Geological structure informs rupture propagation and surface rupture complexity during the 2016 Kaik?ura earthquake, New Zealand: insights for future large earthquake hazard

Abstract

: We summarise the geological setting of complex surface rupture of the 2016 Mw 7.8 Kaikōura earthquake in the Marlborough Tectonic Domain of New Zealand. The event was complex both seismologically and geologically but not totally dissimilar to other large historical events globally. The earthquake occurred in the comprehensively imbricated, steeply-dipping Pahau Terrane crust that exhibits numerous tectonic overprints with diverse faulting styles. The current strike slip faults of the Marlborough Fault System are immature in their structural development and occupy, at least in part, inherited faults of earlier deformation phases. Several of the faults that ruptured in 2016 may connect at seismogenic depths. A listric fault geometry is likely for many of the faults that ruptured in 2016. This interpretation is supported by crustal seismic mapping identifying listric geometries for other large faults within the region. Examination of other historic surface rupturing earthquakes in the Marlborough Tectonic Domain and globally show some complexity but not to the same level of multifault rupture as in 2016. We conclude that multifault ruptures may be enhanced in the Kaikōura region where the Australian plate crust is thinner than farther west and the plate boundary deformation, at rates of >20 mm year –1 , transfers between closely-spaced faults with acute changes in surface geometry and with diverse rupture characteristics. The trend in seismic hazard assessment since 2016 is to include multifault ruptures universally, but this would be inconsistent with historic events in the Marlborough Tectonic Domain. Consideration of geological structure and history may usefully be incorporated into seismic hazard methodology to evaluate when and where multifault source models are indeed appropriate.