Data from a portable dense seismic array deployed on Mt. Vesuvius in May 1994, during a 2D seismic tomography experiment, are analyzed in the present paper. The array consisted of two groups of short period geophones, 4.5 hz natural frequency, formed by 16 and 25 vertical components (plus two horizontal components), distributed along an arc like shape along the summit crater. Stacks of later arrivals, interpreted as reflected phases, provide a significant constraint to a boundary layer located in the depth range 1.5-2.2 km beneath the summit crater with average velocity V=1.8-2.2km/s, interpreted as the top of the limestone basement. The correlation methods applied on microtremor records allowed to infer the shallow velocity structure, up to 400 m, beneath the crater rim.