Mayotte seismic crisis: building knowledge in near real-time by combining land and ocean-bottom seismometers, first results

Jean-Marie Saurel (1) , Eric Jacques (1) , Chastity Aiken (2) , Anne Lemoine (3) , Lise Retailleau (1, 4) , Aude Lavayssière (1) , Océane Foix (2) , Anthony Dofal (1, 5) , Angèle Laurent (1) , Nicolas Mercury (3) , Wayne Crawford (1) , Arnaud Lemarchand (1) , Romuald Daniel (1) , Pascal Pelleau (2) , Maxime Bès de Berc (6) , Grégoire Dectot (3) , Didier Bertil (3) , Agathe Roullé (3) , Céleste Broucke (7) , Alison Colombain (3) , Hélène Jund (7) , Simon Besançon (1) , Pierre Guyavarch (2) , Philippe Kowalski (1, 4) , Mickaël Roudaut (2) , Ronan Apprioual (2) , Jean Battaglia (8) , Soumya Bodihar (1) , Patrice Boissier (1, 4) , Marie Paule Bouin (1) , Christophe Brunet (1, 4) , Kévin Canjamale (1, 4) , Philippe Catherine (1, 4) , Nicolas Desfete (1, 4) , Cécile Doubre (6) , Rémi Dretzen (7) , Tom Dumouche (1) , Philippe Fernagu (2) , Valérie Ferrazzini (1, 4) , Fabrice Fontaine (1, 5) , Arnaud Gaillot (2) , Louis Géli (2) , Cyprien Griot (1, 4) , Marc Grunberg (7) , Emre Can Guzel (9) , Roser Hoste-Colomer (3) , Sophie Lambotte (6) , Frédéric Lauret (1, 4) , Félix Léger (1) , Emmanuel Maros (2) , Aline Peltier (1, 4) , Jérôme Vergne (7) , Claudio Satriano (1) , Frédéric Tronel (3) , Jérôme van Der Woerd (6) , Yves Fouquet (2) , Stephan Jorry (2) , Emmanuel Rinnert (2) , Isabelle Thinon (3) , Nathalie Feuillet (1)

1 IPGP (UMR_7154) - Institut de Physique du Globe de Paris
2 IFREMER - Institut Français de Recherche pour l'Exploitation de la Mer
3 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
4 OVPF - Observatoire Volcanologique du Piton de la Fournaise
5 LGSR - Laboratoire GéoSciences Réunion
6 ITES - Institut Terre Environnement Strasbourg
7 EOST - Ecole et Observatoire des Sciences de la Terre
8 LMV - Laboratoire Magmas et Volcans
9 Faculty of Electrical and Electronics Engineering [Istanbul]

Summary The brutal onset of seismicity offshore Mayotte island North of the Mozambique Channel, Indian Ocean, that occurred in May 2018 caught the population, authorities, and scientific community off guard. Around 20 potentially felt earthquakes were recorded in the first 5 days, up to magnitude Mw 5.9. The scientific community had little pre-existing knowledge of the seismic activity in the region due to poor seismic network coverage. During 2018 and 2019, the MAYOBS/REVOSIMA seismology group was progressively built between four French research institutions to improve instrumentation and data sets to monitor what we know now as an on-going exceptional sub-marine basaltic eruption. After the addition of 3 medium-band stations on Mayotte island and 1 on Grande Glorieuse island in early 2019, the data recovered from the Ocean Bottom Seismometers were regularly processed by the group to improve the location of the earthquakes detected daily by the land network. We first built a new local 1D velocity model and established specific data processing procedures. The local 1.66 low VP/VS ratio we estimated is compatible with a volcanic island context. We manually picked about 125,000 P and S phases on land and sea bottom stations to locate more than 5,000 events between February 2019 and May 2020. The earthquakes outline two separate seismic clusters offshore that we named Proximal and Distal. The Proximal cluster, located 10km offshore Mayotte eastern coastlines, is 20 to 50 km deep and has a cylindrical shape. The Distal cluster start 5 km to the east of the Proximal cluster and extends below Mayotte's new volcanic edifice, from 50 km up to 25 km depth. The two clusters appear seismically separated, however our dataset is insufficient to firmly demonstrate this.

Domaines: Tectonique

Jean-Marie Saurel, Eric Jacques, Chastity Aiken, Anne Lemoine, Lise Retailleau, et al.. Mayotte seismic crisis: building knowledge in near real-time by combining land and ocean-bottom seismometers, first results. Geophysical Journal International, 2021, 228 (2), pp.1281-1293. ⟨10.1093/gji/ggab392⟩. ⟨hal-03397108⟩