Canadian detection and discrimination thresholds for earthquakes and underground explosions in Asia

1969 ◽  
Vol 6 (6) ◽  
pp. 1455-1458 ◽  
Author(s):  
P. W. Basham
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Central Asia ◽  
Body Wave ◽  
Test Site ◽  
Discrimination Threshold ◽  
Nevada Test Site ◽  
Novaya Zemlya ◽  
Seismograph Network

A suite of 33 Asian earthquakes and 36 Central Asia and Novaya Zemlya underground explosions are used to define the minimum detection levels in terms of surface-wave and body-wave magnitudes and the discrimination thresholds of the M versus m discriminant for the Canadian seismograph network. Under low microseismic noise conditions surface-waves can be observed for earthquakes down to m 4.9 and explosions down to m 5.9 for the region near the central Asia test sites. For events above these magnitudes, the M versus m relationships provide reliable discrimination between earthquakes and explosions. Comparison with an intracontinental study leads to the conclusion that the discrimination threshold is limited by path effects and greater distances to events about m 1.0 larger near the Asian test sites than near the Nevada test site.

A method for relocating seismic events using surface waves

1973 ◽  
Vol 63 (4) ◽  
pp. 1305-1313
Author(s):  
S. T. Crough ◽  
R. Van der Voo
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Group Velocity ◽  
Group Velocity Dispersion ◽  
Body Wave ◽  
Test Site ◽  
Seismic Events ◽  
Computer Technique ◽  
Nuclear Explosions ◽  
Reference Event

abstract Seismic events can be relocated relative to a reference event by using the group-velocity dispersion curves of surface waves. Since group velocity is a function of the travel path, surface waves from two events in the same locale should show identical group velocities when viewed at any one seismograph station. A computer technique has been developed for comparing the group-velocity curves of any event with the curves of a reference event and for determining the relocation which causes the curves to best coincide. The method is evaluated by relocating eight intermediate-size nuclear explosions of the Nevada Test Site series. With precise curve fitting, the surface-wave locations are slightly more accurate in southern Nevada than the standard body-wave determinations. The surface-wave origin times are considerably more accurate. In areas of sparse station coverage or of many small earthquakes, the surface-wave method can be expected to improve seismic locations significantly.

Guided Surface Waves on an Elastic Half Space

1971 ◽  
Vol 38 (4) ◽  
pp. 899-905 ◽  
Author(s):  
L. B. Freund
Keyword(s):  
Wave Propagation ◽  
Surface Wave ◽  
Surface Waves ◽  
Half Space ◽  
Body Wave ◽  
Three Dimensional ◽  
Elastic Half Space ◽  
Normal Displacement ◽  
Rigid Barrier ◽  
Wave Disturbances

Three-dimensional wave propagation in an elastic half space is considered. The half space is traction free on half its boundary, while the remaining part of the boundary is free of shear traction and is constrained against normal displacement by a smooth, rigid barrier. A time-harmonic surface wave, traveling on the traction free part of the surface, is obliquely incident on the edge of the barrier. The amplitude and the phase of the resulting reflected surface wave are determined by means of Laplace transform methods and the Wiener-Hopf technique. Wave propagation in an elastic half space in contact with two rigid, smooth barriers is then considered. The barriers are arranged so that a strip on the surface of uniform width is traction free, which forms a wave guide for surface waves. Results of the surface wave reflection problem are then used to geometrically construct dispersion relations for the propagation of unattenuated guided surface waves in the guiding structure. The rate of decay of body wave disturbances, localized near the edges of the guide, is discussed.

P-wave spectra of nevada test site events at near and very near distances: Implications for a near-regional body wave-surface wave discriminant

1976 ◽  
Vol 66 (3) ◽  
pp. 803-825
Author(s):  
William A. Peppin
Keyword(s):  
Scaling Laws ◽  
Body Wave ◽  
Test Site ◽  
P Wave ◽  
Spectral Amplitude ◽  
Source Spectrum ◽  
Wave Spectra ◽  
Nevada Test Site ◽  
Field Source ◽  
Source Spectra

abstract Some 140 P-wave spectra of explosions, earthquakes, and explosion-induced aftershocks, all within the Nevada Test Site, have been computed from wide-band seismic data at close-in (< 30 km) and near-regional (200 to 300 km) distances. Observed near-regional corner frequencies indicate that source corner frequencies of explosions differ little from those of earthquakes of similar magnitude for 3 < ML < 5. Plots of 0.8 to 1.0 Hz Pg spectral amplitude versus 12-sec Rayleigh-wave amplitude show a linear trend with unit slope over three orders of magnitude for explosions; earthquakes fail to be distinguished from explosions on such a plot. These spectra also indicate similar source spectra for explosions in different media (tuff, alluvium, rhyolite) which corroborates Cherry et al. (1973). Close-in spectra of three large explosions indicate that: (1) source corner frequencies of explosions scale with yield in a way significantly different from previously published scaling laws; (2) explosion source spectra in tuff are flat from 0.2 to 1.0 Hz (no overshoot); (3) the far-field source spectrum decays at least as fast as frequency cubed. Taken together, these data indicate that the following factors are not responsible for Peppin and McEvilly's (1974) near-regional discriminant: (a) source dimension, (b) source rise time, or (c) shape of the source spectrum.

3D elastic full-waveform inversion of surface waves in the presence of irregular topography using an envelope-based misfit function

Geophysics ◽  
2018 ◽  
Vol 83 (1) ◽  
pp. R1-R11 ◽  
Author(s):  
Dmitry Borisov ◽  
Ryan Modrak ◽  
Fuchun Gao ◽  
Jeroen Tromp
Keyword(s):  
Surface Wave ◽  
Objective Function ◽  
Surface Waves ◽  
Large Scale ◽  
Body Wave ◽  
Waveform Inversion ◽  
Full Waveform Inversion ◽  
S Wave ◽  
Near Surface ◽  
Full Waveform

Full-waveform inversion (FWI) is a powerful method for estimating the earth’s material properties. We demonstrate that surface-wave-driven FWI is well-suited to recovering near-surface structures and effective at providing S-wave speed starting models for use in conventional body-wave FWI. Using a synthetic example based on the SEG Advanced Modeling phase II foothills model, we started with an envelope-based objective function to invert for shallow large-scale heterogeneities. Then we used a waveform-difference objective function to obtain a higher-resolution model. To accurately model surface waves in the presence of complex tomography, we used a spectral-element wave-propagation solver. Envelope misfit functions are found to be effective at minimizing cycle-skipping issues in surface-wave inversions, and surface waves themselves are found to be useful for constraining complex near-surface features.

Lg magnitudes and yield estimates for underground Novaya Zemlya nuclear explosions

1988 ◽  
Vol 78 (2) ◽  
pp. 873-884
Author(s):  
Otto W. Nuttli
Keyword(s):  
Large Range ◽  
Test Site ◽  
Nevada Test Site ◽  
P Values ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Novaya Zemlya ◽  
Short Period ◽  
Lg Wave ◽  
Range Of Values

Abstract Lg-wave amplitudes of 30 Novaya Zemlya underground nuclear explosions, as recorded by short-period seismographs in Denmark, Finland, Germany, Norway, Spitsbergen, and Sweden, are used to determine mb(Lg) values. Assuming that the mb(Lg) versus explosion yield relation derived from Nevada Test Site data applies to all continental areas, the yields of the explosions are estimated. They cover a large range of values, from 2.5 to 4900 kt. The largest explosion since April 1976 had an estimated yield of 145 kt. The mb(Lg) values, when subtracted from the mb(P) values, can be used to estimate the mb(P) bias between two test sites. In this way, the mb(P) bias between Novaya Zemlya and the Nevada Test Site is estimated to be 0.20 magnitude units.

