Surface Rupture Of Multiple Crustal Faults In The 2016 M-W 7.8 Kaikoura, New Zealand, Earthquake

Multiple (>20) crustal faults ruptured to the ground surface and seafloor in the 14 November 2016 M-w 7.8 Kaikoura earthquake, and many have been documented in detail, providing an opportunity to understand the factors controlling multifault ruptures, including the role of the subduction interface. We present a summary of the surface ruptures, as well as previous knowledge including paleoseismic data, and use these data and a 3D geological model to calculate cumulative geological moment magnitudes (M-w(G)) and seismic moments for comparison with those from geophysical datasets. The earthquake ruptured faults with a wide range of orientations, sense of movement, slip rates, and recurrence intervals, and crossed a tectonic domain boundary, the Hope fault. The maximum net surface displacement was similar to 12 m on the Kekerengu and the Papatea faults, and average displacements for the major faults were 0.7-1.5 m south of the Hope fault, and 5.5-6.4 m to the north. M-w(G) using two different methods are M-w(G) 7.7(-0.2)(+0.3) and the seismic moment is 33%-67% of geophysical datasets. However, these are minimum values and a best estimate M-w(G) incorporating probable larger slip at depth, a 20 km seismogenic depth, and likely listric geometry is M-w(G) 7.8 +/- 0.2, suggests <= 32% of the moment may be attributed to slip on the subduction interface and/or a midcrustal detachment. Likely factors contributing to multifault rupture in the Kaikoura earthquake include (1) the presence of the subduction interface, (2) physical linkages between faults, (3) rupture of geologically immature faults in the south, and (4) inherited geological structure. The estimated recurrence interval for the Kaikoura earthquake is >= 5, 000-10,000 yrs, and so it is a relatively rare event. Nevertheless, these findings support the need for continued advances in seismic hazard modeling to ensure that they incorporate multifault ruptures that cross tectonic domain boundaries.