HR: 14:45h
AN: G23C-06    [Abstracts]
TI: Constraints on Lithospheric Rheology From Fault Displacement Rate Histories and Numerical Experiments
AU: * Lavier, L L
EM: luc@ig.utexas.edu
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Rd 600, Austin, TX 78704 United States
AU: Bennett, R A
AF: Department of Geosciences, University of Arizona, Gould-Simpson Building #77, 1040 E 4th St, Tucson, AZ 85721 United States
AU: Anderson, M L
AF: Department of Geosciences, University of Arizona, Gould-Simpson Building #77, 1040 E 4th St, Tucson, AZ 85721 United States
AU: Matti, J C
AF: U.S. Geological Survey, 520 N. Park Ave, Tucson, AZ 85719 United States
AB: Recent displacement rate and geodetic data on the San Andreas, San Jacinto and eastern California shear zone suggest that changes in the geometry and/or the magnitude of the applied forces on the crust (e.g., a general or local change in fault strike relative to plate motion) can generate strain repartitioning within the crust on time scales of millions to thousands of years. The rates over which this repartitioning takes place in response to changing forces are controlled by the rheological evolution of the lithosphere. We investigate the implications of observed fault displacement histories for the rheology of the lithosphere using 2.5 D numerical experiments of deformation in an analogue system. The numerical technique used allows for the spontaneous formation of elastoplastic shear zones and flow in a Maxwell viscoelastic lower crust. The results show that when a strike slip fault is rotated to strike obliquely to the direction of relative plate motion it causes changes in bending and frictional stresses due to the formation of topography. To accommodate these changes, a conjugate system of oblique-striking strike slip faults develops. The total displacement is then slowly distributed over the new fault system on the time scale of mountain building (i.e. million of years). The rate of change is dependent on the strength of the lithosphere as well as the amount of obliquity applied on the initial strike-slip fault. In other numerical experiments we show that in a system of multiple strike-slip fault zones, displacement rate changes can occur over a time scale of about 100 kyr. This time scale corresponds to the Maxwell time at the brittle ductile transition (BDT). In such a system the lithospheric displacement is alternatively distributed (over 100 kyr) in clusters localized in lower crustal channels and over strike-slip fault zones. We show that the clustering time scale is controlled by the ratio of upper to lower crustal strength. This incomplete exercise shows how displacement rates data sets spanning thousands to millions of years can be used to constrain numerical experiments of lithospheric deformation and, in doing so, place new constraints on the rheology of the lithosphere.
DE: 1206 Crustal movements--interplate (8155)
DE: 1208 Crustal movements--intraplate (8110)
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 1242 Seismic deformations (7205)
SC: Geodesy [G]
MN: 2005 Joint Assembly