LONG‐PERIOD SIGNAL PROCESSING RESULTS FOR THE LARGE APERTURE SEISMIC ARRAY

Geophysics ◽  
1969 ◽  
Vol 34 (3) ◽  
pp. 305-329 ◽  
Author(s):  
J. Capon ◽  
R. J. Greenfield ◽  
R. T. Lacoss
Keyword(s):  
Signal Processing ◽  
Surface Wave ◽  
Maximum Likelihood ◽  
Surface Waves ◽  
Body Wave ◽  
Seismic Array ◽  
Seismic Events ◽  
Long Period ◽  
Large Aperture ◽  
Period Data

The results of a series of off‐line signal processing experiments are presented for long‐period data obtained from the Large Aperture Seismic Array (LASA) located in eastern Montana. The signal‐to‐noise ratio gains obtained with maximum‐likelihood processing, as well as other simpler forms of processing, are presented for body‐wave as well as surface‐wave phases. A discussion of the frequency‐wavenumber characteristics of the noise which led to these results is also given. On the basis of these experiments, several recommendations are made concerning optimum long‐period array configurations and on‐line or off‐line processing methods. The usefulness of maximum‐likelihood processing in suppressing an interfering teleseism is demonstrated. An experiment is given in which maximum‐likelihood processing achieved about 20 db suppression of an interfering teleseism, while simpler forms of processing such as beam‐forming obtained about 11 db. The matched filtering of surface waves using chirp waveforms is shown to be highly effective. A useful discriminant for distinguishing between natural seismic events and underground nuclear explosions, using both the long‐period and short‐period data, was found to be the relationship between the surface‐wave and body‐wave magnitudes. Measurements of this discriminant made on events from four tectonic regions of the earth are presented. It is shown that 60 and 100 percent detectability of surface waves for natural seismic events from the Central Asian‐Kurile Islands‐Kamchatka region occurs at about LASA body‐wave magnitudes 4.5 and 4.9, respectively.

scholarly journals Determining surface-wave magnitudes from regional Nevada Test Site data

1995 ◽  
Vol 120 (2) ◽  
pp. 474-498 ◽  
Author(s):  
Bradley B. Woods ◽  
David G. Harkrider
Keyword(s):  
Surface Wave ◽  
Test Site ◽  
Nevada Test Site

Monitoring nuclear test sites with GERESS

1996 ◽  
Vol 86 (1A) ◽  
pp. 172-190
Author(s):  
M. L. Jost ◽  
J. Schweitzer ◽  
H.-P. Harjes
Keyword(s):  
Test Site ◽  
Nevada Test Site ◽  
Data Set ◽  
Detection Thresholds ◽  
Novaya Zemlya ◽  
Tuamotu Archipelago ◽  
The Future ◽  
Nuclear Tests ◽  
Lop Nor ◽  
Eastern Kazakhstan

Abstract Since the installation of the 25-element GERman Experimental Seismic System (GERESS) array in southeastern Germany in 1990, 36 presumed nuclear tests were recorded by this system: 16 from Nevada, 12 from the Tuamotu Archipelago, 7 from Lop Nor, and 1 from Novaya Zemlya. Also, a chemical calibration experiment at Nevada Test Site (NPE) was observed at the array in 1993. In addition, two presumed nuclear events from Nevada, four from the Tuamotu Archipelago, and six from eastern Kazakhstan were recorded on temporary stations close to the GERESS array during the site survey (1988 to 1989). These latter 12 events were carefully included in this study to broaden the data set. This has been done since the number of underground nuclear tests observable at the GERESS site is not expected to increase significantly in the future because most nuclear powers have adhered to a moratorium on nuclear testing. In addition, we also do not expect that peaceful nuclear explosions (PNE) will be detonated in the future due to reasons of environmental hazard. Concentrating on Nevada Test Site and the Tuamotu Archipelago, a cross-correlation method and a cluster analysis indicate subgroups of the data. These empirical methods clearly discriminate presumed nuclear tests on the islands of Mururoa and Fangataufa. In addition, detection thresholds at GERESS were estimated based on bodywave magnitudes published by ISC: mb = 4.3 for the Nevada Test Site, mb = 3.9 for the Tuamotu Archipelago, mb = 4.6 for Lop Nor, mb = 4.3 for Novaya Zemlya, and mb = 4.4 for eastern Kazakhstan. Clearly, these path-specific detection thresholds deviate substantially from those derived from global amplitude-distance relations (i.e., Gutenberg-Richter). This indicates that a network of seismic stations used for global monitoring purposes may need careful calibration.

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