Apennines Italy Research Articles

Long-term morpho-structural development of major normal fault zones, Gran Sasso area, Central Apennines (Italy)

Although the Central Apennines of Italy are frequently struck by earthquakes related to normal faulting, so far, no detailed regional study into long-term development and mode of normal faulting exists. In this study, we focus on the Assergi fault zone (AFZ) and the Campo Imperatore fault zone (CIFZ) in the Gran Sasso area.Both fault zones are S-dipping and ~ 20 km in length. Range front faults with ~1 km of footwall topography are associated with basins in the hanging wall. To create footwall relief, long-term throw rates of >0.6 mm/a are required. We compared geologic throw with morphologic markers, such as range and triangular facet height, drainage basin size, spacing between drainage basin outlets, and surface offsets. The morphologic analysis allows to distinguish fault sectors that share morphological characteristics but typically include several mapped fault segments. The history of faulting of the CIFZ indicates that normal fault segments first acquire offset at a constant length until reaching a threshold, and then link with neighbouring fault segments into longer fault zones.Our study of the fault zones suggests the following general concept for long-term development of range-front fault morphology and associated slopes: (1) Surface offset by active faulting is followed, or accompanied, by incision of numerous small alluvial-fan catchments with narrow outlet spacing into the fault footwall. (2) Upon further fault growth, large triangular facets separated by gullies develop. By headward and lateral erosion the small fan catchments merge into fewer and larger catchments with larger outlet spacing. (3) During fault dormance, fault scarps degrade to lower-dipping slopes typically veneered by scree. On these slopes, scarps excavated by differential erosion expose Riedel shears of the main faults.

Along-strike variation of fault-related inversion folds within curved thrust systems: The case of the Central-Northern Apennines of Italy

The along-strike variation of fault-related inversion folds within curved thrust systems is documented by presenting cases from the Central-Northern Apennines of Italy. Fold structures are reconstructed by integrating geological field data and structural restoration of various key balanced cross-sections, which are also constrained by the detailed interpretation of panoramic views, geological field mapping, and structural analysis. The lateral variation from fault-bend to fault-propagation folding is promoted by selective reverse reactivation of precursor, mainly rift-related, normal faults preferentially located along the oblique and frontal ramps. Their space variability is identified within single curved thrust systems of three different size testifying a scale-invariant phenomenon. Fault-bend reactivation and fault-propagation shortcut folding produce a characteristic fold interference pattern at the salient apex of the curved thrust system. The transition style depends on the pattern of the inherited normal fault template and on the amount of shortening achieved in the salient zone. The modest amount of shortening resulting from fault-related inversion folding along regional curved thrust systems is consistent with a basement-involved thick-skinned thrusting style. Recognition of fault-related inversion fold styles and of their along-strike variations represents a useful predictive tool when unravelling the kinematic evolution of curved orogenic belts resulting from positive inversion. Inversion fold development modes and their diagnostic features are also important for investigations of subsurface Earth resources.

Assessing active and capable faulting as best practice for post-earthquake reconstruction activities: the Sant’Eutizio Abbey case study, in the epicentral area of the 2016 central Italy seismic sequence

Surface faulting is, together with strong ground shaking, a hazard associated with major earthquake faults. Assessing surface faulting potential of a given active tectonic structure is a fundamental prerequisite to adequately plan the use of territories and to perform new constructions, in order to act practices aimed to mitigate the associated risk. Assessing the surface faulting potential represents also ground for correctly performing re-construction and retrofitting of buildings and infrastructures during post-earthquake activities. We investigated a branch of a major seismogenic normal fault in the central Apennines of Italy, the Campi-Preci fault, along which the monumental Sant’Eutizio Abbey is located. The medieval Abbey is one of the most important cultural/religious edifices of the central Apennines, heavily damaged by the MW 6.5 October 30, 2016, earthquake, focused a few km to the south. Our study, based on field geological, geomorphological and structural survey and trenching investigations revealed that I) the trace of the Campi-Preci active fault branch is not actually located where presently reported in the available literature, II) the supposed morpho-tectonic features (basically, some km-long scarp carved on the Meso-Cenozoic carbonate bedrock), that suggested the presence of the fault segment in the area of the Sant’Eutizio Abbey, are not related to the active fault but are probably associated to a presently inactive reverse fault and III) the Sant’Eutizio Abbey is likely not potentially affected by primary surface faulting. Our work highlights that only a comprehensive multidisciplinary approach allows to correctly assess surface faulting potential in both seismotectonic and engineering perspectives.

