PALEOSEISMICITY OF 2016 MW 7.8 KAIKŌURA EARTHQUAKE FAULTS: WHAT HAVE WE LEARNT AND THE IMPLICATIONS FOR THE NEW ZEALAND SEISMIC HAZARD MODEL

After a very large earthquake like the Mw 7.8 14 November 2016 Kaikōura Earthquake, New Zealand, paleoseismic studies provide a means to better understand the event and past earthquake cycles in the region. The Kaikōura Earthquake was a complex earthquake with multi-fault rupture across two tectonic domains: propagating from the North Canterbury Domain (NCD) northward into the Marlborough Fault System (MFS), broadly spanning a plate boundary transition from continental collision to oblique subduction in the northern South Island. A two-year project funded by the NZ Natural Hazards Research Platform to investigate the paleoseismic records of several faults that ruptured in 2016 is now well advanced. These include the Humps, Leader, Stone Jug and Conway-Charwell faults near the earthquake epicentre, and the Hundalee and Papatea faults, SW and NE of Kaikōura, respectively. The project also seeks to assess the paleoseismic history of the Seaward section of the Hope Fault, which did not substantively rupture in the Kaikōura Earthquake. Results from published studies on other nearby faults and coastal uplift will provide additional data on the context of the Kaikōura Earthquake ruptures across this portion of the plate boundary. Relative soil and luminescence dating, and landscape data are also being collected to help inform fault slip rates. The goals of the project are to assess the Holocene paleoseismicity of this system of faults and to investigate spatio-temporal patterns between paleoseismic records on individual faults. While current data are in preparation, basic geomorphic arguments from existing slip-rate, paleoearthquake and landscape data and inferences, for example, of low- versus high-slip rate faults and short versus long recurrence interval faults involved in 2016, indicate that the specific configuration of the Kaikōura Earthquake was probably a rarity: such a complex pattern of faulting involving the NCD and MFS faults may occur only every 10-20 earthquake cycles of the most active Hope and Kekerengu faults. These observations from earthquake geology are being used to update and refine the New Zealand national seismic hazard model across the northern South Island.