Yield estimation using bandpass-filtered seismograms: Preliminary results using neural networks with mb(Pn), short-time, long-time, and coda energy measurements

1993 ◽  
Vol 83 (2) ◽  
pp. 488-508
Author(s):  
Richard R. Leach ◽  
Farid U. Dowla ◽  
Eileen S. Vergino
Keyword(s):  
Neural Network ◽  
Signal To Noise Ratio ◽  
Linear Regression Analysis ◽  
Test Site ◽  
Signal Frequency ◽  
Yield Estimation ◽  
Lapse Time ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Long Time

Abstract A neural network has been developed to simultaneously use multiple seismic measurements, such as mb(Pn) and coda energy, for estimating yields of underground nuclear explosions. Yield estimation results based on a large number of Nevada Test Site events that were recorded at the broadband seismic stations at Elko, Kanab, Landers, and Mina indicate that different length windows (6, 18, and 200 sec) of seismogram energy are as useful as the mb(Pn) measurement when the seismogram is filtered between 0.5 and 2 Hz. Detailed results of yield estimation trends as a function of signal frequency are also obtained. Yield estimation performance using long lapse time coda energy above 2 Hz is significantly limited by the signal-to-noise ratio (SNR). Performance of the neural network with both mb(Pn) and energy information as input does not significantly exceed the performance of a conventional linear regression analysis that is based only on mb(Pn). Properties of the coda signal as a function of frequency and SNR that might ultimately lead us to the application of a full seismogram with a neural network for accurate seismic yield estimation are discussed.

Yield estimation using regional mb(Pn)

1990 ◽  
Vol 80 (3) ◽  
pp. 656-674 ◽  
Author(s):  
Eileen S. Vergino ◽  
Richard W. Mensing
Keyword(s):  
Large Population ◽  
Test Site ◽  
Yield Estimation ◽  
Nevada Test Site ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Threshold Test ◽  
Using Data ◽  
Yield Threshold ◽  
Test Ban

Abstract Seismic yield estimation at regional distances will become increasingly important in monitoring a Low-Yield Threshold Test Ban (LYTTB). In order to investigate seismic yield estimation using regional data, we have examined regional mb(Pn) values for a large population of Nevada Test Site (NTS) underground nuclear explosions that occurred in widely varying geologic media with a range of yields from less than 1 kt to 300 kt. Magnitude-yield relationships were developed using data from a set of pre-1985 events (calibration set). To obtain an independent estimate of the uncertainty in estimating yields of events at NTS using mb(Pn) alone, the calibrated relationships were applied to a set of post-1984 events (prediction set). We found that the average uncertainty in the yield estimate, based on a weighted combination of the yield estimates from the four Livermore NTS Network (LNN) seismic stations, is about 1.8 (at the 2σ level). If data are available from all four LNN stations, the uncertainty is about 1.7 (at the 2σ level). By including a term for the gas-filled porosity of the rock near the working point in the magnitude-yield relationship, we were able to develop a single relationship valid for events both above and below the water table, as well as those in alluvium and tuff. We have found, however, systematic differences in the relationships for events in Yucca Flat, Pahute Mesa, and Rainier Mesa.

The stability of rms Lg measurements and their potential for accurate estimation of the yields of Soviet underground nuclear explosions

1990 ◽  
Vol 80 (6B) ◽  
pp. 2106-2126
Author(s):  
Roger A. Hansen ◽  
Frode Ringdal ◽  
Paul G. Richards
Keyword(s):  
Soviet Union ◽  
Signal To Noise Ratio ◽  
Test Site ◽  
P Wave ◽  
Accurate Estimation ◽  
Seismic Stations ◽  
Array Data ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Single Station

Abstract Data on underground nuclear explosions have recently become available from modern digital seismic stations installed within the Soviet Union and China. Observations of root mean square (rms) Lg-wave signals for Soviet underground nuclear explosions at the Shagan River Test Site in East Kazakhstan show that the relative amplitudes of the rms signals at stations in Norway, the USSR, and China are very similar for different explosions, the standard deviation of the differences being only about 0.03 in logarithmic units (i.e., magnitude units). This is consistent with earlier observations comparing NORSAR and Graefenberg array data, and the observed scatter is significantly lower than has been reported for Lg data from Nevada Test Site explosions. In view of the excellent correspondence found by Nuttli (1986) and Patton (1988) for Lg versus yield at Nevada, this indicates that rms Lg has a potential for yield estimation with very high accuracy at Shagan River. Our study has shown that: (a) selected stations in the USSR and China, situated at regional distances, provide a much improved signal-to-noise ratio of the Lg phase for events at Shagan River, as compared to NORSAR array data; (b) the scaling of rms Lg amplitudes between different-sized events recorded at the same single station site appears to be consistent with that of NORSAR, indicating a remarkable degree of precision in single station measurements of Lg signal; (c) rms Lg amplitude measurements for the best of these stations may be made at 1.5 to 2.0 magnitude units lower than at NORSAR or Graefenberg, allowing a much lower threshold for Lg-based yield determination; and (d) the P-wave detection capabilities of these single stations do not match those of the NORESS and ARCESS arrays; thus, teleseismic signals continue to be important for detection of small nuclear explosions. Our conclusion is that Lg signals appear to provide an excellent basis for supplying estimates of the yields of nuclear explosions even down to below 1 kt when such signals are recorded at high-quality, digital in-country seismic stations, and when calibrated by access to independent (nonseismic) yield information for a few nuclear explosions at the test sites of interest. In the context of monitoring a low-yield threshold test ban treaty, it will, in addition, be important to take into consideration various environmental conditions in the testing area, such as the possible presence of cavities, and to devise appropriate procedures for on-site observations in this regard.

Study of low-magnitude seismic events near the Novaya Zemlya nuclear test site

1997 ◽  
Vol 87 (6) ◽  
pp. 1563-1575
Author(s):  
Frode Ringdal
Keyword(s):  
Monitoring Network ◽  
Test Site ◽  
Nuclear Test ◽  
P Wave ◽  
Scaling Effects ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Novaya Zemlya ◽  
Source Scaling ◽  
Low Magnitude

Abstract A study of available seismic data shows that all but one of the 42 known underground nuclear explosions at Novaya Zemlya have been detected and located by stations in the global seismic network. During the past 30 years, only one seismic event in this area has been unambiguously classified as an earthquake (1 August 1986, mb = 4.3). Several other small events, most of which are thought to be either chemical explosions or aftereffects of nuclear explosions, have also been detected. Since 1990, a network of sensitive regional arrays has been installed in northern Europe in preparation for the global seismic monitoring network under a comprehensive nuclear test ban treaty (CTBT). This regional network has provided a detection capability for Novaya Zemlya that is shown to be close to mb = 2.5. Three low-magnitude events have been detected and located during this period, as discussed in this article: 31 December 1992 (mb = 2.7), 13 June 1995 (mb = 3.5), and 13 January 1996 (mb = 2.4). To classify the source types of these events has proved very difficult. Thus, even for the mb = 3.5 event in 1995, we have been unable to provide a confident classification of the source as either an earthquake or explosion using the available discriminants. A study of mb magnitude in different frequency bands shows, as expected, that the calculation of mb at regional distances needs to take into account source-scaling effects at high frequencies. Thus, when comparing a 4 to 8 or 8 to 16 Hz filter band to a “teleseismic” 2 to 4 Hz band, the smaller events have, relatively speaking, significantly more high-frequency energy (up to 0.5 mb units) than the larger events. This suggests that a P-wave spectral magnitude scale might be appropriate. The problem of accurately locating small events using a sparse array network is addressed using the 13 January 1996 event, which was detected by only two arrays, as an illustrative example. Our analysis demonstrates the importance of using accurately calibrated regional travel-time curves and, at the same time, illustrates how array processing can be used to identify an interfering phase from a local disturbance, thereby avoiding location errors due to erroneous phase readings.

Evidence of tectonic release from underground nuclear explosions in long-period P waves

1983 ◽  
Vol 73 (2) ◽  
pp. 593-613
Author(s):  
Terry C. Wallace ◽  
Donald V. Helmberger ◽  
Gladys R. Engen
Keyword(s):  
Upper Mantle ◽  
High Stress ◽  
Test Site ◽  
Strike Slip ◽  
Body Waves ◽  
Release Time ◽  
P Waves ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Long Period

abstract In this paper, we study the long-period body waves at regional and upper mantle distances from large underground nuclear explosions at Pahute Mesa, Nevada Test Site. A comparison of the seismic records from neighboring explosions shows that the more recent events have much simpler waveforms than those of the earlier events. In fact, many of the early events produced waveforms which are very similar to those produced by shallow, moderate-size, strike-slip earthquakes; the phase sP is particularly obvious. The waveforms of these explosions can be modeled by assuming that the explosion is accompanied by tectonic release represented by a double couple. A clear example of this phenomenon is provided by a comparison of GREELEY (1966) and KASSERI (1975). These events are of similar yields and were detonated within 2 km of each other. The GREELEY records can be matched by simply adding synthetic waveforms appropriate for a shallow strike-slip earthquake to the KASSERI observations. The tectonic release for GREELEY has a moment of 5 ՠ1024 dyne-cm and is striking approximately 340°. The identification of the sP phase at upper mantle distances indicates that the source depth is 4 km or less. The tectonic release time function has a short duration (less than 1 sec). A comparison of these results with well-studied strike-slip earthquakes on the west coast and eastern Nevada indicate that, if tectonic release is triggered fault motion, then the tectonic release is relatively high stress drop, on the order of several hundred bars. It is possible to reduce these stress drops by a factor of 2 if the tectonic release is a driven fault; i.e., rupturing with the P velocity. The region in which the stress is released for a megaton event has a radius of about 4 km. Pahute Mesa events which are detonated within this radius of a previous explosion have a substantially reduced tectonic release.

