SHALLOW GEOPHYSICAL INVESTIGATION OF TRAIL RIDGE, GEORGIA

Based on both river and shoreline deflections, previous workers have suggested that Trail Ridge, which forms the eastern border of the Okefenokee Swamp, may lie adjacent to a Quaternary fault. Trail Ridge is a paleo- barrier-island complex associated with the Wicomico maximum transgression of sea level in the Plio-Pleistocene. We acquired 3 shallow seismic lines across two N-S-trending escarpments. The more easterly feature is believed to be an ancient terrace and the more westerly feature, along which a spring emerges, may be fault controlled. We used direct and refracted waves to estimate P-wave velocities and layer thickness using a standard layer over a half-space model. Two of the lines show a layer velocity of about 400 m/s and a half-space velocity ranging between 1200 and 1900 m/s, which is likely to correspond to the water table. The layer thickness gradually decreases from E to W from about 4 m to 2 m. Surface-wave analysis indicates the presence of an approximately 3-m-thick layer which has a low S-wave velocity. This layer, at about 4-m depth, may correspond to a water-saturated layer. Preliminary stacking of reflection data shows almost horizontal layering, but additional processing will be done to determine whether they are affected by artifacts. This stage will involve the analysis of synthetic data generated using the information we have determined so far.