Defining a neotectonic fault in the intraplate context is relatively straightforward - the fault must have hosted displacement in the current crusta stress regime. Defining an active fault is far more problematic, depending upon the recurrence of the fault (and nearby faults) and the return period being considered for hazard purposes. This article discusses the term "active" and provides some examples of faults from eastern Australia for emphasis.

In the Cities Project Perth, GA is developing a multi-hazard risk assessment of the Perth metropolitan area. One of the main objectives of the Project is to develop an earthquake hazard and risk model for this area. The hazard model is developed using informaiton about earthquakes, the geology and the local soil characteristics of the region. As part of this process, we will develop several earthquake scenarios with events originating at specific locations in the region. To define an appropriate model of seismicity, the Cities Project initiated an expert debate to discuss and to formulate geological and seismological parameters for the Southwest Seismic Zone and the area around Perth. The debate was followed by a workshop in December 2002 in Canberra where the seismicity model of SW WA was ultimately defined. Further discussion was held following the workshop, culminating in an agreed seismicity model for the region.

Legacy product - no abstract available

This is an article summarising of the earthquake hazard work for 2009-10 for the society's newsletter.

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.

Power point presentation given to a meeting of earthquake hazard model stakeholders, in Sydney on July 22nd 2008.

The inventory of over 200 fault scarps captured in GA's Australian neotectonics database has been used to estimate the maximum magnitude earthquake (Mmax) across the Stable Continental Regions (SCRs) of Australia. This was done by first grouping the scarps according to the spatial divisions described in the recently published neotectonics domain model and calculating the 75th percentile scarp length for each domain. The mean Mmax was then found by averaging the maximum magnitudes predicted from a range of different published relations. Results range between Mw 7.0-7.5±0.2. This suggests that potentially catastrophic earthquakes are possible Australia-wide. These data can form the basis for future seismic hazard assessments, including those for building design codes, both in Australia and analogous SCRs worldwide.

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 Australian Seismological Report 2010 provides a summary of earthquake activity for Australia for 2010. 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 PIRSA describing Seismic Networks and providing Earthquake locations for South Australia.

On the 16 April 2011 (05:31:18 UTC) Geoscience Australia (GA) recorded a ML 5.3 earthquake 50 km west of Bowen in central Queensland. This event was widely felt on the north Queensland coast and was followed by a number of aftershocks, which resulted in GA receiving more than 400 felt reports. Fifty earthquakes of magnitude <5.0 have been recorded in the region between Charters Towers and Mackay since 1900. However, during this same period only one M >5.0 earthquake is recorded; a ML 5.7 event located north of Ravenswood in December 1913. The April 2011 Bowen main shock was quickly followed by five smaller aftershocks ranging in magnitude from ML 3.2 to 4.1. Aftershocks were recorded by permanent seismic stations (e.g. Charters Towers, Eidsvold, Quilpie and Roma), however, the location, magnitude and depth of the smaller events is improved by four temporary stations which were established within four days of the main shock. The temporary sites were deployed between 10 and 48 km from the epicentre of the main shock to maximise the azimuthal coverage. Three-component seismometer and accelerometer data were recorded for a total of six weeks. With this dataset, existing information about several aftershocks was improved.