Effects of rupture complexity on local tsunami inundation: Implications for probabilistic tsunami hazard assessment by example

We investigated the influence of earthquake source complexity on the extent of inundation caused by the resulting tsunami. We simulated 100 scenarios with collocated sources of variable slip on the Hikurangi subduction interface in the vicinity of Hawke's Bay and Poverty Bay in New Zealand and investigated the tsunami effects on the cities of Napier and Gisborne. Rupture complexity was found to have a first-order effect on flow depth and inundation extent for local tsunami sources. The position of individual asperities in the slip distribution on the rupture interface control to some extent how severe inundation will be. However, predicting inundation extent in detail from investigating the distribution of slip on the rupture interface proves difficult. Assuming uniform slip on the rupture interface in tsunami models can underestimate the potential impact and extent of inundation. For example, simulation of an M-w 8.7 to M-w 8.8 earthquake with uniform slip reproduced the area that could potentially be inundated by equivalent nonuniform slip events of M-w 8.4. Deaggregation, to establish the contribution of different sources with different slip distributions to the probabilistic hazard, cannot be performed based on magnitude considerations alone. We propose two predictors for inundation severity based on the offshore tsunami wavefield using the linear wave equations in an attempt to keep costly simulations of full inundation to a minimum.