Fault Block Research Articles

Combined geophysical investigations of the characteristics of a regional fault zone for groundwater development in a basement complex terrain of South-west Nigeria

This paper presents the results of an integrated electrical resistivity and magnetic survey of a strike slip fault in a basement complex terrain with poor well/borehole yield. It aims to characterize the fault zone and determine its geometry, width and depth extent and attitude that will enable an assessment of its prospectivity for groundwater development. The magnetic profiles imaged a fault block characterized by a low (negative) total field magnetic anomaly with a width extent ranging from 112 to 150 m, a depth extent in excess of 150 m and a near vertical disposition. The resistivity structures delineate low resistivity near vertical discontinuities within the high resistivity fresh basement host rock that correlate across the five traverses investigated. The north-western edge of the magnetic fault block and the resistivity anomalous zone correlates with the geo-referenced strike slip fault. The width of the low resistivity zone ranges from 75 to 125 m with depth extent in excess of 150 m. Four subsurface geologic/geoelectric layers were delineated. These include a relatively thin topsoil underlain by a clay/sandy clay weathered basement; a partly weathered/fractured basement column and a basal fresh basement with depth to rock head of 1.6–15.0 m. A zone with thick column (up to 117 m) of partly weathered/fractured basement correlates across the traverses and significantly with the anomalous magnetic and resistivity zones. The study concludes that the thicker region of partly weathered/fractured basement column within the fault zone which is likely to have enhanced permeability and storage capacities has potential for sustainable groundwater development. It also demonstrates the effectiveness of integrated 1D and 2D electrical resistivity imaging and magnetic profiling in structure (fault) identification, characterization, subsurface sequence delineation and groundwater potential assessment in a typical basement complex environment.

Module block fault locating strategy for large-scale photovoltaic arrays

In practical grid-connected photovoltaic systems, faulty modules for small-scale photovoltaic arrays need to be accurately located, while the same strategy to locate each faulty module for large-scale arrays would imply high investment cost due to a large number of sensors needed. Therefore, to reduce the number of sensors and save fault monitoring investment, it suffices to identify where fault happens in a module block, which consists of several modules connected in series. For this purpose, this paper proposes a fault-locating strategy to identify faulty module blocks for large-scale arrays, where voltage sensors are deployed by differentiating the parity of string numbers in the array to acquire the terminal voltages of the module blocks between adjacent strings, and the fault locating rules for open circuit, short circuit, degradation and partial shading faults are formulated. With the help of MATLAB/Simulink platform, the proposed strategy is tested in one small-size array and two large-scale arrays, and the testing results demonstrate that the proposed strategy can locate the single fault case, multiple faults of single-type, as well as mixed faults of different sub-arrays. To summarize, the proposed fault-locating method has higher locating accuracy, lower implementation cost and wiring complexity, and is easily integrable with existing photovoltaic systems.

Tectonics and foreland basin development at the leading edge of the Humber Arm Allochthon, western Newfoundland, Canadian Appalachians

The thrust front of the Northern Appalachians involves Ediacaran rift-related structures of the Laurentian margin that were re-worked in Taconic (Ordovician), Salinic (mainly Silurian) and Acadian (mainly Devonian) deformation events. Much of the thrust front is concealed under the Gulf of St. Lawrence, but Port au Port Peninsula, in western Newfoundland provides a cross-section through the Laurentian passive margin, overlying foreland basins, and the Humber Arm Allochthon. A large area of foreland basin strata is present in areas formerly mapped as Humber Arm Allochthon. Abrupt thickness changes and an abundance of fault-scarp-derived limestone conglomerate indicate that deposition was influenced by block faulting and differential subsidence in a basin undergoing active flexural extension. A coarsening upward trend in the Goose Tickle Group represents a transition from a distal to a proximal sediment source as the Humber Arm Allochthon was emplaced westwards. Goose Tickle Group separates two packages of allochthonous rocks. The West Bay Thrust Sheet, the lower package, represents the leading edge of the Taconic allochthon. Its timing of emplacement is constrained by Darriwilian 3 graptolites both above and below the thrust sheet. Its present-day configuration results from a combination of processes including thrusting, extension by gravity spreading, gravity gliding, and subsequent erosion of material that was deposited in the Goose Tickle Group. The structurally higher Lourdes Thrust Sheet is an out-of-sequence structure associated with Acadian (Devonian) orogenesis. High-angle faults show a protracted history of movement that includes early Taconic flexural extension, Acadian inversion, and later Carboniferous or Mesozoic strike-slip motion. The leading edge of the Humber Arm Allochthon was influenced by both thin-skinned and thick-skinned tectonics throughout the development of the Appalachian orogen.

