Seismic swarms and earthquake activity b-value related to the September 19, 2021, La Palma volcano eruption in Cumbre Vieja, Canary Islands (Spain)

The recent eruption of the Cumbre Vieja Volcanic Ridge in La Palma started on September 19, 2021, after a series of seismic swarms and lasted 85 days. Seismic swarms showed a large variability but could be grouped in two categories: long-term swarms located at subcrustal depth, showing b-values close to 2.2 and low rates (from 4.1 to 56 events/hour) and short-term swarms located at very shallow depths, showing moderate b-values [0.9, 1.6] and high rates (from 58 to 460 events/hour). Magma ascent velocity within the 0-10 km depth range varied between 0.03 and 0.21 km/h. Spatial and temporal characterization of the b-values for the entire magmatic process during the selected study period also indicated three distinct dynamics during a preparation phase starting from at least October 2017-August 2021, the eruptive phase from September 2021-December 2021 and a post-eruption process from the end of the eruption in December 2021-May 2022. These stages with clearly different values reflect two scenarios: one corresponding to the time before the eruption with magma ascending from a 39-km depth to the surface, and a second stage corresponding to the eruption itself which includes two seismicity concentrations within the 30-40 km depth interval and a shallow concentration from 0-20 km, corresponding to the crustal reservoir and movement towards the surface.