Since the Neogene, the Central Mediterranean geodynamics is controlled by the migration of narrow orogenic belts, driven by fast slabs retreat, and the slowly converging Nubian and Eurasian plates. Nowadays, the Calabrian Arc continues its southeast migration in response to the Ionian oceanic plate rollback but at a much slower rate. The Sicilian kinematics has reached a transient state between the ending subduction-collision phase that formed the island, and the steady-state convergence between Africa and Eurasia. This setting explains why Sicily is among the most seismically active region of the Mediterranean, gathering the most destructive historical events recorded in Italy, such as the Noto (1693, Mw ∼ 7.4) and Messina earthquakes (1908, Mw ∼ 7.1). Such tectonic activity has led to numerous studies aimed at evaluating current surface motions at a regional scale using GPS networks. To improve the spatial coverage, we built the first 3D geodetic velocity field over the whole Sicily Island by processing from the Sentinel-1 InSAR time-series. Averaged velocities along the ascending and descending satellite line-of-sight (LOS) were obtained using the Permanent-Scatterer approach (PS-InSAR) over the 2015-2020 period. We converted PS velocity fields into the Nubia reference frame, with the ITRF2014 vertical reference, by adjusting PS to 3D-GPS mean velocities. Reliable GPS velocities were retrieved from time-series of the MAGNET GPS network, leading to about 40selectedsitescoveringSicily and south-west Calabria. Onalltracks, theagreementbetweenPSandGPSLOSvelocitiesisexcellent (rms < 1mm/yr), and derived orbital corrections are robust, except for the western descending track that is only constrained by five GPS data. Since the projected north-south GPS velocity difference along the LOS is about 0.5 mm/yr, we assumed that thenorth-componentoftheground displacementisnegligible. By reducing the problem to a 2D estimation(East and Up component) and using both ascending and descending LOS velocities, we derived the East-andUp-component of the ground deformation within the Nubia-ITRF2014 reference frame. Uncertainties are estimated in the order of 1mm/yr. The results show that the Up-component is consistent with previous works indicating a significant uplift of the Peloritani range (~ 1±0.5 mm/yr) in north-eastern Sicily. Together with the East-component, the whole Peloritani block appears, however, as a coherent tectonic unit and does not show any dislocation along the Tindari line, as suggested by previous structural field observations. Interestingly, PS-InSAR data evidence an eastward tilting of the Hyblean Plateau, with about 1.5 mm/yr of subsidence of the Augusta bay relative to the Vittoria plain, and a 1 to 2 mm/yr of differential vertical motion along the southern coast, between Agrigento and the Licata and Sciacca locations. Although the reconstructed ground motion only captures a short time-window of the seismic cycle, these data represent a major milestone to evaluate the seismic hazard of Sicily.

As part of an ongoing project of mapping, structural studies and fault characterization we present an updated tectonic scheme and data set for the active fault systems that shaped the inner portion of the Apennines north of the Arno river. Geomorphology, stratigraphy of Plio-Quaternary sediments, GPS data, historical and instrumental seismicity have been reviewed and combined with structural studies to define the neotectonic history of the investigated region. Within the studied area, first-order physiographic and structural features allow to define different structural domains related to a set of ranges with a dominant NW-SE direction separated by intramontane or continental/marine morphotectonic depressions of the Lunigiana, Garfagnana, Lucca-Mt.Albano, La Spezia-Carrara and the off-shore Viareggio basin. The main boundary faults and internal fault segments of the different structural domains were described while the Plio-Quaternary sedimentary records has been used to constrain their long to short term deformation and rates, with the aim to improve current Italian catalogues DISS (INGV) and Ithaca (ISPRA) with some utilities for the seismic microzonation local projects. Moreover, our work aims to draw the attention of the scientific community to the seismotectonics of a region in which the seismic hazard is largely considered medium to low despite the occurrence, one century ago, of one of the most destructive earthquakes that have struck the Italian peninsula, the 1920 Fivizzano EQ, with an estimated Mw 6.5 similar to the main shock of the 2016 Central Italy seismic sequence.

Based on the review of the available stratigraphic, tectonic, morphological, geodetic, and seismological data, along with new structural observations, we present a reappraisal of the potential seismogenic faults and fault systems in the inner northwest Apennines, Italy, which was the site, one century ago, of the devastating Mw ~6.5, 1920 Fivizzano earthquake. Our updated fault catalog provides the fault locations, as well as the description of their architecture, large-scale segmentation, cumulative displacements, evidence for recent to present activity, and long-term slip rates. Our work documents that a dense network of active faults, and thus potential earthquake fault sources, exists in the region. We discuss the seismogenic potential of these faults, and propose a general tectonic scenario that might account for their development.

Faults form dense, complex multi‐scale networks generally featuring a master fault and myriads of smaller‐scale faults and fractures off its trace, often referred to as damage. Quantification of the architecture of these complex networks is critical to understanding fault and earthquake mechanics. Commonly, faults are mapped manually in the field or from optical images and topographic data through the recognition of the specific curvilinear traces they form at the ground surface. However, manual mapping is time‐consuming, which limits our capacity to produce complete representations and measurements of the fault networks. To overcome this problem, we have adopted a machine learning approach, namely a U‐Net Convolutional Neural Network (CNN), to automate the identification and mapping of fractures and faults in optical images and topographic data. Intentionally, we trained the CNN with a moderate amount of manually created fracture and fault maps of low resolution and basic quality, extracted from one type of optical images (standard camera photographs of the ground surface). Based on a number of performance tests, we select the best performing model, M Ref , and demonstrate its capacity to predict fractures and faults accurately in image data of various types and resolutions (ground photographs, drone and satellite images and topographic data). M Ref exhibits good generalization capacities, making it a viable tool for fast and accurate mapping of fracture and fault networks in image and topographic data. The M Ref model can thus be used to analyze fault organization, geometry, and statistics at various scales, key information to understand fault and earthquake mechanics.

The Apennines-Sicilian-Maghrebian fold-and-thrust belt originated from the subduction of the Alpine Tethys and the later collision of drifted continental blocks against the African and Apulian paleomargins. From North to South, the Sicilian Fold-and-Thrust Belt (SFTB) is divided in four main tectono-stratigraphic domains: (1) the Calabro-Peloritani terrane, drifted from the European margin, (2) the remnants of the Alpine Tethys accretionary Wedge (ATW) related to the subduction of the Tethys, (3) the folded and thrusted platform (Panormide) and deep-water (Imerese-Sicanian) series of the offscrapped African margin, and (4) the African foreland (Hyblean). Unfortunately, scarce quality seismic lines and outcrops of key tectono-stratigraphic units make the structure and dynamic evolution of the central-eastern part of the SFTB controversial. First, this study outlines through a review of the tectono-stratigraphic evolution of the central-eastern sector of the Sicilian orogen, the major remaining issues concerning: (1) the occurrence of inferred Alpine Tethys units far from the region where the remnants of the ATW outcrop (Nebrodi Mountains); both, in a forearc position above the Peloritani block to the North and in an active foreland context along the present day southern front of the belt; and (2) the diverging tectonic styles, from stacked large-scale tectonic nappes to foreland imbricated thrust systems rooted into a main basal decollement. Secondly, new constraints are given using analogue modeling to test mechanically the hypothesized structural and tectono-stratigraphic evolution of the SFTB. The experiment simulates the orogenic evolution of the SFTB at crustal-scale, from the Oligocene Tethys subduction, to the Middle Miocene-Late Pliocene continental collision between the European and African paleomargins. The tectono-stratigraphic synthesis is used to model the first-order mechanical stratigraphy of the sedimentary units involved in the Sicilian belt, as well as the imprint of the African margin structural inheritance. The experiments succeed in reproducing the general structure and tectono-stratigraphic evolution of the SFTB. In particular, the models support field observations hypothesing a gravity-driven origin of the inferred Alpine Tethys units intercalated within the forearc and foreland syntectonic sedimentation. Moreover, the model testifies of the main tectonic steps that led to the SFTB building. First, a low-tapered accretionary wedge was accreted above the Alpine Tethys oceanic crust from the Oligocene to the Early Miocene. The following underthrusting of the stretched African continental margin and its frontal Panormide platform shortened and thickened the accretionary wedge. This phase provided favorable conditions for significant pulses of reworked Alpine Tethys units that intercalated within the forearc and foredeep successions. During the Middle-Miocene, the decollement of the African Meso-Cenozoic cover (Panormide platform and Imerese-Sicanian deep-water basin) enhanced a deep-seated deformation phase, along with duplexing of the Panormide platform beneath the Alpine Tethys wedge leading to its emersion. Since the Late Messinian, activation of basement faults led to a generalized emersion of the orogenic units through large-wavelength fold culminations accompanied by syntectonic deposition at their southern limbs. Concurrently, the prism front was partly indented to the southeast by the thick and locally already emerged Hyblean platform.

