Damaging earthquakes in Australia and other regions characterised by low seismicity are considered low probability, high consequence events. Uncertainties in modeling earthquake occurrence rates and ground motions pose unique challenges to forecasting seismic hazard in these regions. In 2018 Geoscience Australia released its 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 (AEP) relative to the factors in the Australian earthquake loading standard; the AS1170.4. Due to concerns that the 1/500 AEP hazard factors proposed in the NSHA18 would not assure life safety throughout the continent, the amended AS1170.4 (revised in 2018) retains seismic demands developed in the early 1990s and also introduces a minimum hazard design factor of Z = 0.08 g. The hazard estimates from the NSHA18 have challenged notions of seismic hazard in Australia in terms of the probability of damaging ground motions and raises questions as to whether current practices in probabilistic seismic hazard analysis (PSHA) deliver the outcomes required to protect communities in low-seismicity regions, such as Australia. By contrast, it is also important that the right questions are being asked of hazard modelers in terms of the provision of seismic demand objectives that are fit for purpose. In the United States and Canada, a 1/2475 AEP is used for national hazard maps due to concerns that communities in low-to-moderate seismicity regions are considerably more at risk to extreme ground-motions. The adoption of a 1/2475 AEP seismic demands within the AS1170.4 would bring it in to line with other international building codes in similar tectonic environments and would increase seismic demand factors to levels similar to the 1991 hazard map. This, together with other updates, may be considered for future revisions to the standard. Presented at the Technical Sessions of the 2021 Seismological Society of America Annual Meeting (SSA)

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.

This paper explores the implementation of the Natural Resources Canada’s 5th Generation national seismic hazard model as developed for the National Building Code of Canada (NBCC), within the OpenQuake-engine. It also describes the reconciliation of the differences in hazard estimates relative to the published NBCC values, calculated using GSCFRISK. Source and ground-motion input models developed for the GSCFRISK software were translated to the OpenQuake-engine format for the hazard comparison. In order to successfully undertake this process, several adjustments to the OpenQuake code were needed to mimic the behavior of GSCFRISK. This required the development of new functions for earthquake rupture scaling and ground-motion interpolation. Hazard values estimated using the OpenQuake-engine are generally in good agreement with the 2015 NBCC national-scale hazard values, with differences less than 2-3% typically achieved. Where larger differences arise, they can be rationalized in terms of differences between the behaviours of the two software engines with respect to earthquake rupture length uncertainty and maximum ground-motion integration distance.

Seismic Station ADE Teleseismic times charts. 2002-2008

This catalogue details earthquakes located by South Australian State Government Seismic Monitoring. Earthquake information extends from 1840 to 2017

The Mwp 6.1 Petermann Ranges earthquake that occurred on 20 May, 2016 in the Central Ranges, NT, is the largest onshore earthquake to be recorded in Australia since the 1988 Tennant Creek sequence. While geodetic and geophysical analyses have characterized the extent of surface rupture and faulting mechanism respectively, a comprehensive aftershock characterization has yet to be performed. Data has been acquired from a 12-station temporary seismic network deployed jointly by the ANU and Geoscience Australia (GA), collected from five days following the mainshock to early October. Taking advantage of enhanced automatic detection techniques using the SeisComP3 real-time earthquake monitoring software within the National Earthquake Alerts Centre (NEAC) at GA, we have developed a comprehensive earthquake catalogue for this mainshock-aftershock sequence. Utilising the NonLinLoc location algorithm combined with a Tennant Creek-derived velocity model, we have preliminarily located over 5,800 aftershocks. With additional spatio-temporal analyses and event relocation, our objective will be to use these aftershocks to help delineate the geometry of the headwall rupture along the Woodroffe Thrust. These high-resolution aftershock detection techniques are intended to be implemented in real-time within the NEAC following future significant Australian intraplate earthquakes. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

<p>The 2018 Australian Probabilistic Tsunami Hazard Assessment (PTHA18) was developed by Geoscience Australia to better understand Australia’s tsunami hazard due to earthquakes in the Pacific and Indian Oceans. The PTHA18 contains over a million hypothetical earthquake-tsunami scenarios, with associated return periods which are constrained using historical earthquake data and long-term plate tectonic motions. The tsunami propagation is modelled globally for 36 hours, and results are stored at thousands of sites in deep waters offshore of Australia. Average Return Interval (ARI) estimates are also provided, along with a representation of the associated uncertainties. ARI uncertainties tend to be large because of fundamental limitations in current scientific knowledge regarding the frequency of large earthquakes on global subduction zones. <p>The PTHA18 provides a nationally consistent basis for earthquake-tsunami scenario design, as required for inundation hazard assessments. The results and source-code are also freely available. The current paper aims to provide a short and accessible introduction to the PTHA18 methodology and results, while deliberately limiting technical details which are covered extensively in the associated technical report and code repository.

The preliminary 6th Generation seismic hazard model of Canada (CanadaSHM6-trial) provides the basis for design values proposed for the 2020 edition of the National Building Code of Canada (NBCC2020). Seismic hazard values at a probability level of 2% in 50 years for 679 Canadian localities are provided in an accompanying spreadsheet to supplement the public review of the seismic hazard portion of NBCC2020 scheduled from January to March 2020. The spreadsheet tool provides the ability to select a Canadian locality and visualize seismic hazard values for any value of VS30 (140 - 3000 m/s) and Site Class (E-A). In this document we provide detailed instructions on the use of this spreadsheet. This work will be superseded by a forthcoming Open File, once NBCC2020 is finalized to reflect the final seismic hazard values calculated using CanadaSHM6.

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.