HR: 0800h
AN: S21B-0559    [Abstracts]
TI: Attenuation of Radiated Ground Motion and Stresses from Three-Dimensional Supershear Ruptures
AU: * Bhat, H S
EM: bhat@esag.harvard.edu
AF: School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138, United States
AU: Dunham, E M
EM: edunham@fas.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, United States
AB: Radiating shear and Rayleigh waves from supershear ruptures form Mach fronts that transmit large-amplitude ground motion and stresses to locations far from the fault. We simulate bilateral ruptures on a finite-width vertical strike-slip fault (of width W and half-length L with L >> W) breaking the surface of an elastic half-space, and focus on the wavefield out to distances comparable to L. At distances much smaller than W, two- dimensional plane-strain slip-pulse models (i.e., models in which the lateral extent of the slip zone is unbounded) [Dunham, 2005; Bhat et al., 2007] accurately predict the subsurface wavefield. Amplitudes in the shear Mach wedges of those models are undiminished with distance from the fault. When viewed from distances far greater than W, the fault is accurately modeled as a line source that produces a shear Mach cone and, on the free surface, a Rayleigh Mach wedge. Geometrical spreading of the shear Mach cone occurs radially and amplitudes there decrease with the inverse square-root of distance [Ben-Menahem and Singh, 1987]. The transition between these two asymptotic limits occurs at distances comparable to W. Similar considerations suggest that Rayleigh Mach waves suffer no attenuation in the ideally elastic medium studied here. The rate at which fault strength weakens at the rupture front exerts a strong influence on the off-fault fields only in the immediate vicinity of the fault (for both sub-Rayleigh and supershear ruptures) and at the Mach fronts of supershear ruptures. More rapid weakening generates larger amplitudes at the Mach fronts. A paper has been prepared on this topic, with title the same as for this abstract, by E. M. Dunham and H. S. Bhat, submitted to \it{J. Geophys. Res.}
UR: http://people.deas.harvard.edu/~bhat/documents/DunhamBhatSupershear3dJGR052307.pdf DE: 4255 Numerical modeling (0545, 0560)
DE: 4400 NONLINEAR GEOPHYSICS (3200, 6944, 7839)
DE: 4455 Nonlinear waves, shock waves, solitons (0689, 2487, 3280, 3285, 4275, 6934, 7851, 7852)
DE: 7209 Earthquake dynamics (1242)
DE: 7212 Earthquake ground motions and engineering seismology
SC: Seismology [S]
MN: 2007 Fall Meeting