Fault Deformation Research Articles

Enhancement of Strength and Plasticity by Nanoprecipitation Strengthening and Stacking Fault Deformation in a High Entropy Alloy

Precipitation strengthening can effectively improve the strength of high entropy alloys (HEAs), but usually severely reduces the ductility. In this study, a new interstitial carbon-doped HEA with a nominal composition of Ni33.5(CoFe)55V5Nb5C1.5 at.% was developed. The HEA exhibits a high yield strength of 1244 MPa, ultimate tensile strength of 1553 MPa and excellent elongation of ~ 30%. The stacking fault energy of the matrix is affected by the precipitation of L12-Ni3Nb, which enhances the stacking fault (SF)-induced deformation. Since the Taylor lattice domains are subdivided by the SF networks, the mean free path of dislocation is reduced. The enhanced strain-hardening ability leads to a good combination of strength and ductility.

A validated geomechanical model for the strike-slip restraining bend in Lebanon

Most of the methodologies used to validate complex strike-slip structures mainly rely on comparison with other well-known geological features or analogue laboratory models. This study adopts an approach based on the boundary element method at the regional scale to test the structural interpretation of a complex transpressional mountain range. Lebanon restraining bend represents the most prominent topographic transpressional feature along the Dead Sea Transform (DST). It consists of two mountain ranges: the Mount Lebanon and the Anti-Lebanon ranges. We built a 3D geometrical model of the fault surfaces based on previously studied natural examples, structural maps, satellite images, DEM interpretation and experimental analogue models of restraining bend or transpressional structures. Using a boundary element method, we modelled fault deformation response to the regional stress field. The simulation accurately predicts the shape and magnitude of positive and negative topographic changes and fault slip directions throughout the study area. We propose an original approach, which uses implementation of well-known fault geometries, surface and subsurface data, for structural validation in the complex strike-slip domain. Our results, validated by structural evidences, highlight that various structural styles lead to formation of Mt. Lebanon, Anti-Lebanon and Palmyrides structures. Furthermore, this simulation supports the hypothesis that the restraining bend of the DST formed in the widespread crustal weakness zone developed in the Late Jurassic to Early Createceous. We also propose recent Neogene tectonic evolution of the region based on our modelling and integrated with published U/Pb dating of fault zones and tectonostratigraphic evidence.

Correlation between Seismic Waves Velocity Changes and the Occurrence of Moderate Earthquakes at the Bending of the Eastern Carpathians (Vrancea)

Seismic velocity is the geophysical property that has a key role in characterizing dynamic processes and the state of the stress around the faults, providing valuable information regarding the change in the tectonic regime. The stress in the crust is an important indicator of the possible occurrence of a major earthquake, and the variation of seismic velocities, in time, can provide a clearer picture on the tectonic processes taking place in the region. In the crust, velocities change before, during, and after earthquakes through several mechanisms related to fault deformations, pore pressure, stress changes, and recovery processes. In this study, we investigate the possible correlation between the changes of seismic velocities (Vp/Vs) in time and the occurrence of moderate size crustal and intermediate depth earthquakes from the Vrancea region. Our findings show that there are no significant variations in Vp/Vs for the intermediate depth earthquakes, while crustal events have decreased seismic activity prior to the main earthquake and no high Vp/Vs anomalies. Our results indicate key aspects, and such analyses should be carried out in real-time to continuously explore any unusual pattern pointed out by the seismic velocity changes. Vp/Vs and their standard errors can also be used to describe seismic activity patterns that shape the tectonic evolution of the area.

Alpine Fault‐Related Microstructures and Anisotropy of the Mantle Beneath the Southern Alps, New Zealand

AbstractMantle xenoliths from the Southern Alps, New Zealand, provide insight into the origin of mantle seismic anisotropy related to the Australian‐Pacific plate boundary. Most xenoliths from within 100 km lateral distance of the Alpine Fault are coarse grained, but a small number are finer grained protomylonites. The protomylonites contain connected networks of fine grains with a different crystallographic preferred orientation (CPO) to coarse porphyroclasts in the same xenolith, suggesting that protomylonites and coarse‐grained samples record different deformation kinematics. The CPOs of fine grains in protomylonites have monoclinic symmetry, with the 2‐fold rotation axis normal to a plane that contains olivine [010] and orthopyroxene [100] maxima, suggesting that the protomylonite deformation involved significant simple shear. Some coarse‐grained samples contain unconnected lenses and layers of fine grains with the same CPO as the coarse grains. Microstructures suggest that these fine grains formed by subgrain rotation recrystallization and that protomylonites may represent an up‐strain progression of this microstructure, where the connectivity of fine grains has allowed them to localize shear and develop a new Alpine Fault CPO. The samples tell us about the state of the mantle at 25 Ma, in the early history of the plate boundary. If this suite of samples is representative of the mantle beneath the Alpine Fault in the present day, then we can interpret the complex seismic anisotropy patterns in the lithospheric mantle as representative of blocks containing variably rotated older CPOs juxtaposed by narrow shear zones associated with Alpine Fault deformation.

The 2019 East Coast Slow Slip Event, New Zealand: Spatiotemporal Evolution and Associated Seismicity

Slow slip events (SSEs) are interpreted as the transient quasi-static fault deformation in the deep transition zone from locked to freely slipping in many subduction zones. Using continuous Global Positioning System (cGPS) data collected in New Zealand, we estimate the spatiotemporal evolution model during the 2019 SSE and analyze the influence of subduction interface heterogeneity on seismicity during SSEs at the Hikurangi margin. The results reveal that the 2019 SSE extends from the northern (Gisborne) to the central (Hawke’s Bay) Hikurangi subduction interface and decays rapidly within approximately 3-4 weeks. It releases a total seismic moment of about 4.83 × 1019 N·m (Mw 6.8), with a significant slip in Gisborne and a secondary slip in Hawke’s Bay. The slip depths are similar, but peaks, durations, and rates differ slightly. By combining previous SSEs (2011-2019), diverse characteristics are concluded, i.e., shorter duration and more frequency in Gisborne and relatively longer duration and less frequency in Hawke’s Bay. The seismicity offshore and onshore indicates along-strike variations, which appear to be spatially correlated with the variations in topography, such as subduction seamounts. The heterogeneities on the subduction interface are related to the spatiotemporal distribution of SSEs and seismicity along the Hikurangi margin.

Numerical simulation of fault deformation and seismic activity in the southern Qinghai–Tibet Plateau

The moderate-strong (M ≥ 5, since 1976; or M ≥ 6.5, overall) earthquakes of the north to south trending (NS-trending) faults and their vicinity in the southern Qinghai–Tibet Plateau exhibit prominent spatial concentration distribution characteristics. However, research on the southern Tibet faults is limited. Hence, this study used a two-dimensional viscoelastic finite element model to simulate crustal movement in southern Tibet based on 1991–2015 GPS velocity data. The current deformation field, tectonic stress field, fault slip, and stress accumulation rates distribution were obtained to analyze the relationship between fault activity and earthquake distribution. The results revealed that the simultaneous effected by of the NE-trending compression and uneven EW-trending tension on the study area. Crustal deformation exhibited simultaneous NS-trending compression and EW-trending stretching. The EW- and NWW-trending faults and the NS-trending faults differed in their mechanical properties and movement modes. The NS faults were primarily subjected to extensional stress with normal motion. The remarkable heterogeneity of the fault segments influenced the distribution of moderate-strong earthquakes and types of earthquake ruptures. The concentrated distribution of moderate-strong earthquakes on the NS-trending normal fault and its vicinity depended largely on the high slip rate, strong tensile stress, and geometric strike of the fault segment. This study aids in understanding the heterogeneity in normal fault activity in southern Tibet and is the basis for seismic hazard assessment.

