Revisiting Vs30 as a proxy parameter for site effects: a case study using KIKNET data

The local geology can strongly affect the seismic ground motion at the surface. One standard index used to classify local site effects is the average shear wave velocity in the first 30 meters, namely Vs30. The higher the Vs30 the stiffer the material is and therefore less amplification is expected. However, this index does not map the complexity of the velocity at depth. Indeed, some sites may have close Vs30 values, but quite different velocity distribution at depth. In this study, we propose the ratio between the average shear wave velocity up to depths having at least 800 m/s and Vs30. This ratio gives information about the velocity distribution at depth. Lower ratios mean stronger simi…