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Example of cross-correlation processing between a pair of seismic stations. Non-linearity of recovered maximum amplitudes, shown as a red vertical line, suggests notorious clock drift from 06/04/2018 to 05/05/2018.
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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-de...
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... is based on the CC feature, where causal and acausal parts of a waveform should occur at time lags equal to the time required for a surface wave to travel between two given stations. Temporal variations deviating from this rule ( Figure 5) can indicate the presence of clock errors or notorious data problems unrelated to seismic wave propagation (Stehly et al., 2007). Although this method allows determination of clock drift with subsecond precision, its main limitation is that it is only applicable at relatively short interstation distances, preferably less than ~300 km, due to the attenuation of highfrequency waveforms required for high-quality CC estimation (e.g. ...
Citations
... To pick S-wave arrival times, we rotated the horizontal seismogram components to the radial (R) and transverse (T) coordinate system and picked the S-wave arrivals on transverse components. We assessed the Global Positioning System (GPS) clock stability of all stations used in this study to avoid using stations with GPS clock drifts (Hejrani, Balling, et al., 2017;Hable et al., 2018;Gorbatov et al., 2020). We observed no systemic clock drifts in any of the stations except for AUKSC, for which we have downloaded the corrected data from AusPass Data Centre. ...
The Australian Seismometers in Schools (AuSIS) network operates 50 broadband seismic stations across Australia that are hosted at schools. The instruments augment the Australian National Seismograph Network providing valuable data from urban and regional Australia. The network coverage is quite sparse, but these vital records of rare, moderate Australian earthquakes can improve our understanding of the deformation within the stable continental region of Australia, especially for events with no surface rupture. In this study, we present the feasibility of identifying the fault plane of moderate earthquakes on the Australian continent, using data from the AuSIS network. We examine the fault plane of the September 2021 Mw 5.9 Woods Point earthquake that occurred about 130 km northeast of the Melbourne metropolitan area. We estimate the hypocenter and the centroid moment tensor (CMT) to identify the fault plane from the auxiliary plane in the focal mechanism. We explore a range of 1D models and a 3D Earth model to simulate seismic arrivals and full waveform data. The hypocenter is resolved using P- and S-wave arrivals in a probabilistic framework and the CMT is derived from full waveform modeling through grid search over a set of trial points around the hypocenter. Our solution suggests the mainshock ruptured the depth of 15 ± 4 km, with a strike-slip mechanism striking 348° north on a nearly vertical plane. The high double-couple percentage of this event indicates a simple rupture that propagated from the south (hypocenter) toward the north (centroid) and remained subsurface. This indicates that the causative fault had a deeper structure than the previously known shallow, northwest–southeast-striking faults of the region. The P and T axes deduced from our fault model are notably aligned with the maximum horizontal crustal stress in the region.
... The importance of a national approach to seismic imaging was highlighted by the UNCOVER initiative (AMIRA, 2017). Geoscience Australia (GA) adopted such seismic acquisition as part of (Gorbatov et al. 2020a). ...
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 continental-wide 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 with a strong contrast in crustal thickness to the cratonic zone to the west.
... This highlights the importance of passive seismic data-in this case, Rayleigh-wave dispersion curves-which have the greatest sensitivity to mantle conditions. Over time, programs such as AusArray (Gorbatov et al., 2020) will enhance our passive seismic data collections and increase our ability to image the lithospheric mantle. Except for Figure 2b, results in this abstract reflect the use of Rayleigh-wave phase velocities from Fishwick and Rawlinson (2012), due to a better match with our a priori expectations for LAB structure. ...
... We continue to develop the LitMod platform, and are currently implementing body-wave travel time, potential field and magnetotelluric inversions within the 3D version. Most significantly, our approach has the potential to bring together many world-class, national-scale datasets, including AusArray (Gorbatov et al., 2020), AusLAMP (Duan et al., 2020) and gravity (Bacchin et al., 2008) to image the 3D thermochemical structure of the Australian continent in greater detail. ...
Lithospheric structure and composition have direct relevance for our understanding of mineral prospectivity. Aspects of the lithosphere can be imaged using geophysical inversion or analysed from exhumed samples at the surface of the Earth, but it is a challenge to ensure consistency between competing models and datasets. The LitMod platform provides a probabilistic inversion framework that uses geology as the fabric to unify multiple geophysical techniques and incorporates a priori geochemical information. Here, we present results from the first application of LitMod to the Australian continent. We demonstrate the ability to map important geophysical surfaces, and to differentiate between compositional (e.g. metasomatism) and thermal anomalies. We validate the posterior predictions from our inversion against independent studies, and this highlights the robustness of our results. Finally, we discuss recent technological advances in the implementation of LitMod3D_4INV, and how the model can be used to bring together multiple projects within the Exploring for the Future program to image the lithospheric mantle. The implications of this work extend beyond mineral prospectivity, and will ultimately inform our understanding of energy systems, groundwater and seismic hazard. The mineral systems framework (Wyborn et al., 1994) allows us to reduce the search space for mineral exploration (e.g. Dulfer et al., 2016; Skirrow et al., 2019) by providing a series of testable predictions about lithospheric architecture. Lithospheric features could include broad volumes of metasomatised mantle, crustal-scale fluid pathways, rapid transitions in lithospheric thickness, the influence of plumes, and slab subduction (e.g. Skirrow et al., 2013). These types of features all point towards physical and chemical structures in the lithospheric mantle and sub-lithospheric upper mantle. The main question is: how can we resolve these features within the Australian lithosphere and mantle? Lithospheric architecture information primarily comes from exhumed mantle samples (up to 200 km depth) or geophysical imaging. Individual geophysical inversions have previously been used to identify mineral system components (e.g. Skirrow et al., 2018; Czarnota et al., 2020; Hoggard et al., in press). However, challenges remain-namely, comparison of the results from multiple independent inversions, consistency among geophysical datasets, and compositional matching of mantle xenoliths with laboratory studies. Figure 1 Conceptual diagram of the LitMod platform, including models, input datasets, chi-squared misfits and posterior inference, including uncertainty. Our primary model is mantle major oxide suites, and these are computed between major Earth structures (i.e. the Moho and the lithosphere-asthenosphere boundary [LAB]). Haynes et al., 2020 Exploring for the Future: Extended Abstracts
... To this end, highresolution 3D seismic velocity characterisation of the Australian plate has been identified by the UNCOVER initiative as a priority to improve mineral exploration success. The Australian Government and academia have united under the auspices of the Australian Passive Seismic Array Project (AusArray; Gorbatov et al., 2020). ...
... It would be useful if future development of the tomographic inversion focused on three main areas. Further incorporation of legacy data collections will increase the regional data coverage of our tomographic models (Figure 1; Gorbatov et al., 2020). Application of an irregular meshing scheme would focus structural complexity in areas where it is supported by the data, such as beneath the dense arrays (Burdick et al., 2008). ...
Mineral deposits are the products of lithospheric-scale processes. Imaging the structure and composition of the lithosphere is therefore essential to better understand these systems, and to efficiently target mineral exploration. Seismic techniques have unique sensitivity to velocity variations in the lithosphere and mantle, and are therefore the primary means available for imaging these structures. Here, we present the first stage of Geoscience Australia's passive seismic imaging project (AusArray), developed in the Exploring for the Future program. This includes generation of compressional (P) and shear (S) body-wave tomographic imaging models. Our results, on a continental scale, are broadly consistent with a priori expectations for regional lithospheric structure and the results of previously published studies. However, we also demonstrate the ability to resolve detailed features of the Australian lithospheric mantle underneath the dense seismic deployments of AusArray. Contrasting P- and S-wave velocity trends within the Tennant Creek – Mount Isa region suggest that the lithospheric root may have undergone melt-related alteration. This complements other studies, which point towards high prospectivity for iron oxide–copper–gold mineralisation in the region.
Around the world the Earth’s crust is blanketed to various extents by sediment. For continental regions, knowledge of the distribution and thickness of sediments is crucial for a wide range of applications including seismic hazard, resource potential, and our ability to constrain the deeper crustal geology. Excellent constraints on the sediment thickness can be obtained from borehole drilling or active seismic surveys. However, these approaches are expensive and impractical in remote continental interiors such as central Australia. Recently, a method for estimating the sediment 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. This method uses receiver functions, specifically the time delay of the P-to-S converted phase generated at the sediment-basement interface, relative to the direct-P arrival, to generate a first order estimate of the thickness of sediments. In this work we expand the analysis to the vast array of over 1500 seismic stations across Australia, covering an entire continent and numerous sedimentary basins that span the entire range from Precambrian to present-day. We compare with an established yet separate method to estimate the sediment thickness, which utilises the autocorrelation of the radial receiver functions to ascertain the two-way travel-time of shear waves reverberating in a sedimentary layer. Across the Australian continent the new results match the broad pattern of expected sedimentary features based on the various geological provinces. We are able to delineate the boundaries of many sedimentary basins, such as the Eucla and Murray Basins, which are Cenozoic, and the boundary between the Karumba Basin and the mineral rich Mount Isa Province. Contrasts in seismic delay time across these boundaries are upwards of 0.4 s. The delay signal is found to diminish to <0.1 s for older Proterozoic basins, likely due to compaction and metamorphism of the sediments over time. As an application of the method, a comparison with measurements of sediment thickness from local boreholes allows for a straightforward predictive relationship between the delay time and the cover thickness to be defined. This offers future widespread potential, providing a simple and cheap way to characterise the sediment thickness in under-explored areas from passive seismic data.
