Normal Fault System Research Articles

Influence of Fault System Geometry and Slip Rates on the Relative Role of Coseismic and Interseismic Stresses on Earthquake Triggering and Recurrence Variability

AbstractWe model Coulomb stress transfer (CST) due to 30 strong earthquakes occurring on normal faults since 1509 CE in Calabria, Italy, including the influence of interseismic loading, and compare the results to existing studies of stress interaction from the Central and Southern Apennines, Italy. The three normal fault systems have different geometries and long‐term slip‐rates. We investigate the extent to which stress transfer can influence the occurrence of future earthquakes and what factors may govern the variability in earthquake recurrence in different fault systems. The Calabrian, Central Apennines, and Southern Apennines fault systems have 91%, 73%, and 70% of faults with mean positive cumulative CST in the time considered; this is due to fewer faults across strike, more across strike stress reductions, and greater along‐strike spacing in the three regions respectively. In regions with close along strike spacing or few faults across strike, such as Calabria and Southern Apennines, the stress loading history is mostly dominated by interseismic loading and most faults are positively stressed before an earthquake occur on them (96% of all faults that ruptured in Calabria; 94% of faults in Southern Apennines), and some of the strongest earthquakes occur on faults with the highest mean cumulative stress of all faults prior to the earthquake. In the Central Apennines, where across strike interactions are the predominant process, 79% of earthquakes occur on faults positively stressed. The results highlight that fault system geometry plays a central role in characterizing the stress evolution associated with earthquake recurrence.

Fault Rheology Control on Rupture Propagation and Aftershocks Distribution during the 2016–2017 Central Italy Earthquakes

Abstract The stress released by the large coseismic ruptures and related aftershock sequences is strongly a heterogeneous process. We show highly resolved images of the normal fault system ruptured during the 2016–2017 central Italy earthquake sequence, as obtained by the high-resolution local earthquake tomography allowing relocation of a massive set of aftershocks. We get evidence that lateral changes of elastic properties on the fault planes account for the complexity in the rupture processes during the two Mw > 6 earthquakes. We observe an emergent phase in the first part of the Mw 6.5 rupture, and the coseismic slip becomes large when the rupture breaks through high Poisson ratio portions of the fault. Mainshocks break the fault portions that, although limited and segmented by inherited structural complexity, were dynamically interfering during the faulting episodes. The close repetition of slip on the same relatively high Poisson ratio patch suggests a dynamic weakening of the fault and/or an incomplete stress release during the first mainshock.

Geophysical characteristics of a fault system in the northern Central Range of Taiwan and its applications for geothermal energy exploration

The northern Central Range of Taiwan is a high-potential geothermal region. Since the formations are mainly tight metasandstone and slate, permeable structures associated with faults are commonly considered as conduits of geothermal fluids. This study determines the characteristics and orientations of the permeable fault zones by analyzing the geophysical logs and microresistivity formation image log (FMI) of the JT-4 well in Jentse, an important geothermal area in the northern Central Range. Between 720 and 1480 m measured depth (MD), the effective porosity of the intact host rock is mostly below 3% calculated by the geophysical log. Zones with porosity greater than 5% are only clustered within a few thin intervals. The FMI interpretations show these porous zones are in the interior of the fractured and faulted intervals. These porous fault zones comprise fault damage zones with a high density of open fracture planes and fault cores with porous fault breccias. There is a highly brecciated fault core in 1334–1339 m MD, which would be the most permeable interval of the well. Additionally, some healed fault zones with sealed fractures are observed. The picked drilling-induced tensile fractures signify that the direction of the present-day maximum horizontal principal stress is N40–50°E, and most of the open fractures also strike parallel to the NE–SW direction. The study results show that the open fractures are concentrated in the four fault zones belonging to one major normal fault system. After integrating the orientations and locations of the fault zones, we propose that the permeable normal fault system is about 200 m wide, trends N50–70°E, and dips 70–80° to the NW. The development of the open fractures and the permeable fault system in the northern Central Range may be controlled by the current rifting of the Okinawa Trough offshore northeastern Taiwan. The study exhibits the characteristics of fractured fluid conduits of the regional geothermal system, which will benefit future geothermal exploration in northeastern Taiwan.

