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| | Abstract | | Integrated geophysical surveying was conducted on a levee system part of which was to be excavated for constructing a bridge abutment. The integrated geophysics comprised DC resistivity, OhmMapper resistivity, and high-resolution surface wave surveys along a short line about 200 m set on the levee crest. Resistivity tomography measurement across the levee body was also applied. We conducted resistivity mapping and supplemental short spacing surface wave measurements on the surface after excavation of the levee body. The integrated geophysical surveys clearly delineated a small anomaly featured by high resistivity and high S-wave velocity just at the portion where the levee intersects an old meandering channel. A migrated depth section, obtained from the surface wave data through ordinary S-wave seismic reflection processing, reconstructed clean near-surface structure down to 40 m. The structure was characterized as a steeply dipping unconformity. The estimated depths of the unconformity were well concordant with array piling work results. |
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