Models Aid in Tsunami Planning and Preparation

The Tsunami

On 26 December 2004, a massive earthquake with a magnitude of 9.0 struck Indonesia off the west coast of northern Sumatra. In the nine hours that followed, there were 14 aftershocks with magnitudes between 5.7 and 7.3.

The earthquakes triggered powerful tsunamis with wave heights up to 10m that moved through the Indian Ocean region at over 500km/hr. The tsunami caused widespread death and injuries, displaced thousands and destroyed towns, homes, infrastructure, and livelihoods and wrecked coastal areas. The death toll was up to 273 636 with 220 153 in Indonesia alone. Australia absorbed some of the brunt of the tsunami along the coast of Western Australia. (Emergency Management Australia, 2006)

The tragic events of the Indian Ocean tsunami highlighted limitations in response and alert systems for coastal communities of Western Australia.

A partnership between scientists and decision makers

The Fire and Emergency Services Authority of Western Australia (FESA), established a partnership with Geoscience Australia to improve their knowledge of the tsunami hazard, to understand potential impacts along the coast of Western Australia and to raise community awareness.

Specific scientific questions were developed to fulfil the information requirements of emergency managers and local land-use planners.

These included:

  • what is the maximum credible tsunami or what is the likelihood of a large tsunami?
  • what is the time between the earthquake event and tsunami arrival at the location?
  • what is the extent of inundation from the tsunami impact?
  • what damage is expected?
  • what differences are expected if the tsunami arrives at the location at different tide levels?

How these questions were answered

Geoscience Australia developed numerical models of how tsunamis are generated and how they behave as they propagate from source to shore.

We also worked with data custodians in Western Australia to build models relevant to FESA. The outputs of these models were incorporated into three-dimensional visualisations and GIS-based decision making tools.

How scientific details were provided

The outputs were targeted to provide information to FESA on the specific questions that had been raised, in a way that was easy to understand by emergency managers. To address the question of credible tsunami size and likelihood, FESA was provided with a probabilistic tsunami hazard map for Western Australia. It described the minimum offshore tsunami wave height (at 100m water depth) with a given probability of exceedance. This product was combined with anecdotal evidence of community impact experiences during the Indian Ocean Tsunami in 2004 and FESA's knowledge of Western Australia communities to determine the areas that were selected for a more detailed analysis.

Based on the remaining questions, the following outputs were produced at the determined locations for a number of tsunami selected from the hazard map that were considered to be credible 'worst-case' scenario events:

  • time of tsunami arrival
  • maximum inundation maps
  • maximum flow speed maps; these can assist in understanding the threat of tsunami in both the onshore and offshore environment.

The benefits of working together

The collaborative tsunami risk assessment work between FESA and Geoscience Australia has improved community safety in Western Australia. It allows emergency managers to prioritise planning and mitigation activities for communities that are identified as being at greater risk, and provides initial estimates of tsunami impact based on a selection of representative 'worst-case' scenarios. FESA now understands how a tsunami could affect the length of the Western Australia coastline and also identify potential implications that may compromise emergency response infrastructure.

References

Attorney-General’s Department Disasters Database External site link

Topic contact: hazards@ga.gov.au Last updated: July 9, 2013