The hydrocarbon accumulation potential of Upper Cretaceous to Paleogene in the northern Kaikang trough, Muglad Basin

This paper investigates the characteristics of sedimentary faces, source rocks, and hydrocarbon accumulation in detail within the Paleogene and Upper Cretaceous in the northern Kaikang trough, Muglad Basin. Analysis shows that the fluvial floodplain, delta, and shore-shallow lake facies are well developed in the main formations and several reservoir-cap assemblages are formed. Research on geochemical indicators, hydrocarbon generation, and expulsion potential of source rocks indicated that the thickness of good source rocks in Paleogene ranges from 50 to 200 m and TOC value can reach 0.5–1.3%, but it is immature and has no hydrocarbon generation potential. Nevertheless, the Upper Cretaceous source rocks are mostly matured, but its hydrocarbon generation is limited because of lower TOC (only 0.5–0.8%) and thinner thickness (only 10 m). The main effective source rock is the AG Group in the Lower Cretaceous, which is distributed throughout the area. The evolutionary history shows that most of structures in the central troughs lack hydrocarbon potential, because they were formed since the Paleogene, which are later than the main accumulation period of the AG source rock. The fault terrace zones on both sides of the Kaikang trough have obtained petroleum discovery, but the distribution of oil layers is much complicated. Hydrocarbon accumulation is controlled by formation dips, fault activity intensity, and fault lateral docking characteristics. The weaker active fault block in late period and more effective trap are the key factors to hydrocarbon enrichment at the fault terrace zones. There are two typical reservoir-forming modes; one is the small fault distance reservoir-forming mode of the lower primary reservoir, and the other is the secondary reservoir-forming mode of the upper and middle combination.

Development and growth of basement-involved structural wedges in the northwestern Qaidam Basin, China

Structural wedges contain two connected fault segments, a fore thrust and back thrust, that bound a triangular- or wedge-shaped fault block. Coeval displacements on both faults drive the wedge into surrounding rock, causing distinctive patterns of uplift and folding. We identified a series of thick-skinned structural wedges in northwestern Qaidam Basin, China, where syntectonic strata record deformation timing and kinematics. The Qaidam Basin is located at the northern margin of the Tibetan Plateau and contains more than 100 large anticlinal structures, many of which exhibit characteristics of structural wedges. We interpreted and modeled these structures using seismic reflection data, well logs, surface geological exposures, remote sensing images, and digital elevation data. These wedge structures are distinguished by having elevated and deformed strata in the footwalls of the back thrusts and synclinal folds that extend upward from the wedge tips. With the constraints of fold shape, growth strata, structural relief, and shallow fault geometry, we developed a series of forward models that describe the geometry and kinematic evolution of these wedge structures. The analysis suggests that some of the wedge structures reactivate preexisting normal faults. Our results provide a better understanding of how to identify thick-skinned wedge systems and model their geometry and kinematic evolution, which has implications for studying the tectonic history of the basin. Understanding the geometry and kinematics of the wedge structures is also crucial for petroleum exploration because both hanging-wall and footwall traps constitute an important component of current exploration targets.

Development of Sliding Regimes in Faults and Slow Strain Waves

The paper investigates a model simulating crustal fault dynamics and strain wave generation in a fault block geological medium, the parameters determining sliding regimes in faults, and the physics of transitions between different deformation regimes. The model comprises the most important mechanisms responsible for the interaction of fault walls: friction, geometric irregularities (roughness and asperities on the fault surface), and external load, which govern sliding along the fault. The results of field and laboratory studies of deformation migration on the macro/mesoscale are consistent with the concept of localized deformation propagation in the form of solitary waves (kinks, solitons) and autowaves. The conditions are defined which make possible the transition from the model simulating solitary waves in a conservative medium with low “friction” (soliton-like behavior of the system) toward the model of solitary waves in an active medium with diffusion (autowave-like behavior of the system). Two possible deformation regimes of the fault block structure in the high-friction limit are considered. The fault wall displacement is stopped due to this friction, but the adjacent blocks move relative to each other in the core of the fault. It is shown that in the high-friction limit a perturbed sine-Gordon equation applied for fault dynamics modeling is reduced to a reaction-diffusion equation, whereas the system goes from the soliton regime to the autowave regime. In the case of high friction and a lack of energy supply to the fault from an external source, the transfer of localized deformation is changed by a diffusive dissipation of stress.

Synchronous Distributed Generation Islanding Protection using Paraconsistent Relay

This article presents the intelligent multifunctional protection (IR) relay for systems based on synchronous generators using a paraconsistent neural network. This network woks with degrees of favorable, unfavorable evidence, sensitivity and time. The IR includes islanding, fault detection, fault type recognition and selective fault blocking. The proposed multi-function APL4v IR was tested in a hardware-in-the-loop (HIL) environment. The results show that the proposed IR is superior to the traditional islanding recognition methods regarding reliability, safety and detection time.

Focal validation mechanism for Lombok earthquake with image analysis of satellite radar and crust movement GPS observation

Lombok Earthquake on August 5 and August 19, 2018, traces of deformation were analyzed with satellite image data to determine vertical deformation in the form of uplift on the ground surface. Earthquake wave analysis provides data on the mechanism at the epicenter in the form of a fault, the major forces axis in the form of the P axis, as well as the T axis, in addition to location and strength. The results of the focal analysis showed that the Lombok earthquake was an earthquake on the rising fault, the results of satellite radar image analysis showed the corresponding results, where the maximum increase occurred on the lip of the fault block in the form of a hanging wall. The direction of the acting force is indicated by the Axis P, in accordance with the research results of the Lombok earth crust movement, namely the N-NE Direction.

Morphology and topology of dolostone lithons in the regional Carboneras Fault Zone, Southern Spain

Dolostones in a Neogene strike-slip fault zone are described. Two main types of structural features are recognised: (i) Background deformation in the form of a network of bedding-perpendicular and hybrid conjugate fractures, barren fractures and bedding-parallel stylolites. (ii) Fault-related features include breccias and cataclasites. Orthorhombic rock lithons are generated from the intersection of fracture sets with bedding and/or joints. Lithon size and morphology change across the dolostone fault block gradually producing a tetragonal or isometric shape. The lithons are 1–2 cm in dimension (only ~ 20% outside this range) and have an average cross-sectional aspect ratio of 1.6, irrespective of size or structural position. Topology is analysed using nodes and branches, ranging from isolated (I- node and I-I branch) to connected (Y- and X-nodes, and I-C to C-C branches) respectively. The quantitative description of the geometrical and topological analysis of the dolostone lithons suggest that they become more connected and interact within the dolostone fault blocks. Assessing the change in topology and lithons connectivity have important implications for subsurface reservoirs and aquifers hosted in dolostone-fault zones.

Sedimentary infill of shallow water deltaic sand bodies controlled by small-scale syndepositional faults related paleogeomorphology: Insights from the paleogene Shahejie formation in the Dongying depression, Bohai Bay Basin, Eastern China

