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SEISMICITY OF
THE WESTERN BASIN AND RANGE PROVINCE
[c6, p166]

The advent of plate tectonics and its application to western North America by Atwater (1970) provided a unifying framework for the contemporary tectonics of the western Basin and Range and its interaction with the San Andreas fault system to the west. Deformation within the province reflects soft coupling of the San Andreas fault system to the North American craton and distribution of the relative plate motion - by mechanisms yet unknown - well over 500 km into the continental interior. The ubiquity of normal-fault-bounded ranges throughout the province tends to belie the underlying nature of present-day deformation within the region. Within historical time, this region has undergone nearly equal proportions of extension on normal faults and dextral shear on strike-slip faults.

The earthquake history of the western Basin and Range province is poorly known before the instrumental period, owing to sparse settlement of this high-desert region. The deficiencies of this record are illustrated by the uncertainties associated with fresh-appearing fault scarps discovered in 1911 near the north end of what would become the rupture zone of the 1954 Fairview Peak earthquake. Upon reviewing the scant historical evidence, Slemmons and others (1959) concluded that these scarps formed about 1903. The absence of an event of sufficient size in the instrumental record, however, suggests that the scarp forming event is older (or substantially smaller than M=6). Current understanding of 19th-century seismicity includes an episode of activity along the California-Nevada State line, including a probable rupture of the Olinghouse fault on December 27, 1869 (Sanders and Slemmons, 1979), although this conclusion was questioned by Toppozada and others (1981).

Surface faulting has accompanied numerous earthquakes in the region, the most significant of which are discussed below. Notable additional surface-faulting events include the M=6.3 Excelsior Mountain, Nev., earthquake of 1934 and the ML=5.6 Fort Sage Mountain earthquake of December 14, 1950, located in northeastern California (Gianella, 1957). Ground rupture may have also accompanied the M=6 earthquake of January 24, 1875 (see Gianella, 1957). If so, this observation would move the epicenter listed in Table 6.1 to lat 39-3/4� N., long 120-1/2� W.