Unveiling Exotic Seismic and Hydroacoustic Events Associated with the Activity of the Fani Maoré Submarine Volcano, Mayotte, Indian Ocean

On 10 May 2018, a seismic crisis occurred near Mayotte (Comoros Archipelago, Indian Ocean), and was followed by a significant ground deformation and eastward displacement of the island. Combined with the records of very-long period (VLP) earthquakes, these observations were the first signs of a major submarine volcanic eruption, Fani Maoré, discovered in 2019 approximately 50 km east of Mayotte. The deployment of onshore seismometers and Ocean Bottom Seismometers (OBS) network since 2019 has allowed a better characterisation and classification of the seismicity, including various types of seismic and acoustic signals as volcano-tectonic (VT) earthquakes, long-period (LP) earthquakes, VLP, and hydro-acoustic signals.

In this study, we further investigated the seismic and hydroacoustic activity associated with the Fani Maoré submarine volcano by focusing on the characterization of rare and unconventional seismic signals that are poorly or previously not documented. We concentrated on the October–November 2019 period, when the OBS network was dense and included an OBS station deployed close to the active lava flows. To analyze this dataset, we applied a self-supervised learning (SSL) approach to four-channel time series data, comprising three-component seismometer recordings and a colocated hydrophone.

The SSL-based analysis resulted in the identification of multiple clusters, revealing distinct groups of seismic and acoustic signals. By aggregating these clusters into broader families, we distinguished signals originating from non-volcanic sources (e.g., motor induced signals and whale vocalizations), and families of events clearly associated with the volcanic activity of the Fani Maoré submarine volcano. These include VT and LP earthquakes, impulsive HA signals, drumbeat-like events, tremor-like events and additional signal types whose sources remain uncertain but are likely related to volcanic processes. These results bring new insights in the dynamic of the Fani Maoré volcano, and will allow a better characterization of the involved mechanisms in the seismo-acoustic activity, and improve its monitoring.