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Sample records for s-wave seismic tomography

  1. Upper mantle seismic structure beneath southwest Africa from finite-frequency P- and S-wave tomography

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Yuan, Xiaohui; Tilmann, Frederik

    2015-01-01

    We present a 3D high-resolution seismic model of the southwestern Africa region from teleseismic tomographic inversion of the P- and S- wave data recorded by the amphibious WALPASS network. We used 40 temporary stations in southwestern Africa with records for a period of 2 years (the OBS operated...... inferred from teleseismic shear waves indicate a predominant NE-SW ori- entation for most of the land stations. Current results indicate no evidence for a consistent signature of fossil plume....

  2. Upper mantle seismic structure beneath southwest Africa from finite-frequency P- and S-wave tomography

    Science.gov (United States)

    Youssof, Mohammad; Yuan, Xiaohui; Tilmann, Frederik; Heit, Benjamin; Weber, Michael; Jokat, Wilfried; Geissler, Wolfram; Laske, Gabi; Eken, Tuna; Lushetile, Bufelo

    2015-04-01

    We present a 3D high-resolution seismic model of the southwestern Africa region from teleseismic tomographic inversion of the P- and S- wave data recorded by the amphibious WALPASS network. We used 40 temporary stations in southwestern Africa with records for a period of 2 years (the OBS operated for 1 year), between November 2010 and November 2012. The array covers a surface area of approximately 600 by 1200 km and is located at the intersection of the Walvis Ridge, the continental margin of northern Namibia, and extends into the Congo craton. Major questions that need to be understood are related to the impact of asthenosphere-lithosphere interaction, (plume-related features), on the continental areas and the evolution of the continent-ocean transition that followed the break-up of Gondwana. This process is supposed to leave its imprint as distinct seismic signature in the upper mantle. Utilizing 3D sensitivity kernels, we invert traveltime residuals to image velocity perturbations in the upper mantle down to 1000 km depth. To test the robustness of our tomographic image we employed various resolution tests which allow us to evaluate the extent of smearing effects and help defining the optimum inversion parameters (i.e., damping and smoothness) used during the regularization of inversion process. Resolution assessment procedure includes also a detailed investigation of the effect of the crustal corrections on the final images, which strongly influenced the resolution for the mantle structures. We present detailed tomographic images of the oceanic and continental lithosphere beneath the study area. The fast lithospheric keel of the Congo Craton reaches a depth of ~250 km. Relatively low velocity perturbations have been imaged within the orogenic Damara Belt down to a depth of ~150 km, probably related to surficial suture zones and the presence of fertile material. A shallower depth extent of the lithospheric plate of ~100 km was observed beneath the ocean

  3. Introduction to Seismic Tomography

    Energy Technology Data Exchange (ETDEWEB)

    Rowe, Charlotte Anne [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-11-21

    Tomography is a method of obtaining an image of a 3d object by observing the behavior of energy transmissions through the object. The image is obtained by Interrogating the object with Energy sources at a variety of Locations and observing the Object’s effects on the energy at a Variety of sensors. Tomography was first Used to build 3-dimensional Scans through Human bodies. These Are called computed Tomographic (ct) scans.

  4. 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.

  5. Seismic Tomography of the South Carpathian System

    Science.gov (United States)

    Stuart, G. W.; Ren, Y.; Dando, B. D.; Houseman, G.; Ionescu, C.; Hegedus, E.; Radovanovic, S.; South Carpathian Project Working Group

    2010-12-01

    The South Carpathian Mountain Range is an enigmatic system, which includes one of the most seismically active regions in Europe today. That region, Vrancea in the SE Carpathians, is well studied and its deep structure may be geologically unique, but the mantle structures beneath the western part of the South Carpathian Range are not well resolved by previous tomographic studies. The South Carpathian Project (SCP) is a major temporary deployment (2009-2011) of seismic broadband systems extending across the eastern Pannonian Basin and the South Carpathian Mountains. In this project we aim to map the upper mantle structure in central Europe with the objective of testing geodynamic models of the process that produced extension in the Pannonian, synchronous with convergence and uplift in the Carpathians. Here, we describe initial results of finite-frequency tomography using body waves to image the mantle of the region. We have selected teleseismic earthquakes with magnitude greater than 5.9, which occurred between 2005 and 2010. The data were recorded on 57 temporary stations deployed in the South Carpathian Project, 56 temporary stations deployed in the earlier Carpathian Basins Project (CBP), and 41 permanent broadband stations. The differential travel times are measured in high, intermediate and low frequencies (0.5-2.0 Hz, 0.1-0.5 Hz and 0.03-0.1 Hz for both P-wave, 0.1-0.5 Hz, 0.05-0.1 Hz and 0.02-0.05 Hz for S-wave), and are inverted to produce P and S-wave velocity maps at different depths in the mantle. An extensive zone of high seismic velocities is located in the Mantle Transition zone beneath the Pannonian Basin, and is related to down-welling associated with an earlier phase of continental convergence in the Pannonian region. These results will be used in conjunction with 3D geodynamical modelling to help understand the geological evolution of this region. SCP working group: G. Houseman, G. Stuart, Y. Ren, B. Dando, P. Lorinczi, School of Earth and

  6. Time-dependent seismic tomography

    Science.gov (United States)

    Julian, B.R.; Foulger, G.R.

    2010-01-01

    Of methods for measuring temporal changes in seismic-wave speeds in the Earth, seismic tomography is among those that offer the highest spatial resolution. 3-D tomographic methods are commonly applied in this context by inverting seismic wave arrival time data sets from different epochs independently and assuming that differences in the derived structures represent real temporal variations. This assumption is dangerous because the results of independent inversions would differ even if the structure in the Earth did not change, due to observational errors and differences in the seismic ray distributions. The latter effect may be especially severe when data sets include earthquake swarms or aftershock sequences, and may produce the appearance of correlation between structural changes and seismicity when the wave speeds are actually temporally invariant. A better approach, which makes it possible to assess what changes are truly required by the data, is to invert multiple data sets simultaneously, minimizing the difference between models for different epochs as well as the rms arrival-time residuals. This problem leads, in the case of two epochs, to a system of normal equations whose order is twice as great as for a single epoch. The direct solution of this system would require twice as much memory and four times as much computational effort as would independent inversions. We present an algorithm, tomo4d, that takes advantage of the structure and sparseness of the system to obtain the solution with essentially no more effort than independent inversions require. No claim to original US government works Journal compilation ?? 2010 RAS.

  7. Detecting P and S-wave of Mt. Rinjani seismic based on a locally stationary autoregressive (LSAR) model

    Science.gov (United States)

    Nurhaida, Subanar, Abdurakhman, Abadi, Agus Maman

    2017-08-01

    Seismic data is usually modelled using autoregressive processes. The aim of this paper is to find the arrival times of the seismic waves of Mt. Rinjani in Indonesia. Kitagawa algorithm's is used to detect the seismic P and S-wave. Householder transformation used in the algorithm made it effectively finding the number of change points and parameters of the autoregressive models. The results show that the use of Box-Cox transformation on the variable selection level makes the algorithm works well in detecting the change points. Furthermore, when the basic span of the subinterval is set 200 seconds and the maximum AR order is 20, there are 8 change points which occur at 1601, 2001, 7401, 7601,7801, 8001, 8201 and 9601. Finally, The P and S-wave arrival times are detected at time 1671 and 2045 respectively using a precise detection algorithm.

  8. Upper-mantle velocities below the Scandinavian Mountains from P- and S- wave traveltime tomography

    DEFF Research Database (Denmark)

    Hejrani, Babak; Balling, N.; Jacobsen, B. H.

    2017-01-01

    More than 20000 arrival-times of teleseismic P- and S-waves were measured over a period of more than 10 years in five separate temporary and two permanent seismic networks covering the Scandinavian (Scandes) Mountains and adjacent areas of the Baltic Shield. The relative traveltime residuals were...... inverted to 3D tomograms of P- and S- velocities and the VP/VS ratio. Resolution analysis documents that good 3D resolution is available under the dense network south of 64° latitude (Southern Scandes Mountains), and patchier, but highly useful resolution is available further north, where station coverage...... is more uneven. A pronounced upper-mantle velocity boundary (UMVB), transecting the study region is defined. It runs from SE Norway (east of the Oslo Graben) across the mountains to the Norwegian coast near Trondheim (around the Møre-Trøndelag Fault Complex), from where it follows the coast and runs...

  9. Upper-mantle P- and S- wave velocities across the Northern Tornquist Zone from traveltime tomography

    DEFF Research Database (Denmark)

    Hejrani, Babak; Balling, N.; Jacobsen, B. H.

    2015-01-01

    This study presents P- and S-wave velocity variations for the upper mantle in southern Scandinavia and northern Germany based on teleseismic traveltime tomography. Tectonically, this region includes the entire northern part of the prominent Tornquist Zone which follows along the transition from old...... Precambrian shield units to the east to younger Phanerozoic deep sedimentary basins to the southwest. We combine data from several separate temporary arrays/profiles (276 stations) deployed over a period of about 15 yr and permanent networks (31 stations) covering the areas of Denmark, northern Germany......, southern Sweden and southern Norway. By performing an integrated P- and S-traveltime analysis, we obtain the first high-resolution combined 3-D VP and VS models, including variations in the VP/VS ratio, for the whole of this region of study. Relative station mean traveltime residuals vary within ±1 s for P...

  10. S-Wave Velocity Across Central Mexico Using High Resolution Surface Wave Tomography

    Science.gov (United States)

    Iglesias, A.; Clayton, R. W.; Pérez-Campos, X.; Singh, S. K.; Pacheco, J. F.; García, D.; Valdés-González, C.

    2008-12-01

    The shear wave velocity structure across central Mexico is determined by surface wave dispersion from a dense linear seismic experiment "Mesoamerican Subduction Experiment" (MASE). MASE consisted of 100 portable broadband stations deployed along a line crossing Central Mexico from the Pacific Coast to almost the Gulf of Mexico. Regional records were used to obtain Rayleigh-wave group velocity maps for periods from 5 to 50 s and they show a dramatic variation of velocity (~40%), especially for periods larger of 20 s. Local dispersion curves were reconstructed for each station and inverted to find S-wave velocity by using a simulated annealing algorithm. The results, from inversion, show a significant change, particularly in the lower crust, between the backarc, volcanic arc and forearc regions. The crust in the forearc is thicker and faster than the backarc region. Just below the active Trans Mexican Volcanic Belt (TMVB) (300 km from the coast) is presently a low velocity spot (~3.4 km/s) suggesting presence of anomalous material (probably related to a mantle wedge) as deep as 50 km. The results also show a poorly resolved slab and wedge which correspond to the ones in a model reported recently. The results are supported with consistency checks and resolution tests.

  11. Seismic anisotropy inferred from direct S-wave-derived splitting measurements and its geodynamic implications beneath southeastern Tibetan Plateau

    Science.gov (United States)

    Kant Tiwari, Ashwani; Singh, Arun; Eken, Tuna; Singh, Chandrani

    2017-04-01

    The present study deals with detecting seismic anisotropy parameters beneath southeastern Tibet near Namcha Barwa Mountain using the splitting of direct S waves. We employ the reference station technique to remove the effects of source-side anisotropy. Seismic anisotropy parameters, splitting time delays, and fast polarization directions are estimated through analyses of a total of 501 splitting measurements obtained from direct S waves from 25 earthquakes ( ≥ 5.5 magnitude) that were recorded at 42 stations of the Namcha Barwa seismic network. We observe a large variation in time delays ranging from 0.64 to 1.68 s, but in most cases, it is more than 1 s, which suggests a highly anisotropic lithospheric mantle in the region. A comparison between direct S- and SKS-derived splitting parameters shows a close similarity, although some discrepancies exist where null or negligible anisotropy has been reported earlier using SKS. The seismic stations with hitherto null or negligible anisotropy are now supplemented with new measurements with clear anisotropic signatures. Our analyses indicate a sharp change in lateral variations of fast polarization directions (FPDs) from consistent SSW-ENE or W-E to NW-SE direction at the southeastern edge of Tibet. Comparison of the FPDs with Global Positioning System (GPS) measurements, absolute plate motion (APM) directions, and surface geological features indicates that the observed anisotropy and hence inferred deformation patterns are not only due to asthenospheric dynamics but are a combination of lithospheric deformation and sub-lithospheric (asthenospheric) mantle dynamics. Direct S-wave-based station-averaged splitting measurements with increased back-azimuths tend to fill the coverage gaps left in SKS measurements.

  12. Estimation of earthquake source parameters in the Kachchh seismic zone, Gujarat, India, using three component S-wave spectra

    Science.gov (United States)

    Nagamani, Durgada; Mandal, Prantik

    2017-07-01

    Earthquake source parameters and crustal Q0 values for the 138 selected local events of (Mw{:}2.5{-}4.4) the 2001 Bhuj earthquake sequence have been computed through inversion modelling of S-waves from three-component broadband seismometer data. SEISAN software has been used to locate the identified local earthquakes, which were recorded at least three or more stations of the Kachchh seismological network. Three component spectra of S-wave are being inverted by using the Levenberg-Marquardt non-linear inversion technique, wherein the inversion scheme is formulated based on ω 2 source model. SAC Software (seismic analysis code) is being utilized for calculating three-component displacement and velocity spectra of S-wave. The displacement spectra are used for estimating corner frequency (in Hz) and long period spectral level (in nm-s). These two parameters play a key role in estimating earthquake source parameters. The crustal {Q}0 values have been computed simultaneously for each component of three-component broadband seismograph. The estimated seismic moment (M0) and source radius ( r) using S-wave spectra range from 7.03E+12 to 5.36E+15 N-m and 178.56 to 565.21 m, respectively. The corner frequencies for S-wave vary from 3.025 to 7.425 Hz. We also estimated the radiated energy (ES) using velocity spectra, which is varying from 2.76E+06 to 4.07E+11 Joules. The estimated apparent stress drop and static stress drop values range from 0.01 to 2.56 and 0.53 to 36.79 MPa, respectively. Our study also reveals that estimated Q0 values vary from 119.0 to 7229.5, with an average Q0 value of 701. Another important parameter, by which the earthquake rupture process can be recognized, is Zuniga parameter. It suggests that most of the Kachchh events follow the frictional overshoot model. Our estimated static stress drop values are higher than the apparent stress drop values. And the stress drop values are quite larger for intraplate earthquakes than the interplate earthquakes.

  13. An Objective Rationale for the Choice of Regularisation Parameter with Application to Global Multiple-Frequency S-Wave Tomography

    Science.gov (United States)

    Zaroli, C.; Sambridge, M.; Leveque, J. J.; Debayle, E.; Nolet, G.

    2014-12-01

    In a linear ill-posed inverse problem, the regularisation parameter (damping) controls the balance between minimising both the residual data misfit and the model norm. Poor knowledge of data uncertainties often makes the selection of damping rather arbitrary. To go beyond that subjectivity, an objective rationale for the choice of damping is presented, which is based on the coherency of delay-time estimates in different frequency bands. Our method is tailored to the problem of global Multiple-Frequency Tomography, using a data set of 287078 S-wave delay-times measured in five frequency bands (10, 15, 22, 34, 51 s central periods). Whereas for each ray path the delay-time estimates should vary coherently from one period to the other, the noise most likely is not coherent. Thus, the lack of coherency of the information in different frequency bands is exploited, using an analogy with the cross-validation method, to identify models dominated by noise.In addition, a sharp change of behaviour of the model infinity-norm, as the damping becomes lower than a threshold value, is interpreted as the signature of data noise starting to significantly pollute at least one model component. Models with damping larger than this threshold are diagnosed as being constructed with poor data exploitation.Finally, a preferred model is selected from the remaining range of permitted model solutions. This choice is quasi-objective in terms of model interpretation, as the selected model shows a high degree of similarity with almost all other permitted models. The obtained tomographic model is displayed in mid lower-mantle (660-1910 km depth), and is shown to be mostly compatible with three other recent global shear-velocity models, while significant differences can be noticed. A wider application of the presented rationale should permit us to converge towards more objective seismic imaging of the Earth's mantle, using as much as possible of the relevant structural information in the data

  14. 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

  15. Prediction of subsurface fracture in mining zone of Papua using passive seismic tomography based on Fresnel zone

    Energy Technology Data Exchange (ETDEWEB)

    Setiadi, Herlan; Nurhandoko, Bagus Endar B.; Wely, Woen [WISFIR Lab., Physics of Complex System, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Bandung 40132 (Indonesia); Riyanto, Erwin [PT Freeport Indonesia, Tembagapura, Indonesia herlansetiadi@yahoo.com (Indonesia)

    2015-04-16

    Fracture prediction in a block cave of underground mine is very important to monitor the structure of the fracture that can be harmful to the mining activities. Many methods can be used to obtain such information, such as TDR (Time Domain Relectometry) and open hole. Both of them have limitations in range measurement. Passive seismic tomography is one of the subsurface imaging method. It has advantage in terms of measurements, cost, and rich of rock physical information. This passive seismic tomography studies using Fresnel zone to model the wavepath by using frequency parameter. Fresnel zone was developed by Nurhandoko in 2000. The result of this study is tomography of P and S wave velocity which can predict position of fracture. The study also attempted to use sum of the wavefronts to obtain position and time of seismic event occurence. Fresnel zone tomography and the summation wavefront can predict location of geological structure of mine area as well.

  16. Three-dimensional S-wave velocity model of the Bohemian Massif from Bayesian ambient noise tomography

    Science.gov (United States)

    Valentová, Lubica; Gallovič, František; Maierová, Petra

    2017-10-01

    We perform two-step surface wave tomography of phase-velocity dispersion curves obtained by ambient noise cross-correlations in the Bohemian Massif. In the first step, the inter-station dispersion curves were inverted for each period (ranging between 4 and 20 s) separately into phase-velocity maps using 2D adjoint method. In the second step, we perform Bayesian inversion of the set of the phase-velocity maps into an S-wave velocity model. To sample the posterior probability density function, the parallel tempering algorithm is employed providing over 1 million models. From the model samples, not only mean model but also its uncertainty is determined to appraise the reliable features. The model is correlated with known main geologic structures of the Bohemian Massif. The uppermost low-velocity anomalies are in agreement with thick sedimentary basins. In deeper parts (4-20 km), the S-wave velocity anomalies correspond, in general, to main tectonic domains of the Bohemian Massif. The exception is a stable low-velocity body in the middle of the high-velocity Moldanubian domain and high-velocity body resembling a promontory of the Moldanubian into the Teplá-Barrandian domain. The most pronounced (high-velocity) anomaly is located beneath the Eger Rift that is a part of a Tertiary rift system across Europe.

  17. Insights in P- and S-wave relative traveltime tomography from analysing finite-frequency Fréchet kernels

    Science.gov (United States)

    Maupin, Valérie; Kolstrup, Marianne Lanzky

    2015-09-01

    Regional body-wave tomography, also called ACH tomography, is the inversion of relative traveltime residuals of teleseismic body waves measured at regional networks. We analyse the characteristics of the finite-frequency Fréchet kernels for P and S waves for this kind of tomography. Using a simplified geometry enables us to use the complete Green's function in the expression of the Fréchet kernels and analyse elements, which are usually neglected, like the importance of the near-field terms and the P-wave traveltime sensitivity to shear wave velocity variations. By comparing the kernels of the relative residuals and absolute ones, we show that relative residuals have a reduced sensitivity to heterogeneities of large dimensions, and that this reduction is a generalization of the fact that the average model is not recovered in ACH tomography. This sensitivity reduction affects equally short- and long-period residuals. We show in addition the presence of a sensitivity reduction at large depth for the long-period waves. Kernels and reflectivity impulse responses of the crust are used to analyse if crustal corrections should be made frequency-dependent in finite-frequency regional tomography. We find that in most cases the frequency dependence due to reverberations is substantial, and that in many realistic network configurations ray theory is unlikely to be well appropriate to compute crustal corrections for the long-period waves. We also find that the lateral dimensions of the crust affecting the traveltimes is frequency dependent and reaches, at long periods, 50 km for sedimentary basins and 100 km for Moho depth.

  18. 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 ...

  19. Geological variation in S-wave velocity structures in Northern Taiwan and implications for seismic hazards based on ambient noise analysis

    Science.gov (United States)

    Lai, Ya-Chuan; Huang, Bor-Shouh; Huang, Yu-Chih; Yao, Huajian; Hwang, Ruey-Der; Huang, Yi-Ling; Chang, Wen-Yen

    2014-12-01

    Ambient noise analysis in Northern Taiwan revealed obvious lateral variations related to major geological units. The empirical Green's functions extracted from interstation ambient noise were regarded as Rayleigh waves, from which we analyzed the group velocities for period from 3 to 6 s. According to geological features, we divided Northern Taiwan into seven subregions, for which regionalized group velocities were derived by using the pure-path method. On average, the group velocities in mountain areas were higher than those in the plain areas. We subsequently inverted the S-wave velocity structure for each subregion down to 6 km in depth. Following the analysis, we proposed the first models of geology-dependent shallow S-wave structures in Northern Taiwan. Overall, the velocity increased substantially from west to east; specifically, the mountain areas, composed of metamorphic rocks, exhibited higher velocities than did the coastal plain and basin, which consist of soft sediment. At a shallow depth, the Western Coastal Plain, Taipei Basin, and Ilan Plain displayed a larger velocity gradient than did other regions. At the top 3 km of the model, the average velocity gradient was 0.39 km/s per km for the Western Coastal Plain and 0.15 km/s per km for the Central Range. These S-wave velocity models with large velocity gradients caused the seismic waves to become trapped easily in strata and, thus, the ground motion was amplified. The regionalized S-wave velocity models derived from ambient noises can provide useful information regarding seismic wave propagation and for assessing seismic hazards in Northern Taiwan.

  20. 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.

  1. Application of Genetic Algorithms in Seismic Tomography

    Science.gov (United States)

    Soupios, Pantelis; Akca, Irfan; Mpogiatzis, Petros; Basokur, Ahmet; Papazachos, Constantinos

    2010-05-01

    application of hybrid genetic algorithms in seismic tomography is examined and the efficiency of least squares and genetic methods as representative of the local and global optimization, respectively, is presented and evaluated. The robustness of both optimization methods has been tested and compared for the same source-receiver geometry and characteristics of the model structure (anomalies, etc.). A set of seismic refraction synthetic (noise free) data was used for modeling. Specifically, cross-well, down-hole and typical refraction studies using 24 geophones and 5 shoots were used to confirm the applicability of the genetic algorithms in seismic tomography. To solve the forward modeling and estimate the traveltimes, the revisited ray bending method was used supplemented by an approximate computation of the first Fresnel volume. The root mean square (rms) error as the misfit function was used and calculated for the entire random velocity model for each generation. After the end of each generation and based on the misfit of the individuals (velocity models), the selection, crossover and mutation (typical process steps of genetic algorithms) were selected continuing the evolution theory and coding the new generation. To optimize the computation time, since the whole procedure is quite time consuming, the Matlab Distributed Computing Environment (MDCE) was used in a multicore engine. During the tests, we noticed that the fast convergence that the algorithm initially exhibits (first 5 generations) is followed by progressively slower improvements of the reconstructed velocity models. Thus, to improve the final tomographic models, a hybrid genetic algorithm (GA) approach was adopted by combining the GAs with a local optimization method after several generations, on the basis of the convergence of the resulting models. This approach is shown to be efficient, as it directs the solution search towards a model region close to the global minimum solution.

  2. Time-resolved seismic tomography detects magma intrusions at Mount Etna.

    Science.gov (United States)

    Patanè, D; Barberi, G; Cocina, O; De Gori, P; Chiarabba, C

    2006-08-11

    The continuous volcanic and seismic activity at Mount Etna makes this volcano an important laboratory for seismological and geophysical studies. We used repeated three-dimensional tomography to detect variations in elastic parameters during different volcanic cycles, before and during the October 2002-January 2003 flank eruption. Well-defined anomalous low P- to S-wave velocity ratio volumes were revealed. Absent during the pre-eruptive period, the anomalies trace the intrusion of volatile-rich (>/=4 weight percent) basaltic magma, most of which rose up only a few months before the onset of eruption. The observed time changes of velocity anomalies suggest that four-dimensional tomography provides a basis for more efficient volcano monitoring and short- and midterm eruption forecasting of explosive activity.

  3. AN INVESTIGATION TO DOCUMENT MORROW RESERVOIRS THAT CAN BE BETTER DETECTED WITH SEISMIC SHEAR (S) WAVES THAN WITH COMPRESSIONAL (P) WAVES

    Energy Technology Data Exchange (ETDEWEB)

    Thomas Cottman

    2001-10-19

    Pennsylvanian-age Morrow reservoirs are a key component of a large fluvial-deltaic system that extends across portions of Colorado, Kansas, Oklahoma, and Texas. A problem that operators have to solve in some Morrow plays in this multi-state area is that many of the fluvial channels within the Morrow interval are invisible to seismic compressional (P) waves. This P-wave imaging problem forces operators in such situations to site infill, field-extension, and exploration wells without the aid of 3-D seismic technology. The objective of this project was to develop and demonstrate seismic technology that can improve drilling success in Morrow plays. Current P-wave technology commonly results in 80-percent of Morrow exploration wells not penetrating economic reservoir facies. Studies at Colorado School of Mines have shown that some of the Morrow channels that are elusive as P-wave targets create robust shear (S) wave reflections (Rampton, 1995). These findings caused Visos Energy to conclude that exploration and field development of Morrow prospects should be done by a combination of P-wave and S-wave seismic imaging. To obtain expanded information about the P and S reflectivity of Morrow facies, 9-component vertical seismic profile (9-C VSP) data were recorded at three locations along the Morrow trend. These data were processed to create P and S images of Morrow stratigraphy. These images were then analyzed to determine if S waves offer an alternative to P waves, or perhaps even an advantage over P waves, in imaging Morrow reservoir targets. The study areas where these field demonstrations were done are defined in Figure 1. Well A was in Sherman County, Texas; well B in Clark County, Kansas; and well C in Cheyenne County, Colorado. Technology demonstrated at these sites can be applied over a wide geographical area and influence operators across the multi-state region spanned by Morrow channel plays. The scope of the investigation described here is significant on the

  4. Towards Crustal Structure of Java Island (Sunda Arc) from Ambient Seismic Noise Tomography

    Science.gov (United States)

    Widiyantoro, Sri; Zulhan, Zulfakriza; Martha, Agustya; Saygin, Erdinc; Cummins, Phil

    2015-04-01

    In our previous studies, P- and S-wave velocity structures beneath the Sunda Arc were successfully imaged using a global data set and a nested regional-global tomographic method was employed. To obtain more detailed P- and S-wave velocity structures beneath Java, in the central part of the Sunda Arc, we then used local data sets, i.e. newline from the MErapi AMphibious EXperiment (MERAMEX) and the Meteorological, Climatological and Geophysical Agency (MCGA), as well as employed a double-difference technique for tomographic imaging. The results of the imaging show e.g. that P- and S-wave velocities are significantly reduced in the uppermost mantle beneath central Java. In order to obtain detailed crustal structure information beneath Java, the Ambient Noise Tomography (ANT) method was used. The application of this method to the MERAMEX data has produced a good crustal model beneath central Java. We continue our experiment to image crustal structure of eastern Java. We have used seismic waveform data recorded by 22 MCGA stationary seismographic stations and 25 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms of cross-correlated noise between pairs of seismographic stations. Our preliminary results presented here indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly (as shown by our tomographic images). In future work we will install more seismographic stations in eastern Java as well as in western Java to conduct ANT imaging for the whole of Java Island. The expected result combined with the mantle velocity models resulting from our body wave tomography will allow for accurate location of earthquake hypocenters and determination of regional tectonic structures. Both of these are valuable for understanding seismic hazard in Java, the most densely populated

  5. Seismic Tomography in Reykjanes , SW Iceland

    NARCIS (Netherlands)

    Jousset, Philippe; Blanck, Hanna; Franke, Steven; Metz, M.; Águstsson, K.; Verdel, Arie; Ryberg, T.; Hersir, Gylfi Páll; Weemstra, C.; Bruhn, D.F.; Flovenz, Olafur G

    2016-01-01

    We present tomographic results obtained around geothermal reservoirs using seismic data recorded both on-land Reykjanes, SW-Iceland and offshore along Reykjanes Ridge. We gathered records from a network of 83 seismic stations (including 21 Ocean Bottom Seismometers) deployed between April 2014 and

  6. The Signature of a Small-throw Fault Affecting Unconsolidated Sediments in S-wave Reflection Seismic Data

    NARCIS (Netherlands)

    Carvalho, J.P.; Ghose, R.; Loureiro, A.

    2012-01-01

    The definition of appropriate places for the development of paleoseismic studies is extremely important in earthquake engineering site investigations. The seismic reflection method is routinely used to locate shallow fault segments where these do not outcrop, like in low slip-rate areas where faults

  7. Seismicity and S-wave velocity structure of the crust and the upper mantle in the Baikal rift and adjacent regions

    Science.gov (United States)

    Seredkina, Alena; Kozhevnikov, Vladimir; Melnikova, Valentina; Solovey, Oksana

    2016-12-01

    Correlations between seismicity, seismotectonic deformation (STD) field and velocity structure of the crust and the upper mantle in the Baikal rift and the adjacent areas of the Siberian platform and the Mongol-Okhotsk fold belt have been investigated. The 3D S-wave velocity structure up to the depths of 500 km has been modeled using a representative sample of Rayleigh wave group velocity dispersion curves (about 3200 paths) at periods from 10 to 250 s. The STD pattern has been reconstructed from mechanisms of large earthquakes, and is in good agreement with GPS and structural data. Analysis of the results has shown that most of large shallow earthquakes fall in regions of low S-wave velocities in the uppermost mantle (western Mongolia and areas of recent mountain building in southern Siberia) and in zones of their relatively high lateral variations (northeastern flank of the Baikal rift). In the first case the dominant STD regime is compression manifested in a mixture of thrust and strike-slip deformations. In the second case we observe a general predominance of extension.

  8. On the use of sensitivity tests in seismic tomography

    NARCIS (Netherlands)

    Rawlinson, N.; Spakman, W.|info:eu-repo/dai/nl/074103164

    2016-01-01

    Sensitivity analysis with synthetic models is widely used in seismic tomography as a means for assessing the spatial resolution of solutions produced by, in most cases, linear or iterative nonlinear inversion schemes. The most common type of synthetic reconstruction test is the so-called

  9. Transdimensional Bayesian seismic ambient noise tomography across SE Tibet

    Science.gov (United States)

    Zheng, DingChang; Saygin, Erdinc; Cummins, Phil; Ge, Zengxi; Min, Zhaoxu; Cipta, Athanasius; Yang, Runhai

    2017-02-01

    We analyze seismic ambient noise data recorded at a set of permanent and temporary stations across southeastern Tibet to image crustal structure. High-resolution phase velocity maps are presented based on Transdimensional Bayesian seismic ambient noise tomography. Seismic images exhibit more apparent horizontal heterogeneities and show more detailed information compared to previous studies based on traditional ambient noise tomography. As noted from the phase velocity image at 25 s, the rigid high velocity anomalies beneath the Sichuan Basin and the South China Fold System act as a blockage to crustal material expansion, and the distribution of velocity anomalies contributes to the interpretation of a surface clockwise rotation pattern. Our results imply a more complex distributed low-velocity zone rather than two isolated channels beneath SE Tibet.

  10. P and S Wave Velocity Structure of the Crust and Upper Mantle Under China and Surrounding Areas From Body and Surface Wave Tomography

    Science.gov (United States)

    2008-03-31

    C., Gordon , R.G., Angus, D.F., Stein, S., 1990. Current plate motions . Geophys. J. Int. 101, 425–478. Ekström, G., Tromp, J., Larson, E., 1997...Kennett, B., Priestley, K., 2005. Global azimuthal seismic anisotropy and the unique plate - motion deformation of Australia. Nature 433, 509–512. DeMets ...on mantle convec- tion from seismic tomography. In: M.A. Richards, R. Gordon , R.D. van der Hilst (Eds.). History and Dynamics of Plate Motion . Am

  11. Structural analysis of S-wave seismics around an urban sinkhole: evidence of enhanced dissolution in a strike-slip fault zone

    Directory of Open Access Journals (Sweden)

    S. H. Wadas

    2017-12-01

    Full Text Available In November 2010, a large sinkhole opened up in the urban area of Schmalkalden, Germany. To determine the key factors which benefited the development of this collapse structure and therefore the dissolution, we carried out several shear-wave reflection-seismic profiles around the sinkhole. In the seismic sections we see evidence of the Mesozoic tectonic movement in the form of a NW–SE striking, dextral strike-slip fault, known as the Heßleser Fault, which faulted and fractured the subsurface below the town. The strike-slip faulting created a zone of small blocks ( < 100 m in size, around which steep-dipping normal faults, reverse faults and a dense fracture network serve as fluid pathways for the artesian-confined groundwater. The faults also acted as barriers for horizontal groundwater flow perpendicular to the fault planes. Instead groundwater flows along the faults which serve as conduits and forms cavities in the Permian deposits below ca. 60 m depth. Mass movements and the resulting cavities lead to the formation of sinkholes and dissolution-induced depressions. Since the processes are still ongoing, the occurrence of a new sinkhole cannot be ruled out. This case study demonstrates how S-wave seismics can characterize a sinkhole and, together with geological information, can be used to study the processes that result in sinkhole formation, such as a near-surface fault zone located in soluble rocks. The more complex the fault geometry and interaction between faults, the more prone an area is to sinkhole occurrence.

  12. Ambient Seismic Noise Tomography of Southern Norway

    Science.gov (United States)

    Köhler, Andreas; Weidle, Christian; Maupin, Valerie

    2010-05-01

    The noise cross-correlation technique is especially useful in regions like southern Norway since local seismicity is rare and teleseismic records are not able to resolve the upper crust. Within the TopoScandiaDeep project, which aims to investigate the relation between surface topography and lithosphere-asthenosphere structure, we process seismic broadband data from the temporary MAGNUS network in Southern Norway. The receivers were recording 20 months of continuous data between September 2006 and June 2008. Additionally, permanent stations of the National Norwegian Seismic Network, NORSAR and GSN stations in the region are used. After usual preprocessing steps (filtering, prewhitening, temporal normalization), we compute 820 cross-correlation functions from 41 receivers for three month time windows. Evaluation of the azimuthal and temporal variation of signal to noise ratios and f-k analysis of NORSAR array data shows that the dominant propagation direction of seismic noise is south-west to north, corresponding well to the Norwegian coast line. During summer months, the signal to noise ratios decrease and the azimuthal distribution becomes smoother. Time-frequency analysis is applied to measure Rayleigh and Love wave group velocity dispersion curves between each station pair for each three-month correlation stack. The mean and variance of all dispersion curves is computed for each path. After rejection of low-quality data using a signal to noise ratio, minimum wavelength and velocity variance criterion, we obtain a large number of reliable velocity estimates (about 600) for periods between 2 and 15 seconds, which we invert for group velocity maps at respective periods. At all inverted periods, we find positive and negative velocity anomalies for Rayleigh and Love waves that correlate very well with local surface geology. While higher velocities (+5%) can be associated with the Caledonian nappes in the central part of southern Norway, the Oslo Graben is reflected

  13. Upper-mantle P- and S-wave velocities below Scandinavia and East Greenland from teleseismic traveltime tomography

    DEFF Research Database (Denmark)

    Hejrani, Babak

    2014-01-01

    This dissertation deals with the resolution of P- and S-velocity variations in the upper mantle (down to 600 km) using teleseismic P- and S-wave arrival times. The natural laboratory is the land areas bordering the North Atlantic; the Scandinavian and East Greenland Caledonides and the Northern...... improved resolution when stations follow profiles. The method was tested on the SCANLIPS array across the Scandinavian Peninsula (Paper I). On the data side, I performed a complete reorganization of the in-house MATLAB-based system (Medhus et al., 2012a,b) for handling event extraction, filtering, cross....../VS put important constraints on the required compositional differences in mantle lithosphere and asthenosphere in the region. Second study focused on the Scandinavian Caledonides, using a dense network south of Trondheim (including SCANLIPS profile) and more sparse station coverage to the north. The UMVB...

  14. Global seismic tomography and modern parallel computers

    Directory of Open Access Journals (Sweden)

    A. Piersanti

    2006-06-01

    Full Text Available A fast technological progress is providing seismic tomographers with computers of rapidly increasing speed and RAM, that are not always properly taken advantage of. Large computers with both shared-memory and distributedmemory architectures have made it possible to approach the tomographic inverse problem more accurately. For example, resolution can be quantified from the resolution matrix rather than checkerboard tests; the covariance matrix can be calculated to evaluate the propagation of errors from data to model parameters; the L-curve method can be applied to determine a range of acceptable regularization schemes. We show how these exercises can be implemented efficiently on different hardware architectures.

  15. Illumination of Jakarta Basin with Full Seismic Noise Tomography

    Science.gov (United States)

    Saygin, Erdinc; Fichtner, Andreas; Cummins, Phil; Masturyono, Masturyono

    2015-04-01

    The greater Jakarta area is densely populated with over 20 million residents. The rapid subduction of Australian crust beneath Sundaland, and the alluvial basin covering most of Jakarta increase the seismic hazard that the city is facing during an earthquake. We apply 3D Full Seismic Wave Tomography to invert interstation Green's functions retrieved from stacked correlations of seismic ambient noise recorded at a dense broadband network operated in Jakarta, Indonesia. Over 1200 Green's Functions were used in an iteratively applied adjoint scheme to map 3D velocity structure. The initial model used in the simulations, is derived from the combination of a 2-step procedure of Bayesian tomography and point wise inversions of dispersions curves. The iterative updates on the starting model, reduced the misfits between observed and synthetic Green's functions. Simulations were conducted in a parallelized approach with 128 compute cores. Green's functions were filtered between 0.08 and 0.2 Hz where their signal to noise ration is optimum. Results of the full waveform inversions show a thick very low velocity layer in the north-west part of the city with shortening towards the south east. Shear wave velocities as low as 1 km/s is observed across the region. The resulting model contributes to the quantification of the seismic hazard of Jakarta.

  16. Crosshole seismic tomography across a masonry dam

    Science.gov (United States)

    Wong, Joe

    1995-05-01

    An intensive crosshole seismic survey was done across a 700-foot-long stone-masonry dam. It involved measurements on six connected panels each approximately 100 feet in width extending completely across the dam from abutment to abutment. The objective was to provide tomographic images of P-wave velocity and dynamic elastic moduli of the dam and foundation materials along the axis of the dam. Field seismograms were recorded with an airgun source and hydrophone detectors. Data analysis included interactive time-picking, plotting of common source gathers, and tomographic imaging using an iterative back-propagation technique. Color-coded tomograms of velocity and dynamic Young's modulus were produced and correlated with geological and geophysical data measured on drill core samples. Low values of velocity and dynamic elastic modulus correlated with low RQD and high fracture frequency. The tomograms showed significant variations of mechanical properties in the stone masonry dam and its foundation. The colored tomograms were useful in highlighting zones of weak rock possibly requiring remedial action. They also assisted engineering evaluation of the dam by providing a detailed two-dimensional distribution of mechanical properties which can be used as ground truth data for numerical modeling of stress-strain fields.

  17. Seismic tomography reveals magma chamber location beneath Uturuncu volcano (Bolivia)

    Science.gov (United States)

    Kukarina, Ekaterina; West, Michael; Koulakov, Ivan

    2014-05-01

    Uturuncu volcano belongs to the Altiplano-Puna Volcanic Complex in the central Andes, the product of an ignimbrite ''flare-up''. The region has been the site of large-scale silicic magmatism since 10 Ma, producing 10 major eruptive calderas and edifices, some of which are multiple-eruption resurgent complexes as large as the Yellowstone or Long Valley caldera. Satellite measurements show that the hill has been rising more than half an inch a year for almost 20 years, suggesting that the Uturuncu volcano, which has erupted last time more than 300,000 years ago, is steadily inflating, which makes it fertile ground for study. In 2009 an international multidisciplinary team formed a project called PLUTONS to study Uturuncu. Under this project a 100 km wide seismic network was set around the volcano by seismologists from University of Alaska Fairbanks. Local seismicity is well distributed and provides constraints on the shallow crust. Ray paths from earthquakes in the subducting slab complement this with steep ray paths that sample the deeper crust. Together the shallow and deep earthquakes provide strong 3D coverage of Uturuncu and the surrounding region. To study the deformation source beneath the volcano we performed simultaneous tomographic inversion for the Vp and Vs anomalies and source locations, using the non-linear passive source tomographic code, LOTOS. We estimated both P and S wave velocity structures beneath the entire Uturuncu volcano by using arrival times of P and S waves from more than 600 events registered by 33 stations. To show the reliability of the results, we performed a number of different tests, including checkerboard synthetic tests and tests with odd/even data. Obtained Vp/Vs ratio distribution shows increased values beneath the south Uturuncu, at a depth of about 15 km. We suggest the high ratio anomaly is caused by partial melt, presented in expanding magma chamber, responsible for the volcano inflation. The resulting Vp, Vs and the ratio

  18. Surface wave tomography of Europe from ambient seismic noise

    Science.gov (United States)

    Lu, Yang; Stehly, Laurent; Paul, Anne

    2017-04-01

    We present a European scale high-resolution 3-D shear wave velocity model derived from ambient seismic noise tomography. In this study, we collect 4 years of continuous seismic recordings from 1293 stations across much of the European region (10˚W-35˚E, 30˚N-75˚N), which yields more than 0.8 million virtual station pairs. This data set compiles records from 67 seismic networks, both permanent and temporary from the EIDA (European Integrated Data Archive). Rayleigh wave group velocity are measured at each station pair using the multiple-filter analysis technique. Group velocity maps are estimated through a linearized tomographic inversion algorithm at period from 5s to 100s. Adaptive parameterization is used to accommodate heterogeneity in data coverage. We then apply a two-step data-driven inversion method to obtain the shear wave velocity model. The two steps refer to a Monte Carlo inversion to build the starting model, followed by a linearized inversion for further improvement. Finally, Moho depth (and its uncertainty) are determined over most of our study region by identifying and analysing sharp velocity discontinuities (and sharpness). The resulting velocity model shows good agreement with main geological features and previous geophyical studies. Moho depth coincides well with that obtained from active seismic experiments. A focus on the Greater Alpine region (covered by the AlpArray seismic network) displays a clear crustal thinning that follows the arcuate shape of the Alps from the southern French Massif Central to southern Germany.

  19. A Bayesian approach to linear inverse problems in seismic tomography

    Science.gov (United States)

    Tian, Y.; Zhou, Y.; Chung, J.; Chung, M.; Ning, J.

    2014-12-01

    Seismic tomography is often an ill-posed linear inverse problem and regularization such as damping and smoothing has been widely applied to find an approximate solution to the inverse problem. The "optimal" solution is chosen based on the tradeoff between model norm (or model roughness) and data misfit. The main difficulty associated with this deterministic approach is in determining a balance between model uncertainty and data fit. This can make interpretation of tomographic structures subjective because models at the "corner" of the tradeoff curve often show large variability. In this study, we investigate a Bayesian approach to the linear inverse problem by minimizing an empirical Bayes risk function based on training dataset generated for the tomographic problem. We show that sample average approximation can be used to find optimal spectral filters to solve the linear tomographic problem based on singular value decomposition (SVD). We compare optimal truncated SVD, optimal Tikhonov filtering as well as independent optimal spectral filtering in finite-frequency tomography and ray theoretical tomography using a global dataset of surface-wave dispersion measurements.

  20. 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

  1. Imaging the Earth: Methods and Algorithms for Global Seismic Tomography

    Science.gov (United States)

    Valentine, A. P.; Woodhouse, J. H.

    2010-12-01

    Seismic tomography allows us to image the Earth's interior, and a wide range of tomographic `recipes' have been developed over the past 25 years. To what extent are the features observed in tomographic models influenced by the choices made in setting up the inversion process? Do some recipes lead to more reliable results than others? When is it worth making use of more computationally-expensive methods? We believe that these questions must be answered in order to build and interpret the next generation of tomographic models. Understanding the Earth relies on understanding the tomographic process itself; development must be driven by an appreciation of the strengths and deficiencies of current methods. Robust experimentation is therefore required, to determine the effect and significance of each choice made. We outline a framework in which this may be carried out, illustrated with results from early experiments. We also suggest a new approach to full-waveform seismic data, and introduce the concept of the `waveform slice' -- waveforms extracted from seismograms via carefully-designed selection and processing rules, to target particular regions of the model-space, and allow corresponding improvements in model resolution. Such an approach brings both benefits and challenges, and we consider how these might be mitigated. In particular, we demonstrate results from investigations into methods for automatically assessing the quality of seismic waveforms. Source parameters are often overlooked in tomographic inversion: catalogue parameters are typically used. We have recently shown that this adversely affects the earth models recovered, and that a full treatment of the tomographic inverse problem requires simultaneous determination of sources and structure. We discuss this effect, and illustrate how the choice of inversion algorithm may alter tomographic images.

  2. On the use of sensitivity tests in seismic tomography

    Science.gov (United States)

    Rawlinson, N.; Spakman, W.

    2016-05-01

    Sensitivity analysis with synthetic models is widely used in seismic tomography as a means for assessing the spatial resolution of solutions produced by, in most cases, linear or iterative nonlinear inversion schemes. The most common type of synthetic reconstruction test is the so-called checkerboard resolution test in which the synthetic model comprises an alternating pattern of higher and lower wave speed (or some other seismic property such as attenuation) in 2-D or 3-D. Although originally introduced for application to large inverse problems for which formal resolution and covariance could not be computed, these tests have achieved popularity, even when resolution and covariance can be computed, by virtue of being simple to implement and providing rapid and intuitive insight into the reliability of the recovered model. However, checkerboard tests have a number of potential drawbacks, including (1) only providing indirect evidence of quantitative measures of reliability such as resolution and uncertainty, (2) giving a potentially misleading impression of the range of scale-lengths that can be resolved, and (3) not giving a true picture of the structural distortion or smearing that can be caused by the data coverage. The widespread use of synthetic reconstruction tests in seismic tomography is likely to continue for some time yet, so it is important to implement best practice where possible. The goal of this paper is to develop the underlying theory and carry out a series of numerical experiments in order to establish best practice and identify some common pitfalls. Based on our findings, we recommend (1) the use of a discrete spike test involving a sparse distribution of spikes, rather than the use of the conventional tightly spaced checkerboard; (2) using data coverage (e.g. ray-path geometry) inherited from the model constrained by the observations (i.e. the same forward operator or matrix), rather than the data coverage obtained by solving the forward problem

  3. 2D seismic reflection tomography in strongly anisotropic media

    Science.gov (United States)

    Huang, Guangnan; Zhou, Bing; Li, Hongxi; Zhang, Hua; Li, Zelin

    2014-12-01

    Seismic traveltime tomography is an effective method to reconstruct underground anisotropic parameters. Currently, most anisotropic tomographic methods were developed under the assumption of weak anisotropy. The tomographic method proposed here can be implemented for imaging subsurface targets in strongly anisotropic media with a known tilted symmetry axis, since the adopted ray tracing method is suitable for anisotropic media with arbitrary degree. There are three kinds of reflection waves (qP, qSV and qSH waves) that were separately used to invert the blocky abnormal body model. The reflection traveltime tomographiy is developed here because a surface observation system is the most economical and practical way compared with crosswell and VSP. The numerical examples show that the traveltimes of qP reflection wave have inverted parameters {{c}11},{{c}13},{{c}33} \\text{and} {{c}44} successfully. Traveltimes of qSV reflection wave have inverted parameters {{c}11},{{c}33} \\text{and} {{c}44} successfully, with the exception of the {{c}13}, since it is less sensitive than other parameters. Traveltimes of qSH reflection wave also have inverted parameters {{c}44} \\text{and} {{c}66} successfully. In addition, we find that the velocity sensitivity functions (derivatives of phase velocity with respect to elastic moduli parameters) and raypath illuminating angles have a great influence on the qualities of tomograms according to the inversion of theoretical models. Finally, the numerical examples confirm that the reflection traveltime tomography can be applied to invert strongly anisotropic models.

  4. Location of high seismic activity zones and seismic hazard assessment in Zabrze Bielszowice coal mine using passive tomography

    Energy Technology Data Exchange (ETDEWEB)

    Lurka, A. [Central Mining Institute, Katowice (Poland)

    2008-06-15

    Results of passive tomography calculations are presented to assess rockburst hazard and locate high seismic activity zones in the vicinity of longwall 306 in Zabrze Bielszowice coal mine. The area of study was 1000 m in the X direction by 900 m in the Y direction. The zones of high values of P-wave propagation velocity have been found to correlate with the distribution of large seismic tremors. 8 refs., 7 figs.

  5. Crustal Structure in the Western Part of Romania from Local Seismic Tomography

    Science.gov (United States)

    Zaharia, Bogdan; Grecu, Bogdan; Popa, Mihaela; Oros, Eugen; Radulian, Mircea

    2017-12-01

    The inner part of the Carpathians in Romania belongs to the Carpathians-Pannonian system bordered by the Eastern Carpathians to the north and east, Southern Carpathians to the south and Pannonian Basin to the west. It is a complex tectonic region with differential folding mechanisms, post-collisional kinematics, rheology and thermal properties, including within its area the Apuseni Mountains and the Transylvanian Basin. The purpose of this study is to map the 3-D structure of the crust over this region on the basis of local earthquake data. Input data were recorded during the South Carpathian Project (2009–2011), a successful collaboration between the Institute of Geophysics and Tectonics of the University of Leeds and the National Institute for Earth Physics (NIEP), Romania. A temporary array of 32 broadband seismic stations (10 CMG-40T, 8 CMG-3T and 14 CMG-6TD) was installed across the western part of Romania (spaced at 40 to 50 km intervals) during the project. In addition, 25 stations deployed in the eastern Hungary and Serbia was considered. P- and S-wave arrivals are identified for all the selected events (minimum 7 phases per event with reasonable signal/noise ratio). All the events are first relocated using Joint Hypocentre Determination (JHD) technique. Then the well-located events were inverted to determine the crustal structure using LOTOS algorithm. The lateral variations of the crustal properties as resulted from the tomography image are interpreted in correlation with the station corrections estimated by JHD algorithm and with the post-collisional evolution of the Carpathians-Pannonian system.

  6. About probabilistic integration of ill-posed geophysical tomography and logging data: A knowledge discovery approach versus petrophysical transfer function concepts illustrated using cross-borehole radar-, P- and S-wave traveltime tomography in combination with cone penetration and dielectric logging data

    Science.gov (United States)

    Paasche, Hendrik

    2018-01-01

    Site characterization requires detailed and ideally spatially continuous information about the subsurface. Geophysical tomographic experiments allow for spatially continuous imaging of physical parameter variations, e.g., seismic wave propagation velocities. Such physical parameters are often related to typical geotechnical or hydrological target parameters, e.g. as achieved from 1D direct push or borehole logging. Here, the probabilistic inference of 2D tip resistance, sleeve friction, and relative dielectric permittivity distributions in near-surface sediments is constrained by ill-posed cross-borehole seismic P- and S-wave and radar wave traveltime tomography. In doing so, we follow a discovery science strategy employing a fully data-driven approach capable of accounting for tomographic ambiguity and differences in spatial resolution between the geophysical tomograms and the geotechnical logging data used for calibration. We compare the outcome to results achieved employing classical hypothesis-driven approaches, i.e., deterministic transfer functions derived empirically for the inference of 2D sleeve friction from S-wave velocity tomograms and theoretically for the inference of 2D dielectric permittivity from radar wave velocity tomograms. The data-driven approach offers maximal flexibility in combination with very relaxed considerations about the character of the expected links. This makes it a versatile tool applicable to almost any combination of data sets. However, error propagation may be critical and justify thinking about a hypothesis-driven pre-selection of an optimal database going along with the risk of excluding relevant information from the analyses. Results achieved by transfer function rely on information about the nature of the link and optimal calibration settings drawn as retrospective hypothesis by other authors. Applying such transfer functions at other sites turns them into a priori valid hypothesis, which can, particularly for empirically

  7. Construction of the seismic wave-speed model by adjoint tomography beneath the Japanese metropolitan area

    Science.gov (United States)

    Miyoshi, Takayuki

    2017-04-01

    depth of 30 km. We found distinct low wave-speed patterns in S-wave structure. One of the patterns extends in the E-W direction around a depth of 40 km. This zone was interpreted as the serpentinized mantle above the Philippine Sea slab (e.g. Kamiya and Kobayashi 2000). We also obtained the low wave-speed zone around the depth of 5 km. It seems this area extends along the Median tectonic line and this area is correspond to the sedimentary layer. We thank the NIED for providing seismic data, and also thank the researchers for providing the SPECFEM Cartesian program package.

  8. Multi-Resolution Seismic Tomography Based on Recursive Tessellation Hierarchy

    Energy Technology Data Exchange (ETDEWEB)

    Simmons, N A; Myers, S C; Ramirez, A

    2009-07-01

    A 3-D global tomographic model that reconstructs velocity structure at multiple scales and incorporates laterally variable seismic discontinuities is currently being developed. The model parameterization is node-based where nodes are placed along vertices defined by triangular tessellations of a spheroidal surface. The triangular tessellation framework is hierarchical. Starting with a tetrahexahedron representing the whole globe (1st level of the hierarchy, 24 faces), they divide each triangle of the tessellation into daughter triangles. The collection of all daughter triangles comprises the 2nd level of the tessellation hierarchy and further recursion produces an arbitrary number of tessellation levels and arbitrarily fine node-spacing. They have developed an inversion procedure that takes advantage of the recursive properties of the tessellation hierarchies by progressively solving for shorter wavelength heterogeneities. In this procedure, we first perform the tomographic inversion using a tessellation level with coarse node spacing. They find that a coarse node spacing of approximately 8{sup o} is adequate to capture bulk regional properties. They then conduct the tomographic inversion on a 4{sup o} tessellation level using the residuals and inversion results from the 8{sup o} run. In practice they find that the progressive tomography approach is robust, providing an intrinsic regularization for inversion stability and avoids the issue of predefining resolution levels. Further, determining average regional properties with coarser tessellation levels enables long-wavelength heterogeneities to account for sparsely sampled regions (or regions of the mantle where longer wavelength patterns of heterogeneity suffice) while allowing shorter length-scale heterogeneities to emerge where necessary. They demonstrate the inversion approach with a set of synthetic test cases that mimic the complex nature of data arrangements (mixed-determined inversion) common to most

  9. Seismic traveltime tomography by use of gridpoints discritization; Koshitenho ni yoru danseiha tomography kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Hirai, T.; Watanabe, T.; Sassa, K. [Kyoto University, Kyoto (Japan). Faculty of Engineering

    1996-05-01

    Efforts were made to enhance analytical precision and stabilize the results in seismic traveltime tomography by use of a method wherein the velocity distribution is expressed as a continuous function interpolated by parameters respectively assigned to the gridpoints. In this method, the slowness data are regarded as the parameters respectively assigned to the gridpoints, and the slowness value at a given point is determined after interpolation by the gridpoints surrounding the said point. A method based on the variation principle was used for ray tracing. As the result, it was confirmed that this method determines the ray path and traveltime with high precision. A method of least squares using Lagrange`s multiplier was applied for inversion. Comparison was made between the use of cells and the use of gridpoints in the results of inversions performed for an inclined 4-layer structure model, when it was found that the values involving the boundaries between layers, inclinations of the layers, and velocities of seismic waves are ambiguous with the cells while those with the gridpoints are reconstructed roughly correctly. 5 refs., 7 figs., 1 tab.

  10. Six-degree-of-freedom near-source seismic motions II: examples of real seismogram analysis and S-wave velocity retrieval

    Czech Academy of Sciences Publication Activity Database

    Brokešová, J.; Málek, Jiří

    2015-01-01

    Roč. 19, č. 2 (2015), s. 511-539 ISSN 1383-4649 R&D Projects: GA ČR GAP210/10/0925; GA MŠk LM2010008; GA ČR GAP210/12/2336; GA ČR GA15-02363S Institutional support: RVO:67985891 Keywords : seismic rotation * near-source region * rotational seismometer * microearthquakes * West Bohemia/Vogtland region * Gulf of Corinth * Katla region Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.550, year: 2015

  11. A multidisciplinary approach to landslide structure characterization: integration of seismic tomography survey and high resolution LiDar data with the Sloping Local Base Level method.

    Science.gov (United States)

    Travelletti, Julien; Samyn, Kevin; Malet, Jean-Philippe; Grandjean, Gilles; Jaboyedoff, Michel

    2010-05-01

    A challenge to progress in the understanding of landslides is to precisely define their 3D geometry and structure as an input for volume estimation and further hydro-mechanical modelling. The objective of this work is to present a multidisciplinary approach to the geometrical modelling of the La Valette landslide by integrating seismic tomography survey (P and S wave) and high resolution LiDar data with the Sloping Local Base Level (SLBL) method. The La Valette landslide, triggered in March 1982, is one of the most important slope instability in the South French Alps. Its dimensions are 1380 m length and 290 m width, and the total volume is estimated at 3.5 106 m3. Since 2002, an important activity of the upper part of the landslide is observed, and consisted mainly in the retrogression of the crown through the opening of an important fracture over several meters and rotational slumps. The failed mass is currently loading the upper part of the mudslide and is a potential threat for the 170 residential communities. A seismic tomography survey combined to airborne and terrestrial LiDar data analysis have been carried out to identify the geological structures and discontinuities and characterize the stability of the failing mass. Seismic tomography allows direct and non-intrusive measurements of P and S waves velocities which are key parameters for the analysis of the mechanical properties of reworked and highly fissured masses. 4 seismic lines have been performed (3 of them in the direction of the slope and the other perpendicular). The 2 longest devices are composed of 24 geophones spaced by 5 meters and have a sufficient investigation depth for a large scale characterization of the landslide's structure with depth. The 2 shortest devices, composed of 24 geophones spaced by 2 meters bring information about the fracturing degree between the moving material of the landslide and the competent rock. 100gr of pentrite for each shot were used as seismic sources. The

  12. Evaluation of dynamic properties of soft ground using an S-wave vibrator and seismic cones. Part 2. Vs change during the vibration; S ha vibrator oyobi seismic cone wo mochiita gen`ichi jiban no doteki bussei hyoka. 2. Kashinchu no Vs no henka

    Energy Technology Data Exchange (ETDEWEB)

    Inazaki, T. [Public Works Research Institute, Tsukuba (Japan)

    1997-05-27

    With an objective to measure a behavior of the surface ground during a strong earthquake directly on the actual ground and make evaluation thereon, a proposal was made on an original location measuring and analyzing method using an S-wave vibrator and seismic cones. This system consists of an S-wave vibrator and a static cone penetrating machine, and different types of measuring cones. A large number of measuring cones are inserted initially in the object bed of the ground, and variation in the vibration generated by the vibrator is measured. This method can derive decrease in rigidity rate of the actual ground according to dynamic strain levels, or in other words, the dynamic nonlinearity. The strain levels can be controlled with a range from 10 {sup -5} to 10 {sup -3} by varying the distance from the S-wave vibrator. Furthermore, the decrease in the rigidity rate can be derived by measuring variations in the S-wave velocity by using the plank hammering method during the vibration. Field measurement is as easy as it can be completed in about half a day including preparatory works, and the data analysis is also simple. The method is superior in mobility and workability. 9 figs.

  13. Extending shear-wave tomography for the lower mantle using S and SKS arrival-time data

    NARCIS (Netherlands)

    Widiyantoro, S.; Kennett, B.L.N.; Hilst, R.D. van der

    1998-01-01

    Seismic tomography using S wave travel times faces the difficulty imposed by the interference between S and SKS phases near 83o epicentral distance, as the SKS phase overtakes the S waves in the mantle. If the cross-over is avoided completely by excluding S data beyond 82o then no resolution is

  14. Passive seismic tomography application for cave monitoring in DOZ underground mine PT. Freeport Indonesia

    Energy Technology Data Exchange (ETDEWEB)

    Nurhandoko, Bagus Endar B.; Wely, Woen; Setiadi, Herlan [WISFIR Laboratory, Earth Physics and Complex System Division, Physics Department, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung (Indonesia); Riyanto, Erwin [Geotechnical and Hydrology PT. Freeport Indonesia wonbin-ww@hotmail.com (Indonesia)

    2015-04-16

    It is already known that tomography has a great impact for analyzing and mapping unknown objects based on inversion, travel time as well as waveform inversion. Therefore, tomography has used in wide area, not only in medical but also in petroleum as well as mining. Recently, tomography method is being applied in several mining industries. A case study of tomography imaging has been carried out in DOZ ( Deep Ore Zone ) block caving mine, Tembagapura, Papua. Many researchers are undergoing to investigate the properties of DOZ cave not only outside but also inside which is unknown. Tomography takes a part for determining this objective.The sources are natural from the seismic events that caused by mining induced seismicity and rocks deformation activity, therefore it is called as passive seismic. These microseismic travel time data are processed by Simultaneous Iterative Reconstruction Technique (SIRT). The result of the inversion can be used for DOZ cave monitoring. These information must be used for identifying weak zone inside the cave. In addition, these results of tomography can be used to determine DOZ and cave information to support mine activity in PT. Freeport Indonesia.

  15. 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.

  16. 3-D P- and S-wave velocity structure along the central Alpine Fault, South Island, New Zealand

    Science.gov (United States)

    Guo, B.; Thurber, C. H.; Roecker, S. W.; Townend, J.; Rawles, C.; Chamberlain, C. J.; Boese, C. M.; Bannister, S.; Feenstra, J.; Eccles, J. D.

    2017-05-01

    The Deep Fault Drilling Project (DFDP) on the central Alpine Fault, South Island, New Zealand, has motivated a broad range of geophysical and geological studies intended to characterize the fault system in the locality of the drill site at various scales. In order to better understand the structural features of the central Alpine Fault, we have developed 3-D P- and S-wave velocity (VP and VS) models of the region by double-difference tomography using data sets from multiple seismic networks. In previous work, the quality of the S-wave model has been poor due to the small number of available S-wave picks. We have utilized a new high-accuracy automatic S-wave picker to increase the number of usable S-wave arrivals by more than a factor of two, thereby substantially improving the VS model. Compared to previous studies, our new higher-resolution VP model based on more observations shows a clear VP contrast (higher VP on the southeast hanging wall side) at depths of 5-10 km near the DFDP drill sites. With our better resolved VS model, in the same region, we detect a sharply defined high VS body (VS > 3.7 km s-1) within the hanging wall. Our earthquake relocations reveal the presence of clusters within and around low-velocity zones in the hanging wall southeast of the Alpine Fault. Together with the improved earthquake locations, the P- and S-wave tomography results reveal the Alpine Fault to be marked by a velocity contrast throughout most of the study region. The fault dips southeastwards at about 50° from 5 to 15 km depth, as inferred from the velocity structure, seismicity and observations of fault zone guided waves.

  17. Upper Crustal Structure of Santorini Volcano from Seismic Tomography using the PROTEUS dataset

    Science.gov (United States)

    Heath, B.; Hooft, E. E. E.; Morgan, J. V.; Toomey, D. R.; Nomikou, P.; Papazachos, C. V.; Warner, M.

    2016-12-01

    We present initial travel time tomography results from the PROTEUS experiment (Plumbing Reservoirs Of The Earth Under Santorini), an experiment designed to seismically image magma reservoirs beneath Santorini Volcano (Greece). Few seismic imaging studies have been previously conducted on Santorini and none have investigated the deeper crustal magmatic system. The experiment presents a unique opportunity to seismically probe the plumbing system of a historically active arc volcano because of a relatively thin Aegean crust, permitting easier seismic access to the subvolcanic magmatic system, and because of the ability to use marine air gun sound sources for imaging purposes. The latter provides over 1 million unique station-shot pairs ( 14000 airgun shots, over 100 onshore and offshore seismometers) producing a nearly unparalleled seismic dataset for a continental volcano. Our preliminary travel-time tomography results use tens of thousands of travel-time picks and a 3-D ray tracer to invert for anisotropic velocity structure of the upper 5 km of Santorini Volcano and surrounding tectonic region. Our tomographic images provide new constraints on how differing stages of tectonism and volcanism have shaped the geologic structure of the Aegean Volcanic Arc; specifically, we utilize our seismic dataset as well as the unique bathymetric dataset collected during the PROTEUS experiment to study the relationship between seismic velocity, faulting, and volcanism. These results are the first of a multi-year effort to both seismically image Santorini Volcano and understand how our images compare to other geophysical/geochemical models of Santorini and other analogous volcanoes. This experiment represents an unique opportunity to tomographically investigate the magmatic plumbing of a geochemically and volcanologically well-studied volcano.

  18. Seismic tomography in areas associated with complex near-surface structures

    Science.gov (United States)

    Al-Rufaii, Khalid

    The energy demand of the world is increasing every day, forcing the oil industry to explore for oil hydrocarbon traps in locations where the problem complexity requires special imaging techniques. Dealing with complex near-surface structures is the most challenging problem for land seismic exploration. The seismic waves are often distorted and dispersed by extremely low and rapidly varying velocities, as well as poor or inconsistent coupling amongst shots and receivers. It is not uncommon when the near-surface problem degrades the surface reflection data to a useless level. To treat the problem, I employ a first-arrival seismic tomography to model the near-surface velocity structures. The removal of the induced near-surface distortions on seismic data is based on two principles: layer stripping and surface consistency. Though this approach has been taken by previous workers, our method has several unique features. First, the subsurface is parameterized by a grid of irregularly shaped blocks that mimic the topography and help to reduce the number of model variables. Second, a multi-scale inversion is employed that has been shown to give superior results than the conventional single-scale tomography. Third, the initial reference model is established based on the actual travel-time data, hence greatly reduces the concern for picking a wrong initial model. The accuracy of the first-arrival tomography is verified using various synthetic models simulating the complexity of real near-surface conditions. The method is applied to three field 2-D data sets in very different regions: a land data set from a mountainous thrust area in South America, a marine data set from the Gulf of Mexico, and a long-offset data set from the Tarim Basin in China. In addition, I attempt to implement reflection tomography as an alternative to conventional velocity analysis. Using reflection seismic tomography, we invert for velocity-depth models, which can be used for imaging or time processing

  19. Relation between frequency of seismic wave and resolution of tomography; Danseiha tomography kaiseki ni okeru shuhasu to bunkaino no kankei

    Energy Technology Data Exchange (ETDEWEB)

    Fujimoto, M.; Watanabe, T.; Ashida, Y.; Sassa, K. [Kyoto University, Kyoto (Japan). Faculty of Engineering

    1997-05-27

    With regard to the elastic wave exploration, discussions have been given on the relationship between frequency and resolution in P-wave velocity tomography using the initial travel time. The discussions were carried out by using a new analysis method which incorporates the concept of Fresnel volume into tomography analysis. The following two arrangements were used in the calculation: a cross hole arrangement, in which seismic source and vibration receiving points were arranged so as to surround the three directions of a region extending 250 m in the horizontal direction and 500 m in the vertical direction, and observation is performed between two wells, and a permeation VSP arrangement in which the seismic source is installed on the ground surface and receiving points installed in wells. Restructuring was performed on the velocity structure by using a total of 819 observation travel times. This method has derived results of the restructuring according to frequencies of the seismic source used for the exploration. The resolution shown in the result of the restructuring has become higher as elastic waves with higher frequency are used, and the size of the structure identified from the restructuring result has decreased. This fact reveals that sufficient considerations must be given on frequencies of elastic waves used according to size of objects to be explored. 4 refs., 4 figs.

  20. Searching for the Lost Jurassic and Cretaceous Ocean Basins of the Circum-Arctic Linking Plate Models and Seismic Tomography

    Science.gov (United States)

    Shephard, G. E.; Müller, R.

    2012-12-01

    The tectonic evolution of the circum-Arctic since the breakup of Pangea involves the opening and closing of ocean basins including the Oimyakon, Angayucham, South Anuyi, Amerasia and Eurasia basins. The time-dependent configurations and kinematic history of the basins, adjacent continental terranes, and subduction zones involved are not well understood, and many published tectonic models for particular regions are inconsistent with models for adjacent areas. The age, location, geometry and convergence rates of the subduction zones associated with these ancient ocean basins since at least the Late Jurassic have implications for mantle structure, which can be used as an additional constraint for building plate and plate boundary models. Here we integrate an analysis of both surface and deep mantle observations back to 200 Ma. Based on a digitized set of tectonic features with time-dependent rotational histories we present a refined plate model with topologically closed plate polygons for the circum-Arctic with particular focus on the northern Pacific, Siberian and Alaskan margins (Fig 1). We correlate the location, geometry and timing of subduction zones with associated seismic velocities anomalies from global P and S wave tomography models across different depths. We design a plate model that best matches slabs imaged in seismic tomography in an iterative fashion. This match depends on a combination of relative and absolute plate motions. Therefore we test two end-member absolute plate motion models, evaluating a paleomagnetic model and a model based on hotspot tracks and large igneous provinces. This method provides a novel approach to deciphering the Arctic tectonic history in a global context. Fig 1:Plate reconstruction at 200Ma and 140Ma, visualized using GPlates software. Present-day topography raster (ETOPO2) segmented into major tectonic elements of the circum-Arctic. Plate boundaries delineated in black and selected subduction and arc features labeled in

  1. Steam and Brine Zone Prediction around Geothermal Reservoir Derived from Delay Time Seismic Tomography and Anisotropy Case Study: “PR” Geothermal Field

    Science.gov (United States)

    Hendrawan Palgunadi, Kadek; Nugraha, A. D.; Sule, R.; Meidiana, T.

