On the direct estimation of bedrock depth and time-weighted average VS from surface waves dispersion and HVSR curves

The engineering bedrock depth (h) and time-weighted average shear wave velocity till that depth (VS,h) are recognized to be of primary relevance for earthquake hazard assessment. In fact, in contemporary seismic construction codes, they are regarded as proxys for the site response evaluation. Therefore, time-, cost-efficient and reliable investigation strategies are required for their determination, particularly when numerous surveys have to be interpreted for the reconstruction of the geological setting in large study areas and within micro-zonation studies. With this aim a workflow based on the application of a recently published linear wavelength-depth transformation (W–D transform) is evaluated in this paper. The workflow allows to directly derive both h and VS,h from surface waves dispersion and HVSR curves, avoiding the formal solution of the inverse problem,. Obtained results show for the first time the effectiveness and reliability of the proposed workflow for various bedrock depths and overlying velocity structures, and discuss advantages and drawbacks in its application in relation to the uncertainty of the inversion techniques.