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.

Damaging earthquakes are less frequent in Australia when compared to other weather-related events, but when they do occur close to a community they can cause major damage and injury. This risk to property and life exists for building owners, particularly if the building is of vulnerable construction. The good news is that your building can be retrofitted to improve its earthquake resilience within a sensible budget without compromising its heritage value. This document seeks to show you how. It explains the nature of earthquake risk and provides resources for building owners on how the risk can be reduced for the most vulnerable building construction type: unreinforced masonry.

Even though the Australian continent sits within a major tectonic plate, it is affected by earthquakes. Each year, more than 100 earthquakes measuring 3.0 or more on the Richter scale are felt across Australia, with the majority affecting Western Australia—more than X since 1900. Many of these earthquakes are focused around York. Despite the prevalence of earthquakes in the region, the risks have not consistently been recognised during building design and construction. This means many buildings - particularly older masonry buildings - are susceptible to damage from earthquakes.

While damaging earthquakes are less frequent in Australia when compared to other weather related events, when they do occur close to communities they can cause major damage and injury. This community risk to life, property, social fabric and the local economy is significant. The risk also presents associated challenges for government agencies with a role in emergency response, health care and community recovery both in the short and longer term. For some communities recovery to pre-event conditions may never be fully realised due to the destruction of heritage value that may be central to local business activity. Resources for building resilience to earthquakes need to be prioritised against those needed for other hazards. What are the benefits of earthquake retrofit of high risk buildings to communities and what exemplars of risk management driven from government exist? What resources exist for a business case to be articulated for limited resources and for motivating investment by property owners to reduce their individual risk? This document seeks provide useful answer these questions. It presents information that explains the nature of earthquake hazard in Australia, the risk it presents and vulnerability factors behind it. It also provides information on the effectiveness of retrofit in reducing the impact of earthquakes, emergency management logistics and recovery needs. It further provides links to resources that can be used to advance local programs for building community resilience. The primary focus is the most vulnerable building construction type, unreinforced masonry, but the principles are informative to the address of other high risk building types in communities.

Damaging earthquakes are less frequent in Australia when compared to weather related events, but when they occur close to communities they can cause significant damage and injury. This community risk to life, property, social fabric, valued community heritage and the local economy is significant and is gaining recognition. Some state and local governments are seeking to raise awareness of earthquake risk with property owners and are targeting grants schemes to promote cost shared investment in retrofit activity. Where property owners do take the initiative to address structural deficiencies they need the assistance of design professionals and a skilled construction industry to undertake retrofit with due address of heritage considerations. If you work in either domain, this document will assist you. This document is aimed to be a resource for you when discussing retrofit needs and options with clients and translating their retrofit objectives to detailed design, documentation and implementation. The primary focus is the most vulnerable building construction type in Australia, older unreinforced masonry, but the principles are informative to address other high risk building types. The objective is cost-effective retrofit measures with minimised disruption to occupants that can address a significant portion of the earthquake risk to the building owner and the community more broadly. It presents information that explains the nature of earthquake hazard in Australia, the risk it presents and the vulnerability factors that contribute to it. It further describes the common failure modes that can be highlighted to clients and a range of measures that can be employed to preclude these. It also links to other resources that can be drawn upon in developing tailored design solutions that the construction industry can readily implement.

Contains local, blast and teleseismic event information from SA network. 2002-2017

Seismic data form South Australian Network. Stations: ADE, ALV2, DNL, FR27, GHS, GHSS, GLN, GLN2, HML1, HML2, HTT, KNC, MRAT, MYP, NBK, PLMR, SDAN, STR2, TORR, UT, UTT. Date range,2006-2017, not definitive. Some logs files.

Animation showing Australian Earthquakes since 1964

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.

The 20th May 2016 moment magnitude (MW) 6.1 Petermann earthquake was the 2nd longest single-event historic Australian surface rupture (21 km) and largest MW on-shore earthquake in 28 years. Trench logs from two hand-dug trenches show no evidence of penultimate rupture of surface eolian sediments or underlying calcrete. Available dating of eolian dunes 140 to 500 km away from the Petermann fault indicated eolian deposition during either the last glacial maximum (approximately 20 ka) or a period of aridification at approximately 180 - 200 ka. Ten 10Be cosmogenic nuclide erosion rates of bedrock outcrops at 0 to 50 km from the surface rupture trace are within error of each other between 1.4 to 2.6 mMyr-1. These samples have approximate averaging times between 208 to 419 ka. Bedrock erosion rates, trenching results and interpretation of the landscape history suggest the 2016 event is the only surface rupturing earthquake on the Petermann fault in the last 200 to 400 kyrs, and possibly the first ever on this fault. This finding is consistent with a lack of evidence for penultimate rupture for all eleven historic Australian surface rupturing events, as described by either trenching and/or landscape analysis and bedrock erosion rates. These ‘one-off’ events within Precambrian cratonic Australian crust are not consistent with trenching results and geomorphology of paleo-scarps within the Flinders Ranges and Eastern Australia which indicate multiple recurrent fault offset. Variable fault recurrence behaviour highlights that uniform seismic hazard modelling approaches are not applicable across Stable Continental Regions.