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OCTOBER 3, 1915 (M=7.3)
[c6, p167]

The 1915 Pleasant Valley, Nev., earthquake of October 15, 1915, created a series of spectacular normal-fault scarps in the central Nevada seismic zone of the Basin and Range province ( Figure 6.11 and Figure 6.12). Four major scarps formed during the earthquake, with an aggregate length of 59 km, and reruptured Holocene scarps at the base of the mountain blocks (Wallace, 1984). Fault movement in the earthquake appears to have been purely dip slip and averaged about 2 m on the steeply dipping fault plane. The earthquake was felt from western Utah to the Pacific coast and from northeastern Oregon to the United States-Mexican border. Instrumental measures of the magnitude range from 7.3 to 7-3/4 and exceed the moment magnitude of 7.2 derived from field measurements (MO=6.1x10**27 dyne-cm).

The Pleasant Valley earthquake lies at the north end of a 500-km-long belt of historical surface-faulting earthquakes within the central Nevada seismic zone and Owens Valley fault system. The four major earthquake sequences in this zone since 1872 leave two conspicuous seismic gaps that have been discussed as the potential loci of future major earthquake activity ( Figure 6.11; Wallace, 1984).