Séminaire ISTerre

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Looking Deep Inside the Earth with Seismology

mercredi 29 mai 2024 - 11h00

Hrvoje Tkalčić - Professor at ANU College of Science
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Despite considerable progress in global seismology, mineral physics, geodynamics, paleomagnetism, computational methods and mathematical geophysics, Earth’s inner core remains enigmatic. Indeed, progress in understanding the structure and evolution of the Earth's inner core – a metallic ball about the size of Pluto – has been impeded by the lack of geometric coverage of seismic body waves due to an uneven global distribution of earthquakes and receivers. For example, only recently have we confirmed that its innermost part contains distinct seismic anisotropy. In seeking ways forward, we started experimenting with earthquake coda correlation by comparing digital waveforms recorded at different locations many hours after the onset of large earthquakes. Applying the coda correlation principles proved the inner core’s solidity by unambiguously detecting shear waves spreading through it. We also showed that a single seismograph and global-scale waveform cross-correlations between seismic events (inter-source correlation) could be used to scan planetary cores. Recent advances in tomography led us to the first images of the thermal convection cell at the top of the inner core. Using a growing number of global seismic stations, we observed up-to-fivefold reverberating waves from selected earthquakes along the Earth’s diameter, confirming the existence of the innermost inner core. I will review my group’s most important results and ambitions to date, with brief stops at the Earth’s centre and its various shells, the Outback, the Southern Ocean bottom, Antarctica and Mars. As I hope to demonstrate, the coda-correlation and similar innovative methods – apart from further development and the proliferation of seismic sensors – may play a central role in global and planetary seismology in the coming decades.

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Equipe organisatrice : Ondes et structures

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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