From 1 - 10 / 496
  • In the present study, the relative distributions and stable carbon and hydrogen isotopic compositions of the biomarkers from high grade oil shales (Permian and Carboniferous torbanites) rich in B. braunii fossils (i.e. torbanites) deposited under a range of climatic conditions are stringently scrutinised for any evidence of molecular features which may be characteristic of palaeogeographical location of deposition. Eleven torbanites from Scotland, South Africa and Australia covering the Late Carboniferous to Late Permian have been analysed.

  • The discovery of commercial oil in the Cliff Head-1 well in 2001 set an important milestone in the exploration history of the offshore northern Perth Basin. The region had been largely underexplored before then, partly due to the perception that the Hovea Member, a 10 to 40 m-thick unit straddling the Permian-Triassic boundary (PTB) and recognized as the main source of onshore petroleum accumulations, was not developed offshore (Crostella, 2001). The typing of the Cliff Head oil to the Hovea Member provided evidence that the key onshore petroleum system extends offshore and revitalized exploration in the area with 13 new field wildcat wells drilled since 2002. Three discoveries have been made subsequently further offshore in the Abrolhos Sub-basin with gas retrieved in Frankland-1 and Perseverance-1 and oil and gas in Dunsborough-1. A review of source rock and oil geochemical data was undertaken by Geoscience Australia in the offshore northern Perth Basin as part of a major integrated study aimed at reassessing the basin's prospectivity. This work supports the release of offshore exploration areas W13-19 and W13-20, two major blocks straddling the Houtman and Abrolhos Sub-basins with small portions extending into the Zeewyck and Gascoyne Sub-basins (Fig. 1). Well control is provided by 5 wells from the Wittecarra Terrace in the northern Abrolhos Sub-basin and Houtman-1 in the Houtman Sub-basin.

  • Geoscience Australia has been providing estimates of felt and potential damage radiuses for all earthquakes above magnitude 3.0 since 2002. Similarly, over the last decade, using the hazard modelling software EQRM, GA has produced scenario MMI maps for most Australian cities and several cities in our region. The former uses Empirical relations developed from measuring MMI III, IV, V and VI radiuses from the isoseismal map of ~150 Australian earthquakes. The later using various GMPEs to generate the hazard field and PGA/PGV to MMI conversions to estimate MMI. These two approaches have not previously been directly compared. We have tested the fit with between the empirical MMI areas and the scenario models for several combinations of GMPEs and PGA/PGV to MMI conversions. We also investigate the possible importance of site effects in biasing the empirical data, for which only the minimum and maximum epicentral distance was measured, particularly at low MMI. A scenario model that more accurately reflects the empirical data should be more robust than the current method, for both real-time earthquake advice and scenarios. It should also enable the conversions used to estimate the magnitude of pre-instrumental earthquakes to be tested. Additionally the GMPEs that give the best fit to the empirical data might provide guidance when selecting GMPES for PSHAs and future scenario products.

  • No abstract available

  • Separation of regional and residual components of potential field data is an important step within an interpretation procedure. Separation methods include; curve fitting, filtering, subtraction of specified elements of a global geo-potential model, and local model-based approaches. In a local model-based approach, a source distribution is found that reproduces the observed response to a prescribed level. Sources outside the extent to be considered during subsequent interpretation are identified, and their response is subtracted or "stripped" from the observed response. We apply a form of model-based separation that is based on inversion to a coarse 3D property model enveloping the volume of primary interest. We illustrate the method using gravity data from a portion of the Yilgarn Craton, Western Australia.

  • This paper explores wavelets as a measure of linear complexity. An intro-duction to wavelets is given before applying them to spatial data and trial-ing them as a complexity measure on a vector representation of the Austra-lian coastline. Wavelets are shown to be successful at measuring linear complexity. The technique used breaks a single line into different classes of complexity, and has the advantages that it is objective, automated and fast.

  • The region to the east of Mt Isa has complex electrical conductivity, with conductive basin sediments overlying the deeper Carpentaria Conductivity Anomaly (CCA). Early magnetotelluric (MT) model results show alignment of the CCA with aeromagnetic, gravity and seismic features, together implying that they define the major structural edge of the Mt Isa Block. Profile MT data acquired during the previous 20 years have helped refine the position and depth of the CCA. New MT and deep seismic reflection data have recently been acquired in 2014 along a NW to SE profile, funded by the Geological Survey of Queensland's Greenfields 2020 Program in conjunction with Geoscience Australia. These new data provide further evidence of the complex nature of the crustal conductivity in this region. Induction vectors indicate that the CCA itself is braided into several zones which may define deep-seated fracture systems. Key words: magnetotelluric, electrical conductivity, conductivity anomaly, induction vector, Mt Isa

  • To assess the impacts of climate change on Australian communities, a benchmark is required of the current level of severe wind risk. Phase I of the National Wind Risk Assessment assessed the annualised loss due to severe wind in urban areas across Australia, using the regional design wind speeds as defined in AS/NZS 1170.2 (2002) as a substitute for wind hazard. The regional wind speeds used in the Standard were determined from analysis of long-term records of daily maximum gust wind speeds.In this study, Geoscience Australia has used new statistical models to develop a spatially specific understanding of wind hazard arising from tropical cyclones (TCs), synoptic storms and thunderstorms.

  • Electricity supply to communities and key industries depends upon transmission assets. Transmission lines are linear assets that can be very exposed to wind effects, particularly where they traverse steep topography or open coastal terrain in cyclonic regions. The interconnected nature of the lattice towers and conductors also present complex vulnerabilities. These relate to the direction of wind attack to the conductors and the cascading failure mechanisms in which the failure of a single tower has cascading effects on neighbouring towers. Such behaviour is exacerbated by the finely tuned nature of tower design which serves to minimize cost and reserve strength at design wind speeds. There is a clear need to better quantify the local wind hazard and interdependent vulnerabilities of these critical infrastructure assets in the context of the present severe wind hazard and those projected for the future due to climate change. This paper presents a novel methodology developed for the Critical Infrastructure Protection Modelling and Analysis (CIPMA) capability for assessing local wind speeds and the likelihood of tower failure for a range of transmission tower and conductor types. CIPMA is a program managed by the Federal Attorney-General's Department and Geoscience Australia is leading the technical development. The methodology explicitly addresses the highly direction-sensitive nature of tower/conductor vulnerability which varies greatly. It has involved significant refinements to Geoscience Australia's tropical cyclone wind field modelling which now directly interrogates the assessed local wind speed and direction throughout the duration of a cyclone transit. It has also involved the development of a vulnerability methodology and heuristically derived vulnerability models that are consistent with Australian industry experience and full-scale static tower testing results. This has been achieved through consultation with industry specialists and wind engineering experts engaged in four workshops. The methodology directly considers isolated tower loss along with three interdependent failure mechanisms to give overall likelihoods of failure. Future research directions are described that will further refine this CIPMA capability.