Movement on hidden faults within the Hamilton Basin

Abstract

In May last year Drs Moon and de Lange presented evidence at a School of Science Seminar for the presence of faulting within the surface deposits of the Hamilton Basin, and speculated on the presence of 4 fault zones that may have been active during the last 250,000 years. Since then, with the support of an EQC grant and funding from the Waikato Regional Council, further progress has been made on identifying the location of hidden faults. The results of shallow seismic and initial resistivity surveys indicate more than 20 faults cross the Waikato River, and combined with LiDAR data, the evidence shows that some have been active during the last 16,000 years. Data from oil, gas and coal exploration surveys of the deeper geology of the basin combined with the surface data have shown a pattern of normal listric faults extending from the basement to the surface, which explain the pattern of low hills within the basin. Sites for more intensive investigations using resistivity, GPR, and trenching have been identified, which will be used to determine the faulting history and better constrain the frequency and magnitude of earthquakes for seismic hazard assessment.