A major perturbation of the lower crust is revealed by a DSS experiment carried out across the Campania volcanic region (southern Italy). PmP phases, recorded both at constant offsets by two fan-arrays and along a linear profile intersecting at depth their reflection ranges, provide evidence of a limited structural high in the crust-mantle boundary, located at the center of the 100 km wide area. Such an abrupt lateral variation in the structure of the crust may relate to the difference in volcanic products and eruptions between the two main volcanic centers of the area, Mt. Vesuvius and Campi Flegrei caldera. ¿ American Geophysical Union 1989