In September and October of 2011 Geoscience Australia surveyed part of the offshore northern Perth Basin, in order to map potential sites of natural hydrocarbon seepage. The primary objectives of the survey were to map the spatial distribution of seepage sites and characterise the nature of the seepage at these sites (gas vs oil, macroseepage vs microseepage; palaeo vs modern day seepage) on the basis of: - acoustic signatures in the water column, shallow subsurface and on the seabed; - geochemical signatures in rock and sediment samples and the water column, and; - biological signatures on the seabed.

This job was planned due to a requirement for high accuracy aerial photography to be used as part of a cadastral adjustment program. The high quality laser derived surface means that there would be minimal distortion on the part of the imagery and so it would suit the purpose well. The job was extended beyond the immediate town extents as the council was also interested in floodplain mapping and cadastral adjustment in the surrounds.

The Global Positioning System (GPS) and the Gravity Recovery and Climate Experiment (GRACE) have been used to respectively determine the Earth's surface deformation and gravity changes associated with Glacial Isostatic Adjustment (GIA), which is caused by ongoing stress release of the viscoelastic mantle after removal of the Late Pleistocene ice-sheets. Here we present a joint inversion analysis of the GPS derived radial (vertical) deformation and GRACE derived gravity changes in North America to examine whether the ice-sheets (ICE-5G) and earth models can fit the satellite based observations. The results from a three-layer earth model give a lithosphere thickness of 120~150km, an upper-mantle viscosity of 2.1~3.5 × 10**20 Pa s, and a lower-mantle viscosity of 1.3~1.7 × 10**21 Pa s. More sophisticated models such as introducing a transition zone of 400-670km are not fully resolved with current datasets because there is no significant improvement in fitting observations. Tests of modifying ICE-5G show that a reduction of ice thickness by ~20% in the area west of Hudson Bay and an increase by ~40% in the southeast (Quebec region) are required to fit both observed vertical deformation and gravity changes.

The Great Artesian Basin Water Resource Assessment (the Assessment) provides an analytical framework to assist water managers in the Great Artesian Basin (GAB) to meet National Water Initiative commitments. This report presents the findings of the Assessment for the Central Eromanga region: one of four reporting regions in the Assessment, including the Surat, Central Eromanga, Western Eromanga and Carpentaria regions.

This job is part of the town capture program

Report on the results of using a multibeam sonar to map the Darling River at Menindee

Collaboration between Geoscience Australia and the Attorney Generals Department. The map series depicts local government areas in WA eligible for NDRRA assistance following natural disasters.

Since the Indonesian islands of Sumatra and Java lie adjacent to an active subduction zone and include some of the world's most densely populated areas, the reduction of potential earthquake fatalities through improved building codes and seismic hazard assessments is a high priority. One of the most critical parts of an earthquake hazard assessment is a quantitative description of the level of ground motion generated by an earthquake, also known as Ground Motion Prediction Equations (GMPEs). We have developed a strong ground motion database for of Sumatra and Java. This catalog includes: best-available earthquake catalogue parameters; a compilation of site response information using various techniques; and ground motion parameters commonly used in seismology and engineering applications, such as response spectra. We will show how the database can be used for investigating which published Ground Motion Prediction Equation (GMPE) are appropriate to use for Indonesian earthquake hazard assessment.

3D inversion of potential-field data is a powerful technique for investigating subsurface geology. A common problem for geophysicists performing 3D inversion is acquiring sufficient computational power to produce models that cover the area of interest at an appropriate resolution. Being limited by computing power often means that models are degraded, in either their resolution or scale, to ensure they are computed within available resources. To manage this issue, a collaborative arrangement between Geoscience Australia (GA) and the National Computational Infrastructure (NCI) was established to ensure that geophysical modelling projects are supported by a supercomputing facility. NCI maintain Australia's highest performance supercomputer and 3D inversion modelling has been undertaken with parallelised University of British Columbia - Geophysical Inversion Facility (UBC-GIF) software. Using data from the national gravity and magnetic anomaly maps of Australia, inversions are prepared with the model-based trend removal method to remove the effect of anomalies outside the area of interest. Unconstrained density and magnetic susceptibility models have successfully been built for the Wallaby Plateau and the Capricorn Orogen of Western Australia. Models are regional-scale, high-resolution and generated within reasonable time frames. For example, the Capricorn Orogen model is 480 x 500 x 25 km in volume, contains 6.48 million cells and takes ~30 minutes to run. The Capricorn Orogen model supports the interpretation of recently collected seismic line data and identifies possible sutures separating the Pilbara, Capricorn and Yilgarn regions of Western Australia. Constrained gravity and magnetic inversions have been proposed to support the recently collected Yilgarn-Officer-Musgrave seismic line.

For well over a decade GPS time series have been used as an effective way of densifying a reference frame. During this period numerous advances have been made in the analysis and modelling techniques applied to GPS observations. This has seen GPS time series improve by almost an order of magnitude in accuracy, and has allowed even more challenging applications of GPS time series analysis to be investigated such as glacial isostasy, elastic deformation of the earth's crust due to atmospheric loading and atmospheric tomography. Despite numerous improvements in the GPS analysis technique to handle different error sources there still remains significant long term site-specific biases. The biases are often caused by local multi-path effects and/or near-field antenna phenomena and have an adverse impact on the signal being analysed. Typically the largest effect is seen in the height component or the scale of the reference frame determined by the GPS network. Correction of these site-specific systematic errors can not only remove biases, but will also reduce the phase residual noise level, thus providing a better resolution to distinguish the signal of interest. We will present a technique to detect, and model for long term systematic errors by using one-way phase residuals obtained from a post-processed GPS network. We will then assess the impact of applying these derived individual site models into a re-processed solution for the purposes of reference frame determination at the Regional and Global level. We will also asses the performance of these derived site-specific models for real-time solutions.