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The characterisation of the fracture network is a fundamental step for modelling the circulation of different types of geofluids at multiple scales, including at the reservoir scale. Due to the difficulty of sampling the fracture network with a spatial continuity, fracture networks are often derived from a stochastic approach applied to ground truth parametrized datasets. Classical field methods for collecting and analysing fracture data sets (i.e., scan-lines or scan-areas) have limited sample area and the results might be affected by local factors (e.g., facies variations and faults). In poorly- to non-vegetated regions, field-derived data can be integrated with satellite and aerial images providing a “big-picture” of the study area. The availability of open-source, high-resolution aerial and satellite images (e.g., Google Maps, Bing Maps) coupled with the development of specific software and tools (e.g., NetworkGT; FracPaQ) allow to digitize and analyse very large and spatially continuous data sets of fractures at multiple scales for a single case study.In this work, we test the use of Bing Maps imagery for the analysis of the fracture network affecting the Kuh-e-Asmari anticline, in the Zagros fold-and-thrust belt. The Kuh-e-Asmari anticline is considered as an outcropping analogue of fractured reservoirs and is in a scarcely vegetated area, covered by high resolution open-source aerial images (~2.6 m/pixel). We obtained three different image-derived fracture data sets by manually digitizing the fracture network at three different scales (1:50000, 1:5000, and 1:500) in QGIS. Each data set has been analysed using the NetworkGT plugin within QGIS. In detail, we analysed the orientation, length distribution, abundance, and topology of each fracture network data set, and we have compared the results with structural data from scan-lines performed in the field on the same anticline.Results proved to be scale-dependent, with each scale having its pros and cons, as follows. The 1:50000 data set is the only spatially continuous data set, allows to rapidly map the main tectonic features (e.g., major faults and fracture corridors) but it is not accurate enough in terms of the definition of orientation sets and length analyses. The 1:5000 data set is potentially spatially continuous and allows to analyse fracture and connectivity distributions with high detail, by highlighting strongly fractured/connected elongated zones, possibly representing damage zones of known, previously mapped, fault strands. The 1:500 scale cannot guarantee the spatial continuity of the data set but, if applied to a small area, provide reliable results.Results obtained in this work suggest that the manual interpretation of open-source aerial images is a viable way for the characterization of fracture networks in poorly vegetated areas only if the right scale is chosen. For the case study presented here we suggest interpreting the fracture network at 1:5000 or similar scales. A successful testing of semi-automatic or automatic algorithms for lineament detection is required to perform a spatially continuous interpretation and analysis at the highest possible resolution, and/or to analyse the fracture dataset at multiple scales (more than the 3 investigated here).

The rapid improvements of computer vision–based photogrammetric image processing pipelines (i.e., Structure from Motion–Multi View Stereophotogrammetry: SfM-MVS), coupled with the availability of various low-cost and portable acquisition tools, such as Digital Single-Lens Reflex (DSLR), mirrorless cameras, Unmanned Aerial Vehicle (UAV) and even smartphones, have revolutionized outcrop studies in structural geology and have brought traditional field geology into the digital age. This has had a transformative impact on Virtual Outcrop Models (VOMs), which have been promoted from mostly visualization media to fully interrogable quantitative objects. Among the several applications of VOMs in structural geology, extraction of near planar features (e.g., fracture and bedding surfaces) is one of the most important. Various procedures aimed at this purpose exist, spanning from fully automated segmentation and best fitting of point clouds to the manual picking of 3D polylines on both point clouds and textured meshes.Here we illustrate the pros and cons, best practices, and drawbacks of the main procedures for near planar geological data extraction from VOMs. While automated or supervised recognition and subsequent best-fitting of coplanar patches in point clouds has received remarkable attention, its application generally limits to rare case studies. Indeed, most commonly, geological outcrops do not expose patches of near planar surfaces which are large enough to carry out a robust best fitting, and the structural interpretation of the outcrop only permits manual picking procedures. In the latter case, the use of textured meshes must be preferred to point clouds, and during digitization the accuracy of the textured mesh must be considered, as well as the intrinsic roughness of any geological surfaces. The analysis of coplanarity and collinearity of the picked pointsets may help in identifying traces that diverge from idealized (low) collinear and (high) coplanar configurations. However, typically suggested threshold values often produces small datasets. Nonetheless, the goodness of the extraction of data based merely on the visual inspection of the best-fit plane, handling coplanarity and collinearity in real-time through live computation of best-fit planes from picked pointsets, is often acceptable.

Geothermal heat is a crucial source of renewable energy. Its present and future exploitation can be enhanced by the understanding of the in–situ structural and mineralogical processes and of how these processes may change the reservoir productivity. Fossil hydrothermal system may thus be used as analogues to study in-situ fluid-rock interaction processes in active geothermal systems.We present the results of a structural-mineralogical study carried out in the lithocap of the Allumiere high-sulphidation epithermal system (Tolfa Mountains district, northern Latium, Italy). We integrated measurements of attitude of faults and fractures from field analysis with a virtual outcrop model constructed from drone imagery to model the distribution of major faults at the scale of the entire quarry. We then characterized the textures and mineralogical compositions of the alteration facies using optical petrography, Scanning Electron Microscope (SEM), X-ray diffraction analysis and field-based short-wave infrared (SWIR) spectrometer and we mapped their distribution in relation to major faults orientation.We interpreted that initial argillization was promoted by circulation of highly reactive fluid(s) along a major fluid conduit, probably in the form of a network of fault and fractures. Fluid circulation promotes hydrolytic alteration of the Plio-Quaternary pyroclastic rocks, forming a highly silicified carapace at the immediate vicinity of conduits. Enrichment in alunite and kaolinite increases towards distal areas, which in turn fades out into illite-smectite-bearing zone, where the country rock appears less altered. Latest fracturing and fluid circulation occurs along two major sets of faults, oriented NE-SW and NW-SE that sharply put in contact different mineralogical facies.We propose that initial alteration induces a mineralogical-mechanical zonation that control latest reactivations of the system. Strain localization promotes a massive mineralization of alunite and kaolinite by continuous dissolution and precipitation along major faults.

