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Author: Publisher: ISBN: Category : Languages : en Pages : 21
Book Description
Well-resolved moment tensor solutions reveal information about the sources of seismic waves. Here we introduce a new way of assessing confidence in the regional full moment tensor inversion via the introduction of the network sensitivity solution (NSS). The NSS takes into account the unique station distribution, frequency band, and signal-to-noise ratio of a given event scenario. The NSS compares both a hypothetical pure source (for example an explosion or an earthquake) and the actual data with several thousand sets of synthetic data from a uniform distribution of all possible sources. The comparison with a hypothetical pure source provides the theoretically best-constrained source-type region for a given set of stations, and with it one can determine whether further analysis with the data is warranted. The NSS that employs the actual data gives a direct comparison of all other source-types with the best-fit source. In this way, one can choose a threshold level of fit where the solution is comfortably constrained. The method is tested for the well-recorded nuclear test, JUNCTION, at the Nevada Test Site. Sources that fit comparably well to a hypothetical pure explosion recorded with no noise at the JUNCTION data stations have a large volumetric component and are not described well by a double-couple (DC) source. The NSS using the real data from JUNCTION is even more tightly constrained to an explosion since the data contains some energy that precludes fitting with any type of deviatoric source. We also calculate the NSS for the October 2006 North Korea test and a nearby earthquake, where the station coverage is poor and the event magnitude is small. The earthquake solution is very well fit by a DC source, and the best-fit solution to the nuclear test (M{sub W}4.1) is dominantly explosion.
Author: Publisher: ISBN: Category : Languages : en Pages : 21
Book Description
Well-resolved moment tensor solutions reveal information about the sources of seismic waves. Here we introduce a new way of assessing confidence in the regional full moment tensor inversion via the introduction of the network sensitivity solution (NSS). The NSS takes into account the unique station distribution, frequency band, and signal-to-noise ratio of a given event scenario. The NSS compares both a hypothetical pure source (for example an explosion or an earthquake) and the actual data with several thousand sets of synthetic data from a uniform distribution of all possible sources. The comparison with a hypothetical pure source provides the theoretically best-constrained source-type region for a given set of stations, and with it one can determine whether further analysis with the data is warranted. The NSS that employs the actual data gives a direct comparison of all other source-types with the best-fit source. In this way, one can choose a threshold level of fit where the solution is comfortably constrained. The method is tested for the well-recorded nuclear test, JUNCTION, at the Nevada Test Site. Sources that fit comparably well to a hypothetical pure explosion recorded with no noise at the JUNCTION data stations have a large volumetric component and are not described well by a double-couple (DC) source. The NSS using the real data from JUNCTION is even more tightly constrained to an explosion since the data contains some energy that precludes fitting with any type of deviatoric source. We also calculate the NSS for the October 2006 North Korea test and a nearby earthquake, where the station coverage is poor and the event magnitude is small. The earthquake solution is very well fit by a DC source, and the best-fit solution to the nuclear test (M{sub W}4.1) is dominantly explosion.
Author: Sebastiano D'Amico Publisher: Springer ISBN: 3319773593 Category : Science Languages : en Pages : 751
Book Description
This book first focuses on the explanation of the theory about focal mechanisms and moment tensor solutions and their role in the modern seismology. The second part of the book compiles several state-of-the-art case studies in different seismotectonic settings of the planet.The assessment of seismic hazard and the reduction of losses due to future earthquakes is probably the most important contribution of seismology to society. In this regard, the understanding of reliable determination seismic source and of its uncertainty can play a key role in contributing to geodynamic investigation, seismic hazard assessment and earthquake studies. In the last two decades, the use of waveforms recorded at local-to-regional distances has increased considerably. Waveform modeling has been used also to estimate faulting parameters of small-to-moderate sized earthquakes.
Author: Publisher: ISBN: Category : Languages : en Pages : 11
Book Description
In our previous work the deviatoric and isotropic source components for 17 explosions at the Nevada Test Site, as well as 12 earthquakes and 4 collapses in the surrounding region of the western US, were calculated using a regional time-domain full waveform inversion for the complete moment tensor (Dreger et al., 2008; Ford et al., 2008; Ford et al., 2009a). The events separate into specific populations according to their deviation from a pure double-couple and ratio of isotropic to deviatoric energy. The separation allows for anomalous event identification and discrimination between explosions, earthquakes, and collapses. Confidence regions of the model parameters are estimated from the data misfit by assuming normally distributed parameter values. We developed a new Network Sensitivity Solution (NSS) in which the fit of sources distributed over a source-type plot (Hudson et al., 1989) show the resolution of the source parameters. The NSS takes into account the unique station distribution, frequency band, and signal-to-noise ratio of a given event scenario. The NSS compares both a hypothetical pure source (for example an explosion or an earthquake) and the actual data with several thousand sets of synthetic data from a uniform distribution of all possible sources. The comparison with a hypothetical pure source provides the theoretically best-constrained source-type region for a given set of stations, and with it one can determine whether further analysis with the data is warranted. We apply the NSS to a NTS nuclear explosion, and earthquake, as well as the 2006 North Korean explosion, and a nearby earthquake. The results show that explosions and earthquakes are distinguishable, however the solution space depends strongly on the station coverage. Finally, on May 25, 2009 a second North Korean test took place. Our preliminary results show that the explosive nature of the event may be determined using the regional distance moment tensor method. Results indicate that the 2009 event is approximately 5-6 times larger than the earlier test, with an isotropic moment of about 1.8e+22 dyne cm. We perform a series of inversions for pure double-couple, pure explosion, combined double-couple and explosion, full moment tensor, and damped moment tensor inversions to assess the resolution of the isotropic moment of the event.
