Damaging earthquakes in Australia and other regions characterised by low seismicity are considered low probability but high consequence events. Uncertainties in modelling earthquake occurrence rates and ground motions for damaging earthquakes in these regions pose unique challenges to forecasting seismic hazard, including the use of this information as a reliable benchmark to improve seismic safety within our communities. Key challenges for assessing seismic hazards in these regions are explored, including: the completeness and continuity of earthquake catalogues; the identification and characterisation of neotectonic faults; the difficulties in characterising earthquake ground motions; the uncertainties in earthquake source modelling, and the use of modern earthquake hazard information to support the development of future building provisions. Geoscience Australia recently released its 2018 National Seismic Hazard Assessment (NSHA18). Results from the NSHA18 indicate significantly lower seismic hazard across almost all Australian localities at the 1/500 annual exceedance probability level relative to the factors adopted for the current Australian Standard AS1170.4–2007 (R2018). These new hazard estimates have challenged notions of seismic hazard in Australia in terms of the recurrence of damaging ground motions. Consequently, this raises the question of whether current practices in probabilistic seismic hazard analysis (PSHA) deliver the outcomes required to protect communities and infrastructure assets in low-seismicity regions, such as Australia. This manuscript explores a range of measures that could be undertaken to update and modernise the Australian earthquake loading standard, in light of these modern seismic hazard estimates, including the use of alternate ground-motion exceedance probabilities for assigning seismic demands for ordinary-use structures. The estimation of seismic hazard at any location is an uncertain science, particularly in low-seismicity regions. However, as our knowledge of the physical characteristics of earthquakes improve, our estimates of the hazard will converge more closely to the actual – but unknowable – (time independent) hazard. Understanding the uncertainties in the estimation of seismic hazard is also of key importance, and new software and approaches allow hazard modellers to better understand and quantify this uncertainty. It is therefore prudent to regularly update the estimates of the seismic demands in our building codes using the best available evidence-based methods and models.

The geological structure of southwest Australia comprises a rich, complex record of Precambrian cratonization and Phanerozoic continental breakup. Despite the stable continental cratonic geologic history, over the past five decades the southwest of Western Australia has been the most seismically active region in continental Australia though the reason for this activity is not yet well understood. The Southwest Australia Seismic Network (SWAN) is a temporary broadband network of 27 stations that was designed to both record local earthquakes for seismic hazard applications and provide the opportunity to dramatically improve the rendering of 3-D seismic structure in the crust and mantle lithosphere. Such seismic data are essential for better characterization of the location, depth and attenuation of the regional earthquakes, and hence understanding of earthquake hazard. During the deployment of these 27 broadband instruments, a significant earthquake swarm occurred that included three earthquakes with local magnitude (MLa) ≥ 4.0, and the network was supplemented by an additional six short-term nodal seismometers at 10 separate sites in early 2022, as a rapid deployment to monitor this swarm activity. The SWAN experiment has been continuously recording since late 2020 and will continue into 2023. These data are archived at the FDSN recognized Australian Passive Seismic (AusPass) Data center under network code 2P and will be publicly available in 2025. <b>Citation:</b> Meghan S. Miller, Robert Pickle, Ruth Murdie, Huaiyu Yuan, Trevor I. Allen, Klaus Gessner, Brain L. N. Kennett, Justin Whitney; Southwest Australia Seismic Network (SWAN): Recording Earthquakes in Australia’s Most Active Seismic Zone. <i>Seismological Research Letters </i><b>2023</b>;; 94 (2A): 999–1011. doi: https://doi.org/10.1785/0220220323

This document reports on a Bushfire and Natural Hazards Collaborative Research Centre (BNHCRC) utilisation project that has sought to develop information on the most effective means to address York’s high risk buildings. It has also sought to develop a better understanding of the logistics that would be faced by the state emergency services and the local shire council in a rare but credible earthquake. The utilisation project is entitled “Earthquake Mitigation of WA Regional Towns: York Case Study”, and sits under the over-arching BNHCRC Project A9 “Cost-effective Mitigation Strategy Development for Building Related Earthquake Risk”. The work commenced in January 2018 and was undertaken over a two year period. It involved the University of Adelaide and Geoscience Australia as the CRC research partners, and DFES and the Shire of York as the end users. The WA DPLH has also been a participant, though not a formal BNHCRC end user. The project had the following key components:- • Develop a building, business and demographic exposure database for York with the attributes collected tailored for modelling earthquake impact and for quantifying avoided consequences in economic terms. • Examine the benefits and costs of retrofitting old URM buildings to improve the resilience of them to earthquake. This is to range in scale from individual households and businesses up to the community as a whole. • Prepare earthquake impact scenarios suitable for emergency management planning by DFES and the Shire of York.

We present earthquake ground motions based upon a paleoseismically-validated characteristic earthquake scenario for the ~ 48 km-long Avonmore scarp, which overlies the Meadow Valley Fault, east of Bendigo, Victoria. The results from the moment magnitude MW 7.1 scenario earthquake indicate that ground motions are sufficient to be of concern to nearby mining and water infrastructure. Specifically, the estimated median peak ground acceleration (PGA) exceeds 0.5 g to more than ~ 10 km from the source fault, and a 0.09 g PGA liquefaction threshold is exceeded out to approximately 50-70 kilometres. Liquefaction of susceptible materials, such as mine tailings, may occur to much greater distances. Our study underscores the importance of identifying and characterising potentially active faults in proximity to high failure-consequence dams, including mine tailings dams, particularly in light of the requirement to manage tailing dams for a prolonged period after mine closure. Paper presented at Australian National Committee on Large Dams (ANCOLD) conference 2020, online. (https://leishman.eventsair.com/ancold-2020-online/)

Geoscience Australia and the NSW Department of Industry undertook seismic monitoring of the NSW CSG extraction area in Camden as well as baseline monitoring in the region between 2015 and 2019. Geoscience Australia established and maintained seismic stations to identify of events of greater than ML2.0 within the CSG fields. Three new seismic stations were located near Camden CSG area with two baseline stations in North-West Sydney. This poster details the station builds and seismic monitoring of both the Camden CSG production area and the wider region during the project.

Geoscience Australia provides 24/7 monitoring of seismic activity within Australia and the surrounding region through the National Earthquake Alerts Centre (NEAC). Recent enhancements to the earthquakes@GA web portal now allow users to view felt reports, submitted online – together with reports from other nearby respondents – using the new interactive mapping feature. Using an updated questionnaire based on the US Geological Survey’s Did You Feel It? System, Geoscience Australia now calculate Community Internet Intensities (CIIs) to support near-real-time situational awareness applications. Part of the duty seismologists’ situational awareness and decision support toolkit will be the production of real-time “ShakeMaps.” ShakeMap is a system that provides near-real-time maps of shaking intensity following significant earthquakes. The software ingests online intensity observations and spatially distributed instrumental ground-motions in near-real-time. These data are then interpolated with theoretical predictions to provide a grid of ground shaking for different intensity measure types. Combining these predictions with CIIs provides a powerful tool for rapidly evaluating the likely impact of an earthquake. This paper describes the application of the new felt reporting system and explores its utility for near-real-time ShakeMaps and the provision of situational awareness for significant Australian earthquakes.

The 2018 National Seismic Hazard Assessment of Australia incorporated 19 alternative seismic-source models. The diversity of these models demonstrates the deep epistemic uncertainty that exists with regards to how best to characterize intraplate seismicity. A complex logic tree was developed to incorporate the alternative models into a single hazard model. Similarly, a diverse range of ground-motion models were proposed for use and incorporated using a logic tree. Expert opinion was drawn upon to weight the alternative logic tree branches through a structured expert elicitation process. This process aims to transparently and reproducibly characterize the community distribution of expert estimates for unknown parameters and thereby quantify the epistemic uncertainty around estimates of seismic hazard in Australia. We achieve a multi-model rational consensus where each model, and each expert, is, in accordance with the Australian cultural myth of egalitarianism, given a ‘fair go’. Yet despite this process, we find that the results are not universally accepted. A key issue is a contested boundary between what is scientifically reducible and what remains epistemologically uncertain, with a particular focus on the earthquake catalog. Furthermore, a reduction, on average, of 72% for the 10% in 50 years probability of exceedance peak ground acceleration levels compared with those underpinning existing building design standards, challenges the choice of metrics upon which design codes are based. As questions of epistemic uncertainty are quantified or resolved, changes in our understanding of how the hazard behaves should inform dialogue between scientists, engineers and policy makers, and a re-appraisal of the metrics used to inform risk management decisions of societal importance.

Seismic risk assessment involves the development of fragility functions to express the relationship between ground motion intensity and damage potential. In evaluating the risk associated with the building inventory in a region, it is essential to capture ‘actual’ characteristics of the buildings and group them so that ‘generic building types’ can be generated for further analysis of their damage potential. Variations in building characteristics across regions/countries largely influence the resulting fragility functions, such that building models are unsuitable to be adopted for risk assessment in any other region where a different set of building is present. In this paper, for a given building type (represented in terms of height and structural system), typical New Zealand and US building models are considered to illustrate the differences in structural model parameters and their effects on resulting fragility functions for a set of main-shocks and aftershocks. From this study, the general conclusion is that the methodology and assumptions used to derive basic capacity curve parameters have a considerable influence on fragility curves.

When multiple earthquakes occur within a short period of time, damage may accumulate in a building, affecting its ability to withstand future ground shaking. This study aims to quantify the post-earthquake capacity of a nonductile 4-story concrete building in New Zealand through incremental dynamic analysis of a nonlinear multipledegree-of-freedom simulation model. Analysis results are used to compute fragility curves for the intact and damaged buildings, showing that extensive damage reduces the structure’s capacity to resist seismic collapse by almost 30% percent. The damage experienced by the building in mainshock, can be compared with the ATC-20 building tagging criteria for post-earthquake inspections, the purpose of which is to ensure public safety. Extensively damaged buildings, which are likely be red tagged, pose a significant safety hazard due to decreased strength in future earthquakes. The effect of mainshock damage is also compared for multiple and simplified single-degree-of-freedom models of the same building.

We present a methodology for developing fragilities for mainshock-damaged structures, "aftershock fragility", by performing incremental dynamic analysis (IDA) with a sequence of mainshock-aftershock ground motions. The aftershock fragility herein is distinguished from a conventional fragility for an intact structure. We estimate seismic response of a mainshock-damaged building by performing nonlinear time history analysis with a sequence of mainshock and aftershock ground motions (so-called "back-to-back" dynamic analysis). We perform the back-to-back dynamic analyses for a number of levels of mainshock response/damage, and a number of sequences of mainshock and aftershock ground motions. With estimated seismic responses from the back-to-back dynamic analyses, we compute various damage state transition probabilities, the probability of exceeding a higher damage state from an aftershock given a damage state due to a mainshock. For an illustration of the methodology, we develop an aftershock fragility for a typical New Zealand 5-storey reinforced concrete moment frame building. The building is modeled using a single-degree-of-freedom (SDOF) damped nonlinear oscillator with force-deformation behavior represented by a multi-linear capacity/pushover curve with moderate pinching hysteresis and medium cyclic deterioration.