Striking Faults Research Articles

Directionality of Arias intensity in the Wenchuan Mw 7.9 earthquake, China

There is a strong correlation between Arias intensity and the possibility of earthquake-induced landslides. Since landslides have distinct sliding directions, it is necessary to investigate the directional characteristics of Arias intensity. The free-field recordings from 40 stations within 200 km of fault distance in the Wenchuan Mw 7.9 earthquake were selected for this study. We discovered that the fluctuation of Arias intensity with azimuth exhibits distinct features of cosine (or sine) curve with a period of 180°, and we proposed a theoretical expression (Eq. 3) of Arias intensity considering directionality using the maximum value (Ia100), the minimum value (Ia00), and the polarization direction (Amax). The maximum-to-minimum ratios of Arias intensity (Ia100/Ia00) decrease as fault distance increases and can be represented as a piecewise linear decreasing relationship that declines significantly faster in the near-middle field than in the middle-far field. The polarization directions (Amax) for stations near the epicenter are consistent with the coseismic displacement directions, which should be further validated by testing various faulting styles; an estimated equation for the azimuth of the projection of the trace of fault movement on the ground surface was employed to predict Amax using the fault's strike, dip, and rake. Finally, we provided a framework for constructing empirical directional model of Arias intensity using the traditional attenuation relationship, the empirical relationship of Ia100/Ia00, and the estimated equation of Amax, as well as thereby a method for predicting Newmark displacement considering directionality. There is an imperfect solution for Amax estimation, other than our work would still serve as a point of reference for future research into the regional directionality of Arias intensity.

Formational stages of natural fractures revealed by U-Pb dating and C-O-Sr-Nd isotopes of dolomites in the Ediacaran Dengying Formation, Sichuan Basin, southwest China

Deep core (>4.9 km) from Ediacaran Deng IV Member algal dolomites in the Gaoshiti-Moxi block in the Sichuan Basin, southwest China, reveals multiple generations of dolomite-lined and dolomite-filled opening-mode fractures. Three progressive stages of fracture formation are marked by crosscutting relations visible in the core, by acoustic emission experiments revealing evidence of past stress directions, and by fluid inclusions, U-Pb ages, C-O-Sr-Nd isotope patterns, and rare earth element data for dolomite cements in fractures, which document ages and differing thermal conditions and fluid compositions during fracture. In calcite-filled fractures, U-Pb ages and carbon and oxygen isotope signatures vary greatly, indicating that fractures developed with intensified tectonic activity marked by regional structures and with enhanced diagenetic alteration. In stage I, WNW-striking opening-mode fractures formed that contain dolomite deposits precipitated from basinal fluids between ca. 549 Ma and ca. 532 Ma. At this time, the Sichuan Basin experienced Xingkai taphrogenesis (rifting) from the late Neoproterozoic to early Cambrian. The central Sichuan paleo-uplift was undergoing ENE extension, and preexisting ESE- and nearly E-W−striking faults were oblique to the ENE principal stress orientation. This led to a local stress field favoring dextral shear near fault zones accommodated by the fractures. In stage II, ENE-striking fractures that are younger based on crosscutting relations contain dolomite deposits from basinal fluids with ages from ca. 423 Ma to ca. 411 Ma. Contemporaneous with Xuefeng thrusting, the central Sichuan paleo-uplift was in a NNE-striking transpressional stress field, which likely further generated ENE-striking fractures. In stage III, nearly N-S−striking fractures formed in the Gaoshiti-Moxi block. High-temperature fluids related to the Permian Emeishan large igneous province invaded these fractures from ca. 260 Ma to ca. 256 Ma. At this time, the Sichuan Basin was uplifted under the influence of the Emei taphrogenesis in the late Permian, and the central Sichuan paleo-uplift was subjected to E-W−striking extension. In fractures in these carbonate rocks, micro-computed tomography imaging reveals that macropores (>10 μm, 12.1%−21.8%) and small pores (2−10 μm, 76.6%−86.1%) dominate the dolomite mineral deposits, and that there are few (1.6%−1.8%) micropores or nanopores (<2 μm). Medium-sized throats (1−3 μm) are the main connecting channels. We infer that fractures served as conduits for fluid migration, leading to the dissolution of matrix pores adjacent to the fractures. This secondary porosity not only enhances reservoir storage capacity but also augments reservoir connectivity. Our study shows that in situ U-Pb dating and full-diameter rock acoustic emission data can effectively constrain the timing of fractures. By integrating this information with regional tectonic sequences and fracture diagenetic sequences from combined relative timing, geochemistry, and rock mechanics evidence, we clarify the factors controlling fracture formation.

Radiogenic geothermal systems of Bangka Island, Indonesia: Implications of high heat production and tectonic framework

The presence of geothermal manifestation in Bangka Island (Southeast Sumatra, Indonesia) with the absence of Quaternary volcanic activity and also relatively low seismicity events has raised intriguing questions on the control of the geothermal system in this area. As the regional tectonic setting of Indonesia volcanic geothermal systems has been known, that of non-volcanic geothermal systems such as radiogenic system become an issue to be investigated. This study reports the geochemistry and petrography analysis of Triassic granite related to radiogenic production at the vicinity of hot springs in Bangka Island. Surface temperatures of the Bangka hot springs range from 37 to 70.7 °C and pH values vary between 5.6 and 7.5. These hot springs are discharging either in close to massive granite bodies or occur in between two major NE-SW striking faults zones, i.e., Pemali fault and Payung fault. Our results indicate the average radiogenic heat production of Late Triassic Klabat granite in the northern area ranges from 28.5 to 38.34 μWm−3 and the southern area ranges from 28.3 to 49.5 μWm−3. In comparison to similar granite belt located in Malaysia, heat production of granitoid in Bangka hot springs is four times higher, possibly due to their different granite origins.

The 2022–2023 seismic sequence onshore South Evia, central Greece: evidence for activation of a left-lateral strike-slip fault and regional triggering of seismicity

On 29 November 2022, an earthquake of ML 5.0 (Mw 4.8) occurred onshore South Evia Island (central Greece) preceded by a ML 4.7 (Mw 4.6) event. The pattern of relocated aftershocks indicates the activation of a single, near-vertical fault segment, oriented NW-SE at shallow crustal depths (6–11 km). We suggest that both events ruptured a blind, left-lateral strike-slip fault, about 5 km southeast of village Almyropotamos. We observed that a clear foreshock activity (N=55 events) existed before the two moderate events. The impact of the static stress loading on neighboring fault planes diminishes after a distance of 7 km from the November 2022 epicenters, where the static stress falls below +0.1 bar. We further explore triggering relationships between the 29 November events and the late December 2022 moderate events (ML 4.9) that occurred about 60 km toward NW in the Psachna and Vlahia regions of central Evia. We present evidence of possible delayed dynamic triggering of the late December 2022 central Evia sequence, based on marked changes in seismicity rates and on measured peak ground velocities (PGVs) and peak dynamic strains, both exhibiting local maxima in their map distributions. The causes of the delayed triggering may be related to the well-known geothermal field in central/north Evia and the NW-SE strike of the seismic fault.

A method for locating lightning strikes in distribution lines with multiple branches

A lightning strike fault location (FT) method for multi-terminal overhead lines based on 0-mode 1-mode wave velocity difference is proposed to address the shortcomings of current multi-terminal overhead line positioning methods that are difficult to identify due to multi-terminal GPS time synchronization and reflected traveling waves. Based on the wave velocity difference between 0-mode and 1-mode, single-end ranging is performed, and an FT judgment vector is formed based on the ratio of the ranging results of each monitoring terminal to the inherent length of the line. By analyzing the element features in the FT judgment vector, an FT criterion is proposed, and the FT results of the appropriate monitoring terminal are selected as the final FT. After PSCAD/EMTDC simulation verification, this method is suitable for complex multi-branch overhead lines, and can accurately locate the FT without being affected by time synchronization.

