WorldWideScience

Sample records for aftershocks

  1. Aftershock identification

    OpenAIRE

    Zaliapin, Ilya; Gabrielov, Andrei; 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...

  2. 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.

  3. Mechanical origin of aftershocks.

    Science.gov (United States)

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

    2015-01-01

    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. PMID:26497720

  4. Spatiotemporal correlations of aftershock sequences

    OpenAIRE

    Peixoto, Tiago P.; Doblhoff-Dier, Katharina; 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 H...

  5. 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.

  6. 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...

  7. Larger aftershocks happen farther away: Nonseparability of magnitude and spatial distributions of aftershocks

    Science.gov (United States)

    Elst, Nicholas J.; Shaw, Bruce E.

    2015-07-01

    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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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...

  13. 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

  14. 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).

  15. 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.

  16. How Long is an Aftershock Sequence?

    Science.gov (United States)

    Godano, Cataldo; Tramelli, Anna

    2016-06-01

    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.

  17. 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.

  18. 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.

  19. Aftershock Decay Rates in the Iranian Plateau

    Science.gov (United States)

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

    2016-04-01

    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 uc(Gardner) and uc(Knopoff) (Bull Seismol Soc Am 64:1363-1367, 1974); second, a modified version of this using spatial windowing based on the uc(Wells) and uc(Coppersmith) (Bull Seismol Soc Am 84:974-1002, 1994) relations; and third, the uc(Burkhard) and uc(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 uc(Gardner) and uc(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.

  20. Improved understanding of aftershock triggering by waveform detection of aftershocks with GPU computing

    Science.gov (United States)

    Peng, Z.; Meng, X.; Hong, B.; Yu, X.

    2012-12-01

    Large shallow earthquakes are generally followed by increased seismic activities around the mainshock rupture zone, known as "aftershocks". Whether static or dynamic triggering is responsible for triggering aftershocks is still in debate. However, aftershocks listed in standard earthquake catalogs are generally incomplete immediately after the mainshock, which may result in inaccurate estimation of seismic rate changes. Recent studies have used waveforms of existing earthquakes as templates to scan through continuous waveforms to detect potential missing aftershocks, which is termed 'matched filter technique'. However, this kind of data mining is computationally intensive, which raises new challenges when applying to large data sets with tens of thousands of templates, hundreds of seismic stations and years of continuous waveforms. The waveform matched filter technique exhibits parallelism at multiple levels, which allows us to use GPU-based computation to achieve significant acceleration. By dividing the procedure into several routines and processing them in parallel, we have achieved ~40 times speedup for one Nvidia GPU card compared to sequential CPU code, and further scaled the code to multiple GPUs. We apply this paralleled code to detect potential missing aftershocks around the 2003 Mw 6.5 San Simeon and 2004 Mw6.0 Parkfield earthquakes in Central California, and around the 2010 Mw 7.2 El Mayor-Cucapah earthquake in southern California. In all these cases, we can detect several tens of times more earthquakes immediately after the mainshocks as compared with those listed in the catalogs. These newly identified earthquakes are revealing new information about the physical mechanisms responsible for triggering aftershocks in the near field. We plan to improve our code so that it can be executed in large-scale GPU clusters. Our work has the long-term goal of developing scalable methods for seismic data analysis in the context of "Big Data" challenges.

  1. 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

  2. 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...

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. Comparison of the non-proliferation event aftershocks with other Nevada Test Site events

    International Nuclear Information System (INIS)

    As part of a larger effort to develop technology for on-site inspection of ambiguous underground seismic events, we have been working to identify phenomenology of aftershock seismicity which would be useful for discriminating between nuclear explosions, chemical explosions, earthquakes or other seismic events. Phenomenology we have investigated includes; the spatial distribution of aftershocks, the number of aftershocks as a function of time after the main event, the size of the aftershocks, and waveform frequency content. Our major conclusions are: (1) Depending on local geologic conditions, aftershock production rate two weeks after zero time ranges from 1 to 100 per day. (2) Aftershocks of concentrated chemical explosions such as the NPE are indistinguishable from aftershocks of nuclear explosions. (3) Earthquake and explosion aftershock sequences may be differentiated on the basis of depth, magnitude, and in some cases, frequency content of seismic signals

  9. 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.

  10. The aftershock dynamics of the Sumatra-Andaman earthquake

    Science.gov (United States)

    Guglielmi, A. V.; Zotov, O. D.; Zavyalov, A. D.

    2014-01-01

    The aftershocks of the catastrophic Sumatra-Andaman earthquake of December 26, 2004 ( M = 9.0) are analyzed in the general context of the theory of critical phenomena. The analysis relies on the idea that, according to this theory, critical transitions have two key properties. The first is that the intensity of the fluctuations in a dynamical system monotonically increases with the approach of the bifurcation point, so that at a certain time instant, a sufficiently strong internal pulse initiates the catastrophe. This transition can be treated as spontaneous. The second property is that the reactance of the dynamical system drastically increases on the approach of the bifurcation. Even a weak external perturbation in the near-threshold interval can result in a catastrophe. In this case, it is reasonable to refer to the critical transition as an induced transition. The aftershocks of the Sumatra-Andaman earthquake are likely to demonstrate the typical features of induced seismicity. First, the strongest aftershock ( M = 7.2) occurred 3 h 20 min after the main shock. It could have probably been induced by the round-trip seismic echo. Second, it was found that the spectral density of the aftershock sequence significantly increases at about ˜0.3 mHz, which is close to the frequency of the spheroidal mode 0S2. This suggests that the spheroidal oscillations of the Earth, which are excited by the main seismic shock, modulate the aftershock activity. Both hypotheses are supported by the analysis of the aftershocks of the Tohoku earthquake of March 11, 2011 ( M = 9.0).

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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

  16. 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

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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...

  2. Foreshocks and Aftershocks of the Great 1857 California Earthquake

    OpenAIRE

    Meltzner, Aron J.; Wald, David J.

    1999-01-01

    The San Andreas fault is the longest fault in California and one of the longest strike-slip faults anywhere in the world, yet we know little about many aspects of its behavior before, during, and after large earthquakes. We conducted a study to locate and to estimate magnitudes for the largest foreshocks and aftershocks of the 1857 M 7.9 Fort Tejon earthquake on the central and southern segments of the fault. We began by searching archived first-hand accounts from 1857 through 1862, by groupi...

  3. Relationship Between The Seismicity Parameters of Aftershock Sequences of Earthquakes Which Recently Occurred in Turkey

    International Nuclear Information System (INIS)

    In this study, the relationships between some seismicity parameters of aftershock sequences are investigated with the orthogonal regression method using the aftershock sequences of eight earthquakes occurred in Turkey between 1995 and 2004. Notwithstanding it is calculated a few positive and negative relationships, no relations are observed between some parameters

  4. 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

  5. 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.

  6. 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.

  7. 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.

  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. 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

  11. 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.

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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 ≤  M< 3 mainshocks, the seismicity decay 5 min before the mainshocks is indistinguishable from the decay five minutes afterwards, indicating that the mainshocks have no effect at distances outside their static triggering range. Omori temporal decay, the fundamental signature of 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.

  20. 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".

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. The partitioning of radiated energy and the largest aftershock of seismic sequences occurred in the northeastern Italy and western Slovenia

    Science.gov (United States)

    Gentili, S.; Bressan, G.

    2008-07-01

    We analyzed the most relevant seismic sequences that occurred from 1977 to 2007 in the Friuli-Venezia Giulia region (northeastern Italy) and western Slovenia. The eight aftershock sequences were triggered by low- to moderate-magnitude earthquakes with mainshock duration magnitude ranging from 3.7 to 5.6. The b-value of the Gutenberg-Richter law varies from 0.8 to 1.1. The modified Omori’s modeling of the sequences evidences values of the p exponent ranging from 0.8 to 1.0. Using the Reasenberg and Jones ( Science 243:1173-1176, 1989; Science 265:1251-1252, 1994) approach, we computed the probabilistic estimate of the aftershock rates and the largest aftershock in given time intervals. The difference in magnitude between the mainshock and the largest aftershock is calculated according to the modified Båth law and using an approach that considers the partitioning of the radiated seismic energy between mainshock and aftershocks. The partitioning of the radiated seismic energy appears to play a significant role in the evolution of the sequences. We define the parameter R ES as the ratio between the radiated seismic energy of the mainshock and the summation of the seismic energy radiated by the aftershocks. The difference in magnitude between the mainshock and the largest aftershock, calculated with the parameter R ES, agrees well with the observed difference. In most sequences, the parameter R ES decreases very quickly until the occurrence of the largest aftershock and then becomes constant. By analyzing the values of R ES during the early hours following the mainshock, we found that the R ES values after 24 h are well related to the final ones, calculated on the whole sequence, and to the differences in magnitude between the mainshock and the largest aftershock.

  8. The Mw 8.1 2014 Iquique, Chile, seismic sequence: a tale of foreshocks and aftershocks

    Science.gov (United States)

    Cesca, S.; Grigoli, F.; Heimann, S.; Dahm, T.; Kriegerowski, M.; Sobiesiak, M.; Tassara, C.; Olcay, M.

    2016-03-01

    The 2014 April 1, Mw 8.1 Iquique (Chile) earthquake struck in the Northern Chile seismic gap. With a rupture length of less than 200 km, it left unbroken large segments of the former gap. Early studies were able to model the main rupture features but results are ambiguous with respect to the role of aseismic slip and left open questions on the remaining hazard at the Northern Chile gap. A striking observation of the 2014 earthquake has been its extensive preparation phase, with more than 1300 events with magnitude above ML 3, occurring during the 15 months preceding the main shock. Increasing seismicity rates and observed peak magnitudes accompanied the last three weeks before the main shock. Thanks to the large data sets of regional recordings, we assess the precursor activity, compare foreshocks and aftershocks and model rupture preparation and rupture effects. To tackle inversion challenges for moderate events with an asymmetric network geometry, we use full waveforms techniques to locate events, map the seismicity rate and derive source parameters, obtaining moment tensors for more than 300 events (magnitudes Mw 4.0-8.1) in the period 2013 January 1-2014 April 30. This unique data set of fore- and aftershocks is investigated to distinguish rupture process models and models of strain and stress rotation during an earthquake. Results indicate that the spatial distributions of foreshocks delineated the shallower part of the rupture areas of the main shock and its largest aftershock, well matching the spatial extension of the aftershocks cloud. Most moment tensors correspond to almost pure double couple thrust mechanisms, consistent with the slab orientation. Whereas no significant differences are observed among thrust mechanisms in different areas, nor among thrust foreshocks and aftershocks, the early aftershock sequence is characterized by the presence of normal fault mechanisms, striking parallel to the trench but dipping westward. These events likely occurred

  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. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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

    2016-04-01

    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.

  18. 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.

  19. 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

  20. 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

  1. 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

  2. Implications of rate-and-state friction for properties of aftershock sequence: Quasi-static inherently discrete simulations

    Science.gov (United States)

    Ziv, A.; Rubin, A. M.

    2003-01-01

    [1994] modeled the response to a stress step of a population of faults governed by rate- and state-dependent friction. This model assumes that aftershocks nucleate over areas on the fault that at the time of the main shock are already accelerating toward failure and disregards the effect of interactions among aftershocks. The main objective of this study is to examine consequences of relaxing these underlying assumptions. Aftershock activity is simulated using an inherently discrete earthquake fault model, with a fault surface governed by an approximate constitutive friction law similar to the one used by Dieterich. We find that the governing equations in nondimensional form are a function of three main parameters and explore the effect of these parameters on the simulated catalogs. We derive a simple expression for the time-dependent seismicity response to a stress step that approximates the effect of multiple interactions among aftershocks as a time-dependent stressing rate. Close match is found between the simulated seismicity response to a stress step and that predicted analytically. However, the numerical simulations show that the effect of the main shock is not only to raise the local seismicity rate but also to systematically modify the earthquake size distribution. As a result, the actual seismicity rate change early during the aftershock sequence may be higher than that predicted, whereas seismicity rate late in the sequence may be lower than that predicted. Such a modification of the earthquake size distribution can explain observations of lower b values immediately following a stress step.

  3. 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.

  4. 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%.

  5. 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...

  6. 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

  7. The Hellenic Seismological Network Of Crete (HSNC): Validation and results of the 2013 aftershock sequences

    Science.gov (United States)

    Chatzopoulos, Georgios; Papadopoulos, Ilias; Vallianatos, Filippos

    2015-04-01

    The number and quality of seismological networks in Europe has increased in the past decades. Nevertheless, the need for localized networks monitoring areas of great seismic and scientific interest is constant. Hellenic Seismological Network of Crete (HSNC) covers this need for the vicinity of the South Aegean Sea and Crete Island. In the present work with the use of Z-map software (www.seismo.ethz.ch) the spatial variability of Magnitude of Completeness (Mc) is calculated from HSNC's manual analysis catalogue of events for the period 2011 until today, proving the good coverage of HSNC in the areas. Furthermore the 2013, South Aegean seismicity where two large shallow earthquakes occurred in the vicinity of Crete Island, is discussed. The first event takes place on 15th June 2013 in the front of the Hellenic Arc, south from central Crete, while the second one on 12th October, 2013 on the western part of Crete. The two main shocks and their aftershock sequences have been relocated with the use of hypoinverse earthquake location software and an appropriate crust model. The HSNC identified more than 500 and 300 aftershocks respectively followed after the main events. The detailed construction of aftershocks catalogue permits the applicability of modern theories based on complexity sciences as described recently in the frame of non extensive statistical physics. In addition site effects in the stations locations are presented using event and noise recordings. This work was implemented through the project IMPACT-ARC in the framework of action "ARCHIMEDES III-Support of Research Teams at TEI of Crete" (MIS380353) of the Operational Program "Education and Lifelong Learning" and is co-financed by the European Union (European Social Fund) and Greek national funds References A. Tzanis and F. Vallianatos, "Distributed power-law seismicity changes and crustal deformation in the EW Hellenic Arc", Natural Hazards and Earth Systems Sciences, 3, 179-195, 2003 F. Vallianatos, G

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

    Science.gov (United States)

    Batac, Rene C.

    2016-02-01

    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.

  9. 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).

  10. Distribution and migration of aftershocks of the 2010 Mw 7.4 Ogasawara Islands intraplate normal-faulting earthquake related to a fracture zone in the Pacific plate

    Science.gov (United States)

    Obana, Koichiro; Takahashi, Tsutomu; No, Tetsuo; Kaiho, Yuka; Kodaira, Shuichi; Yamashita, Mikiya; Sato, Takeshi; Nakamura, Takeshi

    2014-04-01

    describe the aftershocks of a Mw 7.4 intraplate normal-faulting earthquake that occurred 150 km east Ogasawara (Bonin) Islands, Japan, on 21 December 2010. It occurred beneath the outer trench slope of the Izu-Ogasawara trench, where the Pacific plate subducts beneath the Philippine Sea plate. Aftershock observations using ocean bottom seismographs (OBSs) began soon after the earthquake and multichannel seismic reflection surveys were conducted across the aftershock area. Aftershocks were distributed in a NW-SE belt 140 km long, oblique to the N-S trench axis. They formed three subparallel lineations along a fracture zone in the Pacific plate. The OBS observations combined with data from stations on Chichi-jima and Haha-jima Islands revealed a migration of the aftershock activity. The first hour, which likely outlines the main shock rupture, was limited to an 80 km long area in the central part of the subsequent aftershock area. The first hour activity occurred mainly around, and appears to have been influenced by, nearby large seamounts and oceanic plateau, such as the Ogasawara Plateau and the Uyeda Ridge. Over the following days, the aftershocks expanded beyond or into these seamounts and plateau. The aftershock distribution and migration suggest that crustal heterogeneities related to a fracture zone and large seamounts and oceanic plateau in the incoming Pacific plate affected the rupture of the main shock. Such preexisting structures may influence intraplate normal-faulting earthquakes in other regions of plate flexure prior to subduction.

  11. Spatial and Temporal Variations of Aftershock Activity of the 23 October 2011 Mw 7.1 Van, Turkey, Earthquake

    Science.gov (United States)

    De Gori, P.; Akinci, A.; Lucente, F.; Malagnini, L.; Kilic, T.

    2012-12-01

    A Mw 7.1 earthquake struck on October 23, 201 the Van Lake region causing vast damage in the cities of Van and Ercis, in Eastern Turkey. The main shock was followed by a very high number of aftershocks: in the first week 114 earthquakes occurred with magnitudes between 4.0 and 4.9 and 7 earthquakes with magnitudes greater than ML 5.0. Within the first month, daily average number of aftershock was around 180 for earthquakes ML>2.0. By 09 December 2011, a total of 6284 aftershocks were recorded by the Prime Ministry Disaster and Emergency Management Presidency (AFAD) permanent network. In this study we take an advantage of this large dataset to examine the spatial and temporal properties of the Van earthquake aftershock activity. In order to do so earthquakes are relocated with the computer code HYPOELLIPSE (Lahr and Snoke, 2001) and a 1D velocity model optimized for the region. The distribution of the relocated aftershocks, with ML >2.5 defines a clear 60-70 km long and 30-35 km wide NE-SW trending structure which is an agreement with the source rupture models derived for the main event. We then derive the spatial distribution of b-value of the Gutenberg-Richter law—as well as complementary seismicity parameters—along the surface projection of the fault plane. Calculations are made for two independent aftershock sub-catalogs before and after where a stable magnitude of completeness is reached. Finally, we correlate the observed b-value patterns with slip distribution models of the main shock obtained through the inversion of seismological and geodetic data.

  12. Finite-fault parameters of the September 1976 M > 5 aftershocks in Friuli (NE Italy)

    Science.gov (United States)

    Moratto, L.; Suhadolc, P.; Costa, G.

    2012-04-01

    On September 1976 four strong aftershocks with M > 5 occurred in the Friuli area (NE Italy) causing more damage with respect to that caused by the M6.4 mainshock that occurred on May 6, 1976. Although many studies have been published on the 1976 Friuli seismic sequence, only recently have finite-fault models based on geological considerations (Galadini et al., 2005; Burrato et al., 2008) been proposed for these aftershocks. The aim of our study is to model the September 1976 seismic sources as finite faults by computing finite-fault synthetic seismograms for several possible proposed fault models and nucleation locations. The seismicity distribution following each of the four events gives us some further information about the areal extent of the related fault and its rupture propagation. About 9000 synthetic seismograms are computed for all the tested fault models adopting the reflectivity technique for an upper cutoff frequency of 1 Hz. A "trial and error" procedure is used to find the best fit between the recorded and computed peak ground acceleration derived from signals filtered at 1 Hz, that identifies the final models. These are selected also on the basis of the existing knowledge of fault traces in the area. The four best-fit models seem to be well related to the main Barcis-Staro Selo fault system, their spatial-temporal sequence evidencing an overall progressive East-to-West migration of the seismic activity related to the 1976 sequence.

  13. 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.

  14. 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.

  15. Introduction: Aftershocked

    DEFF Research Database (Denmark)

    Warner, Cameron; Hindman, Heather; Snellinger, Amanda

    2015-01-01

    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 of...... the role of academia in a time of crisis. Much of what is often lost in the rush to rebuild is nuance and historical context, an understanding of the particularities of place in the form of reflections on the past and its implications for the future. Anthropologists working in sites of disaster have...

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

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

    Science.gov (United States)

    Pollitz, Fred F; Stein, Ross S; Sevilgen, Volkan; Bürgmann, Roland

    2012-10-11

    Large earthquakes trigger very small earthquakes globally during passage of the seismic waves and during the following several hours to days, but so far remote aftershocks of moment magnitude M ≥ 5.5 have not been identified, 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 away. 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. PMID:23023131

  8. Statistical analysis of seismicity and hazard estimation for Italy (mixed approach). Statistical parameters of main shocks and aftershocks in the Italian region

    International Nuclear Information System (INIS)

    The catalog of earthquakes of Italy (1900-1993) is analyzed in the present work. The following problems have been considered: 1) a choice of the operating magnitude, 2) an analysis of data completeness, and 3) a grouping (in time and in space). The catalog has been separated into main shocks and aftershocks. Statistical estimations of seismicity parameters (a,b) are performed for the seismogenetic zones defined by GNDT. The non-standard elements of the analysis performed are: (a) statistical estimation and comparison of seismicity parameters under the condition of arbitrary data grouping in magnitude, time and space; (b) use of a not conventional statistical method for the aftershock identification; the method is based on the idea of optimizing two kinds of errors in the aftershock identification process; (c) use of the aftershock zones to reveal seismically- interrelated seismogenic zones. This procedure contributes to the stability of the estimation of the ''b-value'' Refs, 25 figs, tabs

  9. Aftershocks of the 2010 Mw 7.4 Bonin Islands normal-faulting earthquake: Implication for deformation of the Pacific Plate

    Science.gov (United States)

    Obana, K.; Takahashi, T.; No, T.; Kaiho, Y.; Kodaira, S.; Yamashita, M.; Sato, T.; Noguchi, N.; Nakamura, T.

    2011-12-01

    A Mw 7.4 normal-faulting earthquake occurred 150 km east of Chichi-jima Island, Bonin Islands, Japan on December 21, 2010 (UTC). This is an earthquake occurred within the Pacific plate beneath the outer trench-slope region along the Izu-Ogasawara (Bonin) trench, where the Pacific plate subducts beneath the Philippine Sea plate. According to Japan Meteorological Agency (JMA), the associated tsunami was observed over a wide area along the Pacific coast of Japan. Normal faulting earthquakes in outer trench-slope region are a result of the bending of the incoming/subducting oceanic plates. The bending-related normal faults cutting the oceanic plate are likely associated with hydration of the oceanic plate prior to subduction [e.g., Ranero et al., 2003]. The normal faulting earthquakes can be a key to understand deformation and resulting hydration of the oceanic plate. That is also important for consideration of tsunami generation in shallow outer trench-slope region. Aftershock observation of the 2010 Bonin Islands earthquake were conducted by R/V Kairei of Japan Agency for Marine-Earth Science and Technology (JAMSTEC) using ocean bottom seismographs (OBSs). First OBS was deployed in the source area on December 25, 2010 and retrieved on January 7, 2011. Other 4 OBSs were deployed on January 6 and 7 and retrieved on March 11 and 12, 2011. Overall aftershocks distributed in a 130 km long area extended in a NW-SE direction although Izu-Bonin trench extends N-S direction in this area. Most of the aftershocks were located at depths shallower than 30 km, corresponding to the oceanic crust and the uppermost mantle of the Pacific plate. The aftershocks show a complicated distribution. In the central part of the aftershock area, aftershocks formed three subparallel lines with roughly 15 km intervals oriented NW-SE direction. In the southeastern part of the aftershock area away from the trench, the aftershocks distributed along ESE-WNW direction. We estimated aftershock

  10. 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%.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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.

  19. 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.

  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. 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.

  2. Stress inversion from the focal mechanism solution of Bam earthquake aftershocks (Iran, 2003)

    International Nuclear Information System (INIS)

    Stress determination can be performed by different inversion techniques using fault-slip data resulted from focal mechanism solutions obtained from earthquake shock records. Inversion methods, explicitly or implicitly, use the object function that evaluates the fitness of some assumed stress state to the fault-slip data. The optimal stress state is indicated by the extremum value of the function. Therefore, the process comes down to a peak detection problem. The authors used slip data corresponding to the aftershocks of the Bam earthquake that occurred in Iran in 2003. Several stress states are found in close neighbourhood to the maximum value of the object function. Therefore, the selection of the optimal solution becomes very difficult. To overcome this problem, all the stress states with less than 10% difference from the maximum value of the object function were selected. These states were then categorized according to their stress ratios. Grid points related to the maximum and minimum principal stresses were separately projected on a stereogram. Significant stress states were identified as highly concentrated grid points for each category. The results obtained by this method were compared with those obtained by applying the multiple inverse method. The stress results obtained also matched very closely with the pre-existing fault direction in the region

  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. 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.

  5. 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.

  6. 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.

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

    Science.gov (United States)

    Diansari, Angga Vertika; Purwana, Ibnu; Subakti, Hendri

    2015-04-01

    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.

  8. 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

  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. Sequence-based Parameter Estimation for an Epidemiological Temporal Aftershock Forecasting Model using Markov Chain Monte Carlo Simulation

    Science.gov (United States)

    Jalayer, Fatemeh; Ebrahimian, Hossein

    2014-05-01

    Introduction The first few days elapsed after the occurrence of a strong earthquake and in the presence of an ongoing aftershock sequence are quite critical for emergency decision-making purposes. Epidemic Type Aftershock Sequence (ETAS) models are used frequently for forecasting the spatio-temporal evolution of seismicity in the short-term (Ogata, 1988). The ETAS models are epidemic stochastic point process models in which every earthquake is a potential triggering event for subsequent earthquakes. The ETAS model parameters are usually calibrated a priori and based on a set of events that do not belong to the on-going seismic sequence (Marzocchi and Lombardi 2009). However, adaptive model parameter estimation, based on the events in the on-going sequence, may have several advantages such as, tuning the model to the specific sequence characteristics, and capturing possible variations in time of the model parameters. Simulation-based methods can be employed in order to provide a robust estimate for the spatio-temporal seismicity forecasts in a prescribed forecasting time interval (i.e., a day) within a post-main shock environment. This robust estimate takes into account the uncertainty in the model parameters expressed as the posterior joint probability distribution for the model parameters conditioned on the events that have already occurred (i.e., before the beginning of the forecasting interval) in the on-going seismic sequence. The Markov Chain Monte Carlo simulation scheme is used herein in order to sample directly from the posterior probability distribution for ETAS model parameters. Moreover, the sequence of events that is going to occur during the forecasting interval (and hence affecting the seismicity in an epidemic type model like ETAS) is also generated through a stochastic procedure. The procedure leads to two spatio-temporal outcomes: (1) the probability distribution for the forecasted number of events, and (2) the uncertainty in estimating the

  11. Decay and expansion of the early aftershock activity following the 2011, M_w9.0 Tohoku earthquake

    OpenAIRE

    Lengliné, O.; B. Enescu; Z. Peng; Shiomi, K.

    2012-01-01

    The 2011, M_w9.0 Tohoku earthquake was followed by an abundant amount of seismicity providing a unique opportunity to analyze the triggering mechanism of great earthquakes. Although the Tohoku earthquake occurred close to a dense seismic network, many aftershocks that occurred in the first few hours after the mainshock are not recorded in the earthquake catalogs. Here we use a template waveform approach to recover as many as possible missing events in the first 12 hours following the Tohoku m...

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

    OpenAIRE

    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...

  13. Fault Simulator with Dilatant Effects Used to Investigate Statistics of Foreshocks/Aftershocks, Including Magnitude Dependent Seismic Quiescence

    Science.gov (United States)

    Smith, D. E.; Sacks, S. I.; Rydelek, P. A.

    2011-12-01

    We add dilatant effects to a fault simulator to include physics consistent with observations of seismic quiescence. Using this simulator, we examine precursory and aftershock statistics of major events, changes in b-value, correlations between slip and static stress changes, changes in the in-plane focal mechanisms, and temporal decay of aftershocks. Seismic quiescence has been observed for a number major events including, 1982 Urakawa-Oki earthquake [Taylor et al., 1992], 1994 Hokkaido-Toho-Oki earthquake [Takanami et al., 1996], 1994 Northridge earthquake [Smith and Sacks, 2011], 1995 Kobe earthquake [Enescu et al., 2011], 1988 Spitak earthquake [Wysse and Martirosyan, 1998], and 2011 Tohoku earthquake [Katsumata, in press, 2011]. The physics of dilatancy theory [Nur, 1972; Whitcomb et al., 1973; Scholz et al., 1973], which we include in the simulator, is proposed as an explanation for seismic quiescence [Takanami et al., 1996; Scholz, 2000]. As the fault is loaded toward failure and the stress increases, if the stress is sufficiently high, the rock can begin to dilate. As dilation causes an increase in the rock volume, the pore pressure decreases, the effective normal stress increases, and the fault core strengthens [Rice, 1975]. Because the fault core supports more of the stress, the seismicity of the surrounding region will decrease as is observed. Over time (~2-20 years) the water will percolate back into the fault core from the surrounding region. The pore pressure in the fault core increases again, the normal stress decreases, and failure is encouraged. This dilatant effect on the fault core foreshocks, surrounding quiescence zone, and the aftershocks, can be studied by modifying the fault simulator of Sacks and Rydelek [1995]; Rydelek and Sacks [1996]. Based on simple physics: discrete patches, Coulomb failure, and redistribution of stresses on a specified fault geometry, this simulator (without dilatancy) has already been shown to reproduce Gutenberg

  14. Deep structure of the Chuya's earthquake epicentral zone according to the data on local seismic tomography from aftershocks

    International Nuclear Information System (INIS)

    The upper part of the Earth's crust structure was investigated in the Chuya's earthquake epicentral zone (9.27.2003) according to P- and S-waves travel time from aftershocks. Ray Seismic Tomography using time delays was used for data interpretation. A 3D model of Chuya earthquake focal area (distribution of P- and S-wave velocities and Poisson's coefficient) was designed for the territory of 80x80 km with depth up to 15 km. It was analyzed spatial relation of obtained elasticity parameters for environment with seismicity of observed area. (author)

  15. 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

  16. 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

  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. 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

  19. 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

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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...

  9. Time dependence of statistical parameters: the aftershock sequence of the Friuli 1976 earthquake, northern Italy, and a section of the Montenegro, Yugoslavia, earthquake series 1979

    OpenAIRE

    Gottfried Grünthal; E. Hurtig; E. Ruge

    1982-01-01

    Presents the time dependence of the statistical parameters alpha and beta describing seismic activity with a high time resolution. alpha stands for temporal event intensity and beta determines the distribution of magnitudes. It was studied whether these parameters are indicative as precursory phenomena predicting large aftershocks within the investigated earthquake sequences (Friuli region in 1976 and a section of the Montenegro sequence in 1979). No precursor effect could be found in the b-v...

  10. 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.

  11. 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.

  12. Receiver Function Migration of Broadband Seismograms recorded by the International Maule Aftershock Deployment (IMAD) in Central Chile

    Science.gov (United States)

    Morell, M.; Beck, S. L.; Roecker, S. W.; Meltzer, A.; Russo, R. M.

    2011-12-01

    The Mw=8.8 Maule earthquake that occurred off the coast of Chile on February 27, 2010 is one of the largest megathrust earthquakes ever to be recorded and ruptured ~600 km of the plate boundary. This segment of the Nazca-South America plate boundary is an ideal region to investigate the processes related to the structure of the down-dip edge of the seismogenic zone, forearc wedge and subducting slab. Immediately after the Maule earthquake, international teams from France, Germany, Great Britain and the United States joined Chilean seismologists to install an array of seismic stations between 33°-38.5°S, from the coast to the foothills of the Andes to produce the International Maule Aftershock Deployment (IMAD) data set. These arrays were deployed from mid-March until the end of December 2010 in order to capture and study the aftershocks in and around the rupture zone, and to better understand crustal and mantle wedge structure. We calculated receiver functions (RFs) from P and PP phases and made Common Conversion Point stacks to image the structures in the slab and forearc wedge down to a depth of 100 km. We have identified the oceanic slab Moho on several E-W and N-S profiles at 40 to 60 km depth beneath the array and several discontinuities above the slab in the forearc. These profiles also show a large low-velocity zone beneath the northern half of the array in the forearc. In addition, we are using a 2.5D finite difference teleseismic waveform tomography technique described in Roecker et al. (2010) to image the crust and upper mantle beneath that part of the Chilean Andes occupied by the IMAD array and the earlier TIPTEQ deployment of Rietbrock et al. (2005). While the technique does not require any kind of formal source deconvolution, in sparse deployments we can apply this technique in an RF type migration by normalizing medium sensitivities. Both these techniques will improve our imaging of the down-dip limit of the seismogenic zone, forearc wedge and

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. Source Process of the Mw 5.0 Au Sable Forks, New York, Earthquake Sequence from Local Aftershock Monitoring Network Data

    Science.gov (United States)

    Kim, W.; Seeber, L.; Armbruster, J. G.

    2002-12-01

    On April 20, 2002, a Mw 5 earthquake occurred near the town of Au Sable Forks, northeastern Adirondacks, New York. The quake caused moderate damage (MMI VII) around the epicentral area and it is well recorded by over 50 broadband stations in the distance ranges of 70 to 2000 km in the Eastern North America. Regional broadband waveform data are used to determine source mechanism and focal depth using moment tensor inversion technique. Source mechanism indicates predominantly thrust faulting along 45° dipping fault plane striking due South. The mainshock is followed by at least three strong aftershocks with local magnitude (ML) greater than 3 and about 70 aftershocks are detected and located in the first three months by a 12-station portable seismographic network. The aftershock distribution clearly delineate the mainshock rupture to the westerly dipping fault plane at a depth of 11 to 12 km. Preliminary analysis of the aftershock waveform data indicates that orientation of the P-axis rotated 90° from that of the mainshock, suggesting a complex source process of the earthquake sequence. We achieved an important milestone in monitoring earthquakes and evaluating their hazards through rapid cross-border (Canada-US) and cross-regional (Central US-Northeastern US) collaborative efforts. Hence, staff at Instrument Software Technology, Inc. near the epicentral area joined Lamont-Doherty staff and deployed the first portable station in the epicentral area; CERI dispatched two of their technical staff to the epicentral area with four accelerometers and a broadband seismograph; the IRIS/PASSCAL facility shipped three digital seismographs and ancillary equipment within one day of the request; the POLARIS Consortium, Canada sent a field crew of three with a near real-time, satellite telemetry based earthquake monitoring system. The Polaris station, KSVO, powered by a solar panel and batteries, was already transmitting data to the central Hub in London, Ontario, Canada within

  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)

    Parameswaran, Revathy M.; Rajendran, Kusala

    2016-06-01

    The Great Himalayan earthquakes are believed to originate on the Main Himalayan Thrust, and their ruptures lead to deformation along the Main Frontal Thrust (MFT). The rupture of the April 25, 2015 (Mw 7.8), earthquake was east-directed, with no part relayed to the MFT. The aftershock distribution, coseismic elevation change of ~1 m inferred from the InSAR image, and the spatial correspondence of the subtle surface deformations with PT2, a previously mapped out-of-sequence thrust, lead us to explore the role of structural heterogeneities in constraining the rupture progression. We used teleseismic moment inversion of P- and SH-waves, and Coulomb static stress changes to map the slip distribution, and growth of aftershock area, to understand their relation to the thrust systems. Most of the aftershocks were sourced outside the stress shadows (slip >1.65 m) of the April 25 earthquake. The May 12 (Mw 7.3) earthquake that sourced on a contiguous patch coincides with regions of increased stress change and therefore is the first known post-instrumentation example of a late, distant, and large triggered aftershock associated with any large earthquake in the Nepal Himalaya. The present study relates the slip, aftershock productivity, and triggering of unbroken stress barriers, to potential out-of-sequence thrusts, and suggests the role of stress transfer in generating large/great earthquakes.

  20. 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

  1. Faulting structure above the Main Himalayan Thrust as shown by relocated aftershocks of the 2015 Mw7.8 Gorkha, Nepal, earthquake

    Science.gov (United States)

    Bai, Ling; Liu, Hongbing; Ritsema, Jeroen; Mori, James; Zhang, Tianzhong; Ishikawa, Yuzo; Li, Guohui

    2016-01-01

    The 25 April 2015, Mw7.8 Gorkha, Nepal, earthquake ruptured a shallow section of the Indian-Eurasian plate boundary by reverse faulting with NNE-SSW compression, consistent with the direction of current Indian-Eurasian continental collision. The Gorkha main shock and aftershocks were recorded by permanent global and regional arrays and by a temporary local broadband array near the China-Nepal border deployed prior to the Gorkha main shock. We relocate 272 earthquakes with Mw>3.5 by applying a multiscale double-difference earthquake relocation technique to arrival times of direct and depth phases recorded globally and locally. We determine a well-constrained depth of 18.5 km for the main shock hypocenter which places it on the Main Himalayan Thrust (MHT). Many of the aftershocks at shallower depths illuminate faulting structure in the hanging wall with dip angles that are steeper than the MHT. This system of thrust faults of the Lesser Himalaya may accommodate most of the elastic strain of the Himalayan orogeny.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. Contrasting amount of fluids along the megathrust ruptured by the 2010 Maule earthquake as revealed by a combined analysis of aftershocks and afterslip

    Science.gov (United States)

    Tassara, Andres; Soto, Hugo; Bedford, Jonathan; Moreno, Marcos; Baez, Juan Carlos

    2016-03-01

    We present a novel approach combining time-variable computations of b-value and afterslip to study the postseismic activity following the Mw 8.8 Maule 2010 earthquake. We subdivided the first 392 days after the mainshock into overlapping windows, for which we compared maps of b-value (computed from NEIC seismicity) and afterslip (computed from continuous GPS stations). The correlation between both parameters is weak during the first 2 months when the aftershocks' magnitude of completeness decreases and the number of GPS stations increased. After this early stage, a correlation between both parameters emerges. We interpret this correlated spatiotemporal pattern combining factors proposed to control each parameter separately. This exercise suggests a segmentation of the Maule megathrust. The northern segment is characterized by an increase of afterslip and b-value during the early postseismic phase and then a simultaneous decrease of both parameters, which we interpret as the effect of an ingression of fluids into the megathrust and its subsequent consumption during fault healing. In contrast, the southern segment is characterized by a central region with minimum afterslip and low b-value surrounded by areas that experience mostly seismic afterslip as a consequence of large static stress loaded by the mainshock, suggesting a drier and stronger megathrust where healing was active earlier. Interpreted along with features of the pre- and coseismic phases, our results allow us to propose the existence of two contrasting types of seismic asperities: classical strong stick-slip patches that we link with dry regions of the megathrust, versus weak, wet and conditionally stable frictional patches that could have a range of seismogenic behaviors from creeping and/or locking during the interseismic period, largely contributing with coseismic slip, and concentrating afterslip at their borders. The application of our novel method to other great earthquakes could reveal whether

  16. 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.

  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. The Caribbean after-shock.

    Science.gov (United States)

    Canak, W L; Levy, D

    1988-03-01

    The population of the Caribbean islands, is expected to double by the mid-21st century, placing new pressures on local labor markets and economic resources and increasing the need for social expenditures. Most of this growth will take place in urban areas. Emigration to the US is an increasingly important trend, especially in the Dominican Republic, Haiti, and Jamaica, and local Caribbean economies are linked with labor markets in the US through a system of family remittances. Oil price hikes, escalating debt burdens, and falling export prices have created an economic crisis in the Caribbean since the late 1970s. There has been double-digit inflation, rising unemployment, and only sporadic growth in the gross national product. The Caribbean Basin Initiative, established by the Reagan Administration, provides the Caribbean nations with duty-free export entry to the US market for 12 years and targets manufacturing, tourism, agriculture, and foreign investment for growth. Overall, however, the results of this initiative have been an effective subsidy to US investors and little stimulus for growth in locally owned businesses. Haiti and the Dominican Republic are the islands with the most poverty, while Trinidad and Tobago are the most prosperous. Puerto Rico plays an important role in the Caribbean region, serving as a link between North and South America and between cultural differences. PMID:12280949

  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. 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

  2. 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.

  3. 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."

  4. 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

  5. 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.

  6. 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...

  7. Asymmetric distribution of aftershocks on large faults in California

    Science.gov (United States)

    Zaliapin, Ilya; Ben-Zion, Yehuda

    2011-06-01

    We examine the relations between spatial symmetry properties of earthquake patterns along faults in California (CA) and local velocity structure images to test the hypothesis that ruptures on bimaterial faults have statistically preferred propagation directions. The analysis employs seismic catalogues for 25 fault zones in CA. We distinguish between clustered and homogeneous parts of each catalogue, using a recently introduced earthquake cluster analysis, and examine asymmetry of offspring with respect to parent events within the clustered portion of each catalogue. The results indicate strong asymmetric patterns along large faults with prominent bimaterial interfaces (e.g. sections of the San Andreas Fault), with enhanced activities in the directions predicted for the local velocity contrasts, and absence of significant asymmetry along most other faults. Assuming the observed asymmetric properties of seismicity reflect the properties of the parent earthquake ruptures, the discussed methodology and results can be used to develop refined estimates of seismic shaking hazard associated with individual fault zones.

  8. 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

  9. Seismic Damage Detection for a Masonry Building Using Aftershock Monitoring Data

    OpenAIRE

    ZHOU, Wensong; Li, Hui; MAO, Chenxi; Mevel, Laurent; Ou, Jinping

    2013-01-01

    The problem of detecting structural damage by exploiting vibration signal measurements produced from earthquake excitation is addressed in this work. Following the Wenchuan earthquake of 12 May 2008, a residential masonry building was selected for instrumentation with accelerometers by the Harbin Institute of Technology. This building had been damaged in the Wenchuan earthquake. It represents a rare case of an instrumented building that has been previously damaged, thus serving as a full-scal...

  10. 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.

  11. 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.

  12. 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...

  13. Primitive Rituals, Contemporary Aftershocks: Evocations of the Orientalist ‘Other’ in four productions of 'Le Sacre du printemps'

    OpenAIRE

    Lucy Weir

    2013-01-01

    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, ...

  14. 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...

  15. 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.

  16. 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.

  17. 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...

  18. 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.

  19. Delayed dynamic triggering: Local seismicity leading up to three remote M ≥ 6 aftershocks of the 11 April 2012 M8.6 Indian Ocean earthquake

    Science.gov (United States)

    Johnson, Christopher W.; Bürgmann, Roland

    2016-01-01

    The 11 April 2012 M8.6 strike-slip Indian Ocean earthquake (IOE) was followed by an increase in global seismic activity, with three remote M ≥ 6.0 earthquakes within 24 h. We investigate delayed dynamic triggering by systematically examining three offshore regions hosting these events for changes in microseismic activity preceding the IOE, and during the hours between the IOE surface-wave arrival and the triggered-event candidate. The Blanco Fault Zone, USA, and the Tiburón Fault Zone, Mexico, each host a strike-slip event, and the Michoacán Subduction Zone, Mexico, hosts a reverse event. At these locations we estimate transient Coulomb stresses of ±1-10 kPa during the IOE. Each study area contains a regional seismic network allowing us to examine continuous waveforms at one or more nearby stations. We implement a short-/long-term-average algorithm and template matching to detect events and assess the seismicity with the β-statistic. Our results indicate low-magnitude seismicity in the days prior to the IOE and the occurrence of earthquakes during the surface-wave passage after more than 2 h of transient loading. We find both transtensional tectonic environments respond to the transient stresses with a substantial increase observed in the seismicity rates during the hours after the passage of surface waves. In contrast, seismicity rates remain constant in the subduction zone we investigate during the 14 h delay between the IOE and the large-magnitude earthquake. The seismicity rate increases we observe occur after many hours of dynamic stresses and suggest the long duration of transient loading initiated failure processes leading up to these M ≥ 6.0 events.

  20. 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.

  1. 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).

  2. 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.

  3. Disturbances in equilibrium function after major earthquake

    Science.gov (United States)

    Honma, Motoyasu; Endo, Nobutaka; Osada, Yoshihisa; Kim, Yoshiharu; Kuriyama, Kenichi

    2012-10-01

    Major earthquakes were followed by a large number of aftershocks and significant outbreaks of dizziness occurred over a large area. However it is unclear why major earthquake causes dizziness. We conducted an intergroup trial on equilibrium dysfunction and psychological states associated with equilibrium dysfunction in individuals exposed to repetitive aftershocks versus those who were rarely exposed. Greater equilibrium dysfunction was observed in the aftershock-exposed group under conditions without visual compensation. Equilibrium dysfunction in the aftershock-exposed group appears to have arisen from disturbance of the inner ear, as well as individual vulnerability to state anxiety enhanced by repetitive exposure to aftershocks. We indicate potential effects of autonomic stress on equilibrium function after major earthquake. Our findings may contribute to risk management of psychological and physical health after major earthquakes with aftershocks, and allow development of a new empirical approach to disaster care after such events.

  4. Analyzing the characteristics of focal mechanism solutions of Wenchuan earthquake sequence

    Science.gov (United States)

    Cui, X.; Hu, X.; Xie, F.; Yu, C.; Wang, Y.

    2009-12-01

    We firstly read out initial P wave polarity from the digital wave form data given by Chinese national seismic networks, regional seismic networks, temporary seismic networks as well as some IRIS stations. Then employing improved grid point test method we obtain focal mechanism solutions of the strong aftershocks (M≥4.0) and composite fault plane solutions of the moderate and small aftershocks of Wenchuan earthquake sequence. In order to improve the reliability of focal mechanism solutions, we precisely locate the hypocenter location of aftershocks during the determining of focal mechanism solutions. Most of the aftershocks are thrust faulting or strike slip faulting except few ones. Thrust and predominately thrust aftershocks are distributed along the whole rapture zone except the southwest section, while strike slip aftershocks are distributed mainly in the southwest and the northeast sections. In the section from Beichuan to Pingwu, there are hardly any strike slip aftershocks but thrust and predominately thrust aftershocks. In terms of the azimuths of P axes of the focal mechanism solutions of the aftershocks, we find that the ones of the aftershocks with magnitude above 5.0 show good homogeneity, mainly concentrate on the orientation of NWW-SEE, which is consistent with that of Wenchuan mainshock, while as for aftershocks with magnitude below 4.9, they have two dominant distributions of NWW-SEE (azimuth 280°-310°) and NE-SW (azimuth 40°-70°). It shows that the focal mechanism solutions and their distribution characteristics of Wenchuan earthquake sequence are both complex. From the types and the azimuths of P axes of the focal mechanism solutions of the aftershocks, we can obtain the characteristics of segmentation, which is important to realize the dynamic mechanism of the Wenchuan earthquake sequence.

  5. 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.

  6. Bayesian estimation of the Modified Omori Law parameters for the Iranian Plateau

    Science.gov (United States)

    Ommi, S.; Zafarani, H.; Smirnov, V. B.

    2016-04-01

    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.

  7. 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 L.; Benz, Harley M.; Brown, Lucy; Meltzer, Anne S.

    2013-11-01

    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

  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. Earth science: lasting earthquake legacy

    Science.gov (United States)

    Parsons, Thomas E.

    2009-01-01

    Earthquakes occur within continental tectonic plates as well as at plate boundaries. Do clusters of such mid-plate events constitute zones of continuing hazard, or are they aftershocks of long-past earthquakes?

  10. 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...

  11. 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_...

  12. 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...

  13. 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

  14. 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

  15. Stress triggering of earthquakes: evidence for the 1994 M = 6.7 Northridge, California, shock

    OpenAIRE

    King, G. C. P.; J. Lin; Stein, R.S.

    1994-01-01

    A model of stress transfer implies that earthquakes in 1933 and 1952 increased the Conlomb stress at the site of the 1971 San Fernando earthquake. The 1971 earthquake in turn raised stress and produced aftershocks at the site of the 1987 Whittier Narrows and 1994 Northridge ruptures. The Northridge main shock raised stress in areas where its aftershocks and surface faulting occurred. Together, M ? 6 earthquakes near Los Angeles since 1933 have stressed parts of the Oak Ridge, Sierra Madre, Sa...

  16. Guest editorial for the special issue ‘‘Tectonics of Bay of Bengal and Arabian Sea with special emphasis on coastal and marine geohazards’’

    Digital Repository Service at National Institute of Oceanography (India)

    Murthy, K.S.R.; Chaubey, A.K.; Radhakrishna, M.

    the aftershock sequence of December 26, 2004 mega thrust earthquake and the major swarm event of January 2005 within it from the viewpoint of pore fluid diffusion process. The analysis of r–t plots computed by them suggests that elevated pore pressure triggers... the aftershock sequences including 2005 swarm following the Sumatra earthquake, may have reactivated preexisting fault planes, and produced sites for seabed rupturing. The results have been discussed in light of subduction structure, its implication...

  17. 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...

  18. 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 ...

  19. The enigma of the Arthur's Pass, New Zealand, earthquake 1. Reconciling a variety of data for an unusual earthquake sequence

    Science.gov (United States)

    Abercrombie, R.E.; Webb, T.H.; Robinson, R.; McGinty, P.J.; Mori, J.J.; Beavan, R.J.

    2000-01-01

    The 1994 Arthur's Pass earthquake (Mw6.7) is the largest in a recent sequence of earthquakes in the central South Island, New Zealand. No surface rupture was observed the aftershock distribution was complex, and routine methods of obtaining the faulting orientation of this earthquake proved contradictory. We use a range of data and techniques to obtain our preferred solution, which has a centroid depth of 5 km, Mo=1.3??1019 N m, and a strike, dip, and rake of 221??, 47??, 112??, respectively. Discrepancies between this solution and the Harvard centroid moment tensor, together with the Global Positioning System (GPS) observations and unusual aftershock distribution, suggest that the rupture may not have occurred on a planar fault. A second, strike slip, subevent on a more northerly striking plane is suggested by these data but neither the body wave modeling nor regional broadband recordings show any complexity or late subevents. We relocate the aftershocks using both one-dimensional and three-dimensional velocity inversions. The depth range of the aftershocks (1-10 km) agrees well with the preferred mainshock centroid depth. The aftershocks near the hypocenter suggest a structure dipping toward the NW, which we interpret to be the mainshock fault plane. This structure and the Harper fault, ???15 km to the south appear to have acted as boundaries to the extensive aftershock zone trending NNW-SSE Most of the ML???5 aftershocks, including the two largest (ML6.1 and ML5.7), clustered near the Harper fault and have strike slip mechanisms consistent with motion on this fault and its conjugates. Forward modeling of the GPS data suggests that a reverse slip mainshock, combined with strike slip aftershock faulting in the south, is able to match the observed displacements. The occurrence of this earthquake sequence implies that the level of seismic hazard in the central South Island is greater than previous estimates. Copyright 2000 by the American Geophysical Union.

  20. 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 ...

  1. 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.

  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. 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.

  4. 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

  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. 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.

  8. 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.

  9. Frictional afterslip following the 2005 Nias-Simeulue earthquake, Sumatra.

    Science.gov (United States)

    Hsu, Ya-Ju; Simons, Mark; Avouac, Jean-Philippe; Galetzka, John; Sieh, Kerry; Chlieh, Mohamed; Natawidjaja, Danny; Prawirodirdjo, Linette; Bock, Yehuda

    2006-06-30

    Continuously recording Global Positioning System stations near the 28 March 2005 rupture of the Sunda megathrust [moment magnitude (Mw) 8.7] show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust, with a major fraction of this slip in the up-dip direction from the main rupture. Eleven months after the main shock, afterslip continues at rates several times the average interseismic rate, resulting in deformation equivalent to at least a M(w) 8.2 earthquake. In general, along-strike variations in frictional behavior appear to persist over multiple earthquake cycles. Aftershocks cluster along the boundary between the region of coseismic slip and the up-dip creeping zone. We observe that the cumulative number of aftershocks increases linearly with postseismic displacements; this finding suggests that the temporal evolution of aftershocks is governed by afterslip. PMID:16809533

  10. Random variability explains apparent global clustering of large earthquakes

    Science.gov (United States)

    Michael, A.J.

    2011-01-01

    The occurrence of 5 Mw ≥ 8.5 earthquakes since 2004 has created a debate over whether or not we are in a global cluster of large earthquakes, temporarily raising risks above long-term levels. I use three classes of statistical tests to determine if the record of M ≥ 7 earthquakes since 1900 can reject a null hypothesis of independent random events with a constant rate plus localized aftershock sequences. The data cannot reject this null hypothesis. Thus, the temporal distribution of large global earthquakes is well-described by a random process, plus localized aftershocks, and apparent clustering is due to random variability. Therefore the risk of future events has not increased, except within ongoing aftershock sequences, and should be estimated from the longest possible record of events.

  11. 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.

  12. 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.

  13. 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...

  14. Investigating Fault Slip and Rheology Along the San Andreas Fault in the San Juan Bautista Region

    Science.gov (United States)

    Taira, T.; Burgmann, R.; Nadeau, R. M.; Dreger, D. S.

    2012-12-01

    An improved understanding of the connection between seismic behavior and fault-zone rheology at depth is an essential step toward understanding the underlying mechanics of the faulting process. We investigate the seismicity along the northernmost creeping section of the San Andreas fault near San Juan Bautista (SJB), California, by systematically examining spatiotemporal behaviors of the aftershock sequences following the 12 August 1998 Mw 5.1 SJB earthquake. This 1998 SJB earthquake was the largest historic earthquake in the SJB area and was associated with a large slow slip event. Using a waveform cross-correlation approach (Peng and Zhao, 2009, NatureGeo), we have detected previously uncataloged earthquakes (about 500 events), resolving details of the aftershock activity in a zone at a depth of 9 km about 7 km northwest of the 1998 SJB mainshock. This aftershock zone is marked by one of the highest changes in the seismicity rate, exhibiting a delayed peak (about 20 hours after the mainshock) in the rate of aftershocks preceded by a period of very low rate of aftershocks since the mainshock. Subsequently, the rate of aftershocks shows power-law decay with time for about 1 month, and then the aftershock activity approached the pre-earthquake background level. This temporal behavior of the aftershock activity is different from the predicted aftershock decay based on the model of Dieterich (1994, JGR). Instead, our observation is more consistent with the decay rate of aftershocks occurring in the transition zone between locked and stable slip, as simulated numerically by Kaneko and Lapusta (2008, JGR). Our waveform analysis also identifies over 20 repeating microearthquake sequences (or groups of earthquakes with similar waveforms) associated with the 1998 SJB mainshock. The majority of the sequences have events occurring in the first month of the postseismic period. In other words, they reflect short-lived, accelerated repeater recurrences activated by the 1998 SJB

  15. 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...

  16. 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

  17. 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.

  18. Study on application of the low-frequency electromagnetic signals in earthquake prediction

    International Nuclear Information System (INIS)

    Complete text of publication follows. One week before the Wenchuan Ms8.0 earthquake in Sichuan Province, the ionospheric anomalies was captured by DEMETER satellite, and an abnormal electromagnetic radiation also appeared in ELF band electromagnetic field data. Before and after the main shock and a series of aftershocks, the corresponding anomaly information was captured in ELF electromagnetic observation data. We use spectrum method to inspect the ELF electric field, magnetic field data in frequency band of 0.5Hz ∼39Hz, which is sampled at Longnan seismic station during January 2008 and January 2009. The auto power spectrum of electricity and magnetic field shows sudden jump significantly before Wenchuan earthquake and the aftershocks. The abnormal magnitude is related to the earthquake magnitude and the epicenter distance etc. The electromagnetic anomalies during shocks is bigger than normal month 1∼5 orders of magnitude. A coseismic electromagnetic phenomenon was found in Ms6.1 strong aftershocks of August 1, and 5, 2008 in the Longnan ELF observation. We compared the ELF data to the earthquake data and found that the magnetic field component and the seismic waves arrive simultaneously, but the reaction of electric field component is not obviously. We have predicted two strong aftershocks successfully using the above conclusions.

  19. 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

    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 at the......) 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...

  20. 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.

  1. 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…

  2. 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…

  3. Speaking of Silence: Comments from an Irish Studies Perspective

    DEFF Research Database (Denmark)

    McQuaid, Sara Dybris; Beville, Maria

    2012-01-01

    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....

  4. 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...

  5. 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 ...

  6. 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.

  7. Compressive sensing of frequency-dependent seismic radiation from subduction zone megathrust ruptures

    Science.gov (United States)

    Yao, Huajian; Shearer, Peter M.; Gerstoft, Peter

    2013-01-01

    Megathrust earthquakes rupture a broad zone of the subducting plate interface in both along-strike and along-dip directions. The along-dip rupture characteristics of megathrust events, e.g., their slip and energy radiation distribution, reflect depth-varying frictional properties of the slab interface. Here, we report high-resolution frequency-dependent seismic radiation of the four largest megathrust earthquakes in the past 10 y using a compressive-sensing (sparse source recovery) technique, resolving generally low-frequency radiation closer to the trench at shallower depths and high-frequency radiation farther from the trench at greater depths. Together with coseismic slip models and early aftershock locations, our results suggest depth-varying frictional properties at the subducting plate interfaces. The shallower portion of the slab interface (above ∼15 km) is frictionally stable or conditionally stable and is the source region for tsunami earthquakes with large coseismic slip, deficient high-frequency radiation, and few early aftershocks. The slab interface at intermediate depths (∼15–35 km) is the main unstable seismogenic zone for the nucleation of megathrust quakes, typically with large coseismic slip, abundant early aftershocks, and intermediate- to high-frequency radiation. The deeper portion of the slab interface (∼35–45 km) is seismically unstable, however with small coseismic slip, dominant high-frequency radiation, and relatively fewer aftershocks.

  8. 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.

  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 1.05< p <1.2. Finite sample size affects the variation of the branching ratio estimates. Moreover, we investigate the effect of missing aftershocks 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. 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.

  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. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. Stress triggering of earthquakes: evidence for the 1994 M = 6.7 Northridge, California, shock

    Directory of Open Access Journals (Sweden)

    G. C. P. King

    1994-06-01

    Full Text Available A model of stress transfer implies that earthquakes in 1933 and 1952 increased the Conlomb stress at the site of the 1971 San Fernando earthquake. The 1971 earthquake in turn raised stress and produced aftershocks at the site of the 1987 Whittier Narrows and 1994 Northridge ruptures. The Northridge main shock raised stress in areas where its aftershocks and surface faulting occurred. Together, M ? 6 earthquakes near Los Angeles since 1933 have stressed parts of the Oak Ridge, Sierra Madre, Santa Monica Mountains, Elysian Park, and Newport-Inglewood faults by > 1 bar. While too small to cause earthquakes, these stress changes can trigger events if the crust is already near failure, or advance future earthquake occurrence if it is not.

  18. Synchronization and desynchronization in the Olami-Feder-Christensen earthquake model and potential implications for real seismicity

    Directory of Open Access Journals (Sweden)

    S. Hergarten

    2011-09-01

    Full Text Available The Olami-Feder-Christensen model is probably the most studied model in the context of self-organized criticality and reproduces several statistical properties of real earthquakes. We investigate and explain synchronization and desynchronization of earthquakes in this model in the nonconservative regime and its relevance for the power-law distribution of the event sizes (Gutenberg-Richter law and for temporal clustering of earthquakes. The power-law distribution emerges from synchronization, and its scaling exponent can be derived as τ = 1.775 from the scaling properties of the rupture areas' perimeter. In contrast, the occurrence of foreshocks and aftershocks according to Omori's law is closely related to desynchronization. This mechanism of foreshock and aftershock generation differs strongly from the widespread idea of spontaneous triggering and gives an idea why some even large earthquakes are not preceded by any foreshocks in nature.

  19. A data-based model to locate mass movements triggered by seismic events in Sichuan, China.

    Science.gov (United States)

    de Souza, Fabio Teodoro

    2014-01-01

    Earthquakes affect the entire world and have catastrophic consequences. On May 12, 2008, an earthquake of magnitude 7.9 on the Richter scale occurred in the Wenchuan area of Sichuan province in China. This event, together with subsequent aftershocks, caused many avalanches, landslides, debris flows, collapses, and quake lakes and induced numerous unstable slopes. This work proposes a methodology that uses a data mining approach and geographic information systems to predict these mass movements based on their association with the main and aftershock epicenters, geologic faults, riverbeds, and topography. A dataset comprising 3,883 mass movements is analyzed, and some models to predict the location of these mass movements are developed. These predictive models could be used by the Chinese authorities as an important tool for identifying risk areas and rescuing survivors during similar events in the future. PMID:24085622

  20. 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.

  1. 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.

  2. 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.

  3. Analysis of acoustic-seismic coupling behaviour for CTBT on-site inspection performance improvement

    International Nuclear Information System (INIS)

    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.

  4. 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

  5. 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

  6. The Brief Introduction to the April 14,2010 Yushu M7.1 Earthquake Sequence

    Institute of Scientific and Technical Information of China (English)

    Li Gang; Guo Tieshuan; Wang Huimin

    2010-01-01

    @@ An earthquake with M7.1 occurred in Yushu,Qinghai Province,China,at 07:49 a.m.on April 14,2010,according to the Chinese Seismic Station Network.The sequence is a fore-main-after-shock type sequence.A foreshock with M4.7 occurred 2 hours and 11 minutes before the main shock.There were 12 foreshocks and 2385 aftershocks until June 31,2010.

  7. Study on Inelastic Attenuation and Source Parameters of the Shidian Swarm in 2001

    Institute of Scientific and Technical Information of China (English)

    Liu Lifang; Liu Jie; Su Youjin; Fu Hong

    2007-01-01

    Based on horizontal-component digital seismograms recorded on 6 stations of the Yunnan Regional Digital Network,we inversed the inelastic attenuation in the source region of the Shidian swarm using the Atkinson method and the site responses of the 6 stations 200km around the Shidian epicenters using the Moya method.The observational seistoic waveform data were corrected by removing the propagation,instrument and site effects before the source parameters of the Shidian swarm in 2001 were determined using genetic algorithms.The results are as follows:(1) There is a linear relation between seismic moment and local magnitude.The seismic moment is between 1×1012 and 1014 N·m.The rupture radius of the seismic focus varies from 157m to 973m. The seismic moment and the rupture radius maintain a linear correlation.(2) The corner frequency increases as the seismic moment decreases.Based on the expression between corner frequency and seismic moment using least squares fitting,we can obtain the estimated value of the corner frequency.The time-varying value of the calculated corner frequency minus the estimated corner frequency shows that there were continuous high and low anomalies before the strong aftershocks.(3)The seismic stress drop is in the range of 0.07~1.55MPa.The stress drop seems independent of the local magnitude.The variation of stress drops is high before the occurrence of the strong aftershocks.(4) The depth of aftershocks is mostly in a range from 5km to 10km,which means that energy release of aftershocks is mainly concentrated in this range of depth.

  8. On the complexity of earthquake sequences: a historical seismology perspective based on the L'Aquila seismicity (Abruzzo, Central Italy), 1315-1915

    OpenAIRE

    Guidoboni, E.; EEDIS; Valensise, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia

    2015-01-01

    Most damaging earthquakes come as complex sequences characterized by strong aftershocks, sometimes by foreshocks and often by multiple mainshocks. Complex earthquake sequences have enormous seismic hazard, engineering and societal implications as their impact on buildings and infrastructures may be much more severe at the end of the sequence than just after the mainshock. In this paper we examine whether historical sources can help characterizing the rare earthquake sequences of pre-instrumen...

  9. Rapid response to the earthquake emergency of May 2012 in the Po Plain, northern Italy

    OpenAIRE

    Milena Moretti; et al.

    2012-01-01

    Rapid-response seismic networks are an important element in the response to seismic crises. They temporarily improve the detection performance of permanent monitoring systems during seismic sequences. The improvement in earthquake detection and location capabilities can be important for decision makers to assess the current situation, and can provide invaluable data for scientific studies related to hazard, tectonics and earthquake physics. Aftershocks and the clustering of the locations of s...

  10. TSUNAMIGENIC SOURCE MECHANISM AND EFFICIENCY OF THE MARCH 11, 2011 SANRIKU EARTHQUAKE IN JAPAN

    OpenAIRE

    George Pararas-Carayannis

    2011-01-01

    The great Tohoku earthquake of March 11, 2011 generated a very destructive and anomalously high tsunami. To understand its source mechanism, an examination was undertaken of the seismotectonics of the region and of the earthquake’ focal mechanism, energy release, rupture patterns and spatial and temporal sequencing and clustering of major aftershocks. It was determined that the great tsunami resulted from a combination of crustal deformations of the ocean floor due to up-thrust tectonic motio...

  11. Intelligent Spatial-Clustering of Seismicity in the Vicinity of the Hellenic Seismic Arc

    OpenAIRE

    A. J. Konstantaras; Katsifarakis, E; Maravelakis, E; Skounakis, E; E. Kokkinos; E. Karapidakis

    2012-01-01

    This research paper discusses possible seismic cluster formation and evolution in the vicinity of the Hellenic seismic arc and proposes a graphical user-interface monitoring and analysis tool based on various commercial and self-developed clustering algorithms for cluster discrimination, evolution and visualization. Self-developed algorithms enable the processing of both a) all recorder earthquakes and b) main seismic events alone, excluding foreshocks and aftershocks, by incorporating dynami...

  12. Price-Level Targeting: A Post-Mortem?

    OpenAIRE

    Steven Ambler

    2014-01-01

    Recent research has shown that monetary policy based on price-level targeting has several advantages over the traditional inflation targeting method, particularly in times of economic distress. Although several central banks have been coping with the aftershocks of the 2008 financial crisis for prolonged periods, none has adopted price-level targeting. This Commentary reviews some of the reasons for this in the Canadian and American contexts. The relative mildness of Canada’s 2008-2009 recess...

  13. A billions-of-dollar school - a summarized review of Three Mile Island accident and the lessons learnt from it

    International Nuclear Information System (INIS)

    The well known TMI accident shocked the world and its aftershock has not yet disappeared till now. In this paper, the accident is briefly recalled, its influence on the development of nuclear power estimated and the worldwide activities of drawing lessons from TMI described. Since nuclear power is just starting its steps in our country, lessons learnt from the accident are thought to be of great value to us, and hence listed and discussed. (author)

  14. 3D Seismic Velocity Structure in the Rupture Area of the 2010 Maule Mw=8.8 Earthquake

    Science.gov (United States)

    Hicks, S. P.; Rietbrock, A.; Ryder, I. M.; Nippress, S.; Haberland, C. A.

    2011-12-01

    The 2010 Mw=8.8 Maule, Chile earthquake is one of the largest subduction zone earthquakes ever recorded. Up to now numerous co-seismic and some post-seismic slip models have been published based entirely on seismological, geodetic, or tsunami run-up heights, or combinations of these data. Most of these models use a simplified megathrust geometry derived mainly from global earthquake catalogues, and also simplified models of seismic parameters (e.g. shear modulus). By using arrival times for a vast number of aftershocks that have been recorded on a temporary seismic array, we present a new model for the slab geometry based on earthquake locations together with a new 3D seismic velocity model of the region, for both vp and vp/vs. We analyzed 3552 aftershocks that occurred between 18 March and 24 May 2011, recorded by the International Maule Aftershock Dataset (IMAD) seismic network. Event selection from a catalogue of automatically-determined events was based on 20 or more arrival times, from which at least 10 are S-wave observations. In total over 170,000 arrival times (~125,000 and 45,000 P and S wave arrival times respectively) are used for the tomographic reconstructions. Initially, events were relocated in a 2D velocity model based on a previously published model for the southern end of the rupture area (Haberland et al., 2009). Afterwards a staggered inversion scheme is implemented, starting with a 2D inversion followed by a coarse 3D and a subsequent fine 3D inversion. Based on our preliminary inversions we conclude that aftershock seismicity is mainly concentrated between 20 and 35 km depth along the subduction interface. A second band of seismicity between 40 and 50 km depth is also observed. Low seismic velocities and an increased vp/vs ratio characterize the marine forearc. The obtained velocity model will be discussed.

  15. Deep sea in situ excess pore pressure and sediment deformation off NW Sumatra and its relation with the December 26, 2004 Great Sumatra-Andaman Earthquake

    OpenAIRE

    SULTAN, Nabil; Cattaneo, Antonio; Sibuet, Jean-Claude; Schneider, Jean-Luc

    2009-01-01

    The swath bathymetric data acquired during the "Sumatra Aftershocks" cruise from the Sunda trench in the Indian Ocean to the north of the Sumatra Island imaged several scars and deposits. In situ pore pressure measurements using the Ifremer piezometer and coring demonstrate that high excess pore pressure and sediment deformation was generated by a recent event in the scar of the slope failure zone identified by J.T. Henstock and co-authors. This excess pore pressure is localized in the upper ...

  16. Strong ground motion data from the 1983 Borah Peak, Idaho earthquake recorded at the Idaho National Engineering Laboratory

    International Nuclear Information System (INIS)

    The 1983 Borah Peak, Idaho Earthquake was the largest normal faulting event to occur in the last 20 years. There were no near-field recordings of ground motion during the main shock, however, thirteen accelerographs in a permanent array at the Idaho National Engineering Laboratory (INEL) recorded the event at epicentral distances of 90-110 km. Peak horizontal accelerations (PGA) recorded at accelerographs above ground-floor level range from 0.037 to 0.187 g. Accelerographs at basement and free-field sites recorded as low as 0.022 g and as high as 0.078 g. Peak vertical accelerations range from 0.016 g ground level to 0.059 g above ground floor level. A temporary array of digital seismographs deployed by the US Geological Survey (USGS) in the epicentral area recorded ground motion from six large aftershocks at epicentral distances of 4-45 km; the largest of these aftershocks also triggered four accelerographs in the INEL array. Two separate analyses were used to estimate near-field ground motion. The first analysis uses the attenuation of the aftershock PGA measurements to extrapolate the INEL main shock PGA measurements into the near-field. This estimates an upper limit of 0.8 g for near-field ground motion. In the second analysis, a set of main shock accelerograms were synthesized. Wave propagation effects were determined from aftershock recordings at one of the USGS portable stations and an INEL seismograph station. These effects were removed from one of the INEL main shock acceleration traces. The synthetic accelerograms were derived for a hypothetical station southwest of Mackay, Idaho. The PGA measured from the synthetic accelerograms were 0.08, 0.14, 0.15, 0.23 g. These estimates correlate well with ground motion expected for an area of Intensity VII. 12 references, 8 figures, 1 table

  17. INSTANTANEOUS INVERSION OF 1993 ‘KILLARI’ OVERVIEW OF THE MAHARASHTRA: ANALYSIS GEOLOGY TECTONIC

    OpenAIRE

    Balap Tejeshwini Ramchandra

    2015-01-01

    This paper attempts to summarize the various rebuilding components, with an emphasis on housing, and some of the many features of the project. The aftershock sequence of the September 30th, 1993 Killari earthquake in the Latur district of Maharashtra state, India, recorded by 41 temporary seismograph stations. The local earthquake tomography (LET) method of Thurber (1983) is used. About 1500 P and 1200 S wave travel-times are inverted. This paper provides an overvi w of the large , comprehens...

  18. The 2010 Maule Earthquake: Geophysical Investigations Three Years On

    OpenAIRE

    Frederik Tilmann; D. Lange; K. Lieser; I. Grevemeyer; Jonathan Bedford; M. Moreno; L. Ehlert; Mauro Palo;  MARISCOS Team

    2013-01-01

    On February 27, 2010, the Central Chilean margin ruptured over a length of _400 km in the Mw 8.8 Maule earthquake. The international seismological community responded quickly by organising the International Maule Aftershock Deployment (IMAD) consisting of more than 140 seismological stations from Chile, Germany, France, the USA and the UK. This land seismic network is complemented by 30 ocean bottom seismometers in the northern portion of the rupture, operating from September to December 2012...

  19. Structure and mechanical properties of seismogenic fault zones in carbonates

    OpenAIRE

    Fondriest, Michele

    2014-01-01

    In many seismically active areas (e.g. Italy, Greece) earthquakes, sometimes destructive, nucleate within (aftershocks surely do) and propagate through carbonates in the upper crust (e.g. L’Aquila earthquake, 2009, Mw 6.1). Seismology, geophysics and geodesy furnish key parameters related to the earthquake source (e.g. seismic moment, static stress drop, radiated energy) but lack sufficient resolution to constrain detailed three-dimensional fault zone geometry and coseismic on- and off-fault ...

  20. Crustal heterogeneities beneath the 2011 Talala, Saurashtra earthquake, Gujarat, India source zone: Seismological evidence for neo-tectonics

    Science.gov (United States)

    Singh, A. P.; Mishra, O. P.; Rastogi, B. K.; Kumar, Santosh

    2013-01-01

    During the 1st decade of the 21st century, the study area of Talala, Saurashtra of western India witnessed three damaging earthquakes of moderate magnitude, year 2007 [Mw 5.0; Mw 4.8] and in the year 2011 [Mw 5.1] that generated public panic in the region. The last damaging moderate earthquake of the 20th October 2011 in Talala region (21.09°N;70.45°E), located at about 200 km south to the devastating 2001 Bhuj (23.412°N, 70.232°E) mainshock (Mw 7.6), jolted the entire Saurashtra region of Gujarat. A long series of aftershocks followed hereafter, recorded at nine seismograph/accelerograph stations. Hypocenters of aftershocks were relocated accurately using absolute and relative travel time (double-difference) method. In this study, we, for the first time, determined 3-D tomographic images of the upper crust beneath the 2011 Talala earthquake source zone by inverting about 1135 P and 1125 S wave arrival time data. Estimates of seismic velocities (Vp, Vs) and Poisson's ratio (σ) structures offer a reliable interpretation of crustal heterogeneities and their bearing on geneses of moderate earthquakes and their aftershock sequences beneath the source zone. It is found that the 2011 Talala mainshock hypocenter depth (6 km) is located near the boundary of the low and high velocity (Vp, Vs) and the source zone is associated with low-σ anomalies guarded by the prominent high-σ anomalies along the active fault zone having strike-slip motion beneath the earthquake source zone. The pattern of distribution of (Vp, Vs, σ) and its association with occurrences of aftershocks provide seismological evidence for the neo-tectonics in the region having left lateral strike-slip motion of the fault.

  1. An insight into crack density, saturation rate, and porosity model of the 2001 Bhuj earthquake in the stable continental region of western India

    Science.gov (United States)

    Mishra, O. P.; Singh, A. P.; Kumar, Dinesh; Rastogi, B. K.

    2014-04-01

    The 2001 Bhuj earthquake (Mw 7.6) source zone is examined in the light of crack density (ɛ), saturation rate (ξ) and porosity parameter (ψ) using new data set derived from a large aftershock sequence recorded by the Gujarat seismic network (GSNet) during November, 2006-December, 2009. Processes of rupture initiations of the mainshock and its aftershock sequence are better understood by synthesizing the dynamic snapshots of the source zone using the new dataset. Pattern of crustal heterogeneities associated with high-ɛ, high-ξ and high-ψ anomalies at depths varying from 20 km to 25 km is similar to those of earlier study by Mishra and Zhao (2003). The anomalous zone is found extended distinctly by 50-60 km in the lateral direction, indicating the reinforcement of cracks and fractured volume of rock matrix due to long aftershock sequence since 2001 Bhuj earthquake in the source area. It is inferred that the presence of a fluid-filled fractured rock matrix with super saturation may have affected the structural and seismogenic strengths of the source zone and is still contributing significantly to the geneses of earthquakes in and around the source zone. Anomalous pattern of high-ɛ with wider distribution of high-ξ indicates the existence of micro-cracks in the lower crust, while high-ψ suggests the cementation of cracks through permeation of residual magma/metamorphic fluids into the hypocenter zone. The results suggest that the existence of residual fluids in the fractured rock matrix in the mid to lower crust might have played a key role in triggering the 2001 mainshock and is still responsible for its continued long aftershock sequences.

  2. Physics-based and statistical earthquake forecasting in a continental rift zone: the case study of Corinth Gulf (Greece)

    Science.gov (United States)

    Segou, Margarita

    2016-01-01

    I perform a retrospective forecast experiment in the most rapid extensive continental rift worldwide, the western Corinth Gulf (wCG, Greece), aiming to predict shallow seismicity (depth 4.5 earthquakes correspond to spontaneous events and identify, if possible, different triggering characteristics between aftershock sequences and swarm-type seismicity periods. I find that: (1) ETAS models outperform CRS models in most time intervals achieving very low rejection ratio RN = 6 per cent, when I test their efficiency to forecast the total number of events inside the study area, (2) the best rejection ratio for CRS models reaches RN = 17 per cent, when I use varying target depths and receiver plane geometry, (3) 75 per cent of the 1995 Aigio aftershocks that occurred within the first month can be explained by static stress changes, (4) highly variable performance on behalf of both statistical and physical models is suggested by large confidence intervals of information gain per earthquake and (5) generic ETAS models can adequately predict the temporal evolution of seismicity during swarms. Furthermore, stochastic reconstruction of seismicity makes possible the identification of different triggering processes between specific seismic crises (2001, 2003-04, 2006-07) and the 1995 aftershock sequence. I find that: (1) seismic events with M ≥ 5.0 are not a part of a preceding earthquake cascade, since they are characterized by high probability being a background event (average Pback > 0.8) and (2) triggered seismicity within swarms is characterized by lower event productivity when compared with the corresponding value during aftershock sequences. I conclude that physics-based models contribute on the determination of the `new-normal' seismicity rate at longer time intervals and that their joint implementation with statistical models is beneficial for future operational forecast systems.

  3. GPS Time Series Analysis of Southern California Associated with the 2010 M7.2 El Mayor/Cucapah Earthquake

    Science.gov (United States)

    Granat, Robert; Donnellan, Andrea

    2011-01-01

    The Magnitude 7.2 El-Mayor/Cucapah earthquake the occurred in Mexico on April 4, 2012 was well instrumented with continuous GPS stations in California. Large Offsets were observed at the GPS stations as a result of deformation from the earthquake providing information about the co-seismic fault slip as well as fault slip from large aftershocks. Information can also be obtained from the position time series at each station.

  4. Seismicity associated with the Sumatra-Andaman Islands earthquake of 26 December 2004

    Science.gov (United States)

    Dewey, J.W.; Choy, G.; Presgrave, B.; Sipkin, S.; Tarr, A.C.; Benz, H.; Earle, P.; Wald, D.

    2007-01-01

    The U.S. Geological Survey/National Earthquake Information Center (USGS/ NEIC) had computed origins for 5000 earthquakes in the Sumatra-Andaman Islands region in the first 36 weeks after the Sumatra-Andaman Islands mainshock of 26 December 2004. The cataloging of earthquakes of mb (USGS) 5.1 and larger is essentially complete for the time period except for the first half-day following the 26 December mainshock, a period of about two hours following the Nias earthquake of 28 March 2005, and occasionally during the Andaman Sea swarm of 26-30 January 2005. Moderate and larger (mb ???5.5) aftershocks are absent from most of the deep interplate thrust faults of the segments of the Sumatra-Andaman Islands subduction zone on which the 26 December mainshock occurred, which probably reflects nearly complete release of elastic strain on the seismogenic interplate-thrust during the mainshock. An exceptional thrust-fault source offshore of Banda Aceh may represent a segment of the interplate thrust that was bypassed during the mainshock. The 26 December mainshock triggered a high level of aftershock activity near the axis of the Sunda trench and the leading edge of the overthrust Burma plate. Much near-trench activity is intraplate activity within the subducting plate, but some shallow-focus, near-trench, reverse-fault earthquakes may represent an unusual seismogenic release of interplate compressional stress near the tip of the overriding plate. The interplate-thrust Nias earthquake of 28 March 2005, in contrast to the 26 December aftershock sequence, was followed by many interplate-thrust aftershocks along the length of its inferred rupture zone.

  5. A Nonparametric Bayesian Approach to Seismic Hazard Modeling Using the ETAS Framework

    Science.gov (United States)

    Ross, G.

    2015-12-01

    The epidemic-type aftershock sequence (ETAS) model is one of the most popular tools for modeling seismicity and quantifying risk in earthquake-prone regions. Under the ETAS model, the occurrence times of earthquakes are treated as a self-exciting Poisson process where each earthquake briefly increases the probability of subsequent earthquakes occurring soon afterwards, which captures the fact that large mainshocks tend to produce long sequences of aftershocks. A triggering kernel controls the amount by which the probability increases based on the magnitude of each earthquake, and the rate at which it then decays over time. This triggering kernel is usually chosen heuristically, to match the parametric form of the modified Omori law for aftershock decay. However recent work has questioned whether this is an appropriate choice. Since the choice of kernel has a large impact on the predictions made by the ETAS model, avoiding misspecification is crucially important. We present a novel nonparametric version of ETAS which avoids making parametric assumptions, and instead learns the correct specification from the data itself. Our approach is based on the Dirichlet process, which is a modern class of Bayesian prior distribution which allows for efficient inference over an infinite dimensional space of functions. We show how our nonparametric ETAS model can be fit to data, and present results demonstrating that the fit is greatly improved compared to the standard parametric specification. Additionally, we explain how our model can be used to perform probabilistic declustering of earthquake catalogs, to classify earthquakes as being either aftershocks or mainshocks. and to learn the causal relations between pairs of earthquakes.

  6. Visco-elastic stress triggering model of Tangshan earthquake sequence

    Institute of Scientific and Technical Information of China (English)

    WAN Yong-ge; SHEN Zheng-kang; ZENG Yue-hua; SHENG Shu-zhong; XU Xiao-feng

    2008-01-01

    We calculated the Coulomb failure stress change generated by the 1976 Tangshan earthquake that is projected onto the fault planes and slip directions of large subsequent aftershocks. Results of previous studies on the seismic failure distribution, crustal velocity and viscosity structures of the Tangshan earthquake are used as model constraints. Effects of the local pore fluid pressure and impact of soft medium near the fault are also considered. Our result shows that the subsequent Luanxian and Ninghe earthquakes occurred in the regions with a positive Coulomb failure stress produced by the Tangshan earthquake. To study the triggering effect of the Tangshan, Luanxian, and Ninghe earthquakes on the follow-up small earthquakes, we first evaluate the possible focal mechanisms of small earthquakes according to the regional stress field and co-seismic slip distributions derived from previous studies, assuming the amplitude of regional tectonic stress as 10 MPa. By projecting the stress changes generated by the above three earthquakes onto the possible fault planes and slip directions of small earthquakes, we find that the "butterfly" distribution pattern of increased Coulomb failure stress is consistent with the spatial distribution of follow-up earthquakes, and 95% of the aftershocks occurred in regions where Coulomb failure stresses increase, indicating that the former large earthquakes modulated occurrences of follow-up earthquakes in the Tangshan earthquake sequence. This result has some significance in rapid assessment of aftershock hazard after a large earthquake. If detailed failure distribution, seismogenic fault in the focal area and their slip features can be rapidly determined after a large earthquake, our algorithm can be used to predict the locations of large aftershocks.

  7. Teleseismic observations of the 1976 Friuli, Italy earthquake sequence

    OpenAIRE

    Cipar, John

    1980-01-01

    Teleseismic long-period body and surface waves radiated by the May 6, 1976 Friuli, Italy earthquake and its principal aftershock of September 15, 1976 (09h 21 m) are studied to determine source characteristics. Focal mechanisms along with geological evidence suggest that both events represent the underthrusting of the Friuli Plain beneath the southern Alps. The depths of both earthquakes, estimated by matching synthetic body-wave seismograms to observations, are found to lie between 6 and 10 ...

  8. The 2007 M7.7 Tocopilla northern Chile earthquake sequence: Implications for along-strike and downdip rupture segmentation and megathrust frictional behavior

    Science.gov (United States)

    Schurr, B.; Asch, G.; Rosenau, M.; Wang, R.; Oncken, O.; Barrientos, S.; Salazar, P.; Vilotte, J.-P.

    2012-05-01

    In 2007 a M7.7 earthquake occurred near the town of Tocopilla within the northern Chile seismic gap. Main shock slip, derived from coseismic surface deformation, was confined to the depth range between 30 and 55 km. We relocated ˜1100 events during six months before and one week after the main shock. Aftershock seismicity is first congruent to the main shock slip and then it spreads offshore west and northwest of Mejillones Peninsula (MP). Waveform modeling for 38 aftershocks reveals source mechanisms that are in the majority similar to the main shock. However, a few events appear to occur in the upper plate, some with extensional mechanisms. Juxtaposing the Tocopilla aftershocks with those following the neighboring 1995 Antofagasta earthquake produces a striking symmetry across an EW axis in the center of MP. Events seem to skirt around MP, probably due to a shallower Moho there. We suggest that the seismogenic coupling zone in northern Chile changes its frictional behavior in the downdip direction from unstable to mostly conditionally stable. For both earthquake sequences, aftershocks agglomerate in the conditionally stable region, whereas maximum inter-seismic slip deficit and co-seismic slip occurs in the unstable region. The boundary between the unstable and conditionally stable zones parallels the coastline. We identify a similar segmentation for other earthquakes in Chile and Peru, where the offshore segments break in great M > 8 earthquakes, and the onshore segments in smaller M < 8 earthquakes. Using critical taper analysis, we demonstrate a causal relationship between varying slip behavior on the interface and forearc wedge anatomy that can be attributed to spatial variations in the rate-dependency of friction.

  9. The 2005 volcano-tectonic earthquake swarm in the Andaman Sea: Triggered by the 2004 great Sumatra-Andaman earthquake

    Digital Repository Service at National Institute of Oceanography (India)

    Kundu, B.; Legrand, D.; Gahalaut, K.; Gahalaut, V.K.; Mahesh, P.; KameshRaju, K.A.; Catherine, J.K.; Ambikapthy, A.; Chadha, R.K.

    faulting or hydrothermal cooling which result in an increase in the number of earthquake productivity (Sykes 1970; Nur, 1974). The magnitude distribution of both tectonic and volcanic swarms are described by the Gutenberg-Richter (GR) law, where the b... diffusion law. Many examples of the generation of aftershocks have been explained by the time-dependent pore pressure effect of the postseismic process (e.g., Bell and Nur, 1978; Rudnicki, 2001; Gahalaut et al., 2008), but very few cases of triggered...

  10. A seismotectonic analysis of the Anza Seismic Gap, San Jacinto Fault Zone, Southern California

    OpenAIRE

    Sanders, Chris O.; Kanamori, Hiroo

    1984-01-01

    Small earthquake epicenters near the Anza seismic gap define a 20-km quiescent segment of fault bounded to the northwest and southeast by areas of relatively high seismicity. Recent moderate earthquakes on and near the San Jacinto fault in the gap and their relatively depressed aftershock activity indicate that the fault is seismogenic and highly stressed but locked by some mechanism. The locked nature of the fault may be due to relatively high compressive stress normal to the fault resulting...

  11. The effect of lateral variations of friction on crustal faulting

    Directory of Open Access Journals (Sweden)

    M. Cocco

    1994-06-01

    Full Text Available We propose that lateral variations in fault friction control the heterogeneity of slip observed in large earthquakes, We model these variations using a rate and state-dependent friction law, where we differentiate velocity-weakening into strong and weak-seismic fields, and velocity-strengthening into compliant and viscous fields. The strong-seismic field comprises the seismic slip concentrations, or asperities. The two «intermediate» frictional fields, weak-seismic and compliant, modulate both the tectonic loading and the dynamic rupture process. During the interseismic period, the compliant and viscous regions slip aseismically while the strong-seismic regions remain locked, evolving into stress concentrations that fail only in main shocks. The weak-seismic regions contain most of the interseismic activity and aftershocks, but also «creep seismically», that is, most of the weak-seismic area slips aseismically, actuating the seismicity on the remaining area. This «mixed» frictional behavior can be obtained from a sufficiently heterogenous distribution for the critical slip distance. The interseismic slip provides an inherent rupture resistance: dynamic rupture fronts decelerate as they penetrate into these unloaded compliant or creeping weak-seismic areas, diffusing into broad areas of accelerated afterslip. Aftershocks occur in both the weak-seismic and compliant areas around the fault, but most of the stress is diffused through aseismic slip. Rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area, by reloading weak fault areas that slipped in the main shock and then healed. We test this frictional model by comparing the interevent seismicity and aftershocks to the coseismic slip distribution for the 1966 Parkfield, 1979 Coyote Lake, and 1984 Morgan Hill earthquakes.

  12. Source characteristics of the 1989 Boca del Tocuyo earthquakes in northwestern Venezuela

    OpenAIRE

    Gustavo Malavé; Suárez, G.

    2007-01-01

    The Boca del Tocuyo earthquake of April 30, 1989, has a special significance in assessing the seismic hazard of northern Venezuela and in understanding the complex tectonic deformation in this area. Although it was an event of moderate magnitude (Mw=6.2), the mainshock and its largest aftershock (Mw=5.6) produced considerable damage in low-rise structures, mainly due to soil failure, and induced intense liquefaction in most of the coastal towns near the epicentral area. Both earthquakes show ...

  13. Quasi-synchronous multi-parameter anomalies associated with the 2010–2011 New Zealand earthquake sequence

    OpenAIRE

    Qin, K.; College of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China; Wu, L. X.; Academy of Disaster Reduction and Emergency Management, Ministry of Civil Affairs/Ministry of Education of P.R. China (Beijing Normal University), Beijing, China; De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Meng, J.; College of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing, China; Ma, W. Y.; College of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing, China; Cianchini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia

    2012-01-01

    Positive thermal anomalies about one month before the 3 September 2010 Mw Combining double low line 7.1 New Zealand earthquake and " coincidental" quasi-synchronous fluctuations of GPS displacement were reported. Whether there were similar phenomena associated with the aftershocks? To answer it, the following was investigated: multiple parameters including surface and near-surface air temperature, surface latent heat flux, GPS displacement and soil moisture, using a long-term statistical a...

  14. Unusual low-angle normal fault earthquakes after the 2011 Tohoku-oki megathrust earthquake

    Science.gov (United States)

    Yagi, Yuji; Okuwaki, Ryo; Enescu, Bogdan; Fukahata, Yukitoshi

    2015-06-01

    A few low-angle normal fault earthquakes at approximately the depth of the plate interface, with a strike nearly parallel to the trench axis, were detected immediately after the 2011 Tohoku-oki earthquake. After that, however, no such normal fault events have been observed until the occurrence of the 2014 M W 6.6 Fukushima-oki earthquake. Here we analyze the teleseismic body waveforms of the 2014 Fukushima-oki earthquake. We first compare the observed teleseismic body waves of the 2014 Fukushima-oki earthquake with those of the largest previous low-angle normal fault aftershock ( M W 6.6), which occurred on 12 March 2011, and then estimate the centroid depth and moment tensor solution of the 2014 Fukushima-oki earthquake. The teleseismic body waves and moment tensor solution of the 2014 Fukushima-oki earthquake are similar to those of the 2011 normal fault aftershock, which suggests that the 2014 Fukushima-oki earthquake occurred at a similar depth and had a similar mechanism to that of the 2011 aftershock. We detected five low-angle normal fault aftershocks at approximately the depth of the plate interface, with a strike nearly parallel to the trench axis, and confirmed that all of them except for the 2014 Fukushima-oki earthquake occurred within 17 days after the mainshock. The occurrence of these low-angle normal fault events is likely to reflect the reversal of shear stress due to overshooting of slip during the 2011 Tohoku-oki earthquake. We speculate that a fast but heterogeneous recovery of stress state at the plate interface may explain why these events preferentially occurred immediately after the megathrust event, while one of them occurred with a significant delay. In order to better understand the characteristics of stress state in the crust, we have to carefully observe the ongoing seismic activity around this region.

  15. The Bayamo Earthquake (Cuba) of the 18 October 1551

    OpenAIRE

    Diego Córdoba-Barba; Mario O. Cotilla-Rodríguez

    2010-01-01

    Using contemporary and original documents from the Archivo General de Indias it has been possible to complete the data for the 18 October 1551 earthquake in Cuba. The seism took place at midday, approximately. It had foreshocks and aftershocks. In Bayamo, 7 inhabitants were injured, and the town was severely affected. Maximum seismic intensity was IX degrees on the MSK scale, and the area of perceptibility is estimated at 40,000 km2. Liquefaction processes and soil type in Bayamo contributed ...

  16. Indications for a successively triggered rupture growth underlying the 2000 earthquake swarm in Vogtland/NW Bohemia

    Czech Academy of Sciences Publication Activity Database

    Hainzl, S.; Fischer, Tomáš

    Roč. 107, B12 (2002), s. ESE5-1-ESE5-9. ISSN 0148-0227 R&D Projects: GA ČR GA205/02/0381 Grant ostatní: Deutsche Forschungsgemeinschaft(DE) SCH280/13-1 Institutional research plan: CEZ:AV0Z3012916 Keywords : Vogtland * earthquake swarm * seismicity * aftershocks Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.245, year: 2002

  17. Tectonic "short circuit" of sub-horizontal fluid-saturated bodies as a possible mechanism of the earthquake

    CERN Document Server

    Nechayev, Andrei

    2013-01-01

    An alternative earthquake mechanism is proposed. The traditional stress mechanism of fracture formation assigned a support role. As a proximate cause of the earthquake the destruction of the roofs of sub-horizontal fluid-saturated bodies (SHFB) is considered. This collapse may occur due to redistribution of fluid pressure within the system of SHFB connected by cracks (tectonic or other nature). It can cause both shifts of rock blocks contributing to seismic shocks and various effects characteristic of foreshocks and aftershocks.

  18. Tarapacá intermediate-depth earthquake (Mw 7.7, 2005, northern Chile): A slab-pull event with horizontal fault plane constrained from seismologic and geodetic observations

    OpenAIRE

    Peyrat, S.; J. Campos; De Chabalier, Jean-Bernard; Bonvalot, S.; Bouin, M.-P.; Legrand, D; Nercessian, A; Charade, O.; Patau, G.; Clévédé, E; Kausel, E.; BERNARD, Patrick; Vilotte, J.-P; Perez, A.

    2006-01-01

    International audience [1] A large (Mw 7.7) intermediate-depth earthquake occurred on 13 June 2005 in the Tarapacá region of the northern Chile seismic gap. Source parameters are inferred from teleseismic broadbands, strong motions, GPS and InSAR data. Relocated hypocenter is found at $98 km depth within the subducting slab. The 21-days aftershock distribution, constrained by a postseismic temporary array, indicates a sub-horizontal fault plane lying between the planes of the double seismi...

  19. Rapid Earthquake Characterization Using MEMS Accelerometers and Volunteer Hosts Following the M 7.2 Darfield, New Zealand, Earthquake

    OpenAIRE

    Jesse F. Lawrence; Cochran, Elizabeth S.; Chung, Angela; Kaiser, Anna; Christensen, Carl M.; Allen, Richard; Baker, Jack W.; Fry, Bill; Heaton, Thomas; Kilb, Deborah; Kohler, Monica D.; Taufer, Michela

    2014-01-01

    We test the feasibility of rapidly detecting and characterizing earthquakes with the Quake‐Catcher Network (QCN) that connects low‐cost microelectromechanical systems accelerometers to a network of volunteer‐owned, Internet‐connected computers. Following the 3 September 2010 M 7.2 Darfield, New Zealand, earthquake we installed over 180 QCN sensors in the Christchurch region to record the aftershock sequence. The sensors are monitored continuously by the host computer and send trigger reports ...

  20. Revisiting the global detection capability of earthquakes during the period immediately after a large earthquake: considering the influence of intermediate-depth and deep earthquakes

    OpenAIRE

    Takaki Iwata

    2012-01-01

    This study examines the global earthquake detection capability of the Global Centroid Moment Tensor (GCMT) catalogue during the periods immediately following large earthquakes, including intermediate-depth (70 ≤ depth < 300 km) and deep (300 km ≤ depth) events. We have already shown that the detection capability beyond an aftershock zone degrades remarkably and that this condition persists for several hours after the occurrence of large shallow (depth < 70 km) earthquakes. Because an in...

  1. Modeling Spatial and Temporal Dependencies between Earthquakes

    OpenAIRE

    2000-01-01

    Two new different stochastic models for earthquake occurrence are discussed. Both models are focusing on the spatio-temporal interactions between earthquakes. The parameters of the models are estimated from a Bayesian updating of priors, using empirical data to derive posterior distributions. The first model is a marked point process model in which each earthquake is represented by its magnitude and coordinates in space and time. This model incorporates the occurrence of aftershocks as well a...

  2. Phenomenology of the earth's bow shock system - A summary description of experimental results

    Science.gov (United States)

    Greenstadt, E. W.

    1976-01-01

    Observational data on the earth's bow shock system are classified and characterized. Foreshock components, midshock components, and aftershock components are discussed separately. Schematic representations of the field and plasma particle parameters are elaborated, with attention given to quasi-perpendicular geometry and quasi-parallel geometry. Magnetic pulsation structure is delineated. Schematic profiles of field, particle, and wave behavior through a representative quasi-perpendicular shock crossing are displayed.

  3. Site effects of the Roio basin, L’Aquila

    OpenAIRE

    Bertrand, E.; CETE Méditerranée, Service Risque Sismique, Nice, France; Duval, A.M.; CETE Méditerranée (Centre d'Etudes Techniques de l’Equipement), Laboratoire régional des ponts et chaussées, Nice, France; Régnier, J.; CETE Méditerranée, Laboratoire Central des Ponts et Chaussées (LCPC), Nice, France; Azzara, R. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Bergamaschi, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Bordoni, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Cara, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Cultrera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Di Giulio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Milana, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Salichon, J.; OCA, UMR Géoazur, Sophia-Antipolis, France

    2011-01-01

    During the microzonation studies of the April 6th, 2009 L’Aquila earthquake, we observed local seismic amplifications in the Roio area—a plane separated from L’Aquila city center by mount Luco. Six portable, digital instruments were deployed across the plain from 15 April to mid-May 2009. This array recorded 152 aftershocks. We analyzed the ground motion from these events to determine relative site amplification within the plain and on surrounding ridges. Horizontal over vertic...

  4. Fault Orientation Determination for the 4 March 2008 Taoyuan Earthquake from Dense Near-Source Seismic Observations

    Directory of Open Access Journals (Sweden)

    Min-Hung Shih

    2014-01-01

    Full Text Available On 4 March 2008, a moderate earthquake (ML = 5.2 occurred in southern Taiwan and named as the Taoyuan earthquake, preceded by foreshocks and followed by numerous aftershocks. This earthquake sequence occurred during the TAIGER (TAiwan Integrated GEodynamics Research controlled-source seismic experiment. Consequently, several seismic networks were deployed in the Taiwan area at this time and many stations recorded this earthquake sequence in the near-source region. We archived and processed near-source observations to determine the fault orientation. To locate the events more accurately, station corrections, waveform cross-correlation to pick seismic phases, and a double-difference earthquake location algorithm were used to compute earthquake hypocenters. Over a 50-hour recording period, beginning half an hour before the start of the main shock, 2340 events were identified within the earthquake sequence. The identified aftershocks reveal a clear fault plane with a strike of N37°EN37°E and a dip of 45°SE.45°SE. This plane corresponds to one of the focal mechanism nodal planes determined by the Broadband Array in Taiwan for Seismology (BATS (strike = 37°,37°, dip = 48°,48°, and rake = 96°.96°. Based on the main shock focal mechanism, the aftershock distribution, and the regional geological reports, we suggest that faulting on the northern extension of the major regional active fault, the Chishan Fault, caused the Taoyuan earthquake sequence.

  5. Olyutorsky Earthquake (MW=7.6) on April 20, 2006 (Koryakia, Russia)

    Science.gov (United States)

    Gordeev, E.; Chebrov, V.; Gusev, A.; Levina, V.; Bakhtiarova, G.; Bakhtiarov, V.; Leonov, V.; Pinegina, T.; Konstantinova, T.; Senukov, S.; Kugaenko, Y.

    2006-12-01

    On April 20, 2006, 23:25, large earthquake with magnitude Mw=7.6 occurred in northeastern Russia, directly north- northeast of the Kamchatka Peninsula. This earthquake was named as Olyutorsky earthquake. It occurred in sparsely populated region. About 40 people were injured fortunately nobody was killed. The intensity of ground motions in Mercally scale was about 9 in Korf and 8 in Khailino and Tilichiki. Olyutorsky earthquake was the largest in the Koryak area since beginning of instrumental observations and, according to the preliminary data, caused damage of approximately 0.5 million US dollars to the region. Losses included structural damage to apartment buildings and facilities, schools, daycares and local airport's runways, as well as loss of power and water supplies in several settlements. During the first month after main shock 73 aftershocks with M>=5 were registered. The largest aftershocks had magnitude Mc=6.6 (April 29 and May 22). United team of scientists from Geophysical Survey and Institute of Volcanology and Seismology worked in epicenter area of Olyutorsky earthquake in April-May 2006. Unique seismic and GPS data and photo of destroyed buildings were gathered. Main faults of earthquake were mapped. New digital seismic station and accelerometer were installed in Tilichiki. The focal mechanism of the main shock and biggest aftershocks show the EW-NE direction of the main fault as well as surface faults. This direction is very close to main geological structures and proposed border between North American and Bering tectonic plates.

  6. Ductile gap between the Wenchuan and Lushan earthquakes revealed from the two-dimensional Pg seismic tomography.

    Science.gov (United States)

    Pei, Shunping; Zhang, Haijiang; Su, Jinrong; Cui, Zhongxiong

    2014-01-01

    A high-resolution two-dimensional Pg-wave velocity model is obtained for the upper crust around the epicenters of the April 20, 2013 Ms7.0 Lushan earthquake and the May 12, 2008 Ms8.0 Wenchuan earthquake, China. The tomographic inversion uses 47235 Pg arrival times from 6812 aftershocks recorded by 61 stations around the Lushan and Wenchuan earthquakes. Across the front Longmenshan fault near the Lushan earthquake, there exists a strong velocity contrast with higher velocities to the west and lower velocities to the east. Along the Longmenshan fault system, there exist two high velocity patches showing an "X" shape with an obtuse angle along the near northwest-southeast (NW-SE) direction. They correspond to the Precambrian Pengguan and Baoxing complexes on the surface but with a ~20 km shift, respectively. The aftershock gap of the 2008 Wenchuan and the 2013 Lushan earthquakes is associated with lower velocities. Based on the theory of maximum effective moment criterion, this suggests that the aftershock gap is weak and the ductile deformation is more likely to occur in the upper crust within the gap under the near NW-SE compression. Therefore our results suggest that the large earthquake may be hard to happen within the gap. PMID:25267344

  7. Seismic tomography of the area of the 2010 Beni-Ilmane earthquake sequence, north-central Algeria.

    Science.gov (United States)

    Abacha, Issam; Koulakov, Ivan; Semmane, Fethi; Yelles-Chaouche, Abd Karim

    2014-01-01

    The region of Beni-Ilmane (District of M'sila, north-central Algeria) was the site of an earthquake sequence that started on 14 May 2010. This sequence, which lasted several months, was triggered by conjugate E-W reverse and N-S dextral faulting. To image the crustal structure of these active faults, we used a set of 1406 well located aftershocks events and applied the local tomography software (LOTOS) algorithm, which includes absolute source location, optimization of the initial 1D velocity model, and iterative tomographic inversion for 3D seismic P- and S-wave velocities (and the Vp/Vs ratio), and source parameters. The patterns of P-wave low-velocity anomalies correspond to the alignments of faults determined from geological evidence, and the P-wave high-velocity anomalies may represent rigid blocks of the upper crust that are not deformed by regional stresses. The S-wave low-velocity anomalies coincide with the aftershock area, where relatively high values of Vp/Vs ratio (1.78) are observed compared with values in the surrounding areas (1.62-1.66). These high values may indicate high fluid contents in the aftershock area. These fluids could have been released from deeper levels by fault movements during earthquakes and migrated rapidly upwards. This hypothesis is supported by vertical sections across the study area show that the major Vp/Vs anomalies are located above the seismicity clusters. PMID:25485193

  8. The 10 April 2014 Earthquake in Central Nicaragua: Evidence of Complex Crustal Deformation in Central America

    Science.gov (United States)

    Suarez, G.; Muñoz, A.; Talavera, E.; Tenorio, V.; Farraz, I.; Novelo-Casanova, D. A.; Sánchez, A.

    2014-12-01

    On 10 April 2014 a magnitude Mw 6.1 struck central Nicaragua. The main event and the aftershocks were clearly recorded by the Nicaraguan seismic network. These crustal earthquakes were strongly felt but caused relatively little damage to the city of Managua and to the surrounding cities and towns. This is in sharp contrast to the destructive effects of the 1972 earthquake in the capital city of Managua. The differences in damage stem from the fact that in 1972, the earthquake occurred on a fault beneath the city; in contrast, the 2014 event lies offshore, under Lake Managua. The distribution of aftershocks shows two clusters of seismic activity. In the northwestern part of Lake Managua, an alignment of aftershocks suggests a southeast trending fault. The reported source mechanism suggests right-lateral strike slip motion on a plane with the same azimuth as the aftershock sequence. A second cluster of seismic activity occurred simultaneously, but spatially separated, beneath Apoyeque volcano. There is no clear alignment of the epicenters in this cluster. Seismic scaling relations between magnitude and the fault length predict a length of approximately 10 km for an earthquake of this magnitude. This is in agreement with the extent of the fault defined by the aftershock sequence. The northeast - southwest trending Tiscapa and Ciudad Jardín faults that broke during the 1972 and 1931 Managua earthquakes are orthogonal to the fault where the 10 April earthquake occurred. This set of conjugate faults confirms that Central Nicaragua is being deformed in a complex tectonic style of deformation. The forearc sliver between the trench and the volcanic arc moves to the northwest relative to the Caribbean plate. This deformation, however, does not take place on a single set of faults. The motion is apparently accommodated by a system of conjugate faults: right lateral, strike-slip faults oriented parallel to the volcanic arc and another set of faults trending northeast

  9. Deep Tectonic Tremor in Haiti triggered by the 2010/02/27 Mw8.8 Maule, Chile earthquake

    Science.gov (United States)

    Aiken, C.; Peng, Z.; Douilly, R.; Calais, E.; Deschamps, A.; Haase, J. S.

    2013-05-01

    Tectonic tremors have been observed along major plate-boundary faults around the world. In most of these regions, tremors occur spontaneously (i.e. ambient) or as a result of small stress perturbations from passing surface waves (i.e. triggered). Because tremors are located below the seismogenic zone, a detailed study of their behavior could help to better understand how tectonic movement is accommodated in the deep root of major faults, and the relationship with large earthquakes. Here, we present evidence of triggered tremor in southern Haiti around the aftershock zone of the 2010/01/12 Mw7.0 Haiti earthquake. Following the January mainshock, several groups have installed land and ocean bottom seismometers to record aftershock activity (e.g., De Lepinay et al., 2011). In the following month, the 2010/02/27 Mw8.8 Maule, Chile earthquake occurred and was recorded in the southern Haiti region by these seismic stations. We apply a 5-15 Hz band-pass filter to all seismograms to identify local high-frequency signals during the Chile teleseismic waves. Tremor is identified as non-impulsive bursts with 10-20 s durations that is coherent among different stations and is modulated by surface waves. We also convert the seismic data into audible sounds and use them to distinguish between local aftershocks and deep tremor. We locate the source of the tremor bursts using an envelope cross-correlation method based on travel time differences. Because tremor depth is not well constrained with this method, we set it to 20 km, close to the recent estimate of Moho depth in this region (McNamara et al., 2012). Most tremors are located south of the surface expression of the Enriquillo-Plantain Garden Fault (EPGF), a high-angle southward dipping left-lateral strike-slip fault that marks the boundary between the Gonave microplate and the Caribbean plate, although the location errors are large. Tremor peaks are mostly modulated by Love wave velocity, which is consistent with left

  10. A high-resolution 3D seismic velocity model of the 2010 Mw 8.8 Maule, Chile earthquake rupture zone using land & OBS networks

    Science.gov (United States)

    Hicks, S. P.; Rietbrock, A.; Ryder, I. M.; Miller, M.; Lee, C.

    2013-12-01

    Knowledge of seismic properties along a subduction megathrust can shed light on the composition and structure of rocks along the fault. By comparing seismic velocity structure with models of interseismic locking, co-seismic slip and afterslip, we can begin to understand how physical properties may affect fault dynamics throughout the subduction seismic cycle. The Maule earthquake, which hit the coast of central Chile in 2010, is the 6th largest earthquake ever recorded, rupturing a 500 x 80 km area of the Chilean megathrust. Published models demonstrate a complex bilateral rupture, with most co-seismic slip occurring to the north of the mainshock epicentre, although significant slip likely stopped short of the trench and the continental Moho. Here, we show a new high-resolution 3D velocity model (vp and vp/vs ratio) of the central Chilean margin Our velocity model is based on manually picked P- and S-wave arrival times from 670 aftershocks recorded by the International Maule Aftershock Deployment (IMAD) network. Seismic properties of the marine forearc are poorly understood in subduction zones, but by incorporating picks from two ocean-bottom seismometer (OBS) networks, we can resolve the velocity structure of the megathrust as far as the trench. In total, the catalogue used for the tomographic inversion yields a total of ~50,000 high quality P- and S-wave picks. We analyse the quality of our model by analysis of the resolution matrix and by testing characteristic models. The 3D velocity model shows the main structures associated within a subduction forearc: the marine forearc basin (vp 7.5 km/s), and subducting oceanic crust (vp ~ 7.7 km/s). The plate interface is well defined by relocated aftershock seismicity. P-wave velocities along the megathrust range from 6.5 km/s beneath the marine forearc to 7.7 km/s at the intersection of the megathrust with the continental Moho. We infer several high vp anomalies within the South American forearc that are also expressed

  11. Stress changes on major faults caused by Mw7.9 Wenchuan earthquake, May 12, 2008

    Institute of Scientific and Technical Information of China (English)

    SHAN Bin; XIONG Xiong; ZHENG Yong; DIAO FaQi

    2009-01-01

    On May 12, 2008, a magnitude 7.9 earthquake ruptured the Longmenshan fault system in Sichuan Province, China, collapsing buildings and killing tens of thousands people. As predicted, aftershocks may last for at least one year, and moreover, large aftershocks are likely to occur. Therefore, it is critical to outline the areas with potential aftershocks before reconstruction and re-settling people as to avoid future disasters. It is demonstrated that the redistribution of stress induced by an earthquake should trigger successive seismic activity. Based on static stress triggering theory, we calculated the coseis-mic stress changes on major faults induced by the Wenchuan earthquake, with elastic dislocation the-ory and the multilayered crustal model. We also discuss the stress distribution and its significance for future seismic activity under the impact of the Wenchuan earthquake. It is shown that coulomb failure stress (CFS) increases obviously on the Daofu-Kangding segment of the Xianshuihe Fault, the Maqu and Nanping segment of the Eastern Kunlun Fault, the Qingchuan Fault, southern segment of the Min-jiang Fault, Pengxian-Guanxian Fault, Jiangyou-Guangyuan Fault, and Jiangyou-Guanxian Fault. The increased stress raises the probability of earthquake occurrence on these faults. Since these areas are highly populated, earthquake monitoring and early disaster alarm system are needed. CFS increases with a magnitude of 0.03-0.06 MPa on the Qingchuan Fault, which is close to the northern end of the rapture of Wenchuan earthquake. The occurrence of some strong aftershocks, including three events with magnitude higher than 5.0, indicates that the seismic activities have been triggered by the main shock. Aftershocks seem to migrate northwards. Since the CFS change on the Lueyang-Mianxian Fault located on the NEE of the Qingchuan Fault is rather small (±0.01 MPa), the migration of aftershocks might be terminated in the area near Hanzhong City. The CFS change on the western

  12. Stress changes on major faults caused by M_w7.9 Wenchuan earthquake,May 12,2008

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    On May 12,2008,a magnitude 7.9 earthquake ruptured the Longmenshan fault system in Sichuan Province,China,collapsing buildings and killing tens of thousands people.As predicted,aftershocks may last for at least one year,and moreover,large aftershocks are likely to occur.Therefore,it is critical to outline the areas with potential aftershocks before reconstruction and resettling people as to avoid future disasters.It is demonstrated that the redistribution of stress induced by an earthquake should trigger successive seismic activity.Based on static stress triggering theory,we calculated the coseismic stress changes on major faults induced by the Wenchuan earthquake,with elastic dislocation the-ory and the multilayered crustal model.We also discuss the stress distribution and its significance for future seismic activity under the impact of the Wenchuan earthquake.It is shown that coulomb failure stress(CFS) increases obviously on the Daofu-Kangding segment of the Xianshuihe Fault,the Maqu and Nanping segment of the Eastern Kunlun Fault,the Qingchuan Fault,southern segment of the Min-jiang Fault,Pengxian-Guanxian Fault,Jiangyou-Guangyuan Fault,and Jiangyou-Guanxian Fault.The increased stress raises the probability of earthquake occurrence on these faults.Since these areas are highly populated,earthquake monitoring and early disaster alarm system are needed.CFS increases with a magnitude of 0.03―0.06 MPa on the Qingchuan Fault,which is close to the northern end of the rapture of Wenchuan earthquake.The occurrence of some strong aftershocks,including three events with magnitude higher than 5.0,indicates that the seismic activities have been triggered by the main shock.Aftershocks seem to migrate northwards.Since the CFS change on the Lueyang-Mianxian Fault located on the NEE of the Qingchuan Fault is rather small(±0.01 MPa),the migration of aftershocks might be terminated in the area near Hanzhong City.The CFS change on the western Qinling Fault is around 10 Pa

  13. The 10 April 2014 Nicaraguan Crustal Earthquake: Evidence of Complex Deformation of the Central American Volcanic Arc

    Science.gov (United States)

    Suárez, Gerardo; Muñoz, Angélica; Farraz, Isaac A.; Talavera, Emilio; Tenorio, Virginia; Novelo-Casanova, David A.; Sánchez, Antonio

    2015-11-01

    On 10 April 2014, an M w 6.1 earthquake struck central Nicaragua. The main event and the aftershocks were clearly recorded by the Nicaraguan national seismic network and other regional seismic stations. These crustal earthquakes were strongly felt in central Nicaragua but caused relatively little damage. This is in sharp contrast to the destructive effects of the 1972 earthquake in the capital city of Managua. The differences in damage stem from the fact that the 1972 earthquake occurred on a fault beneath the city; in contrast, the 2014 event lies offshore, under Lake Managua. The distribution of aftershocks of the 2014 event shows two clusters of seismic activity. In the northwestern part of Lake Managua, an alignment of aftershocks suggests a northwest to southeast striking fault, parallel to the volcanic arc. The source mechanism agrees with this right-lateral, strike-slip motion on a plane with the same orientation as the aftershock sequence. For an earthquake of this magnitude, seismic scaling relations between fault length and magnitude predict a sub-surface fault length of approximately 16 km. This length is in good agreement with the extent of the fault defined by the aftershock sequence. A second cluster of aftershocks beneath Apoyeque volcano occurred simultaneously, but spatially separated from the first. There is no clear alignment of the epicenters in this cluster. Nevertheless, the decay of the number of earthquakes beneath Apoyeque as a function of time shows the typical behavior of an aftershock sequence and not of a volcanic swarm. The northeast-southwest striking Tiscapa/Ciudad Jardín and Estadio faults that broke during the 1972 and 1931 Managua earthquakes are orthogonal to the fault where the 10 April earthquake occurred. These orthogonal faults in close geographic proximity show that Central Nicaragua is being deformed in a complex tectonic setting. The Nicaraguan forearc sliver, between the trench and the volcanic arc, moves to the

  14. The 2004 Sumatra Earthquake Mw 9.3: Seismological and Geophysical Investigations in the Andaman-Nicobar Islands

    Science.gov (United States)

    Mooney, W. D.; Kayal, J.

    2007-05-01

    The December 26, 2004 Sumatra-Andaman earthquake (MW 9.3) is the fourth largest event (M>9.0) in the world during the last 100 years. It occurred by thrust faulting on the interplate thrust zone of the subducting India plate and overriding Burma platelet. The main shock rupture, ~1300 km long and ~200 km wide, propagated from north of Sumatra to Andaman - Nicobar Islands; the slow rupture generated Tsunami which killed about 300,000 people. The epicenter of the earthquake is located at 3.90N and 94.260E with a focal depth at 28 km (USGS). This mega seismic event triggered giant tsunamis that devastated the coastal regions of Indonesia, Malaysia, Thailand, Sri Lanka, India, Maldives and even the east coast of Africa. The impact of the tsunami was quite severe in India, in the coasts of Andaman and Nicobar Islands. The Air-base in the Car- Nicobar island was totally devastated by the tsunami and killed about 200 people. Macroseismic survey was carried out by different teams of GSI in North Andaman, Middle Andaman, South Andaman, Havelock Hut Bay and also in the Nicobar Islands. A maximum intensity VIII was recorded in the Andaman Islands. The mega thrust event was followed by an intense aftershock activity spreading over an area extending between 30-140N along the Andaman - Nicobar - Sumatra Island arc region. The aftershocks are distributed northwards from the epicenter of the main shock suggesting a unilateral rupture propagation. The aftershock (M >4.5) area covers a length of about 1300 km and a width of about 200 km, in a 'banana' shape. The national network (IMD) recorded almost all aftershocks M >5.0; about 350 were recorded till 31.01.2005. The Geological Survey of India (GSI) deployed six temporary seismograph stations in the Andaman and Nicobar Islands and also in Havelok and Narkunda (volcanic) islands. About 20,000 aftershocks (M >3.0) were recorded until end of March, 2005. About 1000 aftershocks (M >3.0) located by the GSI network until January 31, 2005

  15. 3D P-wave velocity structure of the crust and relocation of earthquakes in the Lushan, China, source area

    Science.gov (United States)

    Yu, Xiangwei; Wang, Xiaona; Zhang, Wenbo

    2016-04-01

    Many researchers have investigated the Lushan source area with geological and geophysical approaches since the 2013 Lushan, China, earthquake happened. Compared with the previous tomographic studies, we have used a much large data set and an updated tomographic method to determine a small scale three-dimensional P wave velocity structure with spatial resolution less than 5km, which plays the important role for understanding the deep structure and the genetic mechanism beneath the Lushan area. The double difference seismic tomography method is applied to 50,711 absolute first arrival P wave arrival times and 7,294,691 high quality relative P arrival times of 5,285 events of Lushan seismic sequence to simultaneously determine the detailed crustal 3D P wave velocity structure and the hypocenter parameters in the Lushan seismic area. This method takes account of the path anomaly biases explicitly by making full use of valuable information of seismic wave propagation jointly with absolute and relative arrival time data. Our results show that the Lushan mainshock locates at 30.28N, 103.98E, with the depth of 16.38km. The front edge of aftershock in the northeast of mainshock present a spade with a steep dip angle, the aftershocks' extended length is about 12km. In the southwest of Lushan mainshock, the front edge of aftershock in low velocity zone slope gently, the aftershocks' extended length is about 23km. Our high-resolution tomographic model not only displays the general features contained in the previous models, but also reveals some new features. The Tianquan, Shuangshi and Daguan line lies in the transition zone between high velocity anomalies to the southeast and low velocity anomalies to the northwest at the ground surface. An obvious high-velocity anomaly is visible in Daxing area. With the depth increasing, Baoxing high velocity anomaly extends to Lingguan, while the southeast of the Tianquan, Shuangshi and Daguan line still shows low velocity. The high

  16. Impact of Short-term Changes In Earthquake Hazard on Risk In Christchurch, New Zealand

    Science.gov (United States)

    Nyst, M.

    2012-12-01

    The recent Mw 7.1, 4 September 2010 Darfield, and Mw 6.2, 22 February 2011 Christchurch, New Zealand earthquakes and the following aftershock activity completely changed the existing view on earthquake hazard of the Christchurch area. Not only have several faults been added to the New Zealand fault database, the main shocks were also followed by significant increases in seismicity due to high aftershock activity throughout the Christchurch region that is still on-going. Probabilistic seismic hazard assessment (PSHA) models take into account a stochastic event set, the full range of possible events that can cause damage or loss at a particular location. This allows insurance companies to look at their risk profiles via average annual losses (AAL) and loss-exceedance curves. The loss-exceedance curve is derived from the full suite of seismic events that could impact the insured exposure and plots the probability of exceeding a particular loss level over a certain period. Insurers manage their risk by focusing on a certain return period exceedance benchmark, typically between the 100 and 250 year return period loss level, and then reserve the amount of money needed to account for that return period loss level, their so called capacity. This component of risk management is not too sensitive to short-term changes in risk due to aftershock seismicity, as it is mostly dominated by longer-return period, larger magnitude, more damaging events. However, because the secondairy uncertainties are taken into account when calculating the exceedance probability, even the longer return period losses can still experience significant impact from the inclusion of time-dependent earthquake behavior. AAL is calculated by summing the product of the expected loss level and the annual rate for all events in the event set that cause damage or loss at a particular location. This relatively simple metric is an important factor in setting the annual premiums. By annualizing the expected losses

  17. Joint Inversion of Seismic and Geodetic Data for the Source of the 4th March 2010 MW 6.3 Jia-Shian, SW Taiwan, Earthquake

    Science.gov (United States)

    Huang, M.; Dreger, D. S.; Burgmann, R.; Suppe, J.; Hashimoto, M.

    2010-12-01

    The 4th March 2010 Jia-Shian (MW 6.3) earthquake occurred in SW Taiwan and caused moderate damage. According to the Central Weather Bureau (CWB) report, this event is located at a depth of ~23 km under the Central Range. No fault related surface rupture was observed, reflecting an unusually deep source that is relatively rare in west Taiwan. The coseismic GPS measurements show a fan shape pattern with azimuths from SW to NW. The highest observed horizontal displacement is 3.67 cm in the direction of N80°W and is about 20 km far away from the epicenter. We develop finite-source models using a combination of Global Positioning System (GPS), synthetic aperture radar interferometry (InSAR), and seismic strong motion waveform data to understand the rupture process of this event. The preferred model shows a primary slip patch that is about 20 km in diameter with a peak slip of 25.1 cm and total scalar seismic moment of 1.96 × 1018 N m (MW 6.13). This fault geometry is N38°W in strike and 27° dipping to NE. The majority of slip is between 8 and 14 cm located to the NW of the hypocenter, which is very close to the northern end of the active Chi-Shan Fault (CSF) and the high angle reverse Chao-Chou Fault (CCF). Our moment tensor solution using data from the Broadband Array in Taiwan for Seismology (BATS) shows a NW-striking and east dipping thrust with a left-lateral strike-slip component to the focal mechanism, which is close to the current direction of plate motion in Taiwan. The main shock mechanism and the aftershock distribution have different orientations, neither of which is similar to NS or NE-SW trending Chi-Shan and Chao-Chou surface faults. The aftershock sequence extends nearly 25 km into western Foothills striking EW when close to the epicenter but in a NW direction farther west from the epicenter. The different directions from the main shock to the aftershock distribution may imply different fault planes being ruptured during coseismic and postseismic

  18. The 2007 M7.7 Tocopilla northern Chile earthquake sequence - along and across strike rupture segmentation

    Science.gov (United States)

    Schurr, B.; Asch, G.; Motagh, M.; Oncken, O.; Chong Diaz, G.; Barrientos, S. E.; Vilotte, J.

    2010-12-01

    In November 2007 a M7.7 earthquake occurred near the coastal town of Tocopilla in the southern part of a presumed seismic gap extending some 500 km along the northern Chile subduction zone. This major segment last broke in a magnitude ≧8.5 earthquake in 1877. Assuming a complete lock of the interface, it has accumulated more than 8 m of slip deficit. The contiguous segments to the north and south broke in M≧8 earthquakes in 2001 and 1995. Teams from Chile (Universidad Católica del Norte and Universidad de Chile), France (IPGP) and Germany (GFZ) started in 2006 to install semi-permanent multi-parameter observatories within the Integrated Plate Boundary Observatory Chile (IPOC) Initiative to monitor deformation at a variety of spatial and temporal scales in the final stage of the seismic cycle. At the time of the Tocopilla earthquake, 12 sites were equipped with seismic broadband and strong-motion sensors recording both the mainshock and its aftershock series. The earthquake rupture extended for about 160 km from the centre of the Mejillones peninsula (MP) to about 20 km north of the town of Tocopilla. Slip was confined to the depth range 30-55 km and concentrated in two patches in the north and south with a maximum of about 2.6 m. Hence the earthquake released only a fraction of the slip deficit and broke only the down-dip part of the plate interface, with the up-dip limit of the rupture approximately following the coastline. This poses the important question why rupture did not extend offshore, where the interface is presumably locked based on models of long-term interseismic deformation. We relocated more than 1000 aftershocks occurring in the week following the mainshock using hand-picked arrival times, cross-correlation based differential travel times and the double-difference algorithm. Despite the sparseness of the network, the aftershocks sharply define the plate interface. Seismicity in the first 24h is congruent to the slip distribution with the area

  19. Variations of shear wave splitting in the 2008 Wen chuan earthquake region

    Institute of Scientific and Technical Information of China (English)

    DING ZhiFeng; WU Yan; WANG Hui; ZHOU XiaoFeng; LI GuiYin

    2008-01-01

    Through the analysis of S-wave particle motion of local events in the shear wave window, the polarization directions of the faster shear wave and the delay times between the faster and the slower shear waves were derived from seismic recordings at the stations near the fault zones. The shear wave splitting results of seven stations in the area of Longmenshan fault zone reveal spatial variation of the polarization directions of the fast shear wave. The directions at stations in the southeastern side of the Longmenshan fault zone (in the Sichuan Basin area) are in the NE direction, whereas the direction at station PWU (in the Plateau), which is in the northwestern side of the faults, is in the EW direction.Systematic changes of the time delays between two split shear waves were also observed. At station L5501 in the southern end of the aftershock zone, the delay times of the slower shear wave decrease systematically after the main shock. After the main shock, the delay times at station PWU were longer than those before the earthquake. Seismic shear wave splitting is caused mostly by stress-aligned microcracks in the rock below the stations. The results demonstrate changes of local stress field during the main-shock and the aftershocks. The stress in the southern part of Wenchuan seismogenic zone was released by the main-shock and the aftershocks. The crustal stresses were transferred to the northeastern part of the zone, resulting in stress increase at station PWU after the main-shock.

  20. Variations of shear wave splitting in the 2008 Wenchuan earthquake region

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Through the analysis of S-wave particle motion of local events in the shear wave window, the polariza-tion directions of the faster shear wave and the delay times between the faster and the slower shear waves were derived from seismic recordings at the stations near the fault zones. The shear wave split-ting results of seven stations in the area of Longmenshan fault zone reveal spatial variation of the po-larization directions of the fast shear wave. The directions at stations in the southeastern side of the Longmenshan fault zone (in the Sichuan Basin area) are in the NE direction, whereas the direction at station PWU (in the Plateau), which is in the northwestern side of the faults, is in the EW direction. Systematic changes of the time delays between two split shear waves were also observed. At station L5501 in the southern end of the aftershock zone, the delay times of the slower shear wave decrease systematically after the main shock. After the main shock, the delay times at station PWU were longer than those before the earthquake. Seismic shear wave splitting is caused mostly by stress-aligned microcracks in the rock below the stations. The results demonstrate changes of local stress field dur-ing the main-shock and the aftershocks. The stress in the southern part of Wenchuan seismogenic zone was released by the main-shock and the aftershocks. The crustal stresses were transferred to the northeastern part of the zone, resulting in stress increase at station PWU after the main-shock.