Late Quaternary faulting in the southern Matese (Italy): implications for earthquake potential and slip rate variability in the southern Apennines

Abstract. We studied the Gioia Sannitica active normal fault (GF) along the southern Matese fault (SMF) system in the southern Apennines of Italy in detail. The current activity of the fault system and its potential to produce strong earthquakes have been underestimated so far and are now defined here. Precise mapping of the GF fault trace on a 1:20 000 geological map and point and line data on the geometry, kinematics, and slip rate of the faults forming the SMF system are made available in electronic format. The GF, and the entire fault system along the southern Matese mountain front in general, is made of slowly slipping faults with a long active history revealed by the large geologic offsets, mature geomorphology, and complex fault patterns and kinematics. Present activity has resulted in late Quaternary fault scarps resurrecting the foot of the mountain front and Holocene surface faulting. The resurrected mountain front indicates variation in slip rate through time. The slip rate varies along-strike, with a maximum Upper Pleistocene–Holocene slip rate of ∼ 0.5 mm yr−1. Activation of the 11.5 km long GF can produce up to M 6.2 earthquakes. If activated together with the 18.5 km long Ailano–Piedimonte Matese fault (APMF), the seismogenic potential would be M 6.8. The slip history of the two faults is compatible with a contemporaneous rupture. The observed Holocene displacements on the GF and APMF are compatible with activations during some poorly constrained historical earthquakes, such as the 1293 (M 5.8), 1349 (M 6.8; possibly a southern prolongation of the rupture on the Aquae Iuliae fault), and 346 CE earthquakes. A fault rupture during the poorly constrained 847 CE earthquake is also chronologically compatible with the dated displacements.

A Preliminary Assessment of Young Water Fractions in Groundwater from Alluvial Aquifers Facing the Northern Italian Apennines

This study sums up the first estimates of the young water fraction (Fyw; here understood as the percentage proportion of groundwater passing through the well’s screen and younger than approximately 2–3 months) from groundwater collected in 75 wells from alluvial fans facing the northern Italian Apennines of Italy. The Fyw estimates were based on a monthly dataset of water-stable isotopes (oxygen-18 (18O)) from surficial water (9 rivers), while the dataset of groundwater (75 wells) consisted of three-monthly isotopic data. In the cases of surficial water and stable isotopes, these lasted over the period of January 2003 to December 2007, while in the case of groundwater, the data were collected from January 2005 to December 2007. The values of Fyw were estimated by means of a sine-wave fitting technique; the results made evident the presence of unexpectedly reduced differences between groundwater. In particular, shallower groundwater hosted in aquifers from the apical parts of the alluvial fans (i.e., aquifers characterized by the coarsest materials such as gravels and sands, and closest to the recharge areas) showed similar values of Fyw to the deepest aquifers from the distal parts; however, former studies mentioned here evidenced the existence of poorly recharged old groundwater. Our results seem to confirm a complex behavior of these aquifers compared with what had previously been thought.

The influence of slope gradient and gully channel on the run-out behavior of rockslide-debris flow: an analysis on the Verghereto landslide in Italy

Rockslide-debris flow may cause catastrophic damages because of its high speed and long run-out distance. The influences of slope gradient and gully channel on the entrainment, deposition, and run-out behavior of this type of landslide were not sufficiently investigated by previous studies. To achieve a better understanding toward this type of landslide, a recent rockslide-debris flow that occurred in the Northern Apennines of Italy is studied through field investigation and numerical simulation. The run-out process of this landslide is simulated by an improved depth-averaged model, paying special attention to analyzing the influence of slope gradient and gully channel. The simulation results are compared with the detailed field data of entrainment and deposition distributions. It shows that the depth-averaged model can reasonably simulate the entrainment and deposition characteristic of this landslide by adopting different basal friction strengths for the rockslide region and debris flow region. Entrainment occurs in both high and low slope gradient zones. However, entrainment can only be observed in the high slope gradient zones, while in the low gradient zones, the post-failure topography shows accumulation and deposition. The simulation results also demonstrate that the presence of a gully channel is a key factor in determining landslide mobility and run-out distance. In comparison to a landslide with similar size and geological settings but without a gully channel, the run-out distance is much less, and the landslide does not develop into a flow.

Deriving Vp Velocity and Density Properties of Complex Litho-Structural Units from the Analysis of Geophysical Log Data: A Study from the Southern Apennines of Italy

Deriving Vp Velocity and Density Properties of Complex Litho-Structural Units from the Analysis of Geophysical Log Data: A Study from the Southern Apennines of Italy

Constraining the slip rate of Jurassic rift faults through the drowning history of a carbonate platform

Abstract“Classic” field mapping in sedimentary successions, where lithostratigraphy, biostratigraphy and sedimentology meet, still has potential for producing answers to long‐standing problems in basin analysis. In the Northern Apennines of Italy, constraints on the slip rates of Early Jurassic rift faults, related to the embryonic separation of Eurasia and Gondwana, are provided by sedimentology and ammonite biostratigraphy, coupled with the field mapping of exposed tracts of the submarine escarpments and of the clinoform slopes which bordered carbonate footwall blocks. Slip rates of 600–1,000 m/Myr are here computed for Tethyan rift faults, producing >1 km of palaeostructural relief in ~2 million years (earliest Sinemurian: Bucklandi p.p. – Semicostatum p.p. zones).

Field measurements, laboratory tests and empirical relations for investigating the solid-to-fluid transition of a rapid earthflow

Earthflows are widespread phenomena in the Mediterranean area. These landslides involve fine-grained soils and clay-bearing rocks, and despite their low speed are responsible for significant economic losses in vast areas. The dynamics of these landslides is still relatively obscure thus reducing our ability to forecast and mitigate their effects. In this study, we present a methodological approach for the characterization of active earthflows based on the combination of geophysical surveys, laboratory tests, and empirical formulas. Geophysical surveys consist of periodic measurements of Rayleigh wave velocities repeated over time to evaluate the change of stiffness with time of the landslide material. Laboratory tests combine Atterberg limits, fall cone and oedometric tests and allow to constrain the empirical correlations between geophysical and geotechnical properties. The method is designed to obtain relevant data when direct methods like boreholes or geotechnical soundings are not possible for safety reasons, with the aim of investigating the solid-to-fluid transition that can occur in rapid earthflows. We applied this approach to study the Montevecchio landslide (Northern Apennines of Italy), an active earthflow in young marine clays which was affected by multiple reactivations in the recent years. Results show that after a surge the earthflow material is very soft (shear wave velocity in the order of 50–60 m/s) and characterized by a high water content. However, the exact value of the Liquidity Index remains unknown due to the lack of direct measurements and to the uncertainty dictated by the empirical relationships.

Volatile Composition Variability of Arnica montana Wild Populations of Trentino-Alto Adige, Italy, Determined by Headspace-Solid Phase Microextraction.

