HR: 12:05h
AN: S42B-08    [Abstracts]
TI: Nonvolcanic Deep Tremors in the Transform Plate Bounding San Andreas Fault Zone
AU: * Nadeau, R M
EM: nadeau@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall Univ. of California, Berkeley, CA 94720-4760 United States
AU: Dolenc, D
EM: dolenc@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall Univ. of California, Berkeley, CA 94720-4760 United States
AB: Recently, deep ($\sim$ 20 to 40 km) nonvolcanic tremor activity has been observed on convergent plate boundaries in Japan and in the Cascadia region of North America (Obara, 2002; Rodgers and Dragert, 2003; Szeliga et al., 2004). Because of the abundance of available fluids from subduction processes in these convergent zones, fluids are believed to play an important role in the generation of the tremor activity. The transient rates of tremor activity in these regions are also observed to correlate either with the occurrence of larger earthquakes (Obara, 2002) or with geodetically determined transient creep events that release large amounts of strain energy deep beneath the locked Cascadia megathrust (M.M. Miller et al., 2002; Rodgers and Dragert, 2003; Szeliga et al., 2004). These associations suggest that nonvolcanic tremor activity may participate in a fundamental mode of deep moment release and in the triggering of large subduction zone events (Rodgers and Dragert, 2003). We report the discovery of deep ($\sim$ 20 to 45 km) nonvolcanic tremor activity on the transform plate bounding San Andreas Fault (SAF) in central California where, in contrast to subduction zones, long-term deformation directions are horizontal and fluid availability from subduction zone processes is absent. The source region of the SAF tremors lies beneath the epicentral region of the great 1857 magnitude (M) $\sim$ 8, Fort Tejon earthquake whose rupture zone is currently locked (Sieh, 1978). Activity rate transients of the tremors occurring since early 2001 also correlate with seismicity rate variations above the tremor source region.
DE: 7230 Seismicity and seismotectonics
DE: 8107 Continental neotectonics
DE: 7215 Earthquake parameters
DE: 1242 Seismic deformations (7205)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting