Abstract

During the 2016 Mw 7.8 Kaikoura earthquake, the Kekerengu fault ruptured the ground surface and produced a maximum of 12  m of net displacement (dextral slip with minor reverse slip), one of the largest five coseismic surface‐rupture displacements so far observed globally. This study presents the first combined onshore to offshore dataset of coseismic ground‐surface and vertical seabed displacements along a near‐continuous 83‐km‐long strike‐slip dominated earthquake surface rupture of large slip magnitude. Onshore on the Kekerengu, Jordan thrust, Upper Kowhai, and Manakau faults, we measured the displacement of 117 cultural and natural markers in the field and using airborne light detection and ranging (lidar) data. Offshore on the dextral‐reverse Needles fault, multibeam bathymetric and high‐resolution seismic reflection data image a throw of the seabed of up to 3.5±0.2  m. Mean net slip on the total 83  km rupture was 5.5±1  m, this is an unusually large mean slip for the rupture length compared to global strike‐slip surface ruptures. Surveyed linear features that extend across the entire surface‐rupture zone show that it varies in width from 13 to 122 m. These cultural features also reveal the across‐strike distribution of lateral displacement, 80% of which is, on average, concentrated within the central 43% of the rupture zone. Combining the near‐field measurements of fault offset with published, far‐field Interferometric Synthetic Aperture Radar (InSAR), continuous Global Positioning System (GPS), and coastal deformation data suggests partitioning of oblique plate convergence, with a significant portion of coseismic contractional deformation (and uplift) being accommodated off‐fault in the hanging‐wall crust to the northwest of the main rupturing faults.

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