United States

The Northern Apennines are a seismically active accretionary wedge formed in response to the Late Cretaceous-Eocene closure of the Ligurian-Piedmont Ocean and the Oligocene-Miocene collision between Adria and Europe. The wedge is shaped by WNW-ESE-striking, SW-dipping thrusts accommodating bulk top-to-the NE tectonic transport. Since the Late Miocene, thrusting in the belt external domains acted coevally with extension in the western hinterland domain, where crustal thinning is still being accommodated by NW-SE-striking normal faults. The focal mechanism solutions of earthquakes between 8 and 35 km constrain NE-SW shortening in the frontal part of the wedge, whereas extensional tectonics controls the seismicity along the belt’s axial portion and in the hinterland. Atop the deformed accretionary wedge occur the Epiligurian Units, which consist of middle Eocene-upper Miocene bathyal to shallow-water siliciclastic deposits infilling wedge-top basins. A regional unconformity separates pre- and post-Burdigalian sequences within the Epiligurian succession, with sedimentary facies changing from deep marine-to platform environment. Our mesoscale structural analysis shows compressional, extensional, and strike-slip fault arrays affecting extensively all the Epiligurian Units, with distinct structural features. Top-to-the NE, WNW-ESE-striking reverse faults are defined by commonly slickensided planar surfaces decorated by thin damage zones. Top-to-the SE, WSW-ENE-striking reverse faults are, instead, generally devoid of well-developed damage zones. NW-SE and NE-SW-striking normal and oblique faults systematically cut across the reverse faults and accommodate centimetric to metric throws. Common cataclastic and disaggregation deformation bands are associated with NE-SW striking normal faults cutting through Upper Eocene-Lower Oligocene siliciclastic units. On the other hand, calcite veins and fibres locally decorate NW-SE and NE-SW-striking normal and oblique faults in marly post-Burdigalian sequences, attesting to fluid-rock interaction within dilatant rock volumes during faulting. A remote sensing analysis has been performed on tectonic structures mapped at the regional scale and confirms a variable trend distribution and density for both normal and reverse faults within both the pre- and post-Burdigalian sequences. Our results suggest that these wedge-top basins probably evolved independently, influenced by lateral thickness variations of the stratigraphic sequences, erosion, subsidence rates and tectonics in response to regional and local variations of the stress regime within the underlying orogenic prism. We propose that the present-day framework of the Epiligurian Units can be used as a powerful structural-stratigraphic gauge to track down the variation, through time and space, of the tectonic regime and state of stress of the Apennines wedge, with noteworthy implications on its current seismotectonic setting.

SGI 2021

Unveiling the structural architecture of the wedge-top Epiligurian Units in the Northern Apennines

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L'Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS e il Dipartimento di Matematica e Geoscienze dell'Università di Trieste sono orgogliosi di ospitare il 90° Congresso della Società Geologica Italiana a Trieste dal 14 al 16 settembre 2021. La modalità del congresso è interamente online.

Con il motto "Geologia senza frontiere" questo evento mira a promuovere le Scienze della Terra come disciplina scientifica proiettata nel futuro, oltre i confini geografici, politici e disciplinari, per comprendere meglio l'interno del Pianeta Terra e la struttura del sottosuolo, difendere la società da pericolosi eventi geologici, comprendere meglio la variabilità climatica, pianificare l'utilizzo delle georisorse in modo etico e nel rispetto dell'ambiente.


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The National Institute of Oceanography and Experimental Geophysics - OGS and the Department of Mathematics and Geosciences of the University of Trieste are proud to host the 90th Congress of the Italian Geological Society in Trieste on 14-16 September 2021.  The Congress will be held entirely online.

With the motto "Geology Without Borders" this event aims to promote Earth Sciences as a scientific discipline projected into the future, beyond geographical, political and disciplinary boundaries, to better understand the interior of Planet Earth and the structure of the subsurface, defend society from dangerous geological events, better understand climatic variability, plan the use of geo-resources in an ethical way and respecting the environment.


