Evaluation of restoration results on the Antonino and Faustina Temple in Rome through seismic transmission tomography: Comparison of P-wave velocities before and after restoration

To evaluate the state of preservation of two columns of the Pronao of the Antonino and Faustina temple in the Roman forum (Rome, Italy - 141 A.D.), 2D seismic tomography was used. In this paper we describe the results of seismic transmission tomography before and after restoration, comparing sections of the two restored columns. The aim of this work was to test the validity of seismic tomography to guide the restorer during the restoration. We assessed the value of using this method to determine elastic properties in terms of P-wave velocity and, consequently, identify zones with little cracks and fractures, and detect improved dynamic characteristics after the restoration. Considering the dimensions nad shape of the studied objects, particular field and acquisition techniques were adopted. To obtain high-resolution tomograms, we used piezoelectric sensors with high cut-off frequency and short sampling intervals for the recorder unit; furthermore a particular recording technique was used to avoid reading errors (double trigger). The investigated sections are divided into cells, whose dimensions are calculated using Fresnel theory and a priori information. To invert the data we used the Least Square Inversion (LSI) method modified with variable damping factors, taking into account the mean slowness of the marble as constraint. The results of comparing P-wave velocities indicate that transmission tomography is able to detect differences in the elastic properties that occur before and after restoration. These results provide information to evaluate the degree of restoration needed, and to guide and help to improve the work of the restorer.