HR: 14:10h
AN: S33C-03    [Abstracts]
TI: Short Fault Branches as Sources of Seismic Complexities
AU: * Bhat, H S
EM: hbhat@fas.harvard.edu
AF: Division of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Olives, M
EM: molives@deas.harvard.edu
AF: Laboratoire de M‚canique, Ecole Polytechnique, Palaiseau, 91128 France
AU: Olives, M
EM: molives@deas.harvard.edu
AF: Option Sol et Sous-Sol, Ecole des Mines de Paris, Paris, 75006 France
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: Division of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: Department of Earth and Planetray Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Dmowska, R
EM: dmowska@esag.harvard.edu
AF: Division of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Dmowska, R
EM: dmowska@esag.harvard.edu
AF: Department of Earth and Planetray Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AB: We analyze an earthquake rupture propagating along a straight "main" fault that is perturbed by a finite-length branch fault. Such intersections are often encountered in natural events. The predicted effects of the encounter with the branch that we report can be remarkable; it can strongly perturb the propagation velocity on the main fault and, in some cases, even arrest that propagation. From previous studies [Poliakov et al., {\it JGR}, 2002; Kame et al., {\it JGR}, 2003; Bhat et al., {\it BSSA} in press, 2004] it is understood what determines whether rupture begins along such a branch fault, and whether the branch fault captures the rupture path exclusively or if rupture continues on the main fault too. However, in the present case of rupture along a finite-length branch fault, the propagation must stop abruptly at the branch end (we neglect fresh fault generation there). Such a sudden stoppage will radiate significant stress changes [Freund and Fossum, {\it JGR}, 1975; Harris and Day, {\it JGR}, 1993]. What happens when those stress changes reach the main fault? Do finite branches thereby influence the rupture propagation characteristics on the main fault? Those questions are addressed by considering mode II rupture propagation along a planar main fault with a finite branch. We simulate the propagation using a 2D elastodynamic BIE formulation incorporating a slip-weakening Coulomb friction failure criterion. Different parameters used to describe the fault configuration and rupture propagation (inclination of the maximum principal compressional stress with the main fault, inclination of the branch, rupture propagation velocity at the branching point, length of the branch) have different influences on the rupture. While, in some cases, an infinite branch would have completely captured the rupture, thus stopping propagation on the main fault, a finite branch in the same configuration will sometimes allow the rupture to propagate. A finite branch also sometimes induces the stoppage of the rupture on the main fault in cases for which an infinite branch would have let it continue to propagate. In general the finite branch, if not completely ignored by the rupture process on the main fault, introduces sudden deceleration and then acceleration of that rupture propagation. Those will contribute to the high frequency content of radiated ground motions. The branch also introduces complexities in the slip pattern along the main fault, and in the residual distributions of normal and shear stress which remain on the fault after the rupture event. Hence, finite branches can be seen as sources of complexities on small spatial and temporal scales during the dynamic rupture, as possible arrestors of that rupture, and as generators of local stress field non uniformities that may affect nucleation and propagation of future events.
UR: http://esag.harvard.edu/rice/OlivesBhRiDm\_FinBr\_27Aug04.pdf
DE: 7223 Seismic hazard assessment and prediction
DE: 7260 Theory and modeling
DE: 8010 Fractures and faults
DE: 8020 Mechanics
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting