GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 1.2 109 Abruzzi Apennines are affected by almost two sets of NW-SE to N-S trending normal faults,. Focal mechanisms, geodetic data and borehole breakouts (Chiaraluce et al. , 2003; D’Agostino et al. , 2001; Mariucci et al. , 1999) characterize the present stress field as NE-SW extension, related to the persistence of the back-arc extension. Such extension, mainly concentrated along the axial belt, generates NW–SE trending, mainly SW-dipping, seismically active normal faults, bounding graben and half-graben basins. Paleoseismological and historical data suggest that almost all the faults of the western fault set activated during historical time while there is no evidence of recent activation for most of the faults related to the eastern set (Galadini and Galli, 2000). For this reason, these structures have been defined as silent and are considered as probable seismic gaps (Galadini and Galli, 2000). The Abruzzi region was affected in the western active sector by large earthquakes in 1349 (Me 6.5), (Me 6.5), 1456 (Me 7.0), 1461 (Me 6.4), 1654 (Me 6.1), 1703 (Me 6.7), 1706 (Me 6.7), 1762 (Me 6.0) and 1915 (Mw 7.0). The January 13, 1915 earthquake is one of the strongest seismic events in Italy, caused 30,000 victims within a large area surrounding the Fucino basin. The last seismic event occurred in the area on the April 6, 2009 (Mw 6.3) killing 309 people. This earthquake struck the town of L’Aquila, after several months of seismic activity focused in the Aquila basin. Thousands of aftershocks have been recorded. The relative hypocenters are located within the upper 10-20 km of the crust (Chiararaluce et al. , 2011). Seismic activity in this region had been scarce during past few decades, with only three seismic swarms in 1985 (Mw 4.5), 1992 (Mw 3.9) and 1994 (Mw = 4.4). The 7 May 1984 (Mw 5.9) earthquake and its strong 11 May aftershock occurred near the southern end of the study region. In historical times, the faults of the more external extensional alignment also remained blocked and silent (Galadini and Galli, 2000),with the only exception of the September 5, 1950 event (Mw 5.7) occurred near the city of Teramo. Further to the SE, two relatively large earthquakes occurred on the eastern flank of the Maiella Mt. on November 3, 1706 (Mw 6.6) and on September 26, 1933 (Mw 5.7). According to Lavecchia et al. (2010), these earthquakes have both been caused by E-verging reverse faulting underneath the Maiella Mt. Data analysis. The analysis of the available geo-structural, seismic and gravimetric data of the studied area has been carried out under a Geographic Information System (GIS) environment (ArcGis 10.1). The “fault” data set �������� �� � ����� �� ��� ��������������� ���������� ��������� ���� consists of a merge of the Plio-Quaternary structures extracted from the available ���������� ��� ���������� ���� ��� ���� ���������� ������ ����� ��� geological and structural maps and from scientific papers (Fig. 1). The geological and structural maps of reference for our analysis have been the following: ITHACA catalogue Fig. 1 – Map of the faults extracted from literature. Purple: from the CARG project (ISPRA); blue: from Neotectonic Map of Italy 1:500,000 (Ambrosetti et al. , 1987); yellow: fromGaladini et al. (2003); red: from ITHACA project (ISPRA).