3D model
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Tomographic images of Southeast Asia and Australia were created by inverting the travel-times of the Rayleigh wave Green's functions retrieved from cross-correlations of the ambient seismic noise. The travel-times of the Green's functions are inverted with a nonlinear two dimensional inversion scheme to map the seismic velocity perturbations of the Earth. Continuous records from the vertical components of 187 permanent broad-band seismic stations operated from 2007 to 2008 are processed. We limit our picks only for Green's functions with interstation separation between 1o and 60o. This ensures that only wide scale anomalies are included in the tomographic inversions. By employing a nonlinear wavefront tracker for the forward problem, we avoid the artefacts of the deviations from the great circle path assumptions for very long interstation paths. We conduct dispersion measurements of group velocities between 6 and 50 seconds by narrowly filtering the envelopes of the extracted Green's functions. The Rayleigh waves for the selected periods sample the Earth from upper-crust (~9 km) to uppermost mantle (~90 km). The tomographic images reveal heterogeneous structure of Australia marking major sediment deposits on shallow layers and the high-velocity structure of the Western Australia cratons composed of ancient Archaean and Proterozoic blocks. Low velocity zones in deeper layers correlate well with the areas of high heat flow and agree with the results of recent surface wave tomographic studies. The Sunda Arc is characterized by prominent low-velocity zones located below the western tip of Java, Java Sea, and Banda Sea for longer periods.
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Seismic activity in the region around Australia results in a significant tsunami hazard to the coastal areas of Australia. Hence seismicity is monitored in real time by Geoscience Australia (GA), which uses a network of permanent broadband seismometers. Although seismic moment tensor (MT) solutions are routinely determined using 1-D structural models of Earth, we have recently demonstrated that a 3-D model of the Australian continent developed using full waveform tomography significantly improves the determination of MT solutions of earthquakes from tectonically active regions. A complete-waveform, time-domain MT inversion method has been developed using a point-source approximation. We present a suite of synthetic tests using first a 1-D and then a 3-D structural model. We study the feasibility of deploying 3-D versus 1-D Earth structure for the inversion of seismic data and we argue for the advantages of using the 3-D structural model. The 3-D model is superior to the 1-D model, as a number of sensitivity tests show. Current work is focused on a real time automated MT inversion system in Australia relying on Australian and other international stations.
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Exploration models for Rot Rock geothermal energy plays in Australia are based primarily on high-heat producing granites (HHPG) in combination with overlying low-conductivity sedimentary rocks providing the insulator necessary to accumulate elevated temperatures at unusually shallow (therefore accessible) depths. Unknowns in this style of geothermal play include the composition and geometry of the HHPG and thermal properties, and the thickness of the overlying sediments. A series of 3D geological models have been constructed to investigate the range of geometries and compositions that may give rise to prospective Hot Rock geothermal energy plays. A 3D geological map of the Cooper Basin region which contains known HHPG beneath thick sedimentary sequences, has been constructed from gravity inversions and constrained by geological data. The inversion models delineate regions of low density within the basement that are inferred to be granitic bodies. Thermal forward modelling was carried out by incorporating measured and estimated thermal properties to the mapped lithologies. An enhancement of the GeoModeller software is to allow the input thermal properties to be specified as distribution functions. Multiple thermal simulations using Monte-Carlo methods would be carried out from the supplied distributions. Statistical methods will be used to yield the probability estimates of the in-situ heat resource, reducing the risk of exploring for heat. The two thermal modelling techniques can be used as a predictive tool in regions where little or no temperature and geological data are available.
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The lower Darling Valley contains Cenozoic shallow marine, fluvial, lacustrine and aeolian sediments including a number of previously poorly dated Quaternary fluvial units associated with the Darling River and its anabranches. New geomorphic mapping of the Darling floodplain that utilises a high resolution LiDAR dataset and SPOT imagery, has revealed that the Late Quaternary sequence consists of scroll-plain tracts of different ages incised into a higher more featureless mud-dominated floodplain. Samples for OSL (Optically-Stimulated Luminescence) and radiocarbon dating were taken in tractor-excavated pits, from sonic drill cores and from hand-auger holes from a number of scroll-plain and older floodplain sediments in the Menindee region. The youngest, now inactive, scroll-plain phase, associated with the modern Darling River, was active in the period 5-2 ka. A previous anabranch scroll-plain phase has dates around 20ka. Indistinct scroll-plain tracts older than the anabranch system, are evident both upstream and downstream of Menindee and have ages around 30ka. These three scroll-plain tracts intersect just south of Menindee but are mostly separated upstream and downstream of that point. Older dates of 50 ka, 85 ka and >150 ka have been obtained from lateral-migration sediments present beneath the higher mud-dominated floodplain. Establishing a chronology for the Quaternary fluvial landscape has been important for groundwater investigations in the Darling River floodplain area. More specifically, this has assisted in constraining the 3D mapping of floodplain units, helped constrain conceptual models of surface-groundwater interaction, and aided in the assessment of managed aquifer recharge options.
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The Southwest Margin of Australia includes the Paleozoic to Mesozoic Perth basin. Depth-to-basement and basement structure and composition across this region remain poorly understood due to a limited extent of exposed basement outcrop, few wells intersect basement and the lack of resolvable basement horizon in many of the seismic lines. This study uses the integrated modelling and interpretation of all available geophysical and geological datasets to produce new interpretive maps of basement architecture, composition and structural fabric to better characterise the nature of basement across the region. The basement domain, structure and composition maps have been constructed through the integrated interpretation of all available geological and geophysical datasets, including outcrop, wells, geochronology, seismic, gravity, magnetic and bathymetry datasets. These products are predictive tools for better understanding structural reactivation patterns and associated changes in basin geometry through time, as well as variations in basement derived heat flow. A depth-to-basement model was developed using the Spector and Grant method, implemented using custom software. Depths are measured from straight line segments in the azimuthally averaged power density spectrum of sub-sectioned magnetic grids. This allows additional geological and geophysical data (e.g. wells, surface outcrop, gravity and seismic interpretations) to be integrated into the workflow, resulting in a more geologically plausible model. The model provides a new view of Perth basin geometry, not obtainable from seismic data alone, which highlights the location and geometry of key depocentres and provides additional constraints on the possible thickness of pre- and early syn-rift sediments.
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Six deep seismic reflection profiles totalling ~900 km were acquired across the Mount Isa Province in 2006 (Figure 1). Each vibe point was recorded to ~20 s TWT (two-way travel time), which equates to ~60 km depth. The aims of the survey were to develop a 3D model and a geodynamic history of the province, link deep crustal structure with known mineral deposits, and demonstrate the potential of deep seismic surveys in mineral exploration
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Extended abstract reporting on status of geophysical work being conducted within the Remote Eastern Frontiers project.
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The Perth 2008 LiDAR data was captured over the Perth region during February, 2008. The data was acquired by AAMHatch (now AAMGroup) and Fugro Spatial Solutions through a number of separate missions as part of the larger Swan Coast LiDAR Survey that covers the regions of Perth, Peel, Harvey, Bunbury and Busselton. The project was funded by Department of Water, WA for the purposes of coastal inundation modelling and a range of local and regional planning. The data are made available under licence for use by Commonwealth, State and Local Government. The data was captured with point density of 1 point per square metre and overall vertical accuracy has been confirmed at <15cm (68% confidence). The data are available as a number of products including mass point files (ASCII, LAS) and ESRI GRID files with 1m grid spacing. A 2m posting hydrologically enforced digital elevation model (HDEM) and inundation contours has also been derived for low lying coastal areas.
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Predictive 3D geological models of the subsurface can be developed using a range of available tools. Each tool is suited to slightly different problems and datasets. The method described here, using the UBC-GIF inversions algorithms, allows rapid development of models using an objective, automated procedure. It has flexibility to include as little or as much geological information as is available, making it ideal for greenfields exploration or mapping programs. The steps involved are: 1) develop a solid understanding of the expected physical properties; 2) convert geological observations into physical property constraints; 3) perform geologically-constrained inversions; 4) apply geological classifier to recovered 3D physical property models. The procedure is demonstrated for the southern Agnew-Wiluna greenstone belt in WA, a highly mineralised region with a high proportion of surface cover. The predictive 3D lithology models developed for the area are particular effective at mapping the extent of dense mafic and magnetic ultramafic rocks, and provide new insights about their distribution at depth.
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Extended abstract to accompany oral conference presentation. Full version of the short abstract (GEOCAT 70799).