Fault Orientation Trumps Fault Maturity in Controlling Coseismic Rupture Characteristics of the 2021 Maduo Earthquake

AbstractFault maturity has been proposed to exert a first order control on earthquake rupture, yet direct observations linking individual rupture to long‐term fault growth are rare. The 2021 Mw 7.4 Maduo earthquake ruptured the east‐growing end of the slow‐moving (∼1 mm/yr) Jiangcuo fault in north Tibet, providing an opportunity to examine the relation between rupture characteristics and fault structure. Here we combine field and multiple remote sensing techniques to map the surface rupture at cm‐resolution and document comprehensively on‐fault offsets and off‐fault deformation. The 158 km‐long surface rupture consists of misoriented structurally inherited N110°‐striking segments and younger optimally oriented N093°‐striking segments, relative to the regional stress field. Despite being comparatively newly formed, the ∼N093°‐striking fault segments accommodate more localized strain, with up to 3 m on‐fault left‐lateral slip and 25%–50% off‐fault deformation, and possibly faster rupture speed. These results are in contrast with previous findings showing more localized strain and faster rupture speed on more mature fault segments; instead, our observations suggest that fault orientation with respect to the regional stress can exert a more important control than fault maturity on coseismic rupture behavior when both factors are at play.

Adaptive fault enhancement in OVT domain based on anisotropy theory

As a result of the combined influence of multi-stage and multi-directional tectonic activities, the subsurface medium in complex structural areas can easily develop intricate fault systems with varying scales and directions. Post-stack seismic and azimuth-stack attributes have limited precision in recognizing such complex fault systems. In this paper, we propose an adaptive fault enhancement workflow in offset vector tile (OVT) domain based on anisotropy theory to improve the recognition ability of seismic data for multi-directional faults and minor faults. The vertical directions of fault strikes and tectonic strikes estimated by the gradient structure tensor (GST) can be used as sensitive observation azimuths of faults. At the same time, according to the anisotropic forward modeling and real data amplitude variation with offset (AVO) analysis of minor faults in marine shale of Wufeng-Longmaxi formations in Sichuan Basin, China, the incident angles with the largest difference between isotropic and anisotropic reflection coefficients can be used as sensitive incident angles of faults. A new fault enhancement seismic data can be reconstructed from the OVT gathers by traversing the sensitive azimuths and incident angles adaptively. The 3D model and real data indicate that the faults enhanced by the workflow we proposed are clearer in shape, smaller in scale, and richer in details, which is consistent with geology and well.

Simultaneous normal and reverse faulting in reactivating caldera faults: A detailed field structural analysis from Campi Flegrei (southern Italy)

Models of volcanic collapses proposed in the literature rely on combining field examples with analogue and numerical modelling to connect superficial observables to sub-surface volcano-tectonic processes. However, the behaviour of such collapses in an already faulted and fractured medium needs to be better explored.We studied a complex array of normal and reverse faults within the central sector of the active Campi Flegrei caldera, where faults with centimeters-to-meters displacements are hosted in the La Pietra tuff (∼13.5 ka) and the overlying pyroclastic succession of the last ∼5.5 kyr. We analyzed the attitude, kinematics and throw of these structures, employing a UAV-based digital outcrop model. The analysis shows that antithetic normal and reverse faults form in the hanging wall of a pre-existing WNW striking, NNE-dipping master normal fault. Moving northward, the strike of the antithetic faults rotates from WNW to NNW directions, with the latter showing a right-lateral oblique component. The simultaneity and coherence of both kinematics and attitudes are verified by the throw analysis. We associated the formation of this array with the caldera-collapse phase of the Agnano-Monte Spina eruption (∼4.55 ka), which caused off-caldera faulting beyond the main collapsed area.Based on field data, we suggest that during peak caldera-forming phases, wider areas beyond the main caldera scarps can be involved in volcano-tectonic collapses in the presence of a pre-existing fault network and complex tapped reservoirs. This highlights the role of inherited structures in weakening the crust above the magma reservoir that can potentially increase the magnitude and duration of caldera-forming eruptions, as they may induce a broader roof rock subsidence, pressurizing wider regions of the sub-caldera magma system.

