GNGTS 2014 - Atti del 33° Convegno Nazionale

T�� ���������� �� ��� �� ����� ���� ��� ����� ���� �� ������ ������������ �� ������������ he decoupling of the MS wedge from the inner belt is mostly accommodated by extensional/ transtensional deformation at the Irpinia, Benevento and Matese fault zones (���� ������� e.g, Ascione et al. , 2007�� ��� �������� ������ ������� ��� ��� ����� ��� ��� ����� ���� �� ���� ���������� ). The relative motion between the ELA wedge and the inner part of this carbonatic platform is accommodated by ��� ����� ����� ��������� �������������� ����� ������� ��������� two major NW-SE sinistral transtensional fault systems (L’Aquila and Fucino, e.g., Piccardi et al. , 2006). In the northern Apennines, the divergence between the outward extruding RMU wedge and the inner belt is accommodated by extensional/ transtensional deformation at a series of tectonic troughs (Fig. 1; e.g. Piccardi et al. , 2006 and references therein). In a number of papers (Mantovani et al. , 2010, 2012, 2014b; Viti et al. , 2012, 2013) it is argued that the short term development of the tectonic context described above may closely be connected with the spatio-temporal distribution of major historical earthquakes in the Apennine belt. The major aspects of that interpretation are synthetically described in the next section. Short-term kinematics and seismic activity in the Apennine belt. When a major earthquake activates one of the decoupling transtensional faults in the southern Apennines, the MS wedge (being stressed by the Adriatic plate) accelerates, as an effect of post seismic relaxation processes. This enhances its belt-parallel push on the ELA wedge, in the central Apennines. Consequently, shear stress increases at the main L’Aquila and Fucino fault systems in that zone. When a major earthquake occurs at one of those fault systems, the decoupled part of Lazio-Abruzzi platform accelerates, strengthening its belt-parallel push on the RMU wedge in the northern Apennines (Fig. 1). ���� ������ ��� ����� ��� ������� ���������� �� ����� ������ This effect may cause the seismic activation of major faults that border the RMU wedge, located at the outer thrust zones and in the extensional troughs running along the axial part of the belt. The effect of a central Apennine earthquake on the kinematic/tectonic response of the RMU wedge depends on which transtensional fault system is activated �� ��� �� ��������� ���� in the LA platform. When such activation involves the Fucino fault system, the decoupled LA sector is relatively wide and consequently, its belt-parallel push stresses the whole RMU wedge. An example in this sense is provided by the large Avezzano earthquake (M=7.0) which ruptured the Fucino fault in 1915. In response to this event, 7 strong shocks (M > 5.5) have occurred in the northern Apennines in the period 1916-1920 (Viti et al. , 2012, 2013). When instead the L’Aquila fault system activates, only a relatively narrow part of the Lazio- Abruzzi wedge, mainly constituted by the Gran SassoArc and Laga units, is decoupled from the western part of the belt. Consequently, the resulting belt-parallel push exerted by that wedge on the northern Apennines stresses a relatively narrow sector of the RMU wedge. The divergence of that sector from the western part of the northern Apennines, is mainly accommodated by extensional/transtensional deformation at the Norcia-Colfiorito-GualdoTadino-Gubbio- AltaValtiberina (NCGGA) fault system (Fig.1). The analysis of the spatio-temporal distribution of major earthquakes, in the framework of the tectonic setting in the central Mediterranean region, has led Mantovani et al. (2014b) to suggest that seismic activity in the periAdriatic zones tends to migrate from south to north, both along the Dinaric and Apennines belt. Such migration mostly develops during major sequences, each lasting about 200 years, during which seismicity progressively migrates from western Greece to the northernmost Dinarides and more or less simultaneously from Calabria to the eastern Alps. The last, still ongoing, sequence (started around the 1930) has so far involved the southern and central Apennines and the adjacent sector of the northern Apennines. In the southern Apennines, ����� ����� ����������� ���� �������� ����� ��� ����� ���������� ������ �� ��� �� three major earthquakes have occurred along the inner decoupling border of the MS wedge (1930 M=6.6, 1962 M=6.1 and 1980 M=6.9). In the framework of the tectonic context shown in Fig. 1, such events have enhanced shear stress in the central Apennines, causing a displacement of the MS wedge for several tens of centimeters. This has favoured the occurrence of major shocks along the outer compressional border of the Gran Sasso Arc (Maiella 1933, M=6.0, 5.1; Laga units 1943, M=5.8; Gran Sasso 1950, M=5.1, 5.7). This seismicity implies a GNGTS 2014 S essione 1.2 183