V[sub.s30] Structure of Almeria City Using SPAC and MASW Methods and Proxy Correlations

The topographic slope method is an innovative, fast and very low-cost technique for estimating the average S-wave velocity in the upper 30 m (V[sub.s30]) based on the relationship between this quantity and the slope of the ground, obtained using a Digital Elevation Model (DEM). The method is based on the good linear correlations log(V[sub.s30])–log(slope) found experimentally, which, ideally, should be determined for each region. If measured V[sub.s30] data are not available to carry out this fitting for the study area, correlations from other areas could be used, although the reliability of the estimated V[sub.s30] results would be lower. In this article, V[sub.s30] observations are made for the city of Almeria, using Spatial Autocorrelation Surveys (SPAC) and Multichannel Analysis of Surface Waves (MASW), obtaining two types of fitting: (a) linear relationship log(V[sub.s30])–log(slope); and (b) considering additional dependence on geological units. The reliability, evaluated by Multiple R-Squared (MRS), varies between 79.2% in the first case and 87.0% in the second, lowering the mean absolute values of the residuals at the observation points in the first case from 40.0 m/s to 29.0 m/s. Using a more generic correlation obtained for other areas of the world, the mean absolute residuals increase to 74.7 m/s.