Formed in extensional structural system, syndepositional faults are widely distributed in rift basins. Large basinal scale syndepositional faults play important roles in controlling the development and dispersion of depositional systems in rift basins. When it comes to the intensively developed small-scale syndepositional faults related to those large basinal scale syndepositional faults in complex fault blocks, the controlling effects to sedimentary architecture in the finer scale are still not well understood in the depositional systems. Thus, commonly used sedimentary models without considering small-scale syndepositional faults related paleogeomorphology are difficult to apply in complex fault blocks of rift basins. In this study, using the interpretation of 3D seismic profiles, wire-line log curves, and cores, patterns of small-scale syndepositional faults and their related finer scale stratigraphic sequences are described in the upper Es2 member, Shahejie Formation of the W43 complex fault block area, Dongying Depression, Bohai Bay Basin. The syndepositional faults are intensively distributed in the W43 complex fault block area. Based on the interpretation of sequence boundaries, four types of syndepositional faults related paleogeomorphology units were identified. They are named the micro slope break belt, micro-horst belt, and the micro-graben belt. The stacking patterns and development scale of individual deltaic sand bodies in the parasequences are controlled by activity of the syndepositional faults. In the hanging wall area near the syndepositional fault of the micro-step and micro-graben, thickened multi-stage continuously individual sand bodies are deposited controlled by low topography during the depositional period with sufficient sediment supply. In the footwall area of single micro syndepositional fault and micro-horst belt, individual sand bodies became thinner and less aggraded in vertical direction. The small-scale syndepositional fault-related paleogeomorphology is a new important factor that controls the sedimentary architecture of the shallow water deltaic sand bodies in the rift basin. This study provides insights into tectonic control of finer-scale sedimentary architecture and hydrocarbon reservoirs development in continental rift basins.

A Hybrid Three-Level and Modular Multilevel Converter With DC Fault Blocking Capability and Reduced Semiconductor Losses

This article proposes a hybrid three-level converter (H3LC) with AC-side cascaded full-bridge submodules (FBSM) for high voltage direct current (HVDC) transmission. The three-level converter operates at fundamental frequency switching to modulate square-wave output voltages. The AC outputs of the three-level converter are connected to cascaded FBSMs, which shape the square-wave voltages into multilevel sinusoidal voltages at the point of common coupling. Using third-order harmonic voltage injection, the AC-side chainlink voltage can be limited to within a quarter of the DC-side voltage which reduces the number of FBSMs and the associated semiconductor losses. The H3LC is capable of blocking DC pole-to-pole fault using the AC-side FBSMs and the proposed protection branches, each of which consists of a low-loss load-current carrying branch and a main breaker. Simulation studies demonstrate the effectiveness of the proposed converter for independent real and reactive power control as well as DC pole-to-pole fault blocking. Compared to other state-of-the-art HVDC converter topologies with DC fault blocking capability, i.e., the mixed half- and full-bridge modular multilevel converter and the hybrid two-level converter with AC-side cascaded FBSMs, the proposed H3LC provides reduced semiconductor losses due to fundamental frequency switching of the three-level converter and the reduced number of submodules.

Novel flexible HVDC transmission converter station topology with DC fault blocking capability

The conventional half-bridge submodule (HBSM)-based multilevel modular converter (MMC) cannot block DC faults. To solve this problem, a novel flexible overhead-line high-voltage direct current (HVDC) transmission converter station topology is proposed in this study, which provides DC fault blocking capability. By adding blocking submodules (SMs) onto the positive and negative DC buses of a conventional HBSM converter station, a rapid fault current blocking can be achieved in the case of a DC bus short circuit. The DC fault blocking principle of the proposed topology and the rapid fault blocking capability of the blocking SM are analyzed. The quantity of required major components is also calculated. In addition, the IGBT, the system loss and the control complexity quantities are comprehensively compared with those of existing topologies. The validity of the proposed topology is demonstrated based on simulation and experimental studies.

Development characteristics and mechanisms of damage-causing urban ground fissures in Datong City, China

A set of widely developed ground fissures within the Datong Basin, northern China, have inflicted serious damage to farm fields, roads, houses, and building foundations in Datong City. Such emergence of large-scale ground fissures is rare in urban areas. The formation mechanisms of these features were therefore investigated in detail through surveying, mapping, trenching, drilling, and geophysical prospecting. The 11 fissures in Datong City are located on the hanging wall of the Kouquan fault (part of regional horst and graben terrain), and run approximately parallel, with a dominant strike of NE34°–70° and a maximum length of 5.5 km. These structures occur in clear zones with similar directions and lateral distributions on the surface. They possess evident synsedimentary fault characteristics, including y-shaped, trapezoidal, and traction structures in their profiles. The synergistic action of different tectonic factors and groundwater exploitation is responsible for fissure formation. Under the influences of regional tensile stress, upper mantle uplift, and fault block movement, activity along local faults created hidden fracture systems within the hanging wall. The over-exploitation of groundwater in the region subsequently accelerated fracture growth, and varying vertical compressibility of the strata on both sides of the local fault resulted in uneven subsidence on the surface, generating tensile zones and promoting the appearance of fissures at the edges of settlement funnels.