  1. Effects of fluid propagation on occurrence of doublet earthquakes

    Science.gov (United States)

    Mastrolembo V., Brunella; Rinaldi, Antonio Pio; Urpi, Luca; Rivalta, Eleonora; Passarelli, Luigi

    2016-04-01

    Most earthquake sequences consist of a main large event preceded and followed by a series of smaller magnitude quakes commonly referred as to fore- and after-shocks. However, seismic catalogs report many examples of earthquake sequences featuring two or more main events of comparable magnitude Such events are often referred as doublet earthquakes and are particularly observed in environments characterized by a large number of faults. Doublet earthquakes occur all over the world representing a significant issue in terms of seismic hazard assessment after large events. Some examples of doublets are: the 2012 Emilia-Romagna sequence (Italy), during which a magnitude 5.9 event occurred on May 20th, followed by a magnitude 5.8 event on May 29th; the 1992 Landers earthquake in California, which has been associated to the Big Bear earthquake, that hit about three hours later after the mainshock; the 2006 November 15th M8.3 event along the Kuril arc followed by a M8.1 event on 13 January 2007 is one of the largest great doublet earthquake on record. The spatial distribution of aftershocks usually well correlates with the coseismic (static) Coulomb stress change, while the observed time delay of aftershocks, as well as their diffusive-like behavior, have been explained as due to additional physical processes such as post-seismic relaxation, afterslip, poro-elastic effect, as well as induced fluid propagation. In this work we first perform an analysis of the available worldwide seismic catalogs in order to identify a number of doublet earthquakes based on a spatial and temporal distance correlation. Then we perform a parametric study to identify the main characteristics of every couple of events and extrapolate the common relations between time delay, hypocentral distances, geological, as well as hydrogeological parameters and fluids content. Numerical simulations are then carried out to study the time delay occurring between two events as related to hydrogeological and

  2. Site effects by generalized inversion technique using strong motion recordings of the 2008 Wenchuan earthquake

    Science.gov (United States)

    Ren, Yefei; Wen, Ruizhi; Yamanaka, Hiroaki; Kashima, Toshihide

    2013-06-01

    The generalized inversion of S-wave amplitude spectra from the free-field strong motion recordings of the China National Strong Motion Observation Network System (NSMONS) are used to evaluate the site effects in the Wenchuan area. In this regard, a total of 602 recordings from 96 aftershocks of the Wenchuan earthquake with magnitudes of M3.7- M6.5 were selected as a dataset. These recordings were obtained from 28 stations at a hypocenter distance ranging from 30 km to 150 km. The inversion results have been verified as reliable by comparing the site response at station 62WUD using the Generalized Inversion Technique (GIT) and the Standard Spectral Ratio method (SSR). For all 28 stations, the site predominant frequency F p and the average site amplification in different frequency bands of 1.0-5.0 Hz, 5.0-10.0 Hz and 1.0-10.0 Hz have been calculated based on the inversion results. Compared with the results from the horizontal-to-vertical spectral ratio (HVSR) method, it shows that the HVSR method can reasonably estimate the site predominant frequency but underestimates the site amplification. The linear fitting between the average site amplification for each frequency band and the V s20 (the average uppermost-20 m shear wave velocity) shows good correlation. A distance measurement called the asperity distance D Aspt is proposed to reasonably characterize the source-to-site distance for large earthquakes. Finally, the inversed site response is used to identify the soil nonlinearity in the main shock and aftershocks of Wenchuan earthquake. In ten of the 28 stations analyzed in the main shock, the soil behaved nonlinearly, where the ground motion level is apparently beyond a threshold of PGA > 300 cm/s2 or PGV > 20 cm/s, and only one station coded 51SFB has evidence of soil nonlinear behavior in the aftershocks.

  3. Short-term foreshock activity and its value for the earthquake prediction

    Science.gov (United States)

    Orfanogiannaki, Katerina; Daskalaki, Elena; Minadakis, George; Papadopoulos, Gerasimos

    2014-05-01

    Seismicity often occurs in space-time clusters: swarms, short-term foreshocks, aftershocks. Swarms are space-time clusters that do not conclude with a mainshock. Earthquake statistics shows that in areas of good seismicity monitoring foreshocks precede sizeable (M5.5 or more) mainshocks at a rate of about half percent. Therefore, discrimination between foreshocks and swarms is of crucial importance with the aim to use foreshocks as a diagnostic of forthcoming strong mainshock in real-time conditions. We analyzed seismic sequences in Greece and Italy with the application of our algorithm FORMA (Foreshocks-Mainshock-Aftershocks) and discriminate between foreshocks and swarms based on the seismicity significant changes in the space-time-magnitude domains. We support that different statistical properties is a diagnostic of foreshocks (e.g. b-value drop) against swarms (b-value increase). A complementary approach is based on the development of Poisson Hidden Markov Models (PHMM's) which are introduced to model significant temporal seismicity changes. In a PHMM the unobserved sequence of states is a finite-state Markov chain and the distribution of the observation at any time is Poissonian with rate depending only on the current state of the chain. Thus, PHMM allows a region to have varying seismicity rate. PHMM is a promising diagnostic since the transition from one state to another does not only depend on the total number of events involved but also on the current state of the system. A third methodological experiment was performed based on the complex network theory. We found that the earthquake networks examined form a scale-free degree distribution. By computing their basic statistical measures, such as the Average Clustering Coefficient, Mean Path Length and Entropy, we found that they underline the strong space-time clustering of swarms, foreshocks and aftershocks but also their important differences. Therefore, network theory is an additional, promising tool to

  4. Local Wave Propagation in the Kachchh Basin, India: Synergy With the New Madrid Seismic Zone

    Science.gov (United States)

    Langston, C. A.; Kang, D.; Bodin, P.; Horton, S.

    2002-12-01

    Aftershocks of the Mw7.6 Bhuj earthquake are used to infer velocity structure and the nature of wave propagation within the Kachchh Basin, India. The data were collected from a joint MAEC/ISTAR deployment of seismographs within 3 weeks of the main event and from existing broadband stations in the region under the India Meteorological Department. Waveforms are available from events that span the entire thickness of the crust and display a variety of wave propagation effects due to low-velocity near-surface site structure and larger structure of the Mesozoic Kachchh basin. These effects include near-site, high frequency reverberations in P and S waves, Sp and Ps mode conversions, PL waves within the Mesozoic basin, basin S multiples, and surface waves. Surface wave group velocity dispersion yields estimates of basin shear wave velocity, and when coupled to analysis of large observed Sp conversions, give a migrated image of stratigraphy within the Banni plains that agrees favorably with published stratigraphy. Identification of basin structure effects allows constraints to be placed on aftershock source depths that are needed in evaluating standard earthquake locations. Structure models are used to construct Green's functions for determining source parameters through waveform modeling. Although stations of the aftershock network were situated on a variety of sites that varied from consolidated Mesozoic bedrock to unconsolidated recent sediments, all stations show major wave propagation effects due to basin fill that must be included in source parameter estimation. These effects seen in India have many similarities to wave propagation effects observed within the Mississippi embayment from microearthquakes in the New Madrid Seismic Zone (NMSZ) of the central U.S. Joint waveform studies are motivating new ways of understanding wave propagation and source processes within both areas.

  5. Seismicity Following Deep Reverse-Faulting in the Indian Plate: Implications for Gujarat

    Science.gov (United States)

    Bilham, R.; Wallace, K.; Bendick, R.

    2001-12-01

    The catastrophic 1819 Allah Bund M=7.7, 1897 Shillong M=8.1, and 2001 Bhuj M=7.6 earthquakes all occurred on buried steep-dipping reverse faults. Each resulted in shortening of the Indian plate in an approximately NW direction, and each consequently loaded the contiguous plate to the east and west. These locally increased stresses are significant compared to the cumulative geodetically-inferred intraplate loading in the past century. Following the 19th century events these adjacent regions subsequently experienced damaging earthquakes. The Bhuj event itself may have been triggered by, or advanced in time by, stress changes resulting from the 1819 earthquake. There is thus some concern that future seismicity east and west of the Bhuj rupture zone will be stimulated by the recent Bhuj event. Stress changes above buried reverse-faulting is compressive and significant. Data for the early events are too poor to assess depths, however, aftershock activity in the uppermost 8 km following the Bhuj earthquake is remarkably low. One explanation for the absence of shallow aftershock activity is that the Anjar 1956 event may have already released near-surface stress, incrementing the region of the 2001 rupture towards failure. Significant earthquakes (6Bhuj earthquake has placed the Kachchh Peninsula and the Little Rann of Kachchh west and east of the Bhuj epicenter under increased stress, and it is anticipated that these regions are likely to experience heightened seismicity in the next several decades. The locations of large aftershocks immediately following the event are consistent with these inferred stress changes, but of greater concern is the possibility that a major shock (M>7) may now occur 100-200 km east or west of the epicentral region.

  6. Multifractal Omori law for earthquake triggering: new tests on the California, Japan and worldwide catalogues

    Science.gov (United States)

    Ouillon, G.; Sornette, D.; Ribeiro, E.

    2009-07-01

    The Multifractal Stress-Activated model is a statistical model of triggered seismicity based on mechanical and thermodynamic principles. It predicts that, above a triggering magnitude cut-off M0, the exponent p of the Omori law for the time decay of the rate of aftershocks is a linear increasing function p(M) = a0M + b0 of the main shock magnitude M. We previously reported empirical support for this prediction, using the Southern California Earthquake Center (SCEC) catalogue. Here, we confirm this observation using an updated, longer version of the same catalogue, as well as new methods to estimate p. One of this methods is the newly defined Scaling Function Analysis (SFA), adapted from the wavelet transform. This method is able to measure a mathematical singularity (hence a p-value), erasing the possible regular part of a time-series. The SFA also proves particularly efficient to reveal the coexistence and superposition of several types of relaxation laws (typical Omori sequences and short-lived swarms sequences) which can be mixed within the same catalogue. Another new method consists in monitoring the largest aftershock magnitude observed in successive time intervals, and thus shortcuts the problem of missing events with small magnitudes in aftershock catalogues. The same methods are used on data from the worldwide Harvard Centroid Moment Tensor (CMT) catalogue and show results compatible with those of Southern California. For the Japan Meteorological Agency (JMA) catalogue, we still observe a linear dependence of p on M, but with a smaller slope. The SFA shows however that results for this catalogue may be biased by numerous swarm sequences, despite our efforts to remove them before the analysis.

  7. The Beni Haoua, Algeria, Mw 4.9 earthquake: source parameters, engineering, and seismotectonic implications

    Science.gov (United States)

    Abbes, Khadidja; Dorbath, Louis; Dorbath, Catherine; Djeddi, Mohamed; Ousadou, Farida; Maouche, Said; Benkaci, Nassima; Slimani, Abdennasser; Larbes, Said; Bouziane, Djillali

    2016-04-01

    A moderate Mw 4.9 earthquake struck the Beni Haoua (Algeria) coastal area on April 25, 2012. The mainshock was largely recorded by the accelerograph network of the Centre National de Recherche Appliquée en Génie Parasismique (CGS). The same day the earthquake occurred, eight mobile short period stations were deployed through the epicentral area. In this study, we use accelerogram and seismogram data recorded by these two networks. We combined the focal mechanism built from the first motion of P waves and from waveform inversion, and the distribution of aftershocks to well constrain the source parameters. The mainshock is located with a shallow focal depth, ˜9 km, and the focal mechanism shows a nearly pure left lateral strike slip motion, with total seismic moment of 2.8 × 1016 N.m (Mw = 4.9). The aftershocks mainly cluster on a narrow NS strip, starting at the coast up to 3-4 km inland. This cluster, almost vertical, is concentrated between 6 and 10 km depth. The second part of this work concerns the damage distribution and estimated intensity in the epicentral area. The damage distribution is discussed in connection with the observed maximum strong motion. The acceleration response spectrum with 5 % damping of the mainshock and aftershocks give the maximum amplitude in high frequency which directly affects the performance of the high-frequency structures. Finally, we tie this earthquake with the seismotectonic of the region, leading to conclude that it occurred on a N-S transform zone between two major compressional fault zones oriented NE-SW.

  8. Surface expressed subduction earthquake segment boundary and its verification in seismological data

    Science.gov (United States)

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

    2008-12-01

    One of the key questions in seismotectonics is what determines the size of an earthquake rupture and whether the geological and tectonic structure has an influence on rupture dynamics. We have found evidence for a subduction segment boundary on Mejillones Peninsula in Northern Chile expressed in topographic features which form an E-W transect over the peninsula in the area around 23.3°S. This transect subdivides the peninsula in a northern and southern part exhibiting differences in geological and tectonic parameters. Stratigraphic data, morphotectonic structures, fault patterns and age of deformation as well as the coastal uplift on both parts have been examined and showed that the transect might act as a "hinge" line or segment boundary provided that it is a persistent feature over various seismic cycles. Confirmation for this interpretation is coming from seismological data particularly from the intensive study of the aftershock sequence of the M8.0, 1995, Antofagasta earthquake. The main shock hypocenter calculations reflecting the start of the rupture are all located in the area of the proposed segment boundary. Several E-W aligned aftershock hypocentres with strike slip focal mechanism are also congruent with the "hinge"-line over Mejillones Peninsula. Furthermore, a number of seismological parameters, like the seimic b-value, do change at the segment boundary. A very strong support for our hypothesis is coming from the recent M7.8, 2007, Tocopilla earthquake which ruptured the adjacent part of the seismogenic interface north of the Antofagasta earthquake fault plane. Preliminary hypocenter determinations of some aftershocks suggest that the Tocopilla fault plane ends where the Antofagasta fault plane starts, which is again congruent with the proposed segment boundary. In our presentation we would like to summarize the geological evidences and give some new results from the seismological studies of the Tocopilla earthquake.

  9. Short-term earthquake forecasting experiment before and during the L’Aquila (central Italy seismic sequence of April 2009

    Directory of Open Access Journals (Sweden)

    Maura Murru

    2015-03-01

    Full Text Available In this paper, we compare the forecasting performance of several statistical models, which are used to describe the occurrence process of earthquakes in forecasting the short-term earthquake probabilities during the L’Aquila earthquake sequence in central Italy in 2009. These models include the Proximity to Past Earthquakes (PPE model and two versions of the Epidemic Type Aftershock Sequence (ETAS model. We used the information gains corresponding to the Poisson and binomial scores to evaluate the performance of these models. It is shown that both ETAS models work better than the PPE model. However, in comparing the two types of ETAS models, the one with the same fixed exponent coefficient (alpha = 2.3 for both the productivity function and the scaling factor in the spatial response function (ETAS I, performs better in forecasting the active aftershock sequence than the model with different exponent coefficients (ETAS II, when the Poisson score is adopted. ETAS II performs better when a lower magnitude threshold of 2.0 and the binomial score are used. The reason is found to be that the catalog does not have an event of similar magnitude to the L’Aquila mainshock (Mw 6.3 in the training period (April 16, 2005 to March 15, 2009, and the (alpha-value is underestimated, thus the forecast seismicity is underestimated when the productivity function is extrapolated to high magnitudes. We also investigate the effect of the inclusion of small events in forecasting larger events. These results suggest that the training catalog used for estimating the model parameters should include earthquakes of magnitudes similar to the mainshock when forecasting seismicity during an aftershock sequence.

  10. The 2003 M=6.9 Zemmouri, Algeria, Earthquake Brought Thrust and Strike-Slip Faults Near Algiers Closer to Coulomb Failure

    Science.gov (United States)

    Lin, J.; Stein, R. S.; Toda, S.; Meghraoui, M.; Dorbath, C.

    2007-12-01

    We investigate key features of thrust earthquake triggering, inhibition, and clustering associated with the stress transferred by the 2003 M=6.9 Zemmouri quake on an offshore hidden thrust fault in coastal Algeria. A crucial question is whether the seismic hazard increased on the Boumerdes and Thenia faults, which lie just west of the Zemmouri rupture and only 10-20 km from the city of Algiers. The capital city suffered large damaging quakes in A.D. 1365 and 1716, and is today home to 3 million people. Slip on blind thrust faults tend to increase the stress above the source fault and in much of the surrounding crust, whereas slip on surface-cutting thrust faults drops the stress in most of the adjacent crust. We examined the sensitivity of the imparted stress to different published source models of the 2003 Zemmouri event inferred from geodetic and seismic inversions, and focus here on the robust results. We calculate that the 2003 M=6.9 Zemmouri quake brought the Coulomb stress 1.0 bars closer to failure on the reverse Boumerdes and 0.5 bars closer on the right-lateral Thenia faults that bound the populated Mitidja basin, although the Thenia fault may not be tectonically active. The calculated pattern of the stress increase appears consistent with aftershock distribution determined from double difference earthquake tomography by Ayadi et al. (submitted); both of these faults were illuminated by aftershocks during the first three months of the sequence. The East Sahel and Larbaa faults, which lie further to the west, are calculated to have sustained a weak 0.1-bar stress increase and show no associated aftershocks. We also calculate a 1.0-bar stress increase on the NNW-SSE trending vertical right-lateral Kabyle fault located south of the Zemmouri fault, although there is no evidence of recent Quaternary tectonic movement, no geomorphology typical of active zones, and little seismicity along the Kabyle fault.

  11. Complex faulting in the Quetta Syntaxis: fault source modeling of the October 28, 2008 earthquake sequence in Baluchistan, Pakistan, based on ALOS/PALSAR InSAR data

    Science.gov (United States)

    Usman, Muhammad; Furuya, Masato

    2015-09-01

    The Quetta Syntaxis in western Baluchistan, Pakistan, is the result of an oroclinal bend of the western mountain belt and serves as a junction for different faults. As this area also lies close to the left-lateral strike-slip Chaman fault, which marks the boundary between the Indian and Eurasian plates, the resulting seismological behavior of this regime is very complex. In the region of the Quetta Syntaxis, close to the fold and thrust belt of the Sulaiman and Kirthar Ranges, an earthquake with a magnitude of 6.4 (Mw) occurred on October 28, 2008, which was followed by a doublet on the very next day. Six more shocks associated with these major events then occurred (one foreshock and five aftershocks), with moment magnitudes greater than 4. Numerous researchers have tried to explain the source of this sequence based on seismological, GPS, and Environmental Satellite (ENVISAT)/Advanced Synthetic Aperture Radar (ASAR) data. Here, we used Advanced Land Observing Satellite (ALOS)/Phased Array-type L-band Synthetic Aperture Radar (PALSAR) InSAR data sets from both ascending and descending orbits that allow us to more completely detect the deformation signals around the epicentral region. The results indicated that the shock sequence can be explained by two right-lateral and two left-lateral strike-slip faults that also included reverse slip. The right-lateral faults have a curved geometry. Moreover, whereas previous studies have explained the aftershock crustal deformation with a different fault source, we found that the same left-lateral segment of the conjugate fault was responsible for the aftershocks. We thus confirmed the complex surface deformation signals from the moderate-sized earthquake. Intra-plate crustal bending and shortening often seem to be accommodated as conjugate faulting, without any single preferred fault orientation. We also detected two possible landslide areas along with the crustal deformation pattern.

  12. Earthquake and nuclear explosion location using the global seismic network

    International Nuclear Information System (INIS)

    The relocation of nuclear explosions, aftershock sequence and regional seismicity is addressed by using joint hypocenter determination, Lomnitz' distance domain location, and origin time and earthquake depth determination with local observations. Distance domain and joint hypocenter location are used for a stepwise relocation of nuclear explosions in the USSR. The resulting origin times are 2.5 seconds earlier than those obtained by ISC. Local travel times from the relocated explosions are compared to Jeffreys-Bullen tables. P times are found to be faster at 9-300 distances, the largest deviation being around 10 seconds at 13-180. At these distances S travel times also are faster by approximately 20 seconds. The 1977 Sumba earthquake sequence is relocated by iterative joint hypocenter determination of events with most station reports. Simultaneously determined station corrections are utilized for the relocation of smaller aftershocks. The relocated hypocenters indicate that the aftershocks were initially concentrated along the deep trench. Origin times and depths are recalculated for intermediate depth and deep earthquakes using local observations in and around the Japanese Islands. It is found that origin time and depth differ systematically from ISC values for intermediate depth events. Origin times obtained for events below the crust down to 100 km depth are earlier, whereas no general bias seem to exist for origin times of events in the 100-400 km depth range. The recalculated depths for earthquakes shallower than 100 km are shallower than ISC depths. The depth estimates for earthquakes deeper than 100 km were increased by the recalculations

  13. Space-time combined correlation integral and earthquake interactions

    Directory of Open Access Journals (Sweden)

    L. Pietronero

    2004-06-01

    Full Text Available Scale invariant properties of seismicity argue for the presence of complex triggering mechanisms. We propose a new method, based on the space-time combined generalization of the correlation integral, that leads to a self-consistent visualization and analysis of both spatial and temporal correlations. The analysis has been applied on global medium-high seismicity. Results show that earthquakes do interact even on long distances and are correlated in time within defined spatial ranges varying over elapsed time. On that base we redefine the aftershock concept.

  14. Earthquake focal mechanisms and stress inversion in the Irpinia Region (southern Italy)

    OpenAIRE

    Pasquale, Giuseppe; De Matteis, Raffaella; Romeo, Annalisa; Maresca, Rosalba

    2008-01-01

    Abstract The goal of this study was to estimate the stress field acting in the Irpinia Region, an area of southern Italy that has been struck in the past by destructive earthquakes and that is now characterized by low to moderate seismicity. The dataset are records of 2,352 aftershocks following the last strong event: the 23 November 1980 earthquake (M 6.9). The earthquakes were recorded at seven seismic stations, on average, and have been located using a three-dimensi...

  15. Horsemen of the Apocalypse: lessons from the Gulf War.

    Science.gov (United States)

    Boyle, J S; Bunting, S M

    1998-12-01

    War is a major global threat to human health, not only in the immediate effects of death and injury to the people, but also in the damage to infrastructures such as food, water, and power supplies and to social structures that support families, economies, and governments. Iraq's devastating aftershocks from the Gulf War include the physical and psychologic effects of displacement, poverty, famine, disease, and environmental destruction. Early nursing leaders vocally opposed World War I, and contemporary nurses should consider becoming activists in the primary and secondary prevention of this major global health problem. PMID:9845484

  16. Seismic tomography of the area of the 2010 Beni-Ilmane earthquake sequence, north-central Algeria

    OpenAIRE

    Abacha, Issam; Koulakov, Ivan; Semmane, Fethi; Yelles-Chaouche, Abd Karim

    2014-01-01

    The region of Beni-Ilmane (District of M’sila, north-central Algeria) was the site of an earthquake sequence that started on 14 May 2010. This sequence, which lasted several months, was triggered by conjugate E–W reverse and N–S dextral faulting. To image the crustal structure of these active faults, we used a set of 1406 well located aftershocks events and applied the local tomography software (LOTOS) algorithm, which includes absolute source location, optimization of the initial 1D velocity...

  17. A modular steel freeway bridge: design concept and earthquake resistance.

    Science.gov (United States)

    Wattenburg, W H; McCallen, D B; Murray, R C

    1995-04-14

    A modular multilane steel freeway bridge has been constructed from surplus railroad flatcar decks. It can be erected on-site in a few days' time. It has been built and static-load tested for emergency freeway bridge repair. This inexpensive modular bridge may also have broad application around the world for low-cost bridges in areas where funds are limited. On the basis of static-load testing performed by the California Department of Transportation and computer dynamic analysis, this simple modular-design concept has the potential of providing a strong bridge that can withstand the severe aftershocks expected immediately after a major earthquake. PMID:17814794

  18. NSFC Strengthens its Funding in Wenchuan

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    @@ NSFC Earth Sciences Department is about to approve two Director's Fund projects to provide better scientific support to the rescue and relief efforts and collect first-hand data with major scientific significance in post-earthquake Wenchuan County,Sichuan Province.One project is on the relation between the stress field of post-earthquake (M= 8.0) deformation and the strong aftershocks in Wenchuan County and the other is on the field investigation and studies on geological hazards and secondary disasters of blocking up river caused by earthquake in the County.

  19. Rupture processes of the 1999 August 17 Izmit and November 12, Düzce (Turkey) earthquakes

    OpenAIRE

    R. Tibi; Bock, G.; XIA, Y; M. Baumbach; Helmut Grosser; Claus Milkereit; S. Karakisa; S. Zünbül; Rainer Kind; Jochen Zschau;  

    2001-01-01

    We derive the rupture history of the 1999 August 17 Izmit (M-w=7.4) and 1999 November 12 Duzce (M-w=7.1) earthquakes in Turkey from teleseismic body waves using broad-band data of the Global Seismograph Network, aftershock locations and mapped surface breaks. The centroid solutions indicate strike-slip mechanisms for both events. The Izmit earthquake was characterized by rupture propagating predominantly eastwards. It consisted of a main rupture lasting about 25 s followed within 1 min by two...

  20. Study on determination of stress level by seismic stress drops and the stress axis deflections before and after large earthquakes

    Institute of Scientific and Technical Information of China (English)

    WAN Yong-ge

    2006-01-01

    To obtain the stress level at the earthquake source, this paper sets forth the solution of the stress magnitude at the earthquake source by seismic stress drop and the stress axis deflections before and after large earthquakes. The pre-seismic and post-seismic stress direction can be statistically determined by a large collection of foreshock and aftershock focal mechanism data while the stress drop can be determined through the source fracture inversion from seismic wave data or crust deformation data. The paper attempts to make a fundamental contribution to seismic dynamics.

  1. Segmented seismicity of the Mw 6.2 Baladeh earthquake sequence (Alborz mountains, Iran) revealed from regional moment tensors

    DEFF Research Database (Denmark)

    Donner, Stefanie; Rössler, Dirk; Krüger, Frank;

    2013-01-01

    The M w 6.2 Baladeh earthquake occurred on 28 May 2004 in the Alborz Mountains, northern Iran. This earthquake was the first strong shock in this intracontinental orogen for which digital regional broadband data are available. The Baladeh event provides a rare opportunity to study fault geometry...... velocity model, regional waveform data of the mainshock and larger aftershocks (M w  ≥3.3) were inverted for moment tensors. For the Baladeh mainshock, this included inversion for kinematic parameters. All analysed earthquakes show dominant thrust mechanisms at depths between 14 and 26 km, with NW...

  2. Far-field coseismic displacements associated with the great Sumatra earthquakes of December 26, 2004 and March 29, 2005 constrained by Global Positioning System

    Institute of Scientific and Technical Information of China (English)

    WANG Min; ZHANG Peizhen; SHEN Zhengkang; LIU Jie; SUN Hanrong; GAN Weijun; LI Peng

    2006-01-01

    Based on continuous GPS observations within China as well as global GPS tracking network,a calculation has been made of far-field coseismic displacements associated with the December, 2004 (Mw= 9.3) and March, 2005 (Mw= 8.7) earthquakes.The far-field coseismic displacements are associated with the 2004 shock range more than 6000-7000 krn in both north-south and east-west dimensions,and depict an undulated wave pattern of contraction and extension. The coseismic displacements associated with the 2005 event, however, are distributed near the epicentral region, and the event itself may be an aftershock of the 2004 earthquake.

  3. The attenuation mechanism of S-waves in the source zone of the 1999 Chamoli earthquake

    OpenAIRE

    Mukhopadhyay, S.; Department of Earth Sciences, IIT Roorkee, Roorkee 247667, India; Kumar, A.; Department of Earth Sciences, IIT Roorkee, Roorkee 247667, India; Garg, A.; Department of Earth Sciences, IIT Roorkee, Roorkee 247667, India; Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Kayal, J. R.; School of Oceanographic Studies, Jadavpur University, Kolkata 700016, India

    2014-01-01

    In the present study the attenuation mechanism of seismic wave energy in and around the source area of the Chamoli earthquake of 29th March 1999 is estimated using the aftershock data. Most of the analyzed events are from the vicinity of the Main Central Thrust (MCT), which is a well-defined tectonic discontinuity in the Himalayas. Separation of intrinsic (Q 1 i ) and scattering (Q 1 s ) attenuation coefficient is done over the frequencies 1, 2, 4, 8 and 16 Hz using Multiple...

  4. The Zemmouri-Boumerdes Earthquake of May 21st, 2003, Mw=6.8: Source Parameters and Rupture Propagation Study from Teleseismic Data.

    OpenAIRE

    Bezzeghoud, M.; B. Caldeira; borges, JF; Buforn, E.; Maouche, F; Ousadou, A; Khrroubi, A; Harbi, A.; Ayadi, A.

    2004-01-01

    On May 21, 2003, occurred the Zemmouri-Boumerdes earth- quake (Mw=6.8, depth 7km) in a zone characterized by rela- tively moderate and diffuse seismicity. The main shock have been relocated at Zemmouri el Bahri (36.83N,3.65E) close to the continent and the aftershocks sequence (CRAAG mobile stations) gives a distribution in the NE-SW direction with most of the epicenters located on the continent or near the coast. Source mechanism of this event, including fault plane solutions, waveform inver...

  5. ANALISI DELLA RISPOSTA SISMICA LOCALE A SAN GIULIANO DI PUGLIA CON MODELLI 1D, 2D e 3D

    OpenAIRE

    Puglia, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Klin, P.; Centro Ricerche Sismologiche, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Trieste, Italia; Pagliaroli, A.; Dipartimento di Ingegneria Strutturale e Geotecnica, Università di Roma “La Sapienza”, Roma, Italia; Ladina, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Priolo, E.; Centro Ricerche Sismologiche, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Trieste, Italia; Lanzo, G.; Dipartimento di Ingegneria Strutturale e Geotecnica, Università di Roma “La Sapienza”, Roma, Italia; Silvestri, F.; Dipartimento di Ingegneria Idraulica, Geotecnica ed Ambientale, Università degli Studi di Napoli Federico II, Napoli, Italia

    2009-01-01

    The paper reports the comparison between 1D, 2D and 3D numerical simulations of seismic site response at San Giuliano di Puglia (Italy) and the amplification recorded in the aftershocks following the 31.X.2002 Molise earthquake (MW=5.7). The records were taken by mobile stations installed in the historical center on a soft rock outcrop and in the newer part of the town on a marly clay formation. The site response analyses by the 3D model involved a subsoil volume of about a 2000 x 2000 x 1500...

  6. A new insight into crustal heterogeneity beneath the 2001 Bhuj earthquake region of Northwest India and its implications for rupture initiations

    Science.gov (United States)

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

    2012-04-01

    The seismic characteristics of the 2001 Bhuj earthquake (Mw 7.6) has been examined from the proxy indicators, relative size distribution (3D b-value mapping) and seismic tomography using a new data set to understand the role of crustal heterogeneities in rupture initiations of the 2001 Bhuj earthquake of the Gujarat (India), one of the disastrous Indian earthquakes of the new millennium. The aftershocks sequence recorded by 22 seismograph stations of Gujarat Seismic Network (GSNet) during the period from 2006 to 2009, encompassing approximately 80 km × 70 km rupture area had revealed clustering of aftershocks at depth of 5-35 km, which is seismogenic layer responsible for the occurrence of continued aftershocks activity in the study region. The 3D b-value mapping estimated from a total of 3850 precisely located aftershocks with magnitude of completeness Mc ⩾ 2.7 shows that a high b-value region is sandwiched within the main shock hypocenter at the depth of 20-25 km and low b-value region above and below of the 2001 Bhuj main shock hypocenter. Estimates of 3-D seismic velocity (Vp; Vs) and Poisson's ratio (б) structure beneath the region demonstrated a very close correspondence with the b-value mapping that supports the similar physicochemical processes of retaining fluids within the fractured rock matrix beneath the 2001 Bhuj mainshock hypocenter. The overall b-value is estimated close to 1.0 which reveals that seismogenesis is related to crustal heterogeneity, which, in turn also supported by low-Vs and high-б structures. The high b-value and high-б anomaly at the depth of 20-25 km indicate the presence of highly fractured heterogeneous rock matrix with fluid intrusions into it at deeper depth beneath the main shock hypocenter region. Low b-value and high-Vp in the region is observed towards the north-east and north-west of the main shock that might be an indication of the existence of relatively competent rock masses with negligible volume of cracks that

  7. Ground-Motion Scaling in the Kachchh Basin, India, Deduced from

    OpenAIRE

    Malagnini, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Bodin, P.; Center for Earthquake Research and Information University of Memphis; Akinci, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia

    2004-01-01

    We studied the excitation, propagation, and site effects in the Kachchh basin of India by using ground-motion recordings from a temporary seismograph network deployed to study aftershocks of the Mw 7.6 Bhuj earthquake of 26 January 2001. The Kachchh basin has been proposed as a useful analog region for studying hazard in other earthquake-prone but slowly deforming regions, such as the central United States. The earthquakes we studied ranged in size from about M 2 to M 5.2, a...

  8. Tomography of the 2011 Iwaki earthquake (M 7.0) and Fukushima nuclear power plant area

    OpenAIRE

    Tong, P.; Zhao, D.; D. Yang

    2012-01-01

    High-resolution tomographic images of the crust and upper mantle in and around the area of the 2011 Iwaki earthquake (M 7.0) and the Fukushima nuclear power plant are determined by inverting a large number of high-quality arrival times with both the finite-frequency and ray tomography methods. The Iwaki earthquake and its aftershocks mainly occurred in a boundary zone with strong variations in seismic velocity and Poisson's ratio. Prominent low-velocity and high Poisson's ratio zones are reve...

  9. Tomography of the 2011 Iwaki earthquake (M 7.0) and Fukushima nuclear power plant area

    OpenAIRE

    Tong, P.; Zhao, D.; D. Yang

    2011-01-01

    High resolution tomographic images of the crust and upper mantle in and around the area of the 2011 Iwaki earthquake (M 7.0) and the Fukushima nuclear power plant are determined by inverting a large number of high-quality arrival times with both the finite-frequency and ray tomography methods. The Iwaki earthquake and its aftershocks mainly occurred in a boundary zone with strong variations in seismic velocity and Poisson's ratio. Prominent low-velocity and high Poisson's ratio zones are reve...

  10. Employing the Quake-Catcher Network (QCN) to Investigate Site Effects in Christchurch, New Zealand Using the κ Method

    Science.gov (United States)

    Neighbors, C.; Liao, E. J.; Cochran, E. S.; Chung, A. I.; Lawrence, J.; Kaiser, A. E.; Fry, B.; Christensen, C. M.

    2011-12-01

    The 3 September 2010 Mw 7.1 Darfield earthquake was felt over 900 km from the source. The maximum felt-intensity was estimated to be at Modified Mercalli Intensity (MMI) 9 and measured near-field accelerations were found to exceed 1 g. The mainshock damaged or destroyed over 100,000 buildings and spatially variable effects (such as liquefaction, slumping, and amplification) were observed throughout the city of Christchurch. Following the mainshock, a vigorous aftershock sequence has continued for months in the region. To record the aftershocks for early warning and other hazard mitigation efforts, a network of over 192 low-cost, 14-bit accelerometers were deployed in local buildings as part of the Quake-Catcher Network Rapid Aftershock Mobilization Project (RAMP). With a large number of sensors covering a city area of ~300 km2, the RAMP collected vastly more data and at a finer scale relative to the deployment of costly traditional broadband sensors. Recent comparison of the signal-to-noise quality of the 14-bit QCN sensors to the strong motion 24-bit New Zealand GeoNet sensors show similar responses. Initial analyses of the data show that aftershocks of magnitude >M4.5 within 30 km of the hypocentral distance were well recorded by QCN sensors. Utilizing the dense coverage, we investigate local site amplification by analyzing the spectra decay parameter, kappa (κ). Following the routine outlined in Douglas et al. (2010, Pure Appl. Geophys.), whereby a 5-sec S-wave window is used to calculate the Fourier spectra and κ for each station, investigations of κ values between stations are used to estimate site conditions on seismic wave behavior at each location. Results from this study will be compared to work performed by New Zealand researchers using other methods to calculate site response, such as the spectral ratio method. Together, these studies will highlight areas of the Christchurch region that may be more susceptible to ground shaking, which can be used to

  11. Medical electromechatronics

    Science.gov (United States)

    Osipov, Y. M.; Syryamkin, V. I.; Osipov, O. Y.

    2015-11-01

    The first part of the article presentsdevices of rehabilitation electromechatronics.As a research work, the author's team has performed sketch and technical developments on this subject, which are protected by patents of the Russian Federation. The second part providesan overview of medical robotic surgery, which is ideal for imperfections removing.It also describes capabilities of the author's team in development of active driveline based "iron" hands.Scalpels never tremble in the iron hands, which are not afraid of the aftershocks and never get tired.They can perform operations during not less than 48 consecutive hours.

  12. The effect of earthquake-induced radon release on the population in the seismic active regions of Armenia

    International Nuclear Information System (INIS)

    Based on the Spitak earthquake in December 1988, it was found that earthquake causes intensive and prolonged radon splashes, which are manifested appreciably in buildings even if located far from the epicenter of the earthquake. The interval of splashes includes the period starting from the first foreshock and ending by the last aftershock, i.e. several months. The radiation intensity and duration of the effect are in direct correlation with the intensity of the earthquake. The area affected by radiation is larger than the territory of Armenia. The population affected is 12-fold higher than the number of people injured in the Spitak earthquake itself

  13. Application of Second-Moment Source Analysis to Three Problems in Earthquake Forecasting

    Science.gov (United States)

    Donovan, J.; Jordan, T. H.

    2011-12-01

    Though earthquake forecasting models have often represented seismic sources as space-time points (usually hypocenters), a more complete hazard analysis requires the consideration of finite-source effects, such as rupture extent, orientation, directivity, and stress drop. The most compact source representation that includes these effects is the finite moment tensor (FMT), which approximates the degree-two polynomial moments of the stress glut by its projection onto the seismic (degree-zero) moment tensor. This projection yields a scalar space-time source function whose degree-one moments define the centroid moment tensor (CMT) and whose degree-two moments define the FMT. We apply this finite-source parameterization to three forecasting problems. The first is the question of hypocenter bias: can we reject the null hypothesis that the conditional probability of hypocenter location is uniformly distributed over the rupture area? This hypothesis is currently used to specify rupture sets in the "extended" earthquake forecasts that drive simulation-based hazard models, such as CyberShake. Following McGuire et al. (2002), we test the hypothesis using the distribution of FMT directivity ratios calculated from a global data set of source slip inversions. The second is the question of source identification: given an observed FMT (and its errors), can we identify it with an FMT in the complete rupture set that represents an extended fault-based rupture forecast? Solving this problem will facilitate operational earthquake forecasting, which requires the rapid updating of earthquake triggering and clustering models. Our proposed method uses the second-order uncertainties as a norm on the FMT parameter space to identify the closest member of the hypothetical rupture set and to test whether this closest member is an adequate representation of the observed event. Finally, we address the aftershock excitation problem: given a mainshock, what is the spatial distribution of aftershock

  14. Coherent noise, scale invariance and intermittency in large systems

    OpenAIRE

    Sneppen, Kim; Newman, M. E. J.

    1996-01-01

    We introduce a new class of models in which a large number of "agents" organize under the influence of an externally imposed coherent noise. The model shows reorganization events whose size distribution closely follows a power law over many decades, even in the case where the agents do not interact with each other. In addition the system displays "aftershock" events in which large disturbances are followed by a string of others at times which are distributed according to a 1/t law. We also fi...

  15. The 14 November, 2007 Mw 7.8 Tocopilla, northern Chile earthquake within the Iquique seismic gap

    Science.gov (United States)

    Schurr, B.; Motagh, M.; Krüger, F.; Asch, G.; Anderssohn, J.; Sobiesiak, M.; Kind, R.; Sodoudi, F.; Ohrnberger, M.; Chong Díaz, G.; Vilotte, J.; Oncken, O.

    2008-05-01

    A prominent seismic gap persisted in northern Chile between the towns of Antofagasta and Arica for 130 years. This 500 km segment along the South American subduction zone last ruptured in 1877 in a devastating M9 earthquake. On November 14th 2007, an Mw 7.8 earthquake started near the coastal town of Tocopilla to break the southernmost 200 km of the seismic gap. In Tocopilla and several other communities in the backcountry, a majority of the structures were destroyed. Commencing in 2006, in close cooperation between the GFZ Potsdam (Germany), IPG Paris (France), the Universidad Catolica del Norte, Antofagasta and Universidad de Chile, Santiago (Chile), a network of 15 observatories equipped with seismic broadband and strong motion sensors, GPS receivers and magnetotelluric probes is being established to monitor the seismic gap. At the time of the Tocopilla earthquake, 12 sites were already deployed with the seismological instruments. Based on these data we relocate the mainshock and early aftershocks. The surface deformation field derived from InSAR data in Wide Swath and Image modes from ascending and descending tracks will be inverted for a distributed slip model using a grid of rectangular dislocations in an elastic half-space. We use broadband stations at teleseismic distances to image the spatio-temporal characteristics of seismic energy release during the earthquake. This analysis indicates a rupture length of approximately 200 km with almost unilateral southward propagation and a duration of approximately 200s. Rupture terminated on Mejillones Peninsula, exactly where an earlier large earthquake, the Mw 8 1995 Antofagasta event, had its northern limit. This is also where most of the early aftershocks focus. The structure beneath the Mejillones Peninsula seems to form a persistent barrier in the northern Chilean earthquake cycle. Based on our analysis, the fault plane of the Tocopilla earthquake fills roughly the southernmost third of the Iquique seismic gap

  16. Kinematic and dynamic inversion of the 16 December earthquake in Northern Chile

    Science.gov (United States)

    Ruiz, S.; Lancieri, M.; Madariaga, R. I.; Sobiesiak, M.; Campos, J. A.

    2009-12-01

    We study the kinematic and dynamic rupture propagation of the M 6.7, intraplate, intermediate depth, slab push earthquake that occurred 16 December 2007, a month after the large interplate thrust event of Tocopilla, Chile (M 7.7). The occurrence of a slab push event after a large subduction earthquake is well explained by Coulomb stress transfer and crack dynamics. A dense seismic network, equipped with short period and accelerometers was deployed after the event of 14 November 2007 by the Task Force of GFZ Potsdam and the University of Chile in Santiago. This network was in place on December 16 providing the best seismic data set ever recorded for a Chilean earthquake. We have used it to do a detailed study of rupture processes. We localized the main event of December 16 and the aftershocks that occurred within 24 h of the main event. The main event was located at 43 km depth, while the aftershocks distribution covered a circular zone of 5 to 8 km of radius centered on the main shock epicenter and with depth ranging between [39 - 49] km. The aftershocks are distributed on an almost vertical plane that agrees with the almost vertical plane of the fault mechanism (86° dip) and all the aftershock have the same mechanism as the main event. We used eight of the nearest accelerometric records low pass filtered at 1 Hz, two of which were situated right above the hypocenter. We performed a non-linear kinematic inversion based on the neighborhood algorithm (NA) with an L2 norm. The velocity model was derived from previous work by GFZ. The earthquake is very well modeled by a circular rupture of radius between 5 and 8 km that propagated with a very low rupture velocity, that varies between 1 and 2 km/s. We need only a few non-linear parameters to model this event, parameter space has a dimension close to 6. The kinematic solution was validated using a full dynamic inversion method in which the rupture process is modeled using finite differences on a coarse grid with a slip

  17. Earthquakes in Tuhinj Valley (Slovenia) In 1840

    Science.gov (United States)

    Cecić, Ina

    2015-04-01

    A less known damaging earthquake in southern part of Kamnik-Savinja Alps, Slovenia, in 1840 is described. The main shock was on 27 August 1840 with the epicentre in Tuhinj Valley. The maximum intensity was VII EMS-98 in Ljubljana, Slovenia, and in Eisenkappel, Austria. It was felt as far as Venice, Italy, 200 km away. The macroseismic magnitude of the main shock, estimated from the area of intensity VI EMS-98, was 5.0. The effects of the main shock and its aftershocks are described, and an earthquake catalogue for Slovenia in 1840 is provided. Available primary sources (newspaper articles) are presented.

