b'Geophysics in the surveysNewsGeological Survey of Victoria: AEGC 2023 presentationsCombining seismic interpretation and gravity modelling finds new structures in the Otway BasinIn the onshore and nearshore of the western Otway Basin in Victoria, sparse seismic, drilling, and poor outcrop have previously limited the understanding of deeper structures within the basin. After acquiring a new gravity gradiometry survey in 2018-19 (see p. 20, Preview 201), we combined seismic interpretation, gravity inversion and forward modelling methods to identify earlier misinterpretations of deep crustal structures (Figure 1). This approach showed that the previous work in the Portland Trough had underestimated the thickness of the basin sediments and led to re-interpretation. The new work indicates potential for a previously unrecognised early rift sequence of basin sediments in a deeper Portland Trough, and provides regionally consistent, structural context for the nearby Tartwaup Fault and Bridgewater High.Gravity modelling of crooked lineFigure 1.Matt Boyds poster highlights new structures discovered in the Otway Basintraverses to constrain seismic reflection interpretations in thegravity models onto traverse curtains toResolving basement crustal Australian Alps depths of around 60 km (see Figure 2). architecture and extensional The integration of seismic interpretationtectonics using 3D inversion 2D deep crustal seismic reflectionand gravity modelling enablesmodelling of airborne gravity data and ground gravity surveys were acquired along the Southeast Lachlanreinterpretation of crustal architecture,in the Otway Basin region, VictoriaCrustal Transect in 2018 and 2019providing new insights into the Palaeozoic by the Geological Survey of Victoria,geology, geodynamic evolution, andMark McLean presented findings from 3D Geoscience Australia, Geological Surveymineral potential of eastern Victoriainversion modelling of Airborne Gravity of New South Wales and AuScopeand New South Wales, with greaterGradiometry (AGG) data in the Otway Limited (see p 20 & 21 Preview 201, p. 19implications for eastern Australia. Basin region.Preview 202). For more information about this project:The study provides a workflow to The survey route navigates extremewww.earthresources.vic.gov.au/evgi tackle the problem of superposition terrain across the Australian Alps in Victoria. The high degree of line crookedness, rough terrain and contributions from off-line geology, including buried bodies, presented challenges in forward modelling gravity profile data along the traverses.Phil Skladzien and his co-authors used several methods to integrate seismic interpretations and gravity models more closely. Gravity profile modelling results were integrated with seismic interpretation refinements in an iterative workflow. 3D visualisation was used to align surface geology, seismicFigure 2.Final gravity forward models traversing eastern Victoria and southeast NSW projected on to interpretations and projected 2.5 Dseismic section curtains shown with cut-away surface geology extending north.29 PREVIEW APRIL 2023'