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Earth Sciences should be understood not only as necessary for a better understanding of the interior of the planet Earth, but also as a defense of society from dangerous geological events, for the understanding of climatic variations, for the planning and use of georesources in a ethical and respecting and protecting the environment.

poster

In the Northern Ionian Sea, the Calabrian Accretionary Wedge (CAW) is facing directly the subducting Apula plate, mainly made of Mesozoic to Tertiary Carbonate Platform (Del Ben et al., 2010; Volpi et al., 2017). This contribution illuminates the structures and stratigraphic relationships between the frontal part of the orogenic belt, the foredeep and adjacent Apulian foreland. A detailed seismic facies analysis of four multichannel seismic profiles has been carried out to define the tectonic-sedimentary evolution of the study area but without exploration wells not available for these deep offshore area. Seismic interpretation allows to identify four main structural domains: the highly tectonized CAW; the narrow foredeep basin filled by a Pliocene-Holocene subhorizontal succession laying above buried normal faults; the massive carbonate succession of the Apulian Platform showing reef and carbonate platform margin facies; the layered succession of the Apulian Platform characterized by ‘'intra-platform'’ facies in the easternmost portion of the area. Three main regional unconformities with characteristic relationships with structural trends were recognized: i) the Messinian unconformity, related to a regional and significant erosion associated to paleokarst processes on the exposed Mesozoic Apulian Platform, is cut by an array of normal faults in the Apulian foreland and by thrust in the accretionary wedge; ii) the angular and erosive middle Pliocene Unconformity truncates the Lower Pliocene reflectors and is affected by normal faults in the foreland and by compressive tectonics in the CAW; iii) a Jurassic/Cretaceous unconformity in the Apulian foreland is marked by Cretaceous reflectors onlapping the Jurassic carbonate platform. The CAW is characterized by compressive tectonics with several fore-thrusts forming a leading imbricate fan system nearby the orogenic front. The Mesozoic Apulian platform is affected by active extensional tectonics driven by flexural bending since Lower Pliocene (Volpi et al., 2017; Maesano et al., 2020), that probably reactivated old normal faults related to the Permian-Triassic rifting stage. The structural map shows that transpressive and positive inversion tectonics is a common deformational style in the central sector of the foreland, suggesting that the Apulia plate is already part of the Calabrian/Hellenic belt. According to these observations, the compressive tectonics affecting the Apula plate is interpreted as related to shortening processes of both the CAW and Hellenic wedge whose interference plays an important role in defining the tectonic-stratigraphic evolution of the Apula Plate in the Northern Ionian Sea.

The response of the Apula plate to the advancing Calabrian and Hellenic wedges (Northern Ionian Sea): implications for subduction processes and tectono-stratigraphic evolution

