The velocity change caused by the 2004 M 6.0 Parkfield earthquake on the San Andreas Fault
Speaker: Kuei-Mei Lin
Abstract
Three seismic arrays were deployed across and along the San Andreas fault(SAF), before and after 2004 M6.0 Parkfield earthquake. The difference caused by the earthquake on the SAF were discovered from the earthquakes, aftershocks, and explosions data. The data from explosions and microearthquakes in 2002 were recorded by our first array located near Parkfield. The second array, near the San Andreas Fault Observatory at Depth(SAFOD) site, was deployed for six weeks in October and November 2003. The third array was co-sited with first array. It recorded aftershocks for 3 months, and starting at the week after the mainshock of 2004 M 6.0 Parkfield earthquake.
The results show seismic velocity changes. The change is possible that the fault zone has been healing , and it seems the rigidity recovers with time. Measurements for repeated aftershocks show the velocity increased within the rupture zone after the earthquake. Trapped-wave data clearly indicate a decrescent trend in velocity near the fault core and a recovered process of velocities following the mainshock. But we have no evidence for coseismic or postseismic changes in anisotropy parameters.
Reference
Li, Y. G., Chen, P., Cochran, E. S., Vidale, J. E., and Burdette, T., (2006). Seismic evidence for rock damage and healing on the San Andreas Fault associated with the 2004 M6.0 Parkfield earthquake, Bull. Seism. Soc. Am., 96 , 349-363
Cochran, E. S., Li, Y. G., and Vidale, J. E., (2006). Anisotropy in the shallow crust observed around the San Andreas Fault before and after the 2004 M 6.0 Parkfield earthquake, Bull. Seism. Soc. Am., 96 , 364-375