Deep Fault Research Articles

Audio Magnetotelluric and Gravity Investigation of the High-Heat-Generating Granites of Midyan Terrane, Northwest Saudi Arabia

The Midyan Terrane (northwest Saudi Arabia) is characterized by the presence of a massive belt of radioactive granitic rocks and thick sedimentary cover near the coastal areas. The area is greatly influenced by the tectonic activities of the Red Sea and Gulf of Aqaba, implying its high potentiality of geothermal energy. In the present work, geophysical surveys, including audio magnetotelluric and gravity methods, were integrated to investigate the subsurface structural pattern of the study area, which identified regional deep and shallow fault systems and detected the subsurface geometry/extension of the granitic rocks as well as detecting the thickness of the sedimentary basins near the coastal area. A total number of 80 audio magnetotelluric and 246 gravity stations were recorded, analyzed, and interpreted. Two high-potential geothermal targets were indicated: high-heat-generating granites and thick anomalous sedimentary basins near the coastal areas. High-heat-generating granites are significant in terms of enhanced geothermal systems (EGSs) whereas sedimentary basins play a crucial role in the formation of conventional geothermal systems. Both areas require more exploration plans to evaluate the energy potential of geothermal reservoirs. The results also contribute to the identification of the subsurface orientation and geometry of radioactive granites, providing the necessary parameters to enhance a volumetric estimation for geothermal reserves.

Ore-controlling structures of the Qingchengzi Pb-Zn-Au-Ag orefield, northeastern China and significance for deep ore prospecting: Revealed from gravity and magnetic anomalies

Located in the middle of Liaodong Rift, the Qingchengzi orefield is an important Pb-Zn-Ag-Au polymetallic mining area in Northeast China. The Pb-Zn-Au-Ag mineralization mainly occurs in the Liaohe Group strata and is closely related to Indosinian and Yanshanian magmatic intrusive bodies. Currently the Qingchengzi orefield is poorly explored at depths greater than 1500 m, with no large deep concealed gold deposit being discovered yet. This study focused on delineating deep concealed ore-controlling structures from the local gravity and aeromagnetic anomalies in different wavelet orders acquired by the application of discrete wavelet transform (DWT), and evaluating their potential for undiscovered gold-rich polymetallic mineralization in the Qingchengzi orefield. We started from summarizing the characteristics of gravity and magnetic anomalies corresponding to the ore-controlling structures obtained from surface geology, exploration profiles and drilling results. Under the guidance of the correspondence, we interpreted the structural control factors of the tectonic-magmatic metallogenic system for the whole Qingchengzi orefield, such as faults, strata, magmatic bodies and mineralized alteration belts. Based on the spatial relationship between the known deposits and structural factors interpreted from gravity and magnetic anomalies, it is concluded that the gold-rich polymetallic deposits and mineralization are controlled by five major deep regional faults (two in the NE direction and three in the NW direction). Moreover, the borders of the Indosinian and Yanshanian concealed magmatic intrusions, as well as the intersections of deep regional faults are more favorable for the deposition of gold-rich polymetallic minerals. A NNE-trending concealed structure was found in the middle of our study area, connecting the Shuangdinggou, Qingchengzi, Xinling and Gujiagou intrusions, serving as a possible channel for magmatic activities in the Indosinian. The forward modeling results on the gravity and magnetic data of profile L1 indicates that the Liaohe Group strata and the possible Mesozoic concealed intrusion lies beneath the Paleoproterozoic Dadingzi granite. This finding supplements the traditional understanding that the Paleoproterozoic Dadingzi granite is the deepest boundary for ore prospecting, and provides new thoughts searching for deep-seated ore bodies for the Xiaotongjiapuzi ore deposits.

Geoelectric Model of the Northwestern Caucasus: Three-Dimensional Inversion

Interpretation of magnetotelluric observations made within the Northwestern Caucasus, by means of one-dimensional, two-dimensional inversion and three-dimensional mathematical modeling programs, has helped build testing and starting geoelectric models that are necessary to test and adapt the program of three-dimensional inversion of the impedance tensor components. The performed three-dimensional inversion of the experimental magnetotelluric data has significantly changed the parameters of conducting blocks within the folded structures of the region, identified at the previous stages of MT data interpretation. In the resulting three-dimensional geoelectric model, the position of low-resistance blocks correlates with: suture zones, deep faults, mud volcanoes, and domains characterized by an increased absorption of transverse and longitudinal seismic waves. The electrical resistivity of the most low-resistance anomalies is explained by the degree of their saturation with the water fraction of the fluid.

Orenburg Radial-Concentric Structure at Great Depth: Experimental Modeling under Fluid Dynamic Loads and Comparative Analysis of Sandstone Samples from Oil Fields in Western Siberia

The study of the deep structure of the Orenburg radial-concentric structure in the basement of the Russian Platform based on seismotectonic and geomorphological data has been carried out. Interpretation of temporal regional seismic profiles crossing the structure was performed, identifying the main deep faults and measuring their dip angles. It was revealed that the radial-concentric structure is a large flower structure. Its structure involves the main multidirectional deep faults dipping at angles of \(\perp \)60°–85° and limiting horst or reverse fault zones in the basement. The hierarchy of faults structure has been established. Oil and gas fields are confined to the main deep dislocations of the Orenburg structure and represent flower structures of minor sizes. An experimental modeling of the formation of “flower” structures was performed based on the analysis of the results of studies using data from the acoustic emission activity of rocks and under the action of fluid dynamic loads performed at the “UIK-AE” unit (Institute of Geophysics, Ural Branch of RAS, Russia) on sandstone core samples from reservoir rocks of oil fields in Western Siberia. The developed model showed that the formation of flower structures can occur without horizontal shear due to lateral compression and deep pressure. With the help of the seismo-acoustic emission method, characteristic noise was recorded during the formation of cracks in core samples, sound attenuation before splitting, and then its sharp explosive increase from a break in the continuity of the rock. Analysis of the core of wells drilled within the Orenburg radial-concentric structure revealed signs of hydrothermal fluid discharge in the sedimentary cover rocks, such as wavy (or flat) layering, bizarre textures and intervals of breccias, shell-shaped inclusions, stillotite seams, fluid textures. It is concluded that the genesis of the Orenburg radial-concentric structure is associated with the impact of deep heat flows, fluids, high pressure and has a commonality with the explosive ring structures of shields and platforms.

Analyzing the Formation and Evolution of Strike-Slip Faults and Their Controlling Effects on Hydrocarbon Migration and Charging: A Case Study of Tahe Area, Tarim Basin

The Ordovician strike-slip faults system in the Tahe area of the Tarim Basin provides an important opportunity for using 3D seismic data to document the structural characteristics, formation, and evolution of strike-slip faults and their relationship with oil and gas. With high-resolution 3D seismic data, the strike-slip faults are interpreted, classified, and described using the seismic coherence technique. The geometric characteristics, active periods, formation, and evolution process of strike-slip faults are analyzed, and the relationship between strike-slip faults and hydrocarbon accumulation and charging is discussed in this research project. On the map, the primary strike-slip faults on the east and west sides of the Tahe area are relatively sheared to each other, showing an “X” type conjugate fault, and the secondary strike-slip faults are scattered. In the cross-section, the primary strike-slip faults are inserted downward into the Cambrian basement and up to Devonian, and “Single line”, “Y”, “Flower”, and “Parallel lines” structures are observed. Bounded by the top of Ordovician, the deep and shallow parts are vertically segmented, with different structure styles. The switch of the structural style of strike-slip faults is attributed to principal stress. A deep “positive flower” shape of faults was developed in the mid-Ordovician period under the effect of compressive stress. Meanwhile, a shallow “negative flower” shape of faults was developed from the late Ordovician to the mid-Devonian period under tensile stress. The “Compound Flower” shape of deep “positive flower” shape and shallow “negative flower” shape formed by compressive and tensile activities has a wider fracture range, which leads to deep fluid migration and shallow karstification. There are two combinations of deep Ordovician strike-slip faults in the section: “Lower single branch-upper flower type” and “lower single branch-upper single branch type”. The primary faults of the former insertion into the Cambrian basement are associated with homologous secondary faults, while the latter has no derived secondary faults. It has an important impact on reservoir reconstruction and distribution, and the reservoir is controlled by faults. Strike-slip faults not only control the channel of oil and gas migration, but also the horizontal and vertical distribution of oil and gas. The closer the carbonate reservoir is to the primary fault, the more likely it is to form a high yield area. There are four types of oil and gas charging models controlled by strike-slip faults. In the area where the structure is high and the strike-slip faults are sheared relatively to each other, the larger the scale of faults, the more conducive it would be to oil and gas migration and accumulation. Among them, the charging model related to the primary fault has higher oil and gas migration efficiency. This research contributes to analyzing the relationship between strike-slip faults and oil and gas as well as playing a significant role in applications of oil and gas exploration in practical works.

Ore-Bearing Faults of Transpressional–Collisional Kinematics in the Verkhoyansk–Kolyma Fold Belt (Structural Consequences of the Geodynamic Model)

The Verkhoyansk–Kolyma fold-thrust belt is an important metallogenic structure of northeastern Russia. Based on irregularly distributed gold mineralization within this belt two large ore-placer districts are distinguished: the Upper Indigirka district (UID) in the northwest and the Central Kolyma district (CKD) in the southeast. The gold grade in these areas is largely provided by a large fault structure—the ore-controlling Adycha–Taryn deep fault. Along the entire length, this fault changes its kinematic characteristics, from an overthrust reverse fault in the north to a strike-slip reverse fault (Tenka fault) in the south. Such a change of the fault kinematics laterally, in the principal ore-controlling structure, is reflected in the structure of specific ore-bearing faults in ore areas, as we have shown on the example of the Degdekan (CKD) and Drazhnoe (UID) deposits. In the Degdekan deposit, synthetic overthrust reverse faults, which control large-volume deposits of relatively poor ores, are ore-bearing, and, in the Drazhnoe deposit, opposite strike-slip faults contain small-size, superimposed rich ore bodies. The change of ore-bearing faults in different ore areas is explained by their position in the changing stress field that formed at different stages of geodynamic development: (1) associated with the collision of the Kolyma–Omolon superterrane and the Siberian craton and collision with the Alazeya arc (early ore mineralization of the Upper Indigirka ore district) and the Uda–Murgal arc (early disseminated pyrite mineralization of the Central Kolyma ore district) and (2) collision with the Chukchi microcontinent and re-activation of earlier faults (the main gold-sulfide-quartz mineralization of the Yana–Kolyma metallogenic belt)

NEOTECTONIC DISLOCATIONS AT THE BARENTS SEA SHELF AND THEIR GENESIS ACCORDING TO THE MORPHOMETRY OF BATHYMETRY, SEISMIC SECTIONS AND THE DEEP MANTLE STRUCTURE

The paper provides a comprehensive analysis of the morphometric attribute “general curvature” for the bathymetry of the Barents Sea, seismic and seismoacoustic data containing in the wave field patterns tectonic faults emerging to the surface, a fault network of the sedimentary cover confirmed by seismic surveys, and seismotomographic data showing the heterogeneous deep structure by the distribution of seismic wave velocities in the upper mantle. The analysis of these data showed the presence of a causal relation between rheologically heterogeneous and mobile blocks of the upper mantle and the crystalline part of the Earth’s crust with the deep fault network, emerging on the bottom surface and being a relief-forming factor that forms characteristic domains with different textures performed by the morphometric attribute “general curvature”.

Active tectonics in the Calabrian Arc: Insights from the Late Miocene to Recent structural evolution of the Squillace Basin (offshore eastern Calabria)

The Calabrian Arc represents one of the most active sectors of the upper plate of the Tyrrhenian-Ionian subduction system. This research aims to reconstruct the evolution of the Squillace Basin (Ionian offshore of the Calabrian Arc) from the Late Miocene to Recent times and recognise active shallow and deep structures using a multiscale approach. The latter is based on interpreting high-penetration and high-resolution seismic reflection profiles, calibrated with well-log data coupled with bathymetric data and the distribution of instrumental earthquakes. Data highlight three steps in the evolution of the Squillace Basin. A Late Miocene extensional event led to the formation of WNW-ESE oriented horst and half-graben structures. During the Pliocene, deformation was localised in the central and northern sectors of the basin and expressed by a WNW-ESE oriented strike-slip fault and NW-SE normal to trastensional faults, respectively. A transpressional event started in the Early Pleistocene, causing the positive inversion of deep (> 3 km) extensional faults and the formation of NW-SE to WNW-ESE oriented transpressional/reverse faults and related anticlines. The kinematics of these faults agree with the NW-SE oriented left-lateral Albi-Cosenza, Lamezia-Catanzaro and Petilia-Sosti crustal fault zones developed in north Calabria. The results of this work suggest that the transpressional structures in the northwestern sector of the basin likely represent the offshore prolongation of the Albi-Cosenza fault zone. NW-SE to WNW-ESE trending, shallow (<2 km) high-angle normal faults offset the younger deposits. Their depth and direction indicate that these faults are secondary structures formed in the extrados of the anticlines associated with the transpressional faults. The distribution of earthquakes shows events with M > 3 and depth <15 km located in the hanging wall of transpressional faults. The integrated data suggest that these structures are active and probably responsible for the major earthquakes that affected the Ionian offshore.

