An improved equivalent viscoelastic medium method for wave propagation across layered rock masses

Abstract

The behavior of waves propagating through a rock mass is complicated by the discontinuous nature posed by the joints in the rock mass. However, at large scale, the jointed rock mass can be treated as an equivalent continuous medium. The purpose of this paper is to establish a method to determine the equivalent viscoelastic property of rock masses with different seismic quality factors, and to analyze seismic wave propagation across jointed rock masses. Each rock mass contains uniformly distributed joint sets with arbitrary orientation. The equivalent viscoelastic parameters are calculated for a rock mass with different seismic quality factors. The wave propagation equation is then derived for seismic wave across layered rock masses, where the parallel layer interfaces are assumed to be welded. Comparison between the improved equivalent viscoelastic medium method (EVMM) and the existing analytical methods is carried out for two specific cases: reflection at free surface, and transmission across a discontinuous interface between two media. The effects of some parameters, such as the incident angle, the thickness of the layer and the rock mass seismic quality factor, on wave propagation are discussed.