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.

The 10% in 50 year seismic hazard map is the key output from the 2018 National Seismic Hazard Assessment for Australia (NSHA18) as required for consideration by the Standards Australia earthquake loading committee AS1170.4

This ecat record refers to the data described in ecat record 123048. The data, supplied in shapefile format, is an input to the 2018 National Seismic Hazard Assessment for Australia (NSHA18) product (ecat 123020) and the 2018 Probabilistic Tsunami Hazard Assessment for Australia (PTHA18) product (ecat 122789).

This Geoscience Australia Record contains technical data and input files that, when used with the Global Earthquake Model’s (GEM’s) OpenQuake-engine probabilistic seismic hazard analysis software (Pagani et al., 2014), will enable end users to explore and reproduce the 2018 National Seismic Hazard Assessment (NSHA18) of Australia (Allen et al., 2018a). This report describes the NSHA18 input data only and does not discuss the scientific rationale behind the model development. These details are provided in Allen et al. (2018a) and references therein.

Located within an intraplate setting, continental Australia has a relatively low rate of seismicity compared with its surrounding plate boundary regions. However, the plate boundaries to the north and east of Australia host significant earthquakes that can impact Australia. Large plate boundary earthquakes have historically generated damaging ground shaking in northern Australia, including Darwin. Large submarine earthquakes have historically generated tsunami impacting the coastline of Australia. Previous studies of tsunami hazard in Australia have focussed on the threat from major subduction zones such as the Sunda and Kermadec Arcs. Although still subject to uncertainty, our understanding of the location, geometry and convergence rates of these subduction zones is established by global tectonic models. Conversely, actively deforming regions in central and eastern Indonesia, the Papua New Guinea region and the Macquarie Ridge region are less well defined, with deformation being more continuous and less easily partitioned onto discrete known structures. A number of recently published geological, geodetic and seismological studies are providing new insights into present-day active tectonics of these regions, providing a basis for updating earthquake source models for earthquake and tsunami hazard assessment. This report details updates to earthquake source models in active tectonic regions along the Australian plate boundary, with a primary focus on regions to the north of Australia, and a subsidiary focus on the Puyesgur-Macquarie Ridge-Hjort plate boundary south of New Zealand. The motivation for updating these source models is threefold: 1. To update regional source models for the 2018 revision of the Australian probabilistic tsunami hazard assessment (PTHA18); 2. To update regional source models for the 2018 revision of the Australian national seismic hazard assessment (NSHA18); and 3. To provide an updated database of earthquake source models for tsunami hazard assessment in central and eastern Indonesia, in support of work funded through the Department of Foreign Affairs and Trade (DFAT) DMInnovation program.

The 2018 National Seismic Hazard Assessment (NSHA18) aims to provide the most up-to-date and comprehensive understanding of seismic hazard in Australia. As such, NSHA18 includes a range of alternative models for characterising seismic sources and ground motions proposed by members of the Australia earthquake hazard community. The final hazard assessment is a weighted combination of alternative models. This report describes the use of a structured expert elicitation methodology (the ‘Classical Model’) to weight the alternative models and presents the complete results of this process. Seismic hazard assessments are inherently uncertain due to the long return periods of damaging earthquakes relative to the time period of human observation. This is especially the case for low-seismicity regions such as Australia. Despite this uncertainty, there is a demand for estimates of seismic hazard to underpin a range of decision making aimed at reducing the impacts of earthquakes to society. In the face of uncertainty, experts will propose alternative models for the distribution of earthquake occurrence in space, time and magnitude (i.e. seismic source characterisation), and how ground shaking is propagated through the crust (i.e. ground motion characterisation). In most cases, there is insufficient data to independently and quantitatively determine a ‘best’ model. Therefore it is unreasonable to expect, or force, experts to agree on a single consensus model. Instead, seismic hazard assessments should capture the variability in expert opinion, while allowing that not all experts are equally adept. Logic trees, with branches representing mutually exclusive models weighted by expert opinion, can be used to model this uncertainty in seismic hazard assessment. The resulting hazard assessment thereby captures the range of plausible uncertainty given current knowledge of earthquake occurrence in Australia. For the NSHA18, experts were invited to contribute peer-reviewed seismic source models for consideration, resulting in 16 seismic source models being proposed. Each of these models requires values to be assigned to uncertain parameters such as the maximum magnitude earthquake expected. Similarly, up to 20 published ground motion models were identified as being appropriate for characterising ground motions for different tectonic regions in Australia. To weight these models, 17 experts in seismic hazard assessment, representative of the collective expertise of the Australian earthquake hazard community, were invited to two workshops held at Geoscience Australia in March 2017. At these workshops, the experts each assigned weights to alternative models representing their degree of belief that a particular model is the ‘true’ model. The experts were calibrated through a series of questions that tested their knowledge of the subject and ability to assess the limits to their knowledge. These workshops resulted in calibrated weights used to parameterise the final seismic source model and ground motion model logic trees for NSHA18. Through use of a structured expert elicitation methodology these weights have been determined in a transparent and reproducible manner drawing on the full depth of expertise and experience within the Australia earthquake hazard community. Such methodologies have application to a range of uncertain problems beyond the case of seismic hazard assessment presented here.

People in Australia are surprised to learn that hundreds of earthquakes occur below our feet every year. The majority are too small to feel, let alone cause any damage. Despite this, we are not immune to large earthquakes.

High‐resolution optical satellite imagery is used to quantify vertical surface deformation associated with the intraplate 20 May 2016 Mw 6.0 Petermann Ranges earthquake, Northern Territory, Australia. The 21 ± 1‐km‐long NW trending rupture resulted from reverse motion on a northeast dipping fault. Vertical surface offsets of up to 0.7 ± 0.1m distributed across a 0.5‐to‐1‐km‐wide deformation zone are measured using the Iterative Closest Point algorithm to compare preearthquake and postearthquake digital elevation models derived from WorldView imagery. The results are validated by comparison with field‐based observations and interferometric synthetic aperture radar. The pattern of surface uplift is consistent with distributed shear above the propagating tip of a reverse fault, leading to both an emergent fault and folding proximal to the rupture. This study demonstrates the potential for quantifying modest (<1 m) vertical deformation on a reverse fault using optical satellite imagery.

Many mapped faults in the south-eastern highlands of New South Wales and Victoria are associated with apparently youthful topographic ranges, suggesting that active faulting may have played a role in shaping the modern landscape. This has been demonstrated to be the case for the Lake George Fault, ~25 km east of Canberra. The age of fluvial gravels displaced across the fault indicates that relief generation of approximately 250 m has occurred in the last ca. 4 Myr. This data implies a large average slip rate by stable continental region standards (~90 m/Myr assuming a 45 degree dipping fault), and begs the question of whether other faults associated with relief in the region support comparable activity rates. Preliminary results on the age of strath terraces on the Murrumbidgee River proximal to the Murrumbidgee Fault are consistent with tens of metres of fault activity in the last ca. 200 kyr. Further south, significant thicknesses of river gravels are over-thrust by basement rocks across the Tawonga Fault and Khancoban-Yellow Bog Fault. While these sediments remain undated, prominent knick-points in the longitudinal profiles of streams crossing these faults suggest Quaternary activity commensurate with that on the Lake George Fault. More than a dozen nearby faults with similar relief are uncharacterised. Recent seismic hazard assessments for large infrastructure projects concluded that the extant paleoseismic information is insufficient to meaningfully characterise the hazard relating to regional faults in the south-eastern highlands, despite the potential for large earthquakes alluded to above. While fault locations and extents remain inconsistent across scales of geologic mapping, and active fault lengths and slip rates remain largely unquantified, the same conclusion may be drawn for other scales of seismic hazard assessment.

The 6th Generation seismic hazard model of Canada is being developed to generate seismic design values for the 2020 National Building Code of Canada (NBCC2020). Ground-motion models (GMMs) from the Next Generation Attenuation (NGA)-West 2 and NGA-East programs are used and epistemic uncertainty in ground-motion models is captured through the use of a classical weighted logic tree framework. For the first time, seismic hazard is computed directly on primary (e.g. A-E) seismic site classes from their time-averaged shear wave velocities in the upper 30 m of the crust (VS30). This approach simplifies the way end users will determine seismic design values for a given location and site class, while having other technical advantages such as capturing epistemic uncertainty in site amplification models. It will remove the need for separate site amplification look-up tables in the building code, enabling users to simply supply their location and site class to determine seismic design values. In general, the new ground- motion models predict higher hazard in most Canadian localities due to a variable combination of changes in median ground motions, site amplification and aleatory uncertainty.