GeALab is the place where CNR IGAG Researchers work for the following activities:

• Local seismic hazard assessment, even in the case of sites where application of non-invasive methods is necessary (i.e. for cultural heritages);
• Subsoil model reconstructions;
• Definition of the variability of the expected seismic actions linked to the presence of heterogeneity in the subsoil or the presence of particular geomorphological conformations;
• Structural health monitoring of artefacts, including historical and architectural heritages.

The available instrumentation allows the application of geophysical techniques conducted in passive mode (single station noise measurements or according to 2D geometries) and active (MASW and Down-Hole). Array measurements can also be used in non-free field environments: for these latter, it is possible to obtain, and monitor in time, the modal shapes and the dynamic characteristics of the observed systems.

One of the 2D array techniques used by the GeALab team is based on the calculation of the average correlation functions between the seismic noise signals acquired at seismic stations or arrays of geophones. From these latter, it is possible to reconstruct the dispersion curve of a site and to obtain, through appropriate data inversion procedures, the variation with the depth of some mechanical properties (in particular the S waves velocity, VS waves). VS profiles are important for the study of the site effects.

The basic application scheme of all these techniques consists of the following three steps:

1) measuring noise by means of an array of seismic stations or synchronized geophones (seismic antenna) suitably arranged on the surface;

2) estimating the apparent dispersion curve of the Rayleigh surface waves;

3) solving the inverse problem to estimate the waves S velocity profile with depth [Vs (z)], looking for the best-fit between the experimental and theoretical dispersion curve, constraining the analysis with the ellipticity of the Rayleigh waves.