The reflection interface obtained from seismic reflection exploration is actually a sub-interface of wave impedance. Under the existence of fracture, some abnormal phenomenon appear in the reflection stacking profile, for instance, the reflective phase is disturbed, its energy becomes weak, a continuous coherent phase no more exists and reflective interface is irregular in shape etc. It is noted that part of these anomalies in reflection time profiles are corresponding to fault zones, while the most parts are corresponding to micro-cracks, deep-weathered rock, and even sharp deformation of rock. Seismic information is far from enough to distinguish fault zone and common fractures.
Resistivity tomography can provide another kind of information, i.e. electric structures of rock formation. In general, the sediments, water-bearing fracture, fault zone and weathered rock can be revealed distinctly from resistivity tomograms. Based on our resistivity surveys in China, four kinds of fault patterns can be easily distinguished.
Joint survey of resistivity and seismic profiles could provide well-constrained results. In the project of Site Investigation for the Tunnel System in Singapore, joint imaging fracture from seismic and resistivity surveys were performed in 1997. Taking this work as an example, authors discussed relevant methods and results.