The Mw=7.8 earthquake of 15 July, 2009 occurred along a section of the subduction zone south of New Zealand, where the Puysegur Block subducts beneath the Pacific Plate. The orientation of this subduction zone suggests that tsunamis generated along it pose a significant threat to the southeast coast of Australia, but since it had not experienced megathrust rupture until the 15 July event, the question of whether it was accumulating strain energy whose release could result in a large tsunami was open. We have used seismic, tsunami, geodetic and SAR data to study this earthquake and find that it involved primarily thrust motion on a fault plane dipping east at a shallow angle, consistent with expectations for a megathrust earthquake. The ability to use multiple data types to study this earthquake lead to improved ability to resolve parameters such as rupture velocity that are often difficult to constrain with seismic data alone. Seismic array data agree with rupture modelling of broadband waveforms in their prediction of a bilateral component to the earthquake rupture. Also, a tsunami of about 10 cm peak-to-peak amplitude was recorded by two tsunameter buoys in the Tasman Sea west of the epicenter, and we find that the tsunami travel times indicated by these data suggest the earthquake was characterised by a low rupture velocity of around 1 km/s. We will also present comparisons against GPS and InSAR data that further constrain parameters of the rupture. Finally, we will discuss the potential for earthquake activity further south along the Puysegur Trench, which poses a tsunami threat particularly to the eastern coast of Tasmania.

The recently released ISC-GEM catalogue was a joint product of the International Seismological Center (ISC) and the Global Earthquake Model (GEM). In a major undertaking it collated, from a very wide range of sources, the surface and body wave amplitude-period pairs from the pre digital era; digital MS, mb and Mw; collated Mw values for 970 earthquakes not included in the Global CMT catalogue; used these values to determine new non-linear regression relationship between MS and Mw and mb and Mw. They also collated arrival picks, from a very wide range of sources, and used these to recompute the location, initially using the EHB location algorithm then revised using the ISC location algorithm (which primarily refined the depth). The resulting catalogues consists of 18871 events that have been relocated and assigned a direct or indirect estimate of Mw. Its completeness periods are, Ms - 7.5 since 1900, Ms - 6.25 1918 and Ms - 5.5 1960. This catalogue assigns, for the first time, an Mw estimate for several Australian earthquakes. For example the 1968 Meckering earthquake the original ML, mb and MS were 6.9, 6.1 and 6.8, with empirical estimates of Mw being 6.7 or 6.8. The ISC-GEM catalogue assigns an Mw of 6.5. We will present a poster of the Australian events in this ISC_GEM catalogue showing, where available, the original ML, mb, Ms, the recalculated mb and Ms, and the assigned Mw. We will discuss the implications of this work for significant Australian earthquakes.

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.

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.

Deep-seismic reflection data across the Eastern Goldfields Province, northeastern Yilgarn Craton, Western Australia have provided information on the region?s crustal architecture and on several of its highly mineralised regions. The seismic reflection data has imaged several prominent crustal scaled features, including an eastward thickening of the crust across the northeastern Yilgarn Craton, the subdivision of the crust into three broad layers, the presence of a prominent east dip to the majority of the reflections and the interpretation of three east-dipping crustal-penetrating shear zones. These east-dipping shear zones are major structures that subdivide the region into four terranes. Major orogenic gold deposits in the Eastern Goldfields Province are spatially associated with these major structures. The Laverton Tectonic Zone, for example, is a highly mineralised corridor that contains several world-class gold deposits plus many other smaller deposits. Other non crustal-penetrating structures within the area do not appear to be as well endowed as the Laverton structure. In all the major structures a wedge-geometry is formed at the intersection of the east-dipping shear and a low-angle shear zone within its hanging wall. This wedge-geometry forms a suitable trap where the upward and/or sub-horizontal moving fluids were focused into the wedge's apex and then distributed and deposited into the surrounding complexly deformed greenstones.