Crustal flow driving twin domes exhumation and low-angle normal faulting in the Menderes Massif of western Anatolia

Lower crustal flow in regions of post-orogenic extension has been inferred to explain the exhumation of metamorphic core complexes and associated low-angle normal (detachment) fault systems. However, the origin of detachment faults, whether initially formed as high-angle or low-angle shear zones, and the extension is symmetric or asymmetric remains enigmatic. Here, we use numerical modeling constrained by geophysical and geological data to show that symmetric extension in the central Menderes Massif of western Anatolia is accommodated by the crustal flow. Our geodynamic model explains how opposite dipping Gediz and Büyük Menderes detachment faults are formed by ∼40° footwall rotation. Model predictions agree with seismic tomography data that suggests updoming of lower crust beneath the exhumed massifs, represented as “twin domes” and a flat Moho. Our work helps to account for the genetic relation between the exhumation of metamorphic core complexes and low-angle normal faulting in both Cordillera and Aegean orogenic regions and has important implications on crustal dynamics in extensional provinces.

Basin-scale interaction between post-LGM faulting and morpho-sedimentary processes in the S. Eufemia Gulf (Southern Tyrrhenian Sea)

The integrated interpretation of high-resolution multibeam bathymetry, seismic profiles and backscatter data in the S. Eufemia Gulf (SEG; Calabro-Tyrrhenian continental margin, south-eastern Tyrrhenian Sea) documents the relationship between postglacial fault activity and morpho-sedimentary processes. Three systems of active normal faults that affect the seafloor or the shallow subsurface, have been identified: 1) the S. Eufemia fault system located on the continental shelf with fault planes mainly oriented N26E-N40E; 2) the offshore fault system that lies on the continental slope off Capo Suvero with fault planes mainly oriented N28E-N60E; 3) the Angitola Canyon fault system located on the seafloor adjacent to the canyon having fault planes oriented N60E-N85E. The faults produce a belt of linear escarpments with vertical displacement varying from a few decimeters to about 12 m. One of the most prominent active structures is the fault F1 with the highest fault length (about 9.5 km). Two main segments of this fault are identified: a segment characterised by seafloor deformation with metric slip affecting Holocene deposits; a segment characterised by folding of the seafloor. A combined tectono-stratigraphic model of an extensional fault propagation fold is proposed here to explain such different deformation.In addition to the seabed escarpments produced by fault deformation, in the SEG, a strong control of fault activity on recent sedimentary processes is clearly observed. For example, canyons and channels frequently change their course in response to their interaction with main tectonic structures. Moreover, the upper branch of the Angitola Canyon shows straight flanks determined by fault scarps. Tectonics also determined different sediment accumulation rates and types of sedimentation (e.g., the accumulation of hanging wall turbidite deposits and the development of contourite deposits around the Maida Ridge). Furthermore, the distribution of landslides is often connected to main fault scarps and fluids are locally confined in the hanging wall side of faults and can escape at the seabed, generating pockmarks aligned along their footwall.

Late Alpine multistage exhumation of the northwestern Rhodope Metamorphic Complex (northern Rila Mountains, Bulgaria)

AbstractThe Rhodope crystalline massif is an Alpine metamorphic complex exposed across several mountain ranges in southern Bulgaria and northern Greece which has experienced a complex history including continental collision, partial subduction and syn-metamorphic nappe stacking followed by syn- to post-contractional extension. We present new 40Ar/39Ar and fission-track data from samples taken from both sides of the North Rhodopean Detachment that were combined with detailed structural studies to investigate the tectonothermal evolution of the northern Rila Mountains. A migmatite from the hanging wall of the North Rhodopean Detachment yields a 40Ar/39Ar muscovite age of 100.79 ± 0.55 Ma, a zircon fission-track age of 38.6 ± 1.9 Ma, and an apatite fission-track age of 21.4 ± 1.5 Ma. A biotite schist from the footwall of the detachment yields 40Ar/39Ar biotite age of 34.90 ± 0.15 Ma, and zircon and apatite fission-track ages of 35.6 ± 5.6 and 13.3 ± 1.1 Ma, respectively. Our new data give evidence of a multistage exhumation of the study area. Late Early Cretaceous (~ 101 ± 0.6 Ma) cooling of the Variscan high-grade metamorphic basement through 440–400 °C was caused by either erosion of the emplacing thrust sheet, or post-contractional denudation. Fast exhumation along the North Rhodopean Extensional System drove a pulse of increased tectonic denudation and cooling during the Eocene (39–35 Ma). Exhumation of the rocks in the northern part of the Rila Mountains below 110 ± 10 °C during the middle–late Miocene was associated with displacement along a system of normal faults.

Training the creation, visualization and interpretation of fault maps for the subsurface – using tectonic geomorphology

Abstract Fault mapping is essential for understanding subsurface geological structure. However, effective training of students in developing and understanding fault patterns in 3D seismic imagery is impeded by the time-investment needed to acquire competence using software and then creating depth-structure maps of stratal horizons. Here an exercise is laid out that can achieve the desired experience – using the young fault systems of Afar (Djibouti), where former land-surface-defining basalt flows are offset by arrays of normal faults. The top-basalt surface, displayed on GoogleEarth, is in effect a depth-structure map and the gaps (‘fault-loss’) in this surface approximate to exposed fault surfaces. The mapping exercise is described and illustrated here step-wise. The fault system is gradually mapped out to reveal examples of long-continuous faults, branching patterns, relaying faults and isolated fault segments. Alternative criteria for identifying faults can be examined, with analogies in seismic interpretation. This can inform discussion of the approaches and uncertainties inherent in mapping faults in the subsurface. The study may be extended to consider the pattern of early–syn-rift depositional systems. Collectively these tasks can be progressed within an hour or so, providing effective insights into the structure of normal fault systems that cannot be replicated by conventional fieldwork.

Seismicity modulation due to hydrological loading in a stable continental region: a case study from the Jektvik swarm sequence in Northern Norway

SUMMARYSeismic swarms have been observed for more than 40 yr along the coast of Nordland, Northern Norway. However, the detailed spatio-temporal evolution and mechanisms of these swarms have not yet been resolved due to the historically sparse seismic station coverage. An increased number of seismic stations now allows us to study a nearly decade-long sequence of swarms in the Jektvik area during the 2013–2021 time window. Our analysis resolves four major groups of seismic events, each consisting of several spatial clusters, that have distinct spatial and temporal behaviours. Computed focal mechanism solutions are predominantly normal with NNE–SSW strike direction reflecting a near-vertical maximum principal stress and a NW–SE near-horizontal minimum principal stress, which are controlled by local NW–SE extension. We attribute the swarms to fluid-saturated fracture zones that are reactivated due to this local extension. Over the time period, the activity tends to increase between February and May, which coincides with the late winter and beginning of spring time in Norway. We hypothesize that the seismicity is modulated seasonally by hydrological loading from snow accumulation. This transient hydrological load results in elastic deformation that is observed at local Global Navigation Satellite System stations. The loading is shown to promote failure in a critically stressed normal faulting system. Once a segment is activated, it can then also trigger neighboring segments via stress transfer. Our new results point to a close link between lithosphere and hydrosphere contributing to the occurrence of seismic swarm activity in northern Norway.

Preservation of thermal signature of elevated syn-rift heat flow during multiphase extension: a case study from the Duntroon Sub-basin, Great Australian Bight

Quantifying the thermal histories of rift basins is important for evaluating their resource and CO2 storage potential because temperature controls hydrocarbon generation, and the diagenesis of reservoir rocks. However, in many rift basins, it is difficult to obtain evidence for elevated heat flow accompanying rifting, since paleotemperature data from drilled sections typically record heating related to post-rift burial. Here we integrate geochemical, geophysical and petrophysical data from the Duntroon Sub-basin, Great Australian Bight, that show how strain-migration during multiphase extension can preserve the signature of syn-rift elevated geothermal gradients. During the late Jurassic–early Cretaceous, rifting was focussed along ~ESE-striking normal fault systems in the northern part of the Duntroon Sub-basin. During the late Cretaceous, strain migrated to the southwest through the development of normal faults which accommodated the deposition of Upper Cretaceous strata. The Echidna-1 well was drilled into a basement high, in the footwall of a late Cretaceous fault system, penetrating ~2.5 km of Lower Cretaceous strata. Paleotemperature proxies define an early Cretaceous paleogeothermal gradient of ~60°C km−1, substantially higher than the present-day gradient. Our results indicate that preserved Lower Cretaceous strata were more deeply buried by ~1 km of additional section, which was likely eroded during an episode of mid-Cretaceous exhumation associated with the migrating locus of rifting; this enabled the preservation of thermal signature of elevated syn-rift heat flow. Similar evidence is also observed in the Otway Basin, demonstrating the regional extent of elevated syn-rift heat flow along the southern Australian margin.

