The Rose Canyon Fault Zone in San Diego

The Rose Canyon fault bisects the City of San Diego, producing much of the unique beauty of the city with the uplift of Mt. Soledad and subsidence producing the natural harbor of San Diego Bay. Geologic studies demonstrate that the late Quaternary slip rate is in the range of 1-2 mm/yr, which although only a fraction of the plate margin slip budget, has the potential to produce major damage in “America’s finest city”. Paleoseismic trenching in La Jolla and downtown San Diego indicate that the most recent surface rupture occurred only a few hundred years ago, sometime after about AD1523 but prior to the establishment of the SD mission in 1769. Displacement in this earthquake may have been as much as 3m based on 3-dimensional trenching. Using this displacement and slip rate, the average return period should be on the order of 1500 -3000 years, suggesting that San Diego may be safe for the near future. However, limited observations suggest that the Rose Canyon fault behaves in a clustered mode, where earthquakes are clustered in time, rather than in a quasi-periodic fashion. If correct, and considering that the rupture in the past few hundred years appears to have been the first large earthquake in more than five thousand years, San Diego may have recently entered a renewed period of activity