The Deforming Philippines Orogen: Detail of Long Term Strain-Rate and Seismicity Calculations from Neotectonic Kinematic Analysis
W. K. Rucker and P. Bird
Department of Earth and Space Sciences, University of California Los Angeles, Los Angeles, CA 90095- 1567, United States
The Philippines orogen accommodates oblique convergence of Sunda and Phillipine Sea plates which subduct at bounding trenches to the West and East respectively. We integrate GPS campaign results, stress inferences, geologic slip-rate evidence, and tectonic velocity boundary conditions in a finite element model. With program Neokinema we modify background strain-rate to fit internal observations in a weighted least squares method. The preferred model predicts long-term (104-106yr) neotectonic velocities, fault slip-rates, and crustal strainrate (~9.5%/Ma). We report especially high (30%/Ma) long-term anelastic strainrates in the Luzon province where unmapped faults, related to active propagation of the Philippine Fault System, contribute to apparent anelastic strain. We further use model long-term velocity to compose a spatial forecast of seismicity. Compared to 630 events of Mw≥5.5 in the CMT catalog (1976-2005), our area integral of seismicity predicts 752 earthquakes of Mw≥5.5. Largest discrepancies between catalog populations and our spatial likelihood prediction occur in Mindanao province along the Siayan-Sindangan Suture Zone where we predict suture zone where we under forecast seismicity, possibly due to locally sparse constraining data.
AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas