The tragic events of the Indian Ocean tsunami on 26 December 2004 highlighted the need for reliable and effective alert and response sysems for tsunami threat to Australian communities. Geoscience Australia has established collaborative partnerships with state and federal emergency management agencies to support better preparedness and to improve community awareness of tsunami risks.

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Tsunami inundation models are computationally intensive and require high resolution elevation data in the nearshore and coastal environment. In general this limits their practical application to scenario assessments at discrete communiteis. This study explores teh use of moderate resolution (250 m) bathymetry data to support computationally cheaper modelling to assess nearshore tsunami hazard. Comparison with high ersolution models using best available elevation data demonstrates that moderate resolution models are valid (errors in waveheight < 20%) at depths greater than 10m in areas of relatively low sloping, uniform shelf environments. However in steeper and more complex shelf environments they are only valid at depths of 20 m or greater. Modelled arrival times show much less sensitivity to data resolution compared with wave heights and current velocities. It is demonstrated that modelling using 250 m resoltuion data can be useful in assisting emergency managers and planners to prioritse communities for more detailed inundation modelling by reducing uncertainty surrounding the effects of shelf morphology on tsunami propagaion. However, it is not valid for modelling tsunami inundation. Further research is needed to define minimum elevation data requirements for modelling inundation and inform decisions to undertake acquisition of high quality elevaiton data collection.

Along the Aceh-Andaman subduction zone, there was no historical precedent for an event the size of the 2004 Sumatra-Andaman tsunami; therefore, neither the countries affected by the tsunami nor their neighbours were adequately prepared for the disaster. By studying the geological signatures of past tsunamis, the record may be extended by thousands of years, leading to a better understanding of tsunami frequency and magnitude. Sedimentary evidence for the 2004 Sumatra-Andaman tsunami and three predecessor great Holocene tsunamis is preserved on a beach ridge plain on Phra Thong Island, Thailand. Optically stimulated luminescence ages were obtained from tsunami-laid sediment sheets and surrounding morphostratigraphic units. Single-grain results from the 2004 sediment sheet show sizable proportions of near-zero grains, suggesting that the majority of sediment was well-bleached prior to tsunami entrainment or that the sediment was bleached during transport. However, a minimum-age model needed to be applied in order to obtain a near-zero luminescence age for the 2004 tsunami deposit as residual ages were found in a small population of grains. This demonstrates the importance of considering partial bleaching in water-transported sediments. The OSL results from the predecessor tsunami deposits and underlying tidal flat sands show good agreement with paired radiocarbon ages and constrain the average recurrence of large late Holocene tsunami on the western Thai coast to between 500 to 1000 years. This is the first large-scale application of luminescence dating to gain recurrence estimates for large Indian Ocean tsunami. These results increase confidence in the use of OSL to date tsunami-laid sediments, providing an additional tool to tsunami geologists when material for radiocarbon dating is unavailable. Through an understanding of the frequency of past tsunami, OSL dating of tsunami deposits can improve our understanding of tsunami hazard and provide a means of assessing fu

The Attorney General's Department (AGD) has supported Geoscience Australia (GA) to develop inundation models for one South Australia (SA) community with the view of building the tsunami planning and preparation capacity of the SA State Government. The community that was chosen was Victor Harbor, which also includes the townships of Port Elliot and Middleton. These locations were selected in collaboration with the SA State Emergency Service (SES), SA Department of Environment and Natural Resources (DENR) and the Australian Government based on the National Near Shore Tsunami Hazard Assessment [1] that highlighted tsunami amplification near Victor Harbor. Three tsunamigenic events were selected for modelling from the scenario database that was calculated as part of the national offshore probabilistic Probabilistic Tsunami Hazard Aassessment (PTHA) [2]. The events selected are hypothetical and are based on the current understanding of the tsunami hazard. Only earthquake sources are considered as these account for the majority of tsunami that have historically been observed in Australia. The suite of events includes three 'worst-case' or 1 in 10 000 year hazard event from three different source zones; the Puysegur Trench, Java Trench and South Sandwhich Islands Trench. These three source zones were identified from the PTHA to contribute significantly to the offshore tsunami hazard near Victor Harbor.

