EGU2020-6835
https://doi.org/10.5194/egusphere-egu2020-6835
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

High resolution seismic microzonation of San Cristóbal de La Laguna (Tenerife, Spain)

Germán Cervigón Tomico1, Diana Patricia Fernández del Campo2, Efrén Fernández Agudo2, Andres Felipe García Salamanca2,3, Rory Tisdall4, Iván Cabrera-Pérez1, David Martínez van Dorth1, Jean Soubestre1, Garazi Bidaurrazaga Aguirre1, Víctor Ortega Ramos1, Luca D'Auria1,5, and Nemesio M. Pérez1,5,6
Germán Cervigón Tomico et al.
  • 1Instituto Volcanológico de Canarias (INVOLCAN), San Cristóbal de La Laguna, Tenerife, Spain
  • 2Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, Madrid, Spain
  • 3Department of Geoscience, University of Calgary, Alberta, Canada
  • 4School of Environmental Sciences, University of Liverpool, Liverpool, UK
  • 5Instituto Tecnológico y de Energías Renovables (ITER), Granadilla de Abona, Tenerife, Canary Islands, Spain
  • 6Agencia Insular de la Energía de Tenerife (AIET), Granadilla de Abona, Tenerife, Canary Islands, Spain

The majority of casualties associated with historical eruptions on Tenerife (Canary Islands) were linked to the seismicity preceding and accompanying the eruptive activity. Therefore, the volcano-tectonic seismicity constitutes a relevant hazard. Moreover, the tectonics of the archipelago and paleoseismological evidences in the southern part of the island, suggest the possibility of destructive earthquakes on the island and its surroundings.

The complex geology of the island also affects seismic wave propagation and can lead to local seismic amplification phenomena. Actually, a recent moderate earthquake (Ml=4.4) located east of the island, has been recorded by a dense broadband network: Red Sísmica Canaria (C7) operated by Instituto Volcanológico de Canarias (INVOLCAN) showing relevant local seismic amplification effects at different sites. For this reason, in the spring of 2019, INVOLCAN started a research program, named TFsismozon, aimed at characterizing the local seismic response of the urban areas of Tenerife with the aim of mitigating the seismic risk of the island.

The first site selected for this purpose was the town of San Cristóbal de La Laguna, declared World Heritage Site by UNESCO 1999 and partially built over lacustrine sediments, which can be responsible for seismic wave amplification. For this purpose, during the summer of 2019, INVOLCAN realized a dense seismic survey of the town, performing seismic noise measurements on 453 sites located in the downtown and its surroundings, for a total surface of about 11 km2. The measurements were realized by deploying mini-arrays, composed of 3-4 elements, for a duration of 2-3 hours. These measurements were realized with the goals  of obtaining H/V ratios and also to get the surface waves dispersion curves through the cross-correlation of the seismic noise. The amplification frequencies are obtained through the H/V ratio, while the joint inversion of both H/V and dispersion curve data allows for obtaining Vs profiles for each point.

This survey therefore represents the first extensive mapping of seismic amplification effects in the Canary Islands. It also allows for improving the geological models of the town, in particular providing a high-resolution map of the lacustrine deposits on which part of the town lies. The preliminary results of the survey evidenced a clear relation between the sediment thickness and the frequency of the dominant peaks in H/V ratio. Moreover, the preliminary data analysis, on the basis of the H/V ratios, showed that the south-eastern area of the survey may be similar to the lacustrine basin, although previous geological maps indicated the presence of basalts.

How to cite: Cervigón Tomico, G., Fernández del Campo, D. P., Fernández Agudo, E., García Salamanca, A. F., Tisdall, R., Cabrera-Pérez, I., Martínez van Dorth, D., Soubestre, J., Bidaurrazaga Aguirre, G., Ortega Ramos, V., D'Auria, L., and Pérez, N. M.: High resolution seismic microzonation of San Cristóbal de La Laguna (Tenerife, Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6835, https://doi.org/10.5194/egusphere-egu2020-6835, 2020

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Presentation version 2 – uploaded on 04 May 2020
Ortographical errors in one of the author's names corrected
  • CC1: Comment on EGU2020-6835, Hans-Balder Havenith, 04 May 2020

    Dear Germán Cervigón,

     

    you have some double peak H/V results - how do you interprete those double peaks. 

    Do they systematically occur on some areas? ...

    Note, we started working on neighbouring El Hierro. .. volcanic flank collapses.

    chat you soon

    hansbh

    • AC1: Reply to CC1, Germán Cervigón Tomico, 04 May 2020

      Hello, good morning.

      The double peaks occur on areas having a more complex geology. Besides, a hypothesis is that these double peaks points could represent a mixture of alluvial and lacustrine layers over the bedrock.

      However, this map is only a preliminary result in which we only show the maximum peak of the H/V curve. Further analysis aimed at determining 1D S-wave velocity profiles beneath each point is ongoing.

      Glad you commented.

      • CC2: Reply to AC1, Hans-Balder Havenith, 04 May 2020

        I just wanted to tell you that we find systematically double peaks on landslides .. response of the landslide material and of the material (e.g. alluvium) below. 

        • AC2: Reply to CC2, Germán Cervigón Tomico, 04 May 2020

          Thanks, however the investigated area is on a saddle and is not surrounded by relevant reliefs. There are no geological evidences of landslides.

          On the other hand there are plenty of lacustrine deposits. By the way, once the emergency is over we plan to carry out other similar campaigns in different areas of Tenerife, some of them have landslides evidences. Let's keep in touch

Presentation version 1 – uploaded on 03 May 2020 , no comments