Illuminating the Pre-, Co-, and Post-Seismic Phases of the 2016 M7.8 Kaikoura Earthquake With 10 Years of Seismicity

The 2016 M7.8 Kaikoura earthquake is one of the most complex earthquakes in recorded history, with significant rupture of at least 21 crustal faults. Using a matched-filter detection routine, precise cross-correlation pick corrections, and accurate location and relocation techniques, we construct a catalog of 33,328 earthquakes between 2009 and 2020 on and adjacent to the faults that ruptured in the Kaikoura earthquake. We also compute focal mechanisms for 1,755 of the earthquakes used as templates. Using this catalog we reassess the rupture pathway of the Kaikoura earthquake. In particular we show that: (a) the earthquake nucleated on the Humps Fault; (b) there is a likely linking offshore reverse fault between the southern fault system and the Papatea Fault, which could explain the anomalously high slip on the Papatea Fault; (c) the faults that ruptured in the 2013 Cook Strait sequence were reactivated by the Kaikoura earthquake and may have played a role in the termination of the earthquake; and (d) no seismicity on an underlying subduction interface is observed beneath almost all of the ruptured region suggesting that if deformation did occur on the plate interface then it occurred aseismically and did not play a significant role in generating co-seismic ground motion.