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Faulting related to the 1915 earthquakes in Pleasant Valley, Nevada

1984; United States Government Publishing Office; Linguagem: Inglês

10.3133/pp1274ab

2330-7102

Robert E. Wallace, Manuel G. Bonilla, H.A. Villalobos,

Botany and Geology in Latin America and Caribbean

A set of fault scarps was formed during the earthquakes of October 2, 1915, in Pleasant Valley, Nevada.Four main scarps developed in a right-stepping en echelon pattern.From northeast to southwest, they are the China Mountain, Tobin, Pearce, and Sou Hills scarps.A fifth scarp, which formed at the crest of the Stillwater Range, may be of nontectonic origin.The combined length of the scarps is 59 km, the average vertical displacement is 2 m, and the maximum displacement, which occurs on the Pearce scarp, is 5.8 m.Several northwest-striking segments of the scarps have a right-lateral component of displacement, generally less than 1 m but 2 m in one place.Only one instance of a left-lateral component of displacement has been found.The fault plane, exposed in only a few places, dips at angles between 45° and 80° west and northwest.The axis of extension is oriented about N. 65° W.At many places the 1915 scarps formed along an older scarp, and in some places older scarps represent more than one previous event.When displacement events occurred prior to 1915 is not known with certainty because the evidence is ambiguous, but the average recurrence interval for large events is likely measured in thousands of years and probably is less than about 12,000 years.Seismic moment, derived from the scarp dimensions, is 61 x 10 25 dyne/cm, which corresponds to a local magnitude (ML) of 7.2.This estimate is about half a magnitude unit smaller than the one derived from analysis of seismic data.The four scarps lie on the west flanks of four mountain blocks which have tilted to the east.Other mountain blocks, east and west of the 1915 scarps, also have tilted to the east.This pattern raises questions about the mechanism responsible for the faults.At least some may be listric faults.The four scarps lie in a belt 6 km wide and 59 km long that trends N. 25° E. The belt may relate to a deep zone of extension.