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La crise sismique induite à Strasbourg J. Schmittbuhl Sophie Lambotte, Olivier Lengliné, Marc Grunberg, Hélène Jund, Jérôme Vergne, François Cornet†, Cécile Doubre, Frédéric Masson Equipes BCSF-RéNaSS, EOST – ITES, et LabEx G-Eau-Thermie profonde - ITI GeoT Université de Strasbourg/CNRS-INSU 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021 1

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2 1291 testimonies 473 testimonies 871 testimonies Novembre 2019 3,3 22/01/2021 19h33 La Wantzenau 3,9 26/06/2021 5h00 La Wantzenau https://www.franceseisme.fr/

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Strasbourg seismic swarms 3 ~5 km Northern swarm Wells GT1 and GT2 – Vendenheim/Wantzenau Activity : March 2018 – June. 2021 Catalog BCSF-RéNaSS : • 3 eq M >3 ( Mlv 3.9 on 26/6/2021; Mlv 3.6 on 4/12/2020; Mlv 3.3 on 22/1/2021) • 11 eq 23 (Ml 3.0 on 12/11/2019) • 3 eq 2

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Regional sismic networks 4 RESIF (RLBP + RAP) Fonroche (2) et ESG (3) open-access networks (code FR) Fonroche private networks EOST lowcost RaspberryShake network German network 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021

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5 7 RaspberryShake stations 12/11/2019 earthquake 34 stations / 46 phases Citizen seismology project

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6 Northern cluster Southern cluster Seismicity From 2018 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021

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~10 day delay between GT1 well and the southern cluster 7 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021

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8 Depth distribution Northern swarm Southern swarm

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Geological context 9 Robertsau fault A B A B A’ B’ A’ B’ Geological map at a depth of 4000m www.geopotenziale.org N15 N25 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021

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Focal mechanisms FMNEAR (B. Delouis) 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021 10

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Template matching + HypoDD relocations 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021 11

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Southern cluster Robertsau – Nov 2019 12 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021

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Southern cluster HypoDD relocation (zoom) Dip 76° Dip 76° 13

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14 Induced/triggered/natural seismicity ? Classified by BCSF- RéNaSS as ‘induced event’ Davis & Frohlich, SRL, 1993 ? >5 ?

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Northern cluster La Wantzenau – Mar 2018/June 2021 15 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021

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N320 N20 sH sH sh N170 ~30° sh Weakness direction 16 Fracture Friction 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021

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Conclusions o Induced (northern cluster) and triggered (southern cluster) seismicity related to the deep geothermal site (Geoven/Georhin) (12 felt earthquakes 2 first lessons (relevance of the conceptual model, transfer from previous projects, initial knowledge of the reservoir, effective size of the reservoir, injected volumes, project management, risk management, etc) o Future projects: ITI GeoT / ANR PrESENCE (2022-2025) / … J. Schmittbuhl; S. Lambotte; O. Lengliné; M. Grunberg; H. Jund; J. Vergne; F. Cornet; C. Doubre; F. Masson. Induced and triggered seismicity below the city of Strasbourg, France from November 2019 to January 2021. Comptes Rendus. Géoscience, Online first (2021), pp. 1-24. doi : 10.5802/crgeos.71. 17

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Earthquake characteristics 18 [Zang et al, 2014] Strasbourg earthquakes: M3.0/M3.9 L ~ 100-500m D ~ 1-5 cm L D: slip 5èmes Rencontres Scientifiques et Techniques Résif- Epos, Obernai, 15-18 novembre 2021

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RéNaSS-BCSF catalog – circles centered on the GEOVEN well Sismicity history 19