HR: 1340h
AN: S43A-1055    [Abstracts]
TI: Earthquake Fracture Energy and Dynamic Branching of Faults in Mesoscopic and Macroscopic Scales
AU: * Ando, R
EM: ando@ldeo.columbia.edu
AF: LDEO, Columbia University, Seismology Bldg. LDEO, Columbia University,61 Route 9W, Palisades, NY 10964-8000 United States
AU: Yamashita, T
EM: tyama@eps.s.u-tokyo.ac.jp
AF: ERI, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: We investigate a dynamic formation process of secondary branch faults (BFs) bifurcated from a principle slip plane based on multi-scale model introducing a hierarchical fault structure inside a fault zone (consisting of the micro-, meso- and macro-scopic scales). Energy dissipation on the BFs is shown to contribute to the fracture energy Gc that determines rupture velocity of an earthquake in the macroscopic scale. Although Gc becomes proportional to the distance of rupture propagation as far as the distance is short than a critical value, this simple scaling is not satisfied if the rupture is propagated beyond the critical distance that starts a BF propagating spontaneously. In a 2-D infinite elastic medium, it is simulated that a mode II crack under constant stress drop is spontaneously propagated through a straight plane that is assumed to be slightly weaker than the medium off the plane; therefore bifurcations from the original plane are enabled. This is an idealized case of a rupture in a mature fault zone or an intact rock. The linear slip weakening constitutive law is assumed on the slip surfaces as coarse-grained processes occurring in the microscopic scale, which is smaller enough than the minimum length of BFs. We employ the boundary integral equation method (BIEM) having advantage in the treatments of non-planar fault geometry. We observe that there are two distinct types of BFs emerging as the result of dynamic bifurcations of a main-fault (MF) on the original plane. If the propagation distance of the MF is smaller than a critical length, BFs are arrested soon after the initiation and their lengths become proportional to the MF length (self-similar distribution); we refer these BFs as mesoscopic BFs. Also, the rupture velocity of the MF becomes constant here, since energy dissipation on the mesoscopic BFs is proportional to the length of MF. However, once the MF is propagated beyond the critical distance, therefore a BF exceeds a critical length, a BF starts to grow spontaneously into a scale comparable to the MF length; we refer this BF as a macroscopic BF. After emergence of the macroscopic BF, subsequent mesoscopic BFs are shortened, due to the stress shadow effect, and their previously observed self-similar length distribution is violated.
DE: 7209 Earthquake dynamics (1242)
DE: 7290 Computational seismology
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8010 Fractures and faults
DE: 8034 Rheology and friction of fault zones (8163)
SC: Seismology [S]
MN: Fall Meeting 2005