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To better understand the shallow structure of El Hierro island, we determined a 3D S-wave velocity model using Ambient Noise Tomography (ANT). We exploited a dataset recorded by 21 broadband seismic stations deployed at El Hierro island in two surveys realized in 2015 and 2021. This dataset allowed us to obtain empirical Green’s functions by cross-correlating seismic ambient noise signals and retrieving 105 dispersion curves using the frequency-time analysis (FTAN). Then we obtained 2-D Rayleigh wave group velocity maps for periods between 0.6 s and 2.6 s through a non-linear multiscale inversion (Cabrera-Pérez et al, 2021). Finally, we performed depth inversion through a Bayesian transdimensional approach to obtain a 3-D S-wave velocity model. The obtained ANT model is merged with a local earthquake tomography model (García-Yeguas et al, 2014). Our study highlights six relevant seismic velocity anomalies. We observed the presence of three high-velocity zones located in the eastern, western and northern parts of the island, which could be related to intrusive bodies possibly associated with the formation of El Hierro island. We also observed three low-velocity anomalies in the northern and southern parts. The anomaly in the North of the island could be related to loose deposits generated by the El Golfo valley megalandslide. The anomalies in the South could be related to porous and highly fractured materials produced during the more recent volcanic episodes., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The receiver function analysis (RF) is a well-established method to investigate the crustal and upper mantle structure in different geodynamic settings. It is highly sensitive to seismic discontinuities and provides information about P- and S-wave velocities beneath a seismic station.This work aims to study the crust and the upper mantle of La Palma Island up to 50 km of depth by using RF analysis. La Palma is one of the youngest oceanic volcanic islands of the Canary archipelago, with a complex internal structure that makes applying conventional RF challenging. The island was affected in 2021 by the devastating Tajogaite eruption which occurred on the Cumbre Vieja volcano.For this study, we obtained RFs of five stations using multi-taper deconvolution. After that, we applied the transdimensional approach of Bodin et al. (2012) to determine 1D profiles of P- and S-wave velocities and the probability of a discontinuity beneath each station.Each 1D model was interpolated to build a N-S trending seismic section that allowed us to correlate the different discontinuities. We observe a Low-Velocity Zone in the upper mantle beneath the Cumbre Vieja volcano and four different layers with a significant change in their Vp/Vs ratios. These results are compared with the seismicity recorded beneath the island from 2017 until the pre-eruptive phase of the Tajogaite eruption. Hypocenters are mainly located at the base of the crust (10-15 km deep) and in the upper mantle (20-30 km deep), possibly related to the presence of two subcrustal magmatic reservoirs., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Time-lapse monitoring of seismic velocity at a volcanic area can provide important information about the dynamics of the volcanic system and its temporal variability. One standard technique to monitor small changes in the medium is ambient noise interferometry. This technique is based on quantifying relative velocity variations (dv/v) by measuring changes in the ambient noise cross-correlation signal phase. In this study, we demonstrate that together with velocity variations, the study of changes in seismic attenuation (Qc) extracted from ambient noise cross-correlation could be relevant for volcano monitoring. The Qcis determined using the lapse-time dependence method (Calvet and Margerin, 2013), in which, Qcis measured as a function of the coda window length for different onsets of the ambient-noise cross-correlation coda. We apply this technique to the 2021 Cumbre Vieja eruption in La Palma (Canary Islands), which started on Sept. 19th and had a significant social and scientific impact. First, we determine a reference Qcmodel of the Cumbre Vieja volcano using data from Aug. 1st to 31st, 2021. Then, we analyze the spatio-temporal Qcvariations during the nineteen days preceding the eruption, and we compare our results with previously obtained dv/v results. We observe an increase of Qcduring the pre-eruptive phase, corresponding to a dv/v decrease. We hypothesize that the observed correlated Qcincrease and dv/v drop could be explained by the ascent of hydrothermal fluids towards the surface before the eruption., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

In recent years the use of Distributed Acoustic Sensing (DAS) in seismology is gaining extensive usage in different applications. A High-Fidelity DAS system (HDAS) was deployed during the 2021 Tajogaite eruption on Cumbre Volcano (La Palma, Canary Islands), allowing the recording of most of the syn-eruptive and post-eruptive seismicity. The eruption lasted from Sep. 19th until Dec. 13th of 2021. The HDAS was installed on 19th Oct. 2021 and is still operating.The HDAS was installed around 10 km from the eruptive vent and was connected to a submarine fibre optic cable directed toward Tenerife Island. Since then, the HDAS has been recording seismic with a temporal sampling rate of 100 Hz and a spatial sampling rate of 10m for a total length of 30 (first phase) and 50 km using Raman Amplification (last period).The HDAS recorded thousands of local earthquakes as well as regional and teleseismic events. It was revealed to be an excellent tool for volcanic monitoring, allowing a better location of deeper events which location was made difficult by the small aperture of the seismic network of La Palma.The HDAS was also able to record the low-frequency (, The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)