Modeling of the stress perturbation revealed by the seismotectonic analysis of the seismic swarm closest to Mayotte Island during the 2018-to-present volcano-tectonic event

Since May 2018, an exceptional submarine seismic-volcanic activity is still underway to the SE off the island of Mayotte (Indian Ocean, Comoros archipelago). The associated, deep seismicity, at 20-50km below the Moho, is mainly distributed in two swarms. The distal swarm started in May 2018, 30 kilometers to the SE off of Mayotte, with M5 + earthquakes (Lemoine et al., 2020) that migrated towards the new discovered volcano (Lemoine et al., 2020, Feuillet et al. 2021). The proximal swarm located about 15 kilometers SE off Mayotte, started in July 2018 (Mercury et al., 2020). Since February 2019, the seismicity of these two still active swarms is recorded using nearby land stations and ocean bottom seismometers (e.g. Feuillet et al, accepted, 2021, Saurel et al., in revision). Using accurate HypoDD relocations (Hoste-Colomer et al., 2020) we determined focal mechanisms (Jacques et al. 2020). These results showed that a) in map view, the proximal swarm has a hollow donut shape, and in 3D, its eastern half depicts a conical shape; and b) Most of the focal mechanisms of this swarm are predominantly strike-slip or normal and their T axes radiate around the hollow center of the swarm. It seems that locally a process perturbs the regional stress regime. In cross-section, normal faults with steeply inward dipping planes tend to form "en échelon" arrays along the eastern half of the swarm boundary, Jacques et al. (2020) proposed that this pattern could be related to a falling piston (the hollow part of the proximal swarm) with respect to its surrounding deforming wall, causing the observed seismicity and stress perturbation. Feuillet et al. (2021) Jacques et al. (2019), proposed that the proximal swarm occurred in response to the massive lava withdrawal, which built the new volcano. Therefore, using elastic modeling, we tested whether a deflating source below the proximal swarm is capable to promote such stress perturbation and seismic faulting.