GNGTS 2015 - Atti del 34° Convegno Nazionale

is provided by the numerical modeling of post-seismic relaxation induced by major shocks (Viti et al. , 2012, 2013). The fact that a significant mobility, even though slower with respect to the outer belt, also affects the inner sector of the Apennine belt, is related with the motion of the African plate, transmitted by the Calabrian wedge and southern Apennines (e.g., Viti et al. , 2006; Mantovani et al. , 2009, 2015a, 2015b). �� ����������� ������������� ���������� ��� ���������� In particular, belt-parallel shortening has controlled , since the Late Pliocene , the recent-present evolution of the inner sector of the northern Apennines and may account for seismic activity in the central-western Tuscany (Viti et al. , 2015). In this note, we discuss the recent/present development of the outer and inner sectors of the northern Apennines by adopting the belt-parallel shortening as main driving mechanism (section 2 and 3 respectively). Furthermore, we show that the implications of such interpretation are compatible with the short-term kinematic pattern obtained from space geodetic (GPS) measurements (section 4). Belt-parallel shortening in the outer sector of the northernApennines. As argued earlier, the belt-parallel push of the Molise-Sannio wedge is transmitted to the northern Apennines by the eastern sector of the Lazio-Abruzzi platform (LA). However, major evidence suggests that the sector of LA indenting the northern Apennines has become narrower and narrower over time, as tentatively sketched in Fig. 1 (see Viti et al. , 2015 and references therein). In the late Pliocene ����� ���� �� ����� ������������ ���������� ����� ������ ��� ������ �� (Fig. 1a)� �� ����� ������������ ���������� ����� ������ ��� ������ �� , no major longitudinal decoupling fault system was active in LA, so the push of the southern Apennines was transmitted by a large part of that platform. At that time, the northern Apennines were mainly constituted by a system of almost parallel ridges and basins, formed in the late Miocene and early-middle Pliocene extensional tectonic phases�. In the early-middle Pleistocene (Fig. 1b), the activation of the Latina fault system allowed the mobile LA sector (ELA) to decouple from its inner part and accelerate roughly NNW ward. Since then, the indentation of such wedge caused ������� ������ ��� ��������� ������� outward escape and oroclinal bending of main ridges in the northern Apennines. This effect was particularly intense in the zones lying just north of the indenter (i.e., Olevano-Antrodoco, Sabini Mts. and Narni). ��� ������� The oblique divergence between the outward escaping wedges and the inner more stable structures induced transtensional deformation in the zone presently covered by the Roman volcanic products. The plausibility of this hypothesis is supported by the fact that such kind of strain regime, often accompanied by the generation of pull-apart troughs, produce sub-vertical fractures that represent preferential pathways for melt ascent through the upper crust (e.g., Gundmundsson, 2001; Acocella and Funiciello, 2001). In the upper Pleistocene ����� ���� ������������� ���������� ������ �� ������ ���� ��� (Fig. 1c)� ������������� ���������� ������ �� , belt-parallel decoupling inside LA became more and more efficient in the Val Roveto and Fucino fault systems, while the Latina fault system was less and less active. The new configuration of the ELA indenter caused stronger and stronger bending and outward escape of orogenic material in the outer part of the RMU units, also reaching the northern ridges (Catenaia, Luna, Pratomagno and San Benedetto in Fig. 1c). In some zones, the divergence between adjacent ridges, which were undergoing different lateral bending, caused the generation of transtensional troughs. Such mechanism may have formed the Casentino and Upper Tiber troughs, as effect of oroclinal bending in the Romagna-Umbria Apennines. Similarly, oroclinal bending in the Toscana Apennines ����� ��� ��� ���� ������ (Fig. 1c) ��� ���� ������ may have formed the Firenze-Pistoia and Mugello troughs and accelerated the development of the Lunigiana and Garfagnana basins. The fact that oroclinal bending has not affected the westernmost edge of the belt (Ligurian Apennines), can be explained by the absence of late Triassic evaporites at the base of that sector ������ ��������� ��� �������� ����� ���������� ������ (e.g., Ciarapica and Passeri, 2005; Bosellini, 2004). During the last evolutionary phase (���� ���� ��� ���� ����� ��� ������� ���������� �� �� Fig. 1d), the Gran Sasso Arc started developing as an effect of the belt-parallel push of the northeastern sector of the Molise-Sannio wedge. In the inner side of the Gran Sasso Arc (experiencing a transtensional regime), the L’Aquila fault system developed. ����� ��� ���� ����������� ����� ���� ���������� �� ��� �� �������� ��� ����� ��� ���� ����������� ����� ���� ���������� �� ��� �� Since the late Pleistocene (Fig. 1d), decoupling in the LA platform has continued to develop at the Fucino fault, but the most efficient and frequent seismic decoupling GNGTS 2015 S essione 1.2 135

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