Passive Seismic Stratigraphy: A new efficient, fast and economic technique

The HVSR technique enjoyed its greatest popularity in Japan as a fast tool for seismic microzonation, although its capability in this respect is still debated. What appears not questionable is the capability of this technique to retrieve the resonance frequencies of surficial sedimentary layers and to infer from these the relative stratigraphy, which can be transformed into the absolute stratigraphy if at least an approximate estimate of shear wave velocity (VS) is available. In order to exploit this potential in practical stratigraphic applications, we used a new type of ultra-portable high resolution instrument and applied the HVSR technique to 5 different settings: 1) a slope debris in Predappio Alta (Forlì, Northern Apennines), 2) a classical problem of engineering geology: the foundation earths of a damaged building in Vodo di Cadore (Belluno, Eastern Alps), 3) the landslide bodies at Scascoli (Bologna, Northern Apennines), 4) the landslide of Ca’ di Malta (Bologna, Northern Apennines), 5) a study of deep stratigraphy in a sedimentary basin (Casaglia, Ferrara, Po Valley). We found that the HVSR technique a) is an invaluable fast, cheap and fully non invasive stratigraphic tool, b) capable of resolving multiple strata, even in case of low seismic impedance contrast, c) applicable to nonplanar, d) 3-dimensional geometries, e) allowing deep prospections (of the order of 1 km depth) and, finally, f) if stratigraphy is known at some point, capable to provide fast and cheap estimates of average VS.