Séminaire ISTerre

HDR "Magnetic survey modeling for a better understanding of volcanic geothermal systems"

jeudi 25 juin 2026 - 10h00
CLAIRE BOULIGAND - ISTerre
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Magnetic survey modeling for a better understanding of volcanic geothermal systems Magnetic surveys bring important information for the understanding of geothermal systems and for the assessments of their geothermal or mineral resources as wells as potential hazards. As I show with examples from my previous research projects in Yellowstone, at the Soufrière dome of Guadeloupe, or in the western United States, through the imaging of the subsurface magnetization, theses surveys can allow the identification of geological structures and lithologies that influence fluid circulations, provide constrains on the temperature distribution at depth, and be used for the mapping of volumes that have undergone hydrothermal alteration at depth. Over such volcanic areas, the interpretation of the complex magnetic anomaly pattern requires the collection of high-resolution data (i.e. dense and low elevation surveys) over large areas which are sometimes of difficult access. In this context, the recent development of drone magnetic surveys is a major opportunity. The interpretation of these magnetic surveys in terms of a subsurface magnetization model remains a difficult task due to the non-uniqueness of the problem. Simplifying assumptions on the crustal magnetization distribution are therefore needed. At the beginning of my research on geothermal systems, I used modeling and inversion approaches in the Fourier domain, that are applicable for magnetic anomaly grids at constant elevation. This allowed me to invert, depending on the case, for 2D maps of equivalent magnetization below topography, for the topography of a surface characterized by a contrast of magnetization, or for the depth to the bottom of magnetic sources often interpreted as the depth to the Curie temperature isotherm. Such approaches can however not be used for the modeling of data that are sparsely sampled or that are draped over a rugged topography. In particular, these approach cannot be used for the large quantity of new high-resolution drone surveys. For this reason, I also used and developed modeling approaches in the spatial domain. With forward modeling, i showed the importance of topography in the magnetic anomaly pattern over volcanic regions and how this topographic signals can also be used to assess the shallow subsurface magnetization. Based on this observation, in collaboration with the Waves and Structures team and the PhD thesis of Lahcene Bellounis, we initiated the development of a new modeling and inversion code suited for taking high precision topography into account for a reasonable computational cost. These methodological developments bring new opportunities for the interpretation of magnetic surveys over geothermal systems. This new modeling code is now being applied for the inversion of high-resolution drone magnetic data collected over the Krafla Geothermal area. We also plan to adapt this code so it can be used for the joint inversion of magnetic and electrical resistivity data or for the monitoring of subsurface magnetization by the joint inversion of repeat magnetic survey collected at different period of times. Serpentinized ultramafic bodies share similarities with volcanic regions in the sense that their subsurface is strongly magnetized. In collaboration with the mineralogy team, we are therefore using magnetic surveys to investigate the links between mineralogical reactions and the distribution of magnetite at larger lengthscales.

Equipe organisatrice : Géophysique des volcans & géothermie

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

Informations de visio :

https://univ-grenoble-alpes-fr.zoom.us/j/93350459749?pwd=kF1WEAx2GQgzNWJoEIRAQrBpuzGB6i.1

“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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