1D P-velocity models of Mt. Vesuvius volcano from the inversion of TomoVes96 first arrival time data

We applied a revised version of the 1-D t–p inversion method to first P-arrival timesfrom the active seismic experiment performed at Mt. Vesuvius (southern Italy) in 1996 (TomoVes96Project). The main objective of this work is to obtain 1-D velocity models of Mt. Somma-Vesuviusvolcano complex and surrounding area. Moreover we show that combining the 1-D information weprovide a reliable 2-D initial model for perturbative tomographic inversions. Seismic and geologicalsurveys suggest the presence of a refractor associated with the contrast between carbonate basement andvolcanic:alluvial sediments; synthetic simulations, using a realistic topography and carbonate topmorphology, allowed us to study the effect of topography on the retrieved velocity models and to checkthat the 1-D t–p method can also approximately retrieve the refractor depth and velocity contrast. Weanalysed data from 14 on-land shots recorded at stations deployed along the in-profile direction. Wegrouped the obtained models in three subsets according to the geology of the sampling area: Models forcarbonate outcrop area, models for the Campanian Plain surrounding the volcano edifice and models forMt. Somma-Vesuvius volcano complex. The found 1-D P-velocity models show important vertical andlateral variations. Very low velocities (1.5–2.5 km:s) are observed in the upper 200–500 m thick shallowlayer. At greater depths (3 km is the maximum investigated depth) P velocities increase to values in therange of 4–6 km:s which are related to the presence of the carbonatic basement. Finally we interpolatedthe 1-D models to demonstrate an example of misfit for a 2-D interpolated model whose residuals areconfined in a narrow band around zero.