Comparison of VS30 using measured, assigned and proxy values in three cities of Northern Greece

Accurate VS30 estimates are increasingly important in seismically active areas due to their efficacy in site effect analysis for seismic hazard assessment as well as microzonation evaluation and shake maps development. A comparison between different approaches for the time-averaged shear-wave velocity (VS) in the upper 30 m (VS30) is presented. In this study of VS30 a site-to-site or averaged zonation value technique comparison is assessed for proxy-based and measured or assigned values, respectively. Three urban areas of Edessa, Grevena and Xanthi in Northern Greece were selected for this study. The merit of this selection was based on the historical seismicity, geology and geomorphology of these areas. This paper highlights the strong correlation between the proxy-based approach and the assigned average values in zones of common geophysical and geotechnical characteristics within the frame of EC8 site characterization. In addition, on site-by-site comparison proxy-based VS30 values, agree with the ones derived from measured geophysical data. With the exception of areas where shear wave velocity has a high rate increase with depth, as well as, in shallow bedrock above 30 m the proxy tends to underestimate the VS30 value. Higher disagreements are reported when stiffer formations are denoted through geotechnical mapping that are not clarified in the geological map.