The 2005 Tanami Seismic Collaborative Research Project was carried out from May through July 2005 across the Tanami Region of Western Australia and the Northern Territory (Figure 1-1). The survey is a collaborative project between Geoscience Australia, the Geological Survey of Western Australia, the Northern Territory Geological Survey, Newmont Exploration and Tanami Gold NL, and used the facilities of ANSIR (the National Research Facility for Earth Sounding). The seismic results would then be used to test our understanding of the 3D architecture by imaging the regional geology and the key regional structures. Some of these key structures are related to gold mineralisation. The project, through a series of meetings between interested Tanami Region geoscientists, identified a series of traverses (Figure 1-1) that would best define the architecture of the Tanami Region. The proposed traverses were selected based on both scientific and operational criteria. The scientific questions that were considered to be important in understanding the geometry and tectonic history of the Tanami Region are: - What are the geometries and the order of structures such as faults and folds? - Can we identify through-going crustal structures? - What is the relationship of the various stratigraphic packages with the controlling structures? - Are variations in the thickness of formations due to layer-parallel duplication (i.e. thrusting) or the result of growth faults? - What is the relationship of mineralized domains to crustal scale structures? - What is the three-dimensional geometry of granitic bodies? - Can we identify the early Palaeoproterozoic or Archaean basement and its relationship to the rocks included in the Tanami province? - What is the nature of the boundary between the Arunta Inlier and Tanami province, and is it related to the prominent east-west trending gravity ridge? - Can we identify the presence of the mineralized Dead Bullock Formation (DBF) at depth in the WA part of the Tanami province? Thick sequences of the formation are known to be present in the NT part of the province, but there seems to be no outcrop of it on the WA side; why is this so? - Can we identify the possible existence of alteration zones that maybe associated with mineralization in WA. In conjunction with these questions, the proposed traverses would provide depth constraint to the Tanami 3D model that was developed with input by GA, NTGS, and GSWA.

The Australian Seismological Report 2008 provides a summary of earthquake activity for Australia for 2008. It also provides a summary of earthquakes of Magnitude 5+ in the Australian Region, as well as an summary of Magnitude 6+ earthquakes worldwide. It has dedicated state and territory earthquake information including: largest earthquakes in the year; largest earthquakes in the state; and tables detailing all earthquakes detected by Geoscience Australia during the year. There are also contributions from Gary Gibson and Environmental Systems and Services describing Seismic Networks and providing Earthquake locations.

In hard rock regions, a large range of stacking velocities is required to correctly stack reflectors of different dips. Typically, horizontal reflectors stack at 6000 m/s, whereas reflectors with dips of 60 degrees stack at 12,000 m/s. For high fold (vibroseis) data, correct stack of conflicting dips can be achieved by dip moveout (DMO) correction. However, for lower fold (dynamite) data, the sparse offset distribution complicates application of DMO. An alternative technique involves producing stacks with different stacking velocities and stacking these stacks. This technique was applied to two data sets, low fold dynamite from Broken Hill, and high fold vibroseis data from the Lachlan Fold Belt. The Lachlan data set was used as both full 60 fold and 10 fold (reduced by selecting every 6th shot). Velocity analysis, both analytical and empirical, was carried out to determine the stacking velocities. Stacking velocity increases with dip angle (cos-1theta), but the velocity range across which an event stacks coherently increases more rapidly (approximately cos-3theta). The most critical area for analysis is the first 2 seconds of data, due to greater sensitivity of NMO to stacking velocity. The optimum number of stacks is an important consideration, based on the number of stacks in which an event contributes coherently to the sum. A range of stacking algorithms was tested, including nth root stacks and coherency weighting. The Broken Hill stack data showed simultaneous imaging of horizontal and dipping events. For the Lachlan reduced fold data, horizontal and moderate to steeply dipping events were stacked successfully. Comparison of these results with the post-DMO stack of the full 60 fold data demonstrates the validity of the technique.

In hard rock regions, a large range of stacking velocities is required to correctly stack reflectors of different dips. Typically, horizontal reflectors stack at 6000 m/s, whereas reflectors with dips of 60 degrees stack at 12,000 m/s. For high fold (vibrator) data, correct stack of conflicting dips can be achieved by dip moveout (DMO) correction. However, for lower fold (dynamite) data, the sparse offset distribution complicates application of DMO. An alternative technique involves producing stacks with different stacking velocities and stacking these stacks. This technique was applied to two seismic reflection data sets, low fold dynamite from Broken Hill and high fold vibrator data from the Lachlan Fold Belt. The Lachlan data set was used as both full 60/120 fold and reduced 10/20 fold. Velocity analysis, both analytical and empirical, was carried out to determine the range of stacking velocities. Stacking velocity increases with dip angle (cos-1 theta), but the velocity range across which an event stacks coherently increases more rapidly (approximately cos-3 theta for velocities typical of hard rock)). The most critical area for analysis is the first two seconds of data, due to greater sensitivity of NMO to stacking velocity. The optimum number of stacks is an important consideration, based on the number of stacks in which an event contributes coherently to the sum The Broken Hill stack data showed simultaneous imaging of horizontal and dipping events. For the Lachlan reduced fold data set, horizontal and moderate to steeply dipping events were stacked successfully, although not as well as the post-DMO stack of the full fold data. The technique has some problems at the shallowest levels, where the stack can be degraded due to time shifts of events in the individual stacks.

Legacy product - no abstract available

The tau-p velocity imaging method, first developed for obtaining the velocity field from marine multichannel seismic data, has been applied to refracted waves from the regolith in regional seismic reflection surveys on land. The technique converts travel time picks from the refracted wavefield into two-dimensional velocity models, by transforming from time-offset into the tau-p domain. Each arrival is mapped individually, and the `true? velocity and position of the ray turning point is obtained by considering reversed raypaths. Thus the data are transformed directly into a depth or two-way-time image of the subsurface displayed in seismic velocity. The method is extremely fast and involves no interpretive steps or iteration. Ideal datasets contain the refracted wavefield sampled densely and equally in the shot and receiver domains. It was therefore decided to test the application of the method for mapping the velocity structure of a portion of regolith, and to compare the results with those obtained using more conventional methods. The area chosen for study was part of a regional seismic reflection line across the Lachlan River palaeo-valley in central NSW. The data set consisted of the first break picks for 240 channel records with receivers spaced every 40 m and vibe points every 40 m. The velocity images were produced as both time and depth sections and compared with the refractor model based on a one layer solution by the reciprocal method. A low velocity region on the image corresponds to the deepest part of the refractor model, interpreted as the thickest part of the palaeo-valley. Bedrock velocity variations are also mapped but appear more clearly in the refractor velocity profile. While further tuning may be required for land work, the technique has the advantage that velocities can be directly imaged and potentially related to regolith physical properties.

No abstract available

We have used data recorded by a temporary seismograph deployment to infer constraints on the state of crustal stress in the Flinders Ranges in south-central Australia. Previous stress estimates for the region have been poorly constrained due to the lack of large events and limited station coverage for focal mechanisms. New data allowed 65 events with 544 first motions to be used in a stress inversion to estimate the principal stress directions and stress ratio.While our initial inversion suggested that stress in the region was not homogeneous, we found that discarding data for events in the top 2km of the crust resulted in a well-constrained stress orientation that is consistent with the assumption of homogeneous stress throughout the Flinders Ranges. We speculate that the need to screen out shallow events may be due to the presence in the shallow crust of either: (1) small-scale velocity heterogeneity that would bias the ray parameter estimates, or (2) heterogeneity in the stress field itself, possibly due to the influence of the relatively pronounced topographic relief. The stress derived from earthquakes in the Flinders Ranges show an oblique reverse faulting stress regime, which contrasts with the pure thrust and pure strike slip regimes suggested by earlier studies. However, the roughly E-W direction of maximum horizontal compressive stress we obtain supports the conclusion of virtually all previous studies that the Flinders Ranges are undergoing E-W compression due to orogenic events at the boundaries of the Australian and Indian Plates.

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.

The effect of ground motion models, site response and recurrence parameters (a, b, Mmax) on the uncertainty in estimating earthquake hazard have been widely discussed. There has been less discussion on the effect of the choice of source zones and the implied seismicity model. In the current Australian national seismic hazard map we have adopted a 3 layer source zone model. This attempts to capture the variability of the spatial distribution of the seismicity in the stable continental crust of Australia. PSHA has an implied assumption that the spatial distribution of earthquakes within a source zone is either uniform or random - with the random distribution approaching uniformity as it becomes sufficiently dense. At almost any scale in no area of Australia does the seismicity conform to either a random (single Poisson model) or a uniform distribution - it is more clustered. Generally, at least three Poisson models are required to match the observed spatial statistical distribution; typically zones of low, moderate and very high seismicity. Using the full (not declustered catalogue) at least 4 Poisson models are required. In all cases examined there are more bins than expected with <1 and >3 earthquakes and a deficit of bins with 1 or 2 earthquakes. This observaion is consistent with emerging models of earthquakes in stable continents being a non-stationary or episodic, rather than a steady state, process. In order to account for this observation, we use a three layer source zone model, consisting of: a Background layer, with three zones covering 100% of the continent, based on the geological and geophysical properties; a Regional layer, of 25 zones covering ~50% of the continent, based on the pattern of earthquake density; and a Hotspot layer, of 44 zones covering 2% of the continent, based on the areas of sustained intense seismicity. In the final hazard model the maximum of the three hazard values is used, not a weighted average of the three layers.