Source Study of the 1906 San Francisco Earthquake: Comparison with Loma Prieta

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This research will analyze the October 17, 1989, Loma Prieta, California, earthquake source mechanism by comparison with the great 1906 San Francisco earthquake which ruptured the San Andreas fault in the same segment. One of the most interesting and unexpected aspects of the Loma Prieta earthquake is that the mechanism indicated by preliminary results has a significant thrust component (about 1/2 the total) which suggests an uplift of about 1 meter. If the oblique-slip mechanism is characteristic of the events occurring along this segment, we would expect a long-term uplift rate of 1 cm/year, which appears much higher than inferred from the regional geomorphology. The seismograms from the 1906 event will be analyzed to look for the presence of a similar thrust component. This research is a contribution to the National Earthquake Hazard Reduction Program.