The Tertiary Piedmont Basin (TPB) is an episutural basin located on top of the junction between the Western Alps and the Northern Apennines. This work combines geological mapping and interpretation of a seismic line provided by Eni S.p.A. aiming at investigating the sedimentary succession of the Arquata Scrivia-Carrosio area, a key sector separating the Alto Monferrato sector to the west from the Borbera-Curone sub-basin to the east. The seismo-stratigraphic analysis of a 33 km-long SE-NE striking seismic line extending from Carrosio to Alessandria and tied to a well, allowed recognizing seven key stratigraphic surfaces, which define six unconformity-bounded stratigraphic units. These could be tied to the outcrop by identifying component lithostratigraphic units at surface. This works contributes to better understanding of the tectono-sedimentary evolution of this sector of TPB, which can be summarized as follows: during the early Oligocene (Unit 1), coarse-grained deltas (Conglomerati di Savignone and Molare Fms.) established, which passed distally (i.e. to the NE) into turbidites and hyperpycnites (Monastero Fm). Following the swift late Oligocene transgression, these marginal fan deltas were onlapped SE-wards by hemipelagic marlstone, containing isolated channelized turbidites (Unit 2; Gremiasco Fm.). Coarse clastic supply was re-established during the Aquitanian-early Burdigalian, with deposition of confined turbidites, mass transport deposits, and channelized turbidites (Unit 3; Castagnola and Costa Montada Fms). In Unit 4 (Costa Areasa Fm., upper Burdigalian-lower Langhian) a basin plain environment established all over TPB, reflecting an increase of the accommodation space driven by southward tectonic tilting of the basin. A further event of basin inversion is that of the intra-Langhian sea level fall, driven by tectonic uplift to the south and recorded by Unit 5 (upper Langhian-lower Messinian), which comprises a range of shelfal systems (Marne di Cessole, Arenarie di Serravalle and Marne di S.Agata Fossili Fms.) making northward transition into turbidites (Cassinasco Fm.). Lastly, Unit 6 (upper Messinian-Pliocene) encompasses a basal package of conglomerates (Conglomerati di Cassano Spinola Fm.), followed upward by early Pliocene clays (Argille di Lugagnano Fm.), over which the shelf margin prograded depositing the Sabbie d’Asti Fm. In addition, the analysis of velocity data from four additional wells from other sectors of the TPB allowed defining a P-wave velocity and seismic wave propagation model. Besides the increase of velocity with depth, conglomeratic facies were found to show higher velocities (in the range 3500-4200 m/s at depths between 350 and 2800 m) than arenaceous and pelitic facies (in the range 2000-3370 m/s at depths between 350 and 3500 m below surface). Results will help time-depth conversion of seismic lines detailing the subsurface of TPB, contributing to accurate reconstruction of basin fill architecture.

Tectonics and sedimentation interplay in the eastern Tertiary Piedmont Basin (Arquata Scrivia, NW Italy): insights from new seismo-stratigraphic analysis

More than 100 years after the devasting Messina-Reggio Calabria earthquake (M=7.1), the largest seismic event ever recorded in southern Europe in the instrumental epoch, its causative seismic source is still unknown, and the several rupture models proposed in the last decades are far from any shared solution. Data interpretation on a new dataset of sub-seafloor geophysical soundings with unprecedented resolution, relocated seismicity, and Vp model, together with morphotectonic investigations and inverse modelling of available levelling data, provide additional constraints on the deformation mechanisms and seismotectonics of the Strait of Messina area. High-resolution seismic lines in the offshore, along with displaced Quaternary marine terraces on land, point to active deformation along a previously unmapped ~ 34.5 km-long extensional fault. The spatial distribution of relocated earthquakes highlighted that a cut-off of the seismicity occurs within the crustal depth. The seismic discontinuity roughly delineates a foreland-dipping and low-angle discontinuity apparently confirming previous studies predicting low-angle seismogenic sources for the 1908 seismic event. However, according to the overburden stress and the attitude of the discontinuity, stress analysis suggests that a seismic slip is unlikely along it. This, therefore, weakens the hypothesis that a large earthquake may have nucleated along a low-angle discontinuity. Rather, aseismic creeping is instead expected since movement is allowed only by assuming a mechanical weakness of the plane. This mechanical behavior is currently also supported by the large interseismic strain-rate recorded in the area. Both seismic tomography and crustal-to-subcrustal scale 3D-modelling strongly suggest a cause-and-effect relationship between slab retreat, mantle wedging, uplift in the upper plate block, and active extension in the Strait of Messina area. Lithospheric doming of the upper plate is here interpreted to be the main process controlling uplift in the Peloritani Mts. of Sicily and subsidence in the Strait of Messina region where deformation is mainly accommodated by the weak low-angle discontinuity. In this frame, an almost aseismical slip toward the foreland of the low-angle discontinuity is here accounted to produce stress perturbation in the area. Coulomb stress change modelling revealed that simulated normal slip on the foreland-dipping discontinuity can induce additional stress and promote failure in the overlying brittle faults. An excellent fit between calculated and observed subsidence is achieved by geodetic data inversion that resolved a normal slip on the low-angle discontinuity and a transtensional (slightly left-lateral) motion on the 34.5 km-long and previously unknown extensional fault. The fault-length along with the observed seafloor displacement make this tectonic structure as the most likely to have produced large earthquakes in the Strait of Messina area.

