HR: 1340h
AN: GP43A-0838    [Abstracts]
TI: Dynamics of Block Rotations in Strike-Slip Fault Zones: A Perspective from Distinct Element Modelling
AU: * Lichtenberg, K
EM: kiml@levee.wustl.edu
AF: Washington University Washington University, Department of Earth and Planetary Sciences, Campus Box 1169, 1 Brookings Drive, St. Louis, MO 63130-4899 United States
AU: Sonder, L J
EM: leslie.sonder@dartmouth.edu
AF: Dartmouth College, Department of Earth Sciences, 6105 Fairchild Hall, Hanover, NH 03755 United States
AB: Previous studies of the dynamics of deformation in strike-slip fault zones have approximated the deforming lithosphere as a thin sheet of viscous material governed by a power-law rheology. Such models (Sonder et al 1986, Nelson and Jones 1987, Sonder et al 1994) yield relationships between the magnitude and distribution of strike-slip offset and vertical axis rotation that match observations in some shear zones very well (e.g. Las Vegas Valley Shear Zone). However, other shear zones (e.g. North Anatolian Fault and some in the Mojave region) show no rotations or rotations that are inconsistent with that expected from thin-sheet model results using the same offset. In addition, because of their continuum nature, continuum models have limited scope in delineating the dynamics of how block size and brittle strength affect the distribution of offset and rotations in the fault zone. Therefore, we consider a complementary approach. We use a distinct element model (Saltzer 1992, Antonellini 1995) to calculate displacements and rotation of cylindrical blocks distributed in a zone between two rigid boundaries moving at a fixed rate. Forces between blocks are calculated from Hertz's (1896) and Mindlin's (1949) solutions for normal and shear interactions between elastic cylinders; the force balance is integrated over time to yield displacements. We consider the role of several factors, including block size, mechanical strength, and heterogeneity of block size and strength, in controlling the distribution of displacements and vertical-axis block rotations in shear zones.
DE: 8110 Continental tectonics--general (0905)
DE: 8159 Rheology--crust and lithosphere
DE: 1208 Crustal movements--intraplate (8110)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting