Active extension in Val d'Agri area, Southern Apennines, Italy: implications for the geometry of the seismogenic belt

Abstract

S U M M A R YIntegration of geologic, geomorphologic and seismologic data sets is used to reconstruct the recent tectonic evolution and active deformation pattern in the Val d'Agri area, located in the seismically active axial sector of the Southern Apennines (Italy).The western portion of the Apennines thrust belt has been affected by Pliocene-Quaternary extension during easterly roll-back and crustal delamination of the Adriatic slab. The bulk of Quaternary extension has been accommodated by SW-dipping oblique and normal faults, which have attained mature morphologic and structural features and, nowadays, separate mountain ranges from intermontane basins.However, in the present seismogenic belt, coseismic faulting locally occurs on NE-dipping structures, which might cut the inherited Pleistocene landscape.In the Val d'Agri basin, in spite of the large Early-Middle Pleistocene, displacement occurred on SW-dipping faults bordering its eastern flank, our investigations show that the recent basin evolution has been controlled by a NE-dipping fault system (Monti della Maddalena fault system, MMFS). This fault system cuts across the Monti della Maddalena range, west of the Agri valley and has not yet created an evident tectonic landscape.Notwithstanding, fault motion since the Middle Pleistocene might explain geomorphologic and hydrographic anomalies of the Agri river and its valley, where fault-controlled subsidence has captured the river course and produced an aggrading plain within a regional uplift context. Recent and ongoing motion is documented by fault scarplets in loose deposits, 14 C ages of palaeosols and the spatial relation with low to moderate instrumental seismicity. Results from fault kinematic analysis are compatible with fault-plane solutions of local and regional seismic events, and indicate ∼NE-SW oriented extension.Recognition of the MMFS as a potential seismogenic fault increases the longitudinal extent of the NE-dipping, morphologically immature seismic sources in the Southern Apennines and argues against the range-bounding fault model for active extension in the region. The regional size of the NE-dipping seismogenic belt may result from impingement of a mantle wedge beneath the Apenninic chain and possibly track the external front of crustal delamination.

Geological and geophysical characterization of the southeastern side of the High Agri Valley (southern Apennines, Italy)

“…2). These scarps are perpendicular to the strike of the streams and they are aligned to the main trend of the EAFS, which was clearly identified between the villages of Pergola to the north and Viggiano to the south (Cello et al, 2003;Maschio et al, 2005). Thus, we suspect that the NW-SE scarps observed in the field could represent the surface expression of an additional strand of the EAFS.…”

“…In addition, the seismic risk is amplified by the presence of two important human activities, namely the exploitation of the largest productive on-shore oil field in West Europe, managed by the Eni company, and the artificial Pertusillo water reservoir (Stabile et al, 2014a, b). The recognition of the Montemurro Fault, which increases longitudinal extent of the EAFS previously mapped by Cello et al (2003) and Maschio et al (2005), may indeed have significant implications for the local seismic hazard. However, our data do not show whether the EAFS is the seismogenic structure of the High Agri Valley, which remains undefined.…”

“…The HAV was hit by the M 7, 1857 Basilicata earthquake. A seismogenic structure capable of producing large events is alternatively associated with: (1) the Monti della Maddalena Fault System (MMFS) (Pantosti and Valensise, 1988;Maschio et al, 2005;Improta et al, 2010) and (2) the Eastern Agri Fault System (EAFS) (Benedetti et al, 1998;Cello et al, 2003;Giano et al, 2000). The MMFS bounds the HAV to the SW and runs for about 25 km between Pergola and Moliterno villages, whereas the EAFS, which is associated with mature fault-line scarps, bounds the HAV to the NE.…”

“…The MMFS bounds the HAV to the SW and runs for about 25 km between Pergola and Moliterno villages, whereas the EAFS, which is associated with mature fault-line scarps, bounds the HAV to the NE. No detailed definition exists on the length of the EAFS that, based on mapped faults between Pergola and Viggiano villages, is about 25 km (Cello et al, 2003;Maschio et al, 2005). The study area falls in the southeastern part of the HAV, in the territory of Montemurro (Fig.…”

Integrated Morphometric Analysis in GIS Environment Applied to Active Tectonic Areas

“…This earthquake has been localized along the narrow topographic culmination of the chain where the historical destructive seismicity, characterized by extensional focal mechanisms, is concentrated together with the active faults of this portion of the Southern Appenines. Different models have been suggested for the 1857 seismogenetic structure, based on: geological and structural surveys (Borraccini et al, 2002;Cello et al, 2003;Giano et al,1997Giano et al, , 2000; geomorphological analysis (Di Niro et al, 1992, Di Niro andGiano, 1995;Giano, 2011); seismotectonic analysis (Benedetti et al, 1998;Burrato & Valensise, 2008;Improta et al, 2010;Maschio et al 2005;Pantosti and Valensise, 1988;Valensise & Pantosti, 2001a), but there are still some open questions. Indeed in this region, contrasting with the events size, several tectonic and geomorphic factors concur to hide the active extensional seismogenetic faults.…”