HR: 08:30h
AN: G31A-03    [Abstracts]
TI: A History of Slow Slip Events in the Mexican Subduction Zone
AU: * Kostoglodov, V
EM: vladi@servidor.unam.mx
AF: Instituto de Geofisica, Universidad Nacional Autonoma de Mexico, Av. Universidad, 3000, Copilco, Coyoacan, Mexico, D.F 04510, Mexico
AU: Larson, K M
EM: kristinem.larson@gmail.com
AF: Department of Aerospace Engineering Science, University of Colorado, Boulder, CO 80309-0429, United States
AU: Santiago, J A
EM: santiago@ssn.ssn.unam.mx
AF: Instituto de Geofisica, Universidad Nacional Autonoma de Mexico, Av. Universidad, 3000, Copilco, Coyoacan, Mexico, D.F 04510, Mexico
AU: Franco, S I
EM: ivonne@ollin.igeofcu.unam.mx
AF: Instituto de Geofisica, Universidad Nacional Autonoma de Mexico, Av. Universidad, 3000, Copilco, Coyoacan, Mexico, D.F 04510, Mexico
AB: Aseismic slow slip events (SSEs) are a common and important feature of the seismotectonic process in the Mexican subduction zone. Large SSEs have been recorded in the central part of Mexico (Guerrero and Oaxaca states) in 1972, 1979 by tide gauges and later on in 1996, 1998, 2002, and 2006 by GPS network and a long- baseline tiltmeter. Comparing long term mean sea level (MSL) rise, ~4.5 mm/yr, and a secular subsidence rate of the GPS, ~11 mm/yr, in Acapulco tide gauge site, we may conclude that at least 9 mm/yr of vertical deformation is recovering episodically by SSEs (assuming 2.5 mm/yr eustatic MSL). The 1972 SSE was probably the largest observed in Mexico. It produced the vertical uplift of ~140 mm in Acapulco City and a noticeable uplift along the Pacific coast down to the town of Salina Cruz (more than 500 km SW from Acapulco). As the permanent GPS network "SSN-Sismología-UNAM"' was established in 1997 we could reliably register transient slips starting from the 1998 SSE. The last two SSEs of 2001-2002 and 2006 are the best studied. Characteristic duration of these events is 6-12 months. The equivalent magnitude exceeded Mw7.5 in 2002. All SSEs, with the exception of the 1996 event, initiated almost simultaneously in the coast (the NW Guerrero seismic gap) and ~180 km inland. Then SSEs propagated laterally along the strike of the subduction zone. However, the propagation rate of ~2 km/day could be estimated reliably only for the 2002 event. The observations indicate that the areas affected by the 1972 and 2002 slow events may have been greater than ~250x500 km². The shallow, subhorizontal configuration of the plate interface in Guerrero and partly in Oaxaca appears to be a controlling factor for the physical conditions favorable for such extensive SSEs. The entire partially coupled interplate zone in Guerrero is of ~160 km width (starting ~55 km inland from the trench) while the seismogenic, shallowest part of it is only ~40 km wide. Different models involving the elastic half space dislocation concept could not yet definitely resolve between the case of transient slip of the order of 10 cm propagating into the shallow seismogenic zone and the opposite case when the slip of 15-20 cm is totally develops on the deeper transition zone of the plate interface. The hazard estimate of the future large subduction thrust earthquake in Guerrero fairly depends on the answer to this query. Thus a denser GPS network in Guerrero is required before the next SSE.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8150 Plate boundary: general (3040)
SC: Geodesy [G]
MN: 2007 Joint Assembly