EGU2020-318
https://doi.org/10.5194/egusphere-egu2020-318
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

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

Iván Cabrera1,3, Jean Soubestre1, Luca D'Auria1,2, Edoardo Del Pezzo4,5, José Barrancos1,2, Germán D. Padilla1,2, Germán Cervigón1, Monika Przeor1,3, Garazi Bidaurrazaga-Aguirre1, David Martínez van Dorth1, Alba Martín-Lorenzo2, and Nemesio M. Pérez1,2
Iván Cabrera et al.
  • 1Instituto Volcanológico de Canarias (INVOLCAN), Granadilla de Abona, Tenerife, Canary Islands (icabrera@iter.es)
  • 2Instituto Tecnológico y de Energías Renovables (ITER), Granadilla de Abona, Tenerife, Canary Islands, Spain
  • 3Universidad de La Laguna (ULL), San Cristóbal de La Laguna, Tenerife, Canary Islands, Spain
  • 4Istituto Nazionale di Geofisica e Vulcanologia (INGV), Osservatorio Vesuviano. Via Diocleziano 328, 80124 Naples, Italy
  • 5Instituto Andaluz de Geofisica (IAG), Universidad de Granada, Calle Profesor Clavera s/n, Campus de Cartuja, Granada, Spain

Tenerife and La Palma are active volcanic islands belonging to the Canarian archipelago. The island of La Palma is the most occidental and volcanically active island of the archipelago. The youngest volcanic rocks are located in the Cumbre Vieja volcanic complex, a fast-growing North-South ridge in the southern half part of the island. On the other hand, the central part of Tenerife island hosts the Teide composite volcano, the third tallest volcano on Earth measured from the ocean floor. The volcanic system of the island extends along three radial dorsals, where most of the historical eruptions occurred. Those two volcanic islands have potential geothermal resources that could be exploited to increase the percentage of renewable energy in the Canary Islands.

 

The main objective of this work is the use of Ambient Noise Tomography (ANT) to determine high-resolution seismic velocity and attenuation models of the first few kilometres of the crust, in order to detect anomalies potentially related to active geothermal reservoirs. In the case of Tenerife, previous tomographic studies were performed on the island using active seismic data. They allowed to image the structure of the first 8 km depth. However, for the purpose of geothermal exploration, a higher spatial resolution is needed for the first few kilometres and the determination of the shear wave velocity has a particular importance when searching for fluid reservoirs. In the case of La Palma, no seismic tomography was performed yet.

 

To realize the ANT, we deployed temporary broadband seismic networks in the two islands. In total, we deployed seismic stations on 41 measurements points in Tenerife and 23 points in La Palma. The campaigns lasted at least 1 month, using jointly the permanent seismic network Red Sísmica Canaria (C7) operated by INVOLCAN. 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 was performed using a novel non-linear multiscale tomographic approach. The forward modelling of surface waves traveltimes was implemented using a shortest-path algorithm which takes the topography into account. The method consists of progressive non-linear inversion steps at increasing resolution. This technique allows retrieving 2D group velocity models in presence of strong velocity contrasts with up to 100% of relative variation.

 

In parallel with velocity model, we retrieved maps of seismic attenuation (i.e. quality factor Q) retrieved from the coda envelope decay of noise cross-correlations (Q-coda). For each source-receiver pair, a Q-coda value was calculated, and mapped to the target area by using 2D empirical sensitivity kernels for diffusion (Del Pezzo and Ibañez, 2019). We compared 2D velocity and attenuation images at different dominant periods, evidencing structural features for Tenerife and La Palma islands which seem to be relevant for the purpose of geothermal exploration.

How to cite: Cabrera, I., Soubestre, J., D'Auria, L., Del Pezzo, E., Barrancos, J., Padilla, G. D., Cervigón, G., Przeor, M., Bidaurrazaga-Aguirre, G., Martínez van Dorth, D., Martín-Lorenzo, A., and Pérez, N. M.: Velocity and attenuation models of Tenerife and La Palma (Canary Islands, Spain) through Ambient Noise Tomography. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-318, https://doi.org/10.5194/egusphere-egu2020-318, 2019

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Presentation version 1 – uploaded on 02 May 2020
  • CC1: Comment on EGU2020-318, Luca De Siena, 03 May 2020

    Hi everyone, is anisotropic noise distribution affecting coda decay? If not, up to which frequency is it true?

    Best

    Luca De Siena

    • AC1: Reply to CC1, Iván Cabrera Pérez, 03 May 2020

      Hello, following Calvet et al, 2013, we believe that considering the latest windows lags, the amplitude decay is independent from the source. We empirically determined the Q coda up to frequencies for which a reliable exponential amplitude decay was observed.

      Best regards

      Iván Cabrera-Pérez

      • CC2: Reply to AC1, Luca De Siena, 03 May 2020

        Thanks for your answer. In that work they use earthquake sources. They demonstrate that independence from the source is only reached when Qc is constant with source station distance. In this way,  they can apply diffusion theory and use the diffusive kernels. How can you do a similar test with noise data, where noise sources are anisotropic? Maybe a test of Qc versus staton distances?

        Best Wishes,

        Luca 

        • AC2: Reply to CC2, Iván Cabrera Pérez, 04 May 2020

          Hello, indeed, this test can be performed by analyzing the variation of Qc with respect to the interstations distance. We performed this analysis and we didn't observed any relation between the Qc value and the distance between stations.

          Best wishes,

          Iván Cabrera-Pérez

          • CC3: Reply to AC2, Luca De Siena, 04 May 2020

            Great, thanks!

            Luca