Arnica montana is a plant distributed in most of Europe, including the Alpine arc and Apennines in Italy, and traditionally used worldwide for medicinal properties. Twelve natural populations of the species from Trentino-Alto Adige, Italy, were characterized using Headspace-Solid Phase Microextraction analysis for their volatile profile. Fifty-one compounds were detected in flower heads, the most abundant being (E)-Caryophyllene (23.4 %), 2,2,4,6,6-Pentamethylheptane (8.3 %), α- trans-Bergamotene (7.2 %), Germacrene D (5.7 %), and Hexanal (5.3 %). A multivariate analysis performed on the ten most abundant compounds grouped these investigated accessions into five main clusters. Three clusters, comprising together five accessions, were linked to the geographical origin of two collection sites. This work is a complete characterization of volatiles of the species by SPME analysis reported to date. Furthermore, results suggest that the species' volatile profile can be linked to the geographical origin of the natural populations and, therefore, represent a tool for evaluating biodiversity within the species.

Transition from slab roll-back to slab break-off in the central Apennines, Italy: Constraints from the stratigraphic and thermochronologic record

ABSTRACTStratigraphic and thermochronologic data are used to study the processes that shaped the topography of the central Apennines of Italy. These are part of a major, active mountain belt in the center of the Mediterranean area, where several subduction zones control a complex topography. The Apennines were shaped by contraction at the front of the accretionary wedge overlying the subducting Adria microplate followed by extension at the wedge rear in response to eastward slab roll-back. In the central Apennines, intermontane extensional basins on the western flank rise eastward toward the summit. We contribute with new data consisting of 28 (U-Th-Sm)/He and 10 fission track ages on apatites to resolve a complex pattern of thermal histories in time and space, which we interpret as reflecting the transitional state of the orogen, undergoing a two-phase evolution related to initial slab retreat, followed by slab detachment. Along the Tyrrhenian coast, we document cooling from depths ≥3–4 km occurring between 8 and 5 Ma and related to the opening of marine extensional basins. Post–5 Ma, a broader region of the central Apennines exhibits cooling from variable depths, between <2 km in most areas and ≥3–4 km in the northeast, and with different onset times: at ca. 4 Ma in the west, at ca. 2.5 Ma in the center and northeast, and at ca. 1 Ma in the southeast. Between 5 and 2.5 Ma, exhumation is associated with modest topographic growth during the late stages of thrusting. Since 2.5 Ma, exhumation has concurred with the opening of intermontane basins in the west and in the east, with regional topographic growth and erosion, that we interpret to be associated with the locally detaching slab.

The role of post-orogenic normal faulting in hydrocarbon migration in fold-and-thrust belts: Insights from the central Apennines, Italy

The reconstruction of the hydrocarbon migration and entrapment history is fundamental for reducing risks and identifying traps and migration pathways during oil exploration and exploitation in fold-and-thrust belts, which host 14% of the world's discovered oil reserves. Within fold-and thrust belts, faults and folds have fundamental roles in controlling hydrocarbon migration, entrapment, and/or leakage. Past studies have mainly focused on the role of syn-orogenic thrusts, tear faults, and folds in controlling hydrocarbon migration and entrapment. On the contrary, little attention has been dedicated to the role of normal faults in hydrocarbon remobilization during the post-orogenic extension. We combine field and subsurface data with geological evidence from the Ripi oil field, central Apennines (Italy), and propose a conceptual model for hydrocarbon remobilization along post-orogenic normal faults and potential entrapment within shallow reservoirs. Results show that post-orogenic normal faults promoted up-dip hydrocarbon remobilization from oil traps generated during fold-and-thrust belt development. Where pre-orogenic deposits are still covered by syn-orogenic deposits, hydrocarbons moved up-dip along post-orogenic normal faults and impregnated high-porosity sandstone lenses, generating discontinuous and heavy oil reservoirs. On the contrary, where syn-orogenic deposits were eroded in response to orogenic uplift, hydrocarbons leaked at the Earth's surface. Results from this study can be applied to reduce risks during hydrocarbon exploration and appraisal in similar tectonic settings, such as Hellenides and Carpathian fold-and-thrust belts, as well as the southern Apennines of Italy, where the Tempa Rossa and Monte Alpi oil fields, two of the largest onshore oil fields in Western Europe, were discovered in the last decades.