In rift basins, the spatial arrangement of extensional faults can influence the facies and the thickness distribution of the syn- and post-sedimentary infill, which can harbour good potential for geothermal systems. In this framework, unravelling the tectono-stratigraphic evolution of a rift basin is decisive, as it can influence one of the key parameters for planning geothermal doublets: aquifer thickness.In our study, the West Netherlands Basin, located in one of the Netherlands most densely populated areas, is used as a case study. Up to 2022, 14 geothermal doublets were realized in the area, with the main target being the syn-rift deposits of the Late Jurassic Nieuwerkerk Formation. As a NW-SE oriented transtensional basin, the West Netherlands Basin developed as consequence of Mesozoic extensional tectonics, after which it became inverted during the Late Cretaceous and Cenozoic. Using publicly available seismic 3D and well data, our renewed interpretation of the study area shows two important rift events. The first one during the Early-Mid Jurassic and the second one, partly controlled by structures of the former, during the Late Jurassic, coinciding with the deposition of the Nieuwerkerk Formation.Our study adds to the understanding of a multiple stage rifting history in the West Netherlands Basin. This is important, as the process influences reservoir thicknesses and with that, the amount of MW that can be extracted from geothermal aquifers. Therefore, this study forms a bridge between providing an integrated picture of the West Netherlands Basin and how the basins geological history affects its geothermal resources.

A digital outcrop example and associated structural analysis of highly deformed sedimentary strata from the Zagros Belt of Iran is presented. By providing this site in open-access, downloadable format, we aim to make this excellent outcrop exposure accessible to a wide range of geoscientists. Digital data extraction techniques are used to constrain structural interpretations and cross section orientation, as well as kinematic restorations of interpreted structures. Structural analysis protocols provided here are well-suited to learning outcomes associated with digital cross section construction, interpretation and restoration. Complex deformation at the study locality and associated uncertainties in horizon and fault mapping yield interpretation and structural restoration results that are likely non-unique. Interpretation uncertainties are discussed in the context of geoscience education, with specific reference to the need for considering and assessing data quality and underlying geological assumptions. Our workflow and results can be used to bridge the gap between field-based training at undergraduate level and the proficiency in 3D digital environments required of professional geoscientists. By using digital outcrops to achieve learning outcomes, knowledge of underlying geological processes and practical skills in digital data handling and treatment can be effectively communicated to future geoscientists within the virtual environment.

Major advances in smartphones and tablets in terms of their built-in sensors (esp. cameras), available computational power and on-board memory are transforming the role of such devices into the key digital platform around which geological fieldwork is redesigning itself. This digital transition is changing how geoscientists collect and share multimodal-multidimensional field datasets, which can now be readily distributed via standardized exchange formats and online data repositories. The increased accessibility of digital field datasets means that such data products are no longer the sole preserve of geospatial/geoscience specialists, but also students, stakeholders and the general public alike, providing great opportunities for knowledge transfer over the entirety of the research value chain. In the wake of this digital transition, the geological community has welcomed with enthusiasm and curiosity the introduction during 2020 of a native LiDAR scanner equipped on both the iPad Pro and the iPhone 12 Pro. This scanner offers a potential paradigm shift in digital geological fieldwork and puts these devices at the forefront of smartphone assisted fieldwork. In this work, we review progress in smartphone/tablet assisted geological fieldwork and test the iPhone 12 Pro's effectiveness as a replacement for conventional geological field tools. Specifically, we evaluate the geo-location accuracy of the iPhone's Global Navigation Satellite System (GNSS) receiver, the effectiveness of its inertial measurement unit (IMU) and magnetometer for orientation data collection, its photo-video imaging capabilities, and the performance of the device's newly equipped LiDAR in the field. We demonstrate that the performance of the iPhone for orientation and raster image data capture is high, being comparable to analog compass-clinometers and reflex/mirrorless cameras. Whilst location error is within the order of a few meters, the level of accuracy and the fast stabilization of the signal means that, beyond survey grade applications, the iPhone's geo-location capabilities are acceptable for most field cases. With regards to the iPhone's built-in LiDAR scanner, it is an excellent tool for depth assisted camera focusing and for casual 3D outcrop sharing, especially for ‘soft’ applications such as geo-heritage documentation and the production of teaching materials (here we also propose a simple mode of uploading outcrops models in Google Maps). However, the generated 3D models in some cases may be considered overly crude for detailed interrogation, particularly where the fidelity of the surface reconstruction is critical to the analysis (e.g. mesh facet orientation estimation). Based on our review of the evolution of digital field acquisition technologies and on our extensive field testing of the sensor suite integrated within the iPhone 12 Pro, it is clear that the digital transition of geological fieldwork is already mature, whereby smartphone devices have become as indispensable in the field as the geologists' traditional hammer and hand lens.

