A proxy-based model for estimating VS30 in the Iberian Peninsula

Abstract

The time-averaged shear-wave velocity in the upper 30 m of the ground, VS30, is a key soil descriptor for estimating site response despite its recognized limitations. It is employed in both, site-specific probabilistic hazard assessments (PSHAs) and regional seismic codes. This work presents a model for estimating VS30 in the Iberian Peninsula as a function of three proxies: topographic slope, geological age and lithology at each site. Tasks accomplished include: 1) gathering existing Vs profiles and calculating their VS30; 2) defining an adequate set of representative age and lithological groups; 3) classifying the available VS profiles according to these groups; and 4) carrying out a regression analysis between VS30, slopes, age and lithological groups. Based on the regression analysis and the dependency on the slope, some of the initially proposed groups were amalgamated, before proposing the final model. This model considers topographic slope values extracted from a digital elevation model (DEM) with 200 m horizontal resolution, plus six geological age groups and four lithological groups. It provides an estimate of the mean and standard deviation of logVS30 (and hence VS30), which can be used for sites without direct estimates of velocity profiles (and VS30) in the Iberian Peninsula. © 2022 Elsevier Ltd