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.

A new finite volume algorithm to solve the two dimensional shallow water equations on an unstructured triangular mesh has been implemented in the open source ANUGA software, jointly developed by the Australian National University and Geoscience Australia. The algorithm allows for 'discontinuous-elevation', or 'jumps' in the bed profile between neighbouring cells. This has a number of benefits compared with previously implemented 'continuous-elevation' approaches. Firstly it can preserve stationary states at wet-dry fronts, while also permitting simulation of very shallow frictionally dominated flow down slopes as occurs in direct-rainfall flood models. Additionally the use of discontinuous-elevation enables the sharp resolution of rapid changes in the topography associated with e.g. narrow rectangular drainage channels, or buildings, without the computational expense of a very fine mesh. The approach also supports a simple and computationally efficient treatment of river walls. A number of benchmark tests are presented illustrating these features of the algorithm, along with its application to urban flood hazard simulation and comparison with field data.

The disasters caused by tsunamis the last 10 years have highlighted the need for a thorough understanding of the global and regional tsunami hazard and risk. At present, the 2004 and 2011 tsunamis hint that their induced risk are dominated by large infrequent events with possibly long return periods. However, an in-depth understanding of how individual contributions from sources of different strength and frequency govern the hazard and risk is presently not clear. A first global analysis of tsunami hazard using earthquake sources was conducted in 2008 on behalf of the UN-ISDR Global Assessment Report (GAR). Recently, this initiative has resulted in the first, fully probabilistic global tsunami hazard assessment. Economic loss calculations based on building fragility curves largely derived from recent major tsunamis have also been included to assess the risk. Still, this complex assessment is premature. Further efforts are needed, requiring joint expertise covering a wide range of topics such as the understanding of sources, hydrodynamics, probability and statistics, as well as vulnerability and exposure. Therefore, there is a dire need for a joint interdisciplinary effort delivering data and tools that may help decision makers in assessing their tsunami hazard and risk. To this end, we propose to establish a Global Tsunami Model (GTM) that will emphasize tsunami hazard and risk analysis on a global scale. The GTM will be based on the initial work in GAR, but should eventually involve a broader community. The motivation, the needs, and the possible contributors for such a GTM will be discussed.

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 Flood Study Summary Services support discovery and retrieval of flood hazard information. The services return metadata and data for flood studies and flood inundation maps held in the 'Australian Flood Studies Database'. The same information is available through a user interface at http://www.ga.gov.au/flood-study-web/. A 'flood study' is a comprehensive technical investigation of flood behaviour. It defines the nature and extent flood hazard across the floodplain by providing information on the extent, level and velocity of floodwaters and on the distribution of flood flows. Flood studies are typically commissioned by government, and conducted by experts from specialist engineering firms or government agencies. Key outputs from flood studies include detailed reports, and maps showing inundation, depth, velocity and hazard for events of various likelihoods. The services are deliverables fom the National Flood Risk Information Project. The main aim of the project is to make flood risk information accessible from a central location. Geoscience Australia will facilitate this through the development of the National Flood Risk Information Portal. Over the four years the project will launch a new phase of the portal prior to the commencement of each annual disaster season. Each phase will increase the amount of flood risk information that is publicly accessible and increase stakeholder capability in the production and use of flood risk information. flood-study-search returns summary layers and links to rich metadata about flood maps and the studies that produced them. flood-study-map returns layers for individual flood inundation maps. Typically a single layer shows the flood inundation for a particular likelihood or historical event in a flood study area. To retrieve flood inundation maps from these services, we recommend: 1. querying flood-study-search to obtain flood inundation map URIs, then 2. using the flood inundation map URIs to retrieve maps separately from flood-study-map. The ownership of each flood study remains with the commissioning organisation and/or author as indicated with each study, and users of the database should refer to the reports themselves to determine any constraints in their usage.

In the last few years there have been several probabilistic seismic hazard assessments (PSHA) of Adelaide. The resulting 500 year PGA obtained are 0.059, 0.067, 0.109 and 0.141. The differences between the first three are readily accounted for by choice of GMPE, how faults are included and differences in recurrence estimation, with each of these having a similar level of importance. As no GMPEs exist for the Mt Lofty and Flingers Ranges the choices of GMPEs were all based on geological analogies. The choice of at what weighting to include low attenuation, that is a stable continental crust, GMPE was most important. At a return period of 500 year the inclusion of faults was not necessarily significant. The choice of whether the faults behaved with Characteristic or Gutenberg-Richter recurrence statistics had the highest impact on the hazard with the choice of slip rate the next most important. A low slip rate Characteristic fault, while increasing the hazard for longer return periods (i.e. ~2500 years), results in only a minor increase at 500 years. The magnitude frequency distribution b-value for the four studies were 1.043, 0.88, 0.915 and 0.724. For the same activity in the magnitude range of 3.0 to 3.5, the activity level at M 6.0 is an order of magnitude higher for a b-value of 0.724 compared to a b-value of 1.043. This increase in activity rate of larger earthquakes significantly increases the hazard. The average of the first three studies is 0.078±0.022 (0.056 -0.100) g. This range is reflecting the intrinsic uncertainty in calculating PSHAs where many of the inputs are poorly constrained. The results for the highest hazard level PSHA study (i.e. 0.141g) can be explained by their use of a low b-value (i.e. 0.724). M. Leonard1, R. Hoult2, P. Somerville3, G. Gibson2, D. Sandiford2, H. Goldsworthy2, E. Lumantarna2 and S Spiliopoulos1. 1Geoscience Australia, 2The University of Melbourne, 3 URS

The Tropical Cyclone Impact Map provides guidance on areas likely to be impacted by severe winds due to tropical cyclones. The impact zones are generated by Geoscience Australia's Tropical Cyclone Risk Model (TCRM), and are based on the tropical cyclone forecast information published by the Bureau of Meteorology's Tropical Cyclone Warning Centres. TCRM applies a 2-dimensional parametric wind field to the forecast track provided by the Bureau of Meteorology, and translates the wind speeds into an indicator of potential damage to housing. Uncertainty in the forecast track is not included in the product.

With a population of over 250 million people, Indonesia is the fourth most populous country in the world (United Nations, 2013). Indonesia also experiences more earthquakes than any other country in the world (USGS, 2015). Its borders encompass one of the most active tectonic regions on Earth including over 18 000 km of major tectonic plate boundary, more than twice that of Japan or Papua New Guinea (Bird, 2003). The potential for this tectonic activity to impact large populations has been tragically demonstrated by the 20004 Sumatra earthquake and tsunami. In order to inform earthquake risk reduction in Indonesia, a new national earthquake hazard map was developed in 2010 (Irsyam et al., 2010). In this report historical records of damaging earthquakes from the 17th to 19th centuries are used to test our current understanding of earthquake hazard in Indonesia and identify areas where further research is needed. In this report we address the following questions: - How well does our current understanding of earthquake hazard in Indonesia reflect historical activity? - Can we associate major historical earthquakes with known active faults, and are these accounted for in current assessments of earthquake hazard? - Does the current earthquake hazard map predict a frequency and intensity of shaking commensurate with the historical record? - What would the impact of these historical earthquakes be if they were to reoccur today? To help answer questions like these, this report collates historical observations of eight large earthquakes from Java, Bali and Nusa Tenggara between 1699 and 1867. These observations are then used to: - Identify plausible sources for each event; - Develop ground shaking models using the OpenQuake Engine (GEM Foundation, 2015); - Assess the validity of the current national seismic hazard map; and - Estimate fatalities were the historical events to occur today using the InaSAFE (InaSAFE.org, 2015) software.

<div>Severe TC Ilsa crossed the Western Australian coastline approximately 120 km east of Port Hedland on Thursday 13 April 2023. Observations at Bedout Island were the highest wind speeds ever recorded on standard BoM instruments (gust wind speed of 289 km/h). In anticipation of the TC, residents in the mining township of Telfer were evacuated, along with a small number of evacuees in other townships (Marble Bar, South Hedland and Nullagine). As a category 5 TC, the threat of widespread destruction was front of mind for emergency managers in Western Australia.</div><div><br></div><div>Geoscience Australia (GA) has established the National Hazard Impact and Risk Service (NHIRS), which provides quantitative modelled impact forecast information for tropical cyclones, large-scale wind events and earthquakes in Australia. NHIRS has been used by the Department of Fire and Emergency Services (DFES) Intelligence Unit to support operational resource planning for TC events.</div><div><br></div><div>In TC Ilsa, DFES Intelligence (and GA) officers reviewed the impact predictions in the days leading up to landfall. Genuine questions were asked about the level of predicted damage, which was almost negligible across northern WA in spite of the predicted landfall intensity. Why was that the case? Was the service operating as expected? This paper highlights the challenge of educating users on the utility of impact forecasting products and communicating the components that are integrated in the impact forecast. Presented at the 30th Conference of the Australian Meteorological and Oceanographic Society (AMOS) 2024

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)