Unique challenges are faced in modelling faults in intraplate regions for seismic hazard purposes. Low fault slip rates compared to landscape modification rates lead to often poor discoverability of fault sources, and favours incomplete characterisation of rupture behaviours. Irrespective, regional and local test cases have demonstrated that fault sources assigned activity rates consistent with paleoseismic observations have the potential to significantly impact probabilistic seismic hazard assessments in Australia. To reflect this, the 2018 Australian NSHA will for the first time incorporate a fault source model. The model includes over 300 onshore faults, and a handful of offshore faults, which are modelled as simplified planes and assigned a general dip and dip direction. Dips are obtained from seismic-reflection profiles, where available, or inferred by taking into account surface geology and geomorphology, or other fault geometries within similar neotectonic settings. The base of faulting is generally taken as the regional maximum depth of distributed seismicity. Slip rates are calculated from displaced strata of known age, estimated from surface expression, or are extrapolated from other faults within similar neotectonic settings. We construct logic trees to capture epistemic uncertainty in fault source parameters, including magnitude frequency distribution, and the potential for random, periodic or episodic recurrence behaviour. This presentation introduces the new fault source database, the fault source logic tree as it currently exists, and discusses uncertainty in and sensitivity to various elements of the proposed fault source input model.

Four smoothed seismicity models were submitted for consideration to the 2018 National Seismic Hazard Assessment (NSHA18). Three of the models used fixed smoothing bandwidths, each with slightly different implementations, while the fourth used an adaptive smoothing bandwidth that varies spatially based on earthquake density. In this paper we assess the performance of these models at forecasting activity rates over decadal timescales by using part of the earthquake catalogue used for NSHA18 to develop the models and calculating the log-likelihood of the model activity rates against the remainder of the catalogue. We test the performance of the models at forecasting rates of earthquakes of different magnitudes over different lengths of training and forecast periods, and compare the use of non-declustered and declustered earthquake catalogues. We test for time-dependence by running the comparisons sequentially and using an earthquake catalogue randomised in time. The results are used to evaluate and inform the final implementation of the smoothed seismicity models for calculating 10% in 50 year probability ground motion exceedances for the NSHA18. This abstract was submitted and presented to the 2017 Australian Earthquake Engineering Society Conference (AEES) ( https://aees.org.au/2017-aees-conference/)

The 2018 revision of Australia's National Seismic Hazard Assessment (NSHA18) represents a substantial improvement from the 2013 NSHA. In particular, this revision will include a fault source models, an improved and more homogeneous earthquake catalogue, and greater epistemic uncertainty through a call for third party source models. This paper presents updated models of seismicity and ground motion that are currently being developed at Geoscience Australia for the NSHA. We use the OpenQuake software to calculate seismic hazard for Australia and compare with OpenQuake implementations of third-party models and the 2013 NSHA. Weighting of logic tree branches for alternative models are discussed, and how these relate to the fundamental datasets on which they are based. A smoothed seismicity model is developed based on recent seismicity while source models derived from neotectonic fault data consider a much longer time history. Final weightings, including for third party models, will be determined in consultation with members of the Australian seismological community.

The 2018 revision of Australia's National Seismic Hazard Assessment (NSHA) represents a substantial improvement from the 2013 NSHA. In particular, this revision will include active fault models, an improved and more homogeneous earthquake catalogue, and greater epistemic uncertainty through a call for third party source models. This paper presents models of seismicity and ground motion that are currently being developed at Geoscience Australia for the NSHA, as implemented in the OpenQuake software. Weighting of logic tree branches for alternative models are discussed, and how these relate to the fundamental datasets on which they are based. For example, a smoothed seismicity model considers only recent seismicity while source models derived from neotectonic data consider a much longer time history. Final weightings will be determined in consultation with members of the Australian seismological community. This abstract was submitted and presented to the 2016 Australian Earthquake Engineering Society Conference (AEES) ( https://aees.org.au/aees-asian-seismological-commission-conferences/)