Punctiform Breakup and Initial Oceanization in the Central Red Sea Rift

The Central Red Sea Rift is a natural laboratory to study the transition from rifting to spreading. Based on new reflection seismic profiles and gravity modeling, we examined the crustal structure, tectonic evolution, breakup mechanism, and future evolution of the Central Red Sea Rift. Along this rift axis, the breakup of continental lithosphere is discontinuous and the oceanic crust is limited to the axial deeps. The punctiform breakup and formation of deeps is assisted by mantle upwelling and topographic uplift, but the nucleation is directly controlled by the normal-fault system. The discontinuities spaced between axial deeps within the relatively continuous central troughs are presently axial domes or highs and will evolve into new deeps with tectonic subsidence. Isolated deeps will grow and connect with each other to become a continuous central trough, before transitioning into a unified spreading center.

A Reliable Procedure to Estimate the Rupture Propagation Directions from Source Directivity: The 2016–2018 Central Italy Seismic Sequence

Abstract We present a new approach to estimate the predominant direction of rupture propagation during a seismic sequence. A fast estimation of the rupture propagation direction is essential to know the azimuthal distribution of shaking around the seismic source and the associated risks for the earthquake occurrence. The main advantage of the proposed method is that it is conceptually reliable, simple, and fast (near real time). The approach uses the empirical Green’s function technique and can be applied directly to the waveforms without requiring the deconvolution of the instrumental response and without knowing a priori the attenuation model and the orientation of the activated fault system. We apply the method to the 2016–2017 Amatrice-Visso-Norcia high-energy and long-lasting earthquake series in central Italy, which affected a large area up to 80 km along strike, with more than 130,000 events of small-to-moderate magnitude recorded until the end of August 2022. Most of the selected events analyzed in this study have a magnitude greater than 4.4 and only four seismic events have a magnitude in the range of 3.3–3.7. Our results show that the complex activated normal fault system has a rupture direction mainly controlled by the pre-existing normal faults and by the orientation of the reactivated faults. In addition, the preferred direction of rupture propagation is also controlled by the presence of fluid in the pre-existing structural discontinuities. We discuss the possible role of fluids as a cause of bimaterial interface. Another important finding from our analysis is that the spatial evolution of seismicity is controlled by the directivity.

Three-dimensional S-wave velocity structure of the crust and upper mantle for the normal fault system beneath the Yinchuan Basin from joint inversion of receiver function and surface wave

Three-dimensional S-wave velocity structure of the crust and upper mantle for the normal fault system beneath the Yinchuan Basin from joint inversion of receiver function and surface wave

Structural evolution and mechanism of multi-phase rift basins: A case study of the Panyu 4 Sag in the Zhu Ⅰ Depression, Pearl River Mouth Basin, South China Sea

The study of changes in normal fault systems during different rift stages is important to understand the genesis and evolution of multi-phase rift basins, such as the Panyu 4 Sag in the Zhu Ⅰ Depression. Using 2D and 3D seismic data and analogue modelling, the Zhu Ⅰ Depression was characterized as a series of half-grabens bounded by NE-NEE-trending normal faults, it was found to have undergone two phases of the extension during the Paleogene. The Zhu Ⅰ Depression exhibited four fault sets with different strikes, including NNE, NE-NEE, EW, and NWW. The main controlling faults were NE-trending and EW-trending with high activity rates during Rift Phase 1 and Rift Phase 2, respectively. The average azimuths of the dominant strikes for type Ⅰa, type Ⅰb, and type Ⅱ faults were 75°, 85°, and 90°, which revealed that the minimum principal stress (σ3) directions during the rift phases 1 and 2 of the Zhu Ⅰ Depression were SSE (∼165°) and near-EW (∼180°), respectively. Two phases of structural-sedimentary evolution, with different directions and analogue modelling results, illustrated that the Panyu 4 Sag was formed as a superimposed basin under multi-phase anisotropic extension. The structural evolution of the Panyu 4 Sag since the Paleogene was mainly controlled by the combined effects of the Pacific, Eurasian, and Indian plates. Since the orientation of subduction of the Pacific plate changed from NNW to NWW, the stress field shifted from NW-SE-trending tension to S-N-trending tension, causing the superimposition of late near-E-W-oriented structural pattern on the early NE-oriented structural pattern.

Regional significance of normal fault systems in the western Canadian Beaufort Sea (Mackenzie delta)

The Beaufort-Mackenzie fold and thrust belt in Arctic Canada corresponds to the offshore part of the Cordilleran orogen in Yukon and Alaska. Previous tectonic studies in this area focussed on contractional structures, and comparatively little attention has been paid to normal faults, even though they are ubiquitous in the shallow Beaufort Sea. Normal faults dip either seaward or landward and most faults are located on the apex of anticlines. Despite the clear spatial relationship with anticlines, normal faults initiated after fold development as the delta front migrated seaward. Accordingly, Oligocene to Pliocene extensional structures are interpreted as recording gravity-driven deformation superimposed on an existing, mainly Eocene, fold and thrust belt. Several normal faults extend downward onto one of the anticline limbs, but the control of the fold geometry on the dip of the faults (seaward or landward) remains poorly understood. Seismic amplitude anomalies suggest that normal faults acted as fluid (most probably thermogenic gas) migration pathways.

Late Quaternary slip rate of the Fengmenkou-Wuzhiling fault at the southern margin of North China block (S-NCB)

The regional crustal slipping behaviour within the interaction zone of the North China and Qinling blocks reveals the pattern of extensional grabens merging with strike-slip faults and establishes the contribution of these faults to the regional basin generation. In this study, we aimed to assess the active slipping at the Laojing Gou site along the Fengmenkou-Wuzhiling fault (FMK-WZLF), one of the main active faults at the southern margin of North China block (S-NCB), by setting a three-dimensional measurement of the offset in buried paleochannels. Mapping, trenching, and age constraints of the geomorphic and stratigraphy units illustrate three offset paleo-fluvial surfaces since the Late Pleistocene, named S1, S2, and S3, along the fault strike direction. Beneath the surface, the structure of isolated confined paleo-channels C1 and C3 was exposed on the stratigraphy profile, and they were active during 130–75 ka and 2.8–3.0 ka, respectively. We presented a set of adapted scripts for three-dimensional measurements to calculate the lateral and normal tectonic components. The left lateral slip rate for the FMK-WZLF was estimated to be 0.25–0.45 mm/a, and the long-term oblique slipping behaviour generated the scarps in a dip of 70° ± 5° across the fault plane. The oblique slip of the FMK-WZLF, together with the regional E-W and SW-NE striking normal fault system, shapes the northeastward flowing Yiluo river and the southeastward flowing Huai river at S-NCB.

Internal architecture and structural evolution of a horst relay zone from the northern Gulf of Suez rift, Egypt: Implications for syn-rift sedimentation

A remarkable outcrop of an extensional NW-oriented horst block takes place between conjugate normal fault segments at the Akheider-El Ramliya fault block (ARFB), along the northwestern termination of the Gulf of Suez rift. Detailed field geological mapping is accomplished to identify the architecture, linkage style as well as evolution of the encountered normal fault system at the ARFB. The resultant structural model revealed several geometries of normal faults interaction that form soft- and hard-linkage relay zones affecting pre- and syn-rift rock units. Such relay zones are well developed between the boundary faults of the ARFB. Additionally, three E-W oriented fault belts are mapped at the northern, central and southern parts of the ARFB enclosing left-stepping en echelon normal faults, where several relay zones are formed between the overlapped fault segments. Structural analysis and evolution of the mapped area revealed that the overall architecture of the ARFB representing a broad horst relay zone between the conjugate divergent boundary normal faults. Also, two sub-basins have been recognized at the downthrows of the border faults comprising syn-rift Oligocene and Miocene sediments. The results show that these faults are rejuvenated by a continued NE-SW extension through Late Eocene, Oligocene and Miocene times. Additionally, the formed relay zones via growth and propagation of such faults have main controls on syn-sedimentation at the northern Gulf of Suez rift. The results of the present study offer constraints on horst relay zones including, internal structural architecture, geometries and interaction of boundary faults as well as role of inherited structures. Also, it provides an outcrop model for architecture and evolution of similar structural styles (e.g., the Gulf of Suez rift) as well as for subsurface mapping and exploration in extensional relay zones.