Bedding-perpendicular joints striking parallel (longitudinal) and perpendicular (transverse) to both the axis of the hosting anticline and the trend of the foredeep-belt system are widely recognized in fold-and-thrust belts. Their occurrence has been commonly attributed to folding-related processes, such as syn-folding outer-arc extension, although they can also be consistent with a pre-folding foredeep-related fracturing stage. Here we report the pre-folding fracture pattern affecting the Pietrasecca Anticline, in the central Apennines (Italy), resolved by a detailed field structural analysis. Field observations, scan-lines and interpretation of virtual outcrops were used to study the intensity, distribution and the orientations of fracture pattern along the anticline. The fracture pattern of the Pietrasecca Anticline consists of longitudinal and transverse joints, oriented approximately perpendicular to bedding, and of a pre-folding longitudinal pressure-solution cleavage set, which is oblique to bedding regardless of the bedding dip. Cross-cutting relationships show that joints predated the development of the pressure-solution cleavage. Furthermore, joint intensity does not relate to the structural position along the anticline. Taken together, these observations suggest that jointing occurred in a foredeep environment before the Pietrasecca Anticline growth. Our work further demonstrates that joints striking parallel and orthogonal to the main fold axis do not necessarily represent syn-folding deformation structures.

In the West Somali Basin, the classic plate tectonic reconstructions describe an early Cretaceous intraplate deformation of oceanic crust (Hauterivian to Aptian) followed by the activation of a major transform fault (Davie Fracture Zone) displacing Madagascar southward for more than 1000 km. In this contribution, using vintage and new high-resolution 2D, 3D seismic reflection data and exploration wells, we show the first clear images of a poorly known tectonic structure: the Seagap fault. The Seagap fault is represented by a complex fault zone of several hundred kilometres of extent, oriented parallel to the Davie Fracture Zone and defined by segment faults, relay zones and step overs structures. It appears to have continuously acted as left-lateral strike slip fault during the Paleogene and most of the Neogene. From structural and stratigraphic observations of both existing and newly interpreted 3D seismic data, the Seagap appears nucleating as a strike-slip fault by reactivating failed Jurassic oceanic spreading zones. At regional scale the main fault appears to cut the main Neogene pervasive extensional oblique rift structures and at place to re-work some of the major Cenozoic inherited structure, creating apparent restraining bend structure. The sinistral kinematic nature of the transcurrent history, suggests that the Seagap fault acted as an independent feature respect to the Davie Fracture Zone. During the Quaternary the Seagap, which also parallels the seismically active Kerimbas rift, shows reduced offsets and appears to slip with normal displacement. We discuss the tectonic significance of the Seagap fault with respect to both to the major extensional oblique rift structural trend offshore Tanzania and the Davie Fracture Zone.

The Apennines form an active fold and thrust belt that develops as part of the W-Mediterranean subduction zone. The evolution of the collisional system is driven by the retreating subduction of the alpine Tethys, which has caused the migration of compressive fronts and the opening of the Liguro-Provençal and Tyrrhenian back-arc basins, along with the rotation and translation of the Sardinia-Corsica and Calabria blocks. The Apennines make the northern limb of the Apennines-Calabria-Sicily orocline, developed due to the differential SE-ward retreat of the subduction system. In such a context, the central-southern Apennine system develops a foreland basin floored by a subaerial forebulge unconformity followed by a trinity of diachronous lithostratigraphic units: (i) shallow-water carbonates, (ii) hemipelagic marls, and (iii) siliciclastic turbidites. Previous studies have used the following datasets for reconstructing the evolution of the orogenic-foreland basin system: paleomagnetic data; the age of the siliciclastic syn-orogenic deposits filling the foredeep and wedge-top depozones; the age of the late-orogenic extensional basins. In this study, we highlight the importance of dating with high precision the onset of the Apennine orogenesis by means of Sr-isotope stratigraphy applied to the first carbonate sediments overlying the forebulge unconformity. In this regard, we have investigated a transect of the Apennine belt, extending from inner to outer sectors, in order to constrain the timing and style of migration of the belt and foreland basin. Our results show progressive rejuvenation of the forebulge unconformity toward the outer portions of the belt. More importantly, we highlight a time delay between the onset of syn-orogenic shallow-water carbonate deposition and the onset of siliciclastic turbidite deposition that ranges between 1 and 11 myr. In detail, the trends in the delay point at three main evolutive steps: 1) rapid evolution from forebulge to foredeep during the Burdigalian, 2) higher delays from the Serravallian until the latest Miocene, and 3) progressive decrease of the delay from the Zanclean. We associate the different velocity of migration with the differential slab retreat and spreading of the back-arc basins.

Little is still known about the structural fabric of a potential continuation of the East African Rift System (EARS) offshore Tanzania in the West Somali Basin. This continuation has been established mostly through sparse GPS measurements, earthquake slip vector data, spatial distribution of teleseismically detected earthquake focal mechanisms, and some recent seismic reflection data. West of the Davie Ridge (which part of a larger structure named the Davie Fracture Zone) and across its northern extension, regional seismic reflection profiles indicate the occurrence of continental - oceanic crust transition, which is characterized by early Cretaceous reverse faulting localized along deformation corridors. After the Aptian, the seafloor spreading ceased and the Tanzania margin evolved into a passive margin dominated by clastic deep-water deposition. In this contribution, we describe some results obtained from structural mapping of a 3D seismic dataset, calibrated by few explorations well, covering an area located between the Davie Ridge and the continent, south of Mafia Island. The seismic data maps suggest a major structural style change across the Neogene that is still active today. The recent structures are represented by two main interacting fault trends: some NS boundary faults corridors and a NW-SE internal arcuate segmented fault, both depicting a widely and diffused distribution of normal fault (with an overall cumulative amount of horizontal brittle extension ranging between 5 to 10 km). Some of the largest faults appear to reactivate older extensional structures but the general absence of growth faults cutting across the Paleo-Neogene depositional units suggest very recent rift re-activation. The recent rift system appears to show a component of obliquity with respect to the orientation of the Davie Ridge, and to the onshore structure related to the EARS tectonics.

In accretionary convergent margins, the subduction interface is formed by a lower plate décollement above which sediments are scraped off and incorporated into the accretionary wedge. During subduction, the basal décollement is typically located within or at the base of the sedimentary pile. However, the transition to collision implies the accretion of the lower plate continental crust and deformation of its inherited rifted margin architecture. During this stage, the basal décollement may remain confined to shallow structural levels as during subduction or re-localize into the lower plate middle-lower crust. Modes and timing of such re-localization are still poorly understood. We present cases from the Zagros, Apennines, Oman, and Taiwan belts, all of which involve a former rifted margin and point to a marked influence of inherited rift-related structures on the décollement re-localization. A deep décollement level occurs in the outer sectors of all of these belts, i.e., in the zone involving the proximal domain of pre-orogenic rift systems. Older—and shallower—décollement levels are preserved in the upper and inner zones of the tectonic pile, which include the base of the sedimentary cover of the distal portions of the former rifted margins. We propose that thinning of the ductile middle crust in the necking domains during rifting, and its complete removal in the hyperextended domains, hampered the development of deep-seated décollements during the inception of shortening. Progressive orogenic involvement of the proximal rift domains, where the ductile middle crust was preserved upon rifting, favors its reactivation as a décollement in the frontal portion of the thrust system. Such décollement eventually links to the main subduction interface, favoring underplating and the upward motion of internal metamorphic units, leading to their final emplacement onto the previously developed tectonic stack.

The Tyrrhenian back-arc basin developed at the rear of the E-ward migrating Apennine fold-and-thrust belt, with northward decreasing rollback of the subducting Adria slab leading to northward fading of back-arc extension. The northern portion of the Tyrrhenian basin is made of thinned continental crust, whereas in the central/southern portion extension eventually evolved to oceanic crust production. In this framework, a long-lasting debate concerns the existence of a >200 km long transform zone along the 41st parallel, which should separate the two portions of the Tyrrhenian basin. At its eastern termination, a branch of the presumed transform zone enters the Tyrrhenian margin of the Apennine belt and occurs as an accommodation zone made of a ribbon of extensional faults and related basins. This accommodation zone, which separates areas of mutually perpendicular extension directions, is here introduced, described, and named the Ponza-Alife accommodation zone. Interpretation of seismic lines and new structural and stratigraphic data from this accommodation zone have been used to constrain the pre-orogenic and syn-orogenic architecture of the subducting plate and the Plio-Quaternary back-arc extensional stage. Our data indicate that the studied zone retraces a deep-seated transform fault system located in the subducting plate and inherited from an Early Jurassic rifting episode, which caused the lateral juxtaposition of different rift domains in the subducting plate. We propose that during collision and trench retreat, this lateral juxtaposition has controlled differential retreat of the subducting plate across the studied zone, forcing the development of the Ponza-Alife accommodation zone in the overlying back-arc basin's margin.

Fault zones can often display a complex internal structure associated with antithetic faults, branch and tip points, bed rotations, bed-parallel slip surfaces, and subordinate synthetic faults. We explore how these structural complexities may affect the development of fault-related fractures as displacement accumulates. We analysed in detail an incipient fault zone within well-bedded, shallow-water carbonates of the southern Apennines thrust belt (Italy). The fault zone crops out with quasi-complete exposure at a reservoir scale on an inaccessible sub-vertical cliff face, and fault and fracture mapping were carried out on a 3D virtual outcrop model of the exposure built for this study using photogrammetry. Comparing the structure of the fault zone and the density of 9444 mapped fractures allowed us to unravel their spatial relationships. Our results show that the areas of denser fractures coincide with: (i) rock volumes bounded by antithetic faults developed within the fault zone, (ii) branch points between these antithetic faults and fault zone-bounding fault segments, (iii) fault zone-bounding fault segments associated with significant displacement gradients, and (iv) relay zones between subordinate synthetic faults. These findings may aid locating sub-seismic resolution volumes of dense fracturing and associated enhanced permeability within faulted reservoirs.

We combined structural data collected in the field and those obtained from a virtual outcrop model constructed from drone imagery, to perform Discrete Fracture Network (DFN) modelling and to characterize the fracture distribution within the damage zone of the low-displacement (~50 m) carbonate-hosted Pietrasecca Fault (PF) (central Apennines, Italy). Both in the hanging wall and in the footwall damage zones, fractures are vertical and parallel to slightly oblique to the fault strike. Fracture length distributions in the footwall damage zone indicate a high degree of fracture maturity, while in the hanging wall damage zone they indicate a low degree of fracture maturity. Pervasive stylolitization in the hanging wall must have hindered the development of through-going fractures, favoring diffuse fracturing characterized by stylolite-bounded fractures. DFN models suggest that permeabilities are 1–2 orders of magnitude greater in the footwall damage zone than in the hanging wall damage zone. As permeability (10−12 to 10−15 m2) is comparable with those measured in large-displacement (up to 600 m) faults in carbonates, our results show that also damage zones accompanying carbonate faults with ~50 m of displacement could be fracture corridors for efficient fluid flow within subsurface reservoirs. Therefore, we propose that jumps in subsurface permeabilities occurring in many carbonate fractured reservoirs could be associated with to the occurrence of high permeability fracture zones developed within damage zones of low-displacement faults. As the recent advancement in seismic imaging allow the recognition of faults with displacement in the order of a few tens of meters, reservoir geologists and engineers can apply results of this study to better model the subsurface flow pathways near low displacement faults in carbonate reservoirs.