High‐Pressure Mechanical Properties of Talc: Implications for Fault Strength and Slip Processes

AbstractThe hydrous mineral talc is stable over a relatively large P‐T field and can form due to fluid migration and metamorphic reactions in mafic and ultramafic rocks and in faults along plate boundary interfaces. Talc is known to be one of the weakest minerals, making it potentially important for the deformation dynamics and seismic characteristics of faults. However, little is known about talc's mechanical properties at high temperatures under confining pressures greater than 0.5 GPa. We present results of deformation experiments on natural talc cylinders exploring talc rheology under 0.5–1.5 GPa and 400–700°C, P‐T conditions simulating conditions at deep faults and subducted slab interface. At these pressures, the strength of talc is highly temperature‐dependent where the thermal weakening is associated with an increased tendency for localization. The strength of talc and friction coefficient inferred from Mohr circle analysis is between 0.13 at 400°C to ∼0.01 at 700°C. Strength comparison with other phyllosilicates highlights talc as the weakest mineral, a factor of ∼3–4 weaker than antigorite and a factor of ∼2 weaker than chlorite. The observed friction coefficients for talc are consistent with those inferred for subducted slabs and the San Andreas fault. We conclude that the presence of talc may explain the low strength of faults and of subducted slab interface at depths where transient slow slip events occur.

Magneto-mineralogical characteristics of mafite-ultramafites of the Middle Bug River area and Holovaniv suture zone of the Ukrainian Shield (overview)

Mafites and ultramafites manifest in the magnetic field as significant magnetic anomalies due to the high content of magnetite, titanomagnetite and iron-magnesium silicates. Studying the mineralogy and magnetic properties of Archean rocks formed deep in the lower crust and uplifted to the surface allows to understanding the sources of magnetic anomalies. Such rocks are known in the Ukrainian shield, in particular in the Middle Bug River region and in the Holovaniv suture zone (HSZ). We consider mafic-ultramafic assemblages of the rocks of this region, their mineral composition and magnetic characteristics, manifestations in the magnetic field, and the distribution of magnetic minerals. Several mafic-ultramafic associations of different ages, composed of effusive, sedimentary-effusive and intrusive formations, are recognized for the area the Pobuzkiy ore mining region. Most of them were transformed intensively by metamorphism of granulite (to eclogite) facies and by intense tectonic and diaphoretic processes. The main volcanics and volcanogenic-sedimentary rocks belong to the Tivriv stratum of the Paleoarchean Dniester-Bug and Neoarchaean Bug series. Mantle rocks were the protolith of the Tivriv stratum, which are similar in composition to oceanic basalts. The Pavliv stratum is considered as a part of the Dniester-Bug series. It is composed mainly of two-pyroxene crystal schists (sometimes amphibolized, often with significant magnetite content (up to 10 %)), magnetite-orthopyroxene crystal schists, and bodies of ferruginous quartzites. Both series contain gneiss complexes, as well as bodies of basite-hyperbasites. Mafic rocks are mainly represented by hornblende-pyroxene crystal schists and amphibolites. Ultramafite and mafit-ultramafite intrusive bodies were mapped in the central and northern parts of the HSZ where they are presented by rocks of the hyperbasite and gabbro-peridotite formations. The Holovaniv block of the HSZ is spatially coincident with the Holovaniv gravitational maximum and magnetic anomalies, which are probably caused by the rooting of mafit-ultramafits from the upper mantle along deep fault zones. Magnetic sources with increased magnetization were identified within the district of Haivoron. They are associated with pyroxene schists, gneisses, coarse-grained pyroxene schists, and ferruginous quartzites. The high values of magnetic parameters of the rocks of the Haivoron-Zavallya region are explained by the presence of eulysites and magnetite-hypersthene crystal schists. Within the area of occurence of charnockite-enderbite rocks, the magnetic field with increased intensity and a large-mosaic structure is observed. Differentiation of the magnetic properties of the rocks of the upper part of the Earth’s crust, the shape and low power of the sources indicate their possible primary magmatic formation in the form of massifs and dykes with further metamorphic transformations. Magnetite is the main magnetic mineral of mafite-ultramafites according to thermomagnetic analysis and ore microscopy. Several generations of magnetite are observed. Early generations (reliably magmatic) are present in the dark-colored minerals as point inclusions and emulsion discharges along fissures (disintegration structures of solid solutions). The increase of the amount of magnetite in all types of rocks is associated with superimposed secondary transformations. Redistribution of iron occurs in the recrystallization zones with the formation of clusters of secondary coarse-grained magnetite. According to the hypothesis, the magnetite of ferruginous quartzites has metamorphic origin, while the origin of the magnetite of iron-carbonate and iron-siliceous formations is a controversial issue. It depends on the determination of the genesis of the original substance.

Bearing fault diagnosis under various conditions using an incremental learning-based multi-task shared classifier

Rolling bearings are susceptible to failure because of their complex and severe working environments. Deep learning-driven intelligent fault diagnosis methods have been widely introduced and exhibit satisfactory performance. However, bearing fault diagnosis during various working conditions is challenging; catastrophic forgetting occurs when test data are gathered under different conditions. In this paper, we develop an incremental learning-based multi-task shared classifier (IL-MTSC) for bearing fault diagnosis under various conditions. We use a one-dimensional convolutional neural network model as the principal framework. Then, we create a knowledge distillation method that allows the model to retain learned knowledge. Finally, we use a shared classifier that operates under various scenarios to establish a unified structure. The method can continuously learn and preserve knowledge when diagnoses bearing faults under various working conditions. The results show that IL-MTSC optimally diagnoses bearing marks under various conditions.

Characteristics of lineaments using gravity data in the Eastern Cameroon: Structural, hydrogeological and natural risks implications

The East region of the Cameroon is situated in the Adamaoua Yadé Domain, which is composed of CCSZ (Central Cameroon Shear Zone) and Sanaga fault that induced many tectonic movements affecting the studied area. The faults caused by these movements are not yet described. The aim of this work is to improve the knowledge of the tectonic structures in the study area (especially faults) through the exploitation of Bouguer anomaly in view of proposing a structural map that will be useful in the prevention of natural catastrophes related to faults and for hydrogeological prospection. In order to characterize these structures, two methods have been used: the multi-scale analysis of the maxima of the horizontal gradient and the Euler's deconvolution methods. The superposition of Euler's solutions to the maxima of the horizontal gradient extended upwards at several altitudes allowed to highlight the gravity lineaments that are either faults or linear contacts and to draw a structural map of the study area. From the map obtained, thirty eight lineaments have been identified, from which twenty seven linear contacts and eleven faults, which have the depth situated between 5 and 10 km, 15 and 20 km, 15 and 25 km, and 20 and 25 km. The analysis revealed that the deepest faults can constitute a natural risk in the study area. These deep faults require a monitoring within the framework of civil protection. The structural map, combined with the water system and boreholes helped to identify potential productive boreholes. The structural map obtained increases the geologic knowledge of the area and constitutes a useful document in natural risk prevention and the siting of boreholes.

Fault Diagnosis Algorithm of Gearboxes Based on GWO-SCE Adaptive Multi-Threshold Segmentation and Subdomain Adaptation

The data distribution of the vibration signal under different speed conditions of the gearbox is different, which leads to reduced accuracy of fault diagnosis. In this regard, this paper proposes a deep transfer fault diagnosis algorithm combining adaptive multi-threshold segmentation and subdomain adaptation. First of all, in the data acquisition stage, a non-contact, easy-to-arrange, and low-cost sound pressure sensor is used to collect equipment signals, which effectively solves the problems of contact installation limitations and increasingly strict layout requirements faced by traditional vibration signal-based methods. The continuous wavelet transform (CWT) is then used to convert the original vibration signal of the device into time–frequency image samples. Further, to highlight the target fault characteristics of the samples, the gray wolf optimization algorithm (GWO) is combined with symmetric cross entropy (SCE) to perform adaptive multi-threshold segmentation on the image samples. A convolutional neural network (CNN) is then used to extract the common features of the source domain samples and the target domain samples. Additionally, the local maximum mean discrepancy (LMMD) is introduced into the parameter space of the deep fully connected layer of the network to align the sub-field edge distribution of deep features so as to reduce the distribution difference of sub-class fault features under different working conditions and improve the diagnostic accuracy of the model. Finally, to verify the effectiveness of the proposed diagnosis method, a fault preset experiment of the gearbox under variable speed conditions is carried out. The results show that compared to other diagnostic methods, the method in this paper has higher diagnostic accuracy and superiority.

In-situ trace elements and sulfur isotopic analyses of stibnite: Constraints on the genesis of Sb/Sb-polymetallic deposits in southern China

The Xiangzhong metallogenic province (XZMP), the largest polymetallic mineralization province in southern China, is known for its large number of Sb and Sb-polymetallic deposits (>100). In this study, detailed microscope observation, trace element, and sulfur isotopic analyses were performed on stibnite from the Xikuangshan, Woxi, and Banxi deposits in the XZMP to constrain the ore genesis.Stibnite from three deposits appears similar under backscattered electron imaging and has similar major elements contents. Detectable trace elements in stibnite are Fe, Cu, Zn, As, and Pb. Base metals (Cu, Pb, and Zn) are enriched in stibnite from the Woxi deposit but are depleted in stibnite from the Xikuangshan and Banxi deposits. Gold is detectable only in stibnite from the Woxi deposit. Cu, As, and Pb mainly occur as solid solutions within the crystal lattice in stibnite, while micro-scale inclusions of Fe- and/or Zn-rich phases are also observed. The δ34S values of stibnite from three deposits are distinct but with narrow ranges: +6.8 to +10.2 ‰; +5.5 to +6.5 ‰; −4.2 to +0.1 ‰ for the Xikuangshan, Banxi, and Woxi deposits, respectively. The δ34S values of stibnite suggest that the underlying basement rocks are the potential source of sulfur for the Sb mineralization in the Xikuangshan and Banxi districts while sulfur for the Sb mineralization of the Woxi district may have originated from a deep magmatic source. In addition, a positive trend between the δ34S values of stibnite and sampling depth suggests an input of the 34S-rich basin brine during the mineralization in the Woxi district.We propose a genetic model for the Sb mineralization in the XZMP: Fluids rich in Sb, Au, W, Cu, Pb, and Zn related to igneous activities ascended via regional deep faults and mixed with 34S-rich basin brine. Ore minerals of Sb, Au, and W were deposited within structural traps resulting in the Woxi-type deposits. The basement-derived deep fluids driven by orogenic leached Sb and related metals from the basement metamorphic rocks, which migrated via the regional faults and mixed with cold near surface meteoric water to form the Xikuangshan-type deposits.

Creation of a training ground for the complex geological and geophysical study of fracturing within the south-western Crimea (Cape Fiolent, Heraclea Plateau)

A complex of geological and geophysical work was carried out to study fracturing in the Jurassic-Neogene rocks of the Heraclea Plateau, which included a field study of the Georgievsky fault zone, structural and geomorphological analysis; the geophysical complex combined marine seismic and magnetometric studies in combination with ground-based studies using electrotomography, gravimetry and magnetometry. The main object of study was the zone of the deep Georgievsky fault and the feathering tectonic disturbances. As a result of complex studies, the main geological and geophysical criteria for the identification of dangerous fracturing sites have been established: the extremely heterogeneous structure of the upper part of the geoelectric section to depths of 30–40 m according to electrical survey data; seismic data indicate that Miocene limestones have extremely low strength properties in areas of increased fracturing; according to electrical survey data, the water content (humidity) of the upper part of the section changes sharply horizontally; in the karst areas at certain depths, there is a sharp variability in resistivity from the maximum values to the minimum; fracturing develops quite actively under the influence of landslide processes. Especially dangerous are the stretching cracks that occur in areas of positive relief of the base rocks, along which landslide bodies represented by limestones slide.

