A New Approach to Near-Field Probabilistic Tsunami Hazard Analysis in New Zealand, using a Physics-Based Synthetic Earthquake Catalogue.

A tsunami with devastating, wide-reaching consequences affecting New Zealand is a significant hazard that needs to be analyzed and quantified. The Puysegur Subduction Zone to the south, the Hikurangi Margin to the east, and the Tonga-Kermadec Subduction Zone to the north of New Zealand, all have the potential to generate catastrophic tsunamis, like those observed in Sumatra-Andaman in 2004 and Japan in 2011. There are also numerous crustal faults offshore New Zealand that have tsunamigenic potential. While far-field tsunamis occur frequently, here we focus on near-field tsunamis as they have the potential to be more devastating than far-field events, both in their overall size and because there may be little time between the earthquake and the arrival of the resulting tsunami. In the near-field, complexities of the tsunami source are influential on the waves impacting the coast, and it is important to incorporate these effects when assessing probabilistic tsunami hazard and risk. Previous tsunami hazard studies have started to examine this infrequent but potentially deadly hazard, using models of past tsunamis, as well as possible future events assuming the estimated magnitude ranges of the faults concerned. However, physics-based synthetic earthquake catalogues have yet to be used to assess the near-field probabilistic tsunami hazard either globally or in New Zealand. Here, we use a 30,000-year subset of a synthetic earthquake catalogue created using RSQSim (Rate and State Earthquake Simulator). From the RSQSim output, earthquake deformation models were produced for events >M7 and input into COMCOT (Cornell Multi-grid Coupled Tsunami model) to model the resulting tsunamis. A total of 2,595 tsunami simulations were used to obtain preliminary results assessing the near-field tsunami hazard posed to New Zealand's coast. Maximum wave heights at coast ranged from 0.1-28m, with 15% of the maximum wave heights at coast exceeding 5m. Analysis of the hazard over a 2,500-year return period showed that the northern and eastern coasts of the North Island could be impacted by waves up to 8-10m, with the remaining coast being impacted by waves of ~1m. When the 500-year return period is examined, expected wave heights along the east coast of the North Island drop to 1-5m, while wave heights along the remaining coast drop to ~0.5m.