COMBINED SURFACE-WAVE AND RESISTIVITY IMAGING FOR SHALLOW SUBSURFACE CHARACTERIZATION

A method for combining resistivity and surface-wave tomography data has been developed to enhance the near-surface anomalies imaged by both techniques. Efficient acquisition of both dipole-dipole resistivity and multichannel surface-wave data can be accomplished using an automated multi-electrode resistivity meter and a 24-channel engineering seismograph with 18 active channels employed in roll along mode. A 100m survey using a 2m geophone spacing and a 4m electrode separation can be completed in approximately 6 hours. Electrical and seismic data may be combined in a number of ways to enhance various types of anomalies. For example, the product of resistivity and shear-wave velocity Vs (from the surface-wave inversion) can be used to strengthen the contrast of the alluvium/consolidated rock contact in depth-to-bedrock studies. In a floodplain survey in Athens, Ohio, this “product image” enhanced anomalies common to both seismic and resistivity images and suppressed features observed in only one physical property. Thus, in situations where there is a need for increased image strength and/or decreased ambiguity in interpretation, combined surface-wave and electrical resistivity surveys can be effective.