Valeri Korneev
Earth Sciences Division
Lawrence Berkeley National Laboratory
Abstract:
The M6.0 2004 Parkfield and M7.0 1989 Loma Prieta strike-slip earthquakes on the San Andreas Fault (SAF) reveal seismicity peaks in the surrounding crust several months prior to the main events. Earthquakes directly within the SAF zone were intentionally excluded from the analysis because they manifest stress-release processes rather than stress accumulation. The observed increase in seismicity is interpreted as a signature of the increasing stress level in the surrounding crust, while the peak that occurs several months prior to the main event and the subsequent decrease in seismicity are attributed to damage-induced softening processes. Furthermore, in both cases there is a distinctive zone of low seismic activity that surrounds the epicentral region in the pre-event period. The increase of seismicity in the crust surrounding a potential future event and the development of a low-seismicity epicentral zone can be regarded as promising precursory information that could help signal the arrival of large earthquakes.