 × 1018 Nm, and rupture duration of the mainshock is 3.5 s. The focal mechanisms of aftershocks are mainly thrust faulting with a strike-slip component. The geometry of the moment tensors (M w ≥ 3.3) reveals a thrust-faulting regime with NE-SW-trending direction of T axis in the entire activated region. According to high-resolution hypocenter relocation of the eastern Crete earthquake sequence, one main cluster consisting of 352 events is revealed. The aftershock activity in the observation period between 5 January 2015 and 7 July 2015 extends from N to S direction. Seismic cross sections indicate a complex pattern of the hypocenter distribution with the activation of three segments. The subduction interface is clearly revealed with high-resolution hypocenter relocation and moment tensor solution. The best constrained focal depths indicate that the aftershock sequence is mainly confined in the upper plate (depth <40 km) and are ranging from about 4.5 to 39 km depth. A stress tensor inversion of focal mechanism data is performed to obtain a more precise picture of the offshore eastern Crete stress field. The stress tensor inversion results indicate a predominant thrust stress regime with a NW-SE-oriented maximum horizontal compressive stress (S H). According to variance of the stress tensor inversion, to first order, the Crete region is characterized by a homogeneous interplate stress field. We also investigate the Coulomb stress change associated with the mainshock to evaluate any significant enhancement of stresses along Crete and surrounding

  15. Numerical Simulation Study of Re-liquefaction of Artificial Island Induced by Aftershocks%人工岛余震再液化数值模拟研究

    Institute of Scientific and Technical Information of China (English)

    胡记磊; 唐小微; 张西文

    2015-01-01

    主震结束后,余震引起的再液化会对土工结构物带来进一步的严重灾害。以人工岛为研究对象,基于 FE-FD 耦合有限元方法,考虑有无余震、不同余震大小和主余震不同时间间隔因素,探讨对人工岛再液化灾害的影响规律。研究结果表明:主震结束后,随着超孔隙水压力的消散,人工岛砂土层液化区域逐渐减小,余震发生时液化区域又开始扩展,甚至可能大于主震结束时的液化区域面积,且其灾害程度比无余震发生时的要大得多;随着主、余震的时间间隔增加,间隔期的土层固结排水很大程度地提高人工岛的抗再液化能力,当超孔隙水压力消散完后,在相同余震等级情况下很难再次达到完全液化;随着余震峰值加速度的增加,人工岛的沉降量和水平侧移量都随之增加,再次液化时间点会向前提前数秒,主震结束后,随着土层的固结排水,人工岛的沉降会继续增加,甚至超过主震引起的沉降量,而水平侧移的产生主要发生在地震液化过程中,在后续的固结排水中几乎不变;余震发生前,如果人工岛的砂土土层仍处于液化状态,则液化层可能会起到隔震作用,减轻余震对岛体造成的灾害。%Re-liquefaction induced by aftershocks causes serious hazards on soil structures after the end of the main shock.In this study,the influences of aftershocks on an artificial island are discussed based on the FE-FD coupling finite element analysis method at different scales of after-shocks and interval time between the main shock and aftershock.The results indicate that with dissipation of excess pore-water pressure after the main shock,liquefied areas in the sand layer of the artificial island gradually decrease;however,the liquefied areas expand rapidly when an after-shock occurs,and can possibly be larger than the liquefied areas induced by the main shock;the extent of

  16. Aftershock distribution and heterogeneous structure in and around the source area of the 2014 northern Nagano Prefecture earthquake (Mw 6.2) , central Japan, revealed by dense seismic array observation

    Science.gov (United States)

    Kurashimo, E.; Hirata, N.; Iwasaki, T.; Sakai, S.; Obara, K.; Ishiyama, T.; Sato, H.

    2015-12-01

    A shallow earthquake (Mw 6.2) occurred on November 22 in the northern Nagano Prefecture, central Japan. Aftershock area is located near the Kamishiro fault, which is a part of the Itoigawa-Shizuoka Tectonic Line (ISTL). ISTL is one of the major tectonic boundaries in Japan. Precise aftershock distribution and heterogeneous structure in and around the source region of this earthquake is important to constrain the process of earthquake occurrence. We conducted a high-density seismic array observation in and around source area to investigate aftershock distribution and crustal structure. One hundred sixty-three seismic stations, approximately 1 km apart, were deployed during the period from December 3, 2014 to December 21, 2014. Each seismograph consisted of a 4.5 Hz 3-component seismometer and a digital data recorder (GSX-3). Furthermore, the seismic data at 40 permanent stations were incorporated in our analysis. During the seismic array observation, the Japan Meteorological Agency located 977 earthquakes in a latitude range of 35.5°-37.1°N and a longitude range of 136.7°-139.0°E, from which we selected 500 local events distributed uniformly in the study area. To investigate the aftershock distribution and the crustal structure, the double-difference tomography method [Zhang and Thurber, 2003] was applied to the P- and S-wave arrival time data obtained from 500 local earthquakes. The relocated aftershock distribution shows a concentration on a plane dipping eastward in the vicinity of the mainshock hypocenter. The large slip region (asperity) estimated from InSAR analysis [GSI, 2014] corresponds to the low-activity region of the aftershocks. The depth section of Vp structure shows that the high Vp zone corresponds to the large slip region. These results suggest that structural heterogeneities in and around the fault plane may have controlled the rupture process of the 2014 northern Nagano Prefecture earthquake.

  17. Some characteristics of the complex El Mayor-Cucapah, MW7.2, April 4, 2010, Baja California, Mexico, earthquake, from well-located aftershock data from local and regional networks.

    Science.gov (United States)

    Frez, J.; Nava Pichardo, F. A.; Acosta, J.; Munguia, L.; Carlos, J.; García, R.

    2015-12-01

    Aftershocks from the El Mayor-Cucapah (EMC), MW7.2, April 4, 2010, Baja California, Mexico, earthquake, were recorded over two months by a 31 station local array (Reftek RT130 seismographs loaned from IRIS-PASSCAL), complemented by regional data from SCSN, and CICESE. The resulting data base includes 518 aftershocks with ML ≥ 3.0, plus 181 smaller events. Reliable hypocenters were determined using HYPODD and a velocity structure determined from refraction data for a mesa located to the west of the Mexicali-Imperial Valley. Aftershock hypocenters show that the El Mayor-Cucapah earthquake was a multiple event comprising two or three different ruptures of which the last one constituted the main event. The main event rupture, which extends in a roughly N45°W direction, is complex with well-defined segments having different characteristics. The main event central segment, located close to the first event epicenter is roughly vertical, the northwest segment dips ~68°NE, while the two southeast segments dip ~60°SW and ~52°SW, respectively, which agrees with results of previous studies based on teleseismic long periods and on GPS-INSAR. All main rupture aftershock hypocenters have depths above 10-11km and, except for the central segment, they delineate the edges of zones with largest coseismic displacement. The two southern segments show seismicity concentrated below 5km and 3.5km, respectively; the paucity of shallow seismicity may be caused by the thick layer of non-consolidated sediments in this region. The ruptures delineated by aftershocks in the southern regions correspond to the Indiviso fault, unidentified until the occurrence of the EMC earthquake. The first event was relocated together with the aftershocks; the epicenter lies slightly westwards of published locations, but it definitely does not lie on, or close to, the main rupture. The focal mechanism of the first event, based on first arrival polarities, is predominantly strike-slip; the focal plane

  18. Seismotectonics of the April-May 2015 Nepal earthquakes: An assessment based on the aftershock patterns, surface effects and deformational characteristics

    Science.gov (United States)

    Parameswaran, Revathy M.; Natarajan, Thulasiraman; Rajendran, Kusala; Rajendran, C. P.; Mallick, Rishav; Wood, Matthew; Lekhak, Harish C.

    2015-11-01

    Occurrence of the April 25, 2015 (Mw 7.8) earthquake near Gorkha, central Nepal, and another one that followed on May 12 (Mw 7.3), located ∼140 km to its east, provides an exceptional opportunity to understand some new facets of Himalayan earthquakes. Here we attempt to assess the seismotectonics of these earthquakes based on the deformational field generated by these events, along with the spatial and temporal characteristics of their aftershocks. When integrated with some of the post-earthquake field observations, including the localization of damage and surface deformation, it became obvious that although the mainshock slip was mostly limited to the Main Himalayan Thrust (MHT), the rupture did not propagate to the Main Frontal Thrust (MFT). Field evidence, supported by the available InSAR imagery of the deformation field, suggests that a component of slip could have emerged through a previously identified out-of-sequence thrust/active thrust in the region that parallels the Main Central Thrust (MCT), known in the literature as a co-linear physiographic transitional zone called PT2. Termination of the first rupture, triggering of the second large earthquake, and distribution of aftershocks are also spatially constrained by the eastern extremity of PT2. Mechanism of the 2015 sequence demonstrates that the out-of-sequence thrusts may accommodate part of the slip, an aspect that needs to be considered in the current understanding of the mechanism of earthquakes originating on the MHT.

  19. Line-of-sight displacement from ALOS-2 interferometry: Mw 7.8 Gorkha Earthquake and Mw 7.3 aftershock

    Science.gov (United States)

    Lindsey, Eric O.; Natsuaki, Ryo; Xu, Xiaohua; Shimada, Masanobu; Hashimoto, Manabu; Melgar, Diego; Sandwell, David T.

    2015-08-01

    Interferometric synthetic aperture radar (InSAR) is a key tool for the analysis of displacement and stress changes caused by large crustal earthquakes, particularly in remote areas. A challenge for traditional InSAR has been its limited spatial and temporal coverage especially for very large events, whose dimensions exceed the typical swath width of 70-100 km. This problem is addressed by the ALOS-2 satellite, whose PALSAR-2 instrument operates in ScanSAR mode, enabling a repeat time of 2 weeks and a swath width of 350 km. Here we present InSAR line-of-sight displacement data from ALOS-2/PALSAR-2 observations covering the Mw 7.8 Gorkha, Nepal earthquake and its Mw 7.3 aftershock that were acquired within 1 week of each event. The data are made freely available and we encourage their use in models of the fault slip and associated stress changes. The Mw 7.3 aftershock not only extended the rupture area of the main shock toward the east but also left a 20 km gap where the fault has little or no coseismic slip. We estimate this unslipped fault patch has the potential to generate a Mw 6.9 event.

  20. Geodetic model of the 2015 April 25 Mw 7.8 Gorkha Nepal Earthquake and Mw 7.3 aftershock estimated from InSAR and GPS data

    Science.gov (United States)

    Feng, Guangcai; Li, Zhiwei; Shan, Xinjian; Zhang, Lei; Zhang, Guohong; Zhu, Jianjun

    2015-11-01

    We map the complete surface deformation of 2015 Mw 7.8 Gorkha Nepal earthquake and its Mw 7.3 aftershock with two parallel ALOS2 descending ScanSAR paths' and two ascending Stripmap paths' images. The coseismic fault-slip model from a combined inversion of InSAR and GPS data reveals that this event is a reverse fault motion, with a slight right-lateral strike-slip component. The maximum thrust-slip and right-lateral strike-slip values are 5.7 and 1.2 m, respectively, located at a depth of 7-15 km, southeast to the epicentre. The total seismic moment 7.55 × 1020 Nm, corresponding to a moment magnitude Mw 7.89, is similar to the seismological estimates. Fault slips of both the main shock and the largest aftershock are absent from the upper thrust shallower than 7 km, indicating that there is a locking lower edge of Himalayan Main Frontal Thrust and future seismic disaster is not unexpected in this area. We also find that the energy released in this earthquake is much less than the accumulated moment deficit over the past seven centuries estimated in previous studies, so the region surrounding Kathmandu is still under the threaten of seismic hazards.

  1. Time-dependent Induced Seismicity Rates Described with an Epidemic Type Aftershock Sequence Model at The Geysers Geothermal Field, California

    Science.gov (United States)

    Johnson, C. W.; Totten, E. J.; Burgmann, R.

    2015-12-01

    To improve understanding of the link between injection/production activity and seismicity, we apply an Epidemic Type Aftershock Sequence (ETAS) model to an earthquake catalog from The Geysers geothermal field (GGF) between 2005-2015 using >140,000 events and Mc 0.8 . We partition the catalog along a northeast-southwest trending divide, which corresponds to regions of high and low levels of enhanced geothermal stimulation (EGS) across the field. The ETAS model is fit to the seismicity data using a 6-month sliding window with a 1-month time step to determine the background seismicity rate. We generate monthly time series of the time-dependent background seismicity rate in 1-km depth intervals from 0-5km. The average wellhead depth is 2-3 km and the background seismicity rates above this depth do not correlate well with field-wide injected masses over the time period of interest. The auto correlation results show a 12-month period for monthly time series proximal to the average wellhead depths (2-3km and 3-4km) for northwest GGF strongly correlates with field-wide fluid injection masses, with a four-month phase shift between the two depth intervals as fluid migrates deeper. This periodicity is not observed for the deeper depth interval of 4-5 km, where monthly background seismicity rates reduce to near zero. Cross-correlation analysis using the monthly time series for background seismicity rate and the field-wide injection, production and net injection (injection minus production) suggest that injection most directly modulates seismicity. Periodicity in the background seismicity is not observed as strongly in the time series for the southeast field. We suggest that the variation in background seismicity rate is a proxy for pore-pressure diffusion of injected fluids at depth. We deduce that the contrast between the background seismicity rates in the northwest and southeast GGF is a result of reduced EGS activity in the southeast region.

  2. Aftershock mechanisms from the 2010 Mw 8.8 Maule, Chile earthquake: detailed analysis using full waveform inversion

    Science.gov (United States)

    Rietbrock, A.; Hicks, S. P.; Chagas, B.; Detzel, H. A.

    2014-12-01

    Since the earthquake rupture process is extremely heterogeneous, it is vital to understand how structural variations in the overriding plate and downgoing slab may control slip style along the subduction megathrust. The large-scale 3-D geometry of subduction plate boundaries is rapidly becoming well understood; however, the nature of any finer-scale structure along the plate interface remains elusive. A detailed study of earthquake source mechanisms along a megathrust region can shed light on the nature of fine-scale structures along the megathrust. The Mw 8.8 Maule earthquake that struck central Chile in 2010 is the sixth largest earthquake ever recorded. Following the earthquake, there was an international deployment of seismic stations in the rupture area, making this one of the best datasets of an aftershock sequence following a large earthquake. This dataset provides a unique opportunity to perform a detailed study of megathrust earthquake source mechanisms. Based on a high-resolution 3-D velocity model and robust earthquake locations [Hicks et al., 2014], we calculate regional moment tensors using the ISOLA software package [Sokos & Zahradnik, 2008]. We incorporate accelerometer recordings, important for constraining solutions of large earthquakes in the overriding plate. We also validate the robustness of our solutions by assessing the consistency of mechanisms with P-wave polarities observed at both onshore and offshore seismic stations, and compare them to already published solutions. We find that accurate earthquake locations are vital for the fine-scale interpretation of focal mechanisms, particularly for offshore events. Our results show that most moment tensor solutions with thrusting mechanisms have a nodal plane dipping parallel to the subducting plate interface. Interestingly, we also find earthquakes with normal faulting mechanisms lying along to the megathrust plate interface in the south of the rupture area. This finding suggests that megathrust

  3. Detection of Interplate Earthquakes in the Source Area of the 2011 Tohoku Earthquake Using Extensive Seafloor Aftershock Observation Data

    Science.gov (United States)

    Nakatani, Y.; Mochizuki, K.; Shinohara, M.; Yamada, T.; Shiobara, H.; Hino, R.; Azuma, R.; Ito, Y.; Murai, Y.; Sato, T.; Uehira, K.; Shimbo, T.; Yakiwara, H.; Kodaira, S.; Machida, Y.; Hirata, K.; Tsushima, H.

    2015-12-01

    Previous studies on the source process of the 2011 Mw 9.0 Tohoku earthquake have revealed its large coseismic slip along a shallow plate interface to the Japan Trench axis. In order to further understand the complex rupture propagation along the plate interface, it is essential to elucidate recovery process of interplate coupling in the source area after the Tohoku earthquake. Estimating changes in b-values for interplate earthquakes before and after the Tohoku event is one of the available approaches to answer the above issue. To start with, we attempt to automatically detect and determine the location of interplate earthquakes using extensive seafloor aftershock observation data. We used mainly short-period pop-up type ocean bottom seismometers (OBSs) [Shinohara et al., 2011, 2012]. We applied a semblance-based method [Nakatani et al., 2015] to 23 OBSs deployed off Fukushima. A seismic tomography result [Matsubara and Obara, 2011] is used for calculation of P wave traveltimes between OBS stations and given grids along the plate interface. To confirm the validity of our method, we conducted synthetic tests by using a Ricker wavelet with several different sets of signal-to-noise (S/N) ratio and focal depths. As the results, semblance values of earthquakes with focal depths relative to the plate interface of 5 km are comparable to noise level, regardless of S/N ratio. On the other hand, earthquakes along the plate interface have significant peak semblance values. Therefore, our method is effective for detection of interplate earthquakes. We, then, applied the method to several waveforms of interplate events listed in the JMA (Japan Meteorological Agency) catalog and identified epicenters by backprojecting semblance values. We compared our resulted epicenters to those of Shinohara et al. (2011, 2012) which precisely relocated the JMA ones using P- and S-wave arrival times and maximum-likelihood estimate technique. The results show good coincidence between them. In

  4. A statistical analysis on Wenchuan aftershock activity triggered by earth tide%汶川地震余震活动固体潮调制的统计分析

    Institute of Scientific and Technical Information of China (English)

    李金; 蒋海昆

    2011-01-01

    A statistical analysis on Wenchuan aftershock activity triggered by tidal is systematically studied based on Schuster's test, including earthquakes triggered by tidal force, tidal stress and tidal coulomb failure stress. The results show that a group of strong aftershocks which occur at the end of July to early August in 2008 at the north of the Wenchuan are obviously triggered by earth tide. The same conclusion is drawn by Schuster's smooth test of the tidal force, tidal stress and tidal coulomb failure stress. In addition, Wenchuan aftershock activity is obviously triggered by fortnight tide. In the north, the aftershocks happened more frequently in the first quarter and the last quarter of the moon, and in the south, the aftershocks happened more frequently in the first quarter and the last quarter of the moon and the full moon.%基于Schuster检验对汶川地震余震受固体潮的调制触发情况进行了系统的研究,包括对引潮力、潮汐应力和潮汐库仑破裂应力等触发地震情况的分时段分区段研究.结果表明,汶川北段2008年7月底至8月初的一组强余震受潮汐触发明显,引潮力、潮汐正应力及潮汐库仑破裂应力经Schuster检验平滑后均得到基本一致的结果.此外,汶川余震受半月潮的调制非常明显,北段余震多发生于上、下弦时段,南段地震多发生于上、下弦和望时段.

  5. Short-term foreshocks in Southern California and Italy revisited: Observed deviations from the Epidemic-Type Aftershock Sequence (ETAS) Model

    Science.gov (United States)

    Seif, Stefanie; Mignan, Arnaud; Wiemer, Stefan

    2013-04-01

    Numerous studies have suggested that short-term foreshocks observed prior to large earthquakes are undistinguishable from the normal behaviour of seismicity, which is well described for example by the Epidemic-Type Aftershock Sequence (ETAS) model. Here we show that these studies fail to extract abnormal foreshock behaviour due to the much more frequent occurrence of aftershocks in comparison to potential foreshocks, which results in undervaluing the role of foreshocks. We first define mainshocks as earthquakes of magnitude M6+ and use a space-time-magnitude window method with a maximum distance of 10 km to the mainshock, a maximum time range of 3 days before the mainshock and a minimum magnitude M4+ to define foreshocks in Southern California and in Italy. We then compare the observed rate of foreshock-mainshock pairs to the rate expected by ETAS simulations. Similar to previous studies, these results indicate that the foreshock activity observed in real catalogues is compatible with the ETAS model. Definition of foreshocks with a window method is, however, simplistic, since any individual event may be considered a foreshock although it is impossible to distinguish a foreshock from background or aftershock activity at a one-to-one event basis. We extend our foreshock analysis based on the predictions of the Non-Critical Precursory Accelerating Seismicity Theory (NC PAST), which are: (1) foreshocks are due to overloading on the main fault and occur in clusters, the activity of which is significantly higher than background activity, (2) microseismicity (Mguidelines, we systematically investigate foreshock sequences before large earthquakes (M6+) in Southern California and Italy. Using different approaches, we finally show that significant anomalies are observed before some mainshocks (e.g., 1992 Landers, 2009 L'Aquila earthquakes), which are not explained by the ETAS process. Anomalies are defined as any deviation from a Poissonian distribution (which describes the

  6. Estimation of seismic moments from local magnitudes and coda durations for the Cairo earthquake aftershocks recorded at Kottamyia (KEG Broadband station

    Directory of Open Access Journals (Sweden)

    M. F. Abdelwahed

    2003-06-01

    Full Text Available The spectral analysis of fifty-five KEG VBB records from the October 12, 1992 Cairo earthquake source region was performed to obtain the seismic moment. We obtained this parameter in turn to develop empirical local magnitude (ML, seismic moment (Mo, coda duration (D relations for that region. In this study the data consist of Lg-waves on the vertical component seismograms for the recorded earthquakes with ML ranging from 1.7 to 4.7. The derived empirical relation between the seismic moment (Mo and magnitude ML for the aftershocks sequence with 1.7 = ML < 3.5 is Log (Mo = (0.96 ± 0.05 ML + (17.88 ± 0.13. We found a correlation between the coda duration (D and Log of the moment (Log (Mo as follows: Log (Mo = (2.35 ± 0.27 Log (D + (16.33 ± 0.48.

  7. Comparison between Utsu's and Vere-Jones' aftershocks model by means of a computer simulation based on the acceptance-rejection sampling of von Neumann

    Science.gov (United States)

    Reyes, J.; Morales-Esteban, A.; González, E.; Martínez-Álvarez, F.

    2016-07-01

    In this research, a new algorithm for generating a stochastic earthquake catalog is presented. The algorithm is based on the acceptance-rejection sampling of von Neumann. The result is a computer simulation of earthquakes based on the calculated statistical properties of each zone. Vere-Jones states that an earthquake sequence can be modeled as a series of random events. This is the model used in the proposed simulation. Contrariwise, Utsu indicates that the mainshocks are special geophysical events. The algorithm has been applied to zones of Chile, China, Spain, Japan, and the USA. This allows classifying the zones according to Vere-Jones' or Utsu's model. The results have been quantified relating the mainshock with the largest aftershock within the next 5 days (which has been named as Bath event). The results show that some zones fit Utsu's model and others Vere-Jones'. Finally, the fraction of seismic events that satisfy certain properties of magnitude and occurrence is analyzed.

  8. Seismic and Aseismic Slip on the San-Jacinto Fault Near Anza, CA, from Joint Analysis of Strain and Aftershock Data

    Science.gov (United States)

    Inbal, A.; Avouac, J. P.; Ampuero, J. P.

    2014-12-01

    The San-Jacinto Fault (SJF) is the most active fault in southern California, which together with the southern San-Andreas Fault accommodates a large fraction of the motion across the plate boundary. Seismicity along the SJF is distributed over several fault segments with distinct spatio-temporal characteristics. One of these segments, known as the Anza seismic gap, is a 25 km long strand almost devoid of seismicity. In recent years, four M4-5 events occurred SE of the gap. Despite their moderate magnitudes, these earthquakes triggered rich aftershock sequences and pronounced afterslip that lasted for several weeks, and was well captured by nearby PBO borehole strain meters. A similar transient was remotely triggered by the 2010 El Mayor-Cucapah earthquake. Geodetic and seismic observations following a local M5.4 mainshock indicate that afterslip propagated unilaterally towards the NW at speed of about 5 km/day. We infer the distribution of slip via a joint inversion of the aftershock and strain data. Our approach is based on Dieterich's (1994) model relating the evolution of seismicity rate to applied stresses, within the framework of rate-and-state friction. This approach provides resolution power at depths inaccessible to the surface geodetic network. Moreover, it allows us to gain important insights onto the fault mechanical properties. We apply this inversion scheme to episodes that occurred during 2010. Remarkably, we find that the cumulative moment released post-seismically during the locally triggered transient is 5-10 times larger than the moment of the mainshock. We show that the data favour a model in which deep slip transients, which may develop due to local or remote earthquakes, occur on a weak, close-to-velocity-neutral fault. The transients increase the stress along the Anza gap, and trigger earthquakes outside it through static stress transfer.

  9. Coulomb Stress Change and Seismic Hazard of Rift Zones in Southern Tibet after the 2015 Mw7.8 Nepal Earthquake and Its Mw7.3 Aftershock

    Science.gov (United States)

    Dai, Z.; Zha, X.; Lu, Z.

    2015-12-01

    In southern Tibet (30~34N, 80~95E), many north-trending rifts, such as Yadong-Gulu and Lunggar rifts, are characterized by internally drained graben or half-graben basins bounded by active normal faults. Some developed rifts have become a portion of important transportation lines in Tibet, China. Since 1976, eighty-seven >Mw5.0 earthquakes have happened in the rift regions, and fifty-five events have normal faulting focal mechanisms according to the GCMT catalog. These rifts and normal faults are associated with both the EW-trending extension of the southern Tibet and the convergence between Indian and Tibet. The 2015 Mw7.8 Nepal great earthquake and its Mw7.3 aftershock occurred at the main Himalayan Thrust zone and caused tremendous damages in Kathmandu region. Those earthquakes will lead to significant viscoelastic deformation and stress changes in the southern Tibet in the future. To evaluate the seismic hazard in the active rift regions in southern Tibet, we modeled the slip distribution of the 2015 Nepal great earthquakes using the InSAR displacement field from the ALOS-2 satellite SAR data, and calculated the Coulomb failure stress (CFS) on these active normal faults in the rift zones. Because the estimated CFS depends on the geometrical parameters of receiver faults, it is necessary to get the accurate fault parameters in the rift zones. Some historical earthquakes have been studied using the field data, teleseismic data and InSAR observations, but results are in not agreement with each other. In this study, we revaluated the geometrical parameters of seismogenic faults occurred in the rift zones using some high-quality coseismic InSAR observations and teleseismic body-wave data. Finally, we will evaluate the seismic hazard in the rift zones according to the value of the estimated CFS and aftershock distribution.

  10. Rupture Processes of the Mw8.3 Sea of Okhotsk Earthquake and Aftershock Sequences from 3-D Back Projection Imaging

    Science.gov (United States)

    Jian, P. R.; Hung, S. H.; Meng, L.

    2014-12-01

    On May 24, 2013, the largest deep earthquake ever recorded in history occurred on the southern tip of the Kamchatka Island, where the Pacific Plate subducts underneath the Okhotsk Plate. Previous 2D beamforming back projection (BP) of P- coda waves suggests the mainshock ruptured bilaterally along a horizontal fault plane determined by the global centroid moment tensor solution. On the other hand, the multiple point source inversion of P and SH waveforms argued that the earthquake comprises a sequence of 6 subevents not located on a single plane but actually distributed in a zone that extends 64 km horizontally and 35 km in depth. We then apply a three-dimensional MUSIC BP approach to resolve the rupture processes of the manishock and two large aftershocks (M6.7) with no a priori setup of preferential orientations of the planar rupture. The maximum pseudo-spectrum of high-frequency P wave in a sequence of time windows recorded by the densely-distributed stations from US and EU Array are used to image 3-D temporal and spatial rupture distribution. The resulting image confirms that the nearly N-S striking but two antiparallel rupture stages. The first subhorizontal rupture initially propagates toward the NNE direction, while at 18 s later it directs reversely to the SSW and concurrently shifts downward to 35 km deeper lasting for about 20 s. The rupture lengths in the first NNE-ward and second SSW-ward stage are about 30 km and 85 km; the estimated rupture velocities are 3 km/s and 4.25 km/s, respectively. Synthetic experiments are undertaken to assess the capability of the 3D MUSIC BP for the recovery of spatio-temporal rupture processes. Besides, high frequency BP images based on the EU-Array data show two M6.7 aftershocks are more likely to rupture on the vertical fault planes.

  11. 2011 Van earthquake (Mw=7.2) aftershocks using the source spectra an approach to real-time estimation of moment magnitude

    Science.gov (United States)

    Meral Ozel, N.; Kusmezer, A.

    2012-04-01

    The Converging Grid Search (CGS) algorithm was tested on broadband waveforms data from large aftershocks of the October 23, Van earthquake with the hypocentral distances within 0-300 km over a magnitude range of 4.0≤M≤5.6.Observed displacement spectra were virtually well adapted to the Brune's source model in the whole frequency range for many waveforms.The estimated Mw solutions were compared to global CMT catalogue solutions, and were seen to be in good agreement. To estimate Mw from a shear-wave displacement spectrum, an automatic routine named as CGS was applied to attempt to test and develop a method for stable moment magnitude estimation to be used as a real-time operation.The spectra were corrected for average an elastic attenuation and geometrical spreading factors and then were scaled to compute moment at the long period asymptote where the spectral plateau for 0 Hz is flat.For this aim, an automatic procedure was utilized: 1)calculating the displacement spectra for vertical components at a given station, 2)estimating corner frequency and seismic moment using CGS which is based on minimizing the differences between observed and synthetic source spectra, 3)calculating moment magnitude from seismic moment for each station separately, and then are averaged to give the mean values of each event. The best fitting iteration of these parameters was obtained after a few seconds. The noise spectrum was also computed to suggest a comparison between signals to noise ratio before performing the inversion.Weak events with low SNR were excluded from the computations. The method examined on the Van earthquake aftershock dataset proved that it is applicable to have stable and reliable estimates of magnitude for the routine processing within a few seconds from the initial P wave detection though the location estimation is necessary.This allows a fast determination of Mw magnitude and assist to measure physical quantities of the source available for the real time

  12. Simultaneous estimation of earthquake source parameters and crustal value from broadband data of selected aftershocks of the 2001 7.7 Bhuj earthquake

    Indian Academy of Sciences (India)

    A Saha; S Lijesh; P Mandal

    2012-12-01

    This paper presents the simultaneous estimation of source parameters and crustal Q values for small to moderate-size aftershocks ( 2.1–5.1) of the 7.7 2001 Bhuj earthquake. The horizontal-component S-waves of 144 well located earthquakes (2001–2010) recorded at 3–10 broadband seismograph sites in the Kachchh Seismic Zone, Gujarat, India are analyzed, and their seismic corner frequencies, long-period spectral levels and crustal values are simultaneously estimated by inverting the horizontal component of the S-wave displacement spectrum using the Levenberg–Marquardt nonlinear inversion technique, wherein the inversion scheme is formulated based on the -square source spectral model. The static stress drops ( ) are then calculated from the corner frequency and seismic moment. The estimated source parameters suggest that the seismic moment (0) and source radius () of aftershocks are varying from 1.12 × 1012 to 4.00 × 1016 N-m and 132.57 to 513.20 m, respectively. Whereas, estimated stress drops ( ) and multiplicative factor (mo) values range from 0.01 to 20.0 MPa and 1.05 to 3.39, respectively. The corner frequencies are found to be ranging from 2.36 to 8.76 Hz. The crustal S-wave quality factor varies from 256 to 1882 with an average of 840 for the Kachchh region, which agrees well with the crustal value of the seismically active New Madrid region, USA. Our estimated stress drop values are quite large compared to the other similar size Indian intraplate earthquakes, which can be attributed to the presence of crustal mafic intrusives and aqueous fluids in the lower crust as revealed by the earlier tomographic study of the region.

  13. The 2010 Haiti earthquake sequence: new insight of the tectonic pattern from aftershocks and marine geophysical data : Haiti-OBS cruise

    Science.gov (United States)

    Mercier de Lepinay, B. F.; Mazabraud, Y.; Klingelhoefer, F.; Clouard, V.; Hello, Y.; Graindorge, D.; Marcaillou, B.; Crozon, J.; Saurel, J.; Charvis, P.; Mildor, B. S.; Deschamps, A.; Bouin, M.; Perrot, J.

    2010-12-01

    The devastating 2010 Haiti earthquake ruptured only a relatively short segment (~50km) of the Enriquillo-Plantain Garden fault (EPGF) a 600km long strike-slip fault running onland and offshore from Jamaica to Dominican Republic, with apparently no major surface rupture in the epicentral area. Considering the general behavior of such strike-slip fault (i.e. North Anatolian fault, San Andreas fault), we can expect that, following the 2010 earthquake, other large earthquakes will occur in the near future on adjacent segments. To contribute to the multinational scientific effort for a better understanding of the rupture process and the stress relaxation of this earthquake, we organized the Haiti-OBS cruise of the R/V L'Atalante few weeks after the catastrophe (Feb.5 to Feb.15, 2010, from and to Pointe-a-Pitre, Guadeloupe). Our goal was 1) to deploy a temporary network of seismologic stations -21 OBS, Ocean Bottom Seismometer, and 4 onland stations- and 2) to survey the detailed sea-floor features in relation with the deformation pattern of the area (multibeam bathymetry and mud-penetrator). We show that the distribution pattern of the aftershocks as well as the compressive surface structures observed in the geology and onshore/offshore morphology of the area are consistent with a deformation model implying a major left-lateral component along the EPGF, and a strong reverse component. The January 12, 2010 mainshock has been shown as very complex. However, in the first order, the mainshock and the distribution of the aftershocks, better localized by our temporary network, can be explained by the interaction between the strike-slip EPGF system and a blind folds-and-thrusts system. Thus, the general geological setting shows a southern extension until the southern part of the Canal du Sud area of the well-known fold and thrust system of the Hispaniola main block.

  14. Simultaneous estimation of earthquake source parameters and crustal Q value from broadband data of selected aftershocks of the 2001 M w 7.7 Bhuj earthquake

    Science.gov (United States)

    Saha, A.; Lijesh, S.; Mandal, P.

    2012-12-01

    This paper presents the simultaneous estimation of source parameters and crustal Q values for small to moderate-size aftershocks ( M w 2.1-5.1) of the M_{w }7.7 2001 Bhuj earthquake. The horizontal-component S-waves of 144 well located earthquakes (2001-2010) recorded at 3-10 broadband seismograph sites in the Kachchh Seismic Zone, Gujarat, India are analyzed, and their seismic corner frequencies, long-period spectral levels and crustal Q values are simultaneously estimated by inverting the horizontal component of the S-wave displacement spectrum using the Levenberg-Marquardt nonlinear inversion technique, wherein the inversion scheme is formulated based on the ω-square source spectral model. The static stress drops (Δ σ) are then calculated from the corner frequency and seismic moment. The estimated source parameters suggest that the seismic moment ( M 0) and source radius ( r) of aftershocks are varying from 1.12 × 1012 to 4.00 × 1016 N-m and 132.57 to 513.20 m, respectively. Whereas, estimated stress drops (Δ σ) and multiplicative factor ( E mo) values range from 0.01 to 20.0 MPa and 1.05 to 3.39, respectively. The corner frequencies are found to be ranging from 2.36 to 8.76 Hz. The crustal S-wave quality factor varies from 256 to 1882 with an average of 840 for the Kachchh region, which agrees well with the crustal Q value of the seismically active New Madrid region, USA. Our estimated stress drop values are quite large compared to the other similar size Indian intraplate earthquakes, which can be attributed to the presence of crustal mafic intrusives and aqueous fluids in the lower crust as revealed by the earlier tomographic study of the region.

  15. The Pacific and Philippine Sea slabs in contact beneath Tokyo, central Japan: their roles in defining hazardous interaction earthquakes and in limiting the southern extent of Tohoku-oki aftershocks

    Science.gov (United States)

    Okaya, D. A.; Sato, H.; Lavier, L. L.; Tan, E.; Wu, F. T.; Hirata, N.

    2011-12-01

    The M9 Tohoku-oki earthquake produced over 11,000 >M3 aftershocks within the first four months after its 2011 March 11 occurrence date. The majority of these aftershocks define the earthquake source region between the subducting Pacific plate (PAC) and its overlying Eurasian plate (EUR) along the Japan Trench. While this portion of the trench boundary extends southward to the Boso triple junction (latitude ~34.3 oN), the Tohoku-oki aftershocks predominantly terminate at ~35.7 oN. Between these two latitudes there is a marked dropoff in aftershocks, most noticably offshore of Boso Peninsula, eastern Kanto, which we refer to as the off-Boso aftershock gap. Inside this gap, aftershocks that have occurred form two narrow-width streaks that radiate from the triple junction and extend into central Kanto. There is a correlation between the location of the off-Boso aftershock gap and the northern extent of the Philippine Sea plate (PHS). The PHS is sandwiched between the PAC-EUR plates beneath Kanto. While the majority of Tohoku-oki aftershocks occur within the one-slab PAC-EUR system to the north, the off-Boso gap is updip of where the PHS slab is resident inside the PAC-EUR mantle wedge. Furthermore, the northern of the two aftershock streaks spatially correlates with the downdip extent of the PHS with many located at the PHS-PAC contact based on published tomographic/seismicity studies. The presence of PHS changes the conditions of PAC-EUR slip. Preliminary finite-source studies from web sources (e.g., Univ Tokyo, Harvard) show that Tohoku-oki rupture terminated just north of the off-Boso gap. Apparently, the presence of the Philippine Sea plate may have been a contributing factor to inhibiting this rupture from propagating further southward. The megathrust source faults beneath Kanto are associated with the tops of Philippine Sea and Pacific plates. These shallow source faults have been the focus of much recent geological and geophysical study including seismicity and

  16. Coseismic deformation fields and a fault slip model for the Mw7.8 mainshock and Mw7.3 aftershock of the Gorkha-Nepal 2015 earthquake derived from Sentinel-1A SAR interferometry

    Science.gov (United States)

    Zuo, Ronghu; Qu, Chunyan; Shan, XinJian; Zhang, Guohong; Song, Xiaogang

    2016-08-01

    Coseismic deformation fields caused by the moment magnitude (Mw)7.8 mainshock and Mw7.3 aftershock of the 2015 Gorkha-Nepal earthquake are obtained by analyzing Sentinel-1A/IW ascending and descending interferometry data. Results show that the deformation field associated with the Mw7.8 mainshock roughly resembles a prolate ellipse, extending from the epicenter about 20° east by south. The main region of deformation is about 160 km by 110 km, comprising a large southern area of uplift, and a small northern area of subsidence. Assuming that rupture occurred in a homogeneous elastic half-space, the coseismic fault slip models of the mainshock and aftershock are inverted based on a shallow dip fault constrained by the three data sets, Sentinel-1A/IW descending data, ascending data, and ALOS-2 descending data, separately or in combination. Mainshock slip distributions generated from all three data sets are similar, and inversion constrained by all three in combination reveal a comprehensive fault slip model. Indeed, coseismic slip is mainly distributed within a narrow 40 km zone to the north of the Main Frontal Trust (MFT), and at 6-15 km subsurface depth. In addition, the maximum slip in this event was about 5.1 m, the Mw7.8 mainshock ruptured the deep part of the seismogenic zone, while the region between the southern boundary of the rupture area and the MFT remained locked. Therefore, a considerable earthquake risk remains to the south of Kathmandu. The inverted coseismic slip of the Mw7.3 aftershock was concentrated in a small area, close to, and southeast of the epicenter, with maximum displacement of about 3 m. Finally, because there is no overlap between the two slip areas of the mainshock and aftershock, the gap between them, about 15 km in length, has additional potential to generate future earthquakes.

  17. An intermediate-depth tensional earthquake (MW 5.7) and its aftershocks within the Nazca slab, central Chile: A reactivated outer rise fault?

    Science.gov (United States)

    Marot, Marianne; Monfret, Tony; Pardo, Mario; Ranalli, Giorgio; Nolet, Guust

    2012-04-01

    An intermediate-depth earthquake (7 January 2003, Mw 5.7) occurred within the subducting Nazca plate at longitude 70.3°W, latitude 33.8°S and depth 113 km. Its focal mechanism shows normal faulting with a slight strike-slip component. We detected 50 aftershocks within January 2003 using a temporary seismic network installed in the zone. Their local magnitudes Ml range between 1.9 and 3.5, with the strongest events occurring around the mainshock. Their spatial distribution, including the mainshock, defines an area of ~ (35 ± 5) × (10 ± 2) km2, cutting through almost half of the slab's total thickness at an angle of ~ 60° to the slab's surface. This area agrees well with one of the mainshock nodal planes. However, the total seismic area, as defined by the aftershock distribution, is larger than the rupture area normally expected for an earthquake of moderate magnitude. We compare the orientation of the seismic plane with the outer rise fault pattern offshore central Chile and find a correlation with the strike of the seafloor spreading fabric. The seismic sequence shows similarities with other intermediate-depth cases, notably the 13 June 2005 Tarapacá earthquake in northern Chile and similar cases in the Pacific slab beneath Japan. In all these cases, the inferred reactivated fault planes probably originate from the outer rise region, in agreement with the hypothesis that intermediate-depth seismicity is linked to inherited faults. Consequently, even moderate-sized earthquakes can reactivate large areas of inherited faults within slabs at depths > 100 km. Furthermore, the occurrence of multiple other local events (Mw > 5), with similar focal mechanism and depth to the January 2003 event, appear to indicate that the slab becomes mechanically weak ~ 100 km depth. The depth extent in the slab of the reactivated pre-existing faults is likely governed by the slab's bending/unbending stress regime, i.e. the depth to the neutral plane. Dehydration embrittlement is a

  18. Source Fault of the Dec.26, 2003 Bam Earthquake (Mw6.5) in Southeastern Iran Inferred From Aftershock Observation Data by Temporal High-Sensitive-Seismograph Network

    Science.gov (United States)

    Suzuki, S.; Matsushima, T.; Ito, Y.; Hosseini, S. K.; Nakamura, T.; Arash, J.; Sadeghi, H.; Maleki, M.; Aghda, F.

    2004-05-01

    The Bam earthquake occurred in southeastern Iran at 05:26 A.M.(local time) on December 26, 2003 (epicenter: 29.010N, 58.266E, Mo=6.6x10**18Nm, Mw=6.5; ref.1). The earthquake had strike-slip mechanism (strike=175, dip=85, slip=153; ref.2) and source parameters (focal depth=4km, fault dimension=20kmx15km, Dmax=1.0m, stress drop=3.7MPa; ref.2). The earthquake struck the ancient city of Bam and killed more than 40,000 people. It shows that one third of about 120,000 in population in and around Bam city were killed. The main reason of such a big damage may be caused by weak adobe and brick houses; even so, the damage was too much big. We, therefore, are researching other cause of such a big damage. Taking instruments from Japan for this aim we installed 9 high sensitive seismographs and one accelerograph in and around Bam city on February 6-8, 2004. And we observed aftershocks and continue during one month. Reading P and S arriving times of about 100 aftershocks occurring from February 6 to 10, we determined those preliminary hypocenters and magnitudes. Those epicenters (errors<500m) distribute mainly from northeastern Bam city to south direction with about 20km length. It means that the fault of the main shock passed just under eastern half of Bam city where most of houses and buildings were heavily damaged. This fault is about 4 km away west from Bam fault which is presented in geological map (ref.3). A north-south vertical cross-section of the hypocentral distribution (maybe errors < 1km) shows that most of their depths are shallower than 14km and a seismic gap exists in the laterally middle part of their distribution and shallower than 6 km in depth. The shallow seismic gap may correspond to a main fracture zone as shown in the slip distribution figure proposed by Yamanaka (ref.2). This main fracture occurring shallower than about 6 km in depth must be one of causes of the big damage in Bam. (Reference) ref1:USGS,http://neic.usgs.gov/neis/FM/, ref 2: ERI, U. Tokyo

  19. Evaluating the co-production of a near real time Earthquake Aftershock forecasting tool for humanitarian risk assessment and emergency planning

    Science.gov (United States)

    Quinn, Keira; Hope, Max; McCloskey, John; NicBhloscaidh, Mairead; Jimenez, Abigail; Dunlop, Paul

    2015-04-01

    Concern Worldwide and the University of Ulster Geophysics Research Group are engaged in a project to co-produce a suite of software and mapping tools to assess aftershock hazard in near real-time during the emergency response phase of earthquake disaster, and inform humanitarian emergency planning and response activities. This paper uses a social learning approach to evaluate this co-production process. Following Wenger (1999) we differentiate between the earthquake science and humanitarian communities of practice (CoP) along three dimensions: enterprise (the purpose of CoPs and the problems participants are working to address), repertoire (knowledge, skills, language), and identity (values and boundaries). We examine the effectiveness of learning between CoP, focusing on boundary work and objects, and various organisational structures and aspects of the wider political economy of learning that enable and hinder the co-production process. We conclude by identifying a number of ways to more effectively integrate earthquake science into humanitarian decision-making, policy development and programme design.

  20. P and S waves tomographic analysis of the area of El Asnam's 1980 ms 7.3 earthquake (Algeria) from its aftershock sequence

    Science.gov (United States)

    Bellalem, F.; Bounif, M. A.; Koulakov, I.

    2015-01-01

    We present the 3D seismic model of crustal structure and the distribution of seismicity in the El Asnam region (Algeria) where a strong earthquake (M7.3) occurred in 1980. We apply the local earthquake tomography inversion for the data of temporary networks which recorded the aftershocks of the 1980 event. The results of the tomography inversion have been rigorously tested using a number of different tests. The velocity anomalies from the inversion show pronounced low-velocity anomalies in the surface rupture zone associated with El Asnam fault, which are consistent with the finding of the previous studies (Philip and Meghraoui Tectonics 2:17-49, 1983), Ouyed et al. (Nature 292:26-31, 1981). Moreover, we have also reported the high velocities that exist at shallow crustal depths in the El Asnam zone. We have associated this feature to tectonic, geomorphological, and structural settings in the study area. Finally, we hope that the main features of the interpretation summarized in this article will be the basis for further integrated geophysical and tectonic analyses.

  1. Comparison between low-cost and traditional MEMS accelerometers: a case study from the M7.1 Darfield, New Zealand, aftershock deployment

    Directory of Open Access Journals (Sweden)

    Angela Chung

    2011-06-01

    Full Text Available Recent advances in micro-electro-mechanical systems (MEMS sensing and distributed computing techniques have enabled the development of low-cost, rapidly deployed dense seismic networks. The Quake-Catcher Network (QCN uses triaxial MEMS accelerometers installed in homes and businesses to record moderate to large earthquakes. Real-time accelerations are monitored and information is transferred to a central server using open-source, distributed computing software installed on participating computers. Following the September 3, 2010, Mw 7.1 Darfield, New Zealand, earthquake, 192 QCN stations were installed in a dense array in the city of Christchurch and the surrounding region to record the on-going aftershock sequence. Here, we compare the ground motions recorded by QCN accelerometers with GeoNet strong-motion instruments to verify whether low-cost MEMS accelerometers can provide reliable ground-motion information in network-scale deployments. We find that observed PGA and PGV amplitudes and RMS scatter are comparable between the GeoNet and QCN observations. Closely spaced stations provide similar acceleration, velocity, and displacement time series and computed response spectra are also highly correlated, with correlation coefficients above 0.94.

  2. 2011年云南盈江Ms5.8地震及其余震序列重定位%Relocation of mainshock and aftershocks of the 2011 Yingjiang Ms5.8 earthquake in Yunnan

    Institute of Scientific and Technical Information of China (English)

    房立华; 吴建平; 张天中; 黄静; 王长在; 杨婷

    2011-01-01

    使用川滇地区三维走时表和三维速度模型,利用单纯形法对2011年3月10日云南盈江Ms5.8地震进行了重新定位.震中位置为97.901°E,24.677°N;震源深度13.1 km.使用双差定位方法对其余震序列进行了重定位.余震呈现明显的时空分布特征:余震主要分布在大盈江断裂的两侧及中段和北东段的转折处,余震带长度约12 km;余震自西南沿大盈江断裂带北东段向北东方向移动,在大盈江断裂中段和北东段的交界处,余震逐渐向中段断裂移动;余震震源深度有向地表迁移的趋势,主震发生后10个小时内的余震最小深度接近2 km.表明这次地震的破裂已接近地表.结合地震定位结果,作者认为这次地震震中位于盆地内部、深度浅、距县城近是导致本次地震破坏严重的主要原因.%Based on the 3-D travel-time tables and 3-D velocity model of Sichuan -Yunnan region, we relocated the Yingjiang Ms5. 8 earthquake occurred in Yunnan Province on March 10, 2011, by using the simplex algorithm. The relocated mainshock is 97. 901°E, 24. 677°N, and the focal depth is 13.1 km. Aftershocks were relocated by applying the double-difference method. The aftershocks show obviously spatial and temporal variation, and mainly distribute along the two sides of Dayingjiang fault and near the junction of the middle and northeast section of Dayingjiang fault. The length of the aftershock zone is about 12 km. Aftershocks were moving from southwest to northeast along the northeast segment of Dayingjiang fault, while near the junction between the middle and northeast segment of Dayingjiang fault aftershocks were moving to the middle segment of Dayingjiang fault gradually. The focal depths of aftershocks tend to migrate to the surface. The minimum depth of aftershocks in the first 10 hours approached to 2 km, indicating that the rupture is close to the surface. Combined with the relocation result, we analyzed the factors causing damage

  3. Waveform Correlation Based Detection of Aftershocks of the 6 August 2007 4.1 Mw Crandall Canyon Mine Collapse in Central Utah

    Science.gov (United States)

    Koper, K. D.; Kubacki, T. M.; McCarter, M. K.; Pankow, K. L.

    2012-12-01

    On 6 August 2007 at 08:48:40 (UTC) a 3.9 ML seismic event occurred about 22 km ESE of the town of Mount Pleasant in the coal mining district of central Utah [Pechmann et al., 2008]. An epicenter of 39.4675°N, 111.2249°W and source depth of 0.5 km were determined by University of Utah Seismograph Stations (UUSS). It quickly became clear that the seismic event was associated with a catastrophic collapse at the Crandall Canyon coal mine in which six miners were killed. Subsequent moment tensor inversion showed that a pure double-couple mechanism did not fit the observed waveforms and instead a mechanism dominated by a closing crack (which incorporates an isotropic component) and a smaller residual double-couple and/or CLVD source was preferred [Ford et al., 2008]. The full moment tensor had a scalar moment corresponding to 4.1 Mw. In the 60 days following the mine collapse UUSS located 42 seismic events in the immediate source region. These events had magnitudes of 0.8-2.5 Mc and were detected using standard network association procedures with data from permanent stations of the Utah Regional Seismic Network (URSN), as well as 5 temporary seismometers that UUSS installed in the source area within 2-3 days of the main event. Simple inspection of continuous data from the nearest station shows evidence for a much larger number of seismic events, especially in the hours immediately following the collapse. These events originally went undetected because they were too small to be recorded at a significant number of the permanent URSN stations. Here we use waveform correlation methods to formally detect and locate these tiny aftershocks. We performed multi-channel cross-correlation [vanDecar and Crosson, 1990] on the 42 catalog events using data recorded at the nearest permanent broadband URSN station, MTPU, which was located about 19 km to the south of the mine. A 15-s long window starting 5 s before the expected P arrival was used on data that had been bandpass filtered

  4. A Jurassic Shock-Aftershock Earthquake Sequence Recorded by Small Clastic Pipes and Dikes within Dune Cross-Strata, Zion National Park, Utah

    Science.gov (United States)

    Loope, D. B.; Zlotnik, V. A.; Kettler, R. M.; Pederson, D. T.

    2012-12-01

    dune lee slope through a pipe, the erupted sand dried and was buried by climbing wind-ripple strata as the large dune continued to advance downwind. The mapped cluster recording eight distinct seismic events lies within thin-laminated sediment that was deposited by wind ripples during 1 m (~ 1 year) of southeastward dune migration. We conclude that the small pipes and dikes of our study sites are products of numerous >MM 5 earthquakes, some of which recurred at intervals of less than 2 months. We interpret one small cluster of pipes and dikes with well-defined upward terminations as a distinct shock-aftershock sequence. Because the largest modern earthquakes can produce surface liquefaction only up to about 175 km from their epicenters, the Jurassic epicenters must have been well within that distance. The tendency of modern plate boundaries to produce high-frequency aftershocks suggests that the epicenter for this Jurassic sequence lay to the southwest, within the plate boundary zone (not within continental rocks to the east). As eolian dunes steadily migrate over interdune surfaces underlain by water-saturated dune cross-strata, the thin, distinct laminae produced by the wind ripples that occupy dune toes can faithfully record high-frequency seismic events.

  5. Improving back projection imaging with a novel physics-based aftershock calibration approach: A case study of the 2015 Gorkha earthquake

    Science.gov (United States)

    Meng, Lingsen; Zhang, Ailin; Yagi, Yuji

    2016-01-01

    The 2015 Mw 7.8 Nepal-Gorkha earthquake with casualties of over 9000 people was the most devastating disaster to strike Nepal since the 1934 Nepal-Bihar earthquake. Its rupture process was imaged by teleseismic back projections (BP) of seismograms recorded by three, large regional networks in Australia, North America, and Europe. The source images of all three arrays reveal a unilateral eastward rupture; however, the propagation directions and speeds differ significantly between the arrays. To understand the spatial uncertainties of the BP analyses, we analyze four moderate size aftershocks recorded by all three arrays exactly as had been conducted for the main shock. The apparent source locations inferred from BPs are systematically biased from the catalog locations, as a result of a slowness error caused by three-dimensional Earth structures. We introduce a physics-based slowness correction that successfully mitigates the source location discrepancies among the arrays. Our calibrated BPs are found to be mutually consistent and reveal a unilateral rupture propagating eastward at a speed of 2.7 km/s, localized in a relatively narrow and deep swath along the downdip edge of the locked Himalayan thrust zone. We find that the 2015 Gorkha earthquake was a localized rupture that failed to break the entire Himalayan décollement to the surface, which can be regarded as an intermediate event during the interseismic period of larger Himalayan ruptures that break the whole seismogenic zone width. Thus, our physics-based slowness correction is an important technical improvement of BP, mitigating spatial uncertainties and improving the robustness of single and multiarray studies.

  6. Fault systems of the 1971 San Fernando and 1994 Northridge earthquakes, southern California: Relocated aftershocks and seismic images from LARSE II

    Science.gov (United States)

    Fuis, G.S.; Clayton, R.W.; Davis, P.M.; Ryberg, T.; Lutter, W.J.; Okaya, D.A.; Hauksson, E.; Prodehl, C.; Murphy, J.M.; Benthien, M.L.; Baher, S.A.; Kohler, M.D.; Thygesen, K.; Simila, G.; Keller, Gordon R.

    2003-01-01

    We have constructed a composite image of the fault systems of the M 6.7 San Fernando (1971) and Northridge (1994), California, earthquakes, using industry reflection and oil test well data in the upper few kilometers of the crust, relocated aftershocks in the seismogenic crust, and LARSE II (Los Angeles Region Seismic Experiment, Phase II) reflection data in the middle and lower crust. In this image, the San Fernando fault system appears to consist of a decollement that extends 50 km northward at a dip of ???25?? from near the surface at the Northridge Hills fault, in the northern San Fernando Valley, to the San Andreas fault in the middle to lower crust. It follows a prominent aseismic reflective zone below and northward of the main-shock hypocenter. Interpreted upward splays off this decollement include the Mission Hills and San Gabriel faults and the two main rupture planes of the San Fernando earthquake, which appear to divide the hanging wall into shingle- or wedge-like blocks. In contrast, the fault system for the Northridge earthquake appears simple, at least east of the LARSE II transect, consisting of a fault that extends 20 km southward at a dip of ???33?? from ???7 km depth beneath the Santa Susana Mountains, where it abuts the interpreted San Fernando decollement, to ???20 km depth beneath the Santa Monica Mountains. It follows a weak aseismic reflective zone below and southward of the mainshock hypocenter. The middle crustal reflective zone along the interpreted San Fernando decollement appears similar to a reflective zone imaged beneath the San Gabriel Mountains along the LARSE I transect, to the east, in that it appears to connect major reverse or thrust faults in the Los Angeles region to the San Andreas fault. However, it differs in having a moderate versus a gentle dip and in containing no mid-crustal bright reflections.

  7. Seismic source study of the 1989, October 29, Chenoua (Algeria earthquake from aftershocks, broad-band and strong ground motion records

    Directory of Open Access Journals (Sweden)

    L. Rivera

    2003-06-01

    Full Text Available The broad-band teleseismics records of the earthquake of October 29,1989 in Algeria (MW = 6.0 allow a detailed study of the rupture process of this earthquake. The focal mechanism obtained by P and SH modeling corresponds to reverse faulting with a small amount of left-lateral movement along a fault striking 246° and dipping 56°. The rupture is found to be complex with two sub-events separated in time but occurring on the same plane. The lowfrequency records of an accelerometer located some 25 km to the west of the main shock are also better fi tted when the rupture is composed of a double pulse. In the two cases, there is strong evidence for the rupture to propagate from south-west towards north-east.The relocalisation of the main shock by using a master-event technique and the data from Italian and Spanish stations led to the same conclusions. Soon after the main event, a temporary seimic network was installed in the epicentral area. The aftershock clouds defi ne a SW-NE fault dipping to the NW compatible with the results of the modelisations of the teleseismic body-waves and the accelerogram. The focal mechanisms correspond mainly to reverse faulting. The maximum principal direction of the stress tensor obtained from the inversion is about N-S and the minimum is vertical, typical of a compressive regime. The Chenoua earthquake took place on a fault which was not recognized as active. Repeated comparable seismic events on this fault and on the fault that borders the massif to the south explain this intriguing topographic feature.

  8. Self-Organized Criticality in Process of Aftershocks of Lushan Earthquake%芦山地震余震发生及演化的自组织临界机制

    Institute of Scientific and Technical Information of China (English)

    刘春琼; 史凯; 李思川

    2014-01-01

    为探讨芦山7.0级地震余震演化动力机制,应用统计地震学方法,分析了2013年4月20日-6月20日芦山地震余震序列的宏观统计分布规律;基于自组织临界理论,提出了一种新的余震模型,以期阐明相关统计地震学规律的产生动力机制,并深入讨论了该模型的自组织临界性.该余震模型的具体算法是在经典Olami-Feder-Christensen地震模型基础上,引入了应力衰减因子和应力扩散各向异性因子.研究结果表明:芦山7.0级地震余震序列的震级分布遵循Gutenberg-Richter统计规律,幂指数值约为0.766;其余震序列的时间分布遵循Omori统计规律,幂指数值约为2.52.新建模型的数值模拟能同时对芦山地震余震序列呈现出的 Gutenberg-Richter和Omori统计规律给出满意的预测结果,模拟结果与实际情况高度吻合,表明龙门山断裂带处于一种自组织临界状态,芦山地震余震过程实质上是一种自组织临界现象.%The statistical relations of aftershocks following a strong earthquake can give useful information on the dynamical features of seismic processes and the involved geodynamical mechanisms. The sequence of aftershocks of the Lushan Ms7. 0 earthquake,occurred on the Longmenshan tectonic zone in Sichuan Province,China,was analyzed. The analyses of magnitude and temporal statistical distributions in the aftershocks sequence described by the Gutenberg-Richter and Omori laws respectively were performed. To provide a possible explanation of these observed distributions,a novel SOC (self-organized criticality ) model was developed by introducing stress decay coefficient and anisotropic diffusion factor into the Olami-Feder-Christensen model of earthquakes,and the self-organized criticality properties of this novel model were discussed. The research result shows that the aftershocks of the Lushan Earthquake follow the Gutenberg-Richter and Omori laws,and the

  9. Self-Organized Criticality in Process of Aftershocks of Lushan Earthquake%芦山地震余震发生及演化的自组织临界机制

    Institute of Scientific and Technical Information of China (English)

    刘春琼; 史凯; 李思川

    2014-01-01

    为探讨芦山7.0级地震余震演化动力机制,应用统计地震学方法,分析了2013年4月20日-6月20日芦山地震余震序列的宏观统计分布规律;基于自组织临界理论,提出了一种新的余震模型,以期阐明相关统计地震学规律的产生动力机制,并深入讨论了该模型的自组织临界性.该余震模型的具体算法是在经典Olami-Feder-Christensen地震模型基础上,引入了应力衰减因子和应力扩散各向异性因子.研究结果表明:芦山7.0级地震余震序列的震级分布遵循Gutenberg-Richter统计规律,幂指数值约为0.766;其余震序列的时间分布遵循Omori统计规律,幂指数值约为2.52.新建模型的数值模拟能同时对芦山地震余震序列呈现出的 Gutenberg-Richter和Omori统计规律给出满意的预测结果,模拟结果与实际情况高度吻合,表明龙门山断裂带处于一种自组织临界状态,芦山地震余震过程实质上是一种自组织临界现象.%The statistical relations of aftershocks following a strong earthquake can give useful information on the dynamical features of seismic processes and the involved geodynamical mechanisms. The sequence of aftershocks of the Lushan Ms7. 0 earthquake,occurred on the Longmenshan tectonic zone in Sichuan Province,China,was analyzed. The analyses of magnitude and temporal statistical distributions in the aftershocks sequence described by the Gutenberg-Richter and Omori laws respectively were performed. To provide a possible explanation of these observed distributions,a novel SOC (self-organized criticality ) model was developed by introducing stress decay coefficient and anisotropic diffusion factor into the Olami-Feder-Christensen model of earthquakes,and the self-organized criticality properties of this novel model were discussed. The research result shows that the aftershocks of the Lushan Earthquake follow the Gutenberg-Richter and Omori laws,and the

  10. Coseismic Slip Model of the M 7.8 2015 Nepal Earthquake and its M 7.2 Aftershock from Joint Inversion of InSAR and GPS Data

    Science.gov (United States)

    Cheloni, D.; Tolomei, C.; Bignami, C.; D'Agostino, N.; Atzori, S.

    2015-12-01

    We derived a coseismic slip model for the M 7.8 2015 Nepal earthquake on the basis of radar line-of-sight displacements retrieved from RADARSAT, ALOS and SENTINEL interferograms and GPS data. We use the surface trace of the Main Himalayan Thrust (MHT) and moment tensor solution to approximate the earthquake rupture plane with a planar thrust fault having a strike of ~295° and a dip of ~10°. Our rupture model suggests that the slip area is about 120 x 50 km, with the most of the moment release limited to a depth between 10-20 km. Therefore the earthquake did not reach the surface suggesting a marked shallow slip deficit in the slip depth distribution. The earthquake released a seismic moment of 7.88E+20 Nm, corresponding to a Mw 7.88. Adopting the same fault geometry we also estimated the slip distribution related to the M 7.2 aftershock that occurred near the eastern end of the main coseismic asperity. The aftershock rupture model shows a more compact slip area of about 30 x 30 km, releasing a moment of 5.49E+19 Nm and corresponding to a Mw 7.13. We calculated the static stress changes on the assumed fault plane due to the mainshock. The result suggests loading of the fault around the main coseismic patch where indeed most of the aftershocks, comprising the M 7.2 event, were primarily distributed. Future researches will be focused on the up-dip locked portions of the MHT that did not break during the 25 April 2015 Nepal earthquake and the monitoring of the post-seismic phase by means of InSAR and GPS data.

  11. Faulting mechanism of the Campania–Lucania 1980 earthquake, Italy, from high-resolution, 3D velocity structure, aftershock relocation, fault-plane solutions, and post-seismic deformation modeling

    Directory of Open Access Journals (Sweden)

    Roberto Scarpa

    2011-06-01

    Full Text Available

    This study performs a detailed reconstruction of the rupture mechanism of the 1980 Campania–Lucania (southern Italy earthquake. This is achieved by relocation of the main event through computation of fault-plane solutions of the aftershocks, P-wave velocity inversion, and analysis of post-seismic ground deformation, which provide an overall picture of the faulting mechanism. All of these data are in favor of a complex rupture mechanism, as already identified by many studies, which consists of three separate events. The present study defines a graben-like rupture, with the first event rupturing a (>20-km-long segment of a large, high-angle, NE-dipping, SE-NW-striking, normal fault. The two successive ruptures occurred separately, the first along the southern segment, and the second along the northern segment, of a complementary SW-dipping, normal fault. This mechanism is well evidenced by the revised location of the hypocenter of the main event, and the location of the aftershocks and their fault-plane solutions, as well as by the underlying three-dimensional P-wave velocity structure. The model proposed by Amoruso et al. [2005a] that was based on the inversion of co-seismic vertical displacement data is confirmed by the present analyses, as it satisfies all of the available experimental observations, and better constrains the location and fault-plane solutions of the aftershocks, the velocity discontinuities, and the rupture observations at the surface. This conclusion is also supported by analyses of the post-seismic data.

  12. Geodetic Imaging of the Coseismic and Postseismic deformation from the 2015 Mw 7.8 Gorkha Earthquake and Mw 7.3 Aftershock in Nepal with SAR and GPS

    Science.gov (United States)

    Fielding, E. J.; Liang, C.; Agram, P. S.; Sangha, S. S.; Huang, M. H.; Samsonov, S. V.; Owen, S. E.; Moore, A. W.; Rodriguez-Gonzalez, F.; Minchew, B. M.

    2015-12-01

    The 25th of April 2015 Mw 7.8 Gorkha Earthquake in Nepal affected a large area of central Nepal and adjacent parts of India and Tibet. It was followed by a number of large aftershocks, with the largest so far an Mw 7.3 aftershock on the 12th of May 2015. We integrate geodetic measurements from Global Positioning System (GPS) data and synthetic aperture radar (SAR) satellite images to image the three-dimensional vector field of coseismic surface deformation for these two large events. We analyze SAR data from the Copernicus Sentinel-1A satellite operated by the European Space Agency; the RADARSAT-2 satellite operated by MacDonald, Dettwiler and Associates (MDA); and the Advanced Land Observation Satellite-2 (ALOS-2) satellite operated by the Japanese Aerospace Exploration Agency. We combine less precise analysis of large scale displacements from the SAR images of the three satellites by pixel offset tracking or sub-pixel correlation, including the along-track component of surface motion, with the more precise SAR interferometry (InSAR) measurements in the radar line-of-sight direction to estimate all three components of the surface displacement for the mainshock and large aftershock. A large area of central Nepal was pushed southward, due to thrust slip on the Main Himalayan Thrust (MHT) at depth extending about 170 km along-strike. The InSAR measurements show that there was no detectable slip on the shallower part of the MHT up-dip from the large coseismic slip or on other thrust faults in the Himalayas, except for one area of very shallow triggered slip of up to 5 cm on a thrust to the north of the Himalayan Frontal Thrust, during the two event. We also image postseismic deformation after these earthquakes with ongoing continuous GPS measurements and InSAR analysis of the SAR satellite data. Initial analysis of the GPS measurements indicates the most likely process in the first months is afterslip down-dip from the main coseismic slip. Large atmospheric effects in

  13. Discussion on the Aftershock Magnitude of Nantou 7.6 Earthquake in the Taiwan Island%用Corioli力讨论台湾南投7.6级大震的余震强度

    Institute of Scientific and Technical Information of China (English)

    郭增建; 吴瑾冰

    2001-01-01

    The Natou great earthquake in the Taiwan island is caused by a dis location of thrust in the source region with its upper wall slipping toward the west. The Corioli force of this type of dislocation makes both of fault walls c o mpress each other. Therefore, the total energy does not release completely duri n g the mainshock and the magnitudes of the aftershocks are very large. An attemp t to analyze the effect of Corioli force on the aftershock intentisity of the Nat ou great earthquake is made in this paper.%台湾南投大震是震源地方一个逆掩断层错动引起的,上盘向西错动,这种断层错 动的形式其Corioli力效应是使两断层盘相互挤压,因之主震发生时能量释放不彻底,余震 强度较大。 本文试图用Corioli力效应具体讨论台湾南投大震的余震强度。

  14. The regional moment tensor of the 5 May 2014 Chiang Rai earthquake (Mw = 6.5), Northern Thailand, with its aftershocks and its implication to the stress and the instability of the Phayao Fault Zone

    Science.gov (United States)

    Noisagool, Sutthipong; Boonchaisuk, Songkhun; Pornsopin, Patinya; Siripunvaraporn, Weerachai

    2016-09-01

    On 5 May 2014, the largest earthquake in Thailand modern history occurred in Northern Thailand with over a thousand aftershocks. Most of the epicenters are located within the transition area of the Mae Lao segment (north) and Pan segment (central) of the Phayao Fault Zone (PFZ). Good quality data from all events (ML > 4) are only available for the seismic stations closer to the epicenters (geophysical evidence which reveals that the high shear stress Mae Lao segment is likely to slip first producing the main shock on 5 May 2014. The energy transfer between the segments has then led to many aftershocks with mixed mechanisms. At the end, we re-visited the analysis of the former largest earthquake in Northern Thailand in the past decades, the 11 September 1994 event. Its focal mechanism was re-calculated based on the available P-wave polarities. The strike - slip motion should be the mechanism of the earthquake, not the normal motion as originally believed.

  15. Identifying the dynamic characteristics of a dual core-wall and frame building in Chile using aftershocks of the 27 February 2010 (Mw=8.8) Maule, Chile, earthquake

    Science.gov (United States)

    Çelebi, Mehmet; Sereci, Mark; Boroschek, Ruben; Carreño, Rodrigo; Bonelli, Patricio

    2013-01-01

    Following the 27 February 2010 (Mw = 8.8) Offshore Maule, Chile earthquake, a temporary, 16-channel, real-time data streaming array was installed in a recently constructed building in Viña del Mar to capture its responses to aftershocks. The cast-in-place, reinforced concrete building is 16 stories high, with 3 additional basement levels, and has dual system comprising multiple structural walls and perimeter frames. This building was not damaged during the main-shock, but other buildings of similar design in Viña del Mar and other parts of Chile were damaged, although none collapsed. Dynamic characteristics of the building identified from the low-amplitude (PGA of about 2 Gal) response recordings of aftershocks are found to compare well with those determined from modal analyses using a design level FEM model. Distinct “major-axes” translational and torsional fundamental frequencies, as well as frequencies of secondary modes, are identified. Evidence of beating is consistently observed in the response data for each earthquake. Results do not match well with U.S. code formulas.

  16. An experimental approach to non - extensive statistical physics and Epidemic Type Aftershock Sequence (ETAS) modeling. The case of triaxially deformed sandstones using acoustic emissions.

    Science.gov (United States)

    Stavrianaki, K.; Vallianatos, F.; Sammonds, P. R.; Ross, G. J.

    2014-12-01

    Fracturing is the most prevalent deformation mechanism in rocks deformed in the laboratory under simulated upper crustal conditions. Fracturing produces acoustic emissions (AE) at the laboratory scale and earthquakes on a crustal scale. The AE technique provides a means to analyse microcracking activity inside the rock volume and since experiments can be performed under confining pressure to simulate depth of burial, AE can be used as a proxy for natural processes such as earthquakes. Experimental rock deformation provides us with several ways to investigate time-dependent brittle deformation. Two main types of experiments can be distinguished: (1) "constant strain rate" experiments in which stress varies as a result of deformation, and (2) "creep" experiments in which deformation and deformation rate vary over time as a result of an imposed constant stress. We conducted constant strain rate experiments on air-dried Darley Dale sandstone samples in a variety of confining pressures (30MPa, 50MPa, 80MPa) and in water saturated samples with 20 MPa initial pore fluid pressure. The results from these experiments used to determine the initial loading in the creep experiments. Non-extensive statistical physics approach was applied to the AE data in order to investigate the spatio-temporal pattern of cracks close to failure. A more detailed study was performed for the data from the creep experiments. When axial stress is plotted against time we obtain the trimodal creep curve. Calculation of Tsallis entropic index q is performed to each stage of the curve and the results are compared with the ones from the constant strain rate experiments. The Epidemic Type Aftershock Sequence model (ETAS) is also applied to each stage of the creep curve and the ETAS parameters are calculated. We investigate whether these parameters are constant across all stages of the curve, or whether there are interesting patterns of variation. This research has been co-funded by the European Union

  17. Application example: Preliminary Results of ISOLA use to find moment tensor solutions and centroid depth applied to aftershocks of Mw=8.8 February 27 2010, Maule Earthquake

    Science.gov (United States)

    Nacif, S. V.; Sanchez, M. A.

    2013-05-01

    We selected seven aftershocks from Maule earthquake between 33.5°S to 35°S from May to September to find single source inversion. The data were provided by XY Chile Ramp Experiment* which was deployed after great Maule earthquake. Waveform data are from 13 broad band stations chosen from the 58 broad band stations deployed by IRIS-PASCAL from April to September 2010. Stations are placed above the normal subduction section south of ~33.5°S. Events were located with an iterative software called Hypocenter using one dimensional local model, obtained above for the forearc region between 33°S to 35°S. We used ISOLA which is a fortran code with a Matlab interface to obtain moment tensors solutions, optimum position and time of the subevents. Values depth obtained by a grid search of centroid position show range values which are compatibles with the interplate seismogenic zone. Double-Couple focal mechanism solutions (Figure 1) show 4 thrust events which can be associated with that zone. However, only one of them has strike, dip and rake of 358°, 27° and 101 respectively, appropriate to be expected for interplate seismogenic zone. On the other hand, the other 3 events show strike and normal double-couple focal mechanism solutions (Figure 1). This last topic makes association to those events to the contact of the Nazca and South American plate difficult. Nevertheless, in a first stage, their depths may allow possibility of an origin there. * The facilities of the IRIS Data Management System, and specifically the IRIS Data Management Center, were used for access to waveform, metadata or products required in this study. The IRIS DMS is funded through the National Science Foundation and specifically the GEO Directorate through the Instrumentation and Facilities Program of the National Science Foundation under Cooperative Agreement EAR-0552316. Some activities of are supported by the National Science Foundation EarthScope Program under Cooperative Agreement EAR-0733069

  18. 水平面上处理科氏力余震效应%Operation of Aftershock Effect of Corioli' s Force Produced by Earthquake Fault Dislocation on Horizontal Plane

    Institute of Scientific and Technical Information of China (English)

    郭增建

    2012-01-01

    科氏力余震效应对大震后紧急救援时速判最强余震的震级以警惕二次灾害是有意义的。讨论在平面上处理科氏力问题,也就是在震中所在的地图上处理科氏力问题。%It is significant to use the aftershoek effect of Corioli' s force for predicting magnitude of the largest aftershock to make preparation for the second disaster during emergent assistance after main shock. Operation of Corioli' s force produced by earthquake fault dislocation on horizontal plane is discussed, i.e. , operating Corioli' s force on the map where the epicenter is located.

  19. 汶川Mw7.9地震余震序列触发机制研究%Triggering mechanism of aftershocks triggered by Wenchuan Mw7.9 earthquake

    Institute of Scientific and Technical Information of China (English)

    申文豪; 刘博研; 史保平

    2013-01-01

    余震触发机制的Dieterich解析模型被广泛应用于区域地震活动性的定量分析以及依赖时间的概率地震预测模型的建立等方面.基于滑移速率和状态相依赖的摩擦定律和弹簧-滑块模型,从Dieterich断层滑移速率方程出发,给出了静态应力扰动下触发地震的时钟提前或推后的近似解,从而明确地阐明了触发地震的产生机制与断层的演化过程密切相关,并与传统位错模型下库仑应力扰动时间提前或推后量作了比较.采用对数线性拟合方法求得了汶川Mw7.9主震后余震序列持续时间,符合Dieterich理论结果.以汶川余震序列为例,给出了两种不同的应力扰动模式在该余震序列中的应用.结果表明,经典Dieterich扰动解无法给出主震发生后即时余震数量的异常增加,而考虑主震前后剪应力速率变化的Dieterich分段解则可反映出余震发生率及个数随时间的演化特征.%The analytic solution of earthquake triggering mechanism put forward by Dieterich has been widely used in quantitative analysis and description of regional seismic activities,and in the development of time-dependent earthquake prediction model.Based on the spring-slider model with a combination of rateand state-dependent friction,starting from the fault slip rate evolution equation proposed by Dieterich,we have derived the equation called clock advance/delay related to the earthquake faulting instability under the Coulomb stress perturbation.In comparison with the simple dislocation model,the current result suggests that the generation of earthquakes is actually related to the state of fault evolution.For the 2008 Wenchuan Mw7.9 earthquake sequence,we have estimated the possible time duration of aftershocks caused by main shock,both from theoretical inferring and empirical relation,and the result is similar to each other.Furthermore,two different stress change models have been used in the calculations of aftershock

  20. UNBIASED MOMENT-RATE SPECTRA AND ABSOLUTE SITE EFFECTS IN THE KACHCHH BASIN, INDIA, FROM THE ANALYSIS OF THE AFTERSHOCKS OF THE 2001 Mw 7.6 BHUJ EARTHQUAKE

    Energy Technology Data Exchange (ETDEWEB)

    Malagnini, L; Bodin, P; Mayeda, K; Akinci, A

    2005-05-04

    What can be learned about absolute site effects on ground motions and about earthquake source spectra from recordings at temporary seismic stations, none of which could be considered a 'reference' (hard rock) site, for which no geotechnical information is available, in a very poorly instrumented region? This challenge motivated our current study of aftershocks of the 2001 Mw 7.6 Bhuj earthquake, in Western India. Crustal attenuation and spreading relationships based on the same data used here were determined in an earlier study. In this paper we decouple the ambiguity between absolute source radiation and site effects by first computing robust estimates of moment-rate spectra of about 200 aftershocks in each of two depth ranges. Using these new estimates of sourcespectra, and our understanding of regional wave propagation, we extract the absolute site terms of the sites of the temporary deployment. Absolute site terms (one for each component of the ground motion, for each station) are computed in an average sense, via an L{sub 1}-norm minimization, and results for each site are averaged over wide ranges of azimuths and takeoff angles. The Bhuj deployment is characterized by a variable shallow geology, mostly of soft sedimentary units. Vertical site terms in the region were observed to be almost featureless and slightly < 1.0 within wide frequency ranges. As a result, H/V spectral ratios mimic the absolute behaviors of absolute horizontal site terms, and they generally overpredict them. On the contrary, with respect to the results for sedimentary rock sites (limestone, dolomite) obtained by Malagnini et al. (2004), H/V spectral ratios in their study did not have much in common with absolute horizontal site terms. Spectral ratios between the vector sum of the computed horizontal site terms for the temporary deployment with respect to the same quantity computed at the hardest rock station available, BAC1, are seriously biased by its non-flat, non

  1. Seismological evidence of an active footwall shortcut thrust in the Northern Itoigawa-Shizuoka Tectonic Line derived by the aftershock sequence of the 2014 M 6.7 Northern Nagano earthquake

    Science.gov (United States)

    Panayotopoulos, Yannis; Hirata, Naoshi; Hashima, Akinori; Iwasaki, Takaya; Sakai, Shin'ichi; Sato, Hiroshi

    2016-06-01

    A destructive M 6.7 earthquake struck Northern Nagano prefecture on November 22, 2014. The main shock occurred on the Kamishiro fault segment of the northern Itoigawa-Shizuoka Tectonic Line (ISTL). We used data recorded at 41 stations of the local seismographic network in order to locate 2118 earthquakes that occurred between November 18 and November 30, 2014. To estimate hypocenters, we assigned low Vp models to stations within the Northern Fossa Magna (NFM) basin thus accounting for large lateral crustal heterogeneities across the Kamishiro fault. In order to further improve accuracy, the final hypocenter locations were recalculated inside a 3D velocity model using the double-difference method. We used the aftershock activity distribution and focal mechanism solutions of major events in order to estimate the source fault area of the main shock. Our analysis suggests that the shallow part of the source fault corresponds to the surface trace of the Kamishiro fault and dips 30°-45° SE, while the deeper part of the source fault corresponds to the downdip portion of the Otari-Nakayama fault, a high angle fault dipping 50°-65° SE that formed during the opening of the NFM basin in the Miocene. Along its surface trace the Otari-Nakayama fault has been inactive during the late Quaternary. We verified the validity of our model by calculating surface deformation using a simple homogeneous elastic half-space model and comparing it to observed surface deformation from satellite interferometry, assuming large coseismic slip in the areas of low seismicity and small coseismic slip in the areas of high seismicity. Shallowing of the source fault from 50°-65° to 30°-45° in the upper 4 km, in the areas where both surface fault traces are visible, is a result of footwall shortcut thrusting by the Kamishiro fault off the Otari-Nakayama fault.

  2. Persistent fear of aftershocks, impairment of working memory, and acute stress disorder predict post-traumatic stress disorder: 6-month follow-up of help seekers following the L'Aquila earthquake.

    Science.gov (United States)

    Roncone, Rita; Giusti, Laura; Mazza, Monica; Bianchini, Valeria; Ussorio, Donatella; Pollice, Rocco; Casacchia, Massimo

    2013-01-01

    The aim of our 6-month follow-up study was to assess predictors of post-traumatic stress disorder (PTSD) among individuals seeking treatment at the General Hospital Psychiatric Unit within the first month following the L'Aquila earthquake. Clinical, trauma-related and neurocognitive variables were considered. At the 6-month follow-up, 91 (74.5%) out of 122 subjects were re-assessed and administered the Impact of Events Scale-revised (IES-R) for the detection of PTSD according to DSM-IV criteria. Within 4 weeks following the earthquake, patients were assessed with a checklist of traumatic-event-related variables, along with the Stanford Acute Stress Disorder Questionnaire (SASDQ) for the detection of ASD, with a short battery on working (Wechler Memory Scale-R, Digit Forward and Backward) and verbal memory (subtest of Milan Overall Dementia Assessment, MODA). A statistically significant higher proportion of subjects affected by 'partial' ASD showed a PTSD diagnosis (80.6%, N = 29) compared to not diagnosed subjects (40%, N = 22) and a PTSD diagnosis was shown by all the 4 subjects (4.4%) affected by 'full' ASD at the entry in the study. At the 6-month follow-up 56% of the sample could be considered affected by PTSD on the IES-R scale. The results of the logistic regression analysis on our selected predictors indicated that the persistent fear of aftershocks seemed to increase by over 57 times the likelihood of positive estimate of PTSD, followed by impairment of working memory backward (OR 48.2), and having being diagnosed as ASD case in the first 4 week after the earthquake (OR 17.4). This study underlines the importance of identifying PTSD predictors, in order to planning early treatment interventions after natural disasters. PMID:24324929

  3. Preliminary Analysis of Mobile Observation Records for the Aftershocks in the Yushu M7.1 Earthquake%玉树7.1级地震强震动流动观测记录初步分析

    Institute of Scientific and Technical Information of China (English)

    田秀丰; 张璇; 姚凯; 张晓芳; 蒲举

    2014-01-01

    2010年4月14日青海省玉树藏族自治州玉树县发生 M7.1地震。震后在地震现场架设了7台强震动流动观测仪,记录了大量强震动记录。本文收集整理了该次流动观测所获得的强震动记录,对典型记录进行了初步处理,并对记录特点和相关问题进行了分析与讨论。%The Yushu M7.1 earthquake occurred on April 14,2010 in Yushu,the Tibetan autono-mous prefecture of the Qinghai province (E 96.7°,N 33.1°).After the earthquake,we set up seven strong motion mobile observation instruments around the epicenter.As of October 15, 2010,we had captured 71 seismic events and a total of 213 acceleration records,with the maximum magnitude of M4.6.In these records,there were 10 records whose peak ground acceleration was greater than 30 gal,and the maximum peak ground acceleration was 122 gal.The waveform of re-cords was clear and complete,which makes up for the lack of fixed stations and local records near the earthquake zone.It not only offered the quantitative evidence for analysis of the earthquake damage,but also provided important data for the study of the relationship among the peak ground motion,holding time,the spectrum,and macro-seismic intensity.In this paper,we collected and preliminarily processed these records and obtained the speed schedule,Fourier spectrum,and the power spectrum,then analyzed and discussed the recording features and related issues.The results showed that (1)the maximum peak ground acceleration in this mobile observation was 122 gal, and the holding time of vibration was about 5 seconds,with a frequency of 7.2 Hz.This record came from a M3.6 aftershock,and it indicated that a small earthquake may also obtain high peak acceleration.This would appear to be the opposite phenomenon of a high vibration peak with low seismic intensity.In fact,there were many major projects located in the area which had small seismicity background.With the increasing coverage of observation stations

  4. L'Aquila earthquake verdict yields aftershocks

    Science.gov (United States)

    Showstack, Randy

    2012-11-01

    The 22 October verdict by a court in L'Aquila, Italy, convicting seven Italian earthquake experts of manslaughter for failing to provide an adequate seismic warning to residents prior to a damaging quake in the region continues to send shockwaves through the scientific community. A sampling of the scientific community's concern about the verdict, which is likely to be appealed, included a 25 October joint statement from U.S. National Academy of Sciences president Ralph Cicerone and U.K. Royal Society president Sir Paul Nurse that noted "the difficult task facing scientists in dealing with risk communication and uncertainty." The statement continued, "Much as society and governments would like science to provide simple, clear-cut answers to the problems that we face, it is not always possible. Scientists can, however, gather all the available evidence and offer an analysis of the evidence in light of what they do know. The sensible course is to turn to expert scientists who can provide evidence and advice to the best of their knowledge. They will sometimes be wrong, but we must not allow the desire for perfection to be the enemy of good. That is why we must protest the verdict in Italy. If it becomes a precedent in law, it could lead to a situation in which scientists will be afraid to give expert opinion for fear of prosecution or reprisal. Much government policy and many societal choices rely on good scientific advice and so we must cultivate an environment that allows scientists to contribute what they reasonably can, without being held responsible for forecasts or judgments that they cannot make with confidence."

  5. 利用单台波形资料计算大柴旦6.3级地震余震震源机制%USING SEISMIC DATA FROM A SINGLE-STATION TO CALCULATE THE FOCAL MECHANISMS OF THE AFTERSHOCKS OF THE Ms6.3 DACHAIDAN EARTHQUAKE IN NOV. 10, 2008

    Institute of Scientific and Technical Information of China (English)

    张晓清; 何春晖; 张晶; 刘薇; 马震; 文勇

    2012-01-01

    Based on the digital seismic data of the aftershocks of Dachaidan Ms6. 3 earthquake in Nov. 10, 2008, using the three-component seismic data from a single-station, we calculate the focal mechanisms of af- tershocks by the method of the moment tensors inversion. We collect the epicenter parameters published of Dachaidan Ms6.3 earthquake in Nov. 10, 2008 and the digital seismic data of the seismic network in Qinghai region. Through calculated theoretical seismic wave, we can get the velocity structure model of the research ar- ea in this paper by the epicenter parameters of Dachaidan Ms6.3 earthquake. Using this model, we obtain the focal mechanisms of the ME 92.0 aftershocks. We chosed the 160 aftershocks from the digital seismic data and got some results of 85 aftershocks at last, among which, the largest event is ML 4.7, the smallest magnitude is ML 2.0. Through contrast analysis, it almost is similar that we obtain the moment tensor inversion results from a single-station and the five stations. The calculated results show that the focal mechanisms of a small to mod- erate earthquakes can be gotten using the digital seismic data from a single-station.%以2008年11月10日大柴旦Ms6.3级地震余震数字地震波观测资料为基础,运用矩张量反演方法,利用单台三分量波形资料计算余震的震源机制。收集整理大柴旦Ms6.3级地震公认的震源参数结果和青海区域地震台网数字地震波资料,以大柴旦Ms6.3级地震的震源参数作为约束,计算理论地震波来确定该区域的地壳速度模型。以此模型计算ML≥2.0级余震震源机制解。共收集160个余震资料,最后确定了85个余震震源机制解,其中最大震级为朋。4.7,最小震级为ML2.0。进行单台与多台联合矩张量反演结果对比,两种方法所确定的结果相差不大。实际计算表明,在观测资料信噪比较高的情况下,运用单台数字地震波观测资料可以较好

  6. Comparison of duration and spatial and temporal distribution between Ms8.1 Kunlunshan and Ms8.0 Wenchuan earthquake aftershock sequences%Ms8.1昆仑山口西地震和Ms8.0汶川地震余震序列的时空分布特征和持续时间的对比

    Institute of Scientific and Technical Information of China (English)

    刘博研; 史保平

    2012-01-01

    2001年Ms8.1昆仑山口西地震和2008年Ms8.0汶川地震发生在同一构造单元,但其余震序列无论在个数、空间分布,还是持续时间上都表现了显著的差别.余震通常由主震区域内背景场地震活动性受到的扰动所引起,这样的扰动则来自于主震造成的应力场状态的变化.本文从滑移速率和状态相依赖的摩擦定律(Rate- and State-Dependent Friction Law)出发,结合区域主震前后的地震活动性资料,定量地估算了这两个大地震后余震序列可能的持续时间,并对不同模型所得的结果进行了比较和对比.结果表明,汶川地震余震持续时间约为昆仑山口西地震余震持续时间的20倍,这是由于昆仑山口西地震和汶川地震余震序列的个数和持续时间不仅与地震成核过程的状态变化有关,还与作用在断层面上的正应力σN和剪应力加载速率iι的大小有关.主震前后剪应力速率i的差别导致了在相同大小应力扰动△CFS之后的余震的活动性变化率的明显不同,导致了所触发的余震的个数和余震序列的持续时间的巨大差别.通过对昆仑山口西地震和汶川地震余震序列的时空分布特征和持续时间的定量化认识,可以为地震灾害定量评估提供合理和有益的物理参数.%The 2001 MS8. 1 Kunlunshan earthquake and the 2008 MS8. 0 Wenchuan earthquake occurred in the same tectonic unit. There are significant differences in spatial-temporal distribution, number of aftershocks and time duration for the aftershock sequence following these two main shocks. As we all know, aftershocks could be triggered by the regional seismicity change derived from the main shock, which was caused by the Coulomb stress perturbation. Based on the rate- and state-dependent friction law and the seismicity data before and after the mainshocks, we quantitatively estimated the possible aftershock time duration, and compared the results from different approaches

  7. 电影字幕英译策略探究——以《唐山大地震》字幕英译为例%Study on the C-E Translation Strategies of Movie Subtitle---With the Subtitle Translation of Aftershock as an Example

    Institute of Scientific and Technical Information of China (English)

    苏学雷; 田桂娟

    2012-01-01

    《唐山大地震》是一部震撼心灵的电影,在全国公映之后,该影片也被推向国际市场。字幕翻译的质量对影片在国际市场的广泛传播有着直接影响。文章通过对《唐山大地震》字幕翻译进行分析后,指出“压缩”和“删除”是字幕翻译所特有的两种重要翻译策略,同时也指出了该片字幕翻译的不足之处。%Aftershock is a touching movie. After its release across China, it was put into the international market. Therefore, the quality of its subtitle translation has a direct ,effect on its success in the international market. Through the analysis of the subtitle translation in this film, the paper points out that condensation and deletion are two important strategies in subtitle translation and also points out some mistranslations in the subtitle translation of this film.

  8. 基于聚类分析的多尺度相似地震快速识别方法及其在汶川地震东北端余震序列分析中的应用%Quick identification of multilevel similar earthquakes using hierarchical clustering method and its application to Wenchuan northeast aftershock sequence

    Institute of Scientific and Technical Information of China (English)

    王伟涛; 王宝善

    2012-01-01

    相似地震是具有相似波形记录的一组地震,往往以地震丛集的方式发生,而重复地震是一种特殊的相似地震,一般具有相近的震源机制解和几乎重合的破裂面积.对相似地震特别是重复地震的研究是我们认识断层的结构和变化的重要手段.本文提出了一种基于相似度距离概念和聚类分析技术的相似地震识别方法,可以利用单个台站对其记录到的地震事件进行快速的相似地震和重复地震识别.我们将此方法应用于汶川地震东北端的余震序列,获得了该地区相似地震的分布图像,并对其中存在的重复地震的发震机制进行了讨论分析.%Similar earthquakes are a group of earthquakes which have highly similar waveform at one or more seismic stations, they always occur as clusters in a limited space. Repeating earthquakes, as distinguished similar earthquakes, have nearly identical focal mechanism and overlapped rupture area. They provide an important means for studying the structure and property variation of fault systems. Here we present a method, which is based on similarity distance matrix and hierarchical clustering algorithm, to perform multilevel quick identification of similar earthquakes by one single station. We apply this method to Wenchuan northeast aftershock sequence and obtain the spatial and time distribution of different level similar earthquakes. The ability for detecting repeating earthquakes as well as the possible mechanism of burst-type repeating earthquakes in this region are discussed in the end.

  9. Information theory approach to the Landers aftershock sequence

    Science.gov (United States)

    Jiménez, Abigail

    2015-07-01

    The study of seismicity is becoming increasingly important with recent disasters such as the Gorkha event in Nepal in 2015. Our models mostly depend on the information given by a seismic catalog, such as rates of events and magnitudes. It has also been shown that seismicity presents long-range correlations. Here, we think about how they should be introduced in our models. We divide the region into cells and represent their activity as a time series. We then calculate how much information one cell has about the others in a future time. We find that the higher information content is in each cell with itself. By representing the region as a complex network, we can see that the information between distant cells passes thorough hubs that correspond to the main events. So we conclude that long-range interactions should be introduced as the interaction with the mainshocks, not with other cells except, perhaps, in the nearest neighbourhood.

  10. Aftershocks from the Grybauskaite vs. Putin match / Rokas M. Tracevskis

    Index Scriptorium Estoniae

    Tracevskis, Rokas M.

    2010-01-01

    Leedu presidendi Dalia Grybauskaite ja Venemaa peaministri Vladimir Putini kohtumisest Helsingis, kus räägiti ka Mažeikiai naftatehasest (Orlen Lietuva). Poolale kuuluva Orlen Lietuva võimalikust müügist Venemaale

  11. Pakistan’s Public Debt: The shocks and aftershocks

    OpenAIRE

    Gul, Adnan

    2008-01-01

    Public debt is an important means of bridging government financing gaps. Effective and efficient utilization of public debt can increase economic growth. However, excessive reliance on public debt raises macroeconomic problems. A large gap between revenue and expenditure forces a country to obtain debt. Debt thus obtained further deteriorates expenditure side. High level of public debt holds back the government to meet its macroeconomic objectives of economic growth, price stability and a via...

  12. Estimating Spatially Variable Parameters of the Epidemic Type Aftershock Sequence (ETAS) in California

    Science.gov (United States)

    Nandan, Shyam; Ouillon, Guy; Sornette, Didier; Wiemer, Stefan

    2016-04-01

    The ETAS model is widely employed to model the spatio-temporal distribution of earthquakes, generally using spatially invariant parameters, which is most likely a gross simplification considering the extremely heterogeneous structure of the Earth's crust. We propose an efficient method for the estimation of spatially varying parameters, using an expectation maximization (EM) algorithm and spatial Voronoi tessellations. We assume that each Voronoi cell is characterized by a set of eight constant ETAS parameters. For a given number of randomly distributed cells, Vi=1 to N, we jointly invert the ETAS parameters within each cell using an EM algorithm. This process is progressively repeated several times for a given N (which controls the complexity), which is itself increased incrementally. We use the Bayesian Information Criterion (BIC) to rank all the inverted models given their likelihood and complexity and select the top 1% models to compute the average model at any location. Using a synthetic catalog, we also check that the proposed method correctly inverts the known parameters. We apply the proposed method to earthquakes (M>=3) included in the ANSS catalog that occurred within the time period 1981-2016 in the spatial polygon defined by RELM/CSEP around California. The results indicate significant spatial variation of the ETAS parameters. Using these spatially variable estimates of ETAS parameters, we are better equipped to answer some important questions: (1) What is the seismic hazard (both long- and short-term) in a given region? (2) What kind of earthquakes dominate triggering? (3) are there regions where earthquakes are most likely preceded by foreshocks? Last but not the least, a possible correlation of the spatially varying ETAS parameters with spatially variable geophysical properties can lead to an improved understanding of the physics of earthquake triggering beside providing physical meaning to the parameters of the purely statistical ETAS model.

  13. Woody encroachment over 70 years in South African savannahs: overgrazing, global change or extinction aftershock?

    Science.gov (United States)

    Stevens, Nicola; Erasmus, B F N; Archibald, S; Bond, W J

    2016-09-19

    Woody encroachment in 'open' biomes like grasslands and savannahs is occurring globally. Both local and global drivers, including elevated CO2, have been implicated in these increases. The relative importance of different processes is unresolved as there are few multi-site, multi-land-use evaluations of woody plant encroachment. We measured 70 years of woody cover changes over a 1020 km(2) area covering four land uses (commercial ranching, conservation with elephants, conservation without elephants and communal rangelands) across a rainfall gradient in South African savannahs. Different directions of woody cover change would be expected for each different land use, unless a global factor is causing the increases. Woody cover change was measured between 1940 and 2010 using the aerial photo record. Detection of woody cover from each aerial photograph was automated using eCognitions' Object-based image analysis (OBIA). Woody cover doubled in all land uses across the rainfall gradient, except in conservation areas with elephants in low-rainfall savannahs. Woody cover in 2010 in low-rainfall savannahs frequently exceeded the maximum woody cover threshold predicted for African savannahs. The results indicate that a global factor, of which elevated CO2 is the likely candidate, may be driving encroachment. Elephants in low-rainfall savannahs prevent encroachment and localized megafaunal extinction is a probable additional cause of encroachment.This article is part of the themed issue 'Tropical grassy biomes: linking ecology, human use and conservation'. PMID:27502384

  14. Spatial segmentation characteristic of focal mechanism of aftershock sequence of Wenchuan Earthquake

    Institute of Scientific and Technical Information of China (English)

    WANG QinCai; CHEN ZhangLi; ZHENG SiHua

    2009-01-01

    Moment tensor solutions of 88 earthquakes were determined by using the broadband waveform data recorded in six stations within 450 km around the Wenchuan Earthquake sequence by means of the time domain moment tensor inversion method.It was found that the type of the focal mechanism solution is characteristic of obvious spatial segmentation.There are six segments along the main rupture zone from southwest to northeast,where initially the focal mechanism is of main thrust type,finally of main right-lateral strike-slip type and between these two areas there is a transition zone characterized in multiple types of focal mechanisms appearing in turn.Earthquakes of left-lateral strike-slip type perpendicular to the main rupture zone occurred near Xiaoyudong Town.The stress field of each segment is inversed by means of the FMSI program,and it was found that,along the main rupture zone from southwest to northeast,the direction of the maximum principal stress is gradually changing from near EW to NW-SE,and finally changing back to near EW.

  15. The Lisbon earthquake and its aftershocks in European Enlightenment thinking and planning practice

    Science.gov (United States)

    de Meyer, Dirk

    2010-05-01

    From the Old Testament to Hollywood B-movies, from Sodom and Gomorrah to Los Angeles, the city is the topos of cataclysm. The first city-wide catastrophe that would have a major impact on modern European thinking was the earthquake and tsunami that, in 1755, reduced Lisbon to ruins, and killed about one tenth of its population. This paper will look at the contemporary representations of that catastrophe and at its impact on European Enlightenment thinking and urban planning practices. For Voltaire and Kant the Lisbon disaster had a major impact on the development of there philosophical and esthetical concepts. It strenghtend Rousseau in his anti-urban thinking. For many others it gave way to that modern concept that later will be coined by Paul Valéry in his opening sentence of La crise de l'esprit: "we civilizations now know that we are mortal." I will argue more in detail how, contrary to the rebuilding after the fire of London, where both proposed and realised plans hardly represented a radical new way of conceiving a city plan, the Lisbon reconstruction under the direction of the King's Prime Minister Pombal, can be understood as the start of urban planning as a modern practice — as opposed to earlier, architect-directed Renaissance and Baroque planning. On a smaller scale we will look at the implementation, in the aftermath of the earthquake. of new anti-seismic building techniques in Lisbon's new constructions.

  16. Study of Active Faults in the Three Gorges Dam region by Detecting and Relocating Aftershocks

    Science.gov (United States)

    Huang, R.; Zhu, L.; Xu, Y.

    2014-12-01

    Seismicity in the Three Gorges Dam (TGD) region and its adjacent areas increased dramatically as the water- level of the TGD reservoir rises since its completion in 2003. Accordingly, many efforts have been put forward to quantify the seismicity and geological hazards in the region. However, the precise detective of earthquakes, especially for the minor ones, remains difficulty because of sparse distribution of permanent seismic stations. From December 2013 to June 2014, we deployed 30 three-component broadband seismic stations in the TGD region. During the deployment, we recorded two earthquakes of magnitudes lager than 5.0, one occurred on December 16th 2013 in Badong and another on March 30th 2014 in Zigui. We firstly used a sliding-window cross-correlation (SCC) detection technique to supplement the events catalog from the China Earthquake Networks Center. Over 500 new events with ML lager than 0.5 were detected. We then relocated 502 events out of the total 987 events using the double-difference (DD) relocation algorithm. We also determined moment tensors of some large earthquakes using gCAP. The results clearly show two active faults along Yangtze River with dips of 50 degrees and 90 degrees to a maximum depth of 10 km, respectively. And they also reveal that water might have permeated to a depth of 6 km corresponds to the interface of sediments and metamorphic basement beneath Zigui Basin. We thus preliminarily judge that the quakes are triggered by local stress adjustment resulting of fluctuation of Three Gorges reservoir's loading.

  17. A physical model for aftershocks triggered by dislocation on a rectangular fault

    CERN Document Server

    Console, R

    2005-01-01

    We find the static displacement, stress, strain and the modified Columb failure stress produced in an elastic medium by a finite size rectangular fault after its dislocation with uniform stress drop but a non uniform dislocation on the source. The time-dependent rate of triggered earthquakes is estimated by a rate-state model applied to a uniformly distributed population of faults whose equilibrium is perturbated by a stress change caused only by the first dislocation. The rate of triggered events in our simulations is exponentially proportional to the stress change, but the time at which the maximum rate begins to decrease is variable from fractions of hour for positive stress changes of the order of some MPa, up to more than a year for smaller stress changes. As a consequence, the final number of triggered events is proportional to the stress change. The model predicts that the total number of events triggered on a plane containing the fault is proportional to the 2/3 power of the seismic moment. Indeed, th...

  18. Surviving the aftershock: postearthquake access and adherence to HIV treatment among Haiti's tent residents.

    Science.gov (United States)

    Ghose, Toorjo; Boucicaut, Edner; King, Charles; Doyle, Andrea; Shubert, Virginia

    2013-04-01

    In this research we examined how the conditions of Haiti's tent communities, inhabited by those displaced by the January 10, 2010, earthquake, shaped access and adherence to highly active antiretroviral treatment (HAART) for Haitians with HIV. Conditions in the encampments were marked by unhygienic and cramped living spaces, exposure to the elements, a lack of privacy, unavailability of food and clean water, and a dependence on poorly functioning aid agencies. These conditions shaped access and adherence to HAART by (a) exacerbating the stigma of being HIV positive and undermining mental health; (b) presenting logistical challenges to accessing medical care, storing pills, and ingesting them safely and privately; and (c) sustaining a political economy of aid characterized by unequal treatment in major HAART-dispensing centers, unequal circulation of international funds, and the emergence of alternative medical institutions within encampments that could improve future treatment. Policy and intervention implications are discussed.

  19. Woody encroachment over 70 years in South African savannahs: overgrazing, global change or extinction aftershock?

    Science.gov (United States)

    Stevens, Nicola; Erasmus, B F N; Archibald, S; Bond, W J

    2016-09-19

    Woody encroachment in 'open' biomes like grasslands and savannahs is occurring globally. Both local and global drivers, including elevated CO2, have been implicated in these increases. The relative importance of different processes is unresolved as there are few multi-site, multi-land-use evaluations of woody plant encroachment. We measured 70 years of woody cover changes over a 1020 km(2) area covering four land uses (commercial ranching, conservation with elephants, conservation without elephants and communal rangelands) across a rainfall gradient in South African savannahs. Different directions of woody cover change would be expected for each different land use, unless a global factor is causing the increases. Woody cover change was measured between 1940 and 2010 using the aerial photo record. Detection of woody cover from each aerial photograph was automated using eCognitions' Object-based image analysis (OBIA). Woody cover doubled in all land uses across the rainfall gradient, except in conservation areas with elephants in low-rainfall savannahs. Woody cover in 2010 in low-rainfall savannahs frequently exceeded the maximum woody cover threshold predicted for African savannahs. The results indicate that a global factor, of which elevated CO2 is the likely candidate, may be driving encroachment. Elephants in low-rainfall savannahs prevent encroachment and localized megafaunal extinction is a probable additional cause of encroachment.This article is part of the themed issue 'Tropical grassy biomes: linking ecology, human use and conservation'.

  20. Aftershocks of Chile's Earthquake for an Ongoing, Large-Scale Experimental Evaluation

    Science.gov (United States)

    Moreno, Lorenzo; Trevino, Ernesto; Yoshikawa, Hirokazu; Mendive, Susana; Reyes, Joaquin; Godoy, Felipe; Del Rio, Francisca; Snow, Catherine; Leyva, Diana; Barata, Clara; Arbour, MaryCatherine; Rolla, Andrea

    2011-01-01

    Evaluation designs for social programs are developed assuming minimal or no disruption from external shocks, such as natural disasters. This is because extremely rare shocks may not make it worthwhile to account for them in the design. Among extreme shocks is the 2010 Chile earthquake. Un Buen Comienzo (UBC), an ongoing early childhood program in…

  1. Active source monitoring at the Wenchuan fault zone: coseismic velocity change associated with aftershock event and its implication

    Science.gov (United States)

    Yang, Wei; Ge, Hongkui; Wang, Baoshan; Hu, Jiupeng; Yuan, Songyong; Qiao, Sen

    2014-12-01

    With the improvement of seismic observation system, more and more observations indicate that earthquakes may cause seismic velocity change. However, the amplitude and spatial distribution of the velocity variation remains a controversial issue. Recent active source monitoring carried out adjacent to Wenchuan Fault Scientific Drilling (WFSD) revealed unambiguous coseismic velocity change associated with a local M s5.5 earthquake. Here, we carry out forward modeling using two-dimensional spectral element method to further investigate the amplitude and spatial distribution of observed velocity change. The model is well constrained by results from seismic reflection and WFSD coring. Our model strongly suggests that the observed coseismic velocity change is localized within the fault zone with width of ~120 m rather than dynamic strong ground shaking. And a velocity decrease of ~2.0 % within the fault zone is required to fit the observed travel time delay distribution, which coincides with rock mechanical experiment and theoretical modeling.

  2. Scaled Energies of ML > = 5.1 Aftershocks of the 1999 Chi-Chi, Taiwan, Earthquake Measured from Local Seismograms

    Directory of Open Access Journals (Sweden)

    Ming-Wey Huang and Jeen-Hwa Wang

    2009-01-01

    Full Text Available In this study, we measure the seismic radiation energy, Es, and seismic moment, Mo, of twenty-two larger-sized after shocks with 5.1 < = ML < = 6.5 of the 1999 Ms 7.6 Chi-Chi, Taiwan, earthquake from high-quality digital strong-motion data recorded at stations with epicentral distances of less than 50 km through a method proposed by Andrews (1986. We also eliminate the effects on the measures of Es and Mo due to site amplification and finite frequency band width limitation. Comparison of the values of Mo obtained in this study and those listed in the Harvard CMT catalogue shows that _ method to measure Mo from local seismograms is acceptable. The measured values are Es = 2.0 * 10 ^18 _ 8.9 * 10^21 g cm^2 sec^-2 and Mo = 1.3 * 10^23 _ 1.4 * 10^26 g cm sec^-2 cm^-1, which give the scaled energy to be Es/Mo = 7.4 * 10^-6 _ 2.6 * 10^-4. The scaled energies of the 22 events are dependent upon earthquake magnitude, Ms, when both Es and Mo are evaluated from local seismograms; yet, independent of Ms when Mo is estimated from teleseismic data. Scaled energy slightly depends on the depth, h (in km, through the following form: Es/Mo = 1.92 * 10^-5e^0.09h. In addition, the corner frequency, fc, is also measured. Its value ranges from 0.15 to 1.34. The scaling law between Mo and fc is: Mo ~ fc-3.65.

  3. Three-dimensional kinematic depth migration of converted waves: application to the 2002 Molise aftershock sequence (southern Italy)

    OpenAIRE

    Latorre, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; De Gori, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Amato, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Virieux, J.; LGIT, Université Joseph Fourier, Grenoble, France; Monfret, T.; UMR Geosciences Azur, Sophia Antipolis, France

    2008-01-01

    Migration techniques, currently used in seismic exploration, are still scarcely applied in earthquake seismology due to the poor source knowledge and sparse, irregular acquisition geometries. At the crustal scale, classical seismological studies often perform inversions based on the arrival time of primary phases (P- and S-waves), but seldom exploit other information included in seismic records. Here we show how migration techniques can be adapted to earthquake seismology for converted wave a...

  4. Primitive Rituals, Contemporary Aftershocks: Evocations of the Orientalist ‘Other’ in four productions of 'Le Sacre du printemps'

    Directory of Open Access Journals (Sweden)

    Lucy Weir

    2013-12-01

    Full Text Available This paper situates the original choreography of Sacre as a basis for an ongoing exploration of non-Western themes in modern dance, a persistent fascination with the Orientalist ‘Other,’ before exploring the versions choreographed by Wigman, Bausch and Graham in chronological order of their first performances. In analysing different interpretations of the same score, two themes become apparent: first, that this piece heralded the birth of Modernism in classical dance performance, and second, that the driving anti-classical, anti-traditional rhythms that characterise the piece communicate an enduring interest in primitive aesthetics. Accordingly, this discussion takes Nijinsky’s Sacre as a starting point in re-evaluating the influence of primitivism and Otherness on contemporary dance, and represents an early indication of the significance of the Saidian, non-Western ‘Other’ in shaping the evolution of avant-garde dance.

  5. Limits of Declustering Methods for Disentangling Exogenous from Endogenous Events in Time Series with Foreshocks, Main shocks and Aftershocks

    CERN Document Server

    Sornette, D

    2009-01-01

    Many time series in natural and social sciences can be seen as resulting from an interplay between exogenous influences and an endogenous organization. We use a simple (ETAS) model of events occurring sequentially, in which future events are influenced (partially triggered) by past events to ask the question of how well can one disentangle the exogenous events from the endogenous ones. We apply both model-dependant and model-independent stochastic declustering methods to reconstruct the tree of ancestry and estimate key parameters. In contrast with previously reported positive results, we have to conclude that declustered catalogs are rather unreliable for the synthetic catalogs that we have investigated, which contains of the order of thousands of events, typical of realistic applications. The estimated rates of exogenous events suffer from large errors. The key branching ratio $n$, quantifying the fraction of events that have been triggered by previous events, is also badly estimated in general from declust...

  6. Operation Aftershock: the U.S. military disaster response to the Yogyakarta earthquake May through June 2006.

    Science.gov (United States)

    Amundson, Dennis; Lane, David; Ferrara, Elizabeth

    2008-03-01

    The U.S. military has recently been involved in many humanitarian assistance and disaster response missions around the world. This newfound role is in response to the U.S. government's desire to use "medical diplomacy" rather than "military might" to shape its relationship with foreign governments. With each of these humanitarian assistance and disaster response missions, the U.S. military has learned how to more rapidly insert desperately needed services and skill sets into disaster-struck communities, how to arrange for in-country services (translation services, transportation, etc.) that cannot be readily brought in, and how to work closely with foreign governments and nongovernmental organizations to determine their needs and expectations without the U.S. military appearing as if it were trying to establish a permanent presence.

  7. No Major Economic Aftershocks The tragic earthquake shouldn't have much impact on the economy-but problems remain

    Institute of Scientific and Technical Information of China (English)

    BRADLEY GARDNER

    2008-01-01

    @@ While rescue workers and emergency service crews continue sifting through the rubble caused by the devastating earthquake in Sichuan Province last month, financial institutions have been busy figuring out the financial implications of economy, and what can be done to manage the impact.

  8. Reality Aftershock and How to Avert It: Second-Year Teachers' Experiences of Support for Their Professional Development

    Science.gov (United States)

    J.Hobson, Andrew; Ashby, Patricia

    2012-01-01

    Drawing on analyses of data from a large-scale, mixed-method study of new entrants to the teaching profession in England, this article presents new findings on beginner teachers' experiences of post-induction support for their professional development, about which little was previously known. As well as highlighting positive and negative aspects…

  9. Estimation of seismic moments from local magnitudes and coda durations for the Cairo earthquake aftershocks recorded at Kottamyia (KEG) Broadband station

    OpenAIRE

    M. F. Abdelwahed; H. M. Hussein; M. M. Dessokey; E. M. Abdelrahman

    2003-01-01

    The spectral analysis of fifty-five KEG VBB records from the October 12, 1992 Cairo earthquake source region was performed to obtain the seismic moment. We obtained this parameter in turn to develop empirical local magnitude (ML), seismic moment (Mo), coda duration (D) relations for that region. In this study the data consist of Lg-waves on the vertical component seismograms for the recorded earthquakes with ML ranging from 1.7 to 4.7. The derived empirical relation betwee...

  10. 平面上处理科氏力余震效应(续一)%Operation of Aftershock Effect of Corioli' s Force on Horizontal Plane

    Institute of Scientific and Technical Information of China (English)

    郭增建

    2012-01-01

    我国大陆走滑型震源居多。故本文讨论任意走向的走滑型震源的科氏力余震效应。%Earthquakes with strike slip source are predominant in the mainland of China. Afiershock effect of Corioli' s ibrce of strike slip source with random direction is discussed in this paper.

  11. Response of a tall building far from the epicenter of the 11 March 2011 M 9.0 Great East Japan earthquake and aftershocks

    Science.gov (United States)

    Celebi, Mehmet; Okawa, Izuru; Kashima, Toshidate; Koyama, Shin; Iiba, Masanori

    2012-01-01

    The 11 March 2011 M 9.0 Great East Japan earthquake generated significant long-duration shaking that propagated hundreds of kilometers from the epicenter and affected urban areas throughout much of Honshu. Recorded responses of a tall building at 770 km from the epicenter of the mainshock and other related or unrelated events show how structures sensitive to long-period motions can be affected by distant sources. Even when the largest peak input motions to the building is about 3% g, the strong-shaking duration was about 140 s. The 300- to 1000-s prolonged responses of the building are primarily due to a combination of site resonance (e.g. structural fundamental frequency ~0.15 Hz and site frequency ~0.13–0.17 Hz) and low damping (~1–2%) of the structure. Response modification technologies can improve the response of the building during future earthquakes. The need-to-consider risks to such built environments from distant sources are emphasized.

  12. 余震地区桥梁施工过程易损性分析%THE VULNERABILITY ANALYSIS OF BRIDGE CONSTRUCTION IN AFTERSHOCK AREA

    Institute of Scientific and Technical Information of China (English)

    2016-01-01

    震后灾区重建工作中,桥梁等关键基础设施应迅速修复或重建,以满足灾区交通需求.施工过程中,桥梁整体结构体系尚未形成,且短期内余震频发,将严重威胁着结构安全.通过余震序列早期阶段的统计结果,回归出余震发生概率模型,基于概率的地震危险性分析理论(PSHA),提出了桥梁施工过程中易损性指标与考虑施工过程的易损性模型.以汶川地震为例,对一座山区高墩施工整个过程的易损性展开分析,结果表明:余震地区桥梁施工易产生开裂损伤破坏,影响结构耐久性,有必要对强震过后灾区桥梁施工阶段的地震损害风险做专门的评估.

  13. The west Andaman fault and its influence on the aftershock pattern of the recent megathrust earthquakes in the Andaman-Sumatra region

    Digital Repository Service at National Institute of Oceanography (India)

    KameshRaju, K.A.; Murty, G.P.S.; Amarnath, D.; MohanKumar, M.L.

    lithospheric scale boundary and together with other tectonic elements modulates the occurrence of large earthquakes and their rupture pattern. The active strike-slip motion along the WAF, presence of backarc spreading coupled with increased obliquity...

  14. Ground-motion site effects from multimethod shear-wave velocity characterization at 16 seismograph stations deployed for aftershocks of the August 2011 Mineral, Virginia earthquake

    Science.gov (United States)

    Stephenson, William J.; Odum, Jackson K.; McNamara, Daniel E.; Williams, Robert A.; Angster, Stephen J

    2014-01-01

    We characterize shear-wave velocity versus depth (Vs profile) at 16 portable seismograph sites through the epicentral region of the 2011 Mw 5.8 Mineral (Virginia, USA) earthquake to investigate ground-motion site effects in the area. We used a multimethod acquisition and analysis approach, where active-source horizontal shear (SH) wave reflection and refraction as well as active-source multichannel analysis of surface waves (MASW) and passive-source refraction microtremor (ReMi) Rayleigh wave dispersion were interpreted separately. The time-averaged shear-wave velocity to a depth of 30 m (Vs30), interpreted bedrock depth, and site resonant frequency were estimated from the best-fit Vs profile of each method at each location for analysis. Using the median Vs30 value (270–715 m/s) as representative of a given site, we estimate that all 16 sites are National Earthquake Hazards Reduction Program (NEHRP) site class C or D. Based on a comparison of simplified mapped surface geology to median Vs30 at our sites, we do not see clear evidence for using surface geologic units as a proxy for Vs30 in the epicentral region, although this may primarily be because the units are similar in age (Paleozoic) and may have similar bulk seismic properties. We compare resonant frequencies calculated from ambient noise horizontal:vertical spectral ratios (HVSR) at available sites to predicted site frequencies (generally between 1.9 and 7.6 Hz) derived from the median bedrock depth and average Vs to bedrock. Robust linear regression of HVSR to both site frequency and Vs30 demonstrate moderate correlation to each, and thus both appear to be generally representative of site response in this region. Based on Kendall tau rank correlation testing, we find that Vs30 and the site frequency calculated from average Vs to median interpreted bedrock depth can both be considered reliable predictors of weak-motion site effects in the epicentral region.

  15. Coulomb stress change sensitivity due to variability in mainshock source models and receiving fault parameters: A case study of the 2010-2011 Christchurch, New Zealand, earthquakes

    Science.gov (United States)

    Zhan, Zhongwen; Jin, Bikai; Wei, Shengji; Graves, Robert W.

    2011-01-01

    Strong aftershocks following major earthquakes present significant challenges for infrastructure recovery as well as for emergency rescue efforts. A tragic instance of this is the 22 February 2011 Mw 6.3 Christchurch aftershock in New Zealand, which caused more than 100 deaths while the 2010 Mw 7.1 Canterbury mainshock did not cause a single fatality (Figure 1). Therefore, substantial efforts have been directed toward understanding the generation mechanisms of aftershocks as well as mitigating hazards due to aftershocks. Among these efforts are the prediction of strong aftershocks, earthquake early warning, and aftershock probability assessment. Zhang et al. (1999) reported a successful case of strong aftershock prediction with precursory data such as changes in seismicity pattern, variation of b-value, and geomagnetic anomalies. However, official reports of such successful predictions in geophysical journals are extremely rare, implying that deterministic prediction of potentially damaging aftershocks is not necessarily more scientifically feasible than prediction of mainshocks.

  16. Characteristics of the May 12,2008 Wenchuan Ms8.0 Earthquake Sequence and Discussion on Relevant Problems

    Institute of Scientific and Technical Information of China (English)

    Jiang Haikun; Li Mingxiao; Wu Qiong; Song Jin

    2009-01-01

    The aftershock activity of the May 12, 2008 Wenchuan Ms8.0 Earthquake Sequence shows an obvious segmented feature. Most of the large aftershocks were distributed in the north and south parts of the aftershock zone. Thrusting was dominant with a small amount of strike-slip component in the south part. The aftershock activity decayed gradually, presenting the sequence features of a mainshock-aftershock pattern. The north part was the ending area of the maiushock fracture where strike-slipping was dominant, showing an obvious swarm feature. Therefore it became the major area for large aftershocks. The modulation of the earth tide on aftershock activity is remarkable; most large aftershocks occur during the period of flood and neap tide. The time period around 16:00 was the dominant occurring time for large aftershocks. The p-value, a parameter of modified Omori formula, increases gradually with time, and reaches about 1 at the end. Based on previous study, the sequence patterns, magnitude of maximum aftershock, as well as the duration of aftershock activity has been discussed. The primary results also show that the magnitude difference between the maiushockand the maximum aftershock is proportional to the rupture size of the maiushock for huge earthquakes of about Ms8.0. This means that when the magnitudes of the earthquakes are nearly the same, large rupture size corresponds to sufficient energy release.

  17. Spatio-temporal variation and focal mechanism of the Wenchuan Afs8.0 earthquake sequence

    Institute of Scientific and Technical Information of China (English)

    Wanzheng Cheng; Zhiwei Zhang; Xiang Ruan

    2009-01-01

    Based on abundant aftershock sequence data of the Wenchuan Ms8.0 earthquake on May 12, 2008, we studied the spatio-temporal variation process and segmentation rupture characteristic. Dense aftershocks distribute along Longmen-shan central fault zone of NE direction and form a narrow strip with the length of 325 km and the depth between several and 40 km. The depth profile (section of NW direction) vertical to the strike of aftershock zone (NE direction) shows anisomer-ous wedgy distribution characteristic of aftershock concentrated regions; it is related to the force form of the Longmenshan nappe tectonic belt. The stronger aftershocks could be divided into northern segment and southern segment apparently and the focal depths of strong aftershocks in the 50 km area between northern segment and southern segment are shallower. It seems like 'to be going to rupture' segment. We also study focal mechanisms and segmentation of strong aftershocks. The principal compressive stress azimuth of aftershock area is WNW direction and the faulting types of aftershocks at southern and northern segment have the same proportion. Because aftershocks distribute on different secondary faults, their focal mechanisms present complex local tectonic stress field. The faulting of seven strong earthquakes on the Longmenshan central fault is mainly characterized by thrust with the component of right-lateral strike-slip. Meantime six strong aftershocks on the Longmenshan back-range fault and Qingchuan fault present strike-slip faulting. At last we discuss the complex segmentation rupture mechanism of the Wenchuan earthquake.

  18. ELF electromagnetic emissions observed by the DEMETER satellite before the 2008 MS8.0 Wenchuan earthquake and its aftershocks%汶川地震及其余震期间的ELF电磁异常

    Institute of Scientific and Technical Information of China (English)

    张蓓; 曾中超; 方广有; 王东峰

    2010-01-01

    @@ 近些年来利用卫星技术观测地震前的电磁扰动已得到地震学界的广泛关注, 并被认为是研究地震电磁前兆的有效途径之一(Larkina et al, 1989; Parrot, 1994; Serebryakova et al, 1992; Molchanov et al, 1993; Nemec et al, 2008).

  19. Structural context of the 2015 pair of Nepal earthquakes (Mw 7.8 and Mw 7.3): an analysis based on slip distribution, aftershock growth, and static stress changes

    Science.gov (United States)

    Poujol, Marc; Pitra, Pavel; Van Den Driessche, Jean; Tartèse, Romain; Ruffet, Gilles; Paquette, Jean-Louis; Poilvet, Jean-Charles

    2016-07-01

    One of the striking features that characterise the late stages of the Variscan orogeny is the development of gneiss and migmatite domes, as well as extensional Late Carboniferous and Permian sedimentary basins. It remains a matter of debate whether the formation of domes was related to the well-documented late orogenic extension or to the contractional tectonics that preceded. Migmatization and magmatism are expected to predate extension if the domes are compression-related regional anticlines, but they must both precede and be contemporaneous with extension if they are extensional core complexes. In the Montagne Noire area (southern French Massif Central), where migmatization, magmatism and the deformation framework are well documented, the age of the extensional event was unequivocally constrained to 300-290 Ma. Therefore, dating migmatization in this area is a key point for discriminating between the two hypotheses and understanding the Late Palaeozoic evolution of this part of the Variscan belt. For this purpose, a migmatite and an associated anatectic granite from the Montagne Noire dome were dated by LA-ICP-MS (U-Th-Pb on zircon and monazite) and laser probe 40Ar-39Ar (K-Ar on muscovite). Although zircon did not record any Variscan age unequivocally related to compression (380-330 Ma), two age groups were identified from the monazite crystals. A first event, at ca. 319 Ma (U-Th-Pb on monazite), is interpreted as a first stage of migmatization and as the emplacement age of the granite, respectively. A second event at ca. 298-295 Ma, recorded by monazite (U-Th-Pb) and by the muscovite 40Ar-39Ar system in the migmatite and in the granite, could be interpreted as a fluid-induced event, probably related to a second melting event identified through the syn-extensional emplacement of the nearby Montalet leucogranite ca. 295 Ma ago. The ages of these two events post-date the Variscan compression and agree with an overall extensional context for the development of the Montagne Noire dome-shaped massif. Comparison of these results with published chemical (EPMA) dating of monazite from the same rocks demonstrates that the type of statistical treatment applied to EPMA data is crucial in order to resolve different monazite age populations.

  20. 主余震序列作用下钢混框架结构损伤与抗震性能分析%Damage and seismic performance analysis of RC frame structures under mainshock-aftershock earthquake sequences

    Institute of Scientific and Technical Information of China (English)

    张沛洲; 康谨之; 欧进萍

    2014-01-01

    文中提出一种基于主余震序列分析结构抗震性能的方法(MASA),并讨论和给出该方法中各个参数的确定原则,接着应用该方法分别对某单自由度结构与不同延性的多层结构进行主余震序列分析,研究其累积损伤及抗震性能.分析结果表明本文提出的MASA方法简单实用,参数意义明确,为分析和评价结构在主余震序列或其他序列作用下的累积损伤及抗震性能提供了一种新的思路;应用该方法分析得知余震对钢筋混凝土框架结构的抗震性能影响显著,尤其是延性较低的结构,且其影响程度与主震震级直接相关.

  1. Anomalous Power Law Distribution of Total Lifetimes of Branching Processes Relevant to Earthquakes

    CERN Document Server

    Saichev, A

    2004-01-01

    We consider a branching model of triggered seismicity, the ETAS (epidemic-type aftershock sequence) model which assumes that each earthquake can trigger other earthquakes (``aftershocks''). An aftershock sequence results in this model from the cascade of aftershocks of each past earthquake. Due to the large fluctuations of the number of aftershocks triggered directly by any earthquake (``productivity'' or ``fertility''), there is a large variability of the total number of aftershocks from one sequence to another, for the same mainshock magnitude. We study the regime where the distribution of fertilities $\\mu$ is characterized by a power law $\\sim 1/\\mu^{1+\\gamma}$ and the bare Omori law for the memory of previous triggering mothers decays slowly as $\\sim 1/t^{1+\\theta}$, with $0 < \\theta <1$ relevant for earthquakes. Using the tool of generating probability functions and a quasistatic approximation which is shown to be exact asymptotically for large durations, we show that the density distribution of to...

  2. Bayesian estimation of the Modified Omori Law parameters for the Iranian Plateau

    Science.gov (United States)

    Ommi, S.; Zafarani, H.; Smirnov, V. B.

    2016-07-01

    The forecasting of large aftershocks is a preliminary and critical step in seismic hazard analysis and seismic risk management. From a statistical point of view, it relies entirely on the estimation of the properties of aftershock sequences using a set of laws with well-defined parameters. Since the frequentist and Bayesian approaches are common tools to assess these parameter values, we compare the two approaches for the Modified Omori Law and a selection of mainshock-aftershock sequences in the Iranian Plateau. There is a general agreement between the two methods, but the Bayesian appears to be more efficient as the number of recorded aftershocks decreases. Taking into account temporal variations of the b-value, the slope of the frequency-size distribution, the probability for the occurrence of strong aftershock, or larger main shock has been calculated in a finite time window using the parameters of the Modified Omori Law observed in the Iranian Plateau.

  3. Growth of a Structure Connecting the 2010 M 7.2 El Mayor - Cucapah Rupture with the Elsinore Faul

    Science.gov (United States)

    Donnellan, A.; Parker, J. W.

    2015-12-01

    The M 7.2 El Mayor - Cucapah earthquake occurred on 4 April 2010 in the northern part of Baja, Mexico. The rupture extended about 120 km from near the northern tip of the Gulf of California to the US - Mexican border south of the Elsinore fault zone. Most of the aftershocks occurred within days of the main event. On 14 June 2010 a M 5.7 late aftershock occurred 8 km southeast of Ocotillo, CA and is the largest aftershock in the sequence. The right-lateral event occurred in a cluster of aftershocks and was followed by its own aftershock sequence. UAVSAR data were collected for a swath covering the aftershock on 13 April, 2010 just after the El Mayor - Cucapah earthquake and before the earthquake on 21 October 2009. The line was reflown 1 July 2010 after the M 5.7 14 June 2010 aftershock. Data have been continued to be collected semi yearly to yearly since then. Repeat Pass Interferomety (RPI) products spanning the aftershock show the growth of a lineament that with an azimuth of 121.5° or a strike of -58.5°. The interferograms suggest that a stepover develops following the earthquake. The epicenter of the M 5.7 aftershock is proximal to the linear discontinuity in the postseismic interferogram and the mechanism of the event is consistent with slip on this stepover. Inversions for slip on the northeast linear structure that steps west of the mainshock rupture yield a moment magnitude ranging from 5.5 - 5.8, which is consistent with the magnitude of the aftershock. Slip occurs at a depth of 2-10 km on a steeply dipping fault.

  4. 利用格林函数库计算2008年青海大柴旦6.4级地震的余震震源机制%Using Green Function Database and Quick Moment Tensor Inversion Calculating the Focal Mechanism Solution of Aftershocks of Dachaidan Ms6.4 Earthquake in 2008 in Qinghai Province

    Institute of Scientific and Technical Information of China (English)

    刘薇; 张晓清; 石玉成; 文勇; 赵燕杰

    2012-01-01

    通过建立格林函数库可以降低在矩张量反演过程中的计算量,提高获取中小地震震源机制解的速度.运用此方法对2008年11月10日青海大柴旦6.4级地震的地震序列中ML.≥2.0的98个余震进行了震源机制解,在小震矩张量反演中克服了模拟资料无法准确得到小震震源机制解的缺陷,初步探索了运用区域数字地震台网资料确定中小地震震源机制解的方法,并对计算结果给出了解释.%Through establishing the Green function database, the calculation work in the moment tensors inversion method is reduced, and speed for getting focal mechanism solutions of moderate-small earthquakes is improved. Using this method the focal mechanism solutions for 98 events with ML≥2. 0 in 2008, in Qinghai province are calculated. The result is discussed also. The research work is helpful to using regional digital seismograph network data for giving focal mechanism solution of small earthquakes.

  5. Seismotectonic framework of the 2010 February 27 Mw 8.8 Maule, Chile earthquake sequence

    Science.gov (United States)

    Hayes, Gavin P.; Bergman, Eric; Johnson, Kendra J.; Benz, Harley M.; Brown, Lucy; Meltzer, Anne S.

    2013-01-01

    After the 2010 Mw 8.8 Maule earthquake, an international collaboration involving teams and instruments from Chile, the US, the UK, France and Germany established the International Maule Aftershock Deployment temporary network over the source region of the event to facilitate detailed, open-access studies of the aftershock sequence. Using data from the first 9-months of this deployment, we have analyzed the detailed spatial distribution of over 2500 well-recorded aftershocks. All earthquakes have been relocated using a hypocentral decomposition algorithm to study the details of and uncertainties in both their relative and absolute locations. We have computed regional moment tensor solutions for the largest of these events to produce a catalogue of 465 mechanisms, and have used all of these data to study the spatial distribution of the aftershock sequence with respect to the Chilean megathrust. We refine models of co-seismic slip distribution of the Maule earthquake, and show how small changes in fault geometries assumed in teleseismic finite fault modelling significantly improve fits to regional GPS data, implying that the accuracy of rapid teleseismic fault models can be substantially improved by consideration of existing fault geometry model databases. We interpret all of these data in an integrated seismotectonic framework for the Maule earthquake rupture and its aftershock sequence, and discuss the relationships between co-seismic rupture and aftershock distributions. While the majority of aftershocks are interplate thrust events located away from regions of maximum co-seismic slip, interesting clusters of aftershocks are identified in the lower plate at both ends of the main shock rupture, implying internal deformation of the slab in response to large slip on the plate boundary interface. We also perform Coulomb stress transfer calculations to compare aftershock locations and mechanisms to static stress changes following the Maule rupture. Without the

  6. Is Earthquake Triggering Driven by Small Earthquakes?

    CERN Document Server

    Helmstetter, A

    2002-01-01

    Using a catalog of seismicity for Southern California, we measure how the number of triggered earthquakes increases with the earthquake magnitude. The trade-off between this scaling and the distribution of earthquake magnitudes controls the relative role of small compared to large earthquakes. We show that seismicity triggering is driven by the smallest earthquakes, which trigger fewer aftershocks than larger earthquakes, but which are much more numerous. We propose that the non-trivial scaling of the number of aftershocks emerges from the fractal spatial distribution of aftershocks.

  7. 2011 Christchurch, New Zealand Images

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The South Island, New Zealand earthquake occurred as part of the aftershock sequence of the M 7.0 September 3, 2010 Darfield, NZ earthquake. It involved...

  8. 1886 Charleston, USA Images

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Generally referred to as August 31, 1886, as the earthquake occurred at 9:51 pm local time. Eight minutes later there was a severe aftershock. This was the most...

  9. 1988 Leninakan-Spitak-Kirovakan, Armenia Images

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The magnitude 6.9 earthquake shook northwestern Armenia, and was followed four minutes later by a magnitude 5.8 aftershock. The earthquakes affected an area 80...

  10. Renormalization of the ETAS branching model of triggered seismicity from total to observable seismicity

    CERN Document Server

    Saichev, A

    2005-01-01

    Several recent works point out that the crowd of small unobservable earthquakes (with magnitudes below the detection threshold $m_d$) may play a significant and perhaps dominant role in triggering future seismicity. Using the ETAS branching model of triggered seismicity, we apply the formalism of generating probability functions to investigate how the statistical properties of observable earthquakes differ from the statistics of all events. The ETAS (epidemic-type aftershock sequence) model assumes that each earthquake can trigger other earthquakes (``aftershocks''). An aftershock sequence results in this model from the cascade of aftershocks of each past earthquake. The triggering efficiency of earthquakes is assumed to vanish below a lower magnitude limit $m_0$, in order to ensure the convergence of the theory and may reflect the physics of state-and-velocity frictional rupture. We show that, to a good approximation, the ETAS model is renormalized onto itself under what amounts to a decimation procedure $m_...

  11. Power Monopoly Gets a Shock, Foreigners Plug in

    Institute of Scientific and Technical Information of China (English)

    GuMing

    2003-01-01

    China's power industry experienced a violent shakeup at the end of 2002 and is likely to suffer several aftershocks this year, analysts said. Some wonder whether it is time for more foreign capital to enter the industry.

  12. Statistical quantification of time-dependence in the static Coulomb model

    Science.gov (United States)

    Bhloscaidh, M. Nic; McCloskey, J.; Nalbant, S. S.; Bean, C. J.

    2012-04-01

    Statistical tests of the consistency of observed aftershock sequences with the change in Coulomb Failure Function are based on evaluation of the Coulomb index for the aftershock sequence given the calculated spatial distribution of the change in CFF. Tests of the statistical significance of the results require a choice of null hypothesis, which involves estimating the number of aftershocks that would be expected to occur on regions where dCFF>0 by chance (in general it is assumed that this quantity is static). A null hypothesis of this nature will predict a number of "successes" (i.e. events on CFF>0) that is binomially distributed with parameter p, where p is the probability of an event to occur on CFF>0. Here, p depends on the distribution of seismicity that we assume would have occurred in the aftershock period had there been no mainshock. Using the normal approximation to the binomial, the observation can then be expressed as the number of standard deviations from the expected number of successes, z (a transformation to the standard normal distribution), given the chosen null hypothesis. It is also convenient to apply this method to the investigation of suppression of seismicity in regions where CFFdistribution of background seismicity with respect to the dCFF field, which is difficult to estimate with confidence, is strongly dependent on the location of structure and is therefore heterogeneous over the region of interest. Aftershock distributions from other events preceding the mainshock of interest contribute to the observed seismicity in the aftershock period. This introduces spatial heterogeneity (which is not static in time) into the aftershock distribution, which is again unrelated to the dCFF field from the mainshock. Finally, aftershocks in the distribution have their own aftershock sequences. Particularly for large events, this could have the effect of amplifying contributions to either positive or negative dCFF, causing the statistical significance of

  13. A detailed study of the Pernik (Bulgaria) seismic sequence of 2012

    Science.gov (United States)

    Raykova, Plamena; Solakov, Dimcho; Simeonova, Stela; Dimitrova, Liliya

    2014-05-01

    A detailed study of the Pernik (Bulgaria) seismic sequence of 2012 D.Solakov, S.Simeonova ,I. Georgiev, P.Raykova, L.Dimitrova and V.Protopopova National Institute of Geophysics, Geodesy and Geography-BAS, Sofia, Bulgaria The spatial and temporal clustering of aftershocks is the dominant non-random element of seismicity, so that when aftershocks are removed, the remaining activity can be modelled (as first approximation) as a Poisson process. The properties of aftershock sequences (distinct cluster, for example; even aftershocks can have aftershocks) allow time-dependent prediction of aftershock probabilities. Consideration of recent earthquake sequences suggests that aftershocks to large earthquakes although they are still, by definition, smaller events, can be very damaging and should be addressed in emergence planning scenarios. Because of the factors such as location and radiation pattern and the cumulative nature of building damage, aftershocks can cause more damage than the main shock. An earthquake of moment magnitude 5.6 hit Sofia seismic zone, on May 22nd, 2012. The earthquake occurred in the vicinity of Pernik city, at about 25 km south west of the city of Sofia (the capital of Bulgaria). The event was followed by intensive activity. The active area is situated in the central part of western Bulgaria. That is the most populated (more than 1.2 mil. inhabitants), industrial and cultural region of Bulgaria. Seismicity in the zone is related to the marginal neotectonic faults of Sofia graben. The boundaries of the graben are represented by SE-NW fault system with expressive neotectonic activity. This zone is characterized by shallow earthquakes. The strongest known event in the region is the 1858 quake with intensity I0=9-10 MSK. The 1858 earthquake caused heavy destruction in the city of Sofia and the appearance of thermal spring. It is worth mentioning that the seismic sequence of May 2912 occurred in an area characterized by a long quiescence (of 95 years

  14. The 2007 M7.7 Tocopilla northern Chile earthquake sequence: Implications for along-strike and downdip rupture segmentation and megathrust frictional behavior

    OpenAIRE

    Bernd Schurr; Günter Asch; Matthias Rosenau; Rongjiang Wang; Onno Oncken; Barrientos, S.; Salazar, P.; Vilotte, J. P.

    2012-01-01

    In 2007 a M7.7 earthquake occurred near the town of Tocopilla within the northern Chile seismic gap. Mainshock slip, derived from coseismic surface deformation, was confined to the depth range between 30-55 km. We relocated ~1100 events during six months before and one week after the mainshock. Aftershock seismicity is first congruent to the mainshock slip and then it spreads offshore west and northwest of Mejillones Peninsula (MP). Waveform modeling for 38 aftershocks reveals source mechanis...

  15. A Short Term Seismic Hazard Assessment in Christchurch, New Zealand, After the M 7.1, 4 September 2010 Darfield Earthquake: An Application of a Smoothing Kernel and Rate-and-State Friction Model

    OpenAIRE

    Chung-Han Chan; Yih-Min Wu; and Ting-Li Lin

    2012-01-01

    The Mw 6.3, 21 February 2011 Christchurch, New Zealand, earthquake is regarded as an aftershock of the M 7.1, 4 September 2010 Darfield earthquake. However, it caused severe damage in the downtown Christchurch. Such a circumstance points out the importance of an aftershock sequence in seismic hazard evaluation and suggests the re-evaluation of a seismic hazard immediately after a large earthquake occurrence. For this purpose, we propose a probabilistic seismic hazard assessment (PSHA), which ...

  16. The Perugia (Italy) earthquake of April 29,1984: a seismic survey

    OpenAIRE

    Haessler, H.; Gaulon, R.; Rivera, L.; Console, R.; Frogneux, M.; Gasparini, G.; Martel, L.; Patau, G.; Siciliano, M.; A. Cisternas

    1988-01-01

    International audience A field study after the Perugia earthquake of 29 April 1984 provided more than 300 well-recorded events concentrated within two parallel clusters separated by 2 km and trending along the Apenninic direction. The length of the aftershock area is 14 km, focal depths being shallower than 8 km. Relocation of the main event places the epicenter at the southern end of the aftershock zone, suggesting a rupture propagation from SE to NW. Most focal mechanisms are consistent ...

  17. High frequency fall-off of source spectra using Q-free spectra estimation

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    A broadband seismogram may be represented by a convolution of source time function, the propagation operator and the scattering/attenuation operator. As the propagation operator is frequency-independent, and the scattering/attenuation effect may be described by a Q-factor depending on frequency via Q-1=Q-11+(Q2ω)-1, considering a combination of the displacement spectra, the source spectra may directly be estimated, in which the contribution of the Q-value may be eliminated automatically. Using this algorithm, the near-source broadband seismograms of five aftershocks of the 1988 Lancang-Gengma, Yunnan Province, China earthquake were processed. The results for the ML=3.0 and ML=3.5 aftershocks show that for the same earthquake, similar high-frequency fall-off may be obtained from different recording stations. The result for the MS=6.7 aftershock shows that consistent source parameters may be gotten from different seismic stations. The parameters estimated also agree with the results obtained by empirical Green's function approach. The high-frequency spectra of the aftershocks exhibit a typical f-γ fall-off. For the ML=3.0 aftershock,γ≈3 ; for the MS=6.7 and ML=4.0 aftershocks,γ≈2; and for the ML=3.5 and ML=3.0 aftershocks, γ≈2.5. The corner frequency of the MS=6.7 aftershock indicates that it has a small source dimension, implying that it may come from the rupture of a small but strong barrier.

  18. Determination of Fault Plane and Rupture Direction of the April 18, 2008 Earthquake, Mt. Carmel, Illinois

    Science.gov (United States)

    Yang, H.; Chu, R.; Zhu, L.

    2008-12-01

    We located a large number of aftershocks to determine the fault plane of the April 18, 2008, Illinois earthquake.Those aftershocks were detected by a sliding-window cross correlation (SCC) technique that we developed in this study. We applied this technique to continuous waveforms recorded by the Cooperative New Madrid Seismic Network stations. It detected 86 aftershocks down to magnitude 0.8 in the two-week time window following the mainshock, which is twice more than the number of aftershocks reported by the seismic network. Most aftershocks happened within 24 hours of the mainshock. We then relocated all events by the double-difference relocation algorithm. Accurate differential P- and S-wave arrival times were obtained by waveform cross correlation. After relocation, all events are located in a SW-NE line which delineates an N40E oriented strike-slip fault. The fault is nearly vertical down to ~20 km. To determine the direction of mainshock rupture propagation, we used waveforms of a small magnitude aftershock as the empirical Green's functions to estimate source time function of the mainshock. Results show that the rupture propagated nearly horizontally to the north in the fault plane oriented in N30E, consistent with the fault plane determined by earthquakes locations.

  19. Using the 2011 Mw9.0 Tohoku earthquake to test the Coulomb stress triggering hypothesis and to calculate faults brought closer to failure

    Science.gov (United States)

    Toda, Shinji; Lin, Jian; Stein, Ross S.

    2011-01-01

    The 11 March 2011 Tohoku Earthquake provides an unprecedented test of the extent to which Coulomb stress transfer governs the triggering of aftershocks. During 11-31 March, there were 177 aftershocks with focal mechanisms, and so the Coulomb stress change imparted by the rupture can be resolved on the aftershock nodal planes to learn whether they were brought closer to failure. Numerous source models for the mainshock have been inverted from seismic, geodetic, and tsunami observations. Here, we show that, among six tested source models, there is a mean 47% gain in positively-stressed aftershock mechanisms over that for the background (1997-10 March 2011) earthquakes, which serve as the control group. An aftershock fault friction of 0.4 is found to fit the data better than 0.0 or 0.8, and among all the tested models, Wei and Sladen (2011) produced the largest gain, 63%. We also calculate that at least 5 of the seven large, exotic, or remote aftershocks were brought ≥0.3 bars closer to failure. With these tests as confirmation, we calculate that large sections of the Japan trench megathrust, the outer trench slope normal faults, the Kanto fragment beneath Tokyo, and the Itoigawa-Shizuoka Tectonic Line, were also brought ≥0.3 bars closer to failure.

  20. Coulomb static stress changes before and after the 23 October 2011 Van, eastern Turkey, earthquake (MW= 7.1: implications for the earthquake hazard mitigation

    Directory of Open Access Journals (Sweden)

    M. Utkucu

    2013-07-01

    Full Text Available Coulomb stress changes before and after the 23 October 2011 Van, eastern Turkey, earthquake have been analysed using available data related to the background and the aftershock seismicity and the source faults. The coseismic stress changes of the background seismicity had slightly promoted stress over the rupture plane of the 2011 Van earthquake, while it yielded a stress shadow over the Gürpı nar Fault which has been argued to have produced the 7 April 1646 Van earthquake. The stress shadow over the Gürpi nar fault has become more pronounced following the occurrence of the 2011 Van earthquake, meaning that the repetition of the 1646 Van earthquake has been further suppressed. Spatial distribution and source mechanisms of the 2011 Van earthquake's aftershocks have been utilised to define four clusters with regard to their relative location to the mainshock rupture. In addition, the aftershock sequence covers a much broader area toward the northeast. Correlations between the observed spatial patterns of the aftershocks and the coseismic Coulomb stress changes caused by the mainshock are determined by calculating the stress changes over both optimally oriented and specified fault planes. It is shown here that there is an apparent correlation between the mainshock stress changes and the observed spatial pattern of the aftershock occurrence, demonstrating the usefulness of the stress maps in constraining the likely locations of the upcoming aftershocks and mitigating earthquake hazard.

  1. Spatio-temporal point pattern analysis on Wenchuan strong earthquake

    Institute of Scientific and Technical Information of China (English)

    PeijianShi; Jie Liu; ZhenYang

    2009-01-01

    For exploring the aftershock occurrence process of the 2008 Wenchuan strong earthquake, the spatio-temporal point pattern analysis method is employed to study the sequences of aftershocks with magnitude M≥4.0, M≥4.5, and M≥5.0. It is found that these data exhibit the spatio-temporal clustering on a certain distance scale and on a certain time scale. In particular, the space-time interaction obviously strengthens when the distance is less than 60 km and the time is less than 260 h for the first two aftershock sequences; however, it becomes strong when the distance scale is less than 80 km and the time scale is less than 150 h for the last aftershock sequence. The completely spatial randomness analysis on the data regardless of time component shows that the spatial clustering of the aftershocks gradually strengthens on the condition that the distance is less than 60 km. The results are valuable for exploring the occurrence rules of the Wenchuan strong earthquake and for predicting the aftershocks.

  2. The application of the modified form of Bath's law to the North Anatolian Fault Zone

    CERN Document Server

    Yalcin, S E

    2006-01-01

    Earthquakes and aftershock sequences follow several empirical scaling laws: One of these laws is Bath's law for the magnitude of the largest aftershock. In this work, Modified Form of Bath's Law and its application to KOERI data have been studied. Bath's law states that the differences in magnitudes between mainshocks and their largest detected aftershocks are approximately constant, independent of the magnitudes of mainshocks and it is about 1.2. In the modified form of Bath's law for a given mainshock we get the inferred largest aftershock of this mainshock by using an extrapolation of the Gutenberg-Richter frequency-magnitude statistics of the aftershock sequence. To test the applicability of this modified law, 6 large earthquakes that occurred in Turkey between 1950 and 2004 with magnitudes equal to or greater than 6.9 have been considered. These earthquakes take place on the North Anatolian Fault Zone. Additionally, in this study the partitioning of energy during a mainshock-aftershock sequence was also ...

  3. The Characteristic Analysis and Seismic Triggering Study of the M6.2 and M6.1 Dayao Earthquake Sequences in 2003

    Institute of Scientific and Technical Information of China (English)

    Hua Wei; Liu Jie; Zheng Sihua; Chen Zhangli

    2006-01-01

    The high-resolution hypocenter locations of the mainshocks on July 21 (M6.2) and October 16, 2003 ( M6.1 ) and their aftershock sequences are determined in Dayao, Yunnan by using a double-difference earthquake location algorithm. The results show that the epicenters of the two mainshocks are very close to each other and the distribution of the aftershock sequence appears to be very linear. The distribution of the earthquake sequence is very consistent with the focal mechanism, and both malnshocks are of nearly vertical right-lateral fault. Unlike most other double earthquakes in the Yunnan area, the aftershock distribution of the M6.2 and M6.1 Dayao earthquakes does not appear to be a conjugated distribution but to be in a line, and there are some stacks in the two earthquake sequences. It can be inferred that they are all controlled by the same fault. The distribution of aftershocks is asymmetrical with respect to the mainshock location and appears to be unilateral. The aftershocks of the M6.2 mainshock centralize in the northwest of M6.2 earthquake and the aftershocks of the M6.1 earthquake are in the southeast of the mainshock, moreover, the M6.1 earthquake appears to be another rupture on the southeastern extension of the same fault as the M6.2 earthquake. The results of Coulomb failure static stress changes Aσf show that the earthquake on July 21 (M6.2) apparently triggered the earthquake on October 16 (M6.1), the two mainshocks have stress triggering to their off-fault aftershocks to different extents, and the M6.5 earthquake that occurred in Yao'an in 2000 also triggered the occurrence of the two Dayao earthquakes.

  4. Seismotectonics of the May 19, 2011 Simav- Kutahya Earthquake Activity

    Science.gov (United States)

    Komec Mutlu, Ahu

    2014-05-01

    Aftershock sequence of May 19, 2011 Simav earthquake (Mw = 5.8) is relocated with a new 1-D seismic velocity model and focal mechanisms of largest aftershocks are determined. The May 19, 2011 Simav-Kutahya earthquake is occured in the most seismically active region of western Turkey. During six months after the mainshock, more than 5000 earthquakes are recorded and aftershocks followed over a period of almost two years. In this study, more than 7600 aftershocks occured between years 2011 and 2012 with magnitudes greater than 1.8 relocated. Waveform data is collected by 13 three component seismic stations from three different networks (Kandilli Observatory and Earthquake Research Institute (NEMC-National Earthquake Monitoring Center), Prime Ministry Disaster and Emergency Management Presidency, Department of Earthquake and Canakkale Onsekiz Mart University Geophysics Department). These seismic stations are deployed closer than 80 km epicentral distance in the Simav-Kutahya. Average crustal velocity and average crustal thickness for the region are computed as 5.68 km/sn and 37.6 km, respectively. The source mechanism of fifty aftershocks with magnitudes greater than 4.0 are derived from first motion P phases. Analysis of focal mechanisms indicate mainly normal fault motions with oblique slip.

  5. A model of earthquake triggering probabilities and application to dynamic deformations constrained by ground motion observations

    Science.gov (United States)

    Gomberg, J.; Felzer, K.

    2008-01-01

    We have used observations from Felzer and Brodsky (2006) of the variation of linear aftershock densities (i.e., aftershocks per unit length) with the magnitude of and distance from the main shock fault to derive constraints on how the probability of a main shock triggering a single aftershock at a point, P(r, D), varies as a function of distance, r, and main shock rupture dimension, D. We find that P(r, D) becomes independent of D as the triggering fault is approached. When r ??? D P(r, D) scales as Dm where m-2 and decays with distance approximately as r-n with n = 2, with a possible change to r-(n-1) at r > h, where h is the closest distance between the fault and the boundaries of the seismogenic zone. These constraints may be used to test hypotheses about the types of deformations and mechanisms that trigger aftershocks. We illustrate this using dynamic deformations (i.e., radiated seismic waves) and a posited proportionality with P(r, D). Deformation characteristics examined include peak displacements, peak accelerations and velocities (proportional to strain rates and strains, respectively), and two measures that account for cumulative deformations. Our model indicates that either peak strains alone or strain rates averaged over the duration of rupture may be responsible for aftershock triggering.

  6. Fault plane solutions of the January 26th, 2001 Bhuj earthquake sequence

    Indian Academy of Sciences (India)

    Reena De; S G Gaonkar; B V Srirama; Sagina Ram; J R Kayal

    2003-09-01

    A 12-station temporary microearthquake network was established by the Geological Survey of India for aftershock monitoring of the January 26th, 2001 Bhuj earthquake (W 7.6) in the Kutch district of Gujarat state, western India. The epicentres of the aftershocks show two major trends: one in the NE direction and the other in the NW direction. Fault-plane solutions of the best- located and selected cluster of events that occurred along the NE trend, at a depth of 15-38 km, show reverse faulting with a large left-lateral strike-slip motion, which are comparable with the main-shock solution. The NW trending upper crustal aftershocks at depth < 10 km, on the other hand, show reverse faulting with right-lateral strike-slip motion, and the mid crustal and lower crustal aftershocks, at a depth of 15-38 km, show pure reverse faulting as well as reverse faulting with right-lateral and left-lateral strike-slip motions; these solutions are not comparable with the main-shock solution. It is inferred that the intersection of two faults has been the source area for stress concentration to generate the main shock and the aftershocks.

  7. Preliminary report: The Little Skull Mountain earthquake, June 29, 1992

    International Nuclear Information System (INIS)

    The Little Skull Mountain earthquake occurred about 20 km from the potential high level nuclear repository at Yucca Mountain. The magnitude was 5.6, and the focal mechanism indicates normal faulting on a northeast trending structure. There is evidence that the earthquake was triggered by the magnitude MS = 7.5 earthquake in Landers, California, which occurred less than 24 hours earlier. Preliminary locations of the hypocenter and several aftershocks define an L shaped pattern near the southern boundary of the Nevada Test Site. One arm trends to the northeast beneath Little Skull Mountain, and a shorter, more diffuse zone trends to the southeast. The aftershocks are mostly located at depths between 7 km and 11 km, and may suggest a southeast dipping plane. There is no clear correlation with previously mapped surface faulting. The strongest recorded acceleration is about 0.21 g at Lathrop Wells, Nevada, 15 km from the epicenter. An extensive network of aftershock recorders was installed by the Seismological Laboratory, University of Nevada, Reno, by the US Geological Survey, Golden, Colorado, and by Lawrence Livermore Laboratory, Livermore, California. Aftershock experiments are ongoing as of November, 1992, and include experiments to improve location, depth, focal mechanism, and stress drop, study basin and ridge response near the epicenter and at Midway Valley, and study response of a tunnel at Little Skull Mountain. Analysis of this data, which includes thousands of aftershocks, has only begun

  8. PI forecast with or without de-clustering: an experiment for the Sichuan-Yunnan region

    Directory of Open Access Journals (Sweden)

    C. S. Jiang

    2011-03-01

    Full Text Available Pattern Informatics (PI algorithm uses earthquake catalogues for estimating the increase of the probability of strong earthquakes. The main measure in the algorithm is the number of earthquakes above a threshold magnitude. Since aftershocks occupy a significant proportion of the total number of earthquakes, whether de-clustering affects the performance of the forecast is one of the concerns in the application of this algorithm. This problem is of special interest after a great earthquake, when aftershocks become predominant in regional seismic activity. To investigate this problem, the PI forecasts are systematically analyzed for the Sichuan-Yunnan region of southwest China. In this region there have occurred some earthquakes larger than MS 7.0, including the 2008 Wenchuan earthquake. In the analysis, the epidemic-type aftershock sequences (ETAS model was used for de-clustering. The PI algorithm was revised to consider de-clustering, by replacing the number of earthquakes by the sum of the ETAS-assessed probability for an event to be a "background event" or a "clustering event". Case studies indicate that when an intense aftershock sequence is included in the "sliding time window", the hotspot picture may vary, and the variation lasts for about one year. PI forecasts seem to be affected by the aftershock sequence included in the "anomaly identifying window", and the PI forecast using "background events" seems to have a better performance.

  9. Estimating ETAS: the effects of truncation, missing data, and model assumptions

    Science.gov (United States)

    Seif, Stefanie; Mignan, Arnaud; Zechar, Jeremy; Werner, Maximilian; Wiemer, Stefan

    2016-04-01

    The Epidemic-Type Aftershock Sequence (ETAS) model is widely used to describe the occurrence of earthquakes in space and time, but there has been little discussion of the limits of, and influences on, its estimation. What has been established is that ETAS parameter estimates are influenced by missing data (e.g., earthquakes are not reliably detected during lively aftershock sequences) and by simplifying assumptions (e.g., that aftershocks are isotropically distributed). In this article, we investigate the effect of truncation: how do parameter estimates depend on the cut-off magnitude, Mcut, above which parameters are estimated? We analyze catalogs from southern California and Italy and find that parameter variations as a function of Mcut are caused by (i) changing sample size (which affects e.g. Omori's cconstant) or (ii) an intrinsic dependence on Mcut (as Mcut increases, absolute productivity and background rate decrease). We also explore the influence of another form of truncation - the finite catalog length - that can bias estimators of the branching ratio. Being also a function of Omori's p-value, the true branching ratio is underestimated by 45% to 5% for 1.05aftershocks and find that the ETAS productivity parameters (α and K0) and the Omoris c-value are significantly changed only for low Mcut=2.5. We further find that conventional estimation errors for these parameters, inferred from simulations that do not account for aftershock incompleteness, are underestimated by, on average, a factor of six.

  10. A new finite element model in studying earthquake triggering and continuous evolution of stress field

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    In this paper, a new finite element model (FEM) in consideration of regional stress field and an earthquake triggering factor C are proposed for studying earthquake triggering and stress field evolution in an earthquake sequence. The factor C is defined as a ratio between the shear stress and the frictional strength on a slip surface, and it can be used to tell if earthquake is triggered or not. The new FEM and the factor C are used to study the aftershock triggering of the 1976 Tangshan earthquake sequence. The results indicate that the effects of the stress field and the heterogeneity of the Tangshan earthquake fault zone on the aftershock triggering are very important. The aftershocks fallen in the earthquake triggering regions predicted by the new FEM are more than those fallen in the regions of ΔCFS≥ 0 predicted by seismic dislocation theory.

  11. Seismicity and arrival-time residuals from the Victoria Earthquake of June 9, 1980

    Energy Technology Data Exchange (ETDEWEB)

    Wong, V.; Frez, J.

    1981-01-01

    Hypocenter distribution in space and time of the aftershock activity from the Victoria Earthquake of June 9, 1980 was studied. It was concluded that the main event excited aftershocks in several pre-existing nests at the northwest end of the Cerro Prieto Fault, but no significant activity occurred at the immediate neighborhood of the main event. The depth of the aftershocks increases with the distance from the northwest end of the fault and this feature might be related with the higher temperatures and the spreading center located between the ends of the Imperial and Cerro Prieto Faults. The significance of the arrival-times residuals for local and regional stations is discussed both for P and S-waves and the importance of obtaining station corrections is emphasized. The non-uniqueness in determining a structure which minimizes the residuals is illustrated. Two different structures which satisfy the local data are presented.

  12. Dynamic triggering of deep earthquakes within a fossil slab

    Science.gov (United States)

    Cai, Chen; Wiens, Douglas A.

    2016-09-01

    The 9 November 2009 Mw 7.3 Fiji deep earthquake is the largest event in a region west of the Tonga slab defined by scattered seismicity and velocity anomalies. The main shock rupture was compact, but the aftershocks were distributed along a linear feature at distances of up to 126 km. The aftershocks and some background seismicity define a sharp northern boundary to the zone of outboard earthquakes, extending westward toward the Vitiaz deep earthquake cluster. The northern earthquake lineament is geometrically similar to tectonic reconstructions of the relict Vitiaz subduction zone at 8-10 Ma, suggesting the earthquakes are occurring in the final portion of the slab subducted at the now inactive Vitiaz trench. A Coulomb stress change calculation suggests many of the aftershocks were dynamically triggered. We propose that fossil slabs contain material that is too warm for earthquake nucleation but may be near the critical stress susceptible to dynamic triggering.

  13. Comment on "Analysis of the Spatial Distribution between Successive Earthquakes" by Davidsen and Paczuski

    CERN Document Server

    Werner, M J

    2006-01-01

    By analyzing a southern California earthquake catalog, Davidsen and Paczuski [Phys. Rev. Lett. 94, 048501 (2005)] claim to have found evidence contradicting the theory of aftershock zone scaling in favor of scale-free statistics. We present four elements showing that Davidsen and Paczuski's results may be insensitive to the existence of physical length scales associated with aftershock zones or mainshock rupture lengths, so that their claim is unsubstantiated. (i) Their exponent smaller than 1 for a pdf implies that the power law statistics they report is at best an intermediate asymptotic; (ii) their power law is not robust to the removal of 6 months of data around Landers earthquake within a period of 17 years; (iii) the same analysis for Japan and northern California shows no evidence of robust power laws; (iv) a statistical model of earthquake triggering that explicitely obeys aftershock zone scaling can reproduce the observed histogram of Davidsen and Paczuski, demonstrating that their statistic may not ...

  14. Investigation of the temporal fluctuations of the 1960–2010 seismicity of Caucasus

    Directory of Open Access Journals (Sweden)

    L. Telesca

    2012-06-01

    Full Text Available The time-clustering behaviour of the seismicity of the Caucasus spanning from 1960 to 2010 was investigated. The analysis was performed on the whole and aftershock-depleted catalogues by means of the method of Allan Factor, which permits the identification and quantification of time-clustering in point processes. The whole sequence is featured by two scaling regimes with the scaling exponent at intermediate timescales lower than that at high timescales, and a crossover that could be probably linked with aftershock time activiation. The aftershock-depleted sequence is characterized by higher time-clustering degree and the presence of a periodicity probably correlated with the cyclic earth surface load variations on regional and local scales, e.g. with snow melting in Caucasian mountains and large Enguri dam operations. The obtained results were corroborated by the application of two surrogate methods: the random shuffling and the generation of Poissonian sequences.

  15. Importance of direct and indirect triggered seismicity

    CERN Document Server

    Helmstetter, A; Helmstetter, Agnes; Sornette, Didier

    2003-01-01

    Using the simple ETAS branching model of seismicity, which assumes that each earthquake can trigger other earthquakes, we quantify the role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as in the overall level of seismicity in the presence of a constant external seismicity source. We show that, in this model, the proportion of triggered seismicity is equal to the proportion of secondary plus later-generation aftershocks, and is given by the average number of triggered events per earthquake. Based on these results and on the observation that a large fraction of seismicity are triggered earthquakes, we conclude that similarly a large fraction of aftershocks occurring a few hours or days after a mainshock are triggered indirectly by the mainshock.

  16. Test of the Felzer and Brodsky (2006) argument for, and the Richards-Dinger et al (2010) argument against, remote dynamic triggering by small mainshocks

    Science.gov (United States)

    Peng, W.; Toda, S.

    2013-12-01

    To understand earthquake interaction and forecast time-dependent seismic hazard, it is essential to determine whether static or dynamic stress change triggers most aftershocks and subsequent mainshocks. Felzer and Brodsky (2006) argued that the observed linear seismic density of small aftershocks with distance from small mainshocks is a product of the decay of seismic wave amplitude. They conclude that even small shocks can dynamically trigger remote earthquakes at distances more than ten source fault dimensions away. Richards-Dinger et al. (2010) counter-argue that the power law decay is an apparent product from independent aftershocks occurring along a large rupture zone or near-simultaneous occurrence in seismic swarms. To test the argument of Richards-Dinger et al. (2010), we use the Taiwanese earthquake catalog of the Central Weather Bureau Seismic Network, whose quality is as good as that in California and Japan. Further, we take an advantage of the absence of major inland earthquakes and significant swarms in the period, 2001-2011. We follow the methodology of Felzer and Brodsky (2006) for selecting mainshocks using their declustering algorithm, and then seek all shocks that occurred within 5 minutes to make a diagram of linear aftershock density as a function of distance from mainshock. First we select as a ';mainshock' any event that is not preceded by a larger shock within 3 days (t1) and 100 km, and that is not followed by a large shock within 12 hr (t2) and 100 km. The ';mainshocks' and ';aftershocks' are 2≤Mratios of mainshock-aftershock pairs in the Taiwanese catalog, in comparison to California and Japan, are due to lack of any large rupture and the absence of significant swarms in Taiwan, which supports the argument of Richards-Dingers et al. and renders the possibility that these small shocks are dynamically triggered untenable.

  17. Research on the Accurate Location of the 2007 Ms 6. 4 Ning'er, Yunnan Earthquake

    Institute of Scientific and Technical Information of China (English)

    Lu Xian; Zhou Longquan

    2012-01-01

    Five mobile digital seismic stations were set up by the Earthquake Administration of Yunnan Province near the epicenter of the main shock after the Ning'er M6. 4 earthquake on June 3, 2007. In this paper, the aftershock sequence of the Ning'er M6. 4 earthquake is relocated by using the double difference earthquake location method. The data is from the 5 mobile digital seismic stations and the permanent Simao seismic station. The results show that the length of the aftershock sequence is 40kin and the width is 30km, concentrated obviously at the lateral displacement area between the Pu'er fault and the NNE-trending faults, with the majority occurring on the Pu'er fault around the main shock. The depths of aftershocks are from 2kin to 12km, and the predominant distribution is in the depth of 8 ~ 10km. The mean depth is 7. 9kin. The seismic fault dips to the northwest revealed from the profile parallel to this aftershock sequence, which is identical to the dip of the secondary fault of the NE-trending Menglian-Mojiang fault in the earthquake area. There are more earthquakes concentrated in the northwest segment than in the southeast segment, which is perhaps related to the underground medium and faults. The depth profile of the earthquake sequence shows that the relocated earthquakes are mainly located near the Pu'er fault and the seismic faults dip to the southwest, consistent with the dip of the west branch of the Pu'er fault. In all, the fault strike revealed by earthquake relocations matches well with the strike in the focal mechanism solutions. The main shock is in the top of the aftershock sequence and the aftershocks are symmetrically distributed, showing that faulting was complete in both the NE and SW directions.

  18. Båth's law and its relation to the tectonic environment: A case study for earthquakes in Mexico

    Science.gov (United States)

    Rodríguez-Pérez, Q.; Zúñiga, F. R.

    2016-09-01

    We studied 66 mainshocks and their largest aftershocks in the Mexican subduction zone and in the Gulf of California with magnitudes in the range of 5.2 aftershock sequences, we analyze the physics of the mainshock-largest aftershock relationship (Båth's law). The partitioning of energy during a mainshock-aftershock sequence shows that about 96-97% of the energy dissipated in a sequence is associated with the mainshock and the rest is due to aftershocks. Our results for radiated seismic energy and energy-to-moment ratio are partially in agreement with worldwide studies supporting the observation of mechanism dependence of radiated seismic energy. The statistical tests indicate that the only significant difference is for shallow thrust and strike-slip events for these parameters. The statistical comparison of stress drop of shallow thrust versus that of inslab events shows a strongly significant difference with a confidence better than 99%. The comparison of stress drop of shallow thrust events with that of strike-slip events, also indicates a strongly significant difference. We see no dependence of stress drop with magnitude, which is strong evidence of earthquake self-similarity. We do not observe a systematic depth dependence of stress drop. The results also reveal differences in the earthquake rupture among the events. The magnitude difference between the mainshock and the largest aftershock for inslab events is larger than interplate and strike-slip events suggesting focal mechanism dependence of Båth's law. For the case of this parameter, only that for inslab and strike-slip events present a significant difference with 95% confidence.

  19. Brief communication

    Directory of Open Access Journals (Sweden)

    M. Jaboyedoff

    2010-09-01

    Full Text Available Numerous rockfalls were detected in the Las Cuevas valley, Argentina, after the 27 February 2010 earthquake in Chile. Live rockfalls were observed during aftershocks of 11 March 2010. Many rockfall source areas coincide with known thrust fault and some areas presented a rockfall activity even after the tremors. Some rockfalls crossed the National Road 7 but no damages to houses or vehicles were reported. This study illustrates how the 27 February 2010 earthquake impacted on unstable slopes in a valley far from the earthquakes epicentre. It is an interesting addition to previous studies on landslides caused by earthquakes because of the high magnitude of the event and of its aftershocks.

  20. Source characteristics of a moderate earthquake (M 4.9)using empirical Green ’s function technique

    OpenAIRE

    A. K. Abdel-Fattah

    2002-01-01

    The rupture process of a moderate earthquake (M 4.9)on 28th January 1999 was analyzed using velocity records at local distances less than 80 km.The characterization of the rupture process was obtained from studying aftershocks distribution,azimuthal variations of Relative Source Time Functions (RSTFs),and a set of spatio-temporal slip models.RSTFs were retrieved by deconvolution of small aftershock records from those of the mainshock.In addition,velocity P -wave records of the respective even...

  1. A Brief Introduction to the Wenchun Ms8.0 Earthquake Sequence, May 12, 2008

    Institute of Scientific and Technical Information of China (English)

    Li Gang; Guo Tieshuan; Wang Huimin

    2008-01-01

    @@ A total of 190 aftershocks with Ms≥4.0 occurred until May 31, 2008, after the earthquake with Ms8.0 on May 12, 2008, in Wenchuan, Sichuan, according to the Chinese Seismic Station Network (Table 1). Among them, there are 160 events of Ms4.0 - 4.9, 25 events of Ms5.0 - 5.9, and 5 events of Ms6.0 - 6.9. The strongest aftershock is the Qingchuan earthquake with Ms6.4 on May 25. 1 Received on June 3. 2008.

  2. 汶川Ms8.0地震及余震序列重新定位%Relocation of the Wenchuan Ms8.0 Earthquake Sequence

    Institute of Scientific and Technical Information of China (English)

    赵博; 石玉涛; 高原

    2011-01-01

    From the origin time of May 12, 2008, Ms8.0 Wenchuan earthquake to Dec. 31, 2008, more than 10000 aftershocks(M≥2.0) had been recorded by the seismic network in Sichuan and the surrounding provinces. In the paper, the main shock and more than 7000 aftershocks were relocated using the double difference algorithm. The results show that the length of aftershock distribution is about 350 km. In the southwest, the distribution of aftershocks is along the Back-range, the Central and the Front-range of the Longmenshan fault. In the middle, the distribution of aftershocks is along the Central fault. In the North, the aftershocks distributed across the Qingchuanr-Pingwu fault. The depths of aftershocks mainly located in the 10~20 km, and the average depth of aftershocks is 13 km after relocation.%从2008年5月12日汶川8.0级地震发震时刻起到2008年12月31日,四川省及其周边省区布设的区域台网、水库台网以及流动台共记录到10000余次余震序列(M≥2.0).我们采用双差定位法对主震及余震序列进行重新定位,得到7000多个地震的重新定位结果.结果表明,余震分布带长约350 km.在西南部,余震沿龙门山后山、中央以及前山断裂分布;在中段,余震主要沿龙门山中央断裂分布;在北段,余震横穿青川-平武断裂分布.余震震源深度主要分布在10~20 km,重新定位后的平均震源深度为13 km.

  3. Geomorphic and geologic controls of geohazards induced by Nepal's 2015 Gorkha earthquake

    NARCIS (Netherlands)

    Kargel, J. S.; Leonard, G. J.; Shugar, D. H.; Haritashya, U. K.; Bevington, A.; Fielding, E. J.; Fujita, K.; Geertsema, M.; Miles, E. S.; Steiner, J.; Anderson, E.; Bajracharya, S.; Bawden, G. W.; Breashears, D. F.; Byers, A.; Collins, B.; Dhital, M. R.; Donnellan, A.; Evans, T. L.; Geai, M. L.; Glasscoe, M. T.; Green, D.; Gurung, D. R.; Heijenk, R.; Hilborn, A.; Hudnut, K.; Huyck, C.; Immerzeel, W. W.; Liming, Jiang; Jibson, R.; Kääb, A.; Khanal, N. R.; Kirschbaum, D.; Kraaijenbrink, P. D A; Lamsal, D.; Shiyin, Liu; Mingyang, Lv; McKinney, D.; Nahirnick, N. K.; Zhuotong, Nan; Ojha, S.; Olsenholler, J.; Painter, T. H.; Pleasants, M.; Pratima, K. C.; Yuan, Q. I.; Raup, B. H.; Regmi, D.; Rounce, D. R.; Sakai, A.; Donghui, Shangguan; Shea, J. M.; Shrestha, A. B.; Shukla, A.; Stumm, D.; van der Kooij, M.; Voss, K.; Xin, Wang; Weihs, B.; Wolfe, D.; Lizong, Wu; Xiaojun, Yao; Yoder, M. R.; Young, N.