Probabilistic fault displacement hazard analysis of the Anghiari - Città di Castello normal fault (Italy)

Fault displacement is a localized source of hazard for infrastructure located near active and capable faults, such as critical buildings and distributed facilities. This issue can be overcome through zoning and avoidance strategies, but facilities may sometimes not benefit from this option. In the last 20 years, several authors have developed a probabilistic approach to analyse this hazard, known as probabilistic fault displacement hazard analysis (PFDHA), for both principal fault and distributed rupturing. In this work, we apply the approach proposed by YOUNGS et alii (2003) to the Anghiari-Città di Castello fault, a NE-dipping normal fault located in the northern Apennines of Italy, which shows evidence of Quaternary activity. We explore two different rupturing scenarios to obtain displacement hazard curves and maps for different probabilities of exceedance in 200 years at different distances along and from the principal fault trace for both the principal and distributed rupturing. The expected displacement values for the principal fault rupturing are up to 130 cm for a return period of 10,000 years (2% in 200 years), and the distributed rupturing hazard is 3–4% of the principal fault rupturing hazard. It is null in the footwall of the fault and slightly variable in its hanging wall as a function of distance from the fault trace and fault tip. The variability of the distributed rupturing hazard within the first hundreds of metres from the principal fault can assist to define mitigation strategies for existing facilities located in proximity of the fault.

Assessing Forest Structural and Topographic Effects on Habitat Productivity for the Endangered Apennine Brown Bear

Any forest management potentially affects the availability and quality of resources for forest-dwelling wildlife populations, including endangered species. One such species is the Apennine brown bear, a small and unique population living in the central Apennines of Italy. The conservation of this relict bear population is hampered by the lack of knowledge of the fine-scale relationships between productivity of key foods and forest structure, as this prevents the design and implementation of effective forest management plans. To address this issue, we sampled the main structural stand attributes within the bear’s range and used multivariate generalized linear mixed models in a Bayesian framework to relate forest structural attributes to proxies of productivity of key bear foods. We found that hard mast was positively associated with both forest typology and high forest system, but negatively related to both the time elapsed since the last forest utilization and the amount of deadwood. The availability of soft-mast producing species was positively related to past forestry practices but negatively associated with steep slopes historically managed with high tree densities and a low silvicultural disturbance. Our findings also suggest that herb cover was negatively affected by terrain steepness and basal area, while herb productivity was positively affected by northern and southern exposure. Additionally, richness of forest ants was associated with forests characterized by low volume and high density. Our findings confirm that the productivity of natural bear foods is strongly affected by forest structural and topographical characteristics and are relevant as preliminary information for forest management practices to support the long-term conservation of Apennine bears.

Performance of Fiber Reinforced Mortar coating for irregular stone masonry: Experimental and analytical investigations

Nowadays, the application of Fiber Reinforced Mortar (FRM) is widely used for the consolidation and rehabilitation of masonry structures because represents an effective solution in terms of reversibility and applicability. The paper illustrates the results of cyclic diagonal compression tests performed in situ on stone masonry specimens isolated from the walls of a historic building of L’Aquila (Italy). The tested stone masonry is representative of existing structures of the territories of the central Apennines in Italy. Only two of four panels were strengthened by FRM to provide also the reference value of the unreinforced masonry. The FRM comprised a glass-fiber grid embedded in a natural hydraulic lime (NHL)-based mortar applied as a coating to the masonry surfaces as well as carbon shear connectors. The tests were analyzed to derive the shear strength and the shear modulus of the masonry, as well as their evolution during the tests. Moreover, these tests were compared and integrated with a consistent number of experimental data collected in the current literature aiming to validate a new analytical equation for the estimation of the shear strength of the reinforced masonry, merely based on the properties of the unreinforced masonry and the FRM mortar.

