HR: 10:35h
AN: G22A-02 INVITED    [Abstracts]
TI: The Mechanics of Deep Tremor and Slow Slip
AU: * Beroza, G C
EM: beroza@geo.stanford.edu
AF: Department of Geophysics, Stanford University 397 Panama Mall, Stanford, CA 94305-2215, United States
AU: Shelly, D R
EM: dshelly@gmail.com
AF: Berkeley Seismological Lab, University of California, Berkeley 307 McCone Hall, Berkeley, CA 94720-4760, United States
AU: Ide, S
EM: ide@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, University of Tokyo 7-3-1, Hogo, Bunkyo, Tokyo, 113-0033, Japan
AU: Uchide, T
EM: uchide@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, University of Tokyo 7-3-1, Hogo, Bunkyo, Tokyo, 113-0033, Japan
AB: Deep tremor is a weak, extended-duration seismic signal observed episodically on some major faults, often in conjunction with slow slip events. We use borehole Hi-Net data to study tremor beneath Shikoku, Japan and through the use of a matched-filter algorithm, find that it can be explained as a swarm of small, low-frequency earthquakes (LFEs). Precise relocation places these LFEs on the subduction interface, immediately down-dip of the locked portion of the plate boundary. In order to determine the mechanism, we analyze stacked LFE waveforms and compare them with the waveforms of nearby earthquakes of known mechanism within the subducting Philippine Sea Plate. Both P-wave first-motion focal mechanism and the S-wave moment tensor analysis indicates that LFEs are shear slip on a low-angle thrust fault dipping to the northwest. We conclude that LFEs, and hence deep non-volcanic tremor, is generated directly by shear slip on the plate boundary, and represents a seismic signature of the accompanying slow slip events (SSEs). SSEs that accompany tremor have durations of up to weeks. They have been observed in Japan using borehole accelerometers and in Cascadia using GPS. Recently discovered very low frequency earthquakes (VLFs) with characteristic durations of 10s of seconds have been demonstrated to occur as shear slip in the same location as LFEs and SSEs, but with a longer time constant. Taken together, these events define a spectrum of slow shear-slip events spanning 8 orders of magnitude in moment and duration. Borehole observations of seismic/aseismic transients should allow our results from Japan to be generalized to other tectonic settings.
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1299 General or miscellaneous (1709)
DE: 7294 Seismic instruments and networks (0935, 3025)
DE: 7299 General or miscellaneous
SC: Geodesy [G]
MN: 2007 Fall Meeting