Reexamination of geodetic data has shown that aseismic slip occurred on or near the San Andreas fault in the period of about 20 years after 1906. The inferred displacements are comparable to but at greater depths than the sudden slip that occurred at the time of the earthquake. The postseismic slip is constrained only between late 1906 and 1925, and data are insufficient to determine the movements, if any, below about 20 kilometers on the fault. Two independent observations also indicate substantial anomalous crustal deformation away from the fault at least 30 years before the earthquake.
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Strain release mechanism of the 1906 San Francisco earthquake