Migration, housing & disaster: Risk reduction and creation in Southern Italy's Apennines

Outgoing migration flows can influence demand, availability, location and quality of housing in the areas from which they originate, through dynamics such as remittance transfer and investment, cultural change, demographic decline and loss of skilled work. These dynamics may have diverse implications on disaster risk, potentially affecting the occurrence or intensity of some hazardous events and determining the levels of exposure and vulnerability of people and assets.This paper retraces the evolution of the housing stock as a product of outmigration in San Mango sul Calore and Cavallerizzo di Cerzeto, two mountain villages in Italy's Southern Apennines, in the decades preceding recent disasters. Over the second half of the 20th century, both municipalities witnessed intense outmigration, contributing to the expansion of their respective settlements' housing stock and the abandonment of traditional land-use patterns and building practices. These processes shaped hazard exposure and disaster vulnerability of different people in each community, producing a diversity of risk reduction and risk creation outcomes.This paper analyses the context-specific migration trajectories and risk outcomes in the two study areas, framing them through the findings of the global literature on migration, development and DRR, to identify theoretical implications and operational approaches relevant to understanding and addressing migration-housing-risk dynamics. Its insights can support risk reduction in places experiencing intense population outflows and related demographic and physical transformations.

Integrated bio- and carbon isotope stratigraphy of the Campanian–Danian sedimentary succession in Lurestan (Zagros Basin, Iran): Implications for syntectonic facies distribution and basin evolution

In order to investigate the depositional history and facies architecture of the Campanian-Danian interval of the Zagros Basin, the succession of the Gurpi Formation (Fm.) was examined in the Gandab section, southwestern Lurestan Province, through an integrated study of calcareous nannofossils, planktic foraminifera, and bulk carbonate carbon isotopes. Despite the persistent occurrence of reworked fine fraction carbonates as attested by microfossils across the investigated interval, the carbon isotope stratigraphy of Lurestan shows a good correlation with those in the eastern and western Tethys from the Shahneshin section in central Zargos (Fars Province) and Gubbio of northern Apennines in Italy (Gubbio). The succession can be assigned an age range from late Campanian to early Danian based on the integrated stratigraphy. The results from the Gandab section, as well as field observations in more northeasterly areas of Lurestan, point to lateral facies variation of the Campanian–Danian interval associated with tectonic activity during the Late Cretaceous-Paleogene of the Zagros Basin. According to the known distribution of facies across the SW-NE transect of Lurestan and detailed ages delineated in the Gandab section, a schematic model of syntectonic sedimentation and facies distribution is drawn. Our model illustrates how the continental convergence and closure of Neo-Tethys resulted in uplifting/subsiding of the basin floor, shifting in depocenter, significant changes in sedimentary facies, and reworking phenomena in the Lurestan region.

Stone Tools in the High Molise Mountains (Italy): a first Report

In the last decades, several researches focused on the inland areas of Molise Region (Central-Southern Italy) to investigate the occupation and exploitation of this environment during Pleistocene and Holocene.
 The “Molise Survey Project” started in 2015 with the aim to explore, through systematic surveys, an area of 60 square kilometres, chiefly characterized by a mountainous landscape and part of the Central-Southern Italy Apennines. The project seeks to investigate the patterns of human occupation in the mountainous landscape between the provinces of Campobasso and Isernia. The surveys, carried out during the last four years, allowed the identification of 19 prehistoric sites ranging from Palaeolithic to Bronze Age: the archaeological materials belonging to the latter period are being studied by the team of “Paletnologia” of Sapienza University of Rome. This work aims to show the preliminary results of the analysis of the lithic assemblage acquired during the summer of 2016 surveys, focusing on raw material procurement and the related chaîne opératoire, also considering post-depositional agents. The obtained data allowed to reassess the human presence over inland and high-altitude areas of Molise during prehistoric times, stressing a seasonal use of the territory, from Palaeolithic to Late Prehistory, with different patterns of occupation and exploitation.

