Seismic response of adjacent filled parallel rock fractures with dissimilar properties

a r t i c l e i n f o The purpose of this study is to analytically predict and to experimentally investigate the seismic response of adjacent filled parallel rock fractures with dissimilar properties (e.g., fracture thickness and stiffness). The time-domain recursive method is extended to predict that a P-wave propagates normally across the filled parallel fractures using the specific stiffness of each filled fracture and considering multiple wave reflections between the parallel fractures. The split Hopkinson rock bar technique is modified to simulate P-wave propagation normally across the sand-filled parallel fractures and to characterize the stress-closure relation of each sand-filled fracture. The P-wave transmission and the seismic response of the filled parallel fractures are an interactive process. The experimental results show the decreases of loading rate and dominant frequency when the P-wave propagates across each sand-filled fracture. The P-wave transmitted from the first sand-filled fracture strongly affects the seismic response of the second one. The P-wave attenuation in the filled parallel fractures is mainly due to the dynamic compaction of the filling sands. By comparison, the analytical method provides a satisfactory prediction to the experimental result. This study suggests considering the specific stiffness of each filled fracture to precisely predict the seismic response of filled parallel rock fractures. Seismic response of rock fractures is associated not only with a planar contact of country rock walls, but also with a gouge layer of viscoelastic materials filled between the walls. The filling gouges are found to be ubiquitous in rock fractures at all scales (Marone and Scholz, 1989). Gouge formation is mainly due to fragmentation of intact rocks exposed to sliding wear or implosive loading (Wilson et al., 2005). When an incident P-wave propagates, the seismic responses of the filled fractures largely affect how much seismic energy can travel through rock masses and how rock masses can resist the seismic disturbance. Understanding the mechanical and seismic roles of the filled fractures is thus essential to estimate seismic energy attenua-tion and rock mass instability (e. A group of nearly parallel fractures in rock masses is generally known as a set. The seismic response of a set of parallel fractures has been studied using different analytical methods, such as the Perino et al., 2012) and the virtual wave source method (Li et al., 2010). Most of these methods are narrowed to non-filled parallel fractures and conclude that the seismic response of …