Geoscience Australia (GA) has acquired land seismic data for more than 40 years, and since 1980 has acquired in excess of 15 000 km of onshore deep crustal seismic reflection data and numerous 2D seismic refraction profiles. Expertise in magnetotelluric (MT) data is being developed. Many kilometres of seismic reflection data have also been acquired across Australia's offshore regions.

A new catalogue of Australian earthquakes has been complied which contains 28000 earthquakes of which 17000 are considered main-shocks. The catalogue is complete for all of Australia above M5.5 since 1910, M5 since 1960, M4 since 1970 and M3.5 since 1980. In southern Australia it is complete above M3.5 since 1965 and M2 since 1980. Due to the generally sparse network the location uncertainty of Australian earthquakes is high with only 60% of contemporary earthquakes being located with an uncertainty of 10 km or less. This percentage will be smaller for earthquakes prior to 1980 with very few earthquakes prior to 1960 being located to within 10km. Most of the well located earthquakes are in the southern areas of the continent. The depth of Australian earthquakes are mostly between 8 and 18 km, except for the southwest corner of the continent where they are shallower than 5 km. Local magnitude scales were developed for Australia around 1990, prior to which the Richter magnitude scale was generally used. However at 600 km, a typical hypo-central distance in Australia, the Richter formula gives an overestimate of the magnitude of around 0.5 units. This results in the catalogues pre and post the early 1990's possibly being discrepant. The seismicity in some areas of Australia including the southeast corner, Adelaide fold belt, and the northwest corner, has been ongoing at a steady level for at least 100 years. The seismicity in the southwest corner the seismicity jumped by at least six in the 1940s and has been ongoing since then. The seismicity of much of the rest of Australia appears to be dominated by episodic seismicity. These episodes are characterised by a period of high activity lasting 1-10 years normally associated with a large (M>6) earthquake. Following the large earthquake there is often a period of moderate activity lasting a few years to a few decades. Preceding and following each episode is a period of low activity lasting 0.1ka to 10ka. The seismicity during this quiet period is more than an order of magnitude lower than during the period of high activity. Using the earthquakes since 1970, in the new catalogue, Frequency-Magnitude relations were calculated. Gutenberg-Richter a and b values were calculated on an 85 km grid of Australia. Using the a and b values maps of the probability of a magnitude 5 or greater event per year were produced and are very similar to the GSHAP map for Australia. The resulting maps were used to define four large (> 20000km2) seismogenic zones. There are also several other small zones, some of which appear reflect recent episodes and others appear to be long lived. The expected number of magnitude 5 or greater, 6 or greater, strain rate and deformation rate is given for the four zones, the remainder of Australia and the whole Australian continent. Combining estimate of strain from seismic, GPS and SLR data suggests compressive deformation across Australia of 0.6?2.0mm per year.

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.

A detailed assessment of the impact of a far-field tsunami on the Australian coastline was carried out in the Steep Point region of Western Australia following the July 17 2006 Java tsunami. Tsunami inundation and run-up were mapped on the basis of eyewitness accounts, debris lines, vegetation damage and the occurrence of recently deposited fish, starfish, corals and sea urchins well above high-tide mark. A topographic survey using kinematic GPS with accuracies of 0.02 metres in the horizontal and 0.04 metres in the vertical recorded flow depths of between 1-2 m, inundation of up to 200 m inland, and a maximum recorded run-up of 7.9 m AHD (Australian Height Datum). The tsunami impacted the sparsely-populated Steep Point coastline close to low tide. It caused widespread erosion in the littoral zone, extensive vegetation damage and destroyed several campsites. Eyewitnesses reported three waves in the tsunami wave train, the second being the largest. A sand sheet, up to 14 cm thick and tapering landwards over 200 m, was deposited over coastal dunes. The deposits are predominantly composed of moderately well sorted, medium grained carbonate sand with some gravel and organic debris. A basal unconformity defines the boundary between tsunami sediments and underlying aeolian dune sand. Evidence for up to three individual waves is preserved as normally graded sequences mantled by layers of dark grey, organic-rich fine silty sand. Given the strong wind regimes in the area, and the similarity of the underlying dune deposits to the tsunami sediments, it is likely that seasonal erosion will remove all traces of these sediment sheets within years to decades.

Legacy product - no abstract available

Steeply dipping reflectors have been recognised on stack data for the Lachlan Fold Belt (up to 60º) and the Tanami Province (up to 70º), demonstrating that significant dip filtering does not occur during acquisition with regional parameters. DMO correction is essential during processing to correctly image such features. These events appear to be real reflections not reflected refractions or diffractions, as proved by analysis of amplitude, frequency and moveout on shot records. In the Tanami case, the reflection is related to a small circular feature in the potential field image, possibly the expression of a granite stock. Migration proved problematical, as most migration algorithms could not simultaneously migrate the steep dips and remain artefact free in other parts of the section, suggesting that interpretation must be done on multiple sections in such cases.

One of the important inputs to a probabilistic seismic hazard assessment is the expected rate at which earthquakes within the study region. The rate of earthquakes is a function of the rate at which the crust is being deformed, mostly by tectonic stresses. This paper will present two contrasting methods of estimating the strain rate at the scale of the Australian continent. The first method is based on statistically analysing the recently updated national earthquake catalogue, while the second uses a geodynamic model of the Australian plate and the forces that act upon it. For the first method, we show a couple of examples of the strain rates predicted across Australia using different statistical techniques. However no matter what method is used, the measurable seismic strain rates are typically in the range of 10-16s-1 to around 10-18s-1 depending on location. By contrast, the geodynamic model predicts a much more uniform strain rate of around 10-17s-1 across the continent. The level of uniformity of the true distribution of long term strain rate in Australia is likely to be somewhere between these two extremes. Neither estimate is consistent with the Australian plate being completely rigid and free from internal deformation (i.e. a strain rate of exactly zero). This paper will also give an overview of how this kind of work affects the national earthquake hazard map and how future high precision geodetic estimates of strain rate should help to reduce the uncertainty in this important parameter for probabilistic seismic hazard assessments.

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 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.

The 2005 Tanami Seismic Survey consisted of 720 km of deep crustal seismic reflection data acquired along 4 lines. The processing was aimed at obtaining a high quality image of the crust from the Moho to the surface, with particular emphasis on imaging shallow features and steeply dipping reflectors. The key processing steps applied here included refraction and automatic statics, spectral equalisation, detailed velocity analysis pre and post DMO, and omega-x migration. Near surface features were better imaged using a floating datum technique for refraction statics application, with only the residual CDP static applied before NMO correction, and the mean CDP static after migration. Offset regularization of CDP gathers pre DMO employed trace interpolation based on dip coherency which had the dual advantage of improving signal to noise, and normalizing amplitudes in low-fold areas, thus reducing migration smiles.