Seismic reflection prospecting in support to seismic hazard assessment

Abstract:

It has long been observed that a conspicuous of ground shaking variability produced by an earthquake is strictly correlated with local geological conditions. An accurate understanding of subsurface architecture is of paramount importance to evaluate seismic hazard and for the earthquake-resistant design of new engineering projects. In microzonation studies, active and passive seismic methods are largely used to obtain S-wave velocity profiles from the very near-surface to hundreds of meters below the surface. In presence of complex geological settings, the seismic reflection method represents an effective tool able to provide subsoil velocity models for a reliable ground motion prediction. Both P- and S-wave data can be acquired depending on the resolution and the penetration required. From the theoretical point of view, S-waves offer a better resolution than P-waves since shear waves travel slower than compressional waves. Nevertheless, the applicability of reflection seismic by both types of waves is strongly dependent on the near-surface conditions and the geology of the site under investigation. In addition to the subsoil characterization in terms of velocity and geometry, seismic reflection data offer useful information in support of paleoseismological trench location by high-resolution imaging. Some case histories concerning the seismic hazard assessment acquired by OGS in the framework of different projects both onshore and offshore were presented. These data demonstrate that seismic reflection is a very effective and cost-efficient tool to explore the subsoil geology in support of seismic microzonation studies.