2000 yrs of earthquakes inferred from subsidence events on the Imperial fault, California: Effect of lake-level changes and implication for variable slip rates
T. Rockwell, Yann Klinger
Abstract
The Salton Trough has filled repeatedly with freshwater Lake Cahuilla from avulsions of the Colorado River. The relationship between lake fillings and large earthquakes is a topic of debate. From a new study on the Imperial fault applying cone penetrometer soundings, we show that the long hiatus in lake fillings between about ca 100 BCE and 950 CE resulted in accelerated slip in the few hundred years after re-inundation, an observation that is also seen on the San Andreas and southern San Jacinto faults. A regional, basin-wide signal of transient accelerated slip is interpreted to be the result of the effects of increased pore pressure on fault strength resulting from the 100 m of water load during full lake inundations. These results demonstrate the effects of dramatically increasing pore pressure, termed the reservoir induced seismicity effect, on fault activity and explain the current “earthquake drought” on the southernmost section of the San Andreas fault.