Jaime Delano, Andrew Howell, Kate Clark, Tim Stahl, Chris Rollins, Hannu Seebeck, Jack McGrath

Characterizing coastal multi-hazards in tectonically active regions requires considering 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 sea-level 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 repurposes fault source, earthquake rupture, and epistemic uncertainty data from the New Zealand National Seismic Hazard Model (NZ NSHM 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 plays a significant role in forecasted uplift and subsidence hazard; future versions of both the NZ NSHM 2022 and this 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 multi-hazard analysis, particularly in regions with many overlapping seismic sources.