Evidence of a Low-Velocity Zone in the Upper Mantle Beneath Cumbre Vieja Volcano (Canary Islands) Through Receiver Functions Analysis

Oceanic volcanic islands have a complex internal structure due to their geological evolution. La Palma is the second youngest in the Canary Islands. Historical eruptions occurred in the Cumbre Vieja (CV) volcanic system, including the last 2021 Tajogaite eruption. The seismicity before, during, and after the Tajogaite eruption provides valuable information for a better understanding of deep volcanic processes. We applied the receiver function technique to image the crustal and upper mantle structures beneath the CV volcanic complex. We investigated the first 50 km of the lithosphere, identifying various seismic discontinuities. After a thin layer of recent volcanic rocks, we found a layer corresponding to the old oceanic crust. Beneath the Moho, we found a significant decrease in the seismic velocities until about 37 km of depth. This low-velocity layer corresponds to a zone of partial melting with interconnected magmatic chambers that feed the volcanic activity in CV. Oceanic volcanic islands have a complex internal structure. Our study is important to understand volcanic activity in its geodynamic context better. The last eruption occurred in the Cumbre Vieja volcanic complex on La Palma Island (2021) and had an unexpected magnitude in terms of lava volume, explosivity, and a significant impact on the economy and society of the island. This study used receiver function analysis to image the lithosphere up to a depth of 50 km. This seismological technique exploits the recordings of teleseismic events (i.e., earthquakes located between 30 and 90 degrees from the stations) for this purpose. We used an advanced inversion technique to study the structure of the crust and the upper mantle beneath the volcano. The most relevant finding is a zone of anomalous low seismic velocities extending from 13 to 37 km depth. This zone is likely to host partial melt and magma chambers and extends over a much wider and thicker volume than expected from previous studies. Previous studies also identified two magma chambers: the upper one, located at about 10-15 km, and the lower one, beneath 25 km depth. These findings provide new insights into the current paradigms about the internal active oceanic volcanic islands. Receiver function analysis allowed us to image the crustal and upper mantle seismic structure beneath Cumbre Vieja volcano in La Palma Main velocity discontinuities in the crust show the contacts between the recent volcanic rocks, the old oceanic crust and the upper mantle A low-velocity zone extending from the Moho up to about 37 km of depth indicates the presence of a broad zone of partial melting