HR: 14:30h
AN: S43C-02 INVITED     [Abstracts]
TI: Deep Earthquake Mechanics Inferred From Fault-Plane Orientations in Central South America
AU: * Warren, L M
EM: lmwarren@email.arizona.edu
AF: Department of Geosciences, University of Arizona, 1040 E. 4th St., Tucson, AZ 85721, United States
AU: Biryol, C B
EM: cbbiryol@email.arizona.edu
AF: Department of Geosciences, University of Arizona, 1040 E. 4th St., Tucson, AZ 85721, United States
AU: Beck, S L
EM: slbeck@email.arizona.edu
AF: Department of Geosciences, University of Arizona, 1040 E. 4th St., Tucson, AZ 85721, United States
AB: To place constraints on the physical mechanisms of deep earthquakes, we analyze the rupture properties of >30 intraslab earthquakes with M_W ≥ 5.7 in central South America. For each earthquake, we combine a directivity analysis with mapping of the slip distribution to estimate the rupture vector and identify the fault plane. We can distinguish the fault plane of the focal mechanism for ~1/3 of these earthquakes. At intermediate depths, we test whether earthquakes result from dehydration embrittlement reactivating the steep, trenchward- dipping faults of the outer rise. After accounting for the angle of subduction, the outer-rise faults would be approximately vertical. This prediction disagrees with our identified fault planes between 100-300 km depth, which are all subhorizontal. Subhorizontal faults are consistent with only one of the two failure planes expected from the slab stress field, suggesting that the slab fabric or an isobaric rupture process may also influence fault- plane orientations. The occurrence of exclusively subhorizontal faults at intermediate depths agrees with previous studies in the Tonga-Kermadec and Middle America subduction zones. The similarity in results between the three subduction zones despite large differences in temperature, lithospheric thickness, subduction velocity, and subduction angle suggests that the earthquake-generating mechanism is controlled by pressure rather than temperature or other tectonic parameters. Deeper than 300 km, earthquakes slip along both subhorizontal and subvertical fault planes, in agreement with the ambient stress field.
DE: 7215 Earthquake source observations (1240)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: 2007 Joint Assembly