HR: 11:05h
AN: T12C-04    [Abstracts]
TI: Multi-scale Quasi-periodic Rate Changes of Nonvolcanic Tremor at Cholame, CA Following the 2004 Parkfield Mainshock.
AU: * Nadeau, R M
EM: nadeau@seismo.berkeley.edu
AF: U.C. Berkeley Seismological Lab., 211 McCone Hall, Univ. of California, Berkeley, CA 94720, United States
AU: Guilhem, A
EM: aurelie@seismo.berkeley.edu
AF: U.C. Berkeley Seismological Lab., 211 McCone Hall, Univ. of California, Berkeley, CA 94720, United States
AB: In Cascadia and Japan nonvolcanic tremors (NVTs) have shown a remarkable correlation between their activity rates and GPS and tiltmeter measurements of transient deformation in the deep (sub-seismogenic) fault zone. There is also evidence to suggest that stress changes from passing surface waves of large earthquakes may induce NVT activity. These observations suggest that tremor rate changes may be closely related to transient deformation and/or stress changes in the deep fault zone, and that induced stress changes from near-by larger earthquakes could stimulate tremor activity. Here we present observations of the evolution of NVT activity rates in the Cholame, CA area over a multiple year period ending in late 2007 and spanning the occurrence of the 28 September 2004 Parkfield magnitude 6 earthquake. We show: 1) that NVT rates increased significantly following the 2004 Parkfield event, 2) that immediately following the mainshock, rates were highest and then decayed rapidly for several weeks, 3) that following the rapid decay period, overall rates decay much more slowly, and 4) that a pattern of multi-scale quasi-periodic variation in the rates has evoluted over the three year period since the Parkfield mainshock. These observations support the argument that near-by moderate magnitude earthquakes can stimulate deep NVT activity and that such events may have a significant impact on the longer term evolution of near-by NVT activity.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting