From 1 - 10 / 1023
  • This paper describes the methods used to define earthquake source zones and calculate their recurrence parameters (a, b, Mmax). These values, along with the ground motion relations, effectively define the final hazard map. Definition of source zones is a highly subjective process, relying on seismology and geology to provide some quantitative guidance. Similarly the determination of Mmax is often subjective. Whilst the calculation of a and b is quantitative, the assumptions inherent in the available methods need to be considered when choosing the most appropriate one. For the new map we have maximised quantitative input into the definition of zones and their parameters. The temporal and spatial Poisson statistical properties of Australia's seismicity, along with models of intra-plate seismicity based on results from neotectonic, geodetic and computer modelling studies of stable continental crust, suggest a multi-layer source zonation model is required to account for the seismicity. Accordingly we propose a three layer model consisting of three large background seismicity zones covering 100% of the continent, 25 regional scale source zones covering ~50% of the continent, and 44 hotspot zones covering 2% of the continent. A new algorithm was developed to calculate a and b. This algorithm was designed to minimise the problems with both the maximum likelihood method (which is sensitive to the effects of varying magnitude completeness at small magnitudes) and the least squares regression method (which is sensitive to the presence of outlier large magnitude earthquakes). This enabled fully automated calculation of a and b parameters for all sources zones. The assignment of Mmax for the zones was based on the results of a statistical analysis of neotectonic fault scarps.

  • To investigate the standard electrical conductivity profile beneath a continent, we conducted a magnetotelluric (MT) observation with long dipole span near Alice Springs, central Australia. We utilized geomagnetic data acquired at the Alice Springs geomagnetic observatory operated by Geoscience Australia. Using the BIRRP processing code (Chave and Thomson, 2004), we estimated the MT and GDS (geomagnetic depth sounding) transfer functions for periods from 100 to 10 to 6 sec. The MT-compatible response functions converted from GDS response functions are resistive compared to the Canadian Shield (Chave et al., 1993) for periods around 10 to 5 sec. The calculated MT responses also have generally high apparent resistivity values over the entire period range. We inverted the average MT responses into a one-dimensional conductivity profile using Occam inversion (Constable et al., 1987). The resultant conductivity profile is extremely resistive (0.001 to 0.0001 S/m) down to the mantle transition zone. We compared this one-dimensional structure with electrical conductivity profiles predicted from compositional models of the earth's upper mantle by calculating phase diagrams in the CFMAS (CaO-FeO-MgO-Al2O3-SiO2) system. The on-craton and off-craton chemical composition models (Rudnick et al., 1998) were adopted for the tectosphere. The Perple_X (e.g. Connolly, 2005) programs were used to obtain mineral proportions and compositions with depth. The calculated conductivity profiles with on- and off-craton models show significantly larger magnitude than the observed. The result suggests the continental lithosphere (tectosphere) beneath Australia is extremely dry and its temperature profile is cooler than that used in the calculation.

  • Commonwealth Electoral Division of Hasluck - Landcover data with topographer underlay.

  • Climate change is expected to increase severe wind hazard in many regions of the Australian continent with consequences for exposed infrastructure and human populations. The objective of this paper is to provide an initial nationally consistent assessment of wind risk under current climate, utilizing the Australian/New Zealand wind loading standard (AS/NZS 1170.2, 2002) as a measure of the hazard. This work is part of the National Wind Risk Assessment (NWRA), which is a collaboration between the Australian Federal Government (Department of Climate Change and Energy Efficiency) and Geoscience Australia. It is aimed at highlighting regions of the Australian continent where there is high wind risk to residential structures under current climate, and where, if hazard increases under climate change, there will be a greater need for adaptation. This assessment is being undertaken by separately considering wind hazard, infrastructure exposure and the wind vulnerability of residential buildings. The NWRA will provide a benchmark measure of wind risk nationally (current climate), underpinned by the National Exposure Information System (NEXIS; developed by Geoscience Australia) and the wind loading standard. The methodology which determines the direct impact of severe wind on Australian communities involves the parallel development of the understanding of wind hazard, residential building exposure and the wind vulnerability of residential structures. We provide the current climate wind risk, expressed as annualized loss, based on the wind loading standard.

  • In 2008, as part of the Australian Government's Onshore Energy Security Program, Geoscience Australia, acquired deep seismic reflection, wide-angle refraction, magnetotelluric (MT) and gravity data along a 250 km east-west transect that crosses several tectonic domain boundaries in the Gawler Craton and also the western boundary of the South Australian Heat Flow Anomaly (SAHFA). Geophysical datasets provide information on the crustal architecture and evolution of this part of the Archean-Proterozoic Gawler Craton. The wide-angle refraction and MT surveys were designed to supplement deep seismic reflection data, with velocity information for the upper crust, and electrical conductivity distribution from surface to the upper mantle. The seismic image of the crust from reflection data shows variable reflectivity along the line. The upper 2 s of data imaged nonreflective crust; the middle to lower part of the crust is more reflective, with strong, east-dipping reflections in the central part of the section.The 2D velocity model derived from wide-angle data shows velocity variations in the upper crust and can be constrained down to a depth of 12 km. The model consists of three layers overlying basement. The mid-crustal basement interpreted from the reflection data, at 6 km in depth in the western part of the transect and shallowing to 1 km depth in the east, is consistent with the velocity model derived from wide-angle and gravity data. MT modelling shows a relatively resistive deep crust across most of the transect, with more conductive crust at the western end, and near the centre. The enhanced conductivity in the central part of the profile is associated with a zone of high reflectivity in the seismic image. Joined interpretation of seismic data supplemented by MT, gravity and geological data improve geological understanding of this region.

  • Abstract. Severe wind is one of the major natural hazards in Australia. The component contributors to economic loss in Australia with regards to severe wind are tropical cyclones, thunderstorms and sub-tropical (synoptic) storms. Geoscience Australia's Risk and Impact Analysis Group (RIAG) is developing mathematical models to study a number of natural hazards including wind hazard. This paper discusses wind hazard under current and future climate using RIAG's synoptic wind hazard model. This model can be used in non-cyclonic regions of Australia (Region A in the Australian-New Zealand Wind Loading Standard; AS/NZS 1170.2:2002) where the wind hazard is dominated by synoptic and thunderstorm gust winds.

  • This Record presents data collected as part of the ongoing NTGS-GA geochronological collaboration between July 2000 and June 2011 under the National Geoscience Agreement (NGA). This record presents new SHRIMP U-Pb zircon and monazite geochronological results for 18 samples from the Arunta Region, Davenport Province, Simpson Desert and Pine Creek Orogen in the Northern Territory. Five Paleoproterozoic igneous and metasedimentary samples were collected from the Eastern Arunta (ILLOGWA CREEK), and one metasedimentary sample from the eastern Casey Inlier (HALE RIVER). One igneous volcanic sample and two metasedimentary samples are from the Davenport Province (MAPSHEET) and Simpson Desert regions (HAY RIVER), respectively. Ten samples in total were collected from the Pine Creek Orogen; one igneous sample from DARWIN, the remainder being igneous and metasedimentary samples from the Nimbuwah Domain (ALLIGATOR RIVER).

  • User Manual - Australian Flood Studies Database Search

  • These data are the definitive time series data collected at Geoscience Australia's geomagnetic observatories in Australia and Antarctica. Some data are also provided for historic Australian observatories and some observatories operated by New Zealand and Indonesia.

  • One of the important inputs to a probabilistic seismic hazard assessment is the expected rate at which earthquakes within the study region. The rate of earthquakes is a function of the rate at which the crust is being deformed, mostly by tectonic stresses. This paper will present two contrasting methods of estimating the strain rate at the scale of the Australian continent. The first method is based on statistically analysing the recently updated national earthquake catalogue, while the second uses a geodynamic model of the Australian plate and the forces that act upon it. For the first method, we show a couple of examples of the strain rates predicted across Australia using different statistical techniques. However no matter what method is used, the measurable seismic strain rates are typically in the range of 10-16s-1 to around 10-18s-1 depending on location. By contrast, the geodynamic model predicts a much more uniform strain rate of around 10-17s-1 across the continent. The level of uniformity of the true distribution of long term strain rate in Australia is likely to be somewhere between these two extremes. Neither estimate is consistent with the Australian plate being completely rigid and free from internal deformation (i.e. a strain rate of exactly zero). This paper will also give an overview of how this kind of work affects the national earthquake hazard map and how future high precision geodetic estimates of strain rate should help to reduce the uncertainty in this important parameter for probabilistic seismic hazard assessments.