Understanding non-elastic effects in accretionary wedges using the Kaikoura earthquake: Investigating a major potential tsunami hazarard

When an earthquake occurs, elastic energy that has been stored in rocks that have been undergoing gradual distributed deformation is released suddenly along one or more planar discontinuities known as faults. By definition faults are non-elastic, as they relieve stored elastic energy, localising damage. However, where the rocks on either side of the fault are not significantly damaged, horizontal and vertical coseismic surface movement determined from field observations, InSAR, or other techniques may be used to construct an elastic half-space model that predicts the direction and magnitude of slip at a full range of depths on the fault plane. However, in some cases these models are compromised by non-elastic behaviour of rock bodies, leading to inconsistent surface rupture results and likely significant errors in slip-at-depth estimates. Non-elastic effects in this sense may be caused by movements on subsidiary faults, folding of rock strata, change of shape of soft, deformable zones, and viscoelastic deformation of the ductile lower crust; these effects are witnessed most evidently by post-seismic movements, commonly observed in the days to months after large earthquakes, and also by aftershock earthquake events that are located off the main fault. Improving our understanding of these effects is important, as the relationships between fault slip and earthquake magnitude forms a significant component of seismic hazard analysis. In this specific case, improving our model of slip along all faults involved in the 2016 Kaikoura earthquake will enhance models of crustal stress accumulations in this region, key to developing improved short and medium term earthquake forecasts and seismic hazard analysis. Further, developing an improved insight of the mechanisms that pertain in accretionary prisms located above subduction interfaces is highly significant for understanding tsunami generation, both in New Zealand and elsewhere. We have an opportunity to take advantage of recent significant conceptual and processing developments in the field of 3-D strain modelling made at the Earth Observatory of Singapore (EOS), an Institute of Nanyang Technical University, Singapore. Combining geophysical and mathematical skills, the group headed by Asst. Prof. Sylvain Barbot has developed an approach to modelling complexity in crustal deformation that is significantly more computationally efficient than previous numerical approaches. This represents an unprecedented opportunity to take advantage of the very large and complex Kaikoura earthquake of 14th November 2016 to study in detail how accretionary wedges adjust their shapes as the position of tectonic plates, and the different components of the continental-ocean margin, evolve through time. The high quality data that we have collected as part of our on-going NERC urgency award (NE/P021425/1) makes this an attractive research collaboration for the EOS research team, while for us, it significantly extends the scope of our project, providing the opportunity to leverage our results to develop significant discoveries in the fundamental behaviour of fault movement, earthquake generation and landscape evolution. This will add significant value to the existing NERC-funded project, and form the basis for longer term research collaboration, whilst delivering important new information for seismic hazard analysis, helping to build resilience against natural hazards.