    2016-01-01

    The Gorkha earthquake (magnitude 7.8) on 25 April 2015 and later aftershocks struck South Asia, killing ~9000 people and damaging a large region. Supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone, our team undertook a satellite image survey of

  4. Pandas on The Move

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    After surviving the earthquake,China’s panda population face the search for a new home on the afternoon of May 24,with the landing of a China Southern Airlines Boeing 747 at Beijing Capital International Airport, eight pandas from Sichuan Province finally arrived in China’s capital safe from the aftershocks of the May 12 earthquake. The pandas all came from Wolong

  5. The Impact of a Natural Disaster: Under- and Postgraduate Nursing Education Following the Canterbury, New Zealand, Earthquake Experiences

    Science.gov (United States)

    Richardson, S. K.; Richardson, A.; Trip, H.; Tabakakis, K.; Josland, H.; Maskill, V.; Dolan, B.; Hickmott, B.; Houston, G.; Cowan, L.; McKay, L.

    2015-01-01

    While natural disasters have been reported internationally in relation to the injury burden, role of rescuers and responders, there is little known about the impact on education in adult professional populations. A 7.1 magnitude earthquake affected the Canterbury region of New Zealand on 4 September 2010 followed by more than 13,000 aftershocks in…

  6. Variation of stress during the rupture process of the 1995 ML=4.1 Shacheng, Hebei, China, earthquake sequence

    Institute of Scientific and Technical Information of China (English)

    CHEN Xue-zhong; XU Xiang-tong; ZHAI Wen-jie

    2005-01-01

    According to the rupture dynamics of earthquakes, variations of the apparent stress and the difference between the static stress drop and the dynamic stress drop during the rupture of earthquakes are analyzed for the July 20, 1995 ML=4.1 Shacheng, Hebei, China, earthquake sequence. Results obtained show that the apparent stress for mainshock is about 5 MPa, and the average apparent stress for aftershocks 0.047 MPa. During the rupture of the mainshock, the dynamic stress drop is approximately 1.6 times greater than the static stress drop with the difference of nearly 2.7 MPa. The dynamic stress drop is less than the static stress drop for all aftershocks with the average difference of -0.75 MPa. Therefore, when the mainshock occurs the final stress on the focal fault is higher than the dynamic frictional stress, corresponding to that the fault is abruptly locked. When the aftershocks occur the final stress on the focal fault is lower than the dynamic frictional stress, corresponding to that the fault overshoots. It can be seen from the above results that there could be some differences in the physic processes between the mainshock and the aftershocks.

  7. 1999 Nantou, Taiwan Images

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — At least 2,297 people killed, 8,700 injured, 600,000 people left homeless and about 82,000 housing units damaged by the earthquake and larger aftershocks. Damage...

  8. Hadal disturbance in the Japan Trench induced by the 2011 Tohoku-Oki earthquake

    DEFF Research Database (Denmark)

    Oguri, K.; Kawamura, K.; Sakaguchi, A.;

    2013-01-01

    deposition was observed but the surface sediment contained Cs-134 from the Fukushima Dai-ichi nuclear disaster. We argue that diatom blooms observed by remote sensing facilitated rapid deposition of Cs-134 to hadal environment and the aftershocks induced successive sediment disturbances and maintained dense...

  9. Bosnia and Herzegovina Financial Sector Assessment

    OpenAIRE

    World Bank; International Monetary Fund

    2015-01-01

    Bosnia and Herzegovina (BiH) is still dealing with the aftershocks of the global financial crisis that have weakened financial sector asset quality and profitability. System-wide solvency and liquidity indicators appear broadly sound, but significant pockets of vulnerability exist among domestically-owned banks. Banking and insurance oversight have improved since the 2006 financial sector ...

  10. Speaking of Silence: Comments from an Irish Studies Perspective

    DEFF Research Database (Denmark)

    McQuaid, Sara Dybris; Beville, Maria

    2012-01-01

    in a postmodern era of extensive political change on a global scale is proving to be one of the most serious societal challenges, but also in the context of a ‘New Ireland’ which is now reflecting on the aftershock of the Celtic Tiger and what it means to be a contemporary European multi-cultural State....

  11. Aspects of Decision-Making for Risk Reduction during the Prolonged Earthquake Sequence in Canterbury, New Zealand

    Science.gov (United States)

    Wein, A. M.; Potter, S.; Becker, J.; Ratliff, J. L.; Hudson-Doyle, E.

    2014-12-01

    An earthquake sequence is a prolonged natural hazard event. Scientists can dynamically forecast aftershock frequency within bounds of uncertainty. We examine how this capability can be used in decision-making to reduce risk during a period of heightened seismicity. We draw from experience of the Canterbury earthquake sequence initiated by a magnitude 7.1 mainshock on September 4, 2010 near the city of Christchurch, a population of 370,000. The sequence impacted the built, economic, social and natural environments of the Canterbury region. We study the use of aftershock forecasts in decision-making across the roles of policy makers, emergency managers and responders, critical infrastructure providers, insurers, communication officers, scientists, and the public. We held focus groups and interviews involving 53 participants using a semi-structured message centered approach in May and June of 2013. Transcripts from the focus groups and interviews were thematically coded using qualitative analysis. Responses to a pre-questionnaire suggested that aftershock information for decision-making increases slightly in importance throughout the four phases of a disaster - mitigation, preparedness, response and recovery. We summarize our findings from this research, including the use and barriers to the use of aftershock forecasts in decision-making across the disaster phases by roles conflicts of interest that arise in the decision-making hierarchy challenges with providing and using forecasts during a prolonged event. Finally, we reflect on implications for Operational Earthquake Forecasting and how our findings may be generalized to other prolonged hazards.

  12. Interpretation of the Omori Law

    CERN Document Server

    Guglielmi, Anatol V

    2016-01-01

    The known Omori law is presented in the form of differential equation that describes the evolution of the aftershock activity. This equation is derived hypothetically with taking into account deactivation of the faults in epicentral zone of the main shock. A generalization of the Omori law is proposed.

  13. Co-seismic deformation of the crustal Mw=6.3, 2001, Chusmiza, Chile event triggered by the subduction Mw=8.4, 2001, Arequipa, Peru earthquake studied using seismological data

    Science.gov (United States)

    Legrand, D.

    2005-12-01

    The 24 July 2001 Chusmiza, Mw=6.3, Chile earthquake is one of the few recent moderate shallow superficial earthquake in Northern Chile. Different kinds of data (short- and long-period seismograms, accelerograms) have been used to better locate this event with corresponding aftershocks. A special care has been taken to constrain their depth and to determine the focal mechanism of the main shock and aftershock, in particular to discriminate the real fault plane among the 2 nodal planes. These data have been used separately in the respective inverse problem approach, and similar results have been obtained. The main shock and main after-shock have very similar focal mechanism (strike-slip faults with a small normal component) and are both superficial (less than 10 km depth). The main shock fault plane solution (strike,dip,rake)=(14°,53°,-163°), dipping eastwards, has been discriminated among the two nodal planes without ambiguity with accelerograms waveform modelling data. It corresponds to the distribution of aftershocks (with a dip of about 50° and a strike of about N30°E), and local lineaments of azimuth about N35°E

  14. Human Trafficking in Nepal

    DEFF Research Database (Denmark)

    Gyawali, Bishal; Keeling, June; Kallestrup, Per

    2016-01-01

    As Nepal mourns the 1-year commemoration of the April 2015 earthquake and its aftershocks that killed more than 8500 people and left thousands injured and displaced, other more hidden repercussions of the resultant chaotic environment need attention: the increased risk of human trafficking...

  15. Teacher Guidelines for Helping Students after an Earthquake

    Science.gov (United States)

    National Child Traumatic Stress Network, 2013

    2013-01-01

    Being in an earthquake is very frightening, and the days, weeks, and months following are very stressful. Most families recover over time, especially with the support of relatives, friends, and their community. But different families may have different experiences during and after the earthquake, including the experience of aftershocks which may…

  16. The Ahar-Varzaghan (Iran) double earthquakes (Mw 6.5 and 6.2) of August 11th, 2012: A seismotectonic interpretation from regional moment tensors and kinematic parameters

    DEFF Research Database (Denmark)

    Donner, Stefanie; Krüger, Frank; Ghods, Abdolreza;

    2013-01-01

    and almost nothing is known about active structures so far. Here, GPS velocity records are directed to North-East, while the direction changes to direct North south of the NTF. On 11th of August 2012 the region was surprisingly struck by a shallow Mw 6.5 earthquake with pure right-lateral strike...... earthquakes with ML 2.0 were observed. In the eastern part of the earthquake sequence, along 3/4 of the rupture length, the aftershocks concentrated in a depth of about 14 km. In the western part they became shallower with about 7 km depth. On 7th of November a strong aftershock (Mw 5.4) occurred......) operated by the International Institute of Earthquake Engineering and Seismology (IIEES) in Tehran. For half of the studied aftershocks we obtain pure E-W / N-S oriented strike-slip mechanisms. The other half shows oblique thrust mechanisms with an orientation of NE-SW. The analysed aftershocks are located...

  17. A new technique for moment tensor inversion with applications to the 2008 Wenchuan Ms8.0 earthquake sequence

    Institute of Scientific and Technical Information of China (English)

    LIU Chao; ZHANG Yong; XU Li-sheng; CHEN Yun-tai

    2008-01-01

    A Ms8.0 earthquake occurred in Wenchuan County, Sichuan Province, China, on May 12, 2008, and subsequently, numerous aftershocks followed. We obtained the moment tensor solutions and source time functions (STFs) for the Wenchuan earthquake and its seven larger aftershocks (Ms5.0~6.0) by a new technique of moment tensor inversion using the broadband and long-period seismic waveform data from the Global Seismic Network (GSN). Firstly, the theoretical background and technical flow of the new technique was briefly introduced, and an aftershock of the Wenchuan earthquake sequence was employed to illustrate the real procedure for inverting the moment tensor; secondly, the moment tensor solutions and STFs of the eight events, including the main shock, were presented, and finally, the interpretation of the results was made. The agreement of our results with the GCMT results indicates the new approach is efficient and feasible. By using this approach, not only the moment tensor solution can be obtained but also the STF can be retrieved; the inverted STFs indicate that the source rupture process may be com-plicated even for the moderate earthquakes. The inverted focal mechanisms of the Wenchuan earthquake sequence show that the most of the aftershocks occurred in the main faults of the Longmenshan fault zone with predomi-nantly thmstingwith minor right-lateral strike-slip component, but some of them may have occurred in the sub-faults with strike-slip faulting in the vicinity of the main faults.

  18. International Data Centre: Reviewed Event Bulletin vs. Waveform Cross Correlation Bulletin

    CERN Document Server

    Bobrov, Dmitry; Given, Jeffrey; Khukhuudei, Urtnasan; Kitov, Ivan; Sitnikov, Kirill; Spiliopoulos, Spilio; Zerbo, Lassina

    2012-01-01

    Our objective is to assess the performance of waveform cross-correlation technique, as applied to automatic and interactive processing of the aftershock sequence of the 2012 Sumatera earthquake relative to the Reviewed Event Bulletin (REB) issued by the International Data Centre. The REB includes 1200 aftershocks between April 11 and May 25 with body wave magnitudes from 3.05 to 6.19. To automatically recover the sequence, we selected sixteen aftershocks with mb between 4.5 and 5.0. These events evenly but sparsely cover the area of the most intensive aftershock activity as recorded during the first two days after the main shock. In our study, waveform templates from only seven IMS array stations with the largest SNRs estimated for the signals from the main shock were used to calculate cross-correlation coefficients over the entire period of 44 days. Approximately 1000000 detections obtained using cross-correlation were then used to build events according to the IDC definition. After conflict resolution betwe...

  19. Prediction of Seismic Damage-Based Degradation in RC Structures

    DEFF Research Database (Denmark)

    Kirkegaard, Poul Henning; Gupta, Vinay K.; Nielsen, Søren R.K.

    useful correlations of strength and stiffness degradation with damage wherein a simple damage parameter based on maximum and yield displacements and ductility supply ratio has been considered. The proposed model has also been used to demonstrate that ignoring aftershocks in case of impulsive ground...

  20. Hope Against Hardship

    Institute of Scientific and Technical Information of China (English)

    JING XIAOLEI

    2010-01-01

    @@ Li Xupeng had prepared himself for poor conditions when he went to Mianchi,a town in Sichuan Province's Wenchuan County that was hit hard during the devastating May 12,2008 earthquake.But no preparations could prevent the fear that welled up within him as he felt the fast aftershock rumbling beneath his feet.

  1. Earthquake source parameters and fault kinematics in the Eastern California Shear Zone

    CERN Document Server

    Jones, L E; Jones, Laura E.; Helmberger, Donald V.

    1998-01-01

    Based on waveform data from a profile of aftershocks following the north-south trace of the June 28, 1992 Landers rupture across the Mojave desert, we construct a new velocity model for the Mojave region which features a thin, slow crust. Using this model, we obtain source parameters, including depth and duration, for each of the aftershocks in the profile, and in addition, any significant (M>3.7) Joshua Tree--Landers aftershock between April, 1992 and October, 1994 for which coherent TERRAscope data were available. In all, we determine source parameters and stress-drops for 45 significant (M_w > 4) earthquakes associated with the Joshua Tree and Landers sequences, using a waveform grid-search algorithm. Stress drops for these earthquakes appear to vary systematically with location, with respect to previous seismic activity, proximity to previous rupture (i.e., with respect to the Landers rupture), and with tectonic province. In general, for areas north of the Pinto Mountain fault, stress-drops of aftershocks...

  2. Fault plane solutions of the 1993 and 1995 Gulf of Aqaba earthquakes and their tectonic implications

    Directory of Open Access Journals (Sweden)

    E. M. Ibrahim

    1997-06-01

    Full Text Available The stereographic projection of P-wave first motions for the 3 August 1993 Gulf of Aqaba earthquake, its largest aftershock (16 h 33 min, and for the 22 November 1995 earthquake were constructed using the polarity readings of regional and teleseismic stations. The focal mechanism solutions of the 3 August 1993 mainshock and its largest aftershock represent a normal faulting mechanism with some left lateral strike slip component. The nodal planes selected as the fault imply high similarity in strike and dip. They are related to a local fault striking NW-SE and dipping to the SW. The selected fault planes are in good agreement with the aftershock distribution. For the main shock of the 22 November 1995, the fault plane solution displays the same mechanism (normal faulting with left lateral strike slip component with a plane striking N-S and dipping to the west. The fault plane is greatly conformable with the direction of the regional tectonics and also with the aftershock distribution. The main trend of the extension stress pattern is in a NE-SW direction, corresponding to the rifting direction of the Gulf of Suez and may be related to the paleostress along the Gulf of Suez and Aqaba during the Middle to Late Miocene.

  3. Power law distribution of seismic rates: theory and data

    CERN Document Server

    Saichev, A

    2004-01-01

    We report an empirical determination of the probability density functions P(r) of the number r of earthquakes in finite space-time windows for the California catalog, over fixed spatial boxes 5 x 5 km^2 and time intervals dt =1, 10, 100 and 1000 days. We find a stable power law tail P(r) ~ 1/r^{1+mu} with exponent mu \\approx 1.6 for all time intervals. These observations are explained by a simple stochastic branching process previously studied by many authors, the ETAS (epidemic-type aftershock sequence) model which assumes that each earthquake can trigger other earthquakes (``aftershocks''). An aftershock sequence results in this model from the cascade of aftershocks of each past earthquake. We develop the full theory in terms of generating functions for describing the space-time organization of earthquake sequences and develop several approximations to solve the equations. The calibration of the theory to the empirical observations shows that it is essential to augment the ETAS model by taking account of th...

  4. Accurate Location of the Yao'an Earthquake Sequence and the Yongsheng Earthquake Sequence

    Institute of Scientific and Technical Information of China (English)

    Wang Xinling; Liu Jie; Zhang Guomin; Zhao Cuiping

    2006-01-01

    The Yao'an Ms6.5 earthquake occurred on Jan. 15, 2000 and the Yongsheng Ms6.0 earthquake occurred on Oct. 27, 2001 in Yunnan Province, China. They are both located in the middle of the Dian block. Their epicenters are close to each other, the tectonic and strain characters of the earthquakes were similar, and there were many aftershocks after the two main shocks. In order to further study the spatial-temporal distributions and fault rupture characters of the main shocks and aftershocks, the latter are located using the Geiger earthquake location algorithm (Geiger) and the double difference earthquake location algorithm (DD) based on the seismic phase data of the two earthquake sequences. They were recorded by two Near Source Digital Seismic Networks (YNSSN and YSNSSN) deployed by the Yunnan Seismological Bureau (YNSB). Then, two main shock parameters were relocated using DD based on the data of larger magnitude aftershocks and the two main shocks that were recorded by the Kunming Regional Digital Seismic Network (KMSN). Combining the spatialtemporal distributions of the two earthquake sequences, the tectonic and strain characters of earthquakes, the rupture processes of the two aftershock sequences along faults are analyzed and discussed contrastively.

  5. The ANSS response to the Mw 5.8 Central Virginia Seismic Zone earthquake of August 23, 2011

    Science.gov (United States)

    McNamara, D. E.; Horton, S.; Benz, H.; Earle, P. S.; Withers, M. M.; Hayes, G. P.; Kim, W. Y.; Chapman, M. C.; Herrmann, R. B.; Petersen, M. D.; Williams, R. A.

    2011-12-01

    An Mw 5.8 earthquake (depth=6km) occurred on August 23, 2011 (17:51:04 UTC) near Mineral, Virginia, which was widely felt from Maine to Georgia along the eastern seaboard and west to Chicago and western Tennessee. The USGS tallied nearly 142,000 felt reports submitted to the Did You Feel It (DYFI) internet community intensity system, making it the most widely felt earthquake since the web-site began, and demonstrating that more people felt this earthquake than any other in U.S. history. Significant damage was reported in the epicentral area and as far away as Washington D.C. (135 km away); minor damage was reported in Baltimore (200 km). The reverse faulting earthquake occurred on a northeast-striking plane within a region of diffuse seismicity known as the Central Virginia Seismic Zone. Within the first week, the mainshock was followed by 17 aftershocks with magnitude greater than 2, including Mw 4.5, 4.2, and 3.8 events. In the days following the mainshock, 46 portable seismic stations were deployed by several organizations, making this among the best-recorded aftershock sequence in the eastern U.S. Within 24 hours of the mainshock, 8 portable stations were deployed in time to record the largest aftershock to date (M4.5). We will present the results of our post-earthquake response, including attenuation and site amplification observations using portable aftershock station data, details on the initial USGS NEIC post earthquake response products and an assessment of the seismotectonics of the Central Virginia Seismic Zone based on aftershock locations and source parameter modeling of the larger earthquakes.

  6. Seismicity rate changes along the central California coast due to stress changes from the 2003 M 6.5 San Simeon and 2004 M 6.0 Parkfield earthquakes

    Science.gov (United States)

    Aron, A.; Hardebeck, J.L.

    2009-01-01

    We investigated the relationship between seismicity rate changes and modeled Coulomb static stress changes from the 2003 M 6.5 San Simeon and the 2004 M 6.0 Parkfield earthquakes in central California. Coulomb stress modeling indicates that the San Simeon mainshock loaded parts of the Rinconada, Hosgri, and San Andreas strike-slip faults, along with the reverse faults of the southern Los Osos domain. All of these loaded faults, except for the San Andreas, experienced a seismicity rate increase at the time of the San Simeon mainshock. The Parkfield earthquake occurred 9 months later on the loaded portion of the San Andreas fault. The Parkfield earthquake unloaded the Hosgri fault and the reverse faults of the southern Los Osos domain, which both experienced seismicity rate decreases at the time of the Parkfield event, although the decreases may be related to the decay of San Simeon-triggered seismicity. Coulomb stress unloading from the Parkfield earthquake appears to have altered the aftershock decay rate of the southern cluster of San Simeon after-shocks, which is deficient compared to the expected number of aftershocks from the Omori decay parameters based on the pre-Parkfield aftershocks. Dynamic stress changes cannot explain the deficiency of aftershocks, providing evidence that static stress changes affect earthquake occurrence. However, a burst of seismicity following the Parkfield earthquake at Ragged Point, where the static stress was decreased, provides evidence for dynamic stress triggering. It therefore appears that both Coulomb static stress changes and dynamic stress changes affect the seismicity rate.

  7. Vertical stress transfer after large subduction zone earthquakes: 2007 Tocopilla /North Chile case study

    Science.gov (United States)

    Eggert, S.; Sobiesiak, M.; Victor, P.

    2011-12-01

    Large interplate subduction zone earthquakes occur on fault planes within the seismogenic interface which, in the case of Northern Chile, usually start to break at the down dip end of the coupled interface, propagating towards the trench. Although the rupture is a horizontally oriented process, some vertical connectivity between the interface and the upper crust should be expected. We study two clusters of aftershock seismicity from the Mw 7.7, 2007, Tocopilla earthquake in Northern Chile Both clusters seem to align along vertical profiles in the upper crust above the main shock rupture plane. The first cluster has a rather dissipative character at the up-dip limit of the rupture plane in the off-shore area around the Peninsula of Mejillones. It developed in the early stage of the aftershock sequence. The second cluster lies above the pronounced aftershock sequence of a secondary large Mw 6.9 slab-push event on 16th of December 2007. This type of compressional event can occur after large thrust earthquakes. A comparison of the epicentral distribution of the crustal events belonging to the aftershock sequence suggests a possible relation to the Cerro Fortuna Fault in the Coastal Cordillera which is a subsidiary fault strand of the major Atacama Fault Zone. We compute the Coulomb stress change on the respective faults of both clusters analyzed to see where slip is promoted or inhibited due to the slip on the subduction interface. We then combine these results with the spatial and temporal aftershock distribution, focal mechanism solutions, b-value mappings and geological evidences to understand the process behind the ascending seismicity clusters and their relation to the main shock of the major Tocopilla event.

  8. Improving the resolution of the 2010 Haiti earthquake fault geometry using temporary seismometer deployments

    Science.gov (United States)

    Douilly, R.; Haase, J. S.; Ellsworth, W. L.; Bouin, M.; Calais, E.; Symithe, S. J.; Armbruster, J. G.; Mercier De Lepinay, B. F.; Deschamps, A.; Meremonte, M. E.; Hough, S. E.; Saint Louis, M.

    2012-12-01

    Haiti has been the locus of a number of large and damaging historical earthquakes. The recent January 12, 2010, Mw 7.0 earthquake affected cities that were largely unprepared, which resulted in tremendous losses. It was initially assumed that the earthquake ruptured the Enriquillo Plantain Garden Fault (EPGF), a major active structure in southern Haiti, known from geodetic measurements and its geomorphic expression to be capable of producing M7 or larger earthquakes. However, GPS and InSAR data showed that the event ruptured a previously unmapped fault, the Léogâne fault, a north dipping oblique blind thrust located immediately north of the Enriquillo Fault. Following the earthquake several groups installed temporary seismic stations to record aftershocks, including ocean bottom seismometers on either side of the EPGF. We use data from the complete set of stations deployed after the event, on land and offshore, to relocate all aftershocks from 10 February to 24 June 2010, to determine a one-dimensional regional crustal velocity model, and calculate focal mechanisms. The aftershock locations from the combined data set clearly delineate the Léogâne fault, with a geometry close to that inferred from geodetic data. Its strike and dip closely agrees with that of the global centroid moment tensor solution of the mainshock, but it is more steeply dipping than the plane inferred from previously determined finite fault inversions. The aftershocks also delineate a structure with shallower southward dip offshore and to the west of the rupture zone, which could indicate triggered seismicity on the offshore Trois Baies reverse fault. We use first-motion focal mechanisms to clarify the relationship of the fault geometry to the triggered aftershocks.

  9. Mixture of a seismicity model based on the rate-and-state friction and ETAS model

    Science.gov (United States)

    Iwata, T.

    2015-12-01

    Currently the ETAS model [Ogata, 1988, JASA] is considered to be a standard model of seismicity. However, because the ETAS model is a purely statistical one, the physics-based seismicity model derived from the rate-and-state friction (hereafter referred to as Dieterich model) [Dieterich, 1994, JGR] is frequently examined. However, the original version of the Dieterich model has several problems in the application to real earthquake sequences and therefore modifications have been conducted in previous studies. Iwata [2015, Pageoph] is one of such studies and shows that the Dieterich model is significantly improved as a result of the inclusion of the effect of secondary aftershocks (i.e., aftershocks caused by previous aftershocks). However, still the performance of the ETAS model is superior to that of the improved Dieterich model. For further improvement, the mixture of the Dieterich and ETAS models is examined in this study. To achieve the mixture, the seismicity rate is represented as a sum of the ETAS and Dieterich models of which weights are given as k and 1-k, respectively. This mixture model is applied to the aftershock sequences of the 1995 Kobe and 2004 Mid-Niigata sequences which have been analyzed in Iwata [2015]. Additionally, the sequence of the Matsushiro earthquake swarm in central Japan 1965-1970 is also analyzed. The value of k and parameters of the ETAS and Dieterich models are estimated by means of the maximum likelihood method, and the model performances are assessed on the basis of AIC. For the two aftershock sequences, the AIC values of the ETAS model are around 3-9 smaller (i.e., better) than those of the mixture model. On the contrary, for the Matsushiro swarm, the AIC value of the mixture model is 5.8 smaller than that of the ETAS model, indicating that the mixture of the two models results in significant improvement of the seismicity model.

  10. Separating triggered and stress-change induced seismcity

    Science.gov (United States)

    Zhuang, J.

    2013-12-01

    Once a major earthquake occurs, it usually not only triggers a sequence of many aftershock, but also changes the tectonic stress field in the regions nearby. According to the rate and state law (Dieterich, 1994), such stress changes result in a permanent change of the seismicity rate, increment or decrement. However, since aftershock sequence lasts quite a long time before it decays off, it is hard tell whether the high level of seismicity after a big earthquake is the continuation of the aftershock activity or caused by the changes of stress due this big earthquake. In this study, by making use of the space-time ETAS model (Ogata, 1998) and the stochastic declustering method (Zhuang et al., 2002, 2004), I developed a method to separate the seismicity induced by stress-change from the aftershock activity in a probability manner. For example, it is found that the probabilities that Lushan earthquakes belong the background seismcity, aftershock of the Wenchuan earthquake, are stress-change induced seismcity are, respectively, 38% and 12%, 50%. References Dieterich, J.H. (1994) A constitutive law for rate of earthquake production and its application to earthquake clustering, J. Geophys. Res. , 99 , 2601-2618. Ogata, Y. (1998. Space-time point-process models for earthquake occur- rences, Ann. Inst. Stat. Math., 50, 379-402. Zhuang J., Ogata Y. and Vere-Jones D. (2004). Analyzing earthquake clustering features by using stochastic reconstruction. Journal of Geophysical Research, 109, No. B5, B05301, doi:10.1029/2003JB002879. Zhuang J., Ogata Y. and Vere-Jones D. (2002). Stochastic declustering of space-time earthquake occurrences. Journal of the American Statistical Association, 97: 369-380.

  11. Simultaneous Estimation of Earthquake Source Parameters and Site Response from Inversion of Strong Motion Network Data in Kachchh Seismic Zone, Gujarat, India

    Science.gov (United States)

    Dutta, U.; Mandal, P.

    2010-12-01

    Inversion of horizontal components of S-wave spectral data in the frequency range 0.1-10.0 Hz has been carried out to estimate simultaneously the source spectra of 38 aftershocks (Mw 2.93-5.32) of the 2001 Bhuj earthquake (Mw 7.7) and site response at 18 strong motion sites in the Kachchh Seismic Zone, Gujarat, India. The spatial variation of site response (SR) in the region has been studied by averaging the SR values obtained from the inversion in two frequency bands; 0.2-1.8 Hz and 3.0-7.0 Hz, respectively. In 0.2-1.8 Hz frequency band, the high SR values are observed in the southern part of the Kachchh Mainland Fault that had suffered extensively during the 2001 Bhuj Earthquake. However, for 3.0-7.0 Hz band, the area of Jurassic and Quaternary Formations show predominantly high SR. The source spectral data obtained from the inversion were used to estimate various source parameters namely, the seismic moment, stress drop, corner frequency and radius of source rupture by using an iterative least squares inversion approach based on the Marquardt-Levenberg algorithm. It has been observed that the seismic moment and radius of rupture from 38 aftershocks vary between 3.1x10^{13} to 2.0x10^{17} Nm and 226 to 889 m, respectively. The stress drop values from these aftershocks are found to vary from 0.11 to 7.44 MPa. A significant scatter of stress drop values has been noticed in case of larger aftershocks while for smaller magnitude events, it varies proportionally with the seismic moment. The regression analysis between seismic moment and radius of rupture indicates a break in linear scaling around 10^{15.3} Nm. The seismic moment of these aftershocks found to be proportional to the corner frequency, which is consistent for earthquakes with such short rupture length.