Controls on Bending‐Related Faulting Offshore of the Alaska Peninsula

AbstractOceanic plates experience extensive normal faulting as they bend and subduct, enabling fracturing of the incoming lithosphere. Debate remains about the relative importance of pre‐existing faults, plate curvature and other factors controlling the extent and style of bending‐related faulting. The subduction zone off the Alaska Peninsula is an ideal place to investigate controls on bending faulting as the orientation of the abyssal‐hill fabric with respect to the trench and plate curvature vary along the margin. Here, we characterize faulting between longitudes 161°W and 155°W using newly collected multibeam bathymetry data. We also use a compilation of seismic reflection data to constrain patterns of sediment thickness on the incoming plate. Although sediment thickness increases over 1 km from 156°W to 160°W, most sediments were deposited prior to the onset of bending faulting and thus should have limited impact on the expression of bend‐related fault strikes and throws in bathymetry data. Where magnetic anomalies trend subparallel to the trench (<30°) west of ∼156°W, bending faults parallel magnetic anomalies, implying that bending faults reactivate pre‐existing structures. Where magnetic anomalies are highly oblique (>30°) to the trench east of 156°W, no bending faults are observed. Summed fault throws increase to the west, including where pre‐existing structure orientations are constant (between 157 and 161°W), suggesting that another factor such as the increase in slab curvature must influence bending faulting. However, the westward increase in summed fault throws is more abrupt than expected for gradual changes in slab bending alone, suggesting potential feedbacks between pre‐existing structures, slab dip, and faulting.

Refinement of microplate boundaries assisted by integrated gravity analysis: Application to the Caribbean Sea

Under the long-term influence of subduction, collision and strike-slip faults, the Caribbean Sea and its surroundings have evolved complex topography and terranes, making it an excellent site to study the tectonic of microplates. However, some microplate boundaries of this area are still controversial or unclear. Here we employed the widely-used satellite-derived gravity dataset in combination with previous findings to conduct a detailed re-interpretation of tectonic boundaries. A newly proposed product of normalized multi-edge-attributes (PNMEA) with upward-continued free-air gravity anomalies (FGA) is used to constrain deep large-scale boundaries (i.e., oceanic trenches, deformed belts and fault systems). The residual crustal gravity anomalies (RCGA) obtained based on wavelet multi-scale decomposition further reveal density variations within the crust domain. The Tilt angle (TA) of FGA highlights fault strikes and patterns in the near-surface. Consequently, we refine the possible boundaries of microplates within the northern Caribbean boundary zone and the Nicaraguan Rise, and analyze the contact relationships among microplates. The results suggest a triple junction among the Gonave, Hispaniola and Septentrional microplates exists in the Windward Passage, and a zigzag low RCGA in the Mona Passage separates the Hispaniola and Puerto Rico microplates. In addition, the north and south Nicaraguan rises are inclined to be unaffiliated implied by the differences in multiple physical properties. We thus conclude that an integrated analytical approach involving potential-field edge detection and RCGA can provide additional constraints for identification of tectonic or microplate boundaries. Deep-shallow coupling and lithosphere-scale cooling differences may provide new perspectives to explain the complexity of temporal-spatial configuration due to multiple microplate interactions.

Numerical simulations of earthquake rupture induced by pressure perturbation

The subsurface fluid injection can cause pressure increase within faults, leading to earthquake occurrences. However, the factors controlling earthquake rupture due to pressure perturbation remain poorly understood. To resolve this problem, we simulate the physical processes of earthquake nucleation and rupture on strike-slip faults perturbated by pressure migration based on the slip-weakening law. Multiple kinds of factors, including background stress, fluid injection rates, the area of the pressurized region, fault geometry, and fault friction coefficients, are considered in our simulations. Our simulation results reveal that the ratio of shear stress to normal stress rather than their absolute values controls the rupture behavior. With the large stress ratios, high injection rates, and large pressurized areas, earthquakes are prone to propagate as runaway ruptures. Additionally, faults with large aspect ratios of length to width are also favorable for causing runaway ruptures. In contrast, the factors of fault strike, dip angles and friction coefficients have minor influence on rupture behavior.

