Seismic slip, segmentation, and the Loma Prieta Earthquake

We have plotted the cumulative seismic slip projected onto a vertical plane for earthquakes occurring during the last 20 years along 210 km of the San Andreas fault that includes the section that moved in the Loma Prieta earthquake. These plots illustrate the differences in depth and character of the seismicity between the locked and creeping portions of the fault or fault zone and define the segment upon which the Loma Prieta earthquake occurred. Working by analogy from the relation between pre-main shock microseismicity and presumed main shock slip regions at Parkfield and Loma Prieta, we identify a segment on the San Francisco Peninsula where we believe the M 7 1838 earthquake occurred, and which we believe may have accumulated sufficient strain that rupture should be expected in the coming decades.