HR: 14:55h
AN: S33C-06    [Abstracts]
TI: Shock S-Wave Characterization for Kinematic Fault Rupture Models With Constant Supershear Rupture Velocity
AU: * Bernard, P
EM: bernard@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussieu, Paris, 75252 France
AU: Baumont, D
EM: david.baumont@irsn.fr
AF: Institut de Radioprotection et de Suret‚ Nucl‚aire, BP17, Fontenay aux Roses, 92262 France
AB: We present the specific amplitude and waveform characteristics of near-source S-shock-wave generated by a kinematic model of super-shear rupture at constant velocity v. Asymptotic analytical solutions are provided for the shock wave amplitudes, in relationship with the geometrical singularities carried by the S-wave isochrones on the fault plane. The solution is dominated by waves radiated near a critical point source A defined by $cos(\theta)=\beta / v $, where $\theta$ is the angle between the rupture ray and the S-wave ray normal to the rupture front at A, and b is the S-wave velocity. The far-field, dominant shock-wave velocity related to the mode II component of the slip is proportional to the slip velocity at A and to $cos(2\theta) / sin(\theta)$. Thus, the shock-wave front "carries" the motion on the fault plane at large distances, with little attenuation, within a "shock-wave beam" of rays characterized by their angle $\theta$. Numerical calculation of the complete field has been achieved up to 4 Hz, in a homogeneous elastic half-space, and for a vertical strike-slip fault 50 km long equivalent to a magnitude 7.1. It confirms these theoretical developments, and shows that the peak acceleration and velocities are at least twice that of a standard sub-Rayleigh rupture at 10 km, and up to 5 times its value at 30 km. Although the diffusion and diffraction of S-waves in the real crust is expected to reduce the coherence of the shock-wave front and hence its peak amplitude, specially at large distances and for high frequencies, our analytical and numerical developments demonstrates that supershear rupture can produce unusually large levels of ground motion at distances ranging from 10 to a few tens of kilometres, within the shock-wave beam.
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting