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Regional P Coda For Stable Estimates Of Body Wave Magnitude Application To Novaya Zemlya And Nevada Test Site Events
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Book Synopsis Regional P-Coda for Stable Estimates of Body Wave Magnitude: Application to Novaya Zemlya and Nevada Test Site Events by :
Download or read book Regional P-Coda for Stable Estimates of Body Wave Magnitude: Application to Novaya Zemlya and Nevada Test Site Events written by and published by . This book was released on 2008 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: Regional seismic explosion monitoring requires the discrimination of small clandestine nuclear explosions from background earthquakes. most successful teleseismic discriminant, the so-called Ms:mb, discriminant, compares the long-period surface waves magnitude (Ms) with the period P-based body wave magnitude (mb). There are many studies underway to try and extend surface wave magnitude (Ms) estimation to re distances and smaller magnitudes. Another problem that is encountered is how to estimate mb so that the Ms:mb discriminant is meaningful a consistent with teleseismic measures. For small-to-moderate sized events, the teleseismic body wave magnitude, mb(P), cannot be effectively measured due to low signal-to-noise ratio. We develop a stable regional alternative based on the P-coda that scales 1-to-1 with the teleseismic mb(P), but with the advantage of lower variance. Though mb(Lg) and mb(Lg-coda) can be tied to mb(P) for explosions, they overpredict earth magnitudes by ~0.5-1 magnitude units and degrade the performance of the Ms:mb discriminant. In contrast, mb(P-coda) does not exhibit this and can be used to extend Ms:mb to smaller regional events.
Book Synopsis U.S. Arms Control and Disarmament Agency ... Annual Report by : United States. Arms Control and Disarmament Agency
Download or read book U.S. Arms Control and Disarmament Agency ... Annual Report written by United States. Arms Control and Disarmament Agency and published by . This book was released on 1992 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis U.S. Arms Control and Disarmament Agency 1990 and 1991 Annual Reports by : United States. Arms Control and Disarmament Agency
Download or read book U.S. Arms Control and Disarmament Agency 1990 and 1991 Annual Reports written by United States. Arms Control and Disarmament Agency and published by . This book was released on 1993 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Seismological Research Letters written by and published by . This book was released on 2001 with total page 438 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Phenomenology Research Using Past Nevada Test Site Explosion and Earthquake Data by :
Download or read book Phenomenology Research Using Past Nevada Test Site Explosion and Earthquake Data written by and published by . This book was released on 2000 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: We use regional waveform data from the Nevada Test Site (NTS) to investigate phenomenological relationships between recorded amplitude and explosion yield as well as test regional depth estimation procedures. Our goal is to better understand the performance of seismic observables in other regions of monitoring interest, especially at small magnitudes (mb much less than 4.5). Some of the topics we are studying include: stable yield estimation, depth estimation, and Ms:mb performance. We use Lawrence Livermore National Laboratory's NTS explosion database, which consists of several hundred events ranging from approx. 200- to approx. 1500-m depth and yields ranging from a few tenths of a kiloton to the megaton range. In addition to the broadband explosion data, we have a large dataset of well-located earthquakes on the test site with depths ranging from 2 to 17 km and magnitudes ranging between MW 1.5 and 5.7. For yield estimation the relation between teleseismic body wave magnitude (mb) and nuclear explosion yield has been studied extensively over the past several decades for a number of test sites for large (greater than 1 kt) explosions. In this paper we will look at broadband coda, Pg, and Lg from over 260 nuclear explosions to study yield estimation capability by comparing F-factors. For monitoring compliance with a CTBT, small events that are recorded only at regional distances will be used to estimate magnitude and equivalent yield. Past coda studies show that coda-derived magnitudes of earthquakes and explosions are more stable than any direct phase method, including mb(Lg). In fact, single-station coda measurements can be equivalent to a network average of at least ten direct phase measurements over a broad range of frequencies.
Book Synopsis Regional Surface Wave Magnitude and Moment Determination Methods Applied to Nuclear Explosions at the Nevada Test Site by : Bradley B. Woods
Download or read book Regional Surface Wave Magnitude and Moment Determination Methods Applied to Nuclear Explosions at the Nevada Test Site written by Bradley B. Woods and published by . This book was released on 1994 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Coda Spectral Peaking for Nevada Nuclear Test Site Explosions by :
Download or read book Coda Spectral Peaking for Nevada Nuclear Test Site Explosions written by and published by . This book was released on 2007 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have applied the regional S-wave coda calibration technique of Mayeda et al. (2003) to earthquake data in and around the Nevada Test Site (NTS) using 4 regional broadband stations from the LLNL seismic network. We applied the same path and site corrections to tamped nuclear explosion data and averaged the source spectra over the four stations. Narrowband coda amplitudes from the spectra were then regressed against inferred yield based on the regional m{sub b}(Pn) magnitude of Denny et al. (1987), along with the yield formulation of Vergino and Mensing (1990). We find the following: (1) The coda-derived spectra show a peak which is dependent upon emplacement depth, not event size; (2) Source size estimates are stable for the coda and show a dependence upon the near-source strength and gas porosity; (3) For explosions with the same m{sub b}(Pn) or inferred yield, those in weaker material have lower coda amplitudes at 1-3 Hz.