Legacy product - no abstract available

We compare GPS derived geodetic strain rates with estimates from seismic moment release for the Western Australian Seismic Zone. The geodetic strain rates were derived from occupations, in 2002 and 2006, of a 48 site regional network in the SW corner of Australia. The high precision nature of the experiment enabled us to identify 16 sites where antenna errors were the cause of the anomalous displacements. The cause of this is considered to be due to errors in the phase centre of three antennas. The ~1200 km2 study area is one of the most seismically active areas of mid-continental crust worldwide. The geodetic and seismic derived compressional strain-rates are 0.8±0.8 x10-9 yr-1 and 4.9 ±1.9 x10-9 yr-1 (±1) respectively. In effect, the geodetic strain rate would appear to be significantly less than the seismic rate which is amongst the highest of all mid-continental crust rates. With over 95% confidence we can exclude the geodetic and seismic strain rates being the same. This suggests that the contemporary seismic moment release it significantly higher than the long-term moment release. Thus the seismicity of this region is possibly not following the Poissonian behaviour normally observed for inter-plate earthquakes and may be episodic. Thus estimates of the long-term seismic hazard in this area based solely on the earthquake data are likely to be overestimates. Whether the geodetic stain rate reflects the Australian continental average or an intermediate value will require several repeat occupations.

Geoscience Australia (GA) is currently undertaking the process to update the Australian National Earthquake Hazard Map using modern methods and an extended catalogue of Australian earthquakes. This map is a key component of Australia's earthquake loading code. The characterisation of strong ground-shaking using Ground-Motion Prediction Equations (GMPEs) underpins any earthquake hazard assessment. We have recently seen many advances in ground-motion modelling for active tectonic regions. However, the challenge for Australia - as it is for other stable continental regions - is that there are very few ground-motion recordings from large-magnitude earthquakes with which to develop empirically-based GMPEs. Consequently, we need to consider other numerical techniques to develop these models in the absence of these data. Recently published Australian-specific GMPEs which employ these numerical techniques are now available and these will be integrated into GA's future hazard outputs. This paper addresses several fundamental aspects related to ground-motion in Australia that are necessary to consider in the update of the National Earthquake Hazard Map, including: 1) a summary of recent advances of ground-motion modelling in Australia; 2) a comparison of Australian GMPEs against those commonly used in other stable continental regions; 3) a comparison of new GMPEs against their intensity-based counterparts used in the previous hazard map; and 4) the impact of updated attenuation factors on local magnitudes in southeastern Australia. Specific regional and temporal aspects of magnitude calculation techniques across Australia and its affects on the earthquake catalogue will also be addressed.

The year was another marginally below average one with respect to the frequency and magnitude of earthquakes in Australia; there were two of magnitude 5 or more but no large earthquakes of magnitude 6 or more. It was an above average year for major earthquakes worldwide with one great earthquake of maptude M 8.2 and 16 of magnitude M 7.0 or more.

The Southern McArthur Basin, host to the world class McArthur River (HYC) Zn-Pb-Ag deposit, contains an unmetamorphosed, relatively undeformed Palaeoproterozoic to Mesoproterozoic succession of carbonate, siliciclastic and volcanic rocks. Seismic reflection data obtained across this basin have the potential to revolutionise our understanding of the crustal architecture in which this deposit formed. These data were collected in late 2002 as part of a study to examine the fundamental basin architecture of the Southern McArthur Basin and the nature of underlying basement. Much of the seismic program was designed to test geometric models in this area, including tectonostratigraphy, fault systems and basement structure. The results have wider applicability because the basin is considered to be a little deformed analogue of the Western Succession of Mt Isa. The main seismic line (02GA-BT1) was oriented east-west across the Southern McArthur Basin, commenced 15 km west of Borroloola, and extended about 110 km westwards along the Borroloola-Roper Bar road. A short north-south cross line (02GA-BT2), 20 km long, was acquired within the basin itself, in collaboration with AngloAmerican.