Structure, late Quaternary slip rate and earthquake potential of marine reverse faults along the North Westland deformation front, New Zealand
The North Westland deformation front runs offshore for 320 km between Cape Farewell and Hokitika at a distance of 3–30 km from the coast. From marine seismic reflection profiles integrated with published sediment core and coastal uplift data, we infer late Quaternary activity on six major reverse faults. The principal structures are the Cape Foulwind, Kahurangi and Kongahu faults and the newly named Farewell, Elizabeth and Razorback faults. They include Late Cretaceous and Paleogene rift faults that were reactivated as reverse faults during the late Cenozoic. Best estimates of late Quaternary (<120 ka) slip rates for different faults range from 0.05–0.75 mm a–1. Nine potential earthquake sources are identified, including four segments of the Cape Foulwind Fault. They are of length c. 20–120 km, are potentially capable of producing moderate- to large-magnitude earthquakes of Mw 6.7–7.8 and represent a seismic risk to coastal communities. Best estimates of recurrence intervals for individual fault sources range from about 7600 years to 30,400 years, with large uncertainties in slip rates of up to –0.4, +1.0 mm a–1 reflected by the wide range of recurrence intervals.
