HR: 14:40h
AN: S43D-05 INVITED     [Abstracts]
TI: Challenges in Defining Seismogenic Zone Using Geodetic and Structural Observations
AU: * Wang, K
EM: kwang@nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada, 9860 W Saanich Rd, Sidney, BC, V8L 4B2 Canada
AU: Hyndman, R D
EM: rhyndman@nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada, 9860 W Saanich Rd, Sidney, BC, V8L 4B2 Canada
AB: The coseismic fault slip area in recent subduction earthquakes can be determined from seismological, tsumani, and geodetic observations. The coseismic rupture appears to be limited generally by a temperature around 125$\deg$C at the updip end and a temperature around 350$\deg$C or the intersection of the plate interface with the forearc Moho at the downdip end, with significant along-strike variations. Defining the seismogenic zone from interseismic deformation is much more challenging, because of the fewer available observation methods and the poorly understood earthquake cycle deformation process. It is reasonable to expect the rupture zone to be locked in the interseismic period, but the updip and downdip limits of mechanical locking do not usually have clear simple geodetic signatures. Fault motion outside the locked zone is not simply determined by frictional properties and fault stress. Surface deformation changes through the earthquake cycle due to both transient fault slip and viscoelastic stress relaxation. If an elastic dislocation model is used to explain decade- and century-scale viscoelastic interseismic deformation, a more gradual downdip tapering of locking is required to fit geodetic observations long after the most recent earthquake. Rate- and state-dependent friction and nonlinear mantle rock rheology are both important candidates in explaining transient afterslip of duration of days to a few years downdip of coseismic rupture, although their distinction is obscured by strain localization in nonlinear deformation. Newtonian rheology is arguably applicable a few fault dimensions from the rupture zone and several years after the earthquake. Cascadia and Nankai episodic "silent" slips indicate that the forearc material at 30-40 km depths is able to accumulate and release elastic strain energy. It has been proposed that such slip may be shear deformation of a band of km's thickness above the subducting slab (and that the shear band terminates seismogenic zone), but this gives a problem of mass balance. The slip below the forearc Moho is likely along a thin contact zone between the slab and hydrated cold mantle wedge.
DE: 8162 Rheology--mantle
DE: 7209 Earthquake dynamics and mechanics
DE: 1242 Seismic deformations (7205)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting