A signifi cant uncertainty exists in the defi - nition of both surface pattern and subsurface continuity (i.e., coupling vs. decoupling) of active normal faults in the Apennines. In this study, we investigated the epicentral area of the MS = 6.9, 1980 Irpinia earthquake— one of the most destructive historical earthquakes in Italy—based on detailed topography analyses, morphostratigraphic and structural data, and new age constraints from Quaternary deposits. The active tectonic behavior of the study area is controlled by a series of subparallel, mainly WNW-ESE– to NW-SE–trending, dominantly extensional faults spanning over the southern Apennines axial belt. A large part of the active fault strands is characterized by a subdued topographic expression, as a result of the young age of extensional faulting initiation, and of relatively low mean slip rates. In addition, as already known from long historical seismicity records elsewhere, long-lasting quiescence might alternate with clusters of closely spaced, strong earthquakes. The long-term morphostratigraphic record confi rms that long-lasting quiescence may punctuate fault activity, with major implications for seismic hazard assessment. The relatively smallsized cumulative fault throws estimated by surface evidence contrast with subsurface information provided by crustal-scale cross sections and seismological evidence, which both suggest the occurrence at depth of largedisplacement, mature fault zones capable of nucleating large earthquakes. Furthermore, although the surface distribution of active fault strands overlaps the belt affected by present-day low-magnitude seismicity and by large historical earthquakes, a mismatch in the attitude and kinematics of shallow versus deep faults is unraveled by a comparison of surface geological versus seismological data sets. This feature suggests a decoupling between surface and deep fault zones, and that outcropping fault planes cannot always be straightforwardly traced down to hypocentral depths, particularly in fold-andthrust belts characterized by strong rheological contrasts. On the other hand, stress inversion from outcropping active faults and from earthquake focal mechanisms indicates a general consistency of the stress fi eld, thus suggesting that a homogeneous late Quaternary extensional regime produces complex reactivation of the inherited, articulated fault network affecting different structural levels of the southern Apennine

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In the southern Apennines, low-temperature thermochronometry data indicate that exhumation of previous tectonically buried sedimentary units started at around 10 Ma and took place mostly during the last 6 Ma. Relatively high exhumation rates are obtained from apatite fission track (AFT) and (U-Th)/He (AHe) analysis, pointing to a substantial contribution of tectonic processes to rock exhumation besides erosion. Exhumation rates derived from new apatite (U-Th)/He data (AHe) for the last 3 Ma are generally lower than rates determined by AFT data and almost in line with erosion rates inferred from cosmogenic nuclides and sediment yield, thus suggesting that tectonic exhumation was dominant during the older exhumation stages of this region. However, younger cooling ages in the Monte Alpi area from both AFT and AHe analyses point out focused exhumation during the last 3 Ma. Structural and morphotectonic analyses indicate that fast exhumation occurred specifically in this area-where the Apulian Platform reservoir carbonates, elsewhere buried beneath a several kilometer-thick allochthonous cover, are exposed at the surface-as a result of a complex interplay between steep-rooted reverse faulting and shallow low-angle extension. This deformation involved the development of foreland-dipping low-angle normal faults affecting the allochthonous cover units during the late stages of reverse fault-related anticlinal growth in the underlying buried carbonates. Extension of the region triggered focused exhumation in the footwall of the extensional low-angle faults, which was followed by widespread crustal extension and associated development of high-angle normal faults, leading to surface uplift of Monte Alpi.

The present study focuses on the morphotectonic evolution of the axial portion of the Southern Apennine chain between the lower Calore River valley and the northern Camposauro mountain front (Campania Region). A multidisciplinary approach was used, including geomorphological, field‐geology, stratigraphical, morphotectonic, structural, 40Ar/39Ar and tephrostratigraphical data. Results indicate that, from the Lower Pleistocene onwards, this sector of the chain was affected by extensional tectonics responsible for the onset of the sedimentation of Quaternary fluvial, alluvial fan and slope deposits. Fault systems are mainly composed of NW‐SE, NE–SW and W‐E trending strike‐slip and normal faults, associated to NW‐SE and NE–SW oriented extensions. Fault scarps, stratigraphical and structural data and morphotectonic indicators suggest that these faults affected the wide piedmont area of the northern Camposauro mountain front in the Lower Pleistocene–Upper Pleistocene time span. Faults affected both the oldest Quaternary slope deposits (Laiano Synthem, Lower Pleistocene) and the overlying alluvial fan system deposits constrained between the late Middle Pleistocene and the Holocene. The latter are geomorphologically and chrono‐stratigraphically grouped into four generations, I generation: late Middle Pleistocene–early Upper Pleistocene, with tephra layers 40Ar/39Ar dated to 158±6 and 113±7 ka; II generation: Upper Pleistocene, with tephra layers correlated with the Campanian Ignimbrite (39 ka) and with the slightly older Campi Flegrei activity (40Ar/39Ar age 48±7 ka); III generation: late Upper Pleistocene–Lower Holocene, with tephra layers correlated with the Neapolitan Yellow Tuff (~15 ka); IV generation: Holocene in age. The evolution of the first three generations was controlled by Middle Pleistocene extensional tectonics, while Holocene fans do not show evidence of tectonic activity. Nevertheless, considering the moderate to high magnitude historical seismicity of the study area, we cannot rule out that some of the recognized faults may still be active. Copyright © 2018 John Wiley & Sons, Ltd.

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Normalized steepness index (Ksn) of the Aterno drainage network Quaternary continental deposits thickness from geophysical dataScheme of surface and subsurface geological and geophysical data