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Seismic microzonation of San Cristóbal de La Laguna (Tenerife, Canary Islands)

David Martínez van Dorth1,2, Iván Cabrera-Pérez3, Víctor Ortega-Ramos1, Rubén García-Hernández1, Monika Przeor1, Germán D. Padilla1,2, Luca D'Auria1,2, Mercedes Feriche4, and Nemesio M. Pérez1,2

  • Affiliations: 1Instituto Volcanológico de Canarias (INVOLCAN), Puerto de la Cruz, Tenerife, Canary Islands, Spain 2Instituto Tecnológico y de Energías Renovables (ITER), Granadilla de Abona, Tenerife, Canary Islands, Spain 3Department of Earth Sciences, University of Geneva, Geneva, Switzerland 4Instituto Andaluz Interuniversitario de Investigación en Geofísica y Prevención de Desastres Sísmicos, University of Granada, Granada, Spain 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 160

  • Programme No: 2.2.24

  • Theme 2 > Session 2

Abstract

We present a high-resolution seismic microzonation study of San Cristóbal de La Laguna town (Tenerife, Canary Islands), a UNESCO World Heritage Site. This is the second most populated city on the island, with the town composed mainly of 1--3 story buildings. Part of the urban area is inside a valley filled with volcano-sedimentary and lacustrine deposits. The city is also located in a seismically active region, primarily due to the island's volcanic activity. Therefore, it is prone to very shallow earthquakes with magnitudes exceeding 4.0. Henceforth, these facts make it essential to evaluate the local seismic hazard. For this reason, in 2019, we performed a seismic survey using mini-arrays of 3--4 stations at 467 locations to record microtremor for 2 hours. We applied the horizontal-to-vertical spectral ratio (HVSR) method to determine dominant site frequencies. Data were divided into 80-second windows, filtering out noise and analysing the response in the frequency range of 0.25--30 Hz. The HV curves obtained were inverted to estimate the shallow geological layer's thickness and seismic wave velocities. The first results show fundamental frequencies ranging from 0.62 to 11.11 Hz. Low frequencies (1--3 Hz) dominate most of the valley from NE to SW, likely linked to thick volcano-sedimentary and lacustrine deposits and large lava flow layers. High frequencies were observed in the central area, where the historic buildings are currently located and where an old lagoon existed. Double-frequency peaks were observed and associated with thin surface layers of silts and clays that correlate well with geotechnical observations.