The historical record reveals that at least five tsunamis have impacted the Western Australian coast (1993, 1977, 1994, 2004, 2006). We document the geomorphic effects of these tsunamis through field investigations, analysis of pre and post-tsunami satellite imagery, collation of historical reports and recording of eyewitness accounts. The tsunamis had flow depths of less than 3 m, inundation distances of up to several hundred metres and a maximum recorded run-up height of 8 m a.s.l. Geomorphic effects include off-shore and near-shore erosion and extensive vegetation damage. In some cases, vegetated foredunes were severely depleted or completely removed. Gullies and scour pockets up to 1.5 m deep were eroded into topographic highs during tsunami outflow. Eroded sediments were redeposited landward as sediment sheets several centimetres thick. Isolated coral blocks and oyster-encrusted boulders were deposited over coastal dunes. However, boulder ridges were often unaffected by tsunami flow. The extent of inundation from the most recent tsunamis can be distinguished as strandlines of coral rubble and rafted vegetation. It is likely taht these features are ephemeral and seasonal coastal processes will obscure all traces of these signatures within years to decades. Recently reported evidence for Holocene palaeotsunamis on the Western Australian coast suggests significantly larger run-up and inundation than observed in the historical record. The evidence includes signatures such as chevrons dunes that have not been observed to form during historical events. We have compared the geomorphic effects of historical tsunami with reported palaeotsunami evidence from Coral Bay, Cape Range Peninsula and Port Samson. We conclude that much of the postulated palaeotsunami evidence can be explained by more common and ongoing geomorphic processes such as reef evolution, aeolian dune development and archaeological site formation.

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We present the first national probabilistic tsunami hazard assessment (PTHA) for Indonesia. This assessment considers tsunami generated from near-field earthquakes sources around Indonesia as well as regional and far-field sources, to define the tsunami hazard at the coastline. The PTHA methodology is based on the established stochastic event-based approach to probabilistic seismic hazard assessment (PSHA) and has been adapted to tsunami. The earthquake source information is primarily based on the recent Indonesian National Seismic Hazard Map and included a consensus-workshop with Indonesia's leading tsunami and earthquake scientists to finalize the seismic source models and logic trees to include epistemic uncertainty. Results are presented in the form of tsunami hazard maps showing the expected tsunami height at the coast for a given return period, and also as tsunami probability maps, showing the probability of exceeding a tsunami height of 0.5m and 3.0m at the coast. These heights define the thresholds for different tsunami warning levels in the Indonesian Tsunami Early Warning System (Ina-TEWS). The results show that for short return periods (100 years) the highest tsunami hazard is the west coast of Sumatra, the islands of Nias and Mentawai. For longer return periods (>500 years), the tsunami hazard in Eastern Indonesia (north Papua, north Sulawesi) is nearly as high as that along the Sunda Arc. A sensitivity analysis of input parameters is conducted by sampling branches of the logic tree using a monte-carlo approach to constrain the relative importance of each input parameter. These results can be used to underpin evidence-based decision making by disaster managers to prioritize tsunami mitigation such as developing detailed inundation simulations for evacuation planning.

The aim of this document is to: * outline the general process adopted by Geoscience Australia in modelling tsunami inundation for a range of projects conducted in collaboration with Australian and State Government emergency management agencies * allow discoverability of all data used to generate the products for the collaborative projects as well as internal activities.

Recent centuries provide no precedent for the 2004 Indian Ocean tsunami, either on the coasts it devastated or within its source area. The tsunami claimed nearly all of its victims on shores that had gone 200 years or more without a tsunami disaster. The associated earthquake of magnitude 9.2 defied a Sumatra-Andaman catalogue that contains no nineteenth-century or twentieth-century earthquake larger than magnitude 7.9. The tsunami and the earthquake together resulted from a fault rupture 1,500 km long that expended centuries -worth of plate convergence. Here, using sedimentary evidence for tsunamis, we identify probable precedents for the 2004 tsunami at a grassy beach-ridge plain 125 km north of Phuket. The 2004 tsunami, running 2 km across this plain, coated the ridges and intervening swales with a sheet of sand commonly 5-20 cm thick. The peaty soils of two marshy swales preserve the remains of several earlier sand sheets less than 2,800 years old. If responsible for the youngest of these pre-2004 sand sheets, the most recent full-size predecessor to the 2004 tsunami occurred about 550-700 years ago.