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.

The report summarises earthquake and tsunami information worldwide in 1997 but with a focus on Australia for use by scientists, engineers and the public. Maps of the seismicity are presented on a state-by-state basis and isoseismal maps are included for the significant earthquakes.

The tragic events of the 2004 Indian Ocean Tsunami highlighted the real threat posed by tsunamis to coastal communities worldwide. With subduction zones to the north and east of Australia, tsunamis pose a real threat to the Australian coast. Geoscience Australia has been developing methodologies for quantifying the severity of tsunami impacts to assist emergency management authorities in planning for this threat. Tsunami inundation modelling is computationally intensive and is often restricted to a small number of discrete communities. As a result, communities must be prioritised for this detailed modelling. One method for prioritisation is the Probabilistic Tsunami Hazard Assessment (PTHA) of Australia. In the PTHA, tsunamis were modelled from all likely earthquake sources across the deep ocean using a computationally faster linear solution and coarser model domain. Results are considered valid only to the 100 m depth contour, where we calculate return periods for tsunami wave height around Australia and generate a database of tsunami wave forms. However, tsunami waves are shaped considerably by the bathymetry between the 100 m depth contour and the coast, and tsunami behaviour near the coast is therefore highly non-linear, dependent on elevation, coastline shape, wave height, period and momentum. This non-linear reality of the near shore environment raises a number of questions. Is offshore wave height alone the best predictor of onshore tsunami hazard? Analytical solutions to the 1-D shallow water equations exist for predicting wave run-up on plane beaches. Can these be applied to offshore waves to measure inundation potential? Or are other metrics, such as wave energy, more appropriate? Comparisons with results from detailed inundation models will explore the utility of these measures for prioritising communitie

The aim of the present work is to determine to what extent event-specific tsunami amplitude forecasts from different numerical forecast systems differ, and therefore, how the related products from RTSPs might differ. This is done through comparing tsunami amplitudes for a number of different hypothetical tsunami events within the Indian Ocean, from a number of different tsunami scenario databases.

The occurrence of the Indian Ocean Tsunami on 26 December, 2004 has raised concern about the difficulty in determining appropriate tsunami mitigation measures in Australia, due to the lack of information on the tsunami threat. A first step in the development of such measures is a tsunami hazard assessment, which gives an indication of which areas of coastline are most likely to experience tsunami, and how likely such events are. Here we present the results of a probabilistic tsunami hazard assessment for Western Australia (WA). Compared to other parts of Australia, the WA coastline experiences a relatively high frequency of tsunami occurrence. This hazard is due to earthquakes along the Sunda Arc, south of Indonesia. Our work shows that large earthquakes offshore of Java and Sumba are likely to be a greater threat to WA than those offshore of Sumatra or elsewhere in Indonesia. A magnitude 9 earthquake offshore of the Indonesian islands of Java or Sumba has the potential to significantly impact a large part of the West Australian coastline. The level of hazard varies along the coast, but is highest along the coast from Carnarvon to Dampier. Tsunami generated by other sources (e.g. large intra-plate events, volcanoes, landslides and asteroids) were not considered in this study, which limits our hazard assessment to recurrence times of 2000 years or less.