    2017-04-01

    Development of geothermal production can be conducted in several ways, one of them analyses the fracture or crack and structure within the reservoir. Due to low permeability and porosity value within the reservoir in geothermal field. This crack or fracture provide porosity for fluid storage and permeability for fluid movement and play a major role in production from this kind of reservoir. Structure and polarization direction can be derived from anisotropy parameter and seismic velocity parameter in geothermal field. In this study, we used micro-earthquake data of 1,067 events that were recorded by the average of 15 stations during almost 1-year measurement. We used anisotropy parameter using 3-D shear-wave splitting (SWS) tomography method to represent the distribution of anisotropy medium around the geothermal field. Two parameters produced from the S-wave analysis, which is polarization direction and delay time between fast S-wave and slow S-wave. To determine SWS parameters, we used a rotation of horizontal seismogram including N-S component and E-W component. Furthermore, we used short-time fourier transform (STFT) to calculate lag time and time window based on wave periods. Two horizontal components have been rotated from azimuth 0° to 180° with an increment of 1°. Cross-correlation coefficient used every azimuth of two horizontal components based on delay time with predetermined time window obtained by STFT. When cross-correlation coefficient is high, the corresponding value of delay time and azimuth are chosen as the polarization direction and delay time of SWS. Normalized time different divided by total ray length was used to determine the distribution of crack density. Through correlation of seismic velocity model, crack density, and 3-D anisotropy tomography, we can delineate a geothermal reservoir model. Our results show, high degree of anisotropy and crack density occur in the northern and eastern part of “PR” geothermal field for further

  2. Seismic tomography and mixing in the deep earth

    Directory of Open Access Journals (Sweden)

    W. R. Peltier

    1995-01-01

    Full Text Available Recently constructed tomographic models of the lateral heterogeneity of elastic properties in the Earth's mantle are contrasted in terms of their implications concerning the extent to which the endothermic phase transformation at 660 km depth is influencing the radial style of mixing. Previously published whole mantle and split mantle tomographic reconstructions, SH8/WMI3 and SH8/U4L8 respectively, fit the seismic observations equally well but disagree on the extent to which radial mixing may be impeded across this depth horizon. We show that inferences from seismic tomographic images based on the application of diagnostic functions (global and regional variance spectra and the radial correlation function lead to the conclusion that the mantle circulation is whole mantle in style if model SH8/WM13 is employed. The split mantle tomographic inversion SHS/U4L8 leads to the contradictory conclusion that the mantle circulation is significantly impeded across the 660 km depth horizon. This latter interpretation is reinforced when we employ the new higher resolution split mantle model SH12/U7L5 in our calculations. We demonstrate that the depth-dependent radial heat flow delivered by both of the split models implies the existence of a thermal boundary layer at 660 km depth, and therefore significant layering, whereas that delivered by the whole mantle model does not. By insisting that the depth-dependent viscosity profile of the mantle be compatible with the thermal structure if the flow were layered, we argue that the split mantle tomographic inversions lead to a self-consistent description of geodynamic constraints (geoid and postglacial rebound data.

  3. Plume and lithologic profiling with surface resistivity and seismic tomography

    Energy Technology Data Exchange (ETDEWEB)

    Watson, David B [ORNL; Doll, William E. [Battelle; Gamey, Jeff [Battelle; Sheehan, Jacob R [ORNL; Jardine, Philip M [ORNL

    2005-03-01

    Improved surface-based geophysical technologies that are commercially available provide a new level of detail that can be used to guide ground water remediation. Surface-based multielectrode resistivity methods and tomographic seismic refraction techniques were used to image to a depth of approximately 30 m below the surface at the Natural and Accelerated Bioremediation Research Field Research Center. The U.S. Department of Energy (DOE) established the research center on the DOE Oak Ridge Reservation in Oak Ridge, Tennessee, to conduct in situ field-scale studies on bioremediation of metals and radionuclides. Bioremediation studies are being conducted on the saprolite, shale bedrock, and ground water at the site that have been contaminated with nitrate, uranium, technetium, tetrachloroethylene, and other contaminants (U.S. DOE 1997). Geophysical methods were effective in imaging the high-ionic strength plume and in defining the transition zone between saprolite and bedrock zones that appears to have a significant influence on contaminant transport. The geophysical data were used to help select the location and depth of investigation for field research plots. Drilling, borehole geophysics, and ground water sampling were used to verify the surface geophysical studies.

  4. In-situ testing of the liquefaction potential of soft ground using an s-wave vibrator and seismic cones. Part 1. System, concept and preliminary test result; S ha vibrator oyobi seismic cone wo mochiita gen`ichi jiban ekijoka potential no hyoka. 1. System kosei oyobi genchi yosatsu keisoku kekka

    Energy Technology Data Exchange (ETDEWEB)

    Inazaki, T. [Public Works Research Institute, Tsukuba (Japan)

    1996-05-01

    For the purpose of evaluating liquefaction in situ, it was proposed that an S-wave vibrator designed to serve as a source in a reflection exploration method be utilized as a strong vibration generating source, and measurement was conducted in this connection. Equipment used in this test included an S-wave vibrator, static cone penetration machine, and various measuring cones. A multiplicity of measuring cones had been inserted beforehand into the target layers and comparison layers, and changes upon vibrator activation were measured. On a dry bed of the Tonegawa river, a 40m{sup 2} field was set up, and 41 cone penetration tests were conducted, with the cones positioned zigzag at 5m intervals. In this way, the ground structure was disclosed from the surface to the 10m-deep level. For the measurement, 3-component cones and seismic cones were placed at prescribed depths, and fluctuations and waveforms presented by pore water pressure at each level were determined with the vibration source changing its place. It was found that the changes in the pore water pressure exposed to vibration assume characteristic patterns corresponding to the conditions of vibration application. 5 figs., 1 tab.

  5. Deep critical zone weathering at the southern Sierra Nevada Critical Zone Observatory imaged by seismic waveform tomography

    Science.gov (United States)

    Hayes, J. L.; Holbrook, W.; Riebe, C. S.

    2012-12-01

    We present seismic velocity profiles that constrain the extent of weathering and frequency of velocity heterogeneities at depths less than 40 m in the southern Sierra Nevada Critical Zone Observatory (SSCZO) from waveform tomography modeling of a seismic refraction experiment. Near-surface variations in seismic velocity reflect differences in alteration of parent material by chemical, hydrological and biological processes. Previous traveltime tomography models from these data suggest that the depth to bedrock in the SSCZO is typically ~25 m; thus the potential for subsurface water storage in regolith may be a larger component of water storage than previously thought. Traveltime tomography is unable to resolve heterogeneities with horizontal wavelengths less than 10 m, such as those observed along a surveyed road cut beneath our seismic profile. For a higher resolution seismic image, we apply waveform tomography, which is more robust than traveltime tomography at approximating the wave equation and thus should provide images of subsurface heterogeneities such as corestones and fracture networks. This technique uses a weak scattering approximation to account for the amplitude and phase of the recorded waveforms, rather than just the traveltimes. A 48-channel vertical geophone array and hammer source was deployed over a 7 m high road cut with receiver and shot spacing of 2 m and 4 m respectively. The road cut displays lateral variation in weathering from a friable saprolite to coherent granodiorite which are compared to velocity variations modeled using waveform tomography.

  6. Crustal structure of the Southwest Subbasin, South China Sea, from wide-angle seismic tomography and seismic reflection imaging

    Science.gov (United States)

    Yu, Zhiteng; Li, Jiabiao; Ding, Weiwei; Zhang, Jie; Ruan, Aiguo; Niu, Xiongwei

    2017-06-01

    The Southwest Subbasin (SWSB) is an abyssal subbasin in the South China Sea (SCS), with many debates on its neotectonic process and crustal structure. Using two-dimensional seismic tomography in the SWSB, we derived a detailed P-wave velocity model of the basin area and the northern margin. The entire profile is approximately 311-km-long and consists of twelve oceanic bottom seismometers (OBSs). The average thickness of the crust beneath the basin is 5.3 km, and the Moho interface is relatively flat (10-12 km). No high velocity bodies are observed, and only two thin high-velocity structures ( 7.3 km/s) in the layer 3 are identified beneath the northern continent-ocean transition (COT) and the extinct spreading center. By analyzing the P-wave velocity model, we believe that the crust of the basin is a typical oceanic crust. Combined with the high resolution multi-channel seismic profile (MCS), we conclude that the profile shows asymmetric structural characteristics in the basin area. The continental margin also shows asymmetric crust between the north and south sides, which may be related to the large scale detachment fault that has developed in the southern margin. The magma supply decreased as the expansion of the SWSB from the east to the west.

  7. Seismic Structure of Southeast Asia from Full Waveform Seismic Ambient Noise Tomography

    Science.gov (United States)

    Cummins, P. R.; Saygin, E.; Fichtner, A.; Masturyono, M.

    2015-12-01

    We image the lower crust and upper-mantle structure of Southeast Asia with a 3D full waveform adjoint inversion scheme by directly inverting Green's functions retrieved from interstation seismic noise correlations. Synthetic Green's functions are computed at a period range between 10 and 40 s to simulate the wave propagation in the region. Misfits between observed and synthetic waveforms are reduced by iteratively updating model parameters using sensitivity kernels with a conjugate-gradient optimization method. The final model is verified via comparing the simulated waveforms with the recorded earthquakes in the region. The balanced coverage of rays in the region enabled us to image complex structure. The Australian plate is characterized with higher velocities for most of the crust, where most of Indonesia, and its surroundings show complex structure with low velocities. The transition from the oceanic part of the Australian Plate to the continental crust adjacent to the Banda Arc is clearly imaged.

  8. Three-dimensional full-wavefield seismic tomography on field data (Invited)

    Science.gov (United States)

    Warner, M.; Umpleby, A.; Stekl, I.; Guasch, L.

    2010-12-01

    In contrast to conventional seismic tomography, where we minimise the mismatch between observed and calculated seismic travel times, in full-wavefield tomography we seek a model that is able to match the entire observed wavefield, wiggle-for-wiggle. Wavefield tomography has a long history, but it is only recently that advances in algorithms and in hardware have made the technique feasible on realistic-sized datasets in three dimensions. With sponsorship from the petroleum industry, we have developed full 3D codes for anisotropic acoustic, and isotropic elastic, wavefield tomography in the time-domain, and for visco-acoustic tomography in the frequency domain. In both domains, we solve the wave equation using finite differences on a regular mesh; we use explicit time-stepping in the time domain, and use an implicit iterative solver in the frequency domain. The codes are parallelised to run on a cluster of multi-core nodes, and they are able to deal with large irregular 3D datasets efficiently. We report here the results of applying these codes to a 3D ocean-bottom seismic dataset acquired over the Tommeliten oil field in the North Sea. The field data are composed of 1920 four-component ocean-bottom receivers, recording about 30,000 air-gun sources over an area of 12 x 9 km. A low-velocity, high-attenuation gas cloud is located at a depth of 1 to 2 km; this gas cloud partially obscures the geology of the underlying oil field. There is significant anisotropy within the section; vertical and horizontal p-wave velocities can differ by more than 15%. Wavefield tomography is successful in imaging the complex velocity structure in 3D within this gas cloud with a lateral resolution of about 25 m. This resolution is much better than that obtained using reflection travel-time tomography or migration velocity analysis. Subsequent pre-stack reverse-time depth migration of the underlying reflection data demonstrates that the recovered velocity structure is real. It is necessary

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

    Directory of Open Access Journals (Sweden)

    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.

  10. Singular value decomposition-based reconstruction algorithm for seismic traveltime tomography.

    Science.gov (United States)

    Song, L P; Zhang, S Y

    1999-01-01

    A reconstruction method is given for seismic transmission traveltime tomography. The method is implemented via the combinations of singular value decomposition, appropriate weighting matrices, and variable regularization parameter. The problem is scaled through the weighting matrices so that the singular spectrum is normalized. Matching the normalized singular values, a regularization parameter varies within the interval [0, 1], and linearly increases with singular value index from a small, initial value rather than a fixed one to eliminate the impacts of smaller singular values' components. The experimental results show that the proposed method is superior to the ordinary singular value decomposition (SVD) methods such as truncated SVD and Tikhonov regularization.

  11. Wigner functions of s waves

    DEFF Research Database (Denmark)

    Dahl, Jens Peder; Varro, S.; Wolf, A.

    2007-01-01

    We derive explicit expressions for the Wigner function of wave functions in D dimensions which depend on the hyperradius-that is, of s waves. They are based either on the position or the momentum representation of the s wave. The corresponding Wigner function depends on three variables......: the absolute value of the D-dimensional position and momentum vectors and the angle between them. We illustrate these expressions by calculating and discussing the Wigner functions of an elementary s wave and the energy eigenfunction of a free particle....

  12. Crustal Structure of the Gulf of Aden Continental Margins, from Afar to Oman, by Ambient Noise Seismic Tomography

    Science.gov (United States)

    Korostelev, F.; Weemstra, C.; Boschi, L.; Leroy, S. D.; Ren, Y.; Stuart, G. W.; Keir, D.; Rolandone, F.; Ahmed, A.; Al Ganad, I.; Khanbari, K. M.; Doubre, C.; Hammond, J. O. S.; Kendall, J. M.

    2014-12-01

    Continental rupture processes under mantle plume influence are still poorly known although extensively studied. The Gulf of Aden presents volcanic margins to the west, where they are influenced by the Afar hotspot, and non volcanic margins east of longitude 46° E. We imaged the crustal structure of the Gulf of Aden continental margins from Afar to Oman to evaluate the role of the Afar plume on the evolution of the passive margin and its extent towards the East. We use Ambient Noise Seismic Tomography to better understand the architecture and processes along the Gulf of Aden. This recent method, developed in the last decade, allows us to study the seismic signal propagating between two seismic stations. Ambient Noise Seismic Tomography is thus free from artifacts related to the distribution of earthquakes. We collected continuous records from about 200 permanent or temporary stations since 1999 to compute Rayleigh phase velocity maps over the Gulf of Aden.

  13. Full-waveform seismic tomography of the Vrancea, Romania, subduction region

    Science.gov (United States)

    Baron, Julie; Morelli, Andrea

    2017-12-01

    The Vrancea region is one of the few locations of deep seismicity in Europe. Seismic tomography has been able to map lithospheric downwelling, but has not been able yet to clearly discriminate between competing geodynamic interpretations of the geological and geophysical evidence available. We study the seismic structure of the Vrancea subduction zone, using adjoint-based, full-waveform tomography to map the 3D vP and vS structure in detail. We use the database that was built during the CALIXTO (Carpathian Arc Lithosphere X-Tomography) temporary experiment, restricted to the broadband sensors and local intermediate-depth events. We fit waveforms with a cross-correlation misfit criterion in separate time windows around the expected P and S arrivals, and perform 17 iterations of vP and vS model updates (altogether, requiring about 16 million CPU hours) before reaching stable convergence. Among other features, our resulting model shows a nearly vertical, high-velocity body, that overlaps with the distribution of seismicity in its northeastern part. In its southwestern part, a slab appears to dip less steeply to the NW, and is suggestive of ongoing - or recently concluded - subduction geodynamic processes. Joint inversion for vP and vS allow us to address the vP/vS ratio distribution, that marks high vP/vS in the crust beneath the Focsani sedimentary basin - possibly due to high fluid pressure - and a low vP/vS edge along the lower plane of the subducting lithosphere, that in other similar environment has been attributed to dehydration of serpentine in the slab. In spite of the restricted amount of data available, and limitations on the usable frequency pass-band, full-waveform inversion reveals its potential to improve the general quality of imaging with respect to other tomographic techniques - although at a sensible cost in terms of computing resources. Our study also shows that re-analysis of legacy data sets with up-to-date techniques may bring new, useful

  14. Crustal structure of Shatsky Rise from joint refraction and reflection seismic tomography

    Science.gov (United States)

    Korenaga, J.; Sager, W. W.

    2011-12-01

    Shatsky Rise in the western Pacific is one of a few gigantic oceanic plateaus in the world, with a surface area of ˜ 4.8 ± 105~km2 (about the same size as California). In contrast to other large oceanic plateaus formed during the Cretaceous Quite Period, Shatsky Rise formed during the frequent reversals of magnetic polarity, allowing its tectonic environment to be resolved in detail. It was formed at a rapidly spreading ridge-ridge-ridge triple junction, so the effect of lithospheric lid on magma migration is expected to be minimal, thereby facilitating the petrological interpretation of its seismic structure in terms of parental mantle processes. In the summer of 2010, a seismic refraction survey combined with multichannel seismic profiling was conducted across Shatsky Rise. Twenty eight ocean-bottom seismometers were deployed along two crossing perpendicular lines, and all of the instruments were recovered successfully, yielding a large volume of high-quality wide-angle refraction and reflection data, with the source-receiver distance often exceeding 200~km. In this contribution, we present the P-wave velocity structure of the Shatsky Rise crust, which is constructed by joint refraction and reflection travel time tomography, and also discuss its implications for the origin of Shatsky Rise.

  15. Crustal seismic structure beneath the Deccan Traps area (Gujarat, India), from local travel-time tomography

    Science.gov (United States)

    Prajapati, Srichand; Kukarina, Ekaterina; Mishra, Santosh

    2016-03-01

    The Gujarat region in western India is known for its intra-plate seismic activity, including the Mw 7.7 Bhuj earthquake, a reverse-faulting event that reactivated normal faults of the Mesozoic Kachchh rift zone. The Late Cretaceous Deccan Traps, one of the largest igneous provinces on the Earth, cover the southern part of Gujarat. This study is aimed at bringing light to the crustal rift zone structure and likely origin of the Traps based on the velocity structure of the crust beneath Gujarat. Tomographic inversion of the Gujarat region was done using the non-linear, passive-source tomographic algorithm, LOTOS. We use high-quality arrival times of 22,280 P and 22,040 S waves from 3555 events recorded from August 2006 to May 2011 at 83 permanent and temporary stations installed in Gujarat state by the Institute of Seismological Research (ISR). We conclude that the resulting high-velocity anomalies, which reach down to the Moho, are most likely related to intrusives associated with the Deccan Traps. Low velocity anomalies are found in sediment-filled Mesozoic rift basins and are related to weakened zones of faults and fracturing. A low-velocity anomaly in the north of the region coincides with the seismogenic zone of the reactivated Kachchh rift system, which is apparently associated with the channel of the outpouring of Deccan basalt.

  16. Configuration of the Moho discontinuity beneath the Japanese Islands derived from three-dimensional seismic tomography

    Science.gov (United States)

    Matsubara, Makoto; Sato, Hiroshi; Ishiyama, Tatsuya; Van Horne, Anne

    2017-07-01

    The Mohorovičić discontinuity (Moho) is defined on the basis of an abrupt increase in seismic velocity in the lithosphere which has been observed using seismic refraction and receiver function analysis methods worldwide. Moho depth varies regionally and remains a fundamental parameter of crustal structure. We present a new method of mapping the Moho using a 3D seismic tomography model. Since the tomographic method cannot locate discontinuities, we treat the Moho as a zone of high velocity gradient. Maximum lower crust/minimum upper mantle P-wave velocities in Japan are known to be 7.0 km/s and 7.5 km/s, respectively. We map the residual between isovelocity surfaces of 7.0 km/s and 7.5 km/s to find areas where the residual is small, the separation between the surfaces is narrow, and the velocity gradient is high. The Moho is best constrained where the isovelocity surfaces are close together, and under much of Japan, they are 10 km apart. We chose an isovelocity surface of 7.2 km/s as a representative Moho 'proxy' in these areas. Our resulting 'Moho' map under Japan compares favorably with existing regional Moho models that were obtained from controlled-source seismic investigations. The 'Moho' varies from shallow (25-30 km) to deep (> 30 km), and this variability relates to the structural evolution of the Japanese islands: the opening of the Sea of Japan back-arc, ongoing arc-arc collisions at the Hidaka and Izu collision zones, ongoing back-arc extension in Kyushu, and a possible failed back-arc extensional event of Mesozoic age. It is apparent that the Moho is less well-constrained in areas where the crustal structure has been modified by magmatic activity or thickened due to arc-arc collision.

  17. Empirical mode decomposition: a new tool for S-wave detection

    NARCIS (Netherlands)

    P.J. Oonincx

    2002-01-01

    textabstractSeismic signals consist of several typically short energy bursts, waves, exhibiting several patterns in terms of dominant frequency, amplitude and polarisation. Amongst others, a significant wave is the S-wave. To detect such S-waves one can use conventional techniques that are based on

  18. Seismic and Thermal Structure of the Arctic Lithosphere, From Waveform Tomography and Thermodynamic Modelling

    Science.gov (United States)

    Lebedev, S.; Schaeffer, A. J.; Fullea, J.; Pease, V.

    2015-12-01

    Thermal structure of the lithosphere is reflected in the values of seismic velocities within it. Our new tomographic models of the crust and upper mantle of the Arctic are constrained by an unprecedentedly large global waveform dataset and provide substantially improved resolution, compared to previous models. The new tomography reveals lateral variations in the temperature and thickness of the lithosphere and defines deep boundaries between tectonic blocks with different lithospheric properties and age. The shape and evolution of the geotherm beneath a tectonic unit depends on both crustal and mantle-lithosphere structure beneath it: the lithospheric thickness and its changes with time (these determine the supply of heat from the deep Earth), the crustal thickness and heat production (the supply of heat from within the crust), and the thickness and thermal conductivity of the sedimentary cover (the insulation). Detailed thermal structure of the basins can be modelled by combining seismic velocities from tomography with data on the crustal structure and heat production, in the framework of computational petrological modelling. The most prominent lateral contrasts across the Arctic are between the cold, thick lithospheres of the cratons (in North America, Greenland and Eurasia) and the warmer, non-cratonic blocks. The lithosphere of the Canada Basin is cold and thick, similar to old oceanic lithosphere elsewhere around the world; its thermal structure offers evidence on its lithospheric age and formation mechanism. At 150-250 km depth, the central Arctic region shows a moderate low-velocity anomaly, cooler than that beneath Iceland and N Atlantic. An extension of N Atlantic low-velocity anomaly into the Arctic through the Fram Strait may indicate an influx of N Atlantic asthenosphere under the currently opening Eurasia Basin.

  19. Testing & Validating: 3D Seismic Travel Time Tomography (Detailed Shallow Subsurface Imaging)

    Science.gov (United States)

    Marti, David; Marzan, Ignacio; Alvarez-Marron, Joaquina; Carbonell, Ramon

    2016-04-01

    A detailed full 3 dimensional P wave seismic velocity model was constrained by a high-resolution seismic tomography experiment. A regular and dense grid of shots and receivers was use to image a 500x500x200 m volume of the shallow subsurface. 10 GEODE's resulting in a 240 channels recording system and a 250 kg weight drop were used for the acquisition. The recording geometry consisted in 10x20m geophone grid spacing, and a 20x20 m stagered source spacing. A total of 1200 receivers and 676 source points. The study area is located within the Iberian Meseta, in Villar de Cañas (Cuenca, Spain). The lithological/geological target consisted in a Neogen sedimentary sequence formed from bottom to top by a transition from gyspum to silstones. The main objectives consisted in resolving the underground structure: contacts/discontinuities; constrain the 3D geometry of the lithology (possible cavities, faults/fractures). These targets were achieved by mapping the 3D distribution of the physical properties (P-wave velocity). The regularly space dense acquisition grid forced to acquire the survey in different stages and with a variety of weather conditions. Therefore, a careful quality control was required. More than a half million first arrivals were inverted to provide a 3D Vp velocity model that reached depths of 120 m in the areas with the highest ray coverage. An extended borehole campaign, that included borehole geophysical measurements in some wells provided unique tight constraints on the lithology an a validation scheme for the tomographic results. The final image reveals a laterally variable structure consisting of four different lithological units. In this methodological validation test travel-time tomography features a high capacity of imaging in detail the lithological contrasts for complex structures located at very shallow depths.

  20. 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.

  1. Investigation of the foundations of a Byzantine church by three-dimensional seismic tomography

    Science.gov (United States)

    Polymenakos, L.; Papamarinopoulos, S.; Miltiadou, A.; Charkiolakis, N.

    2005-02-01

    Byzantine public buildings are of high historical and cultural value. Churches, in particular, are of high architectural and artistic value because they are built using various materials and construction techniques and may contain significant frescoes and mosaics. The knowledge of the state of foundations and ground material conditions is important for their proper restoration and preservation. Seismic tomography is employed to investigate the foundation structure and ground material of a Byzantine church. Energy sources are placed across the floor of the church and surrounding courts, while recorders are placed in a subterranean crypt. Travel time data are analyzed and processed with a three-dimensional (3D) tomographic inversion software in order to construct seismic velocity images at the foundation and below foundation level. Velocity variations are known to correlate well with the lithological character of the earth materials, thus providing important structural and lithological information. A case study from a Byzantine church of 11th c. A.D. in the suburbs of Athens, Greece, is presented. The objective of this research is the nondestructive investigation of unknown underground structures or void spaces, mainly under the floor of the building. The results are interpreted in terms of the foundation elements as well as of significant variations in the earth material character.

  2. Ambient Seismic Noise Tomography of a Loess High Bank at Dunaszekcső (Hungary)

    Science.gov (United States)

    Szanyi, Gyöngyvér; Gráczer, Zoltán; Győri, Erzsébet; Kaláb, Zdeněk; Lednická, Markéta

    2016-08-01

    Loess high banks along the right side of the Danube in Hungary are potential subjects of landslides. Small scale ambient seismic noise tomography was used at the Dunaszekcső high bank. The aim of the study was to map near surface velocity anomalies since we assume that the formation of tension cracks—which precede landslides—are represented by low velocities. Mapping Rayleigh wave group velocity distribution can help to image intact and creviced areas and identify the most vulnerable sections. The study area lies at the top of the Castle Hill of Dunaszekcső, which was named after Castellum Lugio, a fortress of Roman origin. The presently active head scarp was formed in April 2011, and our study area was chosen to be at its surroundings. Cross-correlation functions of ambient noise recordings were used to retrieve the dispersion curves, which served as the input of the group velocity tomography. Phase cross-correlation and time-frequency phase weighted stacking was applied to calculate the cross-correlation functions. The average Rayleigh wave group velocity at the loess high bank was found to be 171 ms^{-1}. The group velocity map at a 0.1 s period revealed a low-velocity region, whose location coincides with a highly creviced area, where slope failure takes place along a several meter wide territory. Another low velocity region was found, which might indicate a previously unknown loosened domain. The highest velocities were observed at the supposed remnants of Castellum Lugio.

  3. Integrating Seismic Tomography, 3d Spherical Flow Modeling and Plate Reconstructions

    Science.gov (United States)

    Karason, H.; van der Hilst, R.; Hager, B. H.; Replumaz, A.; Tapponnier, P.

    Due to source and receiver distribution and ray geometry, the sampling of Earth's inte- rior structure is very uneven, and consequently the length scale at which structure can be resolved is spatially variable. In our most recent P-wave tomographic model the mantle is imaged at varying length scales, i.e. the grid size of our block parameteriza- tion adapts to the density of data coverage. In particular, detailed images of complex trajectories of convective flow in the upper mantle, across the transition zone and, in some cases, down to mid-mantle depths are obtained beneath many of the seismically active subduction zones. We have also developed a new code to simulate buoyancy driven mantle flow in three dimensions, in spherical geometry and with high spatial (slabs, are tracked through time to build a flow model with depth de- pendent viscosity profiles of the mantle. At the surface, geometrically complex and/or time-varying boundary conditions are easily applied, facilitating integration with sub- duction history. Comparing the tomography to flow modeling inspired by subduction history and vice versa gives an opportunity to constrain both mantle structure and plate reconstruc- tions. We apply this approach to tectonics in SE-Asia, i.e. the subduction associated with the South and South-West motion of the Sunda-block, caused by the collision of India with mainland Asia. The flow modeling allows us to dynamically connect the plate reconstructions, which constrain surface position of the convergent margin at different times in the past, and the tomography, which constrains the morphology of the slabs at depth. This way we can estimate sinking rates, single out subduction scenarios, constrain the viscosity contrast between the upper and lower mantle and explain apparent discrepancies between the two observables. Furthermore, juxtapos- ing the tomography, realistic flow models and inversion tests using the flow models as inputs, illustrates the biases built into

  4. 2D seismic tomography of Somma- Vesuvius. Description of the experiment and preliminary results.

    Directory of Open Access Journals (Sweden)

    G. Milano

    1996-06-01

    Full Text Available A multidisciplinary project for the investigation of Mt. Vesuvius Structure was started in 1993. The core of the project is represented by a high resolution seismic tomography study by using controlled and natura1 sources. The main research objective is to investigate the feeding system of the vo1cano and to retrieve details of the upper crustal structure in the area. A first 2D using seismic experiment was performed in May 1994, with the aim of studing the feasibility of lIsing tomographic techniques for exploring the vo1cano interiors. Particularly, this experiment was designed to obtain information on the optimal sources-receivers configuration and on the depth extension of the volume sampled by shot-generated seismic waves. 66 three-component seismic stations and 16 single-component analogue instruments were installed by several Italian and French groups to record signals generated by three on-land, underground explosions. Sources and geophones were deployed along a 30-km NW-SE profile passing through the volcano crater. Receivers were placed at an average spacing of 250 m in the middle of the recording line and at 500 m outside. The arrival time data base was complemented by first P and S readings of micro earthquakes which occurred in the recent past within the volcano. The first arrival data set was preliminary used to determine the shallow structure of the volcano by applying Thurber's (1983 tomographic inversion technique. This analysis shows evidence for a high-velocity body which extends vertically from about 400 m below the crater down to at least 3000 m and for a shallow 300-500 m thick low-velocity cover which borders the edifice. Data from the distant shot show evidence for arrivals of deep reflected/converted phases and provide information on the deeper structure under the volcano. The results from the interpretation of 2D data are used for planning a 3D tomographic survey which will be cauied out in 1996.

  5. 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.

  6. Investigating the Origin of the Gutenberg Discontinuity With Anisotropic Seismic Tomography (Invited)

    Science.gov (United States)

    Beghein, C.; Yuan, K.; Xing, Z.; Schmerr, N. C.

    2013-12-01

    We present a new tomographic model of seismic anisotropy and velocity beneath the Pacific basin, which reveals changes in seismic anisotropy that coincide with SS precursor detections of the Gutenberg seismic discontinuity (G). We inverted a global dataset composed of anisotropic Love and Rayleigh wave phase velocity maps for fundamental and higher modes (Visser et al., 2008) to obtain a 3-D model of shear-wave velocity, radial anisotropy, and vertically polarized shear wave (SV) azimuthal anisotropy. The higher modes provide greater sensitivity to upper mantle structure than previous models, many of which are based on fundamental modes only. Our model displays multiple layers. The top layer is described by high S-wave velocities, radial anisotropy with VSV>VSH, and azimuthal anisotropy with fast axes that are subparallel to the paleospreading directions. Below, we find a low velocity zone (LVZ) characterized by stronger radial anisotropy (4-5%) and VSH>VSV that extends down to 150-200km. This LVZ is also associated with anomalously strong azimuthal anisotropy of ~5% and fast axes that align with the present-day absolute plate motion (APM). The thickness of the top layer increases with overlying crustal age, following the prediction of a simple half-space cooling model for oceanic lithosphere. We thus assign the interface to the lithosphere-asthenosphere boundary (LAB). The anisotropy within the lithosphere is consistent with olivine lattice preferred orientation (LPO) due to past deformation episodes. The anisotropy in the LVZ/asthenosphere is in agreement with LPO generated by mantle flow-induced shear strain in a channel of lowered viscosity. In many locations, a strong change in anisotropy coincides with where the G has been detected by SS precursors, especially for ages between 30 Ma and 100 Ma. For younger ages (< 30 Ma), the G is at ~50 km depth, mirroring a weak change in azimuthal anisotropy, but deviates from the HSC model and isotropic shear velocity

  7. Reservoir Characterization around Geothermal Field, West Java, Indonesia Derived from 4-D Seismic Tomography

    Science.gov (United States)

    Verdhora Ry, Rexha; Nugraha, A. D.

    2016-01-01

    Observation of micro-seismic events induced by intensive geothermal exploitation in a particular geothermal field, located in West Java region, Indonesia was used to detect the fracture and permeability zone. Using local monitoring seismometer network, tomographic inversions were conducted for the three-dimensional Vp, Vs, and Vp/Vs structure of the reservoir for January - December 2007, January - December 2008, and January - December 2009. First, hypocenters location was relocated using joint hypocenter determination (JHD) method in purpose to estimate best location. Then, seismic tomographic inversions were conducted using delay time tomography for dataset of every year respectively. The travel times passing through the three-dimensional velocity model were calculated using ray tracing pseudo-bending method. Norm and gradient damping were added to constrain blocks without ray and to produce smooth solution model. The inversion algorithm was developed in Matlab environment. Our tomographic inversion results from 3-years of observations indicate the presence of low Vp, low Vs, and low Vp/Vs ratio at depths of about 1 - 3 km below sea level. These features were interpreted may be related to steam-saturated rock in the reservoir area of this geothermal field. The locations of the reservoir area were supported by the data of well- trajectory, where the zones of high Vp/Vs were observed around the injection wells and the zones of low Vp/Vs were observed around the production wells. The extensive low Vp/Vs anomaly that occupies the reservoir is getting stronger during the 3-years study period. This is probably attributed to depletion of pore liquid water in the reservoir and replacement with steam. Continuous monitoring of Vp, Vs, and Vp/Vs is an effective tool for geothermal reservoir characterization and depletion monitoring and can potentially provide information in parts of the reservoir which have not been drilled.

  8. Seismic tomography for charaterization of an ore vein in the research and education mine Reiche Zeche

    Science.gov (United States)

    Winter, Sebastian; Schlüter, Ralf; Hlousek, Felix; Buske, Stefan

    2017-04-01

    A test site for the design, implementation and operation of an underground in-situ bioleaching unit has been installed by the „Biohydrometallurgical Center for Strategic Elements" at the research and education mine "Reiche Zeche" of Technical University Bergakademie Freiberg. For this purpose an ore vein block will be developed and mined with the bio-hydrometallurgical in-situ leaching technology. As a site survey an underground seismic tomography experiment has been performed to investigate the spatial distribution of the ore vein within this block consisting mainly of gneiss and with dimensions of about 30 x 10 meters. The experiment was performed with a sledgehammer as source and 76 three-component receivers with source and receiver point intervals of about 1 m surrounding the approximately rectangular block. High precision laser scanning was performed to obtain accurate source and receiver positions which was particularly necessary to obtain reliable results due to the generally high wave velocities of the gneiss. The resulting seismic data set showed a high signal-to-noise ratio with clear first arrivals which were picked for all source and receiver combinations and subsequently used as input to a first-arrival tomographic inversion scheme. The resulting velocity model has very good ray coverage and shows well resolved high- and low-velocity regions within the block. These regions can be clearly assigned to mapped outcrops of the ore vein along the galleries surrounding the block, including a correlation of low velocities to fractured rock parts as well as high velocities to the undisturbed ore vein core, respectively. In summary the obtained velocity model and the inferred spatial distribution of the ore vein provides a good basis for planning and implementing the actual ore mining step using the envisaged bioleaching technology.

  9. Seismic structure of the upper crust in the Albertine Rift from travel-time and ambient-noise tomography - a comparison

    Science.gov (United States)

    Jakovlev, Andrey; Kaviani, Ayoub; Ruempker, Georg

    2017-04-01

    Here we present results of the investigation of the upper crust in the Albertine rift around the Rwenzori Mountains. We use a data set collected from a temporary network of 33 broadband stations operated by the RiftLink research group between September 2009 and August 2011. During this period, 82639 P-wave and 73408 S-wave travel times from 12419 local and regional earthquakes were registered. This presents a very rare opportunity to apply both local travel-time and ambient-noise tomography to analyze data from the same network. For the local travel-time tomographic inversion the LOTOS algorithm (Koulakov, 2009) was used. The algorithm performs iterative simultaneous inversions for 3D models of P- and S-velocity anomalies in combination with earthquake locations and origin times. 28955 P- and S-wave picks from 2769 local earthquakes were used. To estimate the resolution and stability of the results a number of the synthetic and real data tests were performed. To perform the ambient noise tomography we use the following procedure. First, we follow the standard procedure described by Bensen et al. (2007) as modified by Boué et al. (2014) to compute the vertical component cross-correlation functions between all pairs of stations. We also adapted the algorithm introduced by Boué et al. (2014) and use the WHISPER software package (Briand et al., 2013) to preprocess individual daily vertical-component waveforms. On the next step, for each period, we use the method of Barmin et al. (2001) to invert the dispersion measurements along each path for group velocity tomographic maps. Finally, we adapt a modified version of the algorithm suggested by Macquet et al. (2014) to invert the group velocity maps for shear velocity structure. We apply several tests, which show that the best resolution is obtained at a period of 8 seconds, which correspond to a depth of approximately 6 km. Models of the seismic structure obtained by the two methods agree well at shallow depth of about

  10. Breathing of the Nevado del Ruiz volcano reservoir, Colombia, inferred from repeated seismic tomography.

    Science.gov (United States)

    Vargas, Carlos A; Koulakov, Ivan; Jaupart, Claude; Gladkov, Valery; Gomez, Eliana; El Khrepy, Sami; Al-Arifi, Nassir

    2017-04-10

    Nevado del Ruiz volcano (NRV), Columbia, is one of the most dangerous volcanoes in the world and caused the death of 25,000 people in 1985. Using a new algorithm for repeated tomography, we have found a prominent seismic anomaly with high values of the Vp/Vs ratio at depths of 2-5 km below the surface, which is associated with a shallow magma reservoir. The amplitude and shape of this anomaly changed during the current phase of unrest which began in 2010. We interpret these changes as due to the ascent of gas bubbles through magma and to degassing of the reservoir. In 2011-2014, most of this gas escaped through permeable roof rocks, feeding surface fumarole activity and leading to a gradual decrease of the Vp/Vs ratio in the reservoir. This trend was reversed in 2015-2016 due to replenishment of the reservoir by a new batch of volatile-rich magma likely to sustain further volcanic activity. It is argued that the recurring "breathing" of the shallow reservoir is the main cause of current eruptions at NRV.

  11. The mechanisms underpinning Cenozoic intraplate volcanism in eastern Australia: Insights from seismic tomography and geodynamic modeling

    Science.gov (United States)

    Rawlinson, N.; Davies, D. R.; Pilia, S.

    2017-10-01

    Cenozoic intraplate volcanism is widespread throughout much of eastern Australia and manifests as both age-progressive volcanic tracks and non-age-progressive lava fields. Various mechanisms have been invoked to explain the origin and distribution of the volcanism, but a broad consensus remains elusive. We use results from seismic tomography to demonstrate a clear link between lithospheric thickness and the occurrence, composition, and volume of volcanic outcrop. Furthermore, we find that non-age-progressive lava fields overlie significant cavities in the base of the lithosphere. Based on numerical simulations of mantle flow, we show that these cavities generate vigorous mantle upwellings, which likely promote decompression melting. However, due to the intermittent nature of the lava field volcanics over the last 50 Ma, it is probable that transient mechanisms also operate to induce or enhance melting. In the case of the Newer Volcanics Province, the passage of a nearby plume appears to be a likely candidate. Our results demonstrate why detailed 3-D variations in lithospheric thickness, plate motion, and transient sources of mantle heterogeneity need to be considered when studying the origin of non age-progressive volcanism in continental interiors.

  12. Seismic velocity tomography for CO2 monitor in subsurface geological structures

    Directory of Open Access Journals (Sweden)

    Wasiu O. Raji

    2018-01-01

    Full Text Available The storage of CO2 in depleted hydrocarbon reservoirs and saline water aquifers is a leading solution to Global Warming due to CO2 emission to the atmosphere. The capture of CO2 from major CO2-emitting plants and its storage in underground geological structures has a potential to reduce Global Warming by about 60%. A procedure for monitoring safe and secure storage of CO2 in underground geological structures is demonstrated in this study using seismic velocity tomography. The tomographic method uses first arrival traveltime to estimate velocity of geological structure along the ray path. The inversion procedure utilizes optimized objective function that consists of two parts: (i a part that minimizes the misfit between the observed and inverted data, and (ii a part that enforces the true shape and structure of the real geology. First, the method is applied to invert the velocity structure of a west Texas oilfield, and later to reconstruct the velocity structure of Marmousi models before and after CO2 injection. The results of the tests confirm the appropriateness of the procedure for CO2 monitoring. The inverted velocity tomogram for the post-injection stage shows velocity perturbation due to CO2 presence and the progression in CO2 front. Technology for monitoring CO2 in geological storages as demonstrated in this study is crucial to forestall CO2 leakages and its negative consequences on the environment.

  13. 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.

  14. 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.

    A geophysical survey involving seismic refraction tomography (SRT for mapping 'P' waves was

  15. 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.

  16. Resistivity and Seismic Surface Wave Tomography Results for the Nevşehir Kale Region: Cappadocia, Turkey

    Science.gov (United States)

    Coşkun, Nart; Çakır, Özcan; Erduran, Murat; Arif Kutlu, Yusuf

    2014-05-01

    The Nevşehir Kale region located in the middle of Cappadocia with approximately cone shape is investigated for existence of an underground city using the geophysical methods of electrical resistivity and seismic surface wave tomography together. Underground cities are generally known to exist in Cappadocia. The current study has obtained important clues that there may be another one under the Nevşehir Kale region. Two-dimensional resistivity and seismic profiles approximately 4-km long surrounding the Nevşehir Kale are measured to determine the distribution of electrical resistivities and seismic velocities under the profiles. Several high resistivity anomalies with a depth range 8-20 m are discovered to associate with a systematic void structure beneath the region. Because of the high resolution resistivity measurement system currently employed we were able to isolate the void structure from the embedding structure. Low seismic velocity zones associated with the high resistivity depths are also discovered. Using three-dimensional visualization techniques we show the extension of the void structure under the measured profiles.

  17. Seismic tomography of the Gulf of Corinth: a comparison of methods

    Directory of Open Access Journals (Sweden)

    P. Podvin

    1997-06-01

    first arrival P and S travel-times. The obtained images of this seismically active zone show a south/north asymmetry in agreement with the tectonic context. The transition to high velocity lies between 6 km and 9 km indicating a very thin crust related to the active extension regime.At a local scale, travel-time tomography requires a simultaneous inversion of earthquake positions and velocity structure. We applied a joint iterative inversion scheme where medium parameters and hypocenter parameters were inverted simultaneously. At each step of the inversion, rays between hypocenters and stations were traced, new partial derivatives of travel-time were estimated and scaling between parameters was performed as well. The large sparse linear system modified by the scaling was solved by the LSQR method at each iteration. We compared performances of two different forward techniques. Our first approach was a fast ray tracing based on a paraxial method to solve the two-point boundary value problem. The rays connect sources and stations in a velocity structure described by a 3D B-spline interpolation over a regular grid. The second approach is the finite-difference solution of the eikonal equation with a 3D linear interpolation over a regular grid. The partial derivatives are estimated differently depending on the interpolation method. The reconstructed images are sensitive to the spatial variation of the partial derivatives shown by synthetic examples. We aldo found that a scaling between velocity and hypocenter parameters involved in the linear system to be solved is important in recovering accurate amplitudes of anomalies. This scaling was estimated to be five through synthetic examples with the real configuration of stations and sources. We also found it necessary to scale Pand S velocities in order to recover better amplitudes of S velocity anomaly. The crustal velocity structure of a 50X50X20 km domain near Patras in the Gulf of Corinth (Greece was recovered using

  18. Near‐surface evaluation of Ball Mountain Dam, Vermont, using multi‐channel analysis of surface waves (MASW) and refraction tomography seismic methods on land‐streamer data

    Science.gov (United States)

    Ivanov, Julian M.; Johnson, Carole D.; Lane, John W.; Miller, Richard D.; Clemens, Drew

    2009-01-01

    A limited seismic investigation of Ball Mountain Dam, an earthen dam near Jamaica, Vermont, was conducted using multiple seismic methods including multi‐channel analysis of surface waves (MASW), refraction tomography, and vertical seismic profiling (VSP). The refraction and MASW data were efficiently collected in one survey using a towed land streamer containing vertical‐displacement geophones and two seismic sources, a 9‐kg hammer at the beginning of the spread and a 40‐kg accelerated weight drop one spread length from the geophones, to obtain near‐ and far‐offset data sets. The quality of the seismic data for the purposes of both refraction and MASW analyses was good for near offsets, decreasing in quality at farther offsets, thus limiting the depth of investigation to about 12 m. Refraction tomography and MASW analyses provided 2D compressional (Vp) and shear‐wave (Vs) velocity sections along the dam crest and access road, which are consistent with the corresponding VSP seismic velocity estimates from nearby wells. The velocity sections helped identify zonal variations in both Vp and Vs (rigidity) properties, indicative of material heterogeneity or dynamic processes (e.g. differential settlement) at specific areas of the dam. The results indicate that refraction tomography and MASW methods are tools with significant potential for economical, non‐invasive characterization of construction materials at earthen dam sites.

  19. Subsurface fault geometries in Southern California illuminated through Full-3D Seismic Waveform Tomography (F3DT)

    Science.gov (United States)

    Lee, En-Jui; Chen, Po

    2017-04-01

    More precise spatial descriptions of fault systems play an essential role in tectonic interpretations, deformation modeling, and seismic hazard assessments. The recent developed full-3D waveform tomography techniques provide high-resolution images and are able to image the material property differences across faults to assist the understanding of fault systems. In the updated seismic velocity model for Southern California, CVM-S4.26, many velocity gradients show consistency with surface geology and major faults defined in the Community Fault Model (CFM) (Plesch et al. 2007), which was constructed by using various geological and geophysical observations. In addition to faults in CFM, CVM-S4.26 reveals a velocity reversal mainly beneath the San Gabriel Mountain and Western Mojave Desert regions, which is correlated with the detachment structure that has also been found in other independent studies. The high-resolution tomographic images of CVM-S4.26 could assist the understanding of fault systems in Southern California and therefore benefit the development of fault models as well as other applications, such as seismic hazard analysis, tectonic reconstructions, and crustal deformation modeling.

  20. Evaluation of the rockburst potential in longwall coal mining using passive seismic velocity tomography and image subtraction technique

    Science.gov (United States)

    Hosseini, Navid

    2017-09-01

    Rockburst is a typical dynamic disaster in underground coal mines which its occurrences relate to the mechanical quality of coal seam and surrounding rock mass and also the condition of stress distribution. The main aim of this paper is to study the potential of rockburst in a longwall coal mine by using of passive seismic velocity tomography and image subtraction technique. For this purpose, first by mounting an array of receivers on the surface above the active panel, the mining-induced seismic data as a passive source for several continuous days were recorded. Then, the three-dimensional tomograms using simultaneous iteration reconstruction technique (SIRT) for each day are created and by employing the velocity filtering, the overstressed zones are detected. In addition, the two-dimensional seismic velocity tomograms in coal seam level by slicing the three-dimensional tomograms are obtained. Then the state of stress changes in successive days by applying the image subtraction technique on these two-dimensional tomograms is considered. The results show that the compilation of filtered three-dimensional tomograms and subtracted images is an appropriate approach for detecting the overstressed zones around the panel and subsequent evaluation of rockburst potential. The research conclusion proves that the applied approach in this study in combination with field observations of rock mass status can effectively identify the rockburst-prone areas during the mining operation and help to improve the safety condition.

  1. S wave propagation in acoustic anisotropic media

    Science.gov (United States)

    Stovas, Alexey

    2017-04-01

    The acoustic anisotropic medium can be defined in two ways. The first one is known as a pseudo-acoustic approximation (Alkhalifah, 1998) that is based on the fact that in TI media, P wave propagation is weakly dependent on parameter known as "vertical S-wave velocity" (Thomsen, 1986). The standard way to define the pseudo-acoustic approximation is to set this parameter to zero. However, as it was shown later (Grechka et al., 2004), there is "S wave artifact" in such a medium. Another way is to define the stack of horizontal solid-fluid layers and perform an upscaling based on the Backus (1962) averaging. The stiffness coefficient that responds to "vertical S wave velocity" turns to zero if any of layers has zero vertical S wave velocity. In this abstract, I analyze the S wave propagation is acoustic anisotropic medium and define important kinematic properties such as the group velocity surface and Dix-type equations. The kinematic properties can easily be defined from the slowness surface. In elastic transversely isotropic medium, the equations for P and SV wave slowness surfaces are coupled. Setting "vertical S wave velocity" to zero, results in decoupling of equations. I show that the S wave group velocity surface is given by quasi-astroidal form with the reference astroid defined by vertical and horizontal projections of group velocity. I show that there are cusps attached to both vertical and horizontal symmetry axes. The new S wave parameters include vertical, horizontal and normal moveout velocities. With the help of new parameterization, suitable for S wave, I also derived the Dix-type of equations to define the effective kinematical properties of S waves in multi-layered acoustic anisotropic medium. I have shown that effective media defined from P and S waves have different parameters. I also show that there are certain symmetries between P and S waves parameters and equations. The proposed method can be used for analysis of S waves in acoustic anisotropic

  2. Seismic tomography analysis using finite differential calculation of the eikonal equation and reciplocal principle; Eikonal equation no sabunkaiho to sohan genri wo riyoshita danseiha tomography kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Fujimoto, M.; Ashida, Y.; Watanabe, T.; Sassa, K. [Kyoto University, Kyoto (Japan)

    1996-10-01

    This paper describes the seismic tomography analysis of underground structures using finite differential calculation (FDC) and a reciprocal principle which points out that a propagation path is constant even if a source and receiver are exchanged with each other. Tomography analysis generally determines a ray length across each underground cell structure by ray tracing method to modify each cell slowness (inverse of velocity). Travel time field was determined by FDC of eikonal equation among ray tracing methods, and a wave propagation path was determined by reciprocity of elastic wave to carry out inversion. In conventional methods, since a wave length is assumed to be infinitesimal by ray theory, false modified slowness structures frequently appears depending on the density of a ray. Wave propagates in a certain width, and is affected by environment. The slowness was thus modified on the basis of the wave propagation path with a certain width by using not ray-tracing but reciprocity. By this modification, false structures were hardly found under a fine grid, and several propagation paths could be considered. 6 refs., 9 figs.

  3. Development of S-wave portable vibrator; S ha potable vibrator shingen no kaihatsu

    Energy Technology Data Exchange (ETDEWEB)

    Kaida, Y.; Matsubara, Y. [OYO Corp., Tokyo (Japan); Nijhof, V.; Brouwer, J.

    1996-05-01

    An S-wave portable vibrator to serve as a seismic source has been developed for the purpose of applying the shallow-layer reflection method to the study of the soil ground. The author, et al., who previously developed a P-wave portable vibrator has now developed an S-wave version, considering the advantage of the S-wave over the P-wave in that, for example, the S-wave velocity may be directly compared with the N-value representing ground strength and that the S-wave travels more slowly than the P-wave through sticky soil promising a higher-resolution exploration. The experimentally constructed S-wave vibrator consists of a conventional P-wave vibrator and an L-type wooden base plate combined therewith. Serving as the monitor for vibration is a conventional accelerometer without any modification. The applicability test was carried out at a location where a plank hammering test was once conducted for reflection aided exploration, and the result was compared with that of the plank hammering test. As the result, it was found that after some preliminary treatment the results of the two tests were roughly the same but that both reflected waves were a little sharper in the S-wave vibrator test than in the plank hammering test. 4 refs., 9 figs., 1 tab.

  4. Regional scale tomography in central Mexico. Preliminary results from the correlation of seismic noise

    Science.gov (United States)

    Chávez-García, F.; Quintanar, L.

    2009-04-01

    In addition to local site effects, ground motion from coastal earthquakes on rock sites in central Mexico is amplified in a regional scale, relative to ground motion observed along a direction parallel to the coast. This regional amplification attains a factor of 10 at frequencies that are critical in seismic risk analyses (from 0.2 to at least 2 Hz). This amplification has been related to the irregular crustal structure associated with the presence of the Mexican Volcanic Belt (oblique to the trench along the subduction zone). However, this has not yet been verified. The available models are not well constrained and there is a significant lack of data regarding the crustal structure in this region. Recent publications have shown that the Green's function between two seismic stations may be estimated from the cross-correlation of seismic noise. Most papers have shown that surface wave modes emerge in those correlation functions. The larger the distance between stations, the longer the records of seismic noise that are needed to obtain a useful result. In this paper, we use seismic noise recorded by three different arrays to estimate Rayleigh wave dispersion between stations. two arrays were temporal and one, recently installed, is permanent. The first array consisted of only four stations. It operated continuously for three months in 1997. The second temporary array operated a line of 100 seismic recorders installed perpendicularly to the subduction zone in Mexico, the MASE (Middle American Seismic Experiment) array. From this large array we use data from 18 stations in central Mexico. Finally, we use data from the permanent Mexico basin seismic array, recently installed. We use week- and month-long noise records to compute cross-correlation between vertical components for all possible station pairs. The results show clearly the emergence of clear Rayleigh wave pulses. We use the multiple filter technique to determine group velocities in the period band 4 to 10 s

  5. Seismic and mineralogical structures of the lower mantle from probabilistic tomography

    NARCIS (Netherlands)

    Mosca, I.; Cobden, L.; Deuss, A.; Ritsema, J.; Trampert, J.

    2012-01-01

    One of the most powerful approaches for understanding the 3-D thermo-chemical structure of the lower mantle is to link tomographic models with mineral physics data. This is not straightforward because of strong trade-offs between thermal and chemical structures and their influence on seismic

  6. Upper crustal structure of the North Anatolian Fault Zone from ambient seismic noise Rayleigh and Love wave tomography

    Science.gov (United States)

    Taylor, George; Rost, Sebastian; Houseman, Gregory; Hillers, Gregor

    2017-04-01

    By utilising short period surface waves present in the noise field, we can construct images of shallow structure in the Earth's upper crust: a region that is usually poorly resolved in earthquake tomography. Here, we use data from a dense seismic array (Dense Array for Northern Anatolia - DANA) deployed across the North Anatolian Fault Zone (NAFZ) in the region of the 1999 magnitude 7.6 Izmit earthquake in western Turkey. The NAFZ is a major strike-slip system that extends ˜1200 km across northern Turkey and continues to pose a high level of seismic hazard, in particular to the mega-city of Istanbul. We obtain maps of group velocity variation using surface wave tomography applied to short period (1- 6 s) Rayleigh and Love waves to construct high-resolution images of the upper 5 km of a 70 km x 35 km region centred on the eastern end of the fault segment that ruptured in the 1999 Izmit earthquake. The average Rayleigh wave group velocities in the region vary between 1.8 km/s at 1.5 s period, to 2.2 km/s at 6 s period. The NAFZ bifurcates into northern and southern strands in this region; both are active but only the northern strand moved in the 1999 event. The signatures of both the northern and southern branches of the NAFZ are clearly associated with strong gradients in surface wave group velocity. To the north of the NAFZ, we observe low Rayleigh wave group velocities ( 1.2 km/s) associated with the unconsolidated sediments of the Adapazari basin, and blocks of weathered terrigenous clastic sediments. To the south of the northern branch of the NAFZ, we detect high velocities ( 2.5 km/s) associated with a shallow crystalline basement, in particular a block of metamorphosed schists and marbles that bound the northern branch of the NAFZ.

  7. Combining 3D seismic tomography and ground-penetrating radar to reveal the structure of a megalithic burial tomb

    Science.gov (United States)

    Mendes, Manuela; Caldeira, Bento; Borges, José

    2017-04-01

    This work describes a case study concerning a prehistoric buried tomb (around 3000 years B.C.) located near Évora (Portugal). This monument is a tomb completely buried with only five visible irregular small stones distributed in a circle of 3 meter in diameter. A multi-approach combining 3D seismic tomography and ground-penetrating radar (GPR) have been applied to identify hidden elements and arrangement of the stones, required prior to any excavation work. The methodology for the 3D seismic data acquisition involves a total of 24 shots recorded by four lines, with twelve fixed receivers each one. For the GPR survey was used a 400 MHz antenna which moves along parallel lines with 50 cm separation, over a 30x30 m2 area that contains the buried tomb; the GPR unit was configured to a horizontal rate of 50 scans per meter (1024 samples/scan) and a time window of 60 ns. This multi-approach procedure allowed defining: (i) the housing of the tomb in the basement structure; (ii) the presence of a hidden corridor; (iii) the description of the internal structure of the walls of the tomb; (iv) the state of preservation of the monument. Acknowledgements: This work is co-financed by the European Union through the European Regional Development Fund under COMPETE 2020 (Operational Program for Competitiveness and Internationalization) through the ICT project (UID / GEO / 04683/2013) under the reference POCI-01-0145 -FEDER-007690.

  8. Subduction Zone Dewatering at the Southern End of New Zealand's Hikurangi Margin - Insights from 2D Seismic Tomography

    Science.gov (United States)

    Crutchley, G. J.; Klaeschen, D.

    2016-12-01

    The southern end of New Zealand's Hikurangi subduction margin is characterised by highly-oblique convergence as it makes a southward transition into a right-lateral transform plate boundary. Long-offset seismic data that cross part of the offshore portion of this transition zone give new insight into the nature of the margin. We have carried out two-dimensional pre-stack depth migrations with an iterative reflection tomography to update the velocity field on two seismic lines in this area. The depth-migrated sections show much-improved imaging of faulting within the wedge, and the seismic velocities themselves give clues about the distribution of gas and/or overpressured regions at the plate boundary and within the overlying wedge. A fascinating observation is a major splay fault that has been (or continues to be) a preferred dewatering pathway through the wedge, evidenced by a thermal anomaly that has left its mark on the overlying gas hydrate layer. Another interesting observation is a thick and laterally extensive low velocity zone beneath the subduction interface, which might have important implications for the long-term mechanical stability of the interface. Our on-going work on these data is focused on amplitude versus offset analysis in an attempt to better understand the nature of the subduction interface and also the shallower gas hydrate system. This study is an example of how distinct disturbances of the gas hydrate system can provide insight into subduction zone fluid flow processes that are important for understanding wedge stability and ultimately earthquake hazard.

  9. 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

  10. Electric resistivity and seismic refraction tomography: a challenging joint underwater survey at Äspö Hard Rock Laboratory

    Directory of Open Access Journals (Sweden)

    M. Ronczka

    2017-06-01

    Full Text Available Tunnelling below water passages is a challenging task in terms of planning, pre-investigation and construction. Fracture zones in the underlying bedrock lead to low rock quality and thus reduced stability. For natural reasons, they tend to be more frequent at water passages. Ground investigations that provide information on the subsurface are necessary prior to the construction phase, but these can be logistically difficult. Geophysics can help close the gaps between local point information by producing subsurface images. An approach that combines seismic refraction tomography and electrical resistivity tomography has been tested at the Äspö Hard Rock Laboratory (HRL. The aim was to detect fracture zones in a well-known but logistically challenging area from a measuring perspective. The presented surveys cover a water passage along part of a tunnel that connects surface facilities with an underground test laboratory. The tunnel is approximately 100 m below and 20 m east of the survey line and gives evidence for one major and several minor fracture zones. The geological and general test site conditions, e.g. with strong power line noise from the nearby nuclear power plant, are challenging for geophysical measurements. Co-located positions for seismic and ERT sensors and source positions are used on the 450 m underwater section of the 700 m profile. Because of a large transition zone that appeared in the ERT result and the missing coverage of the seismic data, fracture zones at the southern and northern parts of the underwater passage cannot be detected by separated inversion. Synthetic studies show that significant three-dimensional (3-D artefacts occur in the ERT model that even exceed the positioning errors of underwater electrodes. The model coverage is closely connected to the resolution and can be used to display the model uncertainty by introducing thresholds to fade-out regions of medium and low resolution. A structural

  11. Electric resistivity and seismic refraction tomography: a challenging joint underwater survey at Äspö Hard Rock Laboratory

    Science.gov (United States)

    Ronczka, Mathias; Hellman, Kristofer; Günther, Thomas; Wisén, Roger; Dahlin, Torleif

    2017-06-01

    Tunnelling below water passages is a challenging task in terms of planning, pre-investigation and construction. Fracture zones in the underlying bedrock lead to low rock quality and thus reduced stability. For natural reasons, they tend to be more frequent at water passages. Ground investigations that provide information on the subsurface are necessary prior to the construction phase, but these can be logistically difficult. Geophysics can help close the gaps between local point information by producing subsurface images. An approach that combines seismic refraction tomography and electrical resistivity tomography has been tested at the Äspö Hard Rock Laboratory (HRL). The aim was to detect fracture zones in a well-known but logistically challenging area from a measuring perspective. The presented surveys cover a water passage along part of a tunnel that connects surface facilities with an underground test laboratory. The tunnel is approximately 100 m below and 20 m east of the survey line and gives evidence for one major and several minor fracture zones. The geological and general test site conditions, e.g. with strong power line noise from the nearby nuclear power plant, are challenging for geophysical measurements. Co-located positions for seismic and ERT sensors and source positions are used on the 450 m underwater section of the 700 m profile. Because of a large transition zone that appeared in the ERT result and the missing coverage of the seismic data, fracture zones at the southern and northern parts of the underwater passage cannot be detected by separated inversion. Synthetic studies show that significant three-dimensional (3-D) artefacts occur in the ERT model that even exceed the positioning errors of underwater electrodes. The model coverage is closely connected to the resolution and can be used to display the model uncertainty by introducing thresholds to fade-out regions of medium and low resolution. A structural coupling cooperative inversion

  12. Quantifying uncertainties on the solution model of seismic tomography; Quelle confiance accorder au modele solution de la tomographie de reflexion 3D?

    Energy Technology Data Exchange (ETDEWEB)

    Duffet, C.

    2004-12-01

    Reflection tomography allows the determination of a velocity model that fits the travel time data associated with reflections of seismic waves propagating in the subsurface. A least-square formulation is used to compare the observed travel times and the travel times computed by the forward operator based on a ray tracing. This non-linear optimization problem is solved classically by a Gauss-Newton method based on successive linearization of the forward operator. The obtained solution is only one among many possible models. Indeed, the uncertainties on the observed travel times (resulting from an interpretative event picking on seismic records) and more generally the under-determination of the inverse problem lead to uncertainties on the solution. An a posteriori uncertainty analysis is then crucial to delimit the range of possible solutions that fit, with the expected accuracy, the data and the a priori information. A linearized a posteriori analysis is possible by an analysis of the a posteriori covariance matrix, inverse of the Gauss-Newton approximation of the matrix. The computation of this matrix is generally expensive (the matrix is huge for 3D problems) and the physical interpretation of the results is difficult. Then we propose a formalism which allows to compute uncertainties on relevant geological quantities for a reduced computational time. Nevertheless, this approach is only valid in the vicinity of the solution model (linearized framework) and complex cases may require a non-linear approach. An experimental approach consists in solving the inverse problem under constraints to test different geological scenarios. (author)

  13. Can lower mantle plumes be located using seismic tomography and transition zone topography?

    Science.gov (United States)

    Van Keken, P. E.; Bossmann, A. B.; Ritsema, J. E.; Hwang, Y.; Goes, S. D.

    2012-12-01

    Hotspot volcanism is well explained by fluid dynamical models of plumes rising from great depth in the Earth's mantle. Seismic imaging of these suggested plumes has been difficult and somewhat controversial, as imaged low velocity regions in tomographic models may be due to choices in the inversion techniques. Observations of transition zone topography may be a more robust indication of the presence of hotter-than-normal mantle, but in general the topography of the 670-km phase boundary appears flat, suggesting in part that hotspots have an upper mantle origin. We present new high-resolution finite element models of plumes rising from the core-mantle-boundary using compressible convection with phase changes. Plumes that have a buoyancy flux similar to that of the Hawaiian or Iceland hotspots show a broad high velocity conduit in the lower mantle with significant thinning and time-dependent behavior in the upper mantle. Seismic wave propagation modeling using SHAXI demonstrates that the presence of the low velocity plume causes a distinct later arrival of seismic waves that travel through the upper mantle, but wave front healing renders the strong velocity contrasts in the lower mantle invisible at the Earth's surface. The predicted 400-km phase boundary topography occurs over short wavelengths and is consistent with the observations at a significant number of hotspots. The broad plume anomaly in the uppermost lower mantle causes a slight and very broad uplift of the 670-km topography. This is consistent with the absence of significant topography of 670 as seen by the limited aperture seismic studies. Our modeling suggests that the absence of 670 km topography and difficulties of imaging plumes in tomographic models are inherently due to plume morphology and wave front healing.

  14. Seismic anisotropy of Precambrian lithosphere: Insights from Rayleigh wave tomography of the eastern Superior Craton

    Science.gov (United States)

    Petrescu, Laura; Darbyshire, Fiona; Bastow, Ian; Totten, Eoghan; Gilligan, Amy

    2017-05-01

    The thick, seismically fast lithospheric keels underlying continental cores (cratons) are thought to have formed in the Precambrian and resisted subsequent tectonic destruction. A consensus is emerging from a variety of disciplines that keels are vertically stratified, but the processes that led to their development remain uncertain. Eastern Canada is a natural laboratory to study Precambrian lithospheric formation and evolution. It comprises the largest Archean craton in the world, the Superior Craton, surrounded by multiple Proterozoic orogenic belts. To investigate its lithospheric structure, we construct a frequency-dependent anisotropic seismic model of the region using Rayleigh waves from teleseismic earthquakes recorded at broadband seismic stations across eastern Canada. The joint interpretation of phase velocity heterogeneity and azimuthal anisotropy patterns reveals a seismically fast and anisotropically complex Superior Craton. The upper lithosphere records fossilized Archean tectonic deformation: anisotropic patterns align with the orientation of the main tectonic boundaries at periods ≤110 s. This implies that cratonic blocks were strong enough to sustain plate-scale deformation during collision at 2.5 Ga. Cratonic lithosphere with fossil anisotropy partially extends beneath adjacent Proterozoic belts. At periods sensitive to the lower lithosphere, we detect fast, more homogenous, and weakly anisotropic material, documenting postassembly lithospheric growth, possibly in a slow or stagnant convection regime. A heterogeneous, anisotropic transitional zone may also be present at the base of the keel. The detection of multiple lithospheric fabrics at different periods with distinct tectonic origins supports growing evidence that cratonization processes may be episodic and are not exclusively an Archean phenomenon.

  15. High-resolution shallow seismic tomography of a hydrothermal area: application to the Solfatara, Pozzuoli

    Science.gov (United States)

    Letort, J.; Roux, P.; Vandemeulebrouck, J.; Coutant, O.; Cros, E.; Wathelet, M.; Cardellini, C.; Avino, R.

    2012-06-01

    The Solfatara is one of the major volcanoes of the Phlegrean Fields (Campi Flegrei) volcanic complex, and it is located in a densely populated area a few kilometres west of the city of Naples. It is an active resurgent caldera that has been characterized by a rich history of surface-ground deformation and soil diffuse degassing and fumarolic emissions, which are indications of the top of a hydrothermal plume. A seismic survey was completed in May 2009 for the characterization of the main subsurface features of the Solfatara. Using the complete data set, we have carried out surface wave inversion with high spatial resolution. A classical minimization of a least-squares objective function was first computed to retrieve the dispersion curves of the surface waves. Then, the fitting procedure between the data and a three-sediment-layer forward model was carried out (to a depth of 7 m), using an improved version of the neighbourhood algorithm. The inversion results indicate a NE-SW fault, which is not visible at the surface. This was confirmed by a temperature survey conducted in 2010. A passive seismic experiment localized the ambient noise sources that correlate well with the areas of high CO2 flux and high soil temperatures. Finally, considering that the intrinsic attenuation is proportional to the frequency, a centroid analysis provides an overview of the attenuation of the seismic waves, which is closely linked to the petrophysical properties of the rock. These different approaches that merge complete active and passive seismic data with soil temperature and CO2 flux maps confirm the presence of the hydrothermal system plume. Some properties of the top of the plume are indicated and localized.

  16. Critical zone weathering in the southern Sierra Nevada and Laramie Mountains imaged by seismic tomography

    Science.gov (United States)

    Hayes, J. L.; Holbrook, W. S.; Riebe, C. S.

