This cross agency report, highlights the areas of the central NSW continental slope prone to sediment mass wasting over time. It includes the critical factors which contribute to slope failure including basement geometry, angle of slope and thickness of overlying sediments. Evidence of slope failure are observed through: surficial tension cracks; creep features; faulting; redistribution of sediments, multiple relict slides on the sea floor and erosional surface scars.

The tragic events of the Indian Ocean tsunami on 26 December 2004 highlighted shortcomings in the alert and response systems for tsunami threats to Western Australia's (WA) coastal communities. To improve community awareness and understanding of tsunami hazard and potential impact for Western Australia, the Fire and Emergency Services Authority of WA (FESA) established a collaborative partnership with GA in which science and emergency management expertise was applied to identified communities.

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.

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.

To follow

Landslides can happen on the seafloor, just like on land. Areas of the seafloor that are steep and loaded with sediment are more prone to undersea landslides, such as the edge of the continental slope. When an undersea landslide occurs (perhaps after a nearby earthquake) a large mass of sand, mud and gravel can move down the slope. This movement will draw the water down and may cause a tsunami that will travel across the ocean.

As the tsunami moves across the open ocean it is almost undetectable on the ocean surface. In this example, the tsunami waves are only about half a metre high but have a wavelength of 200 kilometres. Travelling at speeds of up to eight or nine hundred kilometres an hour (the speed of a commercial passenger jet), it will take each wave about 15 minutes to pass a slow moving ship.

As the tsunami leaves the deep water of the open ocean and approaches the shallower waters near the coast, it slows down and may grow in height depending on the shape of the seafloor. A tsunami that is unnoticeable by ships at sea may grow to be several metres or more in height near the coast. Our example tsunami is now 1.5 metres high with a wavelength of 100 kilometres and is moving at about 400 kilometres an hour.

As the Australian plate slowly pushes under the Eurasian plate, massive stresses build up in the crust. These stresses also cause the Eurasian plate to be slowly forced upwards - part of the process that builds the mountains and volcanoes of Indonesia, as well as creating the many earthquakes felt in that region of the world each year. When the stresses get too great, the plates will suddenly slip causing massive movements in the seafloor. The part of the crust nearest to the fault zone rapidly moves upwards by a metre or so, lifting the entire body of water above it. A hundred kilometres away the opposite may happen: the seafloor drops and the ocean above it also falls. These two movements (the sudden rise and fall of the seafloor hundreds of kilometres apart), combine to cause a series of tsunami waves which move away from the line of the fault in both directions.

The Attorney General's Departement has supported Geoscience Australia to develop inundation models for four east coast communities with the view of buildling the tsunami planning and preparation capacity of the Jurisdictions. The aim of this document and accompanying DVD is to report on the approach adopted by each Jurisdiction, the modelling outcomes and supply the underpinning computer scripts and input data.