<div>The Kati Thanda – Lake Eyre Basin (KT–LEB) covers about 1.2 million square kilometres of outback Australia. Although the basin is sparsely populated and relatively undeveloped it hosts nationally significant environmental and cultural heritage, including unique desert rivers, sweeping arid landscapes, and clusters of major artesian springs. The basin experiences climatic extremes that intermittently cycle between prolonged droughts and massive inland floods, with groundwater resources playing a critical role in supporting the many communities, industries, ecological systems, and thriving First Nations culture of the KT–LEB.</div><div><br></div><div>As part of Geoscience Australia’s National Groundwater Systems Project (in the Exploring for the Future Program) this report brings together contemporary data and information relevant to understanding the regional geology, hydrogeology and groundwater systems of Cenozoic rocks and sediments of the KT–LEB. This work represents the first whole-of-basin assessment into these vitally important shallow groundwater resources, which have previously received far less scientific attention than the deeper groundwater systems of the underlying Eromanga Basin (part of the Great Artesian Basin). The new knowledge and insights about the geology and hydrogeology of the basin generated by this study will benefit the many users of groundwater within the region and will help to improve sustainable management and use of groundwater resources across the KT–LEB.</div><div><br></div>

Australia's CO2CRC Otway Site hosts a carbon capture and storage (CCS) demonstration facility that has, to date, injected over 80,000 tonnes of CO2 into two separate geological reservoirs. The reservoir geology is well understood and the site has been the subject of several seismic investigations, though relatively little is known about the near-surface geology and how potential leaks from the injection wells would migrate, particularly within the Port Campbell Limestone. No shallow core has been taken from relevant petroleum wells or water bores, and although there is extensive exposure in the prominent sea cliffs, these are mostly inaccessible. In order to further define the structure and geology of the Port Campbell Limestone at the Otway site, a high-resolution, shallow focused, 3D seismic survey has recently been conducted. The assessment of the near-surface geology described in this paper was used to assist with planning the survey. Using available data, the Port Campbell Limestone is assessed as a series of laterally continuous intercalated limestone, marl, and marly limestones. Interpretation of three previously acquired 3D seismic surveys using a minimum similarity attribute demonstrates evidence for a shallow, steeply east-dipping fault striking approximately NNW-SSE directly below the Otway site. This is observed from approximately 100 m to 380 m depth below surface, where it appears to die out. In the shallow section, the fault is undetectable primarily due to low seismic resolution, and so it is unknown how shallow it propagates. Extrapolation of the fault to the surface projects to between the wells Naylor-1 and CRC-1. A recently acquired high-resolution 3D seismic survey over the study area will allow for this fault to be further delineated. Appeared in the Energy Procedia Journal, Volume 114, Pages 4424-4435, July 2017

Seismicity in the intraplate southwest of Western Australia is poorly understood, despite evidence for potentially damaging earthquakes of magnitude>M6. Identifying stress-focusing geological structures near significant earthquake sequences assists in understanding why these earthquakes occur in seemingly random locations across a region of more than 250 000 km2. On 16 September 2018, an ML5.7 earthquake occurred near Lake Muir in the southwest of Western Australia and was followed by an ML5.4 aftershock. The main earthquake formed a mainly northtrending fault scarp ~5 km in length and with a maximum vertical displacement of ~40 cm. The main event was followed by a series of aftershocks, one of which had a magnitude of ML5.4. Using high-resolution aeromagnetic data, we analyse bedrock geology in a wide area surrounding the new scarp and map a series of major east–west-trending faults segmenting eight distinct geological domains, as well as a network of less prominent northwest-trending faults, one of which aligns with the southern segment of the scarp. Surface faulting, surface deformation and earthquake focal mechanism studies suggest movements on north- and northeast-trending structures. The main shock, the aftershocks, surface faulting and changes in InSAR-derived surface elevation all occur in a region bounded to the south by a prominent northwest-trending fault and to the north by a west-northwest-trending domain-bounding structure. Thus, we interpret the north-trending thrust fault associated with the main Lake Muir event as due to local stress concentration of the regional east–west stress field at the intersection of these structures. Further, we propose that a particularly large west-northwest-trending structure may be broadly focusing stress in the Lake Muir area. These findings encourage similar studies to be undertaken in other areas of Australia’s southwest to further the current understanding of seismic release in the region. <b>Citation: </b>S. Standen, M. Dentith & D. Clark (2021) A geophysical investigation of the 2018 Lake Muir earthquake sequence: reactivated Precambrian structures controlling modern seismicity,<i>Australian Journal of Earth Sciences</i>, 68:5, 717-730, DOI: 10.1080/08120099.2021.1848924

<p>The mechanisms that lead to the localisation of stable continental region (SCR) seismicity, and strain more generally, remain poorly understood. Recent work has emphasised correlations between the historical record of earthquake epicentres and lateral changes in the thickness, composition and/or viscosity (thermal state) of the lithospheric mantle, as inferred from seismic velocity/attenuation constraints. Fluid flow and the distribution of heat production within the crust have also been cited as controls on the location of contemporary seismicity. The plate margin-centric hypothesis that the loading rate of crustal faults can been understood in terms of the strain rate of the underlying lithospheric mantle has been challenged in that a space-geodetic strain signal is yet to be measured in many SCRs. Alternatives involving the release of elastic energy from a pre-stressed lithosphere have been proposed. <p>The Australian SCR crust preserves a rich but largely unexplored record of seismogenic crustal deformation spanning a time period much greater than that provided by the historical record of seismicity. Variations in the distribution, cumulative displacement, and recurrence characteristics of neotectonic faults provide important constraint for models of strain localisation mechanisms within SCR crust, with global application. This paper presents two endmember case studies that illustrate the variation in deformation characteristics encountered within Australian SCR crust, and which demonstrate the range and nature of the constraint that might be imposed on models describing crustal deformation and seismic hazard.