A comparison of cross-hole electrical and seismic data in fractured rock |
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| Authors: | JV Herwanger MH Worthington † R Lubbe † A Binley J Khazanehdari |
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| Institution: | Department of Earth Science and Engineering, Imperial College of Science, Technology and Medicine, Prince Consort Road, London SW7 2BP,;Department of Environmental Science, Lancaster University, Lancaster LA1 4YQ;, and PRIS, PO Box 227, Whiteknights, Reading University, Reading RG6 6AB, UK |
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| Abstract: | Cross‐hole anisotropic electrical and seismic tomograms of fractured metamorphic rock have been obtained at a test site where extensive hydrological data were available. A strong correlation between electrical resistivity anisotropy and seismic compressional‐wave velocity anisotropy has been observed. Analysis of core samples from the site reveal that the shale‐rich rocks have fabric‐related average velocity anisotropy of between 10% and 30%. The cross‐hole seismic data are consistent with these values, indicating that observed anisotropy might be principally due to the inherent rock fabric rather than to the aligned sets of open fractures. One region with velocity anisotropy greater than 30% has been modelled as aligned open fractures within an anisotropic rock matrix and this model is consistent with available fracture density and hydraulic transmissivity data from the boreholes and the cross‐hole resistivity tomography data. However, in general the study highlights the uncertainties that can arise, due to the relative influence of rock fabric and fluid‐filled fractures, when using geophysical techniques for hydrological investigations. |
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