This report describes the 2018 Probabilistic Tsunami Hazard Assessment for Australia (henceforth PTHA18). The PTHA18 estimates the frequency with which tsunamis of any given size occur in deep waters around the Australian coastline. To do this it simulates hundreds of thousands of possible tsunami scenarios from key earthquake sources in the Pacific and Indian Oceans, and models the frequency with which these occur. To justify the PTHA18 methodologies a significant fraction of the report is devoted to testing the tsunami scenarios against historical observations, and comparing the modelled earthquake rates against alternative estimates. Although these test provide significant justification for the PTHA18 results, there remain large uncertainties in “how often” tsunamis occur at many sites. This is due to fundamental limitations in present-day scientific knowledge of how often large earthquakes occur.

This Geoscience Australia Record contains technical data and input files that, when used with the Global Earthquake Model’s (GEM’s) OpenQuake-engine probabilistic seismic hazard analysis software (Pagani et al., 2014), will enable end users to explore and reproduce the 2018 National Seismic Hazard Assessment (NSHA18) of Australia (Allen et al., 2018a). This report describes the NSHA18 input data only and does not discuss the scientific rationale behind the model development. These details are provided in Allen et al. (2018a) and references therein.

Tsunamis are relatively rare in Australia and emergency managers rely on the sharing of information at national forums to assist them to manage the tsunami risk in their own jurisdiction. Emergency managers responsible for tsunami risk management across Australia recently identified the need for national consistency in tsunami hazard information and as a result, a project was initiated to develop national guidelines for tsunami hazard modelling. This presentation will outline the approach adopted to develop these guidelines, focusing on the collaboration of end-users and tsunami modelling practitioners. The guidelines were explicitly designed to facilitate appropriate standards of rigour and improved national consistency in tsunami hazard modelling, without dictating software choices or otherwise suppressing innovative practices (which will evolve over time in concert with improvements in tsunami science). The guidelines focused instead on providing guidance in designing a study suitable for the use-case being considered. Core issues included the treatment of uncertainties in tsunami generation, propagation and inundation modelling, and scenario return periods. Whilst the emergency managers proposed the development of these guidelines, the target audience included any agency would could commission tsunami hazard studies for a particular purpose (e.g. coastal infrastructure owners, insurance), as well as the tsunami modellers conducting such studies. The guidelines will also become a valuable resource for the tsunami modelling community. In many situations, tsunami modelling is conducted by coastal hazard modellers who may not have current understanding of Australia’s tsunami hazard.

The 2018 Probabilistic Tsunami Hazard Assessmetn (PTHA18) outputs are can be accessed following the README instructions here: https://github.com/GeoscienceAustralia/ptha/tree/master/ptha_access

Numerical codes for probabilistic tsunami hazard assessment, available for download in github: https://github.com/GeoscienceAustralia/ptha

PTHA18 estimates the frequency with which tsunamis of any given size occur in deep waters around the Australian coastline. To do this it simulates hundreds of thousands of possible tsunami scenarios from key earthquake sources in the Pacific and Indian Oceans, and models the frequency with which these occur.