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.

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>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>

<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>Finding new mineral deposits hidden beneath the sedimentary cover of Australia has become a national priority, given the country’s economic dependence on natural resources and urgent demand for critical minerals for a sustainable future. A fundamental first step in finding new deposits is to characterise the depth of sedimentary cover. Excellent constraints on the sedimentary thickness can be obtained from borehole drilling or active seismic surveys. However, these approaches are expensive and impractical in the remote regions of Australia. With over three quarters of the continent being covered in sedimentary and unconsolidated material, this poses a significant challenge to exploration.</div><div><br></div><div>Recently, a method for estimating the sedimentary thickness using passive seismic data, the collection of which is relatively simple and low-cost, was developed and applied to seismic stations in South Australia. The method uses receiver functions, specifically the delay time of the P-to-S converted phase generated at the interface of the sedimentary basement, relative to the direct-P arrival, to generate a first order estimate of the thickness of sedimentary cover. In this work we apply the same method to the vast array of seismic stations across Australia, using data from broadband stations in both permanent and temporary networks.&nbsp;We also investigate using the two-way traveltime of shear waves, obtained from the autocorrelation of radial receiver functions, as a related yet separate estimate of sedimentary thickness.&nbsp;</div><div><br></div><div>From the new receiver function delay time and autocorrelation results we are able to identify many features, such as the relatively young Cenozoic Eucla and Murray Basins. Older Proterozoic regions show little signal, likely due to the strong compaction of sediments.&nbsp;A comparison with measurements of sedimentary thickness from local boreholes gives a straightforward predictive relationship between the delay time and the cover thickness, offering a simple and cheap way to characterise the sedimentary thickness in unexplored areas from passive seismic data. This study and some of the data used are funded and supported by the Australian Government's Exploring for the Future program led by Geoscience Australia. Abstract to be submitted to/presented at the American Geophysical Union (AGU) Fall Meeting 2023 (AGU23) - https://www.agu.org/fall-meeting

<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>

To improve exploration success undercover, the UNCOVER initiative identified high-resolution 3D seismic velocity characterisation of the Australian plate as a high priority. To achieve this goal, the Australian Government and academia have united around the Australian Passive Seismic Array Project (AusArray). The aim is to obtain a national half-degree data coverage and an updatable 3D national velocity model, which grows in resolution as more data become available. AusArray combines data collected from the Australian National Seismological Network (ANSN), multiple academic transportable arrays (supported by AuScope and individual grants) and the Seismometers in Schools program. The Exploring for the Future program has enable the unification of these datasets and a doubling of the national rate of data acquisition. Extensive quality control checks have been applied across the AusArray dataset to improve the robustness of subsequent tomographic inversion and interpretation. These data and inversion code framework allow robust national-scale imaging of the Earth to be rapidly undertaken at depths of a few metres to hundreds of kilometres. <b>Citation:</b> Gorbatov, A., Czarnota, K., Hejrani, B., Haynes, M., Hassan, R., Medlin, A., Zhao, J., Zhang, F., Salmon, M., Tkalčić, H., Yuan, H., Dentith, M., Rawlinson, N., Reading, A.M., Kennett, B.L.N., Bugden, C. and Costelloe, M., 2020. AusArray: quality passive seismic data to underpin updatable national velocity models of the lithosphere. 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. http://dx.doi.org/10.11636/135284 <b>Data for this product are available on request from clientservices@ga.gov.au (see data description). Last updated 08/08/2024 - Quote eCat# 135284</b>

In recent years there has been a considerable expansion of deployments of portable seismic stations across Australia, which have been analysed by receiver function or autocorrelation methods to extract estimates of Moho depth. An ongoing program of full-crustal reflection profiles has now provided more than 25,000 km of reflection transects that have been interpreted for Moho structure. The Moho dataset is further augmented by extensive marine reflection results. These new data sources have been combined with earlier refraction and receiver function results to provide full continental coverage, though some desert areas remain with limited sampling. The dense sampling of the Moho indicates the presence of rapid changes in Moho depth and so the Moho surface has been constructed using an approach that allows different weighting and spatial influence depending on the nature of the estimate. The inclusion of Moho results from gravity inversion with low weighting helps to resolve the continent-ocean transition and to provide additional control in the least sampled zones. The refined distribution indicates the presence of widespread smaller-scale variations in Moho structure. Strong lateral contrasts in crustal thickness remain, but some have become more subdued with improved sampling of critical areas. The main differences from earlier results lie in previously poorly sampled regions around the Lake Eyre Basin, where additional passive seismic results indicate somewhat thicker crust though still witha strong contrast in crustal thickness to the cratonic zone to the west. Appeared in Geophysical Journal International, January 2023

Geoscience Australia’s Exploring for the Future program (EFTF) provides precompetitive information to inform decision-making by government, community and industry on the sustainable development of Australia's mineral, energy and groundwater resources. The Australian Passive Seismic Array Project (AusArray) program developed from a long history of passive seismic imaging in Australia involving many contributors. Building on this history, the Australian Government (EFTF), academia and state governments have united around AusArray. The objective is a standardised and quality controlled national passive seismic data coverage and an updatable national seismic velocity model framework that can be used as a background for higher-resolution studies. The AusArray passive seismic data are supplemented with active seismic data that can provide P-wave and S-wave velocity information for the near surface down to about 50 m depth. This near-surface velocity data will provide constraints for some AusArray passive seismic data modelling to obtain more reliable depth models. This document details the active seismic data acquisition using TROMINO® three-axis broadband seismometers using a wireless trigger and hammer source. Equipment packing, field operations, data extraction and preparation, and Multichannel Analysis of Surface Waves (MASW) modelling are described.

The Australian Passive Seismic Array Project (AusArray) program was developed from a long history of passive seismic imaging in Australia involving many contributors. Building on this history, the Australian Government and academia have united around AusArray. The objective is a standardised and quality controlled national passive seismic data coverage and an updatable national seismic velocity model framework that can be used as a background for higher-resolution studies. This document details the field activities and equipment preparation for temporary passive seismic station deployment, service and retrieval. Equipment cleaning and testing and database details are also described. The standard operating procedures applied during these activities were established during the deployment of two temporary passive seismograph arrays under the Australian Government’s Exploring for the Future (EFTF) program. These arrays consisted of 120–130 stations deployed in the Northern Territory and Queensland for over a year in a grid pattern with a lateral spacing of half a degree (~55 km). The temporary passive seismograph stations comprised Nanometrics Trillium Compact 120S broadband seismic sensors connected to a Güralp minimus digitiser. Batteries charged by a solar panel powered both instruments. Each station in the array was serviced, i.e. repairs if required and interim data was retrieved, at least once during the deployment.