  18. Long-term clustering, scaling, and universality in the temporal occurrence of earthquakes

    International Nuclear Information System (INIS)

    Analyzing diverse seismic catalogs, we have determined that the probability densities of the earthquake recurrence times for different spatial areas and magnitude ranges can be described by a unique universal distribution if the time is rescaled with the rate of seismic occurrence, which therefore fully governs seismicity. The shape of the distribution shows the existence of clustering beyond the duration of aftershock bursts, and scaling reveals the self-similarity of the clustering structure in the space-time-magnitude domain. This holds from worldwide to local scales, for quite different tectonic environments and for all the magnitude ranges considered

  19. Long-term clustering, scaling, and universality in the temporal occurrence of earthquakes.

    Science.gov (United States)

    Corral, Alvaro

    2004-03-12

    Analyzing diverse seismic catalogs, we have determined that the probability densities of the earthquake recurrence times for different spatial areas and magnitude ranges can be described by a unique universal distribution if the time is rescaled with the rate of seismic occurrence, which therefore fully governs seismicity. The shape of the distribution shows the existence of clustering beyond the duration of aftershock bursts, and scaling reveals the self-similarity of the clustering structure in the space-time-magnitude domain. This holds from worldwide to local scales, for quite different tectonic environments and for all the magnitude ranges considered. PMID:15089251

  20. Crustal attenuation characteristics in northwestern Turkey in the range from 1 to 10 Hz

    OpenAIRE

    Bindi, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Parolai, S.; GeoForschungsZentrum Potsdam Telegrafenberg; Grosser, H.; GeoForschungsZentrum Potsdam Telegrafenberg; Milkereit, C.; GeoForschungsZentrum Potsdam Telegrafenberg; Karakisa, S.; Ministry of Public Works and Settlement General Directorate of Disaster Affairs Earthquake Research Department

    2006-01-01

    We have analyzed the aftershocks (ML 4.5) following the 1999 Izmit earthquake (Mw 7.4) to infer the frequency-dependent attenuation characteristics of both P and S waves, in the frequency range from 1 to 10 Hz and in the distance range from 10 to 140 km. A linear-predictive model is assumed to describe the spectral amplitudes in terms of attenuation and source contributions. The results show that both P and S waves undergo a strong attenuation along ray paths shorter than 40 k...

  1. Scientific overview and historical context of the 1811-1812 New Madrid earthquake sequence

    OpenAIRE

    Hough, S. E.

    2004-01-01

    The central and eastern United States has experienced only 5 historic earthquakes with Mw 7.0, four during the New Madrid sequence of 1811-1812: three principal mainshocks and the so-called «dawn aftershock» following the first mainshock. Much of the historic earthquake research done in the United States has focused on the New Madrid Seismic Zone (NMSZ), because the largest New Madrid earthquakes may represent the archetype for the most damaging earthquakes to be expected in intraplate region...

  2. The April 2009 L'Aquila (Italy) seismic sequence: recordings in the Anfiteatro Flavio (Colosseum)

    Science.gov (United States)

    Caserta, A.; Marra, F.; Cara, F.; Valente, G.

    2015-12-01

    We show a preliminary study concerning the interaction of the seismic wave-field coming from aftershocks of the 2009 seismic sequence in Abruzzo and the structure of the Anfiteatro Flavio, usually called Colosseum. By using mainly Arias intensity, we assess how the incoming energy beneath the foundations is convoyed into the monument, through what preferential frequencies such process takes place, how the trapped energy increases amplitude vibration with floors. Moreover, we also investigate the role played by the near-surface geology in generating differential motions below the monument foundations. In addition we also check, in a preliminary way, the foundation dynamical behaviour under the action of the incoming wave-field.

  3. Seismic imaging of the 2001 Bhuj Mw7.7 earthquake source zone: b-value, fractal dimension and seismic velocity tomography studies

    Science.gov (United States)

    Mandal, Prantik; Rodkin, Mikhail V.

    2011-11-01

    We use precisely located aftershocks of the 2001 Mw7.7 Bhuj earthquake (2001-2009) to explore the structure of the Kachchh seismic zone by mapping the 3-D distributions of b-value, fractal dimension (D) and seismic velocities. From frequency-magnitude analysis, we find that the catalog is complete above Mw = 3.0. Thus, we analyze 2159 aftershocks with Mw ≥ 3.0 to estimate the 3-D distribution of b-value and fractal dimensions using maximum-likelihood and spatial correlation dimension approaches, respectively. Our results show an area of high b-, D- and Vp/Vs ratio values at 15-35 km depth in the main rupture zone (MRZ), while relatively low b- and D values characterize the surrounding rigid regions and Gedi fault (GF) zone. We propose that higher material heterogeneities in the vicinity of the MRZ and/or circulation of deep aqueous fluid/volatile CO 2 is the main cause of the increased b-, D- and Vp/Vs ratio values at 15-35 km depth. Seismic velocity images also show some low velocity zones continuing in to the deep lower crust, supporting the existence of circulation of deep aqueous fluid / volatile CO 2 in the region (probably released from the eclogitasation of olivine rich lower crustal rocks). The presence of number of high and low velocity patches further reveals the heterogeneous and fractured nature of the MRZ. Interestingly, we observe that Aki (1981)'s relation (D = 2b) is not valid for the spatial b-D correlation of the events in the GF (D 2 = 1.2b) zone. However, the events in the MRZ (D 2 = 1.7b) show a fair agreement with the D = 2b relationship while the earthquakes associated with the remaining parts of the aftershock zone (D 2 = 1.95b) show a strong correlation with the Aki (1981)'s relationship. Thus, we infer that the remaining parts of the aftershock zone are probably behaving like locked un-ruptured zones, where larger stresses accumulate. We also propose that deep fluid involvement may play a key role in generating seismic activity in the

  4. Earthquake triggering along a segmented creeping fault: 1951 ML7.3 Hualien-Taitung earthquake sequence in eastern Taiwan

    Science.gov (United States)

    Chen, H.; Toda, S.; Rau, R.

    2005-12-01

    Understanding of fault interactions along active plate boundaries is significant for improving seismic hazard assessment. As the most destructive seismic episode even known in eastern Taiwan, the 1951 ML 7.3 Hualien-Taitung (H-T), Taiwan earthquake series provide a good opportunity to study earthquake triggering processes along an arc-continent collision boundary. This sequence occurred at first on October 21, 1951 with the ML 7.3 Hualien earthquake located at the northernmost segment of the Longitudinal Valley Fault (LVF) and then triggered three ML >6 events with 10-40 km surface ruptures propagating southward. The first triggered November shock did not occur at the nearby Yuli fault segment but occurred at the ~100-km away creeping Chihshang fault. By calculation of static coulomb stress transfer with the rate/state stress transfer model, we modeled the temporal priority of encouraged rupture on four segments of the LVF. We found that rupture of the Hualien mainshock is unlikely to trigger the neighboring Yuli fault prior to the creeping Chihshang fault; doing so requires that both the Yuli and Chihshang segments having background aftershock duration of less than 2.5 years. We also found that the factor controlling the priority of large triggered events varies with static coulomb stress change loading on a given fault segment. When the loaded coulomb stress change is less than 0.5 bar, the priority is mostly governed by the seismicity rate. The segment with higher seismicity rate corresponds to faster triggering, which is consistent with our observations. When the loaded coulomb stress change larger than 0.5 bar, the aftershock duration plays an important role on the priority, the segment with longer aftershock duration leads to faster triggering. Modeling of the jumping behavior of the 1951 H-T sequence suggests that the along-strike rupture directivity depends on the location and magnitude of the mainshock and seismicity rate and aftershock decaying rate of

  5. The Japanese earthquake of 1978

    International Nuclear Information System (INIS)

    In January 1978, an earthquake of magnitude 7.0 took place off the Pacific coast of Honshu, Japan about 110 km south-west-south of Tokyo, which caused some casualties and property damage. This earthquake was preceded by a large number of foreshocks and followed by many aftershocks. The earthquake itself was not very large as a natural event. However, it did provide a number of lessons on the importance of issuing timely information to the public in order to mitigate the impact of earthquake disasters. (author). 1 fig

  6. 3D Dynamic Rupture Simulation Across a Complex Fault System: the Mw7.0, 2010, Haiti Earthquake

    Science.gov (United States)

    Douilly, R.; Aochi, H.; Calais, E.; Freed, A. M.

    2013-12-01

    Earthquakes ruptures sometimes take place on a secondary fault and surprisingly do not activate an adjacent major one. The 1989 Loma Prieta earthquake is a classic case where rupture occurred on a blind thrust while the adjacent San Andreas Fault was not triggered during the process. Similar to Loma Prieta, the Mw7.0, January 12 2010, Haiti earthquake also ruptured a secondary blind thrust, the Léogâne fault, adjacent to the main plate boundary, the Enriquillo Plantain Garden Fault, which did not rupture during this event. Aftershock relocalizations delineate the Léogâne rupture with two north dipping segments with slightly different dip, where the easternmost segment had mostly dip-slip motion and the westernmost one had mostly strike-slip motion. In addition, an offshore south dipping structure inferred from the aftershocks to the west of the rupture zone coincides with the offshore Trois Baies reverse fault, a region of increase in Coulomb stress increase. In this study, we investigate the rupture dynamics of the Haiti earthquake in a complex fault system of multiple segments identified by the aftershock relocations. We suppose a background stress regime that is consistent with the type of motion of each fault and with the regional tectonic regime. We initiate a nucleation on the east segment of the Léogâne fault by defining a circular region with a 2 km radius where shear stress is slightly greater than the yield stress. By varying friction on faults and background stress, we find a range of plausible scenarios. In the absence of near-field seismic records of the event, we score the different models against the static deformation field derived from GPS and InSAR at the surface. All the plausible simulations show that the rupture propagates from the eastern to the western segment along the Léogâne fault, but not on the Enriquillo fault nor on the Trois Baies fault. The best-fit simulation shows a significant increase of shear stresses on the Trois Baies

  7. Hall-petch law revisited in terms of collective dislocation dynamics.

    Science.gov (United States)

    Louchet, François; Weiss, Jérôme; Richeton, Thiebaud

    2006-08-18

    The Hall-Petch (HP) law, that accounts for the effect of grain size on the plastic yield stress of polycrystals, is revisited in terms of the collective motion of interacting dislocations. Sudden relaxation of incompatibility stresses in a grain triggers aftershocks in the neighboring ones. The HP law results from a scaling argument based on the conservation of the elastic energy during such transfers. The Hall-Petch law breakdown for nanometric sized grains is shown to stem from the loss of such a collective behavior as grains start deforming by successive motion of individual dislocations. PMID:17026245

  8. Earthquakes in Switzerland and surrounding regions during 2007

    International Nuclear Information System (INIS)

    This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2007. During this period, 531 earthquakes and 92 quarry blasts were detected and located in the region under consideration. Of these earthquakes, 30 are aftershocks of the stimulation of a proposed geothermal reservoir beneath the city of Basel in December of 2006. With 20 events with Μι ≥ 2.5, four of which were artificially induced, the seismic activity in the year 2007 was far below the average over the previous 32 years. (author)

  9. Detection of crustal deformation from the Landers earthquake sequence using continuous geodetic measurements

    Science.gov (United States)

    Bock, Yehuda; Agnew, Duncan C.; Fang, Peng; Genrich, Joachim F.; Hager, Bradford H.; Herring, Thomas A.; Hudnut, Kenneth W.; King, Robert W.; Larsen, Shawn; Minster, J.-B.

    1993-01-01

    The first measurements are reported for a major earthquake by a continuously operating GPS network, the permanent GPS Genetic ARRY (PGGA) in southern California. The Landers and Big Bear earthquakes of June 28, 1992 were monitored by daily observations. Ten weeks of measurements indicate significant coseismic motion at all PGGA sites, significant postseismic motion at one site for two weeks after the earthquakes, and no significant preseismic motion. These measurements demonstrate the potential of GPS monitoring for precise detection of precursory and aftershock seismic deformation in the near and far field.

  10. The roles of tectonics in erosion: Fracturing and fragmentation are key, rock uplift is not

    Science.gov (United States)

    Molnar, P.; Anderson, R. S.; Anderson, S. P.

    2005-12-01

    As Gilbert and Dutton recognized in the 19th century, erosion consists of two processes: "the disintegration of the rocks, reducing them to fragments, pebbles, sand, and clay" [Dutton, 1882] and then their transport. Tectonics contributes to both but more importantly to the first. Although many in the geomorphic community subscribe to "the emerging view that erosion rates adjust to high rates of tectonically driven rock uplift" [Montgomery and Brandon, 2002], numerical models are not needed to see that rather than ``driving" erosion, most "rock uplift" results from erosion via isostatic compensation. Relegation of rock uplift to consequence, not cause, of erosion, however, does not deny tectonics a role in erosion. Tectonics plays its key role by fracturing rock. Fractures not only provide avenues for water flow and thus promote weathering of rock, but also generate erodible fragments that can be extracted and transported on hillslopes or by rivers and glaciers. Tectonics does the first part of erosion (as defined by 19th century geologists): disintegration of massive rocks. Faults are not perfect planes; both local roughness and larger scale bends require straining of the adjacent rock masses upon slip on the fault, as shown well by aftershocks of major earthquakes. Although aftershocks of great earthquakes commonly occur on the faults that rupture in mainshocks, within continents many, if not most, aftershocks occur within the larger volume of rock of adjacent blocks that slipped past one another in mainshocks. Thus, they contribute to the dismemberment of these rock volumes into smaller blocks. Scaling rules for earthquakes suggest that dimensions of ruptures for very small earthquakes, Magnitude < -2, can be meters or less. The Gutenberg-Richter recurrence relationship implies that such earthquakes are common, as recordings by high-magnification seismographs in low-noise environments show. The large differences among fault plane solutions of aftershocks and of

  11. The March 2004 Kalamata seismic sequence: a case of efficient seismicity monitoring in the area of Peloponnese, southern Greece, by the Tripoli Seismic Array

    Science.gov (United States)

    Pirli, M.; Voulgaris, N.; Chira, A.; Makropoulos, K.

    2007-01-01

    On March 1, 2004, a moderate earthquake occurred in the vicinity of the town of Kalamata, southern Peloponnese, Greece. The Tripoli Seismic Array (TRISAR), located in the centre of Peloponnese, recorded the mainshock as well as the large number of aftershocks that followed. Only a small number of these events were located by regional seismographic networks. Analysis of the Kalamata seismic sequence and evaluation of the results is presented in this article, as an example of the efficiency of TRISAR in seismicity monitoring and location in the area of Peloponnese.

  12. Seismic site response estimation in the near source region of the 2009 L'Aquila, Italy, Earthquake

    OpenAIRE

    Bertrand, E.; CETE Méditerranée, Service Risque Sismique, Nice, France; Duval, A.-M.; CETE Méditerranée, Service Risque Sismique, Nice, France; Régnier, J.; CETE Méditerranée, Laboratoire Central des Ponts et Chaussées (LCPC), Nice, France; Bordoni, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Cara, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Cultrera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Di Giulio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Milana, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Cogliano, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Fodarella, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Pucillo, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Riccio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Salichon, J.; OCA, UMR Géoazur, Sophia-Antipolis, France

    2010-01-01

    To better estimate the seismic ground motion during the April 6th, 2009 earthquake in L'Aquila, we deployed temporary arrays in the near-source region. Several arrays have been successively set up in the Aterno valley's epicentral area and have recorded the aftershocks that followed the main shock, between April and September. The data has been processed in order to study the spectral ratios of the horizontal component of ground motion at the soil site and at a reference site, as well as t...

  13. Quantifying the Earthquake Clustering that Independent Sources with Stationary Rates (as Included in Current Risk Models) Can Produce.

    Science.gov (United States)

    Fitzenz, D. D.; Nyst, M.; Apel, E. V.; Muir-Wood, R.

    2014-12-01

    The recent Canterbury earthquake sequence (CES) renewed public and academic awareness concerning the clustered nature of seismicity. Multiple event occurrence in short time and space intervals is reminiscent of aftershock sequences, but aftershock is a statistical definition, not a label one can give an earthquake in real-time. Aftershocks are defined collectively as what creates the Omori event rate decay after a large event or are defined as what is taken away as "dependent events" using a declustering method. It is noteworthy that depending on the declustering method used on the Canterbury earthquake sequence, the number of independent events varies a lot. This lack of unambiguous definition of aftershocks leads to the need to investigate the amount of clustering inherent in "declustered" risk models. This is the task we concentrate on in this contribution. We start from a background source model for the Canterbury region, in which 1) centroids of events of given magnitude are distributed using a latin-hypercube lattice, 2) following the range of preferential orientations determined from stress maps and focal mechanism, 3) with length determined using the local scaling relationship and 4) rates from a and b values derived from the declustered pre-2010 catalog. We then proceed to create tens of thousands of realizations of 6 to 20 year periods, and we define criteria to identify which successions of events in the region would be perceived as a sequence. Note that the spatial clustering expected is a lower end compared to a fully uniform distribution of events. Then we perform the same exercise with rates and b-values determined from the catalog including the CES. If the pre-2010 catalog was long (or rich) enough, then the computed "stationary" rates calculated from it would include the CES declustered events (by construction, regardless of the physical meaning of or relationship between those events). In regions of low seismicity rate (e.g., Canterbury before

  14. Soundness confirmation through cold test of the system equipment of HTTR

    International Nuclear Information System (INIS)

    HTTR was established at the Oarai Research and Development Center of Japan Atomic Energy Agency, for the purpose of the establishment and upgrading of high-temperature gas-cooled reactor technology infrastructure. Currently, it performs a safety demonstration test in order to demonstrate the safety inherent in high-temperature gas-cooled reactor. After the Great East Japan Earthquake, it conducted confirmation test for the purpose of soundness survey of facilities and equipment, and it confirmed that the soundness of the equipment was maintained. After two years from the confirmation test, it has not been confirmed whether the function of dynamic equipment and the soundness such as the airtightness of pipes and containers are maintained after receiving the influence of damage or deterioration caused by aftershocks generated during two years or aging. To confirm the soundness of these facilities, operation under cold state was conducted, and the obtained plant data was compared with confirmation test data to evaluate the presence of abnormality. In addition, in order to confirm through cold test the damage due to aftershocks and degradation due to aging, the plant data to compare was supposed to be the confirmation test data, and the evaluation on abnormality of the plant data of machine starting time and normal operation data was performed. (A.O.)

  15. Sensitivity of the Static Earthquake Triggering Mechanism to Elastic Heterogeneity and Main Event Slip

    CERN Document Server

    Maharramov, Musa

    2013-01-01

    This paper has evolved out of our previous work on static stress transfer, where we used the full-space elastostatic Green's tensor to compute the Coulomb stress transfer impact of the Landers earthquake on the Hector Mine event. In this work, we use the elastostatic Green's tensor for an arbitrary layered Earth model with free-surface boundary conditions to study the impact of elastic heterogeneity as well as source-fault slip and geometry on the stress transfer mechanism. Slip distribution and fault geometry of the source have a significant impact on the stress transfer, especially in case of spatially extended triggered events. Maximization of the Coulomb stress transfer function for known aftershocks provides a mechanism for inverting for the source event slip. Heterogeneity of the elastic earth parameters is shown to have a sizeable, but lower-magnitude, impact on the static stress transfer in 3D. The analysis is applied to Landers/Hector Mine and 100 small "aftershocks" of the Landers event. A computati...

  16. Quantitative law describing market dynamics before and after interest-rate change

    International Nuclear Information System (INIS)

    We study the behavior of U.S. markets both before and after U.S. Federal Open Market Commission meetings and show that the announcement of a U.S. Federal Reserve rate change causes a financial shock, where the dynamics after the announcement is described by an analog of the Omori earthquake law. We quantify the rate n(t) of aftershocks following an interest-rate change at time T and find power-law decay which scales as n(t-T)∼(t-T)-Ω, with Ω positive. Surprisingly, we find that the same law describes the rate n'(|t-T|) of 'preshocks' before the interest-rate change at time T. This study quantitatively relates the size of the market response to the news which caused the shock and uncovers the presence of quantifiable preshocks. We demonstrate that the news associated with interest-rate change is responsible for causing both the anticipation before the announcement and the surprise after the announcement. We estimate the magnitude of financial news using the relative difference between the U.S. Treasury Bill and the Federal Funds effective rate. Our results are consistent with the 'sign effect', in which 'bad news' has a larger impact than 'good news'. Furthermore, we observe significant volatility aftershocks, confirming a 'market under-reaction' that lasts at least one trading day.

  17. Seismogenic Structure Beneath Décollement Inferred from 2009/11/5 ML 6.2 Mingjian Earthquake in Central Taiwan

    Directory of Open Access Journals (Sweden)

    Che-Min Lin

    2014-01-01

    Full Text Available One decade after the 1999 Chi-Chi earthquake, central Taiwan experienced more strong ground shaking [Central Weather Bureau (CWB, intensity VII] induced by a ML 6.2 earthquake on 5th November 2009. This earthquake occurred in the Mingjian Township of Nantou County, only 12 km southwest of the Chi-Chi earthquake epicenter. The broadband microearthquake monitoring network operated by the National Center for Research on Earthquake Engineering (NCREE observed numerous aftershocks in the five days following the mainshock. The relocated aftershocks and the mainshock focal mechanism indicated a NE-SW striking fault dipping _ toward the northwest. This fault plane is inside the pre-Miocene basement and the rupture extends from the lower crust to 10 km depth just beneath the basal décollementdécollement of the thin-skinned model that is generally used to explain the regional tectonics in Taiwan. The fault plane is vertically symmetrical with the Chelungpu fault by the basal décollement.décollement. The NW-SE compressive stress of plate collision in Taiwan, as well as the deep tectonic background, resulted in the seismogenic structure of the Mingjian earthquake at this location.

  18. Random stress and Omori's law

    CERN Document Server

    Kagan, Yan Y

    2010-01-01

    We consider two statistical regularities that were used to explain Omori's law of the aftershock rate decay: the Levy and Inverse Gaussian (IGD) distributions. These distributions are thought to describe stress behavior influenced by various random factors: post-earthquake stress time history is described by a Brownian motion. Both distributions decay to zero for time intervals close to zero. But this feature contradicts the high immediate aftershock level according to Omori's law. We propose that these statistical distributions are influenced by the power-law stress distribution near the earthquake focal zone and we derive new distributions as a mixture of power-law stress with the exponent psi and Levy as well as IGD distributions. Such new distributions describe the resulting inter-earthquake time intervals and closely resemble Omori's law. The new Levy distribution has a pure power-law form with the exponent -(1+psi/2) and the mixed IGD has two exponents: the same as Levy for small time intervals and -(1+...

  19. Relocation and seismotectonic interpretation of the 2015 Ossa de Montiel (Albacete, Spain) seismic series.

    Science.gov (United States)

    Cantavella, Juan V.; Gaite, Beatriz; Ruiz, Mario; Romero, Paula; Gómez-García, Clara; Cerdeño, Roberto; Villaseñor, Antonio; Díaz, Jordi; Lozano, Lucía

    2016-04-01

    A moderate earthquake with magnitude Mw 4.7 occurred on February 23, 2015 to the NE of Ossa de Montiel (SE central Spain), in a region with very low seismic activity and poorly monitored by permanent seismic stations. Two days after the event a dense temporary seismic network consisting of 13 stations was deployed in this area until April 6, 2015, allowing to detect more than 500 events inside the network limits. The data gathered from this network along with the data from more distant seismic stations has allowed us to perform a precise hypocentral location of the Ossa de Montiel seismic series. For this location we have manually read the arrival times for all the stations and used relative location techniques based on waveform cross-correlations and a double-difference algorithm. In addition, we have studied the focal mechanism of the main shock and the largest aftershocks using first motion polarities and full waveform inversion. We have found that the mechanism and aftershock distribution is consistent with a NW-SE normal fault with a dip of 40 degrees to the NE at a depth of about 12 km. With these results we analyze the temporal evolution of the seismic sequence and propose a seismotectonic interpretation of a series developed in an area with scarce seismic information to this date.

  20. Remarkable changes in behavior and physiology of laboratory mice after the massive 2011 Tohoku earthquake in Japan.

    Directory of Open Access Journals (Sweden)

    Shuichi Yanai

    Full Text Available A devastating earthquake and tsunami hit Japan on March 11, 2011, followed by several long and intense aftershocks. Laboratory mice housed in the Tokyo, located approximately 330 km south of this earthquake's epicenter, displayed remarkable changes in a variety of behaviors and physiological measures. Although unusual pre-earthquake behaviors have been previously reported in laboratory animals, little is known about behavioral and physiological changes that occur after a great earthquake. In the present study, the effects of Tohoku earthquake on mice behavior were investigated. "Earthquake-experienced" mice displayed a marked increase in food consumption without gaining body weight in response to the earthquake. They also displayed enhanced anxiety, and in a formal fear memory task, showed significantly greater tone- and context-dependent conditioned freezing. Water maze performance of earthquake-experienced mice showed the quicker acquisition of the task, faster swim speed and longer swim distance than the naive mice. Serum corticosterone levels were elevated compared to the naive mice, indicating that the earthquake and aftershocks were stressful for the mice. These results demonstrate that great earthquakes strongly affect mouse behaviors and physiology. Although the effects of a variety of experimental manipulations on mouse behaviors in disease models or in models of higher cognitive functions have been extensively examined, researchers need to be aware how natural phenomena, such as earthquakes and perhaps other natural environmental factors, influence laboratory animal behaviors and physiology.

  1. On temporal and spatial distribution of seismic apparent stresses in Yunnan area

    Institute of Scientific and Technical Information of China (English)

    QIN Jia-zheng; QIAN Xiao-dong

    2006-01-01

    motion is applied to a detailed study on the temporal and spatial distribution of the seismic apparent stresses (σa)for the moderate and small earthquakes and two aftershock sequences in Yunnan area. The results show that there exists an obvious non-homogeneity for the seismic apparent stresses in the spatial distribution. The concentrated regions of the high apparent stresses are related to the active places of the moderate and small earthquakes. Before the Dayao M=6.2 earthquake, there was a period in which the apparent stresses were high and the value was 5times of the average value, 0.25 MPa. The relatively high values of apparent stresses distribute around the epicentral area of the major shock and nearby. It indicates that the variation characteristics of the apparent stresses can be taken as a new kind of criterion for the earthquake-risk forecast. Usually the ratio of the apparent stresses of the aftershock sequence σaA to the ones σaM of main shock is less than 1.0.

  2. Geochemistry of soil gas in the seismic fault zone produced by the Wenchuan Ms 8.0 earthquake, southwestern China.

    Science.gov (United States)

    Zhou, Xiaocheng; Du, Jianguo; Chen, Zhi; Cheng, Jianwu; Tang, Yi; Yang, Liming; Xie, Chao; Cui, Yueju; Liu, Lei; Yi, Li; Yang, Panxin; Li, Ying

    2010-01-01

    The spatio-temporal variations of soil gas in the seismic fault zone produced by the 12 May 2008 Wenchuan Ms 8.0 earthquake were investigated based on the field measurements of soil gas concentrations after the main shock. Concentrations of He, H2, CO2, CH4, O2, N2, Rn, and Hg in soil gas were measured in the field at eight short profiles across the seismic rupture zone in June and December 2008 and July 2009. Soil-gas concentrations of more than 800 sampling sites were obtained. The data showed that the magnitudes of the He and H2 anomalies of three surveys declined significantly with decreasing strength of the aftershocks with time. The maximum concentrations of He and H2 (40 and 279.4 ppm, respectively) were found in three replicates at the south part of the rupture zone close to the epicenter. The spatio-temporal variations of CO2, Rn, and Hg concentrations differed obviously between the north and south parts of the fault zone. The maximum He and H2 concentrations in Jun 2008 occurred near the parts of the rupture zone where vertical displacements were larger. The anomalies of He, H2, CO2, Rn, and Hg concentrations could be related to the variation in the regional stress field and the aftershock activity. PMID:21134257

  3. Comparative Study of Local Magnitude Scales for Central U.S. and Western India

    Science.gov (United States)

    Miao, Q.; Langston, C. A.

    2004-12-01

    Seismic waveform data from 816 aftershocks of 2001 Bhuj Mw 7.7 earthquake, recorded by CERI/STAR aftershock deployment, including eight K2 6-channel dataloggers with 3-component episensor accelerometers and 3-component L-28 geophones, were used to develop a local magnitude scale for Kachchh basin of western India. Results show that the distance correction curve can be expressed as -logA0=1.8286*(r/100.0)-0.0052*(r-100.0)+3.0, displaying weak distance attenuation. This result is much like that of the local magnitude scale for the Central U.S. Both scales show weak distance attenuation, compared with the local magnitude scales for southern California or Tanzania, East Africa, and display a negative K parameter, implying similar patterns of seismic wave spreading in these two regions. These results for local magnitude scales give support to the assertion that the Kachchh basin and New Madrid Seismic Zone are geological analogs inasmuch that ground motion and other seismological results from one area can shed light on similar problems in the other area.

  4. Source parameters of the Bhuj earthquake, India of January 26, 2001 from height and gravity changes

    Science.gov (United States)

    Chandrasekhar, D. V.; Mishra, D. C.; Singh, B.; Vijayakumar, V.; Bürgmann, Roland

    2004-10-01

    Height and gravity measurements observed along a profile across the epicentral area before and after the January 26, 2001, Mw 7.6 Bhuj earthquake show a maximum uplift of 1.57 +/- 0.5 m and a corresponding gravity change of -393 +/- 18 μGal. A best-fit, single-dislocation model inverted from the height-changes using non-linear optimization methods indicates that the high-slip rupture was well contained in the aftershock zone and likely did not break to depths shallower than ~10 km. Source parameters arrived in the present study agree well with those provided by seismic inversions and the distribution of aftershocks. Gravity data over the epicentral area are well modeled by the preferred model; however, a strong influence of shallow hydrological processes is inferred for three sites, two located on the Banni plains, whose mean gravity change ~280 μGal suggests a total mass redistribution of as much as 2.9 Mt.

  5. Teleseismic Source Models and Source Depth Constraints for Events of the Bhuj Earthquake Sequence

    Science.gov (United States)

    Langston, C. A.

    2001-12-01

    Earthquake locations determined from the MAEC/ISTAR deployment in the epicentral region show a distribution of source depths ranging from the base of the crust to about 5km from the surface. Teleseismic P waveform data are collected from GSN and IMS three component stations and array stations to independently place constraints on source depths of events greater than M4.0 using pP-P and sP-P phase times. Joint analysis of local and teleseismic data are also used to determine source mechanisms and to generate an appropriate model for local structure than can be used in the computation of teleseismic Green's functions and subsequent source inversions. Thick Kachchh basin sediments modify the signature of sP, in particular, and produce reverberation effects later in the P waveforms that may be misconstrued as contributions from shallow faulting. Using the M5.8 aftershock waveforms as empirical Green's functions, a relative inversion of mainshock/aftershock surface waves and a standard slip inversion of teleseimic P and S waves are performed to investigate different models of source geometry and slip distribution for the mainshock.

  6. COMPARATIVE NUMERICAL SIMULATION OF THE TOHOKU 2011 TSUNAMI

    Directory of Open Access Journals (Sweden)

    Baranova N.A.

    2015-10-01

    Full Text Available The comparative numerical simulation of generation and propagation of tsunami waves generated by the source of the catastrophic 2011 Tohoku earthquake in Japan was performed based on the Okada model and the dynamic keyboard block model. The initial model is connected with the choice of orientation of longitudinal and transverse ruptures within the source region and the values of displacements along the main fault. A subsequent model is based on the premise that the initial stress distribution along the fault zone affects essentially the character of movements around the earthquake source and takes into account the stress-strain state of keyboard blocks. In the first case of the present study, the earthquake source was designated and constructed based on the parameters of the ten largest aftershocks within a finite time interval, while in the second case the source used included all aftershocks on the first day following the main event. Based on such comparative source simulations and far-field tsunami wave measurements, the results with both models were determined to have close similarities. However, in the near-field zone, the agreement with observable data was not as good. That can be attributed to inaccuracies in the placement of virtual tide gauges relative to real ones, as well as to features of bottom relief near the coast.

  7. Statistical parameters of Bhuj earthquake sequence of January 26th, 2001

    Indian Academy of Sciences (India)

    M A Shaik; Sanjay Srivastava

    2003-09-01

    An intraplate earthquake of magnitude (c) 6.9 (Anon 2001a) struck Bhuj and the adjoining region of Kachchh in Gujarat on January 26th, 2001 at about 0316 hrs (GMT) and was followed by a number of aftershocks. The epicentre of this earthquake was located at 23.4°N and 70.28°E close to the Kachchh mainland fault. The intensity observed around the epicenter was X on the MSK scale. A study of 531 aftershocks, in the magnitude range of 3.0-5.7, recorded at Vadodara Seismological Observatory till March 31st, 2001 has been carried out and various statistical parameters calculated. The total energy released during the study period is calculated to be 8.2 × 1014 joule. Sudden occurrence of the main shock without any foreshock in the same tectonic system is a unique feature of this sequence. The -value (0.86), value of 0-1 (1.2), high 1/0 (0.89) and high value of the decay constant ℎ (0.91), all support the tectonic origin of the present study.

  8. Fertility Heterogeneity as a Mechanism for Power Law Distributions of Recurrence Times

    CERN Document Server

    Saichev, A

    2012-01-01

    We study the statistical properties of recurrence times in the self-excited Hawkes conditional Poisson process, the simplest extension of the Poisson process that takes into account how the past events influence the occurrence of future events. Specifically, we analyze the impact of the power law distribution of fertilities with exponent \\alpha, where the fertility of an event is the number of aftershocks of first generation that it triggers, on the probability distribution function (pdf) f(\\tau) of the recurrence times \\tau between successive events. The other input of the model is an exponential Omori law quantifying the pdf of waiting times between an event and its first generation aftershocks, whose characteristic time scale is taken as our time unit. At short time scales, we discover two intermediate power law asymptotics, f(\\tau) ~ \\tau^{-(2-\\alpha)} for \\tau << \\tau_c and f(\\tau) ~ \\tau^{-\\alpha} for \\tau_c << \\tau << 1, where \\tau_c is associated with the self-excited cascades of aft...

  9. Recent earthquake activity in Trichonis region and its tectonic significance

    Directory of Open Access Journals (Sweden)

    N. DELIBASIS

    1977-06-01

    Full Text Available SUMMARY. - The aftershock activity associated with the central Greece
    (Trichonis Lake earthquake of |une-Dec. 1975, has been studied, with emphasis
    on the time and magnitude distribution. It has been found that the value of b,
    in Gutenberg - R i c h t e r ' s relationship was near the same for the primary as
    well as the secondary or second order aftershocks of the sequences, but depends
    upon the focal depth.
    A correlation between the calculated focal mechanisms and the associated
    stress components to the distribution pattern of meizoseismic effects as well
    as to the geological structure of the seismic region was found.
    The seismic region lies at the top of an anticline which was found moving
    downwards, apparently due to compressional stresses.
    Within the series of three earthquakes the progress of the destruction of
    the buildings was observed and reported. The interest is concentrated to modern
    buildings out of reinforced concrete and infill brick walls. The relatively unexpected
    rather bad performance of the later case of buildings was compared to that
    of the traditional small houses out of brick or stone masonry, the behaviour of
    which may be considered as better from what it was expected.

  10. Stress imparted by the great 2004 Sumatra earthquake shut down transforms and activated rifts up to 400 km away in the Andaman Sea.

    Science.gov (United States)

    Sevilgen, Volkan; Stein, Ross S; Pollitz, Fred F

    2012-09-18

    The origin and prevalence of triggered seismicity and remote aftershocks are under debate. As a result, they have been excluded from probabilistic seismic hazard assessment and aftershock hazard notices. The 2004 M = 9.2 Sumatra earthquake altered seismicity in the Andaman backarc rift-transform system. Here we show that over a 300-km-long largely transform section of the backarc, M≥4.5 earthquakes stopped for five years, and over a 750-km-long backarc section, the rate of transform events dropped by two-thirds, while the rate of rift events increased eightfold. We compute the propagating dynamic stress wavefield and find the peak dynamic Coulomb stress is similar on the rifts and transforms. Long-period dynamic stress amplitudes, which are thought to promote dynamic failure, are higher on the transforms than on the rifts, opposite to the observations. In contrast to the dynamic stress, we calculate that the mainshock brought the transform segments approximately 0.2 bar (0.02 MPa) farther from static Coulomb failure and the rift segments approximately 0.2 bar closer to static failure, consistent with the seismic observations. This accord means that changes in seismicity rate are sufficiently predictable to be included in post-mainshock hazard evaluations. PMID:22949694

  11. Stress imparted by the great 2004 Sumatra earthquake shut down transforms and activated rifts up to 400 km away in the Andaman Sea

    Science.gov (United States)

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

    2012-01-01

    The origin and prevalence of triggered seismicity and remote aftershocks are under debate. As a result, they have been excluded from probabilistic seismic hazard assessment and aftershock hazard notices. The 2004 M = 9.2 Sumatra earthquake altered seismicity in the Andaman backarc rift-transform system. Here we show that over a 300-km-long largely transform section of the backarc, M≥4.5 earthquakes stopped for five years, and over a 750-km-long backarc section, the rate of transform events dropped by two-thirds, while the rate of rift events increased eightfold. We compute the propagating dynamic stress wavefield and find the peak dynamic Coulomb stress is similar on the rifts and transforms. Long-period dynamic stress amplitudes, which are thought to promote dynamic failure, are higher on the transforms than on the rifts, opposite to the observations. In contrast to the dynamic stress, we calculate that the mainshock brought the transform segments approximately 0.2 bar (0.02 MPa) farther from static Coulomb failure and the rift segments approximately 0.2 bar closer to static failure, consistent with the seismic observations. This accord means that changes in seismicity rate are sufficiently predictable to be included in post-mainshock hazard evaluations. PMID:22949694

  12. Triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke

    Science.gov (United States)

    Green, Robert G.; Greenfield, Tim; White, Robert S.

    2015-08-01

    Large earthquakes can generate small changes in static stress: increases that trigger aftershock swarms, or reductions that create a region of reduced seismicity--a stress shadow. However, seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity. This makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks. Dyke intrusions do not generate dynamic stresses, so provide an unambiguous test of the stress shadow hypothesis. Here we use GPS and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath Bárðarbunga Volcano, central Iceland, in August 2014. We find that during dyke emplacement, bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano. We calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke. Our results imply that static stress changes help control earthquake clustering. Similar small static stress changes may be important for triggering seismicity near geothermal areas, regions being hydrofractured and deflating oil and gas fields.

  13. Short-term and imminent geomagnetic anomalies of the Wenchuan Ms8.0 earthquake and exploration on earthquake forecast

    Institute of Scientific and Technical Information of China (English)

    Wuxing Wang; Jianhai Ding; Surong Yu; Yongxian Zhang

    2009-01-01

    The diurnal variation of the geomagnetic vertical component is exhibited mainly by changes of phase and amplitude before strong earthquakes. Based on data recorded by the network of geomagnetic observatories in China for many years, the anomalous features of the appearance time of the minima of diurnal variations (i.e, low-point time) of the geomagnetic vertical components and the variation of their spatial distribution (i.e, phenomena of low-point displacement) have been studied before the Wenchuan Ms8.0 earthquake. The strong aftershocks after two months' quiescence of A/6 aftershocks of the A/s8.0 event were forecasted based on these studies. There are good correlativities between these geomagnetic anomalies and occurrences of earthquakes. It has been found that most earthquakes occur near the boundary line of sudden changes of the low-point time and generally within four days before or after the 27th or 41st day counting from the day of the appearance of the anomaly. In addition, the imminent anomalies in diurnal-variation amplitudes near the epicentral areas have also been studied before the Wenchuan earthquake.

  14. Continental seismic events observed by the MPL vertical DIFAR array

    Energy Technology Data Exchange (ETDEWEB)

    Harris, D.B. [Lawrence Livermore National Lab., CA (United States); D`Spain, G. [Scripps Institution of Oceanography, San Diego, CA (United States). Marine Physical Lab.

    1993-11-01

    The vertical DIFAR array, an underwater acoustic sensor system, deployed by the Marine Physical Laboratory (MPL) was in place over the continental shelf off of Southern California and recorded the HUNTERS TROPHY nuclear test and nearly a score of after-shocks of the Landers/Big Bear earthquakes. Data from this array raise the possibility that detection thresholds for continental events may be significantly lower for arrays over the continental shelf than for arrays in the deep ocean basins. Offshore stations could be used to fill gaps in land-based seismic networks for monitoring the NPT and a CTBT, especially for monitoring non-cooperating nations with large coastlines. This preliminary report provides an analysis of the HUNTERS TROPHY observation as well as one of the Landers aftershocks. The analysis suggests detection thresholds for vertical hydrophone arrays below mb 3.0 at ranges between 3 and 4 degrees, and below mb 4.4 out to 6 degrees. This report also describes two signal processing techniques that enhance the detection potential of short vertical arrays. These methods are deterministic null steering to suppress horizontally propagating ambient ocean noise, and matched field processing for vertically-incident acoustic fields. The latter technique is ideally suited for acoustic fields derived from incident seismic waves, and may be viewed as a {open_quotes}synthetic aperture{close_quotes} approach to increase the effective aperture of the array.

  15. Studying the Sequence of the April 17, 2003 Delingha Earthquake (ML=6.7) by Regional Moment Tensor Inversion

    Science.gov (United States)

    Jiao, W.; Qian, R.; Chan, W.; Zeng, X.; Zhang, M.

