Coseismic and Early Postseismic Deformation of the 2016 Mw 7.8 Kaikōura Earthquake, New Zealand, from Continuous GPS Observations

Abstract

The Mw 7.8 Kaikōura, North Canterbury, New Zealand earthquake, which occurred on 14 November 2016 (local time), was one of the most complex continental earthquakes ever documented and among the largest instrumentally recorded events in New Zealand history. The epicenter was located at the southern termination of the Hikurangi margin, where the subducting Pacific Plate transfers into the dextral Alpine transform fault. In this work, we precisely estimate three-dimensional coseismic and postseismic displacements caused by this event from continuous global navigation satellite systems (GNSS) stations in New Zealand. The Kaikōura earthquake activated significant and diverse coseismic and postseismic deformation on a large spatial scale, located mainly in the southern part of the North Island and the northern part of the South Island. Station CMBL had the largest coseismic offsets and the most remarkable postseismic displacements. The accumulated postseismic displacements at this station reached 13, 7 and 29% of the coseismic values on the east, north and vertical components, respectively, in the first 1.5 years after the mainshock. Integrating our estimated coseismic displacements with previously published coseismic displacements, we inverted for the spatial distribution of coseismic slip and spatiotemporal evolution of postseismic slip. Our optimal coseismic model suggests that rupture occurred both on shallow crustal faults, and to some extent at the southern Hikurangi subduction interface. The GPS-inverted coseismic moment release is equivalent to an Mw 7.9 event. The postseismic slip was not only significantly extended at the subduction interface, but also appeared on the Needles fault. The cumulative moment magnitude is Mw 7.35 in the first 1.5 years after the event, and Mw 7.35, Mw 6.95 and Mw 6.80 during the periods 0.0–0.5, 0.5–1.0 and 1.0–1.5 years, respectively, indicating rapid decay of the postseismic deformation. Comparing the spatial distribution of the postseismic to the coseismic slip, although their direction is similar, the discrepancy between their location is significant: the slip located along the shallow crustal faults activated the coseismic deformation, while the slip located on the deep subduction interface controlled the postseismic deformation.