THE CRUSTAL STRUCTURE OF THE WESTERN PO PLAIN - RECONSTRUCTION FROM INTEGRATED GEOLOGICAL AND SEISMIC DATA

A reflection/refraction seismic experiment performed in 1991 in the we stern Po plain gave basic data to constrain the interpretation of the crustal structures across the Alps/Apennines junction zones, Two diffe rent seismic domains, north and south of the western supposed prosecut ion of the Villalvernia-Varzi line, are evidenced from the interpretat ion of the data. The boundary between the two domains is characterized by strong lateral variations from southern high to northern low veloc ity layers, The northward abrupt deepening of the refractor/reflector basement is followed at depth by a similar deepening of the crust/mant le boundary. The geological interpretation evidences domains with cohe rent and independent evolution at surface level juxtaposed along obliq ue discontinuities cutting across the crust, A peculiar feature is the presence of both crust and mantle north-verging wedges into the crust al structure and the overthrust at depth of the 'alpine' metamorphic c rust onto the 'apenninic' nappes (Monferrato region).