Estimation of pore pressure from seismic velocities

International Nuclear Information System (INIS)

Perez, Zayra; Ojeda, German Y; Mateus, Darwin

2009-01-01

On pore pressure calculations it is common to obtain a profile in a well bore, which is then extrapolated toward offset wells. This practice might generate mistakes on pore pressure measurements, since geological conditions may change from a well bore to another, even into the same basin. Therefore, it is important to use other tools which allow engineers not only to detect and estimate in an indirect way overpressure zones, but also to keep a lateral tracking of possible changes that may affect those values in the different formations. Taking into account this situation, we applied a methodology that estimates formation pressure from 3D seismic velocities by using the Eaton method. First, we estimated formation pore pressure; then, we identified possible overpressure zones. Finally, those results obtained from seismic information were analyzed involving well logs and pore pressure tests, in order to compare real data with prediction based on seismic information from the Colombian foothill.

Influence of apparent wave velocity on seismic performance of a super-long-span triple-tower suspension bridge

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Hao Wang

2015-06-01

Full Text Available As one of the main characteristics of seismic waves, apparent wave velocity has great influence on seismic responses of long-span suspension bridges. Understanding these influences is important for seismic design. In this article, the critical issues concerning the traveling wave effect analysis are first reviewed. Taizhou Bridge, the longest triple-tower suspension bridge in the world, is then taken as an example for this investigation. A three-dimensional finite element model of the bridge is established in ABAQUS, and the LANCZOS eigenvalue solver is employed to calculate the structural dynamic characteristics. Traveling wave effect on seismic responses of these long-span triple-tower suspension bridges is investigated. Envelopes of seismic shear force and moment in the longitudinal direction along the three towers, relative displacements between the towers and the girder, and reaction forces at the bottoms of the three towers under different apparent wave velocities are calculated and presented in detail. The results show that the effect of apparent wave velocity on the seismic responses of triple-tower suspension bridge fluctuates when the velocity is lower than 2000 m/s, and the effects turn stable when the velocity becomes larger. In addition, the effects of traveling wave are closely related to spectral characteristics and propagation direction of the seismic wave, and seismic responses of components closer to the source are relatively larger. Therefore, reliable estimation of the seismic input and apparent wave velocity according to the characteristics of the bridge site are significant for accurate prediction of seismic responses. This study provides critical reference for seismic analysis and design of long-span triple-tower suspension bridges.

Precursory changes in seismic velocity for the spectrum of earthquake failure modes

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Scuderi, M.M.; Marone, C.; Tinti, E.; Di Stefano, G.; Collettini, C.

2016-01-01

Temporal changes in seismic velocity during the earthquake cycle have the potential to illuminate physical processes associated with fault weakening and connections between the range of fault slip behaviors including slow earthquakes, tremor and low frequency earthquakes1. Laboratory and theoretical studies predict changes in seismic velocity prior to earthquake failure2, however tectonic faults fail in a spectrum of modes and little is known about precursors for those modes3. Here we show that precursory changes of wave speed occur in laboratory faults for the complete spectrum of failure modes observed for tectonic faults. We systematically altered the stiffness of the loading system to reproduce the transition from slow to fast stick-slip and monitored ultrasonic wave speed during frictional sliding. We find systematic variations of elastic properties during the seismic cycle for both slow and fast earthquakes indicating similar physical mechanisms during rupture nucleation. Our data show that accelerated fault creep causes reduction of seismic velocity and elastic moduli during the preparatory phase preceding failure, which suggests that real time monitoring of active faults may be a means to detect earthquake precursors. PMID:27597879

Relative Seismic Velocity Variations Correlate with Deformation at Kīlauea Volcano.

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Donaldson, C.; Caudron, C.; Green, R. G.; White, R. S.

2016-12-01

Passive interferometry using ambient seismic noise is an appealing monitoring tool at volcanoes. The continuous nature of seismic noise provides better temporal resolution than earthquake interferometry and ambient noise may be sensitive to changes at depths that do not deform the volcano surface. Despite this, to our knowledge, no studies have yet comprehensively compared deformation and velocity at a volcano over a significant length of time. We use a volcanic tremor source (approximately 0.3 - 1.0 Hz) at Kīlauea volcano as a source for interferometry to measure relative velocity changes with time. The tremor source that dominates the cross correlations is located under the Halema'uma'u caldera at Kīlauea summit. By cross-correlating the vertical component of day-long seismic records between 200 pairs of stations, we extract coherent and temporally consistent coda wave signals with time lags of up to 70 seconds. Our resulting time series of relative velocity shows a remarkable correlation with the tilt record measured at Kīlauea summit. Kīlauea summit is continually inflating and deflating as the level of the lava lake rises and falls. During these deflation-inflation (DI) events the tilt increases (inflation), as the velocity increases, on the scale of days to weeks. In contrast, we also detect a longer-term velocity decrease between 2011-2015 as the volcano slowly inflates. We suggest that variations in velocity result from opening and closing cracks and pores due to changes in magma pressurization. Early modeling results indicate that pressurizing magma reservoirs at different depths can result in opposite changes in compression/extension at the surface. The consistent correlation of relative velocity and deformation in this study provides an opportunity to better understand the mechanism causing velocity changes, which currently limits the scope of passive interferometry as a monitoring tool.

Relating seismicity to the velocity structure of the San Andreas Fault near Parkfield, CA

Science.gov (United States)

Lippoldt, Rachel; Porritt, Robert W.; Sammis, Charles G.

2017-06-01

The central section of the San Andreas Fault (SAF) displays a range of seismic phenomena including normal earthquakes, low-frequency earthquakes (LFE), repeating microearthquakes (REQ) and aseismic creep. Although many lines of evidence suggest that LFEs are tied to the presence of fluids, their geological setting is still poorly understood. Here, we map the seismic velocity structures associated with LFEs beneath the central SAF using surface wave tomography from ambient seismic noise to provide constraints on the physical conditions that control LFE occurrence. Fault perpendicular sections show that the SAF, as revealed by lateral contrasts in relative velocities, is contiguous to depths of 50 km and appears to be relatively localized at depths between about 15 and 30 km. This is consistent with the hypothesis that LFEs are shear-slip events on a deep extension of the SAF. We find that along strike variations in seismic behaviour correspond to changes in the seismic structure, which support proposed connections between fluids and seismicity. LFEs and REQs occur within low-velocity structures, suggesting that the presence of fluids, weaker minerals, or hydrous phase minerals may play an important role in the generation of slow-slip phenomena.

Imaging of 3-D seismic velocity structure of Southern Sumatra region using double difference tomographic method

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Lestari, Titik, E-mail: t2klestari@gmail.com [Meteorological Climatological and Geophysical Agency (MCGA), Jalan Angkasa I No.2 Kemayoran, Jakarta Pusat, 10720 (Indonesia); Faculty of Earth Science and Technology, Bandung Institute of Technology, Jalan Ganesa No.10, Bandung 40132 (Indonesia); Nugraha, Andri Dian, E-mail: nugraha@gf.itb.ac.id [Global Geophysical Research Group, Faculty of Mining and Petroleum Engineering, Bandung Institute of Technology, Jalan Ganesa 10 Bandung 40132 (Indonesia)

2015-04-24

Southern Sumatra region has a high level of seismicity due to the influence of the subduction system, Sumatra fault, Mentawai fault and stretching zone activities. The seismic activities of Southern Sumatra region are recorded by Meteorological Climatological and Geophysical Agency (MCGA’s) Seismograph network. In this study, we used earthquake data catalog compiled by MCGA for 3013 events from 10 seismic stations around Southern Sumatra region for time periods of April 2009 – April 2014 in order to invert for the 3-D seismic velocities structure (Vp, Vs, and Vp/Vs ratio). We applied double-difference seismic tomography method (tomoDD) to determine Vp, Vs and Vp/Vs ratio with hypocenter adjustment. For the inversion procedure, we started from the initial 1-D seismic velocity model of AK135 and constant Vp/Vs of 1.73. The synthetic travel time from source to receiver was calculated using ray pseudo-bending technique, while the main tomographic inversion was applied using LSQR method. The resolution model was evaluated using checkerboard test and Derivative Weigh Sum (DWS). Our preliminary results show low Vp and Vs anomalies region along Bukit Barisan which is may be associated with weak zone of Sumatran fault and migration of partial melted material. Low velocity anomalies at 30-50 km depth in the fore arc region may indicated the hydrous material circulation because the slab dehydration. We detected low seismic seismicity in the fore arc region that may be indicated as seismic gap. It is coincides contact zone of high and low velocity anomalies. And two large earthquakes (Jambi and Mentawai) also occurred at the contact of contrast velocity.

Shear wave velocity versus quality factor: results from seismic noise recordings

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Boxberger, Tobias; Pilz, Marco; Parolai, Stefano

2017-08-01

The assessment of the shear wave velocity (vs) and shear wave quality factor (Qs) for the shallow structure below a site is necessary to characterize its site response. In the past, methods based on the analysis of seismic noise have been shown to be very efficient for providing a sufficiently accurate estimation of the vs versus depth at reasonable costs for engineering seismology purposes. In addition, a slight modification of the same method has proved to be able to provide realistic Qs versus depth estimates. In this study, data sets of seismic noise recorded by microarrays of seismic stations in different geological environments of Europe and Central Asia are used to calculate both vs and Qs versus depth profiles. Analogous to the generally adopted approach in seismic hazard assessment for mapping the average shear wave velocity in the uppermost 30 m (vs30) as a proxy of the site response, this approach was also applied to the quality factor within the uppermost 30 m (Qs30). A slightly inverse correlation between both parameters is found based on a methodological consistent determination for different sites. Consequently, a combined assessment of vs and Qs by seismic noise analysis has the potential to provide a more comprehensive description of the geological structure below a site.

Seismic velocity structure in the lower crust beneath the seismic belt in the San-in district, Southwest Japan

Science.gov (United States)

Tsuda, H.; Iio, Y.; Shibutani, T.

2017-12-01

In the San-in district in Southwest Japan, a linear distribution of the epicenters of microearthquakes is seen along the coast of the Japan Sea (Fig. 1). The linear distribution is known as the seismic belt in the San-in district. Large earthquakes also occurred in the seismic belt. What localizes the earthquake distribution in the San-in district which is located far from the plate boundary? We thought that the model proposed by Iio et al. (2002, 2004) could answer this question. The model is as follows. Viscosity is low in a part of the lower crust, which is called `weak zone'. Stress and strain are concentrated in the upper crust right above the weak zone, due to concentrated deformation in the weak zone, and thus earthquakes occur there. To verify whether the weak zone exists in the lower crust beneath the seismic belt, we estimated the seismic velocity structure there by travel-time tomography. We used the tomography program, FMTOMO (Rawlinson et al., 2006). For the model space, we set the latitude range of 33°-36°N, the longitude range of 131°-136°E (Fig. 1), and the depth range of 0-81 km. The grid intervals are 0.1°×0.1°×7 km. We used arrival times picked by Japan Meteorological Agency (JMA) for earthquakes that occurred in the study area. In addition, we used arrival times manually picked at stations in and around the San-in district for earthquakes that occurred within the Philippine Sea Slab, because they are not included in the JMA data. Since the seismic waves from those earthquakes to the stations in the San-in district pass through the lower crust beneath the San-in district, we expect that these data can improve the resolution there. We revealed that low velocity anomalies exist in the lower crust beneath the seismic belt (Fig. 1). It is inferred that the region of low velocity anomalies is characterized by low viscosity, since velocities of rocks decrease with temperature and/or water content. Therefore, the results of this study support

Seismic site-response characterization of high-velocity sites using advanced geophysical techniques: application to the NAGRA-Net

Science.gov (United States)

Poggi, V.; Burjanek, J.; Michel, C.; Fäh, D.

2017-08-01

The Swiss Seismological Service (SED) has recently finalised the installation of ten new seismological broadband stations in northern Switzerland. The project was led in cooperation with the National Cooperative for the Disposal of Radioactive Waste (Nagra) and Swissnuclear to monitor micro seismicity at potential locations of nuclear-waste repositories. To further improve the quality and usability of the seismic recordings, an extensive characterization of the sites surrounding the installation area was performed following a standardised investigation protocol. State-of-the-art geophysical techniques have been used, including advanced active and passive seismic methods. The results of all analyses converged to the definition of a set of best-representative 1-D velocity profiles for each site, which are the input for the computation of engineering soil proxies (traveltime averaged velocity and quarter-wavelength parameters) and numerical amplification models. Computed site response is then validated through comparison with empirical site amplification, which is currently available for any station connected to the Swiss seismic networks. With the goal of a high-sensitivity network, most of the NAGRA stations have been installed on stiff-soil sites of rather high seismic velocity. Seismic characterization of such sites has always been considered challenging, due to lack of relevant velocity contrast and the large wavelengths required to investigate the frequency range of engineering interest. We describe how ambient vibration techniques can successfully be applied in these particular conditions, providing practical recommendations for best practice in seismic site characterization of high-velocity sites.

Comparison of shear-wave velocity measurements by crosshole, downhole and seismic cone penetration test methods

Energy Technology Data Exchange (ETDEWEB)

Suthaker, N.; Tweedie, R. [Thurber Engineering Ltd., Edmonton, AB (Canada)

2009-07-01

Shear wave velocity measurements are an integral part of geotechnical studies for major structures and are an important tool in their design for site specific conditions such as site-specific earthquake response. This paper reported on a study in which shear wave velocities were measured at a proposed petrochemical plant site near Edmonton, Alberta. The proposed site is underlain by lacustrine clay, glacial till and upper Cretaceous clay shale and sandstone bedrock. The most commonly used methods for determining shear wave velocity include crosshole seismic tests, downhole seismic tests, and seismic cone penetration tests (SCPT). This paper presented the results of all 3 methods used in this study and provided a comparison of the various test methods and their limitations. The crosshole test results demonstrated a common trend of increasing shear wave velocity with depth to about 15 m, below which the velocities remained relatively constant. An anomaly was noted at one site, where the shear wave velocity was reduced at a zone corresponding to clay till containing stiff high plastic clay layers. The field study demonstrated that reasonable agreement in shear wave velocity measurements can be made using crosshole, downhole and seismic tests in the same soil conditions. The National Building Code states that the shear wave velocity is the fundamental method for determining site classification, thus emphasizing the importance of obtaining shear wave velocity measurements for site classification. It was concluded that an SCPT program can be incorporated into the field program without much increase in cost and can be supplemented by downhole or crosshole techniques. 5 refs., 2 tabs., 10 figs.

Seismic Velocity Variation and Evolution of the Upper Oceanic Crust across the Mid-Atlantic Ridge at 1.3°S

Science.gov (United States)

Jian, H.; Singh, S. C.

2017-12-01

The oceanic crust that covers >70% of the solid earth is formed at mid-ocean ridges, but get modified as it ages. Understanding the evolution of oceanic crust requires investigations of crustal structures that extend from zero-age on the ridge axis to old crust. In this study, we analyze a part of a 2000-km-long seismic transect that crosses the Mid-Atlantic Ridge segment at 1.3°S, south of the Chain transform fault. The seismic data were acquired using a 12-km-long multi-sensor streamer and dense air-gun shots. Using a combination of downward continuation and seismic tomography methods, we have derived a high-resolution upper crustal velocity structure down to 2-2.5 km depth below the seafloor, from the ridge axis to 3.5 Ma on both sides of the ridge axis. The results demonstrate that velocities increase at all depths in the upper crust as the crust ages, suggesting that hydrothermal precipitations seal the upper crustal pore spaces. This effect is most significant in layer 2A, causing a velocity increase of 0.5-1 km/s after 1-1.5 Ma, beyond which the velocity increase is very small. Furthermore, the results exhibit a significant decrease in both the frequency and amplitude of the low-velocity anomalies associated with faults beyond 1-1.5 Ma, when faults become inactive, suggesting a linkage between the sealing of fault space and the extinction of hydrothermal activity. Besides, the off-axis velocities are systematically higher on the eastern side of the ridge axis compared to on the western side, suggesting that a higher hydrothermal activity should exist on the outside-corner ridge flank than on the inside-corner flank. While the tomography results shown here cover 0-3.5 Ma crust, the ongoing research will further extend the study area to older crust and also incorporating pre-stack migration and full waveform inversion methods to improve the seismic structure.

Seismic velocity structure of the crust and shallow mantle of the Central and Eastern United States by seismic surface wave imaging

Science.gov (United States)

Pollitz, Fred; Mooney, Walter D.

2016-01-01

Seismic surface waves from the Transportable Array of EarthScope's USArray are used to estimate phase velocity structure of 18 to 125 s Rayleigh waves, then inverted to obtain three-dimensional crust and upper mantle structure of the Central and Eastern United States (CEUS) down to ∼200 km. The obtained lithosphere structure confirms previously imaged CEUS features, e.g., the low seismic-velocity signature of the Cambrian Reelfoot Rift and the very low velocity at >150 km depth below an Eocene volcanic center in northwestern Virginia. New features include high-velocity mantle stretching from the Archean Superior Craton well into the Proterozoic terranes and deep low-velocity zones in central Texas (associated with the late Cretaceous Travis and Uvalde volcanic fields) and beneath the South Georgia Rift (which contains Jurassic basalts). Hot spot tracks may be associated with several imaged low-velocity zones, particularly those close to the former rifted Laurentia margin.

The thin section rock physics: Modeling and measurement of seismic wave velocity on the slice of carbonates

Energy Technology Data Exchange (ETDEWEB)

Wardaya, P. D., E-mail: pongga.wardaya@utp.edu.my; Noh, K. A. B. M., E-mail: pongga.wardaya@utp.edu.my; Yusoff, W. I. B. W., E-mail: pongga.wardaya@utp.edu.my [Petroleum Geosciences Department, Universiti Teknologi PETRONAS, Tronoh, Perak, 31750 (Malaysia); Ridha, S. [Petroleum Engineering Department, Universiti Teknologi PETRONAS, Tronoh, Perak, 31750 (Malaysia); Nurhandoko, B. E. B. [Wave Inversion and Subsurface Fluid Imaging Research Laboratory (WISFIR), Dept. of Physics, Institute of Technology Bandung, Bandung, Indonesia and Rock Fluid Imaging Lab, Bandung (Indonesia)

2014-09-25

This paper discusses a new approach for investigating the seismic wave velocity of rock, specifically carbonates, as affected by their pore structures. While the conventional routine of seismic velocity measurement highly depends on the extensive laboratory experiment, the proposed approach utilizes the digital rock physics view which lies on the numerical experiment. Thus, instead of using core sample, we use the thin section image of carbonate rock to measure the effective seismic wave velocity when travelling on it. In the numerical experiment, thin section images act as the medium on which wave propagation will be simulated. For the modeling, an advanced technique based on artificial neural network was employed for building the velocity and density profile, replacing image's RGB pixel value with the seismic velocity and density of each rock constituent. Then, ultrasonic wave was simulated to propagate in the thin section image by using finite difference time domain method, based on assumption of an acoustic-isotropic medium. Effective velocities were drawn from the recorded signal and being compared to the velocity modeling from Wyllie time average model and Kuster-Toksoz rock physics model. To perform the modeling, image analysis routines were undertaken for quantifying the pore aspect ratio that is assumed to represent the rocks pore structure. In addition, porosity and mineral fraction required for velocity modeling were also quantified by using integrated neural network and image analysis technique. It was found that the Kuster-Toksoz gives the closer prediction to the measured velocity as compared to the Wyllie time average model. We also conclude that Wyllie time average that does not incorporate the pore structure parameter deviates significantly for samples having more than 40% porosity. Utilizing this approach we found a good agreement between numerical experiment and theoretically derived rock physics model for estimating the effective seismic

The thin section rock physics: Modeling and measurement of seismic wave velocity on the slice of carbonates

International Nuclear Information System (INIS)

Wardaya, P. D.; Noh, K. A. B. M.; Yusoff, W. I. B. W.; Ridha, S.; Nurhandoko, B. E. B.

2014-01-01

This paper discusses a new approach for investigating the seismic wave velocity of rock, specifically carbonates, as affected by their pore structures. While the conventional routine of seismic velocity measurement highly depends on the extensive laboratory experiment, the proposed approach utilizes the digital rock physics view which lies on the numerical experiment. Thus, instead of using core sample, we use the thin section image of carbonate rock to measure the effective seismic wave velocity when travelling on it. In the numerical experiment, thin section images act as the medium on which wave propagation will be simulated. For the modeling, an advanced technique based on artificial neural network was employed for building the velocity and density profile, replacing image's RGB pixel value with the seismic velocity and density of each rock constituent. Then, ultrasonic wave was simulated to propagate in the thin section image by using finite difference time domain method, based on assumption of an acoustic-isotropic medium. Effective velocities were drawn from the recorded signal and being compared to the velocity modeling from Wyllie time average model and Kuster-Toksoz rock physics model. To perform the modeling, image analysis routines were undertaken for quantifying the pore aspect ratio that is assumed to represent the rocks pore structure. In addition, porosity and mineral fraction required for velocity modeling were also quantified by using integrated neural network and image analysis technique. It was found that the Kuster-Toksoz gives the closer prediction to the measured velocity as compared to the Wyllie time average model. We also conclude that Wyllie time average that does not incorporate the pore structure parameter deviates significantly for samples having more than 40% porosity. Utilizing this approach we found a good agreement between numerical experiment and theoretically derived rock physics model for estimating the effective seismic wave

New Observations of Seismic Group Velocities in the Western Solomon Islands from Cross-Correlation of Ambient Seismic Noise

Science.gov (United States)

Ku, C. S.; You, S. H.; Kuo, Y. T.; Huang, B. S.; Wu, Y. M.; Chen, Y. G.; Taylor, F. W.

2015-12-01

A MW 8.1 earthquake occurred on 1 April 2007 in the western Solomon Islands. Following this event, a damaging tsunami was induced and hit the Island Gizo where the capital city of Western Province of Solomon Islands located. Several buildings of this city were destroyed and several peoples lost their lives during this earthquake. However, during this earthquake, no near source seismic instrument has been installed in this region. The seismic evaluations for the aftershock sequence, the possible earthquake early warning and tsunami warning were unavailable. For the purpose of knowing more detailed information about seismic activity in this region, we have installed 9 seismic stations (with Trillium 120PA broadband seismometer and Q330S 24bit digitizer) around the rupture zone of the 2007 earthquake since September of 2009. Within a decade, it has been demonstrated both theoretically and experimentally that the Green's function or impulse response between two seismic stations can be retrieved from the cross-correlation of ambient noise. In this study, 6 stations' observations which are more complete during 2011/10 ~ 2012/12 period, were selected for the purpose of the cross-correlation analysis of ambient seismic noise. The group velocities at period 2-20 seconds of 15 station-pairs were extracted by using multiple filter technique (MFT) method. The analyzed results of this study presented significant results of group velocities with higher frequency contents than other studies (20-60 seconds in usually cases) and opened new opportunities to study the shallow crustal structure of the western Solomon Islands.

Three-dimensional seismic velocity structure of Mauna Loa and Kilauea volcanoes in Hawaii from local seismic tomography

Science.gov (United States)

Lin, Guoqing; Shearer, Peter M.; Matoza, Robin S.; Okubo, Paul G.; Amelung, Falk

2016-01-01

We present a new three-dimensional seismic velocity model of the crustal and upper mantle structure for Mauna Loa and Kilauea volcanoes in Hawaii. Our model is derived from the first-arrival times of the compressional and shear waves from about 53,000 events on and near the Island of Hawaii between 1992 and 2009 recorded by the Hawaiian Volcano Observatory stations. The Vp model generally agrees with previous studies, showing high-velocity anomalies near the calderas and rift zones and low-velocity anomalies in the fault systems. The most significant difference from previous models is in Vp/Vs structure. The high-Vp and high-Vp/Vs anomalies below Mauna Loa caldera are interpreted as mafic magmatic cumulates. The observed low-Vp and high-Vp/Vs bodies in the Kaoiki seismic zone between 5 and 15 km depth are attributed to the underlying volcaniclastic sediments. The high-Vp and moderate- to low-Vp/Vs anomalies beneath Kilauea caldera can be explained by a combination of different mafic compositions, likely to be olivine-rich gabbro and dunite. The systematically low-Vp and low-Vp/Vs bodies in the southeast flank of Kilauea may be caused by the presence of volatiles. Another difference between this study and previous ones is the improved Vp model resolution in deeper layers, owing to the inclusion of events with large epicentral distances. The new velocity model is used to relocate the seismicity of Mauna Loa and Kilauea for improved absolute locations and ultimately to develop a high-precision earthquake catalog using waveform cross-correlation data.

The Use Of Seismic Velocities For The Prediction Of Abnormal ...

African Journals Online (AJOL)

Ninety (90) velocity control points derived from seismic data processing were examined and analyzed to evaluate abnormal pressure zones in parts of onshore western Niger - Delta. Compaction trend graphs and a map showing the distribution of top of overpressure were produced. The graphs show that compaction ...

SEISMIC VELOCITY DETERMINATION IN GRAVEL AND SANDS USING PIEZOCRYSTALS

Directory of Open Access Journals (Sweden)

Santamarina Juan Carlos

2008-06-01

Full Text Available The exact determination of seismic waves' propagation velocities has great importance in the geotechnics due to from that it is possible to determine, among other parameters, the dynamic ones: Elasticity E, Rigidity G, Poisson !, compressibility B; as well as to reach a knowledge on the stress-strain behavior for the studied soil samples. The seismic waves transmission considered in tests at laboratory scale carried out in the present work is a phenomenon that produces very small deformation, and so doesn't disturb the material. This allows
to apply the results in a more general scale to study the behavior of soils in situ and to predict their answer to stress.
With the purpose to study the response of particulate material subjected to seismic excitements at small scale, samples of gravels and sands were successively introduced in an odometric cell, exciting them with impulsive signals and registering the corresponding seismograms through general purpose piezoelectric transducers embedded in ends of the cell.
The distance source-receiver was interval increased, which enabled, from the corresponding regression straight lines, to calculate in precise form the propagation velocities (for P waves.
The tests were carried out in samples of dry alluvial soil with three different grain sizes. The respective frequency spectra of the signals were determined for two packing modes: loose and compact, what added information on the medium characteristics.

Seismic Velocity Structure across the Hayward Fault Zone Near San Leandro, California

Science.gov (United States)

Strayer, L. M.; Catchings, R.; Chan, J. H.; Richardson, I. S.; McEvilly, A.; Goldman, M.; Criley, C.; Sickler, R. R.

2017-12-01

In Fall 2016 we conducted the East Bay Seismic Investigation, a NEHRP-funded collaboration between California State University, East Bay and the United State Geological Survey. The study produced a large volume of seismic data, allowing us to examine the subsurface across the East Bay plain and hills using a variety of geophysical methods. We know of no other survey performed in the past that has imaged this area, at this scale, and with this degree of resolution. Initial models show that seismic velocities of the Hayward Fault Zone (HFZ), the East Bay plain, and the East Bay hills are illuminated to depths of 5-6 km. We used explosive sources at 1-km intervals along a 15-km-long, NE-striking ( 055°), seismic line centered on the HFZ. Vertical- and horizontal-component sensors were spaced at 100 m intervals along the entire profile, with vertical-component sensors at 20 m intervals across mapped or suspected faults. Preliminary seismic refraction tomography across the HFZ, sensu lato, (includes sub-parallel, connected, and related faults), shows that the San Leandro Block (SLB) is a low-velocity feature in the upper 1-3 km, with nearly the same Vp as the adjacent Great Valley sediments to the east, and low Vs values. In our initial analysis we can trace the SLB and its bounding faults (Hayward, Chabot) nearly vertically, to at least 2-4 km depth. Similarly, preliminary migrated reflection images suggest that many if not all of the peripheral reverse, strike-slip and oblique-slip faults of the wider HFZ dip toward the SLB, into a curtain of relocated epicenters that define the HFZ at depth, indicative of a `flower-structure'. Preliminary Vs tomography identifies another apparently weak zone at depth, located about 1.5 km east of the San Leandro shoreline, that may represent the northward continuation of the Silver Creek Fault. Centered 4 km from the Bay, there is a distinctive, 2 km-wide, uplifted, horst-like, high-velocity structure (both Vp & Vs) that bounds the

Seismic velocity variation along the Izu-Bonin arc estaimated from traveltime tomography using OBS data

Science.gov (United States)

Obana, K.; Tamura, Y.; Takahashi, T.; Kodaira, S.

2014-12-01

The Izu-Bonin (Ogasawara) arc is an intra-oceanic island arc along the convergent plate boundary between the subducting Pacific and overriding Philippine Sea plates. Recent active seismic studies in the Izu-Bonin arc reveal significant along-arc variations in crustal structure [Kodaira et al., 2007]. The thickness of the arc crust shows a remarkable change between thicker Izu (~30 km) and thinner Bonin (~10 km) arcs. In addition to this, several geological and geophysical contrasts, such as seafloor topography and chemical composition of volcanic rocks, between Izu and Bonin arc have been reported [e.g., Yuasa 1992]. We have conducted earthquake observations using ocean bottom seismographs (OBSs) to reveal seismic velocity structure of the crust and mantle wedge in the Izu-Bonin arc and to investigate origin of the along-arc structure variations. We deployed 40 short-period OBSs in Izu and Bonin area in 2006 and 2009, respectively. The OBS data were processed with seismic data recorded at routine seismic stations on Hachijo-jima, Aoga-shima, and Chichi-jima operated by National Research Institute for Earth Science and Disaster Prevention (NIED). More than 5000 earthquakes were observed during about three-months observation period in each experiment. We conducted three-dimensional seismic tomography using manually picked P- and S-wave arrival time data. The obtained image shows a different seismic velocity structures in the mantle beneath the volcanic front between Izu and Bonin arcs. Low P-wave velocity anomalies in the mantle beneath the volcanic front in the Izu arc are limited at depths deeper than those in the Bonin arc. On the other hand, P-wave velocity in the low velocity anomalies beneath volcanic front in the Bonin arc is slower than that in the Izu arc. These large-scale along-arc structure variations in the mantle could relate to the geological and geophysical contrasts between Izu and Bonin arcs.

Improvements in seismic event locations in a deep western U.S. coal mine using tomographic velocity models and an evolutionary search algorithm

Energy Technology Data Exchange (ETDEWEB)

Adam Lurka; Peter Swanson [Central Mining Institute, Katowice (Poland)

2009-09-15

Methods of improving seismic event locations were investigated as part of a research study aimed at reducing ground control safety hazards. Seismic event waveforms collected with a 23-station three-dimensional sensor array during longwall coal mining provide the data set used in the analyses. A spatially variable seismic velocity model is constructed using seismic event sources in a passive tomographic method. The resulting three-dimensional velocity model is used to relocate seismic event positions. An evolutionary optimization algorithm is implemented and used in both the velocity model development and in seeking improved event location solutions. Results obtained using the different velocity models are compared. The combination of the tomographic velocity model development and evolutionary search algorithm provides improvement to the event locations. 13 refs., 5 figs., 4 tabs.

Peak Ground Velocities for Seismic Events at Yucca Mountain, Nevada

International Nuclear Information System (INIS)

K. Coppersmith; R. Quittmeyer

2005-01-01

This report describes a scientific analysis to bound credible horizontal peak ground velocities (PGV) for the repository waste emplacement level at Yucca Mountain. Results are presented as a probability distribution for horizontal PGV to represent uncertainties in the analysis. The analysis also combines the bound to horizontal PGV with results of ground motion site-response modeling (BSC 2004 [DIRS 170027]) to develop a composite hazard curve for horizontal PGV at the waste emplacement level. This result provides input to an abstraction of seismic consequences (BSC 2004 [DIRS 169183]). The seismic consequence abstraction, in turn, defines the input data and computational algorithms for the seismic scenario class of the total system performance assessment (TSPA). Planning for the analysis is documented in Technical Work Plan TWP-MGR-GS-000001 (BSC 2004 [DIRS 171850]). The bound on horizontal PGV at the repository waste emplacement level developed in this analysis complements ground motions developed on the basis of PSHA results. In the PSHA, ground motion experts characterized the epistemic uncertainty and aleatory variability in their ground motion interpretations. To characterize the aleatory variability they used unbounded lognormal distributions. As a consequence of these characterizations, as seismic hazard calculations are extended to lower and lower annual frequencies of being exceeded, the ground motion level increases without bound, eventually reaching levels that are not credible (Corradini 2003 [DIRS 171191]). To provide credible seismic inputs for TSPA, in accordance with 10 Code of Federal Regulations (CFR) 63.102(j) [DIRS 156605], this complementary analysis is carried out to determine reasonable bounding values of horizontal PGV at the waste emplacement level for annual frequencies of exceedance as low as 10 -8 . For each realization of the TSPA seismic scenario, the results of this analysis provide a constraint on the values sampled from the

Combining deterministic and stochastic velocity fields in the analysis of deep crustal seismic data

Science.gov (United States)

Larkin, Steven Paul

Standard crustal seismic modeling obtains deterministic velocity models which ignore the effects of wavelength-scale heterogeneity, known to exist within the Earth's crust. Stochastic velocity models are a means to include wavelength-scale heterogeneity in the modeling. These models are defined by statistical parameters obtained from geologic maps of exposed crystalline rock, and are thus tied to actual geologic structures. Combining both deterministic and stochastic velocity models into a single model allows a realistic full wavefield (2-D) to be computed. By comparing these simulations to recorded seismic data, the effects of wavelength-scale heterogeneity can be investigated. Combined deterministic and stochastic velocity models are created for two datasets, the 1992 RISC seismic experiment in southeastern California and the 1986 PASSCAL seismic experiment in northern Nevada. The RISC experiment was located in the transition zone between the Salton Trough and the southern Basin and Range province. A high-velocity body previously identified beneath the Salton Trough is constrained to pinch out beneath the Chocolate Mountains to the northeast. The lateral extent of this body is evidence for the ephemeral nature of rifting loci as a continent is initially rifted. Stochastic modeling of wavelength-scale structures above this body indicate that little more than 5% mafic intrusion into a more felsic continental crust is responsible for the observed reflectivity. Modeling of the wide-angle RISC data indicates that coda waves following PmP are initially dominated by diffusion of energy out of the near-surface basin as the wavefield reverberates within this low-velocity layer. At later times, this coda consists of scattered body waves and P to S conversions. Surface waves do not play a significant role in this coda. Modeling of the PASSCAL dataset indicates that a high-gradient crust-mantle transition zone or a rough Moho interface is necessary to reduce precritical Pm

Micro-seismicity and seismic moment release within the Coso Geothermal Field, California

Science.gov (United States)

Kaven, Joern; Hickman, Stephen H.; Davatzes, Nicholas C.

2014-01-01

We relocate 16 years of seismicity in the Coso Geothermal Field (CGF) using differential travel times and simultaneously invert for seismic velocities to improve our knowledge of the subsurface geologic and hydrologic structure. We expand on our previous results by doubling the number of relocated events from April 1996 through May 2012 using a new field-wide 3-D velocity model. Relocated micro-seismicity sharpens in many portions of the active geothermal reservoir, likely defining large-scale fault zones and fluid pressure compartment boundaries. However, a significant fraction of seismicity remains diffuse and does not cluster into sharply defined structures, suggesting that permeability is maintained within the reservoir through distributed brittle failure. The seismic velocity structure reveals heterogeneous distributions of compressional (Vp) and shear (Vs) wave speed, with Vs generally higher in the Main Field and East Flank and Vp remaining relatively uniform across the CGF, but with significant local variations. The Vp/Vs ratio appears to outline the two main producing compartments of the reservoir at depths below mean ground level of approximately 1 to 2.5 km, with a ridge of relatively high Vp/Vs separating the Main Field from the East Flank. Detailed analyses of spatial and temporal variations in earthquake relocations and cumulative seismic moment release in the East Flank reveal three regions with persistently high rates of seismic activity. Two of these regions exhibit sharp, stationary boundaries at the margins of the East Flank that likely represent barriers to fluid flow and advective heat transport. However, seismicity and moment release in a third region at the northern end of the East Flank spread over time to form an elongated NE to SW structure, roughly parallel both to an elongated cluster of seismicity at the southern end of the East Flank and to regional fault traces mapped at the surface. Our results indicate that high

Shear-wave velocity of marine sediments offshore Taiwan using ambient seismic noise

Science.gov (United States)

Lin, Yu-Tse; Lin, Jing-Yi; Kuo-Chen, Hao; Yeh, Yi-Chin; Cheng, Win-Bin

2017-04-01

Seismic ambient noise technology has many advantages over the traditional two-station method. The most important one is that noise is happening all the time and it can be widely and evenly distributed. Thus, the Green's Function of any station pair can be obtained through the data cross-correlation process. Many related studies have been performed to estimate the velocity structures based on the inland area. Only a few studies were reported for the marine area due to the relatively shorter recording time of ocean bottom seismometers (OBS) deployment and the high cost of the marine experiment. However, the understanding about the shear-wave velocity (Vs) of the marine sediments is very crucial for the hazard assessment related to submarine landslides, particularly with the growing of submarine resources exploration. In this study, we applied the ambient noise technique to four OBS seismic networks located offshore Taiwan in the aim of getting more information about the noise sources and having the preliminary estimation for the Vs of the marine sediments. Two of the seismic networks were deployed in the NE part of Taiwan, near the Ryukyu subduction system, whereas the others were in the SW area, on the continental margin rich in gas hydrate. Generally, ambient seismic noise could be associated with wind, ocean waves, rock fracturing and anthropogenic activity. In the southwestern Taiwan, the cross-correlation function obtained from two seismic networks indicate similar direction, suggestion that the source from the south part of the network could be the origin of the noise. However, the two networks in the northeastern Taiwan show various source direction, which could be caused by the abrupt change of bathymetry or the volcanic degassing effect frequently observed by the marine geophysical method in the area. The Vs determined from the dispersion curve shows a relatively higher value for the networks in the Okinawa Trough (OT) off NE Taiwan than that in the

Three-dimensional seismic velocity structure and earthquake relocations at Katmai, Alaska

Science.gov (United States)

Murphy, Rachel; Thurber, Clifford; Prejean, Stephanie G.; Bennington, Ninfa

2014-01-01

We invert arrival time data from local earthquakes occurring between September 2004 and May 2009 to determine the three-dimensional (3D) upper crustal seismic structure in the Katmai volcanic region. Waveforms for the study come from the Alaska Volcano Observatory's permanent network of 20 seismic stations in the area (predominantly single-component, short period instruments) plus a densely spaced temporary array of 11 broadband, 3-component stations. The absolute and relative arrival times are used in a double-difference seismic tomography inversion to solve for 3D P- and S-wave velocity models for an area encompassing the main volcanic centers. The relocated hypocenters provide insight into the geometry of seismogenic structures in the area, revealing clustering of events into four distinct zones associated with Martin, Mageik, Trident-Novarupta, and Mount Katmai. The seismic activity extends from about sea level to 2 km depth (all depths referenced to mean sea level) beneath Martin, is concentrated near 2 km depth beneath Mageik, and lies mainly between 2 and 4 km depth below Katmai and Trident-Novarupta. Many new features are apparent within these earthquake clusters. In particular, linear features are visible within all clusters, some associated with swarm activity, including an observation of earthquake migration near Trident in 2008. The final velocity model reveals a possible zone of magma storage beneath Mageik, but there is no clear evidence for magma beneath the Katmai-Novarupta area where the 1912 eruptive activity occurred, suggesting that the storage zone for that eruption may have largely been evacuated, or remnant magma has solidified.

Waveform tomography images of velocity and inelastic attenuation from the Mallik 2002 crosshole seismic surveys

Energy Technology Data Exchange (ETDEWEB)

Pratt, R.G.; Hou, F. [Queen' s Univ., Kingston, ON (Canada); Bauer, K.; Weber, M. [GeoForschungsZentrum Potsdam, Potsdam (Germany)

2005-07-01

A time-lapse crosshole seismic survey was conducted at the Mallik field in Canada's Northwest Territories as part of the 2002 Mallik Gas Hydrate Production Research Well Program. The acquired data provided information on the distribution of the compressional-velocity and compressional-attenuation properties of the sediments. Waveform tomography extracted that information and provided subwavelength high-resolution quantitative images of the seismic velocity and attenuation from the first repeat survey, using frequencies between 100 Hz and 1000 Hz. A preprocessing flow was applied to the waveform data that includes tube-wave suppression, low-pass filtering, spatial subsampling, time-windowing, and amplitude equalization. Travel times by anisotropic velocity tomography was used to obtain the starting model for the waveform tomography. The gas-hydrate-bearing sediments were seen as laterally, continuous, high-velocity anomalies and were characterized by an increase in attenuation. The velocity images resolved individual layers as thin as a few metres. These layers could be followed across the area of interest. Slight lateral changes in velocity and in the attenuation factor were observed.

Seismic wave attenuation and velocity dispersion in UAE carbonates

Science.gov (United States)

Ogunsami, Abdulwaheed Remi

Interpreting the seismic property of fluids in hydrocarbon reservoirs at low frequency scale has been a cherished goal of petroleum geophysics research for decades. Lately, there has been tremendous interest in understanding attenuation as a result of fluid flow in porous media. Although interesting, the emerging experimental and theoretical information still remain ambiguous and are practically not utilized for reasons not too obscure. Attenuation is frequency dependent and hard to measure in the laboratory at low frequency. This thesis describes and reports the results of an experimental study of low frequency attenuation and velocity dispersion on a selected carbonate reservoir samples in the United Arab Emirates (UAE). For the low frequency measurements, stress-strain method was used to measure the moduli from which the velocity is derived. Attenuation was measured as the phase difference between the applied stress and the strain. For the ultrasonic component, the pulse propagation method was employed. To study the fluid effect especially at reservoir in situ conditions, the measurements were made dry and saturated with liquid butane and brine at differential pressures of up to 5000 psi with pore pressure held constant at 500 psi. Similarly to what has been documented in the literatures for sandstone, attenuation of the bulk compressibility mode dominates the losses in these dry and somewhat partially saturated carbonate samples with butane and brine. Overall, the observed attenuation cannot be simply said to be frequency dependent within this low seismic band. While attenuation seems to be practically constant in the low frequency band for sample 3H, such conclusion cannot be made for sample 7H. For the velocities, significant dispersion is observed and Gassmann generally fails to match the measured velocities. Only the squirt model fairly fits the velocities, but not at all pressures. Although the observed dispersion is larger than Biot's prediction, the fact

Magma replenishment and volcanic unrest inferred from the analysis of VT micro-seismicity and seismic velocity changes at Piton de la Fournaise Volcano

Science.gov (United States)

Brenguier, F.; Rivemale, E.; Clarke, D. S.; Schmid, A.; Got, J.; Battaglia, J.; Taisne, B.; Staudacher, T.; Peltier, A.; Shapiro, N. M.; Tait, S.; Ferrazzini, V.; Di Muro, A.

2011-12-01

Piton de la Fournaise volcano (PdF) is among the most active basaltic volcanoes worldwide with more than one eruption per year on average. Also, PdF is densely instrumented with short-period and broad-band seismometers as well as with GPS receivers. Continuous seismic waveforms are available from 1999. Piton de la Fournaise volcano has a moderate inter-eruptive seismic activity with an average of five detected Volcano-Tectonic (VT) earthquakes per day with magnitudes ranging from 0.5 to 3.5. These earthquakes are shallow and located about 2.5 kilometers beneath the edifice surface. Volcanic unrest is captured on average a few weeks before eruptions by measurements of increased VT seismicity rate, inflation of the edifice summit, and decreased seismic velocities from correlations of seismic noise. Eruptions are usually preceded by seismic swarms of VT earthquakes. Recently, almost 50 % of seismic swarms were not followed by eruptions. Within this work, we aim to gather results from different groups of the UnderVolc research project in order to better understand the processes of deep magma transfer, volcanic unrest, and pre-eruptive magma transport initiation. Among our results, we show that the period 1999-2003 was characterized by a long-term increase of VT seismicity rate coupled with a long-term decrease of seismic velocities. These observations could indicate a long-term replenishment of the magma storage area. The relocation of ten years of inter-eruptive micro-seismicity shows a narrow (~300 m long) sub-vertical fault zone thus indicating a conduit rather than an extended magma reservoir as the shallow magma feeder system. Also, we focus on the processes of short-term volcanic unrest and prove that magma intrusions within the edifice leading to eruptions activate specific VT earthquakes that are distinct from magma intrusions that do not lead to eruptions. We thus propose that, among the different pathways of magma transport within the edifice, only one will

Elements of seismic imaging and velocity analysis – Forward modeling and diffraction analysis of conventional seismic data from the North Sea

DEFF Research Database (Denmark)

Montazeri, Mahboubeh

2018-01-01

comprises important oil and gas reservoirs. By application of well-established conventional velocity analysis methods and high-quality diffraction imaging techniques, this study aims to increase the resolution and the image quality of the seismic data. In order to analyze seismic wave propagation......-outs and salt delineations, which can be extracted from the diffractions. The potential of diffraction imaging techniques was studied for 2D seismic stacked data from the North Sea. In this approach, the applied plane-wave destruction method was successful in order to suppress the reflections from the stacked....... This improved seismic imaging is demonstrated for a salt structure as well as for Overpressured Shale structures and the Top Chalk of the North Sea....

Complex Seismic Anisotropy at the Edges of a Very-low Velocity Province in the Lowermost Mantle

Science.gov (United States)

Wang, Y.; Wen, L.

2005-12-01

A prominent very-low velocity province (VLVP) in the lowermost mantle is revealed, and has been extensively mapped out in recent seismic studies (e.g., Wang and Wen, 2004). Seismic evidence unambiguously indicates that the VLVP is compositionally distinct, and its seismic structure can be best explained by partial melting driven by a compositional change produced in the early Earth's history (Wen, 2001; Wen et. al, 2001; Wang and Wen, 2004). In this presentation, we study the seismic anisotropic behavior inside the VLVP and its surrounding area using SKS and SKKS waveform data. We collect 272 deep earthquakes recorded by more than 80 stations in the Kaapvaal seismic array in southern Africa from 1997 to 1999. Based on the data quality, we choose SKS and SKKS waveform data for 16 earthquakes to measure the anisotropic parameters: the fast polarization direction and the splitting time, using the method of Silver and Chan (1991). A total of 162 high-quality measurements are obtained based on the statistics analysis of shear wave splitting results. The obtained anisotropy exhibits different patterns for the SKS and SKKS phases sampling inside the VLVP and at the edges of the VLVP. When the SKS and SKKS phases sample inside the VLVP, their fast polarization directions exhibit a pattern that strongly correlates with stations, gradually changing from 11°N~to 80°N~across the seismic array from south to north and rotating back to the North direction over short distances for several northernmost stations. The anisotropy pattern obtained from the analysis of the SKKS phases is the same as that from the SKS phases. However, when the SKS and SKKS phases sample at the edges of the VLVP, the measured anisotropy exhibits a very complex pattern. The obtained fast polarization directions change rapidly over a small distance, and they no longer correlate with stations; the measurements obtained from the SKS analysis also differ with those from the SKKS analysis. As the SKS and SKKS

Monitoring changes in seismic velocity related to an ongoing rapid inflation event at Okmok volcano, Alaska

Science.gov (United States)

Bennington, Ninfa; Haney, Matt; De Angelis, Silvio; Thurber, Clifford; Freymueller, Jeff

2015-01-01

Okmok is one of the most active volcanoes in the Aleutian Arc. In an effort to improve our ability to detect precursory activity leading to eruption at Okmok, we monitor a recent, and possibly ongoing, GPS-inferred rapid inflation event at the volcano using ambient noise interferometry (ANI). Applying this method, we identify changes in seismic velocity outside of Okmok’s caldera, which are related to the hydrologic cycle. Within the caldera, we observe decreases in seismic velocity that are associated with the GPS-inferred rapid inflation event. We also determine temporal changes in waveform decorrelation and show a continual increase in decorrelation rate over the time associated with the rapid inflation event. Themagnitude of relative velocity decreases and decorrelation rate increases are comparable to previous studies at Piton de la Fournaise that associate such changes with increased production of volatiles and/ormagmatic intrusion within the magma reservoir and associated opening of fractures and/or fissures. Notably, the largest decrease in relative velocity occurs along the intrastation path passing nearest to the center of the caldera. This observation, along with equal amplitude relative velocity decreases revealed via analysis of intracaldera autocorrelations, suggests that the inflation sourcemay be located approximately within the center of the caldera and represent recharge of shallow magma storage in this location. Importantly, there is a relative absence of seismicity associated with this and previous rapid inflation events at Okmok. Thus, these ANI results are the first seismic evidence of such rapid inflation at the volcano.

Temporal Variability in Seismic Velocity at the Salton Sea Geothermal Field

Science.gov (United States)

Taira, T.; Nayak, A.; Brenguier, F.

2015-12-01

We characterize the temporal variability of ambient noise wavefield and search for velocity changes associated with activities of the geothermal energy development at the Salton Sea Geothermal Field. The noise cross-correlations (NCFs) are computed for ~6 years of continuous three-component seismic data (December 2007 through January 2014) collected at 8 sites from the CalEnergy Subnetwork (EN network) with MSNoise software (Lecocq et al., 2014, SRL). All seismic data are downloaded from the Southern California Earthquake Data Center. Velocity changes (dv/v) are obtained by measuring time delay between 5-day stacks of NCFs and the reference NCF (average over the entire 6 year period). The time history of dv/v is determined by averaging dv/v measurements over all station/channel pairs (252 combinations). Our preliminary dv/v measurement suggests a gradual increase in dv/v over the 6-year period in a frequency range of 0.5-8.0 Hz. The resultant increase rate of velocity is about 0.01%/year. We also explore the frequency-dependent velocity change at the 5 different frequency bands (0.5-2.0 Hz, 0.75-3.0 Hz, 1.0-4.0 Hz, 1.5-6.0 Hz, and 2.0-8.0 Hz) and find that the level of this long-term dv/v variability is increased with increase of frequency (i.e., the highest increase rate of ~0.15%/year at the 0.5-2.0 Hz band). This result suggests that the velocity changes were mostly occurred in a depth of ~500 m assuming that the coda parts of NCFs (~10-40 s depending on station distances) are predominantly composed of scattered surface waves, with the SoCal velocity model (Dreger and Helmberger, 1993, JGR). No clear seasonal variation of dv/v is observed in the frequency band of 0.5-8.0 Hz.

Measurement Of Compressional-Wave Seismic Velocities In 29 Wells At The Hanford Site

International Nuclear Information System (INIS)

Peterson, S.W.

2010-01-01

Check shot seismic velocity surveys were collected in 100 B/C, 200 East, 200-PO-1 Operational Unit (OU), and the Gable Gap areas in order to provide time-depth correlation information to aid the interpretation of existing seismic reflection data acquired at the Hanford Site (Figure 1). This report details results from 5 wells surveyed in fiscal year (FY) 2008, 7 wells in FY 2009, and 17 wells in FY 2010 and provides summary compressional-wave seismic velocity information to help guide future seismic survey design as well as improve current interpretations of the seismic data (SSC 1979/1980; SGW-39675; SGW-43746). Augmenting the check shot database are four surveys acquired in 2007 in support of the Bechtel National, Inc. Waste Treatment Plant construction design (PNNL-16559, PNNL-16652), and check shot surveys in three wells to support seismic testing in the 200 West Area (Waddell et al., 1999). Additional sonic logging was conducted during the late 1970s and early 1980s as part of the Basalt Waste Isolation Program (BWIP) (SSC 1979/1980) and check shot/sonic surveys as part of the safety report for the Skagit/Hanford Nuclear project (RDH/10-AMCP-0164). Check shot surveys are used to obtain an in situ measure of compressional-wave seismic velocity for sediment and rock in the vicinity of the well point, and provide the seismic-wave travel time to geologic horizons of interest. The check shot method deploys a downhole seismic receiver (geophone) to record the arrival of seismic waves generated by a source at the ground surface. The travel time of the first arriving seismic-wave is determined and used to create a time-depth function to correlate encountered geologic intervals with the seismic data. This critical tie with the underlying geology improves the interpretation of seismic reflection profile information. Fieldwork for this investigation was conducted by in house staff during the weeks of September 22, 2008 for 5 wells in the 200 East Area (Figure 2); June 1

Pre-stack estimation of time-lapse seismic velocity changes : an example from the Sleipner CO2-sequestration project

International Nuclear Information System (INIS)

Ghaderi, A.; Landro, M.; Ghaderi, A.

2005-01-01

Carbon dioxide (CO 2 ) is being injected into a shallow sand formation at around a 1,000 metre depth at the Sleipner Field located in the North Sea. It is expected that the CO 2 injected in the bottom of the formation, will form a plume consisting of CO 2 accumulating in thin lenses during migration up through the reservoir. Several studies have been published using stacked seismic data from 1994, 1999, 2001 and 2002. A thorough analysis of post-stack seismic data from the Sleipner CO2-Sequestration Pilot Project was conducted. Interpretation of seismic data is usually done on post-stack data. For a given subsurface reflection point, seismic data are acquired for various incidence angles, typically 40 angles. These 40 seismic signals are stacked together in order to reduce noise. The term pre-stack refers to seismic data prior to this step. For hydrocarbon-related 4-dimensional seismic studies, travel time shift estimations have been used. This paper compared pre-stack and post-stack estimation of average velocity changes based on measured 4-dimensional travel time shifts. It is more practical to compare estimated velocity changes than the actual travel time changes, since the time shifts vary with offset for pre-stack time-lapse seismic analysis. It was concluded that the pre-stack method gives smaller velocity changes when estimated between two key horizons. Therefore, pre-stack travel time analysis in addition to conventional post-stack analysis is recommended. 6 refs., 12 figs

Relationships among seismic velocity, metamorphism, and seismic and aseismic fault slip in the Salton Sea Geothermal Field region

Science.gov (United States)

McGuire, Jeffrey J.; Lohman, Rowena B.; Catchings, Rufus D.; Rymer, Michael J.; Goldman, Mark R.

2015-01-01

The Salton Sea Geothermal Field is one of the most geothermally and seismically active areas in California and presents an opportunity to study the effect of high-temperature metamorphism on the properties of seismogenic faults. The area includes numerous active tectonic faults that have recently been imaged with active source seismic reflection and refraction. We utilize the active source surveys, along with the abundant microseismicity data from a dense borehole seismic network, to image the 3-D variations in seismic velocity in the upper 5 km of the crust. There are strong velocity variations, up to ~30%, that correlate spatially with the distribution of shallow heat flow patterns. The combination of hydrothermal circulation and high-temperature contact metamorphism has significantly altered the shallow sandstone sedimentary layers within the geothermal field to denser, more feldspathic, rock with higher P wave velocity, as is seen in the numerous exploration wells within the field. This alteration appears to have a first-order effect on the frictional stability of shallow faults. In 2005, a large earthquake swarm and deformation event occurred. Analysis of interferometric synthetic aperture radar data and earthquake relocations indicates that the shallow aseismic fault creep that occurred in 2005 was localized on the Kalin fault system that lies just outside the region of high-temperature metamorphism. In contrast, the earthquake swarm, which includes all of the M > 4 earthquakes to have occurred within the Salton Sea Geothermal Field in the last 15 years, ruptured the Main Central Fault (MCF) system that is localized in the heart of the geothermal anomaly. The background microseismicity induced by the geothermal operations is also concentrated in the high-temperature regions in the vicinity of operational wells. However, while this microseismicity occurs over a few kilometer scale region, much of it is clustered in earthquake swarms that last from

Detailed seismic velocity structure of the ultra-slow spread crust at the Mid-Cayman Spreading Center from travel-time tomography and synthetic seismograms

Science.gov (United States)

Harding, J.; Van Avendonk, H. J.; Hayman, N. W.; Grevemeyer, I.; Peirce, C.

2017-12-01

The Mid-Cayman Spreading Center (MCSC), an ultraslow-spreading center in the Caribbean Sea, has formed highly variable oceanic crust. Seafloor dredges have recovered extrusive basalts in the axial deeps as well as gabbro on bathymetric highs and exhumed mantle peridotite along the only 110 km MCSC. Wide-angle refraction data were collected with active-source ocean bottom seismometers in April, 2015, along lines parallel and across the MCSC. Travel-time tomography produces relatively smooth 2-D tomographic models of compressional wave velocity. These velocity models reveal large along- and across-axis variations in seismic velocity, indicating possible changes in crustal thickness, composition, faulting, and magmatism. It is difficult, however, to differentiate between competing interpretations of seismic velocity using these tomographic models alone. For example, in some areas the seismic velocities may be explained by either thin igneous crust or exhumed, serpentinized mantle. Distinguishing between these two interpretations is important as we explore the relationships between magmatism, faulting, and hydrothermal venting at ultraslow-spreading centers. We therefore improved our constraints on the shallow seismic velocity structure of the MCSC by modeling the amplitude of seismic refractions in the wide-angle data set. Synthetic seismograms were calculated with a finite-difference method for a range of models with different vertical velocity gradients. Small-scale features in the velocity models, such as steep velocity gradients and Moho boundaries, were explored systematically to best fit the real data. With this approach, we have improved our understanding of the compressional velocity structure of the MCSC along with the geological interpretations that are consistent with three seismic refraction profiles. Line P01 shows a variation in the thinness of lower seismic velocities along the axis, indicating two segment centers, while across-axis lines P02 and P03

Seismic Wave Velocity in Earth's Shallow Core

Science.gov (United States)

Alexandrakis, C.; Eaton, D. W.

2008-12-01

Studies of the outer core indicate that it is composed of liquid Fe and Ni alloyed with a ~10% fraction of light elements such as O, S or Si. Recently, unusual features, such as sediment accumulation, immiscible fluid layers or stagnant convection, have been predicted in the shallow core region. Secular cooling and compositional buoyancy drive vigorous convection that sustains the geodynamo, although critical details of light-element composition and thermal regime remain uncertain. Seismic velocity models can provide important constraints on the light element composition, however global reference models, such as Preliminary Reference Earth Model (PREM), IASP91 and AK135 vary significantly in the 200 km below the core-mantle boundary. Past studies of the outermost core velocity structure have been hampered by traveltime uncertainties due to lowermost mantle heterogeneities. The recently published Empirical Transfer Function (ETF) method has been shown to reduce the uncertainty using a waveform stacking approach to improve global observations of SmKS teleseismic waves. Here, we apply the ETF method to achieve a precise top-of-core velocity measurement of 8.05 ± 0.03 km/s. This new model accords well with PREM. Since PREM is based on the adiabatic form of the Adams-Williamson equation, it assumes a well mixed (i.e. homogeneous) composition. This result suggests a lack of heterogeneity in the outermost core due to layering or stagnant convection.

Model of the seismic velocity distribution in the upper lithosphere of the Vrancea seismogenic zone and within the adjacent areas

International Nuclear Information System (INIS)

Raileanu, Victor; Bala, Andrei

2002-01-01

The task of this project is to perform a detailed seismic velocity model of the P waves in the crust and upper mantle crossed by the VRANCEA 2001 seismic line and to interpret it in structural terms. The velocity model aims to contribute to a new geodynamical model of the Eastern Carpathians evolution and to a better understanding of the causes of the Vrancea earthquakes. It is performed in cooperation with the University of Karlsruhe, Germany, and University of Bucharest. The Project will be completed in 5 working stages. Vrancea 2001 is the name of the seismic line recorded with about 780 seismic instruments deployed over more then 600 km length from eastern part of Romania (east Tulcea) through Vrancea area to Aiud and south Oradea. 10 big shots with charges from 300 kg to 1500 kg dynamite were detonated along seismic line. Field data quality is from good to very good and it provides information down to the upper mantle levels. Processing of data has been performed in the first stage of present project and it consisted in merging of all individual field records in seismograms for each shotpoint. Almost 800 individual records for each out of the 10 shots were merged in 10 seismograms with about 800 channels. A seismogram of shot point S (25 km NE of Ramnicu Sarat) is given. It is visible a high energy generated by shotpoint S. Pn wave can be traced until the western end of seismic line, about 25 km from source. In the second stage of project an interpretation of seismic data is achieved for the first 5 seismograms from the eastern half of seismic line, from Tulcea to Ramnicu Sarat. It is used a forward modeling procedure. 5 unidimensional (1D) velocity-depth function models are obtained. P wave velocity-depth function models for shotpoints from O to T are presented. Velocity-depth information is extended down to 40 km for shot R and 80 km for shot S. It should noticed the unusually high velocities at the shallow levels for Dobrogea area (O and P shots) and the

Source Inversion of Seismic Events Associated with the Sinkhole at Napoleonville Salt Dome, Louisiana using a 3D Velocity Model

Science.gov (United States)

Nayak, Avinash; Dreger, Douglas S.

2018-05-01

The formation of a large sinkhole at the Napoleonville salt dome (NSD), Assumption Parish, Louisiana, caused by the collapse of a brine cavern, was accompanied by an intense and complex sequence of seismic events. We implement a grid-search approach to compute centroid locations and point-source moment tensor (MT) solutions of these seismic events using ˜0.1-0.3 Hz displacement waveforms and synthetic Green's functions computed using a 3D velocity model of the western edge of the NSD. The 3D model incorporates the currently known approximate geometry of the salt dome and the overlying anhydrite-gypsum cap rock, and features a large velocity contrast between the high velocity salt dome and low velocity sediments overlying and surrounding it. For each possible location on the source grid, Green's functions (GFs) to each station were computed using source-receiver reciprocity and the finite-difference seismic wave propagation software SW4. We also establish an empirical method to rigorously assess uncertainties in the centroid location, MW and source type of these events under evolving network geometry, using the results of synthetic tests with hypothetical events and real seismic noise. We apply the methods on the entire duration of data (˜6 months) recorded by the temporary US Geological Survey network. During an energetic phase of the sequence from 24-31 July 2012 when 4 stations were operational, the events with the best waveform fits are primarily located at the western edge of the salt dome at most probable depths of ˜0.3-0.85 km, close to the horizontal positions of the cavern and the future sinkhole. The data are fit nearly equally well by opening crack MTs in the high velocity salt medium or by isotropic volume-increase MTs in the low velocity sediment layers. We find that data recorded by 6 stations during 1-2 August 2012, right before the appearance of the sinkhole, indicate that some events are likely located in the lower velocity media just outside the

Shear-wave velocity-based probabilistic and deterministic assessment of seismic soil liquefaction potential

Science.gov (United States)

Kayen, R.; Moss, R.E.S.; Thompson, E.M.; Seed, R.B.; Cetin, K.O.; Der Kiureghian, A.; Tanaka, Y.; Tokimatsu, K.

2013-01-01

Shear-wave velocity (Vs) offers a means to determine the seismic resistance of soil to liquefaction by a fundamental soil property. This paper presents the results of an 11-year international project to gather new Vs site data and develop probabilistic correlations for seismic soil liquefaction occurrence. Toward that objective, shear-wave velocity test sites were identified, and measurements made for 301 new liquefaction field case histories in China, Japan, Taiwan, Greece, and the United States over a decade. The majority of these new case histories reoccupy those previously investigated by penetration testing. These new data are combined with previously published case histories to build a global catalog of 422 case histories of Vs liquefaction performance. Bayesian regression and structural reliability methods facilitate a probabilistic treatment of the Vs catalog for performance-based engineering applications. Where possible, uncertainties of the variables comprising both the seismic demand and the soil capacity were estimated and included in the analysis, resulting in greatly reduced overall model uncertainty relative to previous studies. The presented data set and probabilistic analysis also help resolve the ancillary issues of adjustment for soil fines content and magnitude scaling factors.

Crustal velocity structure of central Gansu Province from regional seismic waveform inversion using firework algorithm

Science.gov (United States)

Chen, Yanyang; Wang, Yanbin; Zhang, Yuansheng

2017-04-01

The firework algorithm (FWA) is a novel swarm intelligence-based method recently proposed for the optimization of multi-parameter, nonlinear functions. Numerical waveform inversion experiments using a synthetic model show that the FWA performs well in both solution quality and efficiency. We apply the FWA in this study to crustal velocity structure inversion using regional seismic waveform data of central Gansu on the northeastern margin of the Qinghai-Tibet plateau. Seismograms recorded from the moment magnitude ( M W) 5.4 Minxian earthquake enable obtaining an average crustal velocity model for this region. We initially carried out a series of FWA robustness tests in regional waveform inversion at the same earthquake and station positions across the study region, inverting two velocity structure models, with and without a low-velocity crustal layer; the accuracy of our average inversion results and their standard deviations reveal the advantages of the FWA for the inversion of regional seismic waveforms. We applied the FWA across our study area using three component waveform data recorded by nine broadband permanent seismic stations with epicentral distances ranging between 146 and 437 km. These inversion results show that the average thickness of the crust in this region is 46.75 km, while thicknesses of the sedimentary layer, and the upper, middle, and lower crust are 3.15, 15.69, 13.08, and 14.83 km, respectively. Results also show that the P-wave velocities of these layers and the upper mantle are 4.47, 6.07, 6.12, 6.87, and 8.18 km/s, respectively.

The relationship of seismic velocity structure and surface fracture characteristics of basalt outcrops to rippability estimates

International Nuclear Information System (INIS)

Kay, S.E.; Dougherty, M.E.; Pelton, J.R.

1994-01-01

Seismic velocity has been shown in previous engineering studies to be related to the fracture characteristics and rippability of rock outcrops. However, common methods of measuring seismic velocity in outcrops do not take into account the many possible travel paths for wave propagation and the fact that velocity zones may exist within an outcrop. Presented here are the results of using raytracing inversion of first-arrival travel-time data to map P-velocity structure in basalt outcrops, and also the investigation of the relationship of the mapped velocities to observed surface fractures and hand-sample P-velocities. It is shown that basalt outcrops commonly consist of an irregular near-surface low-velocity zone underlain by higher velocity material; that velocity gradients can exist in outcrops; that hand-sample velocity measurements are typically higher than outcrop-scale measurements; and that the characteristics of surface fractures are empirically related to near-surface P-velocity. All of these findings are relevant to the estimated rippability of rock in geotechnical engineering. The data for this study are derived from eleven sites on basalt outcrops of the Troodos Ophiolite in Cyprus. The basalt types include pillow basalts, massive flows, and a pillow breccia. A commonly available raytracing inversion program (RAYINVR) was used to produce a velocity profile of each outcrop. Different velocity zones were detailed by inverting observed travel times to produce a model of outcrop velocity structure which produces rippability profiles for each outcrop. 16 refs., 9 figs

High resolution Rayleigh wave group velocity tomography in North-China from ambient seismic noise

International Nuclear Information System (INIS)

Fang Lihua; Wu Jianping; Ding Zhifeng; Panza, G.F.

2009-03-01

This study presents the results of the Rayleigh wave group velocity tomography in North-China performed using ambient seismic noise observed at 190 broadband and 10 very broadband stations of the North-China Seismic Array. All available vertical component time-series for the 14 months span between January, 2007 and February, 2008 are cross-correlated to obtain empirical Rayleigh wave Green functions that are subsequently processed, with the multiple filter method, to isolate the group velocity dispersion curves of the fundamental mode of Rayleigh wave. Tomographic maps, with a grid spacing of 0.25 deg. x 0.25 deg., are computed at the periods of 4.5s, 12s, 20s, 28s. The maps at short periods reveal an evident lateral heterogeneity in the crust of North-China, quite well in agreement with known geological and tectonic features. The North China Basin is imaged as a broad low velocity area, while the Taihangshan and Yanshan uplifts and Ordos block are imaged as high velocity zones, and the Quaternary intermountain basins show up as small low-velocity anomalies. The group velocity contours at 4.5s, 12s and 20s are consistent with the Bouguer gravity anomalies measured in the area of the Taihangshan fault, that cuts through the lower crust at least. Most of the historical strong earthquakes (M≥6.0) are located where the tomographic maps show zones with moderate velocity gradient. (author)

Changes in seismic velocity during the first 14 months of the 2004–2008 eruption of Mount St. Helens, Washington

Science.gov (United States)

Hotovec-Ellis, A.J.; Vidale, J.E.; Gomberg, Joan S.; Thelen, Weston A.; Moran, Seth C.

2015-01-01

Mount St. Helens began erupting in late 2004 following an 18 year quiescence. Swarms of repeating earthquakes accompanied the extrusion of a mostly solid dacite dome over the next 4 years. In some cases the waveforms from these earthquakes evolved slowly, likely reflecting changes in the properties of the volcano that affect seismic wave propagation. We use coda-wave interferometry to quantify small changes in seismic velocity structure (usually <1%) between two similar earthquakes and employed waveforms from several hundred families of repeating earthquakes together to create a continuous function of velocity change observed at permanent stations operated within 20 km of the volcano. The high rate of earthquakes allowed tracking of velocity changes on an hourly time scale. Changes in velocity were largest near the newly extruding dome and likely related to shallow deformation as magma first worked its way to the surface. We found strong correlation between velocity changes and the inverse of real-time seismic amplitude measurements during the first 3 weeks of activity, suggesting that fluctuations of pressure in the shallow subsurface may have driven both seismicity and velocity changes. Velocity changes during the remainder of the eruption likely result from a complex interplay of multiple effects and are not well explained by any single factor alone, highlighting the need for complementary geophysical data when interpreting velocity changes.

Transformation of seismic velocity data to extract porosity and saturation values for rocks

International Nuclear Information System (INIS)

Berryman, James G.; Berge, Patricia A.; Bonner, Brian P.

2000-01-01

For wave propagation at low frequencies in a porous medium, the Gassmann-Domenico relations are well-established for homogeneous partial saturation by a liquid. They provide the correct relations for seismic velocities in terms of constituent bulk and shear moduli, solid and fluid densities, porosity and saturation. It has not been possible, however, to invert these relations easily to determine porosity and saturation when the seismic velocities are known. Also, the state (or distribution) of saturation, i.e., whether or not liquid and gas are homogeneously mixed in the pore space, is another important variable for reservoir evaluation. A reliable ability to determine the state of saturation from velocity data continues to be problematic. It is shown how transforming compressional and shear wave velocity data to the (ρ/λ,μ/λ)-plane (where λ and μ are the Lame parameters and ρ is the total density) results in a set of quasi-orthogonal coordinates for porosity and liquid saturation that greatly aids in the interpretation of seismic data for the physical parameters of most interest. A second transformation of the same data then permits isolation of the liquid saturation value, and also provides some direct information about the state of saturation. By thus replotting the data in the (λ/μ, ρ/μ)-plane, inferences can be made concerning the degree of patchy (inhomogeneous) versus homogeneous saturation that is present in the region of the medium sampled by the data. Our examples include igneous and sedimentary rocks, as well as man-made porous materials. These results have potential applications in various areas of interest, including petroleum exploration and reservoir characterization, geothermal resource evaluation, environmental restoration monitoring, and geotechnical site characterization. (c) 2000 Acoustical Society of America

Continental lithospheric subduction and intermediate-depth seismicity: Constraints from S-wave velocity structures in the Pamir and Hindu Kush

Science.gov (United States)

Li, Wei; Chen, Yun; Yuan, Xiaohui; Schurr, Bernd; Mechie, James; Oimahmadov, Ilhomjon; Fu, Bihong

2018-01-01

The Pamir has experienced more intense deformation and shortening than Tibet, although it has a similar history of terrane accretion. Subduction as a primary way to accommodate lithospheric shortening beneath the Pamir has induced the intermediate-depth seismicity, which is rare in Tibet. Here we construct a 3D S-wave velocity model of the lithosphere beneath the Pamir by surface wave tomography using data of the TIPAGE (Tien Shan-Pamir Geodynamic program) and other seismic networks in the area. We imaged a large-scale low velocity anomaly in the crust at 20-50 km depth in the Pamir overlain by a high velocity anomaly at a depth shallower than 15 km. The high velocity anomalies colocate with exposed gneiss domes, which may imply a similar history of crustal deformation, partial melting and exhumation in the hinterland, as has occurred in the Himalaya/Tibet system. At mantle depths, where the intermediate-depth earthquakes are located, a low velocity zone is clearly observed extending to about 180 km and 150 km depth in the Hindu Kush and eastern Pamir, respectively. Moreover, the geometry of the low-velocity anomaly suggests that lower crustal material has been pulled down into the mantle by the subducting Asian and Indian lithospheric mantle beneath the Pamir and Hindu Kush, respectively. Metamorphic processes in the subducting lower crust may cause the intermediate-depth seismicity down to 150-180 km depth beneath the Pamir and Hindu Kush. We inverted focal mechanisms in the seismic zone for the stress field. Differences in the stress field between the upper and lower parts of the Indian slab imply that subduction and detachment of the Indian lithosphere might cause intense seismicity associated with the thermal shear instability in the deep Hindu Kush.

Characteristics of Offshore Hawai';i Island Seismicity and Velocity Structure, including Lo';ihi Submarine Volcano

Science.gov (United States)

Merz, D. K.; Caplan-Auerbach, J.; Thurber, C. H.

2013-12-01

The Island of Hawai';i is home to the most active volcanoes in the Hawaiian Islands. The island's isolated nature, combined with the lack of permanent offshore seismometers, creates difficulties in recording small magnitude earthquakes with accuracy. This background offshore seismicity is crucial in understanding the structure of the lithosphere around the island chain, the stresses on the lithosphere generated by the weight of the islands, and how the volcanoes interact with each other offshore. This study uses the data collected from a 9-month deployment of a temporary ocean bottom seismometer (OBS) network fully surrounding Lo';ihi volcano. This allowed us to widen the aperture of earthquake detection around the Big Island, lower the magnitude detection threshold, and better constrain the hypocentral depths of offshore seismicity that occurs between the OBS network and the Hawaii Volcano Observatory's land based network. Although this study occurred during a time of volcanic quiescence for Lo';ihi, it establishes a basis for background seismicity of the volcano. More than 480 earthquakes were located using the OBS network, incorporating data from the HVO network where possible. Here we present relocated hypocenters using the double-difference earthquake location algorithm HypoDD (Waldhauser & Ellsworth, 2000), as well as tomographic images for a 30 km square area around the summit of Lo';ihi. Illuminated by using the double-difference earthquake location algorithm HypoDD (Waldhauser & Ellsworth, 2000), offshore seismicity during this study is punctuated by events locating in the mantle fault zone 30-50km deep. These events reflect rupture on preexisting faults in the lower lithosphere caused by stresses induced by volcano loading and flexure of the Pacific Plate (Wolfe et al., 2004; Pritchard et al., 2007). Tomography was performed using the double-difference seismic tomography method TomoDD (Zhang & Thurber, 2003) and showed overall velocities to be slower than

3-D Velocity Model of the Coachella Valley, Southern California Based on Explosive Shots from the Salton Seismic Imaging Project

Science.gov (United States)

Persaud, P.; Stock, J. M.; Fuis, G. S.; Hole, J. A.; Goldman, M.; Scheirer, D. S.

2014-12-01

We have analyzed explosive shot data from the 2011 Salton Seismic Imaging Project (SSIP) across a 2-D seismic array and 5 profiles in the Coachella Valley to produce a 3-D P-wave velocity model that will be used in calculations of strong ground shaking. Accurate maps of seismicity and active faults rely both on detailed geological field mapping and a suitable velocity model to accurately locate earthquakes. Adjoint tomography of an older version of the SCEC 3-D velocity model shows that crustal heterogeneities strongly influence seismic wave propagation from moderate earthquakes (Tape et al., 2010). These authors improve the crustal model and subsequently simulate the details of ground motion at periods of 2 s and longer for hundreds of ray paths. Even with improvements such as the above, the current SCEC velocity model for the Salton Trough does not provide a match of the timing or waveforms of the horizontal S-wave motions, which Wei et al. (2013) interpret as caused by inaccuracies in the shallow velocity structure. They effectively demonstrate that the inclusion of shallow basin structure improves the fit in both travel times and waveforms. Our velocity model benefits from the inclusion of known location and times of a subset of 126 shots detonated over a 3-week period during the SSIP. This results in an improved velocity model particularly in the shallow crust. In addition, one of the main challenges in developing 3-D velocity models is an uneven stations-source distribution. To better overcome this challenge, we also include the first arrival times of the SSIP shots at the more widely spaced Southern California Seismic Network (SCSN) in our inversion, since the layout of the SSIP is complementary to the SCSN. References: Tape, C., et al., 2010, Seismic tomography of the Southern California crust based on spectral-element and adjoint methods: Geophysical Journal International, v. 180, no. 1, p. 433-462. Wei, S., et al., 2013, Complementary slip distributions

Seismic velocity uncertainties and their effect on geothermal predictions: A case study

Science.gov (United States)

Rabbel, Wolfgang; Köhn, Daniel; Bahadur Motra, Hem; Niederau, Jan; Thorwart, Martin; Wuttke, Frank; Descramble Working Group

2017-04-01

Geothermal exploration relies in large parts on geophysical subsurface models derived from seismic reflection profiling. These models are the framework of hydro-geothermal modeling, which further requires estimating thermal and hydraulic parameters to be attributed to the seismic strata. All petrophysical and structural properties involved in this process can be determined only with limited accuracy and thus impose uncertainties onto the resulting model predictions of temperature-depth profiles and hydraulic flow, too. In the present study we analyze sources and effects of uncertainties of the seismic velocity field, which translate directly into depth uncertainties of the hydraulically and thermally relevant horizons. Geological sources of these uncertainties are subsurface heterogeneity and seismic anisotropy, methodical sources are limitations in spread length and physical resolution. We demonstrate these effects using data of the EU-Horizon 2020 project DESCRAMBLE investigating a shallow super-critical geothermal reservoir in the Larderello area. The study is based on 2D- and 3D seismic reflection data and laboratory measurements on representative rock samples under simulated in-situ conditions. The rock samples consistently show P-wave anisotropy values of 10-20% order of magnitude. However, the uncertainty of layer depths induced by anisotropy is likely to be lower depending on the accuracy, with which the spatial orientation of bedding planes can be determined from the seismic reflection images.

Shear-wave velocities beneath the Harrat Rahat volcanic field, Saudi Arabia, using ambient seismic noise analysis

Science.gov (United States)

Civilini, F.; Mooney, W.; Savage, M. K.; Townend, J.; Zahran, H. M.

2017-12-01

We present seismic shear-velocities for Harrat Rahat, a Cenozoic bimodal alkaline volcanic field in west-central Saudi Arabia, using seismic tomography from natural ambient noise. This project is part of an overall effort by the Saudi Geological Survey and the United States Geological Survey to describe the subsurface structure and assess hazards within the Saudi Arabian shield. Volcanism at Harrat Rahat began approximately 10 Ma, with at least three pulses around 10, 5, and 2 Ma, and at least several pulses in the Quaternary from 1.9 Ma to the present. This area is instrumented by 14 broadband Nanometrics Trillium T120 instruments across an array aperture of approximately 130 kilometers. We used a year of recorded natural ambient noise to determine group and phase velocity surface wave dispersion maps with a 0.1 decimal degree resolution for radial-radial, transverse-transverse, and vertical-vertical components of the empirical Green's function. A grid-search method was used to carry out 1D shear-velocity inversions at each latitude-longitude point and the results were interpolated to produce pseudo-3D shear velocity models. The dispersion maps resolved a zone of slow surface wave velocity south-east of the city of Medina spatially correlated with the 1256 CE eruption. A crustal layer interface at approximately 20 km depth was determined by the inversions for all components, matching the results of prior seismic-refraction studies. Cross-sections of the 3D shear velocity models were compared to gravity measurements obtained in the south-east edge of the field. We found that measurements of low gravity qualitatively correlate with low values of shear-velocity below 20 km along the cross-section profile. We apply these methods to obtain preliminary tomography results on the entire Arabian Shield.

Comparison of Effective Medium Schemes For Seismic Velocities in Cracked Anisotropic Rock

Science.gov (United States)

Morshed, S.; Chesnokov, E.

2017-12-01

Understanding of elastic properties of reservoir rock is necessary for meaningful interpretation and analysis of seismic measurements. The elastic properties of a rock are controlled by the microstructural properties such as mineralogical composition, pore and crack distribution, texture and pore connectivity. However, seismic scale is much larger than microstructure scale. Understanding of macroscopic properties at relevant seismic scale (e.g. borehole sonic data) comes from effective medium theory (EMT). However, most of the effective medium theories fail at high crack density as the interactions of strain fields of the cracks can't be ignored. We compare major EMT schemes from low to high crack density. While at low crack density all method gives similar results, at high crack density they differ significantly. Then, we focus on generalized singular approximation (GSA) and effective field (EF) method as they allow cracks beyond the limit of dilute concentrations. Additionally, we use grain contact (GC) method to examine the stiffness constants of the rock matrix. We prepare simple models of a multiphase media containing low to high concentrations of isolated pores. Randomly oriented spherical pores and horizontally oriented ellipsoidal (aspect ratio =0.1) pores have been considered. For isolated spherical pores, all the three methods show exactly same or similar results. However, inclusion interactions are different in different directions in case of horizontal ellipsoidal pores and individual stiffness constants differ greatly from one method to another at different crack density. Stiffness constants remain consistent in GSA method whereas some components become unusual in EF method at a higher crack density (>0.15). Finally, we applied GSA method to interpret ultrasonic velocities of core samples. Mineralogical composition from X-ray diffraction (XRD) data and lab measured porosity data have been utilized. Both compressional and shear wave velocities from GSA

Development of a State-Wide 3-D Seismic Tomography Velocity Model for California

Science.gov (United States)

Thurber, C. H.; Lin, G.; Zhang, H.; Hauksson, E.; Shearer, P.; Waldhauser, F.; Hardebeck, J.; Brocher, T.

2007-12-01

We report on progress towards the development of a state-wide tomographic model of the P-wave velocity for the crust and uppermost mantle of California. The dataset combines first arrival times from earthquakes and quarry blasts recorded on regional network stations and travel times of first arrivals from explosions and airguns recorded on profile receivers and network stations. The principal active-source datasets are Geysers-San Pablo Bay, Imperial Valley, Livermore, W. Mojave, Gilroy-Coyote Lake, Shasta region, Great Valley, Morro Bay, Mono Craters-Long Valley, PACE, S. Sierras, LARSE 1 and 2, Loma Prieta, BASIX, San Francisco Peninsula and Parkfield. Our beta-version model is coarse (uniform 30 km horizontal and variable vertical gridding) but is able to image the principal features in previous separate regional models for northern and southern California, such as the high-velocity subducting Gorda Plate, upper to middle crustal velocity highs beneath the Sierra Nevada and much of the Coast Ranges, the deep low-velocity basins of the Great Valley, Ventura, and Los Angeles, and a high- velocity body in the lower crust underlying the Great Valley. The new state-wide model has improved areal coverage compared to the previous models, and extends to greater depth due to the data at large epicentral distances. We plan a series of steps to improve the model. We are enlarging and calibrating the active-source dataset as we obtain additional picks from investigators and perform quality control analyses on the existing and new picks. We will also be adding data from more quarry blasts, mainly in northern California, following an identification and calibration procedure similar to Lin et al. (2006). Composite event construction (Lin et al., in press) will be carried out for northern California for use in conventional tomography. A major contribution of the state-wide model is the identification of earthquakes yielding arrival times at both the Northern California Seismic

Crustal structure beneath discovery bank in the South Scotia Sea from group velocity tomography and seismic reflection data

International Nuclear Information System (INIS)

Vuan, A.; Lodolo, E.; Panza, G.F.

2003-09-01

Bruce, Discovery, Herdman and Jane Banks, all located along the central-eastern part of the South Scotia Ridge (i.e., the Antarctica-Scotia plate boundary), represent isolated topographic reliefs surrounded by relatively young oceanic crust, whose petrological and structural nature is still the subject of speculations due to the lack of resolving data. In the Scotia Sea and surrounding regions negative anomalies of about 34% are reported in large-scale group velocity tomography maps. The spatial resolution (∼500 km) of these maps does not warrant any reliable interpretation of such anomalies. A recent surface wave tomography in the same area, performed using broad band seismic stations and 300 regional events, shows that in the period range from 15 s to 50 s the central-eastern part of the South Scotia Ridge is characterized by negative anomalies of the group velocities as large as 6. The resolution of our data set (∼300 km) makes it possible to distinguish an area (centered at 61 deg S and 36 deg W) with a crust thicker than 25 km, and a shear wave velocity vs. depth profile similar to that found beneath the northern tip of the Antarctic Peninsula and southern South America. Rayleigh and Love wave dispersion curves are inverted in the period range from 15 s to 80 s to obtain shear wave velocity profiles that suggest a continental nature of Discovery Bank. The continental-type crust of this topographic relief is in agreement with the interpretation of a multi-channel seismic reflection profile acquired across this rise. Peculiar acoustic facies are observed in this profile and are interpreted as thinned and faulted continental plateau. The boundaries of the negative group velocity anomalies are marked by a high seismicity rate. Historical normal faulting earthquakes with magnitude around 7 are localised between the low velocity anomaly region in the eastern South Scotia Ridge and the high velocity anomaly region associated with the surrounding oceanic crust

Seismic Technology Adapted to Analyzing and Developing Geothermal Systems Below Surface-Exposed High-Velocity Rocks Final Report

Energy Technology Data Exchange (ETDEWEB)

Hardage, Bob A. [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; DeAngelo, Michael V. [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Ermolaeva, Elena [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Hardage, Bob A. [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Remington, Randy [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Sava, Diana [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Wagner, Donald [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology; Wei, Shuijion [Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology

2013-02-01

The objective of our research was to develop and demonstrate seismic data-acquisition and data-processing technologies that allow geothermal prospects below high-velocity rock outcrops to be evaluated. To do this, we acquired a 3-component seismic test line across an area of exposed high-velocity rocks in Brewster County, Texas, where there is high heat flow and surface conditions mimic those found at numerous geothermal prospects. Seismic contractors have not succeeded in creating good-quality seismic data in this area for companies who have acquired data for oil and gas exploitation purposes. Our test profile traversed an area where high-velocity rocks and low-velocity sediment were exposed on the surface in alternating patterns that repeated along the test line. We verified that these surface conditions cause non-ending reverberations of Love waves, Rayleigh waves, and shallow critical refractions to travel across the earth surface between the boundaries of the fast-velocity and slow-velocity material exposed on the surface. These reverberating surface waves form the high level of noise in this area that does not allow reflections from deep interfaces to be seen and utilized. Our data-acquisition method of deploying a box array of closely spaced geophones allowed us to recognize and evaluate these surface-wave noise modes regardless of the azimuth direction to the surface anomaly that backscattered the waves and caused them to return to the test-line profile. With this knowledge of the surface-wave noise, we were able to process these test-line data to create P-P and SH-SH images that were superior to those produced by a skilled seismic data-processing contractor. Compared to the P-P data acquired along the test line, the SH-SH data provided a better detection of faults and could be used to trace these faults upward to the boundaries of exposed surface rocks. We expanded our comparison of the relative value of S-wave and P-wave seismic data for geothermal

Correlation-based seismic velocity inversion

NARCIS (Netherlands)

Van Leeuwen, T.

2010-01-01

Most of our knowledge of the subsurface comes from the measurement of quantities that are indirectly related to the earth’s structure. Examples are seismic waves, gravity and electromagnetic waves. We consider the use of seismic waves for inference of structural information on an exploration scale.

Derivation of site-specific relationships between hydraulic parameters and p-wave velocities based on hydraulic and seismic tomography

Energy Technology Data Exchange (ETDEWEB)

Brauchler, R.; Doetsch, J.; Dietrich, P.; Sauter, M.

2012-01-10

In this study, hydraulic and seismic tomographic measurements were used to derive a site-specific relationship between the geophysical parameter p-wave velocity and the hydraulic parameters, diffusivity and specific storage. Our field study includes diffusivity tomograms derived from hydraulic travel time tomography, specific storage tomograms, derived from hydraulic attenuation tomography, and p-wave velocity tomograms, derived from seismic tomography. The tomographic inversion was performed in all three cases with the SIRT (Simultaneous Iterative Reconstruction Technique) algorithm, using a ray tracing technique with curved trajectories. The experimental set-up was designed such that the p-wave velocity tomogram overlaps the hydraulic tomograms by half. The experiments were performed at a wellcharacterized sand and gravel aquifer, located in the Leine River valley near Göttingen, Germany. Access to the shallow subsurface was provided by direct-push technology. The high spatial resolution of hydraulic and seismic tomography was exploited to derive representative site-specific relationships between the hydraulic and geophysical parameters, based on the area where geophysical and hydraulic tests were performed. The transformation of the p-wave velocities into hydraulic properties was undertaken using a k-means cluster analysis. Results demonstrate that the combination of hydraulic and geophysical tomographic data is a promising approach to improve hydrogeophysical site characterization.

Seismic Velocity Structure and Improved Seismic Image of the Southern Depression of the Tainan Basin from Pre-Stack Depth Migration

Directory of Open Access Journals (Sweden)

Qunshu Tang Chan Zheng

2010-01-01

Full Text Available In this paper, a velocity model of the Southern Depression of the Tainan Basin is obtained along with its migrated image from an iterative pre-stack depth migration approach. The Cenozoic strata are uniformly layered with velocities varying from ~1.8 to ~3.6 km s-1. However, the general velocity is slightly lower in the NW segment than the SE. Both fractures and burial depth might be the controls of their seismic velocities. There is an unconformable contact between the Cenozoic and underlying Mesozoic strata with an abrupt velocity jump from ~3.2 to ~4.3 km s-1. The Mesozoic strata are recognized with acoustically distinct reflection patterns (chaotic, deformed and discontinuous and complex internal structures (uplift, folds and faults. Their interval velocities range from ~4.3 to ~4.7 km s-1 within a depth from ~3.5 down to ~12.5 km, and the maximum depositional thickness reaches up to 6.5 km. Multiple tectonic events such as collision, subsidence and uplift might be responsible for the complexity of the Mesozoic strata.

Seismic velocity distribution in the vicinity of a mine tunnel at Thabazimbi, South Africa

CSIR Research Space (South Africa)

Wright, C

2000-07-01

Full Text Available Analysis of the refracted arrivals on a seismic reflection profile recorded along the wall of a tunnel at an iron mine near Thabazimbi, South Africa, shows variations in P-wave velocity in dolomite away from the de-stressed zone that vary between 4...

Monitoring Seismic Velocity Change to Explore the Earthquake Seismogenic Structures

Science.gov (United States)

Liao, C. F.; Wen, S.; Chen, C.

2017-12-01

Studying spatial-temporal variations of subsurface velocity structures is still a challenge work, but it can provide important information not only on geometry of a fault, but also the rheology change induced from the strong earthquake. In 1999, a disastrous Chi-Chi earthquake (Mw7.6; Chi-Chi EQ) occurred in central Taiwan and caused great impacts on Taiwan's society. Therefore, the major objective of this research is to investigate whether the rheology change of fault can be associated with seismogenic process before strong earthquake. In addition, after the strike of the Chi-Chi EQ, whether the subsurface velocity structure resumes to its steady state is another issue in this study. Therefore, for the above purpose, we have applied a 3D tomographic technique to obtain P- and S-wave velocity structures in central Taiwan using travel time data provided by the Central Weather Bureau (CWB). One major advantage of this method is that we can include out-of-network data to improve the resolution of velocity structures at deeper depths in our study area. The results show that the temporal variations of Vp are less significant than Vs (or Vp/Vs ratio), and Vp is not prominent perturbed before and after the occurrence of the Chi-Chi EQ. However, the Vs (or Vp/Vs ratio) structure in the source area demonstrates significant spatial-temporal difference before and after the mainshock. From the results, before the mainshock, Vs began to decrease (Vp/Vs ratio was increased as well) at the hanging wall of Chelungpu fault, which may be induced by the increasing density of microcracks and fluid. But in the vicinities of Chi-Chi Earthquake's source area, Vs was increasing (Vp/Vs ratio was also decreased). This phenomenon may be owing to the closing of cracks or migration of fluid. Due to the different physical characteristics around the source area, strong earthquake may be easily nucleated at the junctional zone. Our findings suggest that continuously monitoring the Vp and Vs (or

Uppermost mantle seismic velocity and anisotropy in the Euro-Mediterranean region from Pn and Sn tomography

Science.gov (United States)

Díaz, J.; Gil, A.; Gallart, J.

2013-01-01

In the last 10-15 years, the number of high quality seismic stations monitoring the Euro-Mediterranean region has increased significantly, allowing a corresponding improvement in structural constraints. We present here new images of the seismic velocity and anisotropy variations in the uppermost mantle beneath this complex area, compiled from inversion of Pn and Sn phases sampling the whole region. The method of Hearn has been applied to the traveltime arrivals of the International Seismological Center catalogue for the time period 1990-2010. A total of 579 753 Pn arrivals coming from 12 377 events recorded at 1 408 stations with epicentral distances between 220 km and 1 400 km have been retained after applying standard quality criteria (maximum depth, minimum number of recordings, maximum residual values …). Our results show significant features well correlated with surface geology and evidence the heterogeneous character of the Euro-Mediterranean lithosphere. The station terms reflect the existence of marked variations in crustal thickness, consistent with available Moho depths inferred from active seismic experiments. The highest Pn velocities are observed along a continuous band from the Po Basin to the northern Ionian Sea. Other high velocity zones include the Ligurian Basin, the Valencia Trough, the southern Alboran Sea and central part of the Algerian margin. Most significant low-velocity values are associated to orogenic belts (Betics, Pyrenees, Alps, Apennines and Calabrian Arc, Dinarides-Hellenides), and low-velocity zones are also identified beneath Sardinia and the Balearic Islands. The introduction of an anisotropic term enhances significantly the lateral continuity of the anomalies, in particular in the most active tectonic areas. Pn anisotropy shows consistent orientations subparallel to major orogenic structures, such as Betics, Apennines, Calabrian Arc and Alps. The Sn tomographic image has lower resolution but confirms independently most of the

Crustal composition in the Hidaka Metamorphic Belt estimated from seismic velocity by laboratory measurements

Science.gov (United States)

Yamauchi, K.; Ishikawa, M.; Sato, H.; Iwasaki, T.; Toyoshima, T.

2015-12-01

To understand the dynamics of the lithosphere in subduction systems, the knowledge of rock composition is significant. However, rock composition of the overriding plate is still poorly understood. To estimate rock composition of the lithosphere, it is an effective method to compare the elastic wave velocities measured under the high pressure and temperature condition with the seismic velocities obtained by active source experiment and earthquake observation. Due to an arc-arc collision in central Hokkaido, middle to lower crust is exposed along the Hidaka Metamorphic Belt (HMB), providing exceptional opportunities to study crust composition of an island arc. Across the HMB, P-wave velocity model has been constructed by refraction/wide-angle reflection seismic profiling (Iwasaki et al., 2004). Furthermore, because of the interpretation of the crustal structure (Ito, 2000), we can follow a continuous pass from the surface to the middle-lower crust. We corrected representative rock samples from HMB and measured ultrasonic P-wave (Vp) and S-wave velocities (Vs) under the pressure up to 1.0 GPa in a temperature range from 25 to 400 °C. For example, the Vp values measured at 25 °C and 0.5 GPa are 5.88 km/s for the granite (74.29 wt.% SiO2), 6.02-6.34 km/s for the tonalites (66.31-68.92 wt.% SiO2), 6.34 km/s for the gneiss (64.69 wt.% SiO2), 6.41-7.05 km/s for the amphibolites (50.06-51.13 wt.% SiO2), and 7.42 km/s for the mafic granulite (50.94 wt.% SiO2). And, Vp of tonalites showed a correlation with SiO2 (wt.%). Comparing with the velocity profiles across the HMB (Iwasaki et al., 2004), we estimate that the lower to middle crust consists of amphibolite and tonalite, and the estimated acoustic impedance contrast between them suggests an existence of a clear reflective boundary, which accords well to the obtained seismic reflection profile (Iwasaki et al., 2014). And, we can obtain the same tendency from comparing measured Vp/Vs ratio and Vp/Vs ratio structure model

Velocity variations associated with the large 2010 eruption of Merapi volcano, Java, retrieved from seismic multiplets and ambient noise cross-correlation

Science.gov (United States)

Budi-Santoso, Agus; Lesage, Philippe

2016-07-01

We present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of Merapi volcano. For the first time to our knowledge, the technique of coda wave interferometry is applied to both families of similar events (multiplets) and to correlation functions of seismic noise. About half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified, including 120 similar events that occurred in the last 20 hr preceding the eruption onset. Daily noise cross-correlation functions (NCF) were calculated for the six pairs of short-period stations available. Using the stretching method, we estimate time-series of apparent velocity variation (AVV) for each multiplet and each pair of stations. No significant velocity change is detected until September 2010. From 10 October to the beginning of the eruption on 26 October, a complex pattern of AVV is observed with amplitude of up to ±1.5 per cent. Velocity decrease is first observed from families of deep events and then from shallow earthquakes. In the same period, AVV with different signs and chronologies are estimated from NCF calculated for various station pairs. The location in the horizontal plane of the velocity perturbations related with the AVV obtained from NCF is estimated by using an approach based on the radiative transfer approximation. Although their spatial resolution is limited, the resulting maps display velocity decrease in the upper part of the edifice in the period 12-25 October. After the eruption onset, the pattern of velocity perturbations is significantly modified with respect to the previous one. We interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations. The perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks. Thus the detected AVVs can be considered as precursors of

Two types of SDR recognised in pre-stack velocity analysis of ultra-long-offset seismic reflection data in the South Atlantic

Science.gov (United States)

Collier, J.; McDermott, C.; Lonergan, L.; McDermott, K.; Bellingham, P.

2017-12-01

Our understanding of continental breakup at volcanic margins has lagged behind that of non-volcanic margins in recent years. This is largely due to seismic imaging problems caused by the presence of thick packages of Seaward-Dipping Reflectors (SDRs) in the continent-ocean transition zone. These packages consist of interbedded tholeiitic lava flows, volcanic tuffs and terrestrial sediment that results in scattering, peg-leg multiples and defocusing of seismic energy. Here we analyse three ultra-long-offset (10.2 km), wide-bandwidth (5-100 Hz) seismic reflection profiles acquired by ION-GXT offshore South America during 2009-12 to gain new insights into the velocity structure of the SDRs and hence pattern of magmatism during continental breakup. We observe two seismic velocity patterns within the SDRs. The most landward packages show high velocity anomaly "bulls-eyes" of up to 1 km s-1. These highs occur where the stacked section shows them to thicken at the down-dip end of individual packages that are bounded by faults. All lines show 5-6 velocity highs spaced approximately 10 km apart. We interpret the velocity bulls-eyes as depleted mafic or ultramafic bodies that fed the sub-aerial tholeiitic lava flows during continental stretching. Similar relationships have been observed in outcrop onshore but have not been previously demonstrated in seismic data. The bulls-eye packages pass laterally into SDR packages that show no velocity highs. These packages are not associated with faulting and become more extensive going north towards the impact point of the Tristan da Cunha hotspot. This second type of SDR coincides with linear magnetic anomalies. We interpret these SDRs as the products of sub-aerial oceanic spreading similar to those seen on Iceland and described in the classic "Hinz model" and marine geophysical literature. Our work demonstrates that these SDRs are preceded by ones generated during an earlier phase of mechanical thinning of the continental crust. The

2.5D seismic velocity modelling in the south-eastern Romanian Carpathians Orogen and its foreland

Science.gov (United States)

Bocin, Andrei; Stephenson, Randell; Tryggvason, Ari; Panea, Ionelia; Mocanu, Victor; Hauser, Franz; Matenco, Liviu

2005-12-01

The DACIA-PLAN (Danube and Carpathian Integrated Action on Processes in the Lithosphere and Neotectonics) deep seismic reflection survey was performed in August-September 2001, with the objective of obtaining new information on the deep structure of the external Carpathians nappe system and the architecture of the Tertiary/Quaternary basins developed within and adjacent to the Vrancea zone, including the rapidly subsiding Focsani Basin. The DACIA-PLAN profile is about 140 km long, having a roughly WNW-ESE direction, from near the southeast Transylvanian Basin, across the mountainous south-eastern Carpathians and their foreland to near the Danube River. A high resolution 2.5D velocity model of the upper crust along the seismic profile has been determined from a tomographic inversion of the DACIA-PLAN first arrival data. The results show that the data fairly accurately resolve the transition from sediment to crystalline basement beneath the Focsani Basin, where industry seismic data are available for correlation, at depths up to about 10 km. Beneath the external Carpathians nappes, apparent basement (material with velocities above 5.8 km/s) lies at depths as shallow as 3-4 km, which is less than previously surmised on the basis of geological observations. The first arrival travel-time data suggest that there is significant lateral structural heterogeneity on the apparent basement surface in this area, suggesting that the high velocity material may be involved in Carpathian thrusting.

Structure and Deformation in the Transpressive Zone of Southern California Inferred from Seismicity, Velocity, and Qp Models

Science.gov (United States)

Hauksson, E.; Shearer, P.

2004-12-01

We synthesize relocated regional seismicity and 3D velocity and Qp models to infer structure and deformation in the transpressive zone of southern California. These models provide a comprehensive synthesis of the tectonic fabric of the upper to middle crust, and the brittle ductile transition zone that in some cases extends into the lower crust. The regional seismicity patterns in southern California are brought into focus when the hypocenters are relocated using the double difference method. In detail, often the spatial correlation between background seismicity and late Quaternary faults is improved as the hypocenters become more clustered, and the spatial patterns are more sharply defined. Along some of the strike-slip faults the seismicity clusters decrease in width and form alignments implying that in many cases the clusters are associated with a single fault. In contrast, the Los Angeles Basin seismicity remains mostly scattered, reflecting a 3D distribution of the tectonic compression. We present the results of relocating 327,000 southern California earthquakes that occurred between 1984 and 2002. In particular, the depth distribution is improved and less affected by layer boundaries in velocity models or other similar artifacts, and thus improves the definition of the brittle ductile transition zone. The 3D VP and VP/VS models confirm existing tectonic interpretations and provide new insights into the configuration of the geological structures in southern California. The models extend from the US-Mexico border in the south to the Coast Ranges and Sierra Nevada in the north, and have 15 km horizontal grid spacing and an average vertical grid spacing of 4 km, down to 22 km depth. The heterogeneity of the crustal structure as imaged in both the VP and VP/VS models is larger within the Pacific than the North America plate, reflecting regional asymmetric variations in the crustal composition and past tectonic processes. Similarly, the relocated seismicity is

Spatiotemporal seismic velocity change in the Earth's subsurface associated with large earthquake: contribution of strong ground motion and crustal deformation

Science.gov (United States)

Sawazaki, K.

2016-12-01

It is well known that seismic velocity of the subsurface medium changes after a large earthquake. The cause of the velocity change is roughly attributed to strong ground motion (dynamic strain change), crustal deformation (static strain change), and fracturing around the fault zone. Several studies have revealed that the velocity reduction down to several percent concentrates at the depths shallower than several hundred meters. The amount of velocity reduction correlates well with the intensity of strong ground motion, which indicates that the strong motion is the primary cause of the velocity reduction. Although some studies have proposed contributions of coseismic static strain change and fracturing around fault zone to the velocity change, separation of their contributions from the site-related velocity change is usually difficult. Velocity recovery after a large earthquake is also widely observed. The recovery process is generally proportional to logarithm of the lapse time, which is similar to the behavior of "slow dynamics" recognized in laboratory experiments. The time scale of the recovery is usually months to years in field observations, while it is several hours in laboratory experiments. Although the factor that controls the recovery speed is not well understood, cumulative strain change due to post-seismic deformation, migration of underground water, mechanical and chemical reactions on the crack surface could be the candidate. In this study, I summarize several observations that revealed spatiotemporal distribution of seismic velocity change due to large earthquakes; especially I focus on the case of the M9.0 2011 Tohoku earthquake. Combining seismograms of Hi-net (high-sensitivity) and KiK-net (strong motion), geodetic records of GEONET and the seafloor GPS/Acoustic ranging, I investigate contribution of the strong ground motion and crustal deformation to the velocity change associated with the Tohoku earthquake, and propose a gross view of

Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

Science.gov (United States)

Syracuse, E. M.; Zhang, H.; Maceira, M.

2017-10-01

We present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body wave first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region. Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. Without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.

A California statewide three-dimensional seismic velocity model from both absolute and differential times

Science.gov (United States)

Lin, G.; Thurber, C.H.; Zhang, H.; Hauksson, E.; Shearer, P.M.; Waldhauser, F.; Brocher, T.M.; Hardebeck, J.

2010-01-01

We obtain a seismic velocity model of the California crust and uppermost mantle using a regional-scale double-difference tomography algorithm. We begin by using absolute arrival-time picks to solve for a coarse three-dimensional (3D) P velocity (VP) model with a uniform 30 km horizontal node spacing, which we then use as the starting model for a finer-scale inversion using double-difference tomography applied to absolute and differential pick times. For computational reasons, we split the state into 5 subregions with a grid spacing of 10 to 20 km and assemble our final statewide VP model by stitching together these local models. We also solve for a statewide S-wave model using S picks from both the Southern California Seismic Network and USArray, assuming a starting model based on the VP results and a VP=VS ratio of 1.732. Our new model has improved areal coverage compared with previous models, extending 570 km in the SW-NE directionand 1320 km in the NW-SE direction. It also extends to greater depth due to the inclusion of substantial data at large epicentral distances. Our VP model generally agrees with previous separate regional models for northern and southern California, but we also observe some new features, such as high-velocity anomalies at shallow depths in the Klamath Mountains and Mount Shasta area, somewhat slow velocities in the northern Coast Ranges, and slow anomalies beneath the Sierra Nevada at midcrustal and greater depths. This model can be applied to a variety of regional-scale studies in California, such as developing a unified statewide earthquake location catalog and performing regional waveform modeling.

Shear-wave velocity models and seismic sources in Campanian volcanic areas: Vesuvius and Phlegraean fields

Energy Technology Data Exchange (ETDEWEB)

Guidarelli, M; Zille, A; Sarao, A [Dipartimento di Scienze della Terra, Universita degli Studi di Trieste, Trieste (Italy); Natale, M; Nunziata, C [Dipartimento di Geofisica e Vulcanologia, Universita di Napoli ' Federico II' , Napoli (Italy); Panza, G F [Dipartimento di Scienze della Terra, Universita degli Studi di Trieste, Trieste (Italy); Abdus Salam International Centre for Theoretical Physics, Trieste (Italy)

2006-12-15

This chapter summarizes a comparative study of shear-wave velocity models and seismic sources in the Campanian volcanic areas of Vesuvius and Phlegraean Fields. These velocity models were obtained through the nonlinear inversion of surface-wave tomography data, using as a priori constraints the relevant information available in the literature. Local group velocity data were obtained by means of the frequency-time analysis for the time period between 0.3 and 2 s and were combined with the group velocity data for the time period between 10 and 35 s from the regional events located in the Italian peninsula and bordering areas and two station phase velocity data corresponding to the time period between 25 and 100 s. In order to invert Rayleigh wave dispersion curves, we applied the nonlinear inversion method called hedgehog and retrieved average models for the first 30-35 km of the lithosphere, with the lower part of the upper mantle being kept fixed on the basis of existing regional models. A feature that is common to the two volcanic areas is a low shear velocity layer which is centered at the depth of about 10 km, while on the outside of the cone and along a path in the northeastern part of the Vesuvius area this layer is absent. This low velocity can be associated with the presence of partial melting and, therefore, may represent a quite diffused crustal magma reservoir which is fed by a deeper one that is regional in character and located in the uppermost mantle. The study of seismic source in terms of the moment tensor is suitable for an investigation of physical processes within a volcano; indeed, its components, double couple, compensated linear vector dipole, and volumetric, can be related to the movements of magma and fluids within the volcanic system. Although for many recent earthquake events the percentage of double couple component is high, our results also show the presence of significant non-double couple components in both volcanic areas. (author)

Retrieving robust noise-based seismic velocity changes from sparse data sets: synthetic tests and application to Klyuchevskoy volcanic group (Kamchatka)

Science.gov (United States)

Gómez-García, C.; Brenguier, F.; Boué, P.; Shapiro, N. M.; Droznin, D. V.; Droznina, S. Ya; Senyukov, S. L.; Gordeev, E. I.

2018-05-01

Continuous noise-based monitoring of seismic velocity changes provides insights into volcanic unrest, earthquake mechanisms and fluid injection in the sub-surface. The standard monitoring approach relies on measuring travel time changes of late coda arrivals between daily and reference noise cross-correlations, usually chosen as stacks of daily cross-correlations. The main assumption of this method is that the shape of the noise correlations does not change over time or, in other terms, that the ambient-noise sources are stationary through time. These conditions are not fulfilled when a strong episodic source of noise, such as a volcanic tremor for example, perturbs the reconstructed Green's function. In this paper we propose a general formulation for retrieving continuous time series of noise-based seismic velocity changes without the requirement of any arbitrary reference cross-correlation function. Instead, we measure the changes between all possible pairs of daily cross-correlations and invert them using different smoothing parameters to obtain the final velocity change curve. We perform synthetic tests in order to establish a general framework for future applications of this technique. In particular, we study the reliability of velocity change measurements versus the stability of noise cross-correlation functions. We apply this approach to a complex dataset of noise cross-correlations at Klyuchevskoy volcanic group (Kamchatka), hampered by loss of data and the presence of highly non-stationary seismic tremors.

Accessing the uncertainties of seismic velocity and anisotropy structure of Northern Great Plains using a transdimensional Bayesian approach

Science.gov (United States)

Gao, C.; Lekic, V.

2017-12-01

Seismic imaging utilizing complementary seismic data provides unique insight on the formation, evolution and current structure of continental lithosphere. While numerous efforts have improved the resolution of seismic structure, the quantification of uncertainties remains challenging due to the non-linearity and the non-uniqueness of geophysical inverse problem. In this project, we use a reverse jump Markov chain Monte Carlo (rjMcMC) algorithm to incorporate seismic observables including Rayleigh and Love wave dispersion, Ps and Sp receiver function to invert for shear velocity (Vs), compressional velocity (Vp), density, and radial anisotropy of the lithospheric structure. The Bayesian nature and the transdimensionality of this approach allow the quantification of the model parameter uncertainties while keeping the models parsimonious. Both synthetic test and inversion of actual data for Ps and Sp receiver functions are performed. We quantify the information gained in different inversions by calculating the Kullback-Leibler divergence. Furthermore, we explore the ability of Rayleigh and Love wave dispersion data to constrain radial anisotropy. We show that when multiple types of model parameters (Vsv, Vsh, and Vp) are inverted simultaneously, the constraints on radial anisotropy are limited by relatively large data uncertainties and trade-off strongly with Vp. We then perform joint inversion of the surface wave dispersion (SWD) and Ps, Sp receiver functions, and show that the constraints on both isotropic Vs and radial anisotropy are significantly improved. To achieve faster convergence of the rjMcMC, we propose a progressive inclusion scheme, and invert SWD measurements and receiver functions from about 400 USArray stations in the Northern Great Plains. We start by only using SWD data due to its fast convergence rate. We then use the average of the ensemble as a starting model for the joint inversion, which is able to resolve distinct seismic signatures of

Evaluation of stress and saturation effects on seismic velocity and electrical resistivity - laboratory testing of rock samples

Science.gov (United States)

Vilhelm, Jan; Jirků, Jaroslav; Slavík, Lubomír; Bárta, Jaroslav

2016-04-01

Repository, located in a deep geological formation, is today considered the most suitable solution for disposal of spent nuclear fuel and high-level waste. The geological formations, in combination with an engineered barrier system, should ensure isolation of the waste from the environment for thousands of years. For long-term monitoring of such underground excavations special monitoring systems are developed. In our research we developed and tested monitoring system based on repeated ultrasonic time of flight measurement and electrical resistivity tomography (ERT). As a test site Bedřichov gallery in the northern Bohemia was selected. This underground gallery in granitic rock was excavated using Tunnel Boring Machine (TBM). The seismic high-frequency measurements are performed by pulse-transmission technique directly on the rock wall using one seismic source and three receivers in the distances of 1, 2 and 3 m. The ERT measurement is performed also on the rock wall using 48 electrodes. The spacing between electrodes is 20 centimeters. An analysis of relation of seismic velocity and electrical resistivity on water saturation and stress state of the granitic rock is necessary for the interpretation of both seismic monitoring and ERT. Laboratory seismic and resistivity measurements were performed. One series of experiments was based on uniaxial loading of dry and saturated granitic samples. The relation between stress state and ultrasonic wave velocities was tested separately for dry and saturated rock samples. Other experiments were focused on the relation between electrical resistivity of the rock sample and its saturation level. Rock samples with different porosities were tested. Acknowledgments: This work was partially supported by the Technology Agency of the Czech Republic, project No. TA 0302408

New evidence for the serpentinization of the Palaeozoic basement of southeastern Sicily from joint 3-D seismic velocity and attenuation tomography

Science.gov (United States)

Giampiccolo, E.; Brancato, A.; Manuella, F. C.; Carbone, S.; Gresta, S.; Scribano, V.

2017-12-01

In this study, we derived the first 3-D P-wave seismic attenuation images (QP) as well as new 3-D VP and VP/VS models for the crust in southeastern Sicily. We used a large data set of local seismic events occurring in the time span 1994-2013. The results of this tomographic study have important implications on the seismic behaviour of the region. Based on velocity and attenuation images, we identified distinct volumes characterized by different fluid content, which correlate well with seismicity distribution. Moreover, the obtained velocity and attenuation tomographies help us to provide a more complete picture of the crustal structure of the area. High VP, high QP and high VP/VS values have been obtained in the crustal basement, below a depth of 8 km, and may be interpreted as due to the presence of serpentinized peridotites. Accordingly, the new model for the degree of serpentinization, retrieved from VP values, shows that the basement has an average serpentinization value of 96 ± 3 vol.% at 8 km, decreasing to 44 ± 5 vol.% at about 18-20 km.

Deep Downhole Seismic Testing at the Waste Treatment Plant Site, Hanford, WA. Volume V S-Wave Measurements in Borehole C4996 Seismic Records, Wave-Arrival Identifications and Interpreted S-Wave Velocity Profile.

Energy Technology Data Exchange (ETDEWEB)

Stokoe, Kenneth H.; Li, Song Cheng; Cox, Brady R.; Menq, Farn-Yuh

2007-06-06

Velocity measurements in shallow sediments from ground surface to approximately 370 to 400 feet bgs were collected by Redpath Geophysics using impulsive S- and P-wave seismic sources (Redpath 2007). Measurements below this depth within basalt and sedimentary interbeds were made by UTA between October and December 2006 using the T-Rex vibratory seismic source in each of the three boreholes. Results of these measurements including seismic records, wave-arrival identifications and interpreted velocity profiles are presented in the following six volumes: I. P-Wave Measurements in Borehole C4993 II. P-Wave Measurements in Borehole C4996 III. P-Wave Measurements in Borehole C4997 IV. S-Wave Measurements in Borehole C4993 V. S-Wave Measurements in Borehole C4996 VI. S-Wave Measurements in Borehole C4997 In this volume (V), all S-wave measurements are presented that were performed in Borehole C4996 at the WTP with T-Rex as the seismic source and the Lawrence Berkeley National Laboratory (LBNL) 3-D wireline geophone as the at-depth borehole receiver.

Deep Downhole Seismic Testing at the Waste Treatment Plant Site, Hanford, WA. Volume VI S-Wave Measurements in Borehole C4997 Seismic Records, Wave-Arrival Identifications and Interpreted S-Wave Velocity Profile.

Energy Technology Data Exchange (ETDEWEB)

Stokoe, Kenneth H.; Li, Song Cheng; Cox, Brady R.; Menq, Farn-Yuh

2007-06-06

Velocity measurements in shallow sediments from ground surface to approximately 370 to 400 feet bgs were collected by Redpath Geophysics using impulsive S- and P-wave seismic sources (Redpath 2007). Measurements below this depth within basalt and sedimentary interbeds were made by UTA between October and December 2006 using the T-Rex vibratory seismic source in each of the three boreholes. Results of these measurements including seismic records, wave-arrival identifications and interpreted velocity profiles are presented in the following six volumes: I. P-Wave Measurements in Borehole C4993 II. P-Wave Measurements in Borehole C4996 III. P-Wave Measurements in Borehole C4997 IV. S-Wave Measurements in Borehole C4993 V. S-Wave Measurements in Borehole C4996 VI. S-Wave Measurements in Borehole C4997 In this volume (VI), all S-wave measurements are presented that were performed in Borehole C4997 at the WTP with T-Rex as the seismic source and the Lawrence Berkeley National Laboratory (LBNL) 3-D wireline geophone as the at-depth borehole receiver.

Absolute earthquake locations using 3-D versus 1-D velocity models below a local seismic network: example from the Pyrenees

Science.gov (United States)

Theunissen, T.; Chevrot, S.; Sylvander, M.; Monteiller, V.; Calvet, M.; Villaseñor, A.; Benahmed, S.; Pauchet, H.; Grimaud, F.

2018-03-01

Local seismic networks are usually designed so that earthquakes are located inside them (primary azimuthal gap 180° and distance to the first station higher than 15 km). Errors on velocity models and accuracy of absolute earthquake locations are assessed based on a reference data set made of active seismic, quarry blasts and passive temporary experiments. Solutions and uncertainties are estimated using the probabilistic approach of the NonLinLoc (NLLoc) software based on Equal Differential Time. Some updates have been added to NLLoc to better focus on the final solution (outlier exclusion, multiscale grid search, S-phases weighting). Errors in the probabilistic approach are defined to take into account errors on velocity models and on arrival times. The seismicity in the final 3-D catalogue is located with a horizontal uncertainty of about 2.0 ± 1.9 km and a vertical uncertainty of about 3.0 ± 2.0 km.

Estimating regional pore pressure distribution using 3D seismic velocities in the Dutch Central North Sea Graben

NARCIS (Netherlands)

Winthaegen, P.L.A.; Verweij, J.M.

2003-01-01

The application of the empirical Eaton method to calibrated sonic well information and 3D seismic interval velocity data in the southeastern part of the Central North Sea Graben, using the Japsen (Glob. Planet. Change 24 (2000) 189) normal velocitydepth trend, resulted in the identification of an

Crustal seismicity and the earthquake catalog maximum moment magnitudes (Mcmax) in stable continental regions (SCRs): correlation with the seismic velocity of the lithosphere

Science.gov (United States)

Mooney, Walter D.; Ritsema, Jeroen; Hwang, Yong Keun

2012-01-01

A joint analysis of global seismicity and seismic tomography indicates that the seismic potential of continental intraplate regions is correlated with the seismic properties of the lithosphere. Archean and Early Proterozoic cratons with cold, stable continental lithospheric roots have fewer crustal earthquakes and a lower maximum earthquake catalog moment magnitude (Mcmax). The geographic distribution of thick lithospheric roots is inferred from the global seismic model S40RTS that displays shear-velocity perturbations (δVS) relative to the Preliminary Reference Earth Model (PREM). We compare δVS at a depth of 175 km with the locations and moment magnitudes (Mw) of intraplate earthquakes in the crust (Schulte and Mooney, 2005). Many intraplate earthquakes concentrate around the pronounced lateral gradients in lithospheric thickness that surround the cratons and few earthquakes occur within cratonic interiors. Globally, 27% of stable continental lithosphere is underlain by δVS≥3.0%, yet only 6.5% of crustal earthquakes with Mw>4.5 occur above these regions with thick lithosphere. No earthquakes in our catalog with Mw>6 have occurred above mantle lithosphere with δVS>3.5%, although such lithosphere comprises 19% of stable continental regions. Thus, for cratonic interiors with seismically determined thick lithosphere (1) there is a significant decrease in the number of crustal earthquakes, and (2) the maximum moment magnitude found in the earthquake catalog is Mcmax=6.0. We attribute these observations to higher lithospheric strength beneath cratonic interiors due to lower temperatures and dehydration in both the lower crust and the highly depleted lithospheric root.

Crustal seismicity and the earthquake catalog maximum moment magnitude (Mcmax) in stable continental regions (SCRs): Correlation with the seismic velocity of the lithosphere

Science.gov (United States)

Mooney, Walter D.; Ritsema, Jeroen; Hwang, Yong Keun

2012-12-01

A joint analysis of global seismicity and seismic tomography indicates that the seismic potential of continental intraplate regions is correlated with the seismic properties of the lithosphere. Archean and Early Proterozoic cratons with cold, stable continental lithospheric roots have fewer crustal earthquakes and a lower maximum earthquake catalog moment magnitude (Mcmax). The geographic distribution of thick lithospheric roots is inferred from the global seismic model S40RTS that displays shear-velocity perturbations (δVS) relative to the Preliminary Reference Earth Model (PREM). We compare δVS at a depth of 175 km with the locations and moment magnitudes (Mw) of intraplate earthquakes in the crust (Schulte and Mooney, 2005). Many intraplate earthquakes concentrate around the pronounced lateral gradients in lithospheric thickness that surround the cratons and few earthquakes occur within cratonic interiors. Globally, 27% of stable continental lithosphere is underlain by δVS≥3.0%, yet only 6.5% of crustal earthquakes with Mw>4.5 occur above these regions with thick lithosphere. No earthquakes in our catalog with Mw>6 have occurred above mantle lithosphere with δVS>3.5%, although such lithosphere comprises 19% of stable continental regions. Thus, for cratonic interiors with seismically determined thick lithosphere (1) there is a significant decrease in the number of crustal earthquakes, and (2) the maximum moment magnitude found in the earthquake catalog is Mcmax=6.0. We attribute these observations to higher lithospheric strength beneath cratonic interiors due to lower temperatures and dehydration in both the lower crust and the highly depleted lithospheric root.

Near-surface characterization for seismic exploration based on gravity and resistivity data

Czech Academy of Sciences Publication Activity Database

Mrlina, Jan

(2016), č. článku 41892. [Middle East Geoscience Conference and Exhibition /12./. Manama, 07.03.2016-10.03.2016] Institutional support: RVO:67985530 Keywords : gravity and resistivity surveys * near-surface formations * seismic velocity Subject RIV: DC - Siesmology, Volcanology, Earth Structure

Compositional trends among Kaapvaal Craton garnet peridotite xenoliths and their effects on seismic velocity and density

DEFF Research Database (Denmark)

Schutt, Derek; Lesher, Charles

2010-01-01

garnet and clinopyroxene enrichment. Using the parameterization of Schutt and Lesher (2006) we show that at cratonic mantle temperatures and pressures, orthopyroxene enrichment results in little change in bulk density (ρbulk) and shear-wave velocity (VS), but decreases compressional wave velocities (VP......We examine the modes and compositions of garnet-bearing peridotite xenoliths from the Kaapvaal Craton to quantify factors governing density and seismic velocity variations within metasomatically altered cratonic mantle. Three distinct compositional trends are resolved by principal component...... analysis. The first reflects differences in residue composition resulting from partial melting. The second is associated with orthopyroxene (opx) enrichment, possibly due to silica addition by subduction zone fluids in the source region of the xenoliths. The third principal component reflects garnet...

Multivariate Formation Pressure Prediction with Seismic-derived Petrophysical Properties from Prestack AVO inversion and Poststack Seismic Motion Inversion

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Yu, H.; Gu, H.

2017-12-01

A novel multivariate seismic formation pressure prediction methodology is presented, which incorporates high-resolution seismic velocity data from prestack AVO inversion, and petrophysical data (porosity and shale volume) derived from poststack seismic motion inversion. In contrast to traditional seismic formation prediction methods, the proposed methodology is based on a multivariate pressure prediction model and utilizes a trace-by-trace multivariate regression analysis on seismic-derived petrophysical properties to calibrate model parameters in order to make accurate predictions with higher resolution in both vertical and lateral directions. With prestack time migration velocity as initial velocity model, an AVO inversion was first applied to prestack dataset to obtain high-resolution seismic velocity with higher frequency that is to be used as the velocity input for seismic pressure prediction, and the density dataset to calculate accurate Overburden Pressure (OBP). Seismic Motion Inversion (SMI) is an inversion technique based on Markov Chain Monte Carlo simulation. Both structural variability and similarity of seismic waveform are used to incorporate well log data to characterize the variability of the property to be obtained. In this research, porosity and shale volume are first interpreted on well logs, and then combined with poststack seismic data using SMI to build porosity and shale volume datasets for seismic pressure prediction. A multivariate effective stress model is used to convert velocity, porosity and shale volume datasets to effective stress. After a thorough study of the regional stratigraphic and sedimentary characteristics, a regional normally compacted interval model is built, and then the coefficients in the multivariate prediction model are determined in a trace-by-trace multivariate regression analysis on the petrophysical data. The coefficients are used to convert velocity, porosity and shale volume datasets to effective stress and then

The density, compressibility and seismic velocity of hydrous melts at crustal and upper mantle conditions

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Ueki, K.; Iwamori, H.

2015-12-01

Various processes of subduction zone magmatism, such as upward migration of partial melts and fractional crystallization depend on the density of the hydrous silicate melt. The density and the compressibility of the hydrous melt are key factors for the thermodynamic calculation of phase relation of the hydrous melt, and the geophysical inversion to predict physicochemical conditions of the melting region based on the seismic velocity. This study presents a new model for the calculations of the density of the hydrous silicate melts as a function of T, P, H2O content and melt composition. The Birch-Murnaghan equation is used for the equation of state. We compile the experimentally determined densities of various hydrous melts, and optimize the partial molar volume, compressibility, thermal expansibility and its pressure derivative, and K' of the H2O component in the silicate melt. P-T ranges of the calibration database are 0.48-4.29 GPa and 1033-2073 K. As such, this model covers the P-T ranges of the entire melting region of the subduction zone. Parameter set provided by Lange and Carmichael [1990] is used for the partial molar volume and KT value of the anhydrous silicate melt. K' of anhydrous melt is newly parameterized as a function of SiO2 content. The new model accurately reproduces the experimentally determined density variations of various hydrous melts from basalt to rhyolite. Our result shows that the hydrous melt is more compressive and less dense than the anhydrous melt; with the 5 wt% of H2O in melt, density and KT decrease by ~10% and ~30% from those of the anhydrous melt, respectively. For the application of the model, we calculated the P-wave velocity of the hydrous melt. With the 5 wt% of H2O, P-wave velocity of the silicate melt decreases by >10%. Based on the melt P-wave velocity, we demonstrate the effect of the melt H2O content on the seismic velocity of the partially molten zone of the subduction zone.

Automated seismic waveform location using Multichannel Coherency Migration (MCM)-I. Theory

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Shi, Peidong; Angus, Doug; Rost, Sebastian; Nowacki, Andy; Yuan, Sanyi

2018-03-01

With the proliferation of dense seismic networks sampling the full seismic wavefield, recorded seismic data volumes are getting bigger and automated analysis tools to locate seismic events are essential. Here, we propose a novel Multichannel Coherency Migration (MCM) method to locate earthquakes in continuous seismic data and reveal the location and origin time of seismic events directly from recorded waveforms. By continuously calculating the coherency between waveforms from different receiver pairs, MCM greatly expands the available information which can be used for event location. MCM does not require phase picking or phase identification, which allows fully automated waveform analysis. By migrating the coherency between waveforms, MCM leads to improved source energy focusing. We have tested and compared MCM to other migration-based methods in noise-free and noisy synthetic data. The tests and analysis show that MCM is noise resistant and can achieve more accurate results compared with other migration-based methods. MCM is able to suppress strong interference from other seismic sources occurring at a similar time and location. It can be used with arbitrary 3D velocity models and is able to obtain reasonable location results with smooth but inaccurate velocity models. MCM exhibits excellent location performance and can be easily parallelized giving it large potential to be developed as a real-time location method for very large datasets.

3-D velocity structures, seismicity patterns, and their tectonic implications across the Andean Foreland of San Juan Argentina

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Asmerom, Biniam Beyene

Three-dimensional velocity structures and seismicity patterns have been studied across the Andean Foreland of San Juan Argentina using data acquired by PANDA deployment. Distinct velocity variations are revealed between Precordillera in the west and Pie de Palo in the east. The low velocity anomaly beneath Precordillera is associated with the presence of thick sedimentary rocks and thick sediment cover of Matagusanos valley. Similarly, the high velocity anomaly east of Eastern Precordillera is correlated with the presence of basement rocks. These anomalies are observed from the station corrections of Joint Hypocentral Determination (JHD) analysis. A northeast trending west dipping high velocity anomaly is imaged beneath the southern half of Pie de Palo. This anomaly represents a Grenvillian suture zone formed when Pie de Palo collided with the Precordillera. Relocated seismicity using 3-D Vp and Vs models obtained in this study revealed crustal scale buried faults beneath the Eastern Precordillera and Sierra Pie de Palo. The fault defined by the seismicity extend down to a depth of ˜ 40 km and ~35 km beneath Precordillera and Pie de Palo, respectively, defining the lower bound of the brittle to ductile transition of the crust. These results confirm that present day active crustal thickening involves the entire crust in the tectonic process and results in thick-skinned deformation beneath both the Eastern Precordillera and Pie de Palo. Based on the seismicity pattern, geomorphology, and velocity structures, Sierra Pie de Palo, a basement uplift block, can be divided into two separate semi-blocks separated by a northeast trending fracture zone. The northern block is characterized by a well-defined west dipping fault and low Vp/Vs ratio particularly at a depth of 12 to 16 km, while the southern block shows a poorly-defined east dipping fault with high Vp/Vs ratio at a depth of 20 to 26 km. Spatial distribution of the well-relocated crustal earthquakes along these

A Study on the Compatibility of 3-D Seismic Velocity Structures with Gravity Data of Taiwan

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Horng-Yuan Yen Hsien-Hsiang Hsieh

2010-01-01

Full Text Available The Bouguer anomaly of Taiwan has been revised in this study based on more accurate terrain data provided by the Taiwanese Digital Terrain Model compiled by the Taiwan Forestry Bureau. Three seismic velocity models, those determined by Rau and Wu (1995, Kim et al. (2005, and Wu et al. (2007 respectively, were selected for our study. We converted their velocity models to density models using the relationship between P-wave velocity and rock density proposed by Ludwig et al. (1970 and Barton (1986, and then calculated their corresponding gravity anomalies. According to the correlation coefficient between the Bouguer anomalies calculated from the velocity models and the revised Bouguer anomalies, the Kim et al. model was more compatible with gravity data than the other two velocity models. The differences between the revised gravity anomaly and the calculated gravity anomalies trend toward positive values at elevations higher than 2000 m. This indicates that the velocities at the shallower depths beneath the mountainous area of the three models are overdetermined, i.e., higher than the real velocities. This ratiocination implies that the crustal thickness beneath the Central Range is less than 55 km which was obtained from the velocity models.

Seismic Velocity/Temperature Correlations and a Possible New Geothermometer: Insights from Exploration of a High-Temperature Geothermal System on Montserrat, West Indies

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Graham Alexander Ryan

2014-10-01

Full Text Available In 2013, two production wells were drilled into a geothermal reservoir on Montserrat, W.I. (West Indies Drilling results confirmed the main features of a previously developed conceptual model. The results confirm that below ~220 °C there is a negative correlation between reservoir temperature and seismic velocity anomaly. However, above ~220 °C there is a positive correlation. We hypothesise that anomalous variations in seismic velocity within the reservoir are controlled to first order by the hydrothermal mineral assemblage. This study suggests a new geophysical thermometer which can be used to estimate temperatures in three dimensions with unprecedented resolution and to indicate the subsurface fluid pathways which are the target of geothermal exploitation.

2D Seismic Velocity Modelling in the Southeastern Romanian Carpathians and its Foreland (Vrancea Zone and Focsani Basin)

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Stephenson, R.; Bocin, A.; Tryggvason, A.

2003-12-01

The DACIA-PLAN (Danube and Carpathian Integrated Action on Processes in the Lithosphere and Neotectonics) deep seismic reflection survey was performed in August-September 2001, with the objective of obtaining of new information on the deep structure of the external Carpathians nappes and the architecture of Tertiary/Quaternary basins developed within and adjacent to the seismically-active Vrancea Zone, including the rapidly subsiding Focsani Basin. The DACIA-PLAN profile is about 140 km long, having a roughly NW-SE direction, from near the southeast Transylvanian Basin, across the mountainous southeastern Carpathians and their foreland to near the Danube Dalta. A high resolution 2D velocity model of the upper crust along the seismic profile has been determined from a first-arrival tomographic inversion of the DACIA-PLAN data. The shallowing of Palaeozoic-Mesozoic basement, and related structural heterogeneity within it, beneath the eastern flank of the Focsani Basin is clearly seen. Velocity heterogeneity within the Carpathian nappe belt is also evident and is indicative of internal structural complexity, including the presence of salt bodies and basement involvement in thrusting, thus favouring some current geological models over others. The presence of basement involvement implies the compressional reactivation of pre-existing basement normal faults. Members of the DACIA-PLAN/TomoSeis Working Group (see poster) should be considered as co-authors of this presentation.

Seismic velocity structure of the crust in NW Namibia: Impact of rifting and mantle plume activity

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Bauer, K.; Heit, B.; Muksin, U.; Yuan, X.

2017-12-01

The continental crust in northwestern Namibiamainly was formed during to the Neoproterozoic assembly of Gondwana. The collision of old African and South American cratonic coressuch as the Congo, Kalahari and Rio de la Plata cratons led tothe development of the Pan-African Damara orogen. The fold systemconsists of an intracratonic branch in northern central Namibia (named Damara Belt), and two coast-parallel branches, the Kaoko Belt in northern Namibia and the Gariep Belt in the border region between Namibia and theRepublic of South Africa. During the Early Cretaceous opening of the South Atlantic ocean, the crust in NW Namibia was prominently affected by the Tristan da Cunha mantle plume, as evidenced by the emplacement of the Etendeka continental flood basalts.A local earthquake tomography was carried out in NW Namibia to investigateif and to what degree the deeper continental crust was modified by the magmaticactivity during rifting and the impingement of the Tristan da Cunhamantle plume. We analyzed data from 28 onshore stations of the temporaryWALPASS seismic network. Stations were covering the continental marginaround the landfall of the Walvis Ridge, parts of the Kaoko Belt and Damara Belt,and marginally the southwestern edges of the Congo craton.First arrivals of P and S waves were identified and travel times werepicked manually. 1D inversion was carried out with VELEST to derivestarting models and the initial seismicity distribution, and SIMUL2000was used for the subsequent 3D tomographic inversion. The resultingseismicity distribution mainly follows the structures of the Pan-Africanorogenic belts. The majority of events was localized in the upper crust,but additional seismicity was also found in the deeper crust.An anomaly of increased P velocities is revealed in the deep crust under the Etendekaflood basalt province. Increased P velocities can be explained by mafic and ultra-maficmaterial which intruded in the lower crust. The anomaly appears to be rather

The ascent of magma as determined by seismic tomography. The visualization of velocity structure and magma distribution from upper mantle to upper crust in Hakone volcano, northern Izu peninsula

International Nuclear Information System (INIS)

Abe, Shintaro; Aoyagi, Yasuhira; Toshida, Kiyoshi; Oda, Yoshiya

2003-01-01

Three-dimensional seismic reflection and refraction survey was carried out in Hakone volcanic area, northern part of Izu peninsula. The region is one of the most famous hot spring areas in Japan. Hakone volcano morphologically resembles one big caldera. However, the depression of the volcano consists of several small calderas which has been formed by multiple eruptions. Although sprouts of fumarolic gas and steam are identified in a few areas of the volcano, there is no historical record of volcanic eruption. Main purpose of our study is to determine the 3-dimensional deep velocity structure around the volcano using the seismic tomography processing. We deployed 44 sets of temporal offline seismic stations and a line of multi-channels seismic reflection survey cable. The seismic waves generated by some natural earthquakes and 14 dynamite explosions were observed, and their data were processed for tomography. The observation coverage was 20 km in diameter. Our result demonstrates the usefulness of high dense seismic observation in identifying and locating low velocity zones beneath the particular area. According to our tomography, low velocity zone was identified only in surface layer of the old caldera part of the volcano. We could not identify any remarkable reflector in deeper crust, as the result of wide-angle reflection survey using explosive shots. Moreover, we could not identify any other low velocity zone as far as 32 km depth by incorporating the results of other study. In other words, we think that magma is no longer supplied to Hakone volcanic area. (author)

Crustal thickness and velocity structure across the Moroccan Atlas from long offset wide-angle reflection seismic data: The SIMA experiment

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Ayarza, P.; Carbonell, R.; Teixell, A.; Palomeras, I.; Martí, D.; Kchikach, A.; Harnafi, M.; Levander, A.; Gallart, J.; Arboleya, M. L.; Alcalde, J.; Fernández, M.; Charroud, M.; Amrhar, M.

2014-05-01

The crustal structure and topography of the Moho boundary beneath the Atlas Mountains of Morocco has been constrained by a controlled source, wide-angle seismic reflection transect: the SIMA experiment. This paper presents the first results of this project, consisting of an almost 700 km long, high-resolution seismic profile acquired from the Sahara craton across the High and the Middle Atlas and the Rif Mountains. The interpretation of this seismic data set is based on forward modeling by raytracing, and has resulted in a detailed crustal structure and velocity model for the Atlas Mountains. Results indicate that the High Atlas features a moderate crustal thickness, with the Moho located at a minimum depth of 35 km to the S and at around 31 km to the N, in the Middle Atlas. Upper crustal shortening is resolved at depth through a crustal root where the Saharan crust underthrusts the northern Moroccan crust. This feature defines a lower crust imbrication that, locally, places the Moho boundary at ˜40-41 km depth in the northern part of the High Atlas. The P-wave velocity model is characterized by relatively low velocities, mostly in the lower crust and upper mantle, when compared to other active orogens and continental regions. These low deep crustal velocities together with other geophysical observables such as conductivity estimates derived from MT measurements, moderate Bouguer gravity anomaly, high heat flow, and surface exposures of recent alkaline volcanism lead to a model where partial melts are currently emplaced at deep crustal levels and in the upper mantle. The resulting model supports the existence of a mantle upwelling as mechanism that would contribute significantly to sustain the High Atlas topography. However, the detailed Moho geometry deduced in this work should lead to a revision of the exact geometry and position of this mantle feature and will require new modeling efforts.

Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion

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Davy, R. G.; Morgan, J. V.; Minshull, T. A.; Bayrakci, G.; Bull, J. M.; Klaeschen, D.; Reston, T. J.; Sawyer, D. S.; Lymer, G.; Cresswell, D.

2018-01-01

Continental hyperextension during magma-poor rifting at the Deep Galicia Margin is characterized by a complex pattern of faulting, thin continental fault blocks and the serpentinization, with local exhumation, of mantle peridotites along the S-reflector, interpreted as a detachment surface. In order to understand fully the evolution of these features, it is important to image seismically the structure and to model the velocity structure to the greatest resolution possible. Traveltime tomography models have revealed the long-wavelength velocity structure of this hyperextended domain, but are often insufficient to match accurately the short-wavelength structure observed in reflection seismic imaging. Here, we demonstrate the application of 2-D time-domain acoustic full-waveform inversion (FWI) to deep-water seismic data collected at the Deep Galicia Margin, in order to attain a high-resolution velocity model of continental hyperextension. We have used several quality assurance procedures to assess the velocity model, including comparison of the observed and modeled waveforms, checkerboard tests, testing of parameter and inversion strategy and comparison with the migrated reflection image. Our final model exhibits an increase in the resolution of subsurface velocities, with particular improvement observed in the westernmost continental fault blocks, with a clear rotation of the velocity field to match steeply dipping reflectors. Across the S-reflector, there is a sharpening in the velocity contrast, with lower velocities beneath S indicative of preferential mantle serpentinization. This study supports the hypothesis that normal faulting acts to hydrate the upper-mantle peridotite, observed as a systematic decrease in seismic velocities, consistent with increased serpentinization. Our results confirm the feasibility of applying the FWI method to sparse, deep-water crustal data sets.

Seismic Structure of Perth Basin (Australia) and surroundings from Passive Seismic Deployments

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Issa, N.; Saygin, E.; Lumley, D. E.; Hoskin, T. E.

2016-12-01

We image the subsurface structure of Perth Basin, Western Australia and surroundings by using ambient seismic noise data from 14 seismic stations recently deployed by University of Western Australia (UWA) and other available permanent stations from Geoscience Australia seismic network and the Australian Seismometers in Schools program. Each of these 14 UWA seismic stations comprises a broadband sensor and a high fidelity 3-component 10 Hz geophone, recording in tandem at 250 Hz and 1000 Hz. The other stations used in this study are equipped with short period and broadband sensors. In addition, one shallow borehole station is operated with eight 3 component geophones at depths of between 2 and 44 m. The network is deployed to characterize natural seismicity in the basin and to try and identify any microseismic activity across Darling Fault Zone (DFZ), bounding the basin to the east. The DFZ stretches to approximately 1000 km north-south in Western Australia, and is one of the longest fault zones on the earth with a limited number of detected earthquakes. We use seismic noise cross- and auto-correlation methods to map seismic velocity perturbations across the basin and the transition from DFZ to the basin. Retrieved Green's functions are stable and show clear dispersed waveforms. Travel times of the surface wave Green's functions from noise cross-correlations are inverted with a two-step probabilistic framework to map the absolute shear wave velocities as a function of depth. The single station auto-correlations from the seismic noise yields P wave reflectivity under each station, marking the major discontinuities. Resulting images show the shear velocity perturbations across the region. We also quantify the variation of ambient seismic noise at different depths in the near surface using the geophones in the shallow borehole array.

Near‐surface void detection using a seismic landstreamer and horizontal velocity and attenuation tomography

Science.gov (United States)

Buckley, Sean F.; Lane, John W.

2012-01-01

The detection and characterization of subsurface voids plays an important role in the study of karst formations and clandestine tunnels. Horizontal velocity and attenuation tomography (HVAT) using offset‐fan shooting and a towed seismic land streamer is a simple, rapid, minimally invasive method that shows promise for detecting near‐surface voids and providing information on the orientation of linear voids. HVAT surveys were conducted over a known subsurface steam tunnel on the University of Connecticut Depot Campus, Storrs, Connecticut. First‐arrival travel‐time and amplitude data were used to produce two‐dimensional (2D) horizontal (map view) velocity and attenuation tomograms. In addition, attenuation tomograms were produced based on normalized total trace energy (TTE). Both the velocity and TTE attenuation tomograms depict an anomaly consistent with the location and orientation of the known tunnel; the TTE method, however, requires significantly less processing time, and therefore may provide a path forward to semi‐automated, near real‐time detection of near‐surface voids. Further study is needed to assess the utility of the HVAT method to detect deeper voids and the effects of a more complex geology on HVAT results.

Estimation of seismic velocity in the subducting crust of the Pacific slab beneath Hokkaido, northern Japan by using guided waves

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Shiina, T.; Nakajima, J.; Toyokuni, G.; Kita, S.; Matsuzawa, T.

2014-12-01

A subducting crust contains a large amount of water as a form of hydrous minerals (e.g., Hacker et al., 2003), and the crust plays important roles for water transportation and seismogenesis in subduction zones at intermediate depths (e.g., Kirby et al., 1996; Iwamori, 2007). Therefore, the investigation of seismic structure in the crust is important to understand ongoing physical processes with subduction of oceanic lithosphere. A guided wave which propagates in the subducting crust is recorded in seismograms at Hokkaido, northern Japan (Shiina et al., 2014). Here, we estimated P- and S-wave velocity in the crust with guided waves, and obtained P-wave velocity of 6.6-7.3 km/s and S-wave velocity of 3.6-4.2 km/s at depths of 50-90 km. Moreover, Vp/Vs ratio in the crust is calculated to be 1.80-1.85 in that depth range. The obtained P-wave velocity about 6.6km/s at depths of 50-70 km is consistent with those estimated in Tohoku, northeast Japan (Shiina et al., 2013), and this the P-wave velocity is lower than those expected from models of subducting crustal compositions, such as metamorphosed MORB model (Hacker et al., 2003). In contrast, at greater depths (>80 km), the P-wave velocity marks higher velocity than the case of NE Japan and the velocity is roughly comparable to those of the MORB model. The obtained S-wave velocity distribution also shows characteristics similar to P waves. This regional variation may be caused by a small variation in thermal regime of the Pacific slab beneath the two regions as a result of the normal subduction in Tohoku and oblique subduction in Hokkaido. In addition, the effect of seismic anisotropy in the subducting crust would not be ruled out because rays used in the analysis in Hokkaido propagate mostly in the trench-parallel direction, while those in Tohoku are sufficiently criss-crossed.

Velocity and stress distributions of deep seismic zone under Izu-Bonin, Japan

Science.gov (United States)

Jiang, Guoming; Zhang, Guibin; Jia, Zhengyuan

2017-04-01

Deep earthquakes can provide the deep information of the Earth directly. We have collected the waveform data from 77 deep earthquakes with depth greater than 300 km under Izu-Bonin in Japan. To obtain the velocity structures of P- and S-wave, we have inversed the double-differences of travel times from deep event-pairs. These velocity anomalies can further yield the Poisson's ratio and the porosity. Our results show that the average P-wave velocity anomaly is lower 6%, however the S-wave anomaly is higher 2% than the iasp91 model. The corresponding Poisson's ratio and porosity anomaly are -24% and -4%, respectively, which suggest that the possibility of water in the deep seismic zone is very few and the porosity might be richer. To obtain the stress distribution, we have used the ISOLA method to analyse the non-double-couple components of moment tensors of 77 deep earthquakes. The focal mechanism results show that almost half of all earthquakes have larger double-couple (DC) components, but others have clear isotropic (ISO) or compensated linear vector dipole (CLVD) components. The non-double-couple components (ISO and CLVD) seem to represent the volume around a deep earthquake changes as it occurs, which could be explained the metastable olivine phase transition. All results indicate that the metastable olivine wedge (MOW) might exist in the Pacific slab under the Izu-Bonin region and the deep earthquakes might be induced by the phase change of metastable olivine.

A Two-Radius Circular Array Method: Extracting Independent Information on Phase Velocities of Love Waves From Microtremor Records From a Simple Seismic Array

Science.gov (United States)

Tada, T.; Cho, I.; Shinozaki, Y.

2005-12-01

We have invented a Two-Radius (TR) circular array method of microtremor exploration, an algorithm that enables to estimate phase velocities of Love waves by analyzing horizontal-component records of microtremors that are obtained with an array of seismic sensors placed around circumferences of two different radii. The data recording may be done either simultaneously around the two circles or in two separate sessions with sensors distributed around each circle. Both Rayleigh and Love waves are present in the horizontal components of microtremors, but in the data processing of our TR method, all information on the Rayleigh waves ends up cancelled out, and information on the Love waves alone are left to be analyzed. Also, unlike the popularly used frequency-wavenumber spectral (F-K) method, our TR method does not resolve individual plane-wave components arriving from different directions and analyze their "vector" phase velocities, but instead directly evaluates their "scalar" phase velocities --- phase velocities that contain no information on the arrival direction of waves --- through a mathematical procedure which involves azimuthal averaging. The latter feature leads us to expect that, with our TR method, it is possible to conduct phase velocity analysis with smaller numbers of sensors, with higher stability, and up to longer-wavelength ranges than with the F-K method. With a view to investigating the capabilities and limitations of our TR method in practical implementation to real data, we have deployed circular seismic arrays of different sizes at a test site in Japan where the underground structure is well documented through geophysical exploration. Ten seismic sensors were placed equidistantly around two circumferences, five around each circle, with varying combinations of radii ranging from several meters to several tens of meters, and simultaneous records of microtremors around circles of two different radii were analyzed with our TR method to produce

Seismic Responses of an Added-Story Frame Structure with Viscous Dampers

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Xuansheng Cheng

2014-01-01

Full Text Available The damping ratio of an added-story frame structure is established based on complex damping theory to determine the structure seismic response. The viscous dampers are selected and arranged through target function method. A significant damping effect is obtained when a small velocity index is selected. The seismic responses of a five-floor reinforced concrete frame structure with directly added light steel layers and light steel layers with viscous dampers are compared with the finite element software SAP2000. Calculation results show that, after adding the layers, the structure becomes flexible and the shear in the bottom layer decreases. However, the interlaminar shear of the other layers increases. The seismic response of the added layers is very significant and exhibits obvious whiplash effect. The interstory displacement angles of some layers do not meet the requirements. The seismic response of the structure decreases after the adoption of viscous dampers; thereby seismic requirements are satisfied.

Subsurface investigation on Quarter 27 of May 15th city, Cairo, Egypt using electrical resistivity tomography and shallow seismic refraction techniques

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Sultan Awad Sultan Araffa

2014-12-01

Full Text Available Geophysical tools such as electrical resistivity tomography (ERT and shallow seismic (both P-wave seismic refraction and Multi-channel Analysis of Surface Waves (MASW are interesting techniques for delineating the subsurface configurations as stratigraphy, structural elements, caves and water saturated zones. The ERT technique is used to delineate the contamination, to detect the buried objects, and to quantify some aquifer properties. Eight 2-D (two dimensional electrical resistivity sections were measured using two different configurations (dipole–dipole and Wenner. The spread length is of 96 m and the electrodes spacing are 2, 4 and 6 m, respectively to reach a depth ranging from 13 to 17 m. The results indicate that, the subsurface section is divided into main three geo-electrical units, the first is fractured marl and limestone which exhibits high resistivity values ranging from 40 to 300 ohm m. The second unit is corresponding to marl of moderate resistivity values and the third unit, which is the deeper unit, exhibits very low resistivity values corresponding to clayey marl. The fourth layer is marly clay with water. The presence of clay causes the most geotechnical problems. Fourteen shallow seismic sections (both for P-wave and MASW were carried out using spread of 94 m and geophone spacing of 2 m for each P-wave section. The results demonstrate that the deduced subsurface section consists of four layers, the first layer exhibits very low P-wave velocity ranging from 280 to 420 m/s, the second layer reveals P-wave velocity ranging from 400 to 1200 m/s, the third layer has P-wave velocity ranging from 970 to 2000 m/s and the fourth layer exhibits high velocity ranging from 1900 to 3600 m/s. The ERT and shallow seismic results, reflect the presence of two parallel faults passing through Quarter 27 and trending NW-SE.

Seismic and resistivity anisotropy analysis at the Low-Noise Underground Laboratory (LSBB) of Rustrel (France)

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Zeyen, H. J.; Bereš, J.; Gaffet, S.; Sénéchal, G.; Rousset, D.; Pessel, M.

2011-12-01

Many geological materials exhibit anisotropic behaviour. A limestone massif, especially if cracked with fractures and faults in a predominant orientation is expected to manifest seismic and electric resistivity anisotropy. Seismic velocity within air- or water-filled cracks is smaller than in the rock matrix. Therefore, the velocity parallel to fractures, controlled mainly by the rock matrix, is expected to be faster than perpendicular to the fractures, where waves have to cross fractures and rock matrix. Seismic and resistivity measurements were conducted in three underground galleries of the Low-Noise Underground Gallery (LSBB) in southern France forming a horse-shoe setting. The galleries are located inside a karstic limestone massif. Around 22500 first arrival travel-times were picked and different types of pole-pole and dipole-dipole resistivity measurement were carried out in parallel. Resistivities and velocities vary strongly with direction of observation. The direction of fast velocities is at right angle with the one of slow velocities, a typical sign for anisotropy. Observation of a system of subparallel fractures allows to approximate the actual rock anisotropy by a horizontal transverse isotropy model. The dataset was treated by different approaches, including simple cosine fit, inversion of average anisotropy parameters using a Monte-Carlo approach, isotropic and anisotropic tomography inversion. All of the above confirm the directions of fast and slow velocities (30°N and 120°N respectively) and an anisotropy of about 10%. Common measurements of seismic and resistivity data at different periods of the year will have the potential to determine quantitatively the fracture density and the free water content in this karst massif.

Rippability Assessment of Weathered Sedimentary Rock Mass using Seismic Refraction Methods

Science.gov (United States)

Ismail, M. A. M.; Kumar, N. S.; Abidin, M. H. Z.; Madun, A.

2018-04-01

Rippability or ease of excavation in sedimentary rocks is a significant aspect of the preliminary work of any civil engineering project. Rippability assessment was performed in this study to select an available ripping machine to rip off earth materials using the seismic velocity chart provided by Caterpillar. The research area is located at the proposed construction site for the development of a water reservoir and related infrastructure in Kampus Pauh Putra, Universiti Malaysia Perlis. The research was aimed at obtaining seismic velocity, P-wave (Vp) using a seismic refraction method to produce a 2D tomography model. A 2D seismic model was used to delineate the layers into the velocity profile. The conventional geotechnical method of using a borehole was integrated with the seismic velocity method to provide appropriate correlation. The correlated data can be used to categorize machineries for excavation activities based on the available systematic analysis procedure to predict rock rippability. The seismic velocity profile obtained was used to interpret rock layers within the ranges labelled as rippable, marginal, and non-rippable. Based on the seismic velocity method the site can be classified into loose sand stone to moderately weathered rock. Laboratory test results shows that the site’s rock material falls between low strength and high strength. Results suggest that Caterpillar’s smallest ripper, namely, D8R, can successfully excavate materials based on the test results integration from seismic velocity method and laboratory test.

Velocity Model Analysis Based on Integrated Well and Seismic Data of East Java Basin

Science.gov (United States)

Mubin, Fathul; Widya, Aviandy; Eka Nurcahya, Budi; Nurul Mahmudah, Erma; Purwaman, Indro; Radityo, Aryo; Shirly, Agung; Nurwani, Citra

2018-03-01

Time to depth conversion is an important processof seismic interpretationtoidentify hydrocarbonprospectivity. Main objectives of this research are to minimize the risk of error in geometry and time to depth conversion. Since it’s using a large amount of data and had been doing in the large scale of research areas, this research can be classified as a regional scale research. The research was focused on three horizons time interpretation: Top Kujung I, Top Ngimbang and Basement which located in the offshore and onshore areas of east Java basin. These three horizons was selected because they were assumed to be equivalent to the rock formation, which is it has always been the main objective of oil and gas exploration in the East Java Basin. As additional value, there was no previous works on velocity modeling for regional scale using geological parameters in East Java basin. Lithology and interval thickness were identified as geological factors that effected the velocity distribution in East Java Basin. Therefore, a three layer geological model was generated, which was defined by the type of lithology; carbonate (layer 1: Top Kujung I), shale (layer 2: Top Ngimbang) and Basement. A statistical method using three horizons is able to predict the velocity distribution on sparse well data in a regional scale. The average velocity range for Top Kujung I is 400 m/s - 6000 m/s, Top Ngimbang is 500 m/s - 8200 m/s and Basement is 600 m/s - 8000 m/s. Some velocity anomalies found in Madura sub-basin area, caused by geological factor which identified as thick shale deposit and high density values on shale. Result of velocity and depth modeling analysis can be used to define the volume range deterministically and to make geological models to prospect generation in details by geological concept.

The preliminary results: Internal seismic velocity structure imaging beneath Mount Lokon

Energy Technology Data Exchange (ETDEWEB)

Firmansyah, Rizky, E-mail: rizkyfirmansyah@hotmail.com [Geophysical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung, 40132 (Indonesia); Nugraha, Andri Dian, E-mail: nugraha@gf.itb.ac.id [Global Geophysical Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung, 40132 (Indonesia); Kristianto, E-mail: kris@vsi.esdm.go.id [Center for Volcanology and Geological Hazard Mitigation (CVGHM), Geological Agency, Bandung, 40122 (Indonesia)

2015-04-24

Historical records that before the 17{sup th} century, Mount Lokon had been dormant for approximately 400 years. In the years between 1350 and 1400, eruption ever recorded in Empung, came from Mount Lokon’s central crater. Subsequently, in 1750 to 1800, Mount Lokon continued to erupt again and caused soil damage and fall victim. After 1949, Mount Lokon dramatically increased in its frequency: the eruption interval varies between 1 – 5 years, with an average interval of 3 years and a rest interval ranged from 8 – 64 years. Then, on June 26{sup th}, 2011, standby alert set by the Center for Volcanology and Geological Hazard Mitigation. Peak activity happened on July 4{sup th}, 2011 that Mount Lokon erupted continuously until August 28{sup th}, 2011. In this study, we carefully analyzed micro-earthquakes waveform and determined hypocenter location of those events. We then conducted travel time seismic tomographic inversion using SIMULPS12 method to detemine Vp, Vs and Vp/Vs ratio structures beneath Lokon volcano in order to enhance our subsurface geological structure. During the tomographic inversion, we started from 1-D seismic velocities model obtained from VELEST33 method. Our preliminary results show low Vp, low Vs, and high Vp/Vs are observed beneath Mount Lokon-Empung which are may be associated with weak zone or hot material zones. However, in this study we used few station for recording of micro-earthquake events. So, we suggest in the future tomography study, the adding of some seismometers in order to improve ray coverage in the region is profoundly justified.

Seismic velocity structure of the crust and upper mantle beneath the Texas-Gulf of Mexico margin from joint inversion of Ps and Sp receiver functions and surface wave dispersion

Science.gov (United States)

Agrawal, M.; Pulliam, J.; Sen, M. K.

2013-12-01

The seismic structure beneath Texas Gulf Coast Plain (GCP) is determined via velocity analysis of stacked common conversion point (CCP) Ps and Sp receiver functions and surface wave dispersion. The GCP is a portion of a ocean-continental transition zone, or 'passive margin', where seismic imaging of lithospheric Earth structure via passive seismic techniques has been rare. Seismic data from a temporary array of 22 broadband stations, spaced 16-20 km apart, on a ~380-km-long profile from Matagorda Island, a barrier island in the Gulf of Mexico, to Johnson City, Texas were employed to construct a coherent image of the crust and uppermost mantle. CCP stacking was applied to data from teleseismic earthquakes to enhance the signal-to-noise ratios of converted phases, such as Ps phases. An inaccurate velocity model, used for time-to-depth conversion in CCP stacking, may produce higher errors, especially in a region of substantial lateral velocity variations. An accurate velocity model is therefore essential to constructing high quality depth-domain images. To find accurate velocity P- and S-wave models, we applied a joint modeling approach that searches for best-fitting models via simulated annealing. This joint inversion approach, which we call 'multi objective optimization in seismology' (MOOS), simultaneously models Ps receiver functions, Sp receiver functions and group velocity surface wave dispersion curves after assigning relative weights for each objective function. Weights are computed from the standard deviations of the data. Statistical tools such as the posterior parameter correlation matrix and posterior probability density (PPD) function are used to evaluate the constraints that each data type places on model parameters. They allow us to identify portions of the model that are well or poorly constrained.

Diffraction imaging and velocity analysis using oriented velocity continuation

KAUST Repository

Decker, Luke

2014-08-05

We perform seismic diffraction imaging and velocity analysis by separating diffractions from specular reflections and decomposing them into slope components. We image slope components using extrapolation in migration velocity in time-space-slope coordinates. The extrapolation is described by a convection-type partial differential equation and implemented efficiently in the Fourier domain. Synthetic and field data experiments show that the proposed algorithm is able to detect accurate time-migration velocities by automatically measuring the flatness of events in dip-angle gathers.

Low Velocity Seismic Waves Produced by Stick-Slip Processes During the Drainage of Two Supraglacial Lakes in Greenland

Science.gov (United States)

Kenyon, P. M.; Orantes, E. J.; Grynewize, S.; Tedesco, M.

2016-12-01

The drainage of supraglacial lakes over the Greenland ice sheet has been shown to have a significant impact on ice dynamics and subglacial hydrology. As supraglacial lakes drain, they produce seismic waves that can be detected on both local and regional scales. Studying such waves and the originating phenomena has the potential to advance our understanding of the subglacial processes involved. Here we present the results of an analysis of high frequency seismic waves generated during the drainage of two supraglacial lakes in southwestern Greenland. The two lakes drained by contrasting mechanisms. One (Lake Half Moon) drained slowly by overflow into an existing moulin. Here GPS data, recorded during the drainage, show an increase in ice sheet velocity that begins well before the time of maximum lake depth. The other lake (Lake Ponting) drained suddenly by hydrofracture through the lake bed. In this case, the GPS data show an increase in velocity that is essentially simultaneous with the maximum lake depth. In both cases, vertical component seismograms were obtained from the Greenland Ice Sheet Monitoring Network (GLISN) for several hours before and after the lake drainage. Arrival times were picked manually, using the criterion that an arrival must have a minimum amplitude of twice the noise level. The arrivals were then plotted on graphs of time versus distance from the lake in question. Several linear trends are visible on each graph. The velocities calculated from the slopes of these trends are unexpectedly low. We suggest that one explanation for this might be that the waves are traveling in a layer of till at the base of the ice sheet, that forms a low velocity channel. When compared with GPS and lake depth data, the origin times of the waves coincide with the velocity increase in both cases. Therefore, we conclude that the waves are being generated by stick-slip processes involving the slippage of the ice sheet on an underlying layer of till.

Calibration of the seismic velocity structure and understanding of the fault formation in the environs of the Orkney M5.5 earthquake, South Africa

Science.gov (United States)

Ogasawara, H.; Manzi, M. S.; Durrheim, R. J.; Ogasawara, H.

2017-12-01

In August 2014, the largest seismic event (M5.5) to occur in a South African gold mining district took place near Orkney. The M5.5 event and aftershocks were recorded by strainmeters installed at 3 km depth hundreds of meters above the M5.5 fault, 46 in-mine 4.5Hz triaxial geophone stations at depths of 2-3 km within a hypocentral radius of 2-3 km, and 17 surface strong motion stations (South African Seismograph Network; SANSN) within an epicentral radius of 25 km. Aftershocks were distributed on a nearly vertical plane striking NNW-SSE. The upper edge of this fault was hundreds of meters below the deepest level of the mine. ICDP approved a project "Drilling into seismogenic zones of M2.0-5.5 earthquakes in South African gold mines" to elucidate the details of the events (DSeis; Yabe et al. invited talk in S020 in this AGU). On 1 August 2017 drilling was within a few hundreds of meters of intersecting the M5.5 fault zone. To locate the drilling target accurately it is very important to determine the velocity structure between the seismic events and sensors. We do this by using the interval velocities used to migrate 3D-reflection seismic data that was previously acquired by a mining company to image the gold-bearing reef and any fault structures close to the mining horizon. Less attention was given to the velocities below the mining horizon, as accurate imaging of the geological structure was not as important and very little drilling information was available. We used the known depths of prominent reflectors above the mining horizon to derive the interval velocities needed to convert two-way-travel-time to depth. We constrain the velocity below the mining horizon by comparing the DSeis drilling results with the 3D seismic cube. The geometric data is crucial for the kinematic modeling that Ogasawara et al. (S018 in this AGU) advocates. The efforts will result in a better understanding of the main rupture and aftershocks.

Mapping Deep Low Velocity Zones in Alaskan Arctic Coastal Permafrost using Seismic Surface Waves

Science.gov (United States)

Dou, S.; Ajo Franklin, J. B.; Dreger, D. S.

2012-12-01

Permafrost degradation may be an important amplifier of climate change; Thawing of near-surface sediments holds the potential of increasing greenhouse gas emissions due to microbial decomposition of preserved organic carbon. Recently, the characterization of "deep" carbon pools (several meters below the surface) in circumpolar frozen ground has increased the estimated amount of soil carbon to three times higher than what was previously thought. It is therefore potentially important to include the characteristics and processes of deeper permafrost strata (on the orders of a few to tens of meters below surface) in climate models for improving future predictions of accessible carbon and climate feedbacks. This extension is particularly relevant if deeper formations are not completely frozen and may harbor on-going microbial activity despite sub-zero temperatures. Unfortunately, the characterization of deep permafrost systems is non-trivial; logistics and drilling constraints often limit direct characterization to relatively shallow units. Geophysical measurements, either surface or airborne, are often the most effective tools for evaluating these regions. Of the available geophysical techniques, the analysis of seismic surface waves (e.g. MASW) has several unique advantages, mainly the ability to provide field-scale information with good depth resolution as well as penetration (10s to 100s of m with small portable sources). Surface wave methods are also able to resolve low velocity regions, a class of features that is difficult to characterize using traditional P-wave refraction methods. As part of the Department of Energy (DOE) Next-Generation Ecosystem Experiments (NGEE-Arctic) project, we conducted a three-day seismic field survey (May 12 - 14, 2012) at the Barrow Environmental Observatory, which is located within the Alaskan Arctic Coastal Plain. Even though permafrost at the study site is continuous, ice-rich and thick (>= 350m), our Multichannel Analysis of

Crustal Seismic Anisotropy: Implications for Understanding Crustal Dynamics

Science.gov (United States)

Meltzer, A.; Christensen, N.; Okaya, D.

2003-12-01

The Nanga Parbat - Haramosh massif, in the core of the western syntaxis of the Himalaya, represents a unique exposure of mid-lower continental crust from beneath a collisional orogen. The exhumed core of the massif forms a large scale antiformal structure with axial orientation of N10E and associated lineation directed north-south with near-vertical dips. Laboratory measurements of seismic velocity on a suite of quartzofeldspathic gneisses from the massif show a relatively strong degree of anisotropy, up to 12.5% for compressional waves and up to 21% for shear waves. The degree of velocity anisotropy is primarily a function of mica content and rock fabric strength. The strong anisotropy measured in these rocks should be observable in recorded seismic field data and provides a means of mapping rock fabric at depth provided the rock fabric is coherent over appropriate length scales. An IRIS/PASSCAL deployment of 50 short period instruments recorded local and regional earthquakes to characterize seismicity and determine crustal structure beneath the massif as part of a multidisciplinary NSF Continental Dynamics study investigating the active tectonic processes responsible for exhumation and crustal reworking at Nanga Parbat. Microseismicity at Nanga Parbat is distributed along strike beneath the massif but exhibits a sharp drop-off laterally into adjacent terranes and with depth. This data set is ideal for studying crustal seismic anisotropy because the raypaths are restricted to the crust, sharp onsets in P and S allow for clear identification of arrivals, and source-receiver geometries sample a range of azimuths with respect to structure. Preliminary analysis indicates that the majority of local events exhibit some degree of splitting and that splitting patterns, while complicated, are coherent. While splitting delay normally increases with distance traveled through anisotropic material, the range of delay times can be due to heterogeneity in composition, lateral

Joint inversion of teleseismic P waveforms and surface-wave group velocities from ambient seismic noise in the Bohemian Massif

Czech Academy of Sciences Publication Activity Database

Růžek, Bohuslav; Plomerová, Jaroslava; Babuška, Vladislav

2012-01-01

Roč. 56, č. 1 (2012), s. 107-140 ISSN 0039-3169 R&D Projects: GA ČR GA205/07/1088; GA AV ČR IAA300120709; GA MŠk LM2010008 Institutional research plan: CEZ:AV0Z30120515 Keywords : receiver function * seismic noise * joint inversion * Bohemian Massif * velocity structure Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.975, year: 2012

Construction method and application of 3D velocity model for evaluation of strong seismic motion and its cost performance

International Nuclear Information System (INIS)

Matsuyama, Hisanori; Fujiwara, Hiroyuki

2014-01-01

Based on experiences of making subsurface structure models for seismic strong motion evaluation, the advantages and disadvantages in terms of convenience and cost for several methods used to make such models were reported. As for the details, gravity and micro-tremor surveys were considered to be highly valid in terms of convenience and cost. However, stratigraphy and seismic velocity structure are required to make accurate 3-D subsurface structures. To realize these, methods for directly examining subsurface ground or using controlled tremor sources (at high cost) are needed. As a result, it was summarized that in modeling subsurface structures, some sort of plan including both types of methods is desirable and that several methods must be combined to match one's intended purposes and budget. (authors)

New tomographic images of P- , S- wave velocity and Q on the Philippine Sea Slab beneath Tokyo: Implication to seismotectonics and seismic hazard in the Tokyo metropolitan region

Science.gov (United States)

Hirata, Naoshi; Sakai, Shin'ichi; Nakagawa, Shigeki; Panayotopoulos, Yannis; Ishikawa, Masahiro; Sato, Hiroshi; Kasahara, Keiji; Kimura, Hisanor; Honda, Ryou

2013-04-01

The Central Disaster Management Council of Japan estimates the next great M7+ earthquake in the Tokyo metropolitan region will cause 11,000 fatalities and 112 trillion yen (1 trillion US) economic loss at worst case if it occur beneath northern Tokyo bay with M7.3. However, the estimate is based on a source fault model by conventional studies about the PSP geometry. To evaluate seismic hazard due to the great quake we need to clarify the geometry of PSP and also the Pacific palate (PAP) that subducs beneath PSP. We identify those plates with use of seismic tomography and available deep seismic reflection profiling and borehole data in southern Kanto area. We deployed about 300 seismic stations in the greater Tokyo urban region under the Special Project for Earthquake Disaster Mitigation in Tokyo Metropolitan Area. We obtain clear P- and S- wave velocity (Vp and Vs) and Q tomograms which show a clear image of PSP and PAP. A depth to the top of PSP, 20 to 30 kilometer beneath northern part of Tokyo bay, is about 10 km shallower than previous estimates based on the distribution of seismicity (Ishida, 1992). This shallower plate geometry changes estimations of strong ground motion for seismic hazards analysis within the Tokyo region. Based on elastic wave velocities of rocks and minerals, we interpreted the tomographic images as petrologic images. Tomographic images revealed the presence of two stepwise velocity increase of the top layer of the subducting PSP slab. Rock velocity data reveals that subducting PSP crust transforms from blueschists to amphibolites at depth of 30km and amphibolites to eclogites at depth of 50km, which suggest that dehydration reactions occurs in subducting crust of basaltic compositions during prograde metamorphism and water is released from the subducting PSP crust. Tomograms show evidence for a low-velocity zone (LVZ) beneath the area just north of Tokyo bay. A Q tomogram show a low Q zone in PSP slab. We interpret the LVZ as a

Seismic velocity model of the crust and upper mantle along profile PANCAKE across the Carpathians between the Pannonian Basin and the East European Craton

DEFF Research Database (Denmark)

Starostenko, V.; Janik, T.; Kolomiyets, K.

2013-01-01

the Transcarpathian Depression and the Carpathian Foredeep; and the south-western part of the EEC, including the Trans European Suture Zone (TESZ). Seismic data support a robust model of the Vp velocity structure of the crust. In the PB, the 22-23km thick crust consists of a 2-5km thick sedimentary layer (Vp=2......Results are presented of a seismic wide-angle reflection/refraction survey along a profile between the Pannonian Basin (PB) and the East European Craton (EEC) called PANCAKE. The P- and S-wave velocity model derived can be divided into three sectors: the PB; the Carpathians, including.......4-3.7km/s), 17-20km thick upper crystalline crust (5.9-6.3km/s) and an up to 3km thick lower crustal layer (Vp=6.4km/s). In the central part of the Carpathians, a 10-24km thick uppermost part of the crust with Vp≤6.0km/s may correspond to sedimentary rocks of different ages; several high velocity bodies...

Seismic Tomography of Siyazan - Shabran Oil and Gas Region Of Azerbaijan by Data of The Seismic Stations

Science.gov (United States)

Yetirmishli, Gurban; Guliyev, Ibrahim; Mammadov, Nazim; Kazimova, Sabina; Ismailova, Saida

2016-04-01

The main purpose of the research was to build a reliable 3D model of the structure of seismic velocities in the earth crust on the territory of Siyazan-Shabran region of Azerbaijan, using the data of seismic telemetry stations spanning Siyazan-Shabran region (Siyazan, Altiagaj, Pirgulu, Guba, Khinalig, Gusar), including 7 mobile telemetry seismic stations. Interest to the problem of research seismic tomography caused by applied environmental objectives, such as the assessment of geological risks, engineering evaluation (stability and safety of wells), the task of exploration and mining operations. In the study region are being actively developed oil fields, and therefore, there is a risk of technogenic earthquakes. It was performed the calculation of first arrival travel times of P and S waves and the corresponding ray paths. Calculate 1D velocity model which is the initial model as a set of horizontal layers (velocity may be constant or changed linearly with depth on each layer, gaps are possible only at the boundaries between the layers). Have been constructed and analyzed the horizontal sections of the three-dimensional velocity model at different depths of the investigated region. By the empirical method was proposed density model of the sedimentary rocks at depths of 0-8 km.

Correlation of Crustal Structures and Seismicity Patterns in Northern Appalachians

Science.gov (United States)

Yang, X.; Gao, H.

2017-12-01

The earthquake distributions in northern Appalachians are bounded by major geologically-defined terrane boundaries. There is a distinct seismic gap within Taconic Belt between the Western Quebec Seismic Zone (WQSZ) to the west and the seismically active Ganderia terrane to the east. It is not clear, however, what crustal structures control the characteristics of earthquake clustering in this region. Here we present a newly constructed crustal shear velocity model for the northern Appalachians using Rayleigh wave data extracted from ambient noises. Our tomographic model reveals strongly heterogeneous seismic structures in the crust. We observe multiple NW-dipping patches of high-velocity anomalies in the upper crust beneath the southeastern WQSZ. The upper crust shear velocities in the Ganderia and Avalonia region are generally lower than those beneath the WQSZ. The middle crust has relatively lower velocities in the study area. The earthquakes in the study area are constrained within the upper crust. Most of the earthquake hypocenters within the WQSZ are concentrated along the NW-dipping boundaries separating the high-velocity anomalies. In contrast, most of the earthquake hypocenters in the Ganderia and Avalonia region are diffusely distributed without clear vertical lineaments. The orientations of maximum compressive stresses change from W-E in the Ganderia and Avalonia region to SW-NE in the WQSZ. The contrasts in seismicity, velocity, and stress field across the Taconic Belt indicate that the Taconic Belt terrane may act as a seismically inactive buffer zone in northern Appalachians.

A Centerless Circular Array Method: Extracting Maximal Information on Phase Velocities of Rayleigh Waves From Microtremor Records From a Simple Seismic Array

Science.gov (United States)

Cho, I.; Tada, T.; Shinozaki, Y.

2005-12-01

We have developed a Centerless Circular Array (CCA) method of microtremor exploration, an algorithm that enables to estimate phase velocities of Rayleigh waves by analyzing vertical-component records of microtremors that are obtained with an array of three or five seismic sensors placed around a circumference. Our CCA method shows a remarkably high performance in long-wavelength ranges because, unlike the frequency-wavenumber spectral method, our method does not resolve individual plane-wave components in the process of identifying phase velocities. Theoretical considerations predict that the resolving power of our CCA method in long-wavelength ranges depends upon the SN ratio, or the ratio of power of the propagating components to that of the non-propagating components (incoherent noise) contained in the records from the seismic array. The applicability of our CCA method to small-sized arrays on the order of several meters in radius has already been confirmed in our earlier work (Cho et al., 2004). We have deployed circular seismic arrays of different sizes at test sites in Japan where the underground structure is well documented through geophysical exploration, and have applied our CCA method to microtremor records to estimate phase velocities of Rayleigh waves. The estimates were then checked against "model" phase velocities that are derived from theoretical calculations. For arrays of 5, 25, 300 and 600 meters in radii, the estimated and model phase velocities demonstrated fine agreement within a broad wavelength range extending from a little larger than 3r (r: the array radius) up to at least 40r, 14r, 42r and 9r, respectively. This demonstrates the applicability of our CCA method to arrays on the order of several to several hundreds of meters in radii, and also illustrates, in a typical way, the markedly high performance of our CCA method in long-wavelength ranges. We have also invented a mathematical model that enables to evaluate the SN ratio in a given

Seismic applications in CBM exploration and development

Energy Technology Data Exchange (ETDEWEB)

Richardson, S.E.; Lawton, D.C. [Calgary Univ., AB (Canada)

2002-07-01

This Power Point presentation reviewed seismic methods, coal seam seismology, seismology and coalbed methane (CBM) development, and time-lapse seismic imaging with reference to numerical modelling and physical testing. The issue of resolution versus detection in various seismic methods was discussed. The thinnest resolvable beds are usually about 1.0 m thick. Coal zones with thin seams can be mapped using seismic reflection, but individual seams are difficult to resolve in field data. In terms of coal seismology, it was noted that seismic surveys make it possible to identify seam thickness, field geometry, subsurface structuring and facies changes. Facies model make it possible to determine the depositional environment, coal type, coal quality and lateral continuity. Some successes in coal seismology include the Cedar Hill and Ferron fields in the San Juan Basin. Numerical modelling methods include digital dipole compressional sonic and density well logs through Ardley Coal Zone, P-wave synthetic seismograms generated in SYNTH (MATLAB), and the alteration of density/velocity values to create new seismograms. Another numerical method is to take the difference between original and altered seismograms. It was shown that dewatering causes a decrease in velocity of about 20 per cent, and a 15 per cent decrease in density. Changes as small as 5 per cent in reservoir properties can be successfully imaged. It was concluded that the identification of dewatered zones allow for optimal positioning of development wells. Further physical testing will involve wet and dry p-wave velocities, s-wave velocities will be tested, and velocities will be measured under pressure. 2 tabs., 10 figs.

Permeability and seismic velocity anisotropy across a ductile-brittle fault zone in crystalline rock

Science.gov (United States)

Wenning, Quinn C.; Madonna, Claudio; de Haller, Antoine; Burg, Jean-Pierre

2018-05-01

This study characterizes the elastic and fluid flow properties systematically across a ductile-brittle fault zone in crystalline rock at the Grimsel Test Site underground research laboratory. Anisotropic seismic velocities and permeability measured every 0.1 m in the 0.7 m across the transition zone from the host Grimsel granodiorite to the mylonitic core show that foliation-parallel P- and S-wave velocities systematically increase from the host rock towards the mylonitic core, while permeability is reduced nearest to the mylonitic core. The results suggest that although brittle deformation has persisted in the recent evolution, antecedent ductile fabric continues to control the matrix elastic and fluid flow properties outside the mylonitic core. The juxtaposition of the ductile strain zone next to the brittle zone, which is bounded inside the two mylonitic cores, causes a significant elastic, mechanical, and fluid flow heterogeneity, which has important implications for crustal deformation and fluid flow and for the exploitation and use of geothermal energy and geologic waste storage. The results illustrate how physical characteristics of faults in crystalline rocks change in fault zones during the ductile to brittle transitions.

Seismic safety in conducting large-scale blasts

Science.gov (United States)

Mashukov, I. V.; Chaplygin, V. V.; Domanov, V. P.; Semin, A. A.; Klimkin, M. A.

2017-09-01

In mining enterprises to prepare hard rocks for excavation a drilling and blasting method is used. With the approach of mining operations to settlements the negative effect of large-scale blasts increases. To assess the level of seismic impact of large-scale blasts the scientific staff of Siberian State Industrial University carried out expertise for coal mines and iron ore enterprises. Determination of the magnitude of surface seismic vibrations caused by mass explosions was performed using seismic receivers, an analog-digital converter with recording on a laptop. The registration results of surface seismic vibrations during production of more than 280 large-scale blasts at 17 mining enterprises in 22 settlements are presented. The maximum velocity values of the Earth’s surface vibrations are determined. The safety evaluation of seismic effect was carried out according to the permissible value of vibration velocity. For cases with exceedance of permissible values recommendations were developed to reduce the level of seismic impact.

Influence of joint dip angle on seismic behaviors of rock foundation

International Nuclear Information System (INIS)

Yang, Lei; Gao, Yang; Jiang, Yujing; Li, Bo; Li Shucai

2012-01-01

The seismic response of rock foundation to seismic loads is an important issue to the stability and safety of nuclear power plants. Due to the fact that the discontinuities like joints existing in the rock mass govern principally the deformation and failure behaviors of the rock mass, the influence of discontinuities on the seismic behaviors of rock mass remains as one of the fundamental problems in the safety assessment of nuclear power plants. In this study, the distinct element method (DEM) and finite element method (FEM) were adopted to investigate the seismic responses of rock foundation to a real seismic wave, taking into account the effect of joint dip angle on the deformation and dynamic behaviors of rock foundation. In the DEM simulations, the intact rock has an amplification effect on the amplitudes of seismic waves, while the joints exhibit an attenuation effect on the seismic waves. In the FEM simulations, however, the attenuation effect of joints is not obvious. The dip angle of joints has strong effects on the deformation and dynamic behaviors of rock foundation, in terms that different dip angles lead to obviously different deformation and horizontal stress in the rock foundation when subjected to seismic load. When the dip angle of joints is around 60deg, the seismic velocity, displacement and stress reach the maximums. Therefore, attentions need to be paid on this factor during the seismic design of nuclear power plants. (author)

A comparison of seismic velocity inversion methods for layered acoustics

NARCIS (Netherlands)

Van Leeuwen, T.; Mulder, W.A.

2009-01-01

In seismic imaging, one tries to infer the medium properties of the subsurface from seismic reflection data. These data are the result of an active source experiment, where an explosive source and an array of receivers are placed at the surface. Due to the absence of low frequencies in the data, the

Seismic velocity structure and spatial distribution of reflection intensity off the Boso Peninsula, Central Japan, revealed by an ocean bottom seismographic experiment

Science.gov (United States)

Kono, Akihiro; Sato, Toshinori; Shinohara, Masanao; Mochizuki, Kimihiro; Yamada, Tomoaki; Uehira, Kenji; Shinbo, Takashi; Machida, Yuuya; Hino, Ryota; Azuma, Ryosuke

2016-04-01

Off the Boso Peninsula, central Japan, where the Sagami Trough is in the south and the Japan Trench is in the east, there is a triple junction where the Pacific plate (PAC), the Philippine Sea plate (PHS) and the Honshu island arc (HIA) meet each other. In this region, the PAC subducts beneath the PHS and the HIA, and the PHS subducts beneath the HIA. Due to the subduction of 2 oceanic plates, numerous seismic events took place in the past. In order to understand these events, it is important to image structure of these plates. Hence, many researchers attempted to reveal the substructure from natural earthquakes and seismic experiments. Because most of the seismometers are placed inland area and the regular seismicity off Boso is inactive, it is difficult to reveal the precise substructure off Boso area using only natural earthquakes. Although several marine seismic experiments using active sources were conducted, vast area remains unclear off Boso Peninsula. In order to improve the situation, a marine seismic experiment, using airgun as an active source, was conducted from 30th July to 4th of August, 2009. The survey line has 216 km length and 20 Ocean Bottom Seismometers (OBSs) were placed on it. We estimated 2-D P-wave velocity structure from the airgun data using the PMDM (Progressive Model Development Method; Sato and Kenett, 2000) and the FAST (First Arrival Seismic Tomography ; Zelt and Barton, 1998). Furthermore, we identified the probable reflection phases from the data and estimated the location of reflectors using Travel time mapping method (Fujie et al. 2006). We found some reflection phases from the data, and the reflectors are located near the region where P-wave velocity is 5.0 km/s. We interpret that the reflectors indicate the plate boundary between the PHS and the HIA. The variation of the intensity of reflection along the upper surface of PHS seems to be consistent with the result from previous reflection seismic experiment conducted by Kimura et

Developing a Crustal and Upper Mantle Velocity Model for the Brazilian Northeast

Science.gov (United States)

Julia, J.; Nascimento, R.

2013-05-01

Development of 3D models for the earth's crust and upper mantle is important for accurately predicting travel times for regional phases and to improve seismic event location. The Brazilian Northeast is a tectonically active area within stable South America and displays one of the highest levels of seismicity in Brazil, with earthquake swarms containing events up to mb 5.2. Since 2011, seismic activity is routinely monitored through the Rede Sismográfica do Nordeste (RSisNE), a permanent network supported by the national oil company PETROBRAS and consisting of 15 broadband stations with an average spacing of ~200 km. Accurate event locations are required to correctly characterize and identify seismogenic areas in the region and assess seismic hazard. Yet, no 3D model of crustal thickness and crustal and upper mantle velocity variation exists. The first step in developing such models is to refine crustal thickness and depths to major seismic velocity boundaries in the crust and improve on seismic velocity estimates for the upper mantle and crustal layers. We present recent results in crustal and uppermost mantle structure in NE Brazil that will contribute to the development of a 3D model of velocity variation. Our approach has consisted of: (i) computing receiver functions to obtain point estimates of crustal thickness and Vp/Vs ratio and (ii) jointly inverting receiver functions and surface-wave dispersion velocities from an independent tomography study to obtain S-velocity profiles at each station. This approach has been used at all the broadband stations of the monitoring network plus 15 temporary, short-period stations that reduced the inter-station spacing to ~100 km. We expect our contributions will provide the basis to produce full 3D velocity models for the Brazilian Northeast and help determine accurate locations for seismic events in the region.

Seismicity Characterization and Velocity Structure of Northeast Russia

National Research Council Canada - National Science Library

Mackey, Kevin G; Fujita, Kazuya

2005-01-01

A seismicity catalog and associated list of phases for many events has been compiled for northeast Russia using published and unpublished data from the regional networks operating in eastern Russia...

Simultaneous inversion of seismic velocity and moment tensor using elastic-waveform inversion of microseismic data: Application to the Aneth CO2-EOR field

Science.gov (United States)

Chen, Y.; Huang, L.

2017-12-01

Moment tensors are key parameters for characterizing CO2-injection-induced microseismic events. Elastic-waveform inversion has the potential to providing accurate results of moment tensors. Microseismic waveforms contains information of source moment tensors and the wave propagation velocity along the wavepaths. We develop an elastic-waveform inversion method to jointly invert the seismic velocity model and moment tensor. We first use our adaptive moment-tensor joint inversion method to estimate moment tensors of microseismic events. Our adaptive moment-tensor inversion method jointly inverts multiple microseismic events with similar waveforms within a cluster to reduce inversion uncertainty for microseismic data recorded using a single borehole geophone array. We use this inversion result as the initial model for our elastic-waveform inversion to minimize the cross-correlated-based data misfit between observed data and synthetic data. We verify our method using synthetic microseismic data and obtain improved results of both moment tensors and seismic velocity model. We apply our new inversion method to microseismic data acquired at a CO2-enhanced oil recovery field in Aneth, Utah, using a single borehole geophone array. The results demonstrate that our new inversion method significantly reduces the data misfit compared to the conventional ray-theory-based moment-tensor inversion.

Seismic velocities to characterize the soil-aquifer continuum on the Orgeval experimental basin (France)

Science.gov (United States)

Pasquet, S.; Ludovic, B.; Dhemaied, A.; Flipo, N.; Guérin, R.; Mouhri, A.; Faycal, R.; Vitale, Q.

2013-12-01

Among geophysical methods applied to hydrogeology, seismic prospecting is frequently confined to the characterization of aquifers geometry. The combined study of pressure- (P) and shear- (SH) wave velocities (respectively Vp and Vs) can however provide information about the aquifer parameters, as it is commonly done for most fluids in hydrocarbon exploration. This approach has recently been proposed in sandy aquifers with the estimation of Vp/Vs ratio. In order to address such issues in more complex aquifer systems (e.g. unconsolidated, heterogeneous or low-permeability media) we carried out P- and SH-wave seismic surveys on the Orgeval experimental basin (70 km east from Paris, France). This basin drains a multi-layer aquifer system monitored by a network of piezometers. The upper part of the aquifer system is characterized by tabular layers well delineated all over the basin thanks to Electrical Resistivity Tomography (ERT), Time Domain ElectroMagnetic (TDEM) soundings and wells. But the lateral variability of the intrinsic properties in each layer raises questions regarding the hydrodynamics of the upper aquifer and the validity of interpolations between piezometers. A simple interpretation of P- and SH-wave first arrivals for tabular models provides 1D velocity structures in very good agreement with the stratification anticipated from ERT and nearby geological logs. Vp/Vs ratios show a strong contrast at a depth consistent with the observed water table level, reinforcing the assumption of a free upper aquifer in the area. Similar experiments have to be conducted under different hydrological conditions to validate these observations. Anticipating the need to propose lateral applications of the method, we additionally performed tomographic inversions of the recorded data to retrieve 2D Vp and Vs models. If interpreted independently, both models fail to depict the stratification of the medium and the water table level cannot be straightforwardly identified

High-resolution 3-D S-wave Tomography of upper crust structures in Yilan Plain from Ambient Seismic Noise

Science.gov (United States)

Chen, Kai-Xun; Chen, Po-Fei; Liang, Wen-Tzong; Chen, Li-Wei; Gung, YuanCheng

2015-04-01

The Yilan Plain (YP) in NE Taiwan locates on the western YP of the Okinawa Trough and displays high geothermal gradients with abundant hot springs, likely resulting from magmatism associated with the back-arc spreading as attested by the offshore volcanic island (Kueishantao). YP features NS distinctive characteristics that the South YP exhibits thin top sedimentary layer, high on-land seismicity and significant SE movements, relative those of the northern counterpart. A dense network (~2.5 km station interval) of 89 Texan instruments was deployed in Aug. 2014, covering most of the YP and its vicinity. The ray path coverage density of each 0.015 degree cells are greater than 150 km that could provide the robustness assessment of tomographic results. We analyze ambient noise signals to invert a high-resolution 3D S-wave model for shallow velocity structures in and around YP. The aim is to investigate the velocity anomalies corresponding to geothermal resources and the NS geological distinctions aforementioned. We apply the Welch's method to generate empirical Rayleigh wave Green's functions between two stations records of continuous vertical components. The group velocities of thus derived functions are then obtained by the multiple-filter analysis technique measured at the frequency range between 0.25 and 1 Hz. Finally, we implement a wavelet-based multi-scale parameterization technique to construct 3D model of S-wave velocity. Our first month results exhibit low velocity in the plain, corresponding existing sediments, those of whole YP show low velocity offshore YP and those of high-resolution south YP reveal stark velocity contrast across the Sanshin fault. Key words: ambient seismic noises, Welch's method, S-wave, Yilan Plain

3-D Upper-Mantle Shear Velocity Model Beneath the Contiguous United States Based on Broadband Surface Wave from Ambient Seismic Noise

Science.gov (United States)

Xie, Jun; Chu, Risheng; Yang, Yingjie

2018-05-01

Ambient noise seismic tomography has been widely used to study crustal and upper-mantle shear velocity structures. Most studies, however, concentrate on short period (structure on a continental scale. We use broadband Rayleigh wave phase velocities to obtain a 3-D V S structures beneath the contiguous United States at period band of 10-150 s. During the inversion, 1-D shear wave velocity profile is parameterized using B-spline at each grid point and is inverted with nonlinear Markov Chain Monte Carlo method. Then, a 3-D shear velocity model is constructed by assembling all the 1-D shear velocity profiles. Our model is overall consistent with existing models which are based on multiple datasets or data from earthquakes. Our model along with the other post-USArray models reveal lithosphere structures in the upper mantle, which are consistent with the geological tectonic background (e.g., the craton root and regional upwelling provinces). The model has comparable resolution on lithosphere structures compared with many published results and can be used for future detailed regional or continental studies and analysis.

