Download or read book Nonlinear Modeling of Tectonic Release from Underground Explosions written by and published by . This book was released on 1982 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reversal of teleseismic Rayleigh wave polarity has been observed for some underground explosions in eastern Kazakh, and in some cases the polarity is reversed at all azimuths of observation. We analyze two-dimensional, nonlinear numerical simulations of underground explosions to examine the hypothesis that these phase reversals result from the action of tectonic prestress on the explosion-created nonlinear volume. We conclude that the effect of tectonic prestress on surface wave excitation is potentially large. When a shear prestress of 7.5 MPa (75 bars) is introduced, with horizontal principal stresses more compressive than the vertical principal stress, the explosion Rayleigh wave amplitude is reduced by a factor of 4 (i.e., Ms is reduced by 0.6). The large surface wave reduction is accompanied by no significant perturbation of body wave magnitude (mb). The nonlinear model predictions imply that if tectonic release is modeled elastically as the relaxation of the deviatoric part of the prestress into a spherical cavity, the appropriate cavity radius is approximately 80 percent of the explosion elastic radius.

Download or read book Surface wave Generation by Underground Nuclear Explosions Releasing Tectonic Strain written by and published by . This book was released on 1980 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Seismic surface-wave generation by underground nuclear explosions releasing tectonic strain is studied through a series of synthetic radiation-pattern calculations based on the earthquake-trigger model. From amplitude and phase radiation patterns for 20-s Rayleigh waves, inferences are made about effects on surface-wave magnitude, M/sub s/, and waveform character. The focus of this study is a comparison between two mechanisms of tectonic strain release: strike-slip motion on vertical faults and thrust motion on 45° dipping faults. The results of our calculations show that Rayleigh-wave amplitudes of the dip-slip model at F values between 0.75 and 1.5 are significantly lower than amplitudes of the strike-slip model or of the explosion source alone. This effect translates into M/sub s/ values about 0.5 units lower than M/sub s/ of the explosion alone. Waveform polarity reversals occur in two of four azimuthal quadrants for the strike-slip model and in all azimuths of the dip-slip-thrust model for F values above about 3. A cursory examination of waveforms from presumed explosions in eastern Kazakhstan suggests that releases of tectonic strain are accompanying the detonation of many of these explosions. Qualitatively, the observations seem to favor the dip-slip-thrust model, which, in the case of a few explosions, must have F values above 3.

Download or read book Tectonic Strain Release by Underground Nuclear Explosions written by M. Nafi Toksoz and published by . This book was released on 1975 with total page 241 pages. Available in PDF, EPUB and Kindle. Book excerpt: Static and dynamic methods are developed to study the elastic field produced by earthquake faulting. An earthquake is considered as the slip on a planar fault due to frictional instability. The dynamics of a circular fault model is considered as a circular rupture front that expands subsonically from a nucleation point until it suddenly stops at its final radius. It was found that both the final slip on the fault and the rise time are zero on the edge of the fault and reach their maxima at the center of the fault. This slip-time history is quite different from that of the usual Haskell model where slip and rise time are assumed constant over the fault. The far field radiation due to this fault model was studied. A new method to compute the static near field of a shallow earthquake was developed.

Download or read book A Time Domain Study of Tectonic Strain Release Effects on Seismic Waves from Underground Nuclear Explosions written by K. K. Nakanishi and published by . This book was released on 1982 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Analysis of the Effects of Tectonic Release on Short Period P Waves Observed from Shagan River Explosions written by Brian W. Barker and published by . This book was released on 1987 with total page 65 pages. Available in PDF, EPUB and Kindle. Book excerpt: Large samples of teleseismic P wave amplitude and waveform data recorded from Shagan River underground explosions have been collected and systematically analyzed in an attempt to identify any effects which may correlate with the amount of tectonic release accompanying these explosions. Results of these analyses indicate that these teleseismic P wave data do not provide any unambiguous evidence of effects of tectonic release in the short-period range of interest in m sub b determination. However, the results of a preliminary theoretical analysis indicate that such negative evidence is not definitive in that there are plausible models of tectonic release for which no detectable variations in the observed teleseismic P waveforms are theoretically expected to result from the superposition of these two sources. At the same time, such models of tectonic release predict significant positive bias in the network-averaged m sub b values for explosions accompanied by the mode of tectonic release traditionally associated with the Shagan River test site. Thus, the currently available seismic data do not exclude the possibility that tectonic release may be introducing a positive bias of as much as several tenths of a magnitude unit into the network-averaged m sub b values computed for some Shagan River explositons. Keywords: Explosion seismology; Threshold Test Ban Treaty; Network; USSR; Global Digital Seismic; Seismic body waves; Nuclear explosion detection; Radiation patterns.

Download or read book Tectonic Strain Release by Underground Nuclear Explosions written by M. Nafi Toksoez and published by . This book was released on 1973 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt: Theoretical and observational research has been carried out in order to study tectonic strain. Theoretical calculations for a composite source model consisting of explosive and double couple components were compared to observed surface wave spectral ratios from underground nuclear explosions. A theoretical calculation is presented to explain the observed double couple component associated with tectonic stress release. Results from numerical calculations of induced flow behind island arcs and the associated tectonic stresses are presented. (Author).

Download or read book Surface wave Generation by Underground Nuclear Explosions Releasing Tectonic Strain written by H. J. Patton and published by . This book was released on 1980 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Release of Tectonic Strain by Large Underground Nuclear Detonation written by R. M. Turpening and published by . This book was released on 1973 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: The report describes an attempt to observe SH waves from several large underground nuclear explosions at first-zone distances (

Download or read book Surface Waves from Underground Explosions with Spall Analysis of Elastic and Nonlinear Source Models written by and published by . This book was released on 1981 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt: Anomalous surface wave observations from underground explosions have been widely attributed to the phenomenon of spall, i.e., the detachment and subsequent slapdown of near-surface layers in response to explosion-induced tensile stresses. We argue, on the basis of a simple equivalent-force model, that, while spall can enhance explosion surface waves at very short periods, it cannot contribute significantly to the teleseismic surface waves radiated by underground explosions at periods exceeding about 10 seconds. Previous theoretical results to the contrary are in error, having been based on source models which do not conserve momentum. A nonlinear, two-dimensional (axisymmetric) finite difference simulation of a buried explosion in granite further supports the conclusion that spall cannot contribute to long-period surface waves. The simulation exhibits extensive spall; nonetheless, predicted fundamental mode Rayleigh wave spectra are nearly identical to those obtained from a spherically symmetric simulation (which does not include spall), at periods exceeding about 10 seconds. At shorter periods, the two-dimensional simulation predicts some Rayleigh wave enhancement, compared to the one- dimensional simulation. The maximum enhancement, compared to the one-dimensional simulation. The maximum enhancement, about a factor of 2, occurs at a period of approximately 2.5 seconds. Synthetic long-period Rayleigh wave seismograms, at 3000 km range, show no perceptible phase or amplitude anomalies due to spall. These results are in excellent agreement with the predictions of the equivalent- force model.

Download or read book Explosion Source Model Development in Support of Seismic Monitoring Technologies New Models Accounting for Shock Induced Tensile Failure written by and published by . This book was released on 2008 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: The traditional source model for long-period seismic waves from nuclear explosions consists of a monopole releasing tectonic strain. Tectonic release has been studied since the 1960's, and numerous studies have shown that linear superposition of monopole + double-couple sources can explain many observations of Rayleigh and Love waves. Free surface interactions and the dynamics of shock-wave rebound are responsible for modes of tensile failure which can also lead to permanent deformations affecting long-period excitation. Indeed, the vast majority of nuclear explosions worldwide were conducted under containment conditions that facilitated shock-induced, deep-seated tensile failure. A new source model, which is a superposition of monopole + tectonic release + shock-induced tensile failure, is proposed, the latter source represented by a compensated-linear-vector dipole (CLVD) with vertical axis of symmetry. This CLVD source does not excite Love waves. I draw upon the Toksoz-Kehrer (1972) model for tectonic release where F is an index measuring long-period source strength of the release relative to monopole moment MI. A new index K, analogous to F, is introduced, providing a relative measure of MCLVD, the source strength of tensile failure. MCLVD vanishes for K = 1, and is> 0 in the case of extensional deformation along the vertical axis, e.g., K> 1. Rayleigh waves from the CLVD destructively interfere with waves from the monopole, and polarity reversals occur on all azimuths for K> ~3 in Poisson media. Most Nevada Test Site (NTS) observations support ~1

Download or read book Plate Tectonics and the Discrimination of Underground Explosions from Earthquakes written by Andrew J. Murphy and published by . This book was released on 1975 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the period covered by this semi-annual report (1 January to 30 June 1975), seven general topics of research have been investigated. (1) A study of anomalous events, earthquakes which plot near the explosion population in a (M sub s) - (m sub b) diagram, has concluded that all such anomalous events in the eastern Himalayas are natural earthquakes. (2) A study of a foreshock-mainshock-aftershock sequence is being conducted to determine if there are factors other than source depth focal mechanism that control the surface wave magnitude of small events. (3) Three studies are in progress on the topic of Intraplate Tectonics. (4) A study comparing the motions in a half space near a fault with those which occur in a whole space if the surface were absent has been completed. (5) A study is currently in progress to test the validity of various models of the core-mantle boundary using seismograms synthesized by the Langer method of frequency domain calculations. (6) In another study, the excitation of higher mode surface waves by shallow events is being examined. (7) A study is also under way on the possible interrelation among bouyant zones, great earthquakes, and dynamic boundaries of subduction.

Download or read book Simulation of Teleseismic Body Waves from Underground Explosions Beneath Sloping and Flat Surfaces Using Nonlinear Axisymmetric Finite Difference Calculations written by J. L. Stevens and published by . This book was released on 1991 with total page 57 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Analysis of Teleseismic P Wave Amplitude and Coda Variations for Underground Explosions written by Thorne Lay and published by . This book was released on 1989 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report presents the results of four investigations which have as their common goal, the development and application of techniques for determining near-source contributions to the observed variations in short-period P wave amplitudes, travel times, waveforms and coda for underground explosions. A waveform modeling analysis of long-period teleseismic SH and SV waves from two large underground explosions at the Southern Novaya Zemlya test site indicates that the appropriate equivalent double couple orientation for the tectonic release is vertical strike slip. complete waveform modeling of the SV signals using the method of Baag and Langston allows us to distinguish between the strike slip and 45 deg. dipping thrust geometries. The resulting mechanism and associated F-factors indicate that teleseismic P waves from these events are probably not strongly affected by tectonic release radiation, consistent with the previous coda and P wave amplitude analysis we conducted under our previous contract. (rh).

Download or read book Explosion Source Phenomenology written by Steven R. Taylor and published by American Geophysical Union. This book was released on 1991-01-08 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 65. In March 1989, the Department of Energy (DOE) and the Lawrence Livermore National Laboratory (LLNL) sponsored a symposium on Explosion Source Phenomenology at Lake Tahoe, California. The purpose was to summarize the state of knowledge of the underground explosion source, based on U.S. experience at the Nevada Test Site (NTS). Specifically, the goals were to summarize knowledge of the explosion source, to identify limits of that knowledge and existing problems, and to propose directions of future research and data?]collection efforts.

Download or read book Effects of Tectonic Release on Broadband Regional Distance Bodywaves written by Terry C. Wallace and published by . This book was released on 1987 with total page 69 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although the distortion of explosion long-period waves is documented at upper mantle distances, the signature is much more subtle at regional and near-field distances. We document the robustness of the observation of sP in underground nuclear explosions waveforms of events which have large F factors. Although 'slapdown' has not been added to the synthetic, seismograms, the strong azimuthal variation can be explained by the simple addition of a double couple (tectonic release). We also calibrate the size of tectonic release for 18 Pahute Mesa events by comparing their SH waves with those of two western United States earthquakes. In general, the signature of tectonic release appears to be strongly frequency-dependent. We performed a moment tensor inversion at three Pahute Mesa events (CHESIRE, FARM and POOL) in different frequency bands in an attempt to isolate the 'dispersion' of the deviatoric component of the moment tensor. Although the apparent size of tectonic release source decreases, the orientation appears to be constant. The moments of the tectonic release at regional distance also are inconsistent with near-field estimates. We developed a model for near-field tectonic release, which requires a distributed source (shear dislocation takes place at the elastic radius). Using BOXCAR and HALFBREAK waveforms, we performed a constrained moment tensor inversion to obtain the tectonic release orientation. This near-field orientation is in excellent agreement with the far-field results.

Download or read book RMS Lg Studies of Underground Nuclear Explosions in the U S S R and the U S written by P. G. Richards and published by . This book was released on 1993 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Monitoring the Comprehensive Nuclear Test Ban Treaty Source Processes and Explosion Yield Estimation written by Goran Ekstrom and published by Birkhäuser. This book was released on 2012-12-06 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pure appl. geophys., by 161 nations. Entry of the treaty into force, however, is still uncertain since it requires ratification by all 44 nations that have some nuclear capability and, as of 15 June 2001, only 31 of those nations have done so. Although entry of the CTBT into force is still uncertain, seismologists and scientists in related fields, such as radionuclides, have proceeded with new research on issues relevant to monitoring compliance with it. Results of much of that research may be used by the International Monitoring System, headquartered in Vienna, and by several national centers and individual institutions, to monitor compliance with the CTBT. New issues associated with CTBT monitoring in the 21st century have presented scientists with many new challenges. They must be able to effectively monitor com pliance by several countries that have not previously been nuclear powers. Effective monitoring requires that we be able to detect and locate much smaller nuclear events than ever before and to distinguish them from small earthquakes and other types of explosions. We must have those capabilities in regions that are seismically active and geologically complex, and where seismic waves might not propagate efficiently.