The Strait of Messina: Seismotectonics and the source of the 1908 earthquake

Evidence for the Early Jurassic Western Tethys rifting is in the Alps and the Apennines. This normal faulting phase dismembered a vast carbonate platform (Calcari Grigi and Calcare Massiccio platform) and produced a complex paleogeographic setting made of intrabasinal morphostructural highs and deeper-water basins (i.e. pelagic carbonate platform or PCP/basin system). Basin-fill pelagites and their geometrical and facies variations highlight this complex architecture. There are growing clues for Early Cretaceous, post-rift, synsedimentary normal faults affecting and displacing the margins of PCP, as in the Umbria-Marche-Sabina Domain and the Trento Plateau-Lombardy Basin. Typical stratigraphic and sedimentological features of this syndepositional tectonic phase include: i) the back-stepping of PCP margins, ii) the deposition of calciclastic bodies, iii) the occurrence of neptunian dykes, and iv) the development of angular unconformities. Geological mapping in the Narni-Amelia Ridge allowed to identify field-evidence for this Cretaceous normal faulting. A polygenic breccia (“Mt. Cosce Breccia”) made of clasts of lithologies not younger than the Early Cretaceous, dispersed in a matrix of Maiolica-type facies, rests through an erosional surface on a Jurassic horst-block of Calcare Massiccio. Comparable clastic deposits are embedded in the uppermost part of the Maiolica in hangingwall-basin successions, associated with soft-sediment deformation. Lower Cretaceous pelagites (Maiolica+Marne a Fucoidi) are locally seen onlapping the unroofed Calcare Massiccio, as well as infilling neptunian dykes. Impressive similarities were recognized along the Jurassic western margin (Ballino escarpment) of the Trento Plateau, albeit at a larger scale. Here, a Lower Cretaceous polygenic breccia (Ballino, Pregasio and Prabione breccias) bearing heterometric (up to >20 m across) blocks of Jurassic-Lower Cretaceous deposits referable to the Calcari Grigi Group, the basinal Lombardy Succession and the horst block-top Venetian Succession, occurs. The clasts are dispersed in a Maiolica-type matrix. The breccia rests unconformably on the Calcari Grigi Group and on several Jurassic units of the Lombardy basin-margin succession, and is accompanied by neptunian dykes made of Maiolica facies. Where preserved by Neogene Alpine deformations, Cretaceous normal faults were locally observed, sealed by the calciclastics and the uppermost part of Maiolica. Field-evidence suggests a phase of tectonic instability during the late Early Cretaceous, coeval with the deposition of the uppermost part of Maiolica, affecting PCP-basin systems in both Central Apennines and Southern Alps. Cretaceous faults locally re-activated Jurassic ancestors, locally had a higher angle than Jurassic faults, locally developed as new faults. The result was the displacement and rejuvenation of inherited Early Jurassic escarpments, or the backstepping of PCP-margins producing exhumation of Jurassic structural highs.

Tectono-stratigraphic evolution of Jurassic Tethyan rift basins in the Early Cretaceous: a comparison between the Central Apennines and the Southern Alps