Diamond exploration over the past decade has led to the discovery of a new province of kimberlitic pipes (the Webb Province) in the Gibson Desert of central Australia. The Webb pipes comprise sparse macrocrystic olivine set in a groundmass of olivine, phlogopite, perovskite, spinel, clinopyroxene, titanian‐andradite and carbonate. The pipes resemble ultramafic lamprophyres (notably aillikites) in their mineralogy, major and minor oxide chemistry, and initial ⁸⁷Sr/⁸⁶Sr and εNd‐εHf isotopic compositions. Ion probe U‐Pb geochronology on perovskite (806 ± 22 Ma) indicates the eruption of the pipes was co‐eval with plume‐related magmatism within central Australia (Willouran‐Gairdner Volcanic Event) associated with the opening of the Centralian Superbasin and Rodinia supercontinent break‐up. The equilibration pressure and temperature of mantle‐derived garnet and chromian (Cr) diopside xenocrysts range between 17 and 40 kbar and 750–1320°C and define a paleo‐lithospheric thickness of 140 ± 10 km. Chemical variations of xenocrysts define litho‐chemical horizons within the shallow, middle, and deep sub‐continental lithospheric mantle (SCLM). The shallow SCLM (50–70 km), which includes garnet‐spinel and spinel lherzolite, contains Cr diopside with weakly refertilized rare earth element compositions and unenriched compositions. The mid‐lithosphere (70–85 km) has lower modal abundances of Cr diopside. This layer corresponds to a seismic mid‐lithosphere discontinuity interpreted as pargasite‐bearing lherzolite. The deep SCLM (>90 km) comprises refertilized garnet lherzolite that was metasomatized by a silicate‐carbonatite melt.
Situated on the northern coast of the Indonesian island of Java, Jakarta and its metropolitan area (Greater Jakarta) are subject to significant earthquake hazards from a subduction zone south of Java and nearby active crustal faults. The seismic risk may be even higher because Greater Jakarta resides on a sedimentary basin filled with thick Pliocene-Pleistocene sediments. A comprehensive study of Jakarta Basin's properties and geometry is important for creating robust seismic hazard and risk assessments. The main objective of this study is to develop a 3D model of Jakarta Basin's shallow shear-wave velocity (VS) structure and improve on previous models that did not cover the basin edge due to the extent of data coverage. Between April and October 2018, we deployed a new temporary seismic network to extend the spatial coverage beyond that of a previous deployment in 2013, and sampled 143 locations through sequential deployments of 30 broad-band sensors covering Jakarta and its adjacent areas. We conducted a 2-stage transdimensional Bayesian inversion of Rayleigh wave phase velocity dispersion curves derived from seismic noise. To begin, we applied tomography and constructed 2D phase velocity maps for periods 1–5 s. Then, at each point in a regular grid defined on these maps, we invert each dispersion curve into 1D depth profiles of VS. Finally, these profiles at grid points with ∼2 km spacing are interpolated to form a pseudo-3D VS model. Our results reveal the edge of the Pliocene-Pleistocene sediments along the south. Also, we resolve a basement offset across south Jakarta that we suggest may be related to the western extension of the Baribis Fault (alternatively, the West Java Back-arc Thrust). We recommend using this 3D model of the Jakarta Basin for scenario earthquake ground motion simulations. Such simulations would help establish how important it might be to re-assess seismic hazard and risk in Greater Jakarta so that basin resonance and amplification are considered.
The proliferation of seismic networks in Australia has laid the groundwork for high-resolution probing of the continental crust. Here we develop an updated 3D shear-velocity model using a large dataset containing nearly 30 years of seismic recordings from over 1600 stations. A recently-developed ambient noise imaging workflow enables improved data analysis by integrating asynchronous arrays across the continent. This model reveals fine-scale crustal structures at a lateral resolution of approximately 1-degree in most parts of the continent, highlighted by 1) shallow low velocities (<3.2 km/s) well correlated with the locations of known sedimentary basins, 2) consistently faster velocities beneath discovered mineral deposits, suggesting a whole-crustal control on the mineral deposition process, and 3) distinctive crustal layering and improved characterization of depth and sharpness of the crust-mantle transition. Our model sheds light on undercover mineral exploration and inspires future multi-disciplinary studies for a more comprehensive understanding of the mineral systems in Australia.