Magnitude distribution and clustering properties of the 3-D seismicity in Central Apennines (Italy)

SUMMARYIn this paper we deal with statistical features of earthquakes, seeking possible correlations between the Gutenberg–Richter magnitude distribution and the short-term clustering in an area of the Central Apennines, Italy, where significant seismicity with earthquakes exceeding magnitude 6.0 has been repeatedly observed from 1990 to the present. For this purpose, a recently developed version of the ETAS model, incorporating a 3-D spatial triggering kernel, has been adopted. Our analysis has been carried out representing the b-value and the probability of independence of events on six vertical cross-sections suitably related to the seismic structures that are considered responsible of the seismicity observed in the study area. The results of the statistical analysis of the seismicity in the study area have shown a clear distinction between the western normal low-angle fault system, characterized by eastward dip and the eastern normal fault systems, with westward dip. In the former (Etrurian Fault System; EFS) we found seismicity with a high b-value and high probability of independence, that is a scarce capacity of producing clusters and strong aftershock sequences. The eastern fault systems of our study area are distinguishable in two main distinct systems, which generated two strong seismic sequences in 1997 and 2016–2017. In the former (Colfiorito) sequence the seismicity showed a very low b-value and a modest probability of independence, while in the latter (Central Italy) sequence the b-value was significantly higher and the probability of independence had extremely low values (manifesting a high level of clustering). The much higher b-value of the EFS than the other extensional sources could be caused by its peculiar seismotectonic role of discontinuity at the base of the normal active faulting, and its reduced capacity of accumulating stress. This circumstance may be interpreted by a difference in the rheological properties of these fault systems, possibly also in relation to their present status in the earthquake cycle and the presence of strong aftershock sequences.

Coseismic and early postseismic deformation of the 2020 Nima Mw 6.4 earthquake, central Tibet, from InSAR and GNSS observations

The 2020 Mw6.4 Nima earthquake is one of the largest normal-faulting earthquakes recently occurring north of the Banggong suture zone in remote central Tibet, where geologic investigation of active faults is extremely limited. We analyze jointly InSAR and GNSS observations over 9 months after the Nima earthquake and calculate the coseismic and postseismic displacement. The optimal coseismic slip model suggests this event is the result of moderate-angle down-dip slip on a complex reversed “S-shape” three-segmented structure at fault junctions of the West Yibu-Chaka fault, the Heishi fault, and an unmapped blind fault, with a small component of left-lateral slip. The superposition of seismic waves from faults with different strikes and dips accounted for a large non-double-couple component in the long-period point-source solutions. The geodetic moment released by the mainshock is 6.4 × 1018 N⋅m, equivalent to Mw 6.42. Coseismic rupture concentrated at a depth of 4–15 km, with a peak slip of 1.36 m at 8.5 km depth. The cumulative afterslip moment within 9 months after the mainshock is 1 × 1018 N m, about 15.6% of that released by the mainshock coseismic slip. The afterslips contributed largely to the release of additional strain energy. In addition, shallow creep on the northern part of the blind fault, and deep uplift on the east normal fault system are promoted by stress perturbations. A significant proportion of down-dip coseismic slip spreading to more than 20 km beneath the surface, and deep up-slip afterslip have implications for the rheology of down-dip extension of the dipping faults in northern Tibet. Two obvious stress loading zones of more than 1 bar highlight seismic hazards in the region, especially in the junction between normal faults and ends of the large-size sinistral Riganpei-Co and Jiangai-Zangbu faults. It is necessary to forecast accurately by longer-term afterslip observation over timescales of years for the faults. Compared with previous studies, our results suggest a more complex subsurface fault geometry linking the normal and strike-slip faults and dynamic stress adjustment in this poorly-known region of Tibet.

Multiscale structural analysis of an Epiligurian wedge-top basin: insights into the syn- to post-orogenic evolution of the Northern Apennines accretionary wedge (Italy)

Wedge-top basins represent useful tectonic elements for the characterisation of the evolution of their underlying accretionary wedge in space and time, as their final state of deformation sums up the bulk shortening and structural instability conditions of the wedge. Here, we present the geometric and kinematic patterns of deformation structures deforming the wedge-top Epiligurian basins of the Northern Apennines (Italy). Our main goals are to generate an evolutionary model to account for the syn- to post-orogenic evolution of the Epiligurian basins and to infer the building style of the Northern Apennines wedge during continental collision. Mesoscale structural analysis shows that common and widely distributed thrust and normal fault arrays deform the entire Epiligurian stratigraphic succession infilling the broadly E-vergent wedge-top basins. Thrusts are invariably cut by later NW–SE and NE-SW-striking normal and oblique fault systems characterised by fault planes that mutually intersect at all scales to form polygonal patterns. Remote sensing analysis of the tectonic structures affecting the Epiligurian formations confirms the variable orientation of both thrusts and normal faults within the different studied stratigraphic successions. As a whole, results suggest a polyphase tectonic evolution of the Epiligurian wedge-top basins during the widening of the Northern Apennines accretionary wedge towards the foreland by frontal accretion. The recognised main phases are: (i) syn-orogenic compression accommodating overall tectonic transport towards the eastern quadrants; (ii) post-orogenic extension genetically related to the extension of the inner zone of the Northern Apennines; (iii) more recent extension forming collapse-induced normal faults spatially arranged in polygonal patterns.

КАРТОГРАФУВАННЯ ГОЛОВНОГО РОЗЛОМУ АНТИКЛІНАЛІ МОНТЕ-НЕРОНЕ (МАРКЕ – ПІВНІЧНІ АПЕННІНИ) ТА ВИКОРИСТАННЯ ТЕХНОЛОГІЇ ГІС У МОНІТОРИНГУ ЗЕМЛЕТРУСІВ

In the work, the main fault of the Monte Nerone anticline (Marche – Northern Apennines) was investigated, as well as the study, identification and fixation of faults: the normal fault system in the Monte Nerone area and the search for correlations on the ground of the Monte Nerone fault with the earthquake in the Marche Apennines in 1781. A small-angle eastern normal fault dipping at a small angle in the structure of extensive deformations was interpreted, it was based on the seismic profiles of the crust. Therefore, seismic events registered in this tectonically active zone can be related to this fault, as, for example, recent events in the area of the southern UmbrianMarchean Apennines. The main local tectonic structure is an anticlinorium, oriented in NW-SW, corresponding to the regional Apennine depression, with a longitudinal extension of about 30 km and a wavelength of 5–6 km. The work on sounding the Monte Nerone main fault was developed in several stages: project preparation, terrain surveying, data processing and synthesis. The project included a CTR of the Marche region, a geodetic reference map based on the international ellipsoid centered on Monte Mario (Rome 1940), a geological map at a scale of 1:10 000 and satellite orthophoto plans of the reference areas. Reference layers were created in the work in the form of a shape file to be able to catalog and share the information obtained in the field. These layers included: metadata, data containing measurements, annotation. During the fieldwork, a route and stops were planned where more detailed measurements were made and played the role of landmarks for checking with previously obtained data to confirm or refute the hypothesis. In the route, nine main stops were selected, where reconnaissance of the territory was carried out, geological characteristics of the formation were determined, measurements and recording of the main fault, its direction, angles of dip and extension, slope were carried out. All measurements were recorded in the software environment and previously created database. Using a Bluetooth GPS connected to a tablet PC, accurate tracking of the position where the measurements were made was obtained. With the help of the measurements carried out, it was possible to put forward the hypothesis that the Monte Nero fault extends from the west, starting from La Valle, crossing the western, southern and eastern slopes of Monte Nerone and extending to Monte La Montagnola, continuing to Pietralunga on its entire along the length of about 9.9 km. In addition, having the CTR with the geological map, we were able to confirm certain geological deposits. A 3D terrain model was created in ArcScene software to fully account for the terrain situation. The topography of the area was modeled in relation to the geological situation, the fault was marked, and the collected data were interpreted. Given the 54° dip, 90° inclination of the rocks we measured along the route, it can be assumed that the earthquake was shallow, with a maximum depth of about 10 km.