Abstract

Precise (<1 km) master-event hypocenters of aftershocks of the 4 October 1978 Wheeler Crest, California earthquake have been computed using a good distribution of close-in temporary stations (typically 10 stations, 0 to 20 km from the epicenter, with a coverage gap of less than 180°). Unlike other earthquakes which have occurred near Long Valley since this time, the Wheeler Crest event has a very simple aftershock pattern consistent with rupture at a depth of 15 km on a plane striking north and dipping about 70° to the west. The rupture plane defined by this aftershock pattern is about 5 by 8 km in extent. Focal mechanisms of this event based on first motions of P are consistent with left-lateral strike-slip motion on a plane striking N15°E (Fuis et al., 1979); however Julian (1983) has found a non-double-couple focal mechanism based on teleseismic observations. The simplicity of the aftershock pattern is evidence for this event being a shear dislocation rather than a sudden dyke injection as proposed by Julian (1983). As with events of the ongoing Mammoth Lakes sequence, the proposed rupture surface does not correspond to recognized Holocene/Quaternary faults in this vicinity, but it does appear to be subparallel with trends of the 1980 aftershocks located a few km west (Lide and Ryall, 1985).

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