<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>

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.

<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>

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

<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

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>

This is a collection of continuous seismic records gathered by temporal and semi-permanent seismic deployments where real-time data transmission was not available. Time spans vary from half an hour to more than a year depending on the purpose of the survey. Description of the employed instrumentation and array constellations can be found in the accompanied material. <b>Value: </b>Passive seismic data contains records of soil vibration due to the natural earth movements, ocean, weather, and anthropogenic activities. This data is used in ongoing research to infer national lithospheric structure from depth of a few meters to a hundred kilometres. Derived models are an important source of information for assessment of resource potential and natural hazard. <b>Scope: </b>Over time, surveys have been focused on areas of economic interest, current work of the Australian Passive Seismic Array Project (AusArray) is seeking to create a grid pattern, spaced ~55 km apart, and complemented by semi-permanent higher sensitivity broadband seismic stations. For more information about AusArray click on the following URL: <a href="https://www.ga.gov.au/eftf/minerals/nawa/ausarray">https://www.ga.gov.au/eftf/minerals/nawa/ausarray</a> <b>Data from phase 1 are available on request from clientservices@ga.gov.au - Quote eCat# 135284</b>

<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>Seismic tomography has been used for more than 50 years to map the seismic velocity structure of Earth’s interior. Here, we use data from the Exploring for the Future program, AusArray 2o deployment, to perform ambient noise tomography of the Australian continent. In this approach, stacks of cross-correlations of background seismic noise recorded by pairs of seismometers are employed to extract an approximation to the surface wave trains travelling between the seismometers. We have developed a semi-automatic approach to estimate dispersion properties of surface waves as a function of frequency at 0.01 – 1 Hz and deployed the largest ever network of broadband seismometers across the country to image the continental crust of Australia. In this study, we present an ambient noise tomography map of the Australian continent at 0.4 Hz (2.5 seconds), which is sensitive to the top 3 km of the Earth’s crust. Our model shows improved resolution across the country, for example, we observed a large low-velocity anomaly (~2.5 km/s) which delineates the shape of the entire Caning basin in Western Australia. This basin has never been imaged at this detail before, as previous tomographic studies do not measure surface wave velocity up to 0.4 Hz and do not have stations deployed in this area. The outcome demonstrates the utility of the ambient noise tomography method of imaging first-order features, that could be built upon for resource potential assessments.</div><div><br></div><div><strong>Citation: </strong>Hejrani B., Hassan R., Gorbatov A. & Zhao J., 2024. Towards continental-scale ambient noise tomography of Australia: a preliminary result from AusArray data. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, https://doi.org/10.26186/149637</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>