HR: 1340h
AN: S13B-1298    [Abstracts]
TI: The 2003 M=6.9 Zemmouri, Algeria, Earthquake Brought Thrust and Strike-Slip Faults Near Algiers Closer to Coulomb Failure
AU: * Lin, J
EM: jlin@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543, United States
AU: Stein, R S
EM: rstein@usgs.gov
AF: U.S. Geological Survey, MS 977, 345 Middlefield Road, Menlo Park, CA 94025, United States
AU: Toda, S
EM: s-toda@aist.go.jp
AF: Active Fault Research Center, AIST, Site 7, Higashi, 1-1, Tsukuba, 305-8567, Japan
AU: Meghraoui, M
EM: Mustapha@eost.u-strasbg.fr
AF: EOST-Institut de Physique du Globe de Strasbourg, 5 rue Rene Descartes, Strasbourg, 67084, France
AU: Dorbath, C
EM: catherine.dorbath@eost.u-strasbg.fr
AF: EOST-Institut de Physique du Globe de Strasbourg, 5 rue Rene Descartes, Strasbourg, 67084, France
AB: We investigate key features of thrust earthquake triggering, inhibition, and clustering associated with the stress transferred by the 2003 M=6.9 Zemmouri quake on an offshore hidden thrust fault in coastal Algeria. A crucial question is whether the seismic hazard increased on the Boumerdes and Thenia faults, which lie just west of the Zemmouri rupture and only 10-20 km from the city of Algiers. The capital city suffered large damaging quakes in A.D. 1365 and 1716, and is today home to 3 million people. Slip on blind thrust faults tend to increase the stress above the source fault and in much of the surrounding crust, whereas slip on surface-cutting thrust faults drops the stress in most of the adjacent crust. We examined the sensitivity of the imparted stress to different published source models of the 2003 Zemmouri event inferred from geodetic and seismic inversions, and focus here on the robust results. We calculate that the 2003 M=6.9 Zemmouri quake brought the Coulomb stress 1.0 bars closer to failure on the reverse Boumerdes and 0.5 bars closer on the right-lateral Thenia faults that bound the populated Mitidja basin, although the Thenia fault may not be tectonically active. The calculated pattern of the stress increase appears consistent with aftershock distribution determined from double difference earthquake tomography by Ayadi et al. (submitted); both of these faults were illuminated by aftershocks during the first three months of the sequence. The East Sahel and Larbaa faults, which lie further to the west, are calculated to have sustained a weak 0.1-bar stress increase and show no associated aftershocks. We also calculate a 1.0-bar stress increase on the NNW-SSE trending vertical right-lateral Kabyle fault located south of the Zemmouri fault, although there is no evidence of recent Quaternary tectonic movement, no geomorphology typical of active zones, and little seismicity along the Kabyle fault.
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8108 Continental tectonics: compressional
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 9305 Africa
SC: Seismology [S]
MN: 2007 Fall Meeting