Impacts of a Moderate-Sized Earthquake: The 2023 Magnitude (Mw) 4.7 Leyte, Leyte Earthquake, Philippines

On 15 January 2023, a shallow, moderate earthquake with a magnitude (Mw) of 4.7 and a depth of one kilometer struck the northern part of Leyte Island in the central Philippines. Originating along the northern Leyte segment of the Philippine Fault, a well-established creeping fault, the earthquake caused significant geologic, structural, and socio-economic impacts despite its low magnitude. Probable surface rupture and landslides were reported, leading to a comprehensive field investigation. Our investigation revealed an ~8 km discontinuous surface rupture along the northern Leyte segment of the Philippine Fault, with a maximum left-lateral displacement of 2 cm. This was the first documented occurrence of such a phenomenon associated with an earthquake of a magnitude less than 6, particularly along a creeping fault segment. The maximum ground shaking felt was reported on the PHIVOLCS Earthquake Intensity Scale (PEIS) to be VI (very strong), equivalent to a Modified Mercalli Intensity (MMI) of VI along the fault strike. However, strong motion accelerographs recorded a peak ground acceleration (PGA) of 0.407 g, equivalent to PEIS VIII (very destructive), attributed to local site amplification influenced by subsurface geology. In the area where the local site amplification occurred, limited liquefaction was observed on marshlands with recent and alluvial deposits. Two landslides were observed in the mountainous area west of the fault. Structural damages were noted in areas with PEIS VI intensity and areas transected by the surface rupture. Despite the earthquake’s low magnitude, the event documented significant impacts, including surface ruptures, liquefaction, landslides, and severe structural damage. The peculiarities of this event are attributed to the shallowness of the earthquake source, and local site conditions, including geology, geomorphology, and soil properties, contributed to the severity of the impacts. Moderate in size, this earthquake emphasizes the importance of documenting moderate-sized earthquakes as a tool and guide for medium- and long-term earthquake risk assessment and resiliency.

Regional structural control on the Mont-Dore Plio-Quaternary volcanism (France)

Magma transfer in the upper crust including emplacement at the surface of the Earth, have been regarded as largely controlled by the regional tectonic activity. While this relationship is well highlighted for systems like monogenetic, mostly basaltic, volcanic fields, the tectonic control on the transfer and emplacement of magmas in complex, polygenetic, volcanic systems, remains poorly documented in evolving tectonic settings. The Mont-Dore Plio-Quaternary volcanic complex (4.7 to 0.3 Ma) is one of such polygenetic volcanic fields as it is formed of three successive eruptive cycles: The caldera unit (3.3 to 2.2 Ma); The Aiguiller complex (2.5 to 1.5 Ma) and the Sancy stratovolcano unit (1.5 to 0.3 Ma).Analyzing fractures, fault kinematics and regional lineaments in the Variscan basement, together with attitude of dikes and volcanic centers alignments of the three volcanic units, we document the influence of the brittle structuration of the underlying basement on the volcanism distribution over time while regional stress changed. The late-Variscan N02E0, and secondary N160, striking crustal faults were reactivated since the Oligocene and channeled at depth the magma, while similarly oriented faults and fractures triggered the final storage in the shallow crust and spatial distribution of the volcanic vents. This fault system continued to act from the Miocene to the present-day uplift, associated with new N020E striking, flat-lying, fractures. An exception arises during the upper Miocene while N060E and N135E striking faults enabled the development of the caldera unit in a NW-SE extensional context.The emplacement of the three units from the mid-Pliocene to the end of the Pleistocene while a change in regional stress field conditions emerged at about 2.5 Ma exemplify the control of the brittle Variscan basement on the magmatic activity of the Mont-Dore Plio-Quaternary volcanic complex.

