HR: 1340h
AN: T53A-1120    [Abstracts]
TI: Spatial Variability in Apparent Stress for Subduction Zone Earthquakes Along the Nicoya Peninsula, Costa Rica
AU: * Stankova-Pursley, J
EM: janas@nmt.du
AF: New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, United States
AU: Bilek, S L
EM: sbilek@ees.nmt.edu
AF: New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, United States
AU: Phillips, W S
EM: wsp@lanl.gov
AF: Los Alamos National Laboratory, MS F665, Los Alamos, NM 87545, United States
AU: Newman, A V
EM: anewman@gatech.edu
AF: Georgia Institute of Technology, School of Earth and Atmospheric Sciences, 311 Ferst Drive, Atlanta, GA 30332-0340, United States
AB: Subduction zones around the world release much of the world's seismic energy in mega- thrust earthquakes. This energy release varies in subduction zones around the world, likely related to heterogeneity in the strength of the mega-thrust zone. Here we examine the heterogeneity along the megathrust at the Middle America Trench, focusing on small magnitude earthquakes along the northwestern margin of Costa Rica, Central America. This area is interesting because seismicity patterns vary along strike of the subduction zone and there is heterogeneous topography on the incoming Cocos plate that could affect the strength of the interface. We compute source spectra and thus seismic moment from coda amplitude measurements for over 2200 well-located earthquakes from the Nicoya Peninsula portion of the 1999-2001 CR-SEIZE project. This method of using the coda wave amplitudes provides more stability for the magnitude estimates because we minimize effects of energy distortion from crustal heterogeneity. These values are then used to compute apparent stress for each earthquake. Preliminary results suggest that earthquakes in the northern and central portions of the peninsula have higher apparent stress than those in the southern portion of the peninsula. These differences seem to coincide with the changes in interface dip as well as the subduction of the Fisher seamount group at the southern tip of Nicoya. These apparent stress results suggest that subduction zone interface in the northern and central portions of the peninsula is either stronger or experiences higher friction along its surface than in the southern region.
DE: 7200 SEISMOLOGY
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting