Source parameters of very low frequency events during the Mayotte seismo-volcanic crisis (May 2018–January 2022)

SUMMARY The seismo-volcanic crisis near Mayotte (Comoros archipelago, Indian Ocean)—marked by the discovery of a new submarine volcano east of the island—is characterized by persistent very-low-frequency (VLF) seismic activity. These events feature long-lasting oscillations exceeding 25 min, with dominant spectral peaks at 67 and 167 mHz. We analyse more than 780 repetitive VLF events recorded between June 2018 and January 2022 using a dense local seismic network, including broad-band ocean-bottom hydrophones. To investigate these events, we developed a spectral-based detection algorithm, a 3-D back-projection location method and performed full-waveform modelling. These techniques constrain the temporal evolution, spectral characteristics, and first-order source properties, including source mechanism and geometry. The VLF sources are located at depths of 20–30 km, near the top of the proximal volcano-tectonic swarm, approximately 12 km east of Petite-Terre. The signals likely originate from the resonance of a magma-filled sill, triggered by transient increases in magma pressure and/or aseismic fault slip acting on a piston-like structure within a complex transcrustal magmatic system. Our findings highlight the diagnostic power of advanced seismological methods for imaging deep submarine volcanic processes and provide new insights into magma-tectonic coupling during the Mayotte seismo-volcanic crisis.