2010 Honorary Lecturer, ASEG/SEG Joint Australia
Mapping active faults using 3D ground-penetrating radar and 2D and 3D high-resolution reflection seismology: Examples from New Zealand
Presented by Alan G. Green
Swiss Federal Institute of Technology (ETH)
New Zealand is located along the boundary between the Australian and Pacific tectonic plates. Although there are a large number of faults associated with this plate boundary setting, few have ruptured during the nearly 200 years of European settlement. Yet, paleoseismology provides clear evidence of relatively recent activity on many of them. Knowledge of the shallow structure and other characteristics of these faults is important for understanding the related seismic hazard and risk. Key properties of faults that produce infrequent large earthquakes are usually determined or inferred from paleoseismological investigations of geomorphology, outcrops, trenches, and boreholes. In an attempt to improve our knowledge and understanding of active faults beyond the reach of conventional paleoseismological methods (i.e., deeper than a few meters), we have acquired ground-penetrating radar data across portions of the strike-slip Wellington Fault and extensional Taupo Rift zone on New Zealand's North Island and ground-penetrating radar and high-resolution seismic reflection data across critical parts of the transpressive Alpine Fault zone (the principal plate boundary) and reverse Ostler Fault zone, and numerous reverse faults hidden beneath the young sediments that cover the northwest Canterbury Plains on the South Island. After subjecting our data to diverse processing procedures, the resultant radar, seismic cross-sections, and horizontal slices provide vivid images of the target structures. When combined with age estimates of various formations, we are able to derive strain rates for a number of the faults.