Seismic and aseismic moment budget and implication for the seismic potential of the Parkfield segment of the San Andreas Fault

This study explores methods to assess the seismic potential of a fault based on geodetic measurements, geological information of fault-slip rate, and seismicity data. The methods are applied to the Parkfield section along the San Andreas fault (SAF) at the transition zone between the SAF creeping segment in the north and the locked section of Cholame to the south, where Mw approximately 6 earthquakes occurred every 24.5 yrs on average since the 1857 Mw 7.7 Fort Tejon earthquake. We compare the moment released by the known earthquakes and associated postseismic deformation with the moment deficit accumulated during the interseismic period derived from geodetic measurement of interseismic strain. We find that the recurring Mw 6 earthquakes are insufficient to balance the slip budget. We discuss and evaluate various possible scenarios which might account for the residual moment deficit and implications of the possible magnitude and return period of Mw>6 earthquakes on that fault segment. The most likely explanation is that this fault segment hosts Mw 6.5-7.5 earthquakes, with a return period of 140-300 yrs. Such events could happen as independent earthquakes in conjunction with ruptures of the Carrizo plain segment of the SAF. We show how the results from our analysis can be formally incorporated in probabilistic seismic hazard assessment assuming various magnitude-frequency distribution and renewal time models.