A probabilistic model for coseismic vertical displacement hazard in coastal settings

Characterizing coastal multihazards in tectonically active regions requires consideration of the possible coseismic vertical deformation. Coseismic uplift or subsidence can cause near- instantaneous meter- scale relative sea- level changes that can exacerbate or reverse the effects of ongoing global sealevel rise. In this study, we developed a probabilistic model that forecasts coseismic vertical displacement over 100 years in the Wellington Region of Aotearoa New Zealand. This model builds upon fault source, earthquake rupture, and epistemic uncertainty data from the 2022 New Zealand National 2022) to quantify the amount, direction, and likelihood of vertical displacement from both crustal fault and subduction interface earthquakes. The results of the model show that both crustal fault and subduction sources pose significant (>0.2 m) vertical displacement hazard at most sites. In general, the subduction interface contributes more to subsidence hazard, while crustal faults contribute more to uplift hazard but also contribute to subsidence hazard at specific sites. We find that fault geometry and slip extent play a significant role in forecasted uplift and subsidence hazard. Future versions of both the NZ NSHM 2022 and our probabilistic model may benefit from refinements to fault geometry and simulated earthquake ruptures. The framework developed here can be used to harness regional- scale hazard models for coastal multihazard analysis, particularly in regions with many overlapping seismic sources.