    2011-12-01

    Near-surface variations in seismic velocity reflect differences in physical properties such as density and porosity, which in turn reflect differences in alteration of parent material by exposure to water and biologic activity. Here we present tomographic analysis of the extent of weathering from seismic refraction experiments at two areas underlain by granite: the Southern Sierra Critical Zone Observatory (SSCZO) in the fall of 2010 & 2011 and the Laramie Mountains in the spring of 2010. A 48-channel geophone array and hammer source was deployed in both surveys. In both areas seismic velocities suggest that weathering has progressed to depths of 10 m or more. When coupled with geochemical measurements of the degree of regolith weathering, these depths imply that the potential for subsurface water storage in regolith may be a larger component of the water budget than previously thought at the SSCZO. The velocity of granite bedrock was determined independently in both studies to be ~4 km/s by seismic experiments directly on outcropping granite. Two other ranges of seismic velocities seem consistent between the studies: a saprolite layer of chemically altered but still intact rock (2-4 km/s) and a regolith layer more altered than the underlying saprolite layer (<2 km/s). Using these parameters we tested hypotheses in two different granite-weathering environments. In the SSCZO a velocity-depth profile that crosses a water-saturated meadow and an adjoining forest reveal relatively low gradients in the first ten meters beneath the forest (0.75 km/s per 10 m) and higher gradients beneath the meadow (3 km/s per 10 m). From these observations, we hypothesize that the saturated meadow may provide a reducing environment that inhibits chemical weathering relative to better-drained, more oxidizing conditions in the forest. In the 1.4 Ga Sherman batholith of the Laramie Mountains we observe isolated outcrops of Lincoln Granite within the Sherman Granite. Two 0.5 km profiles

  17. A seismic tomography study of lithospheric structure under the Norwegian Caledonides

    DEFF Research Database (Denmark)

    Hejrani, Babak; Jacobsen, B. H.; Balling, N.

    2012-01-01

    towards the north along the Caledonian Mountains or not? For this purpose we present new results of relative P-wave tomography for the northern SCANLIPS (SCANdinavia Lithosphere ProfileS) profile across the northern part of the Caledonides combined with data from permanent seismological stations...

  18. Geophysical diffraction tomography and waveform inversion: Applications to high resolution seismic data

    Science.gov (United States)

    Gao, F.; Shen, P.; Symes, W. W.; Zelt, C. A.; Levander, A.

    2001-12-01

    We apply two different techniques to analyze high resolution seismic data from surface and borehole measurements made at a groundwater contamination site at Hill Air Force Base, Ogden, Utah. Two vertical seismic profiles and surface data were recorded simultaneously in and between two 15m deep boreholes separated by 21m. The seismic source was a 223 rifle fired on the surface between the two boreholes, generating signals with energy up to ~300Hz. The size of the target area is roughly the order of a few mean wavelengths in the dataset. The relatively large ratio of mean wavelength ( ~5m) to the scale of structural detail in this high-resolution experiment (projecting misfits in the data space into velocity corrections in the model space. In theory, multiple-frequencies and non-uniform data sampling can be handled easily. In the second technique, full waveform inversion, the inverse problem is posed as nonlinear data fitting where the unknown parameters are solved by minimizing the misfit between the predicted data and the observed data. A gradient-type approach is applied to solve these problems in which the Jacobian and its adjoint are calculated for given model and data vectors. We present an explicit finite difference time stepping scheme to compute the forward model and its adjoint. Waveform data fitting driven by finite difference simulations can be based on different physical modeling assumptions, from acoustic to viscoelastic propagation. Our finite difference class defines an operator in the sense of the Hilbert Class Library (HCL), a C++ software package for optimization (Cockenback, and Symes, 1996). A wide range of gradient type inversion algorithms using HCL as a platform can be tested.

  19. Improving reservoir history matching of EM heated heavy oil reservoirs via cross-well seismic tomography

    KAUST Repository

    Katterbauer, Klemens

    2014-01-01

    Enhanced recovery methods have become significant in the industry\\'s drive to increase recovery rates from oil and gas reservoirs. For heavy oil reservoirs, the immobility of the oil at reservoir temperatures, caused by its high viscosity, limits the recovery rates and strains the economic viability of these fields. While thermal recovery methods, such as steam injection or THAI, have extensively been applied in the field, their success has so far been limited due to prohibitive heat losses and the difficulty in controlling the combustion process. Electromagnetic (EM) heating via high-frequency EM radiation has attracted attention due to its wide applicability in different environments, its efficiency, and the improved controllability of the heating process. While becoming a promising technology for heavy oil recovery, its effect on overall reservoir production and fluid displacements are poorly understood. Reservoir history matching has become a vital tool for the oil & gas industry to increase recovery rates. Limited research has been undertaken so far to capture the nonlinear reservoir dynamics and significantly varying flow rates for thermally heated heavy oil reservoir that may notably change production rates and render conventional history matching frameworks more challenging. We present a new history matching framework for EM heated heavy oil reservoirs incorporating cross-well seismic imaging. Interfacing an EM heating solver to a reservoir simulator via Andrade’s equation, we couple the system to an ensemble Kalman filter based history matching framework incorporating a cross-well seismic survey module. With increasing power levels and heating applied to the heavy oil reservoirs, reservoir dynamics change considerably and may lead to widely differing production forecasts and increased uncertainty. We have shown that the incorporation of seismic observations into the EnKF framework can significantly enhance reservoir simulations, decrease forecasting

  20. Directionality analysis and Rayleigh wave tomography of ambient seismic noise in southern Norway

    Science.gov (United States)

    Köhler, Andreas; Weidle, Christian; Maupin, Valérie

    2011-01-01

    We process seismic broad-band data from southern Norway by cross correlation of ambient seismic noise in view of getting a better image of the crustal structure in the area. The main data set sterns from the temporary MAGNUS network which operated continuously from 2006 September to 2008 June. Additionally, data from permanent stations of the National Norwegian Seismic Network, the NORSAR array and GSN stations in the region are used. We compute vertical component cross-correlation functions using 41 receivers for 3-month time windows. Evaluation of the azimuthal and temporal variation of signal-to-noise ratios (SNRs) and f-k analysis of data from NORSAR array between 3 and 25 s period shows that the dominant source areas of seismic noise are located to the west and north of the network during most of the measurement time, which corresponds well to the Norwegian coast line. During summer months, the SNRs decrease but the azimuthal distribution becomes more uniform between 7 and 12 s period, suggesting a more diffuse character of the wavefield. Primary ocean microseisms above 12 s show different dominant source azimuths during this time period compared to the winter months. Time-frequency analysis is applied to measure Rayleigh wave group velocity dispersion curves between each station pair for each 3-month correlation stack and the mean and variance of all dispersion curves is computed for each path. After rejection of low-quality data, a careful analysis shows that the group velocities are not biased by noise directionality. We invert the data for group velocity maps at period bands between 3 and 25 s. At short periods, we find an average Rayleigh wave group speed of about 3 km s-1 and velocity anomalies that correlate very well with local surface geology. While higher velocities (+5 per cent) can be associated with the Caledonian nappes in the central part of southern Norway, the Oslo Graben is reflected by negative velocity anomalies (-3 to -5 per cent). At

  1. Stress barriers controlling lateral migration of magma revealed by seismic tomography

    Science.gov (United States)

    Martí, J.; Villaseñor, A.; Geyer, A.; López, C.; Tryggvason, A.

    2017-01-01

    Understanding how monogenetic volcanic systems work requires full comprehension of the local and regional stresses that govern magma migration inside them and why/how they seem to change from one eruption to another. During the 2011-2012 El Hierro eruption (Canary Islands) the characteristics of unrest, including a continuous change in the location of seismicity, made the location of the future vent unpredictable, so short term hazard assessment was highly imprecise. A 3D P-wave velocity model is obtained using arrival times of the earthquakes occurred during that pre-eruptive unrest and several latter post-eruptive seismic crises not related to further eruptions. This model reveals the rheological and structural complexity of the interior of El Hierro volcanic island. It shows a number of stress barriers corresponding to regional tectonic structures and blocked pathways from previous eruptions, which controlled ascent and lateral migration of magma and, together with the existence of N-S regional compression, reduced its options to find a suitable path to reach the surface and erupt.

  2. 3D seismic traveltime tomography beneath the Pannonian basin: preliminary results

    Science.gov (United States)

    Timkó, Máté; Wéber, Zoltán

    2017-04-01

    The Pannonian basin and the surrounding orogens are located in central Europe and are parts of the Alpine-Carpathian orogenic mountain belts. This is a back-arc basin characterized by a thinned lower crust and an updoming mantle. Benath the basin the Moho discontinuity is not deeper than 30 km and the lithosphere also has smaller thickness ( 80 km) than the continental average. Imaging the velocity structure of the crust and upper mantle may help us to better understand the structure and formation of the Pannonian region. In this study we have estimated the three-dimensional (3D) P-wave velocity structure and Moho geometry beneath the Pannonian Basin by analysing the seismic data from the ISC bulletin using the FMTOMO tomographic inversion software package. The inversion procedure applies the fast marching method for calculating the forward step, and the subspace inversion method to retrieve the model parameters. In the inversion we used local, regional and teleseismic earthquakes as well. Altogether, we had more than 120 thousand P-wave arrival time data of more than 9000 seismic events from the time period between 2004 and 2014. The resulting 3D velocity image highly resembles the known geologic and tectonic structure of the area and is comperable to earlier tomographic images published in the literature. Also, the retrieved velocity anomalies correlate well with the Moho topography, the orogenic belts and the deep basins of the region.

  3. Lower mantle thermal structure deduced from seismic tomography, mineral physics and numerical modelling

    Science.gov (United States)

    Cadek, O.; Yuen, D. A.; Steinbach, V.; Chopelas, A.; Matyska, C.

    1994-01-01

    The long-wavelength thermal anomalies in the lower mantle have been mapped out using several seismic tomographic models in conjunction with thermodynamic parameters derived from high-pressure mineral physics experiments. These parameters are the depth variations of thermal expansivity and of the proportionality factor between changes in density and seismic velocity. The giant plume-like structures in the lower mantle under the Pacific Ocean and Africa have outer fringes with thermal anomalies around 300-400 K, but very high temperatures are found in the center of the plumes near the base of the core-mantle boundary. These extreme values can exceed +1500 K and may reflect large hot thermal anomalies in the lower mantle, which are supported by recent measurements of high melting temperatures of perovskite and iron. Extremely cold anomalies, around -1500 K, are found for anomalies in the deep mantle around the Pacific rim and under South America. Numerical simulations show that large negative thermal anomalies in the mid-lower mantle have modest magnitudes of around -500 K. correlation pattern exists between the present-day locations of cold masses in the lower mantle and the sites of past subduction since the Cretaceous. Results from correlation analysis show that the slab mass-flux in the lower mantle did not conform to a steady-state nature but exhibited time-dependent behavior.

  4. Towards using direct methods in seismic tomography: computation of the full resolution matrix using high-performance computing and sparse QR factorization

    Science.gov (United States)

    Bogiatzis, Petros; Ishii, Miaki; Davis, Timothy A.

    2016-05-01

    For more than two decades, the number of data and model parameters in seismic tomography problems has exceeded the available computational resources required for application of direct computational methods, leaving iterative solvers the only option. One disadvantage of the iterative techniques is that the inverse of the matrix that defines the system is not explicitly formed, and as a consequence, the model resolution and covariance matrices cannot be computed. Despite the significant effort in finding computationally affordable approximations of these matrices, challenges remain, and methods such as the checkerboard resolution tests continue to be used. Based upon recent developments in sparse algorithms and high-performance computing resources, we show that direct methods are becoming feasible for large seismic tomography problems. We demonstrate the application of QR factorization in solving the regional P-wave structure and computing the full resolution matrix with 267 520 model parameters.

  5. Surface Wave Tomography for the Hawaiian PLUME Project and the Seismic Structure of the Hawaiian Swell

    Science.gov (United States)

    Markee, A.; Laske, G.; Orcutt, J. A.; Collins, J. A.; Wolfe, C. J.; Solomon, S. C.; Detrick, R. S.; Bercovici, D. A.; Hauri, E. H.

    2008-12-01

    During the two-stage seismic component of the Hawaiian PLUME (Plume-Lithosphere Undersea Melt Experiment) project from January 2005 through June 2007, we collected continuous seismic data at ten land stations and nearly 70 ocean bottom sites which were occupied with broad-band seismometers. This provides an ideal basis to analyze surface waves across a broad frequency band to image the crust and mantle of the Hawaiian swell. In the first OBS deployment phase from January 2005 through January 2006, 35 sites were occupied in an elongated array centered on the island of Hawaii, with a station spacing of roughly 75~km and an aperture of 500~km. In the second phase from May 2006 through June 2007, 37 sites were occupied in a larger array with a station spacing of roughly 200~km. Our current analysis concentrates on long-period teleseismic Rayleigh waves. During the first phase we collected records from upward of 95 suitable large, shallow earthquakes with scalar seismic moment M0≥ 0.015 × 1020~Nm (MS≥ 5.6) or larger and source depths of 200~km or less. We also identified 70 smaller events with signal levels suitable for analysis. For the second phase, our initial analysis includes 163 larger earthquakes. We currently have over 5000 unique single-station phase measurements for the first deployment stage and 2500 for the second. We use this primary phase database to obtain two-station path-averaged phase velocity curves. These path-averaged dispersion curves are each well constrained by many earthquakes and are internally consistent between 15 and 50~s, allowing us to image the lithosphere and upper asthenosphere. Some larger events provide constraints beyond 100~s, thereby illuminating the lower asthenosphere. Using these dispersion curves we determine path-averaged depth profiles for nearly 300 two-station legs for the first deployment. The analysis of the second stage has provided over 100 legs and is still ongoing. We combine these profiles in an inversion for 3

  6. Can faults become barriers for deep fluid circulation? Insights from high-resolution seismic VSP tomography at the Soultz-sous-Forêts geothermal site

    Science.gov (United States)

    Calò, Marco; Dorbath, Catherine; Lubrano Lavadera, Paul

    2016-09-01

    Vertical Seismic Profile (VSP) surveys are generally used for modelling converted phases of the seismic body waves propagating in the medium allowing the detection of waves interpreted as reflections on steeply dipping reflecting structures such as faults, abrupt lateral changes of lithology, and fractures. At the Enhanced Geothermal System geothermal field of Soultz-sous-Forêts the analysis of data recorded during a VSP experiment allowed describing the presence of at least two structures near the wells. Here we show how seismic tomography method can be applied to the VSP data to reconstruct the 3-D shape of structures in the volume surrounding the geothermal wells. The three-dimensional P wave velocity model obtained shows positive velocity anomalies associated with the main faults observed by the VSP analysis and negative anomalies in the regions affected by massive hydraulic stimulations performed in the past. This pattern can be explained as a different response of the rock volume to the fluid injections where regions marked by relative pre-existing high permeability were less affected by the hydraulic stimulations. This difference in permeability produced regions that could work as barriers for fluid diffusion through the reservoir. Comparisons of our high resolved model with the location of the induced seismicity and with another model obtained using seismic noise correlation give evidence of the presence of these structures and may explain the poor connection between the wells GPK4 and GPK2-GPK3 system.

  7. Deep structure of Porcupine Basin and nature of the Porcupine Median Ridge from seismic refraction tomography

    Science.gov (United States)

    Watremez, L.; Chen, C.; Prada, M.; Minshull, T. A.; O'Reilly, B.; Reston, T. J.; Wagner, G.; Gaw, V.; Klaeschen, D.; Shannon, P.

    2015-12-01

    The Porcupine Basin is a narrow V-shaped failed rifted basin located offshore SW Ireland. It is of Permo-Triassic to Cenozoic age, with the main rifting phase in the Late Jurassic to Early Cretaceous. Porcupine Basin is a key study area to learn about the processes of continental extension and to understand the thermal history of this rifted basin. Previous studies show increasing stretching factors, from less than 1.5 to the North to more than 6 to the South. A ridge feature, the Porcupine Median Ridge, has been identified in the middle of the southernmost part of the basin. During the last three decades, this ridge has been successively interpreted as a volcanic structure, a diapir of partially serpentinized mantle, or a block of continental crust. Its nature still remains debated today. In this study, we use arrival times from refractions and wide-angle reflections in the sedimentary, crustal and mantle layers to image the crustal structure of the thinnest part of the basin, the geometry of the continental thinning from margin to margin, and the Porcupine Median Ridge. The final velocity model is then compared with coincident seismic reflection data. We show that (1) the basin is asymmetric, (2) P-wave velocities in the uppermost mantle are lower than expected for unaltered peridotites, implying upper-mantle serpentinisation, (3) the nature of Porcupine Median Ridge is probably volcanic, and (4) the amount of thinning is greater than shown in previous studies. We discuss the thermal implications of these results for the evolution of this rift system and the processes leading to the formation of failed rifts. This project is funded by the Irish Shelf Petroleum Studies Group (ISPSG) of the Irish Petroleum Infrastructure Programme Group 4.

  8. The preliminary results: Seismic ambient noise Rayleigh wave tomography around Merapi volcano, central Java, Indonesia

    Energy Technology Data Exchange (ETDEWEB)

    Trichandi, Rahmantara, E-mail: rachmantara.tri@gmail.com [Geophysical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, 40132, Bandung (Indonesia); Yudistira, Tedi; Nugraha, Andri Dian [Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung, 40132 (Indonesia); Zulhan, Zulfakriza [Earth Science Graduate Program, Faculty of Earth Science and Technology, Institut Teknologi Bandung, Bandung, 40132 (Indonesia); Saygin, Erdinc [Research School of Earth Sciences, The Australian National University, Canberra ACT 0200 (Australia)

    2015-04-24

    Ambient noise tomography is relatively a new method for imaging the shallow structure of the Earth subsurface. We presents the application of this method to produce a Rayleigh wave group velocity maps around the Merapi Volcano, Central Java. Rayleigh waves group velocity maps were reconstructed from the cross-correlation of ambient noise recorded by the DOMERAPI array which consists 43 broadband seismometers. In the processing stage, we first filtered the observation data to separatethe noise from the signal that dominated by the strong volcanic activities. Next, we cross-correlate the filtered data and stack to obtain the Green’s function for all possible station pairs. Then we carefully picked the peak of each Green’s function to estimate the dispersion trend and appliedMultiple Filter Technique to obtain the dispersion curve. Inter-station group velocity curvesare inverted to produceRayleigh wave group velocity maps for periods 1 to 10 s. The resulted Rayleigh group velocity maps show the interesting features around the Merapi Volcano which generally agree with the previous studies. Merapi-Lawu Anomaly (MLA) is emerged as a relatively low anomaly in our group velocity maps.

  9. Generation of High-Frequency P and S Wave Energy by Rock Fracture During a Buried Explosion

    Science.gov (United States)

    2015-07-20

    speed digital cameras, and monitored the resultant seismic waves using a laser vibrometer (as an ultra-high-frequency seismometer). We originally... laser vibrometers to record particle velocities in the resultant P and S waves. Since no mechanical data was available for candy- glass, we measured...plates photographing them using high-speed digital cameras, and monitoring the resultant seismic waves using laser vibrometers (as an array of

  10. Along-strike variations in the Himalayan orogenic wedge structure in Bhutan from ambient seismic noise tomography

    Science.gov (United States)

    Singer, Julia; Obermann, Anne; Kissling, Eduard; Fang, Hongjian; Hetényi, György; Grujic, Djordje

    2017-04-01

    The geological units and tectonic structure exposed in the Bhutan Himalaya document significant regional variations, expressed primarily as tectonic windows and klippen. The along-strike variations of these structures and their metamorphic grade are usually associated with the formation of local duplexes in the underlying tectonic units. To investigate these variations and their extent in depth, we image the isotropic shear-wave velocity structure of the orogenic wedge by ambient noise tomography. Group velocities are extracted from cross correlations of ambient seismic noise, recorded by the temporary GANSSER network in Bhutan. The upper crustal structure beneath Bhutan is mapped down to 18 km depth by directly inverting Rayleigh-wave group velocity measurements in the period range between 2 and 20 s with a ray tracing based inversion approach. Our results reveal several distinct high shear-wave velocity anomalies (≥3.6 km/s) and reflect the along-strike variations in the upper crustal structure in relation to the alternating tectonic windows and klippen at the surface. In correlation with the surface geology in the northern part of Bhutan, we interpret shallow high shear-wave velocity anomalies as quarzite-dominated rocks or felsic migmatites with large intrusions of leucogranites. High-velocity anomalies in the orogenic wedge in eastern and western Bhutan correlate with the local geometry of the Main Himalayan Thrust and provide evidence for the formation and depth extent of localized duplexes of quartzite dominated lithology in association with the formation of tectonic windows in the Bhutan Himalaya.

  11. Seismic tomography model reveals mantle magma sources of recent volcanic activity at El Hierro Island (Canary Islands, Spain)

    Science.gov (United States)

    García-Yeguas, Araceli; Ibáñez, Jesús M.; Koulakov, Ivan; Jakovlev, Andrey; Romero-Ruiz, M. Carmen; Prudencio, Janire

    2014-12-01

    We present a 3-D model of P and S velocities beneath El Hierro Island, constructed using the traveltime data of more than 13 000 local earthquakes recorded by the Instituto Geográfico Nacional (IGN, Spain) in the period from 2011 July to 2012 September. The velocity models were performed using the LOTOS code for iterative passive source tomography. The results of inversion were thoroughly verified using different resolution and robustness tests. The results reveal that the majority of the onshore area of El Hierro is associated with a high-velocity anomaly observed down to 10-12-km depth. This anomaly is interpreted as the accumulation of solid igneous rocks erupted during the last 1 Myr and intrusive magmatic bodies. Below this high-velocity pattern, we observe a low-velocity anomaly, interpreted as a batch of magma coming from the mantle located beneath El Hierro. The boundary between the low- and high-velocity anomalies is marked by a prominent seismicity cluster, thought to represent anomalous stresses due to the interaction of the batch of magma with crust material. The areas of recent eruptions, Orchilla and La Restinga, are associated with low-velocity anomalies surrounding the main high-velocity block. These eruptions took place around the island where the crust is much weaker than the onshore area and where the melted material cannot penetrate. These results put constraints on the geological model that could explain the origin of the volcanism in oceanic islands, such as in the Canaries, which is not yet clearly understood.

  12. Shallow Faulting in Morelia, Mexico, Based on Seismic Tomography and Geodetically Detected Land Subsidence

    Science.gov (United States)

    Cabral-Cano, E.; Arciniega-Ceballos, A.; Vergara-Huerta, F.; Chaussard, E.; Wdowinski, S.; DeMets, C.; Salazar-Tlaczani, L.

    2013-12-01

    Subsidence has been a common occurrence in several cities in central Mexico for the past three decades. This process causes substantial damage to the urban infrastructure and housing in several cities and it is a major factor to be considered when planning urban development, land-use zoning and hazard mitigation strategies. Since the early 1980's the city of Morelia in Central Mexico has experienced subsidence associated with groundwater extraction in excess of natural recharge from rainfall. Previous works have focused on the detection and temporal evolution of the subsidence spatial distribution. The most recent InSAR analysis confirms the permanence of previously detected rapidly subsiding areas such as the Rio Grande Meander area and also defines 2 subsidence patches previously undetected in the newly developed suburban sectors west of Morelia at the Fraccionamiento Del Bosque along, south of Hwy. 15 and another patch located north of Morelia along Gabino Castañeda del Rio Ave. Because subsidence-induced, shallow faulting develops at high horizontal strain localization, newly developed a subsidence areas are particularly prone to faulting and fissuring. Shallow faulting increases groundwater vulnerability because it disrupts discharge hydraulic infrastructure and creates a direct path for transport of surface pollutants into the underlying aquifer. Other sectors in Morelia that have been experiencing subsidence for longer time have already developed well defined faults such as La Colina, Central Camionera, Torremolinos and La Paloma faults. Local construction codes in the vicinity of these faults define a very narrow swath along which housing construction is not allowed. In order to better characterize these fault systems and provide better criteria for future municipal construction codes we have surveyed the La Colina and Torremolinos fault systems in the western sector of Morelia using seismic tomographic techniques. Our results indicate that La Colina Fault

  13. New Insights on Mt. Etna's Crust and Relationship with the Regional Tectonic Framework from Joint Active and Passive P-Wave Seismic Tomography

    Science.gov (United States)

    Díaz-Moreno, A.; Barberi, G.; Cocina, O.; Koulakov, I.; Scarfì, L.; Zuccarello, L.; Prudencio, J.; García-Yeguas, A.; Álvarez, I.; García, L.; Ibáñez, J. M.

    2017-09-01

    In the Central Mediterranean region, the production of chemically diverse volcanic products (e.g., those from Mt. Etna and the Aeolian Islands archipelago) testifies to the complexity of the tectonic and geodynamic setting. Despite the large number of studies that have focused on this area, the relationships among volcanism, tectonics, magma ascent, and geodynamic processes remain poorly understood. We present a tomographic inversion of P-wave velocity using active and passive sources. Seismic signals were recorded using both temporary on-land and ocean bottom seismometers and data from a permanent local seismic network consisting of 267 seismic stations. Active seismic signals were generated using air gun shots mounted on the Spanish Oceanographic Vessel `Sarmiento de Gamboa'. Passive seismic sources were obtained from 452 local earthquakes recorded over a 4-month period. In total, 184,797 active P-phase and 11,802 passive P-phase first arrivals were inverted to provide three different velocity models. Our results include the first crustal seismic active tomography for the northern Sicily area, including the Peloritan-southern Calabria region and both the Mt. Etna and Aeolian volcanic environments. The tomographic images provide a detailed and complete regional seismotectonic framework and highlight a spatially heterogeneous tectonic regime, which is consistent with and extends the findings of previous models. One of our most significant results was a tomographic map extending to 14 km depth showing a discontinuity striking roughly NW-SE, extending from the Gulf of Patti to the Ionian Sea, south-east of Capo Taormina, corresponding to the Aeolian-Tindari-Letojanni fault system, a regional deformation belt. Moreover, for the first time, we observed a high-velocity anomaly located in the south-eastern sector of the Mt. Etna region, offshore of the Timpe area, which is compatible with the plumbing system of an ancient shield volcano located offshore of Mt. Etna.

  14. Mapping seismic azimuthal anisotropy of the Japan subduction zone

    Science.gov (United States)

    Zhao, D.; Liu, X.

    2016-12-01

    We present 3-D images of azimuthal anisotropy tomography of the crust and upper mantle of the Japan subduction zone, which are determined using a large number of high-quality P- and S-wave arrival-time data of local earthquakes and teleseismic events recorded by the dense seismic networks on the Japan Islands. A tomographic method for P-wave velocity azimuthal anisotropy is modified and extended to invert S-wave travel times for 3-D S-wave velocity azimuthal anisotropy. A joint inversion of the P and S wave data is conducted to constrain the 3-D azimuthal anisotropy of the Japan subduction zone. Main findings of this work are summarized as follows. (1) The high-velocity subducting Pacific and Philippine Sea (PHS) slabs exhibit trench-parallel fast-velocity directions (FVDs), which may reflect frozen-in lattice-preferred orientation of aligned anisotropic minerals formed at the mid-ocean ridge as well as shape-preferred orientation such as normal faults produced at the outer-rise area near the trench axis. (2) Significant trench-normal FVDs are revealed in the mantle wedge, which reflects corner flow in the mantle wedge due to the active subduction and dehydration of the oceanic plates. (3) Obvious toroidal FVDs and low-velocity anomalies exist in and around a window (hole) in the aseismic PHS slab beneath Southwest Japan, which may reflect a toroidal mantle flow pattern resulting from hot and wet mantle upwelling caused by the joint effects of deep dehydration of the Pacific slab and the convective circulation process in the mantle wedge above the Pacific slab. (4) Significant low-velocity anomalies with trench-normal FVDs exist in the mantle below the Pacific slab beneath Northeast Japan, which may reflect a subducting oceanic asthenosphere affected by hot mantle upwelling from the deeper mantle. ReferencesLiu, X., D. Zhao (2016) Seismic velocity azimuthal anisotropy of the Japan subduction zone: Constraints from P and S wave traveltimes. J. Geophys. Res. 121, doi

  15. Measurement of near-surface seismic compressional wave velocities using refraction tomography at a proposed construction site on the Presidio of Monterey, California

    Science.gov (United States)

    Powers, Michael H.; Burton, Bethany L.

    2012-01-01

    The U.S. Army Corps of Engineers is determining the feasibility of constructing a new barracks building on the U.S. Army Presidio of Monterey in Monterey, California. Due to the presence of an endangered orchid in the proposed area, invasive techniques such as exploratory drill holes are prohibited. To aid in determining the feasibility, budget, and design of this building, a compressional-wave seismic refraction survey was proposed by the U.S. Geological Survey as an alternative means of investigating the depth to competent bedrock. Two sub-parallel profiles were acquired along an existing foot path and a fence line to minimize impacts on the endangered flora. The compressional-wave seismic refraction tomography data for both profiles indicate that no competent rock classified as non-rippable or marginally rippable exists within the top 30 feet beneath the ground surface.

  16. Propagation of S-waves Through the Sediments in the Mississippi Embayment

    Science.gov (United States)

    Chiu, S.; Langston, C. A.; Withers, M.

    2005-12-01

    S body waves from microearthquakes in the New Madrid Seismic Zone (NMSZ) are investigated at selected broadband station sites to understand wave propagation through the Mississippi embayment sediments. Earthquake body waveforms display distinctive features that constrain the nature of the body wave local site response and wave propagation within the unconsolidated Mississippi embayment sediments. S-wave resonance effects may infer near-site conditions. Site resonance effects change between individual receivers because of velocity heterogeneity. Travel times of observed S-phases such as S, Sp, and SsShs (the first S-wave reverberation) can be used to estimate the average S-wave slowness and Poisson's ratio within the embayment sediments. An average Poisson's ratio in the range of 0.34 to 0.45 is obtained for selected sites within the central NMSZ. Use of well log data in wave calculations shows that 1-D heterogeneity can be the first-order influence on seismic wave propagation within the Mississippi embayment sediments.

  17. Estimation of S-wave Velocity Structures by Using Microtremor Array Measurements for Subsurface Modeling in Jakarta

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    Mohamad Ridwan

    2014-12-01

    Full Text Available Jakarta is located on a thick sedimentary layer that potentially has a very high seismic wave amplification. However, the available information concerning the subsurface model and bedrock depth is insufficient for a seismic hazard analysis. In this study, a microtremor array method was applied to estimate the geometry and S-wave velocity of the sedimentary layer. The spatial autocorrelation (SPAC method was applied to estimate the dispersion curve, while the S-wave velocity was estimated using a genetic algorithm approach. The analysis of the 1D and 2D S-wave velocity profiles shows that along a north-south line, the sedimentary layer is thicker towards the north. It has a positive correlation with a geological cross section derived from a borehole down to a depth of about 300 m. The SPT data from the BMKG site were used to verify the 1D S-wave velocity profile. They show a good agreement. The microtremor analysis reached the engineering bedrock in a range from 359 to 608 m as depicted by a cross section in the north-south direction. The site class was also estimated at each site, based on the average S-wave velocity until 30 m depth. The sites UI to ISTN belong to class D (medium soil, while BMKG and ANCL belong to class E (soft soil.

  18. Evaluation of seismic tomography images: topography of the 660 km discontinuity and anomalous low velocity zones near the bottom of stagnant slabs

    Science.gov (United States)

    Tajima, Fumiko

    2010-05-01

    Large-scale seismic tomography studies visualized the images of subducting plates as high velocity anomalies (HVA's), which gradually deflect and flatten to form stagnant slabs in the mantle transition zone (MTZ). The production of stagnant slabs was predicted by mineral physicists more than two decades ago, in that the phase transformation of olivine (ringwoodite) to higher pressure phases may be delayed under cold temperature anomaly, and thus the seismic discontinuity at ~660 km be depressed. A number of succeeding studies found variation of the discontinuity depths and interpreted the depressed discontinuities as the evidence of stagnation of subducted cold slabs albeit there are normal discontinuity depths found in the region of HVA's. As part of the supplementary efforts to long-wavelength studies, we carried out waveform modeling of relatively short-wavelength regional body waves (~1Hz, recorded at distances from ~14 to 30 deg) to verify tomographic images focusing on the MTZ structure in the NW Pacific subduction zones. This waveform modeling has resolving power of the structure near the 660 km discontinuity that is contrasting to tomography modeling of travel-time anomalies alone. Our results show discontinuity depth variation and low velocity anomaly (LVA, ~-10%) zones in the vicinity. The LVA zones which were modeled with SV-P conversion and scattering are highly localized with the lateral extent of a few hundred km length and several 10's km width. Recent laboratory experiments show clear difference in the measured properties for olivine and garnet under dry and wet conditions (Ohtani and Litasov, 2006), implying that the seismically observed depression of the discontinuity depth should represent cold ringwoodite (high pressure phase of olivine) under wet condition. As lower mantle minerals have much smaller capacity of water content than in the MTZ, dehydration should occur from further descending slabs at the base of the MTZ. The highly local LVA

  19. Interlobate esker architecture and related hydrogeological features derived from a combination of high-resolution reflection seismics and refraction tomography, Virttaankangas, southwest Finland

    Science.gov (United States)

    Maries, Georgiana; Ahokangas, Elina; Mäkinen, Joni; Pasanen, Antti; Malehmir, Alireza

    2017-05-01

    A novel high-resolution (2-4 m source and receiver spacing) reflection and refraction seismic survey was carried out for aquifer characterization and to confirm the existing depositional model of the interlobate esker of Virttaankangas, which is part of the Säkylänharju-Virttaankangas glaciofluvial esker-chain complex in southwest Finland. The interlobate esker complex hosting the managed aquifer recharge (MAR) plant is the source of the entire water supply for the city of Turku and its surrounding municipalities. An accurate delineation of the aquifer is therefore critical for long-term MAR planning and sustainable use of the esker resources. Moreover, an additional target was to resolve the poorly known stratigraphy of the 70-100-m-thick glacial deposits overlying a zone of fractured bedrock. Bedrock surface as well as fracture zones were confirmed through combined reflection seismic and refraction tomography results and further validated against existing borehole information. The high-resolution seismic data proved successful in accurately delineating the esker cores and revealing complex stratigraphy from fan lobes to kettle holes, providing valuable information for potential new pumping wells. This study illustrates the potential of geophysical methods for fast and cost-effective esker studies, in particular the digital-based landstreamer and its combination with geophone-based wireless recorders, where the cover sediments are reasonably thick.

  20. Segmentation of the Izu-Bonin and Mariana slabs based on the analysis of the Benioff seismicity distribution and regional tomography results

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    K. Jaxybulatov

    2013-01-01

    Full Text Available We present a new model of P and S velocity anomalies in the mantle down to a depth of 1300 km beneath the Izu-Bonin and Mariana (IBM arcs. This model is derived based on tomographic inversion of global travel time data from the revised ISC catalogue. The results of inversion are thoroughly verified using a series of different tests. The obtained model is generally consistent with previous studies by different authors. We also present the distribution of relocated deep events projected to the vertical surface along the IBM arc system. Unexpectedly, the seismicity forms elongated vertical clusters instead of horizontal zones indicating phase transitions in the slab. We propose that these vertical seismicity zones mark zones of intense deformation and boundaries between semi-autonomous segments of the subducting plate. The P and S seismic tomography models consistently display the slab as prominent high-velocity anomalies coinciding with the distribution of deep seismicity. We can distinguish at least four segments which subduct differently. The northernmost segment of the Izu-Bonin arc has the gentlest angle of dipping which is explained by backward displacement of the trench. In the second segment, the trench stayed at the same location, and we observe the accumulation of the slab material in the transition zone and its further descending to the lower mantle. In the third segment, the trench is moving forward causing the steepening of the slab. Finally, for the Mariana segment, despite the backward displacement of the arc, the subducting slab is nearly vertical. Between the Izu-Bonin and Mariana arcs we clearly observe a gap which can be traced down to about 400 km in depth. Based on joint consideration of the tomography results and the seismicity distribution, we propose two different scenarios of the subduction evolution in the IBM zone during the recent time, depending on the reference frame of plate displacements. In the first case, we

  1. Seismic assessment of a temporary deployment in the Kingdom of Bhutan using double-­difference tomography

    Science.gov (United States)

    Perez, C. A.; Velasco, A. A.; Syracuse, E. M.; Maceira, M.; Zhang, H.

    2014-12-01

    The Kingdom of Bhutan is located on the eastern edge of the Himalaya range. As an area of a major continental-continental collision, Bhutan Himalaya has been subject to a considerable amount of deformation and transpression, and it contains features of the five major shear zones of the Himalayas. Extensive seismic analysis of the region, however, is lacking due to sparse coverage and complexity of its crustal structure. We examine seismic event data from a temporary seismic network deployed in the Kingdom of Bhutan (2002-2003) using the double difference tomographic inversion technique TomoFDD, which allows for the joint inversion of event relocations and seismic velocity structure. Our primary focus is on ~200 regional events surrounding the five-station network. The events are located between 86° and 100°E longitude, and 18° and 31°N latitude, and with depths between 10 and 400 km. To extend our model area, we also incorporate GSN stations LSA, KMI, and CHTO. Prior analysis of this dataset consisted of event location, relocation, and 1D velocity modeling. We leverage on previous studies and build a new 3D seismic velocity model of the crust and upper mantle underneath the Bhutan region to gain further insight on the seismicity and crustal assessment.

  2. 3D Traveltime Tomography and 1D Wavefield Inversion of Dense 3D Seismic Refraction Data From a Shallow Groundwater Contamination Site

    Science.gov (United States)

    Zelt, C. A.; Chen, J.; Levander, A.

    2016-12-01

    In 2012 Rice University carried out a shallow seismic survey in Rifle, Colorado where the groundwater was contaminated by vanadium and uranium ore-processing operations ending in 1958. The purpose of the seismic survey is to provide constraints to improve hydrogeologic modeling. The 3-D P-wave survey over 96 m x 60 m included 2158 shots recorded by 384 channels yielding 828,672 traces. An accelerated weight drop provided data with good signal-to-noise ratio (SNR) and a dominant frequency of 60 Hz. The overall good SNR allows for precise picking and an average uncertainty of 0.65 ms was assigned based on an analysis of all reciprocal time differences. Unreliable source triggering necessitated solving for shot time corrections during travelitme tomography, creating a mixed-parameter inverse problem. Several steps in addition to conventional 3-D traveltime tomography were applied to exploit the dense data and precise picking to overcome the data's low frequency content: (1) stacking the arrival-time-corrected traces in offset bins for 1-D reflectivity modeling to constrain discontinuities; (2) reduced smoothing regularization based on the local angular distribution of raypaths; and (3) a frequency-dependent form of traveltime tomography to account for the data's frequency content. Model assessment techniques include: (1) removal of the best and poorest fit data to assess the effect of outliers, (2) a jackknife procedure to estimate the uncertainty of each velocity node, and (3) checkerboard tests to estimate lateral model resolution using random shot and picking errors consistent with the real data. The results show that most of the velocity model has a relative error of less than 2% and lateral resolution of better than 5, 10 and 20 m to depths of 5, 10 and 20 m, respectively. Results include an isovelocity surface that represents the top of the Wasatch formation.

  3. P and S wave responses of bacterial biopolymer formation in unconsolidated porous media

    Science.gov (United States)

    Noh, Dong-Hwa; Ajo-Franklin, Jonathan B.; Kwon, Tae-Hyuk; Muhunthan, Balasingam

    2016-04-01

    This study investigated the P and S wave responses and permeability reduction during bacterial biopolymer formation in unconsolidated porous media. Column experiments with fine sands, where the model bacteria Leuconostoc mesenteroides were stimulated to produce insoluble biopolymer, were conducted while monitoring changes in permeability and P and S wave responses. The bacterial biopolymer reduced the permeability by more than 1 order of magnitude, occupying ~10% pore volume after 38 days of growth. This substantial reduction was attributed to the bacterial biopolymer with complex internal structures accumulated at pore throats. S wave velocity (VS) increased by more than ~50% during biopolymer accumulation; this indicated that the bacterial biopolymer caused a certain level of stiffening effect on shear modulus of the unconsolidated sediment matrix at low confining stress conditions. Whereas replacing pore water by insoluble biopolymer was observed to cause minimal changes in P wave velocity (VP) due to the low elastic moduli of insoluble biopolymer. The spectral ratio analyses revealed that the biopolymer formation caused a ~50-80% increase in P wave attenuation (1/QP) at the both ultrasonic and subultrasonic frequency ranges, at hundreds of kHz and tens of kHz, respectively, and a ~50-60% increase in S wave attenuation (1/QS) in the frequency band of several kHz. Our results reveal that in situ biopolymer formation and the resulting permeability reduction can be effectively monitored by using P and S wave attenuation in the ultrasonic and subultrasonic frequency ranges. This suggests that field monitoring using seismic logging techniques, including time-lapse dipole sonic logging, may be possible.

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

    Science.gov (United States)

    Mandal, Prantik; Rodkin, Mikhail V.

    2011-11-01

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

  5. Seismic tomography inversion in the case that sources and receivers are distributed out of a 2-D plane; Shingen jushinten ga nijigen heimennai ni nai baai no danseiha tomography kaiseki ni kansuru kosatsu

    Energy Technology Data Exchange (ETDEWEB)

    Yokota, T.; Miyazaki, T. [Geological Survey of Japan, Tsukuba (Japan); Rokugawa, S.; Matsushima, J. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering; Ashida, Y. [Kyoto University, Kyoto (Japan). Faculty of Engineering

    1996-10-01

    In the case where sources and receivers are not distributed on a 2-D plane, seismic tomography inversion was studied. In tomography experiments, the existing wells are generally used. In such case, sources and receivers are frequently not distributed on a 2-D plane. The 2.5-D analysis method including 2-D structure and 3-D ray-tracing was thus developed. This method is featured by less memory necessary for ray-tracing calculation, and the same algorithm for velocity determination as 2-D analysis method. In previous methods, since analysis is generally carried out by projecting sources and receivers on a certain assumed 2-D plane, it can derive correct results in the case of constant velocity and straight ray, however, in the other case, it derives incorrect results. Application of 3-D tomography requires a large amount of memory, and falls into poor convergence because of various parameters. The 2.5-D analysis method can avoid these demerits. This analysis method was applied to the data obtained in Ogiri area, Kagoshima prefecture. 5 refs., 3 figs., 2 tabs.

  6. On the potential asthenospheric linkage between Apenninic slab rollback and Alpine topographic uplift: insights from P wave tomography and seismic anisotropy analysis

    Science.gov (United States)

    Malusa', Marco Giovanni; Salimbeni, Simone; Zhao, Liang; Guillot, Stéphane; Pondrelli, Silvia; Margheriti, Lucia; Paul, Anne; Solarino, Stefano; Aubert, Coralie; Dumont, Thierry; Schwartz, Stéphane; Wang, Qingchen; Xu, Xiaobing; Zheng, Tianyu; Zhu, Rixiang

    2017-04-01

    The role of surface and deep-seated processes in controlling the topography of complex plate-boundary areas is a highly debated issue. In the Western Alps, which include the highest summits in Europe, factors controlling topographic uplift still remain poorly understood. In the absence of active convergence, recent works have suggested a potential linkage between slab breakoff and fast uplift, but this hypothesis is ruled out by the down-dip continuity of the Alpine slab documented by recent tomographic images of the upper mantle beneath the Alpine region (Zhao et al. 2016). In order to shed light on this issue, we use a densely spaced array of temporary broadband seismic stations and previously published observations to analyze the seismic anisotropy pattern along the transition zone between the Alps and the Apennines, within the framework of the upper mantle structure unveiled by P wave tomography. Our results show a continuous trend of anisotropy fast axes near-parallel to the western alpine arc, possibly due to an asthenospheric counterflow triggered by the eastward retreat of the Apenninic slab. This trend is located in correspondence of a low velocity anomaly in the European upper mantle, and beneath the Western Alps region characterized by the highest uplift rates, which may suggest a potential impact of mantle dynamics on Alpine topography. We propose that the progressive rollback of the Apenninic slab induced a suction effect and an asthenospheric counterflow at the rear of the unbroken Alpine slab and around its southern tip, as well as an asthenospheric upwelling, mirrored by low P wave velocities, which may have favored the topographic uplift of the Alpine belt from the Mt Blanc to the Ligurian coast. Zhao L. et al., 2016. Continuity of the Alpine slab unraveled by high-resolution P wave tomography. J. Geophys. Res., doi:10.1002/2016JB013310.

  7. Joint interpretation of seismic tomography and new magnetotelluric results provide evidence for support of high topography in the Southern Rocky Mountains and High Plains of eastern Colorado, USA

    Science.gov (United States)

    Feucht, D. W.; Sheehan, A. F.; Bedrosian, P.

    2015-12-01

    A recent magnetotelluric (MT) survey in central Colorado, USA, when interpreted alongside existing seismic tomography, reveals potential mechanisms of support for high topography both regionally and locally. Broadband and long period magnetotelluric data were collected at twenty-three sites along a 330 km E-W profile across the Southern Rocky Mountains and High Plains of central North America as part of the Deep RIFT Electrical Resistivity (DRIFTER) experiment. Remote-reference data processing yielded high quality MT data over a period range of 100 Hz to 10,000 seconds. A prominent feature of the regional geo-electric structure is the Denver Basin, which contains a thick package of highly conductive shales and porous sandstone aquifers. One-dimensional forward modeling was performed on stations within the Denver Basin to estimate depth to the base of this shallow conductor. Those estimates were then used to place a horizontal penalty cut in the model mesh of a regularized two-dimensional inversion. Two-dimensional modeling of the resistivity structure reveals two major anomalous regions in the lithosphere: 1) a high conductivity region in the crust under the tallest peaks of the Rocky Mountains and 2) a lateral step increase in lithospheric resistivity beneath the plains. The Rocky Mountain crustal anomaly coincides with low seismic wave speeds and enhanced heat flow and is thus interpreted as evidence of partial melt and/or high temperature fluids emplaced in the crust by tectonic activity along the Rio Grande Rift. The lateral variation in the mantle lithosphere, while co-located with a pronounced step increase in seismic velocity, appears to be a gradational boundary in resistivity across eastern Colorado and could indicate a small degree of compositional modification at the edge of the North American craton. These inferred conductivity mechanisms, namely crustal melt and modification of mantle lithosphere, likely contribute to high topography locally in the

  8. Investigating Near Surface S-Wave Velocity Properties Using Ambient Noise in Southwestern Taiwan

    Directory of Open Access Journals (Sweden)

    Chun-Hsiang Kuo

    2015-01-01

    Full Text Available Ambient noise is typically used to estimate seismic site effects and velocity profiles instead of earthquake recordings, especially in areas with limited seismic data. The dominant Horizontal to Vertical Spectral Ratio (HVSR frequency of ambient noise is correlated to Vs30, which is the average S-wave velocity in the top 30 m. Vs30 is a widely used parameter for defining seismic amplification in earthquake engineering. HVSR can detect the vertical discontinuity of velocities, that is, the interfaces between hard bedrock and soft sediments. In southwestern Taiwan most strong motion stations are located in the plains and show a dominant frequency lower than 3 Hz. Several stations near the coast have low dominant frequencies of less than 1 Hz. The dominant frequencies are higher than 4 Hz at piedmont stations. The stations in the mountains with dominant frequencies over 8 Hz are typically located on very hard sites. This study analyzed the HVSR characteristics under different seismic site conditions considering the Vs30 from previous study (Kuo et al. 2012. The result implies that HVSRs are a better tool than Vs30 to classify the sites where bedrock is deeper than 30 m. Furthermore, we found a linear correlation between Vs30 and dominant HVSR frequency which could be used as a proxy of Vs30. The Vs30 map in this area was derived using the Engineering Geological Database for Taiwan Strong Motion Instrumentation Program (EGDT. The comparable distribution pattern between the dominant frequency and Vs30 demonstrate that HVSR can recognize S-wave velocity properties at the shallow subsurface.

  9. Monitoring in situ deformation induced by a fluid injection in a fault zone in shale using seismic velocity changes

    Science.gov (United States)

    Rivet, D.; De Barros, L.; Guglielmi, Y.; Castilla, R.

    2015-12-01

    We monitor seismic velocity changes during an experiment at decametric scale aimed at artificially reactivate a fault zone by a high-pressure hydraulic injection in a shale formation of the underground site of Tournemire, South of France. A dense and a multidisciplinary instrumentation, with measures of pressure, fluid flow, strain, seismicity, seismic properties and resistivity allow for the monitoring of this experiment. We couple hydromechanical and seismic observations of the fault and its adjacent areas to better understand the deformation process preceding ruptures, and the role played by fluids. 9 accelerometers recorded repeated hammers shots on the tunnel walls. For each hammer shot we measured small travel time delays on direct P and S waves. We then located the seismic velocity perturbations using a tomography method. At low injection pressure, i.e. P< 15 Bars, we observe an increase of P-waves velocity around the injection, while we measure no change in S waves velocity. When the pressure overcomes 15 Bars, velocity perturbations dramatically increase with both P and S waves affected. A decrease of velocity is observed close to the injection point and is surrounded by regions of increasing velocity. Our observations are consistent with hydromechanical measures. Below 15 Bars, we interpret the P-wave velocity increase to be related to the compression of the fault zone around the injection chamber. Above 15 Bars, we measure a shear and dilatant fault movement, and a rapid increase in the injected fluid flow. At this step, our measures are coherent with a poroelastic opening of the fault with velocities decrease at the injection source and velocities increase related to stress transfer in the far field. Velocity changes prove to be efficient to monitor stress/strain variation in an activated fault, even if these observations might produce complex signals due to the highly contrasted hydromechanical responses in a heterogeneous media such as a fault zone.

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

    Directory of Open Access Journals (Sweden)

    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.

  11. Time-lapse seismic study of levees in southern New Mexico

    Science.gov (United States)

    Ivanov, J.; Miller, R.D.; Stimac, N.; Ballard, R.F.; Dunbar, J. Joseph; Smullen, S. Steve

    2006-01-01

    The primary objective of this work was to measure changes in compressional- (Vp) and shear-wave (Vs) velocities in an earthen levee during a ponding experiment designed to simulate flood conditions on the Rio Grande in south New Mexico. Although similar to such experiment, performed an year earlier on the Rio Grande in south Texas, the levee seismic response results are different. This work was similar to previous Preliminary testing at three levee sites, all within a 1 km radius and each with unique physical, EM, and core characteristics, was completed and a single low-conductivity, highly fractured site was selected for investigation. Several different types of seismic data were recorded. Seismic data analysis techniques appraised included P-refraction tomography and Rayleigh surface-wave analysis using multichannel analysis of surface waves (MASW). P-wave velocity change (decrease) was rapid and isolated to one section within the pool confines, which already had anomalously high velocity most likely related to burrowing animals modification of the levee structure. S-wave velocity change was gradual and could be observed along the whole width of the pond within and below the levee. The results within the levee sand core were consistent with the observations of sand S-wave velocity changed due to saturation. ?? 2005 Society of Exploration Geophysicists.

  12. A Simultaneous Multi-phase Approach to Determine P-wave and S-wave Attenuation of the Crust and Upper Mantle

    Energy Technology Data Exchange (ETDEWEB)

    Pasyanos, M E; Walter, W R; Matzel, E M

    2009-02-26

    We have generalized the methodology of our regional amplitude tomography from the Lg phase to the four primary regional phases (Pn, Pg, Sn, Lg). Differences in the geometrical spreading, source term, site term, and travel paths are accounted for, while event source parameters such as seismic moment are consistent among phases. In the process, we have developed the first regional attenuation model that uses the amplitudes of four regional phases to determine a comprehensive P-wave and S-wave attenuation model of the crust and upper mantle. When applied to an area encompassing the Middle East, eastern Europe, western Asia, south Asia, and northeast Africa for the 1-2 Hz passband, we find large differences in the attenuation of the lithosphere across the region. The tectonic Tethys collision zone has high attenuation, while stable outlying regions have low attenuation. While crust and mantle Q variations are often consistent, we do find several notable areas where they differ considerably, but are appropriate given the region's tectonic history. Lastly, the relative values of Qp and Qs indicate that scattering Q is likely the dominant source of attenuation in the crust at these frequencies.

  13. The Atlas of the Underworld: a catalogue of slab remnants in the mantle imaged by seismic tomography, and their geological interpretation

    Science.gov (United States)

    van der Meer, Douwe; van Hinsbergen, Douwe; Spakman, Wim

    2017-04-01

    Seismic tomography has provided a breakthrough in the analysis of plate tectonic history by allowing to trace now-subducted, ancient lithosphere in the Earth's mantle, where they appear as large positive seismic wave-speed anomalies. Subduction also leaves a geological record that allows for dating the geological period of active subduction. By combining these sources of information, we previously compiled 28 lower-mantle slab remnants and estimated for the timing of onset and end of subduction of these slabs, from which we derived a first-order sinking rate of slabs through the mantle (van der Meer et al., 2010). This constraint on lower mantle slab sinking rates allowed for the development of the first slab mantle reference frame, and was used to constrain of mantle viscosity. Since that first compilation, the plate tectonic and seismological community has made major progress on linking geological history to mantle structure. Slabs were linked to plate tectonic models at regional scale, contributed to understanding of orogenies at local level, and was recently even used as a novel basis for plate kinematic restorations. When analyses were expanded into the Pacific realm it improved our understanding of the presence of seismic scatterers in the sub-Pacific mantle and Pacific LLSVP topography. Expanding the tomographic analysis to a global, whole-mantle scale has led to the calculation of total lateral slab lengths, which was used to calculated corresponding subduction zone lengths through time that provided constraints for plate tectonic activity over the past 235 Myr impacting atmospheric CO2 and providing insights in the link between strontium isotope curves and global sea level. Encouraged by the direct and indirect results of our previous work, we have expanded our analysis to nearly 100 mantle images throughout the upper and lower mantle, which we correlate to 94 subduction systems active in the past 300 Myr. We provide our geological interpretation of these

  14. Experiment for 3-component S-wave reflection survey. Part 3; Sanseibun S ha hanshaho no kiso jikken. 3

    Energy Technology Data Exchange (ETDEWEB)

    Kano, N.; Yamaguchi, K.; Yokota, T.; Kiguchi, T. [Geological Survey of Japan, Tsukuba (Japan)

    1996-10-01

    Anisotropy has been investigated using S-wave as a technique for detecting fractures. In this study, fundamental experiments were carried out with slightly changing the measuring conditions at a place where anisotropy was expected. This paper describes the fundamental data acquisition of anisotropy analysis using S-wave, and a part of the results. The experiments were conducted on the agricultural road in Yamadera district, Matsuyama-machi, Yamagata Prefecture. Two flat unpaved roads meeting at right angles were used as traverse lines. In this place, several reflection surfaces were certainly detected by P-wave, and anisotropy of S-wave was confirmed from the velocity of refracted wave of S-wave. Data were processed for individual traverse lines meeting at right angles. Firstly, signal sweeping, correlation, and vertical superposition were made. Six kinds of data were prepared, i.e., three-component receiving records of data at 0{degree} of generating direction and three-component receiving records of data at 90{degree} of generating direction. Records of T-component at 0{degree} and R-component at 90{degree} were used for processing of the seismic reflection method. These records would be considered to be data of SH-wave and SV-wave, respectively. 4 figs.

  15. 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

  16. Extensive seismic anisotropy in the lower crust of Archean metamorphic terrain, South India, inferred from ambient noise tomography

    Science.gov (United States)

    Das, Ritima; Rai, S. S.

    2017-01-01

    We use Rayleigh and Love wave empirical Green's function (EGF) recovered from the cross correlation of seismic ambient noise to study the spatial distribution of radial anisotropy in the southern India crust. The corresponding dispersion curves in the period 2 to 32 s are measured from ambient noise data recorded at 57 sites, and the strength of anisotropy computed from the discrepancy between shear velocities obtained from Rayleigh (VSV) and Love (VSH) at various depths down to 40 km. In upper crust (up to a depth of 20 km) the region is characterized by anisotropy coefficients of - 2 to + 2% that could be explained due to a combination of fluid-filled open cracks and foliated metamorphic rocks. At deeper levels (beyond 20 km), except for the Archean metamorphic terrain, most part of south India has anisotropies of up to 5%. This may be due to rocks with varying degree of metamorphism. Beneath the Archean metamorphic terrain, the anisotropy is recorded up to 9% in the depth range of 20-40 km. This high anisotropy is unlikely to be the manifestation of any recent geodynamic process, considering that the region has low surface heat flow ( 30 mW/m2). We propose that the observed strong anisotropy in the metamorphic belt of southern India crust could best be explained as due to the presence of micaceous minerals or amphiboles in the deep crust that are formed possibly during the evolution of granulite terrain at 2.5 Ga.

  17. Non-overlapped P- and S-wave Poynting vectors and its solution on Grid Method

    KAUST Repository

    Lu, Yong Ming

    2017-12-12

    Poynting vector represents the local directional energy flux density of seismic waves in geophysics. It is widely used in elastic reverse time migration (RTM) to analyze source illumination, suppress low-wavenumber noise, correct for image polarity and extract angle-domain common imaging gather (ADCIG). However, the P and S waves are mixed together during wavefield propagation such that the P and S energy fluxes are not clean everywhere, especially at the overlapped points. In this paper, we use a modified elastic wave equation in which the P and S vector wavefields are naturally separated. Then, we develop an efficient method to evaluate the separable P and S poynting vectors, respectively, based on the view that the group velocity and phase velocity have the same direction in isotropic elastic media. We furthermore formulate our method using an unstructured mesh based modeling method named the grid method. Finally, we verify our method using two numerical examples.

  18. Rapid changes in magma storage beneath the Klyuchevskoy group of volcanoes inferred from time-dependent seismic tomography

    Science.gov (United States)

    Koulakov, Ivan; Gordeev, Evgeniy I.; Dobretsov, Nikolay L.; Vernikovsky, Valery A.; Senyukov, Sergey; Jakovlev, Andrey; Jaxybulatov, Kayrly

    2013-08-01

    We present the results of time-dependent local earthquake tomography for the Kluchevskoy group of volcanoes in Kamchatka, Russia. We consider the time period from 1999 to 2009, which covers several stages of activity of Kluchevskoy and Bezymianny volcanoes. The results are supported by synthetic tests that recover a common 3D model based on data corresponding to different time windows. Throughout the period, we observe a robust feature below 25 km depth with anomalously high Vp/Vs values (up to 2.2). We interpret this feature as a channel bringing deep mantle materials with high fluid and melt content to the bottom of the crust. This mantle channel directly or indirectly determines the activity of all volcanoes of the Kluchevskoy group. In the crust, we model complex structure that varies over time. During the pre-eruptive period, we detected two levels of potential magma storage: one in the middle crust at 10-12 km depth and one close to the surface just below Kluchevskoy volcano. In 2005, a year of powerful eruptions of Kluchevskoy and Besymiyanny volcanoes, we observe a general increase in Vp/Vs throughout the crust. In the relaxation period following the eruption, the Vp/Vs values are generally low, and no strong anomalous zones in the crust are observed. We propose that very rapid variations in Vp/Vs are most likely due to abrupt changes in the stress and deformation states, which cause fracturing and the active transport of fluids. These fluids drive more fracturing in a positive feedback system that ultimately leads to eruption. We envision the magma reservoirs beneath the Kluchevskoy group as sponge-structured volumes that may quickly change the content of the molten phases as fluids pulse rapidly through the system.

  19. Late Mesozoic magmatic plumbing system in the onshore-offshore area of Hong Kong: Insight from 3-D active-source seismic tomography

    Science.gov (United States)

    Xia, Shaohong; Zhao, Dapeng

    2014-12-01

    We used active source wide-angle seismic data to determine a high-resolution P-wave crustal tomography beneath the onshore-offshore area of Hong Kong at the southern end of a broad belt dominated by the late Mesozoic intrusive and extrusive rocks in the coastal region of Southeast China. The active source data are much more precise than the natural earthquake data and so can be used to study the fine crustal structure. Our results reveal a localized high-velocity anomaly in the lower crust offshore between Hong Kong and Dangan Island, which may reflect basaltic underplating that is closely associated with formation of voluminous silicic eruptions and granitoid plutons in the onshore-offshore area of Hong Kong. Tilted high-velocity zones connecting with the localized high-velocity anomaly in the lower crust are clearly visible in the entire crust beneath Dangan Island and the calderas of Hong Kong. Taking into account the previous geochemical, petrologic and numerical modeling results, we think that the tilted high-velocity zones may be the results of mingling of mafic and felsic end members and extreme degree of crustal partial melt extraction necessary to generate a large amount of extrusive rocks in the calderas, reflecting cooled magma conduits as a manifestation of solidified Late Mesozoic magmatic plumbing system in the crust. Considering the petrologic and geochemical characteristics of the late Mesozoic granites and basalt in Southeast China, we suggest that subduction and dehydration of the paleo-Pacific plate might trigger the basaltic magma underplating and result in extensive crust-mantle interaction, which not only provided necessary heat energy to cause the crustal partial melting, but also added minor mafic materials to the newly generated granitic melts. This model explains our tomographic results as well as the intimate mingling of coeval mafic and silicic magmas in Hong Kong. Intersecting faults could play an important role in forming magma

  20. Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes

    Science.gov (United States)

    Hasegawa, Akira; Nakajima, Junichi

    2017-12-01

    We review studies of intermediate-depth seismicity and seismic imaging of the interior of subducting slabs in relation to slab metamorphism and their implications for the genesis of intermediate-depth earthquakes. Intermediate-depth events form a double seismic zone in the depth range of c. 40-180 km, which occur only at locations where hydrous minerals are present, and are particularly concentrated along dehydration reaction boundaries. Recent studies have revealed detailed spatial distributions of these events and a close relationship with slab metamorphism. Pressure-temperature paths of the crust for cold slabs encounter facies boundaries with large H2O production rates and positive total volume change, which are expected to cause highly active seismicity near the facies boundaries. A belt of upper-plane seismicity in the crust nearly parallel to 80-90 km depth contours of the slab surface has been detected in the cold Pacific slab beneath eastern Japan, and is probably caused by slab crust dehydration with a large H2O production rate. A seismic low-velocity layer in the slab crust persists down to the depth of this upper-plane seismic belt, which provides evidence for phase transformation of dehydration at this depth. Similar low-velocity subducting crust closely related with intraslab seismicity has been detected in several other subduction zones. Seismic tomography studies in NE Japan and northern Chile also revealed the presence of a P-wave low-velocity layer along the lower plane of a double seismic zone. However, in contrast to predictions based on the serpentinized mantle, S-wave velocity along this layer is not low. Seismic anisotropy and pore aspect ratio may play a role in generating this unique structure. Although further validation is required, observations of these distinct low P-wave velocities along the lower seismic plane suggest the presence of hydrated rocks or fluids within that layer. These observations support the hypothesis that dehydration

  1. P-wave and S-wave traveltime residuals in Caledonian and adjacent units of Northern Europe and Greenland

    Science.gov (United States)

    Hejrani, Babak; Balling, Niels; Holm Jacobsen, Bo; Kind, Rainer; Tilmann, Frederik; England, Richard; Bom Nielsen, Søren

    2014-05-01

    This work combines P-wave and S-wave travel time residuals from in total 477 temporary and 56 permanent stations deployed across Caledonian and adjacent units in Northern Europe and Greenland (Tor, Gregersen et al. 2002; SVEKALAPKO, Sandoval et al., 2003; CALAS, Medhus et al, 2012a; MAGNUS, Weidle et al. 2010; SCANLIPS south, England & Ebbing 2012; SCANLIPS north, Hejrani et al. 2012; JULS Hejrani et al. 2013; plus permanent stations in the region). We picked data from 2002 to 2012 (1221 events) using a cross correlation technique on all waveforms recorded for each event. In this way we achieve maximum consistency of relative residuals over the whole region (Medhus et al. 2012b). On the European side 18362 P-wave travel time residuals was delivered. In East Greenland 1735 P-wave residuals were recovered at the Central Fjord array (13 stations) and 2294 residuals from the sparse GLISN-array (23 stations). Likewise, we picked a total of 6034 residuals of the SV phase (For the Tor and SVEKALAPKO projects we used data from Amaru et al. 2008). Relative residuals within the region are mainly due to sub-crustal uppermost mantle velocity anomalies. A dominant subvertical boundary was detected by Medhus et al. (2012), running along the Tornquist zone, east of the Oslo Graben and crossing under high topography of the southern Scandes. We delineated this boundary in more detail, tracking it towards the Atlantic margin north of Trondheim. Further north (Scanlips north), a similar subvertical upper mantle boundary seems to be present close to the coast, coinciding with the edge of the stretched crust. The North German Caledonides were probed by the new JULS (JUtland Lower Saxony) profile which closes the gap between Tor and CALAS arrays. Mantle structure found by the Tor project was confirmed, and modelling was extended to the eastern edge of the North Sea. References: Amaru, M. L., Spakman, W., Villaseñor, A., Sandoval, S., Kissling, E., 2008, A new absolute arrival time data

  2. Off-shell effects in s-wave pion absorption

    Energy Technology Data Exchange (ETDEWEB)

    Hachenberg, F.; Pirnerdouble-dagger, H.J.

    1978-06-01

    The effect of s-wave pion absorption on the pion-nucleus optical potential is calculated. We assume absorption by two uncorrelated nucleons with off-shell pion rescattering. For the pion-nucleon interaction we develop a field theoretic model which can be used on- and off-mass shell. A fully relativistic calculation of the pion polarization operator then gives U/sup opt/ =-4..pi..B/sub orho//sup 2/(2..mu..)/sup -1/, with B/sub 0/= (0.094+i0.036) ..mu../sup -4/, as contribution from s-wave absorption to the optical potential. The imaginary part agrees well with the experimentally determined value, while pion dispersion (real part of B/sub o/) does not explain the observed repulsion of the s-wave pion nucleus interaction. We deomonstrate the relevance of oo-shell dynamics in pion-nucleus scattering. The ratio R/sub s/ of ..pi../sup -/-absorption rates by neutron-proton and proton-proton pairs is much smaller than predicted by on-shell models. For equal numbers of neutrons and protons we get R/sub s/approx. =3.0.We also apply the formalism to s-wave pion production in nucleon-nucleon collisions and obtain qualitative agreement with the data. In particular the longstanding puzzle of the small imaginary pion deuteron scattering length compared to Im B/sub 0/ is explained. Our claculation gives Im a/sub pid/=3.7 x 10/sup -3/..mu../sup -1/.

  3. S-wave velocity structure and tectonic implications of the northwestern sub-basin and Macclesfield of the South China Sea

    Science.gov (United States)

    Wei, Xiaodong; Ruan, Aiguo; Li, Jiabiao; Niu, Xiongwei; Wu, Zhenli; Ding, Weiwei

    2017-06-01

    Based on the optimum P-wave model, the S-wave velocity structure of a wide angle seismic profile (OBS2006-1), across the northwestern sub-basin (NWSB) and the Macclesfield, is simulated by a 2-D ray-tracing method. The results indicate the S-wave velocities in the upper and lower crust of the NWSB are 3.2-3.6 km/s and 3.6-4.0 km/s, with Vp/ Vs ratios of 1.82-1.88 and 1.74-1.82, respectively, which reflect typical oceanic crust characteristics. The S-wave velocity in the upper crust of the NWSB is a little higher in the NNW segment than that in the SSE segment, while the lateral variation of Vp/ Vs ratio is in the opposite. We suggest that the NWSB might have experienced asymmetrical magma flows during sea floor spreading, which may have blurred the magnetic anomaly lineation. The comparison of S-wave velocities along the northern margin of the SCS shows that the west section is different from the east section, and the northwestern margin has a non-volcanic crust structure. The S-wave structures and P-wave velocity models along the northern margin, Macclesfield and Reed Bank show that the Macclesfield might have a conjugate relationship with the Reed Bank.

  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

  5. Intrinsic and scattering attenuation of high-frequency S-waves in the central part of the External Dinarides

    Science.gov (United States)

    Majstorović, Josipa; Belinić, Tena; Namjesnik, Dalija; Dasović, Iva; Herak, Davorka; Herak, Marijan

    2017-09-01

    The central part of the External Dinarides (CED) is a geologically and tectonically complex region formed in the collision between the Adriatic microplate and the European plate. In this study, the contributions of intrinsic and scattering attenuation ( Q i - 1 and Q sc - 1 , respectively) to the total S-wave attenuation were calculated for the first time. The multiple lapse-time window analysis (MLTWA method), based on the assumptions of multiple isotropic scattering in a homogeneous medium with uniformly distributed scatterers, was applied to seismograms of 450 earthquakes recorded at six seismic stations. Selected events have hypocentral distances between 40 and 90 km with local magnitudes between 1.5 and 4.7. The analysis was performed over 11 frequency bands with central frequencies between 1.5 and 16 Hz. Results show that the seismic albedo of the studied area is less than 0.5 and Q i - 1 > Q sc - 1 at all central frequencies and for all stations. These imply that the intrinsic attenuation dominates over scattering attenuation in the whole study area. Calculated total S-wave and expected coda wave attenuation for CED are in a very good agreement with the ones measured in previous studies using the coda normalization and the coda-Q methods. All estimated attenuation factors decrease with increasing frequency. The intrinsic attenuation for CED is among the highest observed elsewhere, which could be due to the highly fractured and fluid-filled carbonates in the upper crust. The scattering and the total S-wave attenuation for CED are close to the average values obtained in other studies performed worldwide. In particular, good agreement of frequency dependence of total attenuation in CED and in the regions that contributed most strong-motion records for ground motion prediction equations used in PSHA in Croatia indicates that those were well chosen and applicable to this area as far as their attenuation properties are concerned.