    2004-12-01

    On April 17, 2003, a strong earthquake of ML = 6.7 occurred to the northwest of the Delingha City, Qinghai Province, northwest China. The epicenter (37o33¡_N, 96o27¡_E) lies in the Zongwulong Mountain, where the Dachaidan-Zongwulong Mountain fault (DZMF) zone runs through. In this study, we analyzed the focal mechanism of the main shock and several strong immediate aftershocks by regional waveform moment tensor inversion. We collected a comprehensive regional waveform data set that includes the broadband waveforms from the China Digital Seismic Network, the GSN, and a portable broadband seismic network deployed in the near regional distance to the earthquake at the time. One very broadband station equipped with the STS-2 seismometer and 24-bit digital data logger was only 80km from the epicenter, which gave tremendous constraint on the mechanism of the aftershock sequence (Fan and Wallace, 1991; Dreger and Helmberger, 1993). Our results show the dominance of the high angle thrust faulting striking NWW-NW. The distribution of the fault plane solutions reflects the turning and/or branching of the DZMF zone in the area, which has been confirmed by the field geological survey.

  16. Abrupt change in the dip of the subducting plate beneath north Chile

    Science.gov (United States)

    Contreras-Reyes, E.; Jara, J.; Grevemeyer, I.; Ruiz, S.; Carrizo, D.

    2012-05-01

    No large tsunamigenic earthquake has occurred in north Chile since 1877 and the region has been largely recognized as a mature seismic gap. At the southern end of the seismic gap, the 2007 Mw7.7 Tocopilla earthquake ruptured the deeper seismogenic interface, whereas the coupled upper interface remained unbroken. Seismological studies onshore show a gently varying dip of 20° to 30° of the downgoing Nazca plate, which extends from the trench down to depths of 40-50km. Here, we study the lithospheric structure of the subduction zone of north Chile at about 22°S, using wide-angle seismic refraction and reflection data from land and sea, complemented by hypocentre data recorded during the 2007 Tocopilla aftershocks. Our data document an abrupt increase in the dip of the subducting plate, from less than 10° to about 22°, at a depth of approximately 20km. The distribution of the 2007 aftershocks indicates that the change in dip acted as a barrier for the propagation of the 2007 earthquake towards the trench, which, in turn, indicates that the subduction megathrust is not only segmented along the trench, but also in the direction of the dip. We propose that large-magnitude tsunamigenic earthquakes must cross the barrier and rupture the entire seismogenic zone.

  17. Observing seismic and silent faulting related to a megathrust earthquake cycle: Deployment of a creepmeter array in N-Chile

    Science.gov (United States)

    Victor, P.; Bach, C.; Walter, T. R.; Krawczyk, C. M.; Gonzalez, G.; Oncken, O.

    2009-04-01

    Convergent plate boundaries at continental margins belong to the tectonically most active areas on earth and are the potential source of devastating earthquakes and tsunamis. While the bulk of strain accumulates along the subduction interface, significant hazardous deformation occurs by fault activity in the overriding crust. Abundant evidence for active surface faulting in northern Chile has been mapped recently, yet deformation rates can only be calculated on long-term time scales (10000 -100000 years) so far and are often too slow (Tocopilla earthquake. The obtained dataset of one year continuous measurement includes large aftershocks of the earthquake. In 2008 several additional instruments were installed. The examination of the one year dataset on the Mejillones site shows a good correlation of daily and annual temperature oscillations with thermal expansion and contraction of the creepmeter. Abrupt sub-millimeter scale displacements after temperature correction correlate with aftershocks of the Tocopilla Earthquake suggesting tectonic movement related to seismic events. The preliminary results may hence imply dynamic triggering of increased fault slip rates.

  18. Numerical modeling of block structure dynamics: Application to the Vrancea region and study of earthquakes sequences in the synthetic catalogs

    International Nuclear Information System (INIS)

    A seismically active region is represented as a system of absolutely rigid blocks divided by infinitely thin plane faults. The interaction of the blocks along the fault planes and with the underlying medium is viscous-elastic. The system of blocks moves as a consequence of prescribed motion of boundary blocks and the underlying medium. When for some part of a fault plane the stress surpasses a certain strength level a stress-drop (''a failure'') occurs. It can cause a failure for other parts of fault planes. The failures are considered as earthquakes. As a result of the numerical simulation a synthetic earthquake catalogue is produced. This procedure is applied for numerical modeling of dynamics of the block structure approximating the tectonic structure of the Vrancea region. By numerical experiments the values of the model parameters were obtained which supplied the synthetic earthquake catalog with the space distribution of epicenters close to the real distribution of the earthquake epicenters in the Vrancea region. The frequency-magnitude relations (Gutenberg-Richter curves) obtained for the synthetic and real catalogs have some common features. The sequences of earthquakes arising in the model are studied for some artificial structures. It is found that ''foreshocks'', ''main shocks'', and ''aftershocks'' could be detected among earthquakes forming the sequences. The features of aftershocks, foreshocks, and catalogs of main shocks are analysed. (author). 5 refs, 12 figs, 16 tabs

  19. The role of post-earthquake structural safety in pre-earthquake retrof in decision: guidelines and applications

    International Nuclear Information System (INIS)

    Critical structures such as hospitals, police stations, local administrative office buildings, and critical lifeline facilities, are expected to be operational immediately after earthquakes. Any rational decision about whether these structures are strong enough to meet this goal or whether pre-empitive retrofitting is needed cannot be made without an explicit consideration of post-earthquake safety and functionality with respect to aftershocks. Advanced Seismic Assessment Guidelines offer improvement over previous methods for seismic evaluation of buildings where post-earthquake safety and usability is a concern. This new method allows engineers to evaluate the like hood that a structure may have restricted access or no access after an earthquake. The building performance is measured in terms of the post-earthquake occupancy classifications Green Tag, Yellow Tag, and Red Tag, defining these performance levels quantitatively, based on the structure's remaining capacity to withstand aftershocks. These color-coded placards that constitute an established practice in US could be replaced by the standard results of inspections (A to E) performed by the Italian Dept. of Civil Protection after an event. The article also shows some applications of these Guidelines to buildings of the largest utility company in California, Pacific Gas and Electric Company (PGE).

  20. The 2003 Boumerdes, Algeria earthquake: Regional moment tensor analysis

    Science.gov (United States)

    Braunmiller, Jochen; Bernardi, Fabrizio

    2005-03-01

    We used regional broadband seismograms to determine seismic moment tensors for the destructive May 21, 2003 Boumerdes (Algeria) Mw = 7.0 earthquake and its larger aftershocks. Fully automatic inversions using near-real time data provided solutions for seven Mw >= 4.7 events within 90 minutes after event occurrence. After adding off-line data, we manually obtained 30 solutions (Mw >= 3.8) from May 2003 to January 2004. All have shallow source depths (6-21 km). The median P-axis orientation (338°) of 24 thrust and four strike-slip events is consistent with Africa-Eurasia plate motion (330°). The main shock hypocenter at 8-10 km depth at the coastline and its shallow southward dip (25° +/- 5°) puts the fault surface trace 15-20 km offshore, consistent with documented seafloor deformation at the base of the continental slope. A main shock rupture length of about 50 km is deduced from first day aftershocks and location of strike-slip events. The strike-slip events probably define the western rupture end and indicate a left-step of main convergence. Fault strike variability of thrust events suggests fault orientation changes and possibly fault segmentation.

  1. Are volatility correlations in financial markets related to Omori processes occurring on all scales?

    CERN Document Server

    Weber, P; Stanley, H E; Vodenska-Chitkushev, I; Wang, F; Havlin, Shlomo; Vodenska-Chitkushev, Irena; Wang, Fengzhong; Weber, Philipp

    2006-01-01

    We analyze the memory in volatility by studying volatility return intervals, defined as the time between two consecutive fluctuations larger than a given threshold, in time periods following stock market crashes. Such an aftercrash period is characterized by the Omori law, which describes the decay in the rate of aftershocks of a given size with time t by a power law with exponent close to 1. A shock followed by such a power law decay in the rate is here called Omori process. Studying several aftercrash time series, we show that the Omori law holds not only after significant market crashes, but also after ``intermediate shocks''. Moreover, we find self-similar features in the volatility. Specifically, within the aftercrash period there are smaller shocks that themselves constitute Omori processes on smaller scales, similar to the Omori process after the large crash. We call these smaller shocks subcrashes, which are followed by their own aftershocks. We also find similar Omori processes after intermediate cra...

  2. Mapping of b-values, earthquake relocation, and Coulomb stress changes during 1992-2007 in the Murindó seismic zone, Colombia

    Science.gov (United States)

    Dionicio, Viviana; Sánchez, John J.

    2012-07-01

    Seismicity in the Murindó seismic zone, Colombia (6° to 8° and - 75.5° to - 78.0°) during 1992-2007 included the occurrence of the M W 6.6 foreshock on October 17, and M W 7.1 mainshock on October 18, 1992, and aftershocks, which caused severe damage throughout the region. We modeled this seismic sequence by means of Coulomb stress changes imparted by slip along two semi-vertical fault planes with left-lateral motion and subdivided slip. Seismicity thereafter (1993-2007) was characterized by earthquakes magnitude in the range 0.7-6.1 for which a magnitude of completeness M C = 2.7 was determined. b-values are relatively high to the south of the study region and relatively low to the north and northwest. The relocation of epicenters indicates that recent seismicity may be occurring on a fault that is yet to be mapped under the Atrato river valley. We conclude that the 1992 seismic sequence was a case of a major earthquake facilitated by the stress changes imparted during a strong rupture the previous day and that the aftershocks and background seismicity in the region can be explained by static Coulomb stress changes up to 50.1 bar. Our results have implications for hazard in Colombia and serve as basis to foster future investigations.

  3. Earthquake simulations with time-dependent nucleation and long-range interactions

    Directory of Open Access Journals (Sweden)

    J. H. Dieterich

    1995-01-01

    Full Text Available A model for rapid simulation of earthquake sequences is introduced which incorporates long-range elastic interactions among fault elements and time-dependent earthquake nucleation inferred from experimentally derived rate- and state-dependent fault constitutive properties. The model consists of a planar two-dimensional fault surface which is periodic in both the x- and y-directions. Elastic interactions among fault elements are represented by an array of elastic dislocations. Approximate solutions for earthquake nucleation and dynamics of earthquake slip are introduced which permit computations to proceed in steps that are determined by the transitions from one sliding state to the next. The transition-driven time stepping and avoidance of systems of simultaneous equations permit rapid simulation of large sequences of earthquake events on computers of modest capacity, while preserving characteristics of the nucleation and rupture propagation processes evident in more detailed models. Earthquakes simulated with this model reproduce many of the observed spatial and temporal characteristics of clustering phenomena including foreshock and aftershock sequences. Clustering arises because the time dependence of the nucleation process is highly sensitive to stress perturbations caused by nearby earthquakes. Rate of earthquake activity following a prior earthquake decays according to Omori's aftershock decay law and falls off with distance.

  4. 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

    Directory of Open Access Journals (Sweden)

    Chung-Han Chan

    2012-01-01

    Full Text Available 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 takes the disturbance of a short-term seismicity rate into account and can be easily applied in comparison with the classical PSHA. In our approach, the treatment of the background seismicity rate is the same as in the zoneless approach, which considers a bandwidth function as a smoothing Kernel in neighboring region of earthquakes. The rate-and-state friction model imparted by the Coulomb stress change of large earthquakes is used to calculate the fault-interaction-based disturbance in seismicity rate for PSHA. We apply this approach to evaluate the seismic hazard in Christchurch after the occurrence of the M 7.1, 4 September 2010 Darfield earthquake. Results show an increase of seismic hazards due to the stress increase in the region around the rupture plane, which extended to Christchurch. This provides a suitable basis for the application of a time-dependent PSHA using updating earthquake information.

  5. Analysis of acoustic-seismic coupling for CTBT on-site inspection support

    International Nuclear Information System (INIS)

    The measurements of weak seismic signals, e.g. aftershock measurements during an on-site inspection for the Comprehensive Nuclear Test-Ban Treaty (CTBT), can be masked by man-made disturbances. These can be caused by airborne signals, like the noises of aircraft or helicopters, which couple to the ground and excite soil vibrations. We have measured sound pressure and corresponding soil vibrations caused by aircraft and by signals produced artificially with a speaker. Methods of acoustic deadening were applied to reduce the incident acoustic power locally. The influence on soil vibrations in different depths below the surface is investigated. The underlying question was whether the coupling of sound happens locally or soil vibrations created in a wide area around the sensor sum up to the total seismic signal. A better understanding of acoustic-seismic coupling can be used to develop guidelines for seismic aftershock measurements in order to improve the performance of on-site inspections for the CTBT.

  6. The Iquique earthquake sequence of April 2014: Bayesian modeling accounting for prediction uncertainty

    Science.gov (United States)

    Duputel, Zacharie; Jiang, Junle; Jolivet, Romain; Simons, Mark; Rivera, Luis; Ampuero, Jean-Paul; Riel, Bryan; Owen, Susan E; Moore, Angelyn W; Samsonov, Sergey V; Ortega Culaciati, Francisco; Minson, Sarah E.

    2016-01-01

    The subduction zone in northern Chile is a well-identified seismic gap that last ruptured in 1877. On 1 April 2014, this region was struck by a large earthquake following a two week long series of foreshocks. This study combines a wide range of observations, including geodetic, tsunami, and seismic data, to produce a reliable kinematic slip model of the Mw=8.1 main shock and a static slip model of the Mw=7.7 aftershock. We use a novel Bayesian modeling approach that accounts for uncertainty in the Green's functions, both static and dynamic, while avoiding nonphysical regularization. The results reveal a sharp slip zone, more compact than previously thought, located downdip of the foreshock sequence and updip of high-frequency sources inferred by back-projection analysis. Both the main shock and the Mw=7.7 aftershock did not rupture to the trench and left most of the seismic gap unbroken, leaving the possibility of a future large earthquake in the region.

  7. Diverse rupture processes in the 2015 Peru deep earthquake doublet.

    Science.gov (United States)

    Ye, Lingling; Lay, Thorne; Kanamori, Hiroo; Zhan, Zhongwen; Duputel, Zacharie

    2016-06-01

    Earthquakes in deeply subducted oceanic lithosphere can involve either brittle or dissipative ruptures. On 24 November 2015, two deep (606 and 622 km) magnitude 7.5 and 7.6 earthquakes occurred 316 s and 55 km apart. The first event (E1) was a brittle rupture with a sequence of comparable-size subevents extending unilaterally ~50 km southward with a rupture speed of ~4.5 km/s. This earthquake triggered several aftershocks to the north along with the other major event (E2), which had 40% larger seismic moment and the same duration (~20 s), but much smaller rupture area and lower rupture speed than E1, indicating a more dissipative rupture. A minor energy release ~12 s after E1 near the E2 hypocenter, possibly initiated by the S wave from E1, and a clear aftershock ~165 s after E1 also near the E2 hypocenter, suggest that E2 was likely dynamically triggered. Differences in deep earthquake rupture behavior are commonly attributed to variations in thermal state between subduction zones. However, the marked difference in rupture behavior of the nearby Peru doublet events suggests that local variations of stress state and material properties significantly contribute to diverse behavior of deep earthquakes. PMID:27386585

  8. Geochemistry of soil gas in the seismic fault zone produced by the Wenchuan Ms 8.0 earthquake, southwestern China

    Directory of Open Access Journals (Sweden)

    Cui Yueju

    2010-12-01

    Full Text Available Abstract The spatio-temporal variations of soil gas in the seismic fault zone produced by the 12 May 2008 Wenchuan Ms 8.0 earthquake were investigated based on the field measurements of soil gas concentrations after the main shock. Concentrations of He, H2, CO2, CH4, O2, N2, Rn, and Hg in soil gas were measured in the field at eight short profiles across the seismic rupture zone in June and December 2008 and July 2009. Soil-gas concentrations of more than 800 sampling sites were obtained. The data showed that the magnitudes of the He and H2 anomalies of three surveys declined significantly with decreasing strength of the aftershocks with time. The maximum concentrations of He and H2 (40 and 279.4 ppm, respectively were found in three replicates at the south part of the rupture zone close to the epicenter. The spatio-temporal variations of CO2, Rn, and Hg concentrations differed obviously between the north and south parts of the fault zone. The maximum He and H2 concentrations in Jun 2008 occurred near the parts of the rupture zone where vertical displacements were larger. The anomalies of He, H2, CO2, Rn, and Hg concentrations could be related to the variation in the regional stress field and the aftershock activity.

  9. Seismic quiescence and increase of the b value preceding the April 16, 2016 M7.3 earthquake in Kumamoto, Japan

    CERN Document Server

    Nanjo, K Z

    2016-01-01

    The 2016 Kumamoto earthquakes consist of a series of seismic activity in central Kumamoto, Japan, which started at the occurrence of an M6.5 quake on April 14, 2016. As a whole, the seismicity after the M6.5 quake is well modeled by the Omori-Utsu law that describes decay of aftershock activity. However, the p value was notably larger than its typical value (p = 1). Further, the p value, when analyzed using data set of longer time period, becomes larger. It is shown that this result is supported by the fact that the number of larger shocks (M >= 3) decreased rapidly in later time periods. Moreover, careful analysis on the spatiotemporal distribution of the b value shows a remarkable increase of the value, especially in the northern part of the aftershock area, which is consistent with the spatial pattern in the decrease of larger shocks. Based on these findings, combined with the results about the stress inversion analysis performed by NIED, we suggest that stress near the Futagawa fault zone had reduced just...

  10. The Cephalonia, Ionian Sea (Greece, sequence of strong earthquakes of January-February 2014: a first report

    Directory of Open Access Journals (Sweden)

    Gerassimos A. Papadopoulos

    2014-05-01

    Full Text Available On 26.1.2014 and 3.2.2014 two strong earthquakes of Mw6.0 and Mw5.9 ruptured the western Cephalonia Isl., Ionian Sea (Greece, at the SSW-wards continuation of the Lefkada segment of the Cephalonia Transform Fault Zone (CTFZ, causing considerable damage and a variety of ground failures. High-precision relocation of the aftershocks implies that the seismogenic layer was of 35 km in length (L striking NNE-SSW, of 10 km maximum in width and 15 km in thickness. Two aftershock spatial clusters were revealed at north (L1~10 km and at south (L2~25 km. However, no time correlation was found between the two clusters and the two strong earthquakes. Fitting the temporal evolution of aftershocks to the Omori-law showed slow aftershock decay. Fault plane solutions produced by moment tensor inversions indicated that the strong earthquakes as well as a plenty of aftershocks (Mw≥4.0 were associated with dextral strikeslip faulting with some thrust component and preferred fault planes striking about NNE-SSW. Average fault plane parameters obtained for the three largest events are: strike 21(±20, dip 65.5(±30, slip 173(±30. Broadband P-wave teleseismic records were inverted for understanding the rupture histories. It was found that the earthquake of 26.1.2014 had a complex source time function with c. 62 cm maximum slip, source duration of ~12 s and downwards rupture. Most of the slip was concentrated on a 13x9 km fault rupture. The earthquake of 3.2.2014 had a relatively simple source time function related with one big patch of slip with maximum slip c. 45 cm, with 10 s source duration. The rupture was directed upwards which along with the shallow focus (~5 km and the simple source time function may explain the significantly larger (0.77 g PGA recorded with the second earthquake with respect to the one recorded (0.56 g with the first earthquake. Most of the slip was concentrated on a 12x6 km fault rupture. Maximum seismic intensity (Im of level VII and VIII

  11. High Resolution Telesesimic P-wave Back-Projection Imaging Using Variable Travel Time Corrections: Characterizing Sub-Events of the Great April 11th 2012 Indian Ocean Intraplate Earthquakes

    Science.gov (United States)

    Kwong, K. B.; Koper, K. D.; Yue, H.; Lay, T.

    2012-12-01

    Two of the largest strike-slip earthquakes ever recorded occurred off the coast of northern Sumatra on April 11th 2012. The Mw 8.7 mainshock and Mw 8.2 aftershock occurred east of the NinetyEast Ridge in the Wharton Basin, a region of intraplate deformation with prominent fracture zones striking NNE-SSW. The relative lack of geodetic and local seismic data compared to other recent great earthquakes make teleseismic data especially important for understanding the rupture properties of these events. We performed short-period P-wave back-projection imaging using independent networks of stations in Europe and Japan. Preliminary images from the two networks showed similarly complex multi-event sources for the mainshock that indicate rupture occurred along both nodal planes of the gCMT solution, consistent with the locations of early aftershocks. Back-projection images of the Mw 8.2 aftershock showed a single, compact, bilateral rupture corresponding to the NNE-SSW nodal plane of the CMT solution [Yue et al., 2012]. Here we improve upon the resolution and accuracy of our initial back-projection images by estimating station specific travel time corrections that vary across the source region [e.g., Ishii et al., 2007]. These corrections are used to compensate for 3D variations in Earth structure that occur between the source region and the seismometers, and act to focus the array beams. We perform multi-channel cross-correlations of P waves recorded for 7 aftershocks that were (1) distributed broadly around the source region and (2) well-observed at seismometers in Europe. For each seismometer in the array, the 8 measured static corrections are smoothly interpolated over the entire source region with a Kriging method to form a travel time correction surface. These surfaces are then used with an otherwise conventional back-projection approach [Xu et al., 2009] to image the ruptures. Our new images are broadly consistent with our original results, indicating that the

  12. Earthquake Occurrence Corretated with the Movement of the Sun and the Moon%地震发生与日月运行之关联

    Institute of Scientific and Technical Information of China (English)

    赵树贤; 许绍燮; 吴平静; 马莉

    2011-01-01

    基于第23、24太阳活动周发生的全球M≥7.8级以上大震数据、汶川余震和智利余震数据.发现:地震的发生与日月位置存在着关联性;地震的发生与太阳风磁场到达地球的优势聚集方向存在着关联性.说明地震的发生与日月运行有关联.所用地震事件有两类:一类为余震--2008-05-12 M8.0汶川地震M≥5.0强余震与2010-02-27 M8.8智利地震M≥5.5强余震;另一类为1997-2010年全球M≥7.8大地震.虽然参与分析的地震事件数不算很多,但从两类各自不同的代表性以及所使用地震震级与地域的跨度,仍可望其结论具有普适性.文中提供了众多地震发生与日月运行关联的证据,其随机发生概率多为10(-4)-10(-6),小概率为不发生事件,但竟然发生了,表明它们之间必定有其非随机的统-成因机制控制.这是本文作者对地震发生的宇宙环境--"天外来客"特别给予重视的立论所在.%Based on the data of global scale large earthquakes (m≥7.8) during the sclar active cycles 23-24, and the data associated with Wenchuan aftershocks and Chile aftershocks, it has been found that there is a relationships between earthqyakes occurrence and positions of Sun and the Moon, and there is a relationship between earthquakes occurrence and main directions of solar wind magnetic field before earthquakes.These facts indicate that earthquake occurrrence is related with the movement of the Sun and the Moon. Two kinds of eqrthquaks events are studied.One is aftershocks including Wenchuan(2008-05-12 M8.0)aftershocks(M≥5.0) and Chile (2010-02-27 M8.8)aftershocks(M≥5.5).Another is global scale large earthquakes(inthe period of 1997-2010,M≥7.8).Even though numbers of earthquakes event cases used are not very large,considering the fact that these earthquakes represent two very different kind of typieal earthquakes and the magnitude and space of those events have a sufficient span,the results provided in here should

  13. Magnitude Scaling of the early displacement for the 2007, Mw 7.8 Tocopilla sequence (Chile)

    Science.gov (United States)

    Lancieri, M.; Fuenzalida, A.; Ruiz, S.; Madariaga, R. I.

    2009-12-01

    We investigate the empirical relationships between the initial portion of P and S-phase and the final event magnitude, on the Tocopilla (Chile) event and its aftershocks. Such correlations, on which real-time magnitude estimation for seismic early warning is founded, have been widely studied on several data sets, merging earthquakes generated in different tectonic settings and recorded with very different networks. The Tocopilla (Mw 7.8) earthquake, occurred along the northern Chile seismic gap on 14 November 2007, provides, together with its aftershocks, a unique opportunity of studying a homogeneous data set in terms of tectonic environment, focal mechanism, and recording network. The preliminary analysis required to build the seismic catalogue includes the automatic identification of more than 570 aftershocks using an automatic phase detector and picker algorithm, and the subsequent location of the events through a non-linear and probabilistic code. The seismic moment (M0) has been calculated by spectral modeling of P and S waves, assuming a Brune omega-square model. This analysis also yields values for the corner frequency and quality factor. The estimated range of moment magnitude for the aftershocks sequence is [2.8 - 6.8]. The correlation between the low pass filtered peak displacement (PD) and the final magnitude has been investigated for 90 events with magnitude greater than 4. These include the main event, its larger aftershock (Mw 6.8 occurred twenty-four hours after the main shock), and seven events with magnitude greater than 5.7. The recovered relationships confirm the observations of Zollo et al. [2006, 2007] of a clear correlation between distance corrected PD and final magnitude in the magnitude range [4.0 - 7.4], when considering time windows of 4 sec of P- or 2 sec of S- wave. In contrast with the previous studies, when examining time windows of 2 sec of P-wave, we surprisingly do not observe any saturation effect for magnitudes greater than 6

  14. Stress analysis for the 2010 Haiti seismic crisis: an example of strain partitioning on a transpressive setting

    Science.gov (United States)

    López-Cuesta, Víctor; Carbó-Gorosabel, Andrés; Muñoz-Martín, Alfonso; Granja Bruña, José Luis; Gárate Pasquín, Jorge; Rodríguez-Zurrunero, Álvaro

    2014-05-01

    The Mw=7 event occurred the 12th of January, 2010 triggered a seismic crisis in the southern Haiti that continued for 3 months. The epicentral region was located in an E-W oriented transpressive plate boundary where the Caribbean and North American plates converge ~20 mm/y trending 070º. The convergence is very oblique yielding a strain partitioning model where coexist E-W trending structures that accommodate the left-lateral strike-slip motion (e. g., Enriquillo-Plantain Garden fault zone; EPGFZ) and NW-SE trending structures that accommodate the compressive motion component (Transhaitian thrust belt; TTB). The main shock occurred at 15 km southward of Port-au-Prince and to 12 km of depth yielding large personal and material damage. Despite of its significant magnitude and relative shallow depth this event did not yield surface rupture complicating the studies about the source fault. The main event was followed by 50 aftershocks with magnitudes between 4.5 and 5 located to the west of the main event along an E-W trending segment of 50 km of length. All the events occurred along the interaction zone between the NW-SE oriented compressive structures of the TTB and E-W strike-slip structures of the EPGFZ. The TTB and the EPGFZ are first-order structures that define the eastern boundary of the Gonave microplate. In this study we show the results of the stress inversion analysis carried out over the focal mechanisms calculated from the centroid tensor method for the main event and 50 aftershocks of the 2010 seismic crisis. Calculated active stress tensors (maximum horizontal stress, Shmax, and stress regime) have been compared with structural data and inter-seismic surface deformations derived from GPS data. The main event was generated by a N084º north-dipping fault plane with a major left-lateral slip component and a reverse component located at the deformation front of the TTB (i. e., Léogâne fault). This reverse oblique fault was activated by a Shmax trending

  15. 2D Modelling of the Gorkha earthquake through the joint exploitation of Sentinel 1-A DInSAR measurements and geological, structural and seismological information

    Science.gov (United States)

    De Novellis, Vincenzo; Castaldo, Raffaele; Solaro, Giuseppe; De Luca, Claudio; Pepe, Susi; Bonano, Manuela; Casu, Francesco; Zinno, Ivana; Manunta, Michele; Lanari, Riccardo; Tizzani, Pietro

    2016-04-01

    A Mw 7.8 earthquake struck Nepal on 25 April 2015 at 06:11:26 UTC, killing more than 9,000 people, injuring more than 23,000 and producing extensive damages. The main seismic event, known as the Gorkha earthquake, had its epicenter localized at ~82 km NW of the Kathmandu city and the hypocenter at a depth of approximately 15 km. After the main shock event, about 100 aftershocks occurred during the following months, propagating toward the south-east direction; in particular, the most energetic shocks were the Mw 6.7 and Mw 7.3 occurred on 26 April and 12 May, respectively. In this study, we model the causative fault of the earthquake by jointly exploiting surface deformation retrieved by the DInSAR measurements collected through the Sentinel 1-A (S1A) space-borne sensor and the available geological, structural and seismological information. We first exploit the analytical solution performing a back-analysis of the ground deformation detected by the first co-seismic S1A interferogram, computed by exploiting the 17/04/2015 and 29/04/2015 SAR acquisitions and encompassing the main earthquake and some aftershocks, to search for the location and geometry of the fault plane. Starting from these findings and by benefiting from the available geological, structural and seismological data, we carry out a Finite Element (FE)-based 2D modelling of the causative fault, in order to evaluate the impact of the geological structures activated during the seismic event on the distribution of the ground deformation field. The obtained results show that the causative fault has a rather complex compressive structure, dipping northward, formed by segments with different dip angles: 6° the deep segment and 60° the shallower one. Therefore, although the hypocenters of the main shock and most of the more energetic aftershocks are located along the deeper plane, corresponding to a segment of the Main Himalayan Thrust (MHT), the FE solution also indicates the contribution of the shallower

  16. Pre-earthquake foreshock activity and its discrimination from swarms (Invited)

    Science.gov (United States)

    Papadopoulos, G. A.; Daskalaki, E.; Minadakis, G.; Orfanogiannaki, K.

    2013-12-01

    Seismicity often occurs in space-time clusters: swarms, short-term foreshocks, aftershocks. Foreshocks calminate with the occurrence of a strong mainshock. However, swarms are space-time clusters that do not conclude with a mainshock. Earthquake statistics shows that in areas of good seismicity monitoring foreshocks precede sizeable (at least M5.5) mainshocks at a rate of about half percent. The discrimination between foreshocks and swarms is of crucial importance for the use of foreshocks as a diagnostic of forthcoming strong mainshock in real-time conditions. We analyze seismic sequences in Greece and in Italy with the application of our algorithm FORMA (Foreshocks-Mainshock-Aftershocks) and discriminate between foreshocks and swarms based on the seismicity significant changes in the space-time-magnitude domains. We support that different statistical properties is a diagnostic of foreshocks (e.g. b-value drop) against swarms (b-value increase). A complementary approach is based on the development of Poisson Hidden Markov Models (PHMM's) which are introduced to model significant temporal seismicity changes. In a PHMM the unobserved sequence of states is a finite-state Markov chain and the distribution of the observation at any time is Poissonian with rate depending only on the current state of the chain. Thus, PHMM allows a region to have varying seismicity rate. PHMM is a promising diagnostic since the transition from one state to another does not only depend on the total number of events involved but also on the current state of the system. A third methodological experiment was performed based on the complex network theory. We found that the earthquake networks examined form a scale-free degree distribution. By computing their basic statistical measures, such as the Average Clustering Coefficient, Mean Path Length and Entropy, we found that they underline the strong space-time clustering of swarms, foreshocks and aftershocks but also their important differences

  17. Source Scaling and Ground Motion of the 2008 Wells, Nevada, earthquake sequence

    Science.gov (United States)

    Yoo, S.; Dreger, D. S.; Mayeda, K. M.; Walter, W. R.

    2011-12-01

    Dynamic source parameters, such as a corner frequency, stress drop, and radiated energy, are one of the most critical factors controlling ground motions at higher-frequencies (generally greater than 1 Hz), which may cause damage to nearby surface structures. Hence, scaling relation of these parameters can play an important role in assessing the seismic hazard for regions in which records of ground motions from potentially damaging earthquakes are not available. On February 21, 2008 at 14:16 (UTC), a magnitude 6 earthquake occurred near Wells, Nevada, where characterized by low rate of seismicity. For their aftershocks, a marked discrepancy between the observed and predicted ground motions from empirical ground motion prediction equation was reported (Petersen et al., 2011). To evaluate and understand these observed ground motions, we investigate the dynamic source parameters and their scaling relation for this earthquake sequence. We estimate the source parameters of the earthquakes using the coda spectral ratio method (Mayeda et al., 2007) and examine the estimates with the observed spectral accelerations at higher frequencies. From the derived source parameters and scaling relation, we compute synthetic ground motions of the earthquakes using fractal composite source model (e.g., Zeng et al., 1994) and compare these synthetic ground motions with the observed ground motions and synthetic ground motions obtained from self-similar source scaling relation. In our preliminary results, we find the stress drops of the aftershocks are systematically 2-5 times lower than a stress drop of the mainshock. This agrees well with systematic overestimation of the predicted ground motions for the aftershocks. The simulated ground motions from the coda-derived scaling relation better explains the observed both weak and strong ground motions than that of from the size independent stress drop scaling relation. Assuming that the scale dependent stress drop is real, at least in some

  18. Seismotectonics of the Antalya Basin and surrounding regions in eastern Mediterranean from 8 to 28 December 2013 Mw 5.0-5.8 earthquake sequence

    Science.gov (United States)

    Görgün, Ethem; Kalafat, Doğan; Kekovalı, Kıvanç

    2016-05-01

    The 8-28 December 2013 Mw 5.0-5.8 Antalya Basin earthquake sequence in eastern Mediterranean is examined. Centroid moment tensors for 16 earthquakes with moment magnitudes (Mw) between 3.6 and 5.8 are determined by applying a waveform inversion method. All earthquakes are shallow focus thrust events at a depth of 40-45 km. The seismic moments (Mo) of the earthquakes are estimated as 4.10 × 1016-5.54 × 1017 N m and rupture durations of the mainshocks are 20-22 s. The focal mechanisms of the aftershocks are mainly thrust faulting with a strike-slip component and reveal NW-SE trending direction of T-axis in the entire activated region. According to high-resolution hypocenter relocation of the Antalya earthquake sequence, seven main clusters are revealed. The aftershock activity in the observation period between 1 December 2013 and 23 January 2015 extends in an N to S direction. A seismic cross-section indicates that a complex pattern of the hypocenter distribution with the activation of seven segments. The westernmost cluster (cluster 1) is associated with a fault plane trending mainly WNW-ESE and dipping vertical, while the cluster 5 is related to a fault plane trending NNE-SSW and dipping towards SSE. The best constrained focal depths indicate that the aftershock sequence is mainly confined in the crust (depth performed to obtain a more precise picture of the Antalya Basin stress field. The stress tensor inversion results indicate a predominant thrust stress regime with a NE-SW oriented maximum horizontal compressive stress (SH). According to variance of the stress tensor inversion, to first order, the Antalya Basin is characterized by a homogeneous interplate stress field. The Coulomb stress change associated with two mainshocks are also investigated to evaluate any significant enhancement of stresses along the Antalya Basin and surrounding regions. Positive lobes with stress of more than 0.4 bars are obtained for two mainshocks, indicating that these values are

  19. Earthquake Forecasts for Gorkha Immediately Following the 25th April, M=7.8 Mainshock

    Science.gov (United States)

    Segkou, M.; Parsons, T.

    2015-12-01

    The M-7.8 Gorkha (Nepal) earthquake on the 25th April, 2015 has shaken the central Himalayan front and immediately raised concerns for the severity of future triggered earthquakes. Here, we implement standard and innovative forecast models to predict the spatio-temporal distribution of triggered events. Key challenges addressed are: 1) the limited information on early aftershocks, 2) the low-productivity aftershock sequence in the near-source area, 3) the off-fault (>250 km) triggered events exemplified by the M=5.4 Xegar event, 3 hrs after the mainshock. We apply short-term empirical/statistical ETAS and physical forecast models, the latter based on the combination of rate/state friction law and Coulomb stresses. Within the physics-based model implementation we seek to evaluate the uncertainty related with the rupture style of triggered events by considering: 1) the geometry of active structures, 2) optimally oriented for failure faults and 3) all-potential faults described by the total stress field. The latter is represented by the full stress tensor before and after the mainshock and our analysis suggests that the preseismic stress magnitudes are still sufficient to cause earthquakes even after modification by the mainshock. The above remark reveals that there are no "stress shadows" affecting the spatial distribution of near-field aftershocks. It is also noted that the method allows for an a-priori determination of the rupture plan of the M=7.3 event, within the limit of uncertainty (20˚). The results show that: (1) ETAS models underestimate the number of observed events, since they heavily base their good performance in small magnitude earthquakes, not available in the first few weeks after the mainshock, (2) far field triggered events are captured only by physics-based forecasts, and (3) the total stress method improves the predictability of larger magnitude events. We conclude that frontier regions benefit from the implementation of physics-based models

  20. Source Functions and Path Effects from Earthquakes in the Farallon Transform Fault Region, Gulf of California, Mexico that Occurred on October 2013

    Science.gov (United States)

    Castro, Raúl R.; Stock, Joann M.; Hauksson, Egill; Clayton, Robert W.

    2016-07-01

    We determined source spectral functions, Q and site effects using regional records of body waves from the October 19, 2013 (M w = 6.6) earthquake and eight aftershocks located 90 km east of Loreto, Baja California Sur, Mexico. We also analyzed records from a foreshock with magnitude 3.3 that occurred 47 days before the mainshock. The epicenters of this sequence are located in the south-central region of the Gulf of California (GoC) near and on the Farallon transform fault. This is one of the most active regions of the GoC, where most of the large earthquakes have strike-slip mechanisms. Based on the distribution of the aftershocks, the rupture propagated northwest with a rupture length of approximately 27 km. We calculated 3-component P- and S-wave spectra from ten events recorded by eleven stations of the Broadband Seismological Network of the GoC (RESBAN). These stations are located around the GoC and provide good azimuthal coverage (the average station gap is 39°). The spectral records were corrected for site effects, which were estimated calculating average spectral ratios between horizontal and vertical components (HVSR method). The site-corrected spectra were then inverted to determine the source functions and to estimate the attenuation quality factor Q. The values of Q resulting from the spectral inversion can be approximated by the relations Q_{P} = 48.1 ± 1.1 f^{0.88 ± 0.04} and Q_{S} = 135.4 ± 1.1 f^{0.58 ± 0.03} and are consistent with previous estimates reported by Vidales-Basurto et al. (Bull Seism Soc Am 104:2027-2042, 2014) for the south-central GoC. The stress drop estimates, obtained using the ω2 model, are below 1.7 MPa, with the highest stress drops determined for the mainshock and the aftershocks located in the ridge zone. We used the values of Q obtained to recalculate source and site effects with a different spectral inversion scheme. We found that sites with low S-wave amplification also tend to have low P-wave amplification, except

  1. Coseismic Coulomb stress changes caused by the Mw6.9 Yutian earthquake in 2014 and its correlation to the 2008 Mw7.2 Yutian earthquake

    Science.gov (United States)

    Li, Yujiang; Chen, Lianwang; Liu, Shaofeng; Yang, Shuxin; Yang, Xingyue; Zhang, Guangwei

    2015-06-01

    A three-dimensional viscoelastic finite element model of the Qinghai-Tibet Plateau and its adjacent regions was used to explore the relationship between the Mw7.2 Yutian earthquake in 2008 and the 2014 Mw6.9 Yutian earthquake. We further analyzed the Coulomb failure stress change caused by the Yutian Mw6.9 earthquake on faults surrounding the Bayan Har block and discussed the relationship between the Coulomb stress change and aftershock distribution. The preliminary results showed that: (1) The Coulomb failure stress change caused by the Mw7.2 Yutian earthquake in 2008, which was projected on the slip direction of the 2014 Yutian Mw6.9 earthquake, exceeded the earthquake triggering threshold of 0.01 MPa, implying an apparent triggering effect. Specifically, the coseismic Coulomb failure stress changes were 0.0167 MPa and 0.0170 MPa when assuming apparent friction coefficients of 0.4 and 0.6, respectively. The Coulomb failure stress changes, including viscoelastic relaxation effects, were 0.0187 MPa and 0.0194 MPa respectively. Combined with the tectonic stressing rate, the Mw6.9 Yutian earthquake in 2014 was advanced 21.4-24.9 years by the 2008 Mw7.2 Yutian earthquake; (2) The stress changes derived from the viscoelastic relaxation effect were much less than that from the coseismic effect, which was possibly interpreted as the shorter elapsed time between the two earthquakes relative to the characteristic time; (3) The Coulomb failure stresses increased on the mid-northern segment of the Altyn Tagh fault, the middle segment of the Mani-Yushu fault and the western segment of the eastern Kunlun fault, which demonstrated increasing seismic potential. In particular, the Coulomb failure stress on the middle segment of the Altyn Tagh fault increased by 2.8 × 103 Pa, the most significant increase. In contrast, the Coulomb failure stress decreased on the western segment of the Mani-Yushu and Minjiang faults, with the western segment of the Mani-Yushu fault dropping by 3

  2. Inference of small-scale Vp/Vs ratio along the rupture area of the Tocopilla earthquake, Northern Chile (Mw 7.7, 14/11/2007)

    Science.gov (United States)

    Tilmann, F. J.; Palo, M.; Schurr, B.

    2014-12-01

    We have inferred the Vp/Vs ratio along the segment of the Peru-Chile subduction margin corresponding to the rupture area of the Tocopilla earthquake (TE, Mw 7.7, 14/11/2007). This event nucleated in Northern Chile and broke the southern ~100 km of the ~500 km Northern Chile Southern Peru seismic gap, which had not seen an earthquake of this magnitude since the M~9 event of 1877. TE activated two main co-seismic slip patches: one around the epicenter and another north-east of the Mejillones Peninsula. We have applied the Lin and Shearer approach [1] to the aftershock sequence of TE. In this approach, the relative time shift between the S phases of a pair of nearby events at one station are plotted as function of the time shift between the P phases of the same pair. The process is repeated for a set of events. If the events are close enough to assume a uniform local Vp/Vs and the P-reciprocal wavefront can be approximated as planar, the points lay on a line, whose slope is an estimation of the local Vp/Vs. The technique is extended to a set of stations demeaning the time shifts from each pair of events. The time shifts are inferred maximizing the cross-correlation function between the event pairs. The technique has been applied to clusters of events sharing similar waveforms and spatially clustered hypocentres. We have adopted a robust linear L2 regression and have assigned a statistical error to the best fit. Most clusters are identified within a sub-vertical branch of the subduction interface hosting a major aftershock (Michilla earthquake, 16/12/2007, Ml 6.8) and its aftershocks. This branch falls inside the subducted Nazca Plate at depths of 40-50 km, north-east of the Mejillones Peninsula, and shows Vp/Vs mostly in the range 1.8-1.9. Clusters close to the Mejillones Peninsula and to the epicenter displays Vp/Vs around 1.7 and 1.8, respectively. References [1] - Lin, G., & Shearer, P. (2007). Estimating local Vp/Vs ratios within similar earthquake clusters

  3. Stress triggering in en echelon thrust ruptures and related tear faults: The 2003 M=6.9 Zemmouri, Algeria, earthquake and fault interactions

    Science.gov (United States)

    Lin, J.; Stein, R. S.; Meghraoui, M.; Toda, S.; Ayadi, A.; Dorbath, C.; Belabbes, S.

    2009-12-01

    The contractional tectonics of northern Algeria is characterized by a series of en echelon thrust faults of moderate lengths (Meghraoui et al., 2000). This tectonic deformation pattern is similar in geometry to other continental thrust fault systems, such as the Coalinga-Kettleman Hills faults in central California, but differs significantly from that of subduction zones, where thrust segments are often more geometrically continuous along the strike of subduction zones. In this study we first illustrate the essential features of stress interaction between earthquakes occurring on en echelon thrust faults and adjacent tear faults. Our model results reveal that earthquakes on en echelon thrust segments could significantly promote strike-slip motion on the intervening tear faults. Furthermore, if the source earthquake has mixed thrust and strike-slip components, the resultant stress increases on the tear faults are even greater. Thus, tear faults may play an important role in stress transfer between adjacent thrust segments. We next examine the stress transferred by the 2003 M=6.9 Zemmouri quake to nearby thrust and strike-slip faults in northern Algeria. Mahsas et al. (2008) illustrated that the observed afterslip in 2003-2005 appears to be concentrated at the upper parts of the 2003 Zemmouri rupture surface. Our calculations support the hypothesis that a significant portion (more than 75%) of the observed afterslip area might have experienced Coulomb stress increases during the Zemmouri main shock. Calculations further reveal that the majority (more than 90%) of the 30 best-relocated aftershocks as determined by Ayadi et al. (2008) also sustained Coulomb stress increases on at least one of their nodal planes. Finally, we calculated that the Zemmouri main shock brought the Coulomb stress 1 bar closer to failure on the adjacent Boumerdes reverse fault and 0.5 bars closer on the right-lateral Thenia faults that bound the Mitidja basin. Both of these faults experienced

  4. Temporal stress changes associated with the 2008 May 29 MW 6 earthquake doublet in the western South Iceland Seismic Zone

    Science.gov (United States)

    Hensch, Martin; Lund, Björn; Árnadóttir, Thóra; Brandsdóttir, Bryndís

    2016-01-01

    On 2008 May 29, two magnitude MW ˜ 6 earthquakes occurred on two adjacent N-S faults in the western South Iceland Seismic Zone. The first main shock was followed approximately 3 s later by the rupture on a parallel fault, about 5 km to the west. An intense aftershock sequence was mostly confined to the western fault and an E-W aligned zone, extending west of the main shock region into the Reykjanes oblique rift. In this study, a total of 325 well-constrained focal mechanisms were obtained using data from the permanent Icelandic SIL seismic network and a temporary network promptly installed in the source region following the main shocks, which allowed a high-resolution stress inversion in short time intervals during the aftershock period. More than 800 additional focal mechanisms for the time period 2001-2009, obtained from the permanent SIL network, were analysed to study stress changes associated with the main shocks. Results reveal a coseismic counter-clockwise rotation of the maximum horizontal stress of 11 ± 10° (95 per cent confidence level) in the main rupture region. From previous fault models obtained by inversion of geodetic data, we estimate a stress drop of about half of the background shear stress on the western fault. With a stress drop of 8-10 MPa, the pre-event shear stress is estimated to 16-20 MPa. The apparent weakness of the western fault may be caused by fault properties, pore fluid pressure and the vicinity of the fault to the western rift zone, but may also be due to the dynamic stress increase on the western fault by the rupture on the eastern fault. Further, a coseismic change of the stress regime-from normal faulting to strike-slip faulting-was observed at the northern end of the western fault. This change could be caused by stress heterogeneities, but may also be due to a southward shift in the location of the aftershocks as compared to prior events.

  5. Source rupture process of the 12 January 2010 Port-au-Prince (Haiti, Mw7.0) earthquake

    Science.gov (United States)

    Borges, José; Caldeira, Bento; Bezzeghoud, Mourad; Santos, Rúben

    2010-05-01

    The Haiti earthquake occurred on tuesday, January 12, 2010 at 21:53:10 UTC. Its epicenter was at 18.46 degrees North, 72.53 degrees West, about 25 km WSW of Haiti's capital, Port-au-Prince. The earthquake was relatively shallow (H=13 km, U.S. Geological Survey) and thus had greater intensity and destructiveness. The earthquake occurred along the tectonic boundary between Caribbean and North America plate. This plate boundary is dominated by left-lateral strike slip motion and compression with 2 cm/year of slip velocity eastward with respect to the North America plate. The moment magnitude was measured to be 7.0 (U.S. Geological Survey) and 7.1 (Harvard Centroid-Moment-Tensor (CMT). More than 10 aftershocks ranging from 5.0 to 5.9 in magnitude (none of magnitude larger than 6.0) struck the area in hours following the main shock. Most of these aftershocks have occurred to the West of the mainshock in the Mirogoane Lakes region and its distribution suggests that the length of the rupture was around 70 km. The Harvard Centroid Moment Tensor (CMT) mechanism solution indicates lefth-lateral strike slip movement with a fault plane trending toward (strike = 251o ; dip = 70o; rake = 28o). In order to obtain the spatiotemporal slip distribution of a finite rupture model we have used teleseismic body wave and the Kikuchi and Kanamori's method [1]. Rupture velocity was constrained by using the directivity effect determined from a set of waveforms well recorded at regional and teleseismic distances [2]. Finally, we compared a map of aftershocks with the Coulomb stress changes caused by the event in the region [3]. [1]- Kikuchi, M., and Kanamori, H., 1982, Inversion of complex body waves: Bull. Seismol. Soc. Am., v. 72, p. 491-506. [2] Caldeira B., Bezzeghoud M, Borges JF, 2009; DIRDOP: a directivity approach to determining the seismic rupture velocity vector. J Seismology, DOI 10.1007/s10950-009-9183-x (http://www.springerlink.com/content/xp524g2225628773/) [3] -King, G. C. P

  6. Real-Time Science on Social Media: The Example of Twitter in the Minutes, Hours, Days after the 2015 M7.8 Nepal Earthquake

    Science.gov (United States)

    Lomax, A.; Bossu, R.; Mazet-Roux, G.

    2015-12-01

    Scientific information on disasters such as earthquakes typically comes firstly from official organizations, news reports and interviews with experts, and later from scientific presentations and peer-reviewed articles. With the advent of the Internet and social media, this information is available in real-time from automated systems and within a dynamic, collaborative interaction between scientific experts, responders and the public. After the 2015 M7.8 Nepal earthquake, Twitter Tweets from earth scientists* included information, analysis, commentary and discussion on earthquake parameters (location, size, mechanism, rupture extent, high-frequency radiation, …), earthquake effects (distribution of felt shaking and damage, triggered seismicity, landslides, …), earthquake rumors (e.g. the imminence of a larger event) and other earthquake information and observations (aftershock forecasts, statistics and maps, source and regional tectonics, seismograms, GPS, InSAR, photos/videos, …).In the future (while taking into account security, false or erroneous information and identity verification), collaborative, real-time science on social media after a disaster will give earlier and better scientific understanding and dissemination of public information, and enable improved emergency response and disaster management.* A sample of scientific Tweets after the 2015 Nepal earthquake: In the first minutes: "mb5.9 Mwp7.4 earthquake Nepal 2015.04.25-06:11:25UTC", "Major earthquake shakes Nepal 8 min ago", "Epicenter between Pokhara and Kathmandu", "Major earthquake shakes Nepal 18 min ago. Effects derived from witnesses' reports". In the first hour: "shallow thrust faulting to North under Himalayas", "a very large and shallow event ... Mw7.6-7.7", "aftershocks extend east and south of Kathmandu, so likely ruptured beneath city", "Valley-blocking landslides must be a very real worry". In the first day: "M7.8 earthquake in Nepal 2hr ago: destructive in Kathmandu Valley and

  7. Waveform cross correlation for seismic monitoring of underground nuclear explosions. Part II: Synthetic master events

    CERN Document Server

    Bobrov, Dmitry; Rozhkov, Mikhail

    2013-01-01

    Waveform cross correlation is an efficient tool for detection and characterization of seismic signals. The efficiency critically depends on the availability of master events. For the purposes of the Comprehensive Nuclear-Test-Ban Treaty, cross correlation can globally reduce the threshold monitoring by 0.3 to 0.4 magnitude units. In seismically active regions, the optimal choice of master events is straightforward. There are two approaches to populate the global grid in aseismic areas: the replication of real masters and synthetic seismograms calculated for seismic arrays of the International Monitoring System. Synthetic templates depend on the accuracy of shape and amplitude predictions controlled by focal depth and mechanism, source function, velocity structure and attenuation along the master/station path. As in Part I, we test three focal mechanisms (explosion, thrust fault, and actual Harvard CMT solution for one of the April 11, 2012 Sumatera aftershocks) and two velocity structures (ak135 and CRUST 2.0...

  8. A Python-based Post-processing Toolset For Seismic Analyses

    CERN Document Server

    Brasier, Steve

    2014-01-01

    This paper discusses the design and implementation of a Python-based toolset to aid in assessing the response of the UK's Advanced Gas Reactor nuclear power stations to earthquakes. The seismic analyses themselves are carried out with a commercial Finite Element solver, but understanding the raw model output this produces requires customised post-processing and visualisation tools. Extending the existing tools had become increasingly difficult and a decision was made to develop a new, Python-based toolset. This comprises of a post-processing framework (aftershock) which includes an embedded Python interpreter, and a plotting package (afterplot) based on numpy and matplotlib. The new toolset had to be significantly more flexible and easier to maintain than the existing code-base, while allowing the majority of development to be carried out by engineers with little training in software development. The resulting architecture will be described with a focus on exploring how the design drivers were met and the suc...

  9. Nonparametric analysis of the time structure of seismicity in a geographic region

    Directory of Open Access Journals (Sweden)

    A. Quintela-del-Río

    2002-06-01

    Full Text Available As an alternative to traditional parametric approaches, we suggest nonparametric methods for analyzing temporal data on earthquake occurrences. In particular, the kernel method for estimating the hazard function and the intensity function are presented. One novelty of our approaches is that we take into account the possible dependence of the data to estimate the distribution of time intervals between earthquakes, which has not been considered in most statistics studies on seismicity. Kernel estimation of hazard function has been used to study the occurrence process of cluster centers (main shocks. Kernel intensity estimation, on the other hand, has helped to describe the occurrence process of cluster members (aftershocks. Similar studies in two geographic areas of Spain (Granada and Galicia have been carried out to illustrate the estimation methods suggested.

  10. Diminishing high-frequency directivity due to a source effect: Empirical evidence from small earthquakes in the Abruzzo region, Italy

    Science.gov (United States)

    Pacor, F.; Gallovič, F.; Puglia, R.; Luzi, L.; D'Amico, M.

    2016-05-01

    The aim of this study is to investigate the directivity effects of ~250 aftershocks (magnitudes 3-5.5) of the Mw 6.1 2009 L'Aquila earthquake (central Italy). To this end, we estimate the apparent source spectra at each station removing path and site effects inferred by standard Generalized Inversion Technique. Then, we evaluate the residuals between the apparent source spectra and the event mean source spectrum at selected frequencies. We investigate azimuthal and frequency dependence of the residuals for 40 events with the best station coverage. For most of events with the strongest directivity effect (Mw 3.4-4.0), we observe a remarkable decrease of the directivity amplification at high frequencies, which has not yet been documented for such relatively small-magnitude events. Since there is negligible distance dependence, we ascribe this observation to a source phenomenon such as significant small-scale rupture propagation complexity.

  11. Spanish sources concerning the 1693 earthquake in Sicily

    Directory of Open Access Journals (Sweden)

    F. Rodriguez de la Torre

    1995-06-01

    Full Text Available When the great 1693 earthquake occurred, Sicily was a viceroyalty of Spain. In order to find primary and direct sources, the Archivo General de Simancas has to be investigated. Due to the lack of extensive and adequate catalogues it is difficult search amongst the millions of documents filed there. The author located among numerous bundles of papers of different Sections. a total of 238 manuscripts (with 850 pages and 4 printed edicts related to the 1693 earthquake. All the gathered information offers good prospects of true knowledge on many aspects related to the seismic catastrophe: perception area. number of victims, ruin of towns, list of aftershocks. reconstruction. health and public order problems, and all those problems that surround a great historic earthquake (economic, political, social and religious.

  12. Study on Source Spectrum for the Yajiang Earthquake Sequence Using S Wave

    Institute of Scientific and Technical Information of China (English)

    Zhang Yongjiu; Cheng Wanzheng

    2004-01-01

    The source parameters of the Yajiang earthquake sequence are calculated based on spectral analysis of S wave data recorded by the Chengdu Digital Seismic Network. Analysis of the source parameters in different periods are made, The obtained results are: ( 1 ) the relationship between Ms (seismic moment), Mw (moment magnitude) and ML (local magnitude), which fits the data of Yajiang earthquake sequence; (2) the decreasing corner frequency from 1.4 before the M5.0 earthquake to 1.3 afterwards, and then to 1.2 after the M6.0 event; (3) the obvious difference in the source parameters between foreshocks and aftershocks, which may be indicators for earthquake prediction.

  13. Surface Displacement of the 17 May 1993 Eureka Valley, California, Earthquake Observed by SAR Interferometry.

    Science.gov (United States)

    Peltzer, G; Rosen, P

    1995-06-01

    Satellite synthetic aperture radar (SAR) interferometry shows that the magnitude 6.1 Eureka Valley earthquake of 17 May 1993 produced an elongated subsidence basin oriented north-northwest, parallel to the trend defined by the aftershock distribution, whereas the source mechanism of the earthquake implies a north-northeast-striking normal fault. The +/-3-millimeter accuracy of the radar-observed displacement map over short spatial scales allowed identification of the main surface rupture associated with the event. These observations suggest that the rupture began at depth and propagated diagonally upward and southward on a west-dipping, north-northeast fault plane, reactivating the largest escarpment in the Saline Range. PMID:17778980

  14. Preseismic and coseismic deformation associated with the Coyote Lake, California, earthquake.

    Science.gov (United States)

    King, N.E.; Savage, J.C.; Lisowski, M.; Prescott, W.H.

    1981-01-01

    The Coyote Lake earthquake (ML=5.9; August 6, 1979; epicenter c100 km SE of San Francisco) occurred on the Calaveras fault within a geodetic network that had been surveyed annually since 1972 to monitor strain accumulation. The rupture surface as defined by aftershocks is a vertical rectangle 20 km in length extending from a depth of 4 km to c12 km. The observed deformation of the geodetic network constrains the average slip to be 0.33 + or - 0.05m right lateral. Although the geodetic data furnished an exceptionally detailed picture of the pre-earthquake deformation, no significant premonitory anomaly associated with the Coyote Lake earthquake can be identified.-Authors

  15. Geomorphic and geologic controls of geohazards induced by Nepal’s 2015 Gorkha earthquake

    Science.gov (United States)

    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.; Kaab, 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.; 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 the earthquakes’ induced geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision-makers. We mapped 4312 coseismic and postseismic landslides. We also surveyed 491 glacier lakes for earthquake damage but found only nine landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions.

  16. Source Model from ALOS-2 ScanSAR of the 2015 Nepal Earthquakes

    Science.gov (United States)

    Liu, Youtian; Ge, Linlin; Ng, Alex Hay-Man

    2016-06-01

    The 2015 Gorkha Nepal Earthquake sequence started with a magnitude Mw 7.8 main shock and continued with several large aftershocks, particularly the second major shock of Mw 7.3. Both earthquake events were captured using ALOS-2 ScanSAR images to determine the coseismic surface deformation and the source models. In this paper, the displacement maps were produced and the corresponding modelling results were discussed. The single fault model of the main shock suggests that there was nearly 6 m of right-lateral oblique slip motion with fault struck of 292° and dipped gently Northeast at 7°, indicating that the main shock was on a thrust fault. Moreover, a single fault model for the Mw 7.3 quake with striking of 312° and dipping of 11° was derived from observed result. Both results showed the fault planes struck generally to South and dipped northeast, which depicted the risks since the main shock occurred.

  17. Engineering geological aspect of Gorkha Earthquake 2015, Nepal

    Science.gov (United States)

    Adhikari, Basanta Raj; Andermann, Christoff; Cook, Kristen

    2016-04-01

    Strong shaking by earthquake causes massif landsliding with severe effects on infrastructure and human lives. The distribution of landslides and other hazards are depending on the combination of earthquake and local characteristics which influence the dynamic response of hillslopes. The Himalayas are one of the most active mountain belts with several kilometers of relief and is very prone to catastrophic mass failure. Strong and shallow earthquakes are very common and cause wide spread collapse of hillslopes, increasing the background landslide rate by several magnitude. The Himalaya is facing many small and large earthquakes in the past i.e. earthquakes i.e. Bihar-Nepal earthquake 1934 (Ms 8.2); Large Kangra earthquake of 1905 (Ms 7.8); Gorkha earthquake 2015 (Mw 7.8). The Mw 7.9 Gorkha earthquake has occurred on and around the main Himalayan Thrust with a hypocentral depth of 15 km (GEER 2015) followed by Mw 7.3 aftershock in Kodari causing 8700+ deaths and leaving hundreds of thousands of homeless. Most of the 3000 aftershocks located by National Seismological Center (NSC) within the first 45 days following the Gorkha Earthquake are concentrated in a narrow 40 km-wide band at midcrustal to shallow depth along the strike of the southern slope of the high Himalaya (Adhikari et al. 2015) and the ground shaking was substantially lower in the short-period range than would be expected for and earthquake of this magnitude (Moss et al. 2015). The effect of this earthquake is very unique in affected areas by showing topographic effect, liquefaction and land subsidence. More than 5000 landslides were triggered by this earthquake (Earthquake without Frontiers, 2015). Most of the landslides are shallow and occurred in weathered bedrock and appear to have mobilized primarily as raveling failures, rock slides and rock falls. Majority of landslides are limited to a zone which runs east-west, approximately parallel the lesser and higher Himalaya. There are numerous cracks in

  18. Radon anomalies preceding earthquakes which occurred in the UK, in summer and autumn 2002

    International Nuclear Information System (INIS)

    During the course of an investigation into domestic radon levels in Northamptonshire, two hourly sampling real-time radon detectors were operated simultaneously in separate locations 2.25 km apart in Northampton, in the English East Midlands, for a 25-week period. This period of operation encompassed the period in September 2002 during which the Dudley earthquake (magnitude - 5.0) and smaller aftershocks occurred in the English West Midlands, UK. We report herein our observations regarding the occurrence of simultaneous short-period radon anomalies and their timing in relation to the Dudley, and other, earthquakes which occurred during the monitoring period. Analysis of the radon time-series reveals a short period when the two time-series displayed simultaneous in-phase short-term (6-9 h) radon anomalies prior to the main Dudley earthquake. Subsequent investigation revealed that a similar period occurred prior to another smaller but recorded earthquake in the English Channel

  19. Rapid Scientific Response as an Educational Opportunity Integrating Geoscience and Advanced Visualization

    Science.gov (United States)

    Oskin, M. E.; Kellogg, L. H.; Team, K.

    2014-12-01

    Natural disasters provide important opportunities to conduct original scientific research. We present the results of a graduate course at the University of California, Davis centered on rapid scientific response to the 24 August magnitude 6.0 South Napa earthquake. Students from both geoscience and computer visualization formed collaborative teams to conduct original research, choosing from diverse research topics including mapping of the surface rupture, both in the field and remotely, production and analysis of three-dimensional scans of offset features, topographic point-cloud differencing, identification and mapping of pre-historic earthquake scarps, analysis of geodetic data for pre-earthquake fault loading rate and modeling of finite fault offset, aftershock distribution, construction and 3D visualization of earth structure and seismic velocity models, shaking intensity from empirical models, and earthquake rupture simulation.

  20. Earthquake source parameters that display the first digit phenomenon

    Science.gov (United States)

    Toledo, P. A.; Riquelme, S. R.; Campos, J. A.

    2015-10-01

    We study the main parameters of earthquakes from the perspective of the first digit phenomenon: the nonuniform probability of the lower first digit different from 0 compared to the higher ones. We found that source parameters like coseismic slip distributions at the fault and coseismic inland displacements show first digit anomaly. We also found the tsunami runups measured after the earthquake to display the phenomenon. Other parameters found to obey first digit anomaly are related to the aftershocks: we show that seismic moment liberation and seismic waiting times also display an anomaly. We explain this finding by invoking a self-organized criticality framework. We demonstrate that critically organized automata show the first digit signature and we interpret this as a possible explanation of the behavior of the studied parameters of the Tohoku earthquake.

  1. Earthquake source parameters which display first digit phenomenon

    Directory of Open Access Journals (Sweden)

    P. A. Toledo

    2015-05-01

    Full Text Available We study main parameters of earthquakes from the perspective of the first digit phenomenon: the nonuniform probability of the lower first digit different from zero compared to the higher ones. We found that source parameters like coseismic slip distributions at the fault and coseismic inland displacements show first digit anomaly. We also found the tsunami runups measured after the earthquake to display the phenomenon. Other parameters found to obey first digit anomaly are related to the aftershocks: we show that seismic moment liberation and seismic waiting times also display an anomaly. We explain this finding by invoking a self-organized criticality frame. We show that critically organized automata show the first digit signature and we interpret this as a possible explanation of the behavior of the studied parameters of the Tohoku earthquake.

  2. Development of light water reactors and cooling systems

    International Nuclear Information System (INIS)

    Development of Light Water Reactors (LWR) started in US. Japan imported this technology from US, and its construction and improvement had been done by adding Japanese original technologies. This article outlined development history of LWR, its plant system and main components, ECCS and accident management. Most operating LWR were those rapidly developed from 1960 to 1970 and associated accident response was so designed for all assumed conditions at that time. At the Fukushima Daiichi nuclear power station, needed works could not be down well due to all losses of AC and DC power, inability to assure plant state at control room under power stoppage, work interruption caused by aftershock and road blockage by Tsunami drift, and accident management was not effective and accident was enlarged. After the Fukushima nuclear accident, enhanced measures against more stringent conditions such as external events should be prepared to assure safety of nuclear power station using latest knowledge. (T. Tanaka)

  3. INSTANTANEOUS INVERSION OF 1993 ‘KILLARI’ OVERVIEW OF THE MAHARASHTRA: ANALYSIS GEOLOGY TECTONIC

    Directory of Open Access Journals (Sweden)

    Balap Tejeshwini Ramchandra

    2015-05-01

    Full Text Available This paper attempts to summarize the various rebuilding components, with an emphasis on housing, and some of the many features of the project. The aftershock sequence of the September 30th, 1993 Killari earthquake in the Latur district of Maharashtra state, India, recorded by 41 temporary seismograph stations. The local earthquake tomography (LET method of Thurber (1983 is used. About 1500 P and 1200 S wave travel-times are inverted. This paper provides an overvi w of the large , comprehensive analysis program initiated by the Government of Maharashtra, shocking earthquake in 1993. The program had as its primary objective the relocation of the 52 most affected villages (over 27,000 houses and the repair and strengthening of another approximately 200,000 houses scattered over 40,000 square kilometers. This very complex rebuilding program has been described in detail in several other reports and is the subject of additional papers.

  4. 3D Visualization of Recent Sumatra Earthquake

    Science.gov (United States)

    Nayak, Atul; Kilb, Debi

    2005-04-01

    Scientists and visualization experts at the Scripps Institution of Oceanography have created an interactive three-dimensional visualization of the 28 March 2005 magnitude 8.7 earthquake in Sumatra. The visualization shows the earthquake's hypocenter and aftershocks recorded until 29 March 2005, and compares it with the location of the 26 December 2004 magnitude 9 event and the consequent seismicity in that region. The 3D visualization was created using the Fledermaus software developed by Interactive Visualization Systems (http://www.ivs.unb.ca/) and stored as a ``scene'' file. To view this visualization, viewers need to download and install the free viewer program iView3D (http://www.ivs3d.com/products/iview3d).

  5. Statistique asymptotique de processus auto-excitatifs spatio-temporels

    OpenAIRE

    Valmy, Larissa; Vaillant, Jean

    2011-01-01

    Nous nous intéressons aux processus ponctuels auto-excitatifs introduits par Ogata en 1998 et discutés par Zhuang et al. (2005). Ce modèle peut être vu comme une extension, dans un premier temps du processus ponctuel présenté par Hawkes en 1971 et, dans un second temps du modèle de type épidémique temporel proposé par Ogata en 1988. Il s'agit du modèle spatio-temporel ETAS (Epidemic Type Aftershock Sequence) intégrant l'aspect spatio-temporel et les marques. Une de ses utilisations est le cal...

  6. Statistical analysis and modeling of seismicity related to the exploitation of geothermal energy

    Science.gov (United States)

    Dinske, Carsten; Langenbruch, Cornelius; Shapiro, Serge

    2016-04-01

    Geothermal energy is an integral and important part of renewables but it is frequently observed that its production induces seismicity. Here we analyse in detail seismicity from two hydrothermal reservoirs in Germany and one hydrothermal field in Italy. We focus on temporal changes of seismicity rates. This study was motivated by the results of numerical simulations. The modeling of stress changes caused by the injection and production of fluids revealed that the seismicity rate should decrease on a long-term perspective which does not match the observed seismicity rates. To understand this mismatch we analyse the waiting time distributions of the seismic events in both time domain (inter event times) and fluid volume domain (inter event volume). We find clear indications that the observed seismicity contains two components: (1) seismicity that is directly triggered by the production and re-injection of fluid, in other words, induced events, and (2) seismicity that is triggered by earthquake interactions also known as aftershock triggering. In order to calibrate and better constrain our numerical simulations using the induced seismicity we apply a catalog declustering the separate the two components and remove the aftershocks from the observed catalogs. We use the magnitude-dependent space-time windowing approach introduced by Gardener and Knopoff (1974) and tested several published algorithms to calculate the windows. We choose the final space-time window for a given catalog based on the waiting time distribution of the events after the declustering. Technically speaking, we suppose that the probability density of waiting times in the fluid volume domain corresponds to a homogeneous Poisson process (HPP, Langenbruch et al., 2011). After catalog declustering, we conclude that the different reservoirs show a comparable response to the production and re-injection of fluids and the additional triggering of seismicity by earthquake interactions. The declustered

  7. High Resolution Long- and Short-Term Earthquake Forecasts for California

    CERN Document Server

    Werner, M J; Jackson, D D; Kagan, Y Y

    2009-01-01

    We present two models for estimating the probabilities of future earthquakes in California, to be tested in the Collaboratory for the Study of Earthquake Predictability (CSEP). The first, time-independent model, modified from Helmstetter et al. (2007), provides five-year forecasts for magnitudes m > 4.95. We show that large quakes occur on average near the locations of small m > 2 events, so that a high-resolution estimate of the spatial distribution of future large quakes is obtained from the locations of the numerous small events. We employ an adaptive spatial kernel of optimized bandwidth and assume a universal, tapered Gutenberg-Richter distribution. In retrospective tests, we show that no Poisson forecast could capture the observed variability. We therefore also test forecasts using a negative binomial distribution for the number of events. We modify existing likelihood-based tests to better evaluate the spatial forecast. Our time-dependent model, an Epidemic Type Aftershock Sequence (ETAS) model modifie...

  8. Sendai Thermal Power Plant (TPP) and New Sendai TPP of Tohoku Electric Power Co. Inc., and Joban-Kyodo Nakoso TPP

    International Nuclear Information System (INIS)

    In order to learn a lesson of emergency management from experiences, disaster damage on Thermal Power Plants (TPPs) from the Tohoku District - off the Pacific Ocean Earthquake and resulting tsunamis were investigated. Sendai TPP and New Sendai TPP of Tohoku Electric Power Co. Inc., and Joban-Kyodo Nakoso TPP were situated within focal region of the earthquake but their damages were different. Sendai TPP had ground motion greater than 700 Gal at the land surface and seismic damage on equipments was concerned in addition to tsunami damage. Ground liquefaction occurred in New Sendai TPP. Nakoso TPP had big aftershocks with land subsidence, which brought about buckling of lower part of stack and tank. After personnel and worker's lifeline were recovered and stabilized, recovery works such as to remove mud and rubbles, inspect and repair damage of equipments, and replacements if necessary were in progress. (T. Tanaka)

  9. Numerical simulation for 1975 Haicheng and 1999 Xiuyan earthquake processes by DDA+FEM

    Institute of Scientific and Technical Information of China (English)

    ZHANG Rui-qing; WEI Fu-sheng; QIAO Cheng-bin; LIN Bang-hui

    2005-01-01

    In this paper, using discontinuous deformation analysis, we simulate numerically the processes of the 1975 Haicheng earthquake and the 1999 Xiuyan earthquake in the tectonic environment of North China where blocks restrict each other by DDA+FEM. Based on the research on the distribution of foreshocks and recent aftershocks of Xiuyan earthquake and the results from our study and other study on Haicheng earthquake, we present a tectonic block model of Haicheng and Xiuyan earthquakes. The results from numerical simulation include the variation of principal stress field released by these two earthquakes, contour patterns of maximum shear stress change, variation patterns of displacement vectors before and after the earthquakes and variation of the earthquake fault slip with time, which agree basically with the focal mechanisms, macroscopic isoseismal and horizontal displacement characters from observations.

  10. Monitoring the West Bohemian earthquake swarm in 2008/2009 by a temporary small-aperture seismic array

    DEFF Research Database (Denmark)

    Hiemer, Stefan; Rössler, Dirk; Scherbaum, Frank

    2012-01-01

    The most recent intense earthquake swarm in West Bohemia lasted from 6 October 2008 to January 2009. Starting 12 days after the onset, the University of Potsdam monitored the swarm by a temporary small-aperture seismic array at 10 km epicentral distance. The purpose of the installation was a...... complete monitoring of the swarm including micro-earthquakes (ML <0).We identify earthquakes using a conventional shortterm average/long-term average trigger combined with sliding-window frequency-wavenumber and polarisation analyses. The resulting earthquake catalogue consists of 14,530 earthquakes...... temporal features (frequency– magnitude distribution, propagation of back azimuth and horizontal slowness, occurrence rate of aftershock sequences and interevent-time distribution) of the recent 2008/2009 earthquake swarm are presented and discussed. Temporal changes of the coefficient of variation (based...

  11. Avalanche criticality during compression of porcine cortical bone of different ages

    Science.gov (United States)

    Baró, Jordi; Shyu, Peter; Pang, Siyuan; Jasiuk, Iwona M.; Vives, Eduard; Salje, Ekhard K. H.; Planes, Antoni

    2016-05-01

    Crack events developed during uniaxial compression of cortical bones cut from femurs of developing pigs of several ages (4, 12, and 20 weeks) generate avalanches. These avalanches have been investigated by acoustic emission analysis techniques. The avalanche energies are power-law distributed over more than four decades. Such behavior indicates the absence of characteristic scales and suggests avalanche criticality. The statistical distributions of energies and waiting times depend on the pig age and indicate that bones become stronger, but less ductile, with increasing age. Crack propagation is equally age-dependent. Older pigs show, on average, larger cracks with a time distribution similar to those of aftershocks in earthquakes, while younger pigs show only statistically independent failure events.

  12. Analogies between the cracking noise of ethanol-damped charcoal and earthquakes

    CERN Document Server

    Ribeiro, H V; Alves, L G A; Santoro, P A; Picoli, S; Lenzi, E K; Mendes, R S

    2015-01-01

    We report on an extensive characterization of the cracking noise produced by charcoal samples when damped with ethanol. We argue that the evaporation of ethanol causes transient and irregularly distributed internal stresses that promotes the fragmentation of samples and mimic some situations found in mining process. The results show that, in general, the most fundamental seismic laws ruling earthquakes (Gutenberg-Richter law, unified scaling law for the recurrence times, Omori's law, productivity law and Bath's law) hold under the conditions of the experiment. Some discrepancies were also identified (a smaller exponent in Gutenberg-Richter law, a stationary behavior in the aftershocks rates for long times and a double power-law relationship in productivity law) and related to the different loading condition. Our results thus corroborate to elucidate the parallel between seismic laws and fracture experiments caused by a more complex loading condition that also occurs in natural and induced seismicity (such as ...

  13. A statistical model for seismic hazard assessment of hydraulic-fracturing-induced seismicity

    Science.gov (United States)

    Hajati, T.; Langenbruch, C.; Shapiro, S. A.

    2015-12-01

    We analyze the interevent time distribution of hydraulic-fracturing-induced seismicity collected during 18 stages at four different regions. We identify a universal statistical process describing the distribution of hydraulic-fracturing-induced events in time. The distribution of waiting times between subsequently occurring events is given by the exponential probability density function of the homogeneous Poisson process. Our findings suggest that hydraulic-fracturing-induced seismicity is directly triggered by the relaxation of stress and pore pressure perturbation initially created by the injection. Therefore, compared to this relaxation, the stress transfer caused by the occurrence of preceding seismic events is mainly insignificant for the seismogenesis of subsequently occurring events. We develop a statistical model to compute the occurrence probability of hydraulic-fracturing-induced seismicity. This model can be used to assess the seismic hazard associated with hydraulic fracturing operations. No aftershock triggering has to be included in the statistical model.

  14. Strong Ground Motion Estimation During the Kutch, India Earthquake

    Science.gov (United States)

    Iyengar, R. N.; Kanth, S. T. G. Raghu

    2006-01-01

    In the absence of strong motion records, ground motion during the 26th January, 2001 Kutch, India earthquake, has been estimated by analytical methods. A contour map of peak ground acceleration (PGA) values in the near source region is provided. These results are validated by comparing them with spectral response recorder data and field observations. It is found that very near the epicenter, PGA would have exceeded 0.6 g. A set of three aftershock records have been used as empirical Green's functions to simulate ground acceleration time history and 5% damped response spectrum at Bhuj City. It is found that at Bhuj, PGA would have been 0.31 g 0.37 g. It is demonstrated that source mechanism models can be effectively used to understand spatial variability of large-scale ground movements near urban areas due to the rupture of active faults.

  15. Spatial damage distribution of August 16, 2003, Inner Mongolia, China, MS=5.9 earth-quake and analysis

    Institute of Scientific and Technical Information of China (English)

    GAO Meng-tan; XU Li-sheng; GUO Wen-sheng; WAN Bo; YU Yan-xiang

    2005-01-01

    The spatial damage distribution of August 16, 2003, Inner Mongolia, China, MS=5.9 earthquake is summarized through field investigation. The moment tensor solution and focal mechanism are inverted using the digital long-period waveform records of China Digital Seismograph Network (CDSN). The relation between the spatial damage distribution and focal mechanism is analyzed according to the focal mechanism, the aftershock distribution and the spatial damage distribution. The possible relation between the characteristics of ground motion and the tectonic background of the source region is discussed in terms of the global ground motion records, historical earthquake documents and the damage distribution. Investigation reveals that the meizoseismal region is in east-west direction, which is consistent with the nodal plane of focal mechanism inversion. The meizoseismal area is relatively large and the damage of single-story adobe houses or masonry houses is more severe. This may have relations with local seismotectonic environment.

  16. Spatio-temporal patterns in ultra-slow domain wall creep dynamics

    CERN Document Server

    Ferrero, Ezequiel E; Giamarchi, Thierry; Kolton, Alejandro B; Rosso, Alberto

    2016-01-01

    In presence of impurities, ferromagnetic and ferroelectric domain walls slide only above a finite external field. Close to this depinning threshold, the wall proceeds by large and abrupt jumps, called avalanches, while, at much smaller field, it creeps by thermal activation. In this work we develop a novel numerical technique that captures the ultra-slow creep regime over huge time scales. We point out the existence of activated events that involve collective reorganizations similar to avalanches, but, at variance with them, display correlated spatio-temporal patterns that resemble the complex sequence of aftershocks observed after a large earthquake. Remarkably, we show that events assembly in independent clusters owning the same scale-free statistics as critical depinning avalanches. This correlated dynamics should be experimentally accessible by magneto-optical imaging of ferro- magnetic films.

  17. Dike intrusions during rifting episodes obey scaling relationships similar to earthquakes.

    Science.gov (United States)

    Passarelli, L; Rivalta, E; Shuler, A

    2014-01-01

    As continental rifts evolve towards mid-ocean ridges, strain is accommodated by repeated episodes of faulting and magmatism. Discrete rifting episodes have been observed along two subaerial divergent plate boundaries, the Krafla segment of the Northern Volcanic Rift Zone in Iceland and the Manda-Hararo segment of the Red Sea Rift in Ethiopia. In both cases, the initial and largest dike intrusion was followed by a series of smaller intrusions. By performing a statistical analysis of these rifting episodes, we demonstrate that dike intrusions obey scaling relationships similar to earthquakes. We find that the dimensions of dike intrusions obey a power law analogous to the Gutenberg-Richter relation, and the long-term release of geodetic moment is governed by a relationship consistent with the Omori law. Due to the effects of magma supply, the timing of secondary dike intrusions differs from that of the aftershocks. This work provides evidence of self-similarity in the rifting process. PMID:24469260

  18. The OBS Survey of Seismogenic Processes: Using 2010 Chile M=8.8 Mega Earthquake as example

    Science.gov (United States)

    Lee, C.; Wei, H.; Wang, S.

    2012-12-01

    In the early morning of February 27, 2010, a mega-earthquake now known as the "Maule Earthquake" (M=8.8) took place in central Chile. In May 1960, Chile was hit by the largest earthquake ever recorded with a magnitude of 9.5. In general, the west coast of Chile is a convergent boundary between the Nazca and South American Plates, with the Nazca Plate subducting beneath the South American Plate in a NE direction. With a convergence rate of 6-7 cm per year, stress accumulates in the lower part of the oceanic plate to a certain extent resulting in huge destructive earthquakes. In 2010, our team deployed two OBS arrays (the A and B arrays), with a total of 33 deployments to record the aftershocks along the rupture area. We collected data for a total of 46 days (July 15 to August 7 for the A array and August 14 to September 6 for the B array). The aim of our study was to analyze the distribution and characteristics of the aftershocks to get a better understanding of the tectonic activity after the main event, and conjecture on the seismogenic processes that occurred during the rupture. Using the Antelope software on the data we picked the P- and S-wave arrivals and located the events. To obtain more accurate earthquake epicenter locations we also applied the HypoDD software. We recognized a total of 3,807 events in 46 days of monitoring (in average of 80 some earthquakes per day) with many of them distributed along both sides of the trench. Immediately behind the trench axis, along the frontal accretionary prism, there is an aseismic zone, possibly due to the high content of water in the sedimentary strata. On the other hand, the paleo-accretionary prism on the landward side of the trench accumulated most of the earthquakes. These events focus at depths of 50-100 km in the subduction zone. This is called the seismogenic zone. The comparison of events before the main shock and the HypoDD results of this study show that most of the events cluster along the edge of the

  19. Outburst Risk of Barrier Lakes in Sichuan, China

    Institute of Scientific and Technical Information of China (English)

    CHENG Genwei; WANG Xiaodan; HE Xiubin; FAN Jihui; FAN Jianrong

    2008-01-01

    34 barrier lakes induced by earthquake have been formed by wedged debris on the river channels after a massive earthquake happening on May 12 in Sichuan, China. Among them, the Tangjiashan Barrier Lake is the largest one. It faces very urgent risk of dam breaking when water level reaches the top and begins overflow in case of storm rainfalls and continually aftershocks, threatening already devastated cities and villages with about 1.5 million people downstream. The outburst of a similar barrier lake occurred in the Minjiang River in 1933, causing a catastrophic flood. Risk analysis indicates that not all barrier lakes are highly dangerous. Only those lakes with very high dams and water to be filled up in short period need to be dealt with immediately.

  20. Can Apparent Stress be Used to Time-Dependent Seismic Hazard Assessment or Earthquake Forecast? An Ongoing Approach in China

    Science.gov (United States)

    Wu, Zhongliang; Jiang, Changsheng; Zhang, Shengfeng

    2016-08-01

    The approach in China since the last 1.5 decade for using apparent stress in time-dependent seismic hazard assessment or earthquake forecast is summarized. Retrospective case studies observe that apparent stress exhibits short-term increase, with time scale of several months, before moderate to strong earthquakes in a large area surrounding the `target earthquake'. Apparent stress is also used to estimate the tendency of aftershock activity. The concept relating apparent stress indirectly to stress level is used to understand the properties of some `precursory' anomalies. Meanwhile, different opinions were reported. Problems in the calculation also existed for some cases. Moreover, retrospective studies have the limitation in their significance as compared to forward forecast test. Nevertheless, this approach, seemingly uniquely carried out in a large scale in mainland China, provides the earthquake catalogs for the predictive analysis of seismicity with an additional degree of freedom, deserving a systematic review and reflection.

  1. Multifractal Omori-Utsu Law for Earthquake Triggering: New Tests on the Harvard and Japanese Catalogs

    CERN Document Server

    Ouillon, G; Sornette, D

    2006-01-01

    The Multifractal Stress-Activated (MSA) model is a statistical model of triggered seismicity based on mechanical and thermodynamic principles. It predicts that, above a triggering magnitude cut-off $M_0$, the exponent $p$ of the Omori-Utsu law for the seismic decay of aftershocks is a linear increasing function $p(M) =a M+b$ of the mainshock magnitude $M$ [Ouillon and Sornette, 2005]. First empirical support for this prediction has been presented for the Southern California SCEC catalog. Here, we confirm this law on the worlwide Harvard CMT and the Japanese JMA catalogs, with similar ranges of variation from $p(M=3)=0.7 \\pm 0.1$ to $p(M=8)=1.1 \\pm 0.2$. However, the statistically significant differences of the slopes $a$, intercepts $b$ and cut-offs $M_0$ suggest different multifractal properties of the three catalogs, likely associated with different thermal and mechanical properties.

  2. The Koryak strong earthquake of April 20 (21), 2006: Preliminary results

    Science.gov (United States)

    Rogozhin, E. A.; Gordeev, E. I.; Chebrov, V. N.

    2007-02-01

    A number of terrain features and objects of the settlements of Tilichiki and Korf and the village of Khailino in the epicentral zone of the strongest earthquake in the north of the Kamchatka region were examined in the first days after the earthquake. Primary and secondary coseismic ruptures were identified on the surface. An outcrop of the seismic source was discovered in the form of an extended seismic fault about 140 km in traceable length. The settlements were inspected for the purpose of elucidating the macroseismic effect, structural maps were compiled, and the main types of ruptures were identified. The network of seismic stations on Kamchatka and in eastern Russia recorded a few thousand aftershocks. The gathered data provide insight into the structure of the source and its tectonic position at the Asian active continental margin.

  3. The Rheology of the Earth in the Intermediate Time Range

    Directory of Open Access Journals (Sweden)

    A. E. SCHEIDEGGER

    1970-06-01

    Full Text Available The evidence bearing upon the rheology of the " tectonically
    significant layers" of the Earth (" tectonosphere " in the intermediate
    time range (4 hours to 15000 years is analyzed. This evidence is
    based upon observations of rock-behavior in the laboratory, of seismic
    aftershock sequences, of Earth tides and of the decay of the Chandler wobble.
    It is shown that of the rheological models (Maxwell-material, Kelvin-material,
    and logarithmically creeping material advocated in the literature, only that
    based on logarithmic creep does not contradict any of the observational
    evidence available to date. In addition, a strength limit may be present.

  4. Fukushima nuclear accident and the social responsibility of science

    International Nuclear Information System (INIS)

    Five months had passed since Fukushima Daiichi Nuclear Power Plant (NPP) accident occurred but still there was no knowing when the accident ended. Released radioactivity seemed to be greater than one million terra Bq and if there occurred an explosive rupture of containment vessel due to the failure of containment vent or occurrence of steam explosion, the amount of released radioactivity might amount to be at least equivalent to or surpass that of Chernobyl NPP accident. There existed still a risk that overheating and meltdown of nuclear fuels might reoccur with loss of cooling due to a possible giant aftershock. This article described total views on significant disaster that the accident brought about on many neighboring residents or wide range of people. After a general discussion about what was social responsibility of scientists, social responsibility of scientists for Fukushima Daiichi NPP accident was discussed. Responsibility of omission was also argued. (T. Tanaka)

  5. Continental dynamics and continental earthquakes

    Institute of Scientific and Technical Information of China (English)

    张东宁; 张国民; 张培震

    2003-01-01

    Two key research projects in geoscience field in China since the IUGG meeting in Birmingham in 1999, the project of "East Asian Continental Geodynamics" and the project of "Mechanism and Prediction of Strong Continental Earthquakes" are introduced in this paper. Some details of two projects, such as their sub-projects, some initial research results published are also given here. Because of the large magnitude of the November 14, 2001 Kunlun Mountain Pass MS=8.1 earthquake, in the third part of this paper, some initial research results are reviewed for the after-shock monitoring and the multi-discipline field survey, the impact and disaster of this earthquake on the construction site of Qinghai-Xizang (Tibet) railway and some other infrastructure.

  6. In situ dynamic tests and seismic records on the RHR system building ENEL-IV nuclear plant/Caorso (Italy)

    International Nuclear Information System (INIS)

    The tests on the RHR Building of the Caorso Nuclear Plant are part of a program of dynamic tests on large structures sponsored by ENEL, which ISMES is presently carrying out. The main purposes of this program are: - to collect information on the effectiveness of different excitation methods; - to set up the most suitable recording and processing technique; - to compare the experimental results with the computed ones, in view of the validation of the adopted computing schemes. The structure has been excited by a mechanical vibrator delivering sinusoidal forces in a frequency range 2 to 20 cps, in conditions of empty, 1/3, 2/3 and completely full pools. The response, recorded by 36 velocity transducers was digitally processed by means of a Fourier Analyzer. Moreover, a number of Friuli earthquake aftershocks could be picked up, and the building response recorded in many points. (Auth.)

  7. Imaging the electrical resistivity structure at the vicinity of Duzce earthquake, Turkey

    International Nuclear Information System (INIS)

    Complete text of publication follows. Wideband (320 - 0.0005 Hz) magnetotellurics (MT) data were collected at 24 sites to form two parallel profiles on both sides of the 1999 Duezce earthquake's epicenter. All eight elements of the impedance tensor were utilized for deriving the three-dimensional (3D) electrical resistivity structure of the earthquake region and its vicinity. Data space modeling inversion technique which provides faster computation due to smaller number of parameters was used to construct a resistivity model for a 68 x 50 x 40 mesh (including 7 air layers) that extends to a depth of 50 km. The modeling results define a high conductivity region toward the east of the epicenter where earlier studies suggested asperities and wide aftershock distribution.

  8. Statistical models for seismic magnitude

    Science.gov (United States)

    Christoffersson, Anders

    1980-02-01

    In this paper some statistical models in connection with seismic magnitude are presented. Two main situations are treated. The first deals with the estimation of magnitude for an event, using a fixed network of stations and taking into account the detection and bias properties of the individual stations. The second treats the problem of estimating seismicity, and detection and bias properties of individual stations. The models are applied to analyze the magnitude bias effects for an earthquake aftershock sequence from Japan, as recorded by a hypothetical network of 15 stations. It is found that network magnitudes computed by the conventional averaging technique are considerably biased, and that a maximum likelihood approach using instantaneous noise-level estimates for non-detecting stations gives the most consistent magnitude estimates. Finally, the models are applied to evaluate the detection characteristics and associated seismicity as recorded by three VELA arrays: UBO (Uinta Basin), TFO (Tonto Forest) and WMO (Wichita Mountains).

  9. Effect of tidal triggering on seismicity in Taiwan revealed by the empirical mode decomposition method

    Directory of Open Access Journals (Sweden)

    H.-J. Chen

    2012-07-01

    Full Text Available The effect of tidal triggering on earthquake occurrence has been controversial for many years. This study considered earthquakes that occurred near Taiwan between 1973 and 2008. Because earthquake data are nonlinear and non-stationary, we applied the empirical mode decomposition (EMD method to analyze the temporal variations in the number of daily earthquakes to investigate the effect of tidal triggering. We compared the results obtained from the non-declustered catalog with those from two kinds of declustered catalogs and discuss the aftershock effect on the EMD-based analysis. We also investigated stacking the data based on in-phase phenomena of theoretical Earth tides with statistical significance tests. Our results show that the effects of tidal triggering, particularly the lunar tidal effect, can be extracted from the raw seismicity data using the approach proposed here. Our results suggest that the lunar tidal force is likely a factor in the triggering of earthquakes.

  10. Fukushima Dai Ichi, into the heart of hell

    International Nuclear Information System (INIS)

    After having mentioned various reports published by Japanese authorities and agencies, but also bodies from other countries to draw lessons from the Fukushima accident and also of course to highlight failures in the nuclear safety organisation in Japan, this article more particularly quotes and comments the content of the report of the hearing of the Fukushima power station's manager. It gives an insight into an engineering organisation plunged into the hell of a nuclear accident. It also gives a more subjective perception of the accident. It appears that the actual chronology of events as it has been established has not been fully perceived by the station's personnel as some data were not available. It gives a picture of an extreme situation made of a lethal level of radioactivity, unbearable temperature in buildings, destroyed and flooded premises, darkness, aftershocks and explosions of reactors

  11. Dynamic inversion of a Slab-push earthquake in Northern Chile

    Science.gov (United States)

    Ruiz, Sergio; Madariaga, Raul; Lancieri, Maria; Sobesiak, Monika

    2010-05-01

    We study the dynamic rupture propagation of a M 6.7 intraplate earthquake that occurred 16 December 2007, a month after a large thrust event of Tocopilla, Chile (M 7.7). The occurrence of a slab push event after a large subduction earthquake is well explained by Coulomb stress transfer models and crack dynamics. A dense seismic network, equipped with short period and accelerometers was deployed after the event of 14 November 2007 by the Task Force of GFZ Potsdam and the University of Chile in Santiago. This network was in place on December 16 providing an excellent data set for this earthquake. We used these data to make a detailed study of rupture processes. We localized the main event of December 16 and the aftershocks that occurred within 24 h of the main event. The main event was located at 43 km depth, while the aftershocks distribution covered a circular zone of 5 to 8 km of radius centred on the main shock epicentre. The aftershocks are distributed on an almost vertical plane that agrees with one of the fault planes of the mechanism (86° dip) and all the aftershock have the same mechanism as the main event. We used nearest accelerometric records in order to do dynamic inversion, two of these accelerometers were situated right above the hypocentre. We performed a non-linear dynamic inversion based on the neighbourhood algorithm (NA) and MonteCarlo methods with an L2 norm. The data was initially filtered in the 0.05-1 Hz. The velocity model was derived from previous work by GFZ. The earthquake was modelled using finite differences on a grid of variable size. Friction was modelled by the standard Ida slip weakening friction law. At each step of the inversion more than 32 full numerical simulations are carried in parallel. These simulations have been optimized in order to reduce the computer time to a minimum. The best models that result from dynamic inversion reduced the variance by more than 30 %, these models ruptured a relatively small zone of the fault

  12. Seismic evidence of conjugate normal faulting: The 1994 Devil Canyon earthquake sequence near Challis, Idaho

    International Nuclear Information System (INIS)

    In this study, the term ''conjugate'' refers to faults that occur in two intersecting sets and coordinated kinematically, with each set being distinctive in both orientation and sense of shear (Davis, 1984). Contemporaneous activity along the conjugate faults is defined as occurring within the time frame of the mainshock-aftershock sequence (three weeks for this sequence and generally less than one month in other observed cases). Detailed recordings of microearthquakes from a dense array of temporary analog seismic stations are analyzed. The focal mechanisms and hypocenter spatial and temporal characteristics are combined with geological information to assess the style, geometry, timing, kinematics, and mechanics of conjugate normal faulting. The characteristics of conjugate normal faulting observed in the Devil Canyon sequence are compared to other conjugate normal faulting sequences, and strike-slip and thrust conjugate sequences worldwide

  13. Background seismicity in Boso Peninsula, Japan: Long-term acceleration, and relationship with slow slip events

    Science.gov (United States)

    Reverso, T.; Marsan, D.; Helmstetter, A.; Enescu, B.

    2016-06-01

    Slow slip events (SSEs) in subduction zones can trigger earthquake swarms, especially at shallow depth. The monitoring of seismicity rates has therefore the potential to help detect and characterize SSEs, and transient changes in coupling. However, the relationship between seismicity rate and slow slip rate during a SSE is unknown and made complicated by aftershock triggering within the swarm. Here we propose to complement geodetic methods with an objective measure of the seismicity rate that is directly associated with changes in slip rate. We show that this measure, applied to known occurrences of SSEs in the Boso area, Japan, yields an estimate, albeit indirect, of their seismic moment, hence their slip rate. We finally prove that the background rate in Boso has been accelerating since 1990; this explains previous observations of the shortening of the recurrence time between SSEs in Boso, that clearly predate the 2011 Mw9.0 Tohoku-Oki earthquake.

  14. What hydrogen explosion brought about? Hydrodynamics load problem related with pressure suppression chamber of Mark-I reactor containment vessel

    International Nuclear Information System (INIS)

    The author insisted pressure increase of containment vessel and hydrogen explosions occurred at Fukushima Daiichi nuclear power plants would be caused or accelerated by earthquakes such as ignition source of hydrogen explosions might be sparks emitted by friction or drop of metal structure due to aftershocks. Mark-I reactor containment vessel had originally difficulties on structural integrity of suppression chamber caused by hydrodynamics load at loss of coolant accident (LOCA) and failures would be possible if earthquake loads were superposed. Probabilistic Safety Analysis (PSA) asserted no need of combination of LOCA and earthquake loads. Quantitative risk assessment method including PSA should be used to upgrade safety with considering tradeoff of multiple candidates. Low value of probability itself did not always assure safety in such as common mode failure of external events. 'Stress test' should be performed with reflecting truly scientific investigation of causes of accidents based on defense in depth design philosophy. (T. Tanaka)

  15. Study of the practical technology about geomagnetic abnormal phenomena tracking

    International Nuclear Information System (INIS)

    Complete text of publication follows. At present, geomagnetic monitoring networks mainly base on large-scale station -type observation in China, and a variety of mobile measurement obtain observational data through regular artificial measuring. For the emphasis earthquake zone densely monitoring abnormal information monitoring about observation stations etc, there is no corresponding model about flexible tracking. The geomagnetic abnormal phenomena tracking system mainly monitor aftershock identify the disturb sources and meet the equipment contrast observation needs. The research project bases on the existing fluxgate magnetometer technology, improving the equipment performance of field observing. We also mention the related technical system such as power supply, communication and monitoring, etc. The wireless data transmission and remote control of instrument is realized by using the GPRS and CDMA wireless network technology.

  16. A synthetic seismicity model for the Middle America Trench

    Science.gov (United States)

    Ward, Steven N.

    1991-01-01

    A novel iterative technique, based on the concept of fault segmentation and computed using 2D static dislocation theory, for building models of seismicity and fault interaction which are physically acceptable and geometrically and kinematically correct, is presented. The technique is applied in two steps to seismicity observed at the Middle America Trench. The first constructs generic models which randomly draw segment strengths and lengths from a 2D probability distribution. The second constructs predictive models in which segment lengths and strengths are adjusted to mimic the actual geography and timing of large historical earthquakes. Both types of models reproduce the statistics of seismicity over five units of magnitude and duplicate other aspects including foreshock and aftershock sequences, migration of foci, and the capacity to produce both characteristic and noncharacteristic earthquakes. Over a period of about 150 yr the complex interaction of fault segments and the nonlinear failure conditions conspire to transform an apparently deterministic model into a chaotic one.

  17. Influence length and space-time correlation between earthquakes

    CERN Document Server

    Tosi, P; Loreto, V; Pietronero, L; Tosi, Patrizia; Rubeis, Valerio De; Loreto, Vittorio; Pietronero, Luciano

    2004-01-01

    Short and long range interactions between earthquakes are attracting increasing interest. Scale invariant properties of seismicity in time, space and energy argue for the presence of complex triggering mechanisms where, like a cascade process, each event produces aftershocks. A definitive method to assess any connection between two earthquakes separated in time and distance does not exist. Here we propose a novel method of data analysis that, based on the space-time combined generalization of the correlation integral leads to a self-consistent visualization and analysis of both spatial and temporal correlations. When analyzing global seismicity we discovered a universal relation linking the spatial Influence Length of a given earthquake to the time elapsed from the event itself. Following an event, time correlations (i.e. causality effects) exist in a region that shrinks over time, suggesting a long-range dissipating stress transfer. A different process is acting in the short-range where events are randomly s...

  18. Fault mirrors in seismically active fault zones: A fossil of small earthquakes at shallow depths

    Science.gov (United States)

    Kuo, Li-Wei; Song, Sheng-Rong; Suppe, John; Yeh, En-Chao

    2016-03-01

    Fault mirrors (FMs) are naturally polished and glossy fault slip surfaces that can record seismic deformation at shallow depths. They are important for investigating the processes controlling dynamic fault slip. We characterize FMs in borehole samples from the hanging wall damage zone of the active Hsiaotungshi reverse fault, Taiwan. Here we report the first documented occurrence of the combination of silica gel and melt patches coating FMs, with the silica gel resembling those observed on experimentally formed FMs that were cataclastically generated. In addition, the melt patches, which are unambiguous indicators of coseismic slip, suggest that the natural FMs were produced at seismic rates, presumably resulting from flash heating at asperities on the slip surfaces. Since flash heating is efficient at small slip, we propose that these natural FMs represent fossils of small earthquakes, formed in either coseismic faulting and folding or aftershock deformation in the active Taiwan fold-and-thrust belt.

  19. Shock-wave compression of silica gel as a model material for comets

    Science.gov (United States)

    Arasuna, Akane; Okuno, Masayuki; Chen, Liliang; Mashimo, Tsutomu; Okudera, Hiroki; Mizukami, Tomoyuki; Arai, Shoji

    2016-03-01

    A shock-wave compression experiment using synthesized silica gel was investigated as a model for a comet impact event on the Earth's surface. The sample shocked at 20.7 GPa showed considerable structural changes, a release of water molecules, and the dehydration of silanol (Si-OH) that led to the formation of a new Si-O-Si network structure containing larger rings (e.g., six-membered ring of SiO4 tetrahedra). The high aftershock temperature at 20.7 GPa, which could be close to 800 °C, influenced the sample structure. However, some silanols, which were presumed to be the mutually hydrogen-bonded silanol group, remained at pressures >20.7 GPa. This type of silanol along with a small number of water molecules may remain even after shock compression at 30.9 GPa, although the intermediate structure of the sample recovered was similar to that of silica glass.

  20. Shock-wave compression of silica gel as a model material for comets

    Science.gov (United States)

    Arasuna, Akane; Okuno, Masayuki; Chen, Liliang; Mashimo, Tsutomu; Okudera, Hiroki; Mizukami, Tomoyuki; Arai, Shoji

    2016-07-01

    A shock-wave compression experiment using synthesized silica gel was investigated as a model for a comet impact event on the Earth's surface. The sample shocked at 20.7 GPa showed considerable structural changes, a release of water molecules, and the dehydration of silanol (Si-OH) that led to the formation of a new Si-O-Si network structure containing larger rings (e.g., six-membered ring of SiO4 tetrahedra). The high aftershock temperature at 20.7 GPa, which could be close to 800 °C, influenced the sample structure. However, some silanols, which were presumed to be the mutually hydrogen-bonded silanol group, remained at pressures >20.7 GPa. This type of silanol along with a small number of water molecules may remain even after shock compression at 30.9 GPa, although the intermediate structure of the sample recovered was similar to that of silica glass.

  1. An eyewitness account of the Bhuj earthquake

    Indian Academy of Sciences (India)

    M K Gupta

    2003-09-01

    The occurrence of a severe earthquake is a rare event with its effect localized in a limited region. There are no prior indications of its occurrence too; hence experiencing such an event is just a matter of chance, which the author had by virtue of his posting at Bhuj. This paper presents a detailed account of observations made in the wake of the Bhuj earthquake of January 26th 2001, describing physical and mental reactions during the earthquake, the post-quake scenario, the nature and cause of damage to buildings, the trend of aftershocks, various deformities, including ruptures and fissures on the surface of the earth, etc. which may be useful for a detailed study of the seismological activity in the region.

  2. A repeating source of infrasound from the Wells, Nevada earthquake sequence

    Energy Technology Data Exchange (ETDEWEB)

    Arrowsmith, Stephen J. [Los Alamos National Laboratory; Whitaker, Rod [Los Alamos National Laboratory; Randall, George [Los Alamos National Laboratory; Burlacu, Relu [UNIV OF UTAH

    2009-01-01

    The Wells, Nevada earthquake of February 21, 2008, generated a complex seismoacoustic wakefield. In addition to epicentral infrasound, the earthquake triggered a secondary source of infrasound, which was also initiated by subsequent aftershocks. By applying simple constraints on the propagation of seismic and infrasound waves, we show that the secondary source is an isolated peak that appears to efficiently generate infrasound through the interaction with seismic surface waves. By measuring peak-to-peak amplitudes of epicentral and secondary arrivals and correcting them for the effects of distance and winds, we find that epicentral arrivals lit with empirical relationships of Mutschlecner and Whitaker (2005) and Le Pichon et al. (2006), which form the basis for a proposed infrasound discriminant (Anderson et al., Pers. Comm.). In contrast, the secondary arrivals are much higher in amplitude, highlighting the importance of being able to separate epicentral and secondary arrivals for infrasonic event discrimination.

  3. On precursory ULF/ELF electromagnetic signatures for the Kobe earthquake on April 12, 2013

    Science.gov (United States)

    Schekotov, A.; Izutsu, J.; Hayakawa, M.

    2015-12-01

    After the 2011 Tohoku earthquake (EQ), there have been numerous aftershocks in the eastern and Pacific Ocean of Japan, but EQs are still rare in the western part of Japan. In this situation a relatively large (magnitude (M) ∼ 6) EQ happened on April 12 (UT), 2013 at a place close to the 1995 Kobe EQ (M ∼ 7), so we have tried to find whether there existed any electromagnetic precursors to this EQ. Two precursory signatures are detected: one is the depression of ULF (ultra-low-frequency, 0.01-0.02 Hz) geomagnetic variations on April 9, and the second is wideband ELF (extremely low frequency) electromagnetic radiation on April 11. These results for the 2013 Kobe EQ are compared with the corresponding results for the former 1995 Kobe EQ.

  4. Geomorphic and geologic controls of geohazards induced by Nepal's 2015 Gorkha earthquake.

    Science.gov (United States)

    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 the earthquakes' induced geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision-makers. We mapped 4312 coseismic and postseismic landslides. We also surveyed 491 glacier lakes for earthquake damage but found only nine landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions. PMID:26676355

  5. Self-organized intermittent plastic flow in bulk metallic glasses

    International Nuclear Information System (INIS)

    Under stress, bulk metallic glasses irreversibly deform through shear banding processes that manifest as serrated flow behavior. These serration events exhibit a shock-and-aftershock, earthquake-like behavior. Statistical analysis shows that the shear avalanches can self-organize to a critical state (SOC). In analogy to the smooth macroscopic-scale crystalline plasticity that arises from the spatio-temporal averages of disruptive earthquake-like events at the nanometer scale, shear avalanches in glassy metals are another model system that can be used to study SOC behavior. With our understanding of SOC behavior, we further demonstrate how to enhance the plasticity of glassy (brittle) materials. It is expected that the findings can be extended to other glassy or brittle materials.

  6. A Political Journey: Brecht’s Distancing Effect as Transforming Proposal of Russian Formalism’s Defamiliarization

    Directory of Open Access Journals (Sweden)

    Lucía Hellín Nistal

    2016-06-01

    Full Text Available In the two first decades of the 20th century, one of the main discoveries of the Russian formalism in their search of literariness is the defamiliarization. This concept place the purpose of literature on estrangement or on the impossibility of automatism. Two decades later, Bertolt Brecht go back to the concept to transform it into the distancing effect which impede the public’s identification with the performed fiction. In this article, we follow the evolution of the defamiliarization, positioned at the hearth of the discussion between formalism and socialist realism initiated on the USSR’s first years, experiencing an aftershock in the German Democratic Republic in the fifties. This itinerary demonstrate the close relation between the dialectic processes of politic and literary systems belonging to the dynamic reality described by Even-Zohar in his polysystem theory.

  7. The American real estate bubble - Trigger for the biggest financial crisis in the last century

    Directory of Open Access Journals (Sweden)

    Vasilka Gaber

    2014-02-01

    Full Text Available In the last years the world was faced with the worst economic crisis since the 1929-33 period which led to a significant decline in the global economy, tumultuous aftershocks of the financial and the real sector, significant shaking of confidence in financial institutions and the stability of the global financial system. This paper focuses on the crisis that began in the summer 2007 in U.S. when increased delinquency on the secondary market for mortgages created turbulence in the secondary market of securities covered by residential credits. The turbulence was then expanded to other markets securities, money market, financial institutions, with knock-on effects that are transmitted to all market segments, by involving the real sector. Under its global effect, this crisis was characterized as comprehensive, complex and global. This paper intends to detect the origin of this crisis and to analyze the potential government mistakes that led to the current world economic state.

  8. Temporal properties of seismicity and largest earthquakes in SE Carpathians

    Directory of Open Access Journals (Sweden)

    S. Byrdina

    2006-01-01

    Full Text Available In order to estimate the hazard rate distribution of the largest seismic events in Vrancea, South-Eastern Carpathians, we study temporal properties of historical and instrumental catalogues of seismicity. First, on the basis of Generalized Extreme Value theory we estimate the average return period of the largest events. Then, following Bak et al. (2002 and Corral (2005a, we study scaling properties of recurrence times between earthquakes in appropriate spatial volumes. We come to the conclusion that the seismicity is temporally clustered, and that the distribution of recurrence times is significantly different from a Poisson process even for times largely exceeding corresponding periods of foreshock and aftershock activity. Modeling the recurrence times by a gamma distributed variable, we finally estimate hazard rates with respect to the time elapsed from the last large earthquake.

  9. New insights into fault activation and stress transfer between en echelon thrusts: The 2012 Emilia, Northern Italy, earthquake sequence

    Science.gov (United States)

    Cheloni, D.; Giuliani, R.; D'Agostino, N.; Mattone, M.; Bonano, M.; Fornaro, G.; Lanari, R.; Reale, D.; Atzori, S.

    2016-06-01

    Here we present the results of the inversion of a new geodetic data set covering the 2012 Emilia seismic sequence and the following 1 year of postseismic deformation. Modeling of the geodetic data together with the use of a catalog of 3-D relocated aftershocks allows us to constrain the rupture geometries and the coseismic and postseismic slip distributions for the two main events (Mw 6.1 and 6.0) of the sequence and to explore how these thrust events have interacted with each other. Dislocation modeling reveals that the first event ruptured a slip patch located in the center of the Middle Ferrara thrust with up to 1 m of reverse slip. The modeling of the second event, located about 15 km to the southwest, indicates a main patch with up to 60 cm of slip initiated in the deeper and flatter portion of the Mirandola thrust and progressively propagated postseismically toward the top section of the rupture plane, where most of the aftershocks and afterslip occurred. Our results also indicate that between the two main events, a third thrust segment was activated releasing a pulse of aseismic slip equivalent to a Mw 5.8 event. Coulomb stress changes suggest that the aseismic event was likely triggered by the preceding main shock and that the aseismic slip event probably brought the second fault closer to failure. Our findings show significant correlations between static stress changes and seismicity and suggest that stress interaction between earthquakes plays a significant role among continental en echelon thrusts.

  10. Natural hazards and self-organized criticality

    International Nuclear Information System (INIS)

    Several natural hazards exhibit power-law behavior on their frequency-size distributions. Self-organized criticality has become a promising candidate that could offer a more in-depth understanding of the origin of temporal and spatial scaling in dissipative nonequilibrium systems. The outcomes of this thesis are presented in three scientific papers followed by a concluding summary and an appendix.In paper (A) we present a semi-phenomenological approach to explain the complex scaling behavior of the Drossel-Schwabl forest-fire model (DS-FFM) in two dimensions. We derive the scaling exponent solely from the scaling exponent of the clusters' accessible perimeter. Furthermore, the unusual transition to an exponential decay is explained both qualitatively and quantitatively. The exponential decay itself could be reproduced at least qualitatively. In paper (B) we extend the DS-FFM towards anthropogenic ignition factors. The main outcomes are an increase of the scaling exponent with decreasing lightning probability as well as a splitting of the partial frequency-size distributions of lightning induced and man made fires. Lightning is identified as the dominant mechanism in the regime of the largest fires. The results could be validated through an analysis of the Canadian Large Fire Database.In paper (C) we obtain an almost complete theory of the Olami-Feder-Christensen (OFC) model's complex spatio-temporal behavior. Synchronization pushes the system towards a critical state and generates the Gutenberg-Richter law. Desynchronization prevents the system from becoming overcritical and generates foreshocks and aftershocks. Our approach also provides a simple explanation of Omori's law. Beyond this, it explains the phenomena of foreshock migration and aftershock diffusion and the occurrence of large earthquakes without any foreshocks. A novel integer algorithm for the numerics is presented in appendix (A).(author)

  11. Historical intensity VIII earthquakes along the Rhone valley (Valais, Switzerland): primary and secondary effects

    International Nuclear Information System (INIS)

    In recent years the upper Rhone Valley has been one of the most intensively investigated regions by the Swiss Seismological Service. The high seismicity in the region encourages research in the seismological field and one main focus has been historical seismology. This report presents the state of the art of our historical investigations by giving an overview of the effects of four damaging earthquakes with intensity larger than VII, for which a fairly large number of documents could be found and analyzed. The overview includes the events of 1584 (Aigle, epicentral intensity VIII), 1755 (Brig, epicentral intensity VIII), 1855 (Visp, epicentral intensity VIII), and 1946 (Sierre, epicentral intensity VIII for the main shock and intensity VII for the largest aftershock). The paper focuses mainly on primary and secondary effects in the epicentral region, providing the key data and a general characterization of the event. Generally, primary effects such as the reaction of the population and impact on buildings took more focus in the past. Thus building damage is more frequently described in historic documents. However, we also found a number of sources describing secondary effects such as landslides, snow avalanches, and liquefaction. Since the sources may be useful, we include citations of these documents. The 1584 Aigle event, for example, produced exceptional movements in the Lake of Geneva, which can be explained by an expanded sub aquatic slide with resultant tsunami and seiche. The strongest of the aftershocks of the 1584 event triggered a destructive landslide covering the villages Corbeyrier and Yvorne, Vaud. All macroseismic data on the discussed events are accessible through the web page of the Swiss Seismological Service (http://www.seismo.ethz.ch). (authors)

  12. An Overview of the Study on Stress Magnitude

    Institute of Scientific and Technical Information of China (English)

    Sheng Shuzhong; Wan Yongge

    2009-01-01

    Crustal stress field holds an important position in geodynamics research, such as in plate motion simulations, uplift of the Qinghai-Xizang (Tibet) Plateau and earthquake preparation and occurrence. However, most of the crustal stress studies emphasize particularly on the determination of stress direction, with little study being done on stress magnitude at present. After reviewing ideas on a stress magnitude study from geological, geophysical and various other aspects, a method to estimate the stress magnitude in the source region according to the deflection of stress direction before and after large earthquakes and the stress drop tensor of earthquake rupture has been developed. The proposed method can also be supplemented by the average apparent stress before and after large earthquakes. The stress direction deflection before and after large earthquakes can be inverted by massive focal mechanisms of foreshocks and aftershocks and the stress drop field generated by the seismic source can be calculated by the detailed distribution of the earthquake's rupture. The mathematical relationship can then be constructed between the stress drop field, where its magnitude and direction are known and the stress tensor before and after large earthquakes, where its direction is known but magnitude is unknown, thereby obtaining the stress magnitude. The average apparent stress before and after large earthquakes can be obtained by using the catalog of broadband radiated energy and seismic moment tensor of foreshocks and aftershocks and the different responses to stress drops. This relationship leads to another estimation of stress magnitude before a large earthquake. The stress magnitude and its error are constrained by combining the two methods, which provide new constraints for the geodyuamics study.

  13. Examining Communities at Risk: Physical and Socioeconomic Impacts of an Earthquake Scenario on the Hayward Fault (The HayWired Scenario)

    Science.gov (United States)

    Dinitz, L.; Wein, A. M.; Johnson, L. A.; Jones, J. L.

    2015-12-01

    This research led by the U.S. Geological Survey aims to inform and stimulate the development of plans and policies in disaster management and hazard mitigation that will help improve the capacity of residents, businesses and communities to rebound from disasters. As was evidenced in the 1994 Northridge earthquake, "ghost towns" emerged in neighborhoods with high concentrations of damaged rental housing. Also, rental properties that served predominantly lower income households had more difficulty financing repairs which led to blight and other long-term community recovery challenges. Our approach is to develop a framework for identifying and spatially analyzing communities at risk of long-term displacement and recovery challenges for an earthquake scenario. The HayWired scenario postulates a M7.05 earthquake on the Hayward Fault in the San Francisco Bay Area with surface fault rupture, liquefaction, landslides, and fires, as well as subsequent aftershocks. The analytical framework relies on the literature and prior disaster experience to identify and systematically combine physical and socioeconomic impacts of the earthquake sequence with pre-existing socioeconomic conditions to identify areas where housing and building damage, lifeline service disruption, and socioeconomic challenges intersect and can potentially lead to long-term displacements of people, businesses, and jobs. Hazus analyses estimate $46 billion in building damage from the HayWired main shock, which increases by 10-25% due to aftershocks. Heavy damage to large apartment buildings exceeds many other housing types, and preliminary analyses identify neighborhoods where these damage concentrations also intersect with concentrations of low income households. Also, in some counties, the estimated population displaced from severely damaged housing far exceeds the number of vacant housing units, which means residents may be forced to move well away from former neighborhoods and even outside the region

  14. Mechanics of Multifault Earthquake Ruptures

    Science.gov (United States)

    Fletcher, J. M.; Oskin, M. E.; Teran, O.

    2015-12-01

    The 2010 El Mayor-Cucapah earthquake of magnitude Mw 7.2 produced the most complex rupture ever documented on the Pacific-North American plate margin, and the network of high- and low-angle faults activated in the event record systematic changes in kinematics with fault orientation. Individual faults have a broad and continuous spectrum of slip sense ranging from endmember dextral strike slip to normal slip, and even faults with thrust sense of dip slip were commonly observed in the aftershock sequence. Patterns of coseismic slip are consistent with three-dimensional constrictional strain and show that integrated transtensional shearing can be accommodated in a single earthquake. Stress inversions of coseismic surface rupture and aftershock focal mechanisms define two coaxial, but permuted stress states. The maximum (σ1) and intermediate (σ2) principal stresses are close in magnitude, but flip orientations due to topography- and density-controlled gradients in lithostatic load along the length of the rupture. Although most large earthquakes throughout the world activate slip on multiple faults, the mechanical conditions of their genesis remain poorly understood. Our work attempts to answer several key questions. 1) Why do complex fault systems exist? They must do something that simple, optimally-oriented fault systems cannot because the two types of faults are commonly located in close proximity. 2) How are faults with diverse orientations and slip senses prepared throughout the interseismic period to fail spontaneously together in a single earthquake? 3) Can a single stress state produce multi-fault failure? 4) Are variations in pore pressure, friction and cohesion required to produce simultaneous rupture? 5) How is the fabric of surface rupture affected by variations in orientation, kinematics, total geologic slip and fault zone architecture?

  15. H/V ratio in Athens and the strong motion at the Ano Liosia site during the 1999 Athens earthquake

    Science.gov (United States)

    Serpetsidaki, A.; Tselentis, G.-A.; Zahradnik, J.

    2003-04-01

    The damaging 1999 Athens earthquake of Mw=5.9 occurred at about 20km from the city center. The intensity distribution in the capital, ranging from V to IX, was quite irregular due to combination of the source, path and site effects. The 30-stations temporary network of the University of Patras, installed in the area of Attica for 50 days, recorded a significant part of the aftershock sequence. The aftershocks not only delineated the mainshock fault plane, but they also provided important site classification. The Horizontal-to-Vertical spectral ratio method was applied, and the most significant amplification (H/V exceeding 4 in the frequency range 1-4Hz) was found at the Ano Liosia site, belonging to the most heavily damaged zones with intensity IX. The site is situated in a shallow basin, whose surface extent is about 4x4 km, and the maximum depth is of about 150 m. Based on geological and geophysical data (Vp, Vs, Q) measured at the site, the numerical modeling of the seismic site response was carried out. The finite-differences technique was used for a 2D modeling, and significant edge effects were revealed, e.g. the amplification by a factor of 3, with respect to the outcropping bedrock. The 1D effects of the sediment layering, modeled by the matrix technique, would produce much weaker amplification, and simpler time history of the response. No recording of the mainshock is available from Ano Liosia. Nevertheless, based on the finite-extent source model validated by the existing strong motion records in Athens, we assume that the bedrock motion in Ano Liosia had its PGA ranging from 0.2 to 0.3 g, resulting from the relatively small epicentral distance (~ 10 km) and the forward source directivity (Serpetsidaki et al., session SM10). When combined with the above discussed site effect, the PGA values in Ano Liosia might locally exceed 0.6g.

  16. Seismological studies carried out by the CEA in connection with the safety of nuclear sites

    International Nuclear Information System (INIS)

    In order to evaluate the seismic risk at nuclear sites, the Department of Nuclear Safety of the French Atomic Energy Commission (CEA) has been conducting a programme of seismological studies for several years past. This programme is aimed at acquiring a better knowledge of seismic phenomena, in particular the spectral distribution of the energy of earthquakes, considered to be the only correct approach to the problem of earthquake protection, as well as a better knowledge of the seismic activity of the areas surrounding nuclear sites. The authors propose defining the design spectrum of the site on the basis of the probable energy at the source, the distance from the epicentre and the transfer function of the geological formations. The need - for the purpose of defining this spectrum - to acquire data on the characteristics of French earthquakes and on regional seismicity led the Department of Nuclear Safety to set up a network of seismic stations. It now has an observatory at the Cadarache Nuclear Research Centre and mobile stations with automatic magnetic recording for studying aftershock sequences and the activity of faults in the vicinity of nuclear sites, and for making the measurements necessary to calculate the transfer functions. With this equipment it was possible to record six aftershocks of the Oleron earthquake on 7 September 1972 close to the epicentre, and to calculate the spectra therefrom. The latter contained a lot of high frequencies, which is in agreement with the data obtained from other sources for earthquakes of low energy. The synthetic spectra calculated on the basis of one magnitude and one distance are in good agreement with the spectra obtained experimentally

  17. Linking megathrust earthquakes to faulting and mineral vein formation in a fossil accretionary complex

    Science.gov (United States)

    Dielforder, Armin; Herwegh, Marco; Berger, Alfons

    2015-04-01

    Geodetic and seismological data recorded at active subduction zones suggest that megathrust earthquakes induce transient stress changes in the upper plate, which shift the wedge into an unstable state and trigger >Mw 6 aftershocks. These stress changes have, however, never been linked to geological structures that are preserved within fossil accretionary wedges, although plate interface of palaeo-subduction zones has been studied. The conditions under which accretionary wedges fail have therefore remained controversial. Here we show that faulting and associated vein formation in the palaeo-accretionary complex of the European Alps record stress changes generated by the subduction earthquake cycle. Our data integrate wedge deformation over millions of years but still demonstrate the dominance of specific fracture modes at different depths within the wedge. We trace the subduction of sediments by means of the 87Sr/86Sr isotope-systematics of mineral veins, which became more radiogenic at deeper levels. By combining our field observations and geochemical data with a dynamic Mohr-Coulomb wedge analysis, we show that early veins were formed in shallow levels by bedding-parallel shear during coseismic compression of the outer wedge. In contrast, later veins originated at deeper levels during normal faulting and extensional fracturing recording coseismic extension of the inner wedge. Our study shows how mineral veins can be used to reveal the dynamics of outer and inner wedges, which response in opposite ways to megathrust earthquakes by compressional and extensional faulting, respectively. We emphasise, that coseismic fracturing implicates an increase in permeability within the hanging wall of megathrusts. Understanding how fractures are generated throughout the subduction earthquake cycle is therefore essential to better contstrain the nature of postseismic fluid flow and to assess the seismic hazard of hydraulically driven aftershocks.

  18. Ground motion amplification at Hotel Montana during the M7.0 2010 Haiti Earthquake: Topography Effects?

    Science.gov (United States)

    Assimaki, D.; Jeong, S.

    2011-12-01

    Unusually severe structural damage was reported during the 2010 M7.0 Haiti earthquake in the vicinity of Hotel Montana, located on top of a ridge in the district of Pétionville. Prompted by the observations, USGS seismic stations were deployed, and aftershock recordings indicated ground motion amplification on the top of the hill compared to adjacent stations on reference site conditions. The presence of topographic relief has been shown to significantly aggravate the consequences of strong ground motion during past events, and topographic amplification was therefore brought forward to justify the observations. We here investigate the role of ground surface geometry in the recorded ground motions and corresponding damage concentration atop the foothill ridge of Hotel Montana by first conducting site-specific simulations that integrate Digital Elevation Maps (DEM) and shear wave velocity profiles collected at the site. Our analyses show that neither topography nor site amplification predictions alone sufficiently explain the ground motion amplification at the site estimated via aftershock recordings. We next conduct simulations of the foothill ridge response with soil layering, and qualitatively demonstrate that the recorded amplification can be attributed to coupling of site and topography effects. This effect, referred to as topography-modified site amplification, describes seismic waves trapped in the soft soil layers of the near surface and simultaneously subjected to sediment-induced reverberations as well as diffraction and scattering. Parametric investigations of the topography-soil amplification coupling effects are then conducted, and results show that when accounting for a soil-bedrock interface at 100m depth, predictions are in excellent quantitative agreement with the observed motion.

  19. Kinematic rupture process of the 2014 Chile Mw 8.1 earthquake constrained by strong-motion, GPS static offsets and teleseismic data

    Science.gov (United States)

    Liu, Chengli; Zheng, Yong; Wang, Rongjiang; Xiong, Xiong

    2015-08-01

    On 2014 April 1, a magnitude Mw 8.1 interplate thrust earthquake ruptured a densely instrumented region of Iquique seismic gap in northern Chile. The abundant data sets near and around the rupture zone provide a unique opportunity to study the detailed source process of this megathrust earthquake. We retrieved the spatial and temporal distributions of slip during the main shock and one strong aftershock through a joint inversion of teleseismic records, GPS offsets and strong motion data. The main shock rupture initiated at a focal depth of about 25 km and propagated around the hypocentre. The peak slip amplitude in the model is ˜6.5 m, located in the southeast of the hypocentre. The major slip patch is located around the hypocentre, spanning ˜150 km along dip and ˜160 km along strike. The associated static stress drop is ˜3 MPa. Most of the seismic moment was released within 150 s. The total seismic moment of our preferred model is 1.72 × 1021 N m, equivalent to Mw 8.1. For the strong aftershock on 2014 April 3, the slip mainly occurred in a relatively compact area, and the major slip area surrounded the hypocentre with the peak amplitude of ˜2.5 m. There is a secondary slip patch located downdip from the hypocentre with the peak slip of ˜2.1 m. The total seismic moment is about 3.9 × 1020 N m, equivalent to Mw 7.7. Between the rupture areas of the main shock and the 2007 November 14 Mw 7.7 Antofagasta, Chile earthquake, there is an earthquake vacant zone with a total length of about 150 km. Historically, if there is no big earthquake or obvious aseismic creep occurring in this area, it has a great potential of generating strong earthquakes with magnitude larger than Mw 7.0 in the future.

  20. Fault interactions and triggering during the 10 January 2012 Mw 7.2 Sumatra earthquake

    Science.gov (United States)

    Fan, Wenyuan; Shearer, Peter M.

    2016-03-01

    The 10 January 2012 Mw 7.2 Sumatra earthquake in the Wharton basin occurred 3 months before the great Mw 8.6 and Mw 8.2 earthquakes in the same region, which had complex ruptures and are the largest strike-slip earthquakes ever recorded. Teleseismic P wave back projection of the Mw 7.2 earthquake images a unilateral rupture lasting ˜40 s without observable frequency dependency (low frequency, 0.05-0.3 Hz, high frequency, 0.3-1 Hz). In addition to radiation bursts during the Mw 7.2 main shock, coherent energy releases from 50 to 75 s and from 100 to 125 s are observed about 143 km northeast of the main shock rupture and landward of the trench. Analysis of globally recorded P waves, in both 0.02-0.05 Hz velocity records and 1-5 Hz stacked envelope functions, confirms the presence of coherent sources during the time windows. The observed energy bursts are likely to be large early aftershocks occurring on or near the subduction interface. Both dynamic and static triggering could have induced these early aftershocks, as they initiated after the surface wave passed by, and the Coulomb stress perturbations from the Mw 7.2 main shock promote earthquakes in the observed locations. The earthquake sequence is a clear example of a seaward-intraplate strike-slip earthquake triggering landward-intraplate earthquakes in the same region, in contrast to previously reported normal-reverse or reverse-normal interactions at subduction zones.