Optimization of W5 fault block surface-active polymer flooding scheme

According to the current situation of the W5 fault block, it is necessary to carry out the surface-active polymer flooding. By physical simulation, the optimal concentration is 1000 mg/L, the optimal slug size is 0.3PV, and the earlier the injection opportunity, the slower the injection rate, the higher the recovery rate. By numerical simulation, the recovery rate of the optimal scheme is 27.2%. Compared with the water flooding, the cumulative oil increase is 3.33 × 104 t, the enhanced oil recovery is 5.74%, the oil-enhancing amount of one ton surface-active polymers is 307.73 t/t, and the ratio of output to input is 16.30.

Timing of Cenozoic Extension in the Southern Stillwater Range and Dixie Valley, Nevada

AbstractThe Dixie Valley fault bounds the east side of the Stillwater Range in west‐central Nevada and last ruptured in 1954. Offset basalts indicate that slip began more recently than ~14 Ma, and prior work has interpreted the southern segment as an active low‐angle normal fault. Oligocene igneous rocks in the southern Stillwater Range were steeply tilted during large‐magnitude extension prior to ~14 Ma. To refine the timing of early extension and the onset of slip on the Dixie Valley fault, we collected two transects of samples for apatite fission track, apatite and zircon (U‐Th)/He (AHe and ZHe), and apatite 4He/3He thermochronometry. Apatite fission track ages from the Oligocene IXL pluton indicate rapid cooling ~18–14 Ma, and AHe and ZHe ages from the Cretaceous La Plata Canyon pluton indicate rapid cooling ~16–19 Ma. We interpret these data to record cooling during rapid extension. AHe ages from the IXL pluton are ~6–8 Ma and record cooling during slip on the Dixie Valley fault. We modeled these ages and 4He/3He spectra from one sample as the result of cooling during exhumation of a tilted fault block at a constant extension rate. The model predicts slip on the Dixie Valley fault beginning ~8 Ma. Although it does not constrain the initial fault dip, the model illustrates how a low‐angle fault requires a higher extension rate to reproduce cooling ages. Consequently, we prefer a high‐angle southern Dixie Valley fault for strain compatibility with the high‐angle northern segment.

Microseismic Noise before and after Strong Earthquakes: Case Study of Chilean Subduction Zone

Abstract—In this work, we study the parameters of microseismic noise in the vicinity of the Chilean subduction zone in order to detect oscillations of a block–fault system, similar to those identified by processing the results of the previous laboratory experiment. The analysis is based on the data recorded by the broadband seismic stations of the international seismic network IRIS. We calculated the spectral parameters of microseismic noise before and after several earthquakes. It is established that before the earthquakes with Мw ≥ 8, the calculated value of spectral centroid decreases by 0.12–0.26 Hz. The decrease in the value of spectral centroid in the range from 0.008 to 0.45 Hz can be as long as up to two days. The proposed approach can be a new instrument useful for real-time monitoring of active faults of various scales.

Coordinated control of HVDC sending system with large-scale DFIG-based wind farm under mono-polar blocking fault

When the mono-polar blocking fault occurs at the line-commutated converter (LCC)-based high voltage direct current (HVDC) transmission system, due to the long switch time of the installed mechanical switching type VAR compensations, the reactive power of the sending alternating current (AC) system will be surplus. Consequently, the voltage of sending AC system will be sharply increased during the switch process of VAR compensations, which may trip off the connected doubly fed induction generator (DFIG)-based wind farm. For ensuring the sending system can operate in stability and security, the power flow and the overvoltage mechanism of sending AC system under mono polar blocking have been investigated firstly. Furthermore, the power controllable operation area of the DFIG system as well as the transient response of the synchronous compensator (SC) and static synchronous compensator (STATCOM) have been researched. Then, a fault ride through control strategy by coordinating the VAR compensations, DFIG-based wind farm, HVDC system converter and SC is designed. The simulation results show that the proposed scheme can significantly restrain the sending AC system’s overvoltage during the switch process of the installed VAR compensators under mono-polar blocking fault, thus, the transient stability of the HVDC sending system can be effectively enhanced.

