Abstract

The seismic cycle in Nevada, corresponding to the re-rupture time for major faults, is of the order of thousands of years long. Following the occurrence of a large (M > 7) earthquake, aftershock activity in the rupture zone continues for about a century. From earthquakes reported in the meizoseismal zones of the 1915 Pleasant Valley and 1954 Dixie Valley earthquakes, it appears that great Nevada earthquakes are also preceded by a moderate increase in seismicity, lasting several decades. Faults considered to be “active” on geologic grounds are distributed fairly evenly over most of the Nevada region, so that fault mapping alone is not enough for determination of seismic potential. In addition, because of the length of the seismic cycle, the distribution of large historic earthquakes is by itself inadequate for seismic regionalization. A better method for this region may be to spatially correlate epicenter lineups for microearthquakes and small earthquakes with mapped geologic faults or lineaments. A correlation of this type based on earthquakes recorded for the period 1970-1974 suggests that a number of northwest-trending zones in an area of west-central Nevada may have high potential for large earthquakes in the future. On the other hand, high seismicity, complex faulting and scattered epicenter distribution in the seismic “gap” between the 1932 Cedar Mountains and 1872 Owens Valley earthquakes suggests that tectonic stress in this zone may be relieved by a continuous series of small-to-moderate earthquakes.

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