Seismicity of San Diego, 1934-1974

abstract Twelve quarry explosions in the city of San Diego have been used to determine the following crustal velocity model for the region around it: h 1 = 1.5 k m α 1 = 3.50 k m / sec β 1 = 1.90 k m / sec ⁡ h 2 = 26.5 k m α 2 = 6.35 k m / sec ⁡ β 2 = 3.65 k m / sec h 3 = ∞ α 3 = 8.00 k m / sec β 3 = 4.60 k m / sec A computer program employing this model has been used to recalculate the epicenters of all events previously located in the San Diego area, utilizing data from the California Institute of Technology seismic network as well as recent new stations within the city. Tests on the accuracy of the location process indicate that over 50 per cent of the solutions can be expected to be within 2 km of the true epicenters and that 90 per cent will be within 4 km. A total of 37 earthquakes can now be identified with some confidence as having occurred within the study area (32.5°-33.0°N, 116.75°-117.5°W) from 1934 through 1974. Some events previously thought to be earthquakes are now found to have been quarry blasts. The great majority of the earthquakes lie either offshore or less than 10 km inland, in regions of known faulting paralleling the Coronado Escarpment and the Rose Canyon fault zone. Three earthquakes are located within 2 km of the La Nacion fault. Nine of the 11 events since 1963 have taken place within or around the south end of San Diego Bay. Depths are poorly controlled, but seem to be generally less than 8 km. Magnitudes range from 2.3 to 3.7.