Diffuse degassing of carbon dioxide at Somma-Vesuvius volcanic complex (Southern Italy) and its relation with regional tectonics

A systematic survey of soil CO2 concentrations was carried out on the flanks of Somma–Vesuvius volcano in order to constrain possible pathways responsible of carbon dioxide diffuse degassing taking place during the present state of quiescence. Measurements were performed at 1162 sites in late winter–spring 2000, highlighting that soil CO2 concentrations range from 50 to 10500 ppmV. A statistical analysis was developed in order to define the threshold value of anomaly and separate the biogenic CO2 component, produced by soil respiration, from the inorganic component of deep provenance. A computer routine was also elaborated to interpret the grid of CO2 anomalous concentration values and define the actual location, orientation and length of degassing structures. The results obtained by this procedure reveal a main control of the regional stress field on the patterns of gas migration. The identified degassing lineaments are typically oriented along the Apenninic (NW–SE) and anti-Apenninic (NE–SW) trends, which are known to govern the past geological and structural evolution of the Campanian Plain and present seismicity and deformation pattern of Mount Vesuvius. A main degassing area was recognized on the eastern and southern flanks of the volcano, which likely relates to the geometry of the underlying carbonate basement, reaching its top (500 m depth) in this sector of the volcano.