For more than half a century, seismic tomography has been used to map the volumetric structure of Earth’s interior, but only recent advances in computation have enabled the application of this technique at scale. Estimates of surface waves that travel between two seismic stations can be reconstructed from a stack of cross-correlations of continuous data recorded by seismometers. Here, we use data from the Exploring for the Future program AusArray deployment to extract this ambient noise signal of Rayleigh waves and use it to image mid- to upper-crustal structure between Tennant Creek and Mount Isa. Our aim was to establish a repeatable, semi-automatic workflow that can be extended to the entire Australian continent and beyond. Shear wave velocity models at 4, 6, 8 and 10 s periods are presented. A strong low-velocity anomaly (2.5 km/s) at a period of 4 s (~2–4 km depth) delineates the outline of the newly discovered, and prospective for hydrocarbons, Carrara Sub-basin. A near-vertical high-velocity anomaly (3.5 km/s) north of Mount Isa extends from the near surface down to ~12 km and merges with northeast-trending anomalies. These elongate features are likely to reflect compositional variations within the mid-crust associated with major structures inferred to be associated with base metal deposits. These outcomes demonstrate the utility of the ambient noise tomography method of imaging first-order features, which feed into resource potential assessments. <b>Citation: </b>Hejrani, B., Hassan, R., Gorbatov, A., Sambridge, M. Hawkins, R., Valentine, A., Czarnota, K. and Zhao, J., 2020. Ambient noise tomography of Australia: application to AusArray deployment. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4. <b>See eCat record <a href="https://dx.doi.org/10.26186/148676">#148676</a> for the updated version of the model package.</b>

<div>Recent studies have demonstrated that understanding the lithospheric structure is crucial for resource exploration, as errors in model interpretation can lead to significant financial losses. Tomographic images play a key role in constructing lithospheric models. Previous seismic tomographic models were developed using sparse broad-band receiver coverage in Australia, limiting the resolution and reliability of these models. Additionally, the source datasets and associated error estimates are often unavailable, making it difficult to assess the accuracy and resolution power of the models. Therefore, there is a growing need for a fully verifiable lithospheric model of Australia that utilizes national-scale legacy data assimilation and the deployment of new seismic stations to ensure standardized and quality-controlled national data coverage. Geoscience Australia has committed to producing such a model using data from improved national station coverage and sharing all results and datasets involved in model building. A relatively uniform station coverage over the Australian landmass has been achieved with the addition of the currently operated 2-degree (~222 km) grid continental-scale Australian Passive Seismic Array Project&nbsp; (AusArray) deployment, which includes stations installed in previously inaccessible regions. Full waveform inversion (FWI) was selected to create the Australian tomographic models.&nbsp;</div><div><br></div><div>Our database combines records obtained across Australia and the surrounding region. It spans from 1997 to 2023. The dataset underwent a thorough quality check and records for 358 earthquakes registered at 660 seismic stations were extracted for further FWI imaging. Our tomographic image reveals well known subduction zones visible as high velocity belts around Australia showing the structure of ~100 km thickness. The Australian lithosphere in the west is of higher seismic velocity than the east, in general, in agreement with the most tomographic models published previously. However, our results exhibit significantly higher granularity than the previous studies. Adding further earthquakes with lower magnitudes and further AusArray data as it becomes available will continue to improve the model accuracy and resolution. Presented at the 2024 Australian Society of Exploration Geophysicists (ASEG) Discover Symposium

The Exploring for the Future program Showcase 2024 was held on 13-16 August 2024. Day 2 - 14th August talks included: <b>Session 1 - Architecture of the Australian Tectonic Plate</b> <a href="https://youtu.be/a8jzTdNdwfk?si=OWNlVR-FLDhF1GVM">AusArray: Australian lithosphere imaging from top to bottom</a> - Dr Alexei Gorbatov <a href="https://youtu.be/j5ox8Ke5n6M?si=YkfDno2xmZXueS1b">AusLAMP: Mapping lithospheric architecture and reducing exploration space in Australia</a> - Jingming Duan <a href="https://youtu.be/qZ6wjzx_dNc?si=NjDEzvqyEeM24-E8">Constraining the thermomechanical and geochemical architecture of the Australian mantle: Using combined analyses of xenolith inventories and seismic tomography</a> - Dr Mark Hoggard <b>Session 2 - Quantitative characterisation of Australia's surface and near surface</b> <a href="https://youtu.be/nPfa_j3_dos?si=mktfIJWXeLElIOK4">AusAEM: The national coverage and sharpening near surface imaging</a> - Dr Anandaroop Ray <a href="https://youtu.be/SU6ak98JvAw?si=DQPovulHa4poqcm0">Unlocking the surface geochemistry of Australia</a> - Phil Main <a href="https://youtu.be/Xtm45CT6e-s?si=JHU7J-ktgVrbj1Ke">Spotlight on the Heavy Mineral Map of Australia</a> - Dr Alex Walker <b>Session 3 – Maps of Australian geology like never before</b> <a href="https://youtu.be/aRISb1YYigU?si=3byJbqW0qRTqCB8-">An Isotopic Atlas of Australia: Extra dimensions to national maps</a> - Dr Geoff Fraser <a href="https://youtu.be/khSy-WAkw-w?si=F-Y67FX3jXN5zZaz">First continental layered geological map of Australia</a> - Dr Guillaume Sanchez <a href="https://youtu.be/Z3GlCJepLK4?si=k_tbaKdmxGBmoSro">An integrated 3D layered cover modelling approach: Towards open-source data and methodologies for national-scale cover modelling</a> - Sebastian Wong View or download the <a href="https://dx.doi.org/10.26186/149800">Exploring for the Future - An overview of Australia’s transformational geoscience program</a> publication. View or download the <a href="https://dx.doi.org/10.26186/149743">Exploring for the Future - Australia's transformational geoscience program</a> publication. You can access full session and Q&A recordings from YouTube here: 2024 Showcase Day 2 - Session 1 - <a href="https://www.youtube.com/watch?v=EHBsq0-pC8c">Architecture of the Australian Tectonic Plate</a> 2024 Showcase Day 2 - Session 2 - <a href="https://youtube.com/watch?v=xih4lbDk-1A">Quantitative characterisation of Australia's surface and near surface</a> 2024 Showcase Day 2 - Session 3 - <a href="https://www.youtube.com/watch?v=qeTLc1K-Cds">Maps of Australian geology like never before</a>

<div>This model is a volumetric representation of receiver function analysis based on common conversion point (CCP) profiles created every 50 km in North-South and East-West directions below the AusArray network (Gorbatov et al., 2020), combining them into one 3D image. The model bounds are: (-21.74, 132.52) - (-17.30, 141.46), geographic projection EPSG:28353. The model file is distributed in ASCII GoCad stratigraphic grid format (SGrid) where units are longitude (meters), latitude (meters), depth (meters) and value of receiver function amplitude.</div><div><br></div><div>Geoscience Australia’s Exploring for the Future program provides precompetitive information to inform decision-making by government, community and industry on the sustainable development of Australia's mineral, energy and groundwater resources. By gathering, analysing and interpreting new and existing precompetitive geoscience data and knowledge, we are building a national picture of Australia’s geology and resource potential. This leads to a strong economy, resilient society and sustainable environment for the benefit of all Australians. This includes supporting Australia’s transition to a low emissions economy, strong resources and agriculture sectors, and economic opportunities and social benefits for Australia’s regional and remote communities. The Exploring for the Future program, which commenced in 2016, is an eight year, $225m investment by the Australian Government.</div>

