Active source tomography at Mt. Vesuvius: Constraints for the magmatic system

[1] Recently, Mt. Vesuvius has been the subject of renewed seismological studies designed to allow the definition of the subsurface structure, focusing on the location and geometry of a presumed shallow magma chamber. The high volcanic risk associated with the activity of Mt. Vesuvius motivates detailed studies to trace a possible magmatic supply at shallow depth that could feed future eruptions. In 1994 and 1996 two active seismic surveys were carried out by an international team of scientists. Body waves from 17 shots executed around the volcano were recorded by dense arrays of seismic stations located across the volcano and extending to the surrounding Apenninic belt. These experiments encountered logistic difficulties due to the highly populated area; nevertheless, a good-quality data set of waveforms was collected. In this work we present the three-dimensional P wave velocity structure of the upper crust beneath Mt. Vesuvius, obtained through tomographic inversion of data collected during the TomoVes active seismic surveys. Due to the geometry of the problem, we used a tomographic technique that allows ray tracing in a complex model with both sharp velocity discontinuities and velocity gradients. The shot and station distribution and the presence of a very shallow velocity discontinuity, producing head wave first arrivals, limited the analysis to the upper 3 km of the crust. The images we obtained show a well-resolved, main axial high-Vp body interpreted as a magmatic intrusion remnant of recent eruptions from the central crater. Lateral branches depart from the central anomaly, possibly indicating the path followed by the magma during lateral eruptions that occurred in the past.