A physical model study of different crack densities

Abstract

Using a seismo-physical modelling technique with controlled crack densities introduced in laboratory, the effect of crack density and shape on seismic shear waves is studied. The physical models used in the experiment are made of epoxy resin with silicon rubber slices embedded in them to simulate the cracks. In the experiments, different degrees of shear-wave splitting can be observed in the media containing orientated cracks at various crack densities. The experimental results show that the fast shear-wave velocity is stable, whereas the slow shear-wave velocity increases with increasing crack density. The time difference between the two split shear waves is dependent mainly on the travel time of the slow shear wave. In the case of lower crack densities (<6%), the relationship between crack density and fast or slow shear-wave velocity agrees well with theoretical prediction. After careful analysis of the wavefield of the slow shear wave, it is found that the effect of crack shape on velocity is less than that on attenuation, which provides another type of method to describe the crack texture and its characteristics.