The Apennines are a retreating collisional belt where the foreland basin system, across large domains, is floored by a subaerial forebulge unconformity developed due to forebulge uplift and erosion. This unconformity is overlain by a diachronous sequence of three lithostratigraphic units made of (a) shallow-water carbonates, (b) hemipelagic marls and shales and (c) siliciclastic turbidites. Typically, the latter two have been interpreted regionally as the onset of syn-orogenic deposition in the foredeep depozone, whereas little attention has been given to the underlying unit. Accordingly, the rate of migration of the central-southern Apennine fold-thrust belt-foreland basin system has been constrained, so far, exclusively considering the age of the hemipelagites and turbidites, which largely post-date the onset of foredeep depozone. In this work, we provide new high-resolution ages obtained by strontium isotope stratigraphy applied to calcitic bivalve shells sampled at the base of the first syn-orogenic deposits overlying the Eocene-Cretaceous pre-orogenic substratum. Integration of our results with published data indicates progressive rejuvenation of the strata sealing the forebulge unconformity towards the outer portions of the fold-thrust belt. In particular, the age of the forebulge unconformity linearly scales with the pre-orogenic position of the analysed sites, pointing to an overall constant migration velocity of the forebulge wave in the last 25 Myr.

Since the advent of affordable consumer-grade cameras over a century ago, photographic images have been the standard medium for capturing and visualizing outcrop-scale geological features. Despite the ubiquity of raster image data capture in routine fieldwork, the development of close-range 3D remote-sensing techniques has led to a paradigm shift in the representation and analysis of rock exposures from two- to three-dimensional forms. The use of geological 3D surface reconstructions in routine fieldwork has, however, been limited by the portability, associated learning curve, and/ or expense of tools required for data capture, visualization, and analysis. Smartphones are rapidly becoming a viable alternative to conventional 3D close-range remote-sensing data capture and visualization platforms, providing a catalyst for the general uptake of 3D outcrop technologies by the geological community, which were up until relatively recently the purview of a relatively small number of geospatial specialists. Indeed, the continuous improvement of smartphone cameras, coupled with their integration with global navigation satellite system (GNSS) and inertial sensors provides 3D reconstructions with comparable accuracy to survey-grade systems. These developments have already led many field geologists to replace reflex cameras, as well as dedicated handheld GNSS receivers and compass clinometers, with smartphones, which offer the equivalent functionality within a single compact platform. Here we demonstrate that through the use of a smartphone and a portable gimbal stabilizer, we can readily generate and register high-quality 3D scans of outcropping geological structures, with the workflow exemplified using a mirror of a seismically active fault. The scan is conducted with minimal effort over the course of a few minutes with limited equipment, thus being representative of a routine situation for a field geologist.

Geotagged smartphone photos can be employed to build digital terrain models using structure from motion-multiview stereo (SfM-MVS) photogrammetry. Accelerometer, magnetometer, and gyroscope sensors integrated within consumer-grade smartphones can be used to record the orientation of images, which can be combined with location information provided by inbuilt global navigation satellite system (GNSS) sensors to geo-register the SfM-MVS model. The accuracy of these sensors is, however, highly variable. In this work, we use a 200 m-wide natural rocky cliff as a test case to evaluate the impact of consumer-grade smartphone GNSS sensor accuracy on the registration of SfM-MVS models. We built a high-resolution 3D model of the cliff, using an unmanned aerial vehicle (UAV) for image acquisition and ground control points (GCPs) located using a differential GNSS survey for georeferencing. This 3D model provides the benchmark against which terrestrial SfM-MVS photogrammetry models, built using smartphone images and registered using built-in accelerometer/gyroscope and GNSS sensors, are compared. Results show that satisfactory post-processing registrations of the smartphone models can be attained, requiring: (1) wide acquisition areas (scaling with GNSS error) and (2) the progressive removal of misaligned images, via an iterative process of model building and error estimation.

The Zagros thrust belt formed due to the convergence between the Arabian and Eurasian plates during the closure of the Neo-Tethys Ocean. GPS measurements show that the northward relative motion of ...

Joint systems in the eastern portion of the Ebro Basin of the eastern Pyrenees enjoy near continuous exposure from the frontal portion of the belt up to the external portion of its associated foredeep. Utilizing orthophoto mosaics of these world class exposures, we have manually digitized over 30 000 joints within a 16 × 50 km study area. The mapped traces exhibit orientations that are dominantly perpendicular to the trend of the belt (transverse) and, subordinately, orthogonal to it (longitudinal). In particular, joints systematically orient perpendicular to the trend of the belt both in the frontal folds and in the inner and central portion of the foredeep basin. Longitudinal joints occur rarely, with a disordered spatial distribution, exhibiting null difference in abundance between the belt and the foredeep. Joint orientations in the external portion of the foredeep become less clustered, with adjacent areas dominated by either transverse or oblique joints. Our data indicates that joints in the studied area formed in the foredeep in response to a foredeep-parallel stretching, which becomes progressively less intense within the external portion of the foredeep. There, the minimum stress direction becomes more variable, evidencing poor contribution of the forebulge-perpendicular stretching on stress organization.

Fault roughness is a general term used to indicate dimension and distribution of fault asperities. Due to the role that fault asperities play on slip dynamics and frictional behavior during the seismic cycle, fault roughness constitutes a key element to understand earthquakes nucleation. Since it is not possible to recover fault roughness from seismogenic sources, faults at surface are generally used as analogues. However, those faults are in most cases subject to weathering and their roughness can lose seismogenic representativeness. Active faults episodically expose “fresh” fault zones constituting the best targets for seismogenic roughness evaluations.Here we present the study conducted on a splay of the Mt. Vettore fault system in the Central Apennines (Italy), along a vertical transect that includes both a weathered and a freshly exposed portion of the fault. The latter was exposed after the dramatic Mw 6.5 shock that hit the area on the 30th of October 2016. We produced a high detailed model of a part of the fault by means of structure from motion-multiview stereo (SfM-MVS) photogrammetry to assess its roughness parameters and to determine how these are affected by weathering. Our results show that weathering increases the value of the fractal parameters. Accordingly, we conclude that using high resolution point clouds it is possible to recognize patches of fault having similar exposition time to weathering.