Coupling mechanism between systematic elastic deformation and gear surface damage

Understanding the coupling mechanism between systematic elastic deformation and gear tooth surface damage is particularly helpful for us to explore the life-cycle surface damage evolution process. A deformable body dynamic model of gear transmission systems is developed to acquire the systematic elastic deformation. Then the equivalent meshing deviation parameters, which are used to quantify the systematic deformation, are imported into a hybrid finite element-analytical contact model to acquire the load distribution under non-ideal meshing conditions. Considering the concurrent effects of surface wear and pitting, a generalized surface damage model is developed based on the transient elastohydrodynamic lubrication theory. An interactive calculation scheme is built to realize the damage simulation over the life-cycle evolution process. Distinguishing from the conventional models, the proposed multi-physics model bridges the macroscopic systematic deformation and microscopic behaviours (local contact state and damage initiation mechanism). A two-staged gear test rig is utilized to verify the proposed model. Based on the proposed model, the coupling mechanism amongst the tribo-dynamic behaviours, systematic elastic deformation and life-cycle fault characteristics are analysed. It is revealed that the bending-induced asymmetric load distribution will lead to severe pitting at one edge of the gear surface; The life-cycle dynamic performance can be significantly improved by optimizing the supporting configuration. This work can provide the theoretical basis for the tooth fault prognosis, physics-based condition monitoring and configuration design.

Present-day crustal strain and major fault slip rates in North China determined using GNSS observations

• A strain model and an elastic block model of North China were established. • The western Ordos and the northern North China exhibited larger strain rates. • The NNE- and NWW-trending faults showed dextral and sinistral slip respectively. • The fault deformation in North China was controlled by neighboring blocks. North China is characterized by numerous faults, where many earthquakes were recorded. However, the fault slip and crustal deformation mechanism underlying the effects of neighboring block motions remain poorly understood. In this study, we first constructed a strain model using global navigation satellite system (GNSS) velocities to analyze the relationship between seismicity and strain. We then constructed a block model based on the fault distribution and GNSS observations to obtain fault slip. The strain and fault slip rates were then used to determine the crustal deformation mechanism in North China. The strain model suggests the western border of the Ordos Block and the northern North China Plain had larger maximum shear strain rates. These areas are located in a transition between positive and negative dilatation rates, which indicate intense crustal deformation. Based on the block model, we found the NNE-trending faults were dominated by dextral slip. The northern and southern borders of the Ordos Block indicate left-lateral motion (0.4–2.5 mm/a), while its western and eastern margins exhibited right-lateral slip (1.0–3.0 mm/a). The periphery of the Ordos Block exhibited normal slip (0.2–3.2 mm/a), except at the southwestern tip. These results suggest that the eastward extrusion of the Tibetan Plateau caused left-lateral shear in North China, which led to sinistral slip of NNE-trending faults. The northward expansion of the northeastern Tibetan Plateau also contributes to sinistral slip along the northern and southern margins of the Ordos Block, as well as dextral slip along its western and eastern margins.

Ground Deformation and Source Fault Model of the Mw 5.7 Xegar (Tibetan Plateau) 2020 Earthquake, Based on InSAR Observation

Ground Deformation and Source Fault Model of the Mw 5.7 Xegar (Tibetan Plateau) 2020 Earthquake, Based on InSAR Observation

Thermochronological constraints on Eocene deformation regime in the Long-Men Shan: Implications for the eastward growth of the Tibetan Plateau

Understanding the spatio-temporal distribution of strain during Cenozoic growth of the Tibetan Plateau is important for constraining the geodynamic processes underpinning plateau formation. Offset Quaternary landforms and historic earthquake data suggest an along-strike change in deformation style for the eastern margin of the Tibetan Plateau, characterized by a transition from ESE-verging shortening to right-lateral shear from the southern to northern segment of the Long-Men Shan fault zone within a distance of ca. 500 km. When and how this along-strike deformation pattern formed is central to understanding the uplift history and spatio-temporal distribution of strain in the eastern margin of the Tibetan Plateau, and the underpinning geodynamics. To address this, we report a suite of low-temperature thermochronology data from the northern segment of Long-Men Shan fault zone that show a contrast in post late Cretaceous cooling and exhumation histories between the hinterland (west of the marginal Yingxiu-Beichuan fault) and foreland sides (east of the fault). Prior to the Eocene (ca. 40 Ma), the hinterland experienced significant exhumation in contrast to minor exhumation on the foreland side, but, post Eocene exhumation accelerated on the foreland side. This change reflects a switch in the deformation regime from shortening to strike-slip-dominated. This switch reduced hinterland rock uplift and tectonic and topographic loading over the foreland basin, leading to accelerated foreland exhumation through isostatic adjustments. A compilation of fault deformation history for the eastern Tibetan Plateau shows a second tectonic transition in the late Miocene, characterized by formation of the south-striking Huya and Minjiang faults. Our results highlight the importance of progressive late Eocene and late Miocene tectonic transitions in shaping the eastern margin of the Tibetan Plateau. • The hinterland and foreland sides of the eastern Tibetan Plateau margin experienced differential Eocene exhumation. • The differential evolution indicates a coeval tectonic transition from shortening-dominated to strike-slip-dominated. • A second tectonic transition is characterized by the late Miocene formation of the Huya and Minjiang faults. • The eastern margin of the Tibetan Plateau is shaped by progressive late Eocene and late Miocene tectonic transitions.

Deepwater fold-thrust belt contraction driven by mixed deformation components

The formation of fold-thrust belts is driven by compressive stresses caused by crustal tectonics, gravity, or a combination of both. The formation mechanism of a single compressive stress component has been thoroughly investigated by laboratory experiments and field observations. It is yet less well established how fold-thrust systems deform under multiple compressional stresses. The formation of the deepwater fold-thrust belt on the northwest Borneo margin has been previously explained by compressive gravity-driven stresses in the south and crustal-driven tectonics in the north. This study focuses on the transition zone between the gravity-driven south and crustal-driven north, and investigates the structural diversity around this transition using 3D seismic-reflection data. Structural interpretation results reveal two structural provinces distinct in deformation styles and structural kinematics within the deepwater fold-thrust belt. Folds and thrusts in each structural province reflect deformation stresses that occurred at different times with different orientation. Structural features in each structural province developed independently and were preserved largely without mixing in the fold-thrust belt, except for an interference zone of ca. 15 km in width. The fold-thrust belt can be interpreted to have formed by a multi-directional compressive stress system and exhibits greater structural heterogeneity than deformation caused by a single-component compressive stress system. Particular deformation characteristics and fault activity in the interference zone reflect a complex disparate compressive stress relationship.

Fault zone architecture and lithology-dependent deformation mechanisms of the Himalayan frontal fold-thrust belt: Insights from the Nahan Thrust, India

Brittle shallow crustal faults typically develop a complex fault zone architecture with distinct structural domains that display diverse microstructures, mineralogy, and deformation mechanisms. The development of such domains is typically controlled by the strength and composition of the protoliths, physical conditions of deformation, fluid ingress, and diachronous fault growth in response to stress accumulation and co-seismic slip. Herein, we studied the microstructure-mineralogy-kinematics of fault rocks in the Nahan Thrust, in the vicinity of the Main Frontal Thrust that represents a tectonically active zone in the Himalayan orogen. The Nahan Thrust is characterized by alternating red and gray gouge layers, and a single black gouge layer. Our results from electron microscopy and X-ray diffractometry indicate that the protolith of the red gouge layers is argillaceous sandstone, whereas that of the gray and black gouge layers is sandstone. Microstructures suggest an initially distributed deformation (aseismic creep), followed by a protracted brittle deformation event, and a later aseismic creep stage. The brittle stage is marked by progressive localization of stress, fracture development, cataclasis, frictional sliding, and seismic slips. The black gouge layer acted as the principal slip zone and exhibited ultrafine bands of micrometer-scale slip zones with vapor escape structures and clay clast aggregates, indicating seismic faulting and frictional heating during seismic slips. The preferential seismic rupture nucleation in the black gouge layer indicates a strong lithological dependence on seismic slip in the Nahan Thrust. We also conclude that heterogeneity within the Nahan Thrust resulted from primary lithological variations of the protoliths.

Response of a continuous pipeline in sand subjected to normal faulting

The pipelines are vulnerable to fault deformation. Acknowledging the responses of pipelines subjected to faulting is a major concern when designing pipelines within the fault zone. In this study, a centrifuge test was conducted to investigate the response of a pipe in sand subjected to normal faulting. The model pipe is a continuous pipe, made of stainless steel. The measured pipe strain and deformation are discussed and compared with those in reverse fault. The results showed that the peak strain occurs at the footwall close to the rupture, where the maximum soil resistance induces. The peak strain leads to wrinkling of the pipe at the location. The crossing of the rupture will accelerate the increase of peak bending strain during faulting. Compared with the pipe subjected to reverse faulting, the pipe in normal fault experiences sooner failure, due to the larger differential soil displacement caused by faster rupture propagation.

Elusive active faults in a low strain rate region (Sicily, Italy): Hints from a multidisciplinary land-to-sea approach

Low Strain Rate regions (LSRrs), i.e., areas undergoing tectonic deformation at rates of 1 mm/yr or less, often host important cities and highly vulnerable anthropogenic assets, and due to their subdued topography and relatively infrequent seismicity, are often considered low seismic hazard areas. Despite this, infrequent but high-magnitude earthquakes in such regions suggest that identifying active structures in the LSRr is one of the primary challenges for both the scientific community and modern societies. In such regions, one of the main issues in identifying active faults is the lack of valuable outcrop data due to erosional/sedimentation rates overwhelming the fault deformation, causing the hidden morphological signature of the tectonic structures.This work proposes a multidisciplinary approach designed to detect active geological structures and their related deformation in such areas. Our approach consists of quantitative morphotectonic, offshore and onshore tectonostratigraphic and GNSS joint analyses. To test this approach, we selected as a natural laboratory the partially offshore northern Sicilian LSRr (southern Italy) in the coastal sector located between the two major cities of Palermo and Termini Imerese. This area includes the compressional structures of the northern sector of the Apennine-Maghrebian fold and thrust belt, presently accommodating the slow Africa-Europe plate convergence.The main results we achieved are 1) new evidence of active tectonic deformation in this region; 2) the 3D modelling of two NNW-trending active faults; 3) the slip rate of a segment of the westernmost of the two detected faults; 4) a newly recorded relative GNSS velocity field; 5) a new morphotectonic map and morphotectonic evolution model of the study area. Our multidisciplinary approach allowed us to shed new light on the active tectonic framework of a slowly deforming area that crosses the physical limit of the coastline.

Phase change-induced internal-external strain of faults during supercritical CO2 leakage

For the long-term safe operation of carbon capture and storage (CCS) projects, the leakage of supercritical carbon dioxide (SC-CO2) along a fault is an important factor that needs to be monitored. To investigate the phase change and fault deformation associated with SC-CO2 leakage along a fault, this study carried out five groups of SC-CO2 leakage experiments at different initial CO2 temperatures. The volume of the CO2 storage container (100 mL), CO2 initial pressure (8.07 MPa) and fault confining pressure (10.5 MPa) were controlled at the same values. The CO2 phase change and fault internal-external strains response were monitored by high-precision fiber Bragg grating sensors throughout the experiment. The results show that (1) Temperature and strains response times were 1 and 2.5 times longer than pressure, respectively. (2) The viscosity greatly influenced the determination of the critical temperature T0 = 45 °C. (3) The fault internal strains were more than twice that of the external one; except for the entrance, the fault internal and external strains states were opposite at the beginning of leakage; all other positions on the fault surface showed compressive strains except for the tensile strains at the entrance. (4) The distribution of the inflection point of temperature–pressure curves may be used as a basis for distinguishing CO2 leakage from faults (near the triple point) or pipes (far from the triple point). This study provides technical and theoretical support for laboratory-scale studies on the mechanism of internal and external strains differences caused by phase transition of SC-CO2 leakage along faults.

Seafloor overthrusting causes ductile fault deformation and fault sealing along the Northern Hikurangi Margin

IODP Site U1518, drilled during IODP Expeditions 372 and 375, penetrated a large-offset (∼6 km) thrust, the Pāpaku fault, rising from a megathrust that hosts recurring slow slip events along the Hikurangi margin. Although drilling intersected the fault zone at only ∼300 m below the seafloor within porous silty mudstone, it exhibits intense tectonic ductile deformation, including finely banded mudstones contorted into decimeter-scale folds; elongate mudstone clasts with grain tail complexes; stacked and truncated silt beds in distorted mudstones; and soft sediment injections. Locally, these ductile features are overprinted by brittle deformation, including normal faults, fracture arrays, and breccias. The more consolidated hanging wall is dominated by brittle structures, whereas the footwall exhibits ductile and brittle deformation that decreases in intensity with depth. The intense tectonic ductile deformation and asymmetric distribution of structures across the fault zone at Site U1518 can be explained by seafloor overthrusting. The emplacement of the hanging wall upon the footwall flat overrode high-porosity, undeformed, and previously unburied sediments, localizing shear deformation within these weak sediments. In contrast, the overconsolidated hanging wall preferentially experienced brittle deformation during folding and displacement. Interstitial pore water geochemical profiles at Site U1518 show a repetition of near-seafloor diagenetic sequences below the fault, consistent with overthrusting of previously unburied strata. The preserved diagenetic profiles in the footwall suggest that overthrusting occurred within the last 50-100 kyr, and indicate little along- or across-fault fluid flow at the location of Site U1518. Thus the Pāpaku fault appears to define a low-permeability seal that restricts footwall consolidation, maintaining locally high pore fluid pressures and low fault strength. If similar low permeability structures occur elsewhere along the margin, they could support regionally high pore pressure conditions favorable to the occurrence of SSEs on the Hikurangi megathrust fault.

Effects of power transformer high-frequency equivalent circuit parameters non-uniformity on fault diagnosis using SFRA test

The electric power transformer is an essential component of an electrical power system because it regulates the voltage level to provide the best possible system operation. Thus, it is important to detect the transformer faults to maintain its reliability as high as possible. The sweep frequency response analysis (SFRA) test is one of the tests which, used to diagnose transformer faults. It determines the fault type by analyzing its response across a wide frequency range. The main advantage of the SFRA test is the detection of mechanical deformation faults since mechanical deformation faults cause the high-frequency equivalent circuit parameters to change which, could be detected easily using the SFRA test. Also, statistical features are defined for this SFRA response used in fault detection and classification. The transformer high-frequency equivalent circuit parameters are non-uniform distributed over discs due to normal leakages and aging. Thus, in the present paper, the non-uniform distribution of the transformer high-frequency equivalent circuit is studied in the SFRA test at different faults and various non-uniformity levels. Finally, when considering the non-uniform distribution of high-frequency equivalent circuit parameters, the results demonstrate that some features are greatly affected, and others are just minimally affected. Depending on how much each feature is affected by the uniformity of high-frequency equivalent circuit parameters, rules of fault diagnosis algorithms based on the SFRA test could be reweighted to improve their accuracy. Also, the obtained results could be compared to real measured data to estimate the actual non-uniformities of transformer parameters.

Deformation faulting and dislocation-cell refinement in a selective laser melted 316L stainless steel

The selective laser melted (SLM) 316L stainless steel (316L SS) has shown superior tensile ductility and doubled yield strength compared to its wrought counterpart. The significantly improved yield strength has been attributed to the unique cellular substructures featured by Cr/Mo-segregation and trapped dislocations. The excellent ductility of SLMed 316L SS has been mainly understood from the pronounced deformation twinning, which, however, is just one of the dominant plastic deformation mechanisms in 316L SS. Here instead, we report two other fundamental deformation micro-mechanisms, i.e., deformation faulting and dislocation cell refinement, in the SLM 316L SS. Our results showed that deformation faulting and dislocation cell refinement characterize the whole tensile deformation significantly except for deformation twinning. These newly found mechanisms synergistically dominated the deformation behavior at low strain levels while deformation faulting and twinning play a crucial role at medium and high strain levels. The pre-existing stacking faults (SFs) in cellular substructure is mainly responsible for the significant deformation faulting. At the early deformation stage, these pre-existing SFs provide faulting nuclei for deformation faulting, leading to wide SFs. These wide SFs in different cellular interiors penetrate the cellular boundaries and overlap as the strain increases, resulting in long stacking fault ribbons (SFRs). We attributed the formation of DCs to the measured medium stacking fault energy (SFE) of ∼18 mJ/m2. Upon straining, equiaxed dislocation cells (DCs) were generated by new dislocation cell walls (DCWs) inside the cellular substructure, and refined by either the dissociation of fully developed DCWs or the continuously formed new DCWs. Together with deformation twinning, these two fundamental deformation mechanisms jointly led to a steady strain hardening rate during tension and thus a superior tensile ductility of the SLM 316L SS with high yield strength. These findings provide new insights into the excellent strength-ductility combination of SLMed 316L SS and the experimental basis for crystal plasticity modeling and simulation, as well.

Determining the Paleostress Regime during the Mineralization Period in the Dayingezhuang Orogenic Gold Deposit, Jiaodong Peninsula, Eastern China: Insights from 3D Numerical Modeling

The Dayingezhuang orogenic gold deposit, located in the northwestern Jiaodong Peninsula, is hosted by the Zhaoping detachment fault, but the paleostress regime during the mineralization period remains poorly understood. In this study, a series of numerical modeling experiments with variable stress conditions were carried out using FLAC3D software to determine the orientation of paleostress and the fluid migration processes during the ore-forming period. The results show that the simple compression or tension stress model led to fluid downward or upward flow along the fault, respectively, accompanying the expansion deformation near the hanging wall or footwall of the Zhaoping fault, which is inconsistent with the known NE oblique mineralization distribution at Dayingezhuang. The reverse and strike-slip model shows that the shear stress was distributed in the gentle dip sites of the fault, and the expansion space occurred in the geometric depression sites of the fault, which is also inconsistent with the known mineralization distribution. The normal and strike-slip model shows that shear stress was distributed in the sites where the fault geometry transforms from steep to gentle. In addition, the expansion deformation zones appeared at sites with dip angles of 35~60° in the footwall and extended along with the NE-trending distribution from shallow to deep levels. The numerical results are quite consistent with the known mineralization, suggesting that the fault movement during the mineralization stage is a combination of the local strike-slip and the NW–SE extension in the Dayingezhuang deposit. Under this stress regime (σ1 NE–SW, σ2 vertical, σ3 NW–SE), the NE dilation zones associated with fault deformation served as channels for the ore-forming fluid migration. Based on the numerical modeling results, the deeper NE levels of the No. 2 orebody in the Dayingezhuang deposit have good prospecting potential. Thus, our study not only highlights that gold mineralization at Dayingezhuang is essentially controlled by the detachment fault geometry associated with certain stress directions but also demonstrates that numerical modeling is a robust tool for identifying potential mineralization.

Fractal-wave nature of the geological environment of coal formation at Donbas

The structure investigation of the fault and folded deformations of sedimentary deposits at Donbas on various scale levels: from microdislocations to large amplitude ones is carried out. It is established that on all scale levels, the lateral frequency of the folds resulting from the wave processes caused by pulsed horizontal tectonic forces in the post-inversion period is seen. According to the parameters of natural and technogenic fault dislocations of Donbas, the authors calculated fractal dimensions for dependencies of lengths, the number of deformations, the surface area of shifters, the distance between the cracks from the scale of maps for individual mines and workings, coal beds and sandstones. The measurements were carried out on micrographs of coal particles, in mining workings, according to the geological maps of Donbas and individual districts. The distributions of fault deformations in the coalrock massif are described by lognormal and power laws, which indicates the fractality of the fault deformation of sedimentary deposits at Donbas, and the differences of fractal dimensions at various scale levels point at its multifractality. The accuracy of the obtained results is confirmed by the similarity of fractal dimensions calculated by various methods. The discrepancy between the values of fractal dimensions at the different scale levels reflects the impact of additional local or regional factors affecting the formation of the basin framework. The obtained data attest to the action of fractal-wave processes, which, being superpositioned on the resulting deposits, formed a complex structure of the sedimentary thickness of Donbas.