Seismic Velocity Variations Observed Prior to the La Palma Volcano Eruption on 19 September 2021, in Cumbre Vieja, Canary Islands (Spain)

In the recent years, coda-wave interferometry from seismic noise correlation functions has been increasingly used for volcanic eruption forecasting through velocity changes observed in the crust. Because La Palma Island in the Canary Archipelago is very well instrumented, we studied the possible velocity variations related to the last Cumbre Vieja eruption on 19 September 2021, aiming to obtain clear variations in the seismic velocity. For this purpose, we used the moving-window cross-spectral analysis technique for seismic noise within the 0.1–1.0 Hz frequency interval for determining two- and single-station cross-component correlations. During the 2018–2022 observation period, we first detected a seasonal seismic velocity variation possibly caused by annual rainfall and the induced pore pressure change. On 12 September 2021, a dramatic decrease in the velocity of −0.15% was detected, leading to the volcanic eruption at Cumbre Vieja seven days later. The results are compatible with those of models proposed for rapid magma migration from a shallow reservoir at 11 km to the surface.