HR: 13:40h
AN: S23D-01    [Abstracts]
TI: Assessment of Well-Constrained Seismicity and Focal Mechanisms in the Andaman- Sumatra-Java Subduction Systems
AU: * Engdahl, E R
EM: engdahl@colorado.edu
AF: E. Robert Engdahl, University of Colorado, Boulder, CO 80309-0390, United States
AU: DeShon, H R
EM: hdeshon@memphis.edu
AF: Heather R. DeShon, University of Memphis - CERI, Memphis, TN 38152, United States
AU: Bilek, S
EM: sbilek@nmt.edu
AF: Susan Bilek, New Mexico Tech, Socorro, NM 87801, United States
AU: Villaseñor, A
EM: antonio@ija.csic.es
AF: Antonio Villaseñor, Institute of Earth Sciences "Jaume Almera" – CSIC, Barcelona, 08028, Spain
AU: Thurber, C H
EM: clifft@geology.wisc.edu
AF: Clifford H. Thurber, University of Wisconsin-Madison, Madison, WI 53706, United States
AB: Most prior studies of regional seismicity in the Andaman-Sumatra-Java subduction zones have been limited to global catalog hypocenters that often have poorly constrained epicenters and depths. More than 8000 teleseismically well-constrained earthquakes occurring along this subduction margin during the period 1918- 2006 are relocated with special attention to focal depth. Reduced uncertainties of epicenters and depths that meet the stringent Engdahl-van der Hilst-Buland (EHB) location quality criteria are on the order of 15 and 10 km, respectively. The patterns arising from these relocations provide important insights into the complex spatio- temporal relationships among earthquakes along these subduction systems. Relocated hypocenters, when combined with CMT focal mechanism data, reveal complex details about subduction zone processes and microplate formation in the region, and help to clarify how strain is accumulated and released. Selected cross sections reveal in finer detail the shallow-dipping interplate zone, back-arc seismicity, and the intraplate seismic zone at depth in the mantle. Broad-scale features such as the abrupt increase in shallow strike-slip activity along the volcanic arc as subduction becomes highly oblique and the decrease in maximum depth of intraslab earthquakes are readily apparent in the global dataset. Offshore central Sumatra, there is a dearth of shallow, underthrusting earthquakes corresponding to the region affected by the 1833 great subduction earthquake; the seismic hazard along this segment of the Sumatra subduction zone remains high. Along Java, reverse fault mechanisms, rather than thrust earthquakes, dominate the shallow subduction zone seismicity. Comparison of relocated aftershocks and slip distributions of two Java tsunami earthquakes (1994 and 2006) in this region shows that most 1994 aftershocks occurred within the slab updip of the mainshock, but the 2006 aftershocks have a more complex pattern. These aftershock locations have implications for models of tsunami earthquake generation.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Seismology [S]
MN: 2007 Fall Meeting