Application of Migration Velocity Using Fourier Transform Approach ...

African Journals Online (AJOL)

Application of velocity by Fourier transform to process 3-D unmigrated seismic sections has been carried out in Fabi Field, Niger Delta – Nigeria. Usually, all seismic events (sections) are characterized by spikes or noise (random or coherent), multiples and shear waves so that when a seismic bed is dipping, the apparent ...

Seismic velocity structure of the forearc in northern Cascadia from Bayesian inversion of teleseismic data

Science.gov (United States)

Gosselin, J.; Audet, P.; Schaeffer, A. J.

2017-12-01

The seismic velocity structure in the forearc of subduction zones provides important constraints on material properties, with implications for seismogenesis. In Cascadia, previous studies have imaged a downgoing low-velocity zone (LVZ) characterized by an elevated P-to-S velocity ratio (Vp/Vs) down to 45 km depth, near the intersection with the mantle wedge corner, beyond which the signature of the LVZ disappears. These results, combined with the absence of a "normal" continental Moho, indicate that the down-going oceanic crust likely carries large amounts of overpressured free fluids that are released downdip at the onset of crustal eclogitization, and are further stored in the mantle wedge as serpentinite. These overpressured free fluids affect the stability of the plate interface and facilitate slow slip. These results are based on the inversion and migration of scattered teleseismic data for individual layer properties; a methodology which suffers from regularization and smoothing, non-uniqueness, and does not consider model uncertainty. This study instead applies trans-dimensional Bayesian inversion of teleseismic data collected in the forearc of northern Cascadia (the CAFÉ experiment in northern Washington) to provide rigorous, quantitative estimates of local velocity structure, and associated uncertainties (particularly Vp/Vs structure and depth to the plate interface). Trans-dimensional inversion is a generalization of fixed-dimensional inversion that includes the number (and type) of parameters required to describe the velocity model (or data error model) as unknown in the problem. This allows model complexity to be inherently determined by data information content, not by subjective regularization. The inversion is implemented here using the reversible-jump Markov chain Monte Carlo algorithm. The result is an ensemble set of candidate velocity-structure models which approximate the posterior probability density (PPD) of the model parameters. The solution

Toward predicting clay landslide with ambient seismic noise

Science.gov (United States)

Larose, E. F.; Mainsant, G.; Carriere, S.; Chambon, G.; Michoud, C.; Jongmans, D.; Jaboyedoff, M.

2013-12-01

Clay-rich pose critical problems in risk management worldwide. The most widely proposed mechanism leading to such flow-like movements is the increase in water pore pressure in the sliding mass, generating partial or complete liquefaction. This solid-to-liquid transition results in a dramatic reduction of mechanical rigidity, which could be detected by monitoring shear wave velocity variations, The ambient seismic noise correlation technique has been applied to measure the variation in the seismic surface wave velocity in the Pont Bourquin landslide (Swiss Alps). This small but active composite earthslide-earthflow was equipped with continuously recording seismic sensors during spring and summer 2010, and then again from fall 2011 on. An earthslide of a few thousand cubic meters was triggered in mid-August 2010, after a rainy period. This article shows that the seismic velocity of the sliding material, measured from daily noise correlograms, decreased continuously and rapidly for several days prior to the catastrophic event. From a spectral analysis of the velocity decrease, it was possible to determine the location of the change at the base of the sliding layer. These results are confirmed by analogous small-scale experiments in the laboratory. These results demonstrate that ambient seismic noise can be used to detect rigidity variations before failure and could potentially be used to predict landslides.

Identification Of Rippability And Bedrock Depth Using Seismic Refraction

Science.gov (United States)

Ismail, Nur Azwin; Saad, Rosli; Nawawi, M. N. M.; Muztaza, Nordiana Mohd; El Hidayah Ismail, Noer; Mohamad, Edy Tonizam

2010-12-01

Spatial variability of the bedrock with reference to the ground surface is vital for many applications in geotechnical engineering to decide the type of foundation of a structure. A study was done within the development area of Mutiara Damansara utilising the seismic refraction method using ABEM MK8 24 channel seismograph. The geological features of the subsurface were investigated and velocities, depth to the underlying layers were determined. The seismic velocities were correlated with rippability characteristics and borehole records. Seismic sections generally show a three layer case. The first layer with velocity 400-600 m/s predominantly consists of soil mix with gravel. The second layer with velocity 1600-2000 m/s is suggested to be saturated and weathered area. Both layers forms an overburden and generally rippable. The third layer represents granite bedrock with average depth and velocity 10-30 m and >3000 m/s respectively and it is non-rippable. Steep slope on the bedrock are probably the results of shear zones.

Identification Of Rippability And Bedrock Depth Using Seismic Refraction

International Nuclear Information System (INIS)

Ismail, Nur Azwin; Saad, Rosli; Nawawi, M. N. M; Muztaza, Nordiana Mohd; El Hidayah Ismail, Noer; Mohamad, Edy Tonizam

2010-01-01

Spatial variability of the bedrock with reference to the ground surface is vital for many applications in geotechnical engineering to decide the type of foundation of a structure. A study was done within the development area of Mutiara Damansara utilising the seismic refraction method using ABEM MK8 24 channel seismograph. The geological features of the subsurface were investigated and velocities, depth to the underlying layers were determined. The seismic velocities were correlated with rippability characteristics and borehole records. Seismic sections generally show a three layer case. The first layer with velocity 400-600 m/s predominantly consists of soil mix with gravel. The second layer with velocity 1600-2000 m/s is suggested to be saturated and weathered area. Both layers forms an overburden and generally rippable. The third layer represents granite bedrock with average depth and velocity 10-30 m and >3000 m/s respectively and it is non-rippable. Steep slope on the bedrock are probably the results of shear zones.

A First Layered Crustal Velocity Model for the Western Solomon Islands: Inversion of Measured Group Velocity of Surface Waves using Ambient Noise Cross-Correlation

Science.gov (United States)

Ku, C. S.; Kuo, Y. T.; Chao, W. A.; You, S. H.; Huang, B. S.; Chen, Y. G.; Taylor, F. W.; Yih-Min, W.

2017-12-01

Two earthquakes, MW 8.1 in 2007 and MW 7.1 in 2010, hit the Western Province of Solomon Islands and caused extensive damage, but motivated us to set up the first seismic network in this area. During the first phase, eight broadband seismic stations (BBS) were installed around the rupture zone of 2007 earthquake. With one-year seismic records, we cross-correlated the vertical component of ambient noise recorded in our BBS and calculated Rayleigh-wave group velocity dispersion curves on inter-station paths. The genetic algorithm to invert one-dimensional crustal velocity model is applied by fitting the averaged dispersion curves. The one-dimensional crustal velocity model is constituted by two layers and one half-space, representing the upper crust, lower crust, and uppermost mantle respectively. The resulted thickness values of the upper and lower crust are 6.4 and 14.2 km, respectively. Shear-wave velocities (VS) of the upper crust, lower crust, and uppermost mantle are 2.53, 3.57 and 4.23 km/s with the VP/VS ratios of 1.737, 1.742 and 1.759, respectively. This first layered crustal velocity model can be used as a preliminary reference to further study seismic sources such as earthquake activity and tectonic tremor.

Seismic Velocity Structure and Depth-Dependence of Anisotropy in the Red Sea and Arabian Shield from Surface Wave Analysis

Energy Technology Data Exchange (ETDEWEB)

Hansen, S; Gaherty, J; Schwartz, S; Rodgers, A; Al-Amri, A

2007-07-25

We investigate the lithospheric and upper mantle structure as well as the depth-dependence of anisotropy along the Red Sea and beneath the Arabian Peninsula using receiver function constraints and phase velocities of surface waves traversing two transects of stations from the Saudi Arabian National Digital Seismic Network. Frequency-dependent phase delays of fundamental-mode Love and Rayleigh waves, measured using a cross-correlation procedure, require very slow shear velocities and the presence of anisotropy throughout the upper mantle. Linearized inversion of these data produce path-averaged 1D radially anisotropic models with about 4% anisotropy in the lithosphere, increasing to about 4.8% anisotropy across the lithosphere-asthenosphere boundary (LAB). Models with reasonable crustal velocities in which the mantle lithosphere is isotropic cannot satisfy the data. The lithospheric lid, which ranges in thickness from about 70 km near the Red Sea coast to about 90 km beneath the Arabian Shield, is underlain by a pronounced low-velocity zone with shear velocities as low as 4.1 km/s. Forward models, which are constructed from previously determined shear-wave splitting estimates, can reconcile surface and body wave observations of anisotropy. The low shear velocity values are similar to many other continental rift and oceanic ridge environments. These low velocities combined with the sharp velocity contrast across the LAB may indicate the presence of partial melt beneath Arabia. The anisotropic signature primarily reflects a combination of plate- and density-driven flow associated with active rifting processes in the Red Sea.

P-wave velocity structure beneath the northern Antarctic Peninsula

Science.gov (United States)

Park, Y.; Kim, K.; Jin, Y.

2010-12-01

We have imaged tomographically the tree-dimensional velocity structure of the upper mantle beneath the northern Antarctic Peninsula using teleseismic P waves. The data came from the seven land stations of the Seismic Experiment in Patagonia and Antarctica (SEPA) campaigned during 1997-1999, a permanent IRIS/GSN station (PMSA), and 3 seismic stations installed at scientific bases, Esperanza (ESPZ), Jubany (JUBA), and King Sejong (KSJ), in South Shetland Islands. All of the seismic stations are located in coast area, and the signal to noise ratios (SNR) are very low. The P-wave model was inverted from 95 earthquakes resulting in 347 ray paths with P- and PKP-wave arrivals. The inverted model shows a strong low velocity anmaly beneath the Bransfield Strait, and a fast anomaly beneath the South Shetland Islands. The low velocity anomaly beneath the Bransfield might be due to a back arc extension, and the fast velocity anomaly beneath the South Shetland Islands could indicates the cold subducted slab.

First results of cross-correlation analysis of ambient seismic noise from the Hellenic Unified Seismic Network

NARCIS (Netherlands)

Panou, Areti; Paulssen, Hanneke; Hatzidimitriou, Panagiotis

2015-01-01

In this study we present phase velocity maps that were obtained from the cross-correlation analysis of ambient seismic noise recorded in the region of Greece.We used one year (2013) of ambient seismic data obtained from the vertical component of 64 broadband permanent seismological stations that are

Seismic microzonation and velocity models of El Ejido area (SE Spain) from the diffuse-field H/V method

Science.gov (United States)

García-Jerez, Antonio; Seivane, Helena; Navarro, Manuel; Piña-Flores, José; Luzón, Francisco; Vidal, Francisco; Posadas, Antonio M.; Aranda, Carolina

2016-04-01

El Ejido town is located in the Campo de Dalías coastal plain (Almería province, SE Spain), emplaced in one of the most seismically active regions of Spain. The municipality has 84000 inhabitants and presented a high growth rate during the last twenty years. The most recent intense seismic activity occurred close to this town was in 1993 and 1994, with events of Mb = 4.9 and Mb = 5.0, respectively. To provide a basis for site-specific hazard analysis, we first carried out a seismic microzonation of this town in terms of predominant periods and geotechnical properties. The predominant periods map was obtained from ambient noise observations on a grid of 250 x 250 m in the main urban area, and sparser measurements on the outskirts. These broad-band records, of about 20 minutes long each, were analyzed by using the horizontal-to-vertical spectral ratio technique (H/V). Dispersion curves obtained from two array measurements of ambient noise and borehole data provided additional geophysical information. All the surveyed points in the town were found to have relatively long predominant periods ranging from 0.8 to 2.3 s and growing towards the SE. Secondary high-frequency (> 2Hz) peaks were found at about the 10% of the points only. On the other hand, Vs30 values of 550 - 650 m/s were estimated from the array records, corresponding to cemented sediments and medium-hard rocks. The local S-wave velocity structure has been inverted from the H/V curves for a subset of the measurement sites. We used an innovative full-wavefield method based on the diffuse-wavefield approximation (Sánchez-Sesma et al., 2011) combined with the simulated annealing algorithm. Shallow seismic velocities and deep boreholes data were used as constraints. The results show that the low-frequency resonances are related with the impedance contrast between several hundred meters of medium-hard sedimentary rocks (marls and calcarenites) with the stiffer basement of the basin, which dips to the SE. These

Applications of seismic spatial wavefield gradient and rotation data in exploration seismology

Science.gov (United States)

Schmelzbach, C.; Van Renterghem, C.; Sollberger, D.; Häusler, M.; Robertsson, J. O. A.

2017-12-01

Seismic spatial wavefield gradient and rotation data have the potential to open up new ways to address long-standing problems in land-seismic exploration such as identifying and separating P-, S-, and surface waves. Gradient-based acquisition and processing techniques could enable replacing large arrays of densely spaced receivers by sparse spatially-compact receiver layouts or even one single multicomponent station with dedicated instruments (e.g., rotational seismometers). Such approaches to maximize the information content of single-station recordings are also of significant interest for seismic measurements at sites with limited access such as boreholes, the sea bottom, and extraterrestrial seismology. Arrays of conventional three-component (3C) geophones enable measuring not only the particle velocity in three dimensions but also estimating their spatial gradients. Because the free-surface condition allows to express vertical derivatives in terms of horizontal derivatives, the full gradient tensor and, hence, curl and divergence of the wavefield can be computed. In total, three particle velocity components, three rotational components, and divergence, result seven-component (7C) seismic data. Combined particle velocity and gradient data can be used to isolate the incident P- or S-waves at the land surface or the sea bottom using filtering techniques based on the elastodynamic representation theorem. Alternatively, as only S-waves exhibit rotational motion, rotational measurements can directly be used to identify S-waves. We discuss the derivations of the gradient-based filters as well as their application to synthetic and field data, demonstrating that rotational data can be of particular interest to S-wave reflection and P-to-S-wave conversion imaging. The concept of array-derived gradient estimation can be extended to source arrays as well. Therefore, source arrays allow us to emulate rotational (curl) and dilatational (divergence) sources. Combined with 7C

Application of seismic refraction tomography for subsurface imaging ...

African Journals Online (AJOL)

Seismic refraction tomography involves the measurement of the travel times of seismic refracted raypaths in order to define an image of seismic velocity in the intervening ground. This technique was used to estimate the depth to the fresh basement, estimate thickness of the weathered basement and to determine the ...

Seismic Wave Propagation from Underground Chemical Explosions: Sensitivity to Velocity and Thickness of a Weathered Layer

Science.gov (United States)

Hirakawa, E. T.; Ezzedine, S. M.

2017-12-01

Recorded motions from underground chemical explosions are complicated by long duration seismic coda as well as motion in the tangential direction. The inability to distinguish the origins of these complexities as either source or path effects comprises a limitation to effective monitoring of underground chemical explosions. With numerical models, it is possible to conduct rigorous sensitivity analyses for chemical explosive sources and their resulting ground motions under the influence of many attributes, including but not limited to complex velocity structure, topography, and non-linear source characteristics. Previously we found that topography can cause significant scattering in the direct wave but leads to relatively little motion in the coda. Here, we aim to investigate the contribution from the low-velocity weathered layer that exists in the shallow subsurface apart from and in combination with surface topography. We use SW4, an anelastic anisotropic fourth order finite difference code to simulate chemical explosive source in a 1D velocity structure consisting of a single weathered layer over a half space. A range of velocity magnitudes are used for the upper weathered layer with the velocities always being lower than that of the granitic underlaying layer. We find that for lower weathered layer velocities, the wave train is highly dispersed and causes a large percentage of energy to be contained in the coda in relation to the entire time series. The percentage of energy contained in the coda grows with distance from the source but saturates at a certain distance that depends on weathered layer velocity and thickness. The saturation onset distance increases with decreasing layer thickness and increasing velocity of the upper layer. Measurements of relative coda energy and coda saturation onset distance from real recordings can provide an additional constraint on the properties of the weathered layer in remote sites as well as test sites like the Nevada

Multi-hole seismic modeling in 3-D space and cross-hole seismic tomography analysis for boulder detection

Science.gov (United States)

Cheng, Fei; Liu, Jiangping; Wang, Jing; Zong, Yuquan; Yu, Mingyu

2016-11-01

A boulder stone, a common geological feature in south China, is referred to the remnant of a granite body which has been unevenly weathered. Undetected boulders could adversely impact the schedule and safety of subway construction when using tunnel boring machine (TBM) method. Therefore, boulder detection has always been a key issue demanded to be solved before the construction. Nowadays, cross-hole seismic tomography is a high resolution technique capable of boulder detection, however, the method can only solve for velocity in a 2-D slice between two wells, and the size and central position of the boulder are generally difficult to be accurately obtained. In this paper, the authors conduct a multi-hole wave field simulation and characteristic analysis of a boulder model based on the 3-D elastic wave staggered-grid finite difference theory, and also a 2-D imaging analysis based on first arrival travel time. The results indicate that (1) full wave field records could be obtained from multi-hole seismic wave simulations. Simulation results describe that the seismic wave propagation pattern in cross-hole high-velocity spherical geological bodies is more detailed and can serve as a basis for the wave field analysis. (2) When a cross-hole seismic section cuts through the boulder, the proposed method provides satisfactory cross-hole tomography results; however, when the section is closely positioned to the boulder, such high-velocity object in the 3-D space would impact on the surrounding wave field. The received diffracted wave interferes with the primary wave and in consequence the picked first arrival travel time is not derived from the profile, which results in a false appearance of high-velocity geology features. Finally, the results of 2-D analysis in 3-D modeling space are comparatively analyzed with the physical model test vis-a-vis the effect of high velocity body on the seismic tomographic measurements.

Uncertainty assessment of 3D instantaneous velocity model from stack velocities

Science.gov (United States)

Emanuele Maesano, Francesco; D'Ambrogi, Chiara

2015-04-01

3D modelling is a powerful tool that is experiencing increasing applications in data analysis and dissemination. At the same time the need of quantitative uncertainty evaluation is strongly requested in many aspects of the geological sciences and by the stakeholders. In many cases the starting point for 3D model building is the interpretation of seismic profiles that provide indirect information about the geology of the subsurface in the domain of time. The most problematic step in the 3D modelling construction is the conversion of the horizons and faults interpreted in time domain to the depth domain. In this step the dominant variable that could lead to significantly different results is the velocity. The knowledge of the subsurface velocities is related mainly to punctual data (sonic logs) that are often sparsely distributed in the areas covered by the seismic interpretation. The extrapolation of velocity information to wide extended horizons is thus a critical step to obtain a 3D model in depth that can be used for predictive purpose. In the EU-funded GeoMol Project, the availability of a dense network of seismic lines (confidentially provided by ENI S.p.A.) in the Central Po Plain, is paired with the presence of 136 well logs, but few of them have sonic logs and in some portion of the area the wells are very widely spaced. The depth conversion of the 3D model in time domain has been performed testing different strategies for the use and the interpolation of velocity data. The final model has been obtained using a 4 layer cake 3D instantaneous velocity model that considers both the initial velocity (v0) in every reference horizon and the gradient of velocity variation with depth (k). Using this method it is possible to consider the geological constraint given by the geometries of the horizons and the geo-statistical approach to the interpolation of velocities and gradient. Here we present an experiment based on the use of set of pseudo-wells obtained from the

Blind test of methods for obtaining 2-D near-surface seismic velocity models from first-arrival traveltimes

Science.gov (United States)

Zelt, Colin A.; Haines, Seth; Powers, Michael H.; Sheehan, Jacob; Rohdewald, Siegfried; Link, Curtis; Hayashi, Koichi; Zhao, Don; Zhou, Hua-wei; Burton, Bethany L.; Petersen, Uni K.; Bonal, Nedra D.; Doll, William E.

2013-01-01

Seismic refraction methods are used in environmental and engineering studies to image the shallow subsurface. We present a blind test of inversion and tomographic refraction analysis methods using a synthetic first-arrival-time dataset that was made available to the community in 2010. The data are realistic in terms of the near-surface velocity model, shot-receiver geometry and the data's frequency and added noise. Fourteen estimated models were determined by ten participants using eight different inversion algorithms, with the true model unknown to the participants until it was revealed at a session at the 2011 SAGEEP meeting. The estimated models are generally consistent in terms of their large-scale features, demonstrating the robustness of refraction data inversion in general, and the eight inversion algorithms in particular. When compared to the true model, all of the estimated models contain a smooth expression of its two main features: a large offset in the bedrock and the top of a steeply dipping low-velocity fault zone. The estimated models do not contain a subtle low-velocity zone and other fine-scale features, in accord with conventional wisdom. Together, the results support confidence in the reliability and robustness of modern refraction inversion and tomographic methods.

Micro-seismic imaging using a source function independent full waveform inversion method

Science.gov (United States)

Wang, Hanchen; Alkhalifah, Tariq

2018-03-01

At the heart of micro-seismic event measurements is the task to estimate the location of the source micro-seismic events, as well as their ignition times. The accuracy of locating the sources is highly dependent on the velocity model. On the other hand, the conventional micro-seismic source locating methods require, in many cases manual picking of traveltime arrivals, which do not only lead to manual effort and human interaction, but also prone to errors. Using full waveform inversion (FWI) to locate and image micro-seismic events allows for an automatic process (free of picking) that utilizes the full wavefield. However, full waveform inversion of micro-seismic events faces incredible nonlinearity due to the unknown source locations (space) and functions (time). We developed a source function independent full waveform inversion of micro-seismic events to invert for the source image, source function and the velocity model. It is based on convolving reference traces with these observed and modeled to mitigate the effect of an unknown source ignition time. The adjoint-state method is used to derive the gradient for the source image, source function and velocity updates. The extended image for the source wavelet in Z axis is extracted to check the accuracy of the inverted source image and velocity model. Also, angle gathers is calculated to assess the quality of the long wavelength component of the velocity model. By inverting for the source image, source wavelet and the velocity model simultaneously, the proposed method produces good estimates of the source location, ignition time and the background velocity for synthetic examples used here, like those corresponding to the Marmousi model and the SEG/EAGE overthrust model.

Micro-seismic imaging using a source function independent full waveform inversion method

KAUST Repository

Wang, Hanchen

2018-03-26

At the heart of micro-seismic event measurements is the task to estimate the location of the source micro-seismic events, as well as their ignition times. The accuracy of locating the sources is highly dependent on the velocity model. On the other hand, the conventional micro-seismic source locating methods require, in many cases manual picking of traveltime arrivals, which do not only lead to manual effort and human interaction, but also prone to errors. Using full waveform inversion (FWI) to locate and image micro-seismic events allows for an automatic process (free of picking) that utilizes the full wavefield. However, full waveform inversion of micro-seismic events faces incredible nonlinearity due to the unknown source locations (space) and functions (time). We developed a source function independent full waveform inversion of micro-seismic events to invert for the source image, source function and the velocity model. It is based on convolving reference traces with these observed and modeled to mitigate the effect of an unknown source ignition time. The adjoint-state method is used to derive the gradient for the source image, source function and velocity updates. The extended image for the source wavelet in Z axis is extracted to check the accuracy of the inverted source image and velocity model. Also, angle gathers is calculated to assess the quality of the long wavelength component of the velocity model. By inverting for the source image, source wavelet and the velocity model simultaneously, the proposed method produces good estimates of the source location, ignition time and the background velocity for synthetic examples used here, like those corresponding to the Marmousi model and the SEG/EAGE overthrust model.

Velocity Model for CO2 Sequestration in the Southeastern United States Atlantic Continental Margin

Science.gov (United States)

Ollmann, J.; Knapp, C. C.; Almutairi, K.; Almayahi, D.; Knapp, J. H.

2017-12-01

The sequestration of carbon dioxide (CO2) is emerging as a major player in offsetting anthropogenic greenhouse gas emissions. With 40% of the United States' anthropogenic CO2 emissions originating in the southeast, characterizing potential CO2 sequestration sites is vital to reducing the United States' emissions. The goal of this research project, funded by the Department of Energy (DOE), is to estimate the CO2 storage potential for the Southeastern United States Atlantic Continental Margin. Previous studies find storage potential in the Atlantic continental margin. Up to 16 Gt and 175 Gt of storage potential are estimated for the Upper Cretaceous and Lower Cretaceous formations, respectively. Considering 2.12 Mt of CO2 are emitted per year by the United States, substantial storage potential is present in the Southeastern United States Atlantic Continental Margin. In order to produce a time-depth relationship, a velocity model must be constructed. This velocity model is created using previously collected seismic reflection, refraction, and well data in the study area. Seismic reflection horizons were extrapolated using well log data from the COST GE-1 well. An interpolated seismic section was created using these seismic horizons. A velocity model will be made using P-wave velocities from seismic reflection data. Once the time-depth conversion is complete, the depths of stratigraphic units in the seismic refraction data will be compared to the newly assigned depths of the seismic horizons. With a lack of well control in the study area, the addition of stratigraphic unit depths from 171 seismic refraction recording stations provides adequate data to tie to the depths of picked seismic horizons. Using this velocity model, the seismic reflection data can be presented in depth in order to estimate the thickness and storage potential of CO2 reservoirs in the Southeastern United States Atlantic Continental Margin.

Seismic equivalents of volcanic jet scaling laws and multipoles in acoustics

Science.gov (United States)

Haney, Matthew M.; Matoza, Robin S.; Fee, David; Aldridge, David F.

2018-04-01

We establish analogies between equivalent source theory in seismology (moment-tensor and single-force sources) and acoustics (monopoles, dipoles and quadrupoles) in the context of volcanic eruption signals. Although infrasound (acoustic waves volcanic eruptions may be more complex than a simple monopole, dipole or quadrupole assumption, these elementary acoustic sources are a logical place to begin exploring relations with seismic sources. By considering the radiated power of a harmonic force source at the surface of an elastic half-space, we show that a volcanic jet or plume modelled as a seismic force has similar scaling with respect to eruption parameters (e.g. exit velocity and vent area) as an acoustic dipole. We support this by demonstrating, from first principles, a fundamental relationship that ties together explosion, torque and force sources in seismology and highlights the underlying dipole nature of seismic forces. This forges a connection between the multipole expansion of equivalent sources in acoustics and the use of forces and moments as equivalent sources in seismology. We further show that volcanic infrasound monopole and quadrupole sources exhibit scalings similar to seismicity radiated by volume injection and moment sources, respectively. We describe a scaling theory for seismic tremor during volcanic eruptions that agrees with observations showing a linear relation between radiated power of tremor and eruption rate. Volcanic tremor over the first 17 hr of the 2016 eruption at Pavlof Volcano, Alaska, obeyed the linear relation. Subsequent tremor during the main phase of the eruption did not obey the linear relation and demonstrates that volcanic eruption tremor can exhibit other scalings even during the same eruption.

Imaging inhomogeneous seismic velocity structure in and around the fault plane of the 2008 Iwate-Miyagi, Japan, Nairiku Earthquake (M7.2) - spatial variation in depth of seismic-aseismic transition and possible high-T/overpressurized fluid distribution

Science.gov (United States)

Okada, T.; Umino, N.; Hasegawa, A.; 2008 Iwate-Miyagi Nairiku Earthquake, G. O.

2008-12-01

A large shallow earthquake (named the 2008 Iwate-Miyagi Nairiku Earthquake) with a JMA magnitude of 7.2 occurred in the central part of NE Japan on June 14, 2008. Focal area of the present earthquake is located in the Tohoku backbone range strain concentration zone (Miura et al., 2004) along the volcanic front. Just after the occurrence of this earthquake, Japanese universities (Hokkaido, Hirosaki, Tohoku, Tokyo, Nagoya, Kyoto, Kochi, Kyusyu, Kagoshima) and NIED deployed a dense aftershock observation network in and around the focal area. Total number of temporal stations is 128. Using data from this dense aftershock observation and other temporary and routinely operated stations, we estimate hypocenter distribution and seismic velocity structure of the crust in and around the focal area of the present earthquake. We determined three-dimensional seismic velocity structure and relocated hypocenters simultaneously using the double- difference tomography method (Zhang and Thurber, 2003). Spatial extent of the aftershock area is about 45 km (NNE-SSW) by 15 km (WNW-ESE). Most of aftershocks are aligned in westward dipping. Shallower extensions of aftershock alignments seem to be located nearly at the coseismic surface deformations, which are along a geological fault, and the surface trace of the active fault (Detana fault). Note that some aftershocks seem to occur off the fault plane of the mainshock. The focal area of the present earthquake is located at a high Vs area. In the lower crust, we found some distinct low-Vs areas. These low velocity zones are located just beneath the strain concentration zones / seismic belts along the backbone range and in the northern Miyagi region. Focal area of the present earthquake is also located just above the low velocity zone in the lower crust. Beneath active volcanoes, these low velocity zones become more distinct and shallower, and aftershocks tend to occur shallower and not occur within such low-velocity zones. These low-velocity

Seismic velocity anisotropy of phyllosilicate-rich rocks: characteristics inferred from experimental and crack-model studies of biotite-rich schist

Science.gov (United States)

Nishizawa, O.; Kanagawa, K.

2010-07-01

Seismic velocity anisotropy of biotite schist (30 per cent-mode biotite) was measured under confining pressures up to 150 MPa. The rock shows weak orthotropy which was altered from transverse isotropy (TI) generated by biotite-preferred orientation. The orthotropy was caused by microfolding in the rock. The velocity increase under confining pressure indicates that most crack planes are aligned parallel to the cleavage planes (silicate sheet) of the oriented biotite minerals. The anisotropy of the rock is basically TI due to both the aligned biotite minerals and cracks, which have a common symmetry axis. We found that other sheet silicate-rich rocks have a similar anisotropy with the biotite schist, in which the TI-type anisotropy is characterized by the slow P- and S-wave velocities along the symmetry axis. This is caused by the preferred orientation of sheet silicate minerals and the extremely slow P- and S-wave velocities along the axis perpendicular to the silicate sheet compared to the directions along the silicate sheet. When rock contains a large percentage of highly oriented sheet silicates, the fast and slow shear waves exchange their polarities at some off-symmetry axis directions, indicating that the qS-wave (quasi-S wave) velocity exceeds the SH-wave velocity. The phase velocity distribution of qS wave shows an asymmetry with respect to the angle from the symmetry axis, which is characterized by a bulge in this distribution located near the symmetric axis. This is inherent to most sheet silicate minerals. When crack density of aligned cracks increases, the P-wave velocity along the symmetry axis decreases considerably. The qS-wave phase velocity in the off-axis directions also decreases, in accordance with the decrease of the P velocity along the symmetry axis. The asymmetry of the qS-wave phase velocity distribution increases as the P-wave velocity decreases along the symmetry axis. This relationship can be well understood by means of Berryman

Seismic rupture study using near-source data: application to seismic hazard assessment

International Nuclear Information System (INIS)

Hernandez, Bruno

2000-01-01

This work presents seismic source studies using near-field data. In accordance with the quality and the quantity of available data we developed and applied various methods to characterize the seismic source. Macro-seismic data are used to verify if simple and robust methods used on recent instrumental earthquakes may provide a good tool to calibrate historical events in France. These data are often used to characterize earthquakes to be taken into account for seismic hazard assessment in moderate seismicity regions. Geodetic data (SAR, GPS) are used to estimate the slip distribution on the fault during the 1992, Landers, California earthquake. These data are also used to precise the location and the geometry of the main events of the 1997, Colfiorito, central Italy, earthquake sequence. Finally, the strong motions contain the most complete information about rupture process. These data are used to discriminate between two possible fault planes of the 1999, north India, Chamoli earthquake. The strong motions recorded close to the 1999, Mexico, Oaxaca earthquake are used to constrain the rupture history. Strong motions a.re also used in combination with geodetic data to access the rupture history of the Landers earthquake and the main events of the Colfiorito seismic sequence. For the Landers earthquake, the data quality and complementarity offered the possibility to describe the rupture development with accuracy. The large heterogeneities in both slip amplitude and rupture velocity variations suggest that the rupture propagates by breaking successive asperities rather than by propagating like a pulse at constant velocity. The rupture front slows as it encounters barriers and accelerates within main asperities. (author)

Depth-dependence of time-lapse seismic velocity change detected by a joint interferometric analysis of vertical array data

Science.gov (United States)

Sawazaki, K.; Saito, T.; Ueno, T.; Shiomi, K.

2015-12-01

In this study, utilizing depth-sensitivity of interferometric waveforms recorded by co-located Hi-net and KiK-net sensors, we separate the responsible depth of seismic velocity change associated with the M6.3 earthquake occurred on November 22, 2014, in central Japan. The Hi-net station N.MKGH is located about 20 km northeast from the epicenter, where the seismometer is installed at the 150 m depth. At the same site, the KiK-net has two strong motion seismometers installed at the depths of 0 and 150 m. To estimate average velocity change around the N.MKGH station, we apply the stretching technique to auto-correlation function (ACF) of ambient noise recorded by the Hi-net sensor. To evaluate sensitivity of the Hi-net ACF to velocity change above and below the 150 m depth, we perform a numerical wave propagation simulation using 2-D FDM. To obtain velocity change above the 150 m depth, we measure response waveform from the depths of 150 m to 0 m by computing deconvolution function (DCF) of earthquake records obtained by the two KiK-net vertical array sensors. The background annual velocity variation is subtracted from the detected velocity change. From the KiK-net DCF records, the velocity reduction ratio above the 150 m depth is estimated to be 4.2 % and 3.1 % in the periods of 1-7 days and 7 days - 4 months after the mainshock, respectively. From the Hi-net ACF records, the velocity reduction ratio is estimated to be 2.2 % and 1.8 % in the same time periods, respectively. This difference in the estimated velocity reduction ratio is attributed to depth-dependence of the velocity change. By using the depth sensitivity obtained from the numerical simulation, we estimate the velocity reduction ratio below the 150 m depth to be lower than 1.0 % for both time periods. Thus the significant velocity reduction and recovery are observed above the 150 m depth only, which may be caused by strong ground motion of the mainshock and following healing in the shallow ground.

Seismic refraction survey of the ANS preferred site

Energy Technology Data Exchange (ETDEWEB)

Davis, R.K. (Automated Sciences Group, Inc., Oak Ridge, TN (United States)); Hopkins, R.A. (Marrich, Inc., Knoxville, TN (United States)); Doll, W.E. (Oak Ridge National Lab., TN (United States))

1992-02-01

Between September 19, 1991 and October 8, 1991 personnel from Martin Marietta Energy Systems, Inc. (Energy Systems), Automated Sciences Group, Inc., and Marrich, Inc. performed a seismic refraction survey at the Advanced Neutron Source (ANS) preferred site. The purpose of this survey was to provide estimates of top-of-rock topography, based on seismic velocities, and to delineate variations in rock and soil velocities. Forty-four seismic refraction spreads were shot to determine top-of-rock depths at 42 locations. Nine of the seismic spreads were shot with long offsets to provide 216 top-of-rock depths for 4 seismic refraction profiles. The refraction spread locations were based on the grid for the ANS Phase I drilling program. Interpretation of the seismic refraction data supports the assumption that the top-of-rock surface generally follows the local topography. The shallow top-of-rock interface interpreted from the seismic refraction data is also supported by limited drill information at the site. Some zones of anomalous data are present that could be the result of locally variable weathering, a localized variation in shale content, or depth to top-of-rock greater than the site norm.

Integrating sequence stratigraphy and rock-physics to interpret seismic amplitudes and predict reservoir quality

Science.gov (United States)

Dutta, Tanima

improves the predictions of shear wave velocities. In addition, we provide empirical relations on normal compaction depth trends of porosity, velocities, and VP/VS ratio for shale and clean sands in shallow, supra-salt sediments in the Gulf of Mexico. Next, we identify probable spatial trends of sand/shale ratio and sorting as predicted by the conventional sequence stratigraphic model in minibasin settings (spill-and-fill model). These spatial trends are evaluated using well data from offshore West Africa, and the same well data are used to calibrate rock physics models (modified soft-sand model) that provide links between P-impedance and quartz/clay ratio, and sorting. The spatial increase in sand/shale ratio and sorting corresponds to an overall increase in P-impedance, and AVO intercept and gradient. The results are used as a guide to interpret sedimentological parameters from seismic attributes, away from the well locations. We present a quantitative link between carbonate cement and seismic attributes by combining stratigraphie cycles and the rock physics model (modified differential effective medium model). The variation in carbonate cement volume in West Africa can be linked with two distinct stratigraphic cycles: the coarsening-upward cycles and the fining-upward cycles. Cemented sandstones associated with these cycles exhibit distinct signatures on P-impedance vs. porosity and AVO intercept vs. gradient crossplots. These observations are important for assessing reservoir properties in the West Africa as well as in other analogous depositional environments. Finally, we investigate the relationship between seismic velocities and time temperature index (TTI) using basin and petroleum system modeling at Rio Muni basin, West Africa. We find that both VP and VS increase exponentially with TTI. The results can be applied to predict TTI, and thereby thermal maturity, from observed velocities.

Global catalog of earthquake rupture velocities shows anticorrelation between stress drop and rupture velocity

Science.gov (United States)

Chounet, Agnès; Vallée, Martin; Causse, Mathieu; Courboulex, Françoise

2018-05-01

Application of the SCARDEC method provides the apparent source time functions together with seismic moment, depth, and focal mechanism, for most of the recent earthquakes with magnitude larger than 5.6-6. Using this large dataset, we have developed a method to systematically invert for the rupture direction and average rupture velocity Vr, when unilateral rupture propagation dominates. The approach is applied to all the shallow (z earthquakes of the catalog over the 1992-2015 time period. After a careful validation process, rupture properties for a catalog of 96 earthquakes are obtained. The subsequent analysis of this catalog provides several insights about the seismic rupture process. We first report that up-dip ruptures are more abundant than down-dip ruptures for shallow subduction interface earthquakes, which can be understood as a consequence of the material contrast between the slab and the overriding crust. Rupture velocities, which are searched without any a-priori up to the maximal P wave velocity (6000-8000 m/s), are found between 1200 m/s and 4500 m/s. This observation indicates that no earthquakes propagate over long distances with rupture velocity approaching the P wave velocity. Among the 23 ruptures faster than 3100 m/s, we observe both documented supershear ruptures (e.g. the 2001 Kunlun earthquake), and undocumented ruptures that very likely include a supershear phase. We also find that the correlation of Vr with the source duration scaled to the seismic moment (Ts) is very weak. This directly implies that both Ts and Vr are anticorrelated with the stress drop Δσ. This result has implications for the assessment of the peak ground acceleration (PGA) variability. As shown by Causse and Song (2015), an anticorrelation between Δσ and Vr significantly reduces the predicted PGA variability, and brings it closer to the observed variability.

Seismic imaging of the shallow subsurface with high frequency seismic measurements

International Nuclear Information System (INIS)

Kaelin, B.; Lawrence Berkeley National Lab., CA

1998-07-01

Elastic wave propagation in highly heterogeneous media is investigated and theoretical calculations and field measurements are presented. In the first part the dynamic composite elastic medium (DYCEM) theory is derived for one-dimensional stratified media. A self-consistent method using the scattering functions of the individual layers is formulated, which allows the calculation of phase velocity, attenuation and waveform. In the second part the DYCEM theory has been generalized for three-dimensional inclusions. The specific case of spherical inclusions is calculated with the exact scattering functions and compared with several low frequency approximations. In the third part log and VSP data of partially water saturated tuffs in the Yucca Mountain region of Nevada are analyzed. The anomalous slow seismic velocities can be explained by combining self-consistent theories for pores and cracks. The fourth part analyzes an air injection experiment in a shallow fractured limestone, which has shown large effects on the amplitude, but small effects on the travel time of the transmitted seismic waves. The large amplitude decrease during the experiment is mainly due to the impedance contrast between the small velocities of gas-water mixtures inside the fracture and the formation. The slow velocities inside the fracture allow an estimation of aperture and gas concentration profiles

Seismic velocities within the sedimentary succession of the Canada Basin and southern Alpha-Mendeleev Ridge, Arctic Ocean: evidence for accelerated porosity reduction?

Science.gov (United States)

Shimeld, John; Li, Qingmou; Chian, Deping; Lebedeva-Ivanova, Nina; Jackson, Ruth; Mosher, David; Hutchinson, Deborah R.

2016-01-01

The Canada Basin and the southern Alpha-Mendeleev ridge complex underlie a significant proportion of the Arctic Ocean, but the geology of this undrilled and mostly ice-covered frontier is poorly known. New information is encoded in seismic wide-angle reflections and refractions recorded with expendable sonobuoys between 2007 and 2011. Velocity–depth samples within the sedimentary succession are extracted from published analyses for 142 of these records obtained at irregularly spaced stations across an area of 1.9E + 06 km2. The samples are modelled at regional, subregional and station-specific scales using an exponential function of inverse velocity versus depth with regionally representative parameters determined through numerical regression. With this approach, smooth, non-oscillatory velocity–depth profiles can be generated for any desired location in the study area, even where the measurement density is low. Practical application is demonstrated with a map of sedimentary thickness, derived from seismic reflection horizons interpreted in the time domain and depth converted using the velocity–depth profiles for each seismic trace. A thickness of 12–13 km is present beneath both the upper Mackenzie fan and the middle slope off of Alaska, but the sedimentary prism thins more gradually outboard of the latter region. Mapping of the observed-to-predicted velocities reveals coherent geospatial trends associated with five subregions: the Mackenzie fan; the continental slopes beyond the Mackenzie fan; the abyssal plain; the southwestern Canada Basin; and, the Alpha-Mendeleev magnetic domain. Comparison of the subregional velocity–depth models with published borehole data, and interpretation of the station-specific best-fitting model parameters, suggests that sandstone is not a predominant lithology in any of the five subregions. However, the bulk sand-to-shale ratio likely increases towards the Mackenzie fan, and the model for this subregion compares

Stress development in heterogenetic lithosphere: Insights into earthquake processes in the New Madrid Seismic Zone

Science.gov (United States)

Zhan, Yan; Hou, Guiting; Kusky, Timothy; Gregg, Patricia M.

2016-03-01

The New Madrid Seismic Zone (NMSZ) in the Midwestern United States was the site of several major M 6.8-8 earthquakes in 1811-1812, and remains seismically active. Although this region has been investigated extensively, the ultimate controls on earthquake initiation and the duration of the seismicity remain unclear. In this study, we develop a finite element model for the Central United States to conduct a series of numerical experiments with the goal of determining the impact of heterogeneity in the upper crust, the lower crust, and the mantle on earthquake nucleation and rupture processes. Regional seismic tomography data (CITE) are utilized to infer the viscosity structure of the lithosphere which provide an important input to the numerical models. Results indicate that when differential stresses build in the Central United States, the stresses accumulating beneath the Reelfoot Rift in the NMSZ are highly concentrated, whereas the stresses below the geologically similar Midcontinent Rift System are comparatively low. The numerical observations coincide with the observed distribution of seismicity throughout the region. By comparing the numerical results with three reference models, we argue that an extensive mantle low velocity zone beneath the NMSZ produces differential stress localization in the layers above. Furthermore, the relatively strong crust in this region, exhibited by high seismic velocities, enables the elevated stress to extend to the base of the ancient rift system, reactivating fossil rifting faults and therefore triggering earthquakes. These results show that, if boundary displacements are significant, the NMSZ is able to localize tectonic stresses, which may be released when faults close to failure are triggered by external processes such as melting of the Laurentide ice sheet or rapid river incision.

6C polarization analysis - seismic direction finding in coherent noise, automated event identification, and wavefield separation

Science.gov (United States)

Schmelzbach, C.; Sollberger, D.; Greenhalgh, S.; Van Renterghem, C.; Robertsson, J. O. A.

2017-12-01

Polarization analysis of standard three-component (3C) seismic data is an established tool to determine the propagation directions of seismic waves recorded by a single station. A major limitation of seismic direction finding methods using 3C recordings, however, is that a correct propagation-direction determination is only possible if the wave mode is known. Furthermore, 3C polarization analysis techniques break down in the presence of coherent noise (i.e., when more than one event is present in the analysis time window). Recent advances in sensor technology (e.g., fibre-optical, magnetohydrodynamic angular rate sensors, and ring laser gyroscopes) have made it possible to accurately measure all three components of rotational ground motion exhibited by seismic waves, in addition to the conventionally recorded three components of translational motion. Here, we present an extension of the theory of single station 3C polarization analysis to six-component (6C) recordings of collocated translational and rotational ground motions. We demonstrate that the information contained in rotation measurements can help to overcome some of the main limitations of standard 3C seismic direction finding, such as handling multiple arrivals simultaneously. We show that the 6C polarisation of elastic waves measured at the Earth's free surface does not only depend on the seismic wave type and propagation direction, but also on the local P- and S-wave velocities just beneath the recording station. Using an adaptation of the multiple signal classification algorithm (MUSIC), we demonstrate how seismic events can univocally be identified and characterized in terms of their wave type. Furthermore, we show how the local velocities can be inferred from single-station 6C data, in addition to the direction angles (inclination and azimuth) of seismic arrivals. A major benefit of our proposed 6C method is that it also allows the accurate recovery of the wave type, propagation directions, and phase

Upper mantle seismic velocity anomaly beneath southern Taiwan as revealed by teleseismic relative arrival times

Science.gov (United States)

Chen, Po-Fei; Huang, Bor-Shouh; Chiao, Ling-Yun

2011-01-01

Probing the lateral heterogeneity of the upper mantle seismic velocity structure beneath southern and central Taiwan is critical to understanding the local tectonics and orogeny. A linear broadband array that transects southern Taiwan, together with carefully selected teleseismic sources with the right azimuth provides useful constraints. They are capable of differentiating the lateral heterogeneity along the profile with systematic coverage of ray paths. We implement a scheme based on the genetic algorithm to simultaneously determine the relative delayed times of the teleseismic first arrivals of array data. The resulting patterns of the delayed times systematically vary as a function of the incident angle. Ray tracing attributes the observed variations to a high velocity anomaly dipping east in the mantle beneath the southeast of Taiwan. Combining the ray tracing analysis and a pseudo-spectral method to solve the 2-D wave propagations, we determine the extent of the anomaly that best fits the observations via the forward grid search. The east-dipping fast anomaly in the upper mantle beneath the southeast of Taiwan agrees with the results from several previous studies and indicates that the nature of the local ongoing arc-continent collision is likely characterized by the thin-skinned style.

The Utility of the Extended Images in Ambient Seismic Wavefield Migration

Science.gov (United States)

Girard, A. J.; Shragge, J. C.

2015-12-01

Active-source 3D seismic migration and migration velocity analysis (MVA) are robust and highly used methods for imaging Earth structure. One class of migration methods uses extended images constructed by incorporating spatial and/or temporal wavefield correlation lags to the imaging conditions. These extended images allow users to directly assess whether images focus better with different parameters, which leads to MVA techniques that are based on the tenets of adjoint-state theory. Under certain conditions (e.g., geographical, cultural or financial), however, active-source methods can prove impractical. Utilizing ambient seismic energy that naturally propagates through the Earth is an alternate method currently used in the scientific community. Thus, an open question is whether extended images are similarly useful for ambient seismic migration processing and verifying subsurface velocity models, and whether one can similarly apply adjoint-state methods to perform ambient migration velocity analysis (AMVA). Herein, we conduct a number of numerical experiments that construct extended images from ambient seismic recordings. We demonstrate that, similar to active-source methods, there is a sensitivity to velocity in ambient seismic recordings in the migrated extended image domain. In synthetic ambient imaging tests with varying degrees of error introduced to the velocity model, the extended images are sensitive to velocity model errors. To determine the extent of this sensitivity, we utilize acoustic wave-equation propagation and cross-correlation-based migration methods to image weak body-wave signals present in the recordings. Importantly, we have also observed scenarios where non-zero correlation lags show signal while zero-lags show none. This may be a valuable missing piece for ambient migration techniques that have yielded largely inconclusive results, and might be an important piece of information for performing AMVA from ambient seismic recordings.

Shallow lunar structure determined from the passive seismic experiment

International Nuclear Information System (INIS)

Nakamura, Y.; Dorman, J.; Duennebier, F.; Lammlein, D.; Latham, G.

1975-01-01

Data relevant to the shallow structure of the Moon obtained at the Apollo seismic stations are compared with previously published results of the active seismic experiments. It is concluded that the lunar surface is covered by a layer of low seismic velocity (Vsub(p) approximately equal to 100 ms -1 ), which appears to be equivalent to the lunar regolith defined previously by geological observations. This layer is underlain by a zone of distinctly higher seismic velocity at all of the Apollo landing sites. The regolith thicknesses at the Apollo 11, 12, and 15 sites are estimated from the shear-wave resonance to be 4.4, 3.7, and 4.4m, respectively. These thicknesses and those determined at the other Apollo sites by the active seismic experiments appear to be correlated with the age determinations and the abundances of extra-lunar components at the sites. (Auth.)

Crosshole seismic measurements to characterise and monitor the internal condition of embankment dams

Energy Technology Data Exchange (ETDEWEB)

Vazinkhoo, S. [Horizon Engineering Inc., North Vancouver, BC (Canada); Gaffran, P. [BC Hydro, Burnaby, BC (Canada)

2002-12-01

A sinkhole was discovered at the Bennett Dam in June 1996. The discovery was immediately followed by an investigation consisting 14 geophysical techniques, of which crosshole seismic testing was the most successful. The Bennett Dam Sinkhole Investigation Project resulted in remedial action which involved compaction grouting to repair the defects. Crosshole seismic testing has been carried out annually since 1996 to verify that the integrity of the repaired zone is being maintained. Large amounts of data have been collected since initial testing to augment other acquired data from more conventional geotechnical techniques. Both data sets have provided a unique opportunity to correlate seismic velocities to mechanical soil properties. The condition of the dam can now be readily assessed through the prediction of seismic velocities for a range of soil properties at any point in the dam. The study has resulted in a better understanding of measured velocities with respect to dam behaviour. Results confirm that seismic velocity testing is a useful, non-intrusive tool for monitoring the performance of embankment dams. 13 refs., 2 tabs., 8 figs.

Rayleigh wave group velocity and shear wave velocity structure in the San Francisco Bay region from ambient noise tomography

Science.gov (United States)

Li, Peng; Thurber, Clifford

2018-06-01

We derive new Rayleigh wave group velocity models and a 3-D shear wave velocity model of the upper crust in the San Francisco Bay region using an adaptive grid ambient noise tomography algorithm and 6 months of continuous seismic data from 174 seismic stations from multiple networks. The resolution of the group velocity models is 0.1°-0.2° for short periods (˜3 s) and 0.3°-0.4° for long periods (˜10 s). The new shear wave velocity model of the upper crust reveals a number of important structures. We find distinct velocity contrasts at the Golden Gate segment of the San Andreas Fault, the West Napa Fault, central part of the Hayward Fault and southern part of the Calaveras Fault. Low shear wave velocities are mainly located in Tertiary and Quaternary basins, for instance, La Honda Basin, Livermore Valley and the western and eastern edges of Santa Clara Valley. Low shear wave velocities are also observed at the Sonoma volcanic field. Areas of high shear wave velocity include the Santa Lucia Range, the Gabilan Range and Ben Lomond Plutons, and the Diablo Range, where Franciscan Complex or Silinian rocks are exposed.

Quantifying seismic anisotropy induced by small-scale chemical heterogeneities

Science.gov (United States)

Alder, C.; Bodin, T.; Ricard, Y.; Capdeville, Y.; Debayle, E.; Montagner, J. P.

2017-12-01

Observations of seismic anisotropy are usually used as a proxy for lattice-preferred orientation (LPO) of anisotropic minerals in the Earth's mantle. In this way, seismic anisotropy observed in tomographic models provides important constraints on the geometry of mantle deformation associated with thermal convection and plate tectonics. However, in addition to LPO, small-scale heterogeneities that cannot be resolved by long-period seismic waves may also produce anisotropy. The observed (i.e. apparent) anisotropy is then a combination of an intrinsic and an extrinsic component. Assuming the Earth's mantle exhibits petrological inhomogeneities at all scales, tomographic models built from long-period seismic waves may thus display extrinsic anisotropy. In this paper, we investigate the relation between the amplitude of seismic heterogeneities and the level of induced S-wave radial anisotropy as seen by long-period seismic waves. We generate some simple 1-D and 2-D isotropic models that exhibit a power spectrum of heterogeneities as what is expected for the Earth's mantle, that is, varying as 1/k, with k the wavenumber of these heterogeneities. The 1-D toy models correspond to simple layered media. In the 2-D case, our models depict marble-cake patterns in which an anomaly in shear wave velocity has been advected within convective cells. The long-wavelength equivalents of these models are computed using upscaling relations that link properties of a rapidly varying elastic medium to properties of the effective, that is, apparent, medium as seen by long-period waves. The resulting homogenized media exhibit extrinsic anisotropy and represent what would be observed in tomography. In the 1-D case, we analytically show that the level of anisotropy increases with the square of the amplitude of heterogeneities. This relation is numerically verified for both 1-D and 2-D media. In addition, we predict that 10 per cent of chemical heterogeneities in 2-D marble-cake models can

Innovations in seismic tomography, their applications and induced seismic events in carbon sequestration

Science.gov (United States)

Li, Peng

This dissertation presents two innovations in seismic tomography and a new discovery of induced seismic events associated with CO2 injection at an Enhanced Oil Recovery (EOR) site. The following are brief introductions of these three works. The first innovated work is adaptive ambient seismic noise tomography (AANT). Traditional ambient noise tomography methods using regular grid nodes are often ill posed because the inversion grids do not always represent the distribution of ray paths. Large grid spacing is usually used to reduce the number of inversion parameters, which may not be able to solve for small-scale velocity structure. We present a new adaptive tomography method with irregular grids that provides a few advantages over the traditional methods. First, irregular grids with different sizes and shapes can fit the ray distribution better and the traditionally ill-posed problem can become more stable owing to the different parameterizations. Second, the data in the area with dense ray sampling will be sufficiently utilized so that the model resolution can be greatly improved. Both synthetic and real data are used to test the newly developed tomography algorithm. In synthetic data tests, we compare the resolution and stability of the traditional and adaptive methods. The results show that adaptive tomography is more stable and performs better in improving the resolution in the area with dense ray sampling. For real data, we extract the ambient noise signals of the seismic data near the Garlock Fault region, obtained from the Southern California Earthquake Data Center. The resulting group velocity of Rayleigh waves is well correlated with the geological structures. High velocity anomalies are shown in the cold southern Sierra Nevada, the Tehachapi Mountains and the Western San Gabriel Mountains. The second innovated work is local earthquake tomography with full topography (LETFT). In this work, we develop a new three-dimensional local earthquake tomography

Seismic excitation by space shuttles

Science.gov (United States)

Kanamori, H.; Mori, J.; Sturtevant, B.; Anderson, D.L.; Heaton, T.

1992-01-01

Shock waves generated by the space shuttles Columbia (August 13, 1989), Atlantis (April 11, 1991) and Discovery (September 18, 1991) on their return to Edwards Air Force Base, California, were recorded by TERRAscope (Caltech's broadband seismic network), the Caltech-U.S.G.S Southern California Seismic Network (SCSN), and the University of Southern California (USC) Los Angeles Basin Seismic Network. The spatial pattern of the arrival times exhibits hyperbolic shock fronts from which the path, velocity and altitude of the space shuttle could be determined. The shock wave was acoustically coupled to the ground, converted to a seismic wave, and recorded clearly at the broadband TERRAscope stations. The acoustic coupling occurred very differently depending on the conditions of the Earth's surface surrounding the station. For a seismic station located on hard bedrock, the shock wave (N wave) was clearly recorded with little distortion. Aside from the N wave, very little acoustic coupling of the shock wave energy to the ground occurred at these sites. The observed N wave record was used to estimate the overpressure of the shock wave accurately; a pressure change of 0.5 to 2.2 mbars was obtained. For a seismic station located close to the ocean or soft sedimentary basins, a significant amount of shock wave energy was transferred to the ground through acoustic coupling of the shock wave and the oceanic Rayleigh wave. A distinct topography such as a mountain range was found effective to couple the shock wave energy to the ground. Shock wave energy was also coupled to the ground very effectively through large man made structures such as high rise buildings and offshore oil drilling platforms. For the space shuttle Columbia, in particular, a distinct pulse having a period of about 2 to 3 seconds was observed, 12.5 s before the shock wave, with a broadband seismograph in Pasadena. This pulse was probably excited by the high rise buildings in downtown Los Angeles which were

Seismicity and seismic hazard in Sabah, East Malaysia from earthquake and geodetic data

Science.gov (United States)

Gilligan, A.; Rawlinson, N.; Tongkul, F.; Stephenson, R.

2017-12-01

While the levels of seismicity are low in most of Malaysia, the state of Sabah in northern Borneo has moderate levels of seismicity. Notable earthquakes in the region include the 1976 M6.2 Lahad Datu earthquake and the 2015 M6 Ranau earthquake. The recent Ranau earthquake resulted in the deaths of 18 people on Mt Kinabalu, an estimated 100 million RM ( US$23 million) damage to buildings, roads, and infrastructure from shaking, and flooding, reduced water quality, and damage to farms from landslides. Over the last 40 years the population of Sabah has increased to over four times what it was in 1976, yet seismic hazard in Sabah remains poorly understood. Using seismic and geodetic data we hope to better quantify the hazards posed by earthquakes in Sabah, and thus help to minimize risk. In order to do this we need to know about the locations of earthquakes, types of earthquakes that occur, and faults that are generating them. We use data from 15 MetMalaysia seismic stations currently operating in Sabah to develop a region-specific velocity model from receiver functions and a pre-existing surface wave model. We use this new velocity model to (re)locate earthquakes that occurred in Sabah from 2005-2016, including a large number of aftershocks from the 2015 Ranau earthquake. We use a probabilistic nonlinear earthquake location program to locate the earthquakes and then refine their relative locations using a double difference method. The recorded waveforms are further used to obtain moment tensor solutions for these earthquakes. Earthquake locations and moment tensor solutions are then compared with the locations of faults throughout Sabah. Faults are identified from high-resolution IFSAR images and subsequent fieldwork, with a particular focus on the Lahad Datau and Ranau areas. Used together, these seismic and geodetic data can help us to develop a new seismic hazard model for Sabah, as well as aiding in the delivery of outreach activities regarding seismic hazard

From the Atlas to the Rif a Crustal seismic image across Morocco: The SIMA & RIFSEIS control source wide-angle seismic reflection data

Science.gov (United States)

Carbonell, Ramon; Ayarza, Puy; Gallart, Josep; Diaz, Jordi; Harnafi, Mimoun; Levander, Alan; Teixell, Antonio

2014-05-01

The velocity structure of the crust and the geometry of the Moho across Morocco has been the main target of two recently acquired wide-angle seismic reflection transects. One is the SIMA experiment which provided seismic constraints beneath the Atlas Mountains and the second has been the RIFSEIS experiment which sampled the RIF orogen. Jointly these controlled source wide-angle seismic reflection data results in an almost 700 km, seismic profile going from the the Sahara craton across the High and Middle Atlas and Rif Mountain till the Gibraltar-Arc (Alboran). Current work on the interpretation of the seismic data-set is based on forward modeling, ray-tracing, as well as low fold wide-angle stacking. The data has resulted in a detailed crustal structure and velocity model for the Atlas Mountains and a 700 km transect revealing the irregular topography of the Moho beneath these two mountain orogens. Results indicate that the High Atlas features a moderate crustal thickness and that shortening is resolved at depth through a crustal root where the Saharan crust under-thrusts below the Moroccan crust, defining a lower crust imbrication which locally places the Moho boundary at, approximately, 40 km depth. The P-wave velocity model is characterized, in averaged, by relatively low velocities. These low deep crustal velocities together with other geophysical observables such as: conductivity estimates derived from Mt measurements; moderate Bouguer gravity anomaly; surface exposures of recent alkaline volcanics; lead the interpretation to propose that partial melts are currently emplaced in the deep crustal levels and in the upper mantle. The Moho discontinuity defines a crust which is in average relatively thin beneath the Atlas which is almost a 4000 m high orogenic belt. The resulting model supports existence of mantle upwelling as a possible mechanism that contributes, significantly, to maintain the High Atlas topography.

Microseismic Velocity Imaging of the Fracturing Zone

Science.gov (United States)

Zhang, H.; Chen, Y.

2015-12-01

Hydraulic fracturing of low permeability reservoirs can induce microseismic events during fracture development. For this reason, microseismic monitoring using sensors on surface or in borehole have been widely used to delineate fracture spatial distribution and to understand fracturing mechanisms. It is often the case that the stimulated reservoir volume (SRV) is determined solely based on microseismic locations. However, it is known that for some fracture development stage, long period long duration events, instead of microseismic events may be associated. In addition, because microseismic events are essentially weak and there exist different sources of noise during monitoring, some microseismic events could not be detected and thus located. Therefore the estimation of the SRV is biased if it is solely determined by microseismic locations. With the existence of fluids and fractures, the seismic velocity of reservoir layers will be decreased. Based on this fact, we have developed a near real time seismic velocity tomography method to characterize velocity changes associated with fracturing process. The method is based on double-difference seismic tomography algorithm to image the fracturing zone where microseismic events occur by using differential arrival times from microseismic event pairs. To take into account varying data distribution for different fracking stages, the method solves the velocity model in the wavelet domain so that different scales of model features can be obtained according to different data distribution. We have applied this real time tomography method to both acoustic emission data from lab experiment and microseismic data from a downhole microseismic monitoring project for shale gas hydraulic fracturing treatment. The tomography results from lab data clearly show the velocity changes associated with different rock fracturing stages. For the field data application, it shows that microseismic events are located in low velocity anomalies. By

Directivity of seismic radiation from a series of line charges

Energy Technology Data Exchange (ETDEWEB)

Ahrens, Thomas J [Lawrence Radiation Laboratory, University of California, Livermore, CA (United States)

1970-05-15

A series of two-dimensional calculations describing the stress wave propagation from a row of line explosive sources, detonated sequentially at a supersonic phase velocity on the surface of various layered (half-space) crustal models, was carried out. Spectral ratios of the resulting free-surface velocities at a series of hypothetical seismic stations were used to calculate directivity functions. As in the case considered earlier by Ben-Menahem (where the source moved subsonically), strong enhancement of certain frequencies in the spectrum of the horizontal component of velocity was obtained. Directivity is especially prominent when the explosion-induced signals are generated in a medium in which the longitudinal elastic wave velocity is comparable to the detonation phase velocity and when the seismic signal being analyzed has been refracted from a higher-velocity, underlying layer. (author)

Three-dimensional P velocity structure in Beijing area

Science.gov (United States)

Yu, Xiang-Wei; Chen, Yun-Tai; Wang, Pei-De

2003-01-01

A detail three-dimensional P wave velocity structure of Beijing, Tianjin and Tangshan area (BTT area) was determined by inverting local earthquake data. In total 16 048 P wave first arrival times from 16048 shallow and mid-depth crustal earthquakes, which occurred in and around the BTT area from 1992 to 1999 were used. The first arrival times are recorded by Northern China United Telemetry Seismic Network and Yanqing-Huailai Digital Seismic Network. Hypocentral parameters of 1 132 earthquakes with magnitude M L=1.7 6.2 and the three-dimensional P wave velocity structure were obtained simultaneously. The inversion result reveals the complicated lateral heterogeneity of P wave velocity structure around BTT area. The tomographic images obtained are also found to explain other seismological observations well.

Instrument Correction and Dynamic Site Profile Validation at the Central United States Seismic Observatory, New Madrid Seismic Zone

Science.gov (United States)

Brengman, C.; Woolery, E. W.; Wang, Z.; Carpenter, S.

2016-12-01

The Central United States Seismic Observatory (CUSSO) is a vertical seismic array located in southwestern Kentucky within the New Madrid seismic zone. It is intended to describe the effects of local geology, including thick sediment overburden, on seismic-wave propagation, particularly strong-motion. The three-borehole array at CUSSO is composed of seismic sensors placed on the surface, and in the bedrock at various depths within the 585 m thick sediment overburden. The array's deep borehole provided a unique opportunity in the northern Mississippi embayment for the direct geological description and geophysical measurement of the complete late Cretaceous-Quaternary sediment column. A seven layer, intra-sediment velocity model is interpreted from the complex, inhomogeneous stratigraphy. The S- and P-wave sediment velocities range between 160 and 875 m/s and between 1000 and 2300 m/s, respectively, with bedrock velocities of 1452 and 3775 m/s, respectively. Cross-correlation and direct comparisons were used to filter out the instrument response and determine the instrument orientation, making CUSSO data ready for analysis, and making CUSSO a viable calibration site for other free-field sensors in the area. The corrected bedrock motions were numerically propagated through the CUSSO soil profile (transfer function) and compared, in terms of both peak acceleration and amplitude spectra, to the recorded surface observations. Initial observations reveal a complex spectral mix of amplification and de-amplification across the array, indicating the site effect in this deep sediment setting is not simply generated by the shallowest layers.

Seismic amplification within the Seattle Basin, Washington State: Insights from SHIPS seismic tomography experiments

Science.gov (United States)

Snelson, C.M.; Brocher, T.M.; Miller, K.C.; Pratt, T.L.; Trehu, A.M.

2007-01-01

Recent observations indicate that the Seattle sedimentary basin, underlying Seattle and other urban centers in the Puget Lowland, Washington, amplifies long-period (1-5 sec) weak ground motions by factors of 10 or more. We computed east-trending P- and S-wave velocity models across the Seattle basin from Seismic Hazard Investigations of Puget Sound (SHIPS) experiments to better characterize the seismic hazard the basin poses. The 3D tomographic models, which resolve features to a depth of 10 km, for the first time define the P- and S-wave velocity structure of the eastern end of the basin. The basin, which contains sedimentary rocks of Eocene to Holocene, is broadly symmetric in east-west section and reaches a maximum thickness of 6 km along our profile beneath north Seattle. A comparison of our velocity model with coincident amplification curves for weak ground motions produced by the 1999 Chi-Chi earthquake suggests that the distribution of Quaternary deposits and reduced velocity gradients in the upper part of the basement east of Seattle have significance in forecasting variations in seismic-wave amplification across the basin. Specifically, eastward increases in the amplification of 0.2- to 5-Hz energy correlate with locally thicker unconsolidated deposits and a change from Crescent Formation basement to pre-Tertiary Cascadia basement. These models define the extent of the Seattle basin, the Seattle fault, and the geometry of the basement contact, giving insight into the tectonic evolution of the Seattle basin and its influence on ground shaking.

Seismic properties of lawsonite eclogites from the southern Motagua fault zone, Guatemala

Science.gov (United States)

Kim, Daeyeong; Wallis, Simon; Endo, Shunsuke; Ree, Jin-Han

2016-05-01

We present new data on the crystal preferred orientation (CPO) and seismic properties of omphacite and lawsonite in extremely fresh eclogite from the southern Motagua fault zone, Guatemala, to discuss the seismic anisotropy of subducting oceanic crust. The CPO of omphacite is characterized by (010)[001], and it shows P-wave seismic anisotropies (AVP) of 1.4%-3.2% and S-wave seismic anisotropies (AVS) of 1.4%-2.7%. Lawsonite exhibits (001) planes parallel to the foliation and [010] axes parallel to the lineation, and seismic anisotropies of 1.7%-6.6% AVP and 3.4%-14.7% AVS. The seismic anisotropy of a rock mass consisting solely of omphacite and lawsonite is 1.2%-4.1% AVP and 1.8%-6.8% AVS. For events that propagate more or less parallel to the maximum extension direction, X, the fast S-wave velocity (VS) polarization is parallel to the Z in the Y-Z section (rotated from the X-Z section), causing trench-normal seismic anisotropy for orthogonal subduction. Based on the high modal abundance and strong fabric of lawsonite, the AVS of eclogites is estimated as ~ 11.7% in the case that lawsonite makes up ~ 75% of the rock mass. On this basis, we suggest that lawsonite in both blueschist and eclogite may play important roles in the formation of complex pattern of seismic anisotropy observed in NE Japan: weak trench-parallel anisotropy in the forearc basin domains and trench-normal anisotropy in the backarc region.

Bayesian seismic AVO inversion

Energy Technology Data Exchange (ETDEWEB)

Buland, Arild

2002-07-01

A new linearized AVO inversion technique is developed in a Bayesian framework. The objective is to obtain posterior distributions for P-wave velocity, S-wave velocity and density. Distributions for other elastic parameters can also be assessed, for example acoustic impedance, shear impedance and P-wave to S-wave velocity ratio. The inversion algorithm is based on the convolutional model and a linearized weak contrast approximation of the Zoeppritz equation. The solution is represented by a Gaussian posterior distribution with explicit expressions for the posterior expectation and covariance, hence exact prediction intervals for the inverted parameters can be computed under the specified model. The explicit analytical form of the posterior distribution provides a computationally fast inversion method. Tests on synthetic data show that all inverted parameters were almost perfectly retrieved when the noise approached zero. With realistic noise levels, acoustic impedance was the best determined parameter, while the inversion provided practically no information about the density. The inversion algorithm has also been tested on a real 3-D dataset from the Sleipner Field. The results show good agreement with well logs but the uncertainty is high. The stochastic model includes uncertainties of both the elastic parameters, the wavelet and the seismic and well log data. The posterior distribution is explored by Markov chain Monte Carlo simulation using the Gibbs sampler algorithm. The inversion algorithm has been tested on a seismic line from the Heidrun Field with two wells located on the line. The uncertainty of the estimated wavelet is low. In the Heidrun examples the effect of including uncertainty of the wavelet and the noise level was marginal with respect to the AVO inversion results. We have developed a 3-D linearized AVO inversion method with spatially coupled model parameters where the objective is to obtain posterior distributions for P-wave velocity, S

Seismic protection

International Nuclear Information System (INIS)

Herbert, R.

1988-01-01

To ensure that a nuclear reactor or other damage-susceptible installation is, so far as possible, tripped and already shut down before the arrival of an earthquake shock at its location, a ring of monitoring seismic sensors is provided around it, each sensor being spaced from it by a distance (possibly several kilometres) such that (taking into account the seismic-shock propagation velocity through the intervening ground) a shock monitored by the sensor and then advancing to the installation site will arrive there later than a warning signal emitted by the sensor and received at the installation, by an interval sufficient to allow the installation to trip and shut down, or otherwise assume an optimum anti-seismic mode, in response to the warning signal. Extra sensors located in boreholes may define effectively a three-dimensional (hemispherical) sensing boundary rather than a mere two-dimensional ring. (author)

In situ anisotropic parameter determination using refraction seismic and VSP methods

Energy Technology Data Exchange (ETDEWEB)

Leslie, J.M.; Lawton, D.C. (Calgary Univ., AB (Canada))

1999-01-01

A prime concern in the time-to-depth conversion of reflection seismic data is seismic anisotropy, because it can produce velocity anomalies in seismic data that mimic the structural plays of interest to the petroleum prospector in both size and shape. Ongoing techniques of time-to-depth conversion of P-wave seismic data do not handle the travel time and velocity distortions caused by seismic anisotropy, particularly in areas of complex geologic structures. To address this problem, the first step is to know which rock units are anisotropic and measure their anisotropic parameters. Laboratory means are available, but there are problems with these mainly with shales because of their fissile nature. In situ measurements are preferable because they yield a more robust value, and at the University of Calgary such measurements were undertaken using refraction seismic and vertical seismic profiling (VSP) methods. Results indicate that the two Thomsen anisotropic parameters of interest can be determined from the VSP experiment, but these values are slightly less than those obtained using the refraction technique. This may be because of the sensitivity of the shot statics which arises from the direct travel time measurement of the technique. The experiment yields another method to measure velocity anisotropy, in situ, where steeply dipping strata outcrop, which allows for the accurate measurement of the anisotropic parameters for use in depth migration routines. 4 refs.

In situ anisotropic parameter determination using refraction seismic and VSP methods

Energy Technology Data Exchange (ETDEWEB)

Leslie, J.M.; Lawton, D.C. [Calgary Univ., AB (Canada)

1999-11-01

A prime concern in the time-to-depth conversion of reflection seismic data is seismic anisotropy, because it can produce velocity anomalies in seismic data that mimic the structural plays of interest to the petroleum prospector in both size and shape. Ongoing techniques of time-to-depth conversion of P-wave seismic data do not handle the travel time and velocity distortions caused by seismic anisotropy, particularly in areas of complex geologic structures. To address this problem, the first step is to know which rock units are anisotropic and measure their anisotropic parameters. Laboratory means are available, but there are problems with these mainly with shales because of their fissile nature. In situ measurements are preferable because they yield a more robust value, and at the University of Calgary such measurements were undertaken using refraction seismic and vertical seismic profiling (VSP) methods. Results indicate that the two Thomsen anisotropic parameters of interest can be determined from the VSP experiment, but these values are slightly less than those obtained using the refraction technique. This may be because of the sensitivity of the shot statics which arises from the direct travel time measurement of the technique. The experiment yields another method to measure velocity anisotropy, in situ, where steeply dipping strata outcrop, which allows for the accurate measurement of the anisotropic parameters for use in depth migration routines. 4 refs.

Seismic Studies

Energy Technology Data Exchange (ETDEWEB)

R. Quittmeyer

2006-09-25

This technical work plan (TWP) describes the efforts to develop and confirm seismic ground motion inputs used for preclosure design and probabilistic safety 'analyses and to assess the postclosure performance of a repository at Yucca Mountain, Nevada. As part of the effort to develop seismic inputs, the TWP covers testing and analyses that provide the technical basis for inputs to the seismic ground-motion site-response model. The TWP also addresses preparation of a seismic methodology report for submission to the U.S. Nuclear Regulatory Commission (NRC). The activities discussed in this TWP are planned for fiscal years (FY) 2006 through 2008. Some of the work enhances the technical basis for previously developed seismic inputs and reduces uncertainties and conservatism used in previous analyses and modeling. These activities support the defense of a license application. Other activities provide new results that will support development of the preclosure, safety case; these results directly support and will be included in the license application. Table 1 indicates which activities support the license application and which support licensing defense. The activities are listed in Section 1.2; the methods and approaches used to implement them are discussed in more detail in Section 2.2. Technical and performance objectives of this work scope are: (1) For annual ground motion exceedance probabilities appropriate for preclosure design analyses, provide site-specific seismic design acceleration response spectra for a range of damping values; strain-compatible soil properties; peak motions, strains, and curvatures as a function of depth; and time histories (acceleration, velocity, and displacement). Provide seismic design inputs for the waste emplacement level and for surface sites. Results should be consistent with the probabilistic seismic hazard analysis (PSHA) for Yucca Mountain and reflect, as appropriate, available knowledge on the limits to extreme ground

Seismic Studies

International Nuclear Information System (INIS)

R. Quittmeyer

2006-01-01

This technical work plan (TWP) describes the efforts to develop and confirm seismic ground motion inputs used for preclosure design and probabilistic safety 'analyses and to assess the postclosure performance of a repository at Yucca Mountain, Nevada. As part of the effort to develop seismic inputs, the TWP covers testing and analyses that provide the technical basis for inputs to the seismic ground-motion site-response model. The TWP also addresses preparation of a seismic methodology report for submission to the U.S. Nuclear Regulatory Commission (NRC). The activities discussed in this TWP are planned for fiscal years (FY) 2006 through 2008. Some of the work enhances the technical basis for previously developed seismic inputs and reduces uncertainties and conservatism used in previous analyses and modeling. These activities support the defense of a license application. Other activities provide new results that will support development of the preclosure, safety case; these results directly support and will be included in the license application. Table 1 indicates which activities support the license application and which support licensing defense. The activities are listed in Section 1.2; the methods and approaches used to implement them are discussed in more detail in Section 2.2. Technical and performance objectives of this work scope are: (1) For annual ground motion exceedance probabilities appropriate for preclosure design analyses, provide site-specific seismic design acceleration response spectra for a range of damping values; strain-compatible soil properties; peak motions, strains, and curvatures as a function of depth; and time histories (acceleration, velocity, and displacement). Provide seismic design inputs for the waste emplacement level and for surface sites. Results should be consistent with the probabilistic seismic hazard analysis (PSHA) for Yucca Mountain and reflect, as appropriate, available knowledge on the limits to extreme ground motion at

Evidence of unfrozen liquids and seismic anisotropy at the base of the polar ice sheets

Science.gov (United States)

Wittlinger, Gérard; Farra, Véronique

2015-03-01

We analyze seismic data from broadband stations located on the Antarctic and Greenland ice sheets to determine polar ice seismic velocities. P-to-S converted waves at the ice/rock interface and inside the ice sheets and their multiples (the P-receiver functions) are used to estimate in-situ P-wave velocity (Vp) and P-to-S velocity ratio (Vp/Vs) of polar ice. We find that the polar ice sheets have a two-layer structure; an upper layer of variable thickness (about 2/3 of the total thickness) with seismic velocities close to the standard ice values, and a lower layer of approximately constant thickness with standard Vp but ∼25% smaller Vs. The lower layer ceiling corresponds approximately to the -30 °C isotherm. Synthetic modeling of P-receiver functions shows that strong seismic anisotropy and low vertical S velocity are needed in the lower layer. The seismic anisotropy results from the preferred orientation of ice crystal c-axes toward the vertical. The low vertical S velocity may be due to the presence of unfrozen liquids resulting from premelting at grain joints and/or melting of chemical solutions buried in the ice. The strongly preferred ice crystal orientation fabric and the unfrozen fluids may facilitate polar ice sheet basal flow.

New seismic source `BLASTER` for seismic survey; Hasaiyaku wo shingen to shite mochiita danseiha tansa

Energy Technology Data Exchange (ETDEWEB)

Koike, G; Yoshikuni, Y [OYO Corp., Tokyo (Japan)

1996-10-01

Built-up weight and vacuole have been conceived as seismic sources without using explosive. There have been problems that they have smaller energy to generate elastic wave than explosive, and that they have inferior working performance. Concrete crushing explosive is tried to use as a new seismic source. It is considered to possess rather large seismic generating energy, and it is easy to handle from the viewpoint of safety. Performance as seismic source and applicability to exploration works of this crushing explosive were compared with four kinds of seismic sources using dynamite, dropping weight, shot-pipe utilizing shot vacuole, and impact by wooden maul. When considered by the velocity amplitude, the seismic generating energy of the crushing explosive of 120 g is about one-fifth of dynamite of 100 g. Elastic wave generated includes less high frequency component than that by dynamite, and similar to that using seismic source without explosive, such as the weight dropping. The maximum seismic receiving distance obtained by the seismic generation was about 100 m. This was effective for the slope survey with the exploration depth between 20 m and 30 m. 1 ref., 9 figs., 2 tabs.

Integrated seismic interpretation of the Carlsberg Fault zone, Copenhagen, Denmark

DEFF Research Database (Denmark)

Nielsen, Lars; Thybo, Hans; Jørgensen, Mette Iwanouw

2005-01-01

the fault zone. The fault zone is a shadow zone to shots detonated outside the fault zone. Finite-difference wavefield modelling supports the interpretations of the fan recordings. Our fan recording approach facilitates cost-efficient mapping of fault zones in densely urbanized areas where seismic normal......We locate the concealed Carlsberg Fault zone along a 12-km-long trace in the Copenhagen city centre by seismic refraction, reflection and fan profiling. The Carlsberg Fault is located in a NNW-SSE striking fault system in the border zone between the Danish Basin and the Baltic Shield. Recent...... earthquakes indicate that this area is tectonically active. A seismic refraction study across the Carlsberg Fault shows that the fault zone is a low-velocity zone and marks a change in seismic velocity structure. A normal incidence reflection seismic section shows a coincident flower-like structure. We have...

Analysis of induced seismicity in geothermal reservoirs – An overview

Science.gov (United States)

Zang, Arno; Oye, Volker; Jousset, Philippe; Deichmann, Nicholas; Gritto, Roland; McGarr, Arthur F.; Majer, Ernest; Bruhn, David

2014-01-01

In this overview we report results of analysing induced seismicity in geothermal reservoirs in various tectonic settings within the framework of the European Geothermal Engineering Integrating Mitigation of Induced Seismicity in Reservoirs (GEISER) project. In the reconnaissance phase of a field, the subsurface fault mapping, in situ stress and the seismic network are of primary interest in order to help assess the geothermal resource. The hypocentres of the observed seismic events (seismic cloud) are dependent on the design of the installed network, the used velocity model and the applied location technique. During the stimulation phase, the attention is turned to reservoir hydraulics (e.g., fluid pressure, injection volume) and its relation to larger magnitude seismic events, their source characteristics and occurrence in space and time. A change in isotropic components of the full waveform moment tensor is observed for events close to the injection well (tensile character) as compared to events further away from the injection well (shear character). Tensile events coincide with high Gutenberg-Richter b-values and low Brune stress drop values. The stress regime in the reservoir controls the direction of the fracture growth at depth, as indicated by the extent of the seismic cloud detected. Stress magnitudes are important in multiple stimulation of wells, where little or no seismicity is observed until the previous maximum stress level is exceeded (Kaiser Effect). Prior to drilling, obtaining a 3D P-wave (Vp) and S-wave velocity (Vs) model down to reservoir depth is recommended. In the stimulation phase, we recommend to monitor and to locate seismicity with high precision (decametre) in real-time and to perform local 4D tomography for velocity ratio (Vp/Vs). During exploitation, one should use observed and model induced seismicity to forward estimate seismic hazard so that field operators are in a position to adjust well hydraulics (rate and volume of the

Ambient seismic noise monitoring of a clay landslide: Toward failure prediction

Science.gov (United States)

Mainsant, Guénolé; Larose, Eric; Brönnimann, Cornelia; Jongmans, Denis; Michoud, Clément; Jaboyedoff, Michel

2012-03-01

Given that clay-rich landslides may become mobilized, leading to rapid mass movements (earthflows and debris flows), they pose critical problems in risk management worldwide. The most widely proposed mechanism leading to such flow-like movements is the increase in water pore pressure in the sliding mass, generating partial or complete liquefaction. This solid-to-liquid transition results in a dramatic reduction of mechanical rigidity in the liquefied zones, which could be detected by monitoring shear wave velocity variations. With this purpose in mind, the ambient seismic noise correlation technique has been applied to measure the variation in the seismic surface wave velocity in the Pont Bourquin landslide (Swiss Alps). This small but active composite earthslide-earthflow was equipped with continuously recording seismic sensors during spring and summer 2010. An earthslide of a few thousand cubic meters was triggered in mid-August 2010, after a rainy period. This article shows that the seismic velocity of the sliding material, measured from daily noise correlograms, decreased continuously and rapidly for several days prior to the catastrophic event. From a spectral analysis of the velocity decrease, it was possible to determine the location of the change at the base of the sliding layer. These results demonstrate that ambient seismic noise can be used to detect rigidity variations before failure and could potentially be used to predict landslides.

Shear wave velocity structure of the Anatolian Plate and surrounding regions using Ambient Noise Tomography

Science.gov (United States)

Delph, J. R.; Beck, S. L.; Zandt, G.; Biryol, C. B.; Ward, K. M.

2013-12-01

volcanism. The Tuz Golu fault has a visible seismic signal down to ~15 km below sea level, and the eastern Inner-Tauride Suture corresponding to the Central Anatolian Fault Zone may extend into the mantle. The Isparta Angle separates the actively extending portion of western Anatolia from the plateau regions in the east, and the largest anomaly (slow velocities) extending into the upper mantle is observed under the western flank of the Isparta Angle, corresponding to the Fethiye-Burdur fault zone. We attribute these slow shear-wave velocities to the effects of complex deformations within the crust as a result of the interactions of the African and Anatolian Plates. In the upper mantle, slow shear-wave velocities are consistent with a slab tear along a STEP fault corresponding to the extensions of the Pliny and Strabo Transform faults, allowing asthenosphere to rise to very shallow depths. The upper mantle beneath the Taurides exhibits very slow shear-wave velocities, in agreement with possible delamination or slab-breakoff (Cosentino et al. 2012) causing rapid uplift in the last 8 million years.

The seismic signatures of the 2009 Shiaolin landslide in Taiwan

Directory of Open Access Journals (Sweden)

Z. Feng

2011-05-01

Full Text Available The Shiaolin landslide occurred on 9 August 2009 after Typhoon Morakot struck Taiwan, claiming over 400 lives. The seismic signals produced by the landslide were recorded by broadband seismic stations in Taiwan. The time-frequency spectra for these signals were obtained by the Hilbert-Huang transform (HHT and were analyzed to obtain the seismic characteristics of the landslide. Empirical mode decomposition (EMD was applied to differentiate weak surface-wave signals from noise and to estimate the surface-wave velocities in the region. The surface-wave velocities were estimated using the fifth intrinsic mode function (IMF 5 obtained from the EMD. The spectra of the earthquake data were compared. The main frequency content of the seismic waves caused by the Shiaolin landslide were in the range of 0.5 to 1.5 Hz. This frequency range is smaller than the frequency ranges of other earthquakes. The spectral analysis of surface waves (SASW method is suggested for characterizing the shear-wave velocities of the strata in the region.

Geophysical and transport properties of reservoir rocks. Final report for task 4: Measurements and analysis of seismic properties

Energy Technology Data Exchange (ETDEWEB)

Cook, N.G.W.

1993-05-01

The principal objective of research on the seismic properties of reservoir rocks is to develop a basic understanding of the effects of rock microstructure and its contained pore fluids on seismic velocities and attenuation. Ultimately, this knowledge would be used to extract reservoir properties information such as the porosity, permeability, clay content, fluid saturation, and fluid type from borehole, cross-borehole, and surface seismic measurements to improve the planning and control of oil and gas recovery. This thesis presents laboratory ultrasonic measurements for three granular materials and attempts to relate the microstructural properties and the properties of the pore fluids to P- and S-wave velocities and attenuation. These experimental results show that artificial porous materials with sintered grains and a sandstone with partially cemented grains exhibit complexities in P- and S-wave attenuation that cannot be adequately explained by existing micromechanical theories. It is likely that some of the complexity observed in the seismic attenuation is controlled by details of the rock microstructure, such as the grain contact area and grain shape, and by the arrangement of the grain packing. To examine these effects, a numerical method was developed for analyzing wave propagation in a grain packing. The method is based on a dynamic boundary integral equation and incorporates generalized stiffness boundary conditions between individual grains to account for viscous losses and grain contact scattering.

Seismic Applications of Energy Dampers

OpenAIRE

Shambhu Sinha

2004-01-01

Damping devices based on the operating principle of high velocity fluid flow through orifices have found numerous applications in the shock and vibration isolation of aerospace and defence systems. The study aims to investigate the feasibility of using energy dissipating fluid viscous dampers in structures to protect against seismic loads and to prove analytically and  experimentally that fluid viscous dampers can improve the seismic capacity of a structure by reducing damage and displacement...

A novel high-pressure vessel for simultaneous observations of seismic velocity and in situ CO2 distribution in a porous rock using a medical X-ray CT scanner

Science.gov (United States)

Jiang, Lanlan; Nishizawa, Osamu; Zhang, Yi; Park, Hyuck; Xue, Ziqiu

2016-12-01

Understanding the relationship between seismic wave velocity or attenuation and CO2 saturation is essential for CO2 storage in deep saline formations. In the present study, we describe a novel upright high-pressure vessel that is designed to keep a rock sample under reservoir conditions and simultaneously image the entire sample using a medical X-ray CT scanner. The pressure vessel is composed of low X-ray absorption materials: a carbon-fibre-enhanced polyetheretherketone (PEEK) cylinder and PEEK vessel closures supported by carbon-fibre-reinforced plastic (CFRP) joists. The temperature was controlled by a carbon-coated film heater and an aramid fibre thermal insulator. The assembled sample cell allows us to obtain high-resolution images of rock samples during CO2 drainage and brine imbibition under reservoir conditions. The rock sample was oriented vertical to the rotation axis of the CT scanner, and seismic wave paths were aligned parallel to the rotation axis to avoid shadows from the acoustic transducers. The reconstructed CO2 distribution images allow us to calculate the CO2 saturation in the first Fresnel zone along the ray path between transducers. A robust relationship between the seismic wave velocity or attenuation and the CO2 saturation in porous rock was obtained from experiments using this pressure vessel.

Seismic Interferometry of Gulf of Mexico Basin Opening (GUMBO) Data: Extraction of Body and Surface Waves with a Mixed-Mode Array

Science.gov (United States)

Thangraj, J. S.; Quiros, D.; Pulliam, J.

2017-12-01

that exhibit dispersive behavior, which we interpret to be Rayleigh waves. Current efforts are focused on extending the spatial range of the airgun-generated seismic energy further inland (> 70 km) by creating more VSG, to obtain a body wave velocity model along the transect. Similarly, we are inverting the Rayleigh waves in the VSG to obtain a shear wave velocity model.

the Preliminary Research Based on Seismic Signals Generated by Hutubi Transmitting Seismic Station with One Large-volume Airgun Array

Science.gov (United States)

Wang, Q.; Su, J.; Wei, Y.; Zhang, W.; Wang, H.; Wang, B.; Ji, Z.

2017-12-01

For studying the subsurface structure and its subtle changes, we built the Hutubi transmitting seismic station with one large-volume airgun array at one artificial water pool in the northern segment of Tianshan mountain, where earthquakes occurred frequently. The airgun array consists of six airguns with every airgun capacity of 2000in3, and the artificial water pool with the top diameter of 100m, bottom diameter of 20m and the depth of 18m.We started the regular excitation experiment with the large-volume airgun source every week since June, 2013. Using seismic signals geneated by the Hutubi airgun source, we made the preliminary research on the airgun source, waveform characteristics and the subsurface velocity changes in the northern Tiansh mountain. The results are as follows: The seismic signal exited by the airgun source is characteristic of low-frequency ,and the dominant frequency is in the range of 2 6Hz. The Hutubi transmitting seismic station can continuously generate long-distance detectable and highly repeatable signals, and the correlation coefficient of sigals is greater than 0.95; and the longest propagation distance arrives to 380km, in addition, the 5000-shot stacked sigal using the phase weighted stack technique can be identified in the station, which is about 1300km from the Hutubi transmitting seismic station. Hutubi large-volume airgun source is fitted to detect and monitor the regional-scale subsurface stress state. Applying correlation test method, we measured weak subsurface velocity changes in the northern Tianshan mountain, and found that the several stations, which are within 150km from the the Hutubi transmitting seismic station, appeared 0.1 0.2% relative velocity changes before the Hutubi MS6.2 earthquake on Dec.8, 2016.

Astor Pass Seismic Surveys Preliminary Report

Energy Technology Data Exchange (ETDEWEB)

Louie, John [UNR; Pullammanappallil, Satish [Optim; Faulds, James; Eisses, Amy; Kell, Annie; Frary, Roxanna; Kent, Graham

2011-08-05

In collaboration with the Pyramid Lake Paiute Tribe (PLPT), the University of Nevada, Reno (UNR) and Optim re-processed, or collected and processed, over 24 miles of 2d seismic-reflection data near the northwest corner of Pyramid Lake, Nevada. The network of 2d land surveys achieved a near-3d density at the Astor Pass geothermal prospect that the PLPT drilled during Nov. 2010 to Feb. 2011. The Bureau of Indian Affairs funded additional seismic work around the Lake, and an extensive, detailed single-channel marine survey producing more than 300 miles of section, imaging more than 120 ft below the Lake bottom. Optim’s land data collection utilized multiple heavy vibrators and recorded over 200 channels live, providing a state-of-the-art reflection-refraction data set. After advanced seismic analysis including first-arrival velocity optimization and prestack depth migration, the 2d sections show clear fault-plane reflections, in some areas as deep as 4000 ft, tying to distinct terminations of the mostly volcanic stratigraphy. Some lines achieved velocity control to 3000 ft depth; all lines show reflections and terminations to 5000 ft depth. Three separate sets of normal faults appear in an initial interpretation of fault reflections and stratigraphic terminations, after loading the data into the OpendTect 3d seismic visualization system. Each preliminary fault set includes a continuous trace more than 3000 ft long, and a swarm of short fault strands. The three preliminary normal-fault sets strike northerly with westward dip, northwesterly with northeast dip, and easterly with north dip. An intersection of all three fault systems documented in the seismic sections at the end of Phase I helped to locate the APS-2 and APS-3 slimholes. The seismic sections do not show the faults connected to the Astor Pass tufa spire, suggesting that we have imaged mostly Tertiary-aged faults. We hypothesize that the Recent, active faults that produced the tufa through hotspring

Modeling the impact of melt on seismic properties during mountain building

Science.gov (United States)

Lee, Amicia L.; Walker, Andrew M.; Lloyd, Geoffrey E.; Torvela, Taija

2017-03-01

Initiation of partial melting in the mid/lower crust causes a decrease in P wave and S wave velocities; recent studies imply that the relationship between these velocities and melt is not simple. We have developed a modeling approach to assess the combined impact of various melt and solid phase properties on seismic velocities and anisotropy. The modeling is based on crystallographic preferred orientation (CPO) data measured from migmatite samples, allowing quantification of the variation of seismic velocities with varying melt volumes, shapes, orientations, and matrix anisotropy. The results show nonlinear behavior of seismic properties as a result of the interaction of all of these physical properties, which in turn depend on lithology, stress regime, strain rate, preexisting rock fabrics, and pressure-temperature conditions. This nonlinear behavior is evident when applied to a suite of samples from a traverse across a migmatitic shear zone in the Seiland Igneous Province, Northern Norway. Critically, changes in solid phase composition and CPO, and melt shape and orientation with respect to the wave propagation direction can result in huge variations in the same seismic property even if the melt fraction remains the same. A comparison with surface wave interpretations from tectonically active regions highlights the issues in current models used to predict melt percentages or partially molten regions. Interpretation of seismic data to infer melt percentages or extent of melting should, therefore, always be underpinned by robust modeling of the underlying geological parameters combined with examination of multiple seismic properties in order to reduce uncertainty of the interpretation.

Seismic-Scale Rock Physics of Methane Hydrate

Energy Technology Data Exchange (ETDEWEB)

Amos Nur

2009-01-08

We quantify natural methane hydrate reservoirs by generating synthetic seismic traces and comparing them to real seismic data: if the synthetic matches the observed data, then the reservoir properties and conditions used in synthetic modeling might be the same as the actual, in-situ reservoir conditions. This approach is model-based: it uses rock physics equations that link the porosity and mineralogy of the host sediment, pressure, and hydrate saturation, and the resulting elastic-wave velocity and density. One result of such seismic forward modeling is a catalogue of seismic reflections of methane hydrate which can serve as a field guide to hydrate identification from real seismic data. We verify this approach using field data from known hydrate deposits.

Two applications of time reversal mirrors: Seismic radio and seismic radar

KAUST Repository

Hanafy, Sherif M.

2011-07-08

Two seismic applications of time reversal mirrors (TRMs) are introduced and tested with field experiments. The first one is sending, receiving, and decoding coded messages similar to a radio except seismic waves are used. The second one is, similar to radar surveillance, detecting and tracking a moving object(s) in a remote area, including the determination of the objects speed of movement. Both applications require the prior recording of calibrationGreen’s functions in the area of interest. This reference Green’s function will be used as a codebook to decrypt the coded message in the first application and as a moving sensor for the second application. Field tests show that seismicradar can detect the moving coordinates ( x(t), y(t), z(t)) of a person running through a calibration site. This information also allows for a calculation of his velocity as a function of location. Results with the seismic radio are successful in seismically detecting and decoding coded pulses produced by a hammer. Both seismic radio and radar are highly robust to signals in high noise environments due to the super-stacking property of TRMs.

Hypocenter relocation along the Sunda arc in Indonesia, using a 3D seismic velocity model

Science.gov (United States)

Nugraha, Andri Dian; Shiddiqi, Hasbi A.; Widiyantoro, Sri; Thurber, Clifford H.; Pesicek, Jeremy D.; Zhang, Haijiang; Wiyono, Samsul H.; Ramadhan, Mohamad; Wandano,; Irsyam, Mahsyur

2018-01-01

The tectonics of the Sunda arc region is characterized by the junction of the Eurasian and Indo‐Australian tectonic plates, causing complex dynamics to take place. High‐seismicity rates in the Indonesian region occur due to the interaction between these tectonic plates. The availability of a denser network of seismometers after the earthquakes of Mw">Mw 9.1 in 2004 and  Mw">Mw 8.6 in 2005 supports various seismic studies, one of which regards the precise relocation of the hypocenters. In this study, hypocenter relocation was performed using a teleseismic double‐difference (DD) relocation method (teletomoDD) combining arrival times of P and S waves from stations at local, regional, and teleseismic distances. The catalog data were taken from the Agency of Meteorology, Climatology, and Geophysics (BMKG) of Indonesia, and the International Seismological Centre (ISC) for the time period of April 2009 to May 2015. The 3D seismic‐wave velocity model with a grid size 1°×1°">1°×1° was used in the travel‐time calculations. Relocation results show a reduction in travel‐time residuals compared with the initial locations. The relocation results better illuminate subducted slabs and active faults in the region such as the Mentawai back thrust and the outer rise in the subduction zone south of Java. Focal mechanisms from the Global Centroid Moment Tensor catalog are analyzed in conjunction with the relocation results, and our synthesis of the results provides further insight into seismogenesis in the region.

Intelligent seismic risk mitigation system on structure building

Science.gov (United States)

Suryanita, R.; Maizir, H.; Yuniorto, E.; Jingga, H.

2018-01-01

Indonesia located on the Pacific Ring of Fire, is one of the highest-risk seismic zone in the world. The strong ground motion might cause catastrophic collapse of the building which leads to casualties and property damages. Therefore, it is imperative to properly design the structural response of building against seismic hazard. Seismic-resistant building design process requires structural analysis to be performed to obtain the necessary building responses. However, the structural analysis could be very difficult and time consuming. This study aims to predict the structural response includes displacement, velocity, and acceleration of multi-storey building with the fixed floor plan using Artificial Neural Network (ANN) method based on the 2010 Indonesian seismic hazard map. By varying the building height, soil condition, and seismic location in 47 cities in Indonesia, 6345 data sets were obtained and fed into the ANN model for the learning process. The trained ANN can predict the displacement, velocity, and acceleration responses with up to 96% of predicted rate. The trained ANN architecture and weight factors were later used to build a simple tool in Visual Basic program which possesses the features for prediction of structural response as mentioned previously.

Pennsylvania seismic monitoring network and related tectonic studies

International Nuclear Information System (INIS)

Alexander, S.S.

1991-06-01

This report summarizes the results of the operation of the Pennsylvania Seismic Monitoring Network during the interval May 1, 1983--March 31, 1985 to monitor seismic activity in Pennsylvania and surrounding areas, to characterize the earthquake activity in terms of controlling tectonic structures and related tectonic stress conditions in the crust, and to obtain improved crustal velocity models for hypocentral determinations. Most of the earthquake activity was concentrated in the Lancaster, PA area. The magnitude 4.2 mainshock that occurred there on April 23, 1984 was the largest ever recorded instrumentally and its intensity of VI places it among the largest in the historic record for that area. Other activity during the monitoring interval of this report was confined to eastern Pennsylvania. The very large number of quarry explosions that occur regularly in Pennsylvania account for most of the seismic events recorded and they provide important crustal velocity data that are needed to obtain accurate hypocenter estimates. In general the earthquakes that occurred are located in areas of past historic seismicity. Block-tectonic structures resulting from pre-Ordovician tectonic displacements appear to influence the distribution of contemporary seismicity in Pennsylvania and surrounding areas. 17 refs., 5 figs

Seismic anisotropies of the Songshugou peridotites (Qinling orogen, central China) and their seismic implications

Science.gov (United States)

Cao, Yi; Jung, Haemyeong; Song, Shuguang

2018-01-01

Though extensively studied, the roles of olivine crystal preferred orientations (CPOs or fabrics) in affecting the seismic anisotropies in the Earth's upper mantle are rather complicated and still not fully known. In this study, we attempted to address this issue by analyzing the seismic anisotropies [e.g., P-wave anisotropy (AVp), S-wave polarization anisotropy (AVs), radial anisotropy (ξ), and Rayleigh wave anisotropy (G)] of the Songshugou peridotites (dunite dominated) in the Qinling orogen in central China, based on our previously reported olivine CPOs. The seismic anisotropy patterns of olivine aggregates in our studied samples are well consistent with the prediction for their olivine CPO types; and the magnitude of seismic anisotropies shows a striking positive correlation with equilibrium pressure and temperature (P-T) conditions. Significant reductions of seismic anisotropies (AVp, max. AVs, and G) are observed in porphyroclastic dunite compared to coarse- and fine-grained dunites, as the results of olivine CPO transition (from A-/D-type in coarse-grained dunite, through AG-type-like in porphyroclastic dunite, to B-type-like in fine-grained dunite) and strength variation (weakening: A-/D-type → AG-type-like; strengthening: AG-type-like → B-type-like) during dynamic recrystallization. The transition of olivine CPOs from A-/D-type to B-/AG-type-like in the forearc mantle may weaken the seismic anisotropies and deviate the fast velocity direction and the fast S-wave polarization direction from trench-perpendicular to trench-oblique direction with the cooling and aging of forearc mantle. Depending on the size and distribution of the peridotite body such as the Songshugou peridotites, B- and AG-type-like olivine CPOs can be an additional (despite minor) local contributor to the orogen-parallel fast velocity direction and fast shear-wave polarization direction in the orogenic crust such as in the Songshugou area in Qinling orogen.

A generic model for the shallow velocity structure of volcanoes

Science.gov (United States)

Lesage, Philippe; Heap, Michael J.; Kushnir, Alexandra

2018-05-01

The knowledge of the structure of volcanoes and of the physical properties of volcanic rocks is of paramount importance to the understanding of volcanic processes and the interpretation of monitoring observations. However, the determination of these structures by geophysical methods suffers limitations including a lack of resolution and poor precision. Laboratory experiments provide complementary information on the physical properties of volcanic materials and their behavior as a function of several parameters including pressure and temperature. Nevertheless combined studies and comparisons of field-based geophysical and laboratory-based physical approaches remain scant in the literature. Here, we present a meta-analysis which compares 44 seismic velocity models of the shallow structure of eleven volcanoes, laboratory velocity measurements on about one hundred rock samples from five volcanoes, and seismic well-logs from deep boreholes at two volcanoes. The comparison of these measurements confirms the strong variability of P- and S-wave velocities, which reflects the diversity of volcanic materials. The values obtained from laboratory experiments are systematically larger than those provided by seismic models. This discrepancy mainly results from scaling problems due to the difference between the sampled volumes. The averages of the seismic models are characterized by very low velocities at the surface and a strong velocity increase at shallow depth. By adjusting analytical functions to these averages, we define a generic model that can describe the variations in P- and S-wave velocities in the first 500 m of andesitic and basaltic volcanoes. This model can be used for volcanoes where no structural information is available. The model can also account for site time correction in hypocenter determination as well as for site and path effects that are commonly observed in volcanic structures.

Estimation of sand dune thickness using a vertical velocity profile

International Nuclear Information System (INIS)

Al-Shuhail, Abdullatif A.

2004-01-01

Previous field and mathematical studies have shown that sand dunes may have vertical velocity profiles (i.e. continuous increase of velocity with depth). Therefore, computing the dunes thickness using conventional seismic refraction methods that assume a vertically homogeneous layer will likely produce some errors. The purpose of this study is to quantify the effect of the vertical velocity profile in a sand dune on the process of thickness estimation using seismic refraction data. First, the time distance (T-X) data of the direct wave in the dune is calculated using a vertical velocity profile, V (z), derived from Hertz-Mindlin contact theory. Then the thickness is estimated from the calculated T-X data, intercept time and velocity of the refractor at the dune's base assuming a constant velocity in the dune. The error in the estimated thickness due to the constant-velocity assumption increases with increasing thickness and decreasing porosity of the dune. For sand dunes with porosities greater than 0.2 and thickness less than 200 meter, the error is less than 15%. (author)

Clustering of velocities in a GPS network spanning the Sierra Nevada Block, the northern Walker Lane Belt, and the Central Nevada Seismic Belt, California-Nevada

Science.gov (United States)

Savage, James C.; Simpson, Robert W.

2013-01-01

The deformation across the Sierra Nevada Block, the Walker Lane Belt, and the Central Nevada Seismic Belt (CNSB) between 38.5°N and 40.5°N has been analyzed by clustering GPS velocities to identify coherent blocks. Cluster analysis determines the number of clusters required and assigns the GPS stations to the proper clusters. The clusters are shown on a fault map by symbols located at the positions of the GPS stations, each symbol representing the cluster to which the velocity of that GPS station belongs. Fault systems that separate the clusters are readily identified on such a map. Four significant clusters are identified. Those clusters are strips separated by (from west to east) the Mohawk Valley-Genoa fault system, the Pyramid Lake-Wassuk fault system, and the Central Nevada Seismic Belt. The strain rates within the westernmost three clusters approximate simple right-lateral shear (~13 nstrain/a) across vertical planes roughly parallel to the cluster boundaries. Clustering does not recognize the longitudinal segmentation of the Walker Lane Belt into domains dominated by either northwesterly trending, right-lateral faults or northeasterly trending, left-lateral faults.

Impact of Reservoir Fluid Saturation on Seismic Parameters: Endrod Gas Field, Hungary

Science.gov (United States)

El Sayed, Abdel Moktader A.; El Sayed, Nahla A.

2017-12-01

Outlining the reservoir fluid types and saturation is the main object of the present research work. 37 core samples were collected from three different gas bearing zones in the Endrod gas field in Hungary. These samples are belonging to the Miocene and the Upper - Lower Pliocene. These samples were prepared and laboratory measurements were conducted. Compression and shear wave velocity were measured using the Sonic Viewer-170-OYO. The sonic velocities were measured at the frequencies of 63 and 33 kHz for compressional and shear wave respectively. All samples were subjected to complete petrophysical investigations. Sonic velocities and mechanical parameters such as young’s modulus, rigidity, and bulk modulus were measured when samples were saturated by 100%-75%-0% brine water. Several plots have been performed to show the relationship between seismic parameters and saturation percentages. Robust relationships were obtained, showing the impact of fluid saturation on seismic parameters. Seismic velocity, Poisson’s ratio, bulk modulus and rigidity prove to be applicable during hydrocarbon exploration or production stages. Relationships among the measured seismic parameters in gas/water fully and partially saturated samples are useful to outline the fluid type and saturation percentage especially in gas/water transitional zones.

Evidence for chaotic fault interactions in the seismicity of the San Andreas fault and Nankai trough

Science.gov (United States)

Huang, Jie; Turcotte, D. L.

1990-01-01

The dynamical behavior introduced by fault interactions is examined here using a simple spring-loaded, slider-block model with velocity-weakening friction. The model consists of two slider blocks coupled to each other and to a constant-velocity driver by elastic springs. For an asymmetric system in which the frictional forces on the two blocks are not equal, the solutions exhibit chaotic behavior. The system's behavior over a range of parameter values seems to be generally analogous to that of weakly coupled segments of an active fault. Similarities between the model simulations and observed patterns of seismicity on the south central San Andreas fault in California and in the Nankai trough along the coast of southwestern Japan.

Seismicity and seismogenic structures of Central Apennines (Italy): constraints on the present-day stress field from focal mechanisms - The SLAM (Seismicity of Lazio-Abruzzo and Molise) project

Science.gov (United States)

Frepoli, Alberto; Battista Cimini, Giovanni; De Gori, Pasquale; De Luca, Gaetano; Marchetti, Alessandro; Montuori, Caterina; Pagliuca, Nicola

2016-04-01

We present new results for the microseismic activity in the Central Apennines recorded from a total of 81seismic stations. The large number of recording sites derives from the combination of temporary and permanent seismic networks operating in the study region. Between January 2009 and October 2013 we recorded 6923 earthquakes with local magnitudes ML ranging from 0.1 to 4.8. We located hypocentres by using a refined 1D crustal velocity model. The majority of the hypocenters are located beneath the axes of the Apenninic chain, while the seismic activity observed along the peri-Tyrrhenian margin is lower. The seismicity extends to a depth of 32 km; the hypocentral depth distribution exhibits a pronounced peak of seismic energy release in the depth range between 8 and 20 km. During the observation period we recorded two major seismic swarms and one seismic sequence in the Marsica-Sorano area in which we have had the largest detected magnitude (ML = 4.8). Fault plane solutions for a total of 600 earthquakes were derived from P-polarities. This new data set consists of a number of focal plane solutions that is about four times the data so far available for regional stress field study. The majority of the focal mechanisms show predominantly normal fault solutions. T-axis trends are oriented NE-SW confirming that the area is in extension. We also derived the azimuths of the principal stress axes by inverting the fault plane solutions and calculated the direction of the maximum horizontal stress, which is mainly sub-vertical oriented. The study region has been historically affected by many strong earthquakes, some of them very destructive. This work can give an important contribution to the seismic hazard assessment in an area densely populated as the city of Rome which is distant around 60 km from the main seismogenic structures of Central Apennine.

Consideration of some difficulties in migration velocity analysis; Migration velocity analysis no shomondai ni kansuru kento

Energy Technology Data Exchange (ETDEWEB)

Akama, K [Japan National Oil Corp., Tokyo (Japan). Technology Research Center; Matsuoka, T [Japan Petroleum Exploration Corp., Tokyo (Japan)

1997-10-22

Concerning migration velocity analysis in the seismic exploration method, two typical techniques, out of velocity analysis techniques using residual moveout in the CIP gather, are verified. Deregowski`s method uses pre-stacking deep-level migration records for velocity analysis to obtain velocities free of spatial inconsistency and not dependent on the velocity structure. This method is very like the conventional DMO velocity analysis method and is easy to understand intuitively. In this method, however, error is apt to be aggravated in the process of obtaining the depth-sector velocity from the time-RMS velocity. Al-Yahya`s method formulates the moveout residual in the CIP gather. This assumes horizontal stratification and a small residual velocity, however, and fails to guarantee convergence in the case of a steep structure or a grave model error. In the updating of the velocity model, in addition, it has to maintain required accuracy and, at the same time, incorporate smoothing to ensure not to deteriorate high convergence. 2 refs., 5 figs.

Permeability and seismic velocity and their anisotropy across the Alpine Fault, New Zealand: An insight from laboratory measurements on core from the Deep Fault Drilling Project phase 1 (DFDP-1)

Science.gov (United States)

Allen, M. J.; Tatham, D.; Faulkner, D. R.; Mariani, E.; Boulton, C.

2017-08-01

The Alpine Fault, a transpressional plate boundary between the Australian and Pacific plates, is known to rupture quasiperiodically with large magnitude earthquakes (Mw 8). The hydraulic and elastic properties of fault zones are thought to vary over the seismic cycle, influencing the nature and style of earthquake rupture and associated processes. We present a suite of laboratory permeability and P (Vp) and S (Vs) wave velocity measurements performed on fault lithologies recovered during the first phase of the Deep Fault Drilling Project (DFDP-1), which sampled principal slip zone (PSZ) gouges, cataclasites, and fractured ultramylonites, with all recovered lithologies overprinted by abundant secondary mineralization, recording enhanced fluid-rock interaction. Core material was tested in three orthogonal directions, orientated relative to the down-core axis and, when present, foliation. Measurements were conducted with pore pressure (H2O) held at 5 MPa over an effective pressure (Peff) range of 5-105 MPa. Permeabilities and seismic velocities decrease with proximity to the PSZ with permeabilities ranging from 10-17 to 10-21 m2 and Vp and Vs ranging from 4400 to 5900 m/s in the ultramylonites/cataclasites and 3900 to 4200 m/s at the PSZ. In comparison with intact country rock protoliths, the highly variable cataclastic structures and secondary phyllosilicates and carbonates have resulted in an overall reduction in permeability and seismic wave velocity, as well as a reduction in anisotropy within the fault core. These results concur with other similar studies on other mature, tectonic faults in their interseismic period.

Seismic structure from multi-channel seismic reflection and wide-angle data of Transect 0E in the Southern Gulf of California

Science.gov (United States)

Paramo, P.; Holbrook, W.; Brown, H.; Lizarralde, D.; Fletcher, J.; Umhoefer, P.; Kent, G.; Harding, A.; Gonzalez, A.; Axen, G.

2005-12-01

We present a velocity model from wide-angle data along with coincident prestack depth migration sections from seismic reflection data collected in the southern Gulf of California. Transect 0E runs NE to SW from the hills of Sierra Madre in mainland Mexico near Mazatlan to approximately 115 km into Gulf of California waters. Wide-angle data were recorded by 9 ocean bottom seismometers, deployed by the R/V New Horizon and 10 Reftek seismometers located along onshore extension of the transect. The average spacing for the OBS and Refteks is ~12 km and shots were fired from the R/V Maurice Ewing at 150 m intervals. Transect 0E crosses what it is believed to be extended continental crust and lies in the initial direction of extension characteristic of the proto-gulf. Preliminary results from the velocity model show upper crustal velocities of 6.1-6.3 km/s and lower crustal velocities of 6.7-7.0 km/s along the entire transect. Seismic velocities and crustal thicknesses observed along transect 0E are characteristic of non-volcanic margins.

Ultra-low velocity zone heterogeneities at the core-mantle boundary from diffracted PKKPab waves

Science.gov (United States)

Ma, Xiaolong; Sun, Xinlei

2017-08-01

Diffracted waves around Earth's core could provide important information of the lowermost mantle that other seismic waves may not. We examined PKKPab diffraction waves from 52 earthquakes occurring at the western Pacific region and recorded by USArray to probe the velocity structure along the core-mantle boundary (CMB). These diffracted waves emerge at distances up to 10° past the theoretical cutoff epicentral distance and show comparable amplitudes. We measured the ray parameters of PKKPab diffraction waves by Radon transform analysis that is suitable for large-aperture arrays. These ray parameters show a wide range of values from 4.250 to 4.840 s/deg, suggesting strong lateral heterogeneities in sampling regions at the base of the mantle. We further estimated the P-wave velocity variations by converting these ray parameters and found the CMB regions beneath the northwestern edge of African Anomaly (Ritsma et al. in Science 286:1925-1928, 1999) and southern Sumatra Islands exhibit velocity reductions up to 8.5% relative to PREM. We suggest that these low velocity regions are Ultra-low velocity zones, which may be related to partial melt or iron-enriched solids.[Figure not available: see fulltext.

Seismic surveys test on Innerhytta Pingo, Adventdalen, Svalbard Islands

Science.gov (United States)

Boaga, Jacopo; Rossi, Giuliana; Petronio, Lorenzo; Accaino, Flavio; Romeo, Roberto; Wheeler, Walter

2015-04-01

We present the preliminary results of an experimental full-wave seismic survey test conducted on the Innnerhytta a Pingo, located in the Adventdalen, Svalbard Islands, Norway. Several seismic surveys were adopted in order to study a Pingo inner structure, from classical reflection/refraction arrays to seismic tomography and surface waves analysis. The aim of the project IMPERVIA, funded by Italian PNRA, was the evaluation of the permafrost characteristics beneath this open-system Pingo by the use of seismic investigation, evaluating the best practice in terms of logistic deployment. The survey was done in April-May 2014: we collected 3 seismic lines with different spacing between receivers (from 2.5m to 5m), for a total length of more than 1 km. We collected data with different vertical geophones (with natural frequency of 4.5 Hz and 14 Hz) as well as with a seismic snow-streamer. We tested different seismic sources (hammer, seismic gun, fire crackers and heavy weight drop), and we verified accurately geophone coupling in order to evaluate the different responses. In such peculiar conditions we noted as fire-crackers allow the best signal to noise ratio for refraction/reflection surveys. To ensure the best geophones coupling with the frozen soil, we dug snow pits, to remove the snow-cover effect. On the other hand, for the surface wave methods, the very high velocity of the permafrost strongly limits the generation of long wavelengths both with these explosive sources as with the common sledgehammer. The only source capable of generating low frequencies was a heavy drop weight system, which allows to analyze surface wave dispersion below 10 Hz. Preliminary data analysis results evidence marked velocity inversions and strong velocity contrasts in depth. The combined use of surface and body waves highlights the presence of a heterogeneous soil deposit level beneath a thick layer of permafrost. This is the level that hosts the water circulation from depth controlling

Development of seismic tomography software for hybrid supercomputers

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Nikitin, Alexandr; Serdyukov, Alexandr; Duchkov, Anton

2015-04-01

Seismic tomography is a technique used for computing velocity model of geologic structure from first arrival travel times of seismic waves. The technique is used in processing of regional and global seismic data, in seismic exploration for prospecting and exploration of mineral and hydrocarbon deposits, and in seismic engineering for monitoring the condition of engineering structures and the surrounding host medium. As a consequence of development of seismic monitoring systems and increasing volume of seismic data, there is a growing need for new, more effective computational algorithms for use in seismic tomography applications with improved performance, accuracy and resolution. To achieve this goal, it is necessary to use modern high performance computing systems, such as supercomputers with hybrid architecture that use not only CPUs, but also accelerators and co-processors for computation. The goal of this research is the development of parallel seismic tomography algorithms and software package for such systems, to be used in processing of large volumes of seismic data (hundreds of gigabytes and more). These algorithms and software package will be optimized for the most common computing devices used in modern hybrid supercomputers, such as Intel Xeon CPUs, NVIDIA Tesla accelerators and Intel Xeon Phi co-processors. In this work, the following general scheme of seismic tomography is utilized. Using the eikonal equation solver, arrival times of seismic waves are computed based on assumed velocity model of geologic structure being analyzed. In order to solve the linearized inverse problem, tomographic matrix is computed that connects model adjustments with travel time residuals, and the resulting system of linear equations is regularized and solved to adjust the model. The effectiveness of parallel implementations of existing algorithms on target architectures is considered. During the first stage of this work, algorithms were developed for execution on

Characterization of a complex near-surface structure using well logging and passive seismic measurements

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Benjumea, Beatriz; Macau, Albert; Gabàs, Anna; Figueras, Sara

2016-04-01

We combine geophysical well logging and passive seismic measurements to characterize the near-surface geology of an area located in Hontomin, Burgos (Spain). This area has some near-surface challenges for a geophysical study. The irregular topography is characterized by limestone outcrops and unconsolidated sediments areas. Additionally, the near-surface geology includes an upper layer of pure limestones overlying marly limestones and marls (Upper Cretaceous). These materials lie on top of Low Cretaceous siliciclastic sediments (sandstones, clays, gravels). In any case, a layer with reduced velocity is expected. The geophysical data sets used in this study include sonic and gamma-ray logs at two boreholes and passive seismic measurements: three arrays and 224 seismic stations for applying the horizontal-to-vertical amplitude spectra ratio method (H/V). Well-logging data define two significant changes in the P-wave-velocity log within the Upper Cretaceous layer and one more at the Upper to Lower Cretaceous contact. This technique has also been used for refining the geological interpretation. The passive seismic measurements provide a map of sediment thickness with a maximum of around 40 m and shear-wave velocity profiles from the array technique. A comparison between seismic velocity coming from well logging and array measurements defines the resolution limits of the passive seismic techniques and helps it to be interpreted. This study shows how these low-cost techniques can provide useful information about near-surface complexity that could be used for designing a geophysical field survey or for seismic processing steps such as statics or imaging.

Bootstrap inversion for Pn wave velocity in North-Western Italy

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C. Eva

1997-06-01

Full Text Available An inversion of Pn arrival times from regional distance earthquakes (180-800 km, recorded by 94 seismic stations operating in North-Western Italy and surrounding areas, was carried out to image lateral variations of P-wave velocity at the crust-mantle boundary, and to estimate the static delay time at each station. The reliability of the obtained results was assessed using both synthetic tests and the bootstrap Monte Carlo resampling technique. Numerical simulations demonstrated the existence of a trade-off between cell velocities and estimated station delay times along the edge of the model. Bootstrap inversions were carried out to determine the standard deviation of velocities and time terms. Low Pn velocity anomalies are detected beneath the outer side of the Alps (-6% and the Western Po plain (-4% in correspondence with two regions of strong crustal thickening and negative Bouguer anomaly. In contrast, high Pn velocities are imaged beneath the inner side of the Alps (+4% indicating the presence of high velocity and density lower crust-upper mantle. The Ligurian sea shows high Pn velocities close to the Ligurian coastlines (+3% and low Pn velocities (-1.5% in the middle of the basin in agreement with the upper mantle velocity structure revealed by seismic refraction profiles.

Velocity and Q Structure of the Quaternary Sediment in Bohai Basin, China

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

2008-12-01

Heavily populated by Beijing and Tianjin cities, Bohai Basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. There have been some studies about three dimensional structure of the lithosphere in this region; however the attenuation (Qp and Qs) of the surfacial quaternary sediment has not been studied at natural seismic frequency (1-10HZ), which is crucial to earthquake hazards study. Borehole seismic records of micro earthquake provide us a good way to study the velocity and Q attenuation of the surfacial structure (0-500m). We found that there are two pulses well separated with simple waveforms while analyzing borehole seismic records from the 2006 Mw4.9 WenAn earthquake sequence. Then we performed waveform modeling with Generalized Ray Theory (GRT) to confirm that the two pulses are direct wave and surface reflected wave, and found that the average Vp and Vs of the top 300m in this region are about 1.83km/s and 0.42km/s while Vp/Vs falls in a high value of 4.4. We also modeled surface reflected wave with Propagating Matrix method to study the value of Qs and the surfacial velocity structure. Our modeling indicates that Qs should be larger than 30, even up to 100, this is quite larger than the typically assumed extremely low Q (~=10) found by Hauksson et al (Hauksson et al, 1987; Blakeslee and Malin, 1991) but much similar to that of Langston (2002). Also, the velocity gradient just beneath the free surface (0-50m) is very large and velocity increases slowly at larger depth. Our modeling demonstrates the value of borehole seismic records in resolving shallow velocity and attenuation structure, and hence their significance in earthquake hazard simulation.

Ambient Seismic Noise Interferometry on the Island of Hawai`i

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Ballmer, Silke

Ambient seismic noise interferometry has been successfully applied in a variety of tectonic settings to gain information about the subsurface. As a passive seismic technique, it extracts the coherent part of ambient seismic noise in-between pairs of seismic receivers. Measurements of subtle temporal changes in seismic velocities, and high-resolution tomographic imaging are then possible - two applications of particular interest for volcano monitoring. Promising results from other volcanic settings motivate its application in Hawai'i, with this work being the first to explore its potential. The dataset used for this purpose was recorded by the Hawaiian Volcano Observatory's permanent seismic network on the Island of Hawai'i. It spans 2.5 years from 5/2007 to 12/2009 and covers two distinct sources of volcanic tremor. After applying standard processing for ambient seismic noise interferometry, we find that volcanic tremor strongly affects the extracted noise information not only close to the tremor source, but unexpectedly, throughout the island-wide network. Besides demonstrating how this long-range observability of volcanic tremor can be used to monitor volcanic activity in the absence of a dense seismic array, our results suggest that care must be taken when applying ambient seismic noise interferometry in volcanic settings. In a second step, we thus exclude days that show signs of volcanic tremor, reducing the dataset to three months, and perform ambient seismic noise tomography. The resulting two-dimensional Rayleigh wave group velocity maps for 0.1 - 0.9 Hz compare very well with images from previous travel time tomography, both, for the main volcanic structures at low frequencies as well as for smaller features at mid-to-high frequencies - a remarkable observation for the temporally truncated dataset. These robust results suggest that ambient seismic noise tomography in Hawai'i is suitable 1) to provide a three-dimensional S-wave model for the volcanoes and 2

Temporal change in shallow subsurface P- and S-wave velocities and S-wave anisotropy inferred from coda wave interferometry

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Yamamoto, M.; Nishida, K.; Takeda, T.

2012-12-01

Recent progresses in theoretical and observational researches on seismic interferometry reveal the possibility to detect subtle change in subsurface seismic structure. This high sensitivity of seismic interferometry to the medium properties may thus one of the most important ways to directly observe the time-lapse behavior of shallow crustal structure. Here, using the coda wave interferometry, we show the co-seismic and post-seismic changes in P- and S-wave velocities and S-wave anisotropy associated with the 2011 off the Pacific coast of Tohoku earthquake (M9.0). In this study, we use the acceleration data recorded at KiK-net stations operated by NIED, Japan. Each KiK-net station has a borehole whose typical depth is about 100m, and two three-component accelerometers are installed at the top and bottom of the borehole. To estimate the shallow subsurface P- and S-wave velocities and S-wave anisotropy between two sensors and their temporal change, we select about 1000 earthquakes that occurred between 2004 and 2012, and extract body waves propagating between borehole sensors by computing the cross-correlation functions (CCFs) of 3 x 3 component pairs. We use frequency bands of 2-4, 4-8, 8-16 Hz in our analysis. Each averaged CCF shows clear wave packets traveling between borehole sensors, and their travel times are almost consistent with those of P- and S-waves calculated from the borehole log data. Until the occurrence of the 2011 Tohoku earthquake, the estimated travel time at each station is rather stable with time except for weak seasonal/annual variation. On the other hand, the 2011 Tohoku earthquake and its aftershocks cause sudden decrease in the S-wave velocity at most of the KiK-net stations in eastern Japan. The typical value of S-wave velocity changes, which are measured by the time-stretching method, is about 5-15%. After this co-seismic change, the S-wave velocity gradually recovers with time, and the recovery continues for over one year following the

Local seismic tomography in Belgium - implications for the geological structure.

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Sichien, E.; Camelbeek, T.; Henriet, J.-P.

2009-04-01

We present the results of a local seismic tomography in Belgium using well-located local earthquakes registered by 37 stations of the permanent seismic network and by mobile stations installed by the Royal Observatory of Belgium. Previous studies did not offer a lot of information on the middle and lower crust. The seismic profiles shot in the region (Belcorp, Decorp, Ecors, …) all show an unreflective middle and lower crust. The gravimetric and magnetic data show the presence of a sharp transition between the Brabant Massive and the Ardennes allochtone, furthermore, a broad positive gravimetric anomaly, is interpreted as a Moho uplift underneath the Campine region. Our results confirm the sharp transition between the Brabant Massif (higher than expected velocities) and the Ardennes allochtone (lower than expected velocities). At 27 km of depth lower crust - upper mantle velocities (7.50 km/s) are found underneath the Campine region and the Eifelplume region, confirming the Moho uplifts to 28 km underneath these regions. At 13 km similar velocities (7.50 km/s) are seen underneath the Eifelplume, they correspond to a lower crust-upper mantle that trusted in the crust during the Variscan orogeny.

Reducing the uncertainty in the fidelity of seismic imaging results

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Zhou, H. W.; Zou, Z.

2017-12-01

A key aspect in geoscientific inversion is quantifying the quality of the results. In seismic imaging, we must quantify the uncertainty of every imaging result based on field data, because data noise and methodology limitations may produce artifacts. Detection of artifacts is therefore an important aspect in uncertainty quantification in geoscientific inversion. Quantifying the uncertainty of seismic imaging solutions means assessing their fidelity, which defines the truthfulness of the imaged targets in terms of their resolution, position error and artifact. Key challenges to achieving the fidelity of seismic imaging include: (1) Difficulty to tell signal from artifact and noise; (2) Limitations in signal-to-noise ratio and seismic illumination; and (3) The multi-scale nature of the data space and model space. Most seismic imaging studies of the Earth's crust and mantle have employed inversion or modeling approaches. Though they are in opposite directions of mapping between the data space and model space, both inversion and modeling seek the best model to minimize the misfit in the data space, which unfortunately is not the output space. The fact that the selection and uncertainty of the output model are not judged in the output space has exacerbated the nonuniqueness problem for inversion and modeling. In contrast, the practice in exploration seismology has long established a two-fold approach of seismic imaging: Using velocity modeling building to establish the long-wavelength reference velocity models, and using seismic migration to map the short-wavelength reflectivity structures. Most interestingly, seismic migration maps the data into an output space called imaging space, where the output reflection images of the subsurface are formed based on an imaging condition. A good example is the reverse time migration, which seeks the reflectivity image as the best fit in the image space between the extrapolation of time-reversed waveform data and the prediction

Seismic reliability assessment methodology for CANDU concrete containment structures-phase 11

International Nuclear Information System (INIS)

Hong, H.P.

1996-07-01

This study was undertaken to verify a set of load factors for reliability-based seismic evaluation of CANDU containment structures in Eastern Canada. Here, the new, site-specific, results of probabilistic seismic hazard assessment (response spectral velocity) were applied. It was found that the previously recommended load factors are relatively insensitive to the new seismic hazard information, and are adequate for a reliability-based seismic evaluation process. (author). 4 refs., 5 tabs., 9 figs

Velocity Gradient Across the San Andreas Fault and Changes in Slip Behavior as Outlined by Full non Linear Tomography

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Chiarabba, C.; Giacomuzzi, G.; Piana Agostinetti, N.

2017-12-01

The San Andreas Fault (SAF) near Parkfield is the best known fault section which exhibit a clear transition in slip behavior from stable to unstable. Intensive monitoring and decades of studies permit to identify details of these processes with a good definition of fault structure and subsurface models. Tomographic models computed so far revealed the existence of large velocity contrasts, yielding physical insight on fault rheology. In this study, we applied a recently developed full non-linear tomography method to compute Vp and Vs models which focus on the section of the fault that exhibit fault slip transition. The new tomographic code allows not to impose a vertical seismic discontinuity at the fault position, as routinely done in linearized codes. Any lateral velocity contrast found is directly dictated by the data themselves and not imposed by subjective choices. The use of the same dataset of previous tomographic studies allows a proper comparison of results. We use a total of 861 earthquakes, 72 blasts and 82 shots and the overall arrival time dataset consists of 43948 P- and 29158 S-wave arrival times, accurately selected to take care of seismic anisotropy. Computed Vp and Vp/Vs models, which by-pass the main problems related to linarized LET algorithms, excellently match independent available constraints and show crustal heterogeneities with a high resolution. The high resolution obtained in the fault surroundings permits to infer lateral changes of Vp and Vp/Vs across the fault (velocity gradient). We observe that stable and unstable sliding sections of the SAF have different velocity gradients, small and negligible in the stable slip segment, but larger than 15 % in the unstable slip segment. Our results suggest that Vp and Vp/Vs gradients across the fault control fault rheology and the attitude of fault slip behavior.

Extremal inversion of lunar travel time data. [seismic velocity structure

Science.gov (United States)

Burkhard, N.; Jackson, D. D.

1975-01-01

The tau method, developed by Bessonova et al. (1974), of inversion of travel times is applied to lunar P-wave travel time data to find limits on the velocity structure of the moon. Tau is the singular solution to the Clairaut equation. Models with low-velocity zones, with low-velocity zones at differing depths, and without low-velocity zones, were found to be consistent with data and within the determined limits. Models with and without a discontinuity at about 25-km depth have been found which agree with all travel time data to within two standard deviations. In other words, the existence of the discontinuity and its size and location have not been uniquely resolved. Models with low-velocity channels are also possible.

Crustal structure and Seismic Hazard studies in Nigeria from ambient noise and earthquakes

Science.gov (United States)

Kadiri, U. A.

2016-12-01

The crust, upper Mantle and seismic hazard studies have been carried out in Nigeria using noise and earthquake data. The data were acquired from stations in Nigeria and international Agencies. Firstly, known depths of sediments in the Lower Benue Trough (LBT) were collected from wells; Resonance frequency (Fo) and average shear-wave velocities (Vs) were then computed using Matlab. Secondly, average velocities were estimated from noise cross-correlation along seismic stations. Thirdly, the moho depths beneath Ife, Kaduna and Nsukka stations were estimated, as well as Vp/Vs ratio using 2009 earthquake with epicenter in Nigeria. Finally, Statistical and Probabilistic Seismic Hazard Assessment (PSHA) were used to compute seismic hazard parameters in Nigeria and its surroundings. The results showed that, soils on the LBT with average shear wave velocity of about 5684m/s would experience more amplification in case of an earthquake, compared to the basement complex in Nigeria. The Vs beneath the seismic stations in Nigeria were also estimated as 288m/s, 1019m/s, 940.6m/s and 255.02m/s in Ife, Nsukka, Awka, and Abakaliki respectively. The average velocity along the station paths was 4.5km/secs, and the Vp, Vs for depths 100-500km profile in parts of South West Nigeria increased from about 5.83-6.42Km/sec and 3.48-6.31km/s respectively with Vp/Vs ratio decreasing from 1.68 to 1.02. Statistical analysis revealed a trend of increasing earthquake occurrence along the Mid-Atlantic Ridge and tending to West African region. The analysis of PSHA shows the likelihood of earthquakes with different magnitudes occurring in Nigeria and other parts West Africa in future. This work is aimed at addressing critical issues regarding sites effect characterization, improved earthquake location and robust seismic hazards assessment for planning in the choice of sites for critical facilities in Nigeria. Keywords: Sediment thickness, Resonance Frequency, Average Velocity, Seismic Hazard, Nigeria

Integrated interpretation of seismic and resistivity images across the «Val d'Agri» graben (Italy

Directory of Open Access Journals (Sweden)

E. Ceragioli

2002-06-01

Full Text Available Val d'Agri is a «recent SSW - NNE graben» located in the middle of the Southern Apennines thrust belt «chain» and emplaced in Plio-Pleistocene.The recent sedimentation of the valley represents a local critical geophysical problem. Several strong near surface velocity anomalies and scattering degrades seismic data in different ways and compromises the seismic visibility. In 1998, ENI and Enterprise, with the contribution of the European Community (ESIT R & D project - Enhance Seismic In Thrust Belt; EU Thermie fund acquired two «experimental seismic and Resistivity lines» across the valley. The purpose of the project was to look for methods able to enhance seismic data quality and optimize the data processing flow for «thrust belt» areas. During the work, it was clear that some part of the seismic data processing flow could be used for the detailed geological interpretation of the near subsurface too. In fact, the integrated interpretation of the near surface tomography velocity/depth seismic section, built for enhancing the resolution of static corrections, with the HR resistivity profile, acquired for enhancing the seismic source coupling, allowed a quite detailed lithological interpretation of the main shallow velocity changes and the 2D reconstruction of the structural setting of the valley.

Estimating the Wet-Rock P-Wave Velocity from the Dry-Rock P-Wave Velocity for Pyroclastic Rocks

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Kahraman, Sair; Fener, Mustafa; Kilic, Cumhur Ozcan

2017-07-01

Seismic methods are widely used for the geotechnical investigations in volcanic areas or for the determination of the engineering properties of pyroclastic rocks in laboratory. Therefore, developing a relation between the wet- and dry-rock P-wave velocities will be helpful for engineers when evaluating the formation characteristics of pyroclastic rocks. To investigate the predictability of the wet-rock P-wave velocity from the dry-rock P-wave velocity for pyroclastic rocks P-wave velocity measurements were conducted on 27 different pyroclastic rocks. In addition, dry-rock S-wave velocity measurements were conducted. The test results were modeled using Gassmann's and Wood's theories and it was seen that estimates for saturated P-wave velocity from the theories fit well measured data. For samples having values of less and greater than 20%, practical equations were derived for reliably estimating wet-rock P-wave velocity as function of dry-rock P-wave velocity.

Rotational motions from the 2016, Central Italy seismic sequence, as observed by an underground ring laser gyroscope

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Simonelli, Andreino; Belfi, Jacopo; Beverini, Nicolò; Di Virgilio, Angela; Maccioni, Enrico; De Luca, Gaetano; Saccorotti, Gilberto; Wassermann, Joachim; Igel, Heiner

2017-04-01

We present analyses of rotational and translational ground motions from earthquakes recorded during October-November, 2016, in association with the Central Italy seismic-sequence. We use co-located measurements of the vertical ground rotation rate from a large ring laser gyroscope (RLG), and the three components of ground velocity from a broadband seismometer. Both instruments are positioned in a deep underground environment, within the Gran Sasso National Laboratories (LNGS) of the Istituto Nazionale di Fisica Nucleare (INFN). We collected dozen of events spanning the 3.5-5.9 Magnitude range, and epicentral distances between 40 km and 80 km. This data set constitutes an unprecedented observation of the vertical rotational motions associated with an intense seismic sequence at local distance. In theory - assuming plane wave propagation - the ratio between the vertical rotation rate and the transverse acceleration permits, in a single station approach, the estimation of apparent phase velocity in the case of SH arrivals or real phase velocity in the case of Love surface waves. This is a standard approach for the analysis of earthquakes at teleseismic distances, and the results reported by the literature are compatible with the expected phase velocities from the PREM model. Here we extend the application of the same approach to local events, thus exploring higher frequency ranges and larger rotation rate amplitudes. We use a novel approach to joint rotation/acceleration analysis based on the continuous wavelet transform (CWT). Wavelet coherence (WTC) is used as a filter for identifying those regions of the time-period plane where the rotation rate and transverse acceleration signals exhibit significant coherence. This allows retrieving estimates of phase velocities over the period range spanned by correlated arrivals. Coherency among ground rotation and translation is also observed throughout the coda of the P-wave arrival, an observation which is interpreted in

A seismic study on cracks in crystalline rock

International Nuclear Information System (INIS)

Israelsson, H.

1981-07-01

This report summarizes results from a field study with in-situ seismic measurements in crystalline rock. It was found that among a few potential seismic techniques the so called cross hole method would probably provide the most powerful capability for detecting cracks and fracture zones. By this method the area between two holes are systematically scanned by seismic raypaths. Seismic signals are generated in one hole by micro explosions and recorded in the other at various combinations of depths. A test sample of scanning data showed a rather dramatic variation of the seismic P-wave velocity (5-6 km/s). Analysis procedures like tomographic imaging was applied to this data set primarily to illustrate the kind of structural mapping such procedures can provide. (Author)

Using the automized system ''section'' to forecast velocity sections using data on borehole velocity measurement and seismic field prospecting

Energy Technology Data Exchange (ETDEWEB)

Dorman, M.I.; Gein, F.F.; Zubairov, F.B.

1981-01-01

A system of automated processing of seismic data is examined which makes it possible to set up rate functions at arbitrary points of a seismic prospecting section or at points conciding with boreholes in which rate measurements have not been completed. The basis for the forecasting method is data on seismic well logging investigations, seismic prospecting and some indirect observations on sections. The bases of a procedure realizing a forecasting method are set forth, as are those requirements which satisfy the system as a whole. The results of using the ''section'' system in a terrestrial section of Western Siberia are set forth.

A lithospheric velocity model for the flat slab region of Argentina from joint inversion of Rayleigh-wave dispersion and teleseismic receiver functions

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Ammirati, J. B.; Alvarado, P. M.; Beck, S. L.

2014-12-01

Receiver Function (RF) analyses using teleseismic P waveforms is a technique to isolate P to S conversions from seismic discontinuities in the lithosphere. Using earthquakes with a good azimuthal distribution, RFs recorded at a three-component seismic station can be inverted to obtain detailed lithospheric velocity structures. The technique, however presents a velocity-depth trade-off, which results in a non-unique model because RFs do not depend on the absolute seismic velocities but rather on relative velocity contrasts. Unlike RF, surface wave dispersion is sensitive to the average shear-wave velocity which makes it well suited for studying long period variations of the lithospheric seismic velocities. We performed a joint inversion of RF and Rayleigh-wave phase velocity dispersion to investigate the structure beneath the SIEMBRA network, a 43-broadband-seismic-station array deployed in the Pampean flat slab region of Argentina. Our results indicate: 1) The presence of several mid-crustal discontinuities probably related with terrane accretion; 2) A high seismic velocity in the lower crust suggesting partial eclogitization; 3) A thicker crust (> 50 km) beneath the western Sierras Pampeanas with an abrupt change in the relative timing of the Moho signal indicating a thinner crust to the east; 4) The presence of the subducting oceanic crust lying at ~100 km depth. We then built a 1D regional velocity model for the flat slab region of Argentina and used it for regional moment tensor inversions for local earthquakes. This technique is notably dependent on small-scale variations of Earth structure when modeling higher frequency seismic waveforms. Eighteen regional focal mechanisms have been determined. Our solutions are in good agreement with GCMT source estimations although our solutions for deep earthquakes systematically resulted in shallower focal depths suggesting that the slab seismicity could be concentrated at the top of the subducting Nazca plate. Solutions

Toe-of-slope of a Cretaceous carbonate platform in outcrop, seismic model and offshore seismic data (Apulia, Italy)

Science.gov (United States)

Bracco Gartner, Guido; Morsilli, Michele; Schlager, Wolfgang; Bosellini, Alfonso

Synthetic seismic models of outcrops in the Early Cretaceous slope of a carbonate platform on the Gargano Promontory (southern Italy) were compared to an offshore seismic section south of the Promontory. Outcrops of the same age on the promontory have the same sequence stratigraphic characteristics as their offshore equivalent, and are the only areas where the transition from platform to basin of Early Cretaceous is exposed on land. Two adjacent outcrop areas were combined into one seismic-scale lithologic model with the aid of photo mosaics, measured sections, and biostratigraphic data. Velocity, density, and porosity measurements on spot samples were used to construct the impedance model. Seismic models were generated by vertical incidence and finite difference programs. The results indicate that the reflections in the seismic model are controlled by the impedance contrast between low porous intervals rich in debris from the platform and highly porous intervals of pelagic lime mudstone, nearly devoid of debris. Finite difference seismic display showed best resemblance with the real seismic data, especially by mapping a drowning unconformity.

A seismic network to investigate the sedimentary hosted hydrothermal Lusi system

Science.gov (United States)

Javad Fallahi, Mohammad; Mazzini, Adriano; Lupi, Matteo; Obermann, Anne; Karyono, Karyono

2016-04-01

The 29th of May 2006 marked the beginning of the sedimentary hosted hydrothermal Lusi system. During the last 10 years we witnessed numerous alterations of the Lusi system behavior that coincide with the frequent seismic and volcanic activity occurring in the region. In order to monitor the effect that the seismicity and the activity of the volcanic arc have on Lusi, we deployed a ad hoc seismic network. This temporary network consist of 10 broadband and 21 short period stations and is currently operating around the Arjuno-Welirang volcanic complex, along the Watukosek fault system and around Lusi, in the East Java basin since January 2015. We exploit this dataset to investigate surface wave and shear wave velocity structure of the upper-crust beneath the Arjuno-Welirang-Lusi complex in the framework of the Lusi Lab project (ERC grant n° 308126). Rayleigh and Love waves travelling between each station-pair are extracted by cross-correlating long time series of ambient noise data recorded at the stations. Group and phase velocity dispersion curves are obtained by time-frequency analysis of cross-correlation functions, and are tomographically inverted to provide 2D velocity maps corresponding to different sampling depths. 3D shear wave velocity structure is then acquired by inverting the group velocity maps.

Double-difference tomography velocity structure in Northern Oklahoma: Evidence for reduced basement velocity in the Nemaha Uplift

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Stevens, N. T.; Keranen, K. M.; Lambert, C.

2016-12-01

Induced seismicity in northern Oklahoma presents risk for infrastructure, but also an opportunity to gain new insights to earthquake processes [Petersen et al., 2016]. Here we present a double-difference tomographic study using TomoDD [Zhang and Thurber, 2003] in northern Oklahoma utilizing records from a dense broadband network over a 1-year period, constituting a catalog of over 10,000 local seismic events. We image a shallow (depth 4 km). We suggest that this low velocity anomaly stems from enhanced fracturing and/or weathering of the basement in the Nemaha uplift in northern Oklahoma. This velocity anomaly is not observed in basement off the shoulders of the structure, particularly to the southeast of the Nemaha bounding fault. Enhanced fracturing, and related increases to permeability, would ease pressure migration from injection wells linked to increased seismicity in the region, and may explain the relative absence of seismicity coincident with this structure compared to it periphery. References Gay, S. Parker, J. (2003), The Nemaha Trend-A System of Compressional Thrust-Fold, Strike-Slilp Structural Features in Kansas and Oklahoma, Part 1, Shale Shak., 9-49. Petersen, M. D., C. S. Mueller, M. P. Moschetti, S. M. Hoover, A. L. Llenos, W. L. Ellsworth, A. J. Michael, J. L. Rubinstein, A. F. McGarr, and K. S. Rukstales (2016), 2016 One-Year Seismic Hazard Forecast for the Central and Eastern United States from Induced and Natural Earthquakes, Open-File Rep., doi:10.3133/OFR20161035. Zhang, H., and C. H. Thurber (2003), Double-difference tomography: The method and its application to the Hayward Fault, California, Bull. Seismol. Soc. Am., 93(5), 1875-1889, doi:10.1785/0120020190.

The seismic investigation of rock properties at the Carwynnen test mine

International Nuclear Information System (INIS)

New, B.M.

1984-11-01

The research described follows on from the seismic velocity tomography carried out previously at this site and describes an attempt to map the rock mass in terms of its attenuative properties. This is done by comparison of the spectral distributions of energy within wave packets observed at various distances from numerous source locations. The method was not found sensitive to the variations in natural rock condition at this site as the spectra were dominated by the effects of man-made openings and rock damage which appeared to control the energy input/output transfer function at each location. The seismic shadow caused by the presence of a major void in the area was clearly identified and suggested that similar observations could considerably enhance the value of velocity tomography techniques. Shear and compressional wave velocities are used to obtain estimates of the dynamic elastic properties of the rock mass. Brief recommendations regarding future seismic research are given. (author)

Geological and Seismic Data Mining For The Development of An Interpretation System Within The Alptransit Project

Science.gov (United States)

Klose, C. D.; Giese, R.; Löw, S.; Borm, G.

Especially for deep underground excavations, the prediction of the locations of small- scale hazardous geotechnical structures is nearly impossible when exploration is re- stricted to surface based methods. Hence, for the AlpTransit base tunnels, exploration ahead has become an essential component of the excavation plan. The project de- scribed in this talk aims at improving the technology for the geological interpretation of reflection seismic data. The discovered geological-seismic relations will be used to develop an interpretation system based on artificial intelligence to predict hazardous geotechnical structures of the advancing tunnel face. This talk gives, at first, an overview about the data mining of geological and seismic properties of metamorphic rocks within the Penninic gneiss zone in Southern Switzer- land. The data results from measurements of a specific geophysical prediction system developed by the GFZ Potsdam, Germany, along the 2600 m long and 1400 m deep Faido access tunnel. The goal is to find those seismic features (i.e. compression and shear wave velocities, velocity ratios and velocity gradients) which show a significant relation to geological properties (i.e. fracturing and fabric features). The seismic properties were acquired from different tomograms, whereas the geolog- ical features derive from tunnel face maps. The features are statistically compared with the seismic rock properties taking into account the different methods used for the tunnel excavation (TBM and Drill/Blast). Fracturing and the mica content stay in a positive relation to the velocity values. Both, P- and S-wave velocities near the tunnel surface describe the petrology better, whereas in the interior of the rock mass they correlate to natural micro- and macro-scopic fractures surrounding tectonites, i.e. cataclasites. The latter lie outside of the excavation damage zone and the tunnel loos- ening zone. The shear wave velocities are better indicators for rock

EVOLUTION OF SOUTHERN AFRICAN CRATONS BASED ON SEISMIC IMAGING

DEFF Research Database (Denmark)

Thybo, Hans; Soliman, Mohammad Youssof Ahmad; Artemieva, Irina

2014-01-01

present a new seismic model for the structure of the crust and lithospheric mantle of the Kalahari Craton, constrained by seismic receiver functions and finite-frequency tomography based on the seismological data from the South Africa Seismic Experiment (SASE). The combination of these two methods...... since formation of the craton, and (3) seismically fast lithospheric keels are imaged in the Kaapvaal and Zimabwe cratons to depths of 300-350 km. Relatively low velocity anomalies are imaged beneath both the paleo-orogenic Limpopo Belt and the Bushveld Complex down to depths of ~250 km and ~150 km...

2.5D S-wave velocity model of the TESZ area in northern Poland from receiver function analysis

Science.gov (United States)

Wilde-Piorko, Monika; Polkowski, Marcin; Grad, Marek

2016-04-01

Receiver function (RF) locally provides the signature of sharp seismic discontinuities and information about the shear wave (S-wave) velocity distribution beneath the seismic station. The data recorded by "13 BB Star" broadband seismic stations (Grad et al., 2015) and by few PASSEQ broadband seismic stations (Wilde-Piórko et al., 2008) are analysed to investigate the crustal and upper mantle structure in the Trans-European Suture Zone (TESZ) in northern Poland. The TESZ is one of the most prominent suture zones in Europe separating the young Palaeozoic platform from the much older Precambrian East European craton. Compilation of over thirty deep seismic refraction and wide angle reflection profiles, vertical seismic profiling in over one hundred thousand boreholes and magnetic, gravity, magnetotelluric and thermal methods allowed for creation a high-resolution 3D P-wave velocity model down to 60 km depth in the area of Poland (Grad et al. 2016). On the other hand the receiver function methods give an opportunity for creation the S-wave velocity model. Modified ray-tracing method (Langston, 1977) are used to calculate the response of the structure with dipping interfaces to the incoming plane wave with fixed slowness and back-azimuth. 3D P-wave velocity model are interpolated to 2.5D P-wave velocity model beneath each seismic station and synthetic back-azimuthal sections of receiver function are calculated for different Vp/Vs ratio. Densities are calculated with combined formulas of Berteussen (1977) and Gardner et al. (1974). Next, the synthetic back-azimuthal sections of RF are compared with observed back-azimuthal sections of RF for "13 BB Star" and PASSEQ seismic stations to find the best 2.5D S-wave models down to 60 km depth. National Science Centre Poland provided financial support for this work by NCN grant DEC-2011/02/A/ST10/00284.

Experiments on seismic metamaterials: molding surface waves.

Science.gov (United States)

Brûlé, S; Javelaud, E H; Enoch, S; Guenneau, S

2014-04-04

Materials engineered at the micro- and nanometer scales have had a tremendous and lasting impact in photonics and phononics. At much larger scales, natural soils civil engineered at decimeter to meter scales may interact with seismic waves when the global properties of the medium are modified, or alternatively thanks to a seismic metamaterial constituted of a mesh of vertical empty inclusions bored in the initial soil. Here, we show the experimental results of a seismic test carried out using seismic waves generated by a monochromatic vibrocompaction probe. Measurements of the particles' velocities show a modification of the seismic energy distribution in the presence of the metamaterial in agreement with numerical simulations using an approximate plate model. For complex natural materials such as soils, this large-scale experiment was needed to show the practical feasibility of seismic metamaterials and to stress their importance for applications in civil engineering. We anticipate this experiment to be a starting point for smart devices for anthropic and natural vibrations.

An experimental study of velocities under pressure for ancient oceanic rocks

Digital Repository Service at National Institute of Oceanography (India)

Sarma, K.V.L.N.S.

Seismic velocities of Indus suture rock types from Dras-Sanko-Kargil, Kashmir Himalaya, as a function of pressure up to 10 kbar were studied. The high-pressure measurements on the rocks reflect the depthwise increase in velocity, and in general...

Anomalous density and elastic properties of basalt at high pressure: Reevaluating of the effect of melt fraction on seismic velocity in the Earth's crust and upper mantle

Science.gov (United States)

Clark, Alisha N.; Lesher, Charles E.; Jacobsen, Steven D.; Wang, Yanbin

2016-06-01

Independent measurements of the volumetric and elastic properties of Columbia River basalt glass were made up to 5.5 GPa by high-pressure X-ray microtomography and GHz-ultrasonic interferometry, respectively. The Columbia River basalt displays P and S wave velocity minima at 4.5 and 5 GPa, respectively, violating Birch's law. These data constrain the pressure dependence of the density and elastic moduli at high pressure, which cannot be modeled through usual equations of state nor determined by stepwise integrating the bulk sound velocity as is common practice. We propose a systematic variation in compression behavior of silicate glasses that is dependent on the degree of polymerization and arises from the flexibility of the aluminosilicate network. This behavior likely persists into the liquid state for basaltic melts resulting in weak pressure dependence for P wave velocities perhaps to depths of the transition zone. Modeling the effect of partial melt on P wave velocity reductions suggests that melt fraction determined by seismic velocity variations may be significantly overestimated in the crust and upper mantle.

Three-Dimensional Shear Wave Velocity Structure of the Peru Flat Slab Subduction Segment

Science.gov (United States)

Knezevic Antonijevic, S.; Wagner, L. S.; Beck, S. L.; Zandt, G.; Long, M. D.

2012-12-01

Recent studies focused on flat slab subduction segments in central Chile (L. S. Wagner, 2006) and Alaska (B. R. Hacker and G. A. Aber, 2012) suggest significant differences in seismic velocity structures, and hence, composition in the mantle wedge between flat and normal "steep" subducting slabs. Instead of finding the low velocities and high Vp/Vs ratios common in normal subduction zones, these studies find low Vp, high Vs, and very low Vp/Vs above flat slabs. This may indicate the presence of dry, cold material in the mantle wedge. In order to investigate the seismic velocities of the upper mantle above the Peruvian flat segment, we have inverted for 2D Rayleigh wave phase velocity maps using data from the currently deployed 40 station PULSE seismic network and some adjacent stations from the CAUGHT seismic network. We then used the sensitivity of surface waves to shear wave velocity structure with depth to develop a 3D shear wave velocity model. This model will allow us to determine the nature of the mantle lithosphere above the flat slab, and how this may have influenced the development of local topography. For example, dry conditions (high Vs velocities) above the flat slab would imply greater strength of this material, possibly making it capable of causing further inland overthrusting, while wet conditions (low Vs) would imply weaker material. This could provide some insight into the ongoing debate over whether the Fitzcarrald arch (along the northern most flank of the Altiplano) could be a topographical response to the subducted Nazca ridge hundred kilometers away from the trench (N. Espurt, 2012, P. Baby, 2005, V. A. Ramos, 2012) or not (J. Martinod, 2005, M. Wipf, 2008, T. Gerya, 2008).

Seismic hazard maps for Haiti

Science.gov (United States)

Frankel, Arthur; Harmsen, Stephen; Mueller, Charles; Calais, Eric; Haase, Jennifer

2011-01-01

We have produced probabilistic seismic hazard maps of Haiti for peak ground acceleration and response spectral accelerations that include the hazard from the major crustal faults, subduction zones, and background earthquakes. The hazard from the Enriquillo-Plantain Garden, Septentrional, and Matheux-Neiba fault zones was estimated using fault slip rates determined from GPS measurements. The hazard from the subduction zones along the northern and southeastern coasts of Hispaniola was calculated from slip rates derived from GPS data and the overall plate motion. Hazard maps were made for a firm-rock site condition and for a grid of shallow shear-wave velocities estimated from topographic slope. The maps show substantial hazard throughout Haiti, with the highest hazard in Haiti along the Enriquillo-Plantain Garden and Septentrional fault zones. The Matheux-Neiba Fault exhibits high hazard in the maps for 2% probability of exceedance in 50 years, although its slip rate is poorly constrained.

Pitfalls in velocity analysis for strongly contrasting, layered media - Example from the Chalk Group, North Sea

Science.gov (United States)

Montazeri, Mahboubeh; Uldall, Anette; Moreau, Julien; Nielsen, Lars

2018-02-01

Knowledge about the velocity structure of the subsurface is critical in key seismic processing sequences, for instance, migration, depth conversion, and construction of initial P- and S-wave velocity models for full-waveform inversion. Therefore, the quality of subsurface imaging is highly dependent upon the quality of the seismic velocity analysis. Based on a case study from the Danish part of the North Sea, we show how interference caused by multiples, converted waves, and thin-layer effects may lead to incorrect velocity estimation, if such effects are not accounted for. Seismic wave propagation inside finely layered reservoir rocks dominated by chalk is described by two-dimensional finite-difference wave field simulation. The rock physical properties used for the modeling are based on an exploration well from the Halfdan field in the Danish sector of the North Sea. The modeling results are compared to seismic data from the study area. The modeling shows that interference of primaries with multiples, converted waves and thin-bed effects can give rise to strong anomalies in standard velocity analysis plots. Consequently, root-mean-square (RMS) velocity profiles may be erroneously picked. In our study area, such mis-picking can introduce errors in, for example, the thickness estimation of the layers near the base of the studied sedimentary strata by 11% to 26%. Tests show that front muting and bandpass filtering cannot significantly improve the quality of velocity analysis in our study. However, we notice that spiking deconvolution applied before velocity analysis may to some extent reduce the impact of interference and, therefore, reduce the risk of erroneous picking of the velocity function.

Reflection seismic methods applied to locating fracture zones in crystalline rock

International Nuclear Information System (INIS)

Juhlin, C.

1998-01-01

The reflection seismic method is a potentially powerful tool for identifying and localising fracture zones in crystalline rock if used properly. Borehole sonic logs across fracture zones show that they have reduced P-wave velocities compared to the surrounding intact rock. Diagnostically important S-wave velocity log information across the fracture zones is generally lacking. Generation of synthetic reflection seismic data and subsequent processing of these data show that structures dipping up towards 70 degrees from horizontal can be reliably imaged using surface seismic methods. Two real case studies where seismic reflection methods have been used to image fracture zones in crystalline rock are presented. Two examples using reflection seismic are presented. The first is from the 5354 m deep SG-4 borehole in the Middle Urals, Russia where strong seismic reflectors dipping from 25 to 50 degrees are observed on surface seismic reflection data crossing over the borehole. On vertical seismic profile data acquired in the borehole, the observed P-wave reflectivity is weak from these zones, however, strong converted P to S waves are observed. This can be explained by the source of the reflectors being fracture zones with a high P wave to S wave velocity ratio compared to the surrounding rock resulting in a high dependence on the angle of incidence for the reflection coefficient. A high P wave to S wave velocity ratio (high Poisson's ratio) is to be expected in fluid filled fractured rock. The second case is from Aevroe, SE Sweden, where two 1 km long crossing high resolution seismic reflection lines were acquired in October 1996. An E-W line was shot with 5 m geophone and shotpoint spacing and a N-S one with 10 m geophone and shotpoint spacing. An explosive source with a charge size of 100 grams was used along both lines. The data clearly image three major dipping reflectors in the upper 200 ms (600 m). The dipping ones intersect or project to the surface at/or close to

Seismic hazard evaluation for major cities in Madagascar

International Nuclear Information System (INIS)

Razafindrakoto, Hoby N.T.; Rambolamanana, Gerard; Panza, Giuliano F.

2009-09-01

The seismic hazard in some areas in Madagascar has been assessed at regional scale in terms of peak ground motion values (displacement, velocity, acceleration) and their periods, following the Neodeterministic approach, based on the computation of realistic synthetic seismograms. The main data input integrates all available tectonic, seismicity and structural model information. The largest peak values are 1.6cm/s for the velocity, 0.03g for the acceleration and more than 0.5cm for the displacement. These values are consistent within a range of macroseismic intensity from VI to VII MCS, and indicate that relatively simple prevention measures and retrofitting actions may guarantee a high safety level and a well sustainable development. (author)

Review on improved seismic imaging with closure phase

KAUST Repository

Schuster, Gerard T.

2014-08-13

The timing and amplitudes of arrivals recorded in seismic traces are influenced by velocity variations all along the associated raypaths. Consequently, velocity errors far from the target can lead to blurred imaging of the target body. To partly remedy this problem, we comprehensively reviewed inverting differential traveltimes that satisfied the closure-phase condition. The result is that the source and receiver statics are completely eliminated in the data and velocities far from the target do not need to be known. We successfully used the phase closure equation for traveltime tomography, refraction statics, migration, refraction tomography, and earthquake location, all of which demonstrated the higher resolution achievable by processing data with differential traveltimes rather than absolute traveltimes. More generally, the stationary version of the closure-phase equation is equivalent to Fermat’s principle and can be derived from the equations of seismic interferometry. In summary, the general closure-phase equation is the mathematical foundation for approximately redatuming sources and/or receivers to the target of interest without the need to accurately know the statics or the velocity model away from the target.

The 2012 Ferrara seismic sequence: Regional crustal structure, earthquake sources, and seismic hazard

Science.gov (United States)

Malagnini, Luca; Herrmann, Robert B.; Munafò, Irene; Buttinelli, Mauro; Anselmi, Mario; Akinci, Aybige; Boschi, E.

2012-10-01

Inadequate seismic design codes can be dangerous, particularly when they underestimate the true hazard. In this study we use data from a sequence of moderate-sized earthquakes in northeast Italy to validate and test a regional wave propagation model which, in turn, is used to understand some weaknesses of the current design spectra. Our velocity model, while regionalized and somewhat ad hoc, is consistent with geophysical observations and the local geology. In the 0.02-0.1 Hz band, this model is validated by using it to calculate moment tensor solutions of 20 earthquakes (5.6 ≥ MW ≥ 3.2) in the 2012 Ferrara, Italy, seismic sequence. The seismic spectra observed for the relatively small main shock significantly exceeded the design spectra to be used in the area for critical structures. Observations and synthetics reveal that the ground motions are dominated by long-duration surface waves, which, apparently, the design codes do not adequately anticipate. In light of our results, the present seismic hazard assessment in the entire Pianura Padana, including the city of Milan, needs to be re-evaluated.

Seismic Linear Noise Attenuation with Use of Radial Transform

Science.gov (United States)

Szymańska-Małysa, Żaneta

2018-03-01

One of the goals of seismic data processing is to attenuate the recorded noise in order to enable correct interpretation of the image. Radial transform has been used as a very effective tool in the attenuation of various types of linear noise, both numerical and real (such as ground roll, direct waves, head waves, guided waves etc). The result of transformation from offset - time (X - T) domain into apparent velocity - time (R - T) domain is frequency separation between reflections and linear events. In this article synthetic and real seismic shot gathers were examined. One example was targeted at far offset area of dataset where reflections and noise had similar apparent velocities and frequency bands. Another example was a result of elastic modelling where linear artefacts were produced. Bandpass filtering and scaling operation executed in radial domain attenuated all discussed types of linear noise very effectively. After noise reduction all further processing steps reveal better results, especially velocity analysis, migration and stacking. In all presented cases signal-to-noise ratio was significantly increased and reflections covered previously by noise were revealed. Power spectra of filtered seismic records preserved real dynamics of reflections.

Uncertainty analysis in seismic tomography

Science.gov (United States)

Owoc, Bartosz; Majdański, Mariusz

2017-04-01

Velocity field from seismic travel time tomography depends on several factors like regularization, inversion path, model parameterization etc. The result also strongly depends on an initial velocity model and precision of travel times picking. In this research we test dependence on starting model in layered tomography and compare it with effect of picking precision. Moreover, in our analysis for manual travel times picking the uncertainty distribution is asymmetric. This effect is shifting the results toward faster velocities. For calculation we are using JIVE3D travel time tomographic code. We used data from geo-engineering and industrial scale investigations, which were collected by our team from IG PAS.

Sunda-Banda Arc Transition: Marine Wide-Angle Seismic Modeling

Science.gov (United States)

Shulgin, A.; Planert, L.; Kopp, H.; Mueller, C.; Lueschen, E.; Engels, M.; Flueh, E.; Djajadihardja, Y.; Sindbad Working Group, T

2008-12-01

The Sunda-Banda Arc transition is the region of active convergence and collision of the Indo-Australian and Eurasian Plates. The style of subduction changes from an oceanic-island arc subduction to a continental- island arc collision. The character of the incoming plate varies from the rough topography of the Roo Rise, to the smooth seafloor of the Abyssal Plain off Bali, Sumbawa. Forearc structures include well-developed forearc basins and an accretionary prism/outer forearc high of variable size and shape. To quantify the variability of structure of the lower plate and the effects on the upper plate a refraction seismic survey was carried during cruise SO190-2. A total of 245 ocean bottom seismometers were deployed along 1020 nm of wide-angle seismic profiles in four major north-south oriented corridors. To assess the velocity structure we used a tomographic method which jointly inverts for refracted and reflected phases. The sedimentary layers of the models, obtained by the analysis of high-resolution MCS data (see Lueschen et al), were incorporated into the starting model. The obtained models exhibit strong changes of the incoming oceanic crust for the different portions of the margin: The westernmost profile off eastern Java shows a crustal thickness of more than 15 km, most likely related to the presence of an oceanic plateau. Profiles off Lombok reveal an oceanic crust of 8-9 km average thickness in the Argo Abyssal Plain. Crustal and upper mantle velocities are slightly decreased within an area of about 50-60 km seaward of the trench, indicating fracturing and related serpentinization due to bending of the oceanic crust and associated normal faulting. The outer forearc high is characterized by velocities of 2.5-5.5 km/s. For the Lombok Basin, the profiles show a sedimentary infill of up to 3.5 km thick and typical sediment velocities of 1.75-3.0 km/s. A reflector at 16 km depth and velocity values of 7.4-7.8 km/s beneath it suggest the presence of a shallow

Seismic rupture modelling, strong motion prediction and seismic hazard assessment: fundamental and applied approaches

International Nuclear Information System (INIS)

Berge-Thierry, C.

2007-05-01

The defence to obtain the 'Habilitation a Diriger des Recherches' is a synthesis of the research work performed since the end of my Ph D. thesis in 1997. This synthesis covers the two years as post doctoral researcher at the Bureau d'Evaluation des Risques Sismiques at the Institut de Protection (BERSSIN), and the seven consecutive years as seismologist and head of the BERSSIN team. This work and the research project are presented in the framework of the seismic risk topic, and particularly with respect to the seismic hazard assessment. Seismic risk combines seismic hazard and vulnerability. Vulnerability combines the strength of building structures and the human and economical consequences in case of structural failure. Seismic hazard is usually defined in terms of plausible seismic motion (soil acceleration or velocity) in a site for a given time period. Either for the regulatory context or the structural specificity (conventional structure or high risk construction), seismic hazard assessment needs: to identify and locate the seismic sources (zones or faults), to characterize their activity, to evaluate the seismic motion to which the structure has to resist (including the site effects). I specialized in the field of numerical strong-motion prediction using high frequency seismic sources modelling and forming part of the IRSN allowed me to rapidly working on the different tasks of seismic hazard assessment. Thanks to the expertise practice and the participation to the regulation evolution (nuclear power plants, conventional and chemical structures), I have been able to work on empirical strong-motion prediction, including site effects. Specific questions related to the interface between seismologists and structural engineers are also presented, especially the quantification of uncertainties. This is part of the research work initiated to improve the selection of the input ground motion in designing or verifying the stability of structures. (author)

Seismic ground motion and hazard assessment of the Greater Accra Metropolitan Area, southeastern Ghana

International Nuclear Information System (INIS)

Amponsah, P.E.; Banoeng-Yakubo, B.K.; Asiedu, D.; Vaccari, F.; Panza, G.F.

2008-08-01

The seismic ground motion of the Greater Accra Metropolitan area has been computed and the hazard zones assessed using a deterministic hybrid approach based on the modal summation and finite difference methods. The seismic ground motion along four profiles located in the Greater Accra Metropolitan Area has been modelled using the 1939 earthquake of magnitude 6.5(M L ) as the scenario earthquake. Synthetic seismic waveforms from which parameters for engineering design such as peak ground acceleration, velocity and spectral amplifications have been produced along the geological cross sections. From the seismograms computed, the seismic hazard of the metropolis, expressed in terms of peak ground acceleration and peak ground velocity have been estimated. The peak ground acceleration estimated in the study ranges from 0.14 - 0.57 g and the peak ground velocity from 9.2 - 37.1cms -1 . The presence of low velocity sediments gave rise to high peak values and amplifications. The maximum peak ground accelerations estimated are located in areas with low velocity formations such as colluvium, continental and marine deposits. Areas in the metropolis underlain by unconsolidated sediments have been classified as the maximum damage potential zone and those underlain by highly consolidated geological materials are classified as low damage potential zone. The results of the numerical simulation have been extended to all areas in the metropolis with similar geological formation. (author)

Integrated seismic analysis of the Chalk Group in eastern Denmark—Implications for estimates of maximum palaeo-burial in southwest Scandinavia

DEFF Research Database (Denmark)

Nielsen, Lars; Boldreel, Lars Ole; Hansen, Thomas Mejer

2011-01-01

Group. The sonic velocities are consistent with the overall seismic layering, although they show additional fine-scale layering. Integration of gamma and sonic log with porosity data shows that seismic velocity is sensitive to clay content. In intervals near boundaries of the refraction model, moderate......The origin of the topography of southwest Scandinavia is subject to discussion. Analysis of borehole seismic velocity has formed the basis for interpretation of several hundred metres of Neogene uplift in parts of Denmark.Here, refraction seismic data constrain a 7.5km long P-wave velocity model...... of the Chalk Group below the Stevns peninsula, eastern part of the Danish Basin. The model contains four layers in the ~860m thick Chalk Group with mean velocities of 2.2km/s, 2.4km/s, 3.1km/s, and 3.9–4.3km/s. Sonic and gamma wireline log data from two cored boreholes represent the upper ~450m of the Chalk...

Seismic waves in 3-D: from mantle asymmetries to reliable seismic hazard assessment

Science.gov (United States)

Panza, Giuliano F.; Romanelli, Fabio

2014-10-01

A global cross-section of the Earth parallel to the tectonic equator (TE) path, the great circle representing the equator of net lithosphere rotation, shows a difference in shear wave velocities between the western and eastern flanks of the three major oceanic rift basins. The low-velocity layer in the upper asthenosphere, at a depth range of 120 to 200 km, is assumed to represent the decoupling between the lithosphere and the underlying mantle. Along the TE-perturbed (TE-pert) path, a ubiquitous LVZ, about 1,000-km-wide and 100-km-thick, occurs in the asthenosphere. The existence of the TE-pert is a necessary prerequisite for the existence of a continuous global flow within the Earth. Ground-shaking scenarios were constructed using a scenario-based method for seismic hazard analysis (NDSHA), using realistic and duly validated synthetic time series, and generating a data bank of several thousands of seismograms that account for source, propagation, and site effects. Accordingly, with basic self-organized criticality concepts, NDSHA permits the integration of available information provided by the most updated seismological, geological, geophysical, and geotechnical databases for the site of interest, as well as advanced physical modeling techniques, to provide a reliable and robust background for the development of a design basis for cultural heritage and civil infrastructures. Estimates of seismic hazard obtained using the NDSHA and standard probabilistic approaches are compared for the Italian territory, and a case-study is discussed. In order to enable a reliable estimation of the ground motion response to an earthquake, three-dimensional velocity models have to be considered, resulting in a new, very efficient, analytical procedure for computing the broadband seismic wave-field in a 3-D anelastic Earth model.

Feasibility study for seismic monitoring of gas injection; Atsunyu gasu monitaringu no kanosei hyoka ni kansuru kenkyu

Energy Technology Data Exchange (ETDEWEB)

Nishida, A.; Ogawa, T.; Yokota, T.; Shimada, N.; Onozuka, S.; Kono, F.; Miyagi, T. [Japan National Oil Corp., Tokyo (Japan)

1998-10-30

In this study, seismic monitoring of injected gas in a carbonate reservoir was investigated using multidisciplinary approach which consisted of geological/reservoir modeling, reservoir flow simulation, rock physics and seismic modeling. A case study was conducted over Lower Cretaceous carbonate reservoir offshore Abu Dhabi. The gas saturation and reservoir pressure data were obtained from the reservoir flow simulation. The velocity data of dry rock samples under the various conditions were also obtained from rock physics study. These outputs were converted to the velocity model using Gassmann's equation. The calculated velocity from Gassmann's equation is well correlated with velocity from laboratory measurements. Therefore we con confirm that the Gassmann's equation is applicable to estimate the velocity of the gas saturated reservoir rock. Based on the velocity model, synthetic seismic sections before and after gas injection were constructed in order to verify the influence of gas flood. As the results, amplitude difference between the two synthetic seismograms was observed at top and bottom reflectors of the reservoir zone. This amplitude variation is caused by both gas saturation change and pressure change. Although further investigation is needed to detect the cause of the variation, this study indicates the possibility of seismic reservoir monitoring. (author)

Rayleigh-wave phase-velocity maps and three-dimensional shear velocity structure of the western US from local non-plane surface wave tomography

Science.gov (United States)

Pollitz, F.F.; Snoke, J. Arthur

2010-01-01

We utilize two-and-three-quarter years of vertical-component recordings made by the Transportable Array (TA) component of Earthscope to constrain three-dimensional (3-D) seismic shear wave velocity structure in the upper 200 km of the western United States. Single-taper spectral estimation is used to compile measurements of complex spectral amplitudes from 44 317 seismograms generated by 123 teleseismic events. In the first step employed to determine the Rayleigh-wave phase-velocity structure, we implement a new tomographic method, which is simpler and more robust than scattering-based methods (e.g. multi-plane surface wave tomography). The TA is effectively implemented as a large number of local arrays by defining a horizontal Gaussian smoothing distance that weights observations near a given target point. The complex spectral-amplitude measurements are interpreted with the spherical Helmholtz equation using local observations about a succession of target points, resulting in Rayleigh-wave phase-velocity maps at periods over the range of 18–125 s. The derived maps depend on the form of local fits to the Helmholtz equation, which generally involve the nonplane-wave solutions of Friederich et al. In a second step, the phase-velocity maps are used to derive 3-D shear velocity structure. The 3-D velocity images confirm details witnessed in prior body-wave and surface-wave studies and reveal new structures, including a deep (>100 km deep) high-velocity lineament, of width ∼200 km, stretching from the southern Great Valley to northern Utah that may be a relic of plate subduction or, alternatively, either a remnant of the Mojave Precambrian Province or a mantle downwelling. Mantle seismic velocity is highly correlated with heat flow, Holocene volcanism, elastic plate thickness and seismicity. This suggests that shallow mantle structure provides the heat source for associated magmatism, as well as thinning of the thermal lithosphere, leading to relatively high

Characteristics of the seismicity of Vesuvius and Campi Flegrei during the year 2000

Directory of Open Access Journals (Sweden)

G. Talarico

2001-06-01

Full Text Available This paper describes the characteristics of the seismicity in the volcanic Neapolitan area during the year 2000 recorded by the monitoring seismic network of the Osservatorio Vesuviano. In particular, a detailed analysis of the seismicity of Vesuvius is presented. We compared the seismic velocity models available for the Vesuvius area locating the earthquakes recorded in the year 2000 and on the basis of the results, we introduce for routine earthquake location the new velocity model obtained by the seismic tomography experiments (TomoVes performed in the area. We also determined the focal mechanisms and analysed the seismicity rate, comparing the results with those obtained for the past years. After the introduction of the new acquisition system at the Osservatorio Vesuviano, a re-calibration of the duration magnitude scale was necessary to avoid biases related to the different instrumental response. Consequently, we re-calibrated the magnitude relation used for the Vesuvius earthquakes, obtaining a new formula to be used for the earthquakes recorded by the new acquisition system. Finally, we give a description of the seismic activity in the Campi Flegrei area during the summer of 2000.

Analysis of induced seismicity at The Geysers geothermal field, California

Science.gov (United States)

Emolo, A.; Maercklin, N.; Matrullo, E.; Orefice, A.; Amoroso, O.; Convertito, V.; Sharma, N.; Zollo, A.

2012-12-01

Fluid injection, steam extraction, and reservoir stimulation in geothermal systems lead to induced seismicity. While in rare cases induced events may be large enough to pose a hazard, on the other hand the microseismicity provides information on the extent and the space-time varying properties of the reservoir. Therefore, microseismic monitoring is important, both for mitigation of unwanted effects of industrial operations and for continuous assessment of reservoir conditions. Here we analyze induced seismicity at The Geysers geothermal field in California, a vapor-dominated field with the top of the main steam reservoir some 1-3 km below the surface. Commercial exploitation began in the 1960s, and the seismicity increased with increasing field development. We focus our analyses on induced seismicity recorded between August 2007 and October 2011. Our calibrated waveform database contains some 15000 events with magnitudes between 1.0 and 4.5 and recorded by the LBNL Geysers/Calpine surface seismic network. We associated all data with events from the NCEDC earthquake catalog and re-picked first arrival times. Using selected events with at least 20 high-quality P-wave picks, we determined a minimum 1-D velocity model using VELEST. A well-constrained P-velocity model shows a sharp velocity increase at 1-2 km depth (from 3 to 5 km/s) and then a gradient-like trend down to about 5 km depth, where velocities reach values of 6-7 km/s. The station corrections show coherent, relatively high, positive travel time delays in the NW zone, thus indicating a strong lateral variation of the P-wave velocities. We determined an average Vp-to-Vs ratio of 1.67, which is consistent with estimates from other authors for the same time period. The events have been relocated in the new model using a non-linear probabilistic methods. The seismicity appears spatially diffused in a 15x10 km2 area elongated in NW-SE direction, and earthquake depths range between 0 and 6 km. As in previous

Developing regionalized models of lithospheric thickness and velocity structure across Eurasia and the Middle East from jointly inverting P-wave and S-wave receiver functions with Rayleigh wave group and phase velocities

Energy Technology Data Exchange (ETDEWEB)

Julia, J; Nyblade, A; Hansen, S; Rodgers, A; Matzel, E

2009-07-06

In this project, we are developing models of lithospheric structure for a wide variety of tectonic regions throughout Eurasia and the Middle East by regionalizing 1D velocity models obtained by jointly inverting P-wave and S-wave receiver functions with Rayleigh wave group and phase velocities. We expect the regionalized velocity models will improve our ability to predict travel-times for local and regional phases, such as Pg, Pn, Sn and Lg, as well as travel-times for body-waves at upper mantle triplication distances in both seismic and aseismic regions of Eurasia and the Middle East. We anticipate the models will help inform and strengthen ongoing and future efforts within the NNSA labs to develop 3D velocity models for Eurasia and the Middle East, and will assist in obtaining model-based predictions where no empirical data are available and for improving locations from sparse networks using kriging. The codes needed to conduct the joint inversion of P-wave receiver functions (PRFs), S-wave receiver functions (SRFs), and dispersion velocities have already been assembled as part of ongoing research on lithospheric structure in Africa. The methodology has been tested with synthetic 'data' and case studies have been investigated with data collected at an open broadband stations in South Africa. PRFs constrain the size and S-P travel-time of seismic discontinuities in the crust and uppermost mantle, SRFs constrain the size and P-S travel-time of the lithosphere-asthenosphere boundary, and dispersion velocities constrain average S-wave velocity within frequency-dependent depth-ranges. Preliminary results show that the combination yields integrated 1D velocity models local to the recording station, where the discontinuities constrained by the receiver functions are superimposed to a background velocity model constrained by the dispersion velocities. In our first year of this project we will (i) generate 1D velocity models for open broadband seismic stations

Seismic properties of fluid bearing formations in magmatic geothermal systems: can we directly detect geothermal activity with seismic methods?

Science.gov (United States)

Grab, Melchior; Scott, Samuel; Quintal, Beatriz; Caspari, Eva; Maurer, Hansruedi; Greenhalgh, Stewart

2016-04-01

Seismic methods are amongst the most common techniques to explore the earth's subsurface. Seismic properties such as velocities, impedance contrasts and attenuation enable the characterization of the rocks in a geothermal system. The most important goal of geothermal exploration, however, is to describe the enthalpy state of the pore fluids, which act as the main transport medium for the geothermal heat, and to detect permeable structures such as fracture networks, which control the movement of these pore fluids in the subsurface. Since the quantities measured with seismic methods are only indirectly related with the fluid state and the rock permeability, the interpretation of seismic datasets is difficult and usually delivers ambiguous results. To help overcome this problem, we use a numerical modeling tool that quantifies the seismic properties of fractured rock formations that are typically found in magmatic geothermal systems. We incorporate the physics of the pore fluids, ranging from the liquid to the boiling and ultimately vapor state. Furthermore, we consider the hydromechanics of permeable structures at different scales from small cooling joints to large caldera faults as are known to be present in volcanic systems. Our modeling techniques simulate oscillatory compressibility and shear tests and yield the P- and S-wave velocities and attenuation factors of fluid saturated fractured rock volumes. To apply this modeling technique to realistic scenarios, numerous input parameters need to be indentified. The properties of the rock matrix and individual fractures were derived from extensive literature research including a large number of laboratory-based studies. The geometries of fracture networks were provided by structural geologists from their published studies of outcrops. Finally, the physical properties of the pore fluid, ranging from those at ambient pressures and temperatures up to the supercritical conditions, were taken from the fluid physics

Seismic imaging of lithospheric discontinuities and continental evolution

Science.gov (United States)

Bostock, M. G.

1999-09-01

Discontinuities in physical properties within the continental lithosphere reflect a range of processes that have contributed to craton stabilization and evolution. A survey of recent seismological studies concerning lithospheric discontinuities is made in an attempt to document their essential characteristics. Results from long-period seismology are inconsistent with the presence of continuous, laterally invariant, isotropic boundaries within the upper mantle at the global scale. At regional scales, two well-defined interfaces termed H (˜60 km depth) and L (˜200 km depth) of continental affinity are identified, with the latter boundary generally exhibiting an anisotropic character. Long-range refraction profiles are frequently characterized by subcontinental mantle that exhibits a complex stratification within the top 200 km. The shallow layering of this package can behave as an imperfect waveguide giving rise to the so-called teleseismic Pn phase, while the L-discontinuity may define its lower base as the culmination of a low velocity zone. High-resolution, seismic reflection profiling provides sufficient detail in a number of cases to document the merging of mantle interfaces into lower continental crust below former collisional sutures and magmatic arcs, thus unambiguously identifying some lithospheric discontinuities with thrust faults and subducted oceanic lithosphere. Collectively, these and other seismic observations point to a continental lithosphere whose internal structure is dominated by a laterally variable, subhorizontal layering. This stratigraphy appears to be more pronounced at shallower lithospheric levels, includes dense, anisotropic layers of order 10 km in thickness, and exhibits horizontal correlation lengths comparable to the lateral dimensions of overlying crustal blocks. A model of craton evolution which relies on shallow subduction as a principal agent of craton stabilization is shown to be broadly compatible with these characteristics.

Time-lapse changes in velocity and anisotropy in Japan's near surface after the 2011 Tohoku earthquake

Science.gov (United States)

Snieder, R.; Nakata, N.

2012-12-01

A strong-motion recording network, KiK-net, helps us to monitor temporal changes in the near surface in Japan. Each KiK-net station has two seismometers at the free surface and in a borehole a few hundred meters deep, and we can retrieve a traveling wave from the borehole receiver to the surface receiver by applying deconvolution based seismic interferometry. KiK-net recorded the 2011 Tohoku earthquake, which is one of the largest earthquakes in recent history, and seismicity around the time of the main shock. Using records of these seismicity and computing mean values of near-surface shear-wave velocities in the periods of January 1--March 10 and March 12--May 26 in 2011, we detect about a 5% reduction in the velocity after the Tohoku earthquake. The area of the velocity reduction is about 1,200 km wide, which is much wider than earlier studies reporting velocity reductions after larger earthquakes. The reduction partly recovers with time. We can also estimate the azimuthal anisotropy by detecting shear-wave splitting after applying seismic interferometry. Estimating mean values over the same periods as the velocity, we find the strength of anisotropy increased in most parts of northeastern Japan, but fast shear-wave polarization directions in the near surface did not significantly change. The changes in anisotropy and velocity are generally correlated, especially in the northeastern Honshu (the main island in Japan).

Hardrock Elastic Physical Properties: Birch's Seismic Parameter Revisited

Science.gov (United States)

Wu, M.; Milkereit, B.

2014-12-01

Identifying rock composition and properties is imperative in a variety of fields including geotechnical engineering, mining, and petroleum exploration, in order to accurately make any petrophysical calculations. Density is, in particular, an important parameter that allows us to differentiate between lithologies and estimate or calculate other petrophysical properties. It is well established that compressional and shear wave velocities of common crystalline rocks increase with increasing densities (i.e. the Birch and Nafe-Drake relationships). Conventional empirical relations do not take into account S-wave velocity. Physical properties of Fe-oxides and massive sulfides, however, differ significantly from the empirical velocity-density relationships. Currently, acquiring in-situ density data is challenging and problematic, and therefore, developing an approximation for density based on seismic wave velocity and elastic moduli would be beneficial. With the goal of finding other possible or better relationships between density and the elastic moduli, a database of density, P-wave velocity, S-wave velocity, bulk modulus, shear modulus, Young's modulus, and Poisson's ratio was compiled based on a multitude of lab samples. The database is comprised of isotropic, non-porous metamorphic rock. Multi-parameter cross plots of the various elastic parameters have been analyzed in order to find a suitable parameter combination that reduces high density outliers. As expected, the P-wave velocity to S-wave velocity ratios show no correlation with density. However, Birch's seismic parameter, along with the bulk modulus, shows promise in providing a link between observed compressional and shear wave velocities and rock densities, including massive sulfides and Fe-oxides.

Near surface velocity and Q S structure of the Quaternary sediment in Bohai basin, China

Science.gov (United States)

Chong, Jiajun; Ni, Sidao

2009-10-01

Heavily populated by Beijing and Tianjin cities, Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. The attenuation ( Q P and Q S) of the surficial Quaternary sediment has not been studied at natural seismic frequency (1-10 Hz), which is crucial to earthquake hazards study. Borehole seismic records of micro earthquake provide us a good way to study the velocity and attenuation of the surficial structure (0-500 m). We found that there are two pulses well separated with simple waveforms on borehole seismic records from the 2006 M W4.9 Wen’an earthquake sequence. Then we performed waveform modeling with generalized ray theory (GRT) to confirm that the two pulses are direct wave and surface reflected wave, and found that the average ν P and ν S of the top 300 m in this region are about 1.8 km/s and 0.42 km/s, leading to high ν P/ ν S ratio of 4.3. We also modeled surface reflected wave with propagating matrix method to constrain Q S and the near surface velocity structure. Our modeling indicates that Q S is at least 30, or probably up to 100, much larger than the typically assumed extremely low Q (˜10), but consistent with Q S modeling in Mississippi embayment. Also, the velocity gradient just beneath the free surface (0-50 m) is very large and velocity increases gradually at larger depth. Our modeling demonstrates the importance of borehole seismic records in resolving shallow velocity and attenuation structure, and hence may help in earthquake hazard simulation.

Shear wave velocities in the upper mantle of the Western Alps: new constraints using array analysis of seismic surface waves

Science.gov (United States)

Lyu, Chao; Pedersen, Helle A.; Paul, Anne; Zhao, Liang; Solarino, Stefano

2017-07-01

It remains challenging to obtain absolute shear wave velocities of heterogeneities of small lateral extension in the uppermost mantle. This study presents a cross-section of Vs across the strongly heterogeneous 3-D structure of the western European Alps, based on array analysis of data from 92 broad-band seismic stations from the CIFALPS experiment and from permanent networks in France and Italy. Half of the stations were located along a dense sublinear array. Using a combination of these stations and off-profile stations, fundamental-mode Rayleigh wave dispersion curves were calculated using a combined frequency-time beamforming approach. We calculated dispersion curves for seven arrays of approximately 100 km aperture and 14 arrays of approximately 50 km aperture, the latter with the aim of obtaining a 2-D vertical cross-section of Vs beneath the western Alps. The dispersion curves were inverted for Vs(z), with crustal interfaces imposed from a previous receiver function study. The array approach proved feasible, as Vs(z) from independent arrays vary smoothly across the profile length. Results from the seven large arrays show that the shear velocity of the upper mantle beneath the European plate is overall low compared to AK135 with the lowest velocities in the internal part of the western Alps, and higher velocities east of the Alps beneath the Po plain. The 2-D Vs model is coherent with (i) a ∼100 km thick eastward-dipping European lithosphere west of the Alps, (ii) very high velocities beneath the Po plain, coherent with the presence of the Alpine (European) slab and (iii) a narrow low-velocity anomaly beneath the core of the western Alps (from the Briançonnais to the Dora Maira massif), and approximately colocated with a similar anomaly observed in a recent teleseismic P-wave tomography. This intriguing anomaly is also supported by traveltime variations of subvertically propagating body waves from two teleseismic events that are approximately located on

The Crustal Structure and Seismicity of Eastern Venezuela

Science.gov (United States)

Schmitz, M.; Martins, A.; Sobiesiak, M.; Alvarado, L.; Vasquez, R.

2001-12-01

Eastern Venezuela is characterized by a moderate to high seismicity, evidenced recently by the 1997 Cariaco earthquake located on the El Pilar Fault, a right lateral strike slip fault which marks the plate boundary between the Caribbean and South-American plates in this region. Recently, the seismic activity seems to migrate towards the zone of subduction of the Lesser Antilles in the northeast, where a mb 6.0 earthquake occurred in October 2000 at 120 km of depth. Periodical changes in the seismic activity are related to the interaction of the stress fields of the strike-slip and the subduction regimes. The seismic activity decreases rapidly towards to the south with some disperse events on the northern edge of the Guayana Shield, related to the Guri fault system. The crustal models used in the region are derived from the information generated by the national seismological network since 1982 and by microseismicity studies in northeastern Venezuela, coinciding in a crustal thickness of about 35 km in depth. Results of seismic refraction measurements for the region were obtained during field campains in 1998 (ECOGUAY) for the Guayana Shield and the Cariaco sedimentary basin and in 2001 (ECCO) for the Oriental Basin. The total crustal thickness decreases from about 45 km on the northern edge of the Guayana Shield to some 36 km close to El Tigre in the center of the Oriental Basin. The average crustal velocity decreases in the same sense from 6.5 to 5.8 km/s. In the Cariaco sedimentary basin a young sedimentary cover of 1 km thickness with a seismic velocity of 2 km/s was derived. Towards the northern limit of the South-American plate, no deep seismic refraction data are available up to now. The improvement of the crustal models used in that region would constitute a step forward in the analysis of the seismic hazard. Seismic refraction studies funded by CONICIT S1-97002996 and S1-2000000685 projects and PDVSA (additional drilling and blasting), recording equipment

Detailed geological characterisation from seismic data

Energy Technology Data Exchange (ETDEWEB)

Peter Hatherly; Binzhong Zhou; Troy Peters; Milovan Urosevic [CRC Mining (Australia)

2009-02-15

The use of seismic reflection surveying continues to grow within Australia's underground coal mining regions of the Sydney and Bowen Basins. For this project, the potential for acoustic impedance inversion to complement the information available from conventional seismic surveys was investigated. Acoustic impedance is defined by the product of seismic P-wave velocity and rock density. The methods of seismic inversion have been developed mainly for the investigation of petroleum reservoirs. Commercial software packages are available and for this project we utilised the Hampson and Russell software available at Curtin University of Technology. For the true amplitude processing of the seismic data, the Promax software operated at Velseis Processing was used. Inversions were undertaken for three 3D seismic surveys and two 2D surveys. The sites were at Grasstree and North Goonyella Mines in the Bowen Basin and at West Cliff and Dendrobium Collieries in the Sydney Basin. An empirical relationship was derived between acoustic impedance and the newly developed Geophysical Strata Rating (GSR). This allows impedance values to be converted into GSR values that have more meaning in geotechnical assessment. To obtain satisfactory inversions, we used the model based approach.

How a joint interpretation of seismic scattering, velocity, and attenuation models explains the nature of the Campi Flegrei (Italy).

Science.gov (United States)

Calo, M.; Tramelli, A.

2017-12-01

Seismic P and S velocity models (and their ratio Vp/Vs) help illuminating the geometrical structure of the bodies and give insight on the presence of water, molten or gas saturated regions. Seismic attenuation represents the anelastic behavior of the medium. Due to its dependence on temperature, fluid contents and cracks presence, this parameter is also largely used to characterize the structures of volcanoes and geothermal areas. Scattering attenuation is related, in the upper crust, to the amount, size and organization of the fractures giving complementary information on the state of the medium.Therefore a joint interpretation of these models provides an exhaustive view of the elastic parameters in volcanic regions. Campi Flegrei is an active Caldera marked by strong vertical deformations of the ground called bradyseisms and several models have been proposed to describe the nature and the geometry of the bodies responsible of the bradyseisms. Here we show Vp, Vp/Vs, Qp and scattering models carried out by applying an enhanced seismic tomography method that combines de double difference approach (Zhang and Thurber, 2003) and the Weigthed Average Method (Calò et al., 2009, Calò et al., 2011, 2013). The data used are the earthquakes recorded during the largest bradyseism crisis of the 80's. Our method allowed to image structures with linear dimension of 0.5-1.2km, resulting in an improvement of the resolving power at least two times of the other published models (e.g. Priolo et al., 2012). The joint interpretation of seismic models allowed to discern small anomalous bodies at shallow depth (0.5-2.0 km) marked by relatively low Vp, high Vp/Vs ratio and low Qp values associated with the presence of shallow geothermal water saturated reservoir from regions with low Vp, low Vp/Vs and low Qp related to the gas saturated part of the reservoir. At deeper depth (2-3.5 km) bodies with high Vp and Vp/Vs and low Qp are associated with magmatic intrusions. The Scattering

Ray-tracing traveltime tomography versus wave-equation traveltime inversion for near-surface seismic land data

KAUST Repository

Fu, Lei

2017-05-11

Full-waveform inversion of land seismic data tends to get stuck in a local minimum associated with the waveform misfit function. This problem can be partly mitigated by using an initial velocity model that is close to the true velocity model. This initial starting model can be obtained by inverting traveltimes with ray-tracing traveltime tomography (RT) or wave-equation traveltime (WT) inversion. We have found that WT can provide a more accurate tomogram than RT by inverting the first-arrival traveltimes, and empirical tests suggest that RT is more sensitive to the additive noise in the input data than WT. We present two examples of applying WT and RT to land seismic data acquired in western Saudi Arabia. One of the seismic experiments investigated the water-table depth, and the other one attempted to detect the location of a buried fault. The seismic land data were inverted by WT and RT to generate the P-velocity tomograms, from which we can clearly identify the water table depth along the seismic survey line in the first example and the fault location in the second example.

S-velocity structure in Cimandiri fault zone derived from neighbourhood inversion of teleseismic receiver functions

Science.gov (United States)

Syuhada; Anggono, T.; Febriani, F.; Ramdhan, M.

2018-03-01

The availability information about realistic velocity earth model in the fault zone is crucial in order to quantify seismic hazard analysis, such as ground motion modelling, determination of earthquake locations and focal mechanism. In this report, we use teleseismic receiver function to invert the S-velocity model beneath a seismic station located in the Cimandiri fault zone using neighbourhood algorithm inversion method. The result suggests the crustal thickness beneath the station is about 32-38 km. Furthermore, low velocity layers with high Vp/Vs exists in the lower crust, which may indicate the presence of hot material ascending from the subducted slab.

Measurements of translation, rotation and strain: new approaches to seismic processing and inversion

NARCIS (Netherlands)

Bernauer, M.; Fichtner, A.; Igel, H.

2012-01-01

We propose a novel approach to seismic tomography based on the joint processing of translation, strain and rotation measurements. Our concept is based on the apparent S and P velocities, defined as the ratios of displacement velocity and rotation amplitude, and displacement velocity and

A repeatable seismic source for tomography at volcanoes

Directory of Open Access Journals (Sweden)

A. Ratdomopurbo

1999-06-01

Full Text Available One major problem associated with the interpretation of seismic signals on active volcanoes is the lack of knowledge about the internal structure of the volcano. Assuming a 1D or a homogeneous instead of a 3D velocity structure leads to an erroneous localization of seismic events. In order to derive a high resolution 3D velocity model ofMt. Merapi (Java a seismic tomography experiment using active sources is planned as a part of the MERAPI (Mechanism Evaluation, Risk Assessment and Prediction Improvement project. During a pre-site survey in August 1996 we tested a seismic source consisting of a 2.5 l airgun shot in water basins that were constructed in different flanks of the volcano. This special source, which in our case can be fired every two minutes, produces a repeatable, identical source signal. Using this source the number of receiver locations is not limited by the number of seismometers. The seismometers can be moved to various receiver locations while the source reproduces the same source signal. Additionally, at each receiver location we are able to record the identical source signal several times so that the disadvantage of the lower energy compared to an explosion source can be reduced by skipping disturbed signals and stacking several recordings.

Seismic, magnetic, and geotechnical properties of a landslide and clinker deposits, Powder River basin, Wyoming and Montana

Science.gov (United States)

Miller, C.H.

1979-01-01

Exploitation of vast coal and other resources in the Powder River Basin has caused recent, rapid increases in population and in commercial and residential development and has prompted land utilization studies. Two aspects of land utilization were studied for this report: (1) the seismic and geotechnical properties of a landslide and (2) the seismic, magnetic, and geotechnical properties of clinker deposits. (1) The landslide seismic survey revealed two layers in the slide area. The upper (low-velocity) layer is a relatively weak mantle of colluvium and unconsolidated and weathered bedrock that ranges in thickness from 3.0 to 7.5 m and has an average seismic velocity of about 390 m/s. It overlies high-velocity, relatively strong sedimentary bedrock that has velocities greater than about 1330 m/s. The low-velocity layer is also present at the other eight seismic refraction sites in the basin; a similar layer has also been reported in the Soviet Union in a landslide area over similar bedrock. The buried contact of the low- and high-velocity layers is relatively smooth and is nearly parallel with the restored topographic surface. There is no indication that any of the high-velocity layer (bedrock) has been displaced or removed. The seismic data also show that the shear modulus of the low-velocity layer is only about one-tenth that of the high-velocity layer and the shear strength (at failure) is only about one-thirtieth. Much of the slide failure is clearly in the shear mode, and failure is, therefore, concluded to be confined to the low-velocity layer. The major immediate factor contributing to landslide failure is apparently the addition of moisture to the low-velocity layer. The study implies that the low-velocity layer can be defined over some of the basin by seismic surveys and that they can help predict or delineate potential slides. Preventative actions that could then be taken include avoidance, dewatering, prevention of saturation, buttressing the toe, and

Superresolution Imaging Using Resonant Multiples and Plane-wave Migration Velocity Analysis

KAUST Repository

Guo, Bowen

2017-08-28

Seismic imaging is a technique that uses seismic echoes to map and detect underground geological structures. The conventional seismic image has the resolution limit of λ/2, where λ is the wavelength associated with the seismic waves propagating in the subsurface. To exceed this resolution limit, this thesis develops a new imaging method using resonant multiples, which produces superresolution images with twice or even more the spatial resolution compared to the conventional primary reflection image. A resonant multiple is defined as a seismic reflection that revisits the same subsurface location along coincident reflection raypath. This reverberated raypath is the reason for superresolution imaging because it increases the differences in reflection times associated with subtle changes in the spatial location of the reflector. For the practical implementation of superresolution imaging, I develop a post-stack migration technique that first enhances the signal-to-noise ratios (SNRs) of resonant multiples by a moveout-correction stacking method, and then migrates the post-stacked resonant multiples with the associated Kirchhoff or wave-equation migration formula. I show with synthetic and field data examples that the first-order resonant multiple image has about twice the spatial resolution compared to the primary reflection image. Besides resolution, the correct estimate of the subsurface velocity is crucial for determining the correct depth of reflectors. Towards this goal, wave-equation migration velocity analysis (WEMVA) is an image-domain method which inverts for the velocity model that maximizes the similarity of common image gathers (CIGs). Conventional WEMVA based on subsurface-offset, angle domain or time-lag CIGs requires significant computational and memory resources because it computes higher dimensional migration images in the extended image domain. To mitigate this problem, I present a new WEMVA method using plane-wave CIGs. Plane-wave CIGs reduce the

Seismic imaging for an ocean drilling site survey and its verification in the Izu rear arc

Science.gov (United States)

Yamashita, Mikiya; Takahashi, Narumi; Tamura, Yoshihiko; Miura, Seiichi; Kodaira, Shuichi

2018-01-01

To evaluate the crustal structure of a site proposed for International Ocean Discovery Program drilling, the Japan Agency for Marine-Earth Science and Technology carried out seismic surveys in the Izu rear arc between 2006 and 2008, using research vessels Kaiyo and Kairei. High-resolution dense grid surveys, consisting of three kinds of reflection surveys, generated clear seismic profiles, together with a seismic velocity image obtained from a seismic refraction survey. In this paper, we compare the seismic profiles with the geological column obtained from the drilling. Five volcaniclastic sedimentary units were identified in seismic reflection profiles above the 5 km/s and 6 km/s contours of P-wave velocity obtained from the velocity image from the seismic refraction survey. However, some of the unit boundaries interpreted from the seismic images were not recognised in the drilling core, highlighting the difficulties of geological target identification in volcanic regions from seismic images alone. The geological core derived from drilling consisted of seven lithological units (labelled I to VII). Units I to V were aged at 0-9 Ma, and units VI and VII, from 1320-1806.5 m below seafloor (mbsf) had ages from 9 to ~15 Ma. The strong heterogeneity of volcanic sediments beneath the drilling site U1437 was also identified from coherence, calculated using cross-spectral analysis between grid survey lines. Our results suggest that use of a dense grid configuration is important in site surveys for ocean drilling in volcanic rear-arc situations, in order to recognise heterogeneous crustal structure, such as sediments from different origins.

Reservoir Changes Derived from Seismic Observations at The Geysers Geothermal Field, CA, USA

Science.gov (United States)

Gritto, R.; Jarpre, S.

2012-04-01

Induced seismicity associated with the exploitation of geothermal fields is used as a tool to characterize and delineate changes associated with injection and production of fluids from the reservoir. At the same time public concern of felt seismicity has led to objections against the operation of geothermal reservoirs in close proximity to population centers. Production at the EGS sites in Basel (Switzerland) was stopped after renewed seismicity caused concern and objection from the public in the city. Operations in other geothermal reservoirs had to be scaled back or interrupted due to an unexpected increase in seismicity (Soultz-sous-forêt, France, Berlín, El Salvador). As a consequence of these concerns and in order to optimize the use of induced seismicity for reservoir engineering purposes, it becomes imperative to understand the relationship between seismic events and stress changes in the reservoir. We will address seismicity trends at The Geysers Geothermal Reservoir, CA USA, to understand the role of historical seismicity associated with past injection of water and/or production of steam. Our analysis makes use of a comprehensive database of earthquakes and associated phase arrivals from 2004 to 2011. A high-precision sub-set of the earthquake data was selected to analyze temporal changes in seismic velocities and Vp/Vs-ratio throughout the whole reservoir. We find relatively low Vp/Vs values in 2004 suggestive of a vapor dominated reservoir. With passing time, however, the observed temporal increase in Vp/Vs, coupled with a decrease in P- and S-wave velocities suggests the presence of fluid-filled fractured rock. Considering the start of a continuous water injection project in 2004, it can be concluded that the fluid saturation of the reservoir has successfully recovered. Preliminary results of 3-D velocity inversions of seismic data appear to corroborate earlier findings that the lowest Vp/Vs estimates are observed in the center of the reservoir

The roles of texture and microstructure for seismic properties and anisotropy of the continental crust

Science.gov (United States)

Almqvist, B. S. G.; Mainprice, D.

2017-12-01

New seismic methods provide images of the continental crust with improved resolution, carrying unique information on the structure and mass transfer regimes within the crust. At the intrinsic scale components contributing to these images are grains and the microfabric, which includes information on grain characteristics. At the extrinsic scale the presence of micro-cracks, fractures and layering are important in controlling seismic velocities. Although the wavelength of a seismic wave is orders of magnitude larger than the intrinsic scale the minerals and microstructures, the interpretations of seismic images are critically dependent on our understanding and quantification of these microscopic constituents. This contribution explores the role of texture and microstructure in governing seismic properties of rocks. We focus on prediction of seismic velocities based on calculations that take into account mineral composition and microfabric of rocks. Emphasis is placed on recent developments in modeling efforts and analytical techniques, which can consider microfabric parameters such as crystallographic preferred orientation (CPO), grain shape, layering and elastic interaction among grains. Static schemes that use Christoffel's equation, and active/dynamic wave propagation methods provide the general techniques to predict seismic velocities. Single crystal elastic constants are essential in predicting seismic properties. However, the database is incomplete considering the variation of crustal mineralogy and lack of data at elevated pressure and temperature conditions occurring in the middle and lower crust. Finally, the method used to measure CPO and microstructure data has an influence on model predictions. Neutron and X-ray goniometry techniques enable investigation of CPO for large sample volumes, but lack other microstructural information. In contrast, electron backscatter diffraction provides data on both CPO and microstructure, but for a relatively small sample

Seismic moment tensor inversion using 3D velocity model and its application to the 2013 Lushan earthquake sequence

Science.gov (United States)

Zhu, Lupei; Zhou, Xiaofeng

2016-10-01

Source inversion of small-magnitude events such as aftershocks or mine collapses requires use of relatively high frequency seismic waveforms which are strongly affected by small-scale heterogeneities in the crust. In this study, we developed a new inversion method called gCAP3D for determining general moment tensor of a seismic source using Green's functions of 3D models. It inherits the advantageous features of the ;Cut-and-Paste; (CAP) method to break a full seismogram into the Pnl and surface-wave segments and to allow time shift between observed and predicted waveforms. It uses grid search for 5 source parameters (relative strengths of the isotropic and compensated-linear-vector-dipole components and the strike, dip, and rake of the double-couple component) that minimize the waveform misfit. The scalar moment is estimated using the ratio of L2 norms of the data and synthetics. Focal depth can also be determined by repeating the inversion at different depths. We applied gCAP3D to the 2013 Ms 7.0 Lushan earthquake and its aftershocks using a 3D crustal-upper mantle velocity model derived from ambient noise tomography in the region. We first relocated the events using the double-difference method. We then used the finite-differences method and reciprocity principle to calculate Green's functions of the 3D model for 20 permanent broadband seismic stations within 200 km from the source region. We obtained moment tensors of the mainshock and 74 aftershocks ranging from Mw 5.2 to 3.4. The results show that the Lushan earthquake is a reverse faulting at a depth of 13-15 km on a plane dipping 40-47° to N46° W. Most of the aftershocks occurred off the main rupture plane and have similar focal mechanisms to the mainshock's, except in the proximity of the mainshock where the aftershocks' focal mechanisms display some variations.

Seismic isolation of nuclear power plants using sliding isolation bearings

Science.gov (United States)

Kumar, Manish

Nuclear power plants (NPP) are designed for earthquake shaking with very long return periods. Seismic isolation is a viable strategy to protect NPPs from extreme earthquake shaking because it filters a significant fraction of earthquake input energy. This study addresses the seismic isolation of NPPs using sliding bearings, with a focus on the single concave Friction Pendulum(TM) (FP) bearing. Friction at the sliding surface of an FP bearing changes continuously during an earthquake as a function of sliding velocity, axial pressure and temperature at the sliding surface. The temperature at the sliding surface, in turn, is a function of the histories of coefficient of friction, sliding velocity and axial pressure, and the travel path of the slider. A simple model to describe the complex interdependence of the coefficient of friction, axial pressure, sliding velocity and temperature at the sliding surface is proposed, and then verified and validated. Seismic hazard for a seismically isolated nuclear power plant is defined in the United States using a uniform hazard response spectrum (UHRS) at mean annual frequencies of exceedance (MAFE) of 10-4 and 10 -5. A key design parameter is the clearance to the hard stop (CHS), which is influenced substantially by the definition of the seismic hazard. Four alternate representations of seismic hazard are studied, which incorporate different variabilities and uncertainties. Response-history analyses performed on single FP-bearing isolation systems using ground motions consistent with the four representations at the two shaking levels indicate that the CHS is influenced primarily by whether the observed difference between the two horizontal components of ground motions in a given set is accounted for. The UHRS at the MAFE of 10-4 is increased by a design factor (≥ 1) for conventional (fixed base) nuclear structure to achieve a target annual frequency of unacceptable performance. Risk oriented calculations are performed for

South Ilan Plain High-Resolution 3-D S-Wave Velocity from Ambient Noise Tomography

Directory of Open Access Journals (Sweden)

Kai-Xun Chen

2016-06-01

Full Text Available The Ilan Plain in northeastern Taiwan is located at a pivotal point where the Ryukyu trench subduction zone, the northern Taiwan crustal stretching zone, and the ongoing arc-continent collision zone converge. In contrast to the North Ilan Plain, the South Ilan Plain exhibits a thin unconsolidated sedimentary layer with depths ranging from 0 - 1 km, high on-land seismicity and significant SE movements relative to Penghu island. We deployed a dense network of 43 short-period vertical component Texan instruments from June to November 2013 in this study, covering most of the South Ilan Plain and its vicinity. We then used the ambient noise tomography method for simultaneous phase and group Rayleigh wave velocity measurements to invert a high-resolution 3-D S-wave for shallow structures (up to a depth of 2.5 km in the South Ilan Plain. We used the fast marching method for ray tracing to deal with ray bending in an inhomogeneous medium. The resulting rays gradually bend toward high velocity zones with increasing number of iterations. The high velocity zone results are modified by more iterations and the resolutions become higher because ray crossings are proportional to ray densities for evenly distributed stations. The final results agreed well with known sedimentary basement thickness patterns. We observed nearly EW trending fast anomalies beneath the mountainous terrain abutting to the South Ilan Plain. The Chingshui location consistently exhibited a low S-wave velocity zone to a depth of 1.5 km.

Joint Inversion of Direct Current Resistivity and Seismic Refraction Data

International Nuclear Information System (INIS)

Kurt, B.B.

2007-01-01

In this study, I assumed the underground consist of horizontal layers. I developed one-dimensional (1D) Direct Current Resistivity (DCR) and seismic refraction inversion code using MATLAB package and attempt to find velocity, resistivity and depth of the layers. The code uses damped least square technique. The code can do inversion on DCR and seismic data either individually or jointly. I tested the joint inversion code on synthetic data. Eventually, I saw that the result of joint inversion is better than the result of individual inversions. The joint inversion found depth of models of each layer and, in addition, velocity and resistivity closer to real values

Slab dehydration in Cascadia and its relationship to volcanism, seismicity, and non-volcanic tremor

Science.gov (United States)

Delph, J. R.; Levander, A.; Niu, F.

2017-12-01

The characteristics of subduction beneath the Pacific Northwest (Cascadia) are variable along strike, leading to the segmentation of Cascadia into 3 general zones: Klamath, Siletzia, and Wrangelia. These zones show marked differences in tremor density, earthquake density, seismicity rates, and the locus and amount of volcanism in the subduction-related volcanic arc. To better understand what controls these variations, we have constructed a 3D shear-wave velocity model of the upper 80 km along the Cascadia margin from the joint inversion of CCP-derived receiver functions and ambient noise surface wave data using 900 temporary and permanent broadband seismic stations. With this model, we can investigate variations in the seismic structure of the downgoing oceanic lithosphere and overlying mantle wedge, the character of the crust-mantle transition beneath the volcanic arc, and local to regional variations in crustal structure. From these results, we infer the presence and distribution of fluids released from the subducting slab and how they affect the seismic structure of the overriding lithosphere. In the Klamath and Wrangelia zones, high seismicity rates in the subducting plate and high tremor density correlate with low shear velocities in the overriding plate's forearc and relatively little arc volcanism. While the cause of tremor is debated, intermediate depth earthquakes are generally thought to be due to metamorphic dehydration reactions resulting from the dewatering of the downgoing slab. Thus, the seismic characteristics of these zones combined with rather sparse arc volcanism may indicate that the slab has largely dewatered by the time it reaches sub-arc depths. Some of the water released during earthquakes (and possibly tremor) may percolate into the overriding plate, leading to slow seismic velocities in the forearc. In contrast, Siletzia shows relatively low seismicity rates and tremor density, with relatively higher shear velocities in the forearc

Study of seismic design bases and site conditions for nuclear power plants

International Nuclear Information System (INIS)

1980-04-01

This report presents the results of an investigation of four topics pertinent to the seismic design of nuclear power plants: Design accelerations by regions of the continental United States; review and compilation of design-basis seismic levels and soil conditions for existing nuclear power plants; regional distribution of shear wave velocity of foundation materials at nuclear power plant sites; and technical review of surface-founded seismic analysis versus embedded approaches

Study of seismic design bases and site conditions for nuclear power plants

Energy Technology Data Exchange (ETDEWEB)

1980-04-01

This report presents the results of an investigation of four topics pertinent to the seismic design of nuclear power plants: Design accelerations by regions of the continental United States; review and compilation of design-basis seismic levels and soil conditions for existing nuclear power plants; regional distribution of shear wave velocity of foundation materials at nuclear power plant sites; and technical review of surface-founded seismic analysis versus embedded approaches.

The Augustine magmatic system as revealed by seismic tomography and relocated earthquake hypocenters from 1994 through 2009

Science.gov (United States)

Syracuse, E.M.; Thurber, C.H.; Power, J.A.

2011-01-01

We incorporate 14 years of earthquake data from the Alaska Volcano Observatory with data from a 1975 controlled-source seismic experiment to obtain the three-dimensional P and S wave velocity structure and the first high-precision earthquake locations at Augustine Volcano to be calculated in a fully three-dimensional velocity model. Velocity tomography shows two main features beneath Augustine: a narrow, high-velocity column beneath the summit, extending from ???2 km depth to the surface, and elevated velocities on the south flank. Our relocation results allow a thorough analysis of the spatio-temoral patterns of seismicity and the relationship to the magmatic and eruptive activity. Background seismicity is centered beneath the summit at an average depth of 0.6 km above sea level. In the weeks leading to the January 2006 eruption of Augustine, seismicity focused on a NW-SE line along the trend of an inflating dike. A series of drumbeat earthquakes occurred in the early weeks of the eruption, indicating further magma transport through the same dike system. During the six months following the onset of the eruption, the otherwise quiescent region 1 to 5 km below sea level centered beneath the summit became seismically active with two groups of earthquakes, differentiated by frequency content. The deep longer-period earthquakes occurred during the eruption and are interpreted as resulting from the movement of magma toward the summit, and the post-eruptive shorter-period earthquakes may be due to the relaxation of an emptied magma tube. The seismicity subsequently returned to its normal background rates and patterns. Copyright 2011 by the American Geophysical Union.

Improving fault image by determination of optimum seismic survey parameters using ray-based modeling

Science.gov (United States)

Saffarzadeh, Sadegh; Javaherian, Abdolrahim; Hasani, Hossein; Talebi, Mohammad Ali

2018-06-01

In complex structures such as faults, salt domes and reefs, specifying the survey parameters is more challenging and critical owing to the complicated wave field behavior involved in such structures. In the petroleum industry, detecting faults has become crucial for reservoir potential where faults can act as traps for hydrocarbon. In this regard, seismic survey modeling is employed to construct a model close to the real structure, and obtain very realistic synthetic seismic data. Seismic modeling software, the velocity model and parameters pre-determined by conventional methods enable a seismic survey designer to run a shot-by-shot virtual survey operation. A reliable velocity model of structures can be constructed by integrating the 2D seismic data, geological reports and the well information. The effects of various survey designs can be investigated by the analysis of illumination maps and flower plots. Also, seismic processing of the synthetic data output can describe the target image using different survey parameters. Therefore, seismic modeling is one of the most economical ways to establish and test the optimum acquisition parameters to obtain the best image when dealing with complex geological structures. The primary objective of this study is to design a proper 3D seismic survey orientation to achieve fault zone structures through ray-tracing seismic modeling. The results prove that a seismic survey designer can enhance the image of fault planes in a seismic section by utilizing the proposed modeling and processing approach.

Homogenization of Electromagnetic and Seismic Wavefields for Joint Inverse Modeling

Science.gov (United States)

Newman, G. A.; Commer, M.; Petrov, P.; Um, E. S.

2011-12-01

A significant obstacle in developing a robust joint imaging technology exploiting seismic and electromagnetic (EM) wave fields is the resolution at which these different geophysical measurements sense the subsurface. Imaging of seismic reflection data is an order of magnitude finer in resolution and scale compared to images produced with EM data. A consistent joint image of the subsurface geophysical attributes (velocity, electrical conductivity) requires/demands the different geophysical data types be similar in their resolution of the subsurface. The superior resolution of seismic data results from the fact that the energy propagates as a wave, while propagation of EM energy is diffusive and attenuates with distance. On the other hand, the complexity of the seismic wave field can be a significant problem due to high reflectivity of the subsurface and the generation of multiple scattering events. While seismic wave fields have been very useful in mapping the subsurface for energy resources, too much scattering and too many reflections can lead to difficulties in imaging and interpreting seismic data. To overcome these obstacles a formulation for joint imaging of seismic and EM wave fields is introduced, where each data type is matched in resolution. In order to accomplish this, seismic data are first transformed into the Laplace-Fourier Domain, which changes the modeling of the seismic wave field from wave propagation to diffusion. Though high frequency information (reflectivity) is lost with this transformation, several benefits follow: (1) seismic and EM data can be easily matched in resolution, governed by the same physics of diffusion, (2) standard least squares inversion works well with diffusive type problems including both transformed seismic and EM, (3) joint imaging of seismic and EM data may produce better starting velocity models critical for successful reverse time migration or full waveform imaging of seismic data (non transformed) and (4

Heterogeneous Structure and Seismicity beneath the Tokyo Metropolitan Area

Science.gov (United States)

Nakagawa, S.; Kato, A.; Sakai, S.; Nanjo, K.; Panayotopoulos, Y.; Kurashimo, E.; Obara, K.; Kasahara, K.; Aketagawa, T.; Kimura, H.; Hirata, N.

2010-12-01

Beneath the Tokyo metropolitan area, the Philippine Sea Plate (PSP) subducts and causes damaged mega-thrust earthquakes. Sato et al. (2005) revealed the geometry of upper surface of PSP, and Hagiwara et al. (2006) estimated the velocity structure beneath Boso peninsula. However, these results are not sufficient for the assessment of the entire picture of the seismic hazards beneath the Tokyo metropolitan area including those due to an intra-slab M7+ earthquake. So, we launched the Special Project for Earthquake Disaster Mitigation in the Tokyo Metropolitan area (Hirata et al., 2009). Proving the more detailed geometry and physical properties (e.g. velocities, densities, attenuation) and stress field within PSP is very important to attain this issue. The core item of this project is a dense seismic array called Metropolitan Seismic Observation network (MeSO-net) for making observations in the metropolitan area (Sakai and Hirata, 2009; Kasahara et al., 2009). We deployed the 249 seismic stations with a spacing of 5 km. Some parts of stations construct 5 linear arrays at interval of 2 km such as Tsukuba-Fujisawa (TF) array, etc. The TF array runs from northeast to southwest through the center of Tokyo. In this study, we applied the tomography method to image the heterogeneous structure under the Tokyo metropolitan area. We selected events from the Japan Meteorological Agency (JMA) unified earthquake list. All data of MeSO-net were edited into event data by the selected JMA unified earthquake list. We picked the P and S wave arrival times. The total number of stations and events are 421 and 1,256, respectively. Then, we applied the double-difference tomography method (Zhang and Thurber, 2003) to this dataset and estimated the fine-scale velocity structure. The grid nodes locate 10 km interval in parallel with the array, 20 km interval in perpendicular to the array; and on depth direction, 5 km interval to a depth of less than 50 km and 10 km interval at a depth of more

New Insights on the Structure of the Cascadia Subduction Zone from Amphibious Seismic Data

Science.gov (United States)

Janiszewski, Helen Anne

A new onshore-offshore seismic dataset from the Cascadia subduction zone was used to characterize mantle lithosphere structure from the ridge to the volcanic arc, and plate interface structure offshore within the seismogenic zone. The Cascadia Initiative (CI) covered the Juan de Fuca plate offshore the northwest coast of the United States with an ocean bottom seismometer (OBS) array for four years; this was complemented by a simultaneous onshore seismic array. Teleseismic data recorded by this array allows the unprecedented imaging of an entire tectonic plate from its creation at the ridge through subduction initiation and back beyond the volcanic arc along the entire strike of the Cascadia subduction zone. Higher frequency active source seismic data also provides constraints on the crustal structure along the plate interface offshore. Two seismic datasets were used to image the plate interface structure along a line extending 100 km offshore central Washington. These are wide-angle reflections from ship-to-shore seismic data from the Ridge-To-Trench seismic cruise and receiver functions calculated from a densely spaced CI OBS focus array in a similar region. Active source seismic observations are consistent with reflections from the plate interface offshore indicating the presence of a P-wave velocity discontinuity. Until recently, there has been limited success in using the receiver function technique on OBS data. I avoid these traditional challenges by using OBS constructed with shielding deployed in shallow water on the continental shelf. These data have quieter horizontals and avoid water- and sediment-multiple contamination at the examined frequencies. The receiver functions are consistently modeled with a velocity structure that has a low velocity zone (LVZ) with elevated P to S-wave velocity ratios at the plate interface. A similar LVZ structure has been observed onshore and interpreted as a combination of elevated pore-fluid pressures or metasediments

Global seismic inversion as the next standard step in the processing sequence

Energy Technology Data Exchange (ETDEWEB)

Maver, Kim G.; Hansen, Lars S.; Jepsen, Anne-Marie; Rasmussen, Klaus B.

1998-12-31

Seismic inversion of post stack seismic data has until recently been regarded as a reservoir oriented method since the standard inversion techniques rely on extensive well control and a detailed user derived input model. Most seismic inversion techniques further requires a stable wavelet. As a consequence seismic inversion is mainly utilised in mature areas focusing of specific zones only after the seismic data has been interpreted and is well understood. By using an advanced 3-D global technique, seismic inversion is presented as the next standard step in the processing sequence. The technique is robust towards noise within the seismic data, utilizes a time variant wavelet, and derives a low frequency model utilizing the stacking velocities and only limited well control. 4 figs.

The seismic cycle at subduction thrusts: 1. Insights from laboratory models

KAUST Repository

Corbi, F.; Funiciello, F.; Moroni, M.; van Dinther, Y.; Mai, Paul Martin; Dalguer, L. A.; Faccenna, C.

2013-01-01

Subduction megathrust earthquakes occur at the interface between the subducting and overriding plates. These hazardous phenomena are only partially understood because of the absence of direct observations, the restriction of the instrumental seismic record to the past century, and the limited resolution/completeness of historical to geological archives. To overcome these restrictions, modeling has become a key-tool to study megathrust earthquakes. We present a novel model to investigate the seismic cycle at subduction thrusts using complementary analog (paper 1) and numerical (paper 2) approaches. Here we introduce a simple scaled gelatin-on-sandpaper setup including realistic tectonic loading, spontaneous rupture nucleation, and viscoelastic response of the lithosphere. Particle image velocimetry allows to derive model deformation and earthquake source parameters. Analog earthquakes are characterized by “quasi-periodic” recurrence. Consistent with elastic theory, the interseismic stage shows rearward motion, subsidence in the outer wedge and uplift of the “coastal area” as a response of locked plate interface at shallow depth. The coseismic stage exhibits order of magnitude higher velocities and reversal of the interseismic deformation pattern in the seaward direction, subsidence of the coastal area, and uplift in the outer wedge. Like natural earthquakes, analog earthquakes generally nucleate in the deeper portion of the rupture area and preferentially propagate upward in a crack-like fashion. Scaled rupture width-slip proportionality and seismic moment-duration scaling verifies dynamic similarities with earthquakes. Experimental repeatability is statistically verified. Comparing analog results with natural observations, we conclude that this technique is suitable for investigating the parameter space influencing the subduction interplate seismic cycle.

The seismic cycle at subduction thrusts: 1. Insights from laboratory models

KAUST Repository

Corbi, F.

2013-04-01

Subduction megathrust earthquakes occur at the interface between the subducting and overriding plates. These hazardous phenomena are only partially understood because of the absence of direct observations, the restriction of the instrumental seismic record to the past century, and the limited resolution/completeness of historical to geological archives. To overcome these restrictions, modeling has become a key-tool to study megathrust earthquakes. We present a novel model to investigate the seismic cycle at subduction thrusts using complementary analog (paper 1) and numerical (paper 2) approaches. Here we introduce a simple scaled gelatin-on-sandpaper setup including realistic tectonic loading, spontaneous rupture nucleation, and viscoelastic response of the lithosphere. Particle image velocimetry allows to derive model deformation and earthquake source parameters. Analog earthquakes are characterized by “quasi-periodic” recurrence. Consistent with elastic theory, the interseismic stage shows rearward motion, subsidence in the outer wedge and uplift of the “coastal area” as a response of locked plate interface at shallow depth. The coseismic stage exhibits order of magnitude higher velocities and reversal of the interseismic deformation pattern in the seaward direction, subsidence of the coastal area, and uplift in the outer wedge. Like natural earthquakes, analog earthquakes generally nucleate in the deeper portion of the rupture area and preferentially propagate upward in a crack-like fashion. Scaled rupture width-slip proportionality and seismic moment-duration scaling verifies dynamic similarities with earthquakes. Experimental repeatability is statistically verified. Comparing analog results with natural observations, we conclude that this technique is suitable for investigating the parameter space influencing the subduction interplate seismic cycle.

Seismic Fracture Characterization Methodologies for Enhanced Geothermal Systems

Energy Technology Data Exchange (ETDEWEB)

Queen, John H. [Hi-Geophysical, Inc., Ponca, OK (United States)

2016-05-09

Executive Summary The overall objective of this work was the development of surface and borehole seismic methodologies using both compressional and shear waves for characterizing faults and fractures in Enhanced Geothermal Systems. We used both surface seismic and vertical seismic profile (VSP) methods. We adapted these methods to the unique conditions encountered in Enhanced Geothermal Systems (EGS) creation. These conditions include geological environments with volcanic cover, highly altered rocks, severe structure, extreme near surface velocity contrasts and lack of distinct velocity contrasts at depth. One of the objectives was the development of methods for identifying more appropriate seismic acquisition parameters for overcoming problems associated with these geological factors. Because temperatures up to 300º C are often encountered in these systems, another objective was the testing of VSP borehole tools capable of operating at depths in excess of 1,000 m and at temperatures in excess of 200º C. A final objective was the development of new processing and interpretation techniques based on scattering and time-frequency analysis, as well as the application of modern seismic migration imaging algorithms to seismic data acquired over geothermal areas. The use of surface seismic reflection data at Brady's Hot Springs was found useful in building a geological model, but only when combined with other extensive geological and geophysical data. The use of fine source and geophone spacing was critical in producing useful images. The surface seismic reflection data gave no information about the internal structure (extent, thickness and filling) of faults and fractures, and modeling suggests that they are unlikely to do so. Time-frequency analysis was applied to these data, but was not found to be significantly useful in their interpretation. Modeling does indicate that VSP and other seismic methods with sensors located at depth in wells will be the most

Georgia-Armenia Transboarder seismicity studies

Science.gov (United States)

Godoladze, T.; Tvaradze, N.; Javakishvili, Z.; Elashvili, M.; Durgaryan, R.; Arakelyan, A.; Gevorgyan, M.

2012-12-01

In the presented study we performed Comprehensive seismic analyses for the Armenian-Georgian transboarder active seismic fault starting on Armenian territory, cutting the state boarder and having possibly northern termination on Adjara-Triealeti frontal structure in Georgia. In the scope of International projects: ISTC A-1418 "Open network of scientific Centers for mitigation risk of natural hazards in the Southern Caucasus and Central Asia" and NATO SfP- 983284 Project "Caucasus Seismic Emergency Response" in Akhalkalaki (Georgia) seismic center, Regional Summer school trainings and intensive filed investigations were conducted. Main goal was multidisciplinary study of the Javakheti fault structure and better understanding seismicity of the area. Young scientists from Turkey, Armenia, Azerbaijan and Georgia were participated in the deployment of temporal seismic network in order to monitor seisimity on the Javakheti highland and particularly delineate fault scarf and identify active seismic structures. In the scope of international collaboration the common seismic database has been created in the southern Caucasus and collected data from the field works is available now online. Javakheti highland, which is located in the central part of the Caucasus, belongs to the structure of the lesser Caucasus and represents a history of neotectonic volcanism existed in the area. Jasvakheti highland is seismicalu active region devastating from several severe earthquakes(1088, 1283, 1899…). Hypocenters located during analogue network were highly scattered and did not describe real pattern of seismicity of the highland. We relocated hypocenters of the region and improved local velocity model. The hypocenters derived from recently deployed local seismic network in the Javakheti highland, clearly identified seismically active structures. Fault plane solutions of analogue data of the Soviet times have been carefully analyzed and examined. Moment tensor inversion were preformed

Seismic monitoring at the Decatur, Ill., CO2 sequestration demonstration site

Science.gov (United States)

Kaven, Joern; Hickman, Stephen H.; McGarr, Arthur F.; Walter, Steve R.; Ellsworth, William L.

2014-01-01

The viability of carbon capture and storage (CCS) to reduce emissions of greenhouse gases depends on the ability to safely sequester large quantities of CO2 over geologic time scales. One concern with CCS is the potential of induced seismicity. We report on ongoing seismic monitoring by the U.S. Geological Survey (USGS) at a CCS demonstration site in Decatur, IL, in an effort to understand the potential hazards posed by injection-induced seismicity associated with geologic CO2 sequestration. At Decatur, super-critical CO2 is injected at 2.1 km depth into the 550-m-thick Mt. Simon Sandstone, which directly overlies granitic basement. The primary sealing cap rock is the Eau Claire Shale, a 100- to 150-m-thick unit at a depth of roughly 1.5 km. The USGS seismic network consists of 12 stations, three of which have surface accelerometers and three-component borehole geophones. We derived a one-dimensional velocity models from a vertical seismic profile acquired by Archer-Daniels-Midland (ADM) and the Illinois State Geological Survey (ISGS) to a depth of 2.2 km, tied into shallow acoustic logs from our borehole stations and assuming a 6 km/sec P-wave velocity for granite below 2.2 km. We further assume a constant ratio of P- to S-wave velocities of 1.83, as derived from velocity model inversions. We use this velocity model to locate seismic events, all of which are within the footprint of our network. So far magnitudes of locatable events range from Mw = -1.52 to 1.07. We further improved the hypocentral precision of microseismic events when travel times and waveforms are sufficiently similar by employing double-difference relocation techniques, with relative location errors less than 80 m horizontally and 100 m vertically. We observe tend to group in three distinct clusters: ∼0.4 to 1.0 km NE, 1.6 to 2.4 km N, and ∼1.8 to 2.6 km WNW from the injection well. The first cluster of microseismicity forms a roughly linear trend, which may represent a pre-existing geologic

Monitoring Seasonal Changes in Permafrost Using Seismic Interferometry

Science.gov (United States)

James, S. R.; Knox, H. A.; Abbott, R. E.

2015-12-01

The effects of climate change in polar regions and their incorporation in global climate models has recently become an area of great interest. Permafrost holds entrapped greenhouse gases, e.g. CO2 and CH4, which are released to the atmosphere upon thawing, creating a positive feedback mechanism. Knowledge of seasonal changes in active layer thickness as well as long term degradation of permafrost is critical to the management of high latitude infrastructures, hazard mitigation, and increasing the accuracy of climate predictions. Methods for effectively imaging the spatial extent, depth, thickness, and discontinuous nature of permafrost over large areas are needed. Furthermore, continuous monitoring of permafrost over annual time scales would provide valuable insight into permafrost degradation. Seismic interferometry using ambient seismic noise has proven effective for recording velocity changes within the subsurface for a variety of applications, but has yet to be applied to permafrost studies. To this end, we deployed 7 Nanometrics Trillium posthole broadband seismometers within Poker Flat Research Range, located 30 miles north of Fairbanks, Alaska in a zone of discontinuous permafrost. Approximately 2 years worth of nearly continuous ambient noise data was collected. Using the python package MSNoise, relative changes in velocity were calculated. Results show high amounts of variability throughout the study period. General trends of negative relative velocity shifts can be seen between August and October followed by a positive relative velocity shift between November and February. Differences in relative velocity changes with both frequency and spatial location are also observed, suggesting this technique is sensitive to permafrost variation with depth and extent. Overall, short and long term changes in shallow subsurface velocity can be recovered using this method proposing seismic interferometry is a promising new technique for permafrost monitoring. Sandia

MASW Seismic Method in Brebu Landslide Area, Romania

Science.gov (United States)

Mihai, Marinescu; Paul, Cristea; Cristian, Marunteanu; Matei, Mezincescu

2017-12-01

This paper is focused on assessing the possibility of enhancing the geotechnical information in perimeters with landslides, especially through applications of the Multichannel Analysis of Surface Waves (MASW) method. The technology enables the determination of the phase velocities of Rayleigh waves and, recursively, the evaluation of shear wave velocities (Vs) related to depth. Finally, using longitudinal wave velocities (Vp), derived from the seismic refraction measurements, in situ dynamic elastic properties in a shallow section can be obtained. The investigation was carried out in the Brebu landslide (3-5 m depth of bedrock), located on the southern flank of the Slanic Syncline (110 km North of Bucharest) and included a drilling program and geotechnical laboratory observations. The seismic refraction records (seismic sources placed at the centre, ends and outside of the geophone spread) have been undertaken on two lines, 23 m and 46 m long respectively) approximately perpendicular to the downslope direction of the landslide and on different local morpho-structures. A Geode Geometrics seismograph was set for 1 ms sampling rate and pulse summations in real-time for five blows. Twenty-four vertical Geometrics SpaceTech geophones (14 Hz resonance frequency) were disposed at 1 m spacing. The seismic source was represented by the impact of an 8kg weight sledge hammer on a metal plate. Regarding seismic data processing, the distinctive feature is related to performing more detailed analyses of MASW records. The proposed procedure consists of the spread split in groups with fewer receivers and several interval-geophones superposed. 2D Fourier analysis, f-k (frequency-wave number) spectrum, for each of these groups assures the information continuity and, all the more, accuracy to pick out the amplitude maximums of the f-k spectra. Finally, combining both values VS (calculated from 2D spectral analyses of Rayleigh waves) and VP (obtained from seismic refraction records

Seismic fragility analysis of a CANDU containment structure for near-fault ground motions

International Nuclear Information System (INIS)

Choi, In Kil; Choun, Young Sun; Seo, Jeong Moon; Ahn, Seong Moon

2005-01-01

The R. G. 1.60 spectrum used for the seismic design of Korean nuclear power plants provides a generally conservative design basis due to its broadband nature. A survey on some of the Quaternary fault segments near Korean nuclear power plants is ongoing. It is likely that these faults will be identified as active ones. If the faults are confirmed as active ones, it will be necessary to reevaluate the seismic safety of the nuclear power plants located near these faults. The probability based scenario earthquakes were identified as near-field earthquakes. In general, the near-fault ground motion records exhibit a distinctive long period pulse like time history with very high peak velocities. These features are induced by the slip of the earthquake fault. Near-fault ground motions, which have caused much of the damage in recent major earthquakes, can be characterized by a pulse-like motion that exposes the structure to a high input energy at the beginning of the motion. It is necessary to estimate the near-fault ground motion effects on the nuclear power plant structures and components located near the faults. In this study, the seismic fragility analysis of a CANDU containment structure was performed based on the results of nonlinear dynamic time-history analyses

A multi-offset vertical profiling (VSP) experiment for anisotropy analysis and imaging

Energy Technology Data Exchange (ETDEWEB)

Grech, G. K.; Lawton, D. [Calgary Univ., AB (Canada)

2000-09-01

Vertical seismic profiling (VSP) and surface seismic data are used to image and locate hydrocarbon targets in the subsurface, hence the importance of assessing which formations exhibit seismic velocity anisotropy and quantify their parameters for use during seismic imaging. The purpose of the experiments described in this paper was to determine whether the multiple dipping thin shale beds overlying the target area in the Rocky Mountain Foothills in southern Alberta exhibit seismic velocity anisotropy and if so, how this phenomenon affects the image of the underlying target. Traveltime inversion of the first arrival data from the multi-offset VSP in the study area has revealed that the Cretaceous shales exhibit velocity anisotropy of about 10 degrees. For a target depth of 3000 m and moderate dips of 30 to 50 degrees in the anisotropic overburden, it would be reasonable to expect a lateral shift in the imaged location of the target of up to 300 m in the up-direction of overlying bedding. 8 refs., 9 figs.

MIGRATIONS OF RELEASED SEISMIC ENERGY IN VARIOUS GEODYNAMIC CONDITIONS

Directory of Open Access Journals (Sweden)

A. V. Novopashina

2018-01-01

Full Text Available The properties of slow seismic activity migration have been revealed by the space-time analysis of the total earthquake energy (LgEsum. Our study of seismic activity covers the fragments of  the Central Asian, Pacific and Alpine seismic belts: the Baikal rift system (BRS, Russia, the San Andreas fault zone (California, USA, the Christchurch fault (New Zealand, the North and East Anatolian faults (Turkey, the Philippine subduction zone, and the central fragment of the Mid-Atlantic oceanic ridge. The chains of LgEsum clusters mark the propagation of the maximum stresses front in the weaker crust areas, the zones of fault dynamic influence, and the regions of conjugated tectonic structures. The migration process is characterized by a periodicity, changes in direction, and similar modular values of the migration rates within a single fault segment (or a fault zone, which is probably related to the mechanical and rheological crust and upper mantle properties. The data analysis shows that a strong earthquake source may occur at a location wherein the front of seismic activity propagates with periodical changes in direction, and such a source can develop within a period that is multiple of the migration fluctuations, probably associated with the influence of external periodic factors. The main periods of migration fluctuations (2–4 years, and 9–13 years, in different ratios are present in the seismic regimes of different seismic belts. The migration rate, as well as the propagation velocity of the maximum stresses front, directly depends on the velocity of movements between the plates in the region.

Future Seismic Constraints on Mercury's Core Composition

Science.gov (United States)

Knibbe, J. S.; Luginbhuel, S. M.; Rivoldini, A.; Kono, Y.; Van Hoolst, T.; van Westrenen, W.

2018-05-01

The composition of Mercury's large core is strongly linked to the planet's origin and magnetic field generation. We present P-wave velocity measurements for liquid Fe-Si and Fe-S metals. A future seismic mission can constrain the core composition.

Examples of invasive and non-invasive methods for estimation of shear-wave velocity profile in Bucharest

International Nuclear Information System (INIS)

Aldea, A.; Albota, E.; Yamanaka, H.; Fukumoto, S.; Poiata, N.

2007-01-01

The estimation of subsurface shear-wave velocity is of major importance for understanding and modelling site-response and surface ground motion. The shear-wave velocity profile strongly influence the shear-wave part of the seismic motion that proved to be the most damaging one. The improvement of input seismic ground motion for design is one of the long-term objectives within the Japan International Cooperation Agency (JICA) Project in Romania. Two approaches were used: installation of a digital seismic network and soil investigations (in situ and in laboratory). National Center for Seismic Risk Reduction (NCSRR, Romania), the implementing agency of JICA Project, performed these activities in cooperation with Japanese partner institutions, and an efficient know-how transfer was achieved. Between the soil investigation activities, a special importance was given to the estimation of shear-wave velocity profile. The present paper presents results from PS logging tests at NCSRR seismic station sites, and from single-station and array microtremor measurements. Other results from PS logging tests, surface-wave method and in situ and laboratory geotechnical investigations are presented in other papers in these proceedings. In future, a joint-collaborative effort of Romanian institutions may allow an improved characterisation of the soil profile beneath Bucharest. (authors)

Assessment of rock mechanical properties and seismic slope stability in variably weathered layered basalts

Science.gov (United States)

Greenwood, William; Clark, Marin; Zekkos, Dimitrios; Von Voigtlander, Jennifer; Bateman, Julie; Lowe, Katherine; Hirose, Mitsuhito; Anderson, Suzanne; Anderson, Robert; Lynch, Jerome

2016-04-01

, as expected, with a pronounced transition occurring at about 1000 mm/yr MAP. We speculate that relatively stiff, sub-horizontal layers that are interbedded with weathered material, may explain the discrepancy between both lower seismic velocities (in the field and the laboratory) and lower unconfined compressive strength, and the interpreted high strength exhibited by the seismic slope response during the Kiholo Bay earthquake. This observation has important consequences on the type of landslides observed in the 2006 earthquake, as well as the landslides that can be expected in future earthquakes.

Study on Rayleigh Wave Inversion for Estimating Shear-wave Velocity Profile

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T.A. Sanny

2003-05-01

Full Text Available Rayleigh wave or ground roll is a noise in seismic body waves. However, how to use this noise for soil characterization is very interesting since Rayleigh wave phase velocity is a function of compression-wave velocity, shear-wave velocity, density and layer thickness. In layered-medium Rayleigh wave velocity also depends on wavelength or frequency, and this phenomenon is called dispersion. Inversion procedure to get shear-wave velocity profile needs a priori information about the solution of the problem to limit the unknown parameters. The Lagrange multiplier method was used to solve the constrained optimization problems or well known as a smoothing parameter in inversion problems. The advantage of our inversion procedure is that it can guarantee the convergence of solution even though the field data is incomplete, insufficient, and inconsistent. The addition of smoothing parameter can reduce the time to converge. Beside numerical stability, the statistical stability is also involved in inversion procedure. In field experiment we extracted ground roll data from seismic refraction record. The dispersion curves had been constructed by applying f-k analysis and f-k dip filtering. The dispersion curves show the dependence of Rayleigh wave phase velocities in layered media to frequency. The synthetic models also demonstrate the stability and the speed of inversion procedure.

Monitoring a temporal change of seismic velocity in a geothermal reservoir; Chinetsu choryuso hendo ni tomonau jishinha sokudo henka kenshutsu no kokoromi

Energy Technology Data Exchange (ETDEWEB)

Sugihara, M; Nishi, Y; Tosha, T [Geological Survey of Japan, Tsukuba (Japan)

1997-10-22

Data derived at the Kakkonda geothermal area were used to discuss functions of monitoring a temporal change of seismic velocity in geothermal reservoir. The data were selected from about 50 microtremors generated in the vicinity of the area during one year in 1986. Two out of the selected microtremors were earthquakes with a magnitude of 2.7 both accompanying small precursor events. The magnitude of 2.7 may be small under normal definition, but the earthquakes are thought relatively strong because the degree of fracture adjacent to the reservoir is concentrated in a small space. This condition could be a cause of expansion of the fracture zone. The analysis was carried out according what is described by Ratdomopurbo and Poupinet. More specifically, certain time sections were taken on each certain time to fit it with the initial movement time of P-waves on two similar earthquakes, cross spectra were calculated, and phase difference in the two earthquakes was evaluated from the phase spectra. As a result, no distinct change was detected in the velocity. 5 figs.

Advances in crosshole seismic instrumentation for dam safety monitoring

Energy Technology Data Exchange (ETDEWEB)

Anderlini, G.; Anderlini, C. [BC Hydro, Burnaby, BC (Canada); Taylor, R. [RST Instruments Ltd., Coquitlam, BC (Canada)

2009-07-01

Since 1996, crosshole shear wave velocity measurements have been performed annually at the WAC Bennett Dam in order to monitor the performance of the dam core and integrity of the 1997 sinkhole repairs. As the testing showed to be responsive to embankment conditions and capable of detecting subtle changes, the testing program was expanded to include the development of an electrical shear wave source capable of carrying out crosshole seismic testing in Mica and Revelstoke Dams over distances of 100 metres and depths of 250 metres. This paper discussed the development and capabilities of the crosshole seismic instrumentation and presented preliminary results obtained during initial testing. Specific topics that were discussed included conventional crosshole seismic equipment; design basics; description of new crosshole seismic equipment; and automated in-situ crosshole seismic system (ACSS) system description and operation. It was concluded that the ACSS and accompanying electrical shear wave source, developed as part of the project, has advanced and improved on traditional crosshole seismic equipment. 7 refs., 9 figs.

Application of the uphole seismic data in the determination of the ...

African Journals Online (AJOL)

A total of 10 uphole data was acquired and analyzed from a seismic prospecting area of the East-Central Niger Delta, Nigeria. The thickness and velocity of the low velocity layer (LVL) was determined. Refraction statics was computed automatically from first break picks using CGG's SDITR interactive programme.

Seismic Velocity Structure of the Pacific Upper Mantle in the NoMelt Region from Finite-Frequency Traveltime Tomography

Science.gov (United States)

Hung, S. H.; Lin, P. Y.; Gaherty, J. B.; Russell, J. B.; Jin, G.; Collins, J. A.; Lizarralde, D.; Evans, R. L.; Hirth, G.

2017-12-01

Surface wave dispersion and magnetotelluric survey from the NoMelt Experiment conducted on 70 Ma central Pacific seafloor revealed an electrically resistive, high shear wave velocity lid of 80 km thick underlain by a non-highly conductive, low-velocity layer [Sarafian et al., 2015; Lin et al., 2016]. The vertical structure of the upper mantle consistent with these observational constraints suggests a plausible convection scenario, where the seismically fast, dehydrated lithosphere preserving very strong fossil spreading fabric moves at a constant plate speed over the hydrated, melt-free athenospheric mantle with the presence of either pressure-driven return flow or thermally-driven small scale circulation. To explore 3-D variations in compressional shear wave velocities related to the lithospheric and asthenospheric mantle dynamics, we employ a multichannel cross correlation method to measure relative traveltime residuals based on the vertical P and traverse S waveforms filtered at 10-33 s from telseismic earthquakes at epicentral distance between 30 and 98 degrees. The obtained P and S residuals show on average peak-to-peak variations of ±0.5 s and ±1 s, respectively, across the NoMelt OBS array. Particularly, the P residuals for most of the events display an asymmetrical pattern with respect to an axis oriented nearly N-S to NE-SW through the array. Preliminary ray-based P tomography results reveal similar asymmetric variations in the uppermost 100 km mantle. To verify the resulting structural features, we will further perform both the P and S traveltime tomography and resolution tests based on a multiscale finite-frequency approach which properly takes into account both the 3D off-path sensitivities of the measured residuals and data-adaptive resolution of the model.

Traveling Wave Resonance and Simplified Analysis Method for Long-Span Symmetrical Cable-Stayed Bridges under Seismic Traveling Wave Excitation

Directory of Open Access Journals (Sweden)

Zhong-ye Tian

2014-01-01

Full Text Available The seismic responses of a long-span cable-stayed bridge under uniform excitation and traveling wave excitation in the longitudinal direction are, respectively, computed. The numerical results show that the bridge’s peak seismic responses vary significantly as the apparent wave velocity decreases. Therefore, the traveling wave effect must be considered in the seismic design of long-span bridges. The bridge’s peak seismic responses do not vary monotonously with the apparent wave velocity due to the traveling wave resonance. A new traveling wave excitation method that can simplify the multisupport excitation process into a two-support excitation process is developed.

Sub-crustal seismic activity beneath Klyuchevskoy Volcano

Science.gov (United States)

Carr, M. J.; Droznina, S.; Levin, V. L.; Senyukov, S.

2013-12-01

Seismic activity is extremely vigorous beneath the Klyuchevskoy Volcanic Group (KVG). The unique aspect is the distribution in depth. In addition to upper-crustal seismicity, earthquakes take place at depths in excess of 20 km. Similar observations are known in other volcanic regions, however the KVG is unique in both the number of earthquakes and that they occur continuously. Most other instances of deep seismicity beneath volcanoes appear to be episodic or transient. Digital recording of seismic signals started at the KVG in early 2000s.The dense local network reliably locates earthquakes as small as ML~1. We selected records of 20 earthquakes located at depths over 20 km. Selection was based on the quality of the routine locations and the visual clarity of the records. Arrivals of P and S waves were re-picked, and hypocentral parameters re-established. Newl locations fell within the ranges outlined by historical seismicity, confirming the existence of two distinct seismically active regions. A shallower zone is at ~20 km depth, and all hypocenters are to the northeast of KVG, in a region between KVG and Shiveluch volcano. A deeper zone is at ~30 km, and all hypocenters cluster directly beneath the edifice of the Kyuchevskoy volcano. Examination of individual records shows that earthquakes in both zones are tectonic, with well-defined P and S waves - another distinction of the deep seismicity beneath KVG. While the upper seismic zone is unquestionably within the crust, the provenance of the deeper earthquakes is enigmatic. The crustal structure beneath KVG is highly complex, with no agreed-upon definition of the crust-mantle boundary. Rather, a range of values, from under 30 to over 40 km, exists in the literature. Similarly, a range of velocity structures has been reported. Teleseismic receiver functions (RFs) provide a way to position the earthquakes with respect to the crust-mantle boundary. We compare the differential travel times of S and P waves from deep

Seismic Travel Time Tomography in Modeling Low Velocity Anomalies between the Boreholes

Science.gov (United States)

Octova, A.; Sule, R.

2018-04-01

Travel time cross-hole seismic tomography is applied to describing the structure of the subsurface. The sources are placed at one borehole and some receivers are placed in the others. First arrival travel time data that received by each receiver is used as the input data in seismic tomography method. This research is devided into three steps. The first step is reconstructing the synthetic model based on field parameters. Field parameters are divided into 24 receivers and 45 receivers. The second step is applying inversion process for the field data that consists of five pairs bore holes. The last step is testing quality of tomogram with resolution test. Data processing using FAST software produces an explicit shape and resemble the initial model reconstruction of synthetic model with 45 receivers. The tomography processing in field data indicates cavities in several place between the bore holes. Cavities are identified on BH2A-BH1, BH4A-BH2A and BH4A-BH5 with elongated and rounded structure. In resolution tests using a checker-board, anomalies still can be identified up to 2 meter x 2 meter size. Travel time cross-hole seismic tomography analysis proves this mothod is very good to describing subsurface structure and boundary layer. Size and anomalies position can be recognized and interpreted easily.

Microseismic monitoring of CO₂-injection-induced seismicity

Energy Technology Data Exchange (ETDEWEB)

Chen, Yu [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Huang, Lianjie [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-10-03

This presentation's Objectives: Studying moment tensors of microseismic sources; Imaging fracture zones and subsurface structure; Obtaining three-dimension seismic velocity model and improved moment tensors.

Application of seismic refraction tomography for tunnel design in Santa Clara Mountain, San Juan, Argentina Application of seismic refraction tomography for tunnel design in Santa Clara Mountain, San Juan, Argentina

Directory of Open Access Journals (Sweden)

Imhof Armando Luis

2011-12-01

Full Text Available

A geophysical survey involving seismic refraction tomography (SRT for mapping 'P' waves was carried out in Sierra Santa Clara, San Juan Province, Argentina in July 2009. The purpose of the geophysical survey was to determine the degree of fracturing and the rigidity of the rock mass through which it is planned to build a 290 m long road tunnel traversing the mountain almost perpendicular to the axis thereof, at around 100 m depth from the summit.

Several difficulties arose from the operational point of view which made it almost impossible to conduct fieldwork in normal circumstances. Firstly, the topography had almost 45° slopes and 100 m research depths which would have involved having had to use explosives to generate seismic waves reaching sensors which had sufficient signal-to-noise ratio for distinguishing them. Legal restrictions regarding the use of explosives on the one hand and insufficient power when using hammer blows on the other made it necessary to design and build a gas-powered gun to achieve the minimum energy (2 kJ required for detecting seismic signals.

Secondly, using conventional interpretation methods involving layered models was inoperable in such geological structures; seismic tomography methods were thus used which make use of the velocity gradient concept (both lateral and in-depth. This allowed mapping subsurface velocity variations in the form of velocity contour lines.

The methodology used with the new seismic waves' source generator, as well as SRT application in this type of geological structure, demonstrated that satisfactory results could be obtained for this kind of geophysical study for geotechnical purposes.

Seismic Imaging of the Source Physics Experiment Site with the Large-N Seismic Array

Science.gov (United States)

Chen, T.; Snelson, C. M.; Mellors, R. J.

2017-12-01

The Source Physics Experiment (SPE) consists of a series of chemical explosions at the Nevada National Security Site. The goal of SPE is to understand seismic wave generation and propagation from these explosions. To achieve this goal, we need an accurate geophysical model of the SPE site. A Large-N seismic array that was deployed at the SPE site during one of the chemical explosions (SPE-5) helps us construct high-resolution local geophysical model. The Large-N seismic array consists of 996 geophones, and covers an area of approximately 2 × 2.5 km. The array is located in the northern end of the Yucca Flat basin, at a transition from Climax Stock (granite) to Yucca Flat (alluvium). In addition to the SPE-5 explosion, the Large-N array also recorded 53 weight drops. Using the Large-N seismic array recordings, we perform body wave and surface wave velocity analysis, and obtain 3D seismic imaging of the SPE site for the top crust of approximately 1 km. The imaging results show clear variation of geophysical parameter with local geological structures, including heterogeneous weathering layer and various rock types. The results of this work are being incorporated in the larger 3D modeling effort of the SPE program to validate the predictive models developed for the site.

Asymptotic Structure of the Seismic Radiation from an Explosive Column

Directory of Open Access Journals (Sweden)

Marco Rosales-Vera

2018-01-01

Full Text Available We study the structure of the seismic radiation in the far field produced by an explosive column. Using an asymptotic solution for the far field of vibration (Heelan’s solution, we find analytical expressions to the peak particle velocity (PPV diagrams. These results are extended to the case of a charge with finite velocity of detonation.

Long Term Seismic Observation in Mariana by OBSs : Double Seismic Zone and Upper Mantle Structure

Science.gov (United States)

Shiobara, H.; Sugioka, H.; Mochizuki, K.; Oki, S.; Kanazawa, T.; Fukao, Y.; Suyehiro, K.

2005-12-01

In order to obtain the deep arc structural image of Mariana, a large-scale seismic observation by using 58 long-term ocean bottom seismometers (LTOBS) had been performed from June 2003 until April 2004, which is a part of the MARGINS program funded by the NSF. Prior to this observation, a pilot long-term seismic array observation was conducted in the same area by using 10 LTOBSs from Oct. 2001 until Feb. 2003. At that time, 8 LTOBSs were recovered but one had no data. Recently, 2 LTOBSs, had troubles in the releasing, were recovered by the manned submersible (Shinkai 6500, Jamstec) for the research of the malfunction in July 2005. By using all 9 LTOBS's data, those are about 11 months long, hypocenter determination was performed and more than 3000 local events were found. Even with the 1D velocity structure based on the iasp91 model, double seismic zones and a systematic shift of epicenters between the PDE and this study were observed. To investigate the detail of hypocenter distribution and the 3D velocity structure, the DD inversion (tomoDD: Zhang and Thurber, 2003) was applied for this data set with the 1D structure initial model except for the crust, which has been surveyed by using a dense airgun-OBS system (Takahashi et al., 2003). The result of relocated hypocenters shows clear double seismic zones until about 200 km depth, a high activity area around the fore-arc serpentine sea-mount, the Big Blue, and a lined focuses along the current ridge axis in the back-arc basin, and the result of the tomography shows a image of subducting slab and a low-Vs region below the same sea-mount mentioned. The wedge mantle structure was not clearly resolved due to the inadequate source-receiver coverage, which will be done in the recent experiment.

Investigation of sinkhole areas in Germany using 2D shear wave reflection seismics and zero-offset VSP

Science.gov (United States)

Tschache, Saskia; Wadas, Sonja; Polom, Ulrich; Krawczyk, Charlotte M.

2017-04-01

Sinkholes pose a serious geohazard for humans and infrastructure in populated areas. The Junior Research Group Subrosion within the Leibniz Institute for Applied Geophysics and the joint project SIMULTAN work on the multi-scale investigation of subrosion processes in the subsurface, which cause natural sinkholes. In two case studies in sinkhole areas of Thuringia in Germany, we applied 2D shear wave reflection seismics using SH-waves with the aim to detect suitable parameters for the characterisation of critical zones. This method has the potential to image near-surface collapse and faulting structures in improved resolution compared to P-wave surveys resulting from the shorter wavelength of shear waves. Additionally, the shear wave velocity field derived by NMO velocity analysis is a basis to calculate further physical parameters, as e.g. the dynamic shear modulus. In both investigation areas, vertical seismic profiles (VSP) were acquired by generating P- and SH-waves (6 component VSP) directly next to a borehole equipped with a 3C downhole sensor. They provide shear and compressional wave velocity profiles, which are used to improve the 2D shear wave velocity field from surface seismics, to perform a depth calibration of the seismic image and to calculate the Vp/Vs ratio. The signals in the VSP data are analysed with respect to changes in polarisation and attenuation with depth and/or azimuth. The VSP data reveal low shear wave velocities of 200-300 m/s in rock layers known to be heavily affected by subrosion and confirm the low velocities calculated from the surface seismic data. A discrepancy of the shear wave velocities is observed in other intervals probably due to unsymmetrical travel paths in the surface seismics. In some VSP data dominant conversion of the direct SH-wave to P-wave is observed that is assumed to be caused by an increased presence of cavities. A potential fault distorting the vertical travel paths was detected by abnormal P-wave first

3D seismic Unterhaching 2009 within hydrothermal exploration and modelling; 3D-Seismik Unterhaching 2009 im Rahmen hydrothermaler Exploration und Modellierung

Energy Technology Data Exchange (ETDEWEB)

Lueschen, Ewald; Dussel, Michael; Thomas, Ruediger; Schulz, Ruediger [Leibniz-Institut fuer Angewandte Geophysik (LIAG), Hannover (Germany)

2011-10-24

Within the exploration of hydrothermal reservoirs, results of 3D reflexion-seismic measurements are presented. These measurements were performed in June / July 2009 according to the vibroseis method on an area of 26.3 square kilometers in the area Unterhaching (Federal Republic of Germany). The 3D seismic survey exhibits much more complex structures than previously known by 2D seismic lines. Subsequent to sinistral transtension (active in the Cretaceous to the Eocene) a short transpression impetus was performed. This is evident from graduated normal faults as well as staggered reverse fault structures and inversion structures in the Upper Jurassic. Top and base of the 600-650 m mighty Malm are well resolved. Brittle fault structures are formed linearly at the top Malm but rounded and chaotic within the Malm. This can be explained by a radical karstification / hydrothermal solution. Several circular structures are interpreted as karstified incursion structures. The seismic facies of the Malm is characterized by a shift from relatively transparent zones, layered fields, scatters and fault zones. This is an expression of smaller and larger reefs, lagoons and reef debris. Reefs are characterized by several seismic attributes. Striking low-velocity zones are oriented along the main fault zones and can be interpreted as zones that are relieved by gap porosity. Azimuth variable processing gives evidence for preferred orientations of fractures on the seismic scale. By means of the 3D seismic diverse geothermal exploration targets can be defined.

Shallow velocity model in the area of Pozzo Pitarrone, Mt. Etna, from single station, array methods and borehole data

Directory of Open Access Journals (Sweden)

Luciano Zuccarello

2016-09-01

Full Text Available Seismic noise recorded by a temporary array installed around Pozzo Pitarrone, NE flank of Mt. Etna, have been analysed with several techniques. Single station HVSR method and SPAC array method have been applied to stationary seismic noise to investigate the local shallow structure. The inversion of dispersion curves produced a shear wave velocity model of the area reliable down to depth of about 130 m. A comparison of such model with the stratigraphic information available for the investigated area shows a good qualitative agreement. Taking advantage of a borehole station installed at 130 m depth, we could estimate also the P-wave velocity by comparing the borehole recordings of local earthquakes with the same event recorded at surface. Further insight on the P-wave velocity in the upper 130 m layer comes from the surface reflected wave observable in some cases at the borehole station. From this analysis we obtained an average P-wave velocity of about 1.2 km/s, compatible with the shear wave velocity found from the analysis of seismic noise.

Seismic imaging of North China: insight into intraplate volcanism and seismotectonics

Science.gov (United States)

Zhao, D.

2004-12-01

We used seismic tomography to study the detailed three-dimensional (3-D) seismic velocity structure of the crust and mantle beneath North China for understanding the intraplate volcanism and seismotectonics of the Asian continent. Two active volcanoes, Changbai and Wudalianchi, exist in Northeast China and they have erupted several times in the last 1000 years. The origin of the active intraplate volcanoes is still unclear. Global tomography shows that the subducting Pacific slab becomes stagnant under NE Asia and strong low-velocity (low-V) anomalies exist in the upper mantle under the two volcanoes (Zhao, 2004). Recently we determined a 3-D P-wave velocity structure under the Changbai volcano using teleseismic data recorded by 19 portable seismic stations in NE China (Zhao et al., 2004). Our result shows a columnar low-V anomaly extending to 400 km depth and high-velocity anomalies in the mantle transition zone with deep-focus earthquakes of about 600 km depth. These results indicatie that the Changbai and Wudalianchi volcanoes are not hotspot like Hawaii but a kind of back-arc volcano related to the deep subduction and stagnancy of the Pacific slab under NE Asia. A detailed 3-D P-wave tomography of the crust and uppermost mantle under the Beijing region is determined by using local earthquake arrival times recorded by the newly installed Chinese Capital Seismic Network with 101 short-period seismic stations coving the region densely and uniformly (Huang and Zhao, 2004). The results show that large crustal earthquakes, such as the 1679 Sanhe earthquake (M 8.0) and the 1976 Tangshan earthquake (M 7.8), generally occurred in high-velocity areas in the upper to middle crust. In the lower crust to the uppermost mantle under the source zones of the large earthquakes, however, low-velocity and high-conductivity anomalies exist, which are considered to be associated with fluids. The fluids in the lower crust may cause the weakening of the seismogenic layer in the upper

Earthquake source studies and seismic imaging in Alaska

Science.gov (United States)

Tape, C.; Silwal, V.

2015-12-01

Alaska is one of the world's most seismically and tectonically active regions. Its enhanced seismicity, including slab seismicity down to 180 km, provides opportunities (1) to characterize pervasive crustal faulting and slab deformation through the estimation of moment tensors and (2) to image subsurface structures to help understand the tectonic evolution of Alaska. Most previous studies of earthquakes and seismic imaging in Alaska have emphasized earthquake locations and body-wave travel-time tomography. In the past decade, catalogs of seismic moment tensors have been established, while seismic surface waves, active-source data, and potential field data have been used to improve models of seismic structure. We have developed moment tensor catalogs in the regions of two of the largest sedimentary basins in Alaska: Cook Inlet forearc basin, west of Anchorage, and Nenana basin, west of Fairbanks. Our moment tensor solutions near Nenana basin suggest a transtensional tectonic setting, with the basin developing in a stepover of a left-lateral strike-slip fault system. We explore the effects of seismic wave propagation from point-source and finite-source earthquake models by performing three-dimensional wavefield simulations using seismic velocity models that include major sedimentary basins. We will use our catalog of moment tensors within an adjoint-based, iterative inversion to improve the three-dimensional tomographic model of Alaska.

History Matching of 4D Seismic Data Attributes using the Ensemble Kalman Filter

KAUST Repository

Ravanelli, Fabio M.

2013-05-01

tomography to map velocities in the interwell region was demonstrated as a potential tool to ensure survey reproducibility and low acquisition cost when compared with full scale surface surveys. This approach relies on the higher velocity sensitivity to fluid displacement at higher frequencies. The velocity effects were modeled using the Biot velocity model. This method provided promising results leading to similar RRMS error reductions when compared with conventional history matched surface seismic data.

Indication to distinguish the burst region of coal gas from seismic data

Energy Technology Data Exchange (ETDEWEB)

Jian-yuan Cheng; Hong-wei Tang; Lin Xu; Yan-fang Li [China Coal Research Institute, Xi' an (China). Xi' an Research Institute

2009-09-15

The velocity of an over-burst coal seam is about 1/3 compared to a normal coal seam based on laboratory test results. This can be considered as a basis to confirm the area of coal and gas burst by seismic exploration technique. Similarly, the simulation result of the theoretical seismic model shows that there is obvious distinction between over-burst coal and normal coal based on the coal reflection's travel-time, energy and frequency. The results from the actual seismic data acquired in the coal and gas over-burst cases is consistent with that of the laboratory and seismic modeling; that is, in the coal and gas burst region, seismic reflection travel time is delayed, seismic amplitude is weakened and seismic frequency is reduced. Therefore, it can be concluded that seismic exploration technique is promising for use in distinguishing coal and gas over-burst regions based on the variation of seismic reflection travel time, amplitude and frequency. 7 refs., 6 figs.

Critical Velocity for Shear Localization in A Mature Mylonitic Rock Analogue

Science.gov (United States)

Takahashi, M.; van den Ende, M.; Niemeijer, A. R.; Spiers, C. J.

2016-12-01

Highly localized slip zones, seen within ductile shear zones developed in nature, such as pseudotachylite bands occurring within mylonites, are widely recognized as evidence for earthquake nucleation and/or propagation within and overprinting the ductile regime. To understand brittle/frictional localization processes in ductile shear zones and to connect these to earthquake nucleation and propagation processes, we performed large velocity step-change tests on a brine-saturated, 80:20 (wt. %) halite and muscovite gouge mixture, after forming a mature mylonitic structure through pressure solution creep at low-velocity. The sharp increase in sliding strength that occurs in response to an instantaneous upward velocity-step (direct effect) is an important parameter in determining the potential for and nature of seismic rupture nucleation. We obtained reproducible results regarding low velocity mechanical behavior compared with previous work of Niemeijer and Spiers, [2006], but also obtained new insights into the effects of sudden increases in slip velocity on localization and strength evolution, at velocities above a specific critical velocity Vc ( 20 μm/sec). We found that once a ductile, mylonitic structure has developed in a shear zone, subsequent cataclastic deformation at high velocity (> Vc) is consistently localized in a narrow zone characterized by fine grains of halite aligned in arrays between foliated muscovite Due to this intense localization, structures presumably developed under low velocity conditions were still preserved in large parts of the gouge body. This switch to localized deformation is controlled by the imposed velocity, and becomes most apparent at velocities over Vc. In addition, the direct effect a decreases rapidly when the velocity exceeds Vc. This implies that slip can localize and accelerate towards seismic velocities more or less instantly once Vc is exceeded. Obtaining a measure for Vc in natural faults is therefore of key importance

Rescaled Range analysis of Induced Seismicity: rapid classification of clusters in seismic crisis

Science.gov (United States)

Bejar-Pizarro, M.; Perez Lopez, R.; Benito-Parejo, M.; Guardiola-Albert, C.; Herraiz, M.

2017-12-01

Different underground fluid operations, mainly gas storing, fracking and water pumping, can trigger Induced Seismicity (IS). This seismicity is normally featured by small-sized earthquakes (M<2.5), although particular cases reach magnitude as great as 5. It has been up for debate whether earthquakes greater than 5 can be triggered by IS or this level of magnitude only corresponds to tectonic earthquakes caused by stress change. Whatever the case, the characterization of IS for seismic clusters and seismic series recorded close but not into the gas storage, is still under discussion. Time-series of earthquakes obey non-linear patterns where the Hurst exponent describes the persistency or anti-persistency of the sequence. Natural seismic sequences have an H-exponent close to 0.7, which combined with the b-value time evolution during the time clusters, give us valuable information about the stationarity of the phenomena. Tectonic earthquakes consist in a main shock with a decay of time-occurrence of seismic shocks obeying the Omori's empirical law. On the contrary, IS does not exhibit a main shock and the time occurrence depends on the injection operations instead of on the tectonic energy released. In this context, the H-exponent can give information about the origin of the sequence. In 2013, a seismic crisis was declared from the Castor underground gas storing located off-shore in the Mediterranean Sea, close to the Northeastern Spanish cost. The greatest induced earthquake was 3.7. However, a 4.2 earthquake, probably of tectonic origin, occurred few days after the operations stopped. In this work, we have compared the H-exponent and the b-value time evolution according to the timeline of gas injection. Moreover, we have divided the seismic sequence into two groups: (1) Induced Seismicity and (2) Triggered Seismicity. The rescaled range analysis allows the differentiation between natural and induced seismicity and gives information about the persistency and long

Attenuation and Velocity Structure in Spain and Morocco: Distinguishing Between Water, Temperature, and Partial Melt

Science.gov (United States)

Bezada, M. J.; Humphreys, E.

2014-12-01

Temperature, melt fraction, and water content affect seismic velocity and attenuation differently. Both are sensitive to temperature, but velocity is more sensitive to melt fraction and attenuation is thought to be more sensitive to water content. For these reasons, combining attenuation measurements with tomographic imaging of velocity structure can help untangle these fields and better resolve lithospheric structure and physical state. We map variations in attenuation beneath Spain and northern Morocco using teleseismic data generated by more than a dozen teleseismic deep-focus earthquakes recorded on a dense array of stations. For each event, we first estimate the source from the best quality recordings. We then apply an attenuation operator to the source estimate, using a range of t* values, to match the record at each station. We invert for a smooth map of t* from the ensemble of measurements. The spatial patterns in t* correlate very well with the tectonic domains in Spain and Morocco. In particular, areas in Spain that resisted deformation during the Variscan and Alpine orogenies produce very little attenuation. Comparing the attenuation map with seismic velocity structure we find that, in Morocco, some areas with strong low-velocity anomalies and recent volcanism do not cause high attenuation. These observations suggest that water content is a more likely cause for seismic attenuation in the study area than temperature, and that the non-attenuative low-velocity anomalies in Morocco are produced by partial mel.

Toward 2D Seismic Wavefield Monitoring: Seismic Gradiometry for Long-Period Seismogram and Short-Period Seismogram Envelope applied to the Hi-net Array

Science.gov (United States)

Maeda, T.; Nishida, K.; Takagi, R.; Obara, K.

2015-12-01

The high-sensitive seismograph network Japan (Hi-net) operated by National Research Institute for Earth Science and Disaster Prevention (NIED) has about 800 stations with average separation of 20 km. We can observe long-period seismic wave propagation as a 2D wavefield with station separations shorter than wavelength. In contrast, short-period waves are quite incoherent at stations, however, their envelope shapes resemble at neighbor stations. Therefore, we may be able to extract seismic wave energy propagation by seismogram envelope analysis. We attempted to characterize seismic waveform at long-period and its envelope at short-period as 2D wavefield by applying seismic gradiometry. We applied the seismic gradiometry to a synthetic long-period (20-50s) dataset prepared by numerical simulation in realistic 3D medium at the Hi-net station layout. Wave amplitude and its spatial derivatives are estimated by using data at nearby stations. The slowness vector, the radiation pattern and the geometrical spreading are extracted from estimated velocity, displacement and its spatial derivatives. For short-periods at shorter than 1 s, seismogram envelope shows temporal and spatial broadening through scattering by medium heterogeneity. It is expected that envelope shape may be coherent among nearby stations. Based on this idea, we applied the same method to the time-integration of seismogram envelope to estimate its spatial derivatives. Together with seismogram envelope, we succeeded in estimating the slowness vector from the seismogram envelope as well as long-period waveforms by synthetic test, without using phase information. Our preliminarily results show that the seismic gradiometry suits the Hi-net to extract wave propagation characteristics both at long and short periods. This method is appealing that it can estimate waves at homogeneous grid to monitor seismic wave as a wavefield. It is promising to obtain phase velocity variation from direct waves, and to grasp wave

Mobile seismic exploration

Energy Technology Data Exchange (ETDEWEB)

Dräbenstedt, A., E-mail: a.draebenstedt@polytec.de, E-mail: rembe@iei.tu-clausthal.de, E-mail: ulrich.polom@liag-hannover.de; Seyfried, V. [Research & Development, Polytec GmbH, Waldbronn (Germany); Cao, X.; Rembe, C., E-mail: a.draebenstedt@polytec.de, E-mail: rembe@iei.tu-clausthal.de, E-mail: ulrich.polom@liag-hannover.de [Institute of Electrical Information Technology, TU Clausthal, Clausthal-Zellerfeld (Germany); Polom, U., E-mail: a.draebenstedt@polytec.de, E-mail: rembe@iei.tu-clausthal.de, E-mail: ulrich.polom@liag-hannover.de [Leibniz Institute of Applied Geophysics, Hannover (Germany); Pätzold, F.; Hecker, P. [Institute of Flight Guidance, TU Braunschweig, Braunschweig (Germany); Zeller, T. [Clausthaler Umwelttechnik Institut CUTEC, Clausthal-Zellerfeld (Germany)

2016-06-28

Laser-Doppler-Vibrometry (LDV) is an established technique to measure vibrations in technical systems with picometer vibration-amplitude resolution. Especially good sensitivity and resolution can be achieved at an infrared wavelength of 1550 nm. High-resolution vibration measurements are possible over more than 100 m distance. This advancement of the LDV technique enables new applications. The detection of seismic waves is an application which has not been investigated so far because seismic waves outside laboratory scales are usually analyzed at low frequencies between approximately 1 Hz and 250 Hz and require velocity resolutions in the range below 1 nm/s/√Hz. Thermal displacements and air turbulence have critical influences to LDV measurements at this low-frequency range leading to noise levels of several 100 nm/√Hz. Commonly seismic waves are measured with highly sensitive inertial sensors (geophones or Micro Electro-Mechanical Sensors (MEMS)). Approaching a laser geophone based on LDV technique is the topic of this paper. We have assembled an actively vibration-isolated optical table in a minivan which provides a hole in its underbody. The laser-beam of an infrared LDV assembled on the optical table impinges the ground below the car through the hole. A reference geophone has detected remaining vibrations on the table. We present the results from the first successful experimental demonstration of contactless detection of seismic waves from a movable vehicle with a LDV as laser geophone.

A P-wave velocity model of the upper crust of the Sannio region (Southern Apennines, Italy

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M. Cocco

1998-06-01

Full Text Available This paper describes the results of a seismic refraction profile conducted in October 1992 in the Sannio region, Southern Italy, to obtain a detailed P-wave velocity model of the upper crust. The profile, 75 km long, extended parallel to the Apenninic chain in a region frequently damaged in historical time by strong earthquakes. Six shots were fired at five sites and recorded by a number of seismic stations ranging from 41 to 71 with a spacing of 1-2 km along the recording line. We used a two-dimensional raytracing technique to model travel times and amplitudes of first and second arrivals. The obtained P-wave velocity model has a shallow structure with strong lateral variations in the southern portion of the profile. Near surface sediments of the Tertiary age are characterized by seismic velocities in the 3.0-4.1 km/s range. In the northern part of the profile these deposits overlie a layer with a velocity of 4.8 km/s that has been interpreted as a Mesozoic sedimentary succession. A high velocity body, corresponding to the limestones of the Western Carbonate Platform with a velocity of 6 km/s, characterizes the southernmost part of the profile at shallow depths. At a depth of about 4 km the model becomes laterally homogeneous showing a continuous layer with a thickness in the 3-4 km range and a velocity of 6 km/s corresponding to the Meso-Cenozoic limestone succession of the Apulia Carbonate Platform. This platform appears to be layered, as indicated by an increase in seismic velocity from 6 to 6.7 km/s at depths in the 6-8 km range, that has been interpreted as a lithological transition from limestones to Triassic dolomites and anhydrites of the Burano formation. A lower P-wave velocity of about 5.0-5.5 km/s is hypothesized at the bottom of the Apulia Platform at depths ranging from 10 km down to 12.5 km; these low velocities could be related to Permo-Triassic siliciclastic deposits of the Verrucano sequence drilled at the bottom of the Apulia

Micro-seismic Imaging Using a Source Independent Waveform Inversion Method

KAUST Repository

Wang, Hanchen

2016-04-18

Micro-seismology is attracting more and more attention in the exploration seismology community. The main goal in micro-seismic imaging is to find the source location and the ignition time in order to track the fracture expansion, which will help engineers monitor the reservoirs. Conventional imaging methods work fine in this field but there are many limitations such as manual picking, incorrect migration velocity and low signal to noise ratio (S/N). In traditional surface survey imaging, full waveform inversion (FWI) is widely used. The FWI method updates the velocity model by minimizing the misfit between the observed data and the predicted data. Using FWI to locate and image microseismic events allows for an automatic process (free of picking) that utilizes the full wavefield. Use the FWI technique, and overcomes the difficulties of manual pickings and incorrect velocity model for migration. However, the technique of waveform inversion of micro-seismic events faces its own problems. There is significant nonlinearity due to the unknown source location (space) and function (time). We have developed a source independent FWI of micro-seismic events to simultaneously invert for the source image, source function and velocity model. It is based on convolving reference traces with the observed and modeled data to mitigate the effect of an unknown source ignition time. The adjoint-state method is used to derive the gradient for the source image, source function and velocity updates. To examine the accuracy of the inverted source image and velocity model the extended image for source wavelet in z-axis is extracted. Also the angle gather is calculated to check the applicability of the migration velocity. By inverting for the source image, source wavelet and the velocity model simultaneously, the proposed method produces good estimates of the source location, ignition time and the background velocity in the synthetic experiments with both parts of the Marmousi and the SEG

Time-lapse refraction seismic tomography for the detection of ground ice degradation

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C. Hilbich

2010-07-01

Full Text Available The ice content of the subsurface is a major factor controlling the natural hazard potential of permafrost degradation in alpine terrain. Monitoring of changes in ice content is therefore similarly important as temperature monitoring in mountain permafrost. Although electrical resistivity tomography monitoring (ERTM proved to be a valuable tool for the observation of ice degradation, results are often ambiguous or contaminated by inversion artefacts. In theory, the sensitivity of P-wave velocity of seismic waves to phase changes between unfrozen water and ice is similar to the sensitivity of electric resistivity. Provided that the general conditions (lithology, stratigraphy, state of weathering, pore space remain unchanged over the observation period, temporal changes in the observed travel times of repeated seismic measurements should indicate changes in the ice and water content within the pores and fractures of the subsurface material. In this paper, a time-lapse refraction seismic tomography (TLST approach is applied as an independent method to ERTM at two test sites in the Swiss Alps. The approach was tested and validated based on a the comparison of time-lapse seismograms and analysis of reproducibility of the seismic signal, b the analysis of time-lapse travel time curves with respect to shifts in travel times and changes in P-wave velocities, and c the comparison of inverted tomograms including the quantification of velocity changes. Results show a high potential of the TLST approach concerning the detection of altered subsurface conditions caused by freezing and thawing processes. For velocity changes on the order of 3000 m/s even an unambiguous identification of significant ice loss is possible.

Subduction factory 1. Theoretical mineralogy, densities, seismic wave speeds, and H2O contents

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Hacker, Bradley R.; Abers, Geoffrey A.; Peacock, Simon M.

2003-01-01

We present a new compilation of physical properties of minerals relevant to subduction zones and new phase diagrams for mid-ocean ridge basalt, lherzolite, depleted lherzolite, harzburgite, and serpentinite. We use these data to calculate H2O content, density and seismic wave speeds of subduction zone rocks. These calculations provide a new basis for evaluating the subduction factory, including (1) the presence of hydrous phases and the distribution of H2O within a subduction zone; (2) the densification of the subducting slab and resultant effects on measured gravity and slab shape; and (3) the variations in seismic wave speeds resulting from thermal and metamorphic processes at depth. In considering specific examples, we find that for ocean basins worldwide the lower oceanic crust is partially hydrated (measurements. Subducted hydrous crust in cold slabs can persist to several gigapascals at seismic velocities that are several percent slower than the surrounding mantle. Seismic velocities and VP/VS ratios indicate that mantle wedges locally reach 60-80% hydration.

Ambient noise tomography across Mount St. Helens using a dense seismic array

KAUST Repository

Wang, Yadong

2017-05-08

We investigated upper crustal structure with data from a dense seismic array deployed around Mount St. Helens for 2 weeks in the summer of 2014. Interstation cross correlations of ambient seismic noise data from the array were obtained, and clear fundamental mode Rayleigh waves were observed between 2.5 and 5 s periods. In addition, higher-mode signals were observed around 2 s period. Frequency-time analysis was applied to measure fundamental mode Rayleigh wave phase velocities, which were used to invert for 2-D phase velocity maps. An azimuth-dependent traveltime correction was implemented to mitigate potential biases introduced due to an inhomogeneous noise source distribution. Reliable phase velocity maps were only obtained between 3 and 4 s periods due to limitations imposed by the array aperture and higher-mode contamination. The phase velocity tomography results, which are sensitive to structure shallower than 6 km depth, reveal an ~10–15% low-velocity anomaly centered beneath the volcanic edifice and peripheral high-velocity anomalies that likely correspond to cooled igneous intrusions. We suggest that the low-velocity anomaly reflects the high-porosity mixture of lava and ash deposits near the surface of the edifice, a highly fractured magmatic conduit and hydrothermal system beneath the volcano, and possibly a small contribution from silicate melt.

Imaging the Chicxulub central crater zone from large scale seismic acoustic wave propagation and gravity modeling

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Fucugauchi, J. U.; Ortiz-Aleman, C.; Martin, R.

2017-12-01

Large complex craters are characterized by central uplifts that represent large-scale differential movement of deep basement from the transient cavity. Here we investigate the central sector of the large multiring Chicxulub crater, which has been surveyed by an array of marine, aerial and land-borne geophysical methods. Despite high contrasts in physical properties,contrasting results for the central uplift have been obtained, with seismic reflection surveys showing lack of resolution in the central zone. We develop an integrated seismic and gravity model for the main structural elements, imaging the central basement uplift and melt and breccia units. The 3-D velocity model built from interpolation of seismic data is validated using perfectly matched layer seismic acoustic wave propagation modeling, optimized at grazing incidence using shift in the frequency domain. Modeling shows significant lack of illumination in the central sector, masking presence of the central uplift. Seismic energy remains trapped in an upper low velocity zone corresponding to the sedimentary infill, melt/breccias and surrounding faulted blocks. After conversion of seismic velocities into a volume of density values, we use massive parallel forward gravity modeling to constrain the size and shape of the central uplift that lies at 4.5 km depth, providing a high-resolution image of crater structure.The Bouguer anomaly and gravity response of modeled units show asymmetries, corresponding to the crater structure and distribution of post-impact carbonates, breccias, melt and target sediments

Air-coupled seismic waves at long range from Apollo launchings.

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Donn, W. L.; Dalins, I.; Mccarty, V.; Ewing, M.; Kaschak , G.

1971-01-01

Microphones and seismographs were co-located in arrays on Skidaway Island, Georgia, for the launchings of Apollo 13 and 14, 374 km to the south. Simultaneous acoustic and seismic waves were recorded for both events at times appropriate to the arrival of the acoustic waves from the source. The acoustic signal is relatively broadband compared to the nearly monochromatic seismic signal; the seismic signal is much more continuous than the more pulse-like acoustic signal; ground loading from the pressure variations of the acoustic waves is shown to be too small to account for the seismic waves; and the measured phase velocities of both acoustic and seismic waves across the local instrument arrays differ by less than 6 per cent and possibly 3 per cent if experimental error is included. It is concluded that the seismic waves are generated by resonant coupling to the acoustic waves along some 10 km of path on Skidaway Island.

Seismic trapped modes in the oroville and san andreas fault zones.

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Li, Y G; Leary, P; Aki, K; Malin, P

1990-08-17

Three-component borehole seismic profiling of the recently active Oroville, California, normal fault and microearthquake event recording with a near-fault three-component borehole seismometer on the San Andreas fault at Parkfield, California, have shown numerous instances of pronounced dispersive wave trains following the shear wave arrivals. These wave trains are interpreted as fault zone-trapped seismic modes. Parkfield earthquakes exciting trapped modes have been located as deep as 10 kilometers, as shallow as 4 kilometers, and extend 12 kilometers along the fault on either side of the recording station. Selected Oroville and Parkfield wave forms are modeled as the fundamental and first higher trapped SH modes of a narrow low-velocity layer at the fault. Modeling results suggest that the Oroville fault zone is 18 meters wide at depth and has a shear wave velocity of 1 kilometer per second, whereas at Parkfield, the fault gouge is 100 to 150 meters wide and has a shear wave velocity of 1.1 to 1.8 kilometers per second. These low-velocity layers are probably the rupture planes on which earthquakes occur.

Note: Rotaphone, a new self-calibrated six-degree-of-freedom seismic sensor

Science.gov (United States)

Brokešová, Johana; Málek, Jiří; Evans, John R.

2012-01-01

We have developed and tested (calibration, linearity, and cross-axis errors) a new six-degree-of-freedom mechanical seismic sensor for collocated measurements of three translational and three rotational ground motion velocity components. The device consists of standard geophones arranged in parallel pairs to detect spatial gradients. The instrument operates in a high-frequency range (above the natural frequency of the geophones, 4.5 Hz). Its theoretical sensitivity limit in this range is 10(-9) m/s in ground velocity and 10(-9) rad/s in rotation rate. Small size and weight, and easy installation and maintenance make the instrument useful for local-earthquake recording and seismic prospecting.

Homogenization and implementation of a 3D regional velocity model in Mexico for its application in moment tensor inversion of intermediate-magnitude earthquakes

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Rodríguez Cardozo, Félix; Hjörleifsdóttir, Vala; Caló, Marco

2017-04-01

Moment tensor inversions for intermediate and small earthquakes (M. < 4.5) are challenging as they principally excite relatively short period seismic waves that interact strongly with local heterogeneities. Incorporating detailed regional 3D velocity models permits obtaining realistic synthetic seismograms and recover the seismic source parameters these smaller events. Two 3D regional velocity models have recently been developed for Mexico, using surface waves and seismic noise tomography (Spica et al., 2016; Gaite et al., 2015), which could be used to model the waveforms of intermediate magnitud earthquakes in this region. Such models are parameterized as layered velocity profiles and for some of the profiles, the velocity difference between two layers are considerable. The "jump" in velocities between two layers is inconvenient for some methods and algorithms that calculate synthetic waveforms, in particular for the method that we are using, the spectral element method (SPECFEM3D GLOBE, Komatitsch y Tromp, 2000), when the mesh does not follow the layer boundaries. In order to make the velocity models more easily implementec in SPECFEM3D GLOBE it is neccesary to apply a homogenization algorithm (Capdeville et al., 2015) such that the (now anisotropic) layer velocities are smoothly varying with depth. In this work, we apply a homogenization algorithm to the regional velocity models in México for implementing them in SPECFEM3D GLOBE, calculate synthetic waveforms for intermediate-magnitude earthquakes in México and invert them for the seismic moment tensor.

High frequency measurement of P- and S-wave velocities on crystalline rock massif surface - methodology of measurement

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Vilhelm, Jan; Slavík, Lubomír

2014-05-01

For the purpose of non-destructive monitoring of rock properties in the underground excavation it is possible to perform repeated high-accuracy P- and S-wave velocity measurements. This contribution deals with preliminary results gained during the preparation of micro-seismic long-term monitoring system. The field velocity measurements were made by pulse-transmission technique directly on the rock outcrop (granite) in Bedrichov gallery (northern Bohemia). The gallery at the experimental site was excavated using TBM (Tunnel Boring Machine) and it is used for drinking water supply, which is conveyed in a pipe. The stable measuring system and its automatic operation lead to the use of piezoceramic transducers both as a seismic source and as a receiver. The length of measuring base at gallery wall was from 0.5 to 3 meters. Different transducer coupling possibilities were tested namely with regard of repeatability of velocity determination. The arrangement of measuring system on the surface of the rock massif causes better sensitivity of S-transducers for P-wave measurement compared with the P-transducers. Similarly P-transducers were found more suitable for S-wave velocity determination then P-transducers. The frequency dependent attenuation of fresh rock massif results in limited frequency content of registered seismic signals. It was found that at the distance between the seismic source and receiver from 0.5 m the frequency components above 40 kHz are significantly attenuated. Therefore for the excitation of seismic wave 100 kHz transducers are most suitable. The limited frequency range should be also taken into account for the shape of electric impulse used for exciting of piezoceramic transducer. The spike pulse generates broad-band seismic signal, short in the time domain. However its energy after low-pass filtration in the rock is significantly lower than the energy of seismic signal generated by square wave pulse. Acknowledgments: This work was partially

Interpretation of interseismic deformations and the seismic cycle associated with large subduction earthquakes

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Trubienko, Olga; Fleitout, Luce; Garaud, Jean-Didier; Vigny, Christophe

2013-03-01

The deformations of the overriding and subducting plates during the seismic cycle associated with large subduction earthquakes are modelled using 2D and 3D finite element techniques. A particular emphasis is put on the interseismic velocities and on the impact of the rheology of the asthenosphere. The distance over which the seismic cycle perturbs significantly the velocities depends upon the ratio of the viscosity in the asthenosphere to the period of the seismic cycle and can reach several thousand km for rheological parameters deduced from the first years of deformation after the Aceh earthquake. For a same early postseismic velocity, a Burger rheology of the asthenosphere implies a smaller duration of the postseismic phase and thus smaller interseismic velocities than a Maxwell rheology. A low viscosity wedge (LVW) modifies very significantly the predicted horizontal and vertical motions in the near and middle fields. In particular, with a LVW, the peak in vertical velocity at the end of the cycle is predicted to be no longer above the deep end of the locked section of the fault but further away, above the continentward limit of the LVW. The lateral viscosity variations linked to the presence at depth of the subducting slab affect substantially the results. The north-south interseismic compression predicted by this preliminary 2D model over more than 1500 km within the Sunda block is in good agreement with the pre-2004 velocities with respect to South-China inferred from GPS observations in Thailand, Malaysia and Indonesia. In Japan, before the Tohoku earthquake, the eastern part of northern Honshu was subsiding while the western part was uplifting. This transition from subsidence to uplift so far away from the trench is well fitted by the predictions from our models involving a LVW. Most of the results obtained here in a 2D geometry are shown to provide a good estimate of the displacements for fault segments of finite lateral extent, with a 3D spherical

Structure of the crust beneath Cameroon, West Africa, from the joint inversion of Rayleigh wave group velocities and receiver functions

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Tokam, Alain-Pierre K.; Tabod, Charles T.; Nyblade, Andrew A.; Julià, Jordi; Wiens, Douglas A.; Pasyanos, Michael E.

2010-11-01

The Cameroon Volcanic Line (CVL) consists of a linear chain of Tertiary to Recent, generally alkaline, volcanoes that do not exhibit an age progression. Here we study crustal structure beneath the CVL and adjacent regions in Cameroon using 1-D shear wave velocity models obtained from the joint inversion of Rayleigh wave group velocities and P-receiver functions for 32 broad-band seismic stations deployed between 2005 January and 2007 February. We find that (1) crustal thickness (35-39km) and velocity structure is similar beneath the CVL and the Pan African Oubanguides Belt to the south of the CVL, (2) crust is thicker (43-48km) under the northern margin of the Congo Craton and is characterized by shear wave velocities >=4.0kms-1 in its lower part and (3) crust is thinner (26-31km) under the Garoua rift and the coastal plain. In addition, a fast velocity layer (Vs of 3.6-3.8kms-1) in the upper crust is found beneath many of the seismic stations. Crustal structure beneath the CVL and the Oubanguides Belt is very similar to Pan African crustal structure in the Mozambique Belt, and therefore it appears not to have been modified significantly by the magmatic activity associated with the CVL. The crust beneath the coastal plain was probably thinned during the opening of the southern Atlantic Ocean, while the crust beneath the Garoua rift was likely thinned during the formation of the Benue Trough in the early Cretaceous. We suggest that the thickened crust and the thick mafic lower crustal layer beneath the northern margin of the Congo Craton may be relict features from a continent-continent collision along this margin during the formation of Gondwana.

Time-lapse seismic waveform modelling and attribute analysis using hydromechanical models for a deep reservoir undergoing depletion

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He, Y.-X.; Angus, D. A.; Blanchard, T. D.; Wang, G.-L.; Yuan, S.-Y.; Garcia, A.

2016-04-01

Extraction of fluids from subsurface reservoirs induces changes in pore pressure, leading not only to geomechanical changes, but also perturbations in seismic velocities and hence observable seismic attributes. Time-lapse seismic analysis can be used to estimate changes in subsurface hydromechanical properties and thus act as a monitoring tool for geological reservoirs. The ability to observe and quantify changes in fluid, stress and strain using seismic techniques has important implications for monitoring risk not only for petroleum applications but also for geological storage of CO2 and nuclear waste scenarios. In this paper, we integrate hydromechanical simulation results with rock physics models and full-waveform seismic modelling to assess time-lapse seismic attribute resolution for dynamic reservoir characterization and hydromechanical model calibration. The time-lapse seismic simulations use a dynamic elastic reservoir model based on a North Sea deep reservoir undergoing large pressure changes. The time-lapse seismic traveltime shifts and time strains calculated from the modelled and processed synthetic data sets (i.e. pre-stack and post-stack data) are in a reasonable agreement with the true earth models, indicating the feasibility of using 1-D strain rock physics transform and time-lapse seismic processing methodology. Estimated vertical traveltime shifts for the overburden and the majority of the reservoir are within ±1 ms of the true earth model values, indicating that the time-lapse technique is sufficiently accurate for predicting overburden velocity changes and hence geomechanical effects. Characterization of deeper structure below the overburden becomes less accurate, where more advanced time-lapse seismic processing and migration is needed to handle the complex geometry and strong lateral induced velocity changes. Nevertheless, both migrated full-offset pre-stack and near-offset post-stack data image the general features of both the overburden and

Shear wave profiles from surface wave inversion: the impact of uncertainty on seismic site response analysis

International Nuclear Information System (INIS)

Boaga, J; Vignoli, G; Cassiani, G

2011-01-01

Inversion is a critical step in all geophysical techniques, and is generally fraught with ill-posedness. In the case of seismic surface wave studies, the inverse problem can lead to different equivalent subsoil models and consequently to different local seismic response analyses. This can have a large impact on an earthquake engineering design. In this paper, we discuss the consequences of non-uniqueness of surface wave inversion on seismic responses, with both numerical and experimental data. Our goal is to evaluate the consequences on common seismic response analysis in the case of different impedance contrast conditions. We verify the implications of inversion uncertainty, and consequently of data information content, on realistic local site responses. A stochastic process is used to generate a set of 1D shear wave velocity profiles from several specific subsurface models. All these profiles are characterized as being equivalent, i.e. their responses, in terms of a dispersion curve, are compatible with the uncertainty in the same surface wave data. The generated 1D shear velocity models are then subjected to a conventional one-dimensional seismic ground response analysis using a realistic input motion. While recent analyses claim that the consequences of surface wave inversion uncertainties are very limited, our test points out that a relationship exists between inversion confidence and seismic responses in different subsoils. In the case of regular and relatively smooth increase of shear wave velocities with depth, as is usual in sedimentary plains, our results show that the choice of a specific model among equivalent solutions strongly influences the seismic response. On the other hand, when the shallow subsoil is characterized by a strong impedance contrast (thus revealing a characteristic soil resonance period), as is common in the presence of a shallow bedrock, equivalent solutions provide practically the same seismic amplification, especially in the

3D velocity structure of upper crust beneath NW Bohemia/Vogtland

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Javad Fallahi, Mohammad; Mousavi, Sima; Korn, Michael; Sens-Schönfelder, Christoph; Bauer, Klaus; Rößler, Dirk

2013-04-01

The 3D structure of the upper crust beneath west Bohemia/Vogtland region, analyzed with travel time tomography and ambient noise surface wave tomography using existing data. This region is characterized by a series of phenomena like occurrence of repeated earthquake swarms, surface exhalation, CO2 enriched fluids, mofettes, mineral springs and enhanced heat flow, and has been proposed as an excellent location for an ICDP drilling project targeted to a better understanding of the crust in an active magmatic environment. We performed a 3D tomography using P-and S-wave travel times of local earthquakes and explosions. The data set were taken from permanent and temporary seismic networks in Germany and Czech Republic from 2000 to 2010, as well as active seismic experiments like Celebration 2000 and quarry blasts. After picking P and S wave arrival times, 399 events which were recorded by 9 or more stations and azimuthal gap<160° were selected for inversion. A simultaneous inversion of P and S wave 1D velocity models together with relocations of hypocenters and station corrections was performed. The obtained minimum 1D velocity model was used as starting model for the 3D Vp and Vp/Vs velocity models. P and S wave travel time tomography employs damped least-square method and ray tracing by pseudo-bending algorithm. For model parametrization different cell node spacings have been tested to evaluate the resolution in each node. Synthetic checkerboard tests have been done to check the structural resolution. Then Vp and Vp/Vs in the preferred 3D grid model have been determined. Earthquakes locations in iteration process change till the hypocenter adjustments and travel time residuals become smaller than the defined threshold criteria. Finally the analysis of the resolution depicts the well resolved features for interpretation. We observed lower Vp/Vs ratio in depth of 5-10 km close to the foci of earthquake swarms and higher Vp/Vs ratio is observed in Saxoturingian zone and

Sparsity- and continuity-promoting seismic image recovery with curvelet frames

NARCIS (Netherlands)

Herrmann, Felix J.; Moghaddam, Peyman; Stolk, C.C.

2008-01-01

A nonlinear singularity-preserving solution to seismic image recovery with sparseness and continuity constraints is proposed. We observe that curvelets, as a directional frame expansion, lead to sparsity of seismic images and exhibit invariance under the normal operator of the linearized imaging

Tomography of core-mantle boundary and lowermost mantle coupled by geodynamics: joint models of shear and compressional velocity

Directory of Open Access Journals (Sweden)

Gaia Soldati

2015-03-01

Full Text Available We conduct joint tomographic inversions of P and S travel time observations to obtain models of delta v_P  and delta v_S in the entire mantle. We adopt a recently published method which takes into account the geodynamic coupling between mantle heterogeneity and core-mantle boundary (CMB topography by viscous flow, where sensitivity of the seismic travel times to the CMB is accounted for implicitly in the inversion (i.e. the CMB topography is not explicitly inverted for. The seismic maps of the Earth's mantle and CMB topography that we derive can explain the inverted seismic data while being physically consistent with each other. The approach involved scaling P-wave velocity (more sensitive to the CMB to density anomalies, in the assumption that mantle heterogeneity has a purely thermal origin, so that velocity and density heterogeneity are proportional to one another. On the other hand, it has sometimes been suggested that S-wave velocity might be more directly sensitive to temperature, while P heterogeneity is more strongly influenced by chemical composition. In the present study, we use only S-, and not P-velocity, to estimate density heterogeneity through linear scaling, and hence the sensitivity of core-reflected P phases to mantle structure. Regardless of whether density is more closely related to P- or S-velocity, we think it is worthwhile to explore both scaling approaches in our efforts to explain seismic data. The similarity of the results presented in this study to those obtained by scaling P-velocity to density suggests that compositional anomaly has a limited impact on viscous flow in the deep mantle.

Evidence of shallow gas in the Queen Charlotte Basin from waveform tomography of seismic reflection data

Energy Technology Data Exchange (ETDEWEB)

Takam Takougang, Eric M.; Calvert, Andrew J. [Simon Fraser University (Canada)], email: eta9@sfu.ca

2011-07-01

The Geological Survey of Canada (GSC) collected eight seismic reflection lines in 1988 across the Queen Charlotte sedimentary basin of western Canada, which is the largest tertiary basin on the west coast. This work furthers the study of the upper part of the basin by using quantitative imaging of its structure through application of 2-D waveform tomography to the limited offset seismic reflection data. With the help of waveform tomography, seismic reflection data has allowed the identification of pockmark structures and pipe-like gas chimney in the recovered velocity and attenuation models. Overall, there is an excellent match between field data and predicted data. and a good match between the sonic log and a 1-D velocity function derived from the 2-D velocity model. This shows that specific preconditioning of the data and a good inversion strategy make it possible to use waveform tomography of relatively short offset reflection data for the imaging of shallow geological features.

The Lusi seismic experiment: An initial study to understand the effect of seismic activity to Lusi

Energy Technology Data Exchange (ETDEWEB)

Karyono, E-mail: karyonosu@gmail.com [Agency for Meteorology, Climatology and Geophysics (BMKG), Jakarta (Indonesia); OSLO University (Norway); Padjadjaran University (UNPAD), Bandung (Indonesia); Mazzini, Adriano; Sugiharto, Anton [OSLO University (Norway); Lupi, Matteo [ETH Zurich (Switzerland); Syafri, Ildrem [Padjadjaran University (UNPAD), Bandung (Indonesia); Masturyono,; Rudiyanto, Ariska; Pranata, Bayu; Muzli,; Widodo, Handi Sulistyo; Sudrajat, Ajat [Agency for Meteorology, Climatology and Geophysics (BMKG), Jakarta (Indonesia)

2015-04-24

The spectacular Lumpur Sidoarjo (Lusi) eruption started in northeast Java on the 29 of May 2006 following a M6.3 earthquake striking the island [1,2]. Initially, several gas and mud eruption sites appeared along the reactivated strike-slip Watukosek fault system [3] and within weeks several villages were submerged by boiling mud. The most prominent eruption site was named Lusi. The Lusi seismic experiment is a project aims to begin a detailed study of seismicity around the Lusi area. In this initial phase we deploy 30 seismometers strategically distributed in the area around Lusi and along the Watukosek fault zone that stretches between Lusi and the Arjuno Welirang (AW) complex. The purpose of the initial monitoring is to conduct a preliminary seismic campaign aiming to identify the occurrence and the location of local seismic events in east Java particularly beneath Lusi.This network will locate small event that may not be captured by the existing BMKG network. It will be crucial to design the second phase of the seismic experiment that will consist of a local earthquake tomography of the Lusi-AW region and spatial and temporal variations of vp/vs ratios. The goal of this study is to understand how the seismicity occurring along the Sunda subduction zone affects to the behavior of the Lusi eruption. Our study will also provide a large dataset for a qualitative analysis of earthquake triggering studies, earthquake-volcano and earthquake-earthquake interactions. In this study, we will extract Green’s functions from ambient seismic noise data in order to image the shallow subsurface structure beneath LUSI area. The waveform cross-correlation technique will be apply to all of recordings of ambient seismic noise at 30 seismographic stations around the LUSI area. We use the dispersive behaviour of the retrieved Rayleigh waves to infer velocity structures in the shallow subsurface.

Imaging Stress Transients and Fault Zone Processes with Crosswell Continuous Active-Source Seismic Monitoring at the San Andreas Fault Observatory at Depth

Science.gov (United States)

Niu, F.; Taira, T.; Daley, T. M.; Marchesini, P.; Robertson, M.; Wood, T.

2017-12-01

Recent field and laboratory experiments identify seismic velocity changes preceding microearthquakes and rock failure (Niu et al., 2008, Nature; Scuderi et al., 2016, NatureGeo), which indicates that a continuous monitoring of seismic velocity might provide a mean of understanding of the earthquake nucleation process. Crosswell Continuous Active-Source Seismic Monitoring (CASSM) using borehole sources and sensors has proven to be an effective tool for measurements of seismic velocity and its temporal variation at seismogenic depth (Silver, et al, 2007, BSSA; Daley, et al, 2007, Geophysics). To expand current efforts on the CASSM development, in June 2017 we have begun to conduct a year-long CASSM field experiment at the San Andreas Fault Observatory at Depth (SAFOD) in which the preceding field experiment detected the two sudden velocity reductions approximately 10 and 2 hours before microearthquakes (Niu et al., 2008, Nature). We installed a piezoelectric source and a three-component accelerometer at the SAFOD pilot and main holes ( 1 km depth) respectively. A seismic pulse was fired from the piezoelectric source four times per second. Each waveform was recorded 150-ms-long data with a sampling rate of 48 kHz. During this one-year experiment, we expect to have 10-15 microearthquakes (magnitude 1-3) occurring near the SAFOD site, and the data collected from the new experiment would allow us to further explore a relation between velocity changes and the Parkfield seismicity. Additionally, the year-long data provide a unique opportunity to study long-term velocity changes that might be related to seasonal stress variations at Parkfield (Johnson et al., 2017, Science). We will report on initial results of the SAFOD CASSM experiment and operational experiences of the CASSM development.

Early arrival waveform inversion of shallow seismic land data

KAUST Repository

Hanafy, Sherif M.; Yu, Han

2013-01-01

, compared to traveltime tomography, EWI can generate a highly resolved velocity tomogram from shallow seismic data. The more accurate EWI tomogram can make an economically important difference in assessing the storage potential of this wadi; in this case we

Should tsunami simulations include a nonzero initial horizontal velocity?

Science.gov (United States)

Lotto, Gabriel C.; Nava, Gabriel; Dunham, Eric M.

2017-08-01

Tsunami propagation in the open ocean is most commonly modeled by solving the shallow water wave equations. These equations require initial conditions on sea surface height and depth-averaged horizontal particle velocity or, equivalently, horizontal momentum. While most modelers assume that initial velocity is zero, Y.T. Song and collaborators have argued for nonzero initial velocity, claiming that horizontal displacement of a sloping seafloor imparts significant horizontal momentum to the ocean. They show examples in which this effect increases the resulting tsunami height by a factor of two or more relative to models in which initial velocity is zero. We test this claim with a "full-physics" integrated dynamic rupture and tsunami model that couples the elastic response of the Earth to the linearized acoustic-gravitational response of a compressible ocean with gravity; the model self-consistently accounts for seismic waves in the solid Earth, acoustic waves in the ocean, and tsunamis (with dispersion at short wavelengths). Full-physics simulations of subduction zone megathrust ruptures and tsunamis in geometries with a sloping seafloor confirm that substantial horizontal momentum is imparted to the ocean. However, almost all of that initial momentum is carried away by ocean acoustic waves, with negligible momentum imparted to the tsunami. We also compare tsunami propagation in each simulation to that predicted by an equivalent shallow water wave simulation with varying assumptions regarding initial velocity. We find that the initial horizontal velocity conditions proposed by Song and collaborators consistently overestimate the tsunami amplitude and predict an inconsistent wave profile. Finally, we determine tsunami initial conditions that are rigorously consistent with our full-physics simulations by isolating the tsunami waves from ocean acoustic and seismic waves at some final time, and backpropagating the tsunami waves to their initial state by solving the

RELIABILITY AND ACCURACY ASSESSMENT OF INVASIVE AND NON- INVASIVE SEISMIC METHODS FOR SITE CHARACTERIZATION: FEEDBACK FROM THE INTERPACIFIC PROJECT

OpenAIRE

Garofalo , F.; Foti , S.; Hollender , F.; Bard , P.-Y.; Cornou , C.; Cox , B.R.; Dechamp , A.; Ohrnberger , M.; Sicilia , D.; Vergniault , C.

2017-01-01

International audience; The InterPacific project (Intercomparison of methods for site parameter and velocity profile characterization) aims to assess the reliability of seismic site characterization methods (borehole and surface wave methods) used for estimating shear wave velocity (VS) profiles and other related parameters (e.g., VS30). Three sites, representative of different geological conditions relevant for the evaluation of seismic site response effects, have been selected: (1) a hard r...

GPS-determined Crustal Deformation of South Korea after the 2011 Tohoku-Oki Earthquake: Straining Heterogeneity and Seismicity

Science.gov (United States)

Ree, J. H.; Kim, S.; Yoon, H. S.; Choi, B. K.; Park, P. H.

2017-12-01

The GPS-determined, pre-, co- and post-seismic crustal deformations of the Korean peninsula with respect to the 2011 Tohoku-Oki earthquake (Baek et al., 2012, Terra Nova; Kim et al., 2015, KSCE Jour. of Civil Engineering) are all stretching ones (extensional; horizontal stretching rate larger than horizontal shortening rate). However, focal mechanism solutions of earthquakes indicate that South Korea has been at compressional regime dominated by strike- and reverse-slip faultings. We reevaluated the velocity field of GPS data to see any effect of the Tohoku-Oki earthquake on the Korean crustal deformation and seismicity. To calculate the velocity gradient tensor of GPS sites, we used a gridding method based on least-square collocation (LSC). This LSC method can overcome shortcomings of the segmentation methods including the triangulation method. For example, an undesirable, abrupt change in components of velocity field occurs at segment boundaries in the segmentation methods. It is also known that LSC method is more useful in evaluating deformation patterns in intraplate areas with relatively small displacements. Velocity vectors of South Korea, pointing in general to 113° before the Tohoku-Oki earthquake, instantly changed their direction toward the epicenter (82° on average) during the Tohoku-Oki earthquake, and then gradually returned to the original position about 2 years after the Tohoku-Oki earthquake. Our calculation of velocity gradient tensors after the Tohoku-Oki earthquake shows that the stretching and rotating fields are quite heterogeneous, and that both stretching and shortening areas exist in South Korea. In particular, after the post-seismic relaxation ceased (i.e., from two years after the Tohoku-Oki earthquake), regions with thicker and thinner crusts tend to be shortening and stretching, respectively, in South Korea. Furthermore, the straining rate is larger in the regions with thinner crust. Although there is no meaningful correlation between

Seismic and thermal structure of the crust and uppermost mantle beneath Antarctica from inversion of multiple seismic datasets

Science.gov (United States)

Wiens, D.; Shen, W.; Anandakrishnan, S.; Aster, R. C.; Gerstoft, P.; Bromirski, P. D.; Dalziel, I.; Hansen, S. E.; Heeszel, D.; Huerta, A. D.; Nyblade, A.; Stephen, R. A.; Wilson, T. J.; Winberry, J. P.; Stern, T. A.

2017-12-01

Since the last decade of the 20th century, over 200 broadband seismic stations have been deployed across Antarctica (e.g., temporary networks such as TAMSEIS, AGAP/GAMSEIS, POLENET/ANET, TAMNNET and RIS/DRIS by U.S. geoscientists as well as stations deployed by Japan, Britain, China, Norway, and other countries). In this presentation, we discuss our recent efforts to build reference crustal and uppermost mantle shear velocity (Vs) and thermal models for continental Antarctica based on those seismic arrays. By combing the high resolution Rayleigh wave dispersion maps derived from both ambient noise and teleseismic earthquakes, together with P receiver function waveforms, we develop a 3-D Vs model for the crust and uppermost mantle beneath Central and West Antarctica to a depth of 200 km. Additionally, using this 3-D seismic model to constrain the crustal structure, we re-invert for the upper mantle thermal structure using the surface wave data within a thermodynamic framework and construct a 3-D thermal model for the Antarctic lithosphere. The final product, a high resolution thermal model together with associated uncertainty estimates from the Monte Carlo inversion, allows us to derive lithospheric thickness and surface heat flux maps for much of the continent. West Antarctica shows a much thinner lithosphere ( 50-90 km) than East Antarctica ( 130-230 km), with a sharp transition along the Transantarctic Mountains (TAM). A variety of geological features, including a slower/hotter but highly heterogeneous West Antarctica and a much faster/colder East Antarctic craton, are present in the 3-D seismic/thermal models. Notably, slow seismic velocities observed in the uppermost mantle beneath the southern TAM are interpreted as a signature of lithospheric foundering and replacement with hot asthenosphere. The high resolution image of these features from the 3-D models helps further investigation of the dynamic state of Antarctica's lithosphere and underlying asthenosphere

Steep-dip seismic imaging of the shallow San Andreas fault near Parkfield.

Science.gov (United States)

Hole, J A; Catchings, R D; St Clair, K C; Rymer, M J; Okaya, D A; Carney, B J

2001-11-16

Seismic reflection and refraction images illuminate the San Andreas Fault to a depth of 1 kilometer. The prestack depth-migrated reflection image contains near-vertical reflections aligned with the active fault trace. The fault is vertical in the upper 0.5 kilometer, then dips about 70 degrees to the southwest to at least 1 kilometer subsurface. This dip reconciles the difference between the computed locations of earthquakes and the surface fault trace. The seismic velocity cross section shows strong lateral variations. Relatively low velocity (10 to 30%), high electrical conductivity, and low density indicate a 1-kilometer-wide vertical wedge of porous sediment or fractured rock immediately southwest of the active fault trace.

Physical properties of the crust along the seismic refraction profile Vrancea'99

International Nuclear Information System (INIS)

Bala, A.; Raileanu, V.; Popa, M.

2002-01-01

The seismic refraction project VRANCEA'99 is a contribution to the German-Romanian Collaborative Research Center (CRC) 461: 'Strong Earthquakes - a Challenge for Geosciences and Civil Engineering' which was launched by the University of Karlsruhe, Germany in collaboration with various research institutes in Romania. Preparations started already in 1998, but the actual field work was carried out in May 1999. The seismic project VRANCEA'99, was jointly organized by Geophysical Institute of Karlsruhe University, GeoForschungsZentrum (GFZ) Potsdam, Germany and National Institute for Earth Physics from Bucharest, Romania. Seismic and seismological data recorded on this profile are used to compute a reliable continuous distribution of seismic velocity ( P wave ) with depth. Nine of the explosions from seismic profile Vrancea'99 were also recorded at the seismological telemetered stations from the national seismic network. These explosions were localized as seismic events using seismologic data and also some data from recording sites with 3D sensors deployed along the profile. Time - distance graphs are used to derive the continuous distribution of velocity with depth between 5 km - 45 km depth by Wiechert - Herglotz method. The crustal 2D model from obtained on the profile VRANCEA'99 was introduced as starting model in a density modeling along the refraction profile. The measured values of Bouguer anomaly along the profile were introduced in the model in order to be compared with the computed Bouguer anomaly. After several iterations, the computed Bouguer anomaly is overlapping well enough the observed Bouguer anomaly along the profile. This certify the chosen model (obtained from seismic forward and inverse modeling) using another method of geophysical modeling. Geologic and tectonic implications of the obtained density model are discussed. (authors)

Regional versus detailed velocity analysis to quantify hydrate and free gas in marine sediments : the south Shetland margin case study

Energy Technology Data Exchange (ETDEWEB)

Tinivella, U.; Loreto, M.F.; Accaino, F. [Inst. Nazionale di Oceanografia di Geofisica Sperimentale, Trieste (Italy)

2008-07-01

The presence of gas hydrate and free gas within marine sediments, deposited along the South Shetland margin, offshore the Antarctic Peninsula, was confirmed by low and high resolution geophysical data, acquired during three research cruises in 1989-1990. Seismic data analysis has demonstrated the presence of a bottom simulating reflector that is very strong and continuous in the eastern part of the margin. This seismic dataset was used in the past to extract detailed velocity information of the shallow structures by using traditional tomographic inversion and jointly tomographic inversion and pre-stack depth migration tool. This paper presented a method to obtain a regional seismic velocity field and information about hydrate and free gas presence in the marine sediments, by using an improved method of the standard analysis of the pre-stack depth migration output. The velocity field was obtained with a layer stripping approach and tomographic inversion of the reflections observed in common image gathering. The paper presented the seismic data and regional and detailed velocity analysis. The results of residual semblance analyses were also presented. Gas phase concentrations were then discussed. The velocity analysis revealed the presence of three main layers characterizing the first kilometer of sediments below the sea floor. In addition, velocity models and related gas-phase sections showed that gas was concentrated in different parts of the profile than where the hydrate was concentrated. This observation confirmed that geological structures and sedimentary processes controlled the gas and hydrate distribution, as observed along other margins. 7 refs., 5 figs.

An analysis of the first-arrival times picked on the DSS and wide-angle seismic section recorded in Italy since 1968

Directory of Open Access Journals (Sweden)

R. Tondi

2004-06-01

Full Text Available We performed an analysis of refraction data recorded in Italy since 1968 in the frame of the numerous deep seismic sounding and wide-angle reflection/refraction projects. The aims of this study are to construct a parametric database including the recording geometric information relative to each profile, the phase pickings and the results of some kinematic analyses performed on the data, and to define a reference 1D velocity model for the Italian territory from all the available refraction data. As concerns the first goal, for each seismic section we picked the P-wave first-arrival-times, evaluated the uncertainties of the arrival-times pickings and determined from each travel time-offset curve the 1D velocity model. The study was performed on 419 seismic sections. Picking was carried out manually by an algorithm which includes the computation of three picking functions and the picking- error estimation. For each of the travel time-offset curves a 1D velocity model has been calculated. Actually, the 1D velocity-depth functions were estimated in three different ways which assume: a constant velocitygradient model, a varying velocity-gradient model and a layered model. As regards the second objective of this work, a mean 1D velocity model for the Italian crust was defined and compared with those used for earthquake hypocentre locations and seismic tomographic studies by different institutions operating in the Italian area, to assess the significance of the model obtained. This model can be used in future works as input for a next joint tomographic inversion of active and passive seismic data.

A comparative study of calculated and measured particle velocities

International Nuclear Information System (INIS)

Tariq, S.M.

2005-01-01

After an explosive is detonated in a blast hole, seismic waves are generated in the ground surrounding the blast hole. These waves cause the particles of rock to oscillate about its position. As the wave attenuate, the particles come back to their original position. The rapidity with which the particles move is called the particle velocity. The peak or maximum velocity is the value which is of prime concern. This value of peak particle velocity can be estimated by the equations determined by the United States Bureau of Mines and by the DUPONT. A research program was conducted by the author at the 'Beck Materials Quarry' situated near Rolla, Missouri, USA. The purpose was to draw a comparison between the predicted and measured particle velocities. It was generally found that the predicted peak particle velocities were quite high as compared to the velocities measured by the Seismographs. (author)

Seismic and potential field studies over the East Midlands

Science.gov (United States)

Kirk, Wayne John

A seismic refraction profile was undertaken to investigate the source of an aeromagnetic anomaly located above the Widmerpool Gulf, East Midlands. Ten shots were fired into 51 stations at c. 1.5km spacing in a 70km profile during 41 days recording. The refraction data were processed using standard techniques to improve the data quality. A new filtering technique, known as Correlated Adaptive Noise Cancellation was tested on synthetic data and successfully applied to controlled source and quarry blast data. Study of strong motion data reveals that the previous method of site calibration is invalid. A new calibration technique, known as the Scaled Amplitude method is presented to provide safer charge size estimation. Raytrace modelling of the refraction data and two dimensional gravity interpretation confirms the presence of the Widmerpool Gulf but no support is found for the postulated intrusion. Two dimensional magnetic interpretation revealed that the aeromagnetic anomaly could be modelled with a Carboniferous igneous source. A Lower Palaeozoic refractor with a velocity of 6.0 km/s is identified at a maximum depth of c. 2.85km beneath the Widmerpool Gulf. Carboniferous and post-Carboniferous sediments within the gulf have velocities between 2.6-5.5 km/s with a strong vertical gradient. At the gulf margins, a refractor with a constant velocity of 5.2 km/s is identified as Dinantian limestone. A low velocity layer of proposed unaltered Lower Palaeozoics is identified beneath the limestone at the eastern edge of the Derbyshire Dome. The existence and areal extent of this layer are also determined from seismic reflection data. Image analysis of potential field data, presents a model identifying 3 structural provinces, the Midlands Microcraton, the Welsh and English Caledonides and a central region of complex linears. This model is used to explain the distribution of basement rocks determined from seismic and gravity profiles.