Relation of geological structure to seismicity at Pahute Mesa, Nevada Test Site

1975 ◽  
Vol 65 (3) ◽  
pp. 747-764
Author(s):  
F. A. McKeown
Keyword(s):  
Source Parameters ◽  
Test Site ◽  
Basin And Range ◽  
Geological Structure ◽  
Cumulative Frequency ◽  
Nevada Test Site ◽  
Nuclear Explosions ◽  
Seismological Data ◽  
Fault Length ◽  
Frequency Magnitude

abstract Some of the abundant and unique geological and seismological data acquired at the Nevada Test Site is integrated with the objectives of (1) resolving some of the ambiguity in explanations of the source of aftershocks of nuclear explosions, and (2) demonstrating the value of using detailed geological and seismological data to infer realistic source parameters of earthquakes. The distribution of epicenters of aftershocks from nuclear explosions at Pahute Mesa suggests that they are related to faults or intersections of faults in the buried ring-fracture zones of calderas rather than to the conspicuous basin-and-range faults exposed at the surface. Histograms of fault length show clearly that faults in a basin-and-range regime differ significantly in length, median length, and distribution of length from faults in a caldera regime. A histogram of fault lengths derived from magnitudes of aftershocks shows both the median and distribution charactersitics of caldera faults rather than of basin-and-range faults. Cumulative frequency-fault length-squared plots also show differences in the two fault regimes, and have slopes, herein called bf slopes, of −0.89 and −1.08 for caldera and basin-and-range faults, respectively. The bf slopes are similar to the average slope of a cumulative frequency-strain plot for aftershocks rather than to the b slopes for cumulative frequency-magnitude plots. Although the significance of b and bf slopes and differences between them are not resolved clearly, it is concluded that the fault length and strain data reflect dimensions of seismic sources rather than energy of seismic events. The principal conclusion of the investigation is that the most obvious geology of a seismically active area may not provide the proper basis for inferring seismicsource parameters.

Earthquakes caused by underground nuclear explosions on Pahute Mesa, Nevada Test Site

1972 ◽  
Vol 62 (5) ◽  
pp. 1319-1341
Author(s):  
R. M. Hamilton ◽  
B. E. Smith ◽  
F. G. Fischer ◽  
P. J. Papanek
Keyword(s):  
Test Site ◽  
Geological Structure ◽  
Earthquake Activity ◽  
Nevada Test Site ◽  
Fault Plane Solutions ◽  
Fault Movement ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Earthquake Sequences ◽  
Frequency Magnitude

Abstract The underground nuclear explosions BENHAM, PURSE, JORUM, and HANDLEY, detonated on Pahute Mesa, initiated earthquake sequences lasting approximately 70, 10, 20, and 60 days, respectively. Earthquakes of magnitude 2.0 or larger in these sequences numbered 2012, 24, 159, and 231, respectively; earthquake magnitudes were all less than 5. The explosion PIPKIN, also detonated on Pahute Mesa, had no apparent effect on seismicity. Ninety-four per cent of the earthquakes with well-determined focal depths occurred at depths shallower than 5 km, and 95 per cent of the located earthquakes were within 14 km of ground zero of the preceding explosion. There is no evidence for explosion-stimulated earthquake activity extending outside the area of Pahute Mesa. The spatial distribution of earthquakes seems to be largely controlled by geological structure; however, the epicenter distribution can be correlated with observed fault movement only for aftershocks of HANDLEY. Fault-plane solutions indicate predominant dip-slip movement in the northern part of the Pahute Mesa area for aftershocks of BENHAM, JORUM, and HANDLEY. In the southern part, dextral strike-slip movement was found for aftershocks of BENHAM and HANDLEY. The frequency-magnitude relations are similar for earthquakes following BENHAM, PURSE, JORUM, and HANDLEY.

scholarly journals Source parameters of earthquakes, and discrimination between earthquakes and nuclear explosions

1968 ◽  
Vol 58 (5) ◽  
pp. 1503-1517
Author(s):  
John B. Davies ◽  
Stewart W. Smith
Keyword(s):  
Fault Plane ◽  
Source Parameters ◽  
Spectral Ratio ◽  
Shallow Earthquake ◽  
Compressional Waves ◽  
Nuclear Explosions ◽  
Deep Earthquakes ◽  
Fracture Velocity ◽  
Fault Length

Abstract The first part of this study describes a technique by which the source parameters of an earthquake can be obtained from the spectrum of compressional waves. The source parameters defined are fault length, fracture velocity, and fault plane attitude. Two large, deep earthquakes are examined using this technique. The source parameters determined compare favorably with those obtained previously using different techniques. In the second section a method is proposed for discrimination between underground explosions and earthquakes. The technique utilizes the ratio of the spectrums of the two classes of events where the path of propagation is common to both. On the basis of the analysis of the SHOAL event and a nearby shallow earthquake it appears that the duration as determined from the spectral ratio is almost 10 times smaller for an explosion than it is for a comparable earthquake.

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.

mb(LgCoda): A stable single station estimator of magnitude

1993 ◽  
Vol 83 (3) ◽  
pp. 851-861 ◽  
Author(s):  
Kevin Mayeda
Keyword(s):  
Water Table ◽  
Source Region ◽  
Test Site ◽  
Strongly Correlated ◽  
Nevada Test Site ◽  
Nuclear Explosions ◽  
Empirical Relations ◽  
Single Station ◽  
Lg Coda ◽  
Lateral Variations

Abstract Stable single-station estimates of magnitude have been made using the 1-Hz Lg coda envelope of regionally recorded nuclear explosions from the Nevada Test Site (NTS). After empirical relations describing the Lg coda envelope were found for each NTS-station path, single station magnitudes based on the Lg coda envelope were made with precision in the range of 0.03 to 0.04 magnitude units, whereas magnitudes based on third peak Lg amplitude, rms Lg amplitude, and Pn amplitude had scatter on the order of 0.15 to 0.2 magnitude units, generally five times larger than the coda scatter. Despite the high station correlations, the magnitude-yield residuals for events above the water table using the network average mb(LgCoda) were only marginally better than the other magnitude estimates, roughly 10% smaller. Magnitude-yield residual for events above the water table between mb(LgCoda) and mb(Lg) are strongly correlated suggesting that the source region properties, such as gas porosity, affect both magnitudes. Using only a single station, the standard deviation for magnitude-yield residuals using mb(LgCoda) were roughly 25% smaller than those derived from mb(Lg) or mb(Pn). These results show that the method is ideally suited to monitoring efforts in sparsely instrumented regions where little is known about the lateral variations of medium properties.

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