Magnetic, gamma-ray and gravity data sets provide vital information for mineral and petroleum explorers as well as researchers studying the geology of the Australian continent. Commonwealth and State and Territory governments have devoted considerable resources to acquiring these data sets and making them available to encourage exploration. Geoscience Australia's geophysical databases contain data acquired by governments, and this report summarises coverages over Australia of these data. On the occasion of the centenary issue of Preview, it is worth reflecting on the advances in the coverage of publicly available magnetic, gamma-ray and gravity data over Australia since the first edition of Preview in February 1986. Since then the areas and resolution of coverages have increased dramatically. Quality of the data through better acquisition and processing techniques has also improved, and new types of data sets added to the explorers' supplies.

No abstract available

The benthic silicate and oxygen fluxes from Moreton Bay sediments were positively correlated (R2 =0.99) and the silicate to organic carbon flux ratio of 0.14 was similar to that for marine diatoms (0.13). The majority (about 75%) of the benthic silicate flux was attributed to the degradation of fresh diatomaceous detritus and the remainder could be contributed from clay (smectite) dissolution in the warm waters (30oC) during these summer months. Biogenic silica in the upper 2 cm of Moreton Bay sediments was enriched (Si:C = 0.35 +/- 0.25) with respect to the Si:C ratio (0.13 +/- 0.04) of dominant diatom populations, and we suggest that this enrichment is the result of the deposition of Si-enriched faecal pellets and diatom aggregates to the sediments. Combined hydrodynamic and biogeochemical processes resulted in distributions of biogenic silica and total organic carbon in the surface sediments that were spatially coincident. A silicate budget for Moreton Bay indicated the following. 1. The benthic input of silicate was balanced approximately by the silicate load to the sediments from primary productivity. 2. Silicate was recycled through diatomaceous phytoplankton about 18 times before it was lost to the ocean. 3. The export of silicate to the Pacific Ocean was about the same as the terrestrial input.

No abstract available

The spectral signature of an about 1 micrometer thick oil slick has been identified from airborne hyperspectral data (HyMap sensor) acquired over a floating oil production facility located on the North West Shelf of Australia. The paper describes spectral characteristrics of the signature and identifies conditions in which it can be observed.

The Lambert-Amery System is the largest glacier-ice shelf system in East Antarctica, draining a significant portion of the ice sheet. Variation in ice sheet discharge from Antarctica or Greenland has an impact on the rate of change in global mean sea level; which is a manifestation of climate change. In conjunction with a measure of ice thickness change, ice sheet discharge can be monitored by determining the absolute velocities of these glaciers. In order to demonstrate the capability of the DORIS system to determine glacier velocities, Geoscience Australia undertook a Pilot Project under the auspices of the International DORIS Service. A DORIS beacon was deployed on the Sorsdal (November 2001 - January 2002 and November 2003 - January 2004) and Mellor (December 2002 - January 2003) glaciers. The DORIS data, transmitted from the autonomously operating ground beacon for each satellite pass, were stored in the receiver on-board the satellite and later downlinked to the DORIS control centres for processing. This paper describes the campaigns that were conducted at the Sorsdal and Mellor glaciers, the data processing standards for modelling the Doppler measurements, precise orbit determination of the satellites using the data from the globally distributed DORIS network, tracking station position and reference frame modelling, the point positioning mode employed for determining the position and velocities of the transmitting beacon antennas located on the glaciers and provides the velocity estimates that have been determined from the analysis of these tracking data. For the Sorsdal 2001/2002 campaign, using SPOT-4 data only, the measured effective horizontal ice motion was estimated to be 30 ± 0.4 cm/day (azimuth of N246°E.± 1º). The inferred velocities for the Sorsdal 2003/2004 campaign, using SPOT-4 and SPOT-5 data, was 5.7 ± 0.8 cm/day (azimuth of N264°E ± 7.5°) for the first eight days and 11.4 ± 1.4 cm/day (azimuth of N241°E ± 1.5°) for the subsequent 21 days. There was a noted decrease in the inferred velocities between the beginning and the end of the observing period. A sub-division of the latter 21 day observing period into three segments showed a decrease in 2-D velocity from 18.3 ± 0.7 cm/day to 11.2 ± 0.7 cm/day and then to 7.4 ± 0.9 cm/day for the first, second and third segments respectively. In comparison, a GPS derived velocity over the time-span of the 2001/2002 Sorsdal campaign gave a mean ice flow rate of 31 cm/day. The GPS velocity was derived from two daily position estimates 65 days apart. The DORIS determination from 26 days of continuous SPOT-4 and SPOT-5 data compared well with the GPS derived velocity. For the 2002/2003 Mellor glacier campaign, using SPOT-4 and SPOT-5 data, the estimated average ice velocity was 104 ± 25 cm/day (azimuth of N33°E ± 0.1º); which compared well with an InSAR derived velocity of between 110 and 137 cm/day. The point positioning technique as implemented in this study was further validated and assessed by replicating the computational process to determine the position and velocity of the permanent International DORIS Service site at Terre Adélie, Antarctica. Through these experiments, it has been successfully demonstrated that the DORIS system is capable of determining the velocities of glaciers with an accuracy of a few cm/day over a period of several weeks; operating in remote regions in an autonomous mode. With an increasing number of DORIS-equipped satellites and multiple daily passes, it has the potential to measure glacial velocities at a high temporal resolution (sub-daily).

No abstract available

No abstract available

No abstract available

We explore the ability of W-phase waveform inversions 4 to recover a first-order coseismic slip distribution for large earthquakes. To date W-phase inversions for point sources provide fast and accurate moment tensor solutions for moderate to large events. We have applied W-phase finite fault inversion to seismic waveforms recorded following the 2010 Maule earthquake (Mw=8.8) and 2011 Tohoku earhquake (Mw = 9.0). Firstly, a W-phase point source inversion was performed to assist us in selecting the data for the finite fault solution. Then, we use a simple linear multiple-time-window method accounting for changes in the rupture velocity with smoothing and moment minimisation constrains to infer slip and rake variations over the fault. Our results describe well the main features of the slip pattern previously found for both events. This suggests that fast slip inversions may be carried out relying purely on W-phase records.