NUMERICAL MODELING OF FAULT-ZONE TRAPPED WAVES - ACOUSTIC CASE

We have obtained numerical results for an acoustic wave propagating in a 3D medium with mixed boundary conditions. The specific model involv es a vertical low-velocity fault zone of varying thickness embedded in an otherwise homogeneous half-space. At the fault-zone boundary, the stress and displacement are continuous; on the free surface, the stres s is zero. A pseudo-spectrum method is employed to achieve sufficient resolution with reasonable computation time on a GRAY. Results show th e development of guided waves trapped in the fault zone. These guided waves display large amplitudes and lengthening waveforms; they propaga te at lower velocity with amplitudes that drop off mainly due to energ y leakage out of the fault zone. As the width of the fault zone varies , the wave energy tends to funnel into the new low-velocity wave guide . At large distance, these guided waves become the dominant arrivals o n seismograms. The waveforms are useful to recover the geometry and pr operties of the fault zone.