Shear-wave Velocity Structure around Teide Volcano: Results Using Microtremors with the SPAC Method and Implications for Interpretation of Geodetic Results

Abstract

Deformation analysis and simulation of volcanic edifices require the construction of models of elastic properties of those structures. In this paper we present an analysis of microtremor measurements recorded during the performance tests of two temporary seismic arrays installed in the eastern portion of the Teide caldera in 1994. We take advantage of recent developments of the SPAC method and use spatial cross-correlation computations to estimate phase velocity dispersion of Rayleigh waves at the location of the arrays. We show that the extension of the standard SPAC method is valid in the case of our data, justifying its use and supporting the generalization of the SPAC method to single station pairs. The phase velocity dispersion curve obtained was inverted to recover the shear-wave profile at the site of the arrays. Our results indicate that the subsoil structure of the caldera is laterally homogeneous at the scale of a few km about the location of the arrays. We obtained about 315 m of volcanic sediments overlying rocks with a shear-wave velocity of 2 km/s. These results are robust and are a starting point to further modelling of deformation, permanent or transient, at this volcanic edifice, which can be useful in the interpretation of different observed fields. In fact, the computation of deformations and gravity changes due to possible volcanic intrusions in two models; one considering the volcanic sediments and the other without considering them, provided different results in the near field.

New Circular-Array Microtremor Techniques to Infer Love-Wave Phase Velocities

“…Meanwhile, the latest years have seen substantial refinement in the SPAC technique, in both theory and practical methodology (e.g., Morikawa et al, 2004;Chávez-García and Luzón, 2005;Wathelet et al, 2005;Asten, 2006;Cho et al, 2006a,b;Okada, 2006;Tada et al, 2007;Cho et al, 2008a,b;Roberts and Asten, 2008;Yokoi and Margaryan, 2008). Its scope of application has also expanded beyond the traditional limit of circular-array geometry (e.g., Bettig et al, 2001;Ohori et al, 2002;Chávez-García et al, 2006;Maresca et al, 2006;Chávez-García, Domínguez, et al, 2007;Chávez-García, Luzón, et al, 2007;Köhler et al, 2007;Parolai et al, 2007).…”

Beyond the SPAC Method: Exploiting the Wealth of Circular-Array Methods for Microtremor Exploration

“…Most typically, the SPAC method requires an odd number of seismic sensors, placed at equal azimuthal intervals around a circle, plus another at its center. In recent years, the SPAC method has attracted increasing attention in the research community, as is evident in the growing quantity of literature written on the subject (e.g., Morikawa et al, 2004;Roberts and Asten, 2004;Chávez-García and Luzón, 2005;Roberts and Asten, 2005;Wathelet et al, 2005;Asten, 2006;Chávez-García et al, 2006;Maresca et al, 2006;Okada, 2006;Shiraishi et al, 2006;Chávez-García, Domínguez, et al, 2007, Chávez-García, Luzón, et al, 2007Köhler et al, 2007). Cho et al (2006a) cast, in the wake of Henstridge (1979), a new light on the theoretical rationale of the SPAC method and developed on its basis a new comprehensive theoretical framework for circular-array methods of microtremor exploration, which is so general in nature that it encompasses both Aki's (1957) and Henstridge's (1979) formulations as special cases.…”

Microtremor Survey Method: A New Approach for Geothermal Exploration

“…Roberts and Asten (2005) used microtremor array (SPAC) measurements to estimate the S-wave velocity profile of Quaternary silts. Chávez-García et al (2007) adopted microtremors to achieve the S-wave velocity structure around the Teide Volcano. Stephenson and Odum (2010) applied the SPAC to characterise the S-wave velocity in the upper 300 m of Salt Lake Valley, Utah.…”