Offshore Mayotte Volcanic Plumbing Revealed by Local Passive Tomography

Abstract:

A new submarine volcano edifice was discovered offshore Mayotte, a part of the Comores volcanic archipelago between Africa and Madagascar. The edifice arose following the beginning of a seismo-volcanic crisis in May 2018. Since the crisis, the region has experienced > 2,000 earthquakes with magnitude ≥ 3.5, and the seismo-volcanic activity continues today, making it one of the longest recorded volcanic sequences. The earthquake locations present the biggest mystery: a main seismic swarm 5-15 km from Petite Terre, between 20-45 km depth, and a new volcanic edifice 40 km east of this main swarm. A secondary seismic swarm is located between the two sites. Significant subsidence of both Mayotte islands has been assigned to the drainage of a magma chamber located beneath the main seismic swarm. However, at present, the earthquake locations and geodetic observations have not been sufficient to image entirely the structure of the volcanic plumbing system. In this study, we construct dVp, dVs and Vp/Vs 3-D velocity models to assess the deeper structure of the Mayotte volcano plumbing system. Using > 3000 earthquakes from an ongoing monitoring effort (https://doi.org/10.18142/291), and a modified 1-D velocity model, we jointly inverted for velocity structures, earthquake locations, origin times, and station corrections using LOTOS software. The calculated 3-D velocity models highlight a complex volcanic system down to 40-50 km depth, composed of several secondary magma chambers connected to each other and to the surface. Velocity anomaly observations confirm hypotheses from previous works, i.e. that a magma chamber is located at the main seismic swarm, and its drainage path is to the East.