GROUND PENETRATING RADAR IMAGING OF A TECTONICALLY ACTIVE, WAVE-INFLUENCED SHORELINE: HAAST, SOUTH WESTLAND, NEW ZEALAND

The Haast landscape is the only significant flat coastal region in the South-West New Zealand World Heritage Area. It has formed by a unique combination of geological, geomorphic and climatic conditions. The Southern Alps rise abruptly from the Haast coastal plain. Along the foot of these mountains runs the Alpine Fault, the boundary between the Pacific and Indo-Australian plates. As these mountains are being eroded, they provide a significant sediment output to the coast which has built the Haast landscape 10 kms seaward from the base of the Alps in the last 6000 years. From the air, a series of linear, forested ridges can be seen running parallel to coast. These ridges are interpreted as representing regional episodes of coastal progradation and dune formation/aggradation from the rapid transport of large post seismic sediment pulses from the mountains that have followed all known Alpine fault earthquakes to at least A.D. 1200.

A Sensors and Software pulseEKKO 100 ground penetrating radar (GPR) system with 50, 100 and 200 MHz antennae was used to test if GPR could image the subsurface stratigraphy of the Haast coastal plain. The processed and interpreted lines collected at select sites showed the progradation of the coastal sedimentary deposits. This research continues on Derald Smith’s earlier work along the Washington and Oregon coastlines, where we were able to image and age the subsurface stratigraphy and map out individual earthquake events.