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Pliocene–Quaternary faults are relevant structures with which to constrain the seismotectonic context and contribute to the evaluation of the seismic hazard of a region. Many of these faults, however, do not show clear surface evidence even when releasing earthquakes. For these reasons they can be extremely dangerous as they receive relatively little attention and can be difficult to identify. From among the various surface geology studies and/or palaeoseismological investigations, we focus our attention on the integration of different datasets such as seismic reflection profiles, surface kinematic data and the relocation of seismological data, which make it possible to identify and characterize active faults whose dimension and earthquake potential would otherwise not be large enough to make them identifiable. We take as an example the Montespertoli NE-trending fault in southern Tuscany (central Italy) with which we associate the 2016 M=3.9 Castelfiorentino earthquake. This structure is part of a wider (in the order of 15–20 km) crustal-scale shear zone, which may be responsible for strong historical earthquakes in the area. [ABSTRACT FROM AUTHOR]

In the Lesina Marina village area, the cropping out gypsum rocks, that rose up from the deep and thick Upper Trias Burano Fm anhydrite layer, have been analyzed to investigate the trigger mechanism for their ascent. In this regard, we focus on the anhydrite-to-gypsum transformation starting from the deep source layer. Indeed, petrographic observations of the widespread corroded anhydrite crystals embedded in these gypsum rocks revealed unequivocal evidences of the anhydrite-to-gypsum transformation. In addition, and referring to gypsum, microstructural features indicate that ductile deformation mechanisms initially operated under higher temperature conditions. This temperature should be close to 107 °C, namely the value of the upper temperature limit of stability of gypsum from Lesina Marina, above which it starts to transform and dehydrate, as revealed by microthermometry heating/dehydration experiments combined with micro-Raman analyses. All these evidences are in favor of the dramatic density decrease and volume increase due to anhydrite-to-gypsum transformation by hydration in the deep source layer; these variations of physical conditions, triggered by hydration, promoted diapirism of the gypsum mass, in other words "hydration diapirism". As revealed by seismic lines interpretation, the diapirism, which gave rise to the Lesina diapir, occurred during Plio-Pleistocene and was genetically related to the Lesina graben-type structure. Hydration at depth was favored by the downward circulation of water-rich fluids channeled in faults, and the gypsum mass used the weakened zone of the southern fault to pierce the overlying Mesozoic and Tertiary sediments. [ABSTRACT FROM AUTHOR]

Abstract: We present new high-resolution swath bathymetric data and multichannel seismic profiles acquired in the Pantelleria graben, one of the three main tectonic depressions forming the Sicily Channel Rift Zone. This region experienced a Late Miocene–Early Pliocene continental extension with the development of NW-trending, fault-bounded troughs, later accompanied by widespread volcanic manifestations. Data support the interpretation that the Pantelleria graben evolution was dominated by two tectonic phases: A lithospheric-scale continental rifting (Early Pliocene), in which the whole graben was formed, and a successive phase (Late Pliocene–Pleistocene) characterized by a magma-assisted extensional mechanism. Ascending magmas within the graben floor seem to migrate from the S–E sector of the depression toward the N–W sector, which is almost entirely floored by igneous material, and where the volcanic edifice of the Pantelleria Island is emerged. The volcanic activity is presently concentrated north of the Pantelleria Island. The tectonic evolution of the Pantelleria graben, characterized by the chronological sequence of events: rifting-doming-volcanism, can be referred to as a ‘passive’ rifting model. Crustal stretching, and subsequent fault development and rifting within the Pelagian block, may have been controlled by slab-pull forces of the northward-subducting African slab. [Copyright &y& Elsevier]

Abstract: The 1997–98 Umbria–Marche earthquake provided a huge amount of good quality seismological data. The geology of the region has been extensively mapped for over a century by geologists from all over the world. The subsurface geology is constrained by a set of seismic reflection profiles and deep boreholes, acquired for oil exploration. The earthquake stimulated the acquisition of many other geological and geophysical data-sets (surface ruptures, structural analysis, geodetic data, geoeletrical data, etc.). As a consequence, the 1997–98 earthquake is one of the best case studies in the world for extensional earthquakes, driving the possibility of building up an integrated model of an extensional system. We use this favourable test-site to discuss the possibility of integrating and connecting the “seismological” faults (i.e. the short term, instantaneous ruptures generated during the earthquakes, representing the effect of a single event) and the “geological faults” (i.e. the long-term, active faults, exposed at the surface, that are the effects of multiple repeated events of faulting). The review of this complex data-set points to an integrated model, where the moderate seismicity of the region is driven by SW-dipping normal faults, whose dip changes with depth, from 60°–70° (the fault surfaces mapped at the surface), to 35°–45° (the fault segments ruptured during the earthquake, at depths of 2–8 km), to less than 20° at depth >8 km. These normal faults are not inherited from previous tectonic events. However, the pre-existing arc-shaped compressional structures act as barriers segmenting the extensional fault system. The depth and thickness of the seismogenic layer is lithologically controlled, since the seismicity is confined within the sedimentary cover and do not penetrate the underlying basement. The mainshocks are located close to the bottom of the seismogenic layer, within the Triassic evaporites. [Copyright &y& Elsevier]

A geophysical survey provides new information on marine features located seaward of Locri-Epizefiri (Locri), an ancient Greek settlement on the Ionian coastal margin in southern Italy. The study supplements previous work by archaeologists who long searched for the site's harbor and recently identified what was once a marine basin that is now on land next to the city walls of Locri. Profiles obtained offshore, between the present coast and outer shelf, made with a high-resolution, seismic subbottom-profiling system, record spatial and temporal variations of buried Holocene deposits. Two of these submerged features are part of a probable now-submerged ship landing facility. The offshore features can be linked to coastline displacements that occurred off Locri: a sea-to-land shift before Greek settlement, followed by a shoreline reversal from the archaeological site back to sea, and more recently, a return landward. The seaward directed coastal shift that occurred after Locri's occupation by Greeks was likely caused by land uplift near the coastal margin and tectonic seaward shift of the coast, as documented along this geologically active sector of the Calabrian Arc. The seismic survey records an angular, hook-shaped, low rise that extends from the present shore and is now buried on the inner shelf. The rise, enclosing a core lens of poorly stratified to transparent acoustic layers, bounds a broad, low-elevation zone positioned immediately seaward of the shoreline. Close proximity of the raised feature to the lowelevation area suggests it may have been a fabricated structure that functioned as a wave-break for a ship-landing site. The study indicates that the basin extended offshore as a function of the coastline's seaward migration during and/or after Greek occupation of Locri. [ABSTRACT FROM AUTHOR]

Normal faults within orogenic belts can be pre-, syn- or post-orogenic features. We studied the Gubbio normal fault (central Italy), which is an example of a pre-orogenic fault reactivated in a post-orogenic stage. The Gubbio Fault is a 22-km-long fault bordering a Quaternary basin and part of an active faults system in the Umbria–Marche region (Central Italy). The interpretation of a set of seismic profiles enables us to reconstruct the fault geometry in detail and to measure displacement and throw distributions along the fault strike. Seismic data indicate that the Gubbio Fault represents an example of multiple reactivation: at least a portion of the fault was active in the Miocene and only a part of the total displacement was achieved in the Quaternary. The reconstruction of the fault geometry at depth shows that the fault is characterised by listric geometry. The fault is also characterised by a bend along strike and structure contours show that this geometry is maintained at depth. As the fault is commonly addressed as presently active, the maximum fault dimensions are correlated to the maximum expected earthquake, and the presence of the fault bend is discussed as a possible barrier to seismic ruptures propagation. [Copyright &y& Elsevier]

In this paper, we investigate the upper crustal structure of the Irpinia region, Southern Apennines thrust belt, Italy, through analysis and joint interpretation of gravity data, seismic reflection lines and subsurface information from many deep wells. The investigated region includes the epicentral area of the 1980 (Ms=6.9) Irpinia earthquake and is one of the Italian regions with the highest seismic hazard. The upper crustal structure is imaged by modeling a series of 15 SW-trending gravity profiles, spaced about 5 km apart, plentifully constrained by seismic reflection lines and wells, thus reducing the inherent ambiguity of the gravity modeling. Despite of the complexity of the modeled Bouguer anomalies, the application of a calibrating procedure to constrain the range of variability of the density values, as well as the use of geometric constraints, results in a good level of stability in the final density cross-sections, which in fact appear coherent both in the density values and in the geometrical features. The inferred model shows important lateral density variations that can be mostly related to NW-trending geologic structures. High-density bodies delineate carbonate platform thrust sheets and broad antiforms involving Mesozoic basinal rocks, while low-density shallow bodies are associated with Pliocene basins. In addition, important density (i.e. lithological) variations are evident along the strike of the range, the most relevant being an abrupt deepening of the Apulia Carbonate Platform in the southeastern part of the investigated region. In the epicentral region of the 1980 event, we find that the geometry of the high-density, high-velocity carbonates of the Apulia Platform appears correlated with the distribution of the aftershocks and with the P-wave velocity anomaly pattern as inferred from a previous local earthquake tomography. The structural highs of the Apulia Platform correspond to high-velocity regions, where aftershocks and coseismic slip of the mainshock are concentrated. This correlation suggests that the Apulia Carbonate Platform geometry played an important role in the rupture propagation and in the aftershock distribution. [Copyright &y& Elsevier]