Fold architecture predisposing deep-seated gravitational slope deformations within a flysch sequence in the Northern Apennines (Italy)

This research illustrates the case of a deep-seated gravitational slope deformation (DSGSD) affecting a folded structure that developed during Miocene tectonics in the Northern Apennines of Italy, deforming a heterogeneous turbiditic sequence characterised by pelitic-marly and arenaceous intervals. The investigated area includes the headwater portion of the Bidente River basin that has experienced intensive valley incision during the late Quaternary and the sizeable Poggio Baldi landslide with failure episodes in 1914 and 2010.The aim of this work was to unravel the local morphostructural setting determined by the interplay between the active DSGSD, inherited fold geometry, and fluvial dynamics. Dip data collection and structural analysis were used to reconstruct the fold geometry. A complex type of fault-propagation fold was outlined, with later breakthrough thrusts causing the backlimb rotation. Gravity-driven geomorphological features were inventoried and displayed on two geological cross-sections together with Geological Strength Index measurements, while their distribution was analysed to conceive a conceptual model for the development of the DSGSD. Fold setting and lithological anisotropies were considered as the predisposing factors of the gravitational slope deformation, whereas the multi-step entrenchment of the Bidente River valley, testified by the presence of the remnants of at least three generations of fluvial erosional terraces, was considered as the main cause of its initiation.Finally, the reconstruction of the original slope topography in the Poggio Baldi area and the results of structural analysis performed in the landslide detachment zone through remote sensing techniques allowed for the estimation of the size of the wedge-shaped rock block which detached in 1914, an event that occurred in the wider frame of the DSGSD.

Fault Pattern and Seismotectonic Style of the Campania – Lucania 1980 Earthquake (Mw 6.9, Southern Italy): New Multidisciplinary Constraints

New fault trace mapping and structural survey of the active faults outcropping within the epicentral area of the Campania-Lucania 1980 normal fault earthquake (Mw6.9) are integrated with a revision of pre-existing earthquake data and with an updated interpretation of the CROP-04 near-vertical seismic profile to reconstruct the surface and depth geometry, the kinematics and stress tensor of the seismogenic fault pattern. Three main fault alignments, organized in high-angle en-echelon segments of several kilometers in length, are identified and characterized. The inner and intermediate ones, i.e. Inner Irpinia (InIF) and Irpinia Faults (IF), dip eastward; the outer Antithetic Fault (AFA) dips westward. Both the InIF and the IF strike NW-SE along the northern and central segments and rotate to W-E along the southern segments for at least 16 km. We provide evidence of surface coseismic faulting (up to 1 m) not recognized before along the E-W segments and document coseismic ruptures with maximum vertical displacement up to ∼1 m where already surveyed from other investigators 40 years ago. Fault/slip data from surface data and a new compilation of focal mechanisms (1980 – 2018) were used for strain and stress analyses to show a coherent NNE-directed least principal stress over time and at different crustal depths, with a crustal-scale deviation from the classic SW-NE tensional direction across the Apennines of Italy. The continuation at depth of the outcropping faults is analyzed along the trace of the CROP-04 profile and with available hypocentral distributions. Integrating all information, a 3D seismotectonic model, extrapolated to the base of the seismogenic layer, is built. It outlines a graben-like structure with a southern E-W bend developed at depth shallower than 10–12 km, at the hanging wall of an extensional NE- to E-dipping extensional basal detachment. In our interpretation, such a configuration implies a control in the stress transfer during the 1980 earthquake ruptures and provides a new interpretation of the second sub-event, occurred at 20 s. Our reconstruction suggests that the latter ruptured a hanging wall NNE-dipping splay of the E-W striking main fault segment and possibly also an antithetic SSW-dipping splay, in two in-sequence episodes.