Probabilistic Tsunami Hazard Assessment (PTHA)

Geoscience Australia has released a new Probabilistic Tsunami Hazard Assessment - the PTHA18. The PTHA18 is freely accessible and is now available to download.

Download PTHA18 

The Probabilistic Tsunami Hazard Assessment (PTHA) models the frequency with which tsunamis of any given size occur around the entire Australian coast, due to subduction earthquakes in the Indian and Pacific Oceans. The PTHA also provides modelled tsunami data for hundreds of thousands of earthquake-tsunami scenarios around Australia.

The PTHA provides vital information to emergency managers to plan and reduce the threat of tsunami on the Australian coast, and for the insurance industry to understand the tsunami risk as an input to pricing insurance premiums.

This information provides a nationally consistent basis for understanding tsunami inundation hazards in Australia. It is important to note that the PTHA does not define the onshore tsunami impact, or the effect of tsunamis on communities. However, understanding the frequency of tsunamis offshore from the PTHA is a key input for developing local tsunami inundation models, in conjunction with additional high-resolution bathymetry and elevation data, to derive evidence-based evacuation plans to improve community safety.  High risk areas can be identified and prioritised for further analysis or to conduct scenarios to improve risk mitigation and community safety at a local, regional and national level.

Geoscience Australia provides essential evidence based information to government and emergency managers around Australia to improve our communities' ability to prepare for, mitigate against and respond to natural disasters. Contact us at hazards@ga.gov.au if you need further information.

Geoscience Australia has released a new Probabilistic Tsunami Hazard Assessment - PTHA18. The PTHA18 is freely accessible and is now available to download.

Download PTHA18 

The last PTHA was completed in 2008. The PTHA18 has been significantly updated to include advances in our understanding of earthquakes and the resulting tsunamis and to provide hazard information for all Australian offshore territories.

Compared with the previous iterations of the PTHA, PTHA18 includes more comprehensive treatment of the natural variability of earthquake size and slip. This has an important impact on the predicted tsunami wave heights and hazard.

The new methodologies have been tested using 10 years of deep ocean tsunami observational data from the Pacific Ocean to confirm they give a realistic depiction of tsunami behaviour. This crucial deep-ocean-observational dataset was unavailable for the previous assessments, as most of the tsunamis in our test-set had not even occurred in 2008.

The new PTHA methodologies also reflect advances in our understanding of how frequently large earthquakes occur, and the uncertainties in these frequencies.  We also provide outputs at many more sites, which make it easier for other modellers to use these results in local scale hazard studies, including major Australian offshore islands and territories.

Given the changes in the method and the available data, there are changes to the wave heights estimated for a given frequency (or frequency for a given wave height) since the last assessment in 2008. We also provide much more information on the uncertainties in these frequencies.

Currently the PTHA does not include non-earthquake sources that can cause a tsunami such as landslides, volcanic activity or meteorological events. Methods for assessing tsunami hazards for these sources are much less well established than for earthquakes both internationally as well as in Australia. Further research is required to underpin a nationally consistent treatment these tsunami sources.

The PTHA18 data is freely accessible and is available to use. Download now.

The PTHA18 consists of:

  • National scale annual exceedance maps derived from over 1 million possible scenarios (the 2008 assessment provided ~80,000 scenarios)
  • At each of the offshore points around Australia and its offshore territories
    • Hazard curves (stage vs exceedance probability)
    • Hazard deaggregation for scenarios and exceedance rates
    • Time series for each possible scenario at that site
    • Initial conditions of the earthquake source for each possible scenario at that site

Geoscience Australia will plan a future update the PTHA18, as we recognise the importance of incorporating best practice and evidence based science. Science and technology is constantly evolving and improving, and we need to ensure the PTHA reflects these advancements so we can ensure Australian communities are as safe as possible from tsunami events.

We welcome your feedback on the current PTHA. Send your feedback to hazards@ga.gov.au.