abstract bibtex

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., JGR, 2002; Kame et al., JGR, 2003; Bhat et al., 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, JGR, 1975; Harris and Day, 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.

@article{bhat2004aconf, Abstract = {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., JGR, 2002; Kame et al., JGR, 2003; Bhat et al., 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, JGR, 1975; Harris and Day, 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.}, Author = {Bhat, H. S. and Olives, M. and Rice, J. R. and Dmowska, R.}, Date-Modified = {2010-07-14 12:50:23 -0700}, Journal = {Eos Trans. AGU}, Keywords = {conference}, Pages = {Abstract S33C-03}, Title = {Short Fault Branches as Sources of Seismic Complexities}, Volume = {85(47), Fall Meet. Suppl.}, Year = {2004}}

Downloads: 0