| Popis: |
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 division of resistivity into shear-wave velocity (from the surface-wave inversion) can be used to strengthen the contrast of the alluvium/consolidated rock contact in depth-to-bedrock studies. Similarly, since the likelihood that a resistivity anomaly represents a void is increased if it also displays low shear-wave velocity, the ratio of resistivity to shear-wave velocity will enhance anomalies due to voids and suppress those arriving from other features. In a floodplain survey in Athens, Ohio, this “combined image” enhanced anomalies common to both seismic and resistivity images and suppressed features observed in only one physical property. Thus, combined surface-wave and electrical resistivity surveys can be effective in situations where the need for increased anomaly strength and/or decreased ambiguity in interpretation are worth the additional field work and processing time. |
