Earthquake Scenario Selection for Tsunami Inundation Hazard Assessment: Guidelines on using the 2018 Probabilistic Tsunami Hazard Assessment in the Pacific

Abstract

Tsunamis can be a dangerous and destructive natural hazard. Pacific nations are particularly exposed and tsunami risk is a serious concern. Tsunami and disaster risk reduction is recognised as a cornerstone of sustainable development by the Australian Department of Foreign Affairs and Trade (DFAT) who co-funded this work with the World Bank. This document provides guidance on how to assess earthquake-generated tsunami inundation hazards for Pacific Island nations. The methods described leverage the 2018 Probabilistic Tsunami Hazard Assessment (PTHA18) developed by Geoscience Australia. The PTHA18 provides a global database of modelled earthquake-tsunami scenarios and frequencies that is shared under a Creative Commons License for the benefit of the global community. When used with tsunami inundation models, the PTHA18 can be used to assess the inundation hazard. The PTHA18 and these guidelines only consider tsunamis generated by undersea earthquakes, which cause the majority of tsunamis worldwide. Other geophysical processes such as landslides and volcanoes can also generate hazardous tsunamis, but require quite different modelling techniques beyond the scope of this work. The intended audience for these guidelines includes scientists, academic institutions, and technical specialists responsible for assessing the tsunami hazard in the Pacific. Concepts are explained within the text and additional detail is provided in both the appendices and through links to online tutorials. We also encourage familiarisation with the relevant research. Two methods are presented to assess the tsunami inundation hazard for a given location: 1. Scenario-based: This is a very flexible method that involves the selection of a subset of tsunami scenarios from the PTHA18. A variety of criteria can be used to guide the scenario selection, including the tsunami frequency estimates in the PTHA18. This method is less computationally intensive than the Monte Carlo sampling method. 2. Monte Carlo sampling: This method allows for rigorous translation of the tsunami frequencies and uncertainties in the PTHA18 to the onshore site of interest. It is less subjective than the scenario-based approach, and can give a more comprehensive representation of the hazard uncertainties implied by PTHA18. This method requires the modelling of hundreds of scenarios and can be very computationally demanding. Both of these methods are widely applicable to the Pacific region, and case studies of tsunami hazard assessments from Pacific Island nations are included. We acknowledge that research into other methodologies is ongoing (e.g. Chock, 2016) and we expect the standards of best practice to evolve with advances in technology and science. We further encourage the open licensing of datasets used to support collective efforts towards community safety in the region.