CONTINUOUS IMAGING OF THE SHALLOW SUBSURFACE FROM A 25 MHZ GPR PROFILE, HORRY COUNTY, SOUTH CAROLINA

South Carolina’s Long Bay is a welded barrier island complex preserving the geologic record of coastal change from past sea-level rise. To better understand the sedimentary architecture, the South Carolina Department of Natural Resources and USGS collected 25 MHz ground penetrating radar (GPR) common offset data throughout Horry County. In this study, we processed and interpreted part of the dataset collected along Carolina Bays Parkway paralleling the shoreline from the SC border southward 38 km. The GPR wave velocity was estimated by the curve-fitting method to hyperbolas in the subsurface as 0.083 m/ns. This velocity gives a maximum depth of 25 meters for the profile. SC-DNR has 20 drill logs along or near the Carolina Bays Parkway that we used to tie the GPR reflections to subsurface lithologies. NOAA LiDAR survey elevations were used to match the GPR surface to the drillhole collar elevation. Strong basal reflectors within the GPR data are present at depths of 10-15 m along the entire profile. These basal reflectors appear to correlate to a boundary between peat-rich sandy sediments and underlying clay-rich sediments. Above the basal reflectors, both datasets show evidence of lateral stratigraphic terminations, as well as the presence of paleochannels. Future efforts will focus on correlating the shore-parallel GPR profile with other GPR profiles oriented perpendicular to the shoreline to extend our stratigraphic framework landward with the goals of better characterizing local aquifers and reconstructing the evolution of the coastline in this area during the Quaternary.