The characteristics of strike-slip faults and their control on hydrocarbon distribution in deep carbonate reservoirs of the central Sichuan Basin

The past decade has witnessed a breakthrough in the gas exploration of deep marine carbonates of the central Sichuan Basin. Deep faults research has also attracted increasing attention, as faulting plays an important role in reservoir control. Previous studies have suggested a developed series of high-angle strike-slip fault systems in the central Sichuan Basin, but correlated exploration activities are limited, as distribution rules and dynamic mechanisms remain unclear. In this study, the spectral decomposition coherence method was used to describe the geometric and kinematic characteristics of these strike-slip faults. Using a comprehensive analysis technique to assess the strike-slip fault tectonic activity history, the formation and evolution processes of strike-slip faults and their control on hydrocarbon distribution were examined. The results showed that the deep strike-slip fault system, mostly distributed in the Dengying Formation, can be divided into four stages, three levels, and three groups of orientation, which controlled the structural framework and shape of the central Sichuan area, as well as the zoning from north to south, and blocking from west to east. The faults showed features of layered deformation and staged evolution in the vertical direction. The segmentation of strike-slip faults strongly controls the quality of fractured vuggy reservoirs. Reservoirs of the hard-linked zone of the strike-slip fault are the most developed, followed by those of soft-linked segments, with translational sections of the strike-slip fault being relatively undeveloped. Strike-slip faults are important hydrocarbon migration paths, and their multistage activities have different controlling effects on hydrocarbon accumulation.

Attention-based deep meta-transfer learning for few-shot fine-grained fault diagnosis

Deep learning-based fault diagnosis methods have made tremendous progress in recent years; however, most of these methods are coarse grained and data demanding that cannot find the root causes of mechanical system failures at a finer granularity with limited fault data. Therefore, in this study, we first investigate the few-shot fine-grained fault diagnosis (FSFGFD) problem, with the aim of identifying novel fine-grained faults under different working conditions using only few samples from each class. To address the difficulties of fine-grained fault feature extraction and poor model generalization to unseen few-shot faults in FSFGFD tasks, a novel attention-based deep meta-transfer learning (ADMTL) method is proposed. First, the failure modes under different working conditions are considered as fine-grained faults, and their raw signals are transformed into time–frequency images. Based on this, an attention mechanism is introduced to guide the feature extractor of the ADMTL on what information to learn. The ADMTL then follows a three-stage learning process of pre-training, meta-transfer, and meta-adaptation to achieve fast adaptation to new fine-grained faults using a priori knowledge gained from known faults. Furthermore, a parameter modulation strategy is employed to adaptively update the pre-trained network during the meta-transfer process. The comprehensive experimental results of three case studies demonstrate the superiority of our method over state-of-the-art methods. The proposed method achieves excellent performance with an average accuracy of 99.08%, 95.86%, and 77.74% for FSFGFD tasks when performing meta-transfer within the same machine and between different machines, respectively.

The Variable Continuous Bimaterial Interface in the San Jacinto Fault Zone Revealed by Dense Seismic Array Analysis of Fault Zone Head Waves

AbstractKey factors controlling earthquake ruptures include fault geometry, continuity, and seismic velocity structure around the fault. We present a novel tool that better informs deep bimaterial fault geometry embedded in distributed damage and seismicity, associated velocity contrasts across the fault, and their correlations with surface complexities. The method employs fault zone head and direct body waves and is applied to recordings from five spatiotemporally different seismic arrays along the complex San Jacinto fault zone (SJFZ) in southern California. We detect and distinguish these signals based on instantaneous phase coherence and relative energy in a cascading manner from one scale array to another. The analysis reveals a &gt;70‐km long continuous bimaterial interface within the SJFZ with several deep northeast dipping fault segments. The northern SJFZ, for instance, locates ∼7 km northeast of its surface expression at 18‐km depth. P‐wave velocity contrasts range from near 0% to &gt;15%, consistent with other bimaterial faults, and differ by a few % depending on fault‐array azimuth, implying directional‐dependent velocity contrasts. S‐wave head waves and velocity contrasts are also imaged for the first time at the southern SJFZ, averaging to 2.9% in agreement with tomography results. The imaged geometry and continuity suggest the SJFZ initiated along remnant tectonic structures and translates to a rupture potential of M &gt; 7.2, i.e., the sizes of its largest paleo‐earthquakes. The P and S contrasts, and their ratios, have important implications for earthquake rupture speed, mode, directivity, and frictional heating along the SJFZ and other major faults globally.

