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  • An assumption of probabilistic seismic hazard assessment is that within each source zone the random earthquakes of the past are considered a good predictor of future seismicity. Random earthquakes suggest a Poisson process. If the source zone does not follow a Poisson process then the resulting PSHA might not be valid. The tectonics of a region will effect its spatial distributions. Earthquakes occurring on a single fault, or uniformly distributed, or clustered or random will each have a distinctive spatial distribution. Here we describe a method for both identifying and delineating earthquake clusters and then characterising them. We divide the region into N cells and by counting the number of earthquakes in each cell we obtain a distribution of the number of cells versus the number of earthquakes per cell. This can then be compared to the theoretical Poisson distribution. Areas which deviate from the theoretical Poisson distribution, can then be delineated. This suggests a statistically robust method for determining source zones. Preliminary results suggest that areas of clustering (eg. SWSZ) can also be modelled as a Poisson process which differs from the larger regional Poisson process. The effect of aftershocks and swarms are also investigated.

  • Natural hazards such as floods, dam breaks, storm surges and tsunamis impact communities around the world every year. To reduce the impact, accurate modelling is required to predict where water will go, and at what speed, before the event has taken place.

  • 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.

  • We present a probabilistic tectonic hazard analysis of a site in the Otway Basin,Victoria, Australia, as part of the CO2CRC Otway Project for CO2 storage risk. The study involves estimating the likelihood of future strong earthquake shaking and associated fault displacements from natural tectonic processes that could adversely impact the storage process at the site. Three datasets are used to quantify the tectonic hazards at the site: (1) active faults; (2) historical seismicity, and; (3) GPS surface velocities. Our analysis of GPS data reveals strain rates at the limit of detectability and not significantly different from zero. Consequently, we do not develop a GPS-based source model for this Otway Basin model. We construct logic trees to capture epistemic uncertainty in both the fault and seismicity source parameters, and in the ground motion prediction. A new feature for seismic hazard modelling in Australia, and rarely dealt with in low-seismicity regions elsewhere, is the treatment of fault episodicity (long-term activity versus inactivity) in the Otway model. Seismic hazard curves for the combined (fault and distributed seismicity) source model show that hazard is generally low, with peak ground acceleration estimates of less than 0.1g at annual probabilities of 10-3-10-4/yr. The annual probability for tectonic displacements of greater than or equal to 1m at the site is even lower, in the vicinity of 10-8-10-9/yr. The low hazard is consistent with the intraplate tectonic setting of the region, and unlikely to pose a significant hazard for CO2 containment and infrastructure.

  • The cost of landslide is underestimated in Australia because their impact and loss are not readily reported or captured. There is no reliable source of data which highlights landslide cost to communities and explains who currently pays for the hazard and how much costs are. The aim of this document is to investigate and analyse landslide costs within a Local Government Area (LGA) in order to highlight the varied landslide associated costs met by the local government, state traffic and rail authorities and the public. It is anticipated this may assist in developing a baseline awareness of the range of landslide costs that are experienced at a local level in Australia. Initial estimates in this study indicate that cumulative costs associated with some landslide sites are well beyond the budget capacity of a local government to manage. Furthermore, unplanned remediation works can significantly disrupt the budget for planned mitigation works over a number of years. Landslide costs also continue to be absorbed directly by individual property owners as well as by infrastructure authorities and local governments. This is a marked distinction from how disaster costs which arise from other natural hazard events, such as flood, bushfire, cyclone and earthquake are absorbed at a local level. It was found that many generic natural hazard cost models are inappropriate for determining landslide costs because of the differences in the types of landslide movement and damage. Further work is recommended to develop a cost data model suitable for capturing consistent landslide cost data. Better quantification of landslide cost is essential to allow for comparisons to be made with other natural hazard events at appropriate levels. This may allow for more informed policy development and decision making across all levels.

  • The inventory of over 200 fault scarps captured in GA's Australian neotectonics database has been used to estimate the maximum magnitude earthquake (Mmax) across the Stable Continental Regions (SCRs) of Australia. This was done by first grouping the scarps according to the spatial divisions described in the recently published neotectonics domain model and calculating the 75th percentile scarp length for each domain. The mean Mmax was then found by averaging the maximum magnitudes predicted from a range of different published relations. Results range between Mw 7.0-7.5±0.2. This suggests that potentially catastrophic earthquakes are possible Australia-wide. These data can form the basis for future seismic hazard assessments, including those for building design codes, both in Australia and analogous SCRs worldwide.

  • Abstract is too large to be pasted here. See TRIM link: D2011-144613

  • The Attorney General's Department (AGD) has supported Geoscience Australia (GA) to develop inundation models for selected Northern Territory communities with the view of building the tsunami planning and preparation capacity of the Northern Territory Government. The communities chosen were Darwin, Palmerston, Wagait Beach and Dundee Beach. These locations were selected in collaboration with the Northern Territory Emergency Service (NTES) and Department of Natural Resources, Environment, The Arts and Sport (NRETAS) and the Australian Government based on a combination of the offshore Probabilistic Tsunami Hazard Assessment of Australia (PTHA)[1], the availability of suitable elevation data and the location of low lying communities. Three tsunamigenic events were selected for modelling from the scenario database that was calculated as part of the national offshore probabilistic tsunami hazard assessment (PTHA) [1]. The events selected are hypothetical and are based on the current understanding of the tsunami hazard. Only earthquake sources are considered as these account for the majority of tsunami. The suite of events includes three 'worst-case' or 1 in 10 000 year hazard events as well as more frequent events. Source zones considered are the Timor Trough, Flores-Wetar Thrust Fault and the Java Trench as these regions make the highest contribution to the offshore tsunami hazard for Darwin.

  • Geoscience Australia has recently released the 2012 version of the National Earthquake Hazard Map of Australia. Among other applications, the map is a key component of Australia's earthquake loading code AS1170.4. In this presentation we will provide an overview of the new maps and how they were put together. The new maps take advantage of the significant improvements in both the data sets and models used for earthquake hazard assessment in Australia since the current map in AS1170.4 was produced. These include: - An additional 20+ years of earthquake observations - Improved methods of declustering earthquake catalogues and calculating earthquake recurrence - Ground motion prediction equations (i.e. attenuation equations) based on observed strong motions instead of intensity - Revised earthquake source zones - Improved maximum magnitude earthquake estimates based on palaeoseismology - The use of open source software for undertaking probabilistic seismic hazard assessment which promotes testability and repeatability Hazard maps will be presented for a range of response spectral acceleration (RSA) periods between 0.0 and 1.0s and for multiple return periods between a few hundred to a few thousand years. These maps will be compared with the current earthquake hazard map in AS1170.4. For a return period of 500 years, the hazard values in the 0.0s RSA period map were generally lower than the hazard values in the current AS1170.4 map. By contrast the 0.2s RSA period hazard values were generally higher.