HR: 08:15h
AN: G31A-02    [Abstracts]
TI: Preliminary Evidence for Non-Volcanic Tremor in the Oaxaca Region, Mexico
AU: * Brudzinski, M R
EM: brudzimr@muohio.edu
AF: Miami University, Geology Department 114 Shideler Hall, Oxford, OH 45056, United States
AU: Cabral-Cano, E
EM: ecabral@igeofcu.unam.mx
AF: UNAM, Instituto de Geofisica Ciudad Universitaria, Mexico, DF 04510, Mexico
AU: Arciniega-Ceballos, A
EM: maac@geofisica.unam.mx
AF: UNAM, Instituto de Geofisica Ciudad Universitaria, Mexico, DF 04510, Mexico
AU: DeMets, C
EM: chuck@geology.wisc.edu
AF: University of Wisconsin, Department of Geology and Geophysics 1215 W. Dayton, Madison, WI 53706, United States
AU: Diaz-Molina, O
EM: oscard@igeofcu.unam.mx
AF: UNAM, Instituto de Geofisica Ciudad Universitaria, Mexico, DF 04510, Mexico
AB: A multi-year deployment of a large aperture seismic and GPS array in southern Mexico, for the purpose of studying the Oaxaca segment of the Middle America subduction zone, entered its second development phase during the summer of 2006. The Oaxaca segment is one of the few places on earth where land-based geophysical observations can be used to study both the locked, seismogenic area of a subduction interface and the region of deeper transitional slip, where episodic tremor and slip may originate. The newly expanded array, consisting of nine broad-band seismic and eleven continuous GPS stations, measures deformation and ground vibrations in the state of Oaxaca and adjacent areas. The seismic array has nominal 100-km spacing and extends from the coast to ~300 km inland. Preliminary analysis of seismic data indicates that the stations are uniformly characterized by low background noise in the non-volcanic tremor passband of 1-5 Hz, accomplishing an important goal of our site selection. Furthermore, we find several periods of non-volcanic tremor coincident on at least three of our seismic stations, including 3 short episodes during the summer of 2006. Based on relative amplitudes of the recordings, these episodes "hopped" from west (late June) to east (late July) of Oaxaca city and then back west again (mid August). The episodes are most prominent at stations ~100 km from the coast, which is consistent with non-volcanic tremor occurring near the zone of transitional motion downdip from the seismogenic zone. As of February 2007, there have been no prominent slip transients recorded by the GPS stations in the Oaxaca array since the seismic recordings began in early June 2006, so it may be that these are small episodes of non-volcanic tremor in which accompanying slow slip is below the current noise level of GPS. This hypothesis will be tested by the next prominent slow slip event in this region, when one would expect to see larger seismic amplitudes from non-volcanic tremor.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7294 Seismic instruments and networks (0935, 3025)
DE: 8104 Continental margins: convergent
SC: Geodesy [G]
MN: 2007 Joint Assembly