An application of seismic tomography method for studying an urban geology problem

Geophysical methods have been used more recurrently within urban geology in the past years. These techniques, when correctly applied, offer a more or less complete frame on the physical and mechanical properties, on discontinuities and on subsurface geometries of investigated mediums. Geophysical prospecting is also used because of its low cost/advantages ratio. Its also capable of overcoming the limits of more classical geognostical investigations (i.e. borehole drilling) that, being localised, can often give results, which are not univocally interpretable, especially for reconstruction of subsurface geometries in complex scenarios. This work presents an example of the use of high resolution, P wave seismic tomography that has been applied within a study intended to securing an anthropic cavity so as to not represent a threat for human lives and possessions. Instability conditions are due to the poor mechanical conditions of existing lithotypes and the high grade of weathering of the lithologies. Proof of poor structural conditions have been the numerous falls of debris during seismic events (i.e. after the seismic event of 1997). Firstly, applicability and intrinsic limitations of the methodology are discussed on the bases of experimental tests conducted in laboratory with the use of ultrasound on materials of different complexity. Eventually, the acquisition techniques and the data processing are discussed, coadiuvated by the use of direct investigations like geological and structural survey, exploration trial pitting and rotary drilling.