HR: 16:00h
AN: S54A-01 INVITED     [Abstracts]
TI: Wedge Dynamics, Forearc Basins, and Seismogenic Zone of Cascadia Megathrust
AU: * Wang, K
EM: kwang@nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Centre, 9860 W Saanich Rd, Sidney, BC V8L 4B2 Canada
AU: Hu, Y
EM: yhu@nrcan.gc.ca
AF: Institute of Earthquake Sciences, China Earthquake Administration, Beijing, 100036 China
AB: A dynamic critical wedge theory has been developed to describe stress changes in submarine wedges in great earthquake cycles. For most subduction zones, the theory postulates that the actively deforming outer wedge overlies the updip velocity-strengthening part of the subduction fault, and the less deformed inner wedge overlies the megathrust seismogenic zone. Coseismic shear-stress increase in the velocity-strengthening zone drives the outer wedge into the critical state, causing episodic fold-and-thrust deformation, but the inner wedge stays in the stable regime throughout earthquake cycles, maintaining a stable environment for the development of forearc sedimentary basins. This is consistent with the globally observed correlation of the location of forearc basins with rupture zones of subduction earthquakes [Wells et al., JGR, 2003]. However, northern/central Cascadia is complicated by recent, exceedingly rapid growth of the accretionary prism. Until mid-Pleistocene, the megathrust seismogenic zone was probably mostly beneath the forearc basins, in agreement with the modern global observations. Rapid wedge growth and consequent megathrust warming over the past Ma have caused the seismogenic zone to move seaward by tens of km, to a position consistent with inferences based on contemporary geodetic observations. With much of the seismogenic zone located seaward of the forearc basins and beneath the upper continental slope, the dynamic taper theory predicts that coseismic deformation should cause extensional structures on the upper slope but accretion and thrusting on the lower slope, consistent with structural observations [McNeill et al., JGR, 1998].
DE: 7209 Earthquake dynamics (1242)
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: Seismology [S]
MN: Fall Meeting 2005