Estimation of Anisotropy from Real SV and SH Seismic Data Acquired in a Circular Acquisition Geometry

This work analyses the Sv and Sh arrivals in an unusual seismic circular acquisition scheme carried out in the area of the village of Arquata del Tronto (Italy), which was almost completely destroyed by a strong sequences of earthquakes in 2016-2017. Using a vibroseis source, the survey consists of two acquisitions: one with the vibration direction parallel to the estimated strike angle of the buried structures; the other with the corresponding perpendicular direction. In both cases, the geophones have the same orientation of the vibrates. From the first break tomography, we obtained the two velocity fields VSv and VSh by separately inverting the corresponding Sv and Sh arrivals from the two data sets. Then, using the VSv/VSh ratio, obtained from each tomography, we applied a method to estimate the degree of anisotropy and the position (strike and dip angles) of the buried structures. The results show a clear presence of anisotropic structures characterized by relatively high Thomsen parameters (ϵ,δ) with a dip angle greater than 45°-50° estimated from the geological studies.