Internal advice on tsunami, earthquake and severe wind hazards for the Vanimo Port region, derived from large-scale hazard assessments. This advice (refer TRIM D2021-52746) was provided to the Australia Pacific Climate Partnership (APCP) as part of Geoscience Australia's (GA's) contributions to the program. (In confidence report to APCP, not for distribution)

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

A multihazard (volcano, earthquake, tsunami) assessment for East New Britain Province, Papua New Guinea.

Using the wind multiplier code (https://pid.geoscience.gov.au/dataset/ga/82481) and an appropriate source of classified terrain data, wind multipliers for all of Queensland at (approximately) 25 metre resolution were created. The wind multipliers have been used to guide impact assessments as part of the Severe Wind Hazard Assessment for Queensland.

Modern geodetic and seismic monitoring tools are enabling the study of moderate-sized earthquake sequences in unprecedented detail. Discrepancies are apparent between the surface deformation envelopes ‘detectable’ using these tools, and ‘visible’ to traditional ground-based methods of observation. As an example, we compare the detectible and visible surface deformation caused by a sequence of earthquakes near Lake Muir in southwest Western Australia in 2018. A shallow MW 5.3 earthquake on the 16th of September 2018 was followed on the 8th of November 2018 by a MW 5.2 event in the same region. Focal mechanisms for the events suggest reverse and strike-slip rupture, respectively. Interferometric Synthetic Aperture Radar (InSAR) analysis of the events suggests that the ruptures are in part spatially coincident and deformed the Earth’s surface over ~ 12 km in an east-west direction and ~ 8 km in a north-south direction. Field mapping, guided by the InSAR results, reveals 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. No surface deformation unique to the second event was identifiable on the ground. New rupture length versus magnitude scaling relationships developed for non-extended cratonic regions as part of this study allow for the distinction between ‘visible’ surface rupture lengths (VSRL) from field-mapping and ‘detectable’ surface rupture lengths (DSRL) from remote sensing techniques such as InSAR, and suggest longer ruptures for a given magnitude than implied by commonly used scaling relationships.

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.

The Australian Flood Studies Database is available on line by Geoscience Australia. The database provides metadata on Australian flood studies and information on flood risk with a digital version where available. The purpose of the document is to guide new users in data entry and uploading of flood studies to a level acceptable for inclusion in the database.

Internal advice on tsunami, earthquake and severe wind hazards for the Kimbe Bay region, derived from large-scale hazard assessments. This advice (refer TRIM D2021-55557) was provided to the Australia Pacific Climate Partnership (APCP) as part of Geoscience Australia's (GA's) contributions to the program. (In confidence report to APCP, not for distribution)

The northwest Australian coastline from Broome to Exmouth has experienced the greatest number of landfalling Tropical Cyclones (TCs) in Australia since records began in 1908 (Bureau of Meteorology, 2020). Despite this, direct impacts of a TC on individual communities are comparatively unusual, especially for severe TCs (category 3-5) as the coastline is sparsely populated. Communities are generally hundreds of kilometres apart, and a TC can cross the coast between them with little impact. However, the highest recorded wind gust in the world was 408 km/h (category 5) at Barrow Island during TC Olivia on 10 April 1996 (Courtney et al., 2012). The highest wind gust on the Australian mainland was 267 km/h (category 4) at Learmonth during TC Vance on 22 March 1999 (Australian Bureau of Meteorology, 2000). This emphasises the fact that no regional centre in WA, with the exception of Exmouth, has experienced a high-end TC impact in the past 30 years, but there is the potential for extreme events to strike these communities. While the impacts of past cyclone events have been well-documented, it is unlikely that communities have experienced the ‘worst-possible’ (either most intense or most damaging) cyclone impact in the past 30 years. To understand the scale of impacts that would occur if a TC were to make a direct impact on any of these communities the West Australian Department of Fire and Emergency Services (DFES) applied for funding through the Natural Disaster Resilience Program. In July 2017 funding was obtained to conduct the Severe Wind Hazard Assessment (SWHA) project. This initiative is aligned with the National Disaster Risk Reduction Framework (Department of Home Affairs, 2018), which outlines a national, comprehensive approach to proactively reducing disaster risk in Australia. To better understand the potential impacts of cyclones and extra-tropical transitioning cyclones on Western Australian communities, the project has modelled a number of scenarios to demonstrate the impacts of realistic, but perhaps not experienced, cyclones for Broome, Port Hedland, South Hedland and Wedgefield, Karratha, Dampier, Roebourne, Wickham and Point Samson, Exmouth, Carnarvon, Geraldton and Perth A consistent message that comes from this analysis is the excellent performance of modern residential construction to withstand the impacts of these scenario TCs. However, a house built to code’s performance is reliant on being maintained during its life so that its resilience is retained; just because a building was built to standard doesn’t mean it has been maintained to that standard. Investigations conducted into previous cyclones demonstrate that houses built pre-1980s (pre-code) under perform and offer lesser protection compared to those houses built to code post-1980s. In line with that the work undertaken in this report shows clearly that communities with a larger proportion of pre-code residential construction will suffer greater damage, due to the greater vulnerability of older building stock. Houses not originally built to current standards cannot, in general, be expected to perform to the current design levels, irrespective of the maintenance level. The only way to increase performance of these older residential buildings is to retrofit to modern standards. The analysis undertaken in the project has provided emergency managers from local, district and State level with a wealth of information on the potential impacts a major cyclone would have on Western Australia. This information has provided opportunity to strengthen planning processes and raise community awareness of mitigation actions that can reduce impacts. This collection comprises reporting and data developed as part of the Severe Wind Hazard Assessment for Western Australia. The collection includes all reports, publications (e.g. conference presentations, posters and news articles, etc.), and data delivered to Department of Fire and Emergency Services (Western Australia).