GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 3.2 645 (3) where n is the number of layers down to depth z , and hi and VSi are the thickness and the velocity of the ith layer, respectively. We obtain couples of wavelength and depth for which the SW phase velocity is equal to VSz and these couples are then interpolated (Fig. 1b). The W/D curve of the simulated model is a straight line in the depth range that belongs to the sand and it presents a break point at the wavelength λ b and at the depth of the sand bottom. Another important observation is that the deviation from linearity starts at a wavelength shallower than Fig. 1 - a) VS (blue solid) models and the corresponding SW dispersion curve (blue dots) plotted as a function of wavelength. The DC follows a power law until a threshold value of wavelength, λ b . b) W/D corresponding to the model of Fig. 1. The curve deviates from linearity at wavelength λ d and presents a break point at wavelength λ b . The break point corresponds to the sand bottom depth. Fig. 2 - a) VS (green solid) and VP (various color solid) models. VS model is kept the same and VP is updated according to Poisson’s ratio that increases from 0.18 to 0.38 with steps of 0.02. b) W/D corresponding to the various velocity models of Fig. 2a.