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Dan Sandiford added Appendix 2. Previous Studies.tex
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\section{Appendix 2. Previous Studies}
\subsection{Comparisons with previous studies}
Studies summarised here are the 2012 Australia Earthquake Hazard Map (AEHM) (Burbidge, 2012), the AUS5 model (Brown and Gibson, 2001) and the active fault study of Somerville et al. (2008). A description of a number of earlier models can be found in Brown and Gibson (2001).
\subsubsection{Aus5}
The Aus5 model was intended to be dynamic model, allowing for the updating of information as well as the addition of new discoveries as they happen (Brown and Gibson, 2001). Substantial changes in inputs and ‘input methodology’ mean that the VEHM is not intended as update of Aus5. In particular, this model does not follow the ‘hierarchical approach’ of Aus5. We have opted for a simpler approach to building zones, and only feel that incorporation of other geophysical observables (i.e. geologic region, depth to moho etc.) is only warranted if a correlation between those and seismicity can be shone. An area zone-only version of Aus5 was compiled with parameters provided by Gary Gibson for comparison. Figure 10 shows the difference between this model and Model 1 (area zones only) in the current study; Figure 9 shows the values of VEHM minus AUS5. In general, AUS5 gives higher hazard values in areas of low seismicity (Melbourne, far east). Compared to Aus5, the VEHM has anomalously high hazard predictions for areas of southwest Gippsland, and the region north of Echuca (southern NSW) due to the high slip rate assigned to the Cadell Fault.
\subsubsection{2012 Australian Earthquake Hazard map}
The 2012 Australian Earthquake Hazard Map has been recommended as a replacement to the current earthquake loading code AS1170.4-2007. The 2012 AEHM represents a very comprehensive study, re-examining a number of the subcomponents of PSHA including catalogue, declustering methodology, area source zone methodology, Ground Motion Prediction Equations, etc.
Apart from using different computational approaches (Monte Carlo probability distribution vs. traditional Cornell-like PSHA), the main difference between the 2012 Australian Earthquake Hazard Map and the current study is that the former does not include any information on ‘active’ faults. The case for either option is probably best described as intuitive, given that the relationship between “active” faults and seismicity appears ambiguous. Some studies have shown that seismic moment release rate (strain rate) is a good fit to geologically-derived uplift rates in southeastern Australia (Braun et al. 2009).
There is a significant discrepancy between hazard values in the Victorian Earthquake Hazard Map models and the Australian Earthquake Hazard Map. For the AEHM, peak Victorian PGA values are ~ 0.1 g, for the 500 year return period, campared to 0.23 g in the VEHM. This is obviously a concern for stakeholders and is there is ongoing work between Geoscience Australia and the University of Melbourne / Australia Geophysical Observing System to reconcile the differences in calculated hazard values. Overwhelmingly though, we believe, it is the use of an ‘enforced’ b-value of 1.0 in ‘hotspot zones’ in the AEHM, (as well as the reduced M_Max in those zones) which lowers the estimated hazard in that model.
These matters will remain a key part of ongoing work on the Victorian Earthquake Hazard Map project in 2014, along with the integration of the map with the GEM project.