  12. Estimates of source parameters of 4.9 Kharsali earthquake using waveform modelling

    Indian Academy of Sciences (India)

    Ajay Paul; Naresh Kumar

    2010-10-01

    This paper presents the computation of time series of the 22 July 2007 4.9 Kharsali earthquake. It occurred close to the Main Central Thrust (MCT)where seismic gap exists.The main shock and 17 aftershocks were located by closely spaced eleven seismograph stations in a network that involved VSAT based real-time seismic monitoring.The largest aftershock of 3.5 and other aftershocks occurred within a small volume of 4 × 4 km horizontal extent and between depths of 10 and 14 km. The values of seismic moment () determined using P-wave spectra and Brune’s model based on 2 spectral shape ranges from 1018 to 1023 dyne-cm.The initial aftershocks occurred at greater depth compared to the later aftershocks.The time series of ground motion have been computed for recording sites using geometric ray theory and Green's function approach.The method for computing time series consists in integrating the far-field contributions of Green's function for a number of distributed point source.The generated waveforms have been compared with the observed ones.It has been inferred that the Kharsali earthquake occurred due to a northerly dipping low angle thrust fault at a depth of 14 km taking strike N279°E, dip 14° and rake 117°. There are two regions on the fault surface which have larger slip amplitudes (asperities)and the rupture which has been considered as circular in nature initiated from the asperity at a greater depth shifting gradually upwards.The two asperities cover only 10%of the total area of the causative fault plane.However,detailed seismic imaging of these two asperities can be corroborated with structural heterogeneities associated with causative fault to understand how seismogenesis is influenced by strong or weak structural barriers in the region.

  13. Tectonic implications and seismicity triggering during the 2008 Baluchistan, Pakistan earthquake sequence

    Science.gov (United States)

    Yadav, R. B. S.; Gahalaut, V. K.; Chopra, Sumer; Shan, Bin

    2012-02-01

    A damaging and widely felt moderate earthquake (Mw 6.4) hit the rural, mountainous region of southwestern Pakistan on October 28, 2008. The main shock was followed by another earthquake of identical magnitude (Mw 6.4) on the next day. The spatial distribution of aftershocks and focal mechanism revealed a NW-SE striking rupture with right-lateral strike-slip motion which is sympathetic to the NNW-SSE striking active mapped Urghargai Fault. The occurrence of strike-slip earthquakes suggests that along with the thrust faults, strike slip faults too are present beneath the fold-and-thrust belt of Sulaiman-Kirthar ranges and accommodates some of the relative motion of the Indian and Eurasian plates. To assess the characteristics of this sequence, the statistical parameters like aftershocks temporal decay, b-value of G-R relationship, partitioning of radiated seismic energy due to aftershocks, and spatial fractal dimension (D-value) have been examined. The b-value is estimated as 1.03 ± 0.42 and suggests the tectonic genesis of the sequence and crustal heterogeneity within rock mass. The low p-value of 0.89 ± 0.07 implies slow decay of aftershocks activity which is probably an evidence for low surface heat flow. A value of spatial fractal dimension of 2.08 ± 0.02 indicates random spatial distribution and that the source is a two-dimensional plane filled-up by fractures. The static coseismic Coulomb stress changes due to the foreshock (Mw 5.3) were found to increase stress by more than 0.04 bars at the hypocenter of the main shock, thus promoting the failure. The cumulative coseismic Coulomb stress changes due to the foreshock and mainshocks suggest that most of the aftershocks occurred in the region of increased Coulomb stress, and to the SE to the mainshock rupture.

  14. Six months later: Testing the Coulomb stress change model by examining calculations made immediately after the 12 May, 2008 Ms=8.0 Wenchuan earthquake

    Science.gov (United States)

    Parsons, T.; Ji, C.; Kirby, E.

    2008-12-01

    On the 12th of May, 2008 a devastating Ms=8.0 earthquake struck the eastern edge of the Tibetan Plateau, collapsing buildings and killing thousands in major cities aligned along the western Sichuan basin in China. After a high-magnitude earthquake like the 12 May event, rearrangement of stresses in the crust commonly causes subsequent damaging earthquakes. The Sichuan basin and surroundings are crossed by major active strike-slip and thrust faults. By 72 hours after the earthquake, coseismic stress changes were calculated on models of those faults, with many showing significant stress increases. Rapid mapping of stress changes was intended to locate fault sections with relatively higher odds of producing the largest aftershocks and to enable prospective testing of the static-stress triggering hypothesis. A recent prospective test of the method was conducted by McCloskey et al. [2005] after the great 2004 Sumatra earthquake, and was validated by a M=8.7 shock that struck three months later in a region calculated to have been stressed by the mainshock. Our test begins at the time peer review was completed, 38 days after the mainshock on 19 June, 2008. Thus aftershocks occurring between that time and the present can be used for prospective testing. As of this writing, in our test region magnitude greater than 4.0 aftershocks have been largely confined to the mainshock rupture zone, with virtually no activity on Sichuan basin faults with calculated stress increases. Examination of magnitude-frequency behavior of the aftershocks suggests either a corner magnitude at about magnitude 6, or a deficiency in the magnitude greater than 6 range. This experiment is ongoing, and time will tell if the Coulomb model is confirmed in the Sichuan region; our conclusion at present is that there has been no validation, and that use of a generalized aftershock forecast model would have been sufficient.

  15. Analysis of the 23 June 2001 Southern Peru Earthquake Using Locally Recorded Seismic Data

    Science.gov (United States)

    Tavera, H.; Comte, D.; Boroschek, R.; Dorbath, L.; Portugal, D.; Haessler, H.; Montes, H.; Bernal, I.; Antayhua, Y.; Salas, H.; Inza, A.; Rodriguez, S.; Glass, B.; Correa, E.; Balmaceda, I.; Meneses, C.

    2001-12-01

    The 23 June 2001, Mw=8.4 southern Peru earthquake ruptured the northern and central part of the previous large earthquake occurred on 13 August 1868, Mw ~9. A detailed analysis of the aftershock sequence was possible due to the deployment of a temporary seismic network along the coast in the Arequipa and Moquegua districts, complementing the Peruvian permanent stations. The deployed temporary network included 10 short period three component stations from the U. of Chile-IRD-France and 7 broad-band seismic stations from the Instituto Geofísico del Perú. This network operated during the first weeks after the mainshock and recorded the major aftershocks like the larger one occurred on 7 July 2001, Mw=7.5, this event defines the southern limit of the rupture area of the 2001 Peruvian earthquake. The majority of the aftershocks shows a thrusting fault focal mechanisms according with the average convergence direction of the subducting Nazca plate, however, normal faulting events are also present in the aftershock sequence like the 5 July 2001, Mw=6.6 one. The depth distribution of the events permitted a detailed definition of the Wadati-Benioff zone in the region. The segment between Ilo and Tacna did not participated in the rupture process of the 2001 southern Peru earthquake. Seismicity located near the political Peruvian-Chilean boundary was reliable determined using the data recorded by the northern Chile permanent network. Analysis of the mainshock and aftershock acelerograms recorded in Arica, northern Chile are also included. The occurrence of the 1995 Antofagasta (Mw=8.0) and the 2001 southern Peru earthquakes suggests that the probability of having a major earthquake in the northern Chile region increased, considering that the previous large earthquake in this region happened in 1877 (Mw ~9), and since that time no earthquake with magnitude Mw>8 had occurred inside of the 1877 estimated rupture area (between Arica and Antofagasta).

  16. TECTONIC AND SEISMOLOGICAL ASPECTS OF THE GREAT JAPAN EARTHQUAKE OF MARCH 11, 2011

    Directory of Open Access Journals (Sweden)

    Ivan N. Tikhonov

    2015-09-01

    Full Text Available The publication presents a review of the structure and seismotectonic features of the Pacific margin of the NorthEastern Honshu Island on the basis of data from seismic reflection and CDP, drilling and detailed seismic studies in view of the megaearthquake (Mw=9.0 which occurred in Japan on March 11, 2011. The megaearthquake is discussed in terms of its position in the succession of the strongest events (M≥7.6 in the area under study within the historical period and in the recent timeline. It is suggested that the period of recurrence is about 40 years for great events and about 1000+ years for megaearthquakes. A number of facts suggesting a probability of a planetaryscale earthquake in the Honshu Island region are revealed. Specifically, a seismic gap with a total length of about 800 km is determined in the study area. It is located southward of 39° north latitude has already manifested aftershocks of the megaearthquake of March 11, 2011. It is probable that the megaearthquake was related to the deep thrust along the Benioff zone and the Oyashio nappe being its structural cap rock in the middle Pacific slope. The sequence of its aftershocks is compared with those of the SumatraAndaman (Mw=9.3, 2004 and Simushir (Mw=8.3, 2006 earthquakes. It is established that development of the aftershock sequences of the first and second events was very similar in time, and development of the areas of aftershock epicentres of the first and third earthquakes is similar in space. The above similarities give grounds to suggest that an aftershock (M~8.0 is possible with a relative shifting from the main shock towards the deep trench.

  17. A fault and seismicity based composite simulation in northern California

    Directory of Open Access Journals (Sweden)

    M. B. Yıkılmaz

    2011-12-01

    Full Text Available We generate synthetic catalogs of seismicity in northern California using a composite simulation. The basis of the simulation is the fault based "Virtual California" (VC earthquake simulator. Back-slip velocities and mean recurrence intervals are specified on model strike-slip faults. A catalog of characteristic earthquakes is generated for a period of 100 000 yr. These earthquakes are predominantly in the range M = 6 to M = 8, but do not follow Gutenberg-Richter (GR scaling at lower magnitudes. In order to model seismicity on unmapped faults we introduce background seismicity which occurs randomly in time with GR scaling and is spatially associated with the VC model faults. These earthquakes fill in the GR scaling down to M = 4 (the smallest earthquakes modeled. The rate of background seismicity is constrained by the observed rate of occurrence of M > 4 earthquakes in northern California. These earthquakes are then used to drive the BASS (branching aftershock sequence model of aftershock occurrence. The BASS model is the self-similar limit of the ETAS (epidemic type aftershock sequence model. Families of aftershocks are generated following each Virtual California and background main shock. In the simulations the rate of occurrence of aftershocks is essentially equal to the rate of occurrence of main shocks in the magnitude range 4 < M < 7. We generate frequency-magnitude and recurrence interval statistics both regionally and fault specific. We compare our modeled rates of seismicity and spatial variability with observations.

  18. Crustal structure and fault geometry of the 2010 Haiti earthquake from temporary seismometer deployments

    Science.gov (United States)

    Douilly, Roby; Haase, Jennifer S.; Ellsworth, William L.; Bouin, Marie‐Paule; Calais, Eric; Symithe, Steeve J.; Armbruster, John G.; Mercier de Lépinay, Bernard; Deschamps, Anne; Mildor, Saint‐Louis; Meremonte, Mark E.; Hough, Susan E.

    2013-01-01

    Haiti has been the locus of a number of large and damaging historical earthquakes. The recent 12 January 2010 Mw 7.0 earthquake affected cities that were largely unprepared, which resulted in tremendous losses. It was initially assumed that the earthquake ruptured the Enriquillo Plantain Garden fault (EPGF), a major active structure in southern Haiti, known from geodetic measurements and its geomorphic expression to be capable of producing M 7 or larger earthquakes. Global Positioning Systems (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data, however, showed that the event ruptured a previously unmapped fault, the Léogâne fault, a north‐dipping oblique transpressional fault located immediately north of the EPGF. Following the earthquake, several groups installed temporary seismic stations to record aftershocks, including ocean‐bottom seismometers on either side of the EPGF. We use data from the complete set of stations deployed after the event, on land and offshore, to relocate all aftershocks from 10 February to 24 June 2010, determine a 1D regional crustal velocity model, and calculate focal mechanisms. The aftershock locations from the combined dataset clearly delineate the Léogâne fault, with a geometry close to that inferred from geodetic data. Its strike and dip closely agree with the global centroid moment tensor solution of the mainshock but with a steeper dip than inferred from previous finite fault inversions. The aftershocks also delineate a structure with shallower southward dip offshore and to the west of the rupture zone, which could indicate triggered seismicity on the offshore Trois Baies reverse fault. We use first‐motion focal mechanisms to clarify the relationship of the fault geometry to the triggered aftershocks.

  19. Integrated Geophysical Characteristics of the 2015 Illapel, Chile, Earthquake

    Science.gov (United States)

    Herman, M. W.; Yeck, W. L.; Nealy, J. L.; Hayes, G. P.; Barnhart, W. D.; Benz, H.; Furlong, K. P.

    2015-12-01

    On September 16th, 2015, an Mw 8.3 earthquake (USGS moment magnitude) ruptured offshore of central Chile, 50 km west of the city of Illapel and 200 km north of Santiago. The earthquake occurred just north of where the Juan Fernandez Ridge enters the subduction zone. In this study, we integrate multiple seismic and geodetic datasets, including multiple-event earthquake relocations; moment tensors of the Illapel mainshock, aftershocks, and prior regional seismicity; finite fault models (FFMs) of the mainshock rupture; subduction zone geometry; Coulomb stress transfer calculations; and co-seismic GPS offsets and InSAR images. These datasets allow us to (a) assess the context of the Illapel earthquake sequence with respect to historical seismicity in central Chile; (b) constrain the relationship between subduction geometry and the kinematic characteristics of the earthquake sequence; and (c) understand the distribution of aftershocks with respect to the rupture zone. Double source W-phase moment tensor analysis indicates the Illapel mainshock rupture began as a smaller Mw ~7.2 thrusting event before growing into a great-sized Mw 8.3 earthquake. Relocated aftershock seismicity is concentrated around the main region of slip, and few aftershocks occur on the megathrust shallower than ~15 km, despite the FFM indicating slip near the trench. This distribution is consistent with the aftershock behavior following the 2010 Maule and 2014 Iquique earthquakes: aftershocks primarily surround the rupture zones and are largely absent from regions of greatest slip. However, in contrast to the recent 2014 Iquique and 2010 Maule events, which ruptured in regions of the Chilean subduction zone that had not had large events in over a century, this earthquake occurred in a section of the subduction zone that hosted a large earthquake as recently as 1943, as well as earlier significant events in 1880 and 1822. At this section of the subduction zone, in addition to the impinging Juan

  20. The East Aegean Sea strong earthquake sequence of October–November 2005: lessons learned for earthquake prediction from foreshocks

    Directory of Open Access Journals (Sweden)

    G. A. Papadopoulos

    2006-01-01

    Full Text Available The seismic sequence of October–November 2005 in the Samos area, East Aegean Sea, was studied with the aim to show how it is possible to establish criteria for (a the rapid recognition of both the ongoing foreshock activity and the mainshock, and (b the rapid discrimination between the foreshock and aftershock phases of activity. It has been shown that before the mainshock of 20 October 2005, foreshock activity is not recognizable in the standard earthquake catalogue. However, a detailed examination of the records in the SMG station, which is the closest to the activated area, revealed that hundreds of small shocks not listed in the standard catalogue were recorded in the time interval from 12 October 2005 up to 21 November 2005. The production of reliable relations between seismic signal duration and duration magnitude for earthquakes included in the standard catalogue, made it possible to use signal durations in SMG records and to determine duration magnitudes for 2054 small shocks not included in the standard catalogue. In this way a new catalogue with magnitude determination for 3027 events was obtained while the standard catalogue contains 1025 events. At least 55 of them occurred from 12 October 2005 up to the occurrence of the two strong foreshocks of 17 October 2005. This implies that foreshock activity developed a few days before the strong shocks of 17 October 2005 but it escaped recognition by the routine procedure of seismic analysis. The onset of the foreshock phase of activity is recognizable by the significant increase of the mean seismicity rate which increased exponentially with time. According to the least-squares approach the b-value of the magnitude-frequency relation dropped significantly during the foreshock activity with respect to the b-value prevailing in the declustered background seismicity. However, the maximum likelihood approach does not indicate such a drop of b. The b-value found for the aftershocks that

  1. A new finite element model in studying earthquake triggering and continuous evolution of stress field

    Institute of Scientific and Technical Information of China (English)

    HU CaiBo; ZHOU YiJie; CAI YongEn

    2009-01-01

    In this paper, a new finite element model (FEM) In consideration of regional stress field and an earthquake triggering factor C are proposed for studying earthquake triggering and stress field evolution in an earthquake sequence. The factor C is defined as a ratio between the shear stress and the frictional strength on a slip surface, and it can be used to tell if earthquake is triggered or not. The new FEM and the factor C are used to study the aftershock triggering of the 1976 Tangshan earthquake sequence. The results indicate that the effects of the stress field and the heterogeneity of the Tangshan earthquake fault zone on the aftershock triggering are very important. The affershocks fallen in the earthquake triggering regions predicted by the new FEM are more than those fallen in the regions of △CFS≥0 predicted by seismic dislocation theory.

  2. Roles of Radon-222 and other natural radionuclides in earthquake prediction

    International Nuclear Information System (INIS)

    The concentration of 222Rn in subsurface waters is one of the natural parameters being investigated to help develop the capability to predict destructive earthquakes. Since 1966, scientists in several nations have sought to link radon variations with ongoing seismic activity, primarily through the dilatancy model for earthquake occurrences. Within the range of these studies, alpha-, beta-, and gamma-radiation detection techniques have been used in both discrete-sampling and continiuous-monitoring programs. These measured techniques are reviewed in terms of instrumentation adapted to seismic-monitoring purposes. A recent Lawrence Berkeley Laboratory study conducted in central California incorporated discrete sampling of wells in the aftershock area of the 1975 Oroville earthquake and continuous monitoring of water radon in a well on the San Andreas Fault. The results presented show short-term radon variations that may be associated with aftershocks and diurnal changes that may reflect earth tidal forces

  3. Increased pressure from rising bubbles as a mechanism for remotely triggered seismicity

    Science.gov (United States)

    Linde, A.T.; Sacks, I.S.; Johnston, M.J.S.; Hill, D.P.; Bilham, R.G.

    1994-01-01

    Aftershocks of large earthquakes tend to occur close to the main rupture zone, and can be used to constrain its dimensions. But following the 1992 Landers earthquake (magnitude M(w) = 7.3) in southern California, many aftershocks were reported in areas remote from the mainshock. Intriguingly, this remote seismicity occurred in small clusters near active volcanic and geothermal systems. For one of these clusters (Long Valley, about 400 km from the Landers earthquake), crustal deformation associated with the seismic activity was also monitored. Here we argue that advective overpressure provides a viable mechanism for remote seismicity triggered by the Landers earthquake. Both the deformation and seismicity data are consistent with pressure increases owing to gas bubbles rising slowly within a volume of magma. These bubbles may have been shaken loose during the passage of seismic waves generated by the mainshock.

  4. Completeness analysis of a seismic catalog

    Energy Technology Data Exchange (ETDEWEB)

    Tinti, S.; Mulargia, F. (Dipartimento di Fisica, Settore di Geofisica, Universita degli Studi di Bologna (Italy))

    A procedure to identify the incompleteness of a seismic catalog is developed. It consists of three steps: aftershock and swarm removal, detection and measure of the relative completeness, and evaluation of the absolute completeness. We assume that aftershock and swarm removal through a time-space window results in a set of independent events which are treated as a stationary Poisson process. Non-stationarities are easily identified by goodness of fit test and are taken as a measure of relative completeness. If absolute completeness of one portion of the catalog is assumed, the true occurrence rate may be evaluated for all magnitudes. The procedure is applied to estimate space-time probability of occurrence of earthquakes in Calabria and Sicily.

  5. Location and local magnitude of the Tocopilla earthquake sequence of Northern Chile

    Science.gov (United States)

    Fuenzalida, A.; Lancieri, M.; Madariaga, R. I.; Sobiesiak, M.

    2010-12-01

    The Northern Chile gap is generally considered to the site of the next megathurst event in Chile. The Tocopilla earthquake of 14 November 2007 (Mw 7.8) and aftershock series broke the southern end of this gap. The Tocopilla event ruptured a narrow strip of 120 km of length and a width that (Peyrat et al.; Delouis et al. 2009) estimated as 30 km. The aftershock sequence comprises five large thrust events with magnitude greater than 6. The main aftershock of Mw 6.7 occurred on November 15, at 15:06 (UTM) seawards of the Mejillones Peninsula. One month later, on December 16 2007, a strong (Mw 6.8) intraplate event with slab-push mechanism occurred near the bottom of the rupture zone. These events represent a unique opportunity for the study of earthquakes in Northern Chile because of the quantity and quality of available data. In the epicentral area, the IPOC network was deployed by GFZ, CNRS/INSU and DGF before the main event. This is a digital, continuously recording network, equipped with both strong-motion and broad-band instrument. On 29 November 2007 a second network named “Task Force” (TF) was deployed by GFZ to study the aftershocks. This is a dense network, installed near the Mejillones peninsula. It is composed by 20 short-period instruments. The slab-push event of 16 december 2007 occurred in the middle of the area covered by the TF network. Aftershocks were detected using an automatic procedure and manually revised in order to pick P and S arrivals. In the 14-28 November period, we detected 635 events recorded at the IPOC network; and a further 552 events were detected between 29 November and 16 December before the slab-push event using the TF network. The events were located using a vertically layered velocity model (Husen et al. 1999), using the NLLoc software of Lomax et al. From the broadband data we estimated the moment magnitude from the displacement spectra of the events. From the short-period instruments we evaluated local magnitudes using the

  6. Correlations between solid tides and worldwide earthquakes MS ≥ 7.0 since 1900

    Directory of Open Access Journals (Sweden)

    Q. H. Xu

    2012-03-01

    Full Text Available Most studies on the correlations between earthquakes and solid tides mainly concluded the syzygies (i.e. new or full moons of each lunar cycle have more earthquakes than other days in the month. We show a correlation between the aftershock sequence of the ML = 6.3 Christchurch, New Zealand, earthquake and the diurnal solid tide. Ms ≥ 7 earthquakes worldwide since 1900 are more likely to occur during the 0°, 90°, 180° or 270° phases (i.e. earthquake-prone phases of the semidiurnal solid earth tidal curve (M2. Thus, the semidiurnal solid tides triggers earthquakes. However, the long-term triggering effect of the lunar periodicity is uncertain. This proposal is helpful in defining possible origin times of aftershocks several days after a mainshock and can be used for warning of subsequent larger shocks.

  7. The systematic study of the stability of forecasts in the rate- and state-dependent model.

    Science.gov (United States)

    De Gaetano, D.; McCloskey, J.; Nalbant, S.

    2012-04-01

    Numerous observations have shown a general spatial correlation between positive Coulomb failure stress changes due to an earthquake and the locations of aftershocks. However this correlation does not give any indication of the rate from which we can infer the magnitude using the Gutenberg-Richter law. Dieterich's rate- and state-dependent model can be used to obtain a forecast of the observed aftershock rate for the space and time evolution of seismicity caused by stress changes applied to an infinite population of nucleating patches. The seismicity rate changes on this model depend on eight parameters: the stressing rate, the amplitude of the stress perturbation, the physical constitutive properties of faults, the spatial parameters (location and radii of the cells), the start and duration of each of the temporal windows as well as the background seismicity rate. The background seismicity is obtained from the epidemic type aftershock sequence model. We use the 1992 Landers earthquake as a case study, using the Southern California Earthquake Data Centre (SCEDC) catalogue, to examine if Dieterich's rate- and state-dependent model can forecast the aftershock seismicity rate. A systematic study is performed on a range of values on all the parameters to test the forecasting ability of this model. The results obtained suggest variable success in forecasting, when varying the values for the parameters, with the spatial and temporal parameters being the most sensitive. Dieterich's rate- and state-dependent model is compared with a well studied null hypothesis, the Omori-Utsu law. This law describes the aftershock rate as a power law in time following the main shock and depends on only three parameters: the aftershock productivity, the elapsed time since the main shock and the constant time shift, all of which can be estimated in the early part of the aftershock sequence and then extrapolated to give a long term rate forecast. All parameters are estimated using maximum

  8. Statistical Studies of Induced and Triggered Seismicity at The Geysers, California

    Science.gov (United States)

    Hawkins, Angela

    This study considers the statistics of induced and triggered seismicity at The Geysers geothermal field, California. Little seismicity was reported before steam extraction began in 1960. In 1980 the residual water associated with power generation was re-injected, producing induced seismicity. Beginning in 1997 large-scale injections of cold water began in order to enhance the generation of steam. This led to an increase in M 1.25 events. The GR and decay statistics will be given. However, in order to separate second-order aftershocks from triggered aftershocks, an additional triggered sequence is studied. The M = 7.2 4/4/10 Baja earthquake had some 34 M >1.25 triggered events in the first hour including a M = 3.37 event.

  9. Precursory transient slip during the 2001 Mw = 8.4 Peru earthquake sequence from continuous GPS

    Science.gov (United States)

    Melbourne, Timothy I.; Webb, Frank H.

    2002-11-01

    Two-hour position estimates from a continuous GPS station located at Arequipa, Peru, document precursory deformation beginning 18 hours prior to an Mw = 7.6 aftershock of the June 23rd 2001 Mw = 8.4 earthquake. This preseismic signal appears on the north and east components as a slow displacement with an amplitude twice that of the subsequent coseismic. Analysis of three years of 18-hour rate measurement shows this signal to be unprecedented and beyond four standard deviations from the mean rate. The best fitting centroid is directionally consistent with slow slip along the plate interface and suggests the preseismic deformation arises from creep near the aftershock rupture. This implies the Nazca-South American plate interface slipped slowly prior to seismogenic faulting. These observations indicate the Mw = 7.6 earthquake grew out of slow slip along the plate interface and clearly demonstrate the breadth of slip rates accommodated by subduction zone plate interfaces.

  10. Analysis of acoustic-seismic coupling behaviour for CTBT on-site inspection performance improvement

    Energy Technology Data Exchange (ETDEWEB)

    Liebsch, Mattes; Knoop, Jan-Frederik [Technische Univ. Dortmund (Germany)

    2013-07-01

    After teleseismic detection of a big underground explosion, during on-site inspections under the Comprehensive Nuclear Test-Ban Treaty (CTBT) weak seismic signals from aftershocks are to be detected. These, however, can be masked by soil vibrations which are caused by acoustic waves which couple to the ground. To analyse the coupling behaviour between acoustic waves and soil vibrations several experiments with different acoustic sources (helicopters, firecrackers, loudspeaker) were performed. Of special interest is the influence of surface waves, excited in a larger area around the sensor, which can superpose constructively at the position of the sensor and can increase the measured seismic signal. A better understanding of the acoustic-seismic coupling can be used to develop guidelines for seismic aftershock measurements, such as a suitable sensor setup, with the goal of reducing or even preventing disturbing signals to improve the performance of on-site inspections for the CTBT.

  11. Rupture process of the 2016 Kumamoto earthquake in relation to the thermal structure around Aso volcano

    Science.gov (United States)

    Yagi, Yuji; Okuwaki, Ryo; Enescu, Bogdan; Kasahara, Amato; Miyakawa, Ayumu; Otsubo, Makoto

    2016-07-01

    We constructed the rupture process model for the 2016 Kumamoto, Japan, earthquake from broadband teleseismic body waveforms (P-waves) by using a novel waveform inversion method that takes into account the uncertainty of Green's function. The estimated source parameters are: seismic moment = 5.1 × 1019 Nm (Mw = 7.1), fault length = 40 km, and fault width = 15 km. The mainshock rupture mainly propagated northeastward from the epicenter, for about 30 km, along an active strike-slip fault. The rupture propagation of the mainshock decelerated and terminated near the southwest side of the Aso volcano; the aftershock activity was low around the northeastern edge of the major slip area. Our results suggest that the rupture process of the mainshock and the distribution of aftershocks were influenced by the high-temperature area around the magma chamber of Mt. Aso.

  12. Technologies and new approaches used by the INGV EMERGEO Working Group for real-time data sourcing and processing during the Emilia Romagna (northern Italy 2012 earthquake sequence

    Directory of Open Access Journals (Sweden)

    Giuliana Alessio

    2012-10-01

    Full Text Available On May 20, 2012, a Ml 5.9 seismic event hit the Emilia Po Plain, triggering intense earthquake activity along a broad area of the Po Plain across the provinces of Modena, Ferrara, Rovigo and Mantova (Figure 1. Nine days later, on May 29, 2012, a Ml 5.8 event occurred roughly 10 km to the SW of the first main shock. These events caused widespread damage and resulted in 26 victims. The aftershock area extended over more than 50 km and was elongated in the WNW-ESE direction, and it included five major aftershocks with 5.1 ≤Ml ≤5.3, and more than 2000 minor events (Figure 1. In general, the seismic sequence was confined to the upper 10 km of the crust. Minor seismicity with depths ranging from 10 km to 30 km extended towards the southern sector of the epicentral area (ISIDe, http://iside.rm.ingv.it/. […