Hydroacoustic sensing of seismic events during the Tajogaite volcanic eruption (La Palma, Spain).

Volcanic processes generate a variety of seismic events that can be detected by both on-land and underwater sensors. During the 2021 subaerial eruption of the Tajogaite volcano on La Palma Island (Canary Islands, NW Africa), an underwater acoustic sensor was strategically deployed to monitor seismic activity. This study presents marine passive acoustic monitoring data from a moored hydrophone deployed offshore at a depth of 77 m and 7 km from the volcanic vent, both during and after the eruption. We compare hydrophone recordings with island's seismic network and earthquake database from the Instituto Geográfico Nacional (IGN). By calculating acoustic metrics and analyzing low-frequency bands (< 100 Hz), we identified 712 impulsive acoustic signals consistent with seismic events recorded in the seismic catalogue. These acoustic signals were double-pulsed, low-frequency (≤ 50 Hz with peak frequencies ≤ 15 Hz) and exhibited sound levels that well correlated with earthquake magnitudes. Our findings demonstrate that shallow-water hydro-acoustics can detect and estimate the magnitude of volcano-tectonic earthquakes in the studied scenario. These results encourage for the integration of hydro-acoustic monitoring in conjunction with on-land seismic stations to enhance the overall monitoring of the investigated volcanic area seismic activity.