Author: Cedric Schmelzbach Publisher: Academic Press ISBN: 012824027X Category : Science Languages : en Pages : 198
Book Description
Formation and Structure of Planets, Volume 62 in the Advances in Geophysics series, highlights new chapters on a variety of topics in the field, including The evolution of multi-method imaging of structures and processes in environmental geophysics, An introduction to variational inference in Geophysical inverse problems, Moment tensor inversion, and more. Provides high-level reviews of the latest innovations in geophysics Written by recognized experts in the field Presents an essential publication for researchers in all fields of geophysics
Author: Publisher: ScholarlyEditions ISBN: 1464963398 Category : Science Languages : en Pages : 4306
Book Description
Issues in Earth Sciences, Geology, and Geophysics: 2011 Edition is a ScholarlyEditions™ eBook that delivers timely, authoritative, and comprehensive information about Earth Sciences, Geology, and Geophysics. The editors have built Issues in Earth Sciences, Geology, and Geophysics: 2011 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Earth Sciences, Geology, and Geophysics in this eBook to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Earth Sciences, Geology, and Geophysics: 2011 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.
Author: Roman Teisseyre Publisher: Springer Science & Business Media ISBN: 3540313370 Category : Science Languages : en Pages : 582
Book Description
This breakthrough book is the first to examine the rotational effects in earthquakes, a revolutionary concept in seismology. Existing models do no yet explain the significant rotational and twisting motions that occur during an earthquake and cause the failure of structures. The rotation and twist effects are investigated and described, and their consequences for designing tall buildings and other important structures are presented. This book will change the way the world views earthquakes.
Author: Andrea Chiang Publisher: ISBN: Category : Languages : en Pages : 125
Book Description
This dissertation demonstrates the utility of the complete waveform regional moment tensor inversion (Dreger and Woods, 2002; Dreger, 2003, Minson and Dreger, 2008) for nuclear event discrimination. I explore the source processes and associated uncertainties for explosions and earthquakes under the effects of limited station coverage, compound seismic sources, assumptions in velocity models and the corresponding Green's functions, and the effects of shallow source depth and free-surface conditions. The motivation to develop better techniques to obtain reliable source mechanism and assess uncertainties is not limited to nuclear monitoring, but they also provide quantitative information about the characteristics of seismic hazards (e.g. Petersen et al., 2014), local and regional tectonics and in-situ stress fields of the region (Hardebeck and Hauksson, 2001; Hardebeck and Michael, 2006). This dissertation begins with the analysis of three sparsely recorded events: the 14 September 1988 US-Soviet Joint Verification Experiment (JVE) nuclear test at the Semipalatinsk test site in Eastern Kazakhstan, and two nuclear explosions at the Chinese Lop Nor test site. We utilize a regional distance seismic waveform method fitting long-period, complete, three-component waveforms jointly with first-motion observations from regional stations and teleseismic arrays. The combination of long period waveforms and first motion observations provides unique discrimination of these sparsely recorded events in the context of the Hudson et al. (1989) source-type diagram. We demonstrate through a series of Jackknife tests and sensitivity analyses that the source-type of the explosions is well constrained. One event, a 1996 Lop Nor shaft explosion, displays large Love waves and possibly reversed Rayleigh waves at one station, indicative of a large tectonic release. We demonstrate the behavior of Network Sensitivity Solutions [NSS] (Ford et al., 2010) for models of tectonic release (Toksöz et al., 1965) and spall-based tensile damage (Patton and Taylor, 2008) over a range of F-factors and K-factors. A potential issue for moment tensor inversion of explosions is that Green's functions have vanishing amplitudes at the free surface. Because explosions are detonated at very shallow depths, this can result in bias in the moment tensor solution (Stevens and Murphy, 2001). It is important to understand these free surface effects on discriminating shallow explosive sources for nuclear monitoring purposes. It may also be important in natural systems that have shallow seismicity such as volcanoes and geothermal systems. To tackle this problem, we examine the effects of the free surface on the moment tensor via synthetic testing, and apply the moment tensor based discrimination method to well-recorded chemical explosions. These shallow chemical explosions represent rather severe source-station geometry in terms of the vanishing traction issues. We show that the combined waveform and first motion method enables the unique discrimination of these events, even though the data include unmodeled single force components resulting from the collapse and blowout of the quarry face immediately following the initial explosion. In contrast, recovering the announced explosive yield using seismic moment estimates from moment tensor inversion remains challenging but we can begin to put error bounds on our moment estimates using the NSS technique. The estimation of seismic source parameters is dependent upon having a well-calibrated velocity model to compute the Green's functions for the inverse problem. Ideally, seismic velocity models are calibrated through broadband waveform modeling (e.g. Dreger and Helmberger, 1990; Bhattacharyya et al., 1999), however in regions of low seismicity velocity models derived from body or surface wave tomography may be employed (e.g. Tape et al., 2010; Shen et al., 2013; Porritt et al. 2014). Whether a velocity model is 1D or 3D, or based on broadband seismic waveform modeling or the various tomographic techniques, the uncertainty in the velocity model can be the greatest source of error in moment tensor inversion. These errors have not been fully investigated for the nuclear discrimination problem. To study the effects of unmodeled structures on the moment tensor inversion, we set up a synthetic experiment where we produce synthetic seismograms for a 3D model (Moschetti et al., 2010) and invert these data using Green's functions computed with a 1D velocity mode (Song et al., 1996) to evaluate the recoverability of input solutions, paying particular attention to biases in the isotropic component. We then evaluate source inversions for real data using Green's functions for 1D and 3D velocity models in which the Green's functions were computed by utilizing the principle of source-receiver reciprocity (Aki and Richards, 2002; Dahlen and Tromp, 1998), and the finite-difference method (Appelo and Petersson, 2008; Eisner and Clayton, 2001; Graves and Wald, 2001). Using the full waveform moment tensor inversion method we analyze earthquakes and explosions at NTS using 1D and 3D Earth models and compare the solutions and associated uncertainties at different frequency bands. The synthetic experiment results indicate that the 1D model assumption is valid for moment tensor inversions at periods as short as 10 seconds for the 1D western U.S. model (Song et al., 1996). The correct earthquake mechanisms and source depth are recovered with statistically insignificant isotropic components as determined by the F-test. Shallow explosions are biased by the theoretical ISO-CLVD tradeoff but the tectonic release component remains low, and the tradeoff can be eliminated with constraints from P wave first motion. Path-calibration to the 1D model can reduce non-double-couple components in earthquakes, non-isotropic components in explosions and composite sources and improve the fit to the data. When we apply the 3D model to real data, at long periods (20-50 seconds), we see good agreement in the solutions between the 1D and 3D models and slight improvement in waveform fits when using the 3D velocity model Green's functions. At high frequencies the advantage of the 3D model is limited except for paths from NTS to the San Francisco Bay, where we see a marked improvement in waveform fit. However, we do not see a clear reduction in source uncertainties when using a 3D model. A larger sample size is required to make useful interpretations about the use of 3D models in estimating source uncertainties. Our results indicate that the 3D model for the western U.S. (Moschetti et al., 2010) still needs further refinement to adequately model wave propagation at high frequencies and that path-averaged 1D models derived from the 3D model may be a more attractive approach than the more costly 3D simulation for short period inversions.
Author: R. Sabadini Publisher: Springer Science & Business Media ISBN: 9401133743 Category : Science Languages : en Pages : 705
Book Description
by K. Lambeck, R. Sabadini and E. B08Chi Viscosity is one of the important material properties of the Earth, controlling tectonic and dynamic processes such as mantle convection, isostasy, and glacial rebound. Yet it remains a poorly resolved parameter and basic questions such as whether the planet's response to loading is linear or non-linear, or what are its depth and lateral variations remain uncertain. Part of the answer to such questions lies in laboratory observations of the rheology of terrestrial materials. But the extrapolation of such measurements from the laboratory environment to the geological environment is a hazardous and vexing undertaking, for neither the time scales nor the strain rates characterizing the geological processes can be reproduced in the laboratory. General rules for this extrapolation are that if deformation is observed in the laboratory at a particular temperature, deformation in geological environments will occur at a much reduced temperature, and that if at laboratory strain rates a particular deformation mechanism dominates over all others, the relative importance of possible mechanisms may be quite different at the geologically encountered strain rates. Hence experimental results are little more than guidelines as to how the Earth may respond to forces on long time scales.
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Author: Sebastiano D'Amico
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Author: Cedric Schmelzbach
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Author: Sean Ricardo Ford
Author: Roman Teisseyre
Author: Andrea Chiang
Author: H. Kanamori
Author: R. Sabadini