Precise Lightning Strike Detection in Overhead Lines Using KL-VMD and PE-SGMD Innovations

When overhead lines are impacted by lightning, the traveling wave of the fault contains a wealth of fault information. The accurate extraction of feature quantities from transient components and their classification are fundamental to the identification of lightning faults. The extraction process may involve modal aliasing, optimal wavelet base issues, and inconsistencies between the lightning strike distance and the fault point. These factors have the potential to impact the effectiveness of recognition. This paper presents a method for identifying lightning strike faults by utilizing Kullback–Leibler (KL) divergence enhanced Variational Mode Decomposition (VMD) and Symmetric Geometry Mode Decomposition (SGMD) improved with Permutation Entropy (PE) to address the aforementioned issues. A model of a 220 kV overhead line is constructed using real faults to replicate scenarios of winding strike, counterstrike, and short circuit. The three-phase voltage is chosen and then subjected to Karenbaren decoupling in order to transform it into zero mode, line mode 1, and line mode 2. The zero-mode voltage is decomposed using KL-VMD and PE-SGMD methods, and the lightning identification criteria are developed based on various transient energy ratios. The research findings demonstrate that the criteria effectively differentiate between winding strike, counterstrike, and short-circuit faults, thus confirming the accuracy and efficacy of the lightning fault identification criteria utilizing KL-VMD and PE-SGMD.

Sediment‐hosted disseminated gold mineralization at the Gegalaw deposit in Central Myanmar

AbstractGegalaw is one of the gold deposits situated in the Sagaing Fault zone, which marks the boundary between the Central Myanmar Basin to the west and the Mogok metamorphic belt to the east. The gold mineralization is mainly confined along northeast striking faults between carbonaceous silty limestone of the Kywethe Chaung Formation and carbonaceous and calcareous shale of the Eocene Male Formation. Hydrothermally induced dissolution breccia associated with progressive silica replacement increase near the northeast trending faults. The hydrothermal alteration associated with the mineralization is silicification in addition to illite‐kaolinite argillic alteration, of which illite is dated by the K‐Ar method as 40.26 ± 0.91 Ma. Sulfide minerals contained in the ores are mainly pyrite and arsenopyrite, with minor to trace amounts of marcasite, chalcopyrite, and sphalerite, among which pyrite and arsenopyrite are the hosts of gold. Pyrite and arsenopyrite are divided into diagenetic and hydrothermal stages, based on their mineral textures. Diagenetic stage pyrites are framboidal (Py1A) and coalescent framboidal (Py1B). Those of the hydrothermal stage are zoned pyrite with porous cores (Py2) and compact rims (Py4). In addition, euhedral homogeneous pyrites with or without compact rim are present (Py3). Some pyrites show pseudomorphs of ilmenite (Py3i) and carbonate minerals, possibly ankerite (Py3c). Arsenopyrites are also divided into porous, sooty arsenopyrite (Apy1), and compact arsenopyrite (Apy2) that co‐exists with Py3 and Py4 pyrites. Electron probe microanalysis for sulfides indicates that Py1A and Py1B are deficient in Fe while Py2, Py3 and Py4 are deficient in S compared to stoichiometry of pyrite. Such deficiencies are compensated by metal ions such as Co2+ and Ni2+ for Py1A, As2+ for Py1B, and As1− for Py2, Py3, and Py4. Arsenic equilibrium temperature of Apy2‐Py3 pairs shows a mode range of 250–270°C. Detected gold concentrations (~650 ppm) in arsenian pyrite (Py2, Py3, and Py4) indicate that gold in pyrite are below the solubility, suggesting that gold is present as solid‐solution in pyrite. Sulfur isotopic values of the pyrites in the unaltered host rocks are −18.9‰ and −8.9‰, and those of the pyrites from the hydrothermal altered rocks range from −17.3‰ to −0.5‰. These similar negative δ34S ranges of the pyrites suggest that the source of sulfur is dominated in biogenic reduction origin. Nevertheless, the two relatively heavier sulfur isotopic values (−4.9‰ and −0.5‰) suggest a contribution of an external hydrothermal fluid source. The research results indicate that gold mineralization occurred by infiltration of auriferous reduced hydrothermal fluids into the carbonaceous silty limestone and carbonaceous and calcareous shale through northeast trending secondary faults of the dextrally moving Sagaing Fault system and the fluids reacted with framboidal pyrite as well as iron‐bearing minerals in the host rocks to precipitate gold‐bearing arsenian pyrite. The age of hydrothermal illite suggests a link to the right‐lateral strike‐slip movement of the Sagaing Fault that is related to the collision of the Indian and Asian plates.

