THE SOMMA-VESUVIUS STRESS-FIELD INDUCED BY REGIONAL TECTONICS - EVIDENCES FROM SEISMOLOGICAL AND MESOSTRUCTURAL DATA

A detailed structural and geophysical study of the Somma-Vesuvius volc anic complex was carried out by integrating mesostructural measurement s, focal mechanisms and shear-wave splitting analysis. Fault-slip and focal mechanism analysis indicate that the volcano is affected by NW-S E-, NE-SW-trending oblique-slip faults and by E-W-trending normal faul ts. Magma chamber(s) responsible for plinian/sub-plinian eruptions (i. e. A.D. 79 and 1631) formed inside the area bounded by E-W-trending no rmal faults. The post-1631 fissural eruptions (i.e. 1794 and 1861) occ urred along the main oblique-slip fault segments. The movements of the Vesuvius faults are mainly related to the regional stress field. A lo cal stress field superposed to the regional one is also present but ev idences of magma or gravity induced stresses are lacking. The local st ress field acts inside the caldera area being related to fault reactiv ation processes. The present-day Vesuvius seismic activity is due to b oth regional and local stress fields. Shear-wave splitting analysis re veals an anisotropic volume due to stress induced cracks NW-SE aligned by faulting processes. Since the depth extent of the ar,isotropic vol ume is at least 6 km b.s.l., we deduce the NW-SE-trending oblique-slip fault system represents the main discontinuity on which lies the volc ano. This discontinuity is responsible for the morphological lowering of the edifice in its southwestern side. (C) 1998 Elsevier Science B.V . All rights reserved.