The Mw 7.8 2016 Kaikoura earthquake ruptured the Kekerengu-Needle fault resulting in the loading of its eastern continuation, the Wairarapa fault. Since the most recent earthquake on Wairarapa occurred in 1855 and is one of the strongest continental earthquakes ever observed, it is critical to assess the seismic potential of the Wairarapa fault, which might be prone to break. Using Lidar data, we examine its bare-earth morphology and reveal ~650 mostly undiscovered offset geomorphic markers. Using a code we developed in earlier work, we automatically measure the lateral and vertical offsets of these markers providing more than 7000 well constrained measurements. The data document the lateral and vertical slip profiles of the 1855 earthquake for the first time and show its total slip reached ~20 m at surface. Modeling the entire offset dataset reveals 7 prior earthquakes ruptured the entire fault, each similarly producing 16.9 ± 1.4 m dextral slip and ~0.6 m vertical slip at surface in the same central bend zone of the fault. Thus, the Wairarapa fault repeatedly produced giant earthquakes and is likely able to produce a similarly strong forthcoming event. The extreme large size of the Wairarapa earthquakes questions our understanding of earthquake physics.

In Central Mediterranean, the Sicilian Fold and Thrust Belt (SFTB) and Calabrian Arc, as well as the whole Apennine-Maghrebian belt, result from the subduction and collision with drifted micro-continental terranes. These terranes detached from the European margin and migrated southeastward in response to Neogene slab roll-back and associated back-arc extension. From N to S, the SFBT is divided in 4 main tectono-stratigraphic domains: (1) the Calabro-Peloritani terrane, drifted from the European margin and detached from the Corso-Sarde block since the back-arc opening of the Tyrrhenian basin, (2) the Neotethyan pelagic cover, constituting the remnants of the Alpine Tethys oceanic accretionary wedge, (3) the folded and thrusted platform (Panormide) and basinal (Imerese-Sicanian) series of the down-going African margin, and (4) the undeformed african margin foreland (Hyblean).The scarce good quality outcrops of key tectono-stratigraphic units and crustal scale seismic lines makes the structural architecture of the SFTB very controversial, as testified by the wide variety of tectonic interpretations (Bianchi et al., 1987; Roure et al., 1990; Bello et al., 2000; Catalano et al., 2013). Major outstanding issues particularly concern: (1) the occurence of Alpine Tethys units far from the region where the remnants of the Tethyan accretionary wedge outcrop (Nebrodi range); in a forearc position above the Peloritani block north of the SFTB and in an active foreland context along the southern front of SFTB; (2) the diverging suggested tectonic styles, from stacked large-scale tectonic nappes to foreland imbricated thrust systems rooted into a main basal décollement; and (3), the deposition environnement of substantial units such as the widespread Numidian Flyschs, from syntectonic foreland basin to wedge-top sedimentation.We used 2D analogue models to investigate the mechanical processes involved in the formation of the SFTB starting from the Oligocene Tethys subduction to the Middle Miocene - Late Pliocene continental collision with the African paleo-margin. Based on a detailed tectono-stratigraphic synthesis, complemented by field observations, we reproduce the first-order mechanical stratigraphy of the sedimentary and basement units involved in the SFTB as well as the structural inheritance of the African margin. Our models also include: syntectonic erosion and sedimentation, syn-orogenic flexure and adjustable material output via a “subduction channel“.The analog models succeed in reproducing the general structure of the SFTB and main tectono-stratigraphic correlations. For instance, the Panormide platform is underthrusted beneath the Alpine Tethys accretionary wedge, then stacked above the Imerese basinal units and belatedly exhumed in response to basement anticlinal stack. Our results also suggest that the Alpine Tethys units couldn’t overthrust the whole African foreland in the Middle Miocene, nor be back-thrusted over the forearc basin during the Burdigalian. We rather favor a gravity-induced sedimentation process inducing reworking of the tethysian sediments at specific building stages of the accretionary wedge. The structural architecture of the modeled orogenic wedge is also consistent with a SFTB growing by frontal accretion and basal underplating of mechanically resistant stratigraphic units rather than by large-scale nappe overthrusting.

The dataset includes: - the image and topographic data used in the study - the ground truth used in the study - the parameters of the model MRef developed in the study - the Supplementary documents and figures discussed in the paper

Many orogens on the planet result from plate convergence involving subduction of a continental margin. The lithosphere is strongly deformed during mountain building involving subduction of a plate composed generally of accreted continental margin units and some fragments of downgoing oceanic crust and mantle. A complex deformation involving strong partitioning of deformation modes and kinematics produces crustal shortening, accompanied by crustal thickening. Partitioning depends on three main factors: (1) rheologic layering of the lithosphere; (2) interaction between tectonics and surface processes; (3) subduction kinematics and 3D geometry of continental margins (oblique convergence, shape of indenters). Here we present an original view and discussion on the impact of deformation partitioning on the structure and evolution of orogens by examining the Taiwan mountain belt as a case study. Major unsolved questions are addressed through geological observations from the Taiwan orogen and insights from analogue models integrating surface processes. Some of these questions include: What is the role played by decollements or weak zones in crustal deformation and what is the impact of structural heterogeneities inherited from the early extensional history of a rifted passive continental margin? What is the relationship between deep underplating, induced uplift and flow of crustal material during erosion (finite strain evolution during wedge growth)? Are syn-convergent normal faults an effect of deformation partitioning and erosion? What is the role of strain partitioning on the location of major seismogenic faults in active mountain belts? What can be learned about the long-term and the present-day evolution of Taiwan?

A significant issue in the study of orogenic systems concerns the roles played by frontal and basal accretion in the construction of orogenic wedges. These different accretion mechanisms result in different thermal histories, with underplated materials experiencing significant heating and deformation during tectonic burial. This work provides new thermal data from Raman spectroscopy of carbonaceous material in combination with structural and stratigraphic observations of the northern Taiwan slate belt to address these questions of wedge development. Sedimentary rocks of the Northern slate belt were deposited on the Chinese continental margin immediately before the onset of the Neogene Taiwan arc-continent collision. In the slates of the northern Hsuehshan Range, a large-scale pop-up structure on the prowedge of the Taiwan Orogen, synorogenic metamorphism has been investigated through analyses of peak temperatures and metamorphic field gradients. Results indicate underthrusting of the margin sediments to similar to 8-km depth with significant folding in two major duplexes occurring before underplating. Such basal accretion is considered responsible for the distinct culmination of the Hsuehshan Range in central Taiwan and its relative uplift with respect to the Backbone Range to the east along the Lishan Fault. A similar underthrusting scenario is also suggested for the Backbone Range Slate Belt. We propose that basal accretion is the predominant mechanism in the growth and evolution of the Taiwan orogenic wedge and may have been achieved through inversion of a graben system on the ancient passive margin during continental subduction.

Southeastern Sicily is characterized by a prominent topography known as the Hyblean Plateau. It is commonly considered as a flexural bulge formed by the northwest plunging of the Hyblean‐Malta platform beneath the Sicilian Fold and Thrust Belt. However its noncylindrical shape and multiphase uplift history correlated to the Late Miocene and Plio‐Pleistocene volcanism outline a possible magmatic control on the Hyblean Plateau topographic expression. We argue, using 2‐D flexural models, that the flexural bending alone is unlikely to explain the high anomalous elevation of the Hyblean Plateau. Moreover, topographic analysis show that the Hyblean Plateau has a dome shape composed of radially tilted preserved surfaces defining individual blocks. The block edges seem to be related to deep‐seated inherited faults. Using an analogue modeling approach, we show that magmatic intrusions beneath the thick Meso‐Cenozoic sedimentary cover can reproduce the first‐order morphology of the Hyblean Plateau when a structural inheritance is imposed. Accordingly, we propose a tectono‐magmatic model that favors mafic sill intrusions as the major uplift source for the topographic anomaly. However, to explain the strong positive Bouguer anomaly, a deeper high‐density intracrustal body is needed. Moho uprising related to Mesozoic rifting or mafic lower crust underplating/intraplating since the Late Cretaceous can be evoked. The small wavelength of the topography and the deep intracrustal mass anomaly makes the lithospheric elastic stresses sufficiently high to maintain a nonisostatic state over the geological time scales.

Several recent studies have suggested that maps of flow length normalized for drainage area called chi (chi) could reveal landscapes in a transient state, which are prone to reorganizations of basin geometry, flow line topology and water divide locations. However, the potentially long timescales associated with the evolution of basin geometry make the capability of chi to predict such reorganization challenging to test in natural settings. Here, we investigate the evolution of experimental drainage networks developed on a wedge coupled to a piedmont and growing in oblique convergence. We use this experimental setting to investigate the relationships between chi maps, the imposed tectonic deformation and the drainage network evolution. As deposition can occur within channels or in the piedmont, our experimental streams deviate from purely bedrock channels for which the chi metric has been initially developed. Yet we show that the large-scale chi pattern of the experimental drainage network is consistent with the imposed deformation field, as similar to 2/3 of the observed chi gradients across water divide are oriented in the expected direction with respect to the imposed deformation. This suggests that chi maps can be used to infer the horizontal component of regional deformation in large-scale natural mountainous fluvial landscapes. In addition, we observe that when a divide affected by a chi gradient migrates, the orientation of the gradient correctly anticipates the sense of landscape reorganization for similar to 2/3 of these divides. (c) 2018 John Wiley & Sons, Ltd.