Seismic effects of the MILROW and CANNIKIN nuclear explosions

1972 ◽  
Vol 62 (6) ◽  
pp. 1411-1423 ◽  
Author(s):  
E. R. Engdahl
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Test Site ◽  
High Gain ◽  
High Yield ◽  
Upper Crust ◽  
Seismic Effects ◽  
Underground Nuclear Explosions ◽  
Low Level ◽  
Nuclear Explosions

abstract Seismic effects of the underground nuclear explosions MILROW (October 1969, about 1 megaton) and CANNIKIN (November 1971, under 5 megatons) were monitored by a network of continuously recording, high-frequency, high-gain seismographs located on Amchitka and nearby islands. Each explosion was immediately followed by hundreds of small, discrete events (mB < 4), of similar focal mechanism and with a characteristic low-frequency signature, which were apparently related to the deterioration of the explosion cavity. This activity intensified, then terminated within minutes of a large, complex multiple event and concurrent formation of a surface subsided area that signaled complete collapse of the explosion cavity (MILROW, 37 hr; CANNIKIN, 38 hr). A number of small explosion-stimulated tectonic events, apparently unrelated to the collapse phenomenon, occurred intermittently for several weeks following each explosion—near the explosion cavity and up to 13 km southeast of CANNIKIN ground zero along the Island. These events were confined to the upper crust of the Island, had characteristic high-frequency signatures, and, near the Rifle Range Fault, had focal mechanisms which could be correlated with pre-existing faulting. The evidence points to a short-term interaction of the explosions with local ambient tectonic stresses. Because these stresses are of relatively low level on Amchitka, the observed seismic effects were significantly less extensive and smaller than similar effects reported from high-yield explosions at the Nevada Test Site. Continuous monitoring of the natural seismicity of the Amchitka region since 1969 has not revealed other evidence for an interaction between either MILROW or CANNIKIN and natural tectonic processes. The structural stability and apparent low level of stress in the upper crust of Amchitka suggest that the Island effectively is seismically decoupled from the active subduction zone below.

Strain effects of nuclear explosions in Nevada

1971 ◽  
Vol 61 (1) ◽  
pp. 55-64 ◽  
Author(s):  
Gary Boucher ◽  
Stephen D. Malone ◽  
E. Fred Homuth
Keyword(s):  
Body Wave ◽  
High Sensitivity ◽  
Test Site ◽  
Strain Effects ◽  
Underground Nuclear Explosions ◽  
Static Strain ◽  
Nuclear Explosions ◽  
Shot Point ◽  
A Minor ◽  
The University

abstract The University of Nevada's three-component quartz-rod strain meter installation at Round Mountain, Nevada (38°42.1′N, 117°04.6′W) has recorded a number of underground nuclear explosions at the Nevada Test Site, beginning with the megaton-sized JORUM event September 16 1969. Both that explosion and the larger HANDLEY event on March 26 1970 produced static strain offsets of a few parts in 109 at Round Mountain. These offsets did not decay within the first few hours after the explosions. In both cases, the strain offsets were in the sense of ground extension radial to the shot point, which is inconsistent with the assumption of a pure compressive source of strain. The strain-change ellipse for the HANDLEY event was found to have a major strain axis of 11 × 10−9 extensional, oriented N 34°W, and a minor axis of 7.4 × 10−9 compressional. A single-component strain meter at Mina, Nevada, (38°26.3′N, 118°9.3′W) was operated for the HANDLEY event, and recorded a strain offset of 2.6 × 10−9 in the direction N 74°E. Strain offsets at the time of the largest collapse events following HANDLEY were observed at Round Mountain. These offsets had the same sense on each component as those following the explosion itself. This is interpreted as support for the hypothesis that the strain changes are tectonic in origin, and the explosion initiates the strain release. Small offsets were observed for three smaller explosions out of a total of 13 studied. The relationship between body-wave magnitude mb and maximum dynamic strains at Round Mountain may be described empirically by the equation Log S = − 13.4 + 1.10 mb. Because of its high sensitivity and stability, the Round Mountain strain meter is capable of obtaining useful measurements of dynamic and static strain effects of intermediate- to large-sized explosions, at distances ranging from 160 to 200 km.

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