Regional seismic reflection data in hard rock areas contains more shallow information than might first be supposed. Here I use a subset of the 2005 Tanami Seismic Survey data to show that near surface features can be defined, including paleochannels, Palaeozoic basins and structures within the Proterozoic basement. Successful imaging depends on correct determination of refraction statics, including identification of refractor branches, and use of a floating or intermediate datum during seismic reflection processing. Recognition of steep stacking velocity gradients associated with surface referenced processing aids velocity analysis and can further delineate areas of thicker regolith in palaeochannels. The first arrival refraction analysis can also be applied in more detail to estimating thickness of regolith and depth to economic basement in areas of sedimentary cover.

A deep seismic reflection and magnetotelluric survey, conducted in 2007, established the architecture and geodynamic framework of north Queensland, Australia. Results based on the interpretation of the deep seismic data include the discovery of a major, west-dipping, Paleoproterozoic (or older) crustal boundary, interpreted the Gidyea Suture Zone, separating relatively nonreflective, thick crust of the Mount Isa Province from thinner, two layered crust to the east. East of the Mount Isa Province, the lower crust is highly reflective and is subdivided into three mappable seismic provinces (Numil, Abingdon and Agwamin) which are not exposed at the surface. To the west of Croydon, a second major crustal boundary also dips west or southwest, offsetting the Moho and extending below it. It is interpreted as the Rowe Fossil Subduction Zone. This marks the boundary between the Numil and Abingdon seismic provinces, and is overlain by the Etheridge Province. The previously unknown Millungera Basin was imaged below the Eromanga-Carpentaria basin system. In the east, the Greenvale and Charters Towers Provinces, part of the Thomson Orogen, have been mapped on the surface as two discrete provinces, but the seismic interpretation raises the possibility that these two provinces are continuous in the subsurface, and also extend northwards to beneath the Hodgkinson Province, originally forming part of an extensive Neoproterozoic-Cambrian passive margin. Continuation of this passive margin at depth beneath the Hodgkinson and Broken River Provinces suggests that these provinces (which formed in an oceanic environment, possibly as an accretionary wedge at a convergent margin) have been thrust westwards onto the older continental passive margin. The Tasman Line, originally defined to represent the eastern limit of Precambrian rocks in Australia, has a complicated geometry in three dimensions, which is related to regional deformational events during the Paleozoic.

Extended abstract of metalogenic implications of seismic and allied results in North Queensland

During May to October 2007 Geoscience Australia in collaboration with the Geological Survey of Queensland contracted Terrex Seismic to undertake the Mt Isa-Georgetown-Charters Towers Deep Seismic Reflection Survey. This survey acquired deep seismic reflection, gravity and magnetotelluric data along three traverses, 07GA-IG1, 07GA-IG2 and 07GA-GC1 (Figure 1). Funding for this survey was provided by Geoscience Australia's Onshore Energy Security Program and Queensland's Smart Mining - Future Prosperity Program, with the aims of the project to image from the eastern edge of the Mt Isa Province across the Georgetown Province and southeast through the Charters Towers region into the Drummond Basin (Figure 1). A fourth traverse (07GA-A1) was funded by AuScope, an initiative established under the National Collaborative Research Infrastructure Strategy to characterise the structure and evolution of the Australian continent. This line imaged from Mareeba to Mt Surprise across the Palmerville Fault (part of the Tasman Line). A total of 1387 km of 2D seismic reflection data were collected to 20 seconds two way travel time over the four lines. The nominal CDP coverage was 60 fold for line 07GA-IG1 and was increased to 75 fold for the remaining three lines. The survey commenced on 19 May 2007 and was completed on 7 October 2007.

Seismic line 07GA-GC1, described here, forms part of the Isa-Georgetown-Charters Towers seismic survey that was acquired in 2007. The seismic line is oriented approximately northwest-southeast and extends from east of Georgetown in the northwest to south of Charters Towers in the southeast (Figure 1). The acquisition costs for this line were provided jointly by the Geological Survey of Queensland and Geoscience Australia, and field logistics and processing were carried out by the Seismic Acquisition and Processing team from Geoscience Australia. Seven discrete geological provinces have been interpreted on this seismic section (Figure 2). Two of these, the Abingdon and Sausage Creek Provinces, only occur in the subsurface. The upper crustal part of the seismic section is dominated by the Etheridge and Cape River Provinces, but the seismic line also crossed the Broken River Province and the Drummond and Burdekin Basins.

Legacy product - no abstract available

This report is a description of velocity data acquired during the summer of 2006/07 on Geoscience Australia's seismic marine reflection, refraction and potential field survey GA302 over the Capel and Faust Basins, Lord Howe Rise. The survey was the final phase of the Australian Government's Big New Oil initiative commenced in 2003 to support acreage release in frontier basins. Previous data over the region are sparsely located, and the present survey will provide explorers with high quality data acquired and processed to modern standards. The Lord Howe Rise is thought to be a continental fragment detached from Australia during the formation of the Tasman Sea. The Capel and Faust Basins are of interest as possible frontier petroleum provinces, and the present work is aimed at improving the confidence of sediment thickness estimation, a critical parameter in evaluating of prospectivity. The study reviews the seismic reflection data from survey GA302, the sonobuoy refraction data acquired, and the stacking velocities from the seismic reflection processing.

The seismic stacking velocity data in the Otway Basin are a useful dataset for calculating depths and sediment thicknesses. This work presents time-depth relationships computed from unsmoothed stacking velocities and compares these with functions obtained from sonobuoy refraction data and exploration well sonic logs. The comparison suggests that a total sediment thickness over-estimate for the Otway Basin of about 15% can be expected from the depths derived from stacking velocities alone. On the other hand, for sediment thickness calculations down to ~3 s two-way travel time below sea floor, stacking velocity data give comparable depths to those obtained from the sonic logs. A piece-wise formula is offered which scales the time-depth function for the Otway Basin in order to compensate for the depth overestimate inherent in using stacking velocities to calculate total sediment thickness.

Seismic line 07GA-IG2, described here, forms part of the Isa-Georgetown-Charters Towers seismic survey that was acquired in 2007. The seismic line is oriented approximately east-west and extends from east of Croydon in the west to near Mt Surprise in the east (Figure 1). The acquisition costs for this line were provided jointly by the Geological Survey of Queensland and Geoscience Australia, and field logistics and processing were carried out by the Seismic Acquisition and Processing team from Geoscience Australia. Three discrete geological provinces have been interpreted on this seismic section (Figure 2). Two of these, the Numil and Abingdon Provinces, only occur in the subsurface. The upper crustal part of the seismic section consists of the Paleo- to Mesoproterozoic Etheridge Province, which here includes the Croydon Volcanic Group in the western part of the Province. In this east-west profile, the crust is essentially two-layered, with a strongly reflective lower crust defining the Numil and Abingdon Provinces and a less reflective upper crust being representative of the Etheridge Province.

As part of its Energy Security Initiative, the Australian Government allocated Geoscience Australia $59 million in August 2006, to undertake a five-year Onshore Energy Security Program. This is designed to deliver precompetitive geoscience data and scientifically-based assessments to reduce the rick in exploration for onshore energy resources, including petroleum, uranium, thorium and geothermal energy. The work is being conducted in collaboration with the State and territory geological surveys and is scheduled for completion in June 2011.