Paleotemperature reconstructions based on vitrinite thermometry data (on the example of the Upper Paleozoic deposits of the Dnieper-Donets depression and the adjacent margins of the Donbas)

The article is devoted to paleotemperature reconstructions based on the data on the reflectance of the vitrinite of coal organic matter in the Upper Paleozoic deposits of the Don-Dnieper trough (within the Dnieper-Donets depression and adjacent parts of the Donbas). It is builds on earlier work on reconstructing the paleogeothermal regime by establishing paleogeothermal gradients and amplitudes of vertical displacements of rock massifs. Paleogeothermal indicators are associated with the geodynamic setting of the subsoil, which determines the intensity and nature of the distribution of heat sources, geological development, and features of the tectonic structure of the region. Based on the results, a map of the distribution of paleotemperatures at a depth of 3 km was constructed. An analysis of the changes and patterns in the distribution of paleotemperatures makes it possible to reveal the role of volcanism, deep faults geodynamics, and lithospheric parameters in the thermal history of the region, as well as to evaluate its thermal field evolution. The presented map, along with the previously published maps of the paleogeothermal gradients and amplitudes of vertical displacements of rock massifs, can be used to demonstrate the features and patterns of the regional distribution of the indicated parameters. It could become a powerful tool in the study of the tectonic and geothermal history of the region.

Magnetic characteristics and tectonic structure of the Earth's crust of the Carpathian oil and gas region as a component of complex hydrocarbon criteria

For the first time, a qualitative and quantitative analysis of the geomagnetic field and oil and gas capacity was performed for the territory of the Carpathian region, which made it possible to reveal the connection of hydrocarbon deposits with the magnetization of the Earth’s crust at the regional and local levels and the features of the deep structure of the Earth’s crust according to seismic data. The regularity of the distribution of oil and gas deposits of the Carpathian oil and gas-bearing region revealed by geomagnetic criteria is confirmed by their connection with regional and local anomalies of the gravity field and heat flow density. According to the analysis of the regional geomagnetic field and magnetic models along the PANCAKE and RomUkrSeis geotraverses, gas fields are located above the magnetic blocks of the middle and lower parts of the Earth’s crust or in their marginal parts, and oil fields are located above practically non-magnetic deep blocks. Under the thrust part of the Carpathian arc, the regional features of the Earth’s crust structures are clearly manifested, namely, starting from the longitude of the city of Rakhiv, the submeridional direction of extension of regional anomalies of magnetic, gravity, and thermal fields and their horizontal gradient zones prevails. The oil and gas potential of the region is in good agreement with this — the gas fields are timed to the minimum values of the regional horizontal gradient of the regional magnetic field, to the increased gradient of Bouguet anomalies, as well as to the minimum values of the horizontal gradient of heat flow density anomalies. In local geophysical fields, gas fields are gravitating: to weakly negative magnetic anomalies and their gradient zones; to negative anomalies of the gravitational field predominantly; to positive anomalies of heat flow density in the northwest, within the area of Trans-European suture zone (without the middle of the Krakovets fault), and negative anomalies in the Carpathian trough. Oil and oil condensate deposits are correlated with a band of positive magnetic field anomalies, negative gravity field anomalies, and increased heat flux density values. The main deep faults of the Carpathian region and the marginal part of the Platform in the first approximation can be considered Velikomostivsko-Chernivetsky, which characterizes the change in the character of magnetic and gravity fields and heat flow density, Rava-Rusky, which reflects the zone of articulation of the Eastern and Western European platforms, Pre-Carpathian — the border of the Pre-Carpathian trough and the Folded Carpathians on the Earth’s surface (as well as the boundary of the Archaean(?)-Paleoproterozoic and Meso-Neoproterozoic crust according to the modern international chronostratigraphic scale), as well as the Transcarpathian fault. On the basis of magnetic and seismic data, the hypothetical depth position of these faults and the possible connection with them of hydrocarbon flows into the upper part of the Earth’s crust are proposed. Therefore, the geomagnetic criteria of the oil and gas bearing capacity of the Earth’s crust of the Carpathian region are agreed based on the results of the study of the gravity field and heat flow density anomalies, which makes it possible to predict the spread of oil and oil condensate and gas and gas condensate deposits according to the regional and local features of these fields in a first approximation.