21, 1986 (M=6.2)
The Chalfant Valley earthquake of July 21, 1986, is the largest event to date in a series of 33 earthquakes of ML>=5 to occur since 1978 in the White Mountain seismic gap (Savage and Cockerham, 1987). Other principal events in this series include the May 25-27, 1980, Mammoth Lakes earthquakes (M=6.1, 5.9, 5.8, 6.0) and the November 23, 1984, Round Valley earthquake (M=5.7). The series of shocks is of interest not only because of its wide geographic distribution in the White Mountain seismic gap but also because of the contemporaneous uplift of Long Valley caldera (Hill and others, 1985). The Chalfant Valley earthquake created a 10+ -km-long zone of fractures with as much as a few centimeters of dextral slip on the frontal-fault zone of the White Mountains (Lienkaemper and others, 1987). The earthquake focal mechanism and aftershock distribution show that the predominately dextral strike-slip displacement associated with this event occurred on a west-dipping fault plane that projects upward to meet the surface break.