Book Synopsis Regional Body-Wave Corrections and Surface-Wave Tomography Models to Improve Discrimination by :
Download or read book Regional Body-Wave Corrections and Surface-Wave Tomography Models to Improve Discrimination written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Our identification research for the past several years has focused on the problem of correctly discriminating small-magnitude explosions from a background of earthquakes, mining tremors, and other events. Small magnitudes lead to an emphasis on regional waveforms. The goal is to reduce the variance within the population of each type of event, while increasing the separation between the explosions and the other event types. We address this problem for both broad categories of seismic waves, body waves, and surface waves. First, we map out the effects of propagation and source size in advance so that they can be accounted for and removed from observed events. This can dramatically reduce the population variance. Second, we try to optimize the measurement process to improve the separation between population types. For body waves we focus on the identification power of the short-period regional phases Pn, Pg, Sn and Lg, and coda that can often be detected down to very small magnitudes. It is now well established that particular ratios of these phases, such as 6- to 8-Hz Pn/Lg, can effectively discriminate between closely located explosions and earthquakes. To extend this discrimination power over broad areas, we developed a revised Magnitude and Distance Amplitude Correction (MDAC2) procedure (Walter and Taylor, 2002). This joint source and path model fits the observed spectra and removes magnitude and distance trends from the data. It allows for the possibility of variable apparent stress scaling in earthquakes, an unresolved issue that is the subject of investigation under separate funding. The MDACZ procedure makes use of the extremely stable coda estimates of Mw for source magnitude and can also use independent Q tomography to help reduce trade-offs in fitting spectra. We can then apply the kriging operation to the MDAC2 residuals to provide full 2-D path corrections by phase and frequency band. These corrections allow the exploration of all possible ratios and multivariate combinations of ratios for their discrimination power. We also make use of the MDAC2 spectra and the noise spectra to determine the expected signal-to-noise value of each phase and use that to optimize the multivariate discriminants as a function of location. We quantify the discrimination power using the misidentified event trade-off curves and an equi-probable measure. In addition to the traditional phases, we are also exploring the application of coda amplitudes in discrimination. Coda-derived spectra can be peaked due to Rg-to-coda scattering, which can indicate an unusually shallow source. For surface waves we have a new high-resolution regional Rayleigh-Wave tomography for the Yellow Sea and Korean Peninsula Region, based on measuring thousands of seismograms. We also continue to make new measurements for our regional Rayleigh and Love wave group velocity tomography models of Western Eurasia and North Africa. These tomography models provide high-resolution maps of group velocity from 10- to 100-s period. The maps also provide estimates of the expected phase spectra of new events that can be used in phase-match filters to compress the expected signals and improve the signal-to-noise ratio on surface wave magnitude (Ms) estimates. Phase match filters in combination with regional Ms formulas can significantly lower the threshold at which Ms can be measured, extending the Ms-mb discriminant. We have measured Ms in western Eurasia for thousands of events at tens of stations, with and without phase match filtering, and found a marked improvement in discrimination. Here we start to quantify the improvement to both discrimination performance and the Ms threshold reduction. The group velocity models also provide constraints on velocity structure, particularly in low seismicity regions. For example we are working with Dr. Bob Henmann and Dr. Charles Ammon to combine tomography derived group velocity curves with station based receiver functions in joint inversions to estimate structure.
