Postseismic deformation following the 2016 Kaikoura earthquake

Abstract

The M7.8 Kaikōura earthquake took place in the northeastern South Island of New Zealand on 14 November 2016. It ruptured within a complex tectonic region, where the subduction along the Hikurangi margin to the north transitions to strike-slip and collision along the Alpine Fault in the south. The earthquake ruptured over 170 km with significant slip along at least 12 major crustal faults and possibly portions of the subduction plate interface beneath the region. In 2018 the Top of the South Island GNSS network was re measures to capture the first 15 months of postseismic response of the region. In addition, several semi continuous GNSS stations were operated to augment the sparse continuous GNSS network. Postseismic deformation following the Kaikōura earthquake shows a large-scale northeast-directed movement with the most rapid deformation observed in the region of Cape Campbell (northeast tip of South Island), coinciding with a large cluster of aftershocks, decaying with time. The overall pattern of deformation is consistent with rapidly decaying slip on a low-angle source at depth, inferred to be the subduction interface beneath the Marlborough region, as well as significant afterslip on crustal faults that ruptured during the earthquake, in particular the Jordan Thrust/Kekerengu and the Needles fault. Majority of the afterslip relating to the subduction interface had decayed off by middle of 2018 with a total moment release equal to a Mw7.4 event. Sites close to the fault rupture still have significant movement suggesting ongoing afterslip on crustal faults.

Paper number: 51 (EQC 18/754)

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