Ambient noise tomography of Gran Canaria island (Canary Islands) for geothermal exploration

This file contains the 3-D S-wave velocity model of Gran Canaria island.

Abstract

Ambient noise tomography has proven to be efficient in resolving shallow earth structures to multiple industrial studies. We applied this technique to understand Gran Canaria island's shallow structure for geothermal exploration proposes. This technique has never been applied on this volcanic island, being one of the most studied recently for geothermal exploration purposes. We determined the first 3D S-wave velocity model of the island using the data from 30 seismic stations installed between October 2019 and February 2020. We performed cross-correlation seismic ambient noise signals recorded by these stations to obtain empirical Green's functions. Then, we retrieved 279 dispersion curves using the frequency-time analysis. Thus, we obtained the 2D group velocity maps applying a non-linear multiscale inversion approach. Finally, we performed the depth inversion using a Bayesian transdimensional inversion to obtain a 3D S-wave velocity model. Our findings reveal five relevant geological structures that are of interest to understanding the island's formation and the presence of anomalies observed in previous studies. We noticed two high-velocity anomalies in the central part of the island, following a northwest-southeast trend that could be related to intrusive volcanic bodies, related to the early phases of the island formation and aligned along the main structural trend of the island. We also observed three low-velocity zones in the island's West, North, East and southwestern parts that could be associated with porous and highly fractured materials produced during the more recent volcanism episodes. Also, we observed a spatial correlation between the conductive anomalies revealed in the resistivity model obtained by a previous geophysical study and the strong lateral gradients in the S-wave velocity model. This could evidence the presence of a hydrothermal circulation and thermal anomalies associated with lateral contacts between different geological units and/or faults.