The NNW-SSE trending Malta Escarpment (MESC) offshore eastern Sicily is accounted to have a significant role in the recent seismotectonic picture of the Western Ionian Basin and the Hyblean foreland domain, where some of the largest and most destructive Mediterranean earthquakes occurred (Boschi et al., 1995; Piatanesi&Tinti, 1998; Bianca et al., 1999; Azzaro&Barbano, 2000; Tinti et al., 2001, 2004; Rovida et al., 2016). Seismic data and bathymetric grids allow to better constrain the recent/active deformation pattern affecting the northern sector of the MESC. Accurate seafloor mapping and seismic profiling point to a 60 km-long, roughly N–S trending and E-dipping extensional faults belt slicing across the Ionian offshore between CataniaSiracusa.The fault belt deformed the seafloor producing up to 60 m-high fault scarps. Near-fault sediment pattern and displacement analysis provide constraints on the through-time faults activity and deformation rate. Fault parameters were achieved by 3D modeling and then used to derive expected magnitudes and their reactivation propensity. Moreover, empirical scaling relationships (Wells & Coppersmith, 1994; Leonard, 2010) point to a high seismic potential for the detected fault. This combined analysis pointed out how the longest (~60 km) and most continuous fault could be capable of generating M > 7 seismic events, putting forward strong seismotectonic implications for the adjacent and densely populated Hyblean Plateau. The expected magnitude and the estimated recurrence time interval (470-537yrs) are compatible with those inferred for large historical earthquakes that occurred in the area. However, by comparing the depicted tectonic pattern with other structural settings concerning passive margin worldwide (e.g., along the Pará-Maranhão Basin in the Brazilian equatorial margin, see Matos, 2000) and considering the occurrence of ductile layers in the sediment section (e.g. evaporites), part of the observed deformations (i.e. the seafloor scarps) should be also charged to large-scale slope instability or generated by accommodation space following salt migration in response to the overlying sediment load. Accordingly, seafloor deformation could be (partially)the result of this kind of process and this issue should be seriously considered in the seismotectonic analysis. Although our study highlights that classical tools used by marine geologists(i.e. high-resolution seismic data and bathymetric grids) work well in detecting offshore faulting, some other significant faults parameters, which are essential in the seismotectonic analysis (e.g. size parameters and slip rate,), need additional approaches to be achieved. In this view, computer-based 3Dmodelling can represent a starting point for further elaborations such as stress/strain analysis, back/forward and dislocation modeling, sediment decompaction, etc.

3D modeling and sequential back-restoration as tools for assessing faults deformation rate in offshore setting and estimation of their seismic potential

The Quaternary marks a time of important change in the tectonic regime that affected the central Apennine chain. The shift from the late Miocene-early Pliocene compressional regime to the late Pliocene-early Pleistocene extensional regime produced surface uplift of the chain, tectonic activity expressed along normal faults, and rapid evolution of the intra-montane basins. The development of several paleosurface levels in the central Apennines suggests the uplift was not constant through time; dating those paleosurfaces is critical for determining how uplift rates and landscapes changed through time. The Aterno and Tirino basins preserve a record of subplanar highlands that can be related to paleosurfaces. Recent studies on the Quaternary deposits in the L’Aquila Basin allowed the identification of the Valle Daria abandonment surface, which marks an important phase of base-level fall of the drainage system that occurred during the early Pleistocene (Gelasian). Although morphostratigraphic analysis well describes the evolution of these two basins during the Quaternary, the knowledge related to the higher paleosurfaces and their meaning in the landscape evolution is still poorly constrained. In this study, we applied advanced morphometric and morphostructural analysis to the Aterno and Tirino basins, with a focus on the identification of the main paleosurfaces, their dating, and reconstructions of the baselevel-fall variations of the drainage system through time. We used a 10-m resolution DEM to map the position and elevation ranges of the flat surfaces, extract the drainage system, and identify knickpoints and low-gradient levels. We then combined the morphometric results with the morphostratigraphy and tectonics of the area to define the paleosurfaces, correlate the levels, and assign them ages. We identified 4 main levels of paleosurfaces, the lowermost (P3 and P4) respectively related to Valle Daria (early Pleistocene, top Gelasian) and the top of Fosso Genzano Synthem (middle Pleistocene), the higher ones (P1 and P2) that have been related to the thrust-top basins of Monte Coppe (latest Messinian) and Rigopiano (late Zanclean). We finally applied linear inversion of the Aterno and Tirino drainage systems to infer the evolution of base-level and find a possible correlation with central Apennine uplift phases. Our results show three main events in the drainage baselevel-fall rate. The first two events occurred at ca. 3 Ma and 2 Ma, in accordance with the uplift and abandonment of P2 and P3, and the middle to late Pleistocene peak in base-level fall that could be related to changes in the Sulmona Basin and Pescara River systems.

