Geometry and post-seismic moment release of the faults that ruptured in the 2016 Kaikōura earthquake

Abstract:

The 2016 M7.8 Kaikōura earthquake was a complex rupture involving multiple faults and crossing two separate tectonic domains. The Kaikōura earthquake was preceded in 2013 by the Cook Strait earthquake sequence that occurred at the northern extent of the Kaikōura rupture. We constructed a 10-year-long catalog of earthquakes that occurred on the faults that ruptured in the Kaikōura earthquake to study how these faults responded to various large regional earthquakes, and how they healed following the Kaikōura rupture. We used a catalog of 2,655 aftershocks with high-quality picks and locations as templates in a long-term matched-filter search from 2009-2019. We correlated these templates with continuous seismic data from 19 stations of New Zealand’s GeoNet network. For all detected events we computed cross-correlation derived picks resulting in a catalog of more than 30,000 earthquakes. Of these, we were able to locate and compute local magnitudes for 27,148 earthquakes. Some earthquakes were not locatable due to having too few P-picks. Our catalog contains earthquakes ranging from ML 0.2 to ML 7.8. We computed time-varying magnitudes of completeness and b-values and observe systematic variations in b-value after both the Cook Strait sequence and the Kaikōura earthquake. By computing high-precision relative relocations we were able to accurately map earthquakes to the more than 20 faults that participated in the Kaikōura rupture. We compare the moment rate for individual faults with relevant geodetic observations and infer the relative proportion of seismic to aseismic moment release. From this we infer the relative healing rates of each fault, and evaluate the evolution of moment release before, during, and after the 2016 Kaikōura earthquake.