A SERIES of TANGIBLE EARTHQUAKES in 2018–2019 in the FOCAL ZONE of the 10-point SPITAK EARTHQUAKE of 1988

The paper presents the results of a study of 2018–2019 tangible seismic events with intensity at the epicenter of 5–6 points and above, that occurred in the focal zone of the 10-point Spitak earthquake of 07.12.1988 with MLH =6.8. Two earthquakes of June 6, 2018, with МL=3.6 and МL=4.3, as well as two shocks on September 10, 2019, with МL=4.7 and with МL=3.9, were felt in the nearest settlements with an intensity of 5 or more points. For three of them, according to the collected macroseismic data, isoseist maps were constructed and macroseismic parameters were determined. The strike of the nodal planes in the earthquake sources is consistent with the direction of elongation of the isoseist system, which, in turn, for three events coincides with the strike of the nearest faults of the Pambak-Sevan system.

Implications of multi-stage deformation on the differential preservation of Lower Paleozoic shale gas in tectonically complex regions: New structural and kinematic constraints from the Upper Yangtze Platform, South China

The strength of tectonic deformation in tectonically complex regions, particularly multi-stage superimposed tectonic regions, can have a significant impact on shale gas preservation conditions. However, differential tectonic deformation has still not been quantitatively constrained, and its impact on the preservation conditions of shale gas is thus poorly understood in the northern Guizhou Province, southwest China. This study investigates the differential preservation conditions of marine shale gas in four eroded synclines (including Shixi, Daozhen, Zhongguan, and Fuyan Synclines) of the northern Guizhou Province. Interpretation of structures in field outcrops, geometry and kinematic analysis, and typical gas reservoir anatomy are combined to quantitatively explore the effect of superimposed deformation on the preservation conditions of shale gas. According to a set of new structural and kinematic constraints, the Riedel shear model for strike-slip faults is firstly conducted in the eroded synclines in the northern Guizhou Province, which innovatively established a linkage between detailed structural analysis and evaluation of shale-gas preservation conditions. We demonstrate that superimposing of deformations plays a role in differential accumulation in eroded synclines. The results indicate that (1) fault strike in the Shixi Syncline is more concentrated than Zhongguan and Fuyan Synclines, whereas fault strikes in the Zhongguan and Fuyan Synclines are more scattered. There is only one direction of maximum principal stress (σ1) in the Shixi and Daozhen Synclines. There are two maximum principal stress directions (σ1) in the Zhongguan and Fuyan Synclines. The Zhongguan and the Fuyan Synclines have tensional environments, whereas the Shixi and the Daozhen Syncline have compressional settings; (2) the formation dip angle, distance to a class II fracture, average detachment layer thickness, intensity of superimposed modifications, and interlimb angle may be positively correlated with gas content; (3) the progressive transformation pattern is established. These findings lay the foundation for the future research on the differential preservation mechanism of eroded synclines and may be useful for enhancing research on worldwide strike-slip faults controlling hydrocarbon accumulation.

Impact of structural geometry of tilted fault blocks on hydrocarbon entrapment and deposition of syn-rift clastic reservoirs: Belayim Marine field (Gulf of Suez rift)

Belayim Marine oilfield is representative of the Gulf of Suez fields with hydrocarbon production from pre-rift and syn-rift reservoirs. Detailed subsurface mapping using a complete 3D seismic and borehole dataset throws light on the trapping mechanisms of tilted fault blocks in rift basins where the strike of the tilted block is parallel to the bounding fault. For such one-way tilted fault traps, linkage of rift-parallel and rift-oblique faults at the updip sides of the tilted blocks is necessary for trap integrity of laterally continuous reservoirs like the Nubia Sandstone. For laterally discontinuous reservoirs like tidal sand bars aligned normal or oblique to the block-bounding faults, a combination trap can be laterally closed by lateral change in facies of the reservoir unit along fault strike. Fault sealing of the proved hydrocarbon traps is mainly through juxtaposition. Shale smearing is valid for thick shale units with reasonable fault displacement and shale gouge is a proven sealing mechanism especially in clay-rich units. The ductile nature of syn-rift sediments leads to fault-propagation folding above the main-bounding faults of tilted fault blocks where folding is the trapping mechanism of these syn-rift reservoirs.The structural geometry of tilted fault blocks also controls the distribution of syn-rift reservoirs as the linkage of rift-parallel and rift-oblique faults controls the entry of main valleys transporting syn-rift clastics into the basin. Longitudinal depressions sculptured at the crests of tilted fault blocks represent another location for deposition of syn-rift reservoirs.

Research on Confidence Analysis Method of Lightning Strike Accidents on Distribution Lines

Currently, lightning is the main cause of power system faults. Due to insufficient equipment and technology, low insulation level, the distribution network being the main part of power outages, and the complex causes of distribution network faults, it is difficult to determine whether each fault in the distribution network is caused by lightning strikes. In this paper, the concept of lightning strike confidence, i.e., the possibility of a line lightning strike fault caused by falling lightning, is proposed, and a lightning strike confidence analysis is performed for a 10 kV distribution line in the mountainous region of South China to determine the possibility of a line lightning strike fault caused by falling lightning based on the lightning locating system data of the distribution line at the moment of the fault. First, the calculation method of the lightning strike confidence is derived; then the distribution law of the distribution line lightning strike confidence, the influence of the ground tilt direction, and ground tilt angle on the distribution line lightning strike confidence are analyzed; finally, the distribution line lightning strike confidence is analyzed by an example.

Methodology for quantitative prediction of low-order faults in rift basins: Dongtai Depression, Subei Basin, China

In eastern China, oil and gas reservoirs mainly have fault block traps. Low-order, small-scale faults are well developed, with small fault displacements and short extension lengths, but are difficult to identify by traditional seismic methods. Based on paleotectonic interpretations, rock mechanics experimental results and stratigraphic data, combined with seismic interpretation, structural evolution and fault activity analysis, a geomechanical model of the Majiazui area in the Dongtai Depression in the Subei Basin is established to construct a three-dimensional model of the paleostress field. Finally, the control of the principal stress, shear stress, and strain energy on the occurrence and development of low-order faults is quantitatively analyzed. This research shows that fault activity was weak during the Funing period (65-53 Ma), became strong during the Dainan period (53-46 Ma) and was strongest during the Sanduo period (46-37 Ma). The Sanduo period was the main period during which the low-order faults in the Majiazui area were formed. The minimum principal stress and strain energy controlled the development of low-order faults in the Majiazui area. The low-order faults are most developed in areas that experience high minimum principal stress and strain energy. In the Sanduo period, the minimum principal stress in the Majiazui area was tensile in the north–south direction, and the maximum principal stress was vertical. In an extensional stress environment, lateral shear stress controls the strike of faults, while vertical shear stress controls the inclination of faults. The faults in the northern Majiazui area are inclined mainly to the south, and the faults in the southern Majiazui area are inclined mainly to the north. These results are of practical importance for evaluating the oil–water relationship in oil-bearing fault blocks, solving the conflict between injection and production wells and improving oil recovery.