13:50 〜 14:15
[SIT18-01] Planetary cores seen by the coda correlation wavefield
★Invited Papers
キーワード：Earth's core, planetary cores, global seismology, coda correlation, seismic wavefield, correlation wavefield
The cores of terrestrial planets and moons are central to understanding their formation, evolution, and dynamic processes, including magnetic field generation and thermochemical evolution. However, probing planetary cores remains challenging due to limited observational data, particularly for bodies like the Moon and Mars. We present innovative seismological techniques to investigate planetary cores and their properties. First, we demonstrate that a single seismograph, combined with global-scale waveform cross-correlations between seismic events, can effectively constrain the sizes of planetary cores. We address the challenge of constructing global inter-source correlograms, which have previously lacked discernible correlation features due to destructive contributions from diverse source mechanisms and source-receiver geometries. We present a rigorous procedure for selecting source mechanisms and geometries, enabling the construction of global inter-source correlograms with prominent correlation features. This method is particularly effective for single-receiver configurations, offering a practical approach to probing the interiors of Earth and other terrestrial bodies using currently affordable resources. Applying this method to Earth and Mars, we measure the radius of the Martian core, highlighting the potential of this technique for exploring planetary interiors with limited resources (1,2).
Furthermore, building on the theoretical and methodological advances in the correlation wavefield, we explore thermochemical inhomogeneities in the Earth’s outer core using the global coda correlation wavefield. We identify a low-velocity torus structure at low latitudes in the outermost outer core, with ~2% lower velocity than the surrounding outer core, and propose a thermochemical origin for this feature (3). This finding provides critical insights into the distribution of light elements and dynamic processes in the outer core. However, it also represents a challenge in bridging seismological observations with geodynamical constraints. Our results underscore the importance of integrating coda correlation data with body-wave and normal-mode analyses to refine models of core composition and dynamics.
By combining global seismological, mineral physics, and geodynamic-modeling data, we will advance the understanding of planetary cores and their role in planetary evolution. The methodologies like the coda correlation wavefield (4) apply to Earth but also offer new avenues for investigating the interiors of other terrestrial bodies, such as the Moon and Mars, as well as insights relevant to ongoing and future planetary missions, contributing to the broader goals of the SEDI and planetary communities.
(1) Wang, S. & H. Tkalčić, Scanning for planetary cores with single-receiver intersource correlations, Nat. Astron., s41550-022-01796-8, 2022.
(2) Wang, S. & H. Tkalčić, On the formation of global inter-source correlations and applications to constrain the interiors of the Earth and other planets, J. Geophys. Res., 128, 8, e2023JB027236, 2023.
(3) Ma, X. & H. Tkalčić, Low seismic velocity torus in the Earth's outer core: Evidence from the coda correlation wavefield, Sci. Adv., 10, 35, 2024.
(4) Tkalčić, H., T-S. Pham, & S. Wang, The Earth's coda correlation wavefield: Rise of the new paradigm and recent advances, Earth-Sci. Rev., 208, 103285, 2020.
Furthermore, building on the theoretical and methodological advances in the correlation wavefield, we explore thermochemical inhomogeneities in the Earth’s outer core using the global coda correlation wavefield. We identify a low-velocity torus structure at low latitudes in the outermost outer core, with ~2% lower velocity than the surrounding outer core, and propose a thermochemical origin for this feature (3). This finding provides critical insights into the distribution of light elements and dynamic processes in the outer core. However, it also represents a challenge in bridging seismological observations with geodynamical constraints. Our results underscore the importance of integrating coda correlation data with body-wave and normal-mode analyses to refine models of core composition and dynamics.
By combining global seismological, mineral physics, and geodynamic-modeling data, we will advance the understanding of planetary cores and their role in planetary evolution. The methodologies like the coda correlation wavefield (4) apply to Earth but also offer new avenues for investigating the interiors of other terrestrial bodies, such as the Moon and Mars, as well as insights relevant to ongoing and future planetary missions, contributing to the broader goals of the SEDI and planetary communities.
(1) Wang, S. & H. Tkalčić, Scanning for planetary cores with single-receiver intersource correlations, Nat. Astron., s41550-022-01796-8, 2022.
(2) Wang, S. & H. Tkalčić, On the formation of global inter-source correlations and applications to constrain the interiors of the Earth and other planets, J. Geophys. Res., 128, 8, e2023JB027236, 2023.
(3) Ma, X. & H. Tkalčić, Low seismic velocity torus in the Earth's outer core: Evidence from the coda correlation wavefield, Sci. Adv., 10, 35, 2024.
(4) Tkalčić, H., T-S. Pham, & S. Wang, The Earth's coda correlation wavefield: Rise of the new paradigm and recent advances, Earth-Sci. Rev., 208, 103285, 2020.