HR: 0800h
AN: U11A-0802    [Abstracts]
TI: Poroelastic Coupling of the Recent M9 and M8.7 Earthquakes in the Sumatra-Andaman Subduction Zone
AU: * Masterlark, T
EM: masterlark@geo.ua.edu
AF: Dept. of Geological Sciences, University of Alabama, 202 Bevill Bldg., Tuscaloosa, AL 35487 United States
AB: This analysis uses poroelastic models to investigate the deformation, stress, and pore pressure generated by the recent M9 2004 and M8.7 2005 earthquakes in the Sumatra-Andaman Subduction Zone (SASZ) and how these events change the likelihood for other earthquakes in the region. Preliminary results suggest that both the spatial and temporal occurrence of the M8.7 earthquake may have been predictable. These results are obtained by estimating the coseismic slip distribution of the M9 earthquake from near-field GPS data. This estimated slip then loads forward poroelastic models that calculate the evolution of deformation, stress, and pore pressure in the SASZ region. Coulomb stress is the change in shear stress (aligned with a specified slip vector) less the sum of the change in the fault normal stress and change in pore pressure, scaled by a coefficient of friction. A static Coulomb stress analysis confirms the M9 event dramatically increased the tendency for slip to occur along the fault of the future M8.7 event. However, static Coulomb stress cannot account for the three-month delay between events. The delay can be accounted for if we understand the evolution of Coulomb stress following the M9 event, which in turn, requires that we understand the poroelastic deformation at work following the M9 event. A finite element model (FEM), which simulates the poroelastic oceanic and continental crust of the SASZ, predicts that pore pressure in the region of the subsequent M8.7 event not only increased during the interval separating the M9 and M8.7 events, but peaked near the end of this interval. The FEM-predicted evolution of Coulomb stress follows a similar path.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 4255 Numerical modeling (0545, 0560)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Union [U]
MN: Fall Meeting 2005