Migration of historical earthquakes in California

Most large earthquakes of magnitude 6.0 in California during 1852–1987 appear to show a southeast-to-northwest tendency of epicenter migration. This finding is consistent with earlier findings ofSavage (1971) for a relatively few large earthquakes along the west coast of North America, and ofWood andAllen (1973) for smaller events along the San Andreas fault in central California. The average speed of migration is approximately 130 km/yr, which is within the range of speeds observed for other major seismic zones in the world. The epicenter migration in California may be the result of some small but broad-scaled episodic strain changes associated with creep waves induced by magma injections at the East Pacific Rise and propagating northwestwardly along a broad transform boundary between the Pacific and North American plates at subseismogenic depths as proposed bySavage (1971).