HR: 0800h
AN: T21A-0375    [Abstracts]
TI: Explaining postseismic and aseismic transient deformation in subduction zones with rate and state friction modeling constrained by lab and geodetic observations
AU: * Liu, Y
EM: yjliu@princeton.edu
AF: Dept. Geosci., Princeton Univ., 308A Guyot Hall, Princeton, NJ 08544, United States
AU: DeDontney, N L
EM: ndedontn@fas.harvard.edu
AF: Dept. Earth Planet. Sci., Harvard Univ., 20 Oxford St., Cambrdige, MA 02138, United States
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: Dept. Earth Planet. Sci. and Sch. Eng. Appl. Sci., Harvard Univ., 29 Oxford St., Cambridge, MA 02138, United States
AB: Rate and state friction, as applied to modeling subduction earthquake sequences, routinely predicts postseismic slip. It also predicts spontaneous aseismic slip transients, at least when pore pressure p is highly elevated near and downdip from the stability transition [Liu and Rice, 2007]. Here we address how to make such postseismic and transient predictions more fully compatible with geophysical observations. For example, lab observations can determine the a, b parameters and state evolution slip L of rate and state friction as functions of lithology and temperature and, with aid of a structural and thermal model of the subduction zone, as functions of downdip distance. Geodetic observations constrain interseismic, postseismic and aseismic transient deformations, which are controlled in the modeling by the distributions of a \barσ and b \barσ (parameters which also partly control the seismic rupture phase), where \barσ = σ - p. Elevated p, controlled by tectonic compression and dehydration, may be constrained by petrologic and seismic observations. The amount of deformation and downdip extent of the slipping zone associated with the spontaneous quasi- periodic transients, as thus far modeled [Liu and Rice, 2007], is generally smaller than that observed during episodes of slow slip events in northern Cascadia and SW Japan subduction zones. However, the modeling was based on lab data for granite gouge under hydrothermal conditions because data is most complete for that case. We here report modeling based on lab data on dry granite gouge [Stesky, 1975; Lockner et al., 1986], involving no or lessened chemical interaction with water and hence being a possibly closer analog to dehydrated oceanic crust, and limited data on gabbro gouge [He et al., 2007], an expected lithology. Both data sets show a much less rapid increase of a-b with temperature above the stability transition (~ 350 ^oC) than does wet granite gouge; a-b increases to ~ 0.08 for wet granite at 600 ^oC, but to only ~ 0.01 in the dry granite and gabbro cases. We find that the lessened high-T a - b does, for the same \barσ, modestly extend the transient slip episodes further downdip, although a majority of slip is still contributed near and in the updip rate-weakening region. However, postseismic slip, for the same \barσ, propagates much further downdip into the rate-strengthening region. To better constrain the downdip distribution of (a - b) \barσ, and possibly a \barσ and L, we focus on the geodetically constrained [Hutton et al., 2001] space-time distribution of postseismic slip for the 1995 Mw = 8.0 Colima-Jalisco earthquake. This is a similarly shallow dipping subduction zone with a thermal profile [Currie et al., 2001] comparable to those that have thus far been shown to exhibit aseismic transients and non-volcanic tremor [Peacock et al., 2002]. We extrapolate the modeled 2-D postseismic slip, following a thrust earthquake with a coseismic slip similar to the 1995 event, to a spatial-temporal 3-D distribution. Surface deformation due to such slips on the thrust fault in an elastic half space is calculated and compared to that observed at western Mexico GPS stations, to constrain the above depth-variable model parameters.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 8020 Mechanics, theory, and modeling
DE: 8034 Rheology and friction of fault zones (8163)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting