Geoscience Australia, together with contributors from the wider Australian seismology community, has produced a National Seismic Hazard Assessment (NSHA18) that is intended as an update to the 2012 National Seismic Hazard Maps (NSHM12; Burbidge, 2012; Leonard et al., 2013). This Geoscience Australia Record provides an overview of the development of the NSHA18. Time-independent, mean seismic design values are calculated on Standards Australia’s AS1170.4 Soil Class Be (at VS30=760 m/s) for the horizontal peak ground acceleration (PGA) and for the geometric mean of the spectral accelerations, Sa(T), for T = 0.1, 0.2, 0.3, 0.5, 1.0, 2.0 and 4.0 s over a 15-km national grid spacing. Hazard curves and uniform hazard spectra are also calculated for key localities. Maps of PGA, in addition to Sa(0.2 s) and Sa(1.0 s) and for a 10% probability of exceedance in 50 years (Figure A). Additional maps and seismic hazard products are provided in a separate Geoscience Australia Record (Allen, 2018).
The NSHA18 update yields many important advances over its predecessors, including:
- the calculation in a full probabilistic framework (Cornell, 1968) using the Global Earthquake Model Foundation’s OpenQuake-engine (Pagani et al., 2014);
- the consistent expression of earthquake magnitudes in terms of moment magnitude, MW;
- inclusion of a national fault-source model based on the Australian Neotectonic Features database (Clark et al., 2016);
- the inclusion of epistemic (i.e. modelling) uncertainty:
- through the use of multiple alternative source models;
- on magnitude-recurrence distributions;
- fault recurrence and clustering models;
- on maximum earthquake magnitudes for both fault and area sources through an expert elicitation workshop; and
- the use of modern ground-motion models, capturing the epistemic uncertainty on ground motion through an expert elicitation workshop.
