HR: 12:05h
AN: S41G-07    [PDF]
TI: Laboratory Earthquake Experiments: The SubRayleigh to the Intersonic Transition
AU: Xia, K
EM: xia@gps.caltech.edu
AF: California Institute of Technology, Seismological Laboratory Mail Code 252-21 1200 E. California Blvd, Pasadena, CA 91125
AU: Xia, K
EM: xia@gps.caltech.edu
AF: California Institute of Technology, Graduate Aeronautical Laboratories 1200 E. California Boulevard Mail Stop 105-50, Pasadena, CA 91125
AU: * Rosakis, A J
EM: rosakis@atlantis.caltech.edu
AF: California Institute of Technology, Graduate Aeronautical Laboratories 1200 E. California Boulevard Mail Stop 105-50, Pasadena, CA 91125
AU: Kanamori, H
EM: hiroo@gps.caltech.edu
AF: California Institute of Technology, Seismological Laboratory Mail Code 252-21 1200 E. California Blvd, Pasadena, CA 91125
AB: We designed a laboratory earthquake model to investigate spontaneous rupture propagation. An important question is how fast a rupture can propagate. Rosakis et al [1999] demonstrated that a shear rupture can propagate at a supershear speed under impact loading; Here, we investigate an earthquake-like shear rupture which is spontaneous in nature. In our experiments, a fault is simulated with two photoelastic plates (Homalite) held together by friction and the far field tectonic loading is simulated by pre-compression. The fault forms a certain angle with the compression axis. A unique design is used for triggering dynamic rupture using an exploding wire technique. With this method, we can control the timing of triggering and initiate spontaneous rupture driven by the applied stress. We observed both subRayleigh and supershear ruptures depending on the magnitude of loading and the orientation of the fault plane with respect to the loading axis. Under proper loading conditions, a shear rupture which initially propagates at the Rayleigh wave speed initiates a secondary rupture at the shear wave front and this secondary rupture propagates at a supershear speed (close to the longitudinal wave speed). Eventually, the two ruptures combine as one supershear rupture. In general, this observation is consistent with the Burridge-Andrews mechanism [Burridge, 1973; Andrews, 1976]. We modified Andrews' theory which relates the supershear initiation distance $\it{L}$ to loading conditions by introducing a dependence of the critical slip distance $d_0$ on normal pressure. This modified theory yields a better agreement with the experimental data. This transition provides a mechanism for nucleation of supershear ruptures in a 2-D problem. Although such transition has been reported for some earthquakes (e.g., 2001 Kunlunshan earthquake), confirmation of it must await further studies.
DE: 1734 Seismology
DE: 7209 Earthquake dynamics and mechanics
DE: 8010 Fractures and faults
DE: 8120 Dynamics of lithosphere and mantle--general
SC: Seismology [S]
MN: 2003 Fall Meeting