a review and some new issues on the theory of the h v technique for ambient vibrations

In spite of the Horizontal-to-Vertical Spectral Ratio (HVSR or H/V) technique obtained by the ambient vibrations is a very popular tool, a full theoretical explanation of it has been not reached yet. A short excursus is here presented on the theoretical models explaining the H/V spectral ratio that have been development in last decades. It leads to the present two main research lines: one aims at describing the H/V curve by taking in account the whole ambient-vibration wavefield, and another just studies the Rayleigh ellipticity. For the first theoretical branch, a comparison between the most recent two models of the ambient-vibration wavefield is presented, which are the Distributed Surface Sources (DSS) one and the Diffuse Field Approach (DFA). A mention is done of the current developments of these models and of the use of the DSS for comparing the H/V spectral ratio definitions present in literature. For the second research branch, some insights about the connection between the so-called osculation points of the Rayleigh dispersion curves and the behaviour of the H/V curve are discussed

Three-dimensional indirect boundary element method for deformation and gravity changes in volcanic areas: Application to Teide volcano (Tenerife, Canary Islands)

Most deformation models of volcanoes assume that the Earth is a linear, elastic, isotropic and homogeneous half-space, although some volcanic areas are associated with significant relief. We investigate the effects of topography on surface deformation and gravity changes caused by a magma intrusion in the Earth's crust. A three-dimensional (3-D) indirect boundary element method (IBEM) that incorporates realistic topographic features is developed in order to perform this analysis. Our results show that the topography alters both the magnitude and pattern of the deformation and gravity signal. As an example of realistic topography, we consider a spherical source of dilatation located at 4 km depth below Teide volcano summit (Tenerife, Canary Islands) in order to simulate the deformation and gravity changes that could be observed at Tenerife if a hypothetical intrusion occurred in the volcanic system. This approach gives a picture of the 3-D topographic effect at Teide that can provide insight in order to improve the geodetic monitoring of the volcano