A new contribution to the geology of the Egyptian Red Sea shelf using geophysical data

ABSTRACTThe study examines the Egyptian Red Sea shelf and throws more light on the structural set‐up and tectonics controlling the general framework of the area and nature of the crust. Herein, an integrated study using gravity and magnetic data with the available seismic reflection lines and wells information was carried out along the offshore area. The Bouguer and reduced‐to‐pole aeromagnetic maps were processed and reinterpreted in terms of rifting and plate tectonics. The qualitative interpretation shows that the offshore area is characterized by positive gravity everywhere that extremely increases towards the centre of the graben, supporting the presence of an intrusive zone below the axial/main trough. The gravity data were confirmed by the presence of high magnetic amplitudes, magnetic linearity and several dipoles concentrated along the rift axis for at least 250 km. The lineament analysis indicates widespread of the Erythrean (Red Sea) trend that was offset/cut by transform faults in the NE direction (Aqaba). The tectonic model suggests the presence of one tensional (N65°E) and two compressional (N15°W, N30°W) phases of tectonism, resulted in six cycles of deformations, classified into three left lateral (N35°E, N15°E and N–S) and three right lateral (N85°W, N45°W and N60°W). The basement relief map reveals a rough basement surface that varies in depth between 1 and 5.6 km. It outlines several offshore basins, separated from each other by ridges. The models show that the basement consists of tilted fault blocks, which vary greatly in depth and composition and slopes generally to the west. They indicate that the coastal plain is underlain by acidic basement blocks (continental crust) with no igneous activity while suggesting elevated basic materials (oceanic crust) below the rift axis. The study suggests that northern Red Sea forms an early stage of seafloor spreading or at least moved past the late stage of continental rifting.

Operation and control of hybrid HVDC system with LCC and full‐bridge MMC connected in parallel

In this study, a new kind of hybrid high-voltage direct current (HVDC) system is proposed. Each terminal of the proposed system consists of one line commutated converter (LCC) and one full-bridge modular multilevel converter (FB-MMC). The LCC and FB-MMC are connected in parallel so that they can share the same transmission line. The active-reactive power capability of the hybrid HVDC system is extended compared with the conventional LCC-HVDC system, and power reversal control without power interruption can be achieved by the coordination control of LCC and FB-MMC. Besides, the proposed hybrid HVDC system is capable of handling DC fault, because both LCC and FB-MMC have DC fault blocking capability. Moreover, the power rating of FB-MMC can be designed to low value while keeping the bulk-power transmission capability of LCC. A two-terminal bipolar hybrid HVDC system is built in PSCAD/EMTDC. The simulation results verify the effectiveness and feasibility of the proposed hybrid topology and corresponding control strategies.

An Improved Modular Multilevel Converter With DC Fault Blocking Capability Based on Half-Bridge Submodules and H-Bridge Circuit

Pole-to-pole dc short circuit fault blocking capability is a major concern when modular multilevel converters (MMCs) are applied in high voltage direct current (HVDC) transmission systems. Traditional MMCs based on half-bridge submodules (HBSMs) cannot block the fault current, thus needing expensive direct current circuit breakers (DCCBs). There are MMCs based on improved submodule topologies that can block dc faults, but usually with significantly increased device cost. This paper proposes an improved HBSM-based MMC (HB-MMC) which needs fewer extra semiconductor devices. The improved HB-MMC is more competitive than other schemes when it comes to investment cost and loss. An H-bridge circuit composed of two director switches and two diode valves is installed around one arm of the HB-MMC, which will not change the direction of current during the normal operation, whereas it can change the direction of the fault current when a pole-to-pole dc short circuits fault is detected. After two director switches have been turned off, a reverse-biased voltage provided by one arm can block the fault current. The topology can be further improved to provide reactive power during faults. Simulation results are presented to validate the features of the proposed improved HB-MMC.