The Mountain Front Flexure is a major structure of the Zagros orogenic system, and is underlain by the deeply rooted and seismically active Mountain Front Fault system. These coupled structural features divide the belt from its foreland and their trace is sinuous, forming salients and recesses. The origin and tectonic significance of the Mountain Front Fault system and its sinuosity are still unclear, with most of hypotheses pointing to a strong structural control exerted by geological inheritances. In this work we combine interpretation of seismic reflection profiles, earthquake data, geomorphic analysis, and geological observations, to build a balanced cross section across the Mountain Front Flexure in the Lurestan region. Our data are suggestive of a hybrid tectonic style for the Lurestan region, characterised by a major and newly developed crustal ramp in the frontal portion of the belt (i.e the Mountain Front Fault) and by the reactivation of steeply dipping pre-existing basin-bounding faults, along with a minor amount of shortening, in the inner area. Specifically, the integration of our results with previous knowledge indicates that the Mountain Front Fault system developed in the necking domain of the Jurassic rift system, ahead of an array of inverted Jurassic extensional faults, in a structural fashion which resembles that of a crustal-scale footwall shortcut. Within this structural context, the sinusoidal shape of the Mountain Front Flexure in the Lurestan area arises from the re-use of the original segmentation of the inverted Jurassic rift system.

Joint systems in the eastern portion of the Ebro Basin of the eastern Pyrenees enjoy near continuous exposure from the frontal portion of the belt up to the external portion of its associated foredeep. Utilizing orthophoto mosaics of these world-class exposures, we have manually digitized over 30 000 joints within a 16 km×50 km study area. The mapped traces exhibit orientations that are dominantly perpendicular to the trend of the belt (transverse) and, subordinately, parallel to the belt (longitudinal). In particular, joints systematically orient perpendicular to the trend of the belt both in the frontal folds and in the inner and central portion of the foredeep basin. Longitudinal joints occur rarely with a disordered spatial distribution, exhibiting null difference in abundance between the belt and the foredeep. Joint orientations in the external portion of the foredeep become less clustered, with adjacent areas dominated by either transverse or oblique joints. Our data indicate that joints in the studied area formed in the foredeep in response to a foredeep-parallel stretching, which becomes progressively less intense within the external portion of the foredeep. There, the minimum stress direction becomes more variable, providing evidence of the poor contribution of the forebulge-perpendicular stretching on stress organization.

In fold and thrust belts developing at convergent margins, the migration of the advancing wedge is accompanied by bulging of the downgoing plate, followed by the development of a foredeep basin filled by a thick succession of syn-orogenic sediments. The transition from forebulge to foredeep marks a key moment in the evolution of the orogenic system. In deep water environments, the record of this transition is typically complete and progressive. Conversely, in the shallow-water/continental environment of many collisional systems, the uplift of the forebulge area can imply emersion and erosion, obliterating the stratigraphic record of key steps of the evolution of the orogenic system. The southern Apennines constitute one of these collisional fold and thrust belts where the development of the forebulge has implied emersion and erosion, with the development of a Miocene forebulge erosional unconformity, accompanied by extensional deformation associated with the bending of the lithosphere during the forebulge stage. In this paper, we use strontium isotope stratigraphy to constrain with unprecedented time-resolution the age of the forebulge unconformity in areas presently incorporated in the northern sector of the southern Apennines fold and thrust belt. Integration of our results and those of previous studies indicates, at the regional scale, a younging toward the foreland of the forebulge unconformity across the belt. Our high-resolution ages also reveal a diachronous onset of the flexural subsidence over short distances, associated with the occurrence of horst and graben structures, possibly resulting from inherited paleotopography along with forebulge extension. This work highlights how high-resolution dating is critical to unravel the evolution of foreland basin systems at different scales.

To unravel how and where coseismic and interseismic deformation impacts the spatial and temporal patterns of rock uplift of the Lurestan sector of the Zagros Mountains, we performed an investigation of the large‐scale features of topography and river network coupled with 2‐D finite element modeling. Geomorphological analysis and constraints from parameters such as elevation, local relief, normalized channel steepness index (ksn), river longitudinal profiles, and transformed river profiles (chi plots) were used to unravel the time‐space distribution of vertical motions. Whereas the much longer timescale over which topography grows and/or rivers respond to tectonic or climatic perturbations with respect to even multiple seismic cycles, the outputs of the finite element model yield fundamental information on the source of the late part of the spatiotemporal evolution of surface uplift recorded by the geomorphology. Model outputs shed new light into the processes controlling relief evolution in an actively growing mountain belt underlain by a major blind thrust. The outputs illustrate how coseismic slip controls localized uplift of a prominent topographic feature—the Mountain Front Flexure—located above the main upper crustal ramp of the principal basement thrust fault of the region, while continuous displacement along the deeper, aseismic portion of the same basement fault controls generalized uplift of the whole crustal block located farther to the NE, in the interior of the orogen.