  6. Elastic-Wavefield Seismic Stratigraphy: A New Seismic Imaging Technology

    Energy Technology Data Exchange (ETDEWEB)

    Bob A. Hardage; Milo M. Backus; Michael V. DeAngelo; Sergey Fomel; Khaled Fouad; Robert J. Graebner; Paul E. Murray; Randy Remington; Diana Sava

    2006-07-31

    The purpose of our research has been to develop and demonstrate a seismic technology that will provide the oil and gas industry a better methodology for understanding reservoir and seal architectures and for improving interpretations of hydrocarbon systems. Our research goal was to expand the valuable science of seismic stratigraphy beyond the constraints of compressional (P-P) seismic data by using all modes (P-P, P-SV, SH-SH, SV-SV, SV-P) of a seismic elastic wavefield to define depositional sequences and facies. Our objective was to demonstrate that one or more modes of an elastic wavefield may image stratal surfaces across some stratigraphic intervals that are not seen by companion wave modes and thus provide different, but equally valid, information regarding depositional sequences and sedimentary facies within that interval. We use the term elastic wavefield stratigraphy to describe the methodology we use to integrate seismic sequences and seismic facies from all modes of an elastic wavefield into a seismic interpretation. We interpreted both onshore and marine multicomponent seismic surveys to select the data examples that we use to document the principles of elastic wavefield stratigraphy. We have also used examples from published papers that illustrate some concepts better than did the multicomponent seismic data that were available for our analysis. In each interpretation study, we used rock physics modeling to explain how and why certain geological conditions caused differences in P and S reflectivities that resulted in P-wave seismic sequences and facies being different from depth-equivalent S-wave sequences and facies across the targets we studied.

  7. Single-station seismic noise measures, microgravity, and 3D electrical tomographies to assess the sinkhole susceptibility: the "Il Piano" area (Elba Island - Italy) case study

    Science.gov (United States)

    Pazzi, Veronica; Di Filippo, Michele; Di Nezza, Maria; Carlà, Tommaso; Bardi, Federica; Marini, Federico; Fontanelli, Katia; Intrieri, Emanuele; Fanti, Riccardo

    2017-04-01

    Sudden subsurface collapse, cavities, and surface depressions, regardless of shape and origin, as well as doline are currently indicate by means of the term "sinkhole". This phenomenon can be classified according to a large variety of different schemes, depending on the dominant formation processes (soluble rocks karstic processes, acidic groundwater circulation, anthropogenic caves, bedrock poor geomechanical properties), and on the geological scenario behind the development of the phenomenon. Considering that generally sinkholes are densely clustered in "sinkhole prone areas", detection, forecasting, early warning, and effective monitoring are key aspects in sinkhole susceptibility assessment and risk mitigation. Nevertheless, techniques developed specifically for sinkhole detection, forecasting and monitoring are missing, probably because of a general lack of sinkhole risk awareness, and an intrinsic difficulties involved in detecting precursory sinkhole deformations before collapse. In this framework, integration of different indirect/non-invasive geophysical methods is the best practice approach. In this paper we present the results of an integrated geophysical survey at "Il Piano" (Elba Island - Italy), where at least nine sinkholes occurred between 2008 and 2014. 120 single-station seismic noise measures, 17 3D electrical tomographies (min area 140.3 m2, max area 10,188.9 m2; min electrode spacing 2 m, max electrode spacing 5 m), 964 measurement of microgravity spaced in a grid of 6 m to 8 m were carried out at the study area. The most likely origin for these sinkholes was considered related to sediment net erosion from the alluvium, caused by downward water circulation between aquifers. Therefore, the goals of the study were: i) obtaining a suitable geological and hydrogeological model of the area; ii) detecting possible cavities which could evolve in sinkholes, and finally iii) assess the sinkhole susceptibility of the area. Among the results of the

  8. Seismic structure of sediments and basement of the Yakutat Terrane offshore southern Alaska from a combined OBS and MCS tomography inversion

    Science.gov (United States)

    van Avendonk, H.; Worthington, L. L.; Christeson, G. L.; Gulick, S. P.; Pavlis, T. L.

    2011-12-01

    The Yakutat terrane is a shallow (approximately 100 m) oceanic plateau that underthrusts southern Alaska in a NW direction. Wide-angle seismic reflections and refractions recorded on OBSs and on the Langseth MCS streamer during the STEEP experiment constrain the seismic velocities in the sediments and shallow basement of the plateau. At the southeast end of STEEP line 1, igneous basement appears to be covered by a 3 kilometer thick layer with velocities of 3.8-5.0 km/s, which could represent metasediments from an old accretionary wedge that was emplaced on the Yakutat Terrane long before this crustal block arrived offshore southern Alaska. Two younger sediment layers form a more continuous cover on the Yakutat terrane. A deeper layer with seismic velocities of 4.0-4.5 km/s may represent well-compacted, possibly pre-glacial sediments. The youngest, glacio-marine sediments of the Yakutat block appear to have a seismic velocity that increases steadily from 2.0 km/s in the southeast to 3.7 km/s in the Pamplona zone in the northwest. This increase in seismic velocity is consistent with dewatering and compaction of these sediments towards the collision zone.

  9. Interrogating the Isabella Anomaly with the Central California Seismic Array

    Science.gov (United States)

    Hansen, S. M.; Schmandt, B.; Dougherty, S. L.; Clayton, R. W.

    2016-12-01

    The Isabella positive velocity anomaly is located in the uppermost mantle beneath the Great Valley of Central California ( 36°N) and was first recognized by seismic tomography efforts in 1980. The geologic interpretation of this feature remains contentious however. The conventional interpretation is that the anomaly is related to the delamination of a dense mafic root associated with the formation of the Sierra Nevada batholith which lies to the east. Alternatively, the anomaly has been interpreted as a fossil slab fragment associated with the stalled subduction of the Monterey microplate which lies offshore. One of the challenges in interpreting the Isabella anomaly is the relatively poor resolution due to a lack of seismic data in and around the Great Valley. To help further constrain the subsurface structure in this region, we deployed a dense line of 40 broadband seismometers in Central California stretching from the Sierra foothills to the coast that recorded data during 2013-2015. Here we report on our on-going research efforts which include body and surface wave tomography as well as scattered wave imaging derived from P and S wave receiver functions. The most prominent feature observed in the receiver function imaging is a high amplitude crustal discontinuity which is observed over 80 km distance. This westward dipping feature begins near the surface beneath the Sierra foothills and reaches 25 km depth beneath the Great Valley. We speculate that this feature represents the top of a high velocity ophiolite body that underlies most of the Great Valley. Receiver functions also suggest the presence of eastward dipping velocity discontinuities in the uppermost mantle (40-80 km) below the western Great Valley. Body wave travel-time measurements indicate that the Isabella anomaly extends west to beneath the coastal range. These observations support the hypothesis that the Isabella anomaly is a slab fragment rather than a piece of delaminating lithosphere.

  10. Investigation of geophysical methods for assessing seepage and internal erosion in embankment dams : a study of through-dam seismic testing at WAC Bennett Dam

    Energy Technology Data Exchange (ETDEWEB)

    Gaffran, P.; Jeffries, M. [BC Hydro, Burnaby, BC (Canada)

    2005-07-15

    Crosshole tomography is used to establish the distribution of seismic velocity between drill holes. The through-dam mode takes advantage of the triangular cross-section of earth embankments, obviating the need for drill holes. Seismic energy, generated on one face of the dam, passes underneath the crest and is detected by sensors arrayed on the opposite face. The sinkholes discovered at WAC Bennett Dam in 1996 provided an opportunity to test the procedure. Using p-wave energy, two series of measurements were conducted, notably one immediately before remediation of one sinkhole, and a second one shortly after the sinkhole was repaired. The known defect was successfully imaged by the first round of measurements. This report presented the results of an investigation of the through-dam seismic method using propagation of seismic waves through a dam from upstream to downstream, or vice-versa. The purpose of the study was to determine if this procedure could characterize the distribution of seismic velocity within a dam in an accurate and cost effective manner. The report presented the methods of velocity testing such as crosshole and downhole, and tomography; and through-dam measurements. Background to the Bennett Dam studies was also provided, with particular reference to the Bennett Dam sinkholes; sinkhole investigations; working hypothesis for sinkhole development; sinkhole number one characterization; and sinkhole remediation. An analysis of compression wave testing at Bennett Dam and shear wave testing was then offered. Other topics that were discussed included field test procedures; methodologies for data processing; p-waves versus s-waves; applicability of the research; and costs of through-dam surveys. It was concluded that under the right circumstances, through-dam seismic testing was capable of detecting changed conditions in an embankment dam. 15 refs., 2 tabs., 41 figs., 1 appendix.

  11. Comparison of an empirical S-wave velocity model and a calculated stress-strain model for a rock mass disturbed by mining

    Science.gov (United States)

    Krawiec, Krzysztof; Czarny, Rafał

    2017-11-01

    In the article a comparison analysis is presented between a numerical model of the stress and deformation state in a rock mass and an S-wave velocity model obtained as a result of in situ measurement. The research was conducted using data from the Jastrzębie and Moszczenica coal mines. The part of the rock mass examined was strongly disturbed by multi-seam exploitation of coal. To obtain the S-wave velocity model 6 hours of ambient seismic noise data were recorded using 11 seismometers. The propagation of the Rayleigh surface wave between the seismometers was reconstructed utilising the seismic interferometry and the cross correlation technique. Estimation of a two dimensional model of the Swave velocity field was performed on the basis of dispersion curves of the Rayleigh wave phase velocity. The stress and deformation field were calculated assuming a plane state of stress with the use of the elastic-plastic Coulomb-Mohr strength criterion. Images of the vertical stress, horizontal stress, vertical strain and horizontal strain as well as the subsidence profile on the model surface were obtained as a result of the calculation. Analysis of the results shows correlation between the field of S-wave velocity and the modelled field of stress and strain.

  12. Comparison of an empirical S-wave velocity model and a calculated stress-strain model for a rock mass disturbed by mining

    Directory of Open Access Journals (Sweden)

    Krawiec Krzysztof

    2017-01-01

    Full Text Available In the article a comparison analysis is presented between a numerical model of the stress and deformation state in a rock mass and an S-wave velocity model obtained as a result of in situ measurement. The research was conducted using data from the Jastrzębie and Moszczenica coal mines. The part of the rock mass examined was strongly disturbed by multi-seam exploitation of coal. To obtain the S-wave velocity model 6 hours of ambient seismic noise data were recorded using 11 seismometers. The propagation of the Rayleigh surface wave between the seismometers was reconstructed utilising the seismic interferometry and the cross correlation technique. Estimation of a two dimensional model of the Swave velocity field was performed on the basis of dispersion curves of the Rayleigh wave phase velocity. The stress and deformation field were calculated assuming a plane state of stress with the use of the elastic-plastic Coulomb-Mohr strength criterion. Images of the vertical stress, horizontal stress, vertical strain and horizontal strain as well as the subsidence profile on the model surface were obtained as a result of the calculation. Analysis of the results shows correlation between the field of S-wave velocity and the modelled field of stress and strain.

  13. A new AVA attribute based on P-wave and S-wave reflectivities for overpressure prediction

    Science.gov (United States)

    Aleardi, Mattia; Mapelli, Luca; Mazzotti, Alfredo

    2017-05-01

    Pore pressure prediction is a key step for safe well drilling operations and is usually performed by deriving a velocity-pressure relationship calibrated to a reference well. However, in the last few decades, other seismic-based methods, such as the Amplitude versus Angle (AVA) technique, have been extended to predict anomalous pressure values. Concerning AVA analysis, in this work, we show that the expected pressure effect on the elastic rock properties is very different from the fluid effect, thus making the classical AVA attributes used for fluid prediction ineffective at highlighting pressure anomalies. Therefore, we propose a new AVA attribute to evidence the decrease in P-wave and S-wave reflectivity that usually occurs when passing from an overlying formation to an underlying overpressured one. This attribute can be easily derived from the intercept and gradient values extracted from the recorded seismic pre-stack data by means of the Shuey equation. To demonstrate the applicability of this new attribute for pore pressure prediction we show examples on synthetic seismic data and three applications to different field datasets over already drilled prospects. In the case of overpressured layers, this attribute shows anomalous responses, thus demonstrating its effectiveness in highlighting anomalous pore pressure regimes. In contrast, no anomalous attribute values are observed in cases characterized by a hydrostatic pore pressure regime.

  14. Local Earthquake Velocity and Attenuation Tomography of the Jalisco, Mexico Region

    Science.gov (United States)

    Watkins, W. D.; Thurber, C. H.; Abbott, E. R.; Brudzinski, M.; Grand, S. P.

    2015-12-01

    The states of Jalisco, Colima, and Michoacan in western Mexico overlie the boundary of the subducting Rivera and Cocos plates, presenting an appealing target for seismological inquiry to better understand the resulting mantle flow and regional volcanism. The different dips between the subducting plates is thought to provide a mantle conduit that has contributed to the Colima Volcanic Complex, but there is considerable debate on the shallowness of the Rivera plate and width of the resulting conduit. With data from the Mapping the Rivera Subduction Zone (MARS) and Colima Deep Seismic Experiment (CODEX) networks, two temporary broadband arrays deployed in the region between 2006-2008, we invert for three-dimensional P- and S- wave velocity and later attenuation structure of the upper ~80 km of the crust and mantle in the Jalisco region. We improve upon previous tomography work by utilizing double-difference tomography, which enables the use of higher-accuracy differential times to sharpen the earthquake locations, and the inclusion of S-wave data. Current models that utilize only analyst-picked phase arrivals from 590 earthquakes yield P-wave high velocity anomalies that suggest a slab under the coastal regions at 15-25 km depth, and low velocity anomalies that may be related to Colima Volcano or other geologic features. Most of the S-wave model is poorly resolved. We will use a newly developed auto-picker to attempt to substantially increase the size of the S-wave dataset and to a lesser extent the P wave dataset, in order to densify ray coverage and improve model resolution. Additionally, we plan to employ the waveforms from this expanded dataset to compute a path attenuation operator for each arrival, which will then be used to invert for 3D P and S-wave attenuation models. The attenuation models combined with the velocity models will provide multiple constraints on physical properties of the crust in this region as well as those of specific geologic features.

  15. The Study on S-Wave Velocity Structure of Upper Crust in Three Gorges Region of Yangtze River

    Science.gov (United States)

    Li, X.; Zhu, P.; Zhou, Q.

    2014-12-01

    The profile of S-wave velocity structure along Badong-Maoping-Tumen is presented using the ambient noise data observed at 10 stations from mobile broadband seismic array which is located at Three Gorges Region. All of available vertical component time series during April and May,2011 have been cross-correlated to estimate the empirical Green functions. Group velocity dispersion curves were measured by applying multiple filtering technique. Using these dispersion curves,we obtain high resolution pure-path dispersions at 0.5-10 second periods. The S-wave velocity structure,which was reconstructed by inverting the pure-path dispersions,reveals the velocity variations of upper crust at Three Gorges Region. Main conclusions are as follows:(1)The velocity variations in the study region have a close relationship with the geological structure and the velocity profile suggests a anticline unit which core area is Huangling block;(2)The relative fast velocity variations beneath Jiuwanxi and its surrounding areas may correspond to the geological structure and earthquake activity there;(3) The high velocity of the upper crustal in Sandouping indicates that the Reservoir Dam of Three Gorges is located at a tectonic stable region.

  16. Flow Properties in Saturated Soils from Differing Behaviour of Dispersive Seismic Velocity and Attenuation

    NARCIS (Netherlands)

    Ghose, R.; Zhubayev, A.

    2012-01-01

    A careful look into the pertinent models of poroelasticity reveals that in water-saturated sediments or soils, the seismic (P and S wave) velocity dispersion and attenuation in the low field-seismic frequency band (20-200 Hz) have a contrasting behaviour in the porosity-permeability domain.Taking

  17. Contrasting behavior between dispersive seismic velocity and attenuation : Advantages in subsoil characterization

    NARCIS (Netherlands)

    Zhubayev, A.; Ghose, R.

    2012-01-01

    A careful look into the pertinent models of poroelasticity reveals that in water-saturated sediments or soils, the seismic (P and S wave) velocity dispersion and attenuation in the low field-seismic frequency band (20–200 Hz) have a contrasting behavior in the porosity-permeability domain. Taking

  18. Constraining Mantle Heterogeneities with Joint Inversions of Seismic, Geodynamic, and Mineral Physics Data

    Science.gov (United States)

    Lu, C.; Grand, S. P.; Forte, A. M.; Simmons, N. A.

    2014-12-01

    Two outstanding goals of solid earth geophysics are to determine the chemical structure of the Earth and to understand the dynamics of its interior. The dynamics of the mantle are controlled by density variations and combined knowledge of density structure and seismic velocities provide the strongest constraints on chemical heterogeneity. Unfortunately, most of the traditional geophysical methods such as seismic tomography and geodynamic modeling alone cannot adequately resolve the density structure within the mantle. Thus, seismic, geodynamic and mineral physics joint inversion methods have been applied to better understand the dynamics of the mantle in recent years (e.g. Simmons et al. 2010). In these joint inversions, P wave and S wave travel times, as well as four convection-related geodynamic observations (free air gravity, tectonic plate motion, dynamic topography, and the excess ellipticity of the core-mantle boundary) can be used to produce 3-D models of density and seismic velocities simultaneously. The approach initially attempts to find a model that assuming temperature controls lateral variations in mantle properties and then to consider more complicated lateral variations that account for the presence of chemical heterogeneity to further fit data. Here we present new joint inversion results include 50% more new S wave travel time data than in previous work and geodynamic data that extend to larger spherical harmonic degrees. In addition, temperature derivatives of P and S velocity and density have been determined using an updated mineral physics dataset. For the first time we include non-linear anelastic temperature effects on velocities in the joint inversion. The anelastic effects decrease the required high density component within the lower mantle superplumes. The hypothesis that temperature variations explain most observed heterogeneity within the mantle is consistent with our data. Reference: Simmons, N. A., A. M. Forte, L. Boschi, and S. P. Grand

  19. Evidence for gas and magmatic sources beneath the Yellowstone volcanic field from seismic tomographic imaging

    Science.gov (United States)

    Husen, Stephan; Smith, Robert B.; Waite, Gregory P.

    2004-03-01

    The 3-D P-wave velocity and P- to S-wave velocity ratio structure of the Yellowstone volcanic field, Wyoming, has been determined from local earthquake tomography using new data from the permanent Yellowstone seismic network. We selected 3374 local earthquakes between 1995 and 2001 to invert for the 3-D P-wave velocity ( Vp) and P-wave to S-wave velocity ratio ( Vp/ Vs) structure. Vp anomalies of small size (15×15 km) are reliably imaged in the northwestern part of the model outside the Yellowstone caldera; inside the caldera only Vp anomalies of large size extending over several grid nodes are reliably imaged. The Vp/ Vs solution is generally poorer due to the low number of S-P arrival times. Only the northwestern part of the model is resolved with confidence; the Vp/ Vs solution also suffers from strong vertical and horizontal velocity smearing. The tomographic images confirm the existence of a low Vp-body beneath the Yellowstone caldera at depths greater than 8 km, possibly representing hot, crystallizing magma. The most striking result of our study is a volume of anomalously low Vp and Vp/ Vs in the northwestern part of the Yellowstone volcanic field at shallow depths of <2.0 km. Theoretical calculations of changes in P- to S-wave velocity ratios indicate that these anomalies can be interpreted as porous, gas-filled rock. The close spatial correlation of the observed anomalies and the occurrence of the largest earthquake swarm in historic time in Yellowstone, 1985, suggest that the gas may have originated as part of magmatic fluids released by crystallization of magma beneath the Yellowstone caldera.

  20. Microtremor exploration for shallow S-wave velocity profiles at stations in local strong motion network in Bursa, Yalova, and Kocaeli in north-western Turkey

    Science.gov (United States)

    Özmen, Özgür Tuna; Yamanaka, Hiroaki; Chimoto, Kosuke; Çeken, Ulubey; Alkan, Mehmet Akif; Tekin, Kudret; Ateş, Erkan

    2017-05-01

    We conducted microtremor array surveys for shallow S-wave velocity profiles at 20 sites in Bursa, Yalova and Kocaeli provinces in the north-western part of Turkey to provide fundamental data to assess the seismic hazard in the area. All of the measurement sites were positioned very close to strong motion stations belonging to the Disaster and Emergency Management Presidency of Turkey (AFAD) in order to further understand site amplification factors in strong motion records. Of the 20 study sites, two were located in Yalova, four in Bursa and 14 in Kocaeli. We temporarily installed two small arrays to obtain simultaneous records of vertical microtremors. Then, the spatial autocorrelation method was applied to retrieve Rayleigh wave phase velocity curves in a frequency range from 1 to 30 Hz from the array records. The phase velocities in the western part of the Kocaeli area are low across a wide frequency range, while relatively high phase velocities are found in the eastern part of the Kocaeli province. The phase velocities in the Yalova and Bursa provinces are widely distributed suggesting large variations in soil conditions. The observed phase velocity curve at each site was inverted to a one-dimensional (1D) S-wave velocity profile to a depth of 100 m, using a hybrid heuristic inversion method. All the S-wave velocity profiles in the eastern Kocaeli area are similar; however, the sites in the western Kocaeli and Yalova-Bursa areas have profiles with different features from the others. Finally, we discuss amplification factors for S-waves using the inverted profiles. The dominant fundamental periods of the amplification factors were distributed in a frequency range from 0.7 to 5 Hz. The profiles obtained are also used to map average S-wave velocities in the study area, with an addition of existing data at strong motion stations of the AFAD.

  1. Tomography from 26 years of seismicity revealing that the spatial extent of the Yellowstone crustal magma reservoir extends well beyond the Yellowstone caldera

    Science.gov (United States)

    Farrell, Jamie; Smith, Robert B.; Husen, Stephan; Diehl, Tobias

    2014-05-01

    The Yellowstone volcanic field has experienced three of Earth's most explosive volcanic eruptions in the last 2.1 Ma. The most recent eruption occurred 0.64 Ma forming the 60 km long Yellowstone caldera. We have compiled earthquake data from the Yellowstone Seismic Network from 1984 to 2011 and tomographically imaged the three-dimensional P wave velocity (Vp) structure of the Yellowstone volcanic system. The resulting model reveals a large, low Vp body, interpreted to be the crustal magma reservoir that has fueled Yellowstone's youthful volcanism. Our imaged magma body is 90 km long, 5-17 km deep, and 2.5 times larger than previously imaged. The magma body extends ~15 km NE of the caldera and correlates with the location of the largest negative gravity anomaly, a -80 mGal gravity low. This new seismic image provides important constraints on the dynamics of the Yellowstone magma system and its potential for future volcanic eruptions and earthquakes.

  2. Tomography of the subducting Cocos plate in central Mexico: Images of a truncated slab

    Science.gov (United States)

    Husker, A. L.; Davis, P. M.

    2007-12-01

    The location of the subducting slab beneath Mexico City and its relation to the Trans-Mexican Volcanic Belt (TMVB) has been unknown because of the absence of deep seismicity that could be used to define the Wadati-Benioff zone. We used data from a temporary seismic network to locate the slab using seismic tomography. A break is seen in the Cocos plate under the TMVB. The break is seen with both P-wave and S-wave tomography and in a constrained tomographic inversion that finds parameters for a simple slab temperature model. The data used are 172 teleseismic earthquakes recorded by the Middle American Subduction Experiment (MASE). MASE was made up of 100 broadband seismometers spaced every 5 km running from Acapulco north through Mexico City almost to the Gulf Coast. In order to determine arrival time differences, Dt, across the array, waveforms were cross correlated. When Dt is plotted with respect to the latitude of the seismometer at which it was recorded, a Dt minimum (early arrivals) is seen near the TMVB. This minimum is shifted northward for back azimuths from the south, and southward for back azimuths from the north. The shift in the Dt minimum is indicative of a fast structure at depth. If there were no break in the slab, the localized minimum would not be seen. Tomography reveals an approximately 50-80 km thick slab diving into the mantle at about 75° to approximately 550 km depth and 375 km inland from Acapulco. We speculate the absence of deep earthquakes is due to low stresses in a young plate that has been truncated at depth.

  3. Seismic activity of Tokyo area and Philippine Sea plate under Japanese Islands

    Science.gov (United States)

    Sakai, S.; Nakagawa, S.; Nanjo, K.; Kasahara, K.; Panayotopoulos, Y.; Tsuruoka, H.; Kurashimo, E.; Obara, K.; Hirata, N.; Kimura, H.; Honda, R.

    2012-12-01

    The Japanese government has estimated the probability of earthquake occurrence with magnitude 7-class during the next 30 years as 70 %. This estimation is based on five earthquakes that occurred in this area in the late 120 years. However, it has been revealed that this region is lying on more complicated tectonic condition due to the two subducted plates and the various types of earthquakes which have been caused by. Therefore, it is necessary to classify these earthquakes into inter-plate earthquakes and intra-plate ones. Then, we have been constructing a seismic observation network since 5 years ago. Tokyo Metropolitan area is a densely populated region of about 40 million people. It is the center of Japan both in politics and in economy. So that human activities have been conducting quite busily, this region is unsuitable for seismic observation. Then, we have decided to make an ultra high dense seismic observation network. We named it the Metropolitan Seismometer Observation Network; MeSO-net. MeSO-net consists of 296 seismic stations. Minimum interval is about 2km and average interval is about 5km.We picked the P- and S-wave arrival times manually. We applied double-difference tomography method to the dataset and estimated the velocity structure. We depicted the plate boundaries from the newly developed velocity model. And, we referred to the locations of the repeating earthquakes, the distributions of normal hypocenters and the focal mechanisms. Our plate model became relatively flat and a little shallower than previous one.Seismicity of Metropolitan area after the M9 event was compared to the one before M9 event. The seismic activity is about 4 times as high as before the M9 event occurred. We examined spatial distribution of the activated seismicity with respect to the newly developed plate configuration. The activated events are located on upper boundaries and they have almost thrust type mechanisms. Recently, a slow slip event has occurred on October in

  4. Onshore seismic amplifications due to bathymetric features

    Science.gov (United States)

    Rodríguez-Castellanos, A.; Carbajal-Romero, M.; Flores-Guzmán, N.; Olivera-Villaseñor, E.; Kryvko, A.

    2016-08-01

    We perform numerical calculations for onshore seismic amplifications, taking into consideration the effect of bathymetric features on the propagation of seismic movements. To this end, the boundary element method is applied. Boundary elements are employed to irradiate waves and, consequently, force densities can be obtained for each boundary element. From this assumption, Huygens’ principle is applied, and since the diffracted waves are built at the boundary from which they are radiated, this idea is equivalent to Somigliana’s representation theorem. The application of boundary conditions leads to a linear system being obtained (Fredholm integral equations). Several numerical models are analyzed, with the first one being used to verify the proposed formulation, and the others being used to estimate onshore seismic amplifications due to the presence of bathymetric features. The results obtained show that compressional waves (P-waves) generate onshore seismic amplifications that can vary from 1.2 to 5.2 times the amplitude of the incident wave. On the other hand, the shear waves (S-waves) can cause seismic amplifications of up to 4.0 times the incident wave. Furthermore, an important result is that in most cases the highest seismic amplifications from an offshore earthquake are located on the shoreline and not offshore, despite the seafloor configuration. Moreover, the influence of the incident angle of seismic waves on the seismic amplifications is highlighted.

  5. Local seismic hazard assessment in explosive volcanic settings by 3D numerical analyses

    Science.gov (United States)

    Razzano, Roberto; Pagliaroli, Alessandro; Moscatelli, Massimiliano; Gaudiosi, Iolanda; Avalle, Alessandra; Giallini, Silvia; Marcini, Marco; Polpetta, Federica; Simionato, Maurizio; Sirianni, Pietro; Sottili, Gianluca; Vignaroli, Gianluca; Bellanova, Jessica; Calamita, Giuseppe; Perrone, Angela; Piscitelli, Sabatino

    2017-04-01

    This work deals with the assessment of local seismic response in the explosive volcanic settings by reconstructing the subsoil model of the Stracciacappa maar (Sabatini Volcanic District, central Italy), whose pyroclastic succession records eruptive phases ended about 0.09 Ma ago. Heterogeneous characteristics of the Stracciacappa maar (stratification, structural setting, lithotypes, and thickness variation of depositional units) make it an ideal case history for understanding mechanisms and processes leading to modifications of amplitude-frequency-duration of seismic waves generated at earthquake sources and propagating through volcanic settings. New geological map and cross sections, constrained with recently acquired geotechnical and geophysical data, illustrate the complex geometric relationships among different depositional units forming the maar. A composite interfingering between internal lacustrine sediments and epiclastic debris, sourced from the rim, fills the crater floor; a 45 meters thick continuous coring borehole was drilled in the maar with sampling of undisturbed samples. Electrical Resistivity Tomography surveys and 2D passive seismic arrays were also carried out for constraining the geological model and the velocity profile of the S-waves, respectively. Single station noise measurements were collected in order to define natural amplification frequencies. Finally, the nonlinear cyclic soil behaviour was investigated through simple shear tests on the undisturbed samples. The collected dataset was used to define the subsoil model for 3D finite difference site response numerical analyses by using FLAC 3D software (ITASCA). Moreover, 1D and 2D numerical analyses were carried out for comparison purposes. Two different scenarios were selected as input motions: a moderate magnitude (volcanic event) and a high magnitude (tectonic event). Both earthquake scenarios revealed significant ground motion amplification (up to 15 in terms of spectral acceleration

  6. Shallow P- and S-wave velocities and site resonances in the St. Louis region, Missouri-Illinois

    Science.gov (United States)

    Williams, R.A.; Odum, J.K.; Stephenson, W.J.; Herrmann, Robert B.

    2007-01-01

    As part of the seismic hazard-mapping efforts in the St. Louis metropolitan area we determined the compressional and shear-wave velocities (Vp and Vs) to about a 40-m depth at 17 locations in this area. The Vs measurements were made using high-resolution seismic refraction and reflection methods. We find a clear difference in the Vs profiles between sites located on the river floodplains and those located in the upland urban areas of St. Louis. Vs30 (average Vs to 30-m depth) values in floodplain areas range from 200 to 290 m/s (NEHRP category D) and contrast with sites on the upland areas of St. Louis, which have Vs30 values ranging from 410 to 785 m/s (NEHRP categories C and B). The lower Vs30 values and earthquake recordings in the floodplains suggest a greater potential for stronger and more prolonged ground shaking in an earthquake. Spectral analysis of a M3.6 earthquake recorded on the St. Louis-area ANSS seismograph network indicates stronger shaking and potentially damaging S-wave resonant frequencies at NEHRP category D sites compared to ground motions at a rock site located on the Saint Louis University campus. ?? 2007, Earthquake Engineering Research Institute.

  7. Seismicity and Improved Velocity Structure in Kuwait

    Energy Technology Data Exchange (ETDEWEB)

    Gok, R M; Rodgers, A J; Al-Enezi, A

    2006-01-26

    relative arrival times. We obtained {approx}1500 absolute P and S arrival times and {approx}3200 P and S wave arrival time differences. Event locations do not change greatly when 3D velocity structure is included. Three-dimensional velocity structure, where resolvable, does not differ greatly from our optimized 1D model, indicating that the improved 1D model is adequate for routine event location. Finally, we calculated moment magnitudes, MW, for nearly 155 events using the coda magnitude technique of Mayeda et al., (2003). The fact that most of the relocated events occur below the known sedimentary structures extending to 7 km suggests that they are tectonic in origin. Shallow events within the sedimentary crust in the (southern) Minagish region may be related to oil field activities, although the current study cannot unambiguously determine the source of current seismicity in Kuwait. The improved velocity model reduces the scatter of travel time residuals relative to the locations reported in the KNSN bulletin and may be used for ground motion prediction and hazard estimate studies in Kuwait.

  8. S-wave attenuation in northeastern Sonora, Mexico, near the faults that ruptured during the earthquake of 3 May 1887 Mw 7.5.

    Science.gov (United States)

    Villalobos-Escobar, Gina P; Castro, Raúl R

    2014-01-01

    We used a new data set of relocated earthquakes recorded by the Seismic Network of Northeastern Sonora, Mexico (RESNES) to characterize the attenuation of S-waves in the fault zone of the 1887 Sonora earthquake (M w 7.5). We determined spectral attenuation functions for hypocentral distances (r) between 10 and 140 km using a nonparametric approach and found that in this fault zone the spectral amplitudes decay slower with distance at low frequencies (f attenuation functions obtained for 23 frequencies (0.4 ≤ f ≤ 63.1 Hz) permit us estimating the average quality factor Q S  = (141 ± 1.1 )f ((0.74 ± 0.04)) and a geometrical spreading term G(r) = 1/r (0.21). The values of Q estimated for S-wave paths traveling along the fault system that rupture during the 1887 event, in the north-south direction, are considerably lower than the average Q estimated using source-station paths from multiple stations and directions. These results indicate that near the fault zone S waves attenuate considerably more than at regional scale, particularly at low frequencies. This may be the result of strong scattering near the faults due to the fractured upper crust and higher intrinsic attenuation due to stress concentration near the faults.

  9. Advanced seismic imaging of overdeepened alpine valleys

    Science.gov (United States)

    Burschil, Thomas; Buness, Hermann; Tanner, David; Gabriel, Gerald; Krawczyk, Charlotte M.

    2017-04-01

    Major European alpine valleys and basins are densely populated areas with infrastructure of international importance. To protect the environment by, e.g., geohazard assessment or groundwater estimation, understanding of the geological structure of these valleys is essential. The shape and deposits of a valley can clarify its genesis and allows a prediction of behaviour in future glaciations. The term "overdeepened" refers to valleys and basins, in which pressurized melt-water under the glacier erodes the valley below the fluvial level. Most overdeepened valleys or basins were thus refilled during the ice melt or remain in the form of lakes. The ICDP-project Drilling Overdeepened Alpine Valleys (DOVE) intends to correlate the sedimentary succession from boreholes between valleys in the entire alpine range. Hereby, seismic exploration is essential to predict the most promising well path and drilling site. In a first step, this DFG-funded project investigates the benefit of multi-component techniques for seismic imaging. At two test sites, the Tannwald Basin and the Lienz Basin, the Leibniz Institute for Applied Geophysics acquired P-wave reflection profiles to gain structural and facies information. Built on the P-wave information, several S-wave reflection profiles were acquired in the pure SH-wave domain as well as 6-C reflection profiles using a horizontal S-wave source in inline and crossline excitation and 3-C receivers. Five P-wave sections reveal the structure of the Tannwald Basin, which is a distal branch basin of the Rhine Glacier. Strong reflections mark the base of the basin, which has a maximum depth of 240 metres. Internal structures and facies vary strongly and spatially, but allow a seismic facies characterization. We distinguish lacustrine, glacio-fluvial, and deltaic deposits, which make up the fill of the Tannwald Basin. Elements of the SH-wave and 6-C seismic imaging correlate with major structures in the P-wave image, but vary in detail. Based on

  10. FWT2D: A massively parallel program for frequency-domain full-waveform tomography of wide-aperture seismic data—Part 1: Algorithm

    Science.gov (United States)

    Sourbier, Florent; Operto, Stéphane; Virieux, Jean; Amestoy, Patrick; L'Excellent, Jean-Yves

    2009-03-01

    This is the first paper in a two-part series that describes a massively parallel code that performs 2D frequency-domain full-waveform inversion of wide-aperture seismic data for imaging complex structures. Full-waveform inversion methods, namely quantitative seismic imaging methods based on the resolution of the full wave equation, are computationally expensive. Therefore, designing efficient algorithms which take advantage of parallel computing facilities is critical for the appraisal of these approaches when applied to representative case studies and for further improvements. Full-waveform modelling requires the resolution of a large sparse system of linear equations which is performed with the massively parallel direct solver MUMPS for efficient multiple-shot simulations. Efficiency of the multiple-shot solution phase (forward/backward substitutions) is improved by using the BLAS3 library. The inverse problem relies on a classic local optimization approach implemented with a gradient method. The direct solver returns the multiple-shot wavefield solutions distributed over the processors according to a domain decomposition driven by the distribution of the LU factors. The domain decomposition of the wavefield solutions is used to compute in parallel the gradient of the objective function and the diagonal Hessian, this latter providing a suitable scaling of the gradient. The algorithm allows one to test different strategies for multiscale frequency inversion ranging from successive mono-frequency inversion to simultaneous multifrequency inversion. These different inversion strategies will be illustrated in the following companion paper. The parallel efficiency and the scalability of the code will also be quantified.

  11. Seismic scanning tunneling macroscope - Elastic simulations and Arizona mine test

    KAUST Repository

    Hanafy, Sherif M.

    2012-01-01

    Elastic seismic simulations and field data tests are used to validate the theory of a seismic scanning tunneling macroscope (SSTM). For nearfield elastic simulation, the SSTM results show superresolution to be better than λ/8 if the only scattered data are used as input data. If the direct P and S waves are muted then the resolution of the scatterer locations are within about λ/5. Seismic data collected in an Arizona tunnel showed a superresolution limit of at least λ/19. These test results are consistent with the theory of the SSTM and suggest that the SSTM can be a tool used by geophysicists as a probe for near-field scatterers.

  12. Locating S-wave sources for the SPE-5 explosion using time reversal methods and a close-in, 1000 sensor network

    Science.gov (United States)

    Myers, S. C.; Pitarka, A.; Mellors, R. J.

    2016-12-01

    The Source Physics Experiment (SPE) is producing new data to study the generation of seismic waves from explosive sources. Preliminary results show that far-field S-waves are generated both within the non-elastic volume surrounding explosive sources and by P- to S-wave scattering. The relative contribution of non-elastic phenomenology and elastic-wave scattering to far-field S-waves has been debated for decades, and numerical simulations based on the SPE experiments are addressing this question. The match between observed and simulated data degrades with event-station distance and with increasing time in each seismogram. This suggests that a more accurate model of subsurface elastic properties could result in better agreement between observed and simulated seismograms. A detailed model of subsurface structure has been developed using geologic maps and the extensive database of borehole logs, but uncertainty in structural details remains high. The large N instrument deployment during the SPE-5 experiment offers an opportunity to use time-reversal techniques to back project the wave field into the subsurface to locate significant sources of scattered energy. The large N deployment was nominally 1000, 5 Hz sensors (500 Z and 500 3C geophones) deployed in a roughly rectangular array to the south and east of the SPE-5 shot. Sensor spacing was nominally 50 meters in the interior portion of the array and 100 meters in the outer region, with two dense lines at 25 m spacing. The array covers the major geologic boundary between the Yucca Flat basin and the granitic Climax Stock in which the SPE experiments have been conducted. Improved mapping of subsurface scatterers is expected to result in better agreement between simulated and observed seismograms and aid in our understanding of S-wave generation from explosions. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

  13. Compilation of a recent seismicity data base of the greater Alpine region from several seismological networks and preliminary 3D tomographic results

    Directory of Open Access Journals (Sweden)

    M. Granet

    1997-06-01

    Full Text Available Local earthquake data collected by seven national and regional seismic networks have been compiled into a travel time catalog of 32341 earthquakes for the period 1980 to 1995 in South-Central Europe. As a prerequisite, a complete and corrected station list (master station list has been prepared according to updated information provided by every network. By simultaneous inversion of some 600 well-locatable events we obtained one-dimensional (1D velocity propagation models for each network. Consequently, these velocity models with appropriate station corrections have been used to obtain high-quality hypocenter locations for events inside and among the station networks. For better control, merging of phase data from several networks was performed as an iterative process where at each iteration two data sets of neighbouring networks or groups of networks were merged. Particular care was taken to detect and correctly identify phase data from events common to data sets from two different networks. In case of reports of the same phase data from more than one network, the phase data from the network owning and servicing the station were used according to the master station list. The merging yielded a data set of 278007 P and 191074 S-wave travel time observations from 32341 events in the greater Alpine region. Restrictive selection (number of P-wave observations >7; gap <160 degrees yielded a data set of about 10000 events with a total of more than 128000 P and 87000 S-wave observations well suited for local earthquake seismic tomography study. Preliminary tomographic results for South-Central Europe clearly show the topography of the crust-mantle boundary in the greater Alpine region and outline the 3D structure of the seismic Ivrea body.

  14. Passive seismic velocity tomography and geostatistical simulation on longwall mining panel / Tomografia pasywna pola prędkości i symulacje geostatystyczne w obrębie pola ścianowego

    Science.gov (United States)

    Hosseini, Navid; Oraee, Kazem; Shahriar, Kourosh; Goshtasbi, Kamran

    2012-10-01

    Generally, the accurate determination of the stress in surrounding rock mass of underground mining area has an important role in stability and ground control. In this paper stress redistribution around the longwall face has been studied using passive seismic velocity tomography based on Simultaneous Iterative Reconstructive Technique (SIRT) and Sequential Gaussian Simulation (SGS). The mining-induced microseismic events are used as a passive source. Since such sources are used, the ray coverage is insufficient and in order to resolve this deficiency, the wave velocity is estimated in a denser network and by the SGS method. Consequently the three-dimensional images of wave velocity are created and sliced into the coal seam. To analyze the variations of stress around the panel during the study period, these images are interpreted. Results show that the state of stress redistribution around the longwall panel can be deduced from these velocity images. In addition, movements of the stressed zones, including front and side abutments and the goaf area, along the longwall face are evident. The applied approach illustrated in this paper can be used as a useful method to monitoring the stress changes around the longwall face continuously. This can have significant safety implications and contribute to improvements in operational productivity

  15. TOMO-ETNA Experiment -Etna volcano, Sicily, investigated with active and passive seismic methods

    Science.gov (United States)

    Luehr, Birger-G.; Ibanez, Jesus M.; Díaz-Moreno, Alejandro; Prudencio, Janire; Patane, Domenico; Zieger, Toni; Cocina, Ornella; Zuccarello, Luciano; Koulakov, Ivan; Roessler, Dirk; Dahm, Torsten

    2017-04-01

    The TOMO-ETNA experiment, as part of the European Union project "MEDiterranean SUpersite Volcanoes (MED-SUV)", was devised to image the crustal structure beneath Etna by using state of the art passive and active seismic methods. Activities on-land and offshore are aiming to obtain new high-resolution seismic images to improve the knowledge of crustal structures existing beneath the Etna volcano and northeast Sicily up to the Aeolian Islands. In a first phase (June 15 - July 24, 2014) at Etna volcano and surrounding areas two removable seismic networks were installed composed by 80 Short Period and 20 Broadband stations, additionally to the existing network belonging to the "Istituto Nazionale di Geofisica e Vulcanologia" (INGV). So in total air-gun shots could be recorded by 168 stations onshore plus 27 ocean bottom instruments offshore in the Tyrrhenian and Ionian Seas. Offshore activities were performed by Spanish and Italian research vessels. In a second phase the broadband seismic network remained operative until October 28, 2014, as well as offshore surveys during November 19 -27, 2014. Active seismic sources were generated by an array of air-guns mounted in the Spanish Oceanographic vessel "Sarmiento de Gamboa" with a power capacity of up to 5.200 cubic inches. In total more than 26.000 shots were fired and more than 450 local and regional earthquakes could be recorded and will be analyzed. For resolving a volcanic structure the investigation of attenuation and scattering of seismic waves is important. In contrast to existing studies that are almost exclusively based on S-wave signals emitted by local earthquakes, here air-gun signals were investigated by applying a new methodology based on the coda energy ratio defined as the ratio between the energy of the direct P-wave and the energy in a later coda window. It is based on the assumption that scattering caused by heterogeneities removes energy from direct P-waves that constitutes the earliest possible

  16. An efficient sequential strategy for realizing cross-gradient joint inversion: method and its application to two-dimensional cross borehole seismic travel time and DC resistivity tomography

    Science.gov (United States)

    Gao, Ji; Zhang, Haijiang

    2018-01-01

    Cross-gradient joint inversion that enforces structural similarity between different models has been widely utilized in jointly inverting different geophysical data types. However, it is a challenge to combine different geophysical inversion systems with the cross-gradient structural constraint into one joint inversion system because they may differ greatly in the model representation, forward modeling, and inversion algorithm. Here we propose a new joint inversion strategy that can avoid this issue. Different models are separately inverted using the existing inversion packages and model structure similarity is only enforced through cross-gradient minimization between two models after each iteration. Although the data fitting and structure similarity enforcing processes are decoupled, our proposed strategy is still able to choose appropriate models to balance the trade-off between geophysical data fitting and structural similarity. This is realized by using model perturbations from separate data inversions to constrain the cross-gradient minimization process. We have tested this new strategy on two-dimensional cross borehole synthetic seismic travel time and DC resistivity datasets. Compared to separate geophysical inversions, our proposed joint inversion strategy fits the separate data sets at comparable levels while at the same time resulting in a higher structural similarity between the velocity and resistivity models.

  17. 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

  18. Environmental process tomography in the United States

    Energy Technology Data Exchange (ETDEWEB)

    Daily, W.; Ramirez, A.

    1994-01-01

    The US Government is supporting development of new technology and transfer of existing technology from other disciplines to apply to the problem. Part of this effort is development of geophysical tools used for underground imaging. These tools are closely related to many of those used in industrial process tomography. Both seismic and electromagnetic methods are used for underground imaging. In either case, sensitivity and resolution are greatly improved by making measurements from boreholes instead of only from the surface. Seismic signals are usually more sensitive to subsurface structure such as lithologic boundaries, but recent work has also shown seismic tomography to be sensitive to the degree of saturation. Electrical methods can be useful for delineation of aquitards such as clay layers. Electrical tomography is shown to be particularly sensitive to movement of fluids such as steam. Examples of both seismic and electromagnetic process tomography will be discussed in relation to environmental remediation of soils and ground water in the United States.

  19. An evaluation of numerical approaches for S-wave component simulation in rock blasting

    Directory of Open Access Journals (Sweden)

    Qidong Gao

    2017-10-01

    Full Text Available The shear wave (S-wave component of the total blast vibration always plays an important role in damage to rock or adjacent structures. Numerical approach has been considered as an economical and effective tool in predicting blast vibration. However, S-wave has not yet attracted enough attention in previous numerical simulations. In this paper, three typical numerical models, i.e. the continuum-based elastic model, the continuum-based damage model, and the coupled smooth particle hydrodynamics (SPH-finite element method (FEM model, were first introduced and developed to simulate the blasting of a single cylindrical charge. Then, the numerical results from different models were evaluated based on a review on the generation mechanisms of S-wave during blasting. Finally, some suggestions on the selection of numerical approaches for simulating generation of the blast-induced S-wave were put forward. Results indicate that different numerical models produce different results of S-wave. The coupled numerical model was the best, for its outstanding capacity in producing S-wave component. It is suggested that the model that can describe the cracking, sliding or heaving of rock mass, and the movement of fragments near the borehole should be selected preferentially, and priority should be given to the material constitutive law that could record the nonlinear mechanical behavior of rock mass near the borehole.

  20. Lithospheric Delamination or Relict Slab Beneath the Former North American Cratonic Margin in Idaho and Oregon? New Constraints From Seismic Tomography.

    Science.gov (United States)

    Stanciu, A. C.; Russo, R. M.; Mocanu, V. I.; VanDecar, J. C.; Hongsresawat, S.; Bremner, P. M.; Torpey, M. E.; Panning, M. P.

    2016-12-01

    We present a new high-resolution P-wave velocity model of the upper mantle beneath the former passive margin of the North American craton in Oregon and Idaho. We identify high velocity anomalies in the central part of the model and low velocity anomalies to the northwest and southeast. Our results derive from an integrated data set of teleseismic P waves recorded at 145 broadband stations, 85 deployed between 2011 and 2013 as part of the IDOR Passive experiment, and 60 USArray-TA stations. We determined 15,000 travel-times using multi-channel cross-correlation (VanDecar and Crosson, 1990). Phanerozoic tectonic events that affected upper mantle seismic structure here include subduction of Farallon and Juan de Fuca lithosphere, accretion of Blue Mountains terranes, Sevier and Laramide orogenies, Idaho batholith formation, Yellowstone and Columbia River volcanism, and Basin and Range extension. Our results indicate a high P-wave velocity anomaly located beneath the Idaho Batholith in west-central Idaho traceable down to 150-200 km depth. A similar anomaly identified by Schmandt and Humphrey (2011) beneath Washington and Montana was interpreted as a slab remnant from the accretion of Siletzia to North America. Alternatively, the fast Vp anomalies are delaminated North American craton lithosphere. Thickened lithosphere may have formed during Farallon subduction, terrane collision and accretion. Crust as much as 55 km thick present during Late Cretaceous (Foster et al., 2001; Gaschnig et al., 2011) is potentially indicative of lithospheric thickening leading to delamination. To the southeast, upper mantle low velocity anomalies occur beneath the Western Snake River Plain. We associate these low velocities with high temperatures generated by the Yellowstone mantle plume system. We observe a low velocity anomaly beneath the Wallowa Mountains starting at 150-200 km extending to depths below the resolution of our model.

  1. Contrasting behavior between dispersive seismic velocity and attenuation: advantages in subsoil characterization.

    Science.gov (United States)

    Zhubayev, Alimzhan; Ghose, Ranajit

    2012-02-01

    A careful look into the pertinent models of poroelasticity reveals that in water-saturated sediments or soils, the seismic (P and S wave) velocity dispersion and attenuation in the low field-seismic frequency band (20-200 Hz) have a contrasting behavior in the porosity-permeability domain. Taking advantage of this nearly orthogonal behavior, a new approach has been proposed, which leads to unique estimates of both porosity and permeability simultaneously. Through realistic numerical tests, the effect of maximum frequency content in data and the integration of P and S waves on the accuracy and robustness of the estimates are demonstrated. © 2012 Acoustical Society of America

  2. 2D Travel-time tomography of downward continued streamer multichannel seismic data followed by a band-limited full waveform inversion. Application to the Alboran basin (SE Iberia)

    Science.gov (United States)

    Gras Andreu, Claudia; Dagnino, Daniel; Estela Jiménez-Tejero, Clara; Meléndez, Adrià; Sallarès, Valentí; Ranero, César

    2017-04-01

    High-resolution velocity models can be retrieved by applying adjoint-state full-waveform inversion (FWI) to controlled source data. However the strong non-linearity of the problem makes the solution strongly dependent on the initial model chosen and on the low frequency content of the seismic source. Besides, typical relatively-short offset multi-channel seismic (MCS) data lacks first -refracted- arrivals that are commonly used to obtain a suitable starting model for FWI. Here we show that this problem can be solved by combining a joint refraction and reflection Travel Time Tomography (TTT) of a re-datumed version of the same data set to obtain an appropriate reference model with the correct low wavenumber on it that is subsequently refined by FWI. The proposed workflow is first described and then applied to MCS data acquired with 6 km-long streamer during the TOPOMED-2011 experiment in the Gulf of Cadiz (SE Iberia). The applied strategy includes as a first step a wave equation-based downward continuation (DC) or redatuming of the MCS data to simulate a sea bottom acquisition geometry, followed by a joint travel-time tomographic inversion of first arrivals identified in the DC data set together with the top of the basement (TOB) reflection from the MCS common mid point gathers to finally perform the multi-scale FWI of the original streamer data using the model obtained by TTT as initial model. The robustness of the Vp and TOB geometry model obtained by joint refraction and reflection TTT is assessed by comparing the results obtained using three independent data sets (different groups of shotgathers). The three models coincide within parameter uncertainty bounds, and the two-way-time transformed TOB geometry is also coincident with the time migrated image. We conclude therefore that the velocity and reflector depth model obtained is robust. The joint DC refraction and reflection travel-time inversion scheme helps to reduce the inherent existing velocity-depth trade

  3. Waveform tomography in geophysics and helioseismology

    NARCIS (Netherlands)

    Cobden, L.J.; Fichtner, A.; Tong, Vincent

    2015-01-01

    Seismic tomography – in which we construct images of a body's interior using seismic waves – is an inverse problem; that is, our goal is to find a model that fits a set of existing data observations. This is much less straightforward than the reverse, forward problem (i.e., generating synthetic data

  4. The transition zone between the Eastern Alps and the Pannonian Basin imaged by ambient noise tomography

    Science.gov (United States)

    Balázs, Brigitta; Szanyi, Gyöngyvér; Gráczer, Zoltán

    2017-04-01

    In the last decades dense seismic networks showed their importance and possibilities in studying the structure of the lithosphere and the upper mantle. In order to better understand the Alps-Apennines-Carpathians-Dinarides orogenic system the AlpArray Seismic Network was created, which is a European, transnational research initiative with more than 600 seismological stations involved. In this work we have studied the transition zone between the Eastern Alpine orogenic zone and the Neogene extensional Pannonian basin system, where topography gradually changes from high mountains into deep sedimentary basins in a relatively short distance. These geological features are associated with strong velocity contrasts. The aim of our research was to map sedimentary and crustal thickness variations and to detect the main structural lines. We have used data from the permanent stations of the studied region together with the AlpArray Network, as well as the temporary stations of the Carpathian Basin Project, which collected data in this area during 2006-2007. Vertical component noise cross-correlation functions were computed and Rayleigh wave dispersion curves were determined using the frequency-time analysis method. Group velocity tomography and S-wave velocity inversion were carried out for the transition zone. The resulting maps reflect the known, large scale geological features and provide unprecedented resolution for the velocity distribution of the area.

  5. Seismic Creep

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Seismic creep is the constant or periodic movement on a fault as contrasted with the sudden erupture associated with an earthquake. It is a usually slow deformation...

  6. Automatic determination of seismic phase arrival times

    Science.gov (United States)

    Kang, T. S.; Kim, M.; Rhie, J.

    2016-12-01

    Determination of P- and S-wave phase arrival times is significant factors in microseismic detection and thus hypocenter source inversion. If analysts try to pick P- and S-wave phase arrival times of microseismic events manually, they are at risk for inconsistency in picking due to subjective determination of P- and S-wave phase arrival times among them and get to spend too much time in doing the job. This study presents a method for the automatic detection of event and determination of arrival times of seismic phases. An implementation of the method is consisting of five steps. The first is the initial declaration of an event in continuous seismic data using a characteristic function which is also designed specifically in this study. The second is the automatic determination of P-wave phase arrival time using the normalized squared-envelope function. The third is the application of three-axis rotation using an energy ratio among three-component seismograms of the event. The fourth is the automatic determination of S-wave phase arrival time. The final step is the removal of falsely determined time in some records using the Wadati diagram which plots S-P times against P-wave phase arrival times over stations used in the picking stage. Application of the method to the continuous waveform data from a temporary broadband seismograph network consisting of 20 stations distributed in Jeju Island shows that the automatic event detection and determination of phase arrival times are carried out with accuracy.

  7. Seismic bearing

    Science.gov (United States)

    Power, Dennis

    2009-05-01

    Textron Systems (Textron) has been using geophones for target detection for many years. This sensing capability was utilized for detection and classification purposes only. Recently Textron has been evaluating multiaxis geophones to calculate bearings and track targets more specifically personnel. This capability will not only aid the system in locating personnel in bearing space or cartesian space but also enhance detection and reduce false alarms. Textron has been involved in the testing and evaluation of several sensors at multiple sites. One of the challenges of calculating seismic bearing is an adequate signal to noise ratio. The sensor signal to noise ratio is a function of sensor coupling to the ground, seismic propagation and range to target. The goals of testing at multiple sites are to gain a good understanding of the maximum and minimum ranges for bearing and detection and to exploit that information to tailor sensor system emplacement to achieve desired performance. Test sites include 10A Site Devens, MA, McKenna Airfield Ft. Benning, GA and Yuma Proving Ground Yuma, AZ. Geophone sensors evaluated include a 28 Hz triax spike, a 15 Hz triax spike and a hybrid triax spike consisting of a 10 Hz vertical geophone and two 28 Hz horizontal geophones. The algorithm uses raw seismic data to calculate the bearings. All evaluated sensors have triaxial geophone configuration mounted to a spike housing/fixture. The suite of sensors also compares various types of geophones to evaluate benefits in lower bandwidth. The data products of these tests include raw geophone signals, seismic features, seismic bearings, seismic detection and GPS position truth data. The analyses produce Probability of Detection vs range, bearing accuracy vs range, and seismic feature level vs range. These analysis products are compared across test sites and sensor types.

  8. Detection of sinkholes or anomalies using full seismic wave fields.

    Science.gov (United States)

    2013-04-01

    This research presents an application of two-dimensional (2-D) time-domain waveform tomography for detection of embedded sinkholes and anomalies. The measured seismic surface wave fields were inverted using a full waveform inversion (FWI) technique, ...

  9. Clustering and interpretation of local earthquake tomography models in the southern Dead Sea basin

    Science.gov (United States)

    Bauer, Klaus; Braeuer, Benjamin

    2016-04-01

    The Dead Sea transform (DST) marks the boundary between the Arabian and the African plates. Ongoing left-lateral relative plate motion and strike-slip deformation started in the Early Miocene (20 MA) and produced a total shift of 107 km until presence. The Dead Sea basin (DSB) located in the central part of the DST is one of the largest pull-apart basins in the world. It was formed from step-over of different fault strands at a major segment boundary of the transform fault system. The basin development was accompanied by deposition of clastics and evaporites and subsequent salt diapirism. Ongoing deformation within the basin and activity of the boundary faults are indicated by increased seismicity. The internal architecture of the DSB and the crustal structure around the DST were subject of several large scientific projects carried out since 2000. Here we report on a local earthquake tomography study from the southern DSB. In 2006-2008, a dense seismic network consisting of 65 stations was operated for 18 months in the southern part of the DSB and surrounding regions. Altogether 530 well-constrained seismic events with 13,970 P- and 12,760 S-wave arrival times were used for a travel time inversion for Vp, Vp/Vs velocity structure and seismicity distribution. The work flow included 1D inversion, 2.5D and 3D tomography, and resolution analysis. We demonstrate a possible strategy how several tomographic models such as Vp, Vs and Vp/Vs can be integrated for a combined lithological interpretation. We analyzed the tomographic models derived by 2.5D inversion using neural network clustering techniques. The method allows us to identify major lithologies by their petrophysical signatures. Remapping the clusters into the subsurface reveals the distribution of basin sediments, prebasin sedimentary rocks, and crystalline basement. The DSB shows an asymmetric structure with thickness variation from 5 km in the west to 13 km in the east. Most importantly, a well-defined body

  10. Active Faults, Modern Seismicity And Block Structure Of Eurasia

    Science.gov (United States)

    Gatinsky, Y.; Rundquist, D.

    2004-12-01

    transit zones being under influence Indostan-Eurasia collision. The earthquake distribution, active fault patterns, and satellite measurements clearly indicate the present-day geodynamic instability of Eurasia. Unfortunately, the problem of the depth at which various blocks are displaced so far remains a matter of debate and the relevant information is still controversial. Some blocks have roots in the lithosphere upper mantle (Qaidam, southeast China), but others such as Tarim, Tien Shan are not divided at the lithosphere level. Hot plumes under western and central Europe are ascending from the sublitosphere mantle at the depth of about 400 km (Grosvenor et al, 1995), and European blocks' displacement can be connected with these plumes. At the same time prevailing depths of earthquake hypocenters (20-40 km) and seismic tomography allow to suggest that most of the blocks are shallow-seated and bounded from below by detachment zones localized at the crust base or within the lithosphere. It is displayed by a marked reduction of S-wave velocities at various levels presumably corresponding to the development of anomalous heated mantle at the base of crustal or crustal-mantle blocks. The presented evidence confirms the idea of lithosphere lamination, which was proved in the latest time by investigations in the frame of the project INDEPTH (Zhao et al., 2001; Li et al., 2003 and others). The Program of the RF President supports this work (project NSH-99.2003.5). ref='http://www.sgm.ru' >http://www.sgm.ru

  11. New onset S wave in pulmonary embolism: revisited (something old and something new)

    Science.gov (United States)

    Gupta, Prabha Nini; Pillai, Siju B; Ahmad, Sajan Z; Babu, Shifas M

    2013-01-01

    We report a case of a young man who had a new onset S wave in lead 1 in his ECG with typical symptoms of acute onset of dyspoena 2 months after an episode of deep vein thrombosis, S wave disappeared 6 days after thrombolysis. We report this case as the clinical course was very typical plus we have reviewed the literature regarding diagnosis and risk stratification of pulmonary embolism for the student, or the casualty medical officer. PMID:24275333

  12. 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

  13. Seismic metamaterials based on isochronous mechanical oscillators

    Energy Technology Data Exchange (ETDEWEB)

    Finocchio, G., E-mail: gfinocchio@unime.it; Garescì, F.; Azzerboni, B. [Department of Electronic Engineering, Industrial Chemistry and Engineering, University of Messina, C.da di Dio, I-98166 Messina (Italy); Casablanca, O.; Chiappini, M. [Istituto Nazionale di Geofisica e Vulcanologia (INGV), Via Vigna Murata 605, 00143 Roma (Italy); Ricciardi, G. [Department of Civil, Informatic, Architectural, and Environmental Engineering and Applied Mathematics, C.da di Dio, I-98166 Messina (Italy); Alibrandi, U. [Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, Singapore 117576 (Singapore)

    2014-05-12

    This Letter introduces a seismic metamaterial (SM) composed by a chain of mass-in-mass system able to filter the S-waves of an earthquake. We included the effect of the SM into the mono dimensional model for the soil response analysis. The SM modifies the soil behavior and in presence of an internal damping the amplitude of the soil amplification function is reduced also in a region near the resonance frequency. This SM can be realized by a continuous structure with inside a 3d-matrix of isochronous oscillators based on a sphere rolling over a cycloidal trajectory.

  14. Optimum Geometry For Roll Along In Seismic Refraction ...

    African Journals Online (AJOL)

    Seismic refraction is mostly used in geotechnical work to determine the velocity of the overburden and the refractor velocity. Roll along, in seismic refraction tomography, is important for three reasons. These are to increase the profile length beyond the distance dictated by the source and the instrument (number of receiver ...

  15. Analysis of P- and S-wave VSP (vertical seismic profile) data from the Salton Sea Geothermal Field

    Energy Technology Data Exchange (ETDEWEB)

    Daley, T.M.

    1987-09-01

    To understand any geophysical data, geologic information is necessary. This thesis will begin with a summary of the geology of the Salton Trough region and the Salton Sea Geothermal Field (SSGF). The information available from the SSSDP will also be summarized. After the geologic summary, the design of the VSP will be discussed, including acquisition equipment and procedures. The data processing procedures and software used will be discussed as a separate section. Processing procedures will also be described at various times in the thesis where more specialized procedures are used. Data analysis makes up the bulk of the thesis and it is divided into a number of sections detailing the basic VSP interpretation, the anisotropy analysis and the fracture detection and orientation analysis. A combined interpretation of the results, with probable geologic causes for observed events, is presented as a separate section from the data analysis. Finally, a summary of results for each of the goals stated above will be given. The reader should note that a large volume of data were collected and various display methods were used (from the standard wiggle-trace to three-component hodographs). Much of these data are left in the appendices with important or representative figures given in the body of the thesis. Also given in the appendices are listings of FORTRAN programs developed in conjunction with the thesis work. 46 refs., 63 figs., 12 tabs.

  16. Ocean acoustic reverberation tomography.

    Science.gov (United States)

    Dunn, Robert A

    2015-12-01

    Seismic wide-angle imaging using ship-towed acoustic sources and networks of ocean bottom seismographs is a common technique for exploring earth structure beneath the oceans. In these studies, the recorded data are dominated by acoustic waves propagating as reverberations in the water column. For surveys with a small receiver spacing (e.g., ocean acoustic reverberation tomography, is developed that uses the travel times of direct and reflected waves to image ocean acoustic structure. Reverberation tomography offers an alternative approach for determining the structure of the oceans and advancing the understanding of ocean heat content and mixing processes. The technique has the potential for revealing small-scale ocean thermal structure over the entire vertical height of the water column and along long survey profiles or across three-dimensional volumes of the ocean. For realistic experimental geometries and data noise levels, the method can produce images of ocean sound speed on a smaller scale than traditional acoustic tomography.

  17. Computation of Green's Function of 3-D Radiative Transport Equations for Non-isotropic Scattering of P and Unpolarized S Waves

    Science.gov (United States)

    Margerin, Ludovic

    2017-11-01

    In this work, I propose to model the propagation of high-frequency seismic waves in the heterogeneous Earth by means of a coupled system of radiative transfer equations for P and S waves. The model describes the propagation of both coherent and diffuse waves in a statistically isotropic heterogeneous medium and takes into account key phenomena such as scattering conversions between propagation modes, scattering anisotropy and absorption. The main limitation of the approach lies in the neglect of the shear wave polarization information. The canonical case of a medium with uniform scattering and absorption properties is studied in details. Using an adjoint formalism, Green's functions (isotropic point source solutions) of the transport equation are shown to obey a reciprocity relation relating the P energy density radiated by an S source to the S energy density radiated by a P source. A spectral method of calculation of the Green's function is presented. Application of Fourier, Hankel and Legendre transforms to time, space and angular variables, respectively, turns the equation of transport into a numerically tractable penta-diagonal linear system of equations. The implementation of the spectral method is discussed in details and validated through one-to-one comparisons with Monte Carlo simulations. Numerical experiments in different propagation regimes illustrate that the ratio between the correlation length of heterogeneities and the incident wavelength plays a key role in the rate of stabilization of the P-to- S energy ratio in the coda. The results suggest that the rapid stabilization of energy ratios observed in the seismic coda is a signature of the broadband nature of crustal heterogeneities. The impact of the texture of the medium on both pulse broadening and generation of converted S wave arrivals by explosion sources is illustrated. The numerical study indicates that smooth media enhance the visibility of ballistic-like S arrivals from P sources.

  18. Computation of Green's Function of 3-D Radiative Transport Equations for Non-isotropic Scattering of P and Unpolarized S Waves

    Science.gov (United States)

    Margerin, Ludovic

    2017-07-01

    In this work, I propose to model the propagation of high-frequency seismic waves in the heterogeneous Earth by means of a coupled system of radiative transfer equations for P and S waves. The model describes the propagation of both coherent and diffuse waves in a statistically isotropic heterogeneous medium and takes into account key phenomena such as scattering conversions between propagation modes, scattering anisotropy and absorption. The main limitation of the approach lies in the neglect of the shear wave polarization information. The canonical case of a medium with uniform scattering and absorption properties is studied in details. Using an adjoint formalism, Green's functions (isotropic point source solutions) of the transport equation are shown to obey a reciprocity relation relating the P energy density radiated by an S source to the S energy density radiated by a P source. A spectral method of calculation of the Green's function is presented. Application of Fourier, Hankel and Legendre transforms to time, space and angular variables, respectively, turns the equation of transport into a numerically tractable penta-diagonal linear system of equations. The implementation of the spectral method is discussed in details and validated through one-to-one comparisons with Monte Carlo simulations. Numerical experiments in different propagation regimes illustrate that the ratio between the correlation length of heterogeneities and the incident wavelength plays a key role in the rate of stabilization of the P-to-S energy ratio in the coda. The results suggest that the rapid stabilization of energy ratios observed in the seismic coda is a signature of the broadband nature of crustal heterogeneities. The impact of the texture of the medium on both pulse broadening and generation of converted S wave arrivals by explosion sources is illustrated. The numerical study indicates that smooth media enhance the visibility of ballistic-like S arrivals from P sources.

  19. In- and outbound spreading of a free-particle s-wave

    DEFF Research Database (Denmark)

    Bialynicki-Birula, i.; Cirone, M. A.; Dahl, Jens Peder

    2002-01-01

    We show that a free quantum particle in two dimensions with zero angular momentum (s wave) in the form of a ring-shaped wave packet feels an attraction towards the center of the ring, leading first to a contraction followed by an expansion. An experiment to demonstrate this effect is also outlined....

  20. Non-triviality matters: examining the interplay between s-wave superconductivity and topological surface states

    NARCIS (Netherlands)

    Snelder, M.

