A selection of images and short animations explaining key aspects of the 2004 Indian Ocean/ Sumatra tsunami, revised and issued for release to the media and other interested organisations on the tenth anniversary of the disaster. This selection updates existing resources previously released by Geoscience Australia.

The development of the Indian Ocean Tsunami Warning and mitigation System (IOTWS) has occurred rapidly over the past few years and there are now a number of centres that perform tsunami modelling within the Indian Ocean, both for risk assessment and for the provision of forecasts and warnings. The aim of this work is to determine to what extent event-specific tsunami forecasts from different numerical forecast systems differ. This will have implications for the inter-operability of the IOTWS. Forecasts from eight separate tsunami forecast systems are considered. Eight hypothetical earthquake scenarios within the Indian Ocean and ten output points at a range of depths were defined. Each forecast centre provided, where possible, time series of sea-level elevation for each of the scenarios at each location. Comparison of the resulting time series shows that the main details of the tsunami forecast, such as arrival times and characteristics of the leading waves are similar. However, there is considerable variability in the value of the maximum amplitude (hmax) for each event and on average, the standard deviation of hmax is approximately 70% of the mean. This variability is likely due to differences in the implementations of the forecast systems, such as different numerical models, specification of initial conditions, bathymetry datasets, etc. The results suggest that it is possible that tsunami forecasts and advisories from different centres for a particular event may conflict with each other. This represents the range of uncertainty that exists in the real-time situation.

The Mw=7.8 earthquake of 15 July, 2009 occurred along a section of the subduction zone south of New Zealand, where the Puysegur Block subducts beneath the Pacific Plate. The orientation of this subduction zone suggests that tsunamis generated along it pose a significant threat to the southeast coast of Australia, but since it had not experienced megathrust rupture until the 15 July event, the question of whether it was accumulating strain energy whose release could result in a large tsunami was open. We have used seismic, tsunami, geodetic and SAR data to study this earthquake and find that it involved primarily thrust motion on a fault plane dipping east at a shallow angle, consistent with expectations for a megathrust earthquake. The ability to use multiple data types to study this earthquake lead to improved ability to resolve parameters such as rupture velocity that are often difficult to constrain with seismic data alone. Seismic array data agree with rupture modelling of broadband waveforms in their prediction of a bilateral component to the earthquake rupture. Also, a tsunami of about 10 cm peak-to-peak amplitude was recorded by two tsunameter buoys in the Tasman Sea west of the epicenter, and we find that the tsunami travel times indicated by these data suggest the earthquake was characterised by a low rupture velocity of around 1 km/s. We will also present comparisons against GPS and InSAR data that further constrain parameters of the rupture. Finally, we will discuss the potential for earthquake activity further south along the Puysegur Trench, which poses a tsunami threat particularly to the eastern coast of Tasmania.

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

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The major tsunamis of the last few years have dramatically raised awareness of the possibility of potentially damaging tsunami reaching the shores of Australia and to the other countries in the region. Here we present three probabilistic hazard assessments for tsunami generated by megathrust earthquakes in the Indian, Pacific and southern Atlantic Oceans. One of the assessments was done for Australia, one covered the island nations in the Southwest Pacific and one was for all the countries surrounding the Indian Ocean Basin

The high risk of natural disasters in developing nations has considerable implications for international aid programs. Natural disasters can significantly compromise development progress and reduce the effectiveness of aid investments. In order to better understand the threat that natural disasters may pose to its development aid program, AusAID commissioned Geoscience Australia to conduct a broad natural hazard risk assessment of the Asia-Pacific region. The assessment included earthquake, volcanic eruption, tsunami, cyclone, flood, landslide and wildfire hazards, with particular attention given to countries the Australian Government considered to be of high priority to its development aid program. Geoscience Australia's preliminary natural hazard risk assessment of the region aimed to help AusAID identify countries and areas at high risk from one or more natural hazards. The frequency of a range of sudden-onset natural hazards was estimated and, allowing for data constraints, an evaluation was made of potential disaster impact. Extra emphasis was placed on relatively rare but high-impact events, such as the December 2004 tsunami, which might not be well documented in the historical record. While a detailed risk assessment was well beyond the scope of this study, it was recognized that some understanding of the potential impact of natural disasters could be achieved through the simple means of developing appropriate overlays of population and hazard. For example, given an estimate of the frequency and magnitude (VEI) at which volcanic eruptions in a certain region occur, the populations impacted could be roughly estimated by considering the average population close enough to a volcano to receive a significant impact from ash fall.

Keynote presentation to cover * the background to tsunami modelling in Australia * what the modelling showed * why the modelling is important to emergency managers * the importance of partnerships * future challenges

Following the tragic events of the Indian Ocean tsunami on 26 December 2004 it became obvious there were shortcomings in the response and alert systems for the threat of tsunami to Western Australia's (WA) coastal communities. The relative risk of a tsunami event to the towns, remote indigenous communities, and infrastructure for the oil, gas and mining industries was not clearly understood in 2004. Consequently, no current detailed response plans for a tsunami event in WA coastal areas existed. The Boxing Day event affected the WA coastline from Bremer Bay on the south coast, to areas north of Exmouth on the north-west coast, with a number of people requiring rescue from abnormally strong currents and rips. There were also reports of personal belongings at some beaches inundated by wave activity. More than 30 cm of water flowed down a coast-side road in Geraldton on the mid-west coast, and Geordie Bay at Rottnest Island (19 km of the coast of Fremantle) experienced five 'tides' in three hours, resulting in boats hitting the ocean bed a number of times. The vivid images of the devastation caused by the 2004 event across a wide geographical area changed the perception of tsunami and achieved an appreciation of the potential enormity of impact from this low frequency but high consequence natural hazard. With WA's proximity to the Sunda Arc, which is widely recognised as a high probability area for intra-plate earthquakes, the need to develop a better understanding of tsunami risk and model the potential social and economic impacts on communities and critical infrastructure along the Western Australian coast, became a high priority. Under WA's emergency management arrangements, the Fire and Emergency Services Authority (FESA) has responsibility for ensuring effective emergency management is in place for tsunami events across the PPRR framework.

In response to the devastating Indian Ocean Tsunami (IOT) that occurred on the 26th of December 2004, Geoscience Australia developed a framework for tsunami risk modelling. The outputs from this methodology have been used by emergency managers throughout Australia. For GA to be confident in the information that is being provided to the various stakeholders' validation of the model and methodology is required. While the huge loss of life from the tsunami was tragic, the IOT did provide a unique opportunity to record the impact of a tsunami on the coast of Western Australia. Eight months after the tsunami a post-disaster survey was conducted at various locations along the coast and maximum run-up was determined from direct observational evidence or anecdotal accounts. In addition tide gauges located in harbours along the coast also recorded the tsunami and provide a timeseries account of the wave heights and frequency of the event. This study employs the tsunami hazard modelling methodology used by Geoscience Australia (GA) to simulate a tsunami scenario based on the source parameters obtained from the Boxing Day earthquake of 2004. The model results are compared to observational evidence from satellite altimetry, inundation surveys and tide gauge data for Geraldton, a community on the Western Australian coast. Results show that the tsunami model provides good estimates of the wave height in deep water and also run up in inundated areas and it importantly matches the timing of the first wave arrivals. However the model fails to reproduce the timeseries data of wave heights observed by a tide gauge in Geraldton harbour. The model does however replicate the occurrence of a late arriving (16 hrs after first arrival) wave packet of high frequency waves. This observation is encouraging since this particular wave packet has been noted elsewhere in the Indian Ocean and caused havoc in harbours many hours after the initial waves had arrived and dissipated.