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This final paper for the session presents the results of the new draft earthquake hazard assessment for Australia and compares them to the previous AS1170.4 hazard values. Draft hazard maps will be presented for several spectral periods (0.0, 0.2 and 1.0 s) at multiple return periods (500, 2500 and 10,000 years). These maps will be compared with both the current earthquake hazard used in AS1170.4 and with other assessments of earthquake hazard in Australia. In general the hazard in the draft map is higher in the western cratonic parts of Australia than it is in the eastern non-cratonic parts of Australia. Where regional source zones are included, peaks in hazard values in the map are generally comparable to those in the current AS1170.4 map. When seismicity 'hotspot zones are included, as described in the previous paper, several of them produce much higher hazard peaks than any in the AS1170.4 map. However, such hotspots do not affect as large an area as many of those in the current AS1170.4 map. Finally, hazard curves for different cities will also be presented and compared to those predicted by the method outlined in AS1170.4.

The first RSTT model for Australia has been developed based on the Australian Seismological Reference Model (AuSREM) that was released in late 2012. The densely-gridded P and S wave distributions of the crust and upper mantle of AuSREM have been simplified and translated into the 7 layer crustal and upper mantle RSTT model. Travel times computed with this RSTT model are evaluated against travel times computed in full 3D through the AuSREM model to assess the impact of the approximations used by RSTT. Location estimates of 5 ground truth earthquakes (GT1, GT2 and GT5) using the global ak135 reference model, the RSTT model and the full 3D travel times are compared. It is found that the RSTT model can reproduce the 3D travel times fairly accurately within its distance of applicability, thereby improving location estimates compared to using a global travel time model like ak135. However the benefit of using RSTT for locating Australian earthquakes is far less than using full 3D travel times, mainly because most stations tend to be further away from the source than the distance of RSTT applicability.

Legacy product - no abstract available

Geoscience Australia has more than 50 years experience in the acquisition of deep crustal onshore seismic data, beginning with analogue low-fold explosive data, progressing through digital explosive data, and finally, in the last 12 years, moving into the digital vibroseis era. Over the years, shot data in a variety of formats has been recovered from a variety of media, both in-house and by external contractors. Processing through to final stack stage was used as a QC tool for transcription of some of the older analogue surveys, and proved so successful that the reprocessed data was released for interpretation. In other cases, more recent digital explosive surveys have benefited from reprocessing using modern processing algorithms. Key modules in Paradigm Geophysical's Disco/Focus software used by Geoscience Australia for reprocessing old data include refraction statics, spectral equalisation, stacking velocity analysis, surface consistent automatic residual statics and coherency enhancement. Coherency enhancement is commonly carried out on both NMO corrected shots and stack sections, with several iterations of NMO and autostatics. With the irregular offset distribution and low fold of legacy explosive data, dip moveout (DMO) correction is not possible, but due to the shorter spreads is not as critical as for modern high fold vibroseis data. Nevertheless, 'poor man's DMO' has proved successful in the shallow section, by the simple expedient of omitting 25% of the traces with the longest offsets.

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.

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.

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.

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

Legacy product - no abstract available