Novel regularized inversion of VLF(R) data and coincident radar sections over a probable fault affecting Carboniferous sedimentary rocks in the Saar region, Germany

Coal mining induced subsidence along the surface trace of faults has caused extensive damage and consequent expense in parts of the Saar, Germany. An ongoing CEC assisted project was established to determine an efficient strategy for the detection of fault traces, prior to undermining, involving geological mapping, lineament analysis and surface and borehole geophysics. We present VLF(R) and GPR (multi-frequency) results from three traverses, 10 m apart, crossing a suspected fault that was subsequently proved by inclined core drilling. The modelled resistivity distribution (VLF) indicates a dipping, blind conductive zone of limited depth extent, while the radar sections reveal a well defined anomalous zone separating contrasting lithologies on either side of the fault. Additional geophysical data (EM conductivity and DC gradient array mapping and sounding) provide supportive evidence of the faulting.