Book Synopsis Government reports annual index by :
Download or read book Government reports annual index written by and published by . This book was released on 199? with total page 1388 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Isotropic and Deviatoric Moment Inversion of Regional Surface Waves from Nevada Test Site Explosions: Implications for Yield Estimation and Seismic Discrimination by : Bradley B. Woods
Download or read book Isotropic and Deviatoric Moment Inversion of Regional Surface Waves from Nevada Test Site Explosions: Implications for Yield Estimation and Seismic Discrimination written by Bradley B. Woods and published by . This book was released on 1995 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: Seismic moments of Nevada Test Site (NTS) explosions were determined from regional surface wave spectra. Two methods were used. In one the moment is solved for assuming only an explosive source, or average scalar moment; in the other a joint inversion for an isotropic (explosive) source plus a constrained double couple moment component representing tectonic strain release (TSR). Although the general moment tensor solution to this joint inversion problem is non-unique, if some assumptions are made concerning the non-isotropic moment components, then the remaining source parameters can be solved by a linear least-squares inversion scheme. We examined the errors in determining the isotropic moment component (M sub I) by this latter method of constrained linear inversion solutions in a canonical study using a theoretical network of long-period (6-60 sec.) surface wave data. The network azimuthal coverage was chosen to represent that of a long-period North American super-network of 55 stations used for the actual NTS events. We compared these errors in moment estimate to those obtained from surface wave magnitude (M sub s) and spectral scalar moment (M sub 0) measurements for the same surface wave observations. For a ratio of M sub expl/M sub eq less than 1.0 we found that the inverted M sub I solution is a much better estimate of the actual isotropic moment than either M sub s or M sub O, and the standard deviation in this estimate is substantially less than that using the other two methods for the great majority of isotropic source + double couple sources. Even when the inversion constraints are off in dip and rake each by 30 deg, the mis-estimate of the isotropic moment is less than 35 percent of the actual value.
Book Synopsis Path-Corrected Body-wave Magnitudes and Yield Estimates of Novaya Zemlya Explosions by :
Download or read book Path-Corrected Body-wave Magnitudes and Yield Estimates of Novaya Zemlya Explosions written by and published by . This book was released on 1991 with total page 73 pages. Available in PDF, EPUB and Kindle. Book excerpt: Along with an extensive data set of worldwide explosions recorded at WWSSN, teleseismic short-period body-wave amplitudes from 28 Novaya Zemlya explosions are measured and analyzed to isolate the propagation characteristics and to derive a better measure of the source size. The separation of path effects from station effects provides direct clues as to how an old fold-belt structure (like Novaya Zemlya) could modulate the short-period P-wave amplitude and travel-time patterns. A strong correlation between P-wave amplitude and L sub g detection at teleseismic distance is also observed. Assuming the basic coupling and the mantle condition at Novaya Zemlya are comparable to those at Eastern Kazakhstan, the m sub b bias relative to NTS at 50KT level using the path-corrected m sub b(P sub max) values is inferred as 0.25 and 0.36 magnitude unit for Novaya Zemlya and Semipalatinsk, respective The m sub b(P sub max) bias of 0.11 between Semipalatinsk and Novaya Zemlya could be largely due to the difference in pP interference at these two test sites. The relative source size determined by Burger et al. (1986) and the theoretical psi infinity:yield scaling are combined to extrapolate our m sub b scaling to the higher end. The resulting yield estimates range from 2 to 2100 KT, with peak values of 550 KT and 65 KT before and after 1976, respectively, which are in reasonable agreement with those in previous studies.
Book Synopsis Monitoring the Comprehensive Nuclear-Test-Ban Treaty by : H.J. Patton
Download or read book Monitoring the Comprehensive Nuclear-Test-Ban Treaty written by H.J. Patton and published by Springer Science & Business Media. This book was released on 2001-09-01 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: Regional seismograms are dominated by the phases Pn, Pg, Sn, and Lg. More often Sn and Lg are used to infer the attenuation structure of the lithosphere. The seismic phase Sn is a high-frequency shear-wave (typically from 1 to 4 Hz and occasionally higher) that travels in the lithospheric mantle above the negative velocity gradient which usually marks the lithosphere-asthenosphere boundary. Sn has been reported out to distances of 35° (e. g. , MOLNAR and OLIVER, 1969; HUESTIS et aI. , 1973). Sn arrives as a high-frequency wave train lasting tens of seconds and up to 1 to 2 minutes. Sn velocities are typically 4. 7 km/s in stable continental and oceanic lithosphere (HUESTIS et al. , 1973) and as low as 4. 3 km/s (KADINSKY-CADE et al. , 1981) in more tectonically active regions. Lg is a complex short period guided wave consisting of high-frequency P and S energy which travels primarily in the earth's crust at frequencies typically between 0. 5 and 5 Hz. It has been modeled as higher-mode Love and Rayleigh waves as well as a sequence of multiply reflected post-critical S waves trapped in a crustal guide (BOUCHON, 1982; KENNETT, 1986; BOSTOCK and KENNETT, 1990). Lg has been observed not to propagate in oceanic or very thin continental crust (PRESS and EWING, 1952; SEARLE, 1975; ZHANG and LAY, 1995).
