Preliminary Report: The Little Skull Mountain Earthquake, June 29, 1992

by John G. Anderson, Univ of Nevada, Reno, United States,
James N. Brune, Univ of Nevada, Reno, United States,
Diane dePolo, Univ of Nevada, Reno, United States,
Joan Gomberg, Univ of Nevada, Reno, United States,
Stephen C. Harmsen, Univ of Nevada, Reno, United States,
Martha K. Savage, Univ of Nevada, Reno, United States,
Anne F. Sheehan, Univ of Nevada, Reno, United States,
Kenneth D. Smith, Univ of Nevada, Reno, United States,

Abstract: The Little Skull Mountain earthquake occurred about 20 km from the potential high level nuclear repository at Yucca Mountain. The magnitude was 5.6, and the focal mechanism indicates normal faulting on a northeast trending structure. There is evidence that the earthquake was triggered by the magnitude MS = 7.5 earthquake in Landers, California, which occurred less than 24 hours earlier. Preliminary locations of the hypocenter and several aftershocks define an `L' shaped pattern near the southern boundary of the Nevada Test Site. One arm trends to the northeast beneath Little Skull Mountain, and a shorter, more diffuse zone trends to the southeast. The aftershocks are mostly located at depths between 7 km and 11 km, and may suggest a southeast dipping plane. There is no clear correlation with previously mapped surface faulting. The strongest recorded acceleration is about 0.21 g at Lathrop Wells, Nevada, 15 km from the epicenter. An extensive network of aftershock recorders was installed by the Seismological Laboratory, University of Nevada, Reno, by the United States Geological Survey, Golden, Colorado, and by Lawrence Livermore Laboratory, Livermore, California. Aftershock experiments are ongoing as of November, 1992, and include experiments to improve location, depth, focal mechanism, and stress drop, study basin and ridge response near the epicenter and at Midway Valley, and study response of a tunnel at Little Skull Mountain. Analysis of this data, which includes thousands of aftershocks, has only begun.

Subject Headings: Earthquakes | Mountains | Seismic tests | Geological faults | Radioactive wastes | Site investigation | Waste sites | Earthquake magnitude scale | North America | United States | Nevada | California

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