Shear wave structural models of Venice Plain, Italy, from Time Cross Correlation of seismic noise

A good knowledge of shear wave (Vs) structural models is required for the realistic modelling of seismic hazard scenarios. Nowadays there are many approaches based on surface wave dispersion evaluation, mainly oriented to the use of controlled source techniques with appropriate shot gathers. Subsoil deep controlled source surveys suffer great logistic problems and costs, due to the amount of source energy they need (e.g. explosive). Otherwise realistic seismic motion evaluation requires the knowledge of Vs structural models even at large depths (e.g. 100–200 m). In this work we use the cross correlation of seismic noise in order to evaluate surface wave dispersion in a passive way, without controlled sources. Cross correlation of seismic noise recordings can be used to infer the impulse response between two points when the so-called noise correlation function (NCF) converges to the impulse response between two receivers, !ltered by the bandwidth of the noise spectrum. The NCF between two noise recording sensors could be in such a way considered as the passive analogous to a shot gather made with active sources in the space between the sensors themselves. In this work we computed the NCF between two sensors using both sea source noise and an anthropic noise source (an airport), in order to infer a Vs structural model pro!le in an area of the Venice Plain (North-East Italy). Rayleigh wave fundamental mode dispersion curve has been extracted from NCF using the Frequency Time Analysis (FTAN) method. The results of the non-linear inversion of dispersion data, in terms of 1D Vs distribution versus depth, are consistent with the geological subsoil conditions of the studied area and represent the !rst shear wave velocities middle deep characterisation of the Venetian hinterland.