Séminaire ISTerre

Investigating regional heterogeneity at the core-mantle boundary and its impact on outer core flow

vendredi 6 janvier 2023 - 14h00
Hannah Rogers - ISTerre
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Currently, there is relatively poor understanding of how the magnetic field is affected by heterogeneity on the core-mantle boundary (CMB) despite increasing evidence of heterogeneity from geochemical, seismic tomography, geomagnetic, and geodynamics studies. An example of heterogeneity are the Large Low seismic Velocity Provinces (LLVPs) that have been identified at the base of the mantle. LLVPs have been proposed to indicate topographic features, thermal variation, regional stratification, or chemical exchange between core and mantle, all of which would affect the flow at the surface of the core and the magnetic field it generates. If spherical harmonic separations are conducted to investigate heterogeneity, a boundary is enforced at the region edge and large amounts of ringing are generated. One way to investigate regional potential fields on a sphere is to use spherical Slepian functions which convert spherical harmonic data into a new localized basis. These functions are constructed by maximizing the power of a function within a specified region where it is orthogonal in both the region and the complementary part of the sphere. This allows for the preferential ranking and selection of a subsection of the functions to be constrained in the region of interest. Spherical Slepian functions are the only functions that achieve a regional separation expressed as a finite sum of spherical harmonics, and in an easily computable framework, depending only on the geometry of the region and maximum spherical harmonic degree. The key contribution of this work is using spherical Slepian functions during the inversions for SV at the core-mantle boundary. Slepian functions provide a novel application of geomagnetic virtual observatory datasets, which allows 20 years of magnetic data from Swarm, CHAMP, and Cryosat to be treated as an even spread of data points in time and space, similar to ground observatory data. We apply altitude-cognizant Slepian functions to core surface SV models by directly inverting from satellite virtual observatory secular variation data into regions of interest. We successfully demonstrate the technique and current short comings by investigating the influence of LLVPs on the movement of liquid iron at the core surface over time. Unwanted spatial leakage is generated at the region edges in the separated SV but to less of an extent than when using spherical harmonic separations.

Equipe organisatrice : Géodynamo

Salle Dolomieu, Maison des Géosciences, 38400 Saint Martin d'Hères

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“Minimalist seismology”: studying earthquakes with sparse instrumentation

jeudi 17 septembre 2026 - 11h00

Mathieu Causse - ISTerre

Equipe organisatrice : Organisation labo

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

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Stable‑to‑dynamic expansion of fault slipping area through fluid injection observed in laboratory experiments using a sub‑meter scale specimen

vendredi 18 septembre 2026 - 14h00

Takatoshi Ito  - Université de Tohoku, Japan

Equipe organisatrice : Mécanique des failles

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

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Tectonics, Mantle Dynamics and Coupled Lithosphere-Mantle-Core Evolution of Earth and Other Rocky Worlds

jeudi 24 septembre 2026 - 11h00

Paul Tackley - ETH Zurich

Equipe organisatrice : Grands Séminaires ISTerre

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

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Tectonics, Mantle Dynamics and Coupled Lithosphere-Mantle-Core Evolution of Earth and Other Rocky Worlds

jeudi 24 septembre 2026 - 11h00

Paul Tackley - ETH Zurich

Equipe organisatrice : Grands Séminaires ISTerre

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

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Apport des expériences analogiques pour la modélisation et le suivi en temps réel de la propagation du magma en profondeur : Exemple du Rift Est Africain

jeudi 1er octobre 2026 - 11h00

Virginie Pinel - ISTerre

Equipe organisatrice : Organisation labo

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

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A t-on encore besoin de plaques pour expliquer la tectonique de la vallée du Rhône et des Alpes Occidentales ?

vendredi 2 octobre 2026 - 11h00

philippe VERNANT - Geosciences Montpellier

Equipe organisatrice : Tectonique active et sismicité

Salle Dolomieu, Maison des Géosciences, 38400 Saint Martin d'Hères

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TBA

vendredi 2 octobre 2026 - 14h00

Hugo Boulze - 

Equipe organisatrice : Cycle sismique et déformations transitoires

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

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TBA

vendredi 9 octobre 2026 - 11h00

Eric Beaucé - ISTerre

Equipe organisatrice : Cycle sismique et déformations transitoires

Salle Dolomieu, Maison des Géosciences, 38400 Saint Martin d'Hères

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TBA

vendredi 20 novembre 2026 - 11h00

Farzaneh Mohammadi - ENS Paris

Equipe organisatrice : Cycle sismique et déformations transitoires

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

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