Beginning in 1980, the number and distribution of telemetered,
high-gain seismic stations operated in California and western Nevada
provided the capability for locating earthquakes of M ≥ 2.0
occurring throughout the broadly-deforming Pacific-North American
plate boundary from the Salton Trough to the Mendocino triple junction
and as far inland as the western Great Basin. Four networks
combine to provide this capability: (1) the 300-station Central
California Network operated by the U.S. Geological Survey from Menlo
Park, CA; (2) the 200-station Southern California Network operated
jointly by the California Institute of Technology (CIT) and the
U. S. Geological Survey from Pasadena, CA; (3) the 40-station
Western Nevada-Eastern California Network operated by the University
of Nevada from Reno, NV; and (4) the 55-station Southern Nevada
Network operated by the U.S. Geological Survey from Golden, CO. The
distribution of earthquake hypocenters located by this combination
of networks for 1980 and 1981 brings into focus detailed seismicity
patterns within the broad bands of earthquake activity that have
persisted for SO years or more based on locations of M ≥ 3
earthquakes from the regional networks operated by CIT and the
University of California, Berkeley, since the early 1930's. The
precise focal parameters of M ≥ 2.0 earthquakes afforded by these
four telemetered networks provide critical constraints on the
kinematics of seismogenic deformation of the western margin of the
North American plate adjacent to the San Andreas transform-fault
system