Abstract
The 2016 moment magnitude (Mw) 7.8 Kaikoura earthquake demonstrated that multiple fault segments can undergo rupture during a single seismic event. Here, we employ Global Positioning System (GPS) observations and geodetic modeling methods to create detailed images of coseismic slip and postseismic afterslip associated with the Kaikoura earthquake. Our optimal geodetic coseismic model suggests that rupture not only occurred on shallow crustal faults but also to some extent at the Hikurangi subduction interface. The GPS-inverted moment release during the earthquake is equivalent to a Mw 7.9 event. The near-field postseismic deformation is mainly derived from right-lateral strike-slip motions on shallow crustal faults. The afterslip did not only significantly extend northeastward on the Needles fault but also appeared at the plate interface, slowly releasing energy over the past 6 months, equivalent to a Mw 7.3 earthquake. Coulomb stress changes induced by coseismic deformation exhibit complex patterns and diversity at different depths, undoubtedly reflecting multi-fault rupture complexity associated with the earthquake. The Coulomb stress can reach several MPa during coseismic deformation, which can explain the trigger mechanisms of afterslip in two high-slip regions and the majority of aftershocks. Based on the deformation characteristics of the Kaikoura earthquake, interseismic plate coverage, and historical earthquakes, we conclude that Wellington is under higher seismic threat after the earthquake and great attention should be paid to potential large earthquake disasters in the near future.
Highlights
On November 13, 2016, a destructive earthquake with Mw 7.8 struck the Kaikoura region, South Island, New Zealand, which triggered large-scale crustal deformation (Hamling et al 2017), thousands of landslides (Gorum and Yildirim 2017), and a widespread tsunami (Power et al 2017)
We used Global Positioning System (GPS) measurements to establish coseismic and postseismic models, investigated Coulomb stress changes, and assessed the seismic hazard associated with the 2016 Mw 7.8 Kaikoura earthquake
Postseismic deformation shows a logarithmic behavior in time and decays slowly in space, with the motion tendency being consistent with coseismic patterns
Summary
On November 13, 2016, a destructive earthquake with Mw 7.8 struck the Kaikoura region, South Island, New Zealand, which triggered large-scale crustal deformation (Hamling et al 2017), thousands of landslides (Gorum and Yildirim 2017), and a widespread tsunami (Power et al 2017). We only consider GPS observations from GeoNet to construct seismic geodetic inversion models and investigate fault movements during the coseismic and postseismic phases of the Kaikoura earthquake. Investigation of the static coseismic deformation suggests that the Kaikoura earthquake mainly destroyed two distinct tectonic domains, showing right-lateral oblique-slip movements in the North Canterbury region and dominantly rightlateral strike-slip motions in the Marlborough fault system (Fig. 4a). Based on our best fits (Fig. 6b and Additional file 1: Figure S2), the first-order patterns of the afterslip show more dextral strike-slip movements on the five crustal faults and visible thrusting motion at the Hikurangi subduction interface. The near-field postseismic deformation is mainly derived from the significant right-lateral strike-slip motions on the shallow crustal faults, whereas the deep-seated afterslip at the Hikurangi subduction interface mostly contributes to mid- and far-field surface deformation. The 6-month afterslip has a cumulative geodetic moment of 1.19 × 1020 Nm, corresponding to 14% of the coseismic moment release and Mw 7.3, assuming a uniform crustal shear modulus of 30 GPa
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