Palaeoearthquake histories across a normal fault system in the southwest Taranaki Peninsula, New Zealand

Abstract

The tectonic origin, palaeoearthquake histories and slip rates during the last c. 26 ka have been examined for six normal faults (referred to here as the Rahotu, Oaonui, Kina, Ihaia, Kiri and Pihama faults) within the Taranaki Rift, New Zealand. A minimum of 13 ground-surface rupturing palaeoearthquakes have been recognised on four of the faults using analysis of displaced late Quaternary stratigraphy and landforms. These data, in combination with 21 new radiocarbon dates, constrain the timing, slip and magnitude of each earthquake. The faults have low throw rates (c. 0.1-0.8 mm a-1) and appear to be buried near the Mt Taranaki volcanic cone. Recurrence intervals between earthquakes on individual faults typically range from 3-10 ka (average c. 6 ka), with single event displacements ranging from c. 0.3-1.5 m (average c. 0.7 m) and corresponding moment magnitudes incorporating estimated fault rupture areas of Mw 6.1-6.6. Recurrence intervals and single event displacements typically vary by up to a factor of three on individual faults, with only the Oaonui Fault providing any evidence for nearcharacteristic slip (of about 0.5 m) during successive earthquakes. The timing and slip of earthquakes on individual faults appears to have been interdependent, with each event decreasing the likelihood of additional earthquakes across the system. © 2010 The Royal Society of New Zealand.