f Anisotropic seismic and electric cross borehole tomography at a hydrogeological test-site

Understanding fluid flow in fractured rock is of importance in many different fields as diverse as the development of oilfields, contaminant transport along fractures and the supply of drinking water. Geophysical tomographic techniques yield structural information on the examined rock mass, e.g. the distribution of seismic velocities in seismic tomography or the distribution of electrical resistivities in electric tomography. The advantages of joint inversion of seismic and electrical data are frequently discussed although there are relatively few examples of field experiments. The main emphasis of this study is the relationship between seismic and electrical anisotropy within fractured rock. It has long been recognised, that the presence of fractures will result in anisotropy of the physical parameters examined. For example electrical current will flow preferentially along fractures, resulting in a high conductivity along the fracture plane and low conductivity perpendicular to the fracture plane. If this anisotropy of physical parameters is not accounted for in the tomographic reconstruction algorithm, the resulting image of the subsurface can be severely distorted. The Reskajeage Quarry Test Site offers the unique opportunity to carry out geophysical experiments and ground truth the results in a well studied hydro-geological locality.