Effect of a fault on explosion-generated ground shock spectra

1968 ◽  
Vol 58 (6) ◽  
pp. 2033-2041
Author(s):  
Frank W. Galbraith
Keyword(s):  
Fault Zone ◽  
High Frequency ◽  
Atomic Energy Commission ◽  
Ground Surface ◽  
Test Site ◽  
Underground Nuclear Explosion ◽  
Nevada Test Site ◽  
High Frequency Response ◽  
The North ◽  
Ground Shock

ABSTRACT Shock spectrum measurements were made for an underground nuclear explosion at the Nevada Test Site of the U. S. Atomic Energy Commission using 29 reed gages. The objective of the measurements was to determine the effect of a fault zone on shock spectra measured at the ground surface and generated by the explosion. The reed gages were located along two gage lines; one extended to the west and crossed the fault at right angles. The other gage line extended to the north and was generally parallel to the fault. The results showed that the fault zone had an effect on vertical spectra but not on horizontal radial spectra. The vertical gage directly on the fault showed significantly lower displacements for all frequencies above 3 cycles per second but showed no apparent effect on the 3 cps displacement. For gages beyond the fault the vertical spectra for frequencies higher than 3 cps were greater than for corresponding gages along the north gage line. It is believed that this was caused by the upthrust base rock on the side of the fault away from the explosion with a resultant decreased thickness of tuff and alluvium. This resulted in less attenuation of high frequency response than was expected.

Distribution, focal mechanisms, and frequency of earthquakes in the Fairview Peak area, Nevada, near the time of the BENHAM explosion

1972 ◽  
Vol 62 (5) ◽  
pp. 1223-1240 ◽  
Author(s):  
B. E. Smith ◽  
J. M. Coakley ◽  
R. M. Hamilton
Keyword(s):  
Fault Plane ◽  
Nuclear Explosion ◽  
Test Site ◽  
Underground Nuclear Explosion ◽  
Nevada Test Site ◽  
Vertical Orientation ◽  
Fault Plane Solutions ◽  
Pressure Axis ◽  
Tension Axis ◽  
The One

Abstract Six portable seismographs were operated for 30 days in a network centered 25 km south of the epicenter of the 1954 Fairview Peak earthquake. The recording period lasted from 15 days before to 15 days after detonation of the one-megaton BENHAM underground nuclear explosion 250 km to the southeast of the Nevada Test Site on December 19, 1968. Approximately 950 earthquakes were detected within about 30 km of the network. No evidence was found that the explosion affected the rate of earthquake occurrence. Locations were computed for 152 earthquakes. The epicentral pattern shows north and northeast trends about 1 to 3 km wide. Focal depths range from 5 to 14 km. The main zones of activity seem to have a near-vertical orientation. Composite fault-plane solutions suggest that faulting within zones is not consistent with a single focal mechanism. Instead, a variety of mechanisms is indicated, consisting primarily of north-striking right-lateral oblique-slip, and northeast-striking dip-slip movements. In both cases, the pressure axis is near vertical and the tension axis is near horizontal, striking about S60°E.

scholarly journals GEOPHYSICAL DATA ON THE CLIMAX STOCK, NEVADA TEST SITE, NYE COUNTY, NEVADA

Geophysics ◽  
1962 ◽  
Vol 27 (5) ◽  
pp. 599-610 ◽  
Author(s):  
John W. Allingham ◽  
Isidore Zietz
Keyword(s):  
Atomic Energy Commission ◽  
Three Dimensional ◽  
Test Site ◽  
Seismic Effect ◽  
Nevada Test Site ◽  
Aeromagnetic Survey ◽  
Surface Samples ◽  
Welded Tuff ◽  
Geophysical Surveys ◽  
Paleozoic Rocks

A granitic stock at Oak Spring, Nevada, was selected in 1960 by the Atomic Energy Commission as a possible site to study the seismic effect of a deep nuclear shot contained in a large volume of rock. Geophysical surveys were conducted to determine the general configuration of the stock, particularly the thickness. The stock intrudes a sequence of carbonate and siliceous sedimentary rocks of Paleozoic age, which are overlain by Tertiary pyroclastic rocks consisting of tuff, welded tuff, and breccia. A three‐dimensional analysis of a detailed aeromagnetic survey indicates that the stock has a shape similar to a truncated cone, the diameter of which increases from about one mile at the surface to at least 6 miles near sea level, 5,000 feet beneath the surface. The stock, therefore, is much larger than indicated by the area of [Formula: see text] square miles exposed at the surface. In addition, computations show that the intrusion has a thickness of at least 13,000 ft. Much of the ambiguity of interpretation was removed from the analysis because susceptibility measurements of cores from recent drilling and remanent magnetization data from surface samples were available. Interpretation of a gravity profile over the stock gives the probable thickness of the overlying alluvial fill and buried tuff, but does not delineate the intrusive from the Paleozoic rocks.

Analysis of high-frequency Pg/Lg ratios from NTS explosions and western U.S. earthquakes

1996 ◽  
Vol 86 (4) ◽  
pp. 1042-1053 ◽  
Author(s):  
Steven R. Taylor
Keyword(s):  
High Frequency ◽  
Nearest Neighbor ◽  
Signal To Noise Ratio ◽  
Lawrence Livermore National Laboratory ◽  
National Laboratory ◽  
Test Site ◽  
Nevada Test Site ◽  
Signal To Noise ◽  
Propagation Effects ◽  
Classification Procedures

Abstract The high-frequency Pg/Lg discriminant is studied between frequencies of 0.5 and 10 Hz using 294 NTS explosions and 114 western U.S. earthquakes recorded at four broadband seismic stations operated by Lawrence Livermore National Laboratory. The stations are located at distances of about 200 to 400 km from the Nevada Test Site (NTS). Event magnitudes ranged from about 2.5 to 6.5, and propagation paths for the earthquakes range from approximately 175 to 1300 km. The discriminant is shown to be very effective and displays improved separation between earthquakes and explosions as frequency is increased. Because of propagation effects, it is important to apply distance corrections directly to the amplitude ratios or to the magnitude-corrected amplitudes prior to computing the ratios. Multivariate discrimination analysis using both maximum-likelihood Gaussian classifiers and a backpropagation neural network show that approximately 95% of the events can be correctly identified. Both classification procedures were designed to handle missing data filled in using a nearest-neighbor algorithm. Except for a few notable exceptions, most of the earthquake misclassifications occur for mb < 4, which is expected for events having reduced signal-to-noise ratios. All of the explosion misclassifications occur for mb < 4, suggesting a source or near-source effect rather than an effect of poor signal-to-noise ratio. The explosions that were misclassified were typically of magnitude large enough to be classified correctly by mb/Ms or Love-wave energy. The main drawback of the Pg/Lg discriminant is that, because of signal-to-noise considerations and propagation effects, the number of measurements are reduced considerably at higher frequencies. It is expected that the problem will be amplified as magnitudes are reduced and event-receiver distances are increased.

Microearthquake activity in Eastern Nevada and death valley California before and after the nuclear explosion Benham

1969 ◽  
Vol 59 (6) ◽  
pp. 2177-2184
Author(s):  
Peter Molnar ◽  
Klaus Jacob ◽  
Lynn R. Sykes
Keyword(s):  
Nuclear Explosion ◽  
Active Regions ◽  
Test Site ◽  
Death Valley ◽  
Tectonic Activity ◽  
Earthquake Activity ◽  
Underground Nuclear Explosion ◽  
Nevada Test Site ◽  
Pronounced Increase ◽  
Before And After

abstract Six portable, high-gain, high-frequency seismographs were operated in Nevada and California for several weeks before and after the underground nuclear explosion Benham to assess the possibility that earthquakes at distances of tens of kilometers or more may be triggered by large underground explosions. A pronounced increase in earthquake activity in the vicinity of the shot point was observed immediately after the detonation and continued for more than a month after the explosion. No significant change in activity within 25 km of any of our instruments northeast of the Nevada Test Site was observed, and the activity in Death Valley recorded after the explosion did not indicate an important increase. These data imply that this particular explosion did not significantly affect the seismicity of the region studied. Throughout the period of observation the seismic activity northeast of the Nevada Test Site was low; an average of about one event per day was detected within about 25 km of each station. This suggests that the current tectonic activity of this part of Nevada is lower than that of western Nevada and of most other tectonically active regions where microearthquake studies have been made.

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