Abstract
The network of seismographs on Earth allows us to gather enough data to reveal the properties of the metallic core hidden in the centre of the planet’s mantle envelope. In contrast, the small number of seismographs deployed on the Moon or Mars limits the sampling of their interiors and makes inferences challenging. Here we show that a single seismograph and global-scale waveform cross-correlations between seismic events can be used to scan planetary cores. We demonstrate that this technique allows us to constrain the sizes of the cores of Earth and Mars and we confirm that the Martian core is large. This technique provides an opportunity to investigate the structure of planetary interiors with currently realizable resources.
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Data availability
The facilities of IRIS-DMC, NEIC, NASA-PDS, the SEIS-InSight data portal and the IPGP Data Center were used for access to seismic-event catalogue, waveforms and related metadata used in this study. Marsquake catalogue and waveform data used in this study are available from ref. 30,34. The earthquake catalogue and waveform data are available from the NEIC catalog (available at https://earthquake.usgs.gov/earthquakes/search/) and IRIS-DMC (available at http://ds.iris.edu/ds/nodes/dmc/data/types/waveform-data/).
Code availability
Codes are publicly available in the Supplementary Information.
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Acknowledgements
We acknowledge NASA (National Aeronautics and Space Administration), CNES (Centre National D’Etudes Spatiales), their partner agencies and Institutions UKSA (United Kingdom Sailing Academy), SSO (Swiss Space Office), DLR (Deutsches Zentrum für Luft- und Raumfahrt), JPL (Jet Propulsion Laboratory), IPGP-CNRS (Institut de Physique du Globe de Paris, Centre National de la Recherche Scientifique), ETHZ (Eidgenössische Technische Hochschule Zürich), IC (Imperial College), MPS-MPG (Max Planck Institute for Solar System Research), the flight operations team at JPL, SISMOC (SEIS on Mars Operations Center), MSDS (Mars SEIS Data Service), IRIS-DMC and PDS (Planetary Data System, NASA) for the development of SEIS and for providing SEED (Standard for the Exchange of Earthquake Data) SEIS data. This study is supported by computational resources provided by the Australian Government through the National Computational Infrastructure facility under the ANU (Australian National University) Merit Allocation Scheme. We would like to acknowledge the ANU PhD Scholarship supporting S.W. through his degree. H.T.’s time on this project is supported through a combination of grants administrated by the ANU.
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Both authors contributed to the results and determined the course of the study based on methodological developments in S.W.’s PhD work under the supervision and guidance of H.T. S.W. processed the seismic data. Both authors contributed to the analyses, interpretation of the results and manuscript writing.
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Extended data
Extended Data Fig. 1 Selections of source mechanisms and source pairs for constructing global inter-source correlograms.
(a) We select thrust events (red beach balls) and exclude events of other source mechanisms (black beach balls). We extract Mw6.5+ earthquakes in 2000–2020 and their source mechanism solutions from the NEIC catalog. The stations (triangles) originate from the Global Seismographic Networks (network codes II and IU). We use two single stations, II.PFO and II.NNA (blue triangles) to showcase single-station inter-source correlograms in Fig. 1. (b) Source pairs selection based on source-receiver geometry. Each source pair is represented by a great-circle path passing through two sources. We select source pairs for which the great-circle paths are <20° spherical distance away from the receiver (II.NNA). Red lines represent the selected source pairs, while the black lines represent the excluded source pairs for the distance ≥20°. We plot randomly downsampled great-circle paths by 10% to avoid intense overlapping.
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Supplementary materials and method details, Figs. 1–38 and Table 1.
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Wang, S., Tkalčić, H. Scanning for planetary cores with single-receiver intersource correlations. Nat Astron 6, 1272–1279 (2022). https://doi.org/10.1038/s41550-022-01796-8
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DOI: https://doi.org/10.1038/s41550-022-01796-8