Probabilistic Assessment of Tsunami Hazards in New Zealand.

Abstract

New Zealand is vulnerable to tsunami from a wide variety of earthquakes and other sources, at distances which range from immediately adjacent to the coast to the other side of the Pacific Ocean. Among those close to New Zealand, earthquakes on the Kermadec, Hikurangi and Puysegur subduction zones all pose significant threats, as do many crustal faults as was demonstrated in the Kaikoura earthquake and tsunami in 2016.

Appropriate mitigation of these hazards is greatly assisted by quantitative probabilistic assessment of the tsunami hazard. For this purpose a National Tsunami Hazard Model has been developed, and continues to evolve, along with procedures to convert estimates of tsunami hazard at the coast into probabilistic tsunami inundation maps. Currently, the hazard model processes tsunami heights using a synthetic catalogue of source events generated according to magnitude-frequency distributions assigned to each source.

Here we present the development of an alternative approach to the estimation of tsunami hazard from local tsunami sources based on generating synthetic catalogues using a physics-based earthquake simulator (RSQSim - Rate and State Earthquake Simulator). This produces a set of complex rupture scenarios, allowing for interactions between faults, including multiple-fault ruptures, and generated in accord with physical constraints on slip rates. We demonstrate how this approach can be used to evaluate tsunami hazard at the coast from local sources, and how it may be used to evaluate inundation hazards, in both cases making use of COMCOT (the Cornell Multi-grid Coupled Tsunami model).