<div><strong>Output Type: </strong>Exploring for the Future Extended Abstract</div><div><br></div><div><strong>Short Abstract:</strong> Under the Exploring for the Future (EFTF) program, Geoscience Australia staff and collaborators engaged with land-connected stakeholders that managed or had an interest in land comprising 56% of the total land mass area of Australia. From 2020 to 2023, staff planning ground-based and airborne geophysical and geological data acquisition projects consulted farmers, National Park rangers and managers, Native Title holders, cultural heritage custodians and other land-connected people to obtain land access and cultural heritage clearances for surveys proposed on over 122,000 parcels of land. Engagement did not always result in field activities proceeding. To support communication with this diverse audience, animations, comic-style factsheets, and physical models, were created to help explain field techniques. While the tools created have been useful, the most effective method of communication was found to be a combination of these tools and open two-way discussions.</div><div><br></div><div><strong>Citation: </strong>Sweeney, M., Kuoni, J., Iffland, D. &amp; Soroka, L., 2024. Improving how we engage with land-connected people about geoscience. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts. Geoscience Australia, Canberra. https://doi.org/10.26186/148760</div>

<div><strong>Output Type:</strong> Exploring for the Future Extended Abstract</div><div><br></div><div><strong>Short Abstract: </strong>Knowledge of lithospheric structure is crucial information for resources exploration and deepening understanding of natural hazards. Available tomographic models of the Australian lithosphere often agree on large scale features, but in detail significant differences remain. Consequently, there is a growing need for a fully verifiable lithospheric model of Australia. Geoscience Australia has committed to develop such a model and share all results and datasets involved in model building. Here we present the first results of a full waveform inversion tomography model of Australia lithosphere down to a period of 70 s potentially able to resolve half wavelengths across continental Australia. Our model is based on seismic records from the National Seismic Network and legacy datasets with the addition of data from the currently deployed continental-scale 2° AusArray survey, which includes stations installed in previously inaccessible areas. We start with 193 earthquakes (moment magnitude (Mw) 6.2–7.5) and add 165 more earthquakes (Mw &gt;5.0) once the model progressed to a period of 70 s. Model resolution will improve over time as more data become available and more time is allowed for computation and quality control. As further iterations continue, and the inversion frequency range expands to higher frequencies, body waves can be exploited in full to constrain the model in detail and provide enough information for all components of the wavefield, building high-resolution tomographic models at a period of 40 s and below. Our model reveals previously observed first order features while revealing finer detail across much of continental Australia.</div><div><br></div><div><strong>Citation: </strong>Holzschuh, J., Gorbatov, A., Hejrani, B., Boehm, C. &amp; Hassan, R., 2024. Tomographic model of the Australian region from seismic full waveform inversion. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, https://doi.org/10.26186/149404</div>

Geoscience Australia, in collaboration with state government agencies, has been collecting magnetotelluric (MT) data as part of the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) for several years. This program aims to map the electrical resistivity of the rock layers, at depths from ten kilometres to hundreds of kilometres, across the entire continent. AusLAMP sites are each about 55 km apart from each other. Locations are chosen in consultation with landholders and other stakeholders to minimise impacts and avoid disturbance.MT data is collected using sensors that record naturally occurring variations of the Earth’s magnetic and electric fields. The equipment does not produce or transmit and signals. After four to six weeks the equipment is retrieved and the site restored to its original condition.

