HR: 12:05h
AN: G32A-08    [Abstracts]
TI: The Stress/Strain/Fault Slip Cycle in Guerrero, Southern Mexico
AU: * Lowry, A R
EM: arlowry@himalaya.colorado.edu
AF: University of Colorado, Department of Physics, Boulder, CO 80309-0390 United States
AU: Larson, K M
EM: Kristine.Larson@colorado.edu
AF: University of Colorado, Department of Aerospace Engineering, Boulder, CO 80309-0429 United States
AU: Kostoglodov, V
EM: vladi@servidor.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria, Del. Coyoacan, Mexico D.F., C.P. 04510 Mexico
AU: Sanchez, O
EM: osvaldo@ollin.igeofcu.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria, Del. Coyoacan, Mexico D.F., C.P. 04510 Mexico
AB: GPS data from the Cocos-North American plate boundary in Guerrero, southern Mexico indicate four large transient slip events or ``silent earthquakes'' since 1992. We have developed an inverse model of the data that characterizes both the slip during events and the subduction megathrust coupling during inter-event times. Among the most robust features of this model are timing of the events and equivalent moment magnitudes of slip. Unlike similar (but smaller) silent earthquakes observed in Cascadia and Japan, interevent times vary significantly, ranging from 0.68 +0.08/-0.10 years to 4.01 +0.11/-0.13 years. Event magnitudes are 7.18 +0.19/-0.08 in 1998, 7.48 +0.01/-0.01 in 2002 and 7.22 +0.02/-0.15 in 2003. Within uncertainties, the pattern of larger events following longer periods of quiescence is similar to expectations for the strain accumulation and release in radiative earthquakes, with the primary difference that frictional coupling and subsequent slip occurs in the ``stable'' slip regime downdip of the seismogenic megathrust. Estimates of the steady-state frictional coupling on the fault, when compared with location and magnitude of the slip events, suggests that these events do not relieve seismogenic strain. If this pattern of behavior is consistent throughout the seismic cycle, the Guerrero segment of the Cocos/North America plate boundary currently has sufficient strain accumulated to generate a magnitude $\sim$7.9 earthquake. In this presentation, we will examine the cycle of stress/strain accumulation and release via frictional coupling and stable slip. We also will present InSAR deformation snapshots of the 1995 aseismic slip event, a slip event apparently initiated by the 1995 $M_w$=7.3 Copala earthquake.
UR: http://anquetil.colorado.edu/$\sim$arlowry/Guerrero/models.html
DE: 7223 Seismic hazard assessment and prediction
DE: 8123 Dynamics, seismotectonics
DE: 8150 Plate boundary--general (3040)
DE: 3210 Modeling
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting