Velocity and attenuation models of Tenerife (Canary Islands, Spain) through Ambient Noise Tomography.

Tenerife island is likely to host geothermal resources which could be potentially exploited to increase the percentage renewable energy of the region . This work is realized in the framework of a wider multidisciplinary research program, carried out by Instituto Volcanológico de Canarias ( INVOLCAN ) , to estimate the geothermal potential of Tenerife, one of the active volcanic islands of the Canarian archipelago. The main objective of this work is the use of ambient noise tomography (ANT) to determine a high-resolution seismic velocity and attenuation model of the first few kilometers to detect anomalies potentially related to active geothermal reservoirs. The purposes of geothermal exploration require reaching a spatial resolution of few kilometers in the areas of the island which are potentially of interest. To realize ANT, we deployed a temporary broadband seismic network of 13 stations in different phases. In total we deployed seismic stations on 41 measurement points, for at least 1 month, operating jointly with the permanent seismic network Red Sísmica Canaria operated by INVOLCAN which currently consists of 18 permanent broadband stations. After performing standard data processing to retrieve Green's functions from cross-correlations of ambient noise, we retrieved the dispersion curves using the FTAN (Frequency Time Analysis) technique. The inversion of dispersion curves to obtain group velocity maps has been performed using a novel non-linear multiscale tomographic approach. This non-linear inversion technique, that use a shortest-path algorithm, allows retrieving 2D group velocity models, also in presence of strong velocity contrasts, with up to 100% of relative variation. The images obtained were eventually compared with Q (seismic quality factor) space distribution. Q was retrieved from the coda envelope decay of the noise cross-correlations (Q-coda). For each source-receiver pair, a Q-coda value was thus calculated, and mapped to the target area through the 2D sensitivity kernels for diffusion. We adopted the same sensitivity kernels for coda waves obtained using a numerical Monte Carlo approach. The preliminary results for 3D velocity and 2D attenuation images island evidence structural features for the island Tenerife which seem to be relevant for the purposes of geothermal exploration.