Paleosurface mapping and Quaternary uplift evolution of the Aterno and Tirino Basins

Proofs of synsedimentary tectonics during the Early Permian in the central Southern Alps (cSA, N Italy) are recorded in the volcanic and terrigenous successions of the Laghi Gemelli Group, which are characterized by the occurrence of abrupt facies variations often associated with coarse-grained deposits. These features are generally attributed to syn-sedimentary tectonic activity demonstrated by the local occurrence of sediments deformation (Berra et al., 2011) such as liquefaction or slumping due to seismic shaking. Detailed fieldwork allowed us to recognize dewatering structures and sedimentary dikes, ball and pillars and small slumps, occurring along hundreds of mesoscopic faults showing meter-scale displacement in correspondence of high-angle conjugate systems as well as domino-style faults, often accompanied by growth structures. These structures are mainly concentrated in the fine-grained sediments of the Pizzo del Diavolo Formation, which were deposited on top of the volcaniclastic succession of the Ca’ Bianca Volcanite and crossed by seismogenic synsedimentary faults. The Permian synsedimentary structures of cSA are mostly associated with high-angle Andersonian normal faults which are combined with low-angle normal faults (LANFs) that developed along the interface between the Permian sedimentary cover and the Variscan basement (Zanchi et al., 2019). This LANFs system is relevant for the Permian hydrothermal circulation, resulting in widespread tourmalinites deposition along fault zones, and locally in U mineralization. According to our structural analysis the Permian tectonic setting is characterized by pure extension, dominated by ENE-WSW striking normal faults inverted during the Alpine shortening as high-angle reverse faults (Zanchetta et al., 2015).

Evidence of syndepositional tectonics during the Early Permian in the Orobic Basin (central Southern Alps, N Italy)

Seismic images are fundamental to interpret subsurface setting on both continental and marine environments. However, in carbonate systems, seismic response can be very difficult to be analyzed due to the petrophysical heterogeneities, being the interpretation particularly complicated when faults are present. In fact, faults rocks are generally characterized by different petrophysical properties with respect to the host rocks. Synthetic seismic forward modeling is a powerful tool to quantifying the seismic response associated with fault-related petrophysical changes, since input parameters can be modified. In this study, field and laboratory measurements are used to analyze the spectrum of the carbonate-bearing fault seismic response. Here, we focused on the carbonate ramp setting outcropping in the Majella Massif since it represents an excellent surface analogue of buried porous and faulted carbonate reservoirs worldwide. Density and porosity were measured through a helium pycnometer on representative fault (damage zone) rocks sampled at increasing distances from fault planes. Investigated damage zone samples, show both increased and decreased porosity with respect to the host rock, depending on the single fault characteristics. A 2D (12 km long) synthetic profile from the platform top to the basin, oriented SSE-NNW, was then carried out in Matlab simulating the outcropping architecture and spatial distribution of the sedimentary facies and of the faults. Together with a proper porosity variation related to facies distribution, the porosity along the damage zones (DZ) of the simulated faults was set according to the laboratory measurements. The low-frequency (40Hz) synthetic seismic profile shows marked diffraction hyperbolas in the modeled fault zones for faults characterized by higher porosity DZ where lower seismic velocity is expected. On the contrary, fault zone characterized by lower porosity DZ with respect to the host rock resulted to give a less clear seismic image. Going into the details, faults with decreased porosity and consequent increased seismic velocity of 1000 m/s in the damage zone respect to the host rock, do not show a visible difference in the seismic response if compared with the seismic image without modified petrophysical characteristics within the faults. On the other hand, faults with increased porosity and decreased seismic velocity of just 500 m/s respect to the host rock, show clear diffraction hyperbolas where their apexes correspond to the fault planes. Ongoing laboratory measurements and simulations changing geometries, thicknesses and orientations of the damage zones, are expected to help in improving the knowledge of fault seismic response. This work helps in bridging the gap between forward modeling and actual seismic imaging with large implications for hydrocarbon-reservoir characterization and the identification of potential CO2 or hydrogen storage sites.

Synthetic seismic forward modeling as a tool to assess the seismic signature of carbonate-bearing fault zones

The Eastern Mediterranean Sea results from an alternation between extensional and contractional phases. Although several geodynamic reconstructions have been proposed, its tectonostratigraphic evolution is still a matter of debate. The main tectonic phases that affected the area were the Mesozoic rifting, followed by a Cenozoic contractional phase, due to the inception of the convergence between Africa and Eurasia and the subduction of the oceanic lithosphere. From the Miocene, the opening of the Red Sea induced a rotation and northward migration of the Arabian Plate. At the same time, the rollback of the subducting oceanic lithosphere in the Central Mediterranean area favoured a westward escape of the Anatolian plate squeezed out by the northward migration of the Arabian Plate. Our study area is located in the easternmost portion of the Mediterranean Sea, offshore Turkey, Cyprus and Syria, on the ancient passive margin of the Tethys between the Arabian continental lithosphere and the African oceanic lithosphere. Along the Cyprus Arc, the Neo-Tethys oceanic crust is subducting toward NE. Most of the authors (Symeou et al. 2018 and references therein) suggested that this system is continuous from Cyprus to Syria. In this work, multi-channel seismic reflection profiles have been used to analyze the basement nature (oceanic vs continental), to recognize potential subduction zones and their lateral continuity, and to reconstruct the contractional events. Our data suggest a continental nature of the basement, excluding a continuous ophiolite complex and subduction in eastern Cyprus offshore. Most of the recent structures evidenced in the area derive from transpressional reactivation of inherited extensional fault systems.

Structural inheritance in the Northeastern Mediterranean basin 

Diagnostic morphological features (e.g. rectilinear seafloor scarps) and lateral offsets of the Upper Quaternary deposits are typically used to infer offshore active faults. These structures are not necessarily capable of producing large earthquakes as they could be shallow and formed in response to local stresses. We present a multiscale approach to reconstruct the structural pattern in offshore areas and distinguish between shallow, non-seismogenic, active faults, and deep blind faults, potentially associated with large seismic release. The approach is based on the interpretation of seismic reflection profiles with different resolution/penetration and the quantitative morphometric analysis of multibeam bathymetry. The site chosen for testing the method is the Sant’Eufemia Gulf (south-eastern Tyrrhenian Sea) because it is a natural laboratory to investigate the relationships between regional and local processes associated with a slab tear fault (e.g. Rosenbaum et al., 2008) and crustal structures controlling the Plio-Quaternary tectonic evolution (e.g. Brutto et al., 2016). Data highlights the occurrence of three major tectonic events since the Late Miocene. The first extensional or transtensional phase occurred during the Late Miocene. Since the Early Pliocene, a right-lateral transpressional event caused the positive inversion of deep (> 3 km) tectonic features, and the formation of NE-SW faults in the central part of the gulf. Also, NNE-SSW to NE-SW trending anticlines (e.g. Maida Ridge) developed in the eastern sector. Since the Early Pleistocene (Calabrian), shallow (< 1.5 km) NNE-SSW oriented structures formed in a left-lateral transtensional regime. The results of this work integrated with literature data indicate that the transpressional/transtensional structures developed in an ~E-W oriented principal displacement zone extending from the Sant’Eufemia Gulf to the Ionian offshore. The strike-slip zone likely represents the upper plate response to the development of a slab tear fault.  The quantitative morphometric and bathymetric analyses indicate that NNE-SSW to NE-SW trending anticlines were negatively reactivated during the last tectonic phase. We suggest that the deep structure below the Maida Ridge may correspond to the seismogenic source of the large magnitude earthquake that struck the Calabrian region in 1905. The multiscale approach contributes to understanding the tectonic imprint of active faults with different hierarchical order developed in a strike-slip zone orthogonal to the Calabrian Arc.

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The response of the Apula plate to the advancing Calabrian and Hellenic wedges (Northern Ionian Sea): implications for subduction processes and tectono-stratigraphic evolution

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