NSW Coast Tsunami Inundation Modelling; Final Report

This report describes earthquake-tsunami inundation hazard modelling for the entire NSW coast including Lord Howe Island, conducted by Geoscience Australia in partnership with the NSW State Emergency Services. The modelling considers tsunamis generated by earthquakes on major Pacific Ocean subduction zones, using the 2018 Australian Probabilistic Tsunami Hazard Assessment (PTHA18) to represent hypothetical tsunamis and their uncertain occurrence rates. Tsunamis generated by other mechanisms are not treated (e.g. landslides, volcanic eruptions, local earthquakes). A NSW-wide inundation model is developed to simulate tsunamis from the earthquake source through to inundation, with testing against 9 historical tsunamis observed at NSW tide gauges between 1960 and 2021. The NSW-wide inundation model is then combined with scenarios and uncertain occurrence-rates from PTHA18 to compute the hazards onshore. A Monte Carlo technique, based on the theory of importance sampling, is developed to make this computationally feasible. The hazard calculations assume the tsunami arrives during a high tide and use a relatively low onshore roughness, so will tend to be conservative. A wide range of output products depicting the rate of inundation and tsunami intensity are developed, along with inundation zones corresponding to tsunami warning categories from the Joint Australian Tsunami Warning Centre. The results can help NSW SES to develop improved NSW-wide tsunami evacuation zones for tsunamis generated by subduction earthquakes in the Pacific.