Il controllo dell’interazione fra strutture sincinematiche a diversa orientazione nella genesi ed evoluzione dei processi sismogenetici: l’esempio della Val di Sangro (Abruzzo).

The “Val di Sangro” earthquake (May 7th, 1984 Ms5.8) and related aftershock sequence are analysed from a seismotectonic point of view. The study is carried out by a carefully relocation of the aftershock sequence and by comparing seismological data with detailed geological information. The aftershocks are located in the hangingwall of the two major normal fault systems of the southeastern Marsica area (Abruzzo, central Italy): the Barrea normal fault system (NNW-SSE trending, WSW-dipping) and the Valle del Sangro right-lateral normal-oblique fault (N100°E trending, SSW-dipping). The CMT focal mechanisms of the main shock (M5.8) and of the largest aftershock (M5.2) point to a NNW-SSE trending extensional main seismogenetic structure. Aftershock epicentres are mostly concentrated within a cluster oriented ENE-WSW. Hypocentres deepen about 60° toward SW in a SW-NE  section and about 80° toward S in a N-S section. The anomalous ENE-WSW distribution of the aftershock volume appears to be controlled by the interference between two non-coaxial, but kinematically compatible, structures: the Barrea fault and the Valle del Sangro fault. The aftershocks are clustered within the rock volume at the hangingwall of both the faults, along the zone of intersection between the two structures. The Barrea fault would also have acted as the main seismogenetic fault structure; the Valle del Sangro fault would have acted as a barrier to the seismogenic rupture process and also as transfer fault for accumulated strain induced by the main shock rupture.