Study of the sub-surface structure of Somma-Vesuvius (Italy) by seismic reflection data

Eleven seismic reflection lines recorded by the Italian Petroleum Agency, Azienda Generale Italiana Petroli (AGIP), in 1982-1984 around the flanks of the Somma-Vesuvius complex were utilized for studying its sub-surface structure. A new seismic reflection profile acquired within the Avellino caldera, at the southwestern edge of the Great Cone of Vesuvius, integrates the AGIP seismic dataset. The new reflection profile allows us to delineate two main reflectors. The first reflector may indicate a SW lateral collapse experienced by the volcano, probably between 35 and 11 ka ago. Evidence of this seismic discontinuity was also found on one AGIP line and on some refraction surveys. Other volcanic structures, such as buried adventive craters, dikes and pyroclastic deposits were detected on the eastern side of the volcanic complex. In particular, two shallow undulated reflectors are interpreted as pyroclastic deposits older than the Campanian Ignimbrite (CI). The study confirmed the presence of NW-SE striking faults crosscutting Vesuvius, which probably played a major role in the genesis of the volcano. Finally, evidence of ring faults was found mainly in the northeastern and southeastern sectors of the volcano. These faults yielded a low signal-to-noise area characterized by high lateral heterogeneity and the presence of a large number of fractures, possibly due to the stress field created by collapse of the volcanic structure.