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.

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.

Comparison of seismic waves generated by different types of source

1963 ◽  
Vol 53 (5) ◽  
pp. 965-978 ◽  
Author(s):  
David E. Willis
Keyword(s):  
Seismic Waves ◽  
Nuclear Explosion ◽  
Test Site ◽  
Frequency Content ◽  
Nevada Test Site ◽  
Different Types ◽  
The Waves ◽  
Source Duration ◽  
Lower Frequencies

Abstract A comparison of the seismic waves generated by a nuclear explosion and an earthquake is discussed. The epicenter of the earthquake was located within the Nevada Test Site. Both events were recorded at the same station with the same type of equipment. The earthquake waves contained slightly lower frequency than the waves generated by the nuclear shot. The early P phases of the shot had larger amplitudes while the phases after Pg for the earthquake were larger. Seismic waves from collapses were generally found to be composed of lower frequencies than the waves from the original shot. Aftershocks of the Hebgen Lake earthquake were found to generate seismic waves whose frequency content was related to the magnitude of the aftershock. Spectral differences in quarry shot recordings that correlate with source duration times are also discussed.

Aftershocks of the Benham nuclear explosion

1969 ◽  
Vol 59 (6) ◽  
pp. 2271-2281
Author(s):  
R. M. Hamilton ◽  
J. H. Healy
Keyword(s):  
Fault Plane ◽  
Nuclear Explosion ◽  
Test Site ◽  
Strike Slip ◽  
Nevada Test Site ◽  
Ground Zero ◽  
Fault Plane Solutions ◽  
Fault Movement ◽  
Near Surface ◽  
Earthquake Distribution

abstract The Benham nuclear explosion, a 1.1 megaton test 1.4 km beneath Pahute Mesa at the Nevada Test Site, initiated a sequence of earthquakes lasting several months. The epicenters of these shocks were located within 13 km of ground zero in several linear zones that parallel the regional fault trends. Focal depths range from near surface to 6 km. The earthquakes are not located in the zone of the major ground breakage. The earthquake distribution and fault plane solutions together indicate that both right-lateral strike-slip fault movement and dip-slip fault movement occurred. The explosion apparently caused the release of natural tectonic strain.

Preliminary results of ground deformation measurements near the CANNIKIN explosion

1972 ◽  
Vol 62 (6) ◽  
pp. 1505-1518 ◽  
Author(s):  
D. D. Dickey ◽  
F. A. McKeown ◽  
R. C. Bucknam
Keyword(s):  
High Speed ◽  
Nuclear Explosion ◽  
Ground Deformation ◽  
Motion Pictures ◽  
Ground Surface ◽  
Underground Nuclear Explosion ◽  
Geological Structures ◽  
Level Lines ◽  
Before And After ◽  
Principal Strains

abstract Ground deformation around the CANNIKIN underground nuclear explosion was studied by means of geodetic measurements, observation of tilt in lakes, and analysis of high-speed motion pictures. The lengths of 53 lines of the order of 1 km long located as many as 7 km from ground zero (GZ) were measured before and after the explosion. Principal strains calculated from the observed changes in length indicate northeast-oriented extension, which is interpreted as reflecting, in part, the release of tectonic strain. Information from an incomplete remeasurement of level lines indicates as much as about 1 m of residual uplift along nearly 2 km of the Bering coast adjacent to the explosion site. Measurements of tilt at six lakes differ in magnitude and direction from the values expected to be produced by expansion of the explosion cavity, but seem to be related to the influence of geological structures near the lakes. High-speed motion pictures indicate that the ground surface in the GZ area had risen vertically about 8 m by 1.4 sec after the explosion and had returned to within about 1 m of its original elevation by 4 sec after the explosion.

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.

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