Hinge Zone Research Articles

Parametric Modeling Method for 3D Symbols of Fold Structures

Most fabrication methods for three-dimensional (3D) geological symbols are limited to two types: directly increasing the dimensionality of a 2D geological symbol or performing appropriate modeling for an actual 3D geological situation. The former can express limited vertical information and only applies to the three-dimensional symbol-making of point mineral symbols, while the latter weakens the difference between 3D symbols and 3D geological models and has several disadvantages, such as high dependence on measured data, redundant 3D symbol information, and low efficiency when displayed in a 3D scene. Generating a 3D geological symbol is represented by the process of constructing a 3D geological model. This study proposes a parametric modeling method for 3D fold symbols according to the complexity and diversity of the fold structures. The method involves: (1) obtaining the location of each cross-section in the symbol model, based on the location parameters; (2) constructing the middle cross-section, based on morphological parameters and the Bezier curve; (3) performing affine transformation according to the morphology of the hinge zone and the middle section to generate the sections at both ends of the fold; (4) generating transition sections of the 3D symbol model, based on morphing interpolation; and (5) connecting the point sets of each transition section and stitching them to obtain a 3D fold-symbol model. Case studies for different typical fold structures show that this method can eliminate excessive dependence on geological survey data in the modeling process and realize efficient, intuitive, and abstract 3D symbol modeling of fold structures based on only a few parameters. This method also applies to the 3D geological symbol modeling of faults, joints, intrusions, and other geological structures and 3D geological modeling of typical geological structures with a relatively simple spatial morphology.

Structural deformation of shale pores in the fold-thrust belt: The Wufeng-Longmaxi shale in the Anchang Syncline of Central Yangtze Block

The gas-rich Wufeng-Longmaxi shale has been intensely deformed within the fold-thrust belt of the Yangtze Block. To better understand the impact of structural deformation on the shale pore system, this paper systematically investigated the matrix components, porosity and pore structures in core samples from theWufeng-Longmaxi shale, newly collected from various structural domains in the first commercial shale gas field of the Central Yangtze Block, the Anchang Syncline. The shale porosity generally showed a positive relationship with total organic carbon content. Nevertheless, even at a constant total organic carbon content, the shale porosity decreased from the syncline limb to the syncline hinge zone and with a decreasing interlimb angle in the syncline hinge zone, which aligned with the structural deformation strain during folding. The artificial axial compression of shale samples also confirmed that the decrease in shale porosity was stronger at an elevated axial compression stress and was relatively higher in samples with higher total organic carbon content. The organic pore size decreased with higher structural deformation strain, but the aspect ratio of the pore shape increased. Even quartz failed to resist the effective stress under the intensive structural deformation, changing the correlation between porosity and quartz from positive to negative. In contrast, pore spaces generated by the slipping between clay flakes under intensive deformation accounted for a positive relationship between clay content and bulk porosity. Considering the shale porosity reduction caused by the intensive structural deformation of shale pores, the Wufeng-Longmaxi shale, that is rich in fracture networks between roof and floor layers, may still be an excellent exploration target in the fold-thrust belt of the Yangtze Block. Cited as: Guo, X., Liu, R., Xu, S., Feng, B., Wen, T., Zhang, T. Structural deformation of shale pores in the fold-thrust belt: The Wufeng-Longmaxi shale in the Anchang Syncline of Central Yangtze Block. Advances in Geo-Energy Research, 2022, 6(6): 515-530. https://doi.org/10.46690/ager.2022.06.08

Digital mapping and GIS-based spatial analyses of the Pur-Banera Group in Rajasthan, India, with special reference to the structural control on base-metal mineralization

GIS-based ‘digital’ maps help to store geological field data in a georeferenced framework that can be easily displayed at map-scale to outcrop-scale, without the need to map an area separately at different scales. In the iron and base-metal (Pb–Zn ± Cu) prospect of Pur-Banera belt in Rajasthan, India, multiple phases of folding and shearing of the host rocks have led to a complex structural pattern. The relationship between deformation and ore (especially the base-metal ore) localization is not well understood, although it is very important for mineral prospecting and mining. To facilitate exploration targeting, a large part of the Pur-Banera belt is mapped by us at different scales, using the ArcGIS™ platform. The resulting map is ‘intelligent’ in nature, as it can display geological field data at different scales by just zooming in and out, and it is possible to retrieve any type of geological data from any outcrop/sector through a specific GIS-query. Photographs and virtual 3D models of an outcrop can be opened through hyperlinks. Geospatially referenced mapping of the Pur-Banera belt demonstrates four phases of folding, of which the F3 folds define the regional structural pattern. Detailed mapping of mineralized bands and gossans indicate that the originally stratiform iron ore is best mined at the F3 hinge zones where these layers are thickest due to repeated folding. In contrast, the primarily stratabound Pb–Zn ± Cu ore has largely remobilized during F2 folding, becoming concentrated in the hinge zone and/or along the axial plane of F2 folds, which are consequently now the best prospect sites for base metals.

Pore Characteristics and Influencing Factors of Marine and Lacustrine Shale in the Eastern Sichuan Basin, China

Although almost all the shale gas in China is exploited from marine shale (Wufeng–Longmaxi Formation) in Sichuan Basin and several prolific wells, it has also been obtained in Jurassic lacustrine shale. However, the reservoir conditions of the lacustrine shale are not well understood, which has impeded a breakthrough regarding lacustrine shale gas in Sichuan Basin. To probe the reservoir conditions of the lacustrine shale in Sichuan Basin, we take the Wufeng–Longmaxi shale and Dongyuemiao shale sampled from wells and outcrops as examples. A series of experiments were conducted, including TOC, XRD, FE-SEM, N2 adsorption, Micro-CT, vitrinite reflectance and bitumen reflectance. The results show that the pores in marine shale are mainly composed of organic-matter-hosted pores (OM pores). However, in the lacustrine shale