Analysis of magnetotelluric data from Las Cañadas caldera (Tenerife, Spain)

Tenerife is the second-largest island in the Canarian archipelago with an area of 2034 km². It consists of three ancient volcanic massifs (Anaga, Adeje and Teno) located at the edges of the island connected by rift zones to the centre of the island, in correspondence of Las Cañadas caldera. The caldera hosts the most relevant topographic element of Tenerife, the volcanic edifice of Teide – Pico Viejo. Previous studies already suggested the presence of geothermal resources inside and around the caldera. For this reason, in the present study, we have applied the magnetotelluric method (MT) in the central part of the island to better understand subsurface structures in this area.

The MT method is a useful tool successfully applied to detect conductive and resistive structures located in the subsoil. It is commonly used in volcanic areas to detect volcano-tectonic features and geothermal systems to evaluate exploitable geothermal resources. Furthermore, continuous magnetotelluric measurements can also be employed for volcanic monitoring, allowing tracking temporal changes of the resistivity because of fluid transfer processes in the volcanic system.

Between 2019 and 2020 we realised a detailed study of Las Cañadas caldera resistivity structure thought 45 magnetotelluric soundings. The instrumentation consisted of four Metronix ADU-08e, equipped with EPF-06 electrodes and MFS-06e magnetic coils, which registered electric and magnetic fields along the N-S and E-W directions. We also installed three remote stations at different times inside the caldera. Depending on the station quality, we obtained the MT response functions for periods of 0.001 – 1000 s. The dimensionality of the data has been analysed using the phase tensor.  The first preliminary results of dimensionality and strike analysis indicate a 1D/2D behaviour for the first layers which present a decreasing resistivity, evolving to a 3D behaviour from 1s and with an increase of resistivity with depth.

Furthermore, we present some results obtained by a permanent MT station to check the possibility of temporal changes in the electrical resistivity. During the time this station was recording two electrical blackouts which took place on the island. This allowed quantitatively estimating the level of anthropogenic electromagnetic noise in the recorded time series.