Using ground-penetrating radar (GPR) to investigate deposits from the Storegga Slide Tsunami and other sand-sheets in the Shetland Islands, UK

Abstract

We use ground-penetrating radar (GPR) to investigate the geometry, inland extent, and continuity of sand layers interpreted as tsunami deposits in the Shetland Islands, UK. Four sites where sand layers within peat deposits are recorded in previous studies provide ground-truth. In addition, we describe survey results from one site where deposits are not exposed, to test the potential of GPR to identify candidate tsunami deposits in areas that are not well documented. Sand layers can be clearly imaged at all five locations because they are interbedded with peat and the contrast in lithology gives a good reflection on GPR profiles, even very thin sand layers, less than 1 cm in thickness, that are beneath the theoretical resolution of the GPR. 2-D and 3-D surveys show that tsunami deposits appear to drape a buried topography. Most sand layers form continuous reflections although some gaps are attributed to later erosion, most likely by streams. Sand layers have been traced up to 150 m inland and 10 m above the present shoreline which is consistent with data from boreholes. If a similar sized event occurred today it would have a devastating impact on the Shetland Islands.