The Great Sumatra-Andaman Earthquake and Indian Ocean Tsunami of 2004 came as a surprise to most of the earth science community. Few were aware of the potential for the subduction zone off Sumatra to generate giant (Mw>= 8.5) earthquakes, or that such an earthquake might generate a large tsunami. In retrospect, important indicators that such an event might occur appear to have not been well appreciated: (1) the tectonic environment of Sumatra was typical of those in which giant earthquakes occur; (2) GPS campaigns, as well as paleogeodetic studies indicated extensive locking of the interplate contact; (3) giant earthquakes were known to have occurred historically. While it is now widely recognised that the risk of another giant earthquake is high off central Sumatra, just east of the 2004 earthquake, there seems to be relatively little concern about the subduction zone to the north, in the northern Bay of Bengal along the coast of Myanmar. It is shown here that similar indicators suggest the potential for giant earthquake activity is high: (1) the tectonic environment is similar to other subduction zones that experience giant megathrust earthquakes; (2) stress and crustal strain observations indicate the seismogenic zone is locked; and, (3) historical earthquake activity indicates that giant tsunamigenic earthquakes have occurred in the past. These are all consistent with active subduction in the Myanmar subduction zone, and it is hypothesized here that the seismogenic zone there extends beneath the Bengal Fan. The results suggest that giant earthquakes do occur off the coast of Myanmar, and that a very large and vulnerable population is thereby exposed to a significant earthquake and tsunami hazard.

Since the 2004 Sumatra-Andaman earthquake and Indian Ocean Tsunami, there has been an increase both in the frequency of large earthquakes, and in the data for monitoring the seismic and sea level disturbances associated with them, especially in the Australasian region. The increased number of high-quality recordings available for these large earthquakes provides an important opportunity to assess methods for rapid determination of their source properties, which potentially could be used to support tsunami warning systems. In this presentation we will consider how well the available data allow us to characterise the rupture of a earthquake, consider how rapidly this could be done, and assess how well the resulting models can be used to predict far-field tsunami waveforms.

Optically stimulated luminescence (OSL) dating of sand sheets provides a chronology of the largest tsunamis in western Thailand over the late Holocene. Four sand sheets deposited by pre-2004 tsunamis were dated by luminescence to 380 ± 50, 990 ± 130, 1410 ± 190 and 2100 ± 260 years ago (at 1-sigma precision). These compare with previous radiocarbon ages of detrital bark high in buried soils (Jankaew et al., 2008), which suggest that the most recent large-scale predecessor to the 2004 tsunami occurred soon after 550-700 cal BP, and that at least three such tsunamis occurred over the past 3000 years. Concordant OSL ages from successive beach ridges (1600 ± 210 to 2560 ± 350 years ago) and tidal flat deposits (2890 ± 390 years ago) provides a set of limiting maximum ages for sand sheet deposition which, when combined with the sand sheet ages, provide a robust average for tsunami recurrence. The ages imply that between 350 to 700 years separates successive tsunamis on the Andaman coast of Thailand with an average tsunami recurrence interval of 550 years. These results show OSL can provide independent estimates of tsunami recurrence for hazard analysis, particularly in areas where suitable material for radiocarbon dating is unavailable.

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.

As part of the Australian Tsunami Warning System Project (2005-09), the Attorney-General's Department funded Geoscience Australia to develop the national offshore Probabilistic Tsunami Hazard Assessment (PTHA). This assessment could then be used by Australian emergency managers in understanding the tsunami hazard to Australia. The national offshore PTHA considers the tsunami hazard posed to the entire Australian coast by tsunami caused by subduction zone earthquakes in the Indian and Pacific Oceans. These regions are known to have produced major tsunamigenic events External site link in recorded history and are the most likely sources of future events. The hazard maps are defined at a bathymetry water depth contour of 100m offshore. This normally falls outside of the Great Barrier Reef or other reef systems. The 100m depth contour is chosen because: Estimating the tsunami closer to the coast requires high resolution bathymetric data which does not always exist for the entire coast estimating the tsunami closer to the coast is a more computational and time intensive task. These maps help to identify the areas which are most likely to be at risk to damaging tsunami waves. However, they cannot be used directly to infer how far a tsunami will inundate onshore (inundation extent), how high above sea level they will reach on land (run-up), the extent of damage or any other onshore phenomena. To estimate the onshore tsunami impact, detailed bathymetry and topography of the specific region concerned is required for input to a detailed inundation model. The catalogue of tsunami events used to derive the national offshore PTHA can be used by emergency managers, researchers and individuals however to develop detailed inundation models at any onshore location.