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.

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><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>

The AusArray program aims to install small temporary passive seismic stations every 200 km across Australia. The seismic stations will passively measure small natural vibrations that travel through the Earth to help scientists understand the distribution and composition of rocks beneath the ground. Seismometers are sensitive instruments used to measure small natural vibrations that travel through the Earth caused by earthquakes, waves breaking on the shore and even wind. The data collected are analysed to create a three-dimensional model of the Earth’s subsurface. Passive seismic data can be used to model the Earth‘s structure, which is used to infer the geological history and assess the resource potential and natural hazards of the region.

<div>The active seismic and passive seismic database contains metadata about Australian land seismic surveys acquired by Geoscience Australia and its collaborative partners. </div><div>For active seismic this is onshore surveys with metadata including survey header data, line location and positional information, and the energy source type and parameters used to acquire the seismic line data. For passive seismic this metadata includes information about station name and location, start and end dates, operators and instruments. Each also contains a field that contains links to the published data. </div><div><br></div><div>The active and passive seismic database is a subset of tables within the larger Geophysical Surveys and Datasets Database and development of these databases was completed as part of the second phase of the Exploring for the Future (EFTF) program (2020-2024). The resource is accessible via the Geoscience Australia Portal&nbsp;(https://portal.ga.gov.au/), under 'Geophysics'. Use 'active seismic' or 'passive seismic' as search terms. </div><div><br></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

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>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

<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>

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>