Past and Possible Future Earthquakes of Significance to the San Diego Region

Abstract

The potential for earthquakes that may significantly affect the San Diego, California, region is examined from the viewpoint of geology, seismic history, and strong ground motion. We have compiled the best available data on slip rates and recurrence times for all major faults in southern California and northern Baja California, identified possible fault segments that might rupture in single earthquakes and obtained repeat times for these events which are consistent with (or at least not contradicted by) trenching studies. The most important faults for San Diego's seismic hazard are the Rose Canyon fault, the Elsinore fault, and faults immediately offshore (Coronado Banks, San Diego trough). There have not been any major earthquakes on any of these nearby faults in historical time, but the geological evidence is clear that such events will eventually occur. San Diego is located on the western flank of the Peninsular Range batholith, and there is weak evidence that attenuation in this batholith might be lower than average for California. We combine the geological data with an attenuation model to obtain an estimate for the occurrence rate of various levels of peak ground acceleration in downtown San Diego from events with moment magnitude greater than about 6. We find that peak accelerations of 10% g to 20% g are expected about once every 100 years. There are considerable uncertainties in this estimate, but nevertheless, strong ground shaking from a magnitude 6.0 or greater earthquake near the populated area would not be a scientific surprise.