Geophysics and Shallow Faults in Unconsolidated Sediments

This paper presents a case study using various geophysical techniques in unconsolidated sediments where shallow faulting is probable and most likely affects ground-water flow. Wenner and dipole-dipole resistivity, ground penetrating radar (GPR), and high resolution reflection seismic data are compared with cone penetrometer (CPT) information, existing monitoring well data and models of anticipated fault styles. The results of this study suggest that (1) the CPT study, combined with monitoring well data may suggest that discontinuities in corrrelatable zones indicate that faulting is present; (2) the addition of Wenner and dipole-dipole data may further suggest that offset zones exist in the shallow subsurface but make it difficult to map specific faults; (3) the high resolution seismic data will image faults to within a few meters of the surface but cannot identify faulting on the scale of our models; (4) offset 100 MHz and 200 MHz common mid-point (CMP) GPR will image features that may be fault planes and strands similar to the models; and (5) the combination of all the tools in this study, particularly the GPR and seismic, may allow for the mapping of small-scale, shallow faults in unconsolidated sediments that affect ground-water flow.