Legacy product - no abstract available

Legacy product - no abstract available

This paper describes the methods used to define earthquake source zones and calculate their recurrence parameters (a, b, Mmax). These values, along with the ground motion relations, effectively define the final hazard map. Definition of source zones is a highly subjective process, relying on seismology and geology to provide some quantitative guidance. Similarly the determination of Mmax is often subjective. Whilst the calculation of a and b is quantitative, the assumptions inherent in the available methods need to be considered when choosing the most appropriate one. For the new map we have maximised quantitative input into the definition of zones and their parameters. The temporal and spatial Poisson statistical properties of Australia's seismicity, along with models of intra-plate seismicity based on results from neotectonic, geodetic and computer modelling studies of stable continental crust, suggest a multi-layer source zonation model is required to account for the seismicity. Accordingly we propose a three layer model consisting of three large background seismicity zones covering 100% of the continent, 25 regional scale source zones covering ~50% of the continent, and 44 hotspot zones covering 2% of the continent. A new algorithm was developed to calculate a and b. This algorithm was designed to minimise the problems with both the maximum likelihood method (which is sensitive to the effects of varying magnitude completeness at small magnitudes) and the least squares regression method (which is sensitive to the presence of outlier large magnitude earthquakes). This enabled fully automated calculation of a and b parameters for all sources zones. The assignment of Mmax for the zones was based on the results of a statistical analysis of neotectonic fault scarps.

Legacy product - no abstract available

Legacy product - no abstract available

Legacy product - no abstract available

Legacy product - no abstract available

Stations on the Australian continent receive a rich mixture of ambient seismic noise from the surrounding oceans and the numerous small earthquakes in the earthquakes belts to the north in Indonesia and east in Tonga-Kermadec as well as more distant source zones. The noise field at a station contains information about the structure in the vicinity of the site and this can be exploited by applying an autocorrelation procedure to continuous records. Continuous vertical component records from 242 stations (permanent and temporary) across the continent have been processed using running windows of 6 hours long with subsequent stacking. A distinctive pulse, with a time delay between 8 and 30 s from zero offset, is found in the autocorrelation results. This pulse has a frequency content between 1.5 and 3 Hz suggesting P-wave multiples trapped in the crust. Synthetic modeling, with control of multiple phases, shows that a local PmP phase can be recovered with the autocorrelation method. We are therefore able to use this identification to map out the depth to Moho across the continent, and obtain results that largely conform to those from previous studies using a combination of data from refraction, reflection profiles and receiver functions. This approach can be used for Moho depth estimation using just vertical component records and effective results can be obtained with temporary deployments of just a few months.

Recent earthquake disasters in Indonesia, such as the 2006 Yogyakarta (Mw 6.3, 5749 deaths) and the 2009 Padang (Mw 7.5, over 1100 deaths) earthquakes, together with a long history of earthquake occurrence suggesting the potential for even more lethal disasters in the future, highlight an urgent need for measures to reduce earthquake fatalities. Better land use planning, emergency management training based on credible earthquake scenarios, and improved building codes are all effective means for reducing earthquake fatalities, but these all need to be underpinned by a reliable earthquake hazard assessment. Moreover, a robust and sustainable process for periodically updating such assessments is needed in order to keep pace with developments in Indonesian geology and seismology that are rapidly improving the level of knowledge of earthquake occurrence and the propagation of seismic waves.

This booklet is an update of Earthquakes in the Canberra Region published by the Australian Geological Survey Organisation (AGSO, now Geoscience Australia) and the ACT Emergency Services Bureau in 1996. As 10 years have passed since the previous booklet was published, it was considered appropriate to produce an updated version which includes the more recent earthquake activity in the ACT and surrounding region. Postage and handling costs will be charged for distribution of this product.