abstract

Seismological observations local to the 1927 earthquake suggest an epicenter for it near 34.6°N, 120.9°W. These observations include S-P times for the immediate aftershocks recorded at four stations in southern California; S-P times reported for the main shock at Berkeley and Lick Observatory by P. Byerly; and a time-decaying (1934 to 1969) zone of seismicity centered offshore of Point Arguello, herein identified as the aftershock zone of the 1927 earthquake. This location is approximately 40 km southwest of the teleseismic location for the 1927 earthquake recently offered by W. Gawthrop, although a location intermediate to the one proposed here and the one by Gawthrop would satisfy uncertainties associated with both locations. Even so, the location farther offshore is suggested by the near absence of strong shaking in the adjacent coastal region, which seemingly precludes a near-coastal location for an earthquake of this magnitude. Furthermore, unpublished teleseismic first-motion data of G. Stewart and analysis of the distortion of a geodetic quadrilateral by J. Savage and W. Prescott argue against a faulting mechanism for the 1927 earthquake that involves predominantly right-lateral slip on a near-coastal and northwesterly striking fault of the San Andreas type.

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