In the Northern Apennines, the upper crust is thinned by a set of east-dipping low-angle normal faults (LANFs): the easternmost and more recent of these LANFs is the Altotiberina Fault (ATF) located in Northern Umbria. The geometry of the ATF has been reconstructed matching surface geology with seismic reflection profiles and borehole data. The fault, whose average dip is ∼20°, borders the Upper Pliocene–Quaternary Tiber basin and has a displacement of about 8 km. The deeper portion of the ATF is located below the axial zone of the Northern Apennines where the strongest instrumental and historical seismicity is recorded; the microseismicity of the region (M<3.0), located between 4 and 14 km in depth, shows a fairly good correlation with the trajectory of the ATF. We apply frictional reactivation theory, under vertical trajectories of σ1, to evaluate the boundary conditions for the brittle activity of the ATF. The fault can be reactivated for low values of differential stress (σ1−σ3<28 MPa), relatively high values of tensile strength of the fault surrounding rocks (T∼10 MPa), and tensile fluid overpressure Pf>σ3 (e.g. λv>0.93). In the peculiar situation of the Northern Apennines, the deep emissions of large amounts of CO2 documented in the area can be entrapped in their ascent by structural seals (e.g. ATF) favouring localised fluid overpressures. The impossibility of sustaining Pf>σ3 for wide fault portions, counteracted by hydraulic fracturing, increased permeability under low effective stress and load weakening behaviour for normal faulting, would prevent the nucleation of moderate ruptures along the fault. The short-lived attainment of Pf>σ3 along small fault portions can account for the microseismic activity located along the ATF, which occurs on rupture surfaces in the range of 10−1–10−3 km2. [Copyright &y& Elsevier]

The Fucino Basin was the greatest lake of the central Italy, which was completely drained at the end of 19th century. The basin is an intramontane half-graben filled by Plio–Quaternary alluvial and lacustrine deposits located in the central part of the Apennines chain, which was formed in Upper Pliocene and in Quaternary time by the extensional tectonic activity.The analysis of the geological surface data allows the definition of several stratigraphic units grouped in Lower Units and Upper Units. The Lower Units (Upper Pliocene) are exposed along the northern and north-eastern basin margins. They consist of open to marginal lacustrine deposits, breccia deposits and fluvial deposits. The Upper Units (Lower Pliocene–Holocene) consist of interbedded marginal lacustrine deposits and fluvial deposits; thick coarse-grained fan-delta deposits are interfingered at the foot of the main relief with fluvial–lacustrine deposits. Most of the thickness of the lacustrine sequences (more than 1000-m thick) is buried below the central part of the Fucino Plain. The basin is bounded by E–W, WSW–ENE and NW–SE fault systems: Velino–Magnola Fault (E–W) and Tremonti–Celano–Aielli Fault (WSW–ENE) and S. Potito–Celano Fault (NW–SE) in the north; the Trasacco Fault, the Pescina–Celano Fault and the Serrone Fault (NW–SE) in the south-east. The geometry and kinematic indicators of these faults indicate normal or oblique movements. The study of industrial seismic profiles across the Fucino Basin gives a clear picture of the subsurface basin geometry; the basin shows triangular-shaped basin-fill geometry, with the maximum deposits thickness toward the main east boundary fault zones that dip south-westward (Serrone Fault, Trasacco Fault, Pescina–Celano Fault).On the basis of geological surface data, borehole stratigraphy and seismic data analysis, it is possible to recognize and to correlate sedimentary and seismic facies. The bottom of the basin is well recognized in the seismic lines available from the good and continuous signals of the top of Meso–Cenozoic carbonate rocks. The shape of sedimentary bodies indicates that the filling of the basin was mainly controlled by normal slip along the NW–SE boundary faults. In fact, the continental deposits are frequently in on-lap contact over the carbonate substratum; several disconformable contacts occurred during the sedimentary evolution of the basin. The main faults (with antithetic and synthetic fault planes) displace the whole sedimentary sequence up to the surface indicating a recent faults'' activity (1915 Avezzano earthquake, Ms=7.0).The stratigraphic and tectonic setting of the Fucino Basin and neighboring areas indicates that the extensional tectonic events have had an important role in driving the structural-sedimentary evolution of the Plio–Quaternary deposits.The geometry of the depositional bodies, of the fault planes and their relationships indicate that the Fucino Basin was formed as a half-graben type structure during Plio–Quaternary extensional events. Some internal complexities are probably related to the fold-and-thrust structures of the Apenninic orogeny formed in Messinian time, in this area, and to a different activity timing of the E–W and WSW–ENE fault systems and the NW–SE fault systems.We believe, based on the similarity of the surface characteristics, that the structural setting of the Fucino Basin can be extrapolated to the other great intramontane basins in Central Italy (e.g. Rieti, L''Aquila, Sulmona, Sora, Isernia basins). [Copyright &y& Elsevier]