Legacy product - no abstract available

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.

The major tsunamis of the last few years in the southern hemisphere have raised awareness of the possibility of potentially damaging tsunami to Australia and countries in the Southwest Pacific region. Here we present a probabilistic hazard assessment for Australia and for the SOPAC countries in the Southwest Pacific for tsunami generated by subduction zone earthquakes. To conduct a probabilistic tsunami hazard assessment, we first need to estimate the likelihood of a tsunamigeneic earthquake occurring. Here we will discuss and present our method of estimate the likely return period a major megathrust earthquake on each of the subduction zones surrounding the Pacific. Our method is based on the global rate of occurrence of such events and the rate of convergence and geometry of each particular subduction zone. This allows us to create a synthetic catalogue of possible megathrust earthquakes in the region with associated probabilities for each event. To calculate the resulting tsunami for each event we create a library of "unit source" tsunami for a set of 100km x 50km unit sources along each subduction zone. For each unit source, we calculate the sea floor deformation by modelling the slip along the unit source as a dislocation in a stratified, linear elastic half-space. This sea floor deformation is then fed into a tsunami propagation model to calculate the wave height off the coast for each unit source. Our propagation model uses a staggered grid, finite different scheme to solve the linear, shallow water wave equations for tsunami propagation. The tsunami from any earthquake in the synthetic catalogue can then be quickly calculated by summing the unit source tsunami from all the unit sources that fall within the rupture zone of the earthquake. The results of these calculations can then be combined with our estimate of the probability of the earthquake to produce hazard maps showing (for example) the probability of a tsunami exceeding a given height offshore from a given stretch of coastline. These hazard maps can then be used to guide emergency managers to focus their planning efforts on regions and countries which have the greatest likelihood of producing a catastrophic tsunami.

The Mwp method provides a rapid estimate of the moment magnitude of an earthquake based on the P-wave arrival. In this paper we present a variation of this method that addresses two problems that are encountered when applying this method in practice. The first is that the magnitude of very large earthquakes that could generate an ocean wide tsunami is generally underestimated. The second is that the method relies on the magnitude of the first significant maximum after the P-arrival in the integrated displacement (ID) seismogram. Identification of the "correct" first maximum generally has to be performed by an analyst, which introduces a subjective step in the algorithm. In this paper we present a variation of the Mwp method that estimates the asymptotic value of the ID caused by the P arrival, rather than the first maximum. Since asymptotic behaviour of the ID is never observed in practice because of seismic background noise, the new method is based on a comparison of the seismic noise signal before the arrival and the signal of the arrival itself. The new algorithm allows a fully automatic and unambiguous moment estimate. We apply the algorithm to observations of 30 strong (Mw>6.0) earthquakes around Australia, and compare the result with the moment magnitudes of these earthquakes as published by the USGS. It is found that the new algorithm is more accurate than the standard Mwp method, especially for very large (Mw>7.5) earthquakes.

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.

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 Indian Ocean tsunami of December 26, 2004 and subsequent smaller events (off Nias in 2005, Java in 2006 and the Solomon Islands in 2007) have increased awareness among emergency management authorities throughout the Pacific of the need for more information regarding the hazard faced by Pacific nations from tsunami. Over the last few years the Australian Government has undertaken an effort to support regional and national efforts in the southwest Pacific to build capacity to respond to seismic and tsunami information. As part of this effort, Geoscience Australia has received support from AusAid to partner with the South Pacific Applied Geoscience Commission (SOPAC) to assist Pacific countries in assessing the tsunami hazard faced by nations in the southwest Pacific. The tsunami threat faced by Pacific island countries consists of a complex mix of tsunami from local, regional and distant sources, whose effects at any particular location in the southwest Pacific are highly dependent on variations in seafloor shape between the source and the affected area. These factors make the design of an effective warning system for the southwest Pacific problematic, because so many scenarios are possible and each scenario's impact on different islands is so varied. In order to provide national governments in the southwest Pacific with the information they need to make informed decisions about tsunami mitigation measures, including development of a warning system, a comprehensive hazard and risk assessment is called for. The aim of the report is to provide a probabilistic tsunami hazard assessment (PTHA) to SOPAC and AusAID to quantify the expected hazard for the SW Pacific nations. It follows a preliminary report of the tsunami hazard (Thomas et al, 2007) that was restricted to maximum credible tsunami events.

The importance of accurate tsunami simulation has increased since the 2004 Sumatra-Andaman earthquake and the Indian Ocean tsunami that followed it, because it is an important tool for inundation mapping and, potentially, tsunami warning. An important source of uncertainty in tsunami simulations is the source model, which is often estimated from some combination of seismic, geodetic or geological data. A magnitude 8.3 earthquake that occurred in the Kuril subduction zone on 15 November, 2006 resulted in the first teletsunamis to be widely recorded by bottom pressure recorders deployed in the northern Pacific Ocean. Because these recordings were unaffected by shallow complicated bathymetry near the coast, this provides a unique opportunity to investigate whether seismic rupture models can be inferred from teleseismic waves with sufficient accuracy to be used to forecast teletsunamis. In this study, we estimated the rupture model of the 2006 Kuril earthquake by inverting the teleseimic waves and used that to model the tsunami source. The tsunami propagation was then calculated by solving the linear long-wave equations. We found that the simulated 2006 Kuril tsunamis compared very well to the ocean bottom recordings when simultaneously using P and long-period surface waves in the earthquake source process inversion.

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.

This relates to the release of ANUGA as open-source software. No abstract required. See http://sourceforge.net/projects/anuga/