For the first time, we obtained high-resolution images of Earth's interior of the La Palma volcanic eruption that occurred in 2021 derived during the eruptive process. We present evidence of a rapid magmatic rise from the base of the oceanic crust under the island to produce an eruption that was active for 85 days. This eruption is interpreted as a very accelerated and energetic process. We used data from 11,349 earthquakes to perform travel-time seismic tomography. We present high-precision earthquake relocations and 3D distributions of P and S-wave velocities highlighting the geometry of magma sources. We identified three distinct structures: (1) a shallow localised region (< 3 km) of hydrothermal alteration; (2) spatially extensive, consolidated, oceanic crust extending to 10 km depth and; (3) a large sub-crustal magma-filled rock volume intrusion extending from 7 to 25 km depth. Our results suggest that this large magma reservoir feeds the La Palma eruption continuously. Prior to eruption onset, magma ascended from 10 km depth to the surface in less than 7 days. In the upper 3 km, melt migration is along the western contact between consolidated oceanic crust and altered hydrothermal material.

Seismic tomography provides a window into magmatic plumbing systems; however, obtaining sufficient data for ‘real-time’ imaging is challenging. Until now, syn-eruptive tomography has not been successfully demonstrated. For the first time, we obtained high-resolution images of Earth's interior during an ongoing volcanic eruption. We used data from 11,349 earthquakes, most of which during La Palma eruption (19 September-13 December, 2021), to perform travel-time seismic tomography. We present high-precision earthquake relocations and 3D distributions of P and S-wave velocities highlighting the geometry of magma sources. We identified three distinct structures: (1) a shallow localised region (< 3 km) of hydrothermal alteration; (2) spatially extensive, consolidated, oceanic crust extending to ~10 km depth and; (3) a large (> 400 km3) sub-crustal magma-filled rock volume intrusion extending from ~7 to 25 km depth. Our results suggest that this large magma reservoir feeds the La Palma eruption continuously for almost three months. Prior to eruption onset, magma ascended from ~10 km depth to the surface in < 7 days. In the upper 3 km, melt migration is along the western contact between consolidated oceanic crust and altered hydrothermal material. Similar structural weaknesses along the eastern contact could potentially cause new eruptive centres in the future.

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On 2 October 2016, a significant seismic swarm of long‐period events was recorded on Tenerife (Canary Islands, Spain). The swarm lasted more than 5 hr and consisted of at least 766 detected events. We found a positive correlation between the amplitude of each event and the preceding interevent time together with a stability of the spectral properties and waveform similarity during most of the swarm duration. Toward the end of the swarm, individual events merged into a continuous tremor. These observations can be explained by postulating an unsteady transonic choked flow within a crack‐like conduit as a source mechanism for this swarm. The flow resulted from a sudden discharge of magmatic fluids from a pressurized reservoir into the hydrothermal system of Tenerife. The injected fluids reached the surface starting about 1 month after the swarm, as evidenced by the macroscopic increase in the diffuse CO2 emissions from the crater of Teide volcano. The lack of ground deformation and the absence of relevant seismicity at depths greater than 10 km exclude the ascent of a basaltic magma batch as a causative source mechanism. Instead, we hypothesize the sudden release of fluids accumulated at the top of a magma chamber as a possible mechanism. Another possibility is the injection of a small batch of mafic magma into a cooling magma chamber, triggering a convective mixing. Both cases imply the presence of a magma chamber at depths greater than 8.6 km. These results have important implications for the development of the volcano monitoring system of Tenerife.

The estimation of the b-value of the Gutenberg–Richter law is of great importance in different seismological applications. However, its estimate is strongly dependent upon selecting a proper temporal and spatial scale, due to the multiscale nature of the seismicity. For this reason, we propose a novel approach (MUltiscale Spatial and Temporal estimation of the B-value [MUST-B]), which allows consistent estimation of the b-value, avoiding subjective “a priori” choices, by considering simultaneously different temporal or spatial scales. A reliable appraisal of the b-value is obtained by applying a robust median over the estimates computed over all the considered scales. We validate the method using a synthetic dataset, showing its superior performances, compared to traditional approaches, in detecting sharp changes in the b-value as well as inconsistently mapping it for highly heterogeneous catalogs. We apply MUST-B to study the temporal and spatial variations of the b-value during the complex 2016–2017 seismic sequence in central Italy, revealing various interesting patterns. In particular, we observe a marked drop of the b-value after the Accumoli (24 August 2016 M 6.0) mainshock. The drop is also observed when realizing a tridimensional mapping of the b-values, showing the drop occurs mainly in the proximity of major earthquake hypocenters. In accordance with previous studies, we interpret these variations as the effect of the release of crustal fluids following the major earthquakes. We maintain that MUST-B can also be applied to other contexts, such as volcanic and induced seismicity, because of its capacity of dealing consistently with highly heterogeneous seismicity patterns.