HR: 0830h
AN: S41C-0086    [PDF]
TI: The Role of Stress Interaction in Thrust and Subduction Earthquakes
AU: Stein, R R
EM: rstein@usgs.gov
AF: U.S. Geological Survey, MS 977, Menlo Park, CA 94025 United States
AU: * Lin, J
EM: jlin@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept Marine Geology & Geophysics, Woods Hole, MA 02543 United States
AB: Key features of thrust earthquake triggering, inhibition, and clustering can be explained by Coulomb stress changes. Whereas slip on surface-cutting thrust faults drops the stress in most of the adjacent crust, slip on blind thrust faults increases the stress on some nearby zones, particularly above the source fault. Blind thrusts can thus trigger slip on secondary faults at shallow depth, and typically produce broadly distributed aftershocks. Short thrust ruptures are effective at triggering earthquakes of similar size on adjacent thrust faults. We calculate that during a progressive thrust sequence in central California during 1982-1985, the Mw=6.7 Coalinga earthquake brought the subsequent 1983 Mw=6.0 Nu¤ez and 1985 Mw=6.0 Kettleman Hills ruptures 10 and 1˙bars closer to Coulomb failure. On a larger scale, slip on major strike-slip faults modulates the stress acting on nearby thrust faults. We calculate that the 1857 Mw=7.9 Fort Tejon San Andreas earthquake and subsequent interseismic slip brought the Coalinga fault ~1 bar closer to failure, and inhibited failure elsewhere on the Coast Ranges thrust faults. The 1857 event also promoted failure on the White Wolf thrust fault by 8 bars, which ruptured in the 1952 Mw=7.3 Kern County shock. The idealized stress-change calculations also explain key features of seismicity accompanying large subduction events. Subduction zone ruptures are calculated to promote normal faulting events in the outer rise, and to promote thrust faulting events on the periphery of the seismic rupture and on its downdip extension. These features are evident in aftershocks of the 1957 Mw=9.1 Aleutian and other large subduction earthquakes. We further examine stress changes on the rupture surface imparted by the 1960 Mw=9.5 and 1995 Mw=8.1 Chile earthquakes, for which detailed slip models are available. Calculated Coulomb stress increases of 2-20-bars correspond closely to sites of aftershocks and postseismic slip, whereas aftershocks are absent where the stress drops by more than 10 bars. We thus argue that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales.
UR: http://quake.wr.usgs.gov/research/deformation/modeling/refs/ross_refs.html
DE: 7209 Earthquake dynamics and mechanics
DE: 7223 Seismic hazard assessment and prediction
DE: 8123 Dynamics, seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting