Fault Shape Research Articles

Relocation of earthquake clusters show seismogenic transverse structures in the Inner Northern Apennines (Italy)

The Inner Northern Apennines (Italy) are a region with a dominant N-S to NNW-SSE fault system, but dissected and offset by several E-W to NE-SW trending structures and lineaments. The knowledge about the nature of these transverse structures, their origin, activity and role in current tectonic motions is limited and debated. To better establish the location, subsurface shape, and kinematics of faults related to the Livorno-Empoli lineament, one of the major transverse structures in the Northern Apennines, we analysed the seismicity in western Tuscany. In the Viareggio Basin we identified and relocated two distinct earthquake clusters as well as calculated 12 new focal mechanisms. The results show that the clusters consisted of several swarms from the years 2006, 2015, 2016 and 2021. The events had a depth between 2 and 15 km and were located along a NE-SW oriented, SE dipping fault system dissecting the Viareggio Basin. Focal mechanisms show oblique normal slip. We interpret the fault system to form a connection between the Viareggio Basin and the Lucca Basin to the east as well as continuing offshore. The results show that the transversal faults of the Inner Northern Apennines are seismogenic, with the length, position and onshore to offshore nature of the fault suggesting reactivation of pre-existing structures.

Observation of broad triangular Frank-type stacking faults and characterization of stacking faults with emission wavelengths below 430 nm in 4H–SiC epitaxial layers

Frank-type stacking faults in 4H–SiC epitaxial layers were investigated using room-temperature photoluminescence mapping and high-angle annular dark-field high-resolution scanning transmission electron microscopy. Remarkably, the intrinsic Frank-type stacking fault (5,2) and intrinsic multilayer Frank-type stacking fault (4,2), which have been reported to have elongated triangular shapes to date, were found to have broader triangular shape, which was typical shape of Shockley-type stacking faults. The shaping of stacking faults could be explained based on the directions of the partial dislocations bounding the stacking faults. Formation models for the intrinsic (5,2) and (4,2) stacking faults were proposed. In addition, we observed Frank-type stacking faults (3,2,2,3) and (3,3) and Shockley-type stacking faults (3,3,3,2,3,2) and (3,2,3,3,3,2), which were not reported before. All of these stacking faults were composed with the stacking numbers 2 and 3 in the Zhdanov notation and showed very close characteristic photoluminescence emission wavelengths of 427–428 nm. Formation models for the stacking faults of (3,2,2,3), (3,3), (3,3,3,2,3,2), and (3,2,3,3,3,2) were proposed, also. Based on the proposed formation models of (4,2) and (3,3) stacking faults, formation models for the Frank-type stacking faults (4,1) and (3,2) were discussed. Finally, we pointed out that the (4,1) Frank-type stacking fault should be the intrinsic not the extrinsic fault, and the (3,2) Frank-type stacking fault is the extrinsic fault.

Assessment of fault damage zones in carbonate rocks based on numerical and sensitivity analyses

Fault damage zones are structural geological domains that can impact a reservoir's fluid flow and geomechanical behavior during the exploration and production phases in the oil and gas industry. Several methodologies have been proposed in the literature to characterize fault damage zones considering earthquake data, geophysical methods and outcrop observations. Based on those data, statistical relationships have been proposed to predict and constrain the width of fault damage zones in the subsurface. Unfortunately, those relationships show significant data dispersion and raise uncertainties regarding the extension of damage zones. A possible explanation for such distribution is the lack of knowledge of other parameters such as lithology and associated diagenesis, depth of faulting, tectonic environment, fault propagation, fault segment linkage and deformation mechanisms. Numerical modeling has emerged as a promising alternative for understanding geological problems. However, few studies have focused on characterizing fault damage zones at depth. This study presents a novel methodology based on the finite element method (FEM) combined with elastoplastic models and fault displacement data to forecast damage zone widths around geological faults on carbonate rocks. Despite the assumptions and simplifications related to the fault shape and displacement profile, this study shows that the proposed models provide a better understanding of the deformation mechanisms that trigger damage zones. Moreover, a sensitivity study considering the proposed methodology shows that in addition to the fault displacements and the carbonate rocks' geomechanical properties, the location of measured damage zone with respect to the fault can significantly impact the assessment of damage zone widths.

Architecture of intraplate strike-slip fault zones in the Yanchang Formation, Southern Ordos Basin, China: Characterization and implications for their control on hydrocarbon enrichment

Commercial discoveries in the Ordos, Tarim, and Sichuan Basins of China have aroused widespread interest in strike-slip fault-controlled reservoirs. The productivity of different wells, however, can vary within one strike-slip fault zone, suggesting that variability in fault zone architecture controls hydrocarbon enrichment. To date, very few studies have finely and quantitatively explored fault zone architecture in the southern Ordos Basin, inhibiting hydrocarbon development. With the goal of understanding the architecture variability and scale of strike-slip fault zones in the subsurface, we carried out a refined and quantitative study of faults in the Jinghe Oilfield in the southern Ordos Basin by integrating outcrops, wellbore cores, well logs, and 3D seismic data. We quantitatively constrained the subsurface damage zone boundaries according to the slope changes in the cumulative CFI (comprehensive fracture index log) curves at logging scale and the cumulative FSI (fault shape index seismic attribute) curves at seismic scale. We proposed a model highlighting the effects of fault segmentation, architectural configuration, and damage zone asymmetry on the variability of fault zone architecture. Results showed that strike-slip faults can be divided into transtensional, pure strike-slip, and transpressional segments along the fault strike, with transtensional and pure strike-slip segments dominant in the Jinghe Oilfield. These segments exhibited six types of geometric structures, forming complex architectures with multi-fault cores and multi-damage zones surrounding the main and secondary faults. Each segment was further complicated by three configurations of gouge, breccia, and damage zones along the fault dip. The damage zone asymmetry further increased the architecture variability, with the fracture density and damage zone width of the hanging wall being greater than those of the footwall. Quantitative analysis showed that the fault zone width was the greatest for transtensional segments, intermediate for transpressional segments, and the lowest for pure strike-slip segments. And there was a positive linear correlation between the fault core width and the fault zone width (including the fault core and damage zone). Fault segmentation and damage zone asymmetry affected the hydrocarbon enrichment along the fault strike and dip within one strike-slip fault zone. We conclude that damage zones in transtensional segments, particularly in hanging walls, are primary targets for hydrocarbon development in the southern Ordos Basin.

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.

Research on Fault Diagnosis of Steel Surface Based on Improved YOLOV5

Steel is an important raw material of fluid components. The technological level limitation leads to the surface faults of the steel, thus the key to improving fluid components quality is to diagnose the faults in steel production. The complex shape and small size of steel surface faults result in the low accuracy of the diagnosis, and the large size of the network leads to poor real-time performance. Therefore, aiming at the problems, an improved YOLOV5 is proposed. Firstly, to reduce the feature information loss, coordinate attention is used to improve YOLOV5, thus the diagnosis ability can be improved. Secondly, to further reduce the loss, a new connection is constructed in YOLOV5, and the detection ability can also be further improved. Thirdly, to improve the real-time performance of the fault diagnosis, YOLOV5 is improved by the lightweight method ShuffleNetV2, and its size can be reduced. Lastly, to further improve the accuracy, the cosine annealing with warm restarts algorithm is used to optimize YOLOV5. The dataset of NEU-DET is verified and testified. The results show that improved YOLOV5 can diagnose steel surface faults with high efficiency and accuracy.

Mapping Cretaceous faults using a convolutional neural network – A field example from the Danish North Sea

The mapping of faults provides essential information on many aspects of seismic exploration, characterisation of reservoirs for compartmentalisation and cap-rock integrity. However, manual interpretation of faults from seismic data is time-consuming and challenging due to limited resolution and seismic noise. In this study, we apply a convolutional neural network trained on synthetic seismic data with planar fault shapes to improve fault mapping in the Lower and Upper Cretaceous sections of the Valdemar Field in the Danish North Sea. Our objective is to evaluate the performance of the neural network model on post-stack seismic data from the Valdemar Field. Comparison with variance and ant-tracking attributes and a manual fault interpretation shows that the neural network predicts faults with more details that may improve the overall geological and tectonic understanding of the study area and add information on potential compartmentalisation that was previously overlooked. However, the neural network is sensitive to seismic noise, which can distort the fault predictions. Therefore, the proposed model should be treated as an additional fault interpretation tool. Nonetheless, the method represents a state-of-the-art fault mapping tool that can be useful for hydrocarbon exploration and CO2 storage site evaluations.

Oligocene magmatic accretion and transtensional tectonics in the Central Basin Fault rift of the West Philippine back-arc basin: New insights from high-resolution multichannel seismic data

High-resolution multichannel seismic transects that span from oceanic crust domains, and the Central Basin Fault rift to the Kyushu-Palau Ridge are utilized to investigate the dynamic mechanism of the Oligocene tectonic evolution in the West Philippine Basin based on an analysis of sismostratigraphic sequences and the geometries of acoustic substrates. In the oceanic domains, the physiography is characterized by ridges and troughs, and the pelagic stratigraphic succession with transparent facies covers the irregular top of the basement. Relatively homogeneous intracrustal reflections probably correspond to an area of abundant magma supply during the major spreading period. However, a widespread discrete, layered and high-amplitude intracrustal reflector is present in the Central Basin Fault rift that can be interpreted as an area of weaker and unstable magma supply after the major spreading period. The first group of reflectors shows typical low-angle fault shapes; the second and third groups of layered intracrustal reflectors are characterized by spatially limited high-amplitude seismic reflections. Inclined and mounded features of the intracrustal reflectors are interpreted as the result of tectonic processes, suggesting the presence of later magmatic accretion and transtensional tectonics within the acoustic substrate. Additionally, in the Kyushu-Palau Ridge, the anticline that appears within the stratigraphic infills of the basins serves as evidence of transtensional faulting. Overall, we propose that the Oligocene tectonic evolution of the West Philippine Basin occurred during a later transcurrent period due to Oligocene magmatic accretion followed by transtensional tectonics. The changes in the magmatic supply rate and tectonic processes of the Central Basin Fault rift may have originated from the compressive process within the Kyushu-Palau Ridge.

Fault shape effect on SH waves using finite element method

In this paper, we analyse how the combination of fault zone shape and material properties affects the propagation of seismic waves in a two-dimensional domain. We focus on SH wave propagation through several faults with different thicknesses and bending radii, but the theory is easily generalized to the three-dimensional case. We show how the density of energy released is mostly a function of the radius and does not depend on the velocity inside a fault zone.

Azimuthally Anisotropic Structure in the Crust and Uppermost Mantle in Central East China and Its Significance to Regional Deformation Around the Tan‐Lu Fault Zone

AbstractSeismic anisotropy can be linked to different mechanisms, structures, and sources. We constrained the 3‐D depth‐dependent shear wave speed isotropic and azimuthally anisotropic structures with Rayleigh wave phase velocity from ambient noise in central Eastern China. We compared the results with other models and found that in the upper crust, the maximum horizontal stress direction differs mainly from the anisotropy that coincides with the strikes of major faults and geologic structures. We inferred that the anisotropy within proximity of faults might be related to fault fabrics, including fractures that strike parallel to the fast axes. The Tan‐Lu Fault controls the anisotropy in the crust to the uppermost mantle. The direction of fast axes in the fault zone is NNE‐SSW to N‐S, coinciding with the fault strike and trend that matches the fault shape on the surface. Southeastern North China craton has a weak anisotropy in the crust and uppermost mantle. The sources are possibly connected to the thrusting, tight trending folds, and dipping thrusts observed to be sub‐parallel to the Dabie Orogenic Belt (DOB). We propose that the NNE‐SSW Zhangbaling uplift group comes from the extension and ductile shearing in the Tan‐Lu Fault zone and the dragging of the northeastern South China Craton in the crust and the uppermost mantle. The N‐S polarized fast axes in the lower crust and uppermost mantle across the Sulu orogen and Xuzhou thrust‐and‐fold belt are the products of the resultant effect of subduction and deep Tan‐Lu faulting.

Characterization of the accommodation zones along restraining and releasing bends from analogue modelling simulating the seagap fault, off-shore Tanzania

The study aims to understand geometry and evolution of accommodation zones along restraining and releasing bends in strike slip systems which is often complex and characterized by sharp change in polarity, resulting in a difficult characterization of traps location. A batch of sandbox modelling experiments was performed using a layered scaled sand material. The setup parameters of the wooden baseplates used in the first two experiments (SS1 and SS2) are basement offset of 6.5 cm/3 cm, 90°/90° stepovers in releasing and restraining bends of total 96 cm length and 25 cm width. The third experiment (SS3) was performed with basement offset of 6.5 cm/3 cm, 156°/126° stepovers in releasing and restraining bends of total 96 cm length and 25 cm width. The experiments were performed with special attention to the role of syn-kinematic sedimentation and the pre-existing structure of the basement. A sequence of pop-up and pull-apart structures was produced. Along the main structures, complex fault trend was compatible with a sinistral riedel distribution and a counterclockwise rotation of pre-existent elements. Change of fault's polarity at depth and dip direction flipping of high angle faults in accommodation zones were clearly observed. Even more, progressive propagation of the pop-up structures produces a spectacular inversion of adjacent extensional structures. Comparing results of the model with the Seagap fault zone, it is possible to put in evidence similar fault orientation and distribution. Internal structures developed were strongly influenced by syn-kinematic sedimentation as observed by characteristic helicoidal shape of growth faults. The analogue models clearly describe how boundary faults of the pull-apart basin along a paired bend, initially characterized by a normal kinematic can be subsequently inverted in the later stages, which can potentially have a strong impact on the petroleum system.

First comparison of the electrical properties of two grid emulators for UVRT test against field measurement

The technical rules for connecting turbines to the medium, high or extra-high voltage grid in Germany require the certification of the UVRT characteristics of wind turbines. The state-of-art voltage divider-based test equipment, also named UVRT-Container, is well equipped for executing UVRT tests in field. To conduct the UVRT in field the full wind turbine should be already installed. A second option to perform UVRT tests are system level test benches. They enable the testing of the nacelle. The components that are not actually present, such as the turbine tower or the blades, are emulated via a mechanical hardware in the loop (HiL) system. In this work, for the first time, the performance of two different grid simulators installed at the DyNaLab at Fraunhofer IWES and at the CWD at RWTH Aachen University is compared with a field measurement of the same type of wind turbine. Thus, not only a system test bench measurement is compared to a field measurement. Rather, two system test benches with individual technical approaches are additionally compared with each other. The focus of this work is to investigate the characteristics of the grid simulators within the steady-state range of the UVRT tests to replicate identical fault shapes on the test benches and in the field.

Nature and Shape of Stacking Faults in 3C‐SiC by Molecular Dynamics Simulations

Classical molecular dynamics simulations are used to investigate the 3D evolution of stacking faults (SFs), including the partial dislocation (PD) loops enclosing them, during growth of 3C‐SiC layers on Si(001). It is shown that the evolution of single PD loops releasing tensile strain during the initial carbonization stage, commonly preceding 3C‐SiC deposition, leads to the formation of experimentally observed V‐ or Δ‐shaped SFs, the key role being played by the differences in the mobilities between Si‐ and C‐terminated PD segments. Nucleation in the adjacent planes of PD loops takes place at later stage of 3C‐SiC deposition, when slightly compressive‐strain conditions are present. It is shown that such a process very efficiently decreases the elastic energy of the 3C‐SiC crystal. The maximum energy decrease is obtained via the formation of triple SFs with common boundaries made up by PD loops yielding a zero total Burgers vector. Obtained results explain the experimentally observed relative abundance of compact microtwin regions in 3C‐SiC layers as compared with the other SF‐related defects.

Recurrent neural networks models for analyzing single and multiple transient faults in combinational circuits

Transient faults analysis is an important step in circuits designing flow. By a fast and accurate scrutiny, it is possible to achieve a cost-effective and soft error tolerant system. In this paper, an efficient and accurate approach is presented to estimate the shapes of transient faults when they are propagating through the gate-level circuits. To provide a reliable prediction of how the shape of a transient fault occurring in a circuit will be, a new method based on recurrent neural networks (RNNs) is proposed. This method can make a confident estimation of the effects that the single/multiple transient faults leave while propagating through a combinational circuit. Results for a sample of 32-bit carry propagation adder shows 22x speed-up with a mean of 0.82 penalty in accuracy loss, compared to the HSPICE simulator.

Forward kinematic modeling of fault-bend folding

We present a forward numerical modeling approach for fault-bend folding based on a velocity description of deformation. The approach incorporates algorithms capable of modeling multiple fault bends of different geometries (e. g. fault bends not stepping up from a detachment), imbricates, and variable velocity-boundary orientations, with corresponding varying slip ratios. When modeling contraction, the approach is capable of reproducing rounded-hinges and parallel folds with localized bed thinning or thickening commonly observed in natural structures. Extensional fault-bend folds can be modeled using the same set of equations, with the minor modification that velocity boundary orientations are defined independently of the fault shape. The modeled structures conserve area, and commonly observed features of extensional fault-bend folds, such as rollover structures with growth, are produced. Thus, we present a unified inclined-shear and flexural-slip general transformation associated with displacement over bends in faults, describing the theoretical framework which we have implemented in the associated program, fbfFor. We show the utility of this kinematic approach by matching seismic reflection examples, analog models, and mechanical models of fault-bend folds to create progressive, balanced kinematic interpretations and gain further insight into the formation of these structures.

Modelling asymmetric deformation along a curved strike-slip basement-fault system

Large-scale curved strike-slip fault systems along which significant amounts of displacement have taken place are common in nature. Scaled analogue experiments were used in this study to investigate strike-slip deformation in cover units above a curved basement-fault system simulated by a rigid plate with an in-built curvature depicting a half-circular fault. The model results show that en-echelon, right-stepping Riedel shears and low-angle synthetic shears (Y-shears) always form at the beginning of deformation, and grow outwards with splay faults, most of which evolve into thrusts at later stages of deformation. Digital image correlation (DIC) analyses of the surface displacement vectors show that a diffuse zone of deformation progressively changes into en-echelon shears, which gradually develop into throughgoing shear zones with further deformation. The geometries of Riedel shears along two sides of the basement fault (i.e. concave and convex sides) show significant differences in fault shape and intersection angles between the faults and the curved basement fault, indicating an asymmetry in deformation with a much wider deformation zone occurring on the concave side. As a result, en-echelon and/or overlapping flower structures develop along the curved basement strike-slip fault system. In particular, Riedel shears with a upward-convex geometry are localised in both sides of the curved basement fault and a continuous reverse oblique-slip fault forms at the concave side. When compared with the geometry of curved strike-slip faults in nature (e.g. the Daliangshan shear zone in Xichang basin and the Red River shear zone in the Yinggehai basin, China) the model results depict the asymmetric evolution pattern of the faults on either side of curved basement faults.

Seismic Analysis of the 2020 Magna, Utah, Earthquake Sequence: Evidence for a Listric Wasatch Fault

AbstractThe 18 March 2020 Mw 5.7 Magna earthquake near Salt Lake City, Utah, offers a rare glimpse into the subsurface geometry of the Wasatch fault system—one of the world's longest active normal faults and a major source of seismic hazard in northern Utah. We analyze the Magna earthquake sequence and resolve oblique‐normal slip on a shallow (30–35°) west‐dipping fault at ~9‐ to 12‐km depth. Combined with near‐surface geological observations of steep dip (~70°), our results support a curved, or listric, fault shape. High‐precision aftershock locations show the activation of multiple, low‐angle (<30–35°) structures, indicating the existence of a complicated fault system. Our observations constrain the deep structure of the Wasatch fault system and suggest that ground shaking in the Salt Lake City region in future Wasatch fault earthquakes may be higher than previously estimated.

Analysis on the Shapes of the Shockley type Stacking Faults Generated by the REDG Effect in the 4H-SiC Power Devices

Analysis on the Shapes of the Shockley type Stacking Faults Generated by the REDG Effect in the 4H-SiC Power Devices

Towards reconciling seismic and geodetic moment estimations: Case Bárðarbunga

Previous studies have found discrepancies concerning the seismic radiation between planar and curved faults: moment tensor (MT) interpretations, seismic moment estimation and waveforms change dramatically when the rupture is not planar. Therefore, assuming a point source on a planar fault for earthquakes in volcanic environments can be an oversimplification that needs to be addressed if we observe some seismological clues. We study MT inversions for the biggest earthquakes during the 2014–2015 collapse of the Bárðarbunga caldera, which show non-double couple solutions, with vertical compression axis. We calculate synthetic seismograms for partial-ring ruptures using an ideal seismic network, and one emulating the existing monitoring network at Bárðarbunga. Observations using distal stations can return a better-constrained seismic moment, but they fail to characterise the dynamics involved. On the other hand, using proximal stations we obtain a reliable representation of the forces involved. However, the seismic moment is systematically overestimated due to the proximity to the curved source and the corresponding focusing effects. Finally, we correct the area of rupture due to fault shape to estimate the real cumulative seismic moment during the caldera collapse. The result shows a closer relationship between seismic and geodetic moment. In particular, both estimations match when we use a realistic rigidity for a volcanic environment.

CNN Based Fault Recognition with Multi-Scale Fusion Attention Mechanism

In geological exploration, seismic data interpretation is very important and its key task is fault detection or recognition. In fact, the accurate recognition of fault shape and distribution plays an important role in oil and gas exploration. With the increasing demand of fault interpretation accuracy in oilfield, traditional manual fault interpretation methods are susceptible to subjective factors of interpreters. With the rapid development of deep learning technique, convolutional neural networks (CNNs) has successfully applied to the complicated tasks of image classification. This paper utilizes proposes a CNN based fault recognition framework with a multi-scale fusion attention mechanism. It is demonstrated by the experimental results that our proposed approach is superior to the traditional methods on both the fault interpretation accuracy and efficiency of 3D seismic images, greatly reducing the risk of oil and gas exploration and development. With a GeForce GTX 1080 GPU, the training processing takes about 4 hours and predicts the faults in a 33×33×33 seismic volume using only tens of milliseconds.