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New Insights Into How the 2016 Mw7.8 Kaikōura (New Zealand) Multi-Fault Earthquake Nucleated, Propagated and Arrested From a Dense 10-Year Earthquake Catalog.

Session: Exploring Rupture Dynamics and Seismic Wave Propagation Along Complex Fault Systems [Poster]

Type: Poster

Date: 4/19/2021

Presentation Time: 03:45 PM Pacific

Description: 

The 2016 M_W7.8 Kaikōura earthquake in northern South Island, New Zealand, was a complex rupture involving at least 13 different faults and spanning two separate tectonic domains. Despite many studies on this earthquake, several fundamental questions remain, including: (1) what structure did the earthquake nucleate on?; (2) how did the rupture propagate through a complex array of faults with large apparent step-overs?; (3) how did the Papatea Fault accommodate significant slip despite its short length?; (4) why did the earthquake arrest at Cook Strait?; (5) what was the role of the underlying subduction interface co-seismically and post-seismically?

To answer these questions we have constructed a 10-year long catalog of well-located earthquakes on and around the faults that ruptured in the Kaikōura earthquake. We used well-constrained Kaikōura aftershocks as templates in a matched-filter search between 2009 and 2019. We were able to compute local magnitudes and precise relocations for 25,877 earthquakes and focal mechanisms for 1,755 template events, providing an unprecedented view of the pre- and post-seismic seismic slip around the Kaikōura earthquake.

Our earthquake catalog highlights the continuity of faults throughout the ruptured region, including offshore thrust faulting linking the southern and northern domains. We also observe an inland continuation of the Papatea Fault, and provide a new interpretation of the large-slip on this fault as the corner at the edge of a thrust block. We demonstrate that the Kaikōura earthquake nucleated on the Humps Fault, and that previous locations were erroneous mostly due to incorrect velocity models. We also show that the faults that ruptured in the 2013 and 2014 Cook Strait earthquake sequence were re-ruptured by the Kaikōura earthquake and the stress-drop from these earthquakes may have played a role in the Kaikōura arrest. Finally, our catalog contains no subduction zone earthquakes beneath the vast majority of the ruptured faults, suggesting that if the interface did slip either co- or post-seismically, it was likely aseismic.

Presenting Author: Calum J. Chamberlain

Student Presenter: No

Authors