HR: 08:00h
AN: T51E-01 INVITED    [Abstracts]
TI: Elastic and Permanent Deformation of Subduction Zone Forearc Systems Driven by Great Earthquakes
AU: * Wang, K
EM: kwang@nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada, 9860 West Saanich Road, Sidney, BC V8L 4B2, Canada
AU: * Wang, K
EM: kwang@nrcan.gc.ca
AF: School of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8P 5C2, Canada
AU: Hu, Y
EM: yanhu@uvic.ca
AF: School of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8P 5C2, Canada
AB: One of the most remarkable characteristics of forearc systems is the structural and morphological contrast between the actively deforming outer wedge and the much less actively deforming inner wedge which is often the host of forearc basins. The dynamic Coulomb wedge model relates this contrast to the process of megathrust earthquakes. According to this model, the outer wedge overlies the shallow aseismic portion of the megathrust, and the inner wedge overlies the seismogenic zone. At the time of a great earthquake, when the seismogenic zone experiences a stress drop, the aseismic shallow segment strengthens to resist seismic rupture. After an earthquake, when the seismogenic zone is fully locked, the shallow segment tends to weaken and relax, which is most directly reflected as post-seismic afterslip. It can be shown that the inner wedge undergoes mostly elastic deformation in earthquake cycles, but the outer wedge alternates between elastic and permanent deformation. The outer wedge stays in a stable state experiencing only elastic deformation when the basal stress is moderately low, but it enters a critical state experiencing permanent deformation when the basal stress increases to a threshold level. The most important mode of the stress increase along this shallow portion of the megathrust is coseismic strengthening. Therefore, at subduction zones hosting great earthquakes, it is the peak basal stress achieved in these earthquakes that controls the taper geometry of the outer wedge. The dynamic Coulomb wedge model offers some other testable predictions regarding the relation between megathrust slip and forearc structure. For example, there should be a tendency for the outer wedge taper to be larger where moment release in great earthquakes is persistently large. The degree of coseismic strengthening of the shallow megathrust segment controls the updip propagation of coseismic slip, affecting details of the wedge geometry. In the case of complete stress relaxation of the shallow megathrust segment during an interseismic period, the outer wedge may enter an extensionally critical state developing normal faults, opposite of the compressively critical state during great earthquakes.
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8020 Mechanics, theory, and modeling
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting