Onset of a submarine eruption east of Mayotte, Comoros archipelago: the first ten months seismicity of the seismo-volcanic sequence (2018-2019)

Since 10 May 2018, an unprecedented seismic activity is observed east of Mayotte Island (France), related to the largest submarine eruption ever recorded with offshore geophysical studies. Using signals from regional and local seismic stations, we build a comprehensive catalog of the local seismicity for the first ten months of the sequence. This catalog includes a total of 2874 events of magnitude (Mlv) ranging from 2.4 to 6.0, with 77% of them relocated using a double difference location procedure. The hypocentral locations over the period May 2018 – February 2019 are highly dependent on the small seismic network available. We therefore compare the locations of later events from a local ocean bottom seismometer network with locations estimated using a similarly small network. Based on the time space evolution and characteristics of the seismicity, five distinct phases can be identified. They correspond to the successive activation of two deep seismic swarms, related to the lithospheric-scale magma ascent up to the seafloor. We also observe progressive deepening of the seismicity interpreted as decompression of a 40 km deep reservoir.