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.

This investigation uses high-resolution optical satellite imagery to quantify vertical surface offsets associated with the intraplate 20 May 2016 Mw 6.0 Petermann Ranges earthquake, Northern Territory, Australia. The ~20 km long NW-trending rupture resulted from reverse motion on a northeast-dipping fault. We measure vertical surface offsets by differencing pre- and post-earthquake digital elevation models (DEMs) derived from in-track stereo Worldview images. This analysis resolves a maximum vertical deformation of 0.8 ? 0.2 m. We validate these results via comparison to field-based observations and interferometric synthetic aperture radar (InSAR). This new method may be particularly useful for remote characterization of earthquake ruptures with larger (>1 m) vertical deformation, where near-rupture InSAR observations are often compromised by decorrelation.

Volcanism of Late Cretaceous–Miocene age is more widespread across the Zealandia continent than previously recognized. New age and geochemical information from widely spaced northern Zealandia seafloor samples can be related to three volcanotectonic regimes: (1) age-progressive, hotspot-style, low-K, alkali-basalt-dominated volcanism in the Lord Howe Seamount Chain. The northern end of the chain (c. 28 Ma) is spatially and temporally linked to the 40–28 Ma South Rennell Trough spreading centre. (2) Subalkaline, intermediate to silicic, medium-K to shoshonitic lavas of >78–42 Ma age within and near to the New Caledonia Basin. These lavas indicate that the basin and the adjacent Fairway Ridge are underlain by continental rather than oceanic crust, and are a record of Late Cretaceous–Eocene intracontinental rifting or, in some cases, speculatively subduction. (3) Spatially scattered, non-hotspot, alkali basalts of 30–18 Ma age from Loyalty Ridge, Lord Howe Rise, Aotea Basin and Reinga Basin. These lavas are part of a more extensive suite of Zealandia-wide, 97–0 Ma intraplate volcanics. Ages of northern Zealandia alkali basalts confirm that a late Cenozoic pulse of intraplate volcanism erupted across both northern and southern Zealandia. Collectively, the three groups of volcanic rocks emphasize the important role of magmatism in the geology of northern Zealandia, both during and after Gondwana break-up. There is no compelling evidence in our dataset for Late Cretaceous–Paleocene subduction beneath northern Zealandia. <b>Citation:</b> N. Mortimer, P.B. Gans, S. Meffre, C.E. Martin, M. Seton, S. Williams, R.E. Turnbull, P.G. Quilty, S. Micklethwaite, C. Timm, R. Sutherland, F. Bache, J. Collot, P. Maurizot, P. Rouillard, N. Rollet, 2018. <i>Regional volcanism of northern Zealandia: post-Gondwana break-up magmatism on an extended, submerged continent</i>, Large Igneous Provinces from Gondwana and Adjacent Regions, S. Sensarma, B. C. Storey, Geological Society, London, Special Publications, <b>463</b>, pp199–226 This article appears in multiple journals (Lyell Collection & GeoScienceWorld)