Smartphones can be regarded as cameras, natively equipped with geolocation and orientation sensors, making them powerful, portable, user-friendly and inexpensive tools for terrestrial structure from motion/multiview stereo photogrammetry (SfM-MVS) surveys. Camera extrinsic parameters (i.e. camera position and orientation), required to produce fully georeferenced SfM-MVS 3D models are available for the majority of smartphone images via inbuilt magnetometer, accelerometer/gyroscope, and global navigation satellite system (GNSS) sensors. The precision of these internal sensors is not yet sufficient to directly use them as input to SfM-MVS photogrammetric reconstructions. However, when the reconstructed scene is significantly greater than the positional error, camera extrinsic parameters can be successfully used to register 3D models during post-processing. We present a survey of a 400 m wide vertical cliff to illustrate a workflow that enables the use of smartphone cameras to generate and fully georeference photogrammetric models without employing ground control points. Survey images were acquired at a distance of ~350 m to the mapped scene using a consumer-grade smartphone. This survey image dataset was subsequently used to build an unreferenced 3D model, which was registered during post-processing using orientation and position metadata tagged to each photograph.

In this work, we present a Google Earth (GE) based virtual field mapping exercise, designed for master’s and bachelor’s students of geology and aimed at supporting or replacing field mapping training courses. The exercise consists of mapping geological limits and faults in a poorly vegetated area of the Lurestan region (Zagros thrust and fold belt). The occurrence of cliff- forming and recessive formations allows students to recognise directly on GE the first order geological structures of the area, which include faults and folds with wavelengths of many kilometers. The provided input data includes a stratigraphic description of the exposed formations, field photographs, and a set of field checkpoints. The material can be provided entirely or partly, depending on the students’ level and workload required. The full dataset is intended for undergraduate students with little or no field experience, while master students are expected to complete the exercise with limited input data. Additionally, the exercise can be limited/focused on sub-areas or extended on the entire area. This virtual mapping exercise is expected to empower students’ ability to visualize, understand and reconstruct 3D geological surfaces; providing an essential tool for future scholars and practitioners.

Fault roughness constitutes a key element in the understanding of earthquake nucleation, and surficial asperities on the fault plane play a critical role in slip dynamics and frictional behavior during the seismic cycle. Since it is not generally feasible to recover fault roughness profiles or maps directly at the seismogenic sources, faults at the Earth’s surface are typically used as analogues. However, these analogue fault surfaces are often subjected to weathering and erosion, which in turn, reduces their representativeness as seismogenic faults. Rupture along active faults episodically exposes “fresh” fault planes at the Earth’s surface, which represent the best available targets for the evaluation of fault roughness generated at seismogenic depths.Here we present a study conducted on a splay of the Mt. Vettore fault system in the Central Apennines, Italy, along a vertical transect that includes both a weathered and freshly exposed portion of the fault. The latter was exposed after the dramatic Mw 6.5 shock that hit the area on 30 October 2016. We have produced a highly detailed model (i.e., point cloud) of a section of the fault using structure from motion-multiview stereo photogrammetry to assess its roughness parameters (i.e., the Hurst fractal parameter) and to determine the extent to which these parameters are affected by weathering assuming that they had similar fractal characteristics when reaching the surface.Our results show that weathering can modify the value of the fractal parameters. In particular, by independently analyzing different patches of the fault, we have observed that the smoother and recently exposed portions have an average Hurst exponent of 0.52 while the average Hurst exponent of zones with more prolonged exposure times is 0.64. Accordingly, we conclude that by using high-resolution point clouds, it is possible to recognize patches of faults having a similar intensity of deterioration attributable to weathering.

The eastern Persian Gulf hosts several salt structures sourced from two different evaporite layers, the Neoproterozoic-Cambrian Hormuz Salt and the Oligocene-Miocene Fars Salt. Based on seismic interpretation, we discuss the kinematics and dynamics of this autochthonous multi-layer salt system for three case studies: the Tunb and Hengam diapirs, and the Taftan salt anticline. Halokinetic sequences related to Hormuz salt evacuation suggest three main stages of evolution: i) onset of Hormuz Salt diapirism (Paleozoic), ii) diapir squeezing, and emplacement of allochthonous Hormuz Salt (Late Cretaceous to Oligocene-Miocene), and iii) development of secondary and tertiary salt welds (Upper Miocene). Since Fars Salt structures are absent in areas devoid of allochthonous Hormuz Salt, our structural model interprets that the driving mechanism for Fars Salt diapirism is directly related to the emplacement of allochthonous Hormuz Salt during the Zagros-Oman contractional event. The related halokinetic sequences suggest that the Fars Salt diapir kinematic style depends on to the timing of Hormuz Salt extrusion with regards to Fars Salt deposition. Our results provide new insight into the interaction between salt structures sourced from two distinct autochthonous salt layers.

In this work, the application of consumer-grade virtual reality (VR) hardware and software to the analysis of digital outcrop data is explored. Here, we utilize a widely available VR hardware platform (HTC Vive) and VR based freeform 3D visual arts software package (Google Tilt Brush), to digitize fault traces from photo-textured digital outcrop models of exposures of the Penrith Sandstone Formation (Lacy's Caves), in northwest England. Using MATLAB routines provided herein, triangular meshes output from Tilt Brush are used as the basis for 3D fracture trace map extraction, which in turn, are used to generate fracture properties (trace length, orientation, areal fracture intensity). We compare the results of this analysis to two equivalent datasets obtained from the Lacy's Caves model using digital outcrop analysis deployed via a conventional flat panel display: namely (1) a 3D trace map extracted using optical ray tracing from manually interpreted calibrated images and (2) 3D traces fitted directly the Lacy's Caves textured mesh using manual polyline interpretation within an established digital outcrop analysis software platform (OpenPlot). Fault statistics obtained using VR based analysis are broadly equivalent to those acquired from 3D trace maps extracted using the flat panel display deployed analyses presented herein. In this case study, it was found that VR based digital outcrop analysis provided faster data acquisition than the comparative pixel-based approach, which requires linkage and merging of traces mapped from multiple contiguous images. Manual raster analysis and optical ray tracing did however provide 3D trace maps with significantly higher areal fault intensity, with VR analysis incurring censoring of finer fault traces, due to the limited resolution of the outcrop model textured mesh. Whilst data acquisition times and resultant fault intensities proved similar between the VR and OpenPlot workflows, it was noted anecdotally, that the VR analysis holds some advantages for the operator when interpreting models exhibiting complex geometries, such as mine workings and caves systems, with the clip point implemented within the viewport of conventional digital outcrop analysis software tools obstructing the user from obtaining an optimum view of the outcrop surface. VR based digital outcrop analysis techniques, such as those presented here, provide an immersive analytical environment to the operator. This allows users to fuse powerful 3D visualizations of photo-realistic outcrop models with geological interpretation and data collection, fulfilling the early promise of ‘virtual outcrops’ as an analytical medium that can emulate traditional fieldwork. It is hoped that this study and its associated code library will facilitate the evaluation of emerging VR technologies for digital outcrop applications, by provided access to VR analytical tools for non-specialists in virtual reality systems. Finally, prospects for the use of VR technology within the field of digital outcrop geology, as well as within the wider geosciences, are also discussed.

Hydrocarbon accumulations in the Plataforma Burgalesa are located in structural traps that resulted from Mesozoic extensional forced folding. Pre-rift Triassic evaporites favoured the structural decoupling between faulted basement rocks and their supra-salt cover, which includes carbonate and fluvial reservoirs. These reservoir levels record severe syn-extension fracturing, related to the stretching of the supra-salt layers as extensional forced folding proceeded. The observed syn-extension fracture pattern has been partly modified by subsequent Cenozoic shortening. The availability of a large data set of seismic profiles, well data, oil shows, and the exposures of reservoir and seal levels, make the Plataforma Burgalesa an outstanding analogue for petroleum plays in extensional settings with supra-salt reservoirs. Here, we provide a reassessment of recently published structural data from the area, including geometry, kinematics, and fracture pattern of the partly inverted extensional forced fold system. We then compare structural features and occurrence of hydrocarbon accumulations, to discuss the implications for structural traps formation in rift basins with an intermediate decollement level.

We describe conjugate systems of shear-enhanced compaction bands oriented oblique to the maximum compressive stress and developed in Paleocene quartz-rich calcarenites formed by the interplay between shearing, mechanical compaction, and dissolution. These deformation bands are located in the footwall of the Cotiella Thrust (Spanish Pyrenees), and strike perpendicular to the local tectonic transport direction. Conjugate shear-enhanced compaction bands are mutually perpendicular in cross-section, forming an angle of 45° with the shallow-dipping bedding; no macroscopic evidence of shearing is found along them. These shear-enhanced compaction bands occur together with less abundant bedding-perpendicular compaction bands, which strike perpendicular to the local transport direction. The described shear-enhanced compaction bands consist of mm-thick tabular structures showing higher concentrations of quartz grains with reduced sizes in respect to the surrounding undeformed rock. Optical microscope and SEM investigations show that the high concentration of quartz clasts within the bands was caused by pressure-enhanced dissolution of calcite. Quartz grains fragmentation is also observed within the bands, with no significant clasts rotation and translation. All these features indicate that the described shear-enhanced compaction bands are hybrid structures developed during layer-parallel shortening associated with the Cotiella Thrust and are characterized by localized dissolution of calcite grains and fragmentation of quartz grains.

The 2017 Mw 7.3 Iran–Iraq earthquake occurred in a region where the pattern of major plate convergence is well constrained, but limited information is available on the seismogenic structures. Geological observations, interpretation of seismic reflection profiles, and well data are used in this paper to build a regional, balanced cross section that provides a comprehensive picture of the geometry and dimensional parameters of active faults in the hypocentral area. Our results indicate (i) the coexistence of thin- and thick-skinned thrusting, (ii) the reactivation of inherited structures, and (iii) the occurrence of weak units promoting heterogeneous deformation within the palaeo-Cenozoic sedimentary cover and partial decoupling from the underlying basement. According to our study, the main shock of the November 2017 seismic sequence is located within the basement, along the low-angle Mountain Front Fault. Aftershocks unzipped the up-dip portion of the same fault. This merges with a detachment level located at the base of the Paleozoic succession, to form a crustal-scale fault-bend anticline. Size and geometry of the Mountain Front Fault are consistent with a down-dip rupture width of 30 km, which is required for an Mw 7.3 earthquake.

We derive the discrete fracture network (DFN) of a Lower Cretaceous carbonate platform succession exposed at Mt. Faito (Southern Apennines), which represents a good outcrop analogue of the coeval productive units of the buried Apulian Platform in the Basilicata oilfields. A stochastic distribution of joints has been derived by sampling at two different scales of observation. At the outcrop scale, we measured fracture attributes by means of scan lines. At a larger scale, we extracted fracture attributes from a 3D model. This multiscale survey showed the occurrence of an arresting bed for through-going fractures, which is characterized by a low relative permeability, determining a vertical compartmentalization. The DFN model, obtained by integrating fieldwork and numerical modelling by means of the 3D-Move® software, shows a well-defined relationship of permeability and fracture porosity with the relative connectivity of the fracture network. The latter is influenced by the length and aperture and to a lesser extent by the fracture intensity. The permeability distribution obtained for our outcrop analogue can be used to inform modelling of the Basilicata oilfield reservoirs, although the different burial history between the exposed Apennine Platform and the buried Apulian Platform must be taken into account.