Simplified Seismic Soil Classification: The VfZ Approach

Abstract

Summary Site effect assessment studies are presently required in seismic prone areas both at the scale of the single construction (building codes) and at the urban scale (seismic microzonation, urban planning). These studies aim at predicting the effect of seismic shaking on structures by modeling the subsoil as an oscillator coupled to another oscillator representing the construction. Since stratigraphic seismic amplification is not related to the absolute rigidity of subsoil but to the existence of impedance contrasts, the standard simplified approaches based on the ‘average’ rigidity of subsoil in the first few meters (e.g. Vs30, VsH) can hardly be effective. Here it is proposed a simplified soil classification that takes into account the basic physical parameters ruling seismic amplification, i.e. the average shear wave velocity of the cover layer, the resonance frequency and the impedance contrast between the cover and the bedrock, in short VfZ. All the modern single station and multichannel surface wave based active and passive techniques can be proficiently used to achieve a simplified soil classification in terms of VfZ. This approach is illustrated through a set of examples.