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Abstract:
Since May 2018, a seismically quiet area offshore the island of Mayotte, Comoros archipelago, has been affected by a complex seismic sequence, including a massive swarm of thousands of earthquakes, long-duration very long period (VLP) signals recorded globally and a large surface deflation recorded by GNSS stations on Mayotte. We systematically analysed regional and global seismological data and local deformation data to provide a detailed picture of a deep, rare magmatic process without any on-site monitoring. We identify and locate ~7000 volcano-tectonic earthquakes (VT) and more than 400 VLPs, and determine the geometry of both faulting and the magma reservoir. Early VTs migrated upward in response to a magmatic dike propagating from Moho depth to the surface, while later events marked the progressive failure of the reservoir’s roof thus triggering its resonance. VLP and deformation analysis suggest that a 10–15 km diameter magmatic body has lost at least 1.3 km3 of magma. This episode represents the deepest monitored drainage of a large reservoir initiating the partial collapse of its roof.
