Geophysical imaging of disrupted coastal dune stratigraphy and possible mechanisms, Haast, South Westland, New Zealand

Abstract

ABSTRACTGeophysical imaging of coastal dune stratigraphy near Haast, South Westland, provides insight into coseismic dune modification on a seismically active coastline. Complementary ground-penetrating radar and electrical imaging responses reveal low-angle features that apparently truncate and offset dune bedding. Complex attribute analysis of the GPR profiles is consistent with truncated bedding. One feature is near-coastal and separates post-seismic dunes that have been attributed to the 1717 Alpine Fault and 1826 Fiordland earthquakes. Another is inland, coincident with an incised stream channel. Superficially, the truncations might be interpreted as erosional features caused by large storms; however, the truncating features penetrate and appear to disrupt the wave base. We therefore suggest the near-coastal truncation is either a translational feature, such as a slide, or more likely an erosional record of a tsunami generated by the 1826 Fiordland earthquake. The inland feature records a previous event, the cause of which needs further investigation.