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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.

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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 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.

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.

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 2004 Sumatra-Andaman Earthquake and Indian Ocean Tsunami shattered the paradigm that guided our understanding of giant subduction zone earthquakes: that massive, magnitude 9+ earthquakes occur only in subduction zones experiencing rapid subduction of young oceanic lithosphere. Although this paradigm forms the basis of discussion of subduction zone earthquakes in earth sciences textbooks, the 2004 earthquake was the final blow in an accumulating body of evidence showing that it was simply an artefact of a sparse and biased dataset (Okal, 2008). This has led to the realization that the only factor known to limit the size of megathrust earthquakes is subduction zone length. This new appreciation of subduction zone earthquake potential has important implications for the southern Asia-Pacific region. This region is transected by many thousands of km of active subduction, including the Tonga-Kermadec, Sunda Arc, and the Makran Subduction zone along the northern margin of the Arabian Sea. Judging from length alone, all of these subduction zones are capable of hosting megathrust earthquakes of magnitude greater than 8.5, and most could host earthquakes as large as the 2004 Sumatra-Andaman earthquake (Mw=9.3). Such events are without historical precedent for many countries bordering the Indian and Pacific Oceans, many of which have large coastal populations immediately proximate to subduction zones. This talk will summarize the current state of knowledge, and lack thereof, of the tsunami hazard in the southern Asia-Pacific region. I will show that 'worst case' scenarios threaten many lives in large coastal communities, but that in most cases the uncertainty in these scenarios is close to 100%. Is the tsunami risk in SE Asia and the SW Pacific really this dire as the worst-case scenarios predict? The answer to this question relies on our ability to extend the record of tsunamis beyond the historical time frame using paleotsunami research.

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.