Abstract

The ML 5.6–5.8 Little Skull Mountain, Nevada, 29 June 1992 earthquake occurred in the southwest portion of Nevada Test Site (NTS) approximately 20 km from Yucca Mountain, a potential site for a high-level radioactive waste repository. The earthquake involved predominantly down-to-the-southeast dip-slip motion with a small left-slip component on a steeply dipping, 70°, northeast-striking fault. The mainshock nucleated near the base of the aftershock zone and ruptured up and to the northeast, and the mainshock rupture and the majority of the aftershock sequence were confined to depths between 6 and 12 km. All three ML 4+ (largest ML 4.5) aftershocks occurred off the mainshock fault plane on secondary structures within the aftershock zone. The nearest strong-motion instrument located 11 km southwest of the epicenter recorded a peak acceleration of 0.206g. The earthquake occurred adjacent to the Rock Valley fault zone within an area of prior concentrated background seismicity and near the intersection of several northeast-striking faults in the southern NTS that have experienced Quaternary motion.

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