Breaking a Subduction-Termination from Top to Bottom: The Large 2016 Kaikōura Earthquake
Abstract
Subduction systems globally terminate, allowing plate-motion to be transferred from the oceanic megathrust onto continental transform faults. The mechanism of this kinematic transition over earthquake timescales is, however, poorly understood due to lack of relevant data. Here, we zoom into the 2016 Mw7.8 Kaikōura Earthquake in New Zealand, the first large instrumentally-recorded earthquake across a subduction-termination, to investigate this mechanism in detail. We find that the Kaikōura Earthquake, unlike standard subduction earthquakes globally, involved a predominance ( 80%) of coseismic-slip on upper-plate faults and minor triggered-slip onto the underlying oceanic subduction-thrust. In the months following the earthquake, the subduction-thrust accommodated most of the earthquake's afterslip down-dip of its co-seismic rupture zone. This top-down strain-release mechanism is in accord with local geological, geodetic and historical seismicity data which suggest that the bulk of plate-convergence (>75%) is accommodated in the upper-plate. We suggest, therefore, that this alternative strain-release mechanism, which is distinct from standard plate-boundary earthquakes, is characteristic of subduction-terminations and results in the majority of seismic/tsunami hazard being on steep near-surface faults.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T41C..02M
- Keywords:
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- 1209 Tectonic deformation;
- GEODESY AND GRAVITYDE: 4430 Complex systems;
- NONLINEAR GEOPHYSICSDE: 8150 Plate boundary: general;
- TECTONOPHYSICSDE: 8158 Plate motions: present and recent;
- TECTONOPHYSICS