GPR IMAGING OF THE SUBSURFACE IN 3D: EXAMPLES FROM A COASTAL SITE (USA) AND AN ARCHAEOLOGICAL SITE (ISRAEL)

To better understand coastal geomorphic sites as well as archaeological sites, ground penetrating radar (GPR) has become a popular and effective method for imaging the subsurface. GPR is based on the propagation of high frequency electromagnetic waves, which are emitted into the ground and are reflected back to the surface in response to differences in the properties of the sediment the waves travel through. Three-dimensional (3D) GPR datasets have been increasingly collected because their results significantly enhance the ability to view, analyze and interpret subsurface stratigraphy. The first site is along the coastline of the Pacific Northwest, USA and as a result of the subduction zone in the area, large earthquakes pose a significant threat. Coseismic subsidence associated with such earthquakes creates erosional scarps into beach face deposits. A GPR grid (225 MHz) was collected over one of these scarps north of Long Beach, WA. The prominent facies that was imaged in the 3D cube is the erosional scarp which was bounded by the associated progradational beach deposits. The 3D views aid in better understanding the extent of erosion due to coseismic subsidence and how the shoreline recovered as the coast rebounded. The second site, Yavne Yam, is in Israel and is an archeologically significant city, located south of Tel Aviv on the Mediterranean Sea. From the first century AD onward, Yavne Yam served as a sea port for the imperial city of Yavne, which is approximately 24 kilometers to the east. A dense GPR grid 6 was collected adjacent to present excavations with both 225 and 450 MHz antennae. Analyses of the GPR data reveal several linear subsurface anomalies that are interpreted as walls. The interpretation of the collected GPR data will be used by site archeologists to guide future excavations.