<div><strong>Output type: </strong>Exploring for the Future Extended Abstract</div><div><br></div><div><strong>Short abstract: </strong>Passive seismic methods serve as versatile tools for probing Earth structure and facilitating new geological and geodynamic insight across vast areas. Tomographic velocity models derived from continental scale passive seismic data are becoming increasingly important in guiding resource exploration into prospective regions. While Australia has been leading this field our existing data coverage and quality is insufficient resulting in large uncertainties in continental scale models. With the aim of robustly constraining Australia’s lithospheric architecture the Exploring for the Future (EFTF) program began collection of a 2° (~220 km spaced) AusArray passive seismic data coverage. There are over 150 broad-band seismometer stations simultaneously deployed across Australia for a period of up to two years - a pioneering effort on a continental scale. The quality assurance/quality control (QA/QC) analysis and deployment approaches, refined during previous 0.5° (~55 km spaced) campaigns, were rigorously applied to prevent data errors or data loss. Advanced standard operating procedures and stakeholder engagement materials were developed and openly shared with broader professional communities to support similar activities, fostering the continued advancement of passive seismic methods in both industry and research. The resulting data will be shared via the eCat system in raw format, accompanied by a StationXML file that holds the QA/QC information. This file can be used to apply QA/QC results to raw waveforms, enabling their use in subsequent analysis and modelling endeavors. Insights from this survey will guide future higher resolution AusArray deployments. &nbsp;</div><div><br></div><div><strong>Citation: </strong>Gorbatov, A., Hejrani, B., Holzschuh, J., Zhao, J., Hassan, R., Cathro, D., Czarnota, K., Kuoni, J., Sweeney, M., Glowacki, J., Murdie, R., O'Donnel, J.P. & Haydon, S.J., 2024. AusArray continent-scale deployment. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, https://doi.org/10.26186/149640 </div>

<div>As part of the first phase (2016-2020) of the Exploring for the Future (EFTF) program, Geoscience Australia deployed 119 broad band seismic stations in northern Australia. This deployment was part of the Australian Passive Seismic Array (AusArray) Project. Data from these stations were used to image the seismic structure using various techniques, including ambient noise tomography (ANT). The first ANT model (Hejrani et al, 2020) was focused on a narrow range of frequencies and used the Hawkins and Sambridge (2019) approach to estimate dispersion curves. This new approach starts from the original work by Aki (1957) to estimate phase velocity in the frequency domain, and then takes a step further to ensure a smooth curve is achieved. In Hejrani et al., (2022), using minimum Signal-to-Noise-Ratio (SNR) threshold of 2, about 4,000 data points (out of 7,000+) were used to generate surface wave velocity maps at a resolution of 1 degree at four frequencies (sensitive to different depths). This model was subsequently updated in September 2021 by using all 7,000+ data points (no SNR threshold) of phase velocity measurements across AusArray year one to provide a 0.25 degree resolution model. All dispersion curves regardless of their quality were utilized. A number of artefacts were identified in that model, which motivated further investigations. During 2022, I developed a new automated and scalable approach to estimate dispersion curves, which was completed in December 2022. This new method starts from the original idea by Aki (1957), but takes a different approach to stabilize the dispersion curves and to avoid cycle skipping. </div><div>This record represents the preferred 2D velocity models for AusArray year one data based on the newly estimated dispersion curves and a comparison with previous models and interpretations; is an update from Hejrani et al. (2020) and should be read in conjunction. Work is currently under way to invert these 2D surface wave models to obtain 3D velocity models for the crust and mantle. Such 3D velocity models would be suitable for joint interpretations with other data such active seismic, gravity and magnetic. The code will be made publicly available at the conclusion of EFTF.</div>

Exploration and management of minerals, energy and groundwater resources requires robust constraints on subsurface geology. Over the last decade the passive seismic technique has grown in popularity as it is one of a handful of non-invasive methods of imaging the subsurface. Given regional imaging relies on comparing records of ground motion between simultaneous deployments of seismometers deployed for over a year, consistency and quality of data collection lies at the heart of this technique. Here, we summarise the standard operating procedures developed by Geoscience Australia over the last 6 years for deployment, servicing and retrieval of passive seismic arrays. Our purpose is to share our experience and thereby contribute to improving the quality of passive seismic data being acquired across Australia. <b>Citation:</b> Holzschuh J., Gorbatov A., Glowacki J., Cooper A. & Cooper C., 2022. AusArray temporary passive seismic station deployment, servicing and retrieval: Geoscience Australia standard operating procedures. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, https://dx.doi.org/10.26186/146999