HR: 1340h
AN: T53A-1110    [Abstracts]
TI: Effects of Initial Stress State on Splay Fault Activation During Dynamic Rupture Propagation
AU: Raoul, S
EM: sraoul@seas.harvard.edu
AF: Ecole et Observ. Sci. Terre, Univ. Strasbourg I, 4 Rue Rene Descartes, Strasbourg, 67084, France
AU: * Templeton, E L
EM: templet@fas.harvard.edu
AF: Sch. Engin. Appl. Sci., Harvard Univ., 29 Oxford, Cambridge, MA 02138,
AU: DeDontney, N
EM: ndedontn@fas.harvard.edu
AF: Dept. Earth Planet. Sci., Harvard Univ., 20 Oxford, Cambridge, MA 02138,
AU: Dmowska, R
EM: dmowska@esag.deas.harvard.edu
AF: Sch. Engin. Appl. Sci., Harvard Univ., 29 Oxford, Cambridge, MA 02138,
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: Dept. Earth Planet. Sci. and Sch. Engin. Appl. Sci., Harvard Univ., 29 Oxford, Cambridge, MA 02138,
AB: Critical tapered wedge concepts suggest that as material is added to the accretionary prism or removed from the forearc, the material overlying the plate interface must deform to maintain a wedge structure. This internal deformation is achieved by slip on splay faults branching from the main detachment. During major thrust earthquakes, splay faults are possibly activated as part of the seismic event. As a rupture propagates updip along the plate interface, it will reach a series of junctions between the shallowly dipping detachment and more steeply dipping splay faults. The amount and distribution of slip on these surfaces will determine the seafloor deformation and the tsunami waveform. Numerical studies by Kame et al. [JGR, 2003] of fault branching during dynamic slip-weakening rupture in 2D plane strain showed that branch activation depends on the initial stress state, rupture velocity at the branching junction, and branch angle. They found that for a constant initial stress state with the maximum principal stress at shallow angles to the main fault, branch activation is favored on the compressional side of the fault for a range of branch angles. By extending the part of their work on modeling the branching behavior in the context of subduction zones, where the angle \Psi that the principal stress makes with the main fault is shallow, we hope to better understand the conditions for splay fault activation and the criteria for significant moment release on the splay. In aid of that, we conduct similar dynamic rupture analyses to those of by Kame et al., but use explicit finite element methods, and take fuller account of overall structure of the zone (rather than focusing just on the branching junction). Recent studies suggest that splay faults may have been activated during the 2004 Sumatra Andaman event [Araki et al., 2005; Sibuet et al., 2007]. Thus, we use a geometry representative of Sumatra [Banerjee et al., 2007] for our modeling. The aim is to understand what stress states and rupture parameters predict seismic splay fault activation, and what not. Based on Kame et al., the orientation \Psi of the most compressive stress at the branch junction is one important parameter. We use the wedge mechanics concepts to guide the choice of initial stress state in the modeling, take the stresses to be depth dependent, and allow for different elastic properties in the wedge and subducting seafloor. We also investigate how the stress state and other model parameters control the partitioning of slip between main and splay faults and what that means for the tsunami waveform.
DE: 7209 Earthquake dynamics (1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8123 Dynamics: seismotectonics
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting