Abstract
SUMMARY Tenerife (Canary Islands, Spain) is a volcanic island dominated by the Teide-Pico Viejo complex, with a summit height of 3718 m. After renewed signs of activity starting in 2004, an active seismic experiment was performed in 2007 to derive a tomographic model and identify seismic anomalies possibly associated with the magmatic system. To complement the tomography, a double beam-forming analysis is applied on two orthogonal 2-D profiles crossing the island to look for evidence of the existence of a magma chamber. Numerical tests allow us to investigate the best measure of coherency between traces, and show that the correlation and nth root semblance methods give better results than the classical semblance. They also demonstrate that the technique is reliable for locating scattering structures at depth, even when the velocity model is imperfect. Applying this technique to the Tenerife data set, two main anomalies can be identified: one at approximately 7–9 km b.s.l. depth in the northern part of the island, and one shallower (1–4 km b.s.l.) beneath the main summit. These structures could be linked to the magmatic system, in good agreement with previous studies. The shallowest one may be the phonolitic storage area feeding the Teide-Pico Viejo complex, while the deepest structure may be related to the basaltic system.
Highlights
Defining the geometry of magma chambers is of critical importance in understanding a volcano’s current state, yet such imagery has proved notoriously difficult (Lees 2007)
A magma chamber is hypothesized as a volume of molten rock with physical properties that are significantly different from the surrounding host rocks: for this reason, it provides a suitable target for imaging via seismic tomography methods (Chouet 2003)
With passive or active sources, based on body wave traveltime or dispersion curve of surface waves to obtain the velocity of the medium, include for example: Campi Flegrei and Vesuvio (Zollo et al 2003; De Natale et al 2004; Vanorio et al 2005), Etna (Pataneet al. 2006), Popocatepetl (De Barros et al 2008; Berger et al 2011), Kilauea (Monteiller et al 2005; Park et al 2007), Deception island (Zandomeneghi et al 2009), Piton de la Fournaise (Prono et al 2009) and Teide (Ibanez et al 2008; Garcıa-Yeguas et al 2012)
Summary
Defining the geometry of magma chambers is of critical importance in understanding a volcano’s current state, yet such imagery has proved notoriously difficult (Lees 2007). A similar method was previously used by Maercklin (2008) in the Campi Flegrei caldera, in the Bay of Pozzuoli (Italy): the study inferred seismic scattering from a shallow buried caldera rim We apply this approach to a data set from Tenerife, the largest and the most inhabited island of the Canary volcanic archipelago (Spain), situated in the North Atlantic Ocean, about 200 km west of Morocco. The application of the method to the Tenerife data set is described in Section 6: two main scattering structures are identified beneath the island Their interpretation as magmatic storage areas is discussed: it is found to be consistent with the two magmatic reservoirs inferred by petrology and other geophysical studies
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