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.

One of the key challenges in assessing earthquake hazard in Australia is understanding the attenuation of ground-motion through the stable continental crust. There are now a handful of ground-motion models (GMMs) that have been developed specifically to estimate ground-motions from Australian earthquakes. These GMMs, in addition to models developed outside Australia, are considered in the 2018 National Seismic Hazard Assessment (NSHA18; Allen et al., 2017). In order to assess the suitability of candidate GMMs for use in the Australian context, ground-motion data forom small-to-moderate Australian earthquakes have been gathered. Both qualitative and quantitative ranking techniques (e.g., Scherbaum et al., 2009) have been applied to determine the suitability of candidate GMMs for use in the NSHA18. This report provides a summary of these ranking techniques and provides a discussion on the utility of these methods for use in seismic hazard assessments in Australia; in particular for the NSHA18. The information supplied herein was provided to participants of the Ground-Motion Characterisation Expert Elicitation workshop, held at Geoscience Australia on 9 March 2017 (Griffin et al., 2018).

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

Modern geodetic and seismic monitoring tools are enabling study of moderate-sized earthquake sequences in unprecedented detail. Here we use a variety of methods to examine surface deformation caused by a sequence of earthquakes near Lake Muir in Southwest Western Australia in late 2018. A shallow MW 5.3 earthquake near Lake Muir on the 16th of September 2018 was followed on the 8th of November by a MW 5.2 event in the same region. Focal mechanisms produced for the events suggest reverse and strike slip rupture, respectively. Recent improvements in the coverage and observation frequency of the Sentinel-1 Synthetic Aperture Radar (SAR) satellite in Australia allowed for the timely mapping of the surface deformation field relating to both earthquakes in unprecedented detail. Interferometric Synthetic Aperture Radar (InSAR) analysis of the events suggest that the ruptures are in part spatially coincident. Field mapping, guided by the InSAR results, revealed that the first event produced an approximately 3 km long and up to 0.5 m high west-facing surface rupture, consistent with slip on a moderately east-dipping fault. Double difference hypocentre relocation of aftershocks using data from rapidly deployed seismic instrumentation confirms an easterly dipping rupture plane for the first event. The aftershocks are predominantly located at the northern end of the rupture where the InSAR suggests vertical displacement was greatest. The November event resulted from rupture on a NE-trending strike slip fault. Anecdotal evidence from local residents suggests that the southern part of the September rupture was ‘freshened’ during the November event, consistent with InSAR results, which indicate that a NW-SE trending structural element accommodated deformation during both events. Comparison of the InSAR-derived deformation field with surface mapping and UAV-derived digital terrain models (corrected to pre-event LiDAR) revealed a surface deformation envelope consistent with the InSAR for the first event, but could not discern deformation unique to the second event.

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 Geoscience Australia’s 2012 National Seismic Hazard Maps (NSHM12; Burbidge, 2012) and its 2013 update (Leonard et al., 2013). The update at this time is intended to take advantage of recent developments in earthquake hazard research and to ensure the hazard model uses evidence-based science. This Geoscience Australia Record provides an overview of the output datasets generated through the development of the NSHA18. Time-independent, mean seismic design values are calculated on Standards Australia’s AS1170.4 Soil Class Be 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 at the10% and 2% probability of exceedance in 50-year hazard levels. Uniform-probability seismic hazard maps of PGA, in addition to all spectral periods, are provided for 10% and 2% probability of exceedance in 50 years. A Python script is provided to enable end users to interpolate hazard curve grids and to export site-specific hazard information given an input location and probability of exceedance (in the case of uniform hazard spectra). Additionally, geographic information system (GIS) datasets are provided to enable end users to view and interrogate the NSHA18 outputs on a spatially enabled platform. This is the most complete data publication for any previous Australian National Seismic Hazard Assessment. It is intended to ensure the NSHA18 outputs are openly available, discoverable and accessible to enable end-users to integrate these data into their own applications.

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.

Geoscience Australia is the Australian Government advisor on the geology and geography of Australia, and develops the National Seismic Hazard Assessment (NSHA). The NSHA defines the level of earthquake ground shaking across Australia that has a likelihood of being exceeded in a given time period. Knowing how the ground-shaking hazard varies across Australia allows high hazard areas to be identified for the development of mitigation strategies so communities can be more resilient to earthquake events. The NSHA provides key information to the Australian Government Building Codes Board, so buildings and infrastructure design standards can be updated to ensure they can withstand earthquake events in Australia. Using the NSHA, decision makers can better consider: • What this could mean for communities in those areas and whether any further action is required • Where to prioritise further efforts • What this could mean for insurance and reinsurance premiums • Identify high and low hazard areas to plan for growth or investment in infrastructure

Sites recording the extinction or extirpation of tropical–subtropical and cool–cold temperate rainforest genera during the Plio–Pleistocene aridification of Australia are scattered across the continent, with most preserving only partial records from either the Pliocene or Pleistocene. The highland Lake George basin is unique in accumulating sediment over c. 4 Ma although interpretation of the plant microfossil record is complicated by its size (950 km2), neotectonic activity and fluctuating water levels. A comparison of this and other sites confirms (1) the extinction of rainforest at Lake George was part of the retreat of Nothofagus-gymnosperm communities across Australia during the Plio–Pleistocene; (2) communities of warm- and cool-adapted rainforest genera growing under moderately warm-wet conditions in the Late Pliocene to Early Pleistocene have no modern analogues; (3) the final extirpation of rainforest taxa at Lake George occurred during the Middle Pleistocene; and (4) the role of local wildfires is unresolved although topography, and, elsewhere, possibly edaphic factors allowed temperate rainforest genera to persist long after these taxa became extinct or extirpated at low elevations across much of eastern Australia. Araucaria, which is now restricted to the subtropics–tropics in Australia, appears to have survived into Middle Pleistocene time at Lake George, although the reason remains unclear. <b>Citation:</b> Macphail Mike, Pillans Brad, Hope Geoff, Clark Dan (2020) Extirpations and extinctions: a plant microfossil-based history of the demise of rainforest and wet sclerophyll communities in the Lake George basin, Southern Tablelands of NSW, south-east Australia. <i>Australian Journal of Botany </i>68, 208-228.

<p>The mechanisms that lead to the localisation of stable continental region (SCR) seismicity, and strain more generally, remain poorly understood. Recent work has emphasised correlations between the historical record of earthquake epicentres and lateral changes in the thickness, composition and/or viscosity (thermal state) of the lithospheric mantle, as inferred from seismic velocity/attenuation constraints. Fluid flow and the distribution of heat production within the crust have also been cited as controls on the location of contemporary seismicity. The plate margin-centric hypothesis that the loading rate of crustal faults can been understood in terms of the strain rate of the underlying lithospheric mantle has been challenged in that a space-geodetic strain signal is yet to be measured in many SCRs. Alternatives involving the release of elastic energy from a pre-stressed lithosphere have been proposed. <p>The Australian SCR crust preserves a rich but largely unexplored record of seismogenic crustal deformation spanning a time period much greater than that provided by the historical record of seismicity. Variations in the distribution, cumulative displacement, and recurrence characteristics of neotectonic faults provide important constraint for models of strain localisation mechanisms within SCR crust, with global application. This paper presents two endmember case studies that illustrate the variation in deformation characteristics encountered within Australian SCR crust, and which demonstrate the range and nature of the constraint that might be imposed on models describing crustal deformation and seismic hazard.