Séminaire ISTerre

Complex Earthquake Triggering in the Ibaraki Region by the 2011 Mw9.0 Tokoku-Oki Earthquake

mardi 14 septembre 2021 - 14h00
Asaf Inbal - Tel Aviv University
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The importance of aftershocks in redistributing crustal stresses has been known for several decades. However, a growing body of evidence also highlights the role of transient aseismic slip for triggering of large earthquakes. These slip transients may spontaneously nucleate around the site of the future rupture, or may be triggered remotely. Triggered aseismic off-fault transients generated on frictionally heterogeneous faults can cause damaging earthquakes. Only in a few cases, however, the off-fault deformation field is captured with sufficient spatio-temporal resolution, allowing one to elucidate the complex interactions leading to a large, destructive remote aftershock. One such case is the March to April 2011 seismic sequence in Ibaraki prefecture, Japan, which occurred shortly after the Mw9.0 Tohoku-Oki mainshock. This sequence lasted for about a month, and calumniated with the 11 April 2011 Mw6.7 Iwaki-Fukushima earthquake, which ruptured a pair of shallow sub-parallel inland normal faults that were unfavorably oriented with respect to Tohoku-Oki co-seismic strain regime. To constrain the processes responsible for rupture under seemingly unfavorable conditions, we analyze the GPS-derived strain field in Ibaraki during the month preceding the Mw6.7. We find that most of the local deformation in this time period is accommodated aseismically, and that the ratio of the aseismic-to-seismic moment release is largest in the two sub-regions neighboring the Mw6.7 source area. That pre-Mw6.7 strain distribution is only partially compatible with slip along the shallow normal faults in Ibaraki, but is consistent with motion along a deep-seated splay fault that branches from the subduction interface beneath Ibaraki. Our modeling suggests that, to account for the strain accumulated between March 11 and April 11, 2011, the shallow portion of the splay fault must have slipped aseismically by about 40 cm. Thus, the Tohoku mainshock initiated a chain-reaction in Ibaraki, whereby triggered slip on the splay fault induced stresses on shallow normal faults, whose activation eventually led to the Mw6.7 Iwaki-Fukushima rupture.

Equipe organisatrice : Cycle sismique et déformations transitoires

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

“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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