HR: 1340h
AN: T33B-0551    [Abstracts]
TI: Extensional Subduction Earthquakes and Aseismic Slip Transients at Guerrero, Mexico, Observations and Numerical Study by a 2D Rate and State Model
AU: Dmowska, R
EM: dmowska@esag.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Dmowska, R
EM: dmowska@esag.harvard.edu
AF: Division of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: * Liu, Y
EM: liu@esag.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: Division of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AB: To investigate the possible signatures of stress transfer by aseismic slip transients within major subduction zones, and their effects on seismic hazard, we studied spatial-temporal seismicity variations for appropriately chosen time spans that bracket detected transients in the Mexico (Guerrero), Cascadia, and Japan (Bungo Channel) subduction zones. We found, for the large 2001-2002 Guerrero transient, a pattern suggesting that it acted as a means of communication between an extensional seismicity cluster downdip in the slab and later thrust seismicity in the shallow seismogenic zone. Similar time dependence between such slab and thrust zone seismicity clusters, along the same convergent margin, had been observed previously (Dmowska et al., 1988), and transients may provide an explanation for that. We therefore performed a related 2D numerical investigation of subduction earthquake sequences, adopting the Dieterich-Ruina version of rate and state friction. Friction properties, which are temperature-dependent, were made depth-dependent by incorporating appropriate thermal profiles of the subduction interface, chosen to approximate the SW Japan and Mexico subduction zones. Without a stress perturbation from extensional events, periodic large thrust earthquakes occur based on the assumed 2D modeling parameters. We represent the effects of an in-slab extensional event by imposing on the thrust interface, within the interseismic period, the static stress changes due to such normal-fault slip. Simulations with the two profiles show similar results. We found that induced transients and the timing of future thrust earthquakes are affected by three factors associated with the stress perturbation, namely, (1) the stage in the interseismic period, (2) the location along the subduction fault, and (3) the perturbation magnitude. Generally, sequential transients appear if the perturbation is introduced in the early stage of an interseismic period and, if large transient slips have occurred, the next thrust earthquake is delayed as compared to the unperturbed case. Sequential transients tend to migrate toward the velocity-weakening to velocity-strengthening transition zone, even if the perturbation is first introduced much further downdip of that region. Increases in the stress perturbation magnitude amplify the slip rate of the first induced transient, but have little effect on future transients and thrust earthquakes. In all simulated cases, the initial periodic earthquake pattern is resumed in a couple of earthquake cycles after the perturbation. Stress and slip rate evolution along the interplate interface shows that, in our simulations, a thrust earthquake occurs only when the stress peak, due to loading from downdip, reaches a well-locked depth that depends on the modeling parameters. This may help to understand why more transients are induced when the perturbation occurs at an early interseismic stage.
DE: 3225 Numerical approximations and analysis (4260)
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: Fall Meeting 2005