Morfotettonica dei rilievi a nord della Conca Aquilana

Abstract

The paper presents preliminary results obtained with a comparative morfostructural and seismological analysis of elements observed in the area between the northern border of the L'Aquila Basin and Mt. S. Franco (Abruzzo, central Italy). This area is characterized by an important set of NW-SE trendingextensional faults that generally dip towards the SW; some of these faults bound the L'Aquila basin to the NE and others delimit elongated tectonic or tectono-karstic depressions within the mountains (the largest being those at the foot of Mt. Stabiata and Mt. San Franco). Many of the faults show evidence of recent tectonic activity, such as fault scarps in recent deposits, fault escarpments with scarplets at the base, triangular facets, anomalies in the hydrographic network and gravity-controlled tectonic effects on reliefs. These elements probably evolved during high magnitude seismic events, as is suggested by studies on the effects of the 1703 L'Aquila earthquake. Abruzzo has been affected by several intermediate to high magnitude earthquakes of intensity I ≥ Vlll MCS, like the 1703 L'Aquila earthquake (I = X MCS). Since 1992, seismic activity has been recorded by a local network which presently consists of 14 digital stations distributed over the entire Abruzzo territory. From 1992 to 1994 seismicity was characterized by two swarms which occurred in August 1992 (Mmax = 3.9) and June 1994 (Mmax=3.7). Many events of the first swarm were located exactly in the area between Mt. San Franco and Mt. Stabiata. The projection of all the hypocen-tres onto an E-W oriented cross-section indicates that focal depths were located within the first 15 km; this type of focal volumes are typical of earthquakes occurring in the south-central Apennines. Fault plane solutions calculated for a selected number of events indicate predominantly normal fault mechanisms with T axes oriented NE-SW (anti-Apenninic direction).