Seismic hazard models, commonly produced through probabilistic seismic hazard analysis, are used to establish earthquake loading requirements for the built environment. However, there is considerable uncertainty in developing seismic hazard models, which require assumptions on seismicity rates and ground-motion models (GMMs) based on the best evidence available to hazard analysts. This paper explores several area-based tests of long-term seismic hazard forecasts for the Australian continent. ShakeMaps are calculated for all earthquakes of MW 4.25 and greater within approximately 200 km of the Australian coastline using the observed seismicity in the past 50 years (1970-2019). A “composite ShakeMap” is generated that extracts the maximum peak ground acceleration “observed” in this 50-year period for any site within the continent. The fractional exceedance area of this composite map is compared with four generations of Australian seismic hazard maps for a 10% probability of exceedance in 50 years (~1/500 annual exceedance probability) developed since 1990. In general, all these seismic hazard models appear to be conservative relative to the observed ground motions that are estimated to have occurred in the last 50 years. To explore aspects of possible prejudice in this study, the variability in ground-motion exceedance was explored using the Next Generation Attenuation-East GMMs developed for the central and eastern United States. The sensitivity of these results is also tested with the interjection of a rare scenario earthquake with an expected regional recurrence of approximately 5,000 - 10,000 years. While these analyses do not provide a robust assessment of the performance of the candidate seismic hazard for any given location, they do provide—to the first order—a guide to the performance of the respective maps at a continental scale. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

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 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

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.

A database of recordings from moderate-to-large magnitude earthquakes is compiled for earthquakes in western and central Australia. Data are mainly recorded by Australian National Seismograph Network (ANSN), complemented with data from temporary deployments, and covering the period of 1990 to 2019. The dataset currently contains 1497 earthquake recordings from 164 earthquakes with magnitudes from MW 2.5 to 6.1, and hypocentral distances up to 1500 km. The time-series data are consistently processed to correct for the instrument response and to reduce the effect of background noise. A range of ground-motion parameters in the time and frequency domains are calculated and stored in the database. Numerous near-source recordings exceed peak accelerations of 0.10 g and range up to 0.66 g, while the maximum peak velocity of the dataset exceeds 27 cm/s. In addition to its utility for engineering design, the dataset compiled herein will improve characterisation of ground-motion attenuation in the region and will provide an excellent supplement to ground-motion datasets collected in analogue seismotectonic regions worldwide. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

At its nearest, northern Australia is just over 400 km from an active convergent plate margin. This complex and unique tectonic region combines active subduction and the collision of the Sunda-Banda Arc with the Precambrian North Australian Craton (NAC) near the Timor Trough and continues through to the New Guinea Highlands. Ground-motions generated from earthquakes on these structures have particular significance for northern Australian communities and infrastructure projects, with several large earthquakes in the Banda Arc region having caused ground-shaking-related damage in the northern Australian city of Darwin over the historical period. There are very few, if any, present-day tectonic analogs where cold cratonic crust abuts a convergent tectonic margin with subduction and continent-continent collision. Ground motions recorded from earthquakes in typical subduction environments are highly attenuated as they travel through young sediments associated with forearc accretionary prisms and volcanic back-arc regions. In contrast, seismic energy from earthquakes in the northern Australian plate margin region are efficiently channelled through the low-attenuation NAC, which acts as a waveguide for high-frequency earthquake shaking. As such, it is difficult to select models appropriate to the region for seismic hazard assessments. The development of a far-field ground-motion model to support future seismic hazard assessments for northern Australia is discussed. In general, the new model predicts larger ground motions in Australia from plate margin sources than models used for the 2018 National Seismic Hazard Assessment of Australia, none of which were considered fully appropriate for the tectonic environment. Short-period ground motions are strongly dependent on hypocentral depth and are significantly higher than predictions from commonly-used intraslab ground-motion models at comparable distances. The depth dependence in ground motion diminishes with increasing spectra periods. <b>Cite this article as</b> Allen, T. I. (2021). A Far-Field Ground-Motion Model for the North Australian Craton from Plate-Margin Earthquakes, <i>Bull. Seismol. Soc. Am. </i><b> 112</b>, 1041–1059, doi: 10.1785/0120210191

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.

The 6th Generation Seismic Hazard Model of Canada (CanadaSHM6) provides the basis for seismic design values proposed by Natural Resources Canada for the 2020 edition of the National Building Code of Canada (NBCC 2020). This Open File includes OpenQuake compatible source model files that will generate seismic hazard values as currently being proposed. Once NBCC 2020 is finalized, this report will be superseded by a subsequent Open File, to document the final model used to generate seismic hazard values using CanadaSHM6 for NBCC 2020.

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.

You may not realise it but, on average, Australia is rattled every few days by an earthquake of magnitude 3 or above. We don’t feel every small tremor that happens, but the larger earthquakes are powerful enough to cause serious damage to buildings and infrastructure, putting our community’s safety at risk.