    2015-01-01

    The main focus of this thesis is to understand the correlations present at the s-wave/three-dimensional topological insulator interface both theoretically and experimentally. In the future, devices containing these kind of interfaces can be used to create and manipulate a Majorana zero-energy mode

  1. Seismic Symphonies

    Science.gov (United States)

    Strinna, Elisa; Ferrari, Graziano

    2015-04-01

    The project started in 2008 as a sound installation, a collaboration between an artist, a barrel organ builder and a seismologist. The work differs from other attempts of sound transposition of seismic records. In this case seismic frequencies are not converted automatically into the "sound of the earthquake." However, it has been studied a musical translation system that, based on the organ tonal scale, generates a totally unexpected sequence of sounds which is intended to evoke the emotions aroused by the earthquake. The symphonies proposed in the project have somewhat peculiar origins: they in fact come to life from the translation of graphic tracks into a sound track. The graphic tracks in question are made up by copies of seismograms recorded during some earthquakes that have taken place around the world. Seismograms are translated into music by a sculpture-instrument, half a seismograph and half a barrel organ. The organ plays through holes practiced on paper. Adapting the documents to the instrument score, holes have been drilled on the waves' peaks. The organ covers about three tonal scales, starting from heavy and deep sounds it reaches up to high and jarring notes. The translation of the seismic records is based on a criterion that does match the highest sounds to larger amplitudes with lower ones to minors. Translating the seismogram in the organ score, the larger the amplitude of recorded waves, the more the seismogram covers the full tonal scale played by the barrel organ and the notes arouse an intense emotional response in the listener. Elisa Strinna's Seismic Symphonies installation becomes an unprecedented tool for emotional involvement, through which can be revived the memory of the greatest disasters of over a century of seismic history of the Earth. A bridge between art and science. Seismic Symphonies is also a symbolic inversion: the instrument of the organ is most commonly used in churches, and its sounds are derived from the heavens and

  2. Structure of central and southern Mexico from velocity and attenuation tomography

    OpenAIRE

    Chen, Ting; Robert W. Clayton

    2012-01-01

    The 3D V_p, V_p/_Vs, P- and S-wave attenuation structure of the Cocos subduction zone in Mexico is imaged using earthquakes recorded by two temporary seismic arrays and local stations. Direct P wave arrivals on vertical components and direct S wave arrivals on transverse components from local earthquakes are used for velocity imaging. Relative delay times for P and PKP phases from teleseismic events are also used to obtain a deeper velocity structure beneath the southern seismic array. Using ...

  3. Geometry of the Arabia-Somalia Plate Boundary into Afar: Preliminary Results from the Seismic Profile Across the Asal Rift (Djibouti)

    Science.gov (United States)

    Vergne, J.; Doubre, C.; Mohamed, K.; Tiberi, C.; Leroy, S.; Maggi, A.

    2010-12-01

    In the Afar Depression, the Asal-Ghoubbet Rift in Djibouti is a young segment on land at the propagating tip of the Aden Ridge. This segment represents an ideal laboratory to observe the mechanisms of extension and the structural evolutions involved, from the continental break-up to the first stage of oceanic spreading. However, we lack first order information about the crustal and upper mantle structure in this region, which for example prevent detailed numerical modeling of the deformations observed at the surface from GPS or InSAR. Moreover the current permanent network is not well suited to precisely constrain the ratio of seismic/aseismic deformation and to characterize the active deformation and the rifting dynamics. Since November 2009 we have maintained a temporary network of 25 seismic stations deployed along a 150 km-long profile. Because we expect rapid variations of the lithospheric structure across the 10 km-wide central part of the rift, we gradually decreased the inter-stations spacing to less than 1 km in the middle section of the profile. In order to obtain a continuous image of the plate boundary, from the topographic surface to the upper mantle, several techniques and methods will be applied: P and S wave receiver functions, tomographies based on body waves, surface waves and seismic noise correlation, anisotropy, and finally a gravity-seismic joint inversion. We present some preliminary results deduced from the receiver functions applied to the data acquired during the first months of the experiment. We migrate several sets of receiver functions computed in various frequency bands to resolve both mantle interfaces and fine scale structures within the thin crust in the center of the rift. These first images confirm a rapid variation of the Moho depth on both sides of the rift and a very complex lithospheric structure in the central section with several low velocity zones within the top 50km that might correspond to magma lenses.

  4. Imaging the state of the rock mass in the Kiirunavaara iron ore mine, Sweden, using local event tomography

    Science.gov (United States)

    Lund, Björn; Berglund, Karin; Tryggvason, Ari; Dineva, Savka; Jonsson, Linda

    2017-04-01

    Induced seismic events in a mining environment are a potential hazard, but they can be used to gain information about the rock mass in the mine which otherwise would be very difficult to obtain. In this study we use approximately 1.2 million mining induced seismic events in the Kiirunavaara iron ore mine in northernmost Sweden to image the rock mass using local event travel-time tomography. In addition, relocation of the events significantly improves the possibility to infer structural information and rock damage. The Kiirunavaara mine is one of the largest underground iron ore mines in the world. The ore body is a magnetite sheet of 4 km length, with an average thickness of 80 m, which dips approximately 55° to the east. Mining production is now at a depth of 785 - 855 m. During 2015 the seismic system in the mine recorded on average approximately 1,000 local seismic events per day. The events are of various origins such as shear slip on fractures, non-shear events and blasts, with magnitudes of up to 2.5. We use manually picked P- and S-waves in the tomography and we require that both phases are present as we found that events from the routine processing need screening for anomalous P- versus S-travel times, indicating occasional erroneous phase associations. For the tomography we use the 3D local earthquake tomography code PStomo_eq (Tryggvason et al., 2002), which we adjusted to the mining scale. The study volume is 1.2 x 1.8 x 1.8 km and the velocity model grid size is 10x10x10 meter. The tomographic images show clearly defined regions of high and low velocities. Low velocity zones are associated with mapped clay zones and areas of mined out ore, and also with the near-ore tunnel infrastructure in the foot-wall. We also see how the low S-velocity anomaly continues to depth below the current mining levels, following the inferred direction of the ore. The tomography shows higher P- and S-velocities in the foot-wall away from the areas of mine infrastructure. We

  5. Crust-mantle coupling mechanism in Cameroon, West Africa, revealed by 3D S-wave velocity and azimuthal anisotropy

    Science.gov (United States)

    Ojo, Adebayo Oluwaseun; Ni, Sidao; Chen, Haopeng; Xie, Jun

    2018-01-01

    To understand the depth variation of deformation beneath Cameroon, West Africa, we developed a new 3D model of S-wave isotropic velocity and azimuthal anisotropy from joint analysis of ambient seismic noise and earthquake surface wave dispersion. We found that the Cameroon Volcanic Line (CVL) is well delineated by slow phase velocities in contrast with the neighboring Congo Craton, in agreement with previous studies. Apart from the Congo Craton and the Oubanguides Belt, the uppermost mantle revealed a relatively slow velocity indicating a thinned or thermally altered lithosphere. The direction of fast axis in the upper crust is mostly NE-SW, but trending approximately N-S around Mt. Oku and the southern CVL. The observed crustal azimuthal anisotropy is attributed to alignment of cracks and crustal deformation related to magmatic activities. A widespread zone of weak-to-zero azimuthal anisotropy in the mid-lower crust shows evidence for vertical mantle flow or isotropic mid-lower crust. In the uppermost mantle, the fast axis direction changed from NE-SW to NW-SE around Mt. Oku and northern Cameroon. This suggests a layered mechanism of deformation and revealed that the mantle lithosphere has been deformed. NE-SW fast azimuths are observed beneath the Congo Craton and are consistent with the absolute motion of the African plate, suggesting a mantle origin for the observed azimuthal anisotropy. Our tomographically derived fast directions are consistent with the local SKS splitting results in some locations and depths, enabling us to constrain the origin of the observed splitting. The different feature of azimuthal anisotropy in the upper crust and the uppermost mantle implies decoupling between deformation of crust and mantle in Cameroon.

  6. Seismic Tomography of the Near Solar Surface

    Indian Academy of Sciences (India)

    Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately.

  7. Study on P-wave and S-wave velocity in dry and wet sandstones of Tushka region, Egypt

    Directory of Open Access Journals (Sweden)

    Mohamed A. Kassab

    2015-03-01

    The derived equations can be used for the prediction of P-wave velocity of wet rock samples from the P-wave velocity of dry rock samples, and the S-wave velocity of wet rock samples can be predicted from the S-wave velocity of dry rock samples. A strong linear correlation between P-wave velocity and S-wave velocity of dry rock samples and between P-wave velocity and S-wave velocity of wet rock samples was found. The resulting linear equations can be used for the estimation of S-wave velocity from the P-wave velocity in the case of both dry and wet rock samples.

  8. Laboratory measurements of seismic velocity anisotropy of salt diapirs: Implications for wellbore stability and seismic processing

    Science.gov (United States)

    Vargas-Meleza, Liliana; Healy, David

    2013-04-01

    A set of ten evaporite samples collected from outcrops in a single diapiric province in Cape Breton Island (Canada) have been tested for seismic velocity anisotropy using three methods: 1) conventional ultrasonic pulse transmission method, where velocities are found from the travel times and the known dimensions of the samples. In order to obtain the entire suite of elastic constants, both P- and S-wave velocity measurements were taken in three different directions of cuboid rock samples. Velocities have been measured under dry, ambient conditions of temperature and pressure in halite-, gypsum- and anhydrite-dominated samples; 2) optical microscopy and scanning electron microscopy on thin sections to define the spatial distribution of minerals, their crystallographic preferred orientations (CPO); and 3) a numerical 'rock-recipe' approach based on Tatham et al. (2008) to calculate seismic velocity anisotropy using arbitrary composites of evaporite minerals and different CPOs. These three methods are then compared to understand the controlling factors of the anisotropic elastic properties. The elasticity data are used to guide geomechanical modeling for wellbore stability and to provide insights for the seismic data processing and seismic imaging of salt diapirs. Reference Tatham, D.J., Lloyd, G.E., Butler, R.W.H. and Casey, M, 2008, Amphibole and lower crustal seismic properties: Earth and Planetary Science Letters, 267, 118-128.

  9. The gamma gamma --> pi + pi - S wave in the CELLO experiment

    Science.gov (United States)

    Kaloshin, A. E.; Persikov, V. M.

    1993-10-01

    We analyze the CELLO angular distributions $\\gamma\\gamma\\rightarrow\\pi^+\\pi^-$ with the unitary model \\cite{KS-86} for helicity 2 amplitude. In contrast to previous analysis \\cite{CELLO} we do not see any QED damping. The obtained S--wave does not contradict to low--energy theorem and demonstrates more clealy the resonance--like behaviour near 1.3 Gev.

  10. S WAVE IN PULMONARY EMBOLISM, A NEW ECG SIGN TO AID THROMBOLYSIS

    Directory of Open Access Journals (Sweden)

    Thomas John

    2012-11-01

    Full Text Available Acute pulmonary embolism is a devastating disease that often leads to mortality . Previous investigators have found that thrombolysis reduces mortality in men but not significantly in women with pulmonary embolism. Many of the previous studies are with tenecteplase and alteplase. Here, we describe intra - venous thrombolysis with streptokinase in seven patients with pulmonary embolism who survived including two women. Further, we have one patient who had a new onset of S wave in lead I which subsequently disappeared after embolectomy. We also comment on the usefulness of shock sign in 2 deciding on thrombolysis .We propose a new sign for noninvasive assessment of need for thrombolysis in pulmonary embolism. New onset S wave in Lead I in pulmonary embolism can be used as a new sign for deciding the need for thrombolysis. When added to the shock sign it can be used in the emergency deparment to decide the need for thrombolysis. Further, there are no clear end points as to when to stop thrombolysis. In all 4 patients we switched to heparin when spontaneous bleeding or oozing started. In all 4 patients subsequent CT scans showed that the patient has mild to moderate resolution of the pulmonary embolism and patients remained stable and have been discharged and are under regular follow up. Hence we propose that bleeding can be used as an end point for thrombolysis in acute pulmonary embolism. We also describe a patient who had new onset S wave that disappeared after successful pulmonary embolectomy. Probably, the S wave is a marker of main pulmonary artery branch occlusions.

  11. APPLICATION OF A HEURISTIC METHOD FOR THE ESTIMATION OF S-WAVE VELOCITY STRUCTURE

    Directory of Open Access Journals (Sweden)

    Alfaro Castillo Andrés José

    2006-08-01

    Full Text Available The assessment of local site effects is one of the most important subjects in Engineering Seismology. In order to perform an assessment, it is necessary to determine the S-wave velocity structure of the site. Additionally, in some basins, it is very important to know the deep sedimentary structure, due to the amplification phenomena of low frequency waves. There are several techniques to achieve this purpose; probably the most inexpensive technique is using the vertical component of microtremors measured with an array of seismographs. The phase velocity of Rayleigh waves is inverted to an S-wave velocity (Vs profile  using optimization techniques. Most of the time, least square methods have been applied in the inversion.Recently, heuristic methods have also been used for the estimation of the S-wave velocity structure from microtremor.In this study seven arrays of microtremors in the city of Tsukuba city were performed, located to the NE edge of Kanto Basin, in order to estimate the deep S-wave velocity structure. The spatial autocorrelationmethod SPAC was used to determine phase velocity dispersion curves in the frequency range from 0.3-2.5 Hz. The determination of Vs profiles reached a depth of 750 m. Two methods were used to estimate the Swavevelocity structure: Inversion method and a heuristic method via the combination of Downhill Simplex Algorithm with a Very Fast Simulated Annealing Method. Comparisons with Vs from the existent resultsfrom PS-logging tests at the center of the array showed the reliability of the heuristic method.

  12. Seismic Structure of Southern African Cratons

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Artemieva, Irina; Levander, Alan

    2014-01-01

    Cratons are extremely stable continental crustal areas above thick depleted lithosphere. These regions have remained largely unchanged for more than 2.5 Ga. This study presents a new seismic model of the seismic structure of the crust and lithospheric mantle constrained by seismic receiver...... functions and finite-frequency tomography based on data from the South Africa Seismic Experiment (SASE). Combining the two methods provides high vertical and lateral resolution. The main results obtained are (1) the presence of a highly heterogeneous crustal structure, in terms of thickness, composition (as...... shown by estimated Vp/Vs), and sharpness of the discontinuities, (2) observation of an unexpectedly strong crustal azimuthal anisotropy, and (3) a fast lithospheric keel of the Kaapvaal Craton which reaches depths of 300-350 km and relatively slow anomalies beneath both the paleo-orogenic Limpopo Belt...

  13. S/WAVES: The Radio and Plasma Wave Investigation on the STEREO Mission

    Science.gov (United States)

    Bougeret, J. L.; Goetz, K.; Kaiser, M. L.; Bale, S. D.; Kellogg, P. J.; Maksimovic, M.; Monge, N.; Monson, S. J.; Astier, P. L.; Davy, S.; Dekkali, M.; Hinze, J. J.; Manning, R. E.; Aguilar-Rodriguez, E.; Bonnin, X.; Briand, C.; Cairns, I. H.; Cattell, C. A.; Cecconi, B.; Eastwood, J.; Ergun, R. E.; Fainberg, J.; Hoang, S.; Huttunen, K. E. J.; Krucker, S.; Lecacheux, A.; MacDowall, R. J.; Macher, W.; Mangeney, A.; Meetre, C. A.; Moussas, X.; Nguyen, Q. N.; Oswald, T. H.; Pulupa, M.; Reiner, M. J.; Robinson, P. A.; Rucker, H.; Salem, C.; Santolik, O.; Silvis, J. M.; Ullrich, R.; Zarka, P.; Zouganelis, I.

    2008-04-01

    This paper introduces and describes the radio and plasma wave investigation on the STEREO Mission: STEREO/WAVES or S/WAVES. The S/WAVES instrument includes a suite of state-of-the-art experiments that provide comprehensive measurements of the three components of the fluctuating electric field from a fraction of a hertz up to 16 MHz, plus a single frequency channel near 30 MHz. The instrument has a direction finding or goniopolarimetry capability to perform 3D localization and tracking of radio emissions associated with streams of energetic electrons and shock waves associated with Coronal Mass Ejections (CMEs). The scientific objectives include: (i) remote observation and measurement of radio waves excited by energetic particles throughout the 3D heliosphere that are associated with the CMEs and with solar flare phenomena, and (ii) in-situ measurement of the properties of CMEs and interplanetary shocks, such as their electron density and temperature and the associated plasma waves near 1 Astronomical Unit (AU). Two companion papers provide details on specific aspects of the S/WAVES instrument, namely the electric antenna system (Bale et al., Space Sci. Rev., 2007) and the direction finding technique (Cecconi et al., Space Sci. Rev., 2007).

  14. Experimental Study of S-wave Propagation Through a Filled Rock Joint

    Science.gov (United States)

    Liu, Tingting; Li, Jianchun; Li, Haibo; Li, Xinping; Zheng, Yun; Liu, Hui

    2017-10-01

    This experimental study proposes a Split Shear Plates model to investigate the effects of a filled joint on S-wave attenuation. A dynamic impact is used to create frictional slip and generate an incident S-wave. The filled joint is simulated using a sand layer between two rock plates. Normal stress is applied to the filled joint, and semiconductor strain gauges are arranged on the two plates to measure the strain. Verification tests are conducted to validate the reliability of the experimental results. A series of tests is performed to investigate the influence of the normal stress, filled thickness and particle size of the filling materials on the S-wave propagation. The transmission coefficients of the filled joints are smaller than those of the non-filled joints because of the attenuation associated with the filling materials. Additionally, the transmission coefficients exhibit a stronger correlation with the normal stress than with the filled thickness or particle size. The transmission coefficients increase at a decreasing rate as normal pressure increases.

  15. 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

  16. Global Adjoint Tomography

    Science.gov (United States)

    Bozdag, Ebru; Lefebvre, Matthieu; Lei, Wenjie; Peter, Daniel; Smith, James; Komatitsch, Dimitri; Tromp, Jeroen

    2015-04-01

    We will present our initial results of global adjoint tomography based on 3D seismic wave simulations which is one of the most challenging examples in seismology in terms of intense computational requirements and vast amount of high-quality seismic data that can potentially be assimilated in inversions. Using a spectral-element method, we incorporate full 3D wave propagation in seismic tomography by running synthetic seismograms and adjoint simulations to compute exact sensitivity kernels in realistic 3D background models. We run our global simulations on the Oak Ridge National Laboratory's Cray XK7 "Titan" system taking advantage of the GPU version of the SPECFEM3D_GLOBE package. We have started iterations with initially selected 253 earthquakes within the magnitude range of 5.5 simulations having resolution down to ~27 s to invert for a transversely isotropic crust and mantle model using a non-linear conjugate gradient algorithm. The measurements are currently based on frequency-dependent traveltime misfits. We use both minor- and major-arc body and surface waves by running 200 min simulations where inversions are performed with more than 2.6 million measurements. Our initial results after 12 iterations already indicate several prominent features such as enhanced slab (e.g., Hellenic, Japan, Bismarck, Sandwich), plume/hotspot (e.g., the Pacific superplume, Caroline, Yellowstone, Hawaii) images, etc. To improve the resolution and ray coverage, particularly in the lower mantle, our aim is to increase the resolution of numerical simulations first going down to ~17 s and then to ~9 s to incorporate high-frequency body waves in inversions. While keeping track of the progress and illumination of features in our models with a limited data set, we work towards to assimilate all available data in inversions from all seismic networks and earthquakes in the global CMT catalogue.

  17. Sensitivity analysis of P-waves and S-waves to gas hydrate in the Shenhu area using OBS

    Science.gov (United States)

    Xing, Lei; Liu, Xueqin; Zhang, Jin; Liu, Huaishan; Zhang, Jing; Li, Zizheng; Wang, Jianhua

    2018-02-01

    Compared to towed streamers, ocean-bottom seismometers (OBS) obtain both S-wave data and richer wavefield information. In this paper, the induced polarization method is used to conduct wavefield separation on OBS data obtained from the Shenhu area in the South China Sea. A comparison of the changes in P- and S-waves, and a comprehensive analysis of geological factors within the area, enable analysis and description of the occurrence of natural gas hydrate in the study area. Results show an increase in P-wave velocity when natural gas hydrate exists in the formation, whereas the S-wave velocity remains almost constant, as S-waves can only propagate through the rock skeleton. Therefore, the bottom-simulating reflection (BSR) response of the P-wave is better than that of the S-wave in the frequency analysis profile. In a wide-angle section, the refractive wave of the hydrate layer is evident when using P-wave components but identification is difficult with S-wave components. This velocity model illustrates the sensitivity of P- and S-wave components to gas hydrate. The use of this polarization method and results of analysis provide technical and theoretical support for research on hydrate deposits and other geological features in the Shenhu area.

  18. 3D velocity distribution of P- and S-waves in a biotite gneiss, measured in oil as the pressure medium: Comparison with velocity measurements in a multi-anvil pressure apparatus and with texture-based calculated data

    Science.gov (United States)

    Lokajíček, T.; Kern, H.; Svitek, T.; Ivankina, T.

    2014-06-01

    Ultrasonic measurements of the 3D velocity distribution of P- and S-waves were performed on a spherical sample of a biotite gneiss from the Outokumpu scientific drill hole. Measurements were done at room temperature and pressures up to 400 and 70 MPa, respectively, in a pressure vessel with oil as a pressure medium. A modified transducer/sample assembly and the installation of a new mechanical system allowed simultaneous measurements of P- and S-wave velocities in 132 independent directions of the sphere on a net in steps of 15°. Proper signals for P- and S-waves could be recorded by coating the sample surface with a high-viscosity shear wave gel and by temporal point contacting of the transmitter and receiver transducers with the sample surface during the measurements. The 3D seismic measurements revealed a strong foliation-related directional dependence (anisotropy) of P- and S-wave velocities, which is confirmed by measurements in a multi-anvil apparatus on a cube-shaped specimen of the same rock. Both experimental approaches show a marked pressure sensitivity of P- and S-wave velocities and velocity anisotropies. With increasing pressure, P- and S-wave velocities increase non-linearly due to progressive closure of micro-cracks. The reverse is true for velocity anisotropy. 3D velocity calculations based on neutron diffraction measurements of crystallographic preferred orientation (CPO) of major minerals show that the intrinsic bulk anisotropy is basically caused by the CPO of biotite constituting about 23 vol.% of the rock. Including the shape of biotite grains and oriented low-aspect ratio microcracks into the modelling increases bulk anisotropy. An important finding from this study is that the measurements on the sample sphere and on the sample cube displayed distinct differences, particularly in shear wave velocities. It is assumed that the differences are due to the different geometries of the samples and the configuration of the transducer-sample assembly

  19. A new tomographic image on the Philippine Sea Slab beneath Tokyo - Implication to seismic hazard in the Tokyo metropolitan region -

    Science.gov (United States)

    Hirata, N.; Sakai, S.; Nakagawa, S.; Ishikawa, M.; Sato, H.; Kasahara, K.; Kimura, H.; Honda, R.

    2012-12-01

    In central Japan, the Philippine Sea plate (PSP) subducts beneath the Tokyo metropolitan region. Devastating M8-class earthquakes occurred on the upper surface of the Philippine Sea plate (SPS), examples of which are the Genroku earthquake of 1703 (magnitude M=8.0) and the Kanto earthquake of 1923 (M=7.9), which had 105,000 fatalities. A M7 or greater (M7+) earthquake in this region at present has high potential to produce devastating loss of life and property with even greater global economic repercussions although it is smaller than the megathrust type M8-class earthquakes. This great earthquake is evaluated to occur with a probability of 70 % in 30 years by the Earthquake Research Committee of Japan. The M7+ earthquakes may occur either on the upper surface or intra slab of PSP. The Central Disaster Management Council of Japan estimates the next great M7+ earthquake 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) 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

  20. Difference of horizontal-to-vertical spectral ratios of observed earthquakes and microtremors and its application to S-wave velocity inversion based on the diffuse field concept

    Science.gov (United States)

    Kawase, Hiroshi; Mori, Yuta; Nagashima, Fumiaki

    2018-01-01

    We have been discussing the validity of using the horizontal-to-vertical spectral ratios (HVRs) as a substitute for S-wave amplifications after Nakamura first proposed the idea in 1989. So far a formula for HVRs had not been derived that fully utilized their physical characteristics until a recent proposal based on the diffuse field concept. There is another source of confusion that comes from the mixed use of HVRs from earthquake and microtremors, although their wave fields are hardly the same. In this study, we compared HVRs from observed microtremors (MHVR) and those from observed earthquake motions (EHVR) at one hundred K-NET and KiK-net stations. We found that MHVR and EHVR share similarities, especially until their first peak frequency, but have significant differences in the higher frequency range. This is because microtremors mainly consist of surface waves so that peaks associated with higher modes would not be prominent, while seismic motions mainly consist of upwardly propagating plain body waves so that higher mode resonances can be seen in high frequency. We defined here the spectral amplitude ratio between them as EMR and calculated their average. We categorize all the sites into five bins by their fundamental peak frequencies in MHVR. Once we obtained EMRs for five categories, we back-calculated EHVRs from MHVRs, which we call pseudo-EHVRs (pEHVR). We found that pEHVR is much closer to EHVR than MHVR. Then we use our inversion code to invert the one-dimensional S-wave velocity structures from EHVRs based on the diffuse field concept. We also applied the same code to pEHVRs and MHVRs for comparison. We found that pEHVRs yield velocity structures much closer to those by EHVRs than those by MHVRs. This is natural since what we have done up to here is circular except for the average operation in EMRs. Finally, we showed independent examples of data not used in the EMR calculation, where better ground structures were successfully identified from p

  1. S-wave K- pi+ system in D+ ---> K- pi+ pi+ decays from Fermilab E791

    Energy Technology Data Exchange (ETDEWEB)

    Meadows, B.T.; /Cincinnati U.

    2005-06-01

    A new approach to the analysis of three body decays is presented. Model-independent results are obtained for the S-wave K{pi} amplitude as a function of K{pi} invariant mass. These are compared with results from K{sup -}{pi}{sup +} elastic scattering, and the prediction of the Watson theorem, that the phase behavior be the same below K{eta}' threshold, is tested. Contributions from I = 1/2 and I = 3/2 are not resolved in this study. If I = 1/2 dominates, however, the Watson theorem does not describe these data well.

  2. Charge independence, charge symmetry breaking in the S-wave nucleon-nucleon interaction, and renormalization

    Energy Technology Data Exchange (ETDEWEB)

    Alvaro Calle Cordon,Manuel Pavon Valderrama,Enrique Ruiz Arriola

    2012-02-01

    We study the interplay between charge symmetry breaking and renormalization in the NN system for S-waves. We find a set of universality relations which disentangle explicitly the known long distance dynamics from low energy parameters and extend them to the Coulomb case. We analyze within such an approach the One-Boson-Exchange potential and the theoretical conditions which allow to relate the proton-neutron, proton-proton and neutron-neutron scattering observables without the introduction of extra new parameters and providing good phenomenological success.

  3. The s-Wave Neutron Strength Function in the Deformed Region

    OpenAIRE

    Izumi, FURUOYA; Ryuzo, NAKASIMA; Department of Physics, Hosei University

    1983-01-01

    The effect of the doorway states on the s-wave neutron strength function of the deformed nucleus is examined. It is found that the shape of the 4-s giant resonance in the strength function is reproduced fairly well by both effects of the doorway states and the coupled channels. In particular, the irregular hump ranging from A=160 to A=170 cannot be interpreted by coupled channel calculation alone but by additional effect of the doorway states. As an example of the isotopic trend, the numerica...

  4. A compendium of P- and S-wave velocities from surface-to-borehole logging; summary and reanalysis of previously published data and analysis of unpublished data

    Science.gov (United States)

    Boore, David M.

    2003-01-01

    For over 28 years, the U.S. Geological Survey (USGS) has been acquiring seismic velocity and geologic data at a number of locations in California, many of which were chosen because strong ground motions from earthquakes were recorded at the sites. The method for all measurements involves picking first arrivals of P- and S-waves from a surface source recorded at various depths in a borehole (as opposed to noninvasive methods, such as the SASW method [e.g., Brown et al., 2002]). The results from most of the sites are contained in a series of U.S. Geological Survey Open-File Reports (see References). Until now, none of the results have been available as computer files, and before 1992 the interpretation of the arrival times was in terms of piecemeal interval velocities, with no attempt to derive a layered model that would fit the travel times in an overall sense (the one exception is Porcella, 1984). In this report I reanalyze all of the arrival times in terms of layered models for P- and for S-wave velocities at each site, and I provide the results as computer files. In addition to the measurements reported in the open-file reports, I also include some borehole results from other reports, as well as some results never before published. I include data for 277 boreholes (at the time of this writing; more will be added to the web site as they are obtained), all in California (I have data from boreholes in Washington and Utah, but these will be published separately). I am also in the process of interpreting travel time data obtained using a seismic cone penetrometer at hundreds of sites; these data can be interpreted in the same way of those obtained from surface-to-borehole logging. When available, the data will be added to the web site (see below for information on obtaining data from the World Wide Web (WWW)). In addition to the basic borehole data and results, I provide information concerning strong-motion stations that I judge to be close enough to the boreholes

  5. Dependence of s-waves on continuous dimension: The quantum oscillator and free systems

    Energy Technology Data Exchange (ETDEWEB)

    Wolf, K.B. [Centro de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, Apartado Postal 48-3, Cuernavaca, Morelos 62251 (Mexico); Aceves-de-la-Cruz, F. [Departamento de Fisica, CUCEI, Universidad de Guadalajara, Av. Revolucion 1500, Guadalajara, Jalisco 44430 (Mexico)

    2006-12-15

    Wavefunctions with rotational symmetry (i.e., zero angular momentum) in D dimensions, are called s-waves. In quantum quadratic systems (free particle, harmonic and repulsive oscillators), their radial parts obey Schroedinger equations with a fictitious centrifugal (for integer D{>=}4) or centripetal (for D = 2) potential. These Hamiltonians close into the three-dimensional Lorentz algebra so(2,1), whose exceptional interval corresponds to the critical range of continuous dimensions 0s-waves in D>0 dimensions. (Abstract Copyright [2006], Wiley Periodicals, Inc.)

  6. Single gap s-wave superconductivity in Nb{sub 2}PdS{sub 5}

    Energy Technology Data Exchange (ETDEWEB)

    Shruti [School of Physical Sciences, JNU, New Delhi (India); Goyal, R.; Awana, V.P.S. [CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012 (India); Patnaik, S., E-mail: spatnaik@mail.jnu.ac.in [School of Physical Sciences, JNU, New Delhi (India)

    2016-05-15

    Highlights: • In this paper, we report on pairing symmetry and superconducting gap in recently discovered superconductor Nb2PdS5. • This is a remarkable superconductor with highest ever reported Hc2/Tc ratio of ∼3. • In some theoretical studies, such effects have been ascribed to multiband effects and possible p-wave superconductivity. • However our penetration depth data is well ascribed to a single gap nodeless S-wave superconductivity. - Abstract: Superconducting order parameter and its symmetry are important parameters towards deciphering the pairing mechanism in newly discovered superconducting systems. We report a study on penetration depth measurement on Nb{sub 2}PdS{sub 5} that has recently been reported with extremely high upper critical field with possible triplet pairing mechanism. Our data show that at low temperatures the change in penetration depth Δλ is best fitted with BCS s-wave model for single gap with zero-temperature value of the superconducting energy gap Δ{sub 0} = 1.05 meV, corresponding to the ratio 2Δ{sub 0}/k{sub B}T{sub c} = 3.9 ± 0.18. The superfluid density in the entire temperature range is well described by single gap with gap ratio 2Δ{sub 0}/k{sub B}T{sub c} = 4.1 ± 0.13 for λ(0) = 225 nm.

  7. Relativistic corrections to the form factors of Bc into S -wave charmonium

    Science.gov (United States)

    Zhu, Ruilin; Ma, Yan; Han, Xin-Ling; Xiao, Zhen-Jun

    2017-05-01

    We investigate the form factors of Bc meson into S -wave charmonium within the nonrelativistic QCD effective theory and obtain the next-to-leading order relativistic corrections to the form factors, where both the Bc meson and the charmonium are treated as the nonrelativistic bound states. Treating the charm quark as a light quark in the limit mc/mb→0 , some form factors are identical at the maximum recoil point, which are consistent with the predictions in the heavy-quark effective theory and the large-energy effective theory. Considering that the branching ratios of Bc+→J /ψ Ds+ and Bc+→J /ψ Ds*+ have been measured by the LHCb and ATLAS Collaborations recently, we employ the form factors of Bc meson into S -wave charmonium at the next-to-leading order accuracy to these two decay channels and obtain more precise predictions of their decay rates. Numerical results indicate that the factorizable diagrams dominate the contribution in these two channels, while the color-suppressed and the annihilation diagrams contribute less than 10 percent. Our results are consistent with the LHCb and ATLAS data.

  8. Extended s-wave superfluid of repulsively interacting three-component fermionic atoms in optical lattices

    Science.gov (United States)

    Suga, Sei-Ichiro; Inaba, Kensuke

    2014-03-01

    We investigate pairing symmetry of the superfluid state in repulsively interacting three-component (colors) fermionic atoms in optical lattices. This superfluid state appears, when two of the color-dependent three repulsions are much stronger than the other close to half filling. We evaluate the effective pairing interaction by collecting random-phase-approximation-type diagrams and ladder diagrams, and solve the Eliashberg equation within weak-coupling theory in square optical lattices. We find that pairing symmetry is an extended s-wave, although in the phase diagram the superfluid state is adjacent to the color-density wave or paired Mott insulator at half filling. The k-dependence of the superfluid order parameter is caused by quantum fluctuations of the staggered color-density wave. When the difference in the three repulsions is decreased, paring symmetry changes from an extended s-wave to a d-wave. We expect 6Li, 171Yb, 173Yb atoms and their mixtures in optical lattices to be possible candidates for observing this superfluid state. This work was supported by Grants-in-Aid for Scientific Research (C) (No. 23540467) and (B) (No. 25287104) from the Japan Society for the Promotion of Science.

  9. Adjoint tomography of the crust and upper mantle structure beneath the Kanto region using broadband seismograms

    KAUST Repository

    Miyoshi, Takayuki

    2017-10-04

    A three-dimensional seismic wave speed model in the Kanto region of Japan was developed using adjoint tomography for application in the effective reproduction of observed waveforms. Starting with a model based on previous travel time tomographic results, we inverted the waveforms obtained at seismic broadband stations from 140 local earthquakes in the Kanto region to obtain the P- and S-wave speeds Vp and Vs. Additionally, all centroid times of the source solutions were determined before the structural inversion. The synthetic displacements were calculated using the spectral-element method (SEM) in which the Kanto region was parameterized using 16 million grid points. The model parameters Vp and Vs were updated iteratively by Newton’s method using the misfit and Hessian kernels until the misfit between the observed and synthetic waveforms was minimized. Computations of the forward and adjoint simulations were conducted on the K computer in Japan. The optimized SEM code required a total of 6720 simulations using approximately 62,000 node hours to obtain the final model after 16 iterations. The proposed model reveals several anomalous areas with extremely low-Vs values in comparison with those of the initial model. These anomalies were found to correspond to geological features, earthquake sources, and volcanic regions with good data coverage and resolution. The synthetic waveforms obtained using the newly proposed model for the selected earthquakes showed better fit than the initial model to the observed waveforms in different period ranges within 5–30 s. This result indicates that the model can accurately predict actual waveforms.

  10. Adjoint tomography of the crust and upper mantle structure beneath the Kanto region using broadband seismograms

    Science.gov (United States)

    Miyoshi, Takayuki; Obayashi, Masayuki; Peter, Daniel; Tono, Yoko; Tsuboi, Seiji

    2017-12-01

    A three-dimensional seismic wave speed model in the Kanto region of Japan was developed using adjoint tomography for application in the effective reproduction of observed waveforms. Starting with a model based on previous travel time tomographic results, we inverted the waveforms obtained at seismic broadband stations from 140 local earthquakes in the Kanto region to obtain the P- and S-wave speeds V p and V s . Additionally, all centroid times of the source solutions were determined before the structural inversion. The synthetic displacements were calculated using the spectral-element method (SEM) in which the Kanto region was parameterized using 16 million grid points. The model parameters V p and V s were updated iteratively by Newton's method using the misfit and Hessian kernels until the misfit between the observed and synthetic waveforms was minimized. Computations of the forward and adjoint simulations were conducted on the K computer in Japan. The optimized SEM code required a total of 6720 simulations using approximately 62,000 node hours to obtain the final model after 16 iterations. The proposed model reveals several anomalous areas with extremely low- V s values in comparison with those of the initial model. These anomalies were found to correspond to geological features, earthquake sources, and volcanic regions with good data coverage and resolution. The synthetic waveforms obtained using the newly proposed model for the selected earthquakes showed better fit than the initial model to the observed waveforms in different period ranges within 5-30 s. This result indicates that the model can accurately predict actual waveforms. [Figure not available: see fulltext.

  11. Combined teleseismic imaging of the structure of southern African cratons using P-receiver functions and P-and S-finite-frequency tomography

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Thybo, Hans; Levander, Alan

    2011-01-01

    We present a seismic model of the South-African cratonic region obtained by combining receiver functions and teleseismic P and S traveltime tomography. We determined receiver functions (RFs) for 82 stations by iterative deconvolution. Based on HK analysis (Zhou and Kananmori, JGR,2001), we measure...... bands (1, 0.5 and 0.25 Hz for P and 0.1, 0.05 and 0.02 Hz for S) to obtain 3-D P- and S-wave perturbation models for the upper mantle. Crustal corrections are based on the RF models. Tests showed that our dataset is able to resolve structure of 3°x3° up to 400 km depth. The high-velocity cratonic roots...... extend to 300-350 km depth. Lower velocities are detected below the Bushveld complex and the mobile belts. The model also suggests a stratified structure, since we found a low velocity zone (LVZ) at about 170 km depth in the cratonic areas. SdP RFs and surface-wave tomography are in progress and should...

  12. 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

    for the recent moderate size earthquakes and the results are in an agreement with paleo-trenching data showing normal fault mechanism on the south and strake slip on the northern edge of the fault. Local seismic tomography of Javakheti area has been performed in order to improve 3D structure of the region.

  13. Advanced Seismic While Drilling System

    Energy Technology Data Exchange (ETDEWEB)

    Robert Radtke; John Fontenot; David Glowka; Robert Stokes; Jeffery Sutherland; Ron Evans; Jim Musser

    2008-06-30

    . An APS Turbine Alternator powered the SeismicPULSER{trademark} to produce two Hz frequency peak signals repeated every 20 seconds. Since the ION Geophysical, Inc. (ION) seismic survey surface recording system was designed to detect a minimum downhole signal of three Hz, successful performance was confirmed with a 5.3 Hz recording with the pumps running. The two Hz signal generated by the sparker was modulated with the 3.3 Hz signal produced by the mud pumps to create an intense 5.3 Hz peak frequency signal. The low frequency sparker source is ultimately capable of generating selectable peak frequencies of 1 to 40 Hz with high-frequency spectra content to 10 kHz. The lower frequencies and, perhaps, low-frequency sweeps, are needed to achieve sufficient range and resolution for realtime imaging in deep (15,000 ft+), high-temperature (150 C) wells for (a) geosteering, (b) accurate seismic hole depth, (c) accurate pore pressure determinations ahead of the bit, (d) near wellbore diagnostics with a downhole receiver and wired drill pipe, and (e) reservoir model verification. Furthermore, the pressure of the sparker bubble will disintegrate rock resulting in an increased overall rates of penetration. Other applications for the SeismicPULSER{trademark} technology are to deploy a low-frequency source for greater range on a wireline for Reverse Vertical Seismic Profiling (RVSP) and Cross-Well Tomography. Commercialization of the technology is being undertaken by first contacting stakeholders to define the value proposition for rig site services utilizing SeismicPULSER{trademark} technologies. Stakeholders include national oil companies, independent oil companies, independents, service companies, and commercial investors. Service companies will introduce a new Drill Bit SWD service for deep HTHP wells. Collaboration will be encouraged between stakeholders in the form of joint industry projects to develop prototype tools and initial field trials. No barriers have been identified

  14. Estimation of S-wave site response in and around Delhi region from ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Unless otherwise men- tioned, the site amplification SAF will mean those computed using SSR (standard or normalized) and. GINV from horizontal component amplitude spec- tra only. 4. Results and discussion. The recent sequence of earthquakes has highlighted the level of seismic hazard and vulnerability of the. Table 2.

  15. Seismologic study of Los Humeros geothermal field, Puebla, Mexico. Part II: Seismic tomography by attenuation of coda waves (Qc-1) of local earthquakes; Estudio sismologico del campo geotermico de Los Humeros, Puebla, Mexico. Parte II: Tomografia sismica por atenuacion a partir de ondas de coda (Qc-1) de sismos locales

    Energy Technology Data Exchange (ETDEWEB)

    Antayhua, Yanet; Lermo, Javier [Instituto de Ingenieria, Universidad Nacional Autonoma de Mexico, D.F (Mexico); Carlos, Vargas [Departamento de Geociencias, Universidad Nacional de Colombia (Colombia)]. E-mail: jles@pumas.iingen.unam.mx

    2008-07-15

    In the Los Humeros geothermal field, Puebla, seismic tomography has been studied using the attenuation of coda waves (Qc{sup -1}). Ninety-five local earthquakes (Md{<=}3.6) have been used with depths up to 4.0 km registered in the seismic network stations from December 1997 to December 2004. A simple backscattering model was used, filtered in four ranks of frequencies (2, 4, 6, and 8 Hz) and one window of 5 seconds. For the 3D-representation, we used an approximation based on first-order scattering of ellipsoids. The results show that values of Qc for the used frequencies have a frequency dependency shown in the equation: Qc=24{+-}12f{sup 0.86}{+-}{sup 0.06}, where the low values of Qc were observed in the zone of higher seismic and tectonic activity and in the location of injection and production wells. The high values are located in the periphery of the geothermal field. The distribution of the Qc{sup -1} attenuation in 3D and 2D shows the anomalies of high-seismic attenuation are located in the north, south, and southwestern ends of the zone presently under operation, at depths greater than 2.5 km. [Spanish] Para realizar la tomografia sismica por atenuacion de ondas de coda (Qc{sup -1}) en el campo geotermico de Los Humeros, Puebla, se han utilizado 95 sismos locales (Md{<=}3.6) con profundidades hasta 4.0 km, registrados en las estaciones de su red sismica, durante el periodo de diciembre 1997 a diciembre 2004. Se utilizo el modelo de retrodispersion simple, filtrados en cuatro rangos de frecuencias (2, 4, 6, y 8 Hz) y una ventana de 5 segundos. Para la representacion en 3D, se utilizo una aproximacion basada en elipsoides que representan dispersion de primer orden. Los resultados muestran que los valores de Qc para las frecuencias utilizadas tienen una dependencia con la frecuencia de la forma: Qc=24{+-}12f{sup 0.86}{+-}{sup 0.06}, donde los valores bajos de Qc fueron observados en la zona de mayor actividad sismica y en la ubicacion de pozos inyectores y

  16. Analytical calculation for the gluon fragmentation into spin-triplet S -wave quarkonium

    Science.gov (United States)

    Zhang, Peng; Ma, Yan-Qing; Chen, Qian; Chao, Kuang-Ta

    2017-11-01

    Fragmentation is the dominant mechanism for hadron production with high transverse momentum. For spin-triplet S -wave heavy quarkonium production, contribution of gluon fragmenting to color-singlet channel has been numerically calculated since 1993. However, there is still no analytic expression available up to now because of its complexity. In this paper, we calculate both polarization-summed and polarized fragmentation functions of gluon fragmenting to a heavy quark-antiquark pair with quantum number S3 1 [1 ] . Our calculations are performed in two different frameworks. One is the widely used nonrelativistic QCD factorization, and the other is the newly proposed soft gluon factorization. In either case, we calculate at both leading order and next-to-leading order in velocity expansion. All of our final results are presented in terms of compact analytic expressions.

  17. Upper mantle thermal variations beneath the Transantarctic Mountains inferred from teleseismic S-wave attenuation

    Science.gov (United States)

    Lawrence, Jesse F.; Wiens, Douglas A.; Nyblade, Andrew A.; Anandakrishan, Sridhar; Shore, Patrick J.; Voigt, Donald

    2006-02-01

    This study examines teleseismic S-wave attenuation variations between the Ross Sea in West Antarctica and Vostok Subglacial Highlands in East Antarctica. These analyses indicate that δt* is ~1 second greater beneath the Ross Sea than East Antarctica, with the transition occurring beneath the Transantarctic Mountains. While the structure is non-unique, low attenuation beneath East Antarctica is consistent with thick subcontinental lithosphere (>=250 km) and negligible asthenosphere. In contrast, the Ross Sea possesses a thin lithosphere underlain by thick, highly anelastic asthenosphere. Independent temperature estimates from velocity and quality factor indicate that the mantle is 200-400°C colder beneath East Antarctica than the Ross Sea between 80 and 220 km depth. The temperature variation beneath the Transantarctic Mountains may have assisted in the asymmetric uplift of the mountains. Attenuation and velocity anomalies within East Antarctica may delineate regions of elevated temperature, representing recently modified sections between older lithospheric blocks.

  18. Dynamical Shiba states from precessing magnetic moments in an s -wave superconductor

    Science.gov (United States)

    Kaladzhyan, Vardan; Hoffman, Silas; Trif, Mircea

    2017-05-01

    We study theoretically the dynamics of a Shiba state forming around precessing classical spin in an s -wave superconductor. Utilizing a rotating wave description for the precessing magnetic impurity, we find the resulting Shiba bound state quasienergy and the spatial extension of the Shiba wave function. We show that such a precession pertains to dc charge and spin currents flowing through a normal STM tip tunnel coupled to the superconductor in the vicinity of the impurity. We calculate these currents and find that they strongly depend on the magnetic impurity precession frequency, precession angle, and on the position of the Shiba energy level in the superconducting gap. The resulting charge current is found to be proportional to the difference between the electron and hole wave functions of the Shiba state, being a direct measure for such an asymmetry. By dynamically driving the impurity one can infer the spin dependence of the Shiba states in the absence of a spin-polarized STM tip.

  19. Reflection imaging of the Moon's interior using deep-moonquake seismic interferometry

    NARCIS (Netherlands)

    Nishitsuji, Y.; Rowe, CA; Wapenaar, C.P.A.; Draganov, D.S.

    2016-01-01

    The internal structure of the Moon has been investigated over many years using a variety of seismic methods, such as travel time analysis, receiver functions, and tomography. Here we propose to apply body-wave seismic interferometry to deep moonquakes in order to retrieve zero-offset reflection

  20. Bayesian inference of Earth's radial seismic structure from body-wave traveltimes using neural networks

    NARCIS (Netherlands)

    de Wit, R.W.L.; Valentine, A.P.; Trampert, J.

    2013-01-01

    How do body-wave traveltimes constrain the Earth's radial (1-D) seismic structure? Existing 1-D seismological models underpin 3-D seismic tomography and earthquake location algorithms. It is therefore crucial to assess the quality of such 1-D models, yet quantifying uncertainties in seismological

  1. Global imaging of the Earth's deep interior: seismic constraints on (an)isotropy, density and attenuation

    NARCIS (Netherlands)

    Trampert, J.; Fichtner, A.

    2013-01-01

    Seismic tomography is the principal tool to probe the deep interior of the Earth. Models of seismic anisotropy induced by crystal alignment provide insight into the underlying convective motion, and variations of density allow us to discriminate between thermal and compositional heterogeneities.

  2. Measurements of Seismic Anisotropy in Synthetic Rocks with Controlled Crack Geometry and Different Crack Densities

    Science.gov (United States)

    Ding, Pinbo; Di, Bangrang; Wang, Ding; Wei, Jianxin; Li, Xiangyang

    2017-05-01

    Seismic anisotropy can help to extract azimuthal information for predicting crack alignment, but the accurate evaluation of cracked reservoir requires knowledge of degree of crack development, which is achieved through determining the crack density from seismic or VSP data. In this research we study the dependence of seismic anisotropy on crack density, using synthetic rocks with controlled crack geometries. A set of four synthetic rocks containing different crack densities is used in laboratory measurements. The crack thickness is 0.06 mm and the crack diameter is 3 mm in all the cracked rocks, while the crack densities are 0.00, 0.0243, 0.0486, and 0.0729. P and S wave velocities are measured by an ultrasonic investigation system at 0.5 MHz while the rocks are saturated with water. The measurements show the impact of crack density on the P and S wave velocities. Our results are compared to the theoretical prediction of Chapman (J App Geophys 54:191-202, 2003) and Hudson (Geophys J R Astron Soc 64:133-150, 1981). The comparison shows that measured velocities and theoretical results are in good quantitative agreement in all three cracked rocks, although Chapman's model fits the experimental results better. The measured anisotropy of the P and S wave in the four synthetic rocks shows that seismic anisotropy is directly proportional to increasing crack density, as predicted by several theoretical models. The laboratory measurements indicate that it would be effective to use seismic anisotropy to determine the crack density and estimate the intensity of crack density in seismology and seismic exploration.

  3. Robotization in Seismic Acquisition

    NARCIS (Netherlands)

    Blacquière, G.; Berkhout, A.J.

    2013-01-01

    The amount of sources and detectors in the seismic method follows "Moore’s Law of seismic data acquisition", i.e., it increases approximately by a factor of 10 every 10 years. Therefore automation is unavoidable, leading to robotization of seismic data acquisition. Recently, we introduced a new

  4. S-wave triggering of tremor beneath the Parkfield, California, section of the San Andreas fault by the 2011 Tohoku, Japan earthquake: observations and theory

    Science.gov (United States)

    Hill, David P.; Peng, Zhigang; Shelly, David R.; Aiken, Chastity

    2013-01-01

    The dynamic stresses that are associated with the energetic seismic waves generated by the Mw 9.0 Tohoku earthquake off the northeast coast of Japan triggered bursts of tectonic tremor beneath the Parkfield section of the San Andreas fault (SAF) at an epicentral distance of ∼8200  km. The onset of tremor begins midway through the ∼100‐s‐period S‐wave arrival, with a minor burst coinciding with the SHSH arrival, as recorded on the nearby broadband seismic station PKD. A more pronounced burst coincides with the Love arrival, followed by a series of impulsive tremor bursts apparently modulated by the 20‐ to 30‐s‐period Rayleigh wave. The triggered tremor was located at depths between 20 and 30 km beneath the surface trace of the fault, with the burst coincident with the S wave centered beneath the fault 30 km northwest of Parkfield. Most of the subsequent activity, including the tremor coincident with the SHSH arrival, was concentrated beneath a stretch of the fault extending from 10 to 40 km southeast of Parkfield. The seismic waves from the Tohoku epicenter form a horizontal incidence angle of ∼14°, with respect to the local strike of the SAF. Computed peak dynamic Coulomb stresses on the fault at tremor depths are in the 0.7–10 kPa range. The apparent modulation of tremor bursts by the small, strike‐parallel Rayleigh‐wave stresses (∼0.7  kPa) is likely enabled by pore pressure variations driven by the Rayleigh‐wave dilatational stress. These results are consistent with the strike‐parallel dynamic stresses (δτs) associated with the S, SHSH, and surface‐wave phases triggering small increments of dextral slip on the fault with a low friction (μ∼0.2). The vertical dynamic stresses δτd do not trigger tremor with vertical or oblique slip under this simple Coulomb failure model.

  5. Urban shear-wave reflection seismics: Reconstruction support by combined shallow seismic and engineering geology investigations

    Science.gov (United States)

    Polom, U.; Guenther, A.; Arsyad, I.; Wiyono, P.; Krawczyk, C. M.

    2009-12-01

    After the big 2004 Sumatra-Andaman earthquake, the massive reconstruction activities in the Aceh province (Northern Sumatra) were promoted by the Republic of Indonesia and the Federal Ministry of Economic Cooperation and Development. The aims of the project MANGEONAD (Management of Georisk Nanggroe Aceh Darussalam). are to establish geoscientific on the ground support for a sustainable development and management of save building constructions, lifelines, infrastructure and also natural resources. Therefore, shallow shear-wave reflection seismics was applied in close combination to engineering geology investigations in the period between 2005-2009 since depth and internal structure of the Krueng Aceh River delta (mainly young alluvial sediments) were widely unknown. Due to the requirements in the densely populated Banda Aceh region, lacking also traffic infrastructure, a small and lightweight engineering seismic setup of high mobility and high subsurface resolution capability was chosen. The S-wave land streamer system with 48 channels was applied successfully together with the ELVIS vibratory source using S- and P-waves on paved roads within the city of Banda Aceh. The performance of the S-wave system enabled the detailed seismic investigation of the shallow subsurface down to 50-150 m depth generating shaking frequencies between 20 Hz to 200 Hz. This also provides depth information extending the maximum depths of boreholes and Standard Penetrometer Testings (SPT), which could only be applied to max. 20 m depth. To integrate the results gained from all three methods, and further to provide a fast statistical analysis tool for engineering use, the Information System Engineering Geology (ISEG, BGR) was developed. This geospatial information tool includes the seismic data, all borehole information, geotechnical SPT and laboratory results from samples available in the investigation area. Thereby, the geotechnical 3D analysis of the subsurface units is enabled. The

  6. Integrated seismic tools to delineate Pliocene gas-charged geobody, offshore west Nile delta, Egypt

    Science.gov (United States)

    Othman, Adel A. A.; Bakr, Ali; Maher, Ali

    2017-06-01

    Nile delta province is rapidly emerging as a major gas province; commercial gas accumulations have been proved in shallow Pliocene channels of El-Wastani Formation. Solar gas discovery is one of the Turbidities Slope channels within the shallow Pliocene level that was proved by Solar-1 well. The main challenge of seismic reservoir characterization is to discriminate between Gas sand, Water sand and Shale, and extracting the gas-charged geobody from the seismic data. A detailed study for channel connectivity and lithological discrimination was established to delineate the gas charged geobody. Seismic data, being non-stationary in nature, have varying frequency content in time. Spectral decomposition of a seismic signal aims to characterize the time-dependent frequency response of subsurface rocks and reservoirs for imaging and mapping of bed thickness and geologic discontinuities. Spectral decomposition unravels the seismic signal into its constituent frequencies. A crossplot between P-wave Impedance (Ip) and S-wave Impedance (Is) derived from well logs (P-wave velocity, S-wave velocity and density) can be used to discriminate between gas-bearing sand, water-bearing sand, and shale. From Ip vs. Is crossplot, clear separation occurs in the P-impedance so post stack inversion is enough to be applied. Integration between Inversion results and Ip vs. Is crossplot cutoffs help to generate 3D lithofacies cubes, which is used to extract facies geobodies.

  7. S-wave \\gamma\\gamma\\to \\pi\\pi and f_0(980)\\to \\pi\\pi

    OpenAIRE

    Oller, J. A.; Roca, L.; Schat, C.

    2008-01-01

    We report on a dispersion relation for the \\gamma\\gamma\\to (\\pi\\pi)_I S-wave in isospin I emphasizing the low energy region. The f_0(980) signal that emerges in \\gamma\\gamma\\to \\pi\\pi is also discussed. Our results could be used to distinguish between different \\pi\\pi isoscalar S-wave parameterizations. We also calculate the width of the \\sigma resonance to \\gamma\\gamma and obtain the value \\Gamma(\\sigma\\to\\gamma\\gamma)=(1.68\\pm 0.15) KeV. Finally, we elaborate on the size of the f_0(980) cou...

  8. Using micro-seismicity and seismic velocities to map subsurface geologic and hydrologic structure within the Coso geothermal field, California

    Science.gov (United States)

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

    2012-01-01

    Geothermal reservoirs derive their capacity for fluid and heat transport in large part from faults and fractures. Micro-seismicity generated on such faults and fractures can be used to map larger fault structures as well as secondary fractures that add access to hot rock, fluid storage and recharge capacity necessary to have a sustainable geothermal resource. Additionally, inversion of seismic velocities from micro-seismicity permits imaging of regions subject to the combined effects of fracture density, fluid pressure and steam content, among other factors. We relocate 14 years of seismicity (1996-2009) in the Coso geothermal field using differential travel times and simultaneously invert for seismic velocities to improve our knowledge of the subsurface geologic and hydrologic structure. We utilize over 60,000 micro-seismic events using waveform cross-correlation to augment to expansive catalog of P- and S-wave differential travel times recorded at Coso. We further carry out rigorous uncertainty estimation and find that our results are precise to within 10s of meters of relative location error. We find that relocated micro-seismicity outlines prominent, through-going faults in the reservoir in some cases. We also find that a significant portion of seismicity remains diffuse and does not cluster into more sharply defined major structures. The seismic velocity structure reveals heterogeneous distributions of compressional (Vp) and shear (Vs) wave speed, with Vp generally lower in the main field when compared to the east flank and Vs varying more significantly in the shallow portions of the reservoir. The Vp/Vs ratio appears to outline the two main compartments of the reservoir at depths of -0.5 to 1.5 km (relative to sea-level), with a ridge of relatively high Vp/Vs separating the main field from the east flank. In the deeper portion of the reservoir this ridge is less prominent. Our results indicate that high-precision relocations of micro-seismicity can provide

  9. Upper Mississippi embayment shallow seismic velocities measured in situ

    Science.gov (United States)

    Liu, Huaibao P.; Hu, Y.; Dorman, J.; Chang, T.-S.; Chiu, J.-M.

    1997-01-01

    Vertical seismic compressional- and shear-wave (P- and S-wave) profiles were collected from three shallow boreholes in sediment of the upper Mississippi embayment. The site of the 60-m hole at Shelby Forest, Tennessee, is on bluffs forming the eastern edge of the Mississippi alluvial plain. The bluffs are composed of Pleistocene loess, Pliocene-Pleistocene alluvial clay and sand deposits, and Tertiary deltaic-marine sediment. The 36-m hole at Marked Tree, Arkansas, and the 27-m hole at Risco, Missouri, are in Holocene Mississippi river floodplain sand, silt, and gravel deposits. At each site, impulsive P- and S-waves were generated by man-made sources at the surface while a three-component geophone was locked downhole at 0.91-m intervals. Consistent with their very similar geology, the two floodplain locations have nearly identical S-wave velocity (VS) profiles. The lowest VS values are about 130 m s-1, and the highest values are about 300 m s-1 at these sites. The shear-wave velocity profile at Shelby Forest is very similar within the Pleistocene loess (12m thick); in deeper, older material, VS exceeds 400 m s-1. At Marked Tree, and at Risco, the compressional-wave velocity (VP) values above the water table are as low as about 230 m s-1, and rise to about 1.9 km s-1 below the water table. At Shelby Forest, VP values in the unsaturated loess are as low as 302 m s-1. VP values below the water table are about 1.8 km s-1. For the two floodplain sites, the VP/VS ratio increases rapidly across the water table depth. For the Shelby Forest site, the largest increase in the VP/VS ratio occurs at ???20-m depth, the boundary between the Pliocene-Pleistocene clay and sand deposits and the Eocene shallow-marine clay and silt deposits. Until recently, seismic velocity data for the embayment basin came from earthquake studies, crustal-scale seismic refraction and reflection profiles, sonic logs, and from analysis of dispersed earthquake surface waves. Since 1991, seismic data

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

    Science.gov (United States)

    Nielsen, Lars; Thybo, Hans; Jørgensen, Mette I.

    2005-08-01

    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 recorded seismic signals in a fan geometry from shots detonated both inside the low-velocity fault zone and up to ~500 m away from the fault zone. The seismic energy was recorded on three receiver arrays (1.5- to 2.4-km-long arcs) across the expected location of the ~400- to 700-m-wide fault zone at distances of up to ~7 km from the shots. Shots detonated inside the fault zone result in (1) weak and delayed first arrivals on the receivers located inside the fault zone compared to earlier and stronger first arrivals outside the fault zone; (2) strong guided P and S waves as well as surface waves inside 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 incidence and refraction profiling are not feasible.

  11. 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.

  12. Type-I and type-II topological nodal superconductors with s -wave interaction

    Science.gov (United States)

    Huang, Beibing; Yang, Xiaosen; Xu, Ning; Gong, Ming

    2018-01-01

    Topological nodal superconductors with protected gapless points in momentum space are generally realized based on unconventional pairings. In this work we propose a minimal model to realize these topological nodal phases with only s -wave interaction. In our model the linear and quadratic spin-orbit couplings along the two orthogonal directions introduce anisotropic effective unconventional pairings in momentum space. This model may support different nodal superconducting phases characterized by either an integer winding number in BDI class or a Z2 index in D class at the particle-hole invariant axes. In the vicinity of the nodal points the effective Hamiltonian can be described by either type-I or type-II Dirac equations, and the Lifshitz transition from type-I nodal phases to type-II nodal phases can be driven by external in-plane magnetic fields. We show that these nodal phases are robust against weak impurities, which only slightly renormalizes the momentum-independent parameters in the impurity-averaged Hamiltonian, thus these phases are possible to be realized in experiments with real semi-Dirac materials. The smoking-gun evidences to verify these phases based on scanning tunneling spectroscopy method are also briefly discussed.

  13. Region-specific S-wave attenuation for earthquakes in northwestern Iran

    Science.gov (United States)

    Heidari, Reza; Mirzaei, Noorbakhsh

    2017-11-01

    In this study, continuous wavelet transform is applied to estimate the frequency-dependent quality factor of shear waves, Q S , in northwestern Iran. The dataset used in this study includes velocigrams of more than 50 events with magnitudes between 4.0 and 6.5, which have occurred in the study area. The CWT-based method shows a high-resolution technique for the estimation of S-wave frequency-dependent attenuation. The quality factor values are determined in the form of a power law as Q S ( f) = (147 ± 16) f 0.71 ± 0.02 and (126 ± 12) f 0.73 ± 0.02 for vertical and horizontal components, respectively, where f is between 0.9 and 12 Hz. Furthermore, in order to verify the reliability of the suggested Q S estimator method, an additional test is performed by using accelerograms of Ahar-Varzaghan dual earthquakes on August 11, 2012, of moment magnitudes 6.4 and 6.3 and their aftershocks. Results indicate that the estimated Q S values from CWT-based method are not very sensitive to the numbers and types of waveforms used (velocity or acceleration).

  14. Electrodynamics of s-Wave Superconductors Using First-Order Formalism

    Directory of Open Access Journals (Sweden)

    Naoum Karchev

    2017-06-01

    Full Text Available In this paper we give a derivation of a system of equations which generalize the London brothers and Ginzburg–Landau systems of equations, to describe the electrodynamics of s-wave superconductors. First, we consider a relativistically covariant theory in terms of gauge four-vector electromagnetic potential and scalar complex field. We use the first-order formalism to obtain the supplemented Maxwell equations for gauge-invariant electric, magnetic, four-vector fields and the modulus of the superconducting order parameter. The new four-vector field appears in some of the equations as a gauge-invariant super-current, and in other ones, while gauge invariant, as a four-vector electromagnetic potential. This dual contribution of the new four-vector field is the basis of the electrodynamics of superconductors. We focus on the system of equations with time-independent fields. The qualitative analysis shows that the applied magnetic field suppresses the superconductivity, while the applied electric field impacts oppositely, supporting it. Secondly, we consider time-dependent non-relativistic Ginzburg–Landau theory.

  15. Determination of the pion-nucleon coupling constant and s-wave scattering lengths

    CERN Document Server

    Samaranayake, V K

    1972-01-01

    Presently available values of D/sub +or-/, the real parts of the pi /sup +or-/p elastic scattering amplitudes in the forward direction in the laboratory frame, obtained by extrapolation of experimental data to the forward direction, have been fitted up to a pion lab. kinetic energy of 2 GeV using forward dispersion relation. A substantial number of data points have to be discarded to obtain a reasonable goodness of fit. Above 300 MeV the values of D/sub +or-/ obtained from the CERN phase shift analysis are strongly favoured compared with those from the Saclay analysis. The final results for the pion-nucleon coupling constant and s-wave scattering lengths are: 10/sup 3/f/sup 2 /=76.3+or-2.0, 10/sup 3/D/sub +/( mu )=-102.4+or-5.2, 10/sup 3/D/sub - /( mu )=104.8+or-5.4, 10/sup 3/(a/sub 1/-a/sub 3/)=270.6+or-11.3, 10 /sup 3/(a/sub 1/+2a/sub 3/)=3.1+or-8.0. The errors quoted take account of experimental uncertainties and also attempt to include systematic errors arising from the unphysical continuum and from the v...

  16. Symmetry reduction and boundary modes for Fe chains on an s-wave superconductor.

    Science.gov (United States)

    Chen, Yu-Qin; Wu, Yi-Ming; Liu, Xiong-Jun

    2016-11-30

    We investigate the superconducting phases and boundary modes for a quasi-1D system formed by up to three Fe chains on an s-wave superconductor, motivated by a recent experiment. While the Rashba type spin-orbit coupling together with a magnetic ordering is necessary to drive the system to be of nontrivial topology, we show that the onsite [Formula: see text] spin-orbit term, inter-chain diagonal hopping couplings, and magnetic disorders in the Fe chains are crucial in determining the symmetry classes of superconducting phases, which can be topologically trivial or nontrivial in different parameter regimes. In general multiple low-energy Andreev bound states, as well as a single Majorana zero mode if the phase is topological, are obtained in the ends of Fe chains. The nontrivial symmetry reduction mechanism is uncovered to provide an understanding of the present results, and may explain the zero-bias peak observed in the experiment. The present study can be applied to generic multiple-chain system.

  17. Relationship between the focal mechanism of magnitude ML 3.3 seismic event induced by mining and distribution of peak ground velocity

    Directory of Open Access Journals (Sweden)

    Dubiński Józef

    2017-01-01

    Full Text Available The relationship between seismic radiation pattern generated by a strong mining induced seismic event and the distribution of peak ground velocity in the epicenter area has been presented. It was a seismic event with the local magnitude ML = 3.3 occurred on June 21, 2016 in the Upper Silesian Coal Basin (USCB in Marcel Mine. Calculated values of the peak ground velocity, taking into account the amplification coefficient, were the basis for the development of the PGVHamp map. The resulting distribution of PGVHamp isolines and the measured velocity amplitudes point to significant differences. That fact indicates that some additional factors can impact on the seismic effect observed on the surface. One of them could be a focal mechanism of seismic event. Focal mechanism of the M=3.3 induced seismic tremor, were calculated by the moment tensor inversion method. The tremor was characterized by a normal slip mechanism with 87% shear component. Comparison of seismic pattern for S-wave at individual stations allowed confirms a relation between directionality of the seismic radiation pattern for S-wave and the recorded peak ground velocities and explain the observed anomaly.

  18. Relationship between the focal mechanism of magnitude ML 3.3 seismic event induced by mining and distribution of peak ground velocity

    Science.gov (United States)

    Dubiński, Józef; Stec, Krystyna; Mutke, Grzegorz

    2017-11-01

    The relationship between seismic radiation pattern generated by a strong mining induced seismic event and the distribution of peak ground velocity in the epicenter area has been presented. It was a seismic event with the local magnitude ML = 3.3 occurred on June 21, 2016 in the Upper Silesian Coal Basin (USCB) in Marcel Mine. Calculated values of the peak ground velocity, taking into account the amplification coefficient, were the basis for the development of the PGVHamp map. The resulting distribution of PGVHamp isolines and the measured velocity amplitudes point to significant differences. That fact indicates that some additional factors can impact on the seismic effect observed on the surface. One of them could be a focal mechanism of seismic event. Focal mechanism of the M=3.3 induced seismic tremor, were calculated by the moment tensor inversion method. The tremor was characterized by a normal slip mechanism with 87% shear component. Comparison of seismic pattern for S-wave at individual stations allowed confirms a relation between directionality of the seismic radiation pattern for S-wave and the recorded peak ground velocities and explain the observed anomaly.

  19. Mid-European seismic attenuation anomaly

    Science.gov (United States)

    Málek, Jiří; Brokešová, Johana; Vackář, Jiří

    2017-08-01

    Macroseismic studies of various historical earthquakes with epicenters in the Eastern Alps region have shown a significant elongation of isoseismals in the North-West direction. Such an anomalous attenuation of seismic waves in Central Europe is investigated on the basis of instrumental records of two moderate-size earthquakes in the Vienna Basin, which occurred in September and October 2013. It has been found that for both earthquakes the peak amplitudes of both velocity and acceleration are considerably higher to the North-West of the epicenters compared to the other directions. The peak ground velocity amplitudes at comparable epicentral distances but different azimuths may vary by as much as one order of magnitude. The inspection of individual seismograms suggests that the phenomenon is associated mainly with the propagation of S waves. Significant differences in frequency content of the seismic waves radiated to different azimuths are also demonstrated. The maximum predominant frequency was not observed at stations closest to the epicenters but about 250 km away, in the Bohemian Massif. The possible causes of these observations are briefly discussed on the basis of an elementary data analysis but further research and in-depth analysis is required to elucidate the causes of these phenomena.

  20. Seismicity within the Irpinia Fault System As Monitored By Isnet (Irpinia Seismic Network) and Its Possible Relation with Fluid Storage

    Science.gov (United States)

    Festa, G.; Zollo, A.; Amoroso, O.; Ascione, A.; Colombelli, S.; Elia, L.; Emolo, A.; Martino, C.; Mazzoli, S.; Orefice, A.; Russo, G.

    2014-12-01

    ISNet (http://isnet.fisica.unina.it) is deployed in Southern Apennines along the active fault system responsible for the 1980, M 6.9 Irpinia earthquake. ISNet consists of 32 seismic stations equipped with both strong motion and velocimetric instruments (either broadband or short-period), with the aim of capture a broad set of seismic signals, from ambient noise to strong motion. Real time and near real time procedures run at ISNet with the goal of monitoring the seismicity, check possible space-time anomalies, detect seismic sequences and launch an earthquake early warning in the case of potential significant ground shaking in the area. To understand the role of fluids on the seismicity of the area, we investigated velocity and attenuation models. The former is built from accurate cross-correlation picking and S wave detection based onto polarization analysis. Joint inversion of both P and S arrival times is then based on a linearized multi-scale tomographic approach. Attenuation is instead obtained from inversion of displacement spectra, deconvolving for the source effect. High VP/VS and QS/QP >1 were found within a ~15 km wide rock volume where intense microseismicity is located. This indicates that concentration of seismicity is possibly controlled by high pore fluid pressure. This earthquake reservoir may come from a positive feedback between the seismic pumping that controls the fluid transmission through the fractured damage zone and the low permeability of cross fault barrier, increasing the fluid pore pressure within the fault bounded block. In this picture, sequences mostly occur at the base of this fluid rich layer. They show an anomalous pattern in the earthquake occurrence per magnitude classes; main events evolve with a complex source kinematics, as obtained from backprojection of apparent source time functions, indicating possible directivity effects. In this area sequences might be the key for understanding the transition between the deep

  1. Macroscopic quantum tunneling and quasiparticle-tunneling blockade effect in s-wave/d-wave hybrid junctions

    NARCIS (Netherlands)

    Kawabata, S.; Kawabata, S.; Golubov, Alexandre Avraamovitch; Ariando, A.; Verwijs, C.J.M.; Verwijs, C.J.M.; Hilgenkamp, Johannes W.M.; Kirtley, J.R.

    2007-01-01

    We have theoretically investigated macroscopic quantum tunneling (MQT) and the influence of nodal quasiparticles and zero energy bound states (ZESs) on MQT in s-wave/d-wave hybrid Josephson junctions. In contrast to d-wave/d-wave junctions, the low-energy quasiparticle dissipation resulting from

  2. Observability of surface Andreev bound states in a topological insulator in proximity to an s-wave superconductor

    NARCIS (Netherlands)

    Snelder, M.; Asano, Y.; Golubov, Alexandre Avraamovitch; Brinkman, Alexander

    2015-01-01

    To guide experimental work on the search for Majorana zero-energy modes, we calculate the superconducting pairing symmetry of a three-dimensional topological insulator in combination with an s-wave superconductor. We show how the pairing symmetry changes across different topological regimes. We

  3. Feasibility of using P- and S-wave Attenuation for Monitoring of Bacterial Clogging in Unconsolidated Sediments

    Science.gov (United States)

    Noh, D. H.

    2015-12-01

    Accumulation of bacterial biopolymers in porous media is known to decrease permeability by several orders of magnitude, referred to as bioclogging, thereby altering the hydraulic flow systems of porous media. Successful microbial bioclogging treatments require geophysical monitoring techniques to provide appropriate spatial and temporal information on bacterial growth and activities in the subsurface; such monitoring datasets can be used to evaluate the status of plugged reservoir sections and optimize re-treatment if the plug degrades. This study investigated the variations of P- and S-wave attenuation of porous media for monitoring in-situ accumulation of bacterial biopolymers in sediments. Column experiments, where Leuconostoc mesenterorides were stimulated to produce the insoluble polysaccharide biopolymer (referred to as dextran) in a sand pack, were performed while monitoring changes in permeability as well as P- and S-wave responses. P-wave responses at ultrasonic and sub-ultrasonic frequency ranges (i.e., hundreds of kHz and tens of kHz) and S-wave responses at several kHz were acquired using ultrasonic transducers and bender elements during accumulation of the biopolymer. The permeability of the sand pack was reduced by more than one order of magnitude while the insoluble biopolymer, dextran, produced by Leuconostoc mesenteroides occupied ~10% pore volume. The amplitude of the P-wave signals decreased at the both ultrasonic (hundreds of kHz) and sub-ultrasonic (tens of kHz) frequency ranges; and the spectral ratio calculations confirmed an increase in P-wave attenuation (1/QP) in the both frequency ranges. The amplitude of the S-wave signals significantly increased during the increase in S-wave velocity, possibly due to the increased shear stiffness of the medium. However, the spectral ratio calculation suggested an increase in S-wave attenuation (1/QS) in the several kHz band. The observed changes in permeability and P- and S-wave attenuation were

  4. Regional Seismic Methods of Identifying Explosions

    Science.gov (United States)

    Walter, W. R.; Ford, S. R.; Pasyanos, M.; Pyle, M. L.; Hauk, T. F.

    2013-12-01

    A lesson from the 2006, 2009 and 2013 DPRK declared nuclear explosion Ms:mb observations is that our historic collection of data may not be representative of future nuclear test signatures (e.g. Selby et al., 2012). To have confidence in identifying future explosions amongst the background of other seismic signals, we need to put our empirical methods on a firmer physical footing. Here we review the two of the main identification methods: 1) P/S ratios and 2) Moment Tensor techniques, which can be applied at the regional distance (200-1600 km) to very small events, improving nuclear explosion monitoring and confidence in verifying compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Amplitude ratios of seismic P-to-S waves at sufficiently high frequencies (~>2 Hz) can identify explosions among a background of natural earthquakes (e.g. Walter et al., 1995). However the physical basis for the generation of explosion S-waves, and therefore the predictability of this P/S technique as a function of event properties such as size, depth, geology and path, remains incompletely understood. Calculated intermediate period (10-100s) waveforms from regional 1-D models can match data and provide moment tensor results that separate explosions from earthquakes and cavity collapses (e.g. Ford et al. 2009). However it has long been observed that some nuclear tests produce large Love waves and reversed Rayleigh waves that complicate moment tensor modeling. Again the physical basis for the generation of these effects from explosions remains incompletely understood. We are re-examining regional seismic data from a variety of nuclear test sites including the DPRK and the former Nevada Test Site (now the Nevada National Security Site (NNSS)). Newer relative amplitude techniques can be employed to better quantify differences between explosions and used to understand those differences in term of depth, media and other properties. We are also making use of the Source Physics

  5. 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.

  6. 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.

  7. Dynamics of nanoparticules detected at 1 AU by S/WAVES onboard STEREO spacecraft

    Science.gov (United States)

    Belheouane, Soraya; Issautier, Karine; Meyer-Vernet, Nicole; Le Chat, Gaétan; Czechowski, Andrzej; Zaslavsky, Arnaud; Zouganelis, Yannis; Mann, Ingrid

    In order to interpret in detail the S/WAVES data on the interplanetary nanodust discovered by STEREO at 1 AU [Meyer-Vernet et al., 2009], we study the dynamics of nanoparticles in the inner interplanetary medium as well as the distribution of their velocities and directions of arrival, with a model based on [Czechowski and Mann, 2012]. We deduce the charges released by their impacts on the STEREO spacecraft at 1 AU and their dependence on the position of the spacecraft on their orbits. The model studies nanoparticles of size equal or smaller than about 70 nm, assumed to be created via collisional fragmentation of dust grains of larger size moving on keplerian orbits, and sublimation of dust, meteoroids and comets. The nanoparticles are released near the Sun with initial velocities close to keplerian, and mainly subjected to the Lorentz force calculated with a simple solar wind model. A part of the nanoparticles is accelerated to high speeds of the order of 300 km/s, thereby providing impact charges between 10(-14) and 10(-11) Cb [Belheouane, 2014] which enable them to be detected by S/WAVES, whereas another part is trapped within about 0.2 AU from the Sun. We discuss how the fluxes and direction of arrival at 1 AU are expected to change in function of the solar cycle. These results enable us to interpret in detail the STEREO/WAVES observations [Zaslavsky et al., 2012]; [Pantellini et al., 2013]; [Le Chat et al., 2013]. Belheouane, S. (2014). Nanoparticules dans le vent solaire, observations spatiales et theorie. PhD thesis, Pierre and Marie Curie University UPMC. Czechowski, A. and Mann, I. (2012). Nanodust Dynamics in Interplanetary Space, chapter Nanodust Dynamics in Interplanetary Space. Springer Berlin Heidelberg. Le Chat, G., Zaslavsky, A., Meyer-Vernet, N., Issautier, K., Belheouane, S., Pantellini, F., Maksimovic, M., Zouganelis, I., Bale, S., and Kasper, J. (2013). Interplanetary Nanodust Detection by the Solar Terrestrial Relations Observatory/WAVES Low

  8. Seismic Imaging and Monitoring

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Lianjie [Los Alamos National Laboratory

    2012-07-09

    I give an overview of LANL's capability in seismic imaging and monitoring. I present some seismic imaging and monitoring results, including imaging of complex structures, subsalt imaging of Gulf of Mexico, fault/fracture zone imaging for geothermal exploration at the Jemez pueblo, time-lapse imaging of a walkway vertical seismic profiling data for monitoring CO{sub 2} inject at SACROC, and microseismic event locations for monitoring CO{sub 2} injection at Aneth. These examples demonstrate LANL's high-resolution and high-fidelity seismic imaging and monitoring capabilities.

  9. Effect of Velocity of Detonation of Explosives on Seismic Radiation

    Science.gov (United States)

    Stroujkova, A. F.; Leidig, M.; Bonner, J. L.

    2014-12-01

    We studied seismic body wave generation from four fully contained explosions of approximately the same yields (68 kg of TNT equivalent) conducted in anisotropic granite in Barre, VT. The explosions were detonated using three types of explosives with different velocities of detonation (VOD): Black Powder (BP), Ammonium Nitrate Fuel Oil/Emulsion (ANFO), and Composition B (COMP B). The main objective of the experiment was to study differences in seismic wave generation among different types of explosives, and to determine the mechanism responsible for these differences. The explosives with slow burn rate (BP) produced lower P-wave amplitude and lower corner frequency, which resulted in lower seismic efficiency (0.35%) in comparison with high burn rate explosives (2.2% for ANFO and 3% for COMP B). The seismic efficiency estimates for ANFO and COMP B agree with previous studies for nuclear explosions in granite. The body wave radiation pattern is consistent with an isotropic explosion with an added azimuthal component caused by vertical tensile fractures oriented along pre-existing micro-fracturing in the granite, although the complexities in the P- and S-wave radiation patterns suggest that more than one fracture orientation could be responsible for their generation. High S/P amplitude ratios and low P-wave amplitudes suggest that a significant fraction of the BP source mechanism can be explained by opening of the tensile fractures as a result of the slow energy release.

  10. Quantifying the effects of sediment deposition and compaction on seismic properties

    Energy Technology Data Exchange (ETDEWEB)

    Andersen, Charlotte Faust

    2010-10-15

    Due to the increased complexity of the remaining reservoirs, improved quantitative predictions of reservoir properties are needed to reduce the cost and risk of drilling a well. Along with the development of more advanced techniques for measuring and processing seismic data, quantification of reservoir properties from seismic data has now become possible to a greater extent. Extracted or modeled seismic properties like P- and S-wave velocities, acoustic impedance and the Vp/Vs ratio can be converted to reservoir properties through the use of suitable rock physics models. The main reservoir properties that will yield information about the potential economic value of the reservoir are the following: lithology, porosity, permeability, pressure, temperature and hydrocarbon saturation. At the well position, these properties can be found from well-log interpretations, but the properties will vary spatially and rock physics models are needed to predict and validate the corresponding changes in the seismic signature when we move away from the well. Geological processes such as sediment deposition and mechanical and chemical compaction are believed to impact on the physical and seismic properties to a considerable extent. Quantifications of the relations between geological processes and seismic properties will therefore improve the predictions from seismic data, both in the evolution of hydrocarbon prospects and in the monitoring of hydrocarbon-producing reservoirs, which is the objective of this thesis. (AG)

  11. Seismic Catalogue and Seismic Network in Haiti

    Science.gov (United States)

    Belizaire, D.; Benito, B.; Carreño, E.; Meneses, C.; Huerfano, V.; Polanco, E.; McCormack, D.

    2013-05-01

    The destructive earthquake occurred on January 10, 2010 in Haiti, highlighted the lack of preparedness of the country to address seismic phenomena. At the moment of the earthquake, there was no seismic network operating in the country, and only a partial control of the past seismicity was possible, due to the absence of a national catalogue. After the 2010 earthquake, some advances began towards the installation of a national network and the elaboration of a seismic catalogue providing the necessary input for seismic Hazard Studies. This paper presents the state of the works carried out covering both aspects. First, a seismic catalogue has been built, compiling data of historical and instrumental events occurred in the Hispaniola Island and surroundings, in the frame of the SISMO-HAITI project, supported by the Technical University of Madrid (UPM) and Developed in cooperation with the Observatoire National de l'Environnement et de la Vulnérabilité of Haiti (ONEV). Data from different agencies all over the world were gathered, being relevant the role of the Dominican Republic and Puerto Rico seismological services which provides local data of their national networks. Almost 30000 events recorded in the area from 1551 till 2011 were compiled in a first catalogue, among them 7700 events with Mw ranges between 4.0 and 8.3. Since different magnitude scale were given by the different agencies (Ms, mb, MD, ML), this first catalogue was affected by important heterogeneity in the size parameter. Then it was homogenized to moment magnitude Mw using the empirical equations developed by Bonzoni et al (2011) for the eastern Caribbean. At present, this is the most exhaustive catalogue of the country, although it is difficult to assess its degree of completeness. Regarding the seismic network, 3 stations were installed just after the 2010 earthquake by the Canadian Government. The data were sent by telemetry thought the Canadian System CARINA. In 2012, the Spanish IGN together

  12. Assessment of dynamic material properties of intact rocks using seismic wave attenuation: an experimental study

    Science.gov (United States)

    Wanniarachchi, W. A. M.; Ranjith, P. G.; Perera, M. S. A.; Rathnaweera, T. D.; Lyu, Q.; Mahanta, B.

    2017-10-01

    The mechanical properties of any substance are essential facts to understand its behaviour and make the maximum use of the particular substance. Rocks are indeed an important substance, as they are of significant use in the energy industry, specifically for fossil fuels and geothermal energy. Attenuation of seismic waves is a non-destructive technique to investigate mechanical properties of reservoir rocks under different conditions. The attenuation characteristics of five different rock types, siltstone, shale, Australian sandstone, Indian sandstone and granite, were investigated in the laboratory using ultrasonic and acoustic emission instruments in a frequency range of 0.1-1 MHz. The pulse transmission technique and spectral ratios were used to calculate the attenuation coefficient (α) and quality factor (Q) values for the five selected rock types for both primary (P) and secondary (S) waves, relative to the reference steel sample. For all the rock types, the attenuation coefficient was linearly proportional to the frequency of both the P and S waves. Interestingly, the attenuation coefficient of granite is more than 22% higher than that of siltstone, sandstone and shale for both P and S waves. The P and S wave velocities were calculated based on their recorded travel time, and these velocities were then used to calculate the dynamic mechanical properties including elastic modulus (E), bulk modulus (K), shear modulus (µ) and Poisson's ratio (ν). The P and S wave velocities for the selected rock types varied in the ranges of 2.43-4.61 km s-1 and 1.43-2.41 km h-1, respectively. Furthermore, it was observed that the P wave velocity was always greater than the S wave velocity, and this confirmed the first arrival of P waves to the sensor. According to the experimental results, the dynamic E value is generally higher than the static E value obtained by unconfined compressive strength tests.

  13. Computed Tomography (CT) -- Sinuses

    Medline Plus

    Full Text Available ... News Physician Resources Professions Site Index A-Z Computed Tomography (CT) - Sinuses Computed tomography (CT) of the sinuses ... of CT of the Sinuses? What is CT (Computed Tomography) of the Sinuses? Computed tomography, more commonly known ...

  14. Near Surface Structure of the Frijoles Strand of the San Gregorio Fault, Point Año Nuevo, San Mateo County, California, from Seismic Imaging

    Science.gov (United States)

    Campbell, L.; Catchings, R. D.; Rymer, M. J.; Goldman, M.; Weber, G. E.

    2012-12-01

    The San Gregorio Fault Zone (SGFZ) is one of the major faults of the San Andreas Fault (SAF) system in the San Francisco Bay region of California. The SGFZ is nearly 200 km long, trends subparallel to the SAF, and is located primarily offshore with two exceptions- between Point Año Nuevo and San Gregorio Beach and between Pillar Point and Moss Beach. It has a total width of 2 to 3 km and is comprised of seven known fault strands with Quaternary activity, five of which also demonstrate late Holocene activity. The fault is clearly a potential source of significant earthquakes and has been assigned a maximum likely magnitude of 7.3. To better understand the structure, geometry, and shallow-depth P-wave velocities associated with the SGFZ, we acquired a 585-m-long, high-resolution, combined seismic reflection and refraction profile across the Frijoles strand of the SGFZ at Point Año Nuevo State Park. Both P- and S-wave data were acquired, but here we present only the P-wave data. We used two 60-channel Geometrics RX60 seismographs and 120 40-Hz single-element geophones connected via cable to record Betsy Seisgun seismic sources (shots). Both shots and geophones were approximately co-located and spaced at 5-m intervals along the profile, with the shots offset laterally from the geophones by 1 m. We measured first-arrival refractions from all shots and geophones to develop a seismic refraction tomography velocity model of the upper 70 m. P-wave velocities range from about 600 m/s near the surface to more than 2400 m/s at 70 m depth. We used the refraction tomography image to infer the depth to the top of the groundwater table on the basis of the 1500 m/s velocity contour. The image suggests that the depth, along the profile, to the top of groundwater varies by about 18 m, with greater depth on the west side of the fault. At about 46 m depth, a 60- to 80-m-wide, low-velocity zone, which is consistent with faulting, is observed southwest of the Frijoles strand of the

  15. Imaging Seismic Reflections

    NARCIS (Netherlands)

    op 't Root, T.J.P.M.; Op 't Root, Timotheus Johannes Petrus Maria

    2011-01-01

    The goal of reflection seismic imaging is making images of the Earth subsurface using surface measurements of reflected seismic waves. Besides the position and orientation of subsurface reflecting interfaces it is a challenge to recover the size or amplitude of the discontinuities. We investigate

  16. Homogenization of seismic surface wave profiling in highly heterogeneous improved ground

    Science.gov (United States)

    Lin, C.; Chien, C.

    2012-12-01

    Seismic surface wave profiling is gaining popularity in engineering practice for determining shear-wave velocity profile since the two-station SASW (Spectral Analysis of Surface Wave) was introduced. Recent developments in the multi-station approach (Multi-station Analysis of Surface Wave, MASW) result in several convenient commercial tools. Unlike other geophysical tomography methods, the surface wave method is essentially a 1-D method assuming horizontally-layered medium. Nevertheless, MASW is increasingly used to map lateral variation of S-wave velocity by multiple surveys overlooking the effect of lateral heterogeneity. MASW typically requires long receiver spread in order to have enough depth coverage. The accuracy and lateral resolution of 2-D S-wave velocity imaging by surface wave is not clear. Many geotechnical applications involves lateral variation in a scale smaller than the geophone spread and wave length. For example, soft ground is often improved to increase strength and stiffness by methods such as jet grouting and stone column which result in heterogeneous ground with improved columns. Experimental methods (Standard Penetration Test, sampling and laboratory testing, etc.) used to assess such ground improvement are subjected to several limitations such as small sampling volume, time-consuming, and cost ineffectiveness. It's difficult to assess the average property of the improved ground and the actual replacement ratio of ground improvement. The use of seismic surface wave method for such a purpose seems to be a good alternative. But what MASW measures in such highly heterogeneous improved ground remains to be investigated. This study evaluated the feasibility of MASW in highly heterogeneous ground with improved columns and investigated the homogenization of shear wave velocity measured by MASW. Field experiments show that MASW testing in such a composite ground behaves similar to testing in horizontally layered medium. It seems to measure some sort

  17. Determination of the s-wave pion-nucleon threshold scattering parameters from the results of experiments on pionic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Oades, G.C. [Institute of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Rasche, G. [Institut fuer Theoretische Physik der Universitaet, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland); Woolcock, W.S. [Department of Theoretical Physics, IAS, Australian National University, Canberra, ACT 0200 (Australia); Matsinos, E. [Varian Medical Systems Imaging Laboratory GmbH, Taefernstrasse 7, CH-5405 Baden-Daettwil (Switzerland)], E-mail: evangelos.matsinos@varian.com; Gashi, A. [Mediscope AG, Alfred Escher-Str. 27, CH-8002 Zuerich (Switzerland)

    2007-10-01

    We give the conversion equations which lead from experimental values of the 3p{yields}1s transition energy in pionic hydrogen and the total width of the 1s level to values of the s-wave threshold scattering parameters for the processes {pi}{sup -}p{yields}{pi}{sup -}p and {pi}{sup -}p{yields}{pi}{sup 0}n respectively. Using a three-channel potential model, we then calculate the electromagnetic corrections to these quantities, which remove the effects of the Coulomb interaction, the external mass differences and the presence of the {gamma}n channel. We give the s-wave scattering parameters obtained from the present experimental data and these electromagnetic corrections. Finally we discuss the implications for isospin invariance.

  18. Chiral dynamics, S-wave contributions and angular analysis in D → ππl anti ν

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Yu-Ji; Wang, Wei; Zhao, Shuai [Shanghai Jiao-Tong University, INPAC, Shanghai Key Laboratory for Particle Physics and Cosmology, Department of Physics and Astronomy, Shanghai (China)

    2017-07-15

    We present a theoretical analysis of the D{sup -} → π{sup +}π{sup -}l anti ν and anti D{sup 0} → π{sup +}π{sup 0}l anti ν decays. We construct a general angular distribution which can include arbitrary partial waves of ππ. Retaining the S-wave and P-wave contributions we study the branching ratios, forward-backward asymmetries and a few other observables. The P-wave contribution is dominated by ρ{sup 0} resonance, and the S-wave contribution is analyzed using the unitarized chiral perturbation theory. The obtained branching fraction for D → ρlν, at the order 10{sup -3}, is consistent with the available experimental data. The S-wave contribution has a branching ratio at the order of 10{sup -4}, and this prediction can be tested by experiments like BESIII and LHCb. Future measurements can also be used to examine the π-π scattering phase shift. (orig.)

  19. A study on seismicity and seismic hazard for Karnataka State

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 121; Issue 2. A study on seismicity and seismic hazard for Karnataka State. T G Sitharam Naveen ... This paper presents a detailed study on the seismic pattern of the state of Karnataka and also quantifies the seismic hazard for the entire state. In the present work, ...

  20. Delineation of seismic source zones based on seismicity parameters ...

    Indian Academy of Sciences (India)

    The delineation of seismic source zones plays an important role in the evaluation of seismic hazard. In most of the studies the seismic source delineation is done based on geological features. In the present study, an attempt has been made to delineate seismic source zones in the study area (south India) based on the ...

  1. Assessing attenuation characteristics prevailing in a seismic prone area of North Eastern Region, India

    Science.gov (United States)

    Bora, Nilutpal; Biswas, Rajib; Bora, Dipok K.

    2017-12-01

    Microearthquake spectra from the Kopili region, one of the seismic prone areas of northeast India, are examined to observe the effect of attenuation on these spectra. The spectral ratio method is utilized in order to estimate Q values for both P and S waves in the subsurface layer wherein the ratio of spectral amplitudes at lower and higher frequencies are taken into consideration for six stations at varying epicentral distances. Average values of Q p and Q s are computed to be ∼481 ± 36 and 966 ± 98, respectively. Q s/Q p having a value greater than 1 is contemplated in major parts of Kopili and the neighboring area, which can be ascribed to underlying sediment deposits. The estimates of attenuation parameters are well substantiated by site geology. The values obtained in this study are in good conformity with the worldwide average. The estimates will help in seismic hazard estimation of this seismically active area.

  2. Fracture detection, mapping, and analysis of naturally fractured gas reservoirs using seismic technology. Final report, November 1995

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1995-10-01

    Many basins in the Rocky Mountains contain naturally fractured gas reservoirs. Production from these reservoirs is controlled primarily by the shape, orientation and concentration of the natural fractures. The detection of gas filled fractures prior to drilling can, therefore, greatly benefit the field development of the reservoirs. The objective of this project was to test and verify specific seismic methods to detect and characterize fractures in a naturally fractured reservoir. The Upper Green River tight gas reservoir in the Uinta Basin, Northeast Utah was chosen for the project as a suitable reservoir to test the seismic technologies. Knowledge of the structural and stratigraphic geologic setting, the fracture azimuths, and estimates of the local in-situ stress field, were used to guide the acquisition and processing of approximately ten miles of nine-component seismic reflection data and a nine-component Vertical Seismic Profile (VSP). Three sources (compressional P-wave, inline shear S-wave, and cross-line, shear S-wave) were each recorded by 3-component (3C) geophones, to yield a nine-component data set. Evidence of fractures from cores, borehole image logs, outcrop studies, and production data, were integrated with the geophysical data to develop an understanding of how the seismic data relate to the fracture network, individual well production, and ultimately the preferred flow direction in the reservoir. The multi-disciplinary approach employed in this project is viewed as essential to the overall reservoir characterization, due to the interdependency of the above factors.

  3. Seismic Wave Propagation on the Tablet Computer

    Science.gov (United States)

    Emoto, K.

    2015-12-01

    Tablet computers widely used in recent years. The performance of the tablet computer is improving year by year. Some of them have performance comparable to the personal computer of a few years ago with respect to the calculation speed and the memory size. The convenience and the intuitive operation are the advantage of the tablet computer compared to the desktop PC. I developed the iPad application of the numerical simulation of the seismic wave propagation. The numerical simulation is based on the 2D finite difference method with the staggered-grid scheme. The number of the grid points is 512 x 384 = 196,608. The grid space is 200m in both horizontal and vertical directions. That is the calculation area is 102km x 77km. The time step is 0.01s. In order to reduce the user waiting time, the image of the wave field is drawn simultaneously with the calculation rather than playing the movie after the whole calculation. P and S wave energies are plotted on the screen every 20 steps (0.2s). There is the trade-off between the smooth simulation and the resolution of the wave field image. In the current setting, it takes about 30s to calculate the 10s wave propagation (50 times image updates). The seismogram at the receiver is displayed below of the wave field updated in real time. The default medium structure consists of 3 layers. The layer boundary is defined by 10 movable points with linear interpolation. Users can intuitively change to the arbitrary boundary shape by moving the point. Also users can easily change the source and the receiver positions. The favorite structure can be saved and loaded. For the advance simulation, users can introduce the random velocity fluctuation whose spectrum can be changed to the arbitrary shape. By using this application, everyone can simulate the seismic wave propagation without the special knowledge of the elastic wave equation. So far, the Japanese version of the application is released on the App Store. Now I am preparing the

  4. Muon Tomography of Deep Reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Bonneville, Alain H.; Kouzes, Richard T.

    2016-12-31

    Imaging subsurface geological formations, oil and gas reservoirs, mineral deposits, cavities or magma chambers under active volcanoes has been for many years a major quest of geophysicists and geologists. Since these objects cannot be observed directly, different indirect geophysical methods have been developed. They are all based on variations of certain physical properties of the subsurface that can be detected from the ground surface or from boreholes. Electrical resistivity, seismic wave’s velocities and density are certainly the most used properties. If we look at density, indirect estimates of density distributions are performed currently by seismic reflection methods - since the velocity of seismic waves depend also on density - but they are expensive and discontinuous in time. Direct estimates of density are performed using gravimetric data looking at variations of the gravity field induced by the density variations at depth but this is not sufficiently accurate. A new imaging technique using cosmic-ray muon detectors has emerged during the last decade and muon tomography - or muography - promises to provide, for the first time, a complete and precise image of the density distribution in the subsurface. Further, this novel approach has the potential to become a direct, real-time, and low-cost method for monitoring fluid displacement in subsurface reservoirs.

  5. Structure of Suasselkä Postglacial Fault in northern Finland obtained by analysis of ambient seismic noise

    Science.gov (United States)

    Afonin, Nikita; Kozlovskaya, Elena

    2016-04-01

    Understanding inner structure of seismogenic faults and their ability to reactivate is particularly important in investigating the continental intraplate seismicity regime. In our study we address this problem using analysis of ambient seismic noise recorded by the temporary DAFNE array in northern Fennoscandian Shield. The main purpose of the DAFNE/FINLAND passive seismic array experiment was to characterize the present-day seismicity of the Suasselkä post-glacial fault (SPGF) that was proposed as one potential target for the DAFNE (Drilling Active Faults in Northern Europe) project. The DAFNE/FINLAND array comprised the area of about 20 to 100 km and consisted of 8 short-period and 4 broad-band 3-component autonomous seismic stations installed in the close vicinity of the fault area. The array recorded continuous seismic data during September, 2011-May, 2013. Recordings of the array have being analyzed in order to identify and locate natural earthquakes from the fault area and to discriminate them from the blasts in the Kittilä Gold Mine. As a result, we found several dozens of natural seismic events originating from the fault area, which proves that the fault is still seismically active. In order to study the inner structure of the SPGF we use cross-correlation of ambient seismic noise recorded by the array. Analysis of azimuthal distribution of noise sources demonstrated that that during the time interval under consideration the distribution of noise sources is close to the uniform one. The continuous data were processed in several steps including single station data analysis, instrument response removal and time-domain stacking. The data were used to estimate empirical Green's functions between pairs of stations in the frequency band of 0.1-1 Hz and to calculate correspondent surface wave dispersion curves. After that S-wave velocity models were obtained as a result of dispersion curves inversion using Geopsy software. The results suggest that the area of

  6. In-mine electrical resistance tomography for imaging the continuity of tabular orebodies

    CSIR Research Space (South Africa)

    Van Schoor, Abraham M

    2006-09-01

    Full Text Available One of the strengths of the electrical resistance tomography (ERT) technique is its flexibility in terms of survey geometries. In this paper an unconventional and novel ERT application that is geometrically analogous to in-seam seismic tomography...

  7. Theoretical basis of the amplitude source location method for volcano-seismic signals

    Science.gov (United States)

    Morioka, Hanae; Kumagai, Hiroyuki; Maeda, Takuto

    2017-08-01

    The source location method using high-frequency seismic amplitudes based on the assumption of isotropic radiation of S waves has been used successfully to locate seismic events and tremor at volcanoes. This amplitude source location (ASL) method overcomes the limitations of traditional hypocenter determination methods that use onset arrival times and has great potential to improve volcano-seismic monitoring and the investigation of source processes of volcano-seismic signals. However, theoretical justification of the basic assumption used in the ASL method has not been provided in previous studies. In this study, we tested the ASL method by using seismic waveforms simulated with a finite difference method in realistic heterogeneous volcanic structures with intrinsic attenuation and topography. Our results showed that ASL determinations were successful when using waveforms characterized by multiple scattering that can be approximated by the diffusion model. We found that the energy solution of the diffusion model provided an amplitude-distance relation that is similar to that used in the ASL method. Our results suggest that the ASL method is applicable to high-frequency seismograms in highly heterogeneous media with transport mean free paths of 103 m or smaller and strong intrinsic attenuation. These medium parameters are consistent with those estimated at various volcanoes. Our study validates the basic assumption of the ASL method and justifies its use to locate the sources of high-frequency seismic signals observed at volcanoes.

  8. 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.

  9. Lattice preferred orientation of talc and implications for seismic anisotropy in subduction zones

    Science.gov (United States)

    Lee, Jungjin; Jung, Haemyeong; Klemd, Reiner

    2017-04-01

    Since hydrous phases such as talc and serpentine are elastically very anisotropic, the lattice preferred orientation (LPO) of both minerals when formed in the mantle wedge or the subducting slab can cause large seismic anisotropies in subduction zones. Although, fabric studies of talc-associated phases (e.g., serpentine, amphibole) have been reported, up to now no quantitative measurements of the talc LPO have been conducted. In order to examine the LPO of talc, SEM/EBSD analyses were performed on highly deformed garnet-chloritoid-talc schists from the Makbal UHP terrane in the Tianshan orogen (Kazakhstan). These rocks underwent subduction-related eclogite-facies metamorphism corresponding to a burial depth of ca. 92 km (P ≅ 2.9 GPa). The samples contain between 20 and 40 vol. % talc. The LPO results showed that talc has a strong alignment of [001] axes subnormal to the foliation and, in addition, the [100] and [010] axes display a weak concentration with a girdle subparallel to the foliation. The seismic anisotropy of the polycrystalline talc was calculated using the obtained LPO and the pressure-dependent elastic constants of single-crystal talc. The magnitude of the seismic anisotropy of talc due to its LPO was 68‒69 % for P-waves and 21‒23 % for S-waves under the ambient pressure. The seismic anisotropies of talc decreased to 36‒37 % for P-waves and 13‒17 % for S-waves under high pressure (2.9 GPa), however they still remained high. The polarization direction of vertically propagating fast S-waves of the talc was trench-parallel and it was influenced by the strength of talc LPO of both [100] and [010] axes, pressure, and the dipping angle of the subducting slab. Our results indicate that the presence of strong LPO of talc in the hydrated mantle can contribute significantly to the trench-parallel seismic anisotropy and long delay time of S-waves observed in many subduction zones.

  10. BUILDING 341 Seismic Evaluation

    Energy Technology Data Exchange (ETDEWEB)

    Halle, J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-06-15

    The Seismic Evaluation of Building 341 located at Lawrence Livermore National Laboratory in Livermore, California has been completed. The subject building consists of a main building, Increment 1, and two smaller additions; Increments 2 and 3.

  11. Seismic Creep, USA Images

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Seismic creep is the constant or periodic movement on a fault as contrasted with the sudden rupture associated with an earthquake. It is a usually slow deformation...

  12. Detailed seismic intensity in Morioka area; Moriokashi ni okeru shosai shindo bunpu

    Energy Technology Data Exchange (ETDEWEB)

    Saito, T.; Yamamoto, H.; Settai, H. [Iwate University, Iwate (Japan). Faculty of Engineering; Yamada, T. [Obayashi Road Construction Co. Ltd., Tokyo (Japan)

    1996-10-01

    To reveal a seismic intensity distribution in individual areas, a large-scale detailed seismic intensity survey was conducted in Morioka City through questionnaire, as to the Hokkaido Toho-oki (HE) earthquake occurred on October 4, 1994 with a record of seismic intensity 4 at Morioka, and the Sanriku Haruka-oki (SH) earthquake occurred on December 28, 1994 with a record of seismic intensity 5 at Morioka. A relationship was also examined between the seismic intensity distribution and the properties of shallow basement in Morioka City. The range of seismic intensity was from 2.9 to 4.6 and the difference was 1.7 in the case of HE earthquake, and the range was from 3.1 to 5.0 and the difference was 1.9 in the case of SH earthquake. There were large differences in the seismic intensity at individual points. Morioka City has different geological structures in individual areas. There were differences in the S-wave velocity in the surface layer ranging from 150 to 600 m/sec, which were measured using a plate hammering seismic source at 76 areas in Morioka City. These properties of surface layers were in harmony with the seismic intensity distribution obtained from the questionnaire. For the observation of short frequency microtremors at about 490 points in the city, areas with large amplitudes, mean maximum amplitudes of vertical motion components more than 0.1 mkine were distributed in north-western region and a part of southern region. 4 refs., 9 figs., 1 tab.

  13. A future for drifting seismic networks

    Science.gov (United States)

    Simons, F. J.; Nolet, G.; Babcock, J.

    2007-12-01

    One-dimensional, radial Earth models are sufficiently well constrained to accurately locate earthquakes and calculate the paths followed by seismic rays. The differences between observations and theoretical predictions of seismograms in such Earth models can be used to reconstruct the three-dimensional wave speed distribution in the regions sampled by the seismic waves, by the technique of seismic tomography. Caused by thermal, compositional, and textural variations, wave speed anomalies remain the premier data source to fully understand the structure and evolution of our planet, from the scale of mantle convection and the mechanisms of heat transfer from core to surface to the international between the deep Earth and surface processes such as plate motion and crustal deformation. Unequal geographical data coverage continues to fundamentally limit the quality of tomographic reconstructions of seismic wave speeds in the interior of the Earth. Only at great cost can geophysicists overcome the difficulties of placing seismographs on the two thirds of the Earth's surface that is covered by oceans. The lack of spatial data coverage strongly hampers the determination of the structure of the Earth in the uncovered regions: all 3-D Earth models are marked by blank spots in areas, distributed throughout the Earth, where little or no information can be obtained. As a possible solution to gaining equal geographic data coverage, we have developed MERMAID, a prototype mobile receiver that could provide an easy, cost-effective way to collect seismic data in the ocean. It is a modification of the robotic floating instruments designed and used by oceanographers. Like them, MERMAID spends its life at depth but is capable of surfacing using a pump and bladder. We have equipped it with a hydrophone to record water pressure variations induced by compressional (P) waves. Untethered and passively drifting, such a floating seismometer will surface upon detection of a "useful" seismic

  14. Investigating Seismic Wave Scattering in Heterogeneous Environments and Implications for Seismic Imaging

    Science.gov (United States)

    Bongajum, Emmanuel Leinyuy

    2011-07-01

    Inhomogeneities in the earth (fractures, layering, shape, composition) are responsible for seismic wave scattering and contribute towards amplitude, travel time, frequency and spectral fluctuations observed in seismic records. This thesis presents findings that complement our understanding of seismic scattering and imaging in heterogeneous media. Interest focused on probing the correlation between spatial variations in attributes that characterize the state (physical, chemical) of rocks and seismic waveform data with consideration towards potential implications for seismic survey design to optimize imaging, imaging with converted waves, microseismic monitoring, velocity modeling and imaging of lithological boundaries. The highlights of the research strategy include: • The use of stochastic methods to build realistic earth models that characterize the 1D, 2D and 3D spatial variations in rock properties. These petrophysical earth models are conditioned by experimental ("hard") data such as geology, wave velocities and density from case study areas like the Bosumtwi impact crater and the base metal deposits in Nash Creek (Canada) and Thompson (Canada). The distributions of the sulfide mineralization at Nash Creek and at Thompson represent two end members of the heterogeneity spectrum. While the sulfide mineralization at Nash Creek is highly disseminated in nature, the sulfide rich zones at Thompson occur as well defined volumes (lens-shaped) having a strong density contrast with respect to the host rocks. • Analysis of modeled forward (transmitted) and backward scattered wave propagation in the heterogeneous earth models. As a result of a study aimed at correlating resonant frequencies to scale length parameters, it is observed that the efficiency of the spectral ratio method is undermined by its sensitivity to the interference between P- and S-waves as well as the impedance contrast. It is also demonstrated that travel time of direct arrivals (transmitted waves

  15. 3D Seismic Experimentation and Advanced Processing/Inversion Development for Investigations of the Shallow Subsurface

    Energy Technology Data Exchange (ETDEWEB)

    Levander, Alan Richard [Rice Univ., Houston, TX (United States). Earth Science Department; Zelt, Colin A. [Rice Univ., Houston, TX (United States). Earth Science Department

    2015-03-17

    The work plan for this project was to develop and apply advanced seismic reflection and wide-angle processing and inversion techniques to high resolution seismic data for the shallow subsurface to seismically characterize the shallow subsurface at hazardous waste sites as an aid to containment and cleanup activities. We proposed to continue work on seismic data that we had already acquired under a previous DoE grant, as well as to acquire additional new datasets for analysis. The project successfully developed and/or implemented the use of 3D reflection seismology algorithms, waveform tomography and finite-frequency tomography using compressional and shear waves for high resolution characterization of the shallow subsurface at two waste sites. These two sites have markedly different near-surface structures, groundwater flow patterns, and hazardous waste problems. This is documented in the list of refereed documents, conference proceedings, and Rice graduate theses, listed below.

  16. Spectral-element seismic wave propagation on emerging HPC architectures

    Science.gov (United States)

    Peter, Daniel; Liu, Qiancheng; Komatitsch, Dimitri

    2017-04-01

    Seismic tomography is the most prominent approach to infer physical properties of Earth's internal structures such as compressional- and shear-wave speeds, anisotropy and attenuation. Using seismic signals from ground-motion records, recent advances in full-waveform inversions require increasingly accurate simulations of seismic wave propagation in complex 3D media to provide access to the complete 3D seismic wavefield. However, such numerical simulations are computationally expensive and need high-performance computing (HPC) facilities for further improving the current state of knowledge. During recent years, new multi- and many-core architectures such as graphics processing units (GPUs) have been added to available large HPC systems. GPU-accelerated computing together with advances in multi-core central processing units (CPUs) can greatly accelerate scientific applications. To employ a wide variety of hardware accelerators for seismic wave propagation simulations, we incorporated a code generation tool BOAST into an existing spectral-element code package SPECFEM3D_GLOBE. This allows us to use meta-programming of computational kernels and generate optimized source code for both CUDA and OpenCL languages, running simulations on either CUDA or OpenCL hardware accelerators. We show here benchmark applications of seismic wave propagation on GPUs and CPUs, comparing performances on emerging hardware architectures.

  17. SEISMIC AND ROCK PHYSICS DIAGNOSTICS OF MULTISCALE RESERVOIR TEXTURES

    Energy Technology Data Exchange (ETDEWEB)

    Gary Mavko

    2004-08-01

    As part of our study on ''Relationships between seismic properties and rock microstructure'', we have continued our work on analyzing well logs and microstructural constraints on seismic signatures. We report results of three studies in this report. The first one deals with fractures and faults that provide the primary control on the underground fluid flow through low permeability massive carbonate rocks. Fault cores often represent lower transmissibility whereas the surrounding damaged rocks and main slip surfaces are high transmissibility elements. We determined the physical properties of fault rocks collected in and around the fault cores of large normal faults in central Italy. After studying the P- and S-wave velocity variation during cycles of confining pressure, we conclude that a rigid pore frame characterizes the fault gouge whereas the fractured limestone comprises pores with a larger aspect ratio. The second study was to characterize the seismic properties of brine as its temperature decreases from 25 C to -21 C. The purpose was to understand how the transmitted wave changes with the onset of freezing. The main practical reason for this experiment was to use partially frozen brine as an analogue for a mixture of methane hydrate and water present in the pore space of a gas hydrate reservoir. In the third study we analyzed variations in dynamic moduli in various carbonate reservoirs. The investigations include log and laboratory data from velocity, porosity, permeability, and attenuation measurements.

  18. Multi-phase Temporal Seismic Imaging of a Slope Stability Mitigation Project at Newby Island Sanitary Landfill, San Jose, California

    Science.gov (United States)

    Treece, B. J.; Catchings, R.; Reed, D.; Goldman, M.

    2014-12-01

    Without slope stability mitigation, liquefaction-induced settlement in bay mud and Pleistocene alluvial deposits may lead to the collapse of levee walls surrounding sanitary landfills that are located adjacent to the San Francisco Bay. To analyze the effectiveness of a slope stability mitigation project involving deep soil mixing at Newby Island Sanitary Landfill in San Jose, California, we acquired P- and S-wave seismic surveys along a transect through the mitigated region during, and two years after, completion of the mitigation project. Deep soil mixing involves the injection of a cement slurry in augered holes, resulting in groups of soil-cement columns (elements) that are intended to increase the strength and rigidity of the subsurface materials. For our seismic investigations, we used accelerated-weight-drop (AWD) and hammer impacts to generate P- and S-wave seismic sources, respectively, at 57 geophone locations, spaced 5 m apart. The resulting seismic data were recorded using 40-Hz, vertical-component (P-wave) and 4.5-Hz, horizontal-component (S-wave) sensors. Initially, we developed tomographic refraction (velocity) images along a progressive transition from a yet-to-be-mitigated area into a more recently mitigated area, located along the base of a steep slope composed of compacted landfill. The initial survey revealed an increase in seismic velocity in the treated area, seismic velocity increases with curing time for soil-cement elements, and a high-velocity zone beneath the active injection zone. The influence of the mitigation was most apparent from increases in Vp/Vs and Poisson's ratios. To assess the long-term effects of the mitigation project, an identical, follow-up survey was acquired in July 2014, 23 months after the initial survey. We present a comparative analysis of the tomographic images from the two surveys, variations in Vp/Vs and Poisson's ratios over time, and a comparison of in situ, time-varying seismic parameters with laboratory

  19. Seismic Consequence Abstraction

    Energy Technology Data Exchange (ETDEWEB)

    M. Gross

    2004-10-25

    The primary purpose of this model report is to develop abstractions for the response of engineered barrier system (EBS) components to seismic hazards at a geologic repository at Yucca Mountain, Nevada, and to define the methodology for using these abstractions in a seismic scenario class for the Total System Performance Assessment - License Application (TSPA-LA). A secondary purpose of this model report is to provide information for criticality studies related to seismic hazards. The seismic hazards addressed herein are vibratory ground motion, fault displacement, and rockfall due to ground motion. The EBS components are the drip shield, the waste package, and the fuel cladding. The requirements for development of the abstractions and the associated algorithms for the seismic scenario class are defined in ''Technical Work Plan For: Regulatory Integration Modeling of Drift Degradation, Waste Package and Drip Shield Vibratory Motion and Seismic Consequences'' (BSC 2004 [DIRS 171520]). The development of these abstractions will provide a more complete representation of flow into and transport from the EBS under disruptive events. The results from this development will also address portions of integrated subissue ENG2, Mechanical Disruption of Engineered Barriers, including the acceptance criteria for this subissue defined in Section 2.2.1.3.2.3 of the ''Yucca Mountain Review Plan, Final Report'' (NRC 2003 [DIRS 163274]).

  20. Anisotropy of S wave velocity in the lowermost mantle using broad-band data recorded at Syowa in Antarctica

    Science.gov (United States)

    Usui, Y.; Hiramatsu, Y.; Furumoto, M.; Kanao, M.

    2003-12-01

    We investigate the velocity structure of the lowermost mantle (D") beneath the Antarctic Ocean. We analyze seismograms from 16 deep earthquakes in south Pacific subduction zones from 1990 to 2001 recorded by STS-1 broad-band seismographs at Syowa station in Antarctica. The source-receiver combinations span distances range 85\\deg-95\\deg with associated S waves passing through D" beneath the Antarctic ocean. Differential travel times of split S waves are estimated to be up to 2s, showing that longitudinal components (SV) energy arrives earlier than transverse components (SH) energy. The absence of significant splitting for S waves with turning points more than four hundred kilometers above the core-mantle boundary (CMB) indicates that anisotropy is localized within the D" region. Differential travel times among S, ScS and SKS phases and waveform modeling are used to construct the velocity structure in D". We calculate synthetic waveforms by the Direct Solution Method (DSM: Geller and Ohminato, 1994; Geller and Takeuchi, 1995). SH shows a double arrival at the epicentral distance near 89\\deg. However SV in this range remains a single arrival. Isotropic model_@can not explain these observation. We find that synthetics for transverse isotropic models with SH velocity discontinuity (SYYM model) explain well the observed differential travel times and waveforms. The thickness of the anisotropic zone, where SH wave is faster up to 2.0% than SV wave, estimated to be about 350 km. This study region corresponds to the high velocity region at the lowermost mantle by tomographic studies (Kuo et al., 2000; Masters et al., 2000). This kind of transverse anisotropy correlates with high velocity regions where paleo-slabs may descend into the lower mantle (Kendall and Silver, 1996; Garnero and Lay, 1997). We conclude that these observations may be explained by an anisotropic D" layer and D" layer anisotropy is attributed to the paleo-slab material subducted during 120Myr-180Myr.

  1. Bulk evidence for single-Gap s-wave superconductivity in the intercalated graphite superconductor C6Yb.

    Science.gov (United States)

    Sutherland, Mike; Doiron-Leyraud, Nicolas; Taillefer, Louis; Weller, Thomas; Ellerby, Mark; Saxena, S S

    2007-02-09

    We report measurements of the in-plane electrical resistivity rho and thermal conductivity kappa of the intercalated graphite superconductor C6Yb down to temperatures as low as Tc/100. When a field is applied along the c axis, the residual electronic linear term kappa0/T evolves in an exponential manner for Hc1s-wave order parameter, and is a strong argument against the possible existence of multigap superconductivity.

  2. Changes in seismic anisotropy shed light on the nature of the Gutenberg discontinuity

    OpenAIRE

    Beghein, C; Yuan, K; Schmerr, N; Xing, Z

    2014-01-01

    The boundary between the lithosphere and asthenosphere is associated with a platewide high-seismic velocity "lid" overlying lowered velocities, consistent with thermal models. Seismic body waves also intermittently detect a sharp velocity reduction at similar depths, the Gutenberg (G) discontinuity, which cannot be explained by temperature alone. We compared an anisotropic tomography model with detections of the G to evaluate their context and relation to the lithosphere-asthenosphere boundar...

  3. Modeling Three-Dimensional Upper Mantle Seismic Anisotropy with Higher Mode Surface Waves

    OpenAIRE

    Yuan, Kaiqing

    2014-01-01

    This dissertation presents a new 3-D global upper mantle model of elastic anisotropy obtained from surface wave seismic tomography. This research contributes to our understanding of deep Earth structure. The two main results are the following: (1) Our work unravels the presence of azimuthal seismic anisotropy in the mantle transition zone, to greater depths than previously found, thereby challenging common views of mantle deformation mechanisms. It also reveals a striking correlation between ...

  4. Seismic anisotropy from compositional banding in granulites from the deep magmatic arc of Fiordland, New Zealand

    Science.gov (United States)

    Cyprych, Daria; Piazolo, Sandra; Almqvist, Bjarne S. G.

    2017-11-01

    We present calculated seismic velocities and anisotropies of mafic granulites and eclogites from the Cretaceous deep lower crust (∼40-65 km) of Fiordland, New Zealand. Both rock types show a distinct foliation defined by cm-scale compositional banding. Seismic properties are estimated using the Asymptotic Expansion Homogenisation - Finite Element (AEH-FE) method that, unlike the commonly used Voigt-Reuss-Hill homogenisation, incorporates the phase boundary network into calculations. The predicted mean P- and S-wave velocities are consistent with previously published data for similar lithologies from other locations (e.g., Kohistan Arc), although we find higher than expected anisotropies (AVP ∼ 5.0-8.0%, AVS ∼ 3.0-6.5%) and substantial S-wave splitting along foliation planes in granulites. This seismic signature of granulites results from a density and elasticity contrast between cm-scale pyroxene ± garnet stringers and plagioclase matrix rather than from crystallographic orientations alone. Banded eclogites do not show elevated anisotropies as the contrast in density and elastic constants of garnet and pyroxene is too small. The origin of compositional banding in Fiordland granulites is primarily magmatic and structures described here are expected to be typical for the base of present day magmatic arcs. Hence, we identify a new potential source of anisotropy within this geotectonic setting.

  5. Structure and seismicity of the upper mantle using deployments of broadband seismographs in Antarctica and the Mariana Islands

    Science.gov (United States)

    Barklage, Mitchell

    . We investigate seismic velocity structure of the upper mantle across the Central Mariana subduction system using data from the 2003-2004 Mariana Subduction Factory Imaging Experiment. This 11-month experiment consisted of 20 broadband seismic stations deployed on islands and 58 semi-broadband ocean bottom seismographs deployed across the forearc, island arc, and back-arc spreading center. We determine Vp and Vp/Vs structure on a three dimensional grid using over 25,000 local travel time observations as well as over 2000 teleseismic arrival times determined by waveform cross correlation. The mantle wedge is characterized by a region of low velocity and high Vp/Vs beneath the forearc, an inclined zone of low velocity underlying the volcanic front, and a broad region of low velocity beneath the back-arc spreading center. The slow velocity anomalies are strongest at roughly 20-30 km depth in the forearc, 60-70 km depth beneath the volcanic arc, and 20-30 km beneath the back-arc spreading center. The slow velocity anomalies beneath the arc and back-arc appear as separate and distinct features in our images, with a small channel of connectivity occurring at approximately 75 km depth. The subducting Pacific plate is characterized by high seismic velocities. An exception occurs in the forearc beneath the big blue seamount and at the top of the slab at roughly 80 km depth where slow velocities are observed. We interpret the forearc anomalies to represent a region of large scale serpentinization of the mantle whereas the arc and back-arc anomalies represent regions of high temperature with a small amount of increased water content and/or melt and constrain the source regions in the mantle for arc and back-arc lavas. We investigate the double seismic zone (dsz) beneath the Central Mariana Arc using data from a land-sea array of 58 ocean bottom seismographs and 20 land seismographs deployed during 2003-2004. Nearly 600 well-recorded earthquakes were located using a P and S wave

  6. Determination of Focal Mechanisms of Non-Volcanic Tremors Based on S-Wave Polarization Data Corrected for the Effects of Anisotropy

    Science.gov (United States)

    Imanishi, K.; Uchide, T.; Takeda, N.

    2014-12-01

    We propose a method to determine focal mechanisms of non-volcanic tremors (NVTs) based on S-wave polarization angles. The successful retrieval of polarization angles in low S/N tremor signals owes much to the observation that NVTs propagate slowly and therefore they do not change their location immediately. This feature of NVTs enables us to use a longer window to compute a polarization angle (e.g., one minute or longer), resulting in a stack of particle motions. Following Zhang and Schwartz (1994), we first correct for the splitting effect to recover the source polarization angle (anisotropy-corrected angle). This is a key step, because shear-wave splitting distorts the particle motion excited by a seismic source. We then determine the best double-couple solution using anisotropy-corrected angles of multiple stations. The present method was applied to a tremor sequence at Kii Peninsula, southwest Japan, which occurred at the beginning of April 2013. A standard splitting and polarization analysis were subject to a one-minute-long moving window to determine the splitting parameters as well as anisotropy-corrected angles. A grid search approach was performed at each hour to determine the best double-couple solution satisfying one-hour average polarization angles. Most solutions show NW-dipping low-angle planes consistent with the plate boundary or SE-dipping high-angle planes. Because of 180 degrees ambiguity in polarization angles, the present method alone cannot distinguish compressional quadrant from dilatational one. Together with the observation of very low-frequency earthquakes near the present study area (Ito et al., 2007), it is reasonable to consider that they represent shear slip on low-angle thrust faults. It is also noted that some of solutions contain strike-slip component. Acknowledgements: Seismograph stations used in this study include permanent stations operated by NIED (Hi-net), JMA, Earthquake Research Institute, together with Geological Survey of

  7. Ambient noise tomography reveals basalt and sub-basalt velocity structure beneath the Faroe Islands, North Atlantic

    Science.gov (United States)

    Sammarco, Carmelo; Cornwell, David G.; Rawlinson, Nicholas

    2017-11-01

    Ambient noise tomography is applied to seismic data recorded by a portable array of seismographs deployed throughout the Faroe Islands in an effort to illuminate basalt sequences of the North Atlantic Igneous Province, as well as underlying sedimentary layers and Precambrian basement. Rayleigh wave empirical Green's functions between all station pairs are extracted from the data via cross-correlation of long-term recordings, with phase weighted stacking implemented to boost signal-to-noise ratio. Dispersion analysis is applied to extract inter-station group travel-times in the period range 0.5-15 s, followed by inversion for period-dependent group velocity maps. Subsequent inversion for 3-D shear wave velocity reveals the presence of significant lateral heterogeneity (up to 25%) in the crust. Main features of the final model include: (i) a near-surface low velocity layer, interpreted to be the Malinstindur Formation, which comprises subaerial compound lava flows with a weathered upper surface; (ii) a sharp velocity increase at the base of the Malinstindur Formation, which may mark a transition to the underlying Beinisvørð Formation, a thick laterally extensive layer of subaerial basalt sheet lobes; (iii) a low velocity layer at 2.5-7.0 km depth beneath the Beinisvørð Formation, which is consistent with hyaloclastites of the Lopra Formation; (iv) an upper basement layer between depths of 5-9 km and characterized by S wave velocities of approximately 3.2 km/s, consistent with low-grade metamorphosed sedimentary rocks; (v) a high velocity basement, with S wave velocities in excess of 3.6 km/s. This likely reflects the presence of a crystalline mid-lower crust of Archaean continental origin. Compared to previous interpretations of the geological structure beneath the Faroe Islands, our new results point to a more structurally complex and laterally heterogeneous crust, and provide constraints which may help to understand how continental fragments are rifted from the

  8. 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

  9. Computed Tomography (CT) - Spine

    Science.gov (United States)

    ... Professions Site Index A-Z Computed Tomography (CT) - Spine Computed tomography (CT) of the spine is a ... the Spine? What is CT Scanning of the Spine? Computed tomography, more commonly known as a CT ...

  10. Borehole P- and S-wave velocity at thirteen stations in Southern California

    Science.gov (United States)

    Gibbs, James F.; Boore, David M.; Tinsley, John C.; Mueller, Charles S.

    2001-01-01

    The U.S. Geological Survey (USGS), as part of a program to acquire seismic velocity data at locations of strong-ground motion in earthquakes (e.g., Gibbs et al., 2000), has investigated thirteen additional sites in the Southern California region. Of the thirteen sites, twelve are in the vicinity of Whittier, California, and one is located in San Bernardino, California. Several deployments of temporary seismographs were made after the Whittier Narrows, California earthquake of 1 October 1987 (Mueller et al., 1988). A deployment, between 2 October and 9 November 1987, was the motivation for selection of six of the drill sites. Temporary portable seismographs at Hoover School (HOO), Lincoln School (LIN), Corps of Engineers Station (NAR), Olive Junior High School (OLV), Santa Anita Golf Course (SAG), and Southwestern Academy (SWA) recorded significant aftershock data. These portable sites, with the exception of Santa Anita Golf Course, were co-sited with strong-motion recorders. Stations at HOO, Lincoln School Whittier (WLB), Saint Paul High School (STP), Alisos Adult School (EXC), Cerritos College Gymnasium (CGM), Cerritos College Physical Science Building (CPS), and Cerritos College Police Building (CPB) were part of an array of digital strong-motion stations deployed from "bedrock" in Whittier to near the deepest part of the Los Angeles basin in Norwalk. Although development and siting of this new array (partially installed at the time of this writing) was generally motivated by the Whittier Narrows earthquake, these new sites (with the exception of HOO) were not part of any Whittier Narrows aftershock deployments. A similar new digital strong-motion site was installed at the San Bernardino Fire Station during the same time frame. Velocity data were obtained to depths of about 90 meters at two sites, 30 meters at seven sites, and 18 to 25 meters at four sites. Lithology data from the analysis of cuttings and samples was obtained from the two 90-meter deep holes and

  11. GyPSuM: A Detailed Tomographic Model of Mantle Density and Seismic Wave Speeds

    Energy Technology Data Exchange (ETDEWEB)

    Simmons, N A; Forte, A M; Boschi, L; Grand, S P

    2010-03-30

    GyPSuM is a tomographic model fo mantle seismic shear wave (S) speeds, compressional wave (P) speeds and detailed density anomalies that drive mantle flow. the model is developed through simultaneous inversion of seismic body wave travel times (P and S) and geodynamic observations while considering realistic mineral physics parameters linking the relative behavior of mantle properties (wave speeds and density). Geodynamic observations include the (up to degree 16) global free-air gravity field, divergence of the tectonic plates, dynamic topography of the free surface, and the flow-induced excess ellipticity of the core-mantle boundary. GyPSuM is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution. Models of the density field from Earth's free oscillations have provided great insight into the density configuration of the mantle; but are limited to very long-wavelength solutions. Alternatively, simply scaling higher resolution seismic images to density anomalies generates density fields that do not satisfy geodynamic observations. The current study provides detailed density structures in the mantle while directly satisfying geodynamic observations through a joint seismic-geodynamic inversion process. Notable density field observations include high-density piles at the base of the superplume structures, supporting the fundamental results of past normal mode studies. However, these features are more localized and lower amplitude than past studies would suggest. When we consider all seismic anomalies in GyPSuM, we find that P and S-wave speeds are strongly correlated throughout the mantle. However, correlations between the high-velocity S zones in the deep mantle ({approx} 2000 km depth) and corresponding P-wave anomalies are very low suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies. Nevertheless, they argue that temperature variations are

  12. P Wave and S Wave Acoustic Velocities of Partial Molten Peridotite at Mantle P-T and MHz Frequencies

    Science.gov (United States)

    Weidner, D. J.; Li, L.; Whitaker, M. L.; Triplett, R.

    2016-12-01

    The speed that acoustic waves travel in a partially molten peridotite are crucial parameters to detect not only the presence of melt in the Earth's deep interior, but also understand many issues about the structure and dynamics of the mantle. Technical challenges have hindered such measurements in the laboratory. Here we report the experimental results on the ultrasonic acoustic wave velocities in a partial molten peridotite using multi-anvil high pressure apparatus located at beamline BM6 Advance Photon Source. We use the newly installed ultrasonic equipment using the pulse-echo-overlap method coupled with D-DIA device. X-ray radiography is used to measure sample length at high P-T. The X-ray diffraction spectrum is used to determine the pressure and sample conditions. Precise measurements of P and S wave velocities are obtained at 60 and 35 MHz respectively and are nearly simultaneous. We use a double reflector method to enable measurement of elastic wave velocities of cold-pressed polycrystalline sample which is sintered in situ at high P-T. Experiments were carried out up to 3 GPa and 1500 oC. Our preliminary results indicate that the KLB1 peridotite sample experienced a few percent decrease of both p and s wave velocities as partial melting occurs. The data define a small decrease in the bulk modulus as well as the shear modulus upon melting. This implies that dynamic melting is a significant process at megahertz frequencies.

  13. Modeling of low-frequency seismic waves in a shallow sea using the staggered grid difference method

    Science.gov (United States)

    Lu, Zaihua; Zhang, Zhihong; Gu, Jiannong

    2017-09-01

    Elastic waves in the seabed generated by low-frequency noise radiating from ships are known as ship seismic waves and can be used to detect and identify ships. To obtain the propagation characteristics of ship seismic waves, an algorithm for calculating seismic waves at the seafloor is presented based on the staggered-grid finite difference method. The accuracy of the algorithm was tested by comparison with analytical solutions. Numerical simulation of seismic waves generated by a low-frequency point sound source in a typical shallow sea environment was carried out. Using various source frequencies and locations in the numerical simulation, we show that the seismic waves in the near field are composed mostly of transmitted S-waves and interface waves while transmitted P-waves are weak near the seafloor. However, in the far field, the wave components of the seismic wave are mainly normal modes and interface waves, with the latter being relatively strong in the waveforms. As the source frequency decreases, the normal modes become smaller and the interface waves dominate the time series of the seismic waves.

  14. Deformation fabrics of natural blueschists and implications for seismic anisotropy in subducting oceanic crust

    Science.gov (United States)

    Kim, Daeyeong; Katayama, Ikuo; Michibayashi, Katsuyoshi; Tsujimori, Tatsuki

    2013-09-01

    Investigations of microstructures are crucial if we are to understand the seismic anisotropy of subducting oceanic crust, and here we report on our systematic fabric analyses of glaucophane, lawsonite, and epidote in naturally deformed blueschists from the Diablo Range and Franciscan Complex in California, and the Hida Mountains in Japan. Glaucophanes in the analyzed samples consist of very fine grains that are well aligned along the foliation and have high aspect ratios and strong crystal preferred orientations (CPOs) characterized by a (1 0 0)[0 0 1] pattern. These characteristics, together with a bimodal distribution of grain sizes from some samples, possibly indicate the occurrence of dynamic recrystallization for glaucophane. Although lawsonite and epidote display high aspect ratios and a strong CPO of (0 0 1)[0 1 0], the occurrence of straight grain boundaries and euhedral crystals indicates that rigid body rotation was the dominant deformation mechanism. The P-wave (AVP) and S-wave (AVS) seismic anisotropies of glaucophane (AVP = 20.4%, AVS = 11.5%) and epidote (AVP = 9.0%, AVS = 8.0%) are typical of the crust; consequently, the fastest propagation of P-waves is parallel to the [0 0 1] maxima, and the polarization of S-waves parallel to the foliation can form a trench-parallel seismic anisotropy owing to the slowest VS polarization being normal to the subducting slab. The seismic anisotropy of lawsonite (AVP = 9.6%, AVS = 19.9%) is characterized by the fast propagation of P-waves subnormal to the lawsonite [0 0 1] maxima and polarization of S-waves perpendicular to the foliation and lineation, which can generate a trench-normal anisotropy. The AVS of lawsonite blueschist (5.6-9.2%) is weak compared with that of epidote blueschist (8.4-11.1%). Calculations of the thickness of the anisotropic layer indicate that glaucophane and lawsonite contribute to the trench-parallel and trench-normal seismic anisotropy beneath NE Japan, but not to that beneath the Ryukyu

  15. 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.

  16. Retrieval of P wave Basin Response from Autocorrelation of Seismic Noise-Jakarta, Indonesia

    Science.gov (United States)

    Saygin, E.; Cummins, P. R.; Lumley, D. E.

    2016-12-01

    Indonesia's capital city, Jakarta, is home to a very large (over 10 million), vulnerable population and is proximate to known active faults, as well as to the subduction of Australian plate, which has a megathrust at abut 300 km distance, as well as intraslab seismicity extending to directly beneath the city. It is also located in a basin filled with a thick layer of unconsolidated and poorly consolidated sediment, which increases the seismic hazard the city is facing. Therefore, the information on the seismic velocity structure of the basin is crucial for increasing our knowledge of the seismic risk. We undertook a passive deployment of broadband seismographs throughout the city over a 3-month interval in 2013-2014, recording ambient seismic noise at over 90 sites for intervals of 1 month or more. Here we consider autocorrelations of the vertical component of the continuously recorded seismic wavefield across this dense network to image the shallow P wave velocity structure of Jakarta, Indonesia. Unlike the surface wave Green's functions used in ambient noise tomography, the vertical-component autocorrelograms are dominated by body wave energy that is potentially sensitive to sharp velocity contrasts, which makes them useful in seismic imaging. Results show autocorrelograms at different seismic stations with travel time variations that largely reflect changes in sediment thickness across the basin. We also confirm the validity our interpretation of the observed autocorrelation waveforms by conducting 2D finite difference full waveform numerical modeling for randomly distributed seismic sources to retrieve the reflection response through autocorrelation.

  17. Integrated Near-Surface Seismic and Geoelectrical Mapping of the Concealed Carlsberg Fault zone, Copenhagen, Denmark

    Science.gov (United States)

    Nielsen, L.; Thybo, H.; Jorgensen, M. I.

    2004-12-01

    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. We locate the concealed Carlsberg Fault zone along a 12 km long trace in the Copenhagen city center by seismic refraction, reflection and fan profiling. We supplement our seismic investigations with multi-electrode geoelectrical profiling. The seismic refraction study shows that the Carlsberg 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 structure. We have recorded seismic signals in a fan geometry from shots detonated both inside the low-velocity fault zone and up to about 500 m away from the fault zone. The seismic energy was recorded on three receiver arrays (1.5-2.4 km long arcs) across the expected location of the 400-700 m wide fault zone at distances of up to 7 km from the shots. Shots detonated inside the fault zone result in: 1) weak and delayed first arrivals on the receivers located inside the fault zone compared to earlier and stronger first arrivals outside the fault zone; 2) strong guided P- and S-waves as well as surface waves inside the fault zone. The fault zone is a shadow zone to shots detonated outside the fault zone. Finite-difference wavefield modeling 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-incidence and refraction profiling are not feasible. The geoelectrical measurements show that the fault zone is characterized by low resistivities (lower than 5 ohmm), indicating that the fault zone is fractured and water-filled. This interpretation is supported by hydrological measurements conducted by others, which show that the Carlsberg Fault zone is highly permeable.

  18. Attenuation of seismic waves in Central Egypt

    Directory of Open Access Journals (Sweden)

    Mamdouh Abbas Morsy

    2013-06-01

    Full Text Available Attenuation of seismic waves in central Egypt had never been studied before. The results of the research on the seismic attenuation are based upon the information collected by the seismological network from 1998 to 2011. 855 earthquakes were selected from the Egyptian seismological catalog, with their epicenter distances between 15 and 150 km, their magnitudes ranging from 2 and 4.1 and focal depths reaching up to 30 km. The first systematic study of attenuation derived from the P-, S- and coda wave in the frequency range 1–24 Hz is presented. In the interpretation of the results both single and multiple scattering in a half space are considered. The single scattering model proposed by Sato (1977 was used. Two methods, the coda (Qc and the Multiple Lapse Time Window (MLTW method are used. The aim of this study is to validate these interpretations in the region and to try to identify the effects of attenuation due to intrinsic (Qi and scattering attenuation (Qsc. The mean Qc value calculated was Qc = (39 ± 1f1.0±0.009. The average Qc at 1.5 Hz is (53 ± 6 and Qc = (900 ± 195 at 24 Hz with Qo ranging between 23 and 107, where η ranging between 0.9 and 1.3. The quality factor (Q was estimated from spectra of P- and S-waves by applying a spectral ratio technique. The results show variations in Qp and QS as a function of frequency, according to the power law Q = 56η1.1. The seismic albedo is 0.7 at all stations and it mean that the earthquake activity is due to tectonic origin. The attenuation and frequency dependency for different paths and the correlation of the results with the geotectonic of the region are presented. The Qc values were calculated and correlated with the geology and tectonics of the area. The relatively low Qo and the high frequency dependency agree with the values of a region characterized by a low tectonic activity and vise versa.

  19. Controllable seismic source

    Energy Technology Data Exchange (ETDEWEB)

    Gomez, Antonio; DeRego, Paul Jeffrey; Ferrell, Patrick Andrew; Thom, Robert Anthony; Trujillo, Joshua J.; Herridge, Brian

    2015-09-29

    An apparatus for generating seismic waves includes a housing, a strike surface within the housing, and a hammer movably disposed within the housing. An actuator induces a striking motion in the hammer such that the hammer impacts the strike surface as part of the striking motion. The actuator is selectively adjustable to change characteristics of the striking motion and characteristics of seismic waves generated by the impact. The hammer may be modified to change the physical characteristics of the hammer, thereby changing characteristics of seismic waves generated by the hammer. The hammer may be disposed within a removable shock cavity, and the apparatus may include two hammers and two shock cavities positioned symmetrically about a center of the apparatus.

  20. Controllable seismic source

    Energy Technology Data Exchange (ETDEWEB)

    Gomez, Antonio; DeRego, Paul Jeffrey; Ferrel, Patrick Andrew; Thom, Robert Anthony; Trujillo, Joshua J.; Herridge, Brian

    2014-08-19

    An apparatus for generating seismic waves includes a housing, a strike surface within the housing, and a hammer movably disposed within the housing. An actuator induces a striking motion in the hammer such that the hammer impacts the strike surface as part of the striking motion. The actuator is selectively adjustable to change characteristics of the striking motion and characteristics of seismic waves generated by the impact. The hammer may be modified to change the physical characteristics of the hammer, thereby changing characteristics of seismic waves generated by the hammer. The hammer may be disposed within a removable shock cavity, and the apparatus may include two hammers and two shock cavities positioned symmetrically about a center of the apparatus.

  1. Source mechanisms of mining-related seismic events in the Far West Rand, South Africa

    CSIR Research Space (South Africa)

    Kassa, BB

    2009-09-01

    Full Text Available Meeting and Exhibition Swaziland, 16 - 18 September 2009, pages 69 - 72 Source mechanisms of mining-related seismic events in the Far West Rand, South Africa BB Kassa1, J Julià2, AA Nyblade2 and RJ Durrheim1,3 1University of the Witwatersrand... layer between the gold- bearing reefs, the forward problem can be formulated as [Trifu et al., 2000; Julia et al., 2009] u=cF:M where u = vector of spectral displacements, c = 1/(4pV3R), ρ = density, V = P- or S-wave velocity, R = hypocentral...

  2. Double-Difference Tomography for Sequestration MVA

    Energy Technology Data Exchange (ETDEWEB)

    Westman, Erik

    2008-12-31

    Analysis of synthetic data was performed to determine the most cost-effective tomographic monitoring system for a geologic carbon sequestration injection site. Double-difference tomographic inversion was performed on 125 synthetic data sets: five stages of CO2 plume growth, five seismic event regions, and five geophone arrays. Each resulting velocity model was compared quantitatively to its respective synthetic velocity model to determine an accuracy value. The results were examined to determine a relationship between cost and accuracy in monitoring, verification, and accounting applications using double-difference tomography. The geophone arrays with widely-varying geophone locations, both laterally and vertically, performed best. Additionally, double difference seismic tomography was performed using travel time data from a carbon sequestration site at the Aneth oil field in southeast Utah as part of a Department of Energy initiative on monitoring, verification, and accounting (MVA) of sequestered CO2. A total of 1,211 seismic events were recorded from a borehole array consisting of 22 geophones. Artificial velocity models were created to determine the ease with which different CO2 plume locations and sizes can be detected. Most likely because of the poor geophone arrangement, a low velocity zone in the Desert Creek reservoir can only be detected when regions of test site containing the highest ray path coverage are considered. MVA accuracy and precision may be improved through the use of a receiver array that provides more comprehensive ray path coverage.

  3. Seismic source characterisation of a Tunnel Boring Machine (TBM)

    Science.gov (United States)

    Kreutzer, Ingrid; Brückl, Ewald; Radinger, Alexander

    2015-04-01

    The Tunnel Seismic While Drilling (TSWD) method aims at predicting continuously the geological situation ahead of the tunnel without disturbing the construction work. Thereby the Tunnel Boring Machine (TBM) itself is used as seismic source. The cutting process generates seismic waves radiating into the rock mass and vibrations propagating to the main bearing of the cutter head. These vibrations are monitored and used as pilot signal. For the processing and interpretation it was hypothesized so far that the TBM acts like a single force. To prove this assumption the radiation pattern of several TBM's under construction were investigated. Therefore 3-components geophones were installed at the surface, which were situated directly above the tunnel axes and also with lateral offset. Additional, borehole geophones were placed in the wall of one tube of a two-tube tunnel. The geophones collected the forward and backward radiated wave field, as the TBM, operating in the other tube, passed their positions. The obtained seismic data contains continuous records over a range of 600 m of the TBM position. The offsets vary from 25 m to 400 m and the frequency ranges from 20-250 Hertz. The polarisation of the p-wave and the s-wave and their amplitude ratio were determined and compared with modelled seismograms with different source mechanism. The results show that the description of the source mechanism by a single force can be used as a first order approximation. More complex radiation pattern including tensile forces and several source locations like the transmission of reaction forces over the gripper to the tunnel wall are further tested and addressed.

  4. Soil Profiles and Seismic Loading

    Directory of Open Access Journals (Sweden)

    Janotka, V.

    2006-01-01

    Full Text Available The contribution estimates different geotechnical profiles of site condition change and their influences on the computed seismic response spectra and time histories final values and forms applying on the seismic structures loading. The mentioned problems methodics attitude solution is based on the computed seismic motion parameters.

  5. Seismic Data Processing and the Characterization of a Gas Hydrate Bearing Zone Offshore of Southwestern Taiwan

    Directory of Open Access Journals (Sweden)

    Hui Deng

    2006-01-01

    Full Text Available Various seismic attributes of gas hydrate bearing sediments were analyzed in the accretionary prism offshore of southwestern Taiwan utilizing seismic imaging, velocity analysis, AVO analysis, and AVO inversion of large offset seismic data. A bottom-simulating reflector (BSR is clearly observed on the seismic section with a reversed polarity compared to that of the seabed reflection. Instantaneous amplitude sectioning clearly shows lateral variations of the BSR. The zero-phase waveform of the BSR is distinct and the weak reflectors above the BSR can be observed on the instantaneous phase section. AVO analysis shows the absolute value of the negative BSR amplitude increasing with offset. A low P-wave interval velocity layer was found below the strong BSR by detailed velocity analysis. Both the P (normal incident P-wave reflection coefficient and G (AVO gradient values are highly negative for the strong BSR on the P and G sections, and they lie in the third quadrant of the P and G cross-plot section. The P+G (reflectivity of Poisson¡¦s ratio value is also negative on the P+G section and the P-G (normal incident S-wave reflection coefficient value is approximately zero on the P-G section along the same strong BSR. All the seismic characters described above suggest that a gas hydrate layer exists together with a free gas layer below it along strong BSRs in the area offshore southwestern Taiwan.

  6. High-frequency seismic wave propagation within the heterogeneous crust: effects of seismic scattering and intrinsic attenuation on ground motion modelling

    Science.gov (United States)

    Takemura, Shunsuke; Kobayashi, Manabu; Yoshimoto, Kazuo

    2017-09-01

    For practical modelling of high-frequency (>1 Hz) seismic wave propagation, we analysed the apparent radiation patterns and attenuations of P and S waves using observed Hi-net velocity seismograms for small-to-moderate crustal earthquakes in the Chugoku region, southwestern Japan. By comparing observed and simulated seismograms, we estimated practical parameter sets of crustal small-scale velocity heterogeneity and intrinsic attenuations of P and S waves (QP.int-1 and QS.int-1). Numerical simulations of seismic wave propagation were conducted via the finite-difference method using a 1-D crustal velocity structure model with additional 3-D small-scale velocity heterogeneity and intrinsic attenuation. The estimated crustal small-scale velocity heterogeneity is stochastically characterized by an exponential-type power spectral density function with correlation length of 1 km and root-mean-square value of 0.03. Estimated QP.int-1 and QS.int-1 values range from 10-2.6 to 10-2.0 and 10-2.8 to 10-2.4, respectively, indicating QP.int-1 > QS.int-1 for high frequencies (>1 Hz). Intrinsic attenuation dominates over scattering attenuation, which is caused by small-scale velocity heterogeneity. The crustal parameters obtained in this study are useful for evaluating peak ground velocities and coda envelopes for moderate crustal earthquakes via physical-based simulations using a 3-D heterogeneous structure model.

  7. Improving the Monitoring, Verification, and Accounting of CO{sub 2} Sequestered in Geologic Systems with Multicomponent Seismic Technology and Rock Physics Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Alkan, Engin; DeAngelo, Michael; Hardage, Bob; Sava, Diana; Sullivan, Charlotte; Wagner, Donald

    2012-12-31

    Research done in this study showed that P-SV seismic data provide better spatial resolution of geologic targets at our Appalachian Basin study area than do P-P data. This finding is important because the latter data (P-P) are the principal seismic data used to evaluate rock systems considered for CO{sub 2} sequestration. The increase in P-SV{sub 1} resolution over P-P resolution was particularly significant, with P-SV{sub 1} wavelengths being approximately 40-percent shorter than P-P wavelengths. CO{sub 2} sequestration projects across the Appalachian Basin should take advantage of the increased resolution provided by converted-shear seismic modes relative to P-wave seismic data. In addition to S-wave data providing better resolution of geologic targets, we found S-wave images described reservoir heterogeneities that P-P data could not see. Specifically, a channel-like anomaly was imaged in a key porous sandstone interval by P-SV{sub 1} data, and no indication of the feature existed in P-P data. If any stratigraphic unit is considered for CO{sub 2} storage purposes, it is important to know all heterogeneities internal to the unit to understand reservoir compartmentalization. We conclude it is essential that multicomponent seismic data be used to evaluate all potential reservoir targets whenever a CO{sub 2} storage effort is considered, particularly when sequestration efforts are initiated in the Appalachian Basin. Significant differences were observed between P-wave sequences and S- wave sequences in data windows corresponding to the Oriskany Sandstone, a popular unit considered for CO{sub 2} sequestration. This example demonstrates that S-wave sequences and facies often differ from P-wave sequences and facies and is a principle we have observed in every multicomponent seismic interpretation our research laboratory has done. As a result, we now emphasis elastic wavefield seismic stratigraphy in our reservoir characterization studies, which is a science based on the

  8. Characterization of U.S. Wave Energy Converter (WEC) Test Sites: A Catalogue of Met-Ocean Data.

    Energy Technology Data Exchange (ETDEWEB)

    Dallman, Ann Renee; Neary, Vincent Sinclair

    2014-10-01

    This report presents met - ocean data and wave energy characteristics at three U.S. wave energy converter (WEC) test and potential deployment sites . Its purpose is to enable the compari son of wave resource characteristics among sites as well as the select io n of test sites that are most suitable for a developer's device and that best meet their testing needs and objectives . It also provides essential inputs for the design of WEC test devices and planning WEC tests, including the planning of deployment and op eration s and maintenance. For each site, this report catalogues wave statistics recommended in the (draft) International Electrotechnical Commission Technical Specification (IEC 62600 - 101 TS) on Wave Energy Characterization, as well as the frequency of oc currence of weather windows and extreme sea states, and statistics on wind and ocean currents. It also provides useful information on test site infrastructure and services .

  9. Determination of the {ital S}-wave scattering length in pionic deuterium with a high resolution crystal spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Chatellard, D.; Egger, J.; Jeannet, E. [Institut de Physique de l`Universite, Breguet 1, CH-2000 Neuchatel (Switzerland); Badertscher, A.; Bogdan, M.; Goudsmit, P.F.A.; Leisi, H.J.; Matsinos, E.; Schroeder, H.; Sigg, D.; Zhao, Z.G. [Institut fuer Teilchenphysik der Eidgenoessische Technische Hochschule Zuerich, CH-5232 Villigen PSI (Switzerland); Aschenauer, E.C.; Gabathuler, K.; Hauser, P.; Simons, L.M. [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Rusi, A.J.; Hassani, E. [Ecole Mohammadia des Ingenieurs, Rabat (Morocco)

    1995-05-22

    The pionic deuterium 3{ital P}{minus}1{ital S} x-ray transition was measured with a quartz crystal spectrometer in combination with a cyclotron trap and charge coupled device detectors. The strong interaction shift and total decay width of the 1{ital S} level are {epsilon}{sub 1{ital S}}(shift)=2.48{plus_minus}0.10 eV (repulsive), {Gamma}{sub 1{ital S}}(width)=1.02{plus_minus}0.21 eV, where the statistical and systematic errors were added linearly. They yield the total pionic deuterium {ital S}-wave scattering length: {ital a}{sub {pi}{sup {minus}}{ital d}}= {minus}0.0264({plus_minus}0.0011)+{ital i}0.0054({plus_minus}0.0011){ital m}{sub {pi}}{sup {minus}1}.

  10. Theory of edge states in a quantum anomalous Hall insulator/spin-singlet s-wave superconductor hybrid system

    Science.gov (United States)

    Ii, Akihiro; Yada, Keiji; Sato, Masatoshi; Tanaka, Yukio

    2011-06-01

    We study the edge states for a quantum anomalous Hall system (QAHS) coupled with a spin-singlet s-wave superconductor through the proximity effect, and clarify the topological nature of them. When we consider a superconducting pair potential induced in the QAHS, there appear topological phases with nonzero Chern numbers, i.e., N=1 and N=2, where Andreev bound states appear as chiral Majorana edge modes. We calculate the energy spectrum of the edge modes and the resulting local density of states. It is found that the degenerate chiral Majorana edge modes for N=2 are lifted off by applying a Zeeman magnetic field parallel to the interface or the shift of the chemical potential by doping. The degeneracy of the chiral Majorana edge modes and its lifting are explained by two different winding numbers defined at the time-reversal invariant point of the edge momentum.

  11. Pre-seismic, co-seismic and post-seismic displacements associated ...

    Indian Academy of Sciences (India)

    Pre-seismic, co-seismic and post-seismic displacements associated with the Bhuj 2001 earthquake derived from recent and historic geodetic data. Sridevi Jade M Mukul I A Parvez M B Ananda P D Kumar V K Gaur R Bendick R Bilham F Blume K Wallace I A Abbasi M Asif Khan S Ulhadi. Volume 112 Issue 3 September ...

  12. 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.

  13. Understanding induced seismicity

    NARCIS (Netherlands)

    Elsworth, Derek; Spiers, Christopher J.|info:eu-repo/dai/nl/304829323; Niemeijer, Andre R.|info:eu-repo/dai/nl/370832132

    2016-01-01

    Fluid injection–induced seismicity has become increasingly widespread in oil- and gas-producing areas of the United States (1–3) and western Canada. It has shelved deep geothermal energy projects in Switzerland and the United States (4), and its effects are especially acute in Oklahoma, where

  14. Degree 16 model of S-wave heterogeneity in the upper mantle determined by the Direct Solution Method

    Science.gov (United States)

    Hara, T.

    2001-12-01

    We determine degree 16 model of S-wave heterogeneity in the upper mantle by waveform inversion of long period surface wave data. We use the Direct Solution Method (DSM. Hara et al., [1991]) for theoretical calculations. Although the high accuracy of the DSM can improve the accuracy of earth models (Hara and Geller [2000]), the resolution of the model is still limited due to its heavy computational requirements (e.g., Hara and Geller [2000] obtained an degree 8 model of the upper mantle S-wave velocity). It is necessary to improve the DSM computational efficiency to raise the model resolution. Recently, Hara [2000] implemented the DSM codes on vector-parallel supercomputer to find that the improvement of_@computational efficiency is almost proportional to the number of processing elements. In the present study, we apply these codes to analyses of surface wave data in the frequency band 2-4mHz. The upper mantle is divided into three layers (11-216 km, 216-421 km, and 421-671 km), and the lateral heterogeneity is expanded using spherical harmonics up to degree 16. Long wavelength features of this new model are similar to the model of Hara and Geller [2000]. There is a good correlation between low velocities and hot spot distributions in the shallow upper mantle (11-216 km). There are low velocities in the transition zone under some hot spots (e.g., south Pacific), which suggests that it is possible to trace temperature and/or chemical heterogeneities related to hot spots by surface wave studies.

  15. Long term monitoring of the micro-seismicity along the Main Marmara Fault, Turkey using template matching

    Science.gov (United States)

    Matrullo, Emanuela; Lengliné, Olivier; Schmittbuhl, Jean; Karabulut, Hayrullah; Bouchon, Michel

    2017-04-01

    The Main Marmara Fault (MMF) represents a 150 km un-ruptured segment of the North Anatolian Fault located below the Marmara Sea. It poses a significant hazard for the large cities surrounding the region and in particular for the megalopolis of Istanbul. The seismic activity has been continuously monitored since 2007 by various seismic networks. For this purpose it represents an extraordinary natural laboratory to study in details the whole seismicity bringing insights into the geometry of the faults systems at depth and mechanical properties at various space-time scales. Waveform similarity-based analysis is performed on the continuous recordings to construct a refined catalog of earthquakes from 2009 to 2014. High-resolution relocation was applied using the double-difference algorithm, using cross-correlation differential travel-time data. Seismic moment magnitudes (Mw) have been computed combining the inversion of earthquake S-wave displacement spectra for the larger events and the estimation of the relative size of multiplets using the singular value decomposition (SVD) thanks the highly coherent waveforms. The obtained catalog of seismicity includes more than 15,000 events. The seismicity strongly varying along the strike and depth exhibits a complex structure that confirms the segmentation of the fault with different mechanical behavior (Schmittbuhl et al., GGG, 2016). In the central part of the Marmara Sea, seismicity is poor and scattered. To the east, in the Cinarcick basin, along the MMF, the seismicity is mainly located around 8-15 km in depth, except at both ends of this basin where the seismicity extends vertically up to surface. In the Yalova and Gemlik region (to the east not on the MMF) the seismicity is distributed over a wide range of depth (from surface to 15 km deep) and is characterized by several clusters vertically elongated. The spatio-temporal evolution of earthquake sequences, which repeatedly occur in specific sub-areas, and the seismic

  16. Back-Projecting Volcano and Geyser Seismic Signals to Sources

    Science.gov (United States)

    Kelly, C. L.; Lawrence, J. F.; Ebinger, C. J.

    2015-12-01

    Volcanic and hydrothermal systems are generally characterized by persistent, low-amplitude seismic "noise" with no clear onset or end. Outside of active eruptions and earthquakes, which tend to occur only a small fraction of the time, seismic records and spectrograms from these systems are dominated by long-duration "noise" (typically around 1-5Hz) generated by ongoing processes in the systems' subsurface. Although it has been shown that these low-amplitude signals can represent a series of overlapping low-magnitude displacements related to fluid and volatile movement at depth, because of their "noisy" properties compared to typical active or earthquake sources they are difficult to image using traditional seismic techniques (i.e. phase-picking). In this study we present results from applying a new ambient noise back-projection technique to improve seismic source imaging of diffuse signals found in volcanic and hydrothermal systems. Using this new method we show how the distribution of all seismic sources - particularly sources associated with volcanic tremor - evolves during a proposed intrusion in early June 2010 at Sierra Negra Volcano on the Galápagos Archipelago off the coast of Ecuador. We use a known velocity model for the region (Tepp et al., 2014) to correlate and back-project seismic signals from all available receiver-pairs to potential subsurface source locations assuming bending raypaths and accounting for topography. We generate 4D time-lapsed images of the source field around Sierra Negra before, during and after the proposed intrusion and compare the consistency of our observations with previously identified seismic event locations and tomography results from the same time period. Preliminary results from applying the technique to a dense grid of geophones surrounding a periodically erupting geyser at El Tatio Geyser Field in northern Chile (>2000 eruptions recorded) will also be presented.

  17. In situ seismic velocity changes in Southern Iceland

    Science.gov (United States)

    Bjarnason, Ingi Th.; Menke, William; Þorbjarnardóttir, Bergþóra S.; Kjartansson, Einar; Guðmundsson, Gunnar

    2017-04-01

    Detecting in situ velocity changes in the crust of the earth before significant earthquakes (pre-seismic changes), for the purpose of predicting earthquakes, has been described as the Holy Grail of seismology, i.e. highly desirable goal but with elusive results. Pre-seismic signals of the order of 10-20%, reported in the 1960ies and 1970ies, have not been convincingly reproduced. Lower level (0.5-3.5%) coseismic and postseismic in situ changes have, however, repeatedly been reported. Due to lack of seismicity prior to significant earthquakes, adequate data are often lacking to test the hypothesis of pre-seismic signals. Using earthquake data in order to detect such signals, errors in earthquake locations and velocity models may give a false-positive temporal signals. For the detection of a low level ( 1.0%) pre-seismic change, good knowledge of seismic structure, high accuracy of earthquake locations, and a continuous high level of seismicity are important factors. The local seismic network of the Icelandic Meteorology Office, the SIL network, is in many respects ideal for studying in situ pre-seismic changes before significant earthquakes. Since the beginning of its operation in 1991, four earthquakes of magnitude 6.0 and greater have occurred in the region, which may have caused pre-seismic velocity changes in the crust. The original design of the network had a high clock accuracy (±1 ms). S-waves tend to be very clear, and successful 1D velocity model (SIL model) has been used to locate earthquakes in the area, suggesting relatively simple velocity structure in spite of active tectonic setting. Earthquakes in Southern Iceland during the period 1991 to 2000 are being analyzed. The period includes two large earthquakes in year 2000, both of them of the magnitude 6.5. The analysis involves improving earthquake locations in order to determine if in situ changes do exist in the area (down to 0.5% significance level), with the ultimate goal of locating them at

  18. Seismic Imaging and Seismicity Analysis in Beijing-Tianjin-Tangshan Region

    Directory of Open Access Journals (Sweden)

    Xiangwei Yu

    2011-01-01

    Full Text Available In this study a new tomographic method is applied to over 43,400 high-quality absolute direct P arrival times and 200,660 relative P arrival times to determine detailed 3D crustal velocity structures as well as the absolute and relative hypocenter parameters of 2809 seismic events under the Beijing-Tianjin-Tangshan region. The inferred velocity model of the upper crust correlates well with the surface geological and topographic features in the BTT region. In the North China Basin, the depression and uplift areas are imaged as slow and fast velocities, respectively. After relocation, the double-difference tomography method provides a sharp picture of the seismicity in the BTT region, which is concentrated along with the major faults. A broad low-velocity anomaly exists in Tangshan and surrounding area from 20 km down to 30 km depth. Our results suggest that the top boundary of low-velocity anomalies is at about 25.4 km depth. The event relocations inverted from double-difference tomography are clusted tightly along the Tangshan-Dacheng Fault and form three clusters on the vertical slice. The maximum focal depth after relocation is about 25 km depth in the Tangshan area.

  19. High Voltage Seismic Generator

    Science.gov (United States)

    Bogacz, Adrian; Pala, Damian; Knafel, Marcin

    2015-04-01

    This contribution describes the preliminary result of annual cooperation of three student research groups from AGH UST in Krakow, Poland. The aim of this cooperation was to develop and construct a high voltage seismic wave generator. Constructed device uses a high-energy electrical discharge to generate seismic wave in ground. This type of device can be applied in several different methods of seismic measurement, but because of its limited power it is mainly dedicated for engineering geophysics. The source operates on a basic physical principles. The energy is stored in capacitor bank, which is charged by two stage low to high voltage converter. Stored energy is then released in very short time through high voltage thyristor in spark gap. The whole appliance is powered from li-ion battery and controlled by ATmega microcontroller. It is possible to construct larger and more powerful device. In this contribution the structure of device with technical specifications is resented. As a part of the investigation the prototype was built and series of experiments conducted. System parameter was measured, on this basis specification of elements for the final device were chosen. First stage of the project was successful. It was possible to efficiently generate seismic waves with constructed device. Then the field test was conducted. Spark gap wasplaced in shallowborehole(0.5 m) filled with salt water. Geophones were placed on the ground in straight line. The comparison of signal registered with hammer source and sparker source was made. The results of the test measurements are presented and discussed. Analysis of the collected data shows that characteristic of generated seismic signal is very promising, thus confirms possibility of practical application of the new high voltage generator. The biggest advantage of presented device after signal characteristics is its size which is 0.5 x 0.25 x 0.2 m and weight approximately 7 kg. This features with small li-ion battery makes

  20. Passive Seismic Imaging

    Science.gov (United States)

    Artman, B. W.

    2003-12-01

    Traditionally, passive seismology connotes the use of earthquake signals from continuously recording receivers. Small time windows around the arrivals of earthquakes are then analyzed in myriad fashion. I will distinguish from this body of work, the notion of passive seismic imaging, which requires no knowledge of the time or characteristics of a source event. Instead, by using the ambient noise in the subsurface with all orders of scattering and thus randomized directionality, passive seismic imaging can produce results analogous to conventional controlled source experiments. Mathematical proof of the concept of passive seismic imaging has been presented in the literature from several foundations. The results reduce to the simple concept of cross-correlating many long recordings within a simultaneously deployed array. This generates panels with the kinematics of a shot-gather from a standard reflection seismic acquisition effort. Results from synthetic data sets show the validity of the method for point diffractor, and layered earth models. Noting the similarity of form of the standard approach to produce shot-gathers with the imaging condition of shot-profile migration, I then show that migrating the raw passive seismic data without the correlation step produces the the correct image. The synthetic data from above is used to demonstrate the technique. By comparison, this image is of better quality, and demands less compute time, than migrating the data having been cross-correlated first. Finally, both techniques are used to process a 2x2 meter, 72-channel array recorded on the beach sand of Monterey Bay, California. Approximately one meter below the sand, a six inch diameter plastic pipe was buried to serve as a target.

  1. Appropriate conditions to realize a p -wave superfluid state starting from a spin-orbit-coupled s -wave superfluid Fermi gas

    Science.gov (United States)

    Yamaguchi, T.; Inotani, D.; Ohashi, Y.

    2017-05-01

    We theoretically investigate a spin-orbit-coupled s -wave superfluid Fermi gas, to examine the time evolution of the system, after an s -wave pairing interaction is replaced by a p -wave one at t =0 . In our recent paper [T. Yamaguchi, D. Inotani, and Y. Ohashi, J. Phys. Soc. Jpn. 86, 013001 (2017), 10.7566/JPSJ.86.013001], we proposed that this manipulation may realize a p -wave superfluid Fermi gas because the p -wave pair amplitude that is induced in the s -wave superfluid state by a parity-broken antisymmetric spin-orbit interaction gives a nonvanishing p -wave superfluid order parameter, immediately after the p -wave interaction is turned on. In this paper, using a time-dependent Bogoliubov-de Gennes theory, we assess this idea under various conditions with respect to the s -wave and p -wave interaction strengths, as well as the spin-orbit coupling strength. From these, we clarify that the momentum distribution of Fermi atoms in the initial s -wave state (t gas physics, our results may provide a possible way to accomplish this.

  2. Hydrogeological response to tele-seismic events with underground water level precision monitoring data

    Science.gov (United States)

    Gorbunova, Ella; Vinogradov, Evgeny; Besedina, Alina; Kabychenko, Nikolay; Svintsov, Igor

    2015-04-01

    Underground water level precision monitoring has been being carried out in the IDG RAS experimental area "Mikhnevo" in step with barometric pressure measuring since February of 2008. Seismic events registration is being realized with small aperture seismic array "Mikhnevo" and STS-2 seismometer. Complex processing of original hydrological and seismic data allows to mark out hydrological responses to large earthquakes (Mw>7.5) seismic waves propagation throw aseismic region - central area of Russian Plate. GPO "Mikhnevo" is located within South part of Moscow artesian basin in the North-East part of Prioksko-Terrasny biosphere reserve out of intensive anthropogenic impact zone. Wellbore unseals index aquifer in the interval of 91-115 m. An aquifer is characterized with season level variations. Water containing rocks are presented with nonuniform fractured limestones. In IDG RAS step-by-step methodic of experimental data handling was devised. First preliminary comparison of 1 Hz frequency seismic and hydrological data is being carried out for hydrogeological response to large earthquakes (Mw>7.5) seismic waves propagation marking out. On basis of these data main types and parameters of waves registered in seismic and hydrological data are being identified and representative periods for geological medium response to tele-seismic events analysis are being selected. In the area of GPO "Mikhnevo" we traced geological response to disastrous earthquakes that took place 02/27/2011 near Central Chile Coast and 03/11/11 near Honshu Island east coast that is presented being smoothed in underground water level. Tele-seismic events differs in intensity, signal duration and post-seismic effect. Significant water level harmonic oscillations are coupled with surface and S-waves arrival, where vertical component prevails First hydrological responses were registered in the time of S-wave propagation 28 minutes after Honshu earthquake beginning and 39 minutes after Chile earthquake

  3. Extending Regional Seismic Travel Time (RSTT) Tomography to New Regions

    Science.gov (United States)

    2011-09-01

    layers overlay a mantle velocity profile that is simplified to two parameters: velocity at the Moho and a linear velocity gradient with depth. By... Moho depth of the starting model. (b) An example velocity/depth profile as defined at each node. The mantle portion of the profile is specified by...follows the contour of the Moho (e.g., Hearn, 1984). The head wave assumption results in poor travel time prediction at far-regional distance (>~700 km

  4. Modeling of the Sedimentary Interbedded Basalt Stratigraphy for the Idaho National Laboratory Probabilistic Seismic Hazard Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Suzette Payne

    2007-08-01

    This report summarizes how the effects of the sedimentary interbedded basalt stratigraphy were modeled in the probabilistic seismic hazard analysis (PSHA) of the Idaho National Laboratory (INL). Drill holes indicate the bedrock beneath INL facilities is composed of about 1.1 km of alternating layers of basalt rock and loosely consolidated sediments. Alternating layers of hard rock and “soft” loose sediments tend to attenuate seismic energy greater than uniform rock due to scattering and damping. The INL PSHA incorporated the effects of the sedimentary interbedded basalt stratigraphy by developing site-specific shear (S) wave velocity profiles. The profiles were used in the PSHA to model the near-surface site response by developing site-specific stochastic attenuation relationships.

  5. Modeling of the Sedimentary Interbedded Basalt Stratigraphy for the Idaho National Laboratory Probabilistic Seismic Hazard Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Suzette Payne

    2006-04-01

    This report summarizes how the effects of the sedimentary interbedded basalt stratigraphy were modeled in the probabilistic seismic hazard analysis (PSHA) of the Idaho National Laboratory (INL). Drill holes indicate the bedrock beneath INL facilities is composed of about 1.1 km of alternating layers of basalt rock and loosely consolidated sediments. Alternating layers of hard rock and “soft” loose sediments tend to attenuate seismic energy greater than uniform rock due to scattering and damping. The INL PSHA incorporated the effects of the sedimentary interbedded basalt stratigraphy by developing site-specific shear (S) wave velocity profiles. The profiles were used in the PSHA to model the near-surface site response by developing site-specific stochastic attenuation relationships.

  6. Geotechnical Parameters from Seismic Measurements: Two Field Examples from Egypt and Saudi Arabia

    KAUST Repository

    Khalil, Mohamed H.

    2016-03-18

    © 2016 EEGS. Geotechnical parameters were used to determine subsurface rock quality for construction purposes. We summarize the mathematical relationships used to calculate the geotechnical parameters from P- and S-wave velocities and density values. These relationships are applied to two field examples; the first is a regional seismic study in Egypt and the second is a 2-D seismic profile recorded in Saudi Arabia. Results from both field examples are used to determine the subsurface rock quality and locate zones that should be avoided during construction. We suggest combining all geotechnical parameters into one map using a normalized-weighted relation, which helps to locate the zones with high versus low rock quality for engineering purposes.

  7. Structure of the Suasselkä postglacial fault in northern Finland obtained by analysis of local events and ambient seismic noise

    Science.gov (United States)

    Afonin, Nikita; Kozlovskaya, Elena; Kukkonen, Ilmo; Dafne/Finland Working Group

    2017-04-01

    Understanding the inner structure of seismogenic faults and their ability to reactivate is particularly important in investigating the continental intraplate seismicity regime. In our study we address this problem using analysis of local seismic events and ambient seismic noise recorded by the temporary DAFNE array in the northern Fennoscandian Shield. The main purpose of the DAFNE/FINLAND passive seismic array experiment was to characterize the present-day seismicity of the Suasselkä postglacial fault (SPGF), which was proposed as one potential target for the DAFNE (Drilling Active Faults in Northern Europe) project. The DAFNE/FINLAND array comprised an area of about 20 to 100 km and consisted of eight short-period and four broadband three-component autonomous seismic stations installed in the close vicinity of the fault area. The array recorded continuous seismic data during September 2011-May 2013. Recordings of the array have being analysed in order to identify and locate natural earthquakes from the fault area and to discriminate them from the blasts in the Kittilä gold mine. As a result, we found a number of natural seismic events originating from the fault area, which proves that the fault is still seismically active. In order to study the inner structure of the SPGF we use cross-correlation of ambient seismic noise recorded by the array. Analysis of azimuthal distribution of noise sources demonstrated that during the time interval under consideration the distribution of noise sources is close to the uniform one. The continuous data were processed in several steps including single-station data analysis, instrument response removal and time-domain stacking. The data were used to estimate empirical Green's functions between pairs of stations in the frequency band of 0.1-1 Hz and to calculate corresponding surface wave dispersion curves. The S-wave velocity models were obtained as a result of dispersion curve inversion. The results suggest that the area of

  8. In situ seismic measurements in claystone at Tournemire (France)

    Science.gov (United States)

    Zillmer, M.; Marthelot, J.-M.; Gélis, C.; Cabrera, J.; Druivenga, G.

    2014-12-01

    Compressional and shear wave seismic measurements were performed in an old railway tunnel and in galleries excavated in a 250-m-thick Toarcian claystone formation in the Tournemire experimental station (France). Three component (3C) geophones and three orthogonal orientations of the vibroseismic force source were used. Additionally, vertical seismic profiling (VSP) measurements were recorded with a 3C borehole geophone, a hydrophone and a microphone in a 159 m deep borehole (ID180) in the tunnel. The seismic data show that Toarcian claystone has strong transverse isotropy (TI) with a vertical symmetry axis. The qP, SH and qSV wave propagation velocities in horizontal directions-the plane of isotropy of the TI medium-are measured as 3550, 1850 and 1290 m s-1, respectively. The zero-offset VSP reveals that only one shear wave propagates in the vertical (depth) direction and the P- and S-wave velocities are 3100 and 1375 m s-1, respectively. Four elastic moduli of the TI medium are determined from the seismic velocities and from the bulk density of 2.53 g cm-3: c11 = 31.9 GPa, c33 = 24.3 GPa, c44 = 4.5 GPa and c66 = 8.7 GPa. A walkaway VSP with the borehole geophone at 50 m depth in borehole ID180 and shot points in the galleries leads to oblique seismic ray paths which allow us to determine the fifth elastic modulus of the TI medium to c13 = 16 GPa. The tube wave recorded by a hydrophone in the water filled lower part of the borehole propagates with 1350 m s-1, which confirms the estimate of the elastic constant c66. The analysis of body wave and surface wave data from a seismic experiment in Galerie Est shows reflections from several fracture zones in the gallery floor. The thickness of the excavation damaged zone (EDZ) in the floor of Galerie Est is estimated to 0.7 m.

  9. Stress-dependent elastic properties of shales—laboratory experiments at seismic and ultrasonic frequencies

    Science.gov (United States)

    Szewczyk, Dawid; Bauer, Andreas; Holt, Rune M.

    2018-01-01

    Knowledge about the stress sensitivity of elastic properties and velocities of shales is important for the interpretation of seismic time-lapse data taken as part of reservoir and caprock surveillance of both unconventional and conventional oil and gas fields (e.g. during 4-D monitoring of CO2 storage). Rock physics models are often developed based on laboratory measurements at ultrasonic frequencies. However, as shown previously, shales exhibit large seismic dispersion, and it is possible that stress sensitivities of velocities are also frequency dependent. In this work, we report on a series of seismic and ultrasonic laboratory tests in which the stress sensitivity of elastic properties of Mancos shale and Pierre shale I were investigated. The shales were tested at different water saturations. Dynamic rock engineering parameters and elastic wave velocities were examined on core plugs exposed to isotropic loading. Experiments were carried out in an apparatus allowing for static-compaction and dynamic measurements at seismic and ultrasonic frequencies within single test. For both shale types, we present and discuss experimental results that demonstrate dispersion and stress sensitivity of the rock stiffness, as well as P- and S-wave velocities, and stiffness anisotropy. Our experimental results show that the stress-sensitivity of shales is different at seismic and ultrasonic frequencies, which can be linked with simultaneously occurring changes in the dispersion with applied stress. Measured stress sensitivity of elastic properties for relatively dry samples was higher at seismic frequencies however, the increasing saturation of shales decreases the difference between seismic and ultrasonic stress-sensitivities, and for moist samples stress-sensitivity is higher at ultrasonic frequencies. Simultaneously, the increased saturation highly increases the dispersion in shales. We have also found that the stress-sensitivity is highly anisotropic in both shales and that in

  10. On the feasibility and use of teleseismic P wave coda autocorrelation for mapping shallow seismic discontinuities

    Science.gov (United States)

    Phạm, Thanh-Son; Tkalčić, Hrvoje

    2017-05-01

    Seismic body waves from distant earthquakes, which propagate near vertically beneath recording stations, provide tools for imaging shallow Earth structures with high vertical resolution. The most commonly used techniques such as P and S wave receiver functions utilize mode conversions from P to S waves or vice versa to retrieve information on the gradients of elastic properties in the crust and upper mantle. Here we demonstrate the feasibility and advantage of utilizing reflection signals through an improved method of teleseismic P wave coda autocorrelation. We recover clear reflections independently on vertical and radial components, which provide complementary constraints on the subsurface structures. Field data from two stations from different geological settings are analyzed, one of which is an ice station in Antarctica and the other is a bedrock station on the Kaapvaal craton in South Africa. The results from both analyses show the feasibility of the method to unveil P and S wave reflection signals from the ice-rock interface and the Moho discontinuity. Extensive synthetic experiments are set up to corroborate our results.

  11. Assessing the Comprehensive Seismic Earth Model using normal mode data

    Science.gov (United States)

    Koelemeijer, Paula; Afanasiev, Michael; Fichtner, Andreas; Gokhberg, Alexey

    2016-04-01

    Advances in computational resources and numerical methods allow the simulation of realistic seismic wave propagation through complex media, while ensuring that the complete wave field is correctly represented in synthetic seismograms. This full waveform inversion is widely applied on regional and continental scales, where particularly dense data sampled can be achieved leading to an increased resolution in the obtained model images. On a global scale, however, full waveform tomography is still and will continue to be limited to longer length scales due to the large computational costs. Normal mode tomography provides an alternative fast full waveform approach for imaging seismic structures in a global way. Normal modes are not limited by the poor station-earthquake distribution and provide sensitivity to density structure. Using normal modes, a more robust long wavelength background model can be obtained, leading to more accurate absolute velocity models for tectonic and mineral physics interpretations. In addition, it is vital to combine all seismic data types across accessible periods to obtain a more complete, consistent and interpretable image of the Earth's interior. Here, we aim to combine the globally sensitive long period normal modes with shorter period full waveform modelling within the multi-scale framework of the Comprehensive Seismic Earth Model (CSEM). The multi-scale inversion framework of the CSEM allows exploitation of the full waveform capacity on both sides of the seismic spectrum. As the CSEM includes high-resolution subregions with velocity variations at much shorter wavelengths than normal modes could constrain, the question arises whether these small-scale variations are noticeable in normal mode data, and which modes respond in particular. We report here on experiments in which we address these questions. We separately investigate the effects of small-scale variations in shear-wave velocity and compressional wave velocity compared to the

  12. Seismic investigations in downtown Copenhagen, Denmark

    Science.gov (United States)

    Martinez, K.; Mendoza, J. A.; Olsen, H.

    2009-12-01

    Near surface geophysics are gaining widespread use in major infrastructure projects with respect to geotechnical and engineering applications. The development of data acquisition, processing tools and interpretation methods have optimized survey production, reduced logistics costs and increase results reliability of seismic surveys during the last decades. However, the use of geophysical methods under urban environments continues to face challenges due to multiple noise sources and obstacles inherent to cities. A seismic investigation was conducted in Copenhagen aiming to produce information needed for hydrological, geotechnical and groundwater modeling assessments related to the planned Cityringen underground metro project. The particular objectives were a) map variations in subsurface Quaternary and limestone properties b) to map for near surface structural features. The geological setting in the Copenhagen region is characterized by several interlaced layers of glacial till and meltwater sand deposits. These layers, which are found unevenly distributed throughout the city and present in varying thicknesses, overlie limestone of different generations. There are common occurrences of incised valley structures containing localized instances of weathered or fractured limestone. The surveys consisted of combined seismic reflection and refraction profiles accounting for approximately 13 km along sections of the projected metro line. The data acquisition was carried out using standard 192 channels arrays, receiver groups with 5 m spacing and a Vibroseis as a source at 5 m spacing. In order to improve the resolution of the data, 29 Walkaway-Vertical Seismic Profiles were performed at selected wells along the surface seismic lines. The refraction data was processed with travel-time tomography and the reflection data underwent standard interpretation. The refraction data inversion was performed twofold; a surface refraction alone and combined with the VSP data. Three

  13. Waveform modeling of the seismic response of a mid-ocean ridge axial melt sill

    Science.gov (United States)

    Xu, Min; Stephen, R. A.; Canales, J. Pablo

    2017-12-01

    Seismic reflections from axial magma lens (AML) are commonly observed along many mid-ocean ridges, and are thought to arise from the negative impedance contrast between a solid, high-speed lid and the underlying low-speed, molten or partially molten (mush) sill. The polarity of the AML reflection ( P AML P) at vertical incidence and the amplitude vs offset (AVO) behavior of the AML reflections (e.g., P AML P and S-converted P AML S waves) are often used as a diagnostic tool for the nature of the low-speed sill. Time-domain finite difference calculations for two-dimensional laterally homogeneous models show some scenarios make the interpretation of melt content from partial-offset stacks of P- and S-waves difficult. Laterally heterogeneous model calculations indicate diffractions from the edges of the finite-width AML reducing the amplitude of the AML reflections. Rough seafloor and/or a rough AML surface can also greatly reduce the amplitude of peg-leg multiples because of scattering and destructive interference. Mid-crustal seismic reflection events are observed in the three-dimensional multi-channel seismic dataset acquired over the RIDGE-2000 Integrated Study Site at East Pacific Rise (EPR, cruise MGL0812). Modeling indicates that the mid-crustal seismic reflection reflections are unlikely to arise from peg-leg multiples of the AML reflections, P-to- S converted phases, or scattering due to rough topography, but could probably arise from deeper multiple magma sills. Our results support the identification of Marjanović et al. (Nat Geosci 7(11):825-829, 2014) that a multi-level complex of melt lenses is present beneath the axis of the EPR.

  14. 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

  15. Seismic imaging of Southern African cratons

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad

    Cratonic regions are the oldest stable parts of continents that hold most of Earth’s mineral resources. There are several open questions regarding their formation and evolution. In this PhD study, passive source seismic methods have been used to investigate the crustal and lithosphere structures...... of the southern African regions. Some of the main research problems that have been dealt with during this research are about (1) the heterogeneity scale of crustal structure and composition, (2) the depth extent of the cratonic keels and their layering, and (3) the strength of crustal anisotropy. The core...... of this research was based on Ps- and Sp- receiver functions analysis to determine crustal thickness while finite-frequency traveltime tomography is utilized to model 3D heterogeneity in the upper mantle. Combining the two methods provides high vertical and lateral resolution....

  16. An Automated Approach for the Determination of the Seismic Moment Tensor in Mining Environments

    Science.gov (United States)

    Wamboldt, Lawrence R.

    A study was undertaken to evaluate an automated process to invert for seismic moment tensors from seismic data recorded in mining environments. The data for this study was recorded at Nickel Rim South mine, Sudbury, Ontario. The mine has a seismic monitoring system manufactured by ESG Solutions that performs continuous monitoring of seismicity. On average, approximately 400 seismic events are recorded each day. Currently, data are automatically processed by ESG Solution's software suite during acquisition. The automatic processors pick the P- and/or S-wave arrivals, locate the events and solve for certain source parameters, excluding the seismic moment tensor. In order to solve for the moment tensor, data must be manually processed, which is laborious and therefore seldom performed. This research evaluates an automatic seismic moment tensor inversion method and demonstrates some of the difficulties (through inversions of real and synthetic seismic data) of the inversion process. Results using the method are also compared to the inversion method currently available from ESG Solutions, which requires the manual picking of first-motion polarities for every event. As a result of the extensive synthetic testing of the automatic inversion program, as well as the inversion of real seismic data, it is apparent that there are key parameters requiring greater accuracy in order to increase the reliability of the automation. These parameters include the source time function definition, source location (in turn requiring more accurate and precise knowledge of the earth media), arrival time picks and an attenuation model to account for ray-path dependent filtering of the source time function. In order to improve the automatic method three key pieces of research are needed: (1) studying various location algorithms (and the effects of increasing earth model intricacy) and automatic time picking to improve source location methods, (2) studying how the source time pulse can be

  17. High-Resolution Analysis of Seismicity Induced at Berlín Geothermal Field, El Salvador

    Science.gov (United States)

    Kwiatek, G.; Bulut, F.; Dresen, G. H.; Bohnhoff, M.

    2012-12-01

    We investigate induced microseismic activity monitored at Berlín Geothermal Field, El Salvador, during a hydraulic stimulation. The site was monitored for a time period of 17 months using thirteen 3-component seismic stations located in shallow boreholes. Three stimulations were performed in the well TR8A with a maximum injection rate and well head pressure of 160l/s and 130bar, respectively. For the entire time period of our analysis, the acquisition system recorded 581 events with moment magnitudes ranging between -0.5 and 3.7. The initial seismic catalog provided by the operator was substantially improved: 1) We re-picked P- and S-wave onsets and relocated the seismic events using the double-difference relocation algorithm based on cross-correlation derived differential arrival time data. Forward modeling was performed using a local 1D velocity model instead of homogeneous full-space. 2) We recalculated source parameters using the spectral fitting method and refined the results applying the spectral ratio method. We investigated the source parameters and spatial and temporal changes of the seismic activity based on the refined dataset and studied the correlation between seismic activity and production. The achieved hypocentral precision allowed resolving the spatiotemporal changes in seismic activity down to a scale of a few meters. The application of spectral ratio method significantly improved the quality of source parameters in a high-attenuating and complex geological environment. Of special interest is the largest event (Mw3.7) and its nucleation process. We investigate whether the refined seismic data display any signatures that the largest event is triggered by the shut-in of the well. We found seismic activity displaying clear spatial and temporal patterns that could be easily related to the amount of water injected into the well TR8A and other reinjection wells in the investigated area. The migration of seismicity outside of injection point is observed

  18. Lattice preferred orientation of amphibole in amphibolites from Jenner Headland and Ring Mt. in California and implications for seismic anisotropy

    Science.gov (United States)

    Kim, Junha; Jung, Haemyeong

    2017-04-01

    Seismic anisotropy in the crust which is observed throughout the world can be attributed to lattice preferred orientation (LPO) of elastically anisotropic minerals. Although amphibole has smaller elastic anisotropy than that of mica, it takes a large proportion of deep crust and sufficiently anisotropic. Therefore, to understand the seismic anisotropy of lower crust, we studied amphibolites from Jenner Headland and Ring Mt. in California. All samples are well-foliated amphibolites constituting dominantly amphibole, plagioclase and other minor minerals such as garnet, epidote, biotite, and titanite. Chemical compositions of these minerals were analyzed by EPMA, and LPO of minerals was determined by using SEM/EBSD technique at the Tectonophysics Laboratory in Seoul National University. Almost all samples showed that [100] axes of amphibole are aligned normal to the foliation and [001] axes are subparallel to the lineation, which is called Type-I LPO of amphibole (Ko & Jung, 2015). All axes of plagioclase showed almost random distributions. Seismic anisotropy was calculated from the LPOs of minerals. P-wave velocity anisotropy of amphibole was in the range of 15.9‒20.9% and maximum S-wave anisotropy was in the range of 13.1‒19.7%. For horizontal flow, seismic velocity of P-wave is slowest in the direction subnormal to foliation and fastest subparallel to lineation. Polarization direction of vertically propagating fast S-wave is subnormal to lineation. Shear wave anisotropy (AVs) is also lowest subnormal to lineation. When we consider dipping angle of flow at 45° assuming 2D corner flow model, polarization direction of fast S-wave is normal to lineation. Seismic anisotropies of whole rock were weaker than those of amphibole. Our results suggest that LPO of amphibole can strongly induce low-velocity and anisotropic layers in the deep crust causing a large seismic anisotropy depending on the direction of seismic wave propagation. Ko, B. and Jung, H., 2015, Crystal

  19. Joint Cross Well and Single Well Seismic Studies at Lost Hills, California

    Energy Technology Data Exchange (ETDEWEB)

    Gritto, Roland; Daley, Thomas M.; Myer, Larry R.

    2002-06-25

    A series of time-lapse seismic cross well and single well experiments were conducted in a diatomite reservoir to monitor the injection of CO{sub 2} into a hydrofracture zone, based on P- and S-wave data. A high-frequency piezo-electric P-wave source and an orbital-vibrator S-wave source were used to generate waves that were recorded by hydrophones as well as three-component geophones. The injection well was located about 12 m from the source well. During the pre-injection phase water was injected into the hydrofrac-zone. The set of seismic experiments was repeated after a time interval of 7 months during which CO{sub 2} was injected into the hydrofractured zone. The questions to be answered ranged from the detectability of the geologic structure in the diatomic reservoir to the detectability of CO{sub 2} within the hydrofracture. Furthermore it was intended to determine which experiment (cross well or single well) is best suited to resolve these features. During the pre-injection experiment, the P-wave velocities exhibited relatively low values between 1700-1900 m/s, which decreased to 1600-1800 m/s during the post-injection phase (-5%). The analysis of the pre-injection S-wave data revealed slow S-wave velocities between 600-800 m/s, while the post-injection data revealed velocities between 500-700 m/s (-6%). These velocity estimates produced high Poisson ratios between 0.36 and 0.46 for this highly porous ({approx} 50%) material. Differencing post- and pre-injection data revealed an increase in Poisson ratio of up to 5%. Both, velocity and Poisson estimates indicate the dissolution of CO{sub 2} in the liquid phase of the reservoir accompanied by a pore-pressure increase. The single well data supported the findings of the cross well experiments. P- and S-wave velocities as well as Poisson ratios were comparable to the estimates of the cross well data. The cross well experiment did not detect the presence of the hydrofracture but appeared to be sensitive to overall

  20. Simultaneous prestack seismic inversion in a carbonate reservoir

    Directory of Open Access Journals (Sweden)

    Rafael Amaral Cataldo

    Full Text Available Abstract We applied a method of Simultaneous Prestack Seismic Inversion (SPSI in a hydrocarbon field located in the Campos Basin, Brazil. The goal was to study the application of this method to Albian carbonate rocks of the Quissamã Formation. Based on what is found in nearby fields, this Formation potentially contains hydrocarbon accumulations that can be revealed with the inverted models. P-wave velocity (Vp, S-wave velocity (Vs and density (ρ curves along seven wells were used as inputs to construct 3-D initial models of acoustic impedance (Zp, shear impedance (Zs and ρ. Wells without Vs and ρ curves had those values calculated from well-established equations. Final 3-D models were calculated from deviations in linear relationships between the logarithms of Zs and Zp, as well as between ρ and Zp, which were merged with the initial models. Interpretations of the inversion results were conducted based on patterns found along well logs such as resistivity (ILD, gamma ray (GR, density (RHOB, neutron porosity (NPHI and sonic (DT. These analyses provided criteria to select the best inverted models. These models show low impedance anomalies that are consistent with previous studies performed with the well logs. One well in particular was interpreted as having high potential to contain hydrocarbons. This well shows an impedance pattern that allowed us to highlight other areas with the same pattern throughout the entire seismic volume.

  1. Comparison of seismic sources for shallow seismic: sledgehammer and pyrotechnics

    Directory of Open Access Journals (Sweden)

    Brom Aleksander

    2015-10-01

    Full Text Available The pyrotechnic materials are one of the types of the explosives materials which produce thermal, luminous or sound effects, gas, smoke and their combination as a result of a self-sustaining chemical reaction. Therefore, pyrotechnics can be used as a seismic source that is designed to release accumulated energy in a form of seismic wave recorded by tremor sensors (geophones after its passage through the rock mass. The aim of this paper was to determine the utility of pyrotechnics for shallow seismic engineering. The work presented comparing the conventional method of seismic wave excitation for seismic refraction method like plate and hammer and activating of firecrackers on the surface. The energy released by various sources and frequency spectra was compared for the two types of sources. The obtained results did not determine which sources gave the better results but showed very interesting aspects of using pyrotechnics in seismic measurements for example the use of pyrotechnic materials in MASW.

  2. Comparison of seismic sources for shallow seismic: sledgehammer and pyrotechnics

    Science.gov (United States)

    Brom, Aleksander; Stan-Kłeczek, Iwona

    2015-10-01

    The pyrotechnic materials are one of the types of the explosives materials which produce thermal, luminous or sound effects, gas, smoke and their combination as a result of a self-sustaining chemical reaction. Therefore, pyrotechnics can be used as a seismic source that is designed to release accumulated energy in a form of seismic wave recorded by tremor sensors (geophones) after its passage through the rock mass. The aim of this paper was to determine the utility of pyrotechnics for shallow seismic engineering. The work presented comparing the conventional method of seismic wave excitation for seismic refraction method like plate and hammer and activating of firecrackers on the surface. The energy released by various sources and frequency spectra was compared for the two types of sources. The obtained results did not determine which sources gave the better results but showed very interesting aspects of using pyrotechnics in seismic measurements for example the use of pyrotechnic materials in MASW.

  3. Crustal seismic anisotropy and structure from textural and seismic investigations in the Cycladic region, Greece

    Science.gov (United States)

    Cossette, Élise; Schneider, David; Audet, Pascal; Grasemann, Bernhard

    2016-04-01

    Seismic anisotropy data are often used to resolve rock structures and deformation styles in the crust based on compilations of rock properties that may not be representative of the exposed geology. We use teleseismic receiver functions jointly with in situ rock property data to constrain the seismic structure and anisotropy of the crust in the Cyclades, Greece, located in the back arc region of the Hellenic subduction zone. Crystallographic preferred orientations (CPOs) via electron backscatter diffraction (EBSD) analyses were measured on a suite of samples representative of different structural depths along the West Cycladic Detachment System; average seismic properties of the rocks were calculated with the Voigt-Reuss-Hill average of the single minerals' elastic stiffness tensor. The calcitic and quartzitic rocks have P- and S-wave velocity anisotropies (AVp, AVs) averaging 8.1% and 7.1%, respectively. The anisotropy increases with depth represented by blueschist assemblages, with AVp averaging 20.3% and AVs averaging 14.5% due to the content of aligned glaucophane and mica, which strongly control the seismic properties of the rocks. Localized anisotropies of very high magnitude are caused by the presence of mica schists as they possess the strongest anisotropies, with values of ~25% for AVp and AVs. The direction of the fast and slow P-wave velocities occur parallel and perpendicular to the foliation, respectively, for most samples. The fast propagation has the same NE-SW orientation as the lithospheric stretching direction present in the Cyclades since the Late Oligocene. The maximum shear wave anisotropy is subhorizontal, similarly concordant with mineral alignment that developed during back-arc extension. Our results strongly favor radial anisotropy in the Aegean mid-crust over azimuthal anisotropy. The receiver function data indicate that the Moho is relatively flat at 25 km depth in the south and deepens to 33 km in the north, consistent with previous

  4. The shallow seismic structure of the Larderello geothermal field (Italy) as seen from Receiver Function analysis

    Science.gov (United States)

    Piana Agostinetti, Nicola; Licciardi, Andrea; Piccinini, Davide; Mazzarini, Francesco; Musumeci, Giovanni; Saccorotti, Gilberto

    2017-04-01

    The Larderello field (Tuscany, Italy) is the oldest example in the world of geothermal energy exploitation for industrial purposes. Despite its century long history of exploration and exploitation, the deep structure (4-8km depth) of the Larderello field is still poorly known, due to (a) the lack of resolution of the applied exploration techniques and (b) the lack of interest in the investigation of deep geothermal reservoirs, given the abundant amount of energy extracted from the shallow reservoirs. Recently, the increasing demand of green-energy promoted a renewed interest in the geothermal industrial sector, which translated into new exploration efforts, especially to obtain a detailed characterization of deep geothermal sources. We investigate the seismic structure of the Larderello geothermal field using Receiver Function (RF) analysis. Crustal seismic structures are routinely investigated using the RF methodology, where teleseismic P-wave are analysed to extract P-to-S converted phases that can be related to the propagation of the P-wave across a seismic discontinuity. We compute RF from 26 seismic stations, belonging to both temporary and permanent networks: the GAPSS and RETREAT experiments and the Italian Seismic Network. The RF data-set is migrated at depth and decomposed into azimuthal harmonics. Computing the first, k=0, and the second, k=1, harmonics allows to separate the "isotropic" contribution, due to the change of the isotropic properties of the sampled materials (recorded on the k=0 harmonics), from the "anisotropic" contribution, where the energy is related to the propagation of the P-wave through anisotropic materials (recorded on the k=1 harmonics). Preliminary results allow us: (1) to infer the position of the main S-wave velocity discontinuities in the study area, mainly a shallow Tyrrhenian Moho and a very-low S-wave velocity body in the center of the Larderello dome, at about 5-15km depth; and (2) to map the presence of anisotropic

  5. Gasgeochemical indicators seismic activity

    Science.gov (United States)

    Obzhirov, Anatoly

    2017-10-01

    Laboratory of Gasgeochemistry of POI FEB RAS is studying gas distribution in lithosphere, hydrosphere and atmosphere from 1977 years. Method consist is sampling from its in expedition, take gas from samples of sediment, water and atmosphere to use method degassing and analysis gas in chromatograph, to measure CH4, C2-C4, O2, N2, H2, He and some time Rn. Gas is using like indicators to search oil-gas deposits, gas hydrate, mapping zones faults, to determine seismic activity, to calculate green house gas (CH4, CO2). The next geological, geophysics and hydro-acoustics characteristics assist which help to explain to form methane bubbles fluxes and gas hydrate in the Okhotsk Sea. The methane fluxes are mostly located in the zones faults and it increase in period seismic activity.

  6. 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.

  7. Bayesian inversion of refraction seismic traveltime data

    Science.gov (United States)

    Ryberg, T.; Haberland, Ch

    2018-03-01

    We apply a Bayesian Markov chain Monte Carlo (McMC) formalism to the inversion of refraction seismic, traveltime data sets to derive 2-D velocity models below linear arrays (i.e. profiles) of sources and seismic receivers. Typical refraction data sets, especially when using the far-offset observations, are known as having experimental geometries which are very poor, highly ill-posed and far from being ideal. As a consequence, the structural resolution quickly degrades with depth. Conventional inversion techniques, based on regularization, potentially suffer from the choice of appropriate inversion parameters (i.e. number and distribution of cells, starting velocity models, damping and smoothing constraints, data noise level, etc.) and only local model space exploration. McMC techniques are used for exhaustive sampling of the model space without the need of prior knowledge (or assumptions) of inversion parameters, resulting in a large number of models fitting the observations. Statistical analysis of these models allows to derive an average (reference) solution and its standard deviation, thus providing uncertainty estimates of the inversion result. The highly non-linear character of the inversion problem, mainly caused by the experiment geometry, does not allow to derive a reference solution and error map by a simply averaging procedure. We present a modified averaging technique, which excludes parts of the prior distribution in the posterior values due to poor ray coverage, thus providing reliable estimates of inversion model properties even in those parts of the models. The model is discretized by a set of Voronoi polygons (with constant slowness cells) or a triangulated mesh (with interpolation within the triangles). Forward traveltime calculations are performed by a fast, finite-difference-based eikonal solver. The method is applied to a data set from a refraction seismic survey from Northern Namibia and compared to conventional tomography. An inversion test

  8. Establishing seismic design criteria to achieve an acceptable seismic margin

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, R.P. [RPK Structural Mechanics Consulting, Inc., Yorba Linda, CA (United States)

    1997-01-01

    In order to develop a risk based seismic design criteria the following four issues must be addressed: (1) What target annual probability of seismic induced unacceptable performance is acceptable? (2). What minimum seismic margin is acceptable? (3) Given the decisions made under Issues 1 and 2, at what annual frequency of exceedance should the Safe Shutdown Earthquake ground motion be defined? (4) What seismic design criteria should be established to reasonably achieve the seismic margin defined under Issue 2? The first issue is purely a policy decision and is not addressed in this paper. Each of the other three issues are addressed. Issues 2 and 3 are integrally tied together so that a very large number of possible combinations of responses to these two issues can be used to achieve the target goal defined under Issue 1. Section 2 lays out a combined approach to these two issues and presents three potentially attractive combined resolutions of these two issues which reasonably achieves the target goal. The remainder of the paper discusses an approach which can be used to develop seismic design criteria aimed at achieving the desired seismic margin defined in resolution of Issue 2. Suggestions for revising existing seismic design criteria to more consistently achieve the desired seismic margin are presented.

  9. Estimation of subsurface structures in a Minami Noshiro 3D seismic survey region by seismic-array observations of microtremors; Minami Noshiro sanjigen jishin tansa kuikinai no hyoso kozo ni tsuite. Bido no array kansoku ni yoru suitei

    Energy Technology Data Exchange (ETDEWEB)

    Okada, H.; Ling, S.; Ishikawa, K. [Hokkaido University, Sapporo (Japan); Tsuburaya, Y.; Minegishi, M. [Japan National Oil Corp., Tokyo (Japan). Technology Research Center

    1997-05-27

    Japan National Oil Corporation Technology Research Center has carried out experiments on the three-dimensional seismic survey method which is regarded as an effective means for petroleum exploration. The experiments were conducted at the Minami Noshiro area in Akita Prefecture. Seismometer arrays were developed in radii of 30 to 300 m at seven points in the three-dimensional seismic exploration region to observe microtremors. The purpose is to estimate S-wave velocities from the ground surface to the foundation by using surface waves included in microtremors. Estimation of the surface bed structure is also included in the purpose since this is indispensable in seismic exploration using the reflection method. This paper reports results of the microtremor observations and the estimation on S-wave velocities (microtremor exploration). One or two kinds of arrays with different sizes composed of seven observation points per area were developed to observe microtremors independently. The important point in the result obtained in the present experiments is that a low velocity bed suggesting existence of faults was estimated. It will be necessary to repeat experiments and observations in the future to verify whether this microtremor exploration method has that much of exploration capability. For the time being, however, interest is addressed to considerations on comparison with the result of 3D experiments using the reflection method. 4 refs., 7 figs.

  10. An upper-mantle S-wave velocity model for Northern Europe from Love and Rayleigh group velocities

    Science.gov (United States)

    Weidle, Christian; Maupin, Valérie

    2008-12-01

    A model of upper-mantle S-wave velocity and transverse anisotropy beneath northwestern Europe is presented, based on regional surface wave observations. Group velocities for both Love and Rayleigh surface waves are measured on waveform data from international and regional data archives (including temporary deployments) and then inverted for group velocity maps, using a method accounting for Fresnel zone sensitivity. The group velocity variations are larger than in global reference maps, and we are able to resolve unprecedented details. We then apply a linear inversion scheme to invert for local 1-D shear wave velocity profiles which are consequently assembled to a 3-D model. By choosing conservative regularization parameters in the 2-D inversion, we ensure the smoothness of the group velocity maps and hence of the resulting 3-D shear wave speed model. To account for the different tectonic regimes in the study region and investigate the sensitivity of the 1-D inversions to inaccuracies in crustal parameters, we analyse inversions with different reference models of increasing complexity (pure 1-D, 3-D crust/1-D mantle and pure 3-D). We find that all inverted models are very consistent at depths below 70 km. At shallower depths, the constraints put by the reference models, primarily Moho depth which we do not invert for, remain the main cause for uncertainty in our inversion. The final 3-D model shows large variations in S-wave velocity of up to +/-12 per cent. We image an intriguing low-velocity anomaly in the depth range 70-150 km that extends from the Iceland plume beneath the North Atlantic and in a more than 400 km wide channel under Southern Scandinavia. Beneath Southern Norway, the negative perturbations are around 10 per cent with respect to ak135, and a shallowing of the anomaly is indicated which could be related to the sustained uplift of Southern Scandinavia in Neogene times. Furthermore, our upper-mantle model reveals good alignment to ancient plate

  11. Topography of the 410 km and 660 km discontinuities beneath the Japan Sea and adjacent regions by analysis of multiple-ScS waves

    Science.gov (United States)

    Wang, Xin; Li, Juan; Chen, Qi-Fu

    2017-02-01

    The northwest Pacific subduction region is an ideal location to study the interaction between the subducting slab and upper mantle discontinuities. Due to the sparse distribution of seismic stations in the sea, previous studies mostly focus on mantle transition zone (MTZ) structures beneath continents or island arcs, leaving the vast area of the Japan Sea and Okhotsk Sea untouched. In this study, we analyzed multiple-ScS reverberation waves, and a common-reflection-point stacking technique was applied to enhance consistent signals beneath reflection points. A topographic image of the 410 km and 660 km discontinuities is obtained beneath the Japan Sea and adjacent regions. One-dimensional and 3-D velocity models are adapted to obtain the "apparent" and "true" depth. We observe a systematic pattern of depression ( 10-20 km) and elevation ( 5-10 km) of the 660, with the topography being roughly consistent with the shift of the olivine-phase transition boundary caused by the subducting Pacific plate. The behavior of the 410 is more complex. It is generally 5-15 km shallower at the location where the slab penetrates and deepened by 5-10 km oceanward of the slab where a low-velocity anomaly is observed in tomography images. Moreover, we observe a wide distribution of depressed 410 beneath the southern Okhotsk Sea and western Japan Sea. The hydrous wadsleyite boundary caused by the high water content at the top of the MTZ could explain the depression. The long-history trench rollback motion of Pacific slab might be responsible for the widely distributed depression of the 410 ranging upward and landward from the slab.

  12. Deformation fabrics of blueschist facies phengite-rich, epidote-glaucophane schists from Ring Mountain, California and implications for seismic anisotropy in subduction zone

    Science.gov (United States)

    Jung, H.; HA, Y.; Raymond, L. A.

    2016-12-01

    In many subduction zones, strong seismic anisotropy is observed. A part of the seismic anisotropy can be attributed to the subducting oceanic crust, which is transformed to blueschist facies rocks under high-pressure, high-temperature conditions. Because glaucophane, epidote, and phengite constituting the glaucophane schists are very anisotropic elastically, seismic anisotropy in the oceanic crust in hot subduction zones can be attributed to the lattice preferred orientation (LPO) of these minerals. We studied deformation fabrics and seismic properties of phengite-rich, epidote-glaucophane schists from the Franciscan Complex of Ring Mountain, California. The blueschist samples are mainly composed of glaucophane, epidote, and phengite, with minor garnet, titanite, and chlorite. Some samples contain abundant phengite (up to 40 %). We determined LPOs of minerals using SEM/EBSD and calculated seismic anisotropy of minerals and whole rocks. LPOs of glaucophane have [001] axes aligned subparallel to lineation, and both (110) poles and [100] axes subnormal to foliation. Epidote [001] axes are aligned subnormal to foliation, with both (110) and (010) poles subparallel to lineation. LPOs of phengite are characterized by maxima of [001] axes subnormal to foliation, and both (110) and (010) poles and [100] axes aligned in a girdle subparallel to foliation. Phengite showed much stronger seismic anisotropy (AVP = 42%, max.AVS = 37%) than glaucophane or epidote. Glaucophane schist with abundant phengite showed much stronger seismic anisotropy (AVP = 30%, max.AVS = 23%) than epidote-glaucophane schist without phengite (AVP = 13%, max.AVS = 9%). Therefore, phengite clearly can significantly affect seismic anisotropy of whole rocks. When the subduction angle of phengite-rich blueschist facies rocks is considered for a 2-D corner flow model, the polarization direction of fast S-waves for vertically propagating S-waves changed to a nearly trench-parallel direction for the subduction

  13. Seismic survey considerations in glaciology

    OpenAIRE

    Hofstede, Coen

    2015-01-01

    Seismic surveying of glaciers give both englacial and subglacial physical information and is as such an important tool in glaciology. In comparison with the collection of radar data, mainly performed from airborne platforms, seismic data acquisition is a time consuming process practiced in small survey areas and used less frequent. Over the last six years, AWI developed an effective strategy to collect seismic data on glaciers, ice sheets and ice shelves, at a high production rate with a smal...

  14. Perseids permanent seismic downhole system

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2005-07-01

    PERSEIDS{sup TM} describes a permanent seismic downhole system. In that system, geo-phones are either cemented or mounted on tubing and coupled to the casing through a bow-string. Perseids{sup TM} is ideal for both passive and active seismic monitoring, to visualize bypass areas, gas cap and aquifer expansion. It can be combined with {mu}SICS{sup TM} software to record, process and interpret micro-seismic activity.

  15. Retrieving impulse response function amplitudes from the ambient seismic field

    Science.gov (United States)

    Viens, Loïc; Denolle, Marine; Miyake, Hiroe; Sakai, Shin'ichi; Nakagawa, Shigeki

    2017-07-01

    Seismic interferometry is now widely used to retrieve the impulse response function of the Earth between two distant seismometers. The phase information has been the focus of most passive imaging studies, as conventional seismic tomography uses traveltime measurements. The amplitude information, however, is harder to interpret because it strongly depends on the distribution of ambient seismic field sources and on the multitude of processing methods. Our study focuses on the latter by comparing the amplitudes of the impulse response functions calculated between seismic stations in the Kanto sedimentary basin, Japan, using several processing techniques. This region provides a unique natural laboratory to test the reliability of the amplitudes with complex wave propagation through the basin, and dense observations from the Metropolitan Seismic Observation network. We compute the impulse response functions using the cross correlation, coherency and deconvolution techniques of the raw ambient seismic field and the cross correlation of 1-bit normalized data. To validate the amplitudes of the impulse response functions, we use a shallow Mw 5.8 earthquake that occurred on the eastern edge of Kanto Basin and close to a station that is used as the virtual source. Both S and surface waves are retrieved in the causal part of the impulse response functions computed with all the different techniques. However, the amplitudes obtained from the deconvolution method agree better with those of the earthquake. Despite the expected wave attenuation due to the soft sediments of the Kanto Basin, seismic amplification caused by the basin geometry dominates the amplitudes of S and surface waves and is captured by the ambient seismic field. To test whether or not the anticausal part of the impulse response functions from deconvolution also contains reliable amplitude information, we use another virtual source located on the western edge of the basin. We show that the surface wave amplitudes

  16. Computed Tomography (CT) -- Sinuses

    Medline Plus

    Full Text Available ... the Sinuses? What is CT (Computed Tomography) of the Sinuses? Computed tomography, more commonly known as a ... of page What are some common uses of the procedure? CT of the sinuses is primarily used ...

  17. Flat lens for seismic waves

    CERN Document Server

    Brule, Stephane; Guenneau, Sebastien

    2016-01-01

    A prerequisite for achieving seismic invisibility is to demonstrate the ability of civil engineers to control seismic waves with artificially structured soils. We carry out large-scale field tests with a structured soil made of a grid consisting of cylindrical and vertical holes in the ground and a low frequency artificial source (< 10 Hz). This allows the identification of a distribution of energy inside the grid, which can be interpreted as the consequence of an effective negative refraction index. Such a flat lens reminiscent of what Veselago and Pendry envisioned for light opens avenues in seismic metamaterials to counteract the most devastating components of seismic signals.

  18. Seismic hazard estimation of northern Iran using smoothed seismicity

    Science.gov (United States)

    Khoshnevis, Naeem; Taborda, Ricardo; Azizzadeh-Roodpish, Shima; Cramer, Chris H.

    2017-07-01

    This article presents a seismic hazard assessment for northern Iran, where a smoothed seismicity approach has been used in combination with an updated seismic catalog and a ground motion prediction equation recently found to yield good fit with data. We evaluate the hazard over a geographical area including the seismic zones of Azerbaijan, the Alborz Mountain Range, and Kopeh-Dagh, as well as parts of other neighboring seismic zones that fall within our region of interest. In the chosen approach, seismic events are not assigned to specific faults but assumed to be potential seismogenic sources distributed within regular grid cells. After performing the corresponding magnitude conversions, we decluster both historical and instrumental seismicity catalogs to obtain earthquake rates based on the number of events within each cell, and smooth the results to account for the uncertainty in the spatial distribution of future earthquakes. Seismicity parameters are computed for each seismic zone separately, and for the entire region of interest as a single uniform seismotectonic region. In the analysis, we consider uncertainties in the ground motion prediction equation, the seismicity parameters, and combine the resulting models using a logic tree. The results are presented in terms of expected peak ground acceleration (PGA) maps and hazard curves at selected locations, considering exceedance probabilities of 2 and 10% in 50 years for rock site conditions. According to our results, the highest levels of hazard are observed west of the North Tabriz and east of the North Alborz faults, where expected PGA values are between about 0.5 and 1 g for 10 and 2% probability of exceedance in 50 years, respectively. We analyze our results in light of similar estimates available in the literature and offer our perspective on the differences observed. We find our results to be helpful in understanding seismic hazard for northern Iran, but recognize that additional efforts are necessary to

  19. Assessment of local seismic response of the Stracciacappa maar (Central Italy)

    Science.gov (United States)

    Moscatelli, Massimiliano; Simionato, Maurizio; Gaudiosi, Iolanda; Sottili, Gianluca; Pagliaroli, Alessandro; Sirianni, Pietro; Pileggi, Domenico; Avalle, Alessandra; Giallini, Silvia; Razzano, Roberto; Mancini, Marco; Vignaroli, Gianluca; Piscitelli, Sabatino; Bellanova, Jessica; Calamita, Giuseppe; Perrone, Angela; Lanzo, Giuseppe

    2016-04-01

    In this work, we face the definition of a subsoil model aimed at the local seismic response assessment of the Stracciacappa maar (Sabatini Volcanic District, central Italy) (e.g., De Rita and Zanetti, 1986; Marra et al., 2014). The pyroclastic succession of Stracciacappa records two main hydromagmatic eruptive phases ended about 0.09 Ma ago (e.g., Sottili et al., 2010). The preserved crater, with a diameter of about 1500 meters and a crater floor of about 30-40 m, hosted a lake until it was drained in AD 1834. In the framework of the cooperation between CNR IGAG and Italian Department of Civil Protection (DPC) of the Presidency of Council of Ministers (DPC funds 2014), a multidisciplinary approach including detailed stratigraphic and geophysical study has been carried out in the Stracciacappa maar and surrounding areas. New geological map and cross sections illustrate the complex geometric relationships between the thick pyroclastic surge succession, showing diffuse sandwave structures, and even meter-sized lava ballistic. A composite interdigitation between lacustrine and epiclastic debris sediments fills the crater floor. A continuous coring borehole was drilled inside the crater, 45 meters deep from the wellhead, with sampling of undisturbed samples. In addition, four MASW and one SCPTU test were carried out, in order to define the velocity profile of the s-waves within the lacustrine deposits. This Vs profile was then extended at higher depths by using the results of four 2D seismic passive arrays. Moreover, in order to define the resonance frequency of sedimentary covers via the HVSR technique, twenty-eight measurements were carried out with digital sensor Tromino® and seven measurements were performed with a Lennartz® Le-3D/5s sensor with Lennartz Marslite® digitizer. Finally, three electrical resistivity tomography tests, with a total length of about 3500 meters, were carried out with the purpose of constraining the subsoil model. Regarding the non linear

  20. A Robust MEMS Based Multi-Component Sensor for 3D Borehole Seismic Arrays

    Energy Technology Data Exchange (ETDEWEB)

    Paulsson Geophysical Services

    2008-03-31

    The objective of this project was to develop, prototype and test a robust multi-component sensor that combines both Fiber Optic and MEMS technology for use in a borehole seismic array. The use such FOMEMS based sensors allows a dramatic increase in the number of sensors that can be deployed simultaneously in a borehole seismic array. Therefore, denser sampling of the seismic wave field can be afforded, which in turn allows us to efficiently and adequately sample P-wave as well as S-wave for high-resolution imaging purposes. Design, packaging and integration of the multi-component sensors and deployment system will target maximum operating temperature of 350-400 F and a maximum pressure of 15000-25000 psi, thus allowing operation under conditions encountered in deep gas reservoirs. This project aimed at using existing pieces of deployment technology as well as MEMS and fiber-optic technology. A sensor design and analysis study has been carried out and a laboratory prototype of an interrogator for a robust borehole seismic array system has been assembled and validated.

  1. Imaging architecture of the Jakarta Basin, Indonesia with transdimensional inversion of seismic noise

    Science.gov (United States)

    Saygin, E.; Cummins, P. R.; Cipta, A.; Hawkins, R.; Pandhu, R.; Murjaya, J.; Masturyono, Irsyam, M.; Widiyantoro, S.; Kennett, B. L. N.

    2016-02-01

    In order to characterize the subsurface structure of the Jakarta Basin, Indonesia, a dense portable seismic broad-band network was operated by The Australian National University (ANU) and the Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) between October 2013 and February 2014. Overall 96 locations were sampled through successive deployments of 52 seismic broad-band sensors at different parts of the city. Oceanic and anthropogenic noises were recorded as well as regional and teleseismic earthquakes. We apply regularized deconvolution to the recorded ambient noise of the vertical components of available station pairs, and over 3000 Green's functions were retrieved in total. Waveforms from interstation deconvolutions show clear arrivals of Rayleigh fundamental and higher order modes. The traveltimes that were extracted from group velocity filtering of fundamental mode Rayleigh wave arrivals, are used in a 2-stage Transdimensional Bayesian method to map shear wave structure of subsurface. The images of S wave speed show very low velocities and a thick basin covering most of the city with depths up to 1.5 km. These low seismic velocities and the thick basin beneath the city potentially cause seismic amplification during a subduction megathrust or other large earthquake close to the city of Jakarta.

  2. Seismic retrofit guidelines for Utah highway bridges.

    Science.gov (United States)

    2009-05-01

    Much of Utahs population dwells in a seismically active region, and many of the bridges connecting transportation lifelines predate the rigorous seismic design standards that have been developed in the past 10-20 years. Seismic retrofitting method...

  3. The influence of backfill on seismicity

    CSIR Research Space (South Africa)

    Hemp, DA

    1990-09-01

    Full Text Available , that the seismicity has been reduced in areas where backfill had been placed. A factor complicating the evaluation of backfill on seismicity is the effect of geological structures on seismicity....

  4. Body wave travel times and amplitudes for present-day seismic model of Mars

    Science.gov (United States)

    Raevskiy, Sergey; Gudkova, Tamara

    At the moment Martian interior structure models are constrained by the satellite observational data (the mass, the moment of inertia factor, the Love number k _{2}) (Konopliv et al., 2011) and high pressure experimental data (Bertka and Fei, 1997). Seismological observations could provide unparalleled capability for studying Martian interiors. Future missions include seismic experiments on Mars (Lognonné et al., 2012). The main instrument for these seismic experiments is a broadband seismometer (Robert et al., 2012). When seismic measurements are not yet available, physically consistent interior models, characterized by properties of relevant minerals, make possible to study of the seismic response of the planet. \\To estimate travel times for direct P, S, core reflected PcP, ScS and core refracted PKP body waves as a function of epicentral distance and hypocentral depth, as well as their amplitudes at the surface for a given marsquake, software product was developed in MatLab, as it encompasses many plotting routines that plot resulting travel times and ray paths. The computational results have been compared with the program TTBox (Knapmeyer, 2004). The code computes seismic ray paths and travel times for a one-dimentional spherical interior model (density and seismic velocities are functions of a radius only). Calculations of travel times tables for direct P, S, core reflected PcP, ScS and core refracted PKP waves and their amplitudes are carried out for a trial seismic model of Mars M14_3 from (Zharkov et al., 2009): the core radius is 1800 km, the thickness of the crust is 50 km. Direct and core reflected P and S waves are recorded to a maximum epicentral distance equal to about 100(°) , and PKP arrivals can be detected for epicental distances larger than 150(°) . The shadow zone is getting wider in comparison with previous results (Knapmeyer, 2010), as the liquid core radius of the seismic model under consideration is larger. Based on the estimates of

  5. Computed Tomography (CT) -- Head

    Medline Plus

    Full Text Available ... News Physician Resources Professions Site Index A-Z Computed Tomography (CT) - Head Computed tomography (CT) of the head uses special x-ray ... Head? What is CT Scanning of the Head? Computed tomography, more commonly known as a CT or CAT ...

  6. Seismic velocity and crustal thickness inversions: Moon and Mars

    Science.gov (United States)

    Drilleau, Melanie; Blanchette-Guertin, Jean-François; Kawamura, Taichi; Lognonné, Philippe; Wieczorek, Mark

    2017-04-01

    We present results from new inversions of seismic data arrival times acquired by the Apollo active and passive experiments. Markov chain Monte Carlo inversions are used to constrain (i) 1-D lunar crustal and upper mantle velocity models and (ii) 3-D lateral crustal thickness models under the Apollo stations and the artificial and natural impact sites. A full 3-D model of the lunar crustal thickness is then obtained using the GRAIL gravimetric data, anchored by the crustal thicknesses under each Apollo station and impact site. To avoid the use of any seismic reference model, a Bayesian inversion technique is implemented. The advantage of such an approach is to obtain robust probability density functions of interior structure parameters governed by uncertainties on the seismic data arrival times. 1-D seismic velocities are parameterized using C1-Bézier curves, which allow the exploration of both smoothly varying models and first-order discontinuities. The parameters of the inversion include the seismic velocities of P and S waves as a function of depth, the thickness of the crust under each Apollo station and impact epicentre. The forward problem consists in a ray tracing method enabling both the relocation of the natural impact epicenters, and the computation of time corrections associated to the surface topography and the crustal thickness variations under the stations and impact sites. The results show geology-related differences between the different sites, which are due to contrasts in megaregolith thickness and to shallow subsurface composition and structure. Some of the finer structural elements might be difficult to constrain and might fall within the uncertainties of the dataset. However, we use the more precise LROC-located epicentral locations for the lunar modules and Saturn-IV upper stage artificial impacts, reducing some of the uncertainties observed in past studies. In the framework of the NASA InSight/SEIS mission to Mars, the method developed in

  7. Experimental monitoring of the hydro-mechanical state of a discontinuity using controlled source seismic method

    Science.gov (United States)

    Place, Joachim; Blake, Oshaine; Rietbrock, Andreas; Faulkner, Dan

    2013-04-01

    Great earthquakes often occur in crystalline rocks, and basement rocks can host geothermal and hydrocarbon resources. In such rocks, the fluid storage and transfer properties depend mainly on the natural fault and fracture networks. Therefore, it is of primary importance to characterise the physical properties of the fault zones in order to better understand the seismogenic processes and how the resources can be exploited. Seismic waves are known to be sensitive to many parameters which evolve depending on the fault response to stresses and fluid type. Therefore seismic methods show a great potential to monitor the hydro-mechanical state of structures remotely, with no need for drilling through the structures. We developed a basic experimental approach at sample scale to monitor the mechanical coupling through a discontinuity between a granite sample in contact with a piece of steel, when the effective pressure (Peff) and the nature of the filling fluid vary. Piezoceramics utilised both as sources and sensors are located on the steel (in which the attenuation is assumed to be zero) and both generate and record the P and S wave fields reflected off the discontinuity at normal incidence. This permits the normal (Bn) and tangential (Bt) fracture compliances to be calculated after Schoenberg's linear slip theory from the measurement of P-P and S-S reflection coefficients. The roughness of the sample surface, as well as the effect of fluid type (air or water) and Peff were studied. Under dry conditions, it is observed that the poorer the contact area, the higher Bn and Bt, meaning that the seismic energy of P and S waves is less transmitted. Increasing the effective pressure decreases the compliances, which is interpreted as the effect of the closure of the voids at the interface; this permits more seismic energy to be transmitted through the interface. It is also observed that Bn is significantly higher than Bt at low Peff (energy of compressional waves through the

  8. Crustal Seismic Attenuation in Germany Measured with Acoustic Radiative Transfer Theory

    Science.gov (United States)

    Gaebler, Peter J.; Eulenfeld, Tom; Wegler, Ulrich

    2017-04-01

    This work is carried out in the context of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). As part of this treaty a verification regime was introduced to detect, locate and characterize nuclear explosion testings. The study of seismology can provide essential information in the form of broadband waveform recordings for the identification and verification of these critical events. A profound knowledge of the Earth's subsurface between source and receiver is required for a detailed description of the seismic wave field. In addition to underground parameters such as seismic velocity or anisotropy, information about seismic attenuation values of the medium are required. Goal of this study is the creation of a comprehensive model of crustal seismic attenuation in Germany and adjacent areas. Over 20 years of earthquake data from the German Central Seismological Observatory data archive is used to estimate the spatial dependent distribution of seismic intrinsic and scattering attenuation of S-waves for frequencies between 0.5 and 20 Hz. The attenuation models are estimated by fitting synthetic seismogram envelopes calculated with acoustic radiative transfer theory to observed seismogram envelopes. This theory describes the propagation of seismic S-energy under the assumption of multiple isotropic scattering, the crustal structure of the scattering medium is hereby represented by a half-space model. We present preliminary results of the spatial distribution of intrinsic attenuation represented by the absorption path length, as well as of scattering attenuation in terms of the mean free path and compare the outcomes to results from previous studies. Furthermore catalog magnitudes are compared to moment magnitudes estimated during the inversion process. Additionally site amplification factors of the stations are presented.

  9. Earthquake damage orientation to infer seismic parameters in archaeological sites and historical earthquakes

    Science.gov (United States)

    Martín-González, Fidel

    2018-01-01

    Studies to provide information concerning seismic parameters and seismic sources of historical and archaeological seismic events are used to better evaluate the seismic hazard of a region. This is of especial interest when no surface rupture is recorded or the seismogenic fault cannot be identified. The orientation pattern of the earthquake damage (ED) (e.g., fallen columns, dropped key stones) that affected architectonic elements of cities after earthquakes has been traditionally used in historical and archaeoseismological studies to infer seismic parameters. However, in the literature depending on the authors, the parameters that can be obtained are contradictory (it has been proposed: the epicenter location, the orientation of the P-waves, the orientation of the compressional strain and the fault kinematics) and authors even question these relations with the earthquake damage. The earthquakes of Lorca in 2011, Christchurch in 2011 and Emilia Romagna in 2012 present an opportunity to measure systematically a large number and wide variety of earthquake damage in historical buildings (the same structures that are used in historical and archaeological studies). The damage pattern orientation has been compared with modern instrumental data, which is not possible in historical and archaeoseismological studies. From measurements and quantification of the orientation patterns in the studied earthquakes, it is observed that there is a systematic pattern of the earthquake damage orientation (EDO) in the proximity of the seismic source (fault trace) (EDO in these earthquakes is normal to the fault trend (±15°). This orientation can be generated by a pulse of motion that in the near fault region has a distinguishable acceleration normal to the fault due to the polarization of the S-waves. Therefore, the earthquake damage orientation could be used to estimate the seismogenic fault trend of historical earthquakes studies where no instrumental data are available.

  10. Seismic Characterization of the Jakarta Basin

    Science.gov (United States)

    Cipta, A.; Saygin, E.; Cummins, P. R.; Masturyono, M.; Rudyanto, A.; Irsyam, M.

    2015-12-01

    Jakarta, Indonesia, is home to more than 10 million people. Many of these people live in seismically non-resilient structures in an area that historical records suggest is prone to earthquake shaking. The city lies in a sedimentary basin composed of Quaternary alluvium that experiences rapid subsidence (26 cm/year) due to groundwater extraction. Forecasts of how much subsidence may occur in the future are dependent on the thickness of the basin. However, basin geometry and sediment thickness are poorly known. In term of seismic hazard, thick loose sediment can lead to high amplification of seismic waves, of the kind that led to widespread damage in Mexico city during the Michoacan Earthquake of 1985. In order to characterize basin structure, a temporary seismograph deployment was undertaken in Jakarta in Oct 2013- Jan 2014. A total of 96 seismic instrument were deployed throughout Jakarta were deployed throughout Jakarta at 3-5 km spacing. Ambient noise tomography was applied to obtain models of the subsurface velocity structure. Important key, low velocity anomalies at short period (<8s) correspond to the main sedimentary sub-basins thought to be present based on geological interpretations of shallow stratigraphy in the Jakarta Basin. The result shows that at a depth of 300 m, shear-wave velocity in the northern part (600 m/s) of the basin is lower than that in the southern part. The most prominent low velocity structure appears in the northwest of the basin, down to a depth of 800 m, with velocity as low as 1200 m/s. This very low velocity indicates the thickness of sediment and the variability of basin geometry. Waveform computation using SPECFEM2D shows that amplification due to basin geometry occurs at the basin edge and the thick sediment leads to amplification at the basin center. Computation also shows the longer shaking duration occurrs at the basin edge and center of the basin. The nest step will be validating the basin model using earthquake events

  11. Early arrival waveform inversion of shallow seismic land data

    KAUST Repository

    Hanafy, Sherif M.

    2013-09-22

    We estimate the near-surface velocity distribution over Wadi Qudaid in Saudi Arabia by applying early arrival waveform inversion (EWI) to shallow seismic land data collected with source-receiver offsets no longer than 232 m. The main purpose is to characterize the shallow subsurface for its water storage and reuse potential. To enhance the accuracy of EWI, we extracted a natural source wavelet from the data, and also corrected for the attenuation effects with an estimated factor Q. Results suggest that, 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 find an increase of 18% of storage potential in the EWI tomogram relative to the traveltime tomogram. This approach suggests that FWI might be a more accurate means for economically characterizing the water storage potential for wadis’ throughout the world.

  12. Seismic monitoring in the oceans by autonomous floats

    Science.gov (United States)

    Sukhovich, Alexey; Bonnieux, Sébastien; Hello, Yann; Irisson, Jean-Olivier; Simons, Frederik J.; Nolet, Guust

    2015-08-01

    Our understanding of the internal dynamics of the Earth is largely based on images of seismic velocity variations in the mantle obtained with global tomography. However, our ability to image the mantle is severely hampered by a lack of seismic data collected in marine areas. Here we report observations made under different noise conditions (in the Mediterranean Sea, the Indian and Pacific Oceans) by a submarine floating seismograph, and show that such floats are able to fill the oceanic data gap. Depending on the ambient noise level, the floats can record between 35 and 63% of distant earthquakes with a moment magnitude M>=6.5. Even magnitudes noise conditions. The serendipitous recording of an earthquake swarm near the Indian Ocean triple junction enabled us to establish a threshold magnitude between 2.7 and 3.4 for local earthquakes in the noisiest of the three environments.

  13. Mine-induced seismicity at East-Rand proprietary mines

    CSIR Research Space (South Africa)

    Milev, AM

    1995-09-01

    Full Text Available Mining results in seismic activity of varying intensity, from small micro seismic events to larger seismic events, often associated with significant seismic induced damages. This work deals with the understanding of the present seismicity...

  14. Meaning of Interior Tomography

    CERN Document Server

    Wang, Ge

    2013-01-01

    The classic imaging geometry for computed tomography is for collection of un-truncated projections and reconstruction of a global image, with the Fourier transform as the theoretical foundation that is intrinsically non-local. Recently, interior tomography research has led to theoretically exact relationships between localities in the projection and image spaces and practically promising reconstruction algorithms. Initially, interior tomography was developed for x-ray computed tomography. Then, it has been elevated as a general imaging principle. Finally, a novel framework known as omni-tomography is being developed for grand fusion of multiple imaging modalities, allowing tomographic synchrony of diversified features.

  15. Automatic Seismic Signal Processing

    Science.gov (United States)

    1982-02-04

    81-04 4 February 1982 AUTOMATIC SEISMIC SIGNAL PROCESSING FINAL TECHNICAL REPORT i j Contract F08606-80.C-0021" PREPARED BY ILKKA NOPONEN, ROBERT SAX...PERFORMING ORG. REPORT NUMBER SAS-FR-81-04 7. AUTHOR(e) a. CONTRACT OR GRANT NUMBER(e) F08606- 80-C-0021 ILKKA NOPONEN, ROBERT SAX AND F 6 C0 STEVEN...observed, as also Swindell and Snell (1977), that the distribu- tion of x was slightly skewed, we used the median of x instead of aver- age of x for U(x

  16. Seismic risk perception test

    Science.gov (United States)

    Crescimbene, Massimo; La Longa, Federica; Camassi, Romano; Pino, Nicola Alessandro

    2013-04-01

    The perception of risks involves the process of collecting, selecting and interpreting signals about uncertain impacts of events, activities or technologies. In the natural sciences the term risk seems to be clearly defined, it means the probability distribution of adverse effects, but the everyday use of risk has different connotations (Renn, 2008). The two terms, hazards and risks, are often used interchangeably by the public. Knowledge, experience, values, attitudes and feelings all influence the thinking and judgement of people about the seriousness and acceptability of risks. Within the social sciences however the terminology of 'risk perception' has become the conventional standard (Slovic, 1987). The mental models and other psychological mechanisms which people use to judge risks (such as cognitive heuristics and risk images) are internalized through social and cultural learning and constantly moderated (reinforced, modified, amplified or attenuated) by media reports, peer influences and other communication processes (Morgan et al., 2001). Yet, a theory of risk perception that offers an integrative, as well as empirically valid, approach to understanding and explaining risk perception is still missing". To understand the perception of risk is necessary to consider several areas: social, psychological, cultural, and their interactions. Among the various research in an international context on the perception of natural hazards, it seemed promising the approach with the method of semantic differential (Osgood, C.E., Suci, G., & Tannenbaum, P. 1957, The measurement of meaning. Urbana, IL: University of Illinois Press). The test on seismic risk perception has been constructed by the method of the semantic differential. To compare opposite adjectives or terms has been used a Likert's scale to seven point. The test consists of an informative part and six sections respectively dedicated to: hazard; vulnerability (home and workplace); exposed value (with reference to

  17. Comparisons of seismic interferometry by cross correlation, deconvolution, and cross coherence

    Science.gov (United States)

    Chojnacki, John T.

    Ambient noise seismic interferometry (ANSI) has been applied widely for geophysical investigations including earthquake tomography, civil engineering and seismic exploration purposes. Comparing this approach with the traditional active seismic survey, the application of ANSI is cost effective, environmentally friendly and easily repeatable. Conventional seismic interferometry by cross correlating wavefields recorded at different receivers has already obtained fruitful results. Even though the application of seismic interferometry (SI) by cross correlation has been successful, different methods for the processing workflow such as cross coherence and deconvolution have been conducted in an effort to improve the resolution. While these three methods have been evaluated for shear wave imaging of the near surface using surface waves by other authors, no conclusive study has been performed to compare the results from these methods for reflection surveys. In this study, by considering three common methods of retrieving a virtual seismic record, I compare the methods and analyze the results with respect to their signal-to-noise ratios. I applied ANSI to numerically modeled data to retrieve reflection responses for both base and repeat surveys monitoring the time-lapse changes of the impedance at the top of a reservoir before and after CO2 injection. The retrieved seismic response by the three methods including cross correlation, deconvolution and cross coherence are also compared for the field noise data recorded near the CO2 storage site in Ketzin, Germany. While all three provide adequate results in noise-free synthetic data examples, the cross coherence method yielded improved images using real data.

  18. Locating the Origin of Scattered Waves By Simulating Time Reversal of the Seismic Wavefield

    Science.gov (United States)

    Myers, S. C.; Pitarka, A.; Sjogreen, B.; Petersson, A.; Simmons, N. A.; Johannesson, G.

    2014-12-01

    The Source Physics Experiment (SPE) is a series of underground chemical explosions at the Nevada National Security Site (NNSS) that are improving our physical understanding how explosion sources generate seismic waves. Better understanding the origin of S-waves from explosions is a primary goal of the SPE. Even at distances of a few kilometers from the SPE sources, seismic recordings include arrivals of unknown origin that could originate as S-waves at the explosive source or from topographic and subsurface scatterers. Back propagation of time reversed seismograms has been used to determine the location of seismic events (e.g. Tromp et al., 2005; Larmat et al., 2006), and Myers et al. (2007) demonstrated that the time-reversal method can be used to determine the origin of direct and scattered waves in seismic simulations. In this study we identify the origin of distinct features in synthetic seismograms that are generated by elastic, finite-difference simulation of seismic propagation from SPE explosions through a model that has been developed specifically for the SPE. The SPE model includes 3-dimensional velocity discontinuities at geologic boundaries, as well as free-surface topography. Although the largest arrivals in the synthetic seismograms are expected to originate at the explosion source, other prominent features are likely to originate as scattered energy from model discontinuities. Scattering sources in the SPE model that are needed in order to match synthetic seismograms to field recordings of SPE shots will be identified. Conversely, model structures may be removed if they result in disagreement between synthetic seismograms and field recordings. Ultimately, we plan to constrain the origin of prominent features in field recordings of SPE shots by directly using the field recordings as inputs to time reversal simulations. Direct use of field recordings will require development of methods that account for the uncertainty of the seismic model through which

  19. Seismic hazard maps of Italy

    Directory of Open Access Journals (Sweden)

    A. Rebez

    1998-06-01

    Full Text Available The Italian "Gruppo Nazionale per la Difesa dai Terremoti" has conducted a project in recent years for assessing seismic hazard in the national territory to be used as a basis for the revision of the current seismic zonation. In this project the data on the major earthquakes were reassessed and a new earthquake data file prepared. Definition of a seismotectonic model for the whole territory, based on a structural-kinematic analysis of Italy and the surrounding regions, led to the definition of 80 seismogenic zones, for which the geological and seismic characteristics were determined. Horizontal PGA and macroseismic intensity were used as seismicity parameters in the application of the Cornell probabilistic approach. The main aspects of the seismic hazard assessment are here described and the results obtained are presented and discussed. The maps prepared show the various aspects of seismic hazard which need to be considered for a global view of the problem. In particular, those with a 475-year return period, in agreement with the specifications of the new seismic Eurocode EC8, can be considered basic products for a revision of the present national seismic zonation.

  20. Seismic attenuation imaging with causality

    NARCIS (Netherlands)

    Hak, B.; Mulder, W.A.

    2010-01-01

    Seismic data enable imaging of the Earth, not only of velocity and density but also of attenuation contrasts. Unfortunately, the Born approximation of the constant-density visco-acoustic wave equation, which can serve as a forward modelling operator related to seismic migration, exhibits an

  1. Seismic microzonation of Bangalore, India

    Indian Academy of Sciences (India)

    encompassing Bangalore Mahanagara. Palike (BMP) has been chosen as the study area. Seismic hazard analysis and microzonation of. Bangalore are addressed in three parts: in the first part, estimation of seismic hazard is done using seismotectonic and geological information. Second part deals with site ...

  2. Seismic Data Gathering and Validation

    Energy Technology Data Exchange (ETDEWEB)

    Coleman, Justin [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-02-01

    Three recent earthquakes in the last seven years have exceeded their design basis earthquake values (so it is implied that damage to SSC’s should have occurred). These seismic events were recorded at North Anna (August 2011, detailed information provided in [Virginia Electric and Power Company Memo]), Fukushima Daichii and Daini (March 2011 [TEPCO 1]), and Kaswazaki-Kariwa (2007, [TEPCO 2]). However, seismic walk downs at some of these plants indicate that very little damage occurred to safety class systems and components due to the seismic motion. This report presents seismic data gathered for two of the three events mentioned above and recommends a path for using that data for two purposes. One purpose is to determine what margins exist in current industry standard seismic soil-structure interaction (SSI) tools. The second purpose is the use the data to validated seismic site response tools and SSI tools. The gathered data represents free field soil and in-structure acceleration time histories data. Gathered data also includes elastic and dynamic soil properties and structural drawings. Gathering data and comparing with existing models has potential to identify areas of uncertainty that should be removed from current seismic analysis and SPRA approaches. Removing uncertainty (to the extent possible) from SPRA’s will allow NPP owners to make decisions on where to reduce risk. Once a realistic understanding of seismic response is established for a nuclear power plant (NPP) then decisions on needed protective measures, such as SI, can be made.

  3. Seismic imaging with incoherent wavefields

    NARCIS (Netherlands)

    Berkhout, A.J.; Verschuur, D.J.; Blacquière, G.

    2009-01-01

    In blended seismic acquisition incoherent source arrays are used to generate the seismic response. The blended shot records can be directly fed into a shot record migration scheme with a more advanced imaging condition. Blended shot records can also be simulated in the processing phase. In the

  4. Advances in Rotational Seismic Measurements

    Energy Technology Data Exchange (ETDEWEB)

    Pierson, Robert [Applied Technology Associates, Albuquerque, NM (United States); Laughlin, Darren [Applied Technology Associates, Albuquerque, NM (United States); Brune, Robert [Applied Technology Associates, Albuquerque, NM (United States)

    2016-10-19

    Rotational motion is increasingly understood to be a significant part of seismic wave motion. Rotations can be important in earthquake strong motion and in Induced Seismicity Monitoring. Rotational seismic data can also enable shear selectivity and improve wavefield sampling for vertical geophones in 3D surveys, among other applications. However, sensor technology has been a limiting factor to date. The US Department of Energy (DOE) and Applied Technology Associates (ATA) are funding a multi-year project that is now entering Phase 2 to develop and deploy a new generation of rotational sensors for validation of rotational seismic applications. Initial focus is on induced seismicity monitoring, particularly for Enhanced Geothermal Systems (EGS) with fracturing. The sensors employ Magnetohydrodynamic (MHD) principles with broadband response, improved noise floors, robustness, and repeatability. This paper presents a summary of Phase 1 results and Phase 2 status.

  5. Attenuation Characteristics of High Frequency Seismic Waves in Southern India

    Science.gov (United States)

    Sivaram, K.; Utpal, Saikia; Kanna, Nagaraju; Kumar, Dinesh

    2017-07-01

    We present a systematic study of seismic attenuation and its related Q structure derived from the spectral analysis of P-, S-waves in the southern India. The study region is separated into parts of EDC (Eastern Dharwar Craton), Western Dharwar Craton (WDC) and Southern Granulite Terrain (SGT). The study is carried out in the frequency range 1-20 Hz, using a single-station spectral ratio technique. We make use of about 45 earthquakes, recorded in a network of about 32 broadband 3-component seismograph-stations, having magnitudes ( M L) varying from 1.6 to 4.5, to estimate the average seismic body wave attenuation quality factors; Q P and Q S. Their estimated average values are observed to be fitting to the power law form of Q = Q 0 f n . The averaged power law relations for Southern Indian region (as a whole) are obtained as Q P = (95 ± 1.12) f (1.32±0.01); Q S = (128 ± 1.84) f (1.49±0.01). Based on the stations and recorded local earthquakes, for parts of EDC, WDC and SGT, the average power law estimates are obtained as: Q P = (97 ± 5) f (1.40±0.03), Q S = (116 ± 1.5) f (1.48±0.01) for EDC region; Q P = (130 ± 7) f (1.20±0.03), Q S = (103 ± 3) f (1.49±0.02) for WDC region; Q P = (68 ± 2) f (1.4±0.02), Q S = (152 ± 6) f (1.48±0.02) for SGT region. These estimates are weighed against coda Q ( Q C) estimates, using the coda decay technique, which is based on a weak backscattering of S-waves. A major observation in the study of body wave analysis is the low body wave Q ( Q 0 0.5) and Q S/ Q P ≫ 1, suggesting lateral stretches of dominant scattering mode of seismic wave propagation. This primarily could be attributed to possible thermal anomalies and spread of partially fluid-saturated rock-masses in the crust and upper mantle of the southern Indian region, which, however, needs further laboratory studies. Such physical conditions might partly be correlated to the active seismicity and intraplate tectonism, especially in SGT and EDC regions, as per the

  6. Multi-Attribute Seismic/Rock Physics Approach to Characterizing Fractured Reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Gary Mavko

    2004-11-30

    Most current seismic methods to seismically characterize fractures in tight reservoirs depend on a few anisotropic wave propagation signatures that can arise from aligned fractures. While seismic anisotropy can be a powerful fracture diagnostic, a number of situations can lessen its usefulness or introduce interpretation ambiguities. Fortunately, laboratory and theoretical work in rock physics indicates that a much broader spectrum of fracture seismic signatures can occur, including a decrease in P- and S-wave velocities, a change in Poisson's ratio, an increase in velocity dispersion and wave attenuation, as well as well as indirect images of structural features that can control fracture occurrence. The goal of this project was to demonstrate a practical interpretation and integration strategy for detecting and characterizing natural fractures in rocks. The approach was to exploit as many sources of information as possible, and to use the principles of rock physics as the link among seismic, geologic, and log data. Since no single seismic attribute is a reliable fracture indicator in all situations, the focus was to develop a quantitative scheme for integrating the diverse sources of information. The integrated study incorporated three key elements: The first element was establishing prior constraints on fracture occurrence, based on laboratory data, previous field observations, and geologic patterns of fracturing. The geologic aspects include analysis of the stratigraphic, structural, and tectonic environments of the field sites. Field observations and geomechanical analysis indicates that fractures tend to occur in the more brittle facies, for example, in tight sands and carbonates. In contrast, strain in shale is more likely to be accommodated by ductile flow. Hence, prior knowledge of bed thickness and facies architecture, calibrated to outcrops, are powerful constraints on the interpreted fracture distribution. Another important constraint is that

  7. Micromachined silicon seismic transducers

    Energy Technology Data Exchange (ETDEWEB)

    Barron, C.C.; Fleming, J.G.; Sniegowski, J.J.; Armour, D.L.; Fleming, R.P.

    1995-08-01

    Batch-fabricated silicon seismic transducers could revolutionize the discipline of CTBT monitoring by providing inexpensive, easily depolyable sensor arrays. Although our goal is to fabricate seismic sensors that provide the same performance level as the current state-of-the-art ``macro`` systems, if necessary one could deploy a larger number of these small sensors at closer proximity to the location being monitored in order to compensate for lower performance. We have chosen a modified pendulum design and are manufacturing prototypes in two different silicon micromachining fabrication technologies. The first set of prototypes, fabricated in our advanced surface- micromachining technology, are currently being packaged for testing in servo circuits -- we anticipate that these devices, which have masses in the 1--10 {mu}g range, will resolve sub-mG signals. Concurrently, we are developing a novel ``mold`` micromachining technology that promises to make proof masses in the 1--10 mg range possible -- our calculations indicate that devices made in this new technology will resolve down to at least sub-{mu}G signals, and may even approach to 10{sup {minus}10} G/{radical}Hz acceleration levels found in the low-earth-noise model.

  8. Seismic event classification system

    Science.gov (United States)

    Dowla, Farid U.; Jarpe, Stephen P.; Maurer, William

    1994-01-01

    In the computer interpretation of seismic data, the critical first step is to identify the general class of an unknown event. For example, the classification might be: teleseismic, regional, local, vehicular, or noise. Self-organizing neural networks (SONNs) can be used for classifying such events. Both Kohonen and Adaptive Resonance Theory (ART) SONNs are useful for this purpose. Given the detection of a seismic event and the corresponding signal, computation is made of: the time-frequency distribution, its binary representation, and finally a shift-invariant representation, which is the magnitude of the two-dimensional Fourier transform (2-D FFT) of the binary time-frequency distribution. This pre-processed input is fed into the SONNs. These neural networks are able to group events that look similar. The ART SONN has an advantage in classifying the event because the types of cluster groups do not need to be pre-defined. The results from the SONNs together with an expert seismologist's classification are then used to derive event classification probabilities.

  9. Local earthquake tomography of the Jalisco, Mexico region

    Science.gov (United States)

    Watkins, W. David; Thurber, Clifford H.; Abbott, Elizabeth R.; Brudzinski, Michael R.

    2018-01-01

    The states of Jalisco, Colima, and Michoacán in western Mexico overlie the boundary of the subducting Rivera and Cocos plates, presenting an ideal target for seismological inquiry to better understand the resulting mantle flow and regional volcanism. The different dips between the two subducting plates are thought to provide a mantle conduit that has contributed to the Colima Volcanic Complex (CVC), but there is considerable debate on the depth of the Rivera plate and width of the resulting conduit. With data from the Mapping the Rivera Subduction Zone (MARS) and Colima Deep Seismic Experiment (CODEX) networks, two temporary broadband arrays deployed in the region between 2006 and 2008, we inverted for three-dimensional P- and S-wave velocity as well as Vp/Vs structure of the upper 70 km of the crust and mantle in the Jalisco region. Using a newly-developed automatic P- and S-wave picker, we increased P picks by 74% and S picks by more than a factor of four compared to a database of manual picks for the 803 earthquakes used in the inversion. Additional relocated earthquakes extending to the trench are consistent with previous interpretations of the Rivera and Cocos plate interfaces. Areas of high Vp/Vs above both subducting slabs suggest the presence of fluids resulting from dehydration of subducted material. Extensive crustal seismicity occurs near these anomalies. A zone of high Vp/Vs is also present under the CVC. We also compare the results of different methods for obtaining Vp/Vs: a direct inversion for Vp/Vs from S minus P times versus simply dividing the Vp model by the Vs model. We find direct inversions of S minus P times to be more reliable.

  10. Determining resolvability of mantle plumes with synthetic seismic modeling

    Science.gov (United States)

    Maguire, R.; Van Keken, P. E.; Ritsema, J.; Fichtner, A.; Goes, S. D. B.

    2014-12-01

    Hotspot volcanism in locations such as Hawaii and Iceland is commonly thought to be associated with plumes rising from the deep mantle. In theory these dynamic upwellings should be visible in seismic data due to their reduced seismic velocity and their effect on mantle transition zone thickness. Numerous studies have attempted to image plumes [1,2,3], but their deep mantle origin remains unclear. In addition, a debate continues as to whether lower mantle plumes are visible in the form of body wave travel time delays, or whether such delays will be erased due to wavefront healing. Here we combine geodynamic modeling of mantle plumes with synthetic seismic waveform modeling in order to quantitatively determine under what conditions mantle plumes should be seismically visible. We model compressible plumes with phase changes at 410 km and 670 km, and a viscosity reduction in the upper mantle. These plumes thin from greater than 600 km in diameter in the lower mantle, to 200 - 400 km in the upper mantle. Plume excess potential temperature is 375 K, which maps to seismic velocity reductions of 4 - 12 % in the upper mantle, and 2 - 4 % in the lower mantle. Previous work that was limited to an axisymmetric spherical geometry suggested that these plumes would not be visible in the lower mantle [4]. Here we extend this approach to full 3D spherical wave propagation modeling. Initial results using a simplified cylindrical plume conduit suggest that mantle plumes with a diameter of 1000 km or greater will retain a deep mantle seismic signature. References[1] Wolfe, Cecily J., et al. "Seismic structure of the Iceland mantle plume." Nature 385.6613 (1997): 245-247. [2] Montelli, Raffaella, et al. "Finite-frequency tomography reveals a variety of plumes in the mantle." Science 303.5656 (2004): 338-343. [3] Schmandt, Brandon, et al. "Hot mantle upwelling across the 660 beneath Yellowstone." Earth and Planetary Science Letters 331 (2012): 224-236. [4] Hwang, Yong Keun, et al

  11. 3-D Seismic Velocity Structure of the Hawaii Hotspot from Joint Inversion of Body Wave and Surface Wave data

    Science.gov (United States)

    Cheng, C.; Allen, R. M.; Porritt, R. W.

    2012-12-01

    The Hawaii hotspot and the associated chain of islands have been long regarded as the case example of a deep-rooted mantle plume. However the efforts to detect a thermal plume seismically have been inconclusive. In this study we combine the complementary sensitivities of body- and surface-waves in order to improve resolution of mantle structure beneath Hawaii. Adding surface-wave constraints to the body wave inversion improves the resolution of the crustal and upper mantle structure. We used data from the deployment of temporary broadband ocean-bottom seismometers (OBS) of the Hawaiian Plume-Lithosphere Undersea Melt Experiment (PLUME) together with data from the on-shore stations in order to make the most complete dataset available. In a first step, we obtained stable and reliable OBS orientations over a range of earthquake back-azimuths using teleseismic P-wave particle motions. Due to the high noise of the OBS data in some frequency bands, we began by filtering in the period band of 0.04-1Hz. Using the proper channel orientations, we measured ~800 S-wave relative arrival times (direct S and SKS phases) on the SV component using muti-channel cross correlation. We applied the two-plane wave tomography method to generate surface wave phase velocity information. We use surface waves from 71 events with magnitude greater than 5.8 to generate phase velocity maps from 25 sec to 100 sec. These maps clearly show the low velocities beneath the islands surrounded by relatively high phase velocity. The pure S wave inversion result shows the 3-D structure beneath the PLUME array to a depth of 1000km and reveals a several-hundred-kilometer-wide region of low velocities beneath Hawaii that dips to the southeast. The low velocities continue downward through the mantle transition zone and extend into the uppermost lower-mantle where our resolution begins to degrade. These images are consistent with the interpretation that the Hawaiian hotspot is the result of an upwelling high

  12. seismic-py: Reading seismic data with Python

    Directory of Open Access Journals (Sweden)

    2008-08-01

    Full Text Available The field of seismic exploration of the Earth has changed
    dramatically over the last half a century. The Society of Exploration
    Geophysicists (SEG has worked to create standards to store the vast
    amounts of seismic data in a way that will be portable across computer
    architectures. However, it has been impossible to predict the needs of the
    immense range of seismic data acquisition systems. As a result, vendors have
    had to bend the rules to accommodate the needs of new instruments and
    experiment types. For low level access to seismic data, there is need for a
    standard open source library to allow access to a wide range of vendor data
    files that can handle all of the variations. A new seismic software package,
    seismic-py, provides an infrastructure for creating and managing drivers for
    each particular format. Drivers can be derived from one of the known formats
    and altered to handle any slight variations. Alternatively drivers can be
    developed from scratch for formats that are very different from any previously
    defined format. Python has been the key to making driver development easy
    and efficient to implement. The goal of seismic-py is to be the base system
    that will power a wide range of experimentation with seismic data and at the
    same time provide clear documentation for the historical record of seismic
    data formats.

  13. Characterization of seismic properties across scales: from the laboratory- to the field scale

    Science.gov (United States)

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

    2016-04-01

    modulus K(ω) and shear modulus G(ω), from which the P- and S-wave velocities V P(ω) and V S(ω) and the quality factors QP(ω) and QS(ω) of fluid saturated fractured rock volumes can be estimated. These volumes are much larger and contain more complex structures than the rock samples investigated in the laboratory. Thus, the derived quantities describe the elastic and anelastic (energy loss due to wave induced fluid flow) short-term deformation induced by seismic waves at scales that are relevant for field-scale seismic exploration projects.

  14. Turbocharging Quantum Tomography

    Energy Technology Data Exchange (ETDEWEB)

    Blume-Kohout, Robin J. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Gamble, John King [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Nielsen, Erik [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Maunz, Peter Lukas Wilhelm [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Scholten, Travis L. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Rudinger, Kenneth Michael [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)

    2015-01-01

    Quantum tomography is used to characterize quantum operations implemented in quantum information processing (QIP) hardware. Traditionally, state tomography has been used to characterize the quantum state prepared in an initialization procedure, while quantum process tomography is used to characterize dynamical operations on a QIP system. As such, tomography is critical to the development of QIP hardware (since it is necessary both for debugging and validating as-built devices, and its results are used to influence the next generation of devices). But tomography suffers from several critical drawbacks. In this report, we present new research that resolves several of these flaws. We describe a new form of tomography called gate set tomography (GST), which unifies state and process tomography, avoids prior methods critical reliance on precalibrated operations that are not generally available, and can achieve unprecedented accuracies. We report on theory and experimental development of adaptive tomography protocols that achieve far higher fidelity in state reconstruction than non-adaptive methods. Finally, we present a new theoretical and experimental analysis of process tomography on multispin systems, and demonstrate how to more effectively detect and characterize quantum noise using carefully tailored ensembles of input states.

  15. Seismic Constraints on Slab Interaction With the Transition Zone

    Science.gov (United States)

    Lekic, V.; Reif, C.; Dziewonski, A. M.; Sheehan, A.; van Summeren, J.

    2006-12-01

    Over the past decade, seismic tomography has revealed that subducting lithospheric slabs interact with the transition zone in a variety of ways, directly penetrating into the lower mantle in some locations, while stagnating in others. Here, we present preliminary results of attempts to characterize and quantify the stagnation of slab material in the transition zone initiated at the 2006 Cooperative Institute for Deep Earth Research (CIDER) workshop. Providing seismic constraints on slab interaction with the transition zone is essential for verifying dynamic calculations that examine to what degree slabs are hindered from penetrating through the 660 km seismic discontinuity. First we compute the tomographic signature of an end-member mantle model in which 100 km thick slabs descend from the upper to lower mantle without deformation / stagnation in the transition zone. We then compare the amplitude of the predicted shear velocity anomaly with that observed in the most recent Scripps, Berkeley, Harvard, Caltech, and UT Austin global tomographic models. We find that in the western Pacific slab material is accumulating within the transition zone, while under South America, the slabs appear to enter the lower mantle unhindered. This accumulation of slab material in the transition zone indicates that some mechanism is temporarily delaying it from passing into the lower mantle. This finding is consistent with comparisons of power spectra of the observed models in and below the transition zone, which indicate that the pattern of seismic heterogeneity changes drastically across the 660 km discontinuity. Furthermore, the focal mechanisms of deep (>400 km) earthquakes from the Harvard Centroid Moment Tensor project provide a wealth of information on slab deformation within the transition zone. We have systematically compared the orientations of earthquake compressional axes to the slab orientations (as defined by the Wadati-Benioff zone) for all regions of deep seismicity. The

  16. Unwrapped phase inversion for near surface seismic data

    KAUST Repository

    Choi, Yun Seok

    2012-11-04

    The Phase-wrapping is one of the main obstacles of waveform inversion. We use an inversion algorithm based on the instantaneous-traveltime that overcomes the phase-wrapping problem. With a high damping factor, the frequency-dependent instantaneous-traveltime inversion provides the stability of refraction tomography, with higher resolution results, and no arrival picking involved. We apply the instantaneous-traveltime inversion to the synthetic data generated by the elastic time-domain modeling. The synthetic data is a representative of the near surface seismic data. Although the inversion algorithm is based on the acoustic wave equation, the numerical examples show that the instantaneous-traveltime inversion generates a convergent velocity model, very similar to what we see from traveltime tomography.

  17. Muon Tomography for Geological Repositories.

    Science.gov (United States)

    Woodward, D.; Kudryavtsev, V.; Gluyas, J.; Clark, S. J.; Thompson, L. F.; Klinger, J.; Spooner, N. J.; Blackwell, T. B.; Pal, S.; Lincoln, D. L.; Paling, S. M.; Mitchell, C. N.; Benton, C.; Coleman, M. L.; Telfer, S.; Cole, A.; Nolan, S.; Chadwick, P.

    2015-12-01

    Cosmic-ray muons are subatomic particles produced in the upper atmosphere in collisions of primary cosmic rays with atoms in air. Due to their high penetrating power these muons can be used to image the content (primarily density) of matter they pass through. They have already been used to image the structure of pyramids, volcanoes and other objects. Their applications can be extended to investigating the structure of, and monitoring changes in geological formations and repositories, in particular deep subsurface sites with stored CO2. Current methods of monitoring subsurface CO2, such as repeat seismic surveys, are episodic and require highly skilled personnel to operate. Our simulations based on simplified models have previously shown that muon tomography could be used to continuously monitor CO2 injection and migration and complement existing technologies. Here we present a simulation of the monitoring of CO2 plume evolution in a geological reservoir using muon tomography. The stratigraphy in the vicinity of the reservoir is modelled using geological data, and a numerical fluid flow model is used to describe the time evolution of the CO2 plume. A planar detection region with a surface area of 1000 m2 is considered, at a vertical depth of 776 m below the seabed. We find that one year of constant CO2 injection leads to changes in the column density of about 1%, and that the CO2 plume is already resolvable with an exposure time of less than 50 days. The attached figure show a map of CO2 plume in angular coordinates as reconstructed from observed muons. In parallel with simulation efforts, a small prototype muon detector has been designed, built and tested in a deep subsurface laboratory. Initial calibrations of the detector have shown that it can reach the required angular resolution for muon detection. Stable operation in a small borehole within a few months has been demonstrated.

  18. The forecast of mining-induced seismicity and the consequent risk of damage to the excavation in the area of seismic event

    Directory of Open Access Journals (Sweden)

    Jan Drzewiecki

    2017-01-01

    Full Text Available The Central Mining Institute has developed a method for forecasting the amount of seismic energy created by tremors induced by mining operations. The results of geophysical measurements of S wave velocity anomalies in a rock mass or the results of analytic calculations of the values of pressure on the horizon of the elastic layers are used in the process of calculating the energy. The calculation program which has been developed and adopted has been modified over recent years and it now enables not only the prediction of the energy of dynamic phenomena induced by mining but also the forecasting of the devastating range of seismic shock. The results obtained from this calculation, usually presented in a more readable graphic form, are useful for the macroscopic evaluation of locations that are potential sources of seismic energy. Forecasting of the maximum energy of seismic shock without prior knowledge of the location of the shock's source, does not allow shock attenuation that results from, for example, a distance of tremor source from the excavation which will be affected by seismic energy, to be taken into consideration. The phenomena of energy dissipation, which is taken into account in the forecasts, create a new quality of assessment of threat to the excavation. The paper presents the principle of a method of forecasting the seismic energy of a shock and the risk of damage to the excavation as a result of the impact of its energy wave. The solution assumes that the source of the energy shock is a resilient layer in which the sum of the gravitational stresses, resulting from natural disturbances and those induced by the conducted or planned mining exploitation, is estimated. The proposed solution assumes a spherical model for the tremor source, for which seismic energy is forecasted as a function of the longwall advance and the elementary value of seismic energy destroying the excavation. Subsequently, the following are calculated for the

  19. QLg tomography in Gujarat, Western India

    Science.gov (United States)

    Aggarwal, Sandeep Kumar; Khan, Prosanta Kumar

    2016-10-01

    We propose a novel Lg attenuation tomography model (QLg tomography) for the state of Gujarat, Western India, using earthquake data recorded by the Gujarat Seismic Network, operated by the Institute of Seismological Research in Gandhinagar. The waveform dataset consist of 400 3-component recordings, produced by 60 earthquakes with magnitude (ML) spanning from 3.6 to 5.1, recorded at 60 seismic stations having epicentral distances spanning between 200 and 500 km. Spectral amplitude decays for Lg wave displacement were obtained by generalized inversion at 17 frequencies spanning between 0.9 and 9 Hz. Lg wave propagation efficiency was measured by Lg/Pn spectral ratio categorizing as efficient ratio ≥6 for 86%, intermediate ratio of 3-6 for 10% and inefficient ratio Gujarat. Average power-law attenuation relationship obtained for Gujarat as QLg(f) = 234f0.64, which corresponds to high attenuation in comparison to peninsular India shield region and other several regions around the world. QLg tomography resolves the highly attenuating crust of extremely fractured Saurashtra region and tectonically active Kachchh region. The Gujarat average attenuation is also lying in between them. The low attenuation in Cambay and Narmada rift basins and extremely low attenuation in patch of Surendranagar area is identified. This study is the first attempt and can be utilized as pivotal criteria for scenario hazard assessment, as maximum hazard has been reported in highly attenuating tectonically active Kachchh region and in low attenuating Cambay, Narmada and Surendranagar regions. The site and source terms are also obtained along with the QLg inversion. The estimated site responses are comparable with observed local geological condition and agree with the previously reported site amplifications at the same sites. The source terms are comparable with local magnitude estimated from Network. The Mw (Lg) is nearly equivalent to ML (GSN) and the slight differences are noted for larger

  20. Updated Colombian Seismic Hazard Map

    Science.gov (United States)

    Eraso, J.; Arcila, M.; Romero, J.; Dimate, C.; Bermúdez, M. L.; Alvarado, C.

    2013-05-01

    The Colombian seismic hazard map used by the National Building Code (NSR-98) in effect until 2009 was developed in 1996. Since then, the National Seismological Network of Colombia has improved in both coverage and technology providing fifteen years of additional seismic records. These improvements have allowed a better understanding of the regional geology and tectonics which in addition to the seismic activity in Colombia with destructive effects has motivated the interest and the need to develop a new seismic hazard assessment in this country. Taking advantage of new instrumental information sources such as new broad band stations of the National Seismological Network, new historical seismicity data, standardized global databases availability, and in general, of advances in models and techniques, a new Colombian seismic hazard map was developed. A PSHA model was applied. The use of the PSHA model is because it incorporates the effects of all seismic sources that may affect a particular site solving the uncertainties caused by the parameters and assumptions defined in this kind of studies. First, the seismic sources geometry and a complete and homogeneous seismic catalog were defined; the parameters of seismic rate of each one of the seismic sources occurrence were calculated establishing a national seismotectonic model. Several of attenuation-distance relationships were selected depending on the type of seismicity considered. The seismic hazard was estimated using the CRISIS2007 software created by the Engineering Institute of the Universidad Nacional Autónoma de México -UNAM (National Autonomous University of Mexico). A uniformly spaced grid each 0.1° was used to calculate the peak ground acceleration (PGA) and response spectral values at 0.1, 0.2, 0.3, 0.5, 0.75, 1, 1.5, 2, 2.5 and 3.0 seconds with return periods of 75, 225, 475, 975 and 2475 years. For each site, a uniform hazard spectrum and exceedance rate curves were calculated. With the results, it is

  1. Seismic hazard assessment: Issues and alternatives

    Science.gov (United States)

    Wang, Z.

    2011-01-01

    Seismic hazard and risk are two very important concepts in engineering design and other policy considerations. Although seismic hazard and risk have often been used inter-changeably, they are fundamentally different. Furthermore, seismic risk is more important in engineering design and other policy considerations. Seismic hazard assessment is an effort by earth scientists to quantify seismic hazard and its associated uncertainty in time and space and to provide seismic hazard estimates for seismic risk assessment and other applications. Although seismic hazard assessment is more a scientific issue, it deserves special attention because of its significant implication to society. Two approaches, probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA), are commonly used for seismic hazard assessment. Although PSHA has been pro-claimed as the best approach for seismic hazard assessment, it is scientifically flawed (i.e., the physics and mathematics that PSHA is based on are not valid). Use of PSHA could lead to either unsafe or overly conservative engineering design or public policy, each of which has dire consequences to society. On the other hand, DSHA is a viable approach for seismic hazard assessment even though it has been labeled as unreliable. The biggest drawback of DSHA is that the temporal characteristics (i.e., earthquake frequency of occurrence and the associated uncertainty) are often neglected. An alternative, seismic hazard analysis (SHA), utilizes earthquake science and statistics directly and provides a seismic hazard estimate that can be readily used for seismic risk assessment and other applications. ?? 2010 Springer Basel AG.

  2. Deep seismic investigation of crustal extensional structures in the Danish Basin along the ESTRID-2 profile

    DEFF Research Database (Denmark)

    Sandrin, Alessandro; Thybo, Hans

    2008-01-01

    The crust and uppermost mantle in the Danish Basin are investigated by modelling the P-wave velocity distribution along the north-south trending seismic profile ESTRID-2. Seismic tomography and ray inversion modelling demonstrate a variable depth to the top of the crystalline crust, from ~10 km...... to magmatic underplating. The occurrence of a large crustal mafic intrusion associated with magmatic underplating may be related to extensional/transtensional tectonism in the Tornquist Fan area in the Late Palaeozoic. The extensional event probably caused the opening of a plumbing system for intrusion...

  3. First-arrival traveltime tomography for anisotropic media using the adjoint-state method

    KAUST Repository

    Waheed, Umair bin

    2016-05-27

    Traveltime tomography using transmission data has been widely used for static corrections and for obtaining near-surface models for seismic depth imaging. More recently, it is also being used to build initial models for full-waveform inversion. The classic traveltime tomography approach based on ray tracing has difficulties in handling large data sets arising from current seismic acquisition surveys. Some of these difficulties can be addressed using the adjoint-state method, due to its low memory requirement and numerical efficiency. By coupling the gradient computation to nonlinear optimization, it avoids the need for explicit computation of the Fréchet derivative matrix. Furthermore, its cost is equivalent to twice the solution of the forward-modeling problem, irrespective of the size of the input data. The presence of anisotropy in the subsurface has been well established during the past few decades. The improved seismic images obtained by incorporating anisotropy into the seismic processing workflow justify the effort. However, previous literature on the adjoint-state method has only addressed the isotropic approximation of the subsurface. We have extended the adjoint-state technique for first-arrival traveltime tomography to vertical transversely isotropic (VTI) media. Because δ is weakly resolvable from surface seismic alone, we have developed the mathematical framework and procedure to invert for vNMO and η. Our numerical tests on the VTI SEAM model demonstrate the ability of the algorithm to invert for near-surface model parameters and reveal the accuracy achievable by the algorithm.

  4. Upper mantle structure at Walvis Ridge from Pn tomography

    Science.gov (United States)

    Ryberg, Trond; Braeuer, Benjamin; Weber, Michael

    2017-10-01

    Passive continental margins offer the unique opportunity to study the processes involved in continental extension and break-up. Within the LISPWAL (LIthospheric Structure of the Namibian continental Passive margin at the intersection with the Walvis Ridge from amphibious seismic investigations) project, combined on- and offshore seismic experiments were designed to characterize the Southern African passive margin at the Walvis Ridge in northern Namibia. In addition to extensive analysis of the crustal structures, we carried out seismic investigations targeting the velocity structure of the upper mantle in the landfall region of the Walvis Ridge with the Namibian coast. Upper mantle Pn travel time tomography from controlled source, amphibious seismic data was used to investigate the sub-Moho upper mantle seismic velocity. We succeeded in imaging upper mantle structures potentially associated with continental break-up and/or the Tristan da Cunha hotspot track. We found mostly coast-parallel sub-Moho velocity anomalies, interpreted as structures which were created during Gondwana break-up.

  5. Artificial seismic acceleration

    Science.gov (United States)

    Felzer, Karen R.; Page, Morgan T.; Michael, Andrew J.

    2015-01-01

    In their 2013 paper, Bouchon, Durand, Marsan, Karabulut, 3 and Schmittbuhl (BDMKS) claim to see significant accelerating seismicity before M 6.5 interplate mainshocks, but not before intraplate mainshocks, reflecting a preparatory process before large events. We concur with the finding of BDMKS that their interplate dataset has significantly more fore- shocks than their intraplate dataset; however, we disagree that the foreshocks are predictive of large events in particular. Acceleration in stacked foreshock sequences has been seen before and has been explained by the cascade model, in which earthquakes occasionally trigger aftershocks larger than themselves4. In this model, the time lags between the smaller mainshocks and larger aftershocks follow the inverse power law common to all aftershock sequences, creating an apparent acceleration when stacked (see Supplementary Information).

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  7. High-resolution seismic profiles of the active wedge thrusts in the Toyama basin, central Japan

    Science.gov (United States)

    Kato, Naoko; Sato, Hiroshi; Ishiyama, Tatsuya

    2017-04-01

    Thick-Neogene sediments accumulated in the Toyama basin, Miocene failed rift formed in the opening stage of the Sea of Japan. Due to the shortening deformation since the Pliocene, NE-trending reverse faults and folds have been developed to form active fault systems. Evaluation of seismic hazards requires understanding the relationship between active fault and seismic source fault is important. To obtain complete image of the active seismogenic source fault system, we carried out the high-resolution seismic profiling across the active faults in the Toyama basin, together with the deep seismic reflection profiling (KT01: Ishiyama et al., 2016). Seismic data were acquired using two vibrator trucks (IVI, EnviroVib) and a Mini-vib (IVI T15000). Shot and receiver intervals are 10 and 12.5 m respectively. The seismic data were processed using conventional CMP-reflection methods. The obtained seismic sections across the Takashozu and Isurugi faults portrays the growth strata associated with the Plio-Quaternary reverse faulting. The seismic sections show that both structures are formed as wedge thrusts at shallower structural levels. P-wave velocity profiles obtained by refraction tomography accords well to the geologic interpretation as a wedge thrust. The depth of thrust tip of main thrust is 0.6 km to 1.5 km and located in the syn rift Miocene mudstone. As the main anticline was formed by the deep-seated thrust, this shallow thrust played a secondary role for this anticline. Our results demonstrate that high-resolution seismic profiles help to reveal source fault geometry and their activity.

  8. A Bayesian approach to the real-time estimation of magnitude from the early P and S wave displacement peaks

    Science.gov (United States)

    Lancieri, M.; Zollo, A.

    2008-12-01

    It has been shown that the initial portion of P and S wave signals can provide information about the final earthquake magnitude in a wide magnitude range. This observation opens the perspective for the real-time determination of source parameters. In this paper we describe a probabilistic evolutionary approach for the real-time magnitude estimation which can have a potential use in earthquake early warning. The technique is based on empirical prediction laws correlating the low-frequency peak ground displacement measured in a few seconds after the P and/or S phase arrival and the final event magnitude. The evidence for such a correlation has been found through the analysis of 256 shallow crustal events in the magnitude range Mjma 4-7.1 located over the entire Japanese archipelago. The peak displacement measured in a 2-s window from the first P phase arrival correlates with magnitude in the range M = [4-6.5]. While a possible saturation effect above M ≃ 6.5 is observed, it is less evident in an enlarged window of 4 s. The scaling of S peaks with magnitude is instead also observed at smaller time lapses (i.e., 1 s) after the first S arrival. The different scaling of P and S peaks with magnitude when measured in a 2-s window is explained in terms of different imaged rupture surface by the early portion of the body wave signals. We developed a technique to estimate the probability density function (PDF) of magnitude, at each time step after the event origin. The predicted magnitude value corresponds to the maximum of PDF, while its uncertainty is given by the 95% confidence bound. The method has been applied to the 2007 (Mjma = 6.9) Noto Hanto and 1995 (Mjma = 7.3) Kobe earthquakes. The results of this study can be summarized as follows: (1) The probabilistic algorithm founded on the predictive model of peak displacement versus final magnitude is able to provide a fast and robust estimation of the final magnitude. (2) The information available after a few seconds

  9. Surface-Wave Tomography of Yucca Flat, Nevada

    Science.gov (United States)

    Toney, L. D.; Abbott, R. E.; Knox, H. A.; Preston, L. A.; Hoots, C. R.

    2016-12-01

    In 2015, Sandia National Laboratories conducted an active-source seismic survey of Yucca Flat, Nevada, on the Nevada National Security Site. The Yucca Flat basin hosted over 900 nuclear tests between 1951 and 1992. Data from this survey will help characterize seismic propagation effects of the area, informing models for the next phase of the Source Physics Experiments. The survey source was a 13,000-kg weight-drop at 91 locations along a 19-km N-S transect and 56 locations along an 11-km E-W transect. Over 350 three-component 2-Hz geophones were variably spaced at 10, 20, and 100 m along each line. We employed roll-along survey geometry to ensure 10-m receiver spacing within 2 km of the source. Phase velocity surface-wave analysis via the refraction-microtremor (ReMi) method was previously performed on this data in order to obtain an S-wave velocity model of the subsurface. However, the results of this approach were significantly impacted in areas where ray paths were proximate to underground nuclear tests, resulting in a spatially incomplete model. We have processed the same data utilizing group velocities and the multiple filter technique (MFT), with the hope that the propagation of wave groups is less impacted by the disrupted media surrounding former tests. We created a set of 30 Gaussian band-pass filters with scaled relative passbands and central frequencies ranging from 1 to 50 Hz. We picked fundamental Rayleigh wave arrivals from the filtered data; these picks were then inverted for 2D S-wave velocity along the transects. The new S-wave velocity model will be integrated with previous P-wave tomographic results to yield a more complete model of the subsurface structure of Yucca Flat. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  10. Experimental Observation of Non-'S-Wave' Superconducting Behavior in Bulk Superconducting Tunneling Junctions of Yba2Cu3O7-δ

    Directory of Open Access Journals (Sweden)

    Leandro Jose Guerra

    1998-06-01

    Full Text Available Evidence of non-s-wave superconductivity from normal tunneling experiments in bulk tunneling junctions of YBa2Cu3O7-δ is presented. The I-V and dI/dV characteristics of bulk superconducting tunneling junctions of YBa2Cu3O7-δ have been measured at 77.0K and clear deviation from s-wave superconducting behavior has been observed. The result agrees with d-wave symmetry, and interpreting the data in this way, the magnitude of the superconducting energy gap, 2Δ, is found to be (0.038 ± 0.002 eV. Comparing this energy gap with Tc (2Δ/kB Tc = 5.735, indicates that these high-Tc superconductors are strongly correlated materials, which in contrast with BCS-superconductors are believed to be weakly correlated.

  11. SEISMIC ANALYSIS FOR PRECLOSURE SAFETY

    Energy Technology Data Exchange (ETDEWEB)

    E.N. Lindner

    2004-12-03

    The purpose of this seismic preclosure safety analysis is to identify the potential seismically-initiated event sequences associated with preclosure operations of the repository at Yucca Mountain and assign appropriate design bases to provide assurance of achieving the performance objectives specified in the Code of Federal Regulations (CFR) 10 CFR Part 63 for radiological consequences. This seismic preclosure safety analysis is performed in support of the License Application for the Yucca Mountain Project. In more detail, this analysis identifies the systems, structures, and components (SSCs) that a