The Application of Ground Penetrating Radar in Delineating Shore Platform Morphology: A Case Study from Wellington, New Zealand

摘要

Ground penetrating radar (GPR) is a new technique in field sciences and is now commonly applied to studies of coastal dunes and beaches. The technique has yet to be applied on hard rocky coasts, and its ability to discern subsurface stratigraphy has great potential for investigating landform evolution on tectonically active shorelines where erosional surfaces are often buried by sediments derived from marine and nonmarine sources. In this study, we test the resolution of a 100- and 250-MHz GPR system on a series of Holocene uplifted shore platforms and gravel beaches in Wellington, New Zealand. The sediment thickness at the sites investigated ranged from a thin veneer to many meters and is composed of a mix of sand and gravel-sized material. It was found that the 100-MHz antenna did not have the resolution of the 250-MHz antenna and could not distinguish the buried platform surface. Using the 250-MHz antenna, bedding features within the unconsolidated sediment and the bedrock-sediment interface could be discerned. The high relief of the bedrock (meter scale), which outcropped on the surface, and the presence of buried boulders caused significant interference to the radar profiles through the creation of multiple and hyperbolic reflections. Despite these reflections, the GPR was able to quantify the morphology of the buried shore platform, thus indicating the utility of this technique for rocky coast research.