Distributed displacement on the Papatea fault from the 2016 Mw 7.8 Kaikōura earthquake and implications for hazard planning

ABSTRACT The distribution of ground motion, displacement, and secondary hazards around active faults is defined by the interaction of tectonic and site characteristics including fault kinematics. As a result of this complexity, recommendations for fault setback distances or avoidance zones are necessarily simplified. We observed distributed vertical coseismic displacement from the 2016 Mw 7.8 Kaikōura earthquake up to c. 500 m on either side of the sinistral-reverse Papatea fault. On average, c. 32% (2.13 m) of vertical displacement was measured at distances >50 m from the Papatea fault. Additionally, in places, there is strong asymmetry where displacement was accommodated over a wider area in the hanging wall of the fault, a common observation around many dip-slip fault ruptures globally. We compare the distribution of displacement around the Papatea fault to the current fault avoidance zone and find that increasing the size of the fault avoidance zone by 10 m captures 11% more area with a high gradient of vertical displacement. Given these results and similar findings for other faults globally, we recommend that existing standards for fault avoidance zones be evaluated to ensure their ongoing efficacy.