Seismic Body Waves from Surface Faults

Abstract

The seismic body waves at large distances from a propagating fault near a free surface in an elastic half-space are investigated both in the frequency domain and in the time domain. The results are presented in an analytical form. The fault is simulated by a distribution of double couples of body forces on the fault plane with an appropriate time shift in accordance with the velocity and the direction of the rupture. Two representative cases are considered for the geometry of the fault. The first is a strike-slip fault propagating horizontally along the free surface and the second is a dip-slip fault propagating vertically towards the free surface. It is shown that the effect of the fault finiteness in the horizontal direction on the spectra is characterized by vanishing amplitude and π phase change at particular frequencies. No such simple characteristics exist in the vertical direction. It is demonstrated for the second fault model that the reflected wave of the latest arrival is a very energetic event.