Book Synopsis Discrimination Among Small Magnitude Events on Nevada Test Site by : William A. Peppin
Download or read book Discrimination Among Small Magnitude Events on Nevada Test Site written by William A. Peppin and published by . This book was released on 1973 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: Broadband data (.02 to 20 Hz) from the University of California Lawrence Livermore Laboratory four-station seismic array, deployed at close range (less than 500 km) azimuthally about Nevada Test Site (NTS), allow investigation of the body wave-surface wave discriminant between explosion and earthquakes for small events confined to NTS, extending previous results to magnitudes around 3.5. It is found that natural earthquakes, explosion collapses, and explosion aftershocks all are distinct from explosions, and that the populations do not seem to converge at the low magnitudes. Also, for explosions, there is no change in the slope of the Pn versus Rayleigh wave amplitude relation over more than three orders of magnitude. Since the non-explosion events are shallow, of low magnitude, and of different source types, differences in source dimension, focal depth, and focal mechanism appear inadequate to explain the discriminant at small magnitudes (Author).
Book Synopsis Analysis of the November 1999 Dead Sea Calibration Shots by :
Download or read book Analysis of the November 1999 Dead Sea Calibration Shots written by and published by . This book was released on 2000 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: In November 1999 three chemical explosions were conducted in the Dead Sea for the purposes of calibrating the International Monitoring System (IMS) for the Comprehensive Nuclear-Test-Ban Treaty (CTBT). These shots were organized and conducted by the Geophysical Institute of Israel (GII). Large chemical explosions are the most valuable form of ground truth as the location, depth and origin time are very well known. We focus on the two largest shots (M{sub w} ≥ 3.6) and performed several types of analysis of the regional recordings and travel times of these shots. These data provide valuable new information about the region and offer an opportunity to test monitoring strategies. A crustal and uppermost mantle velocity model was inferred from the travel times of the regional phases: Pn, Pg and Sg. This effort utilized a grid search method to find suitable models of the structure. Results indicate that the crust is relatively thin (32 km) with lower than average crustal velocities (mean V{sub P} = 6.1-6.2 km/s). We located each shot treating the other shot as a calibration explosion. Locations were computed using both station static corrections and kriged correction surfaces. Results show that the locations with static corrections can be better or worse than the locations without corrections. However, the locations with kriged correction surfaces are consistently better than those without corrections or with static corrections because kriging properly accounts for residual statistics. Measures of the S-wave coda for regional events provide a stable estimate of event size (moment magnitude, M{sub w}) and the event source spectrum. S-wave coda envelope amplitudes were calibrated to moments estimated from long-period waveform modeling. We measured moment and body-wave magnitudes and source spectra for many events in the region. The Dead Sea shots show spectral peaking associated with shallow events. Finally, analysis of regional broadband recordings from the Saudi Arabian National Seismic Network reveals spectral scalloping associated with the bubble pulse. The observed bubble pulse periods are consistent with theoretical predictions.
Book Synopsis Analysis of Short-Period P-Coda Measurements for Presumed Underground Nuclear Explosions in Eurasia by : D. R. Baumgardt
Download or read book Analysis of Short-Period P-Coda Measurements for Presumed Underground Nuclear Explosions in Eurasia written by D. R. Baumgardt and published by . This book was released on 1984 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: Characteristics of P-coda measurements at NORSAR were investigated for presumed underground nuclear explosions in the Soviet Union. For explosions in the Semipalatinsk region, coda magnitudes, measured in the time domain in 5-second windows averaged over 50 seconds of P coda, were found to vary by about 0.1 magnitude units across NORSAR as compared with about 0.2 to 0.3 units for P-wave magnitudes. Also, array-averaged estimates of coda magnitude varied more smoothly with time into the coda than single channel estimates. This result indicates that local subarray scattering causes random perturbations in coda levels which are smoothed out by the averaging process. NORSAR P-coda magnitudes, like the Lg measurements of Rindal (1983), are more consistent with network averaged P-wave magnitudes than NORSAR single-channel magnitudes. There is some indication that Lg measurements may be slightly better than P-coda measurements in terms of reducing scatter and bias. In the analysis of P-codas from seismic events north of the Caspian Sea, codas of presumed explosions in the Astrakhan region are more intense and variable as a function of time into the coda than those for events near Azgir. These differences are attributed to lateral variations in geologic structure in the Pri-Caspian salt basin.
Book Synopsis U.S. National Report to International Union of Geodesy and Geophysics, 1987-1990 by :
Download or read book U.S. National Report to International Union of Geodesy and Geophysics, 1987-1990 written by and published by . This book was released on 1991 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Cause of the Body-wave Surface-wave Discriminant Between Earthquakes and Underground Nuclear Explosions at Near-regional Distances by : William Alan Peppin
Download or read book The Cause of the Body-wave Surface-wave Discriminant Between Earthquakes and Underground Nuclear Explosions at Near-regional Distances written by William Alan Peppin and published by . This book was released on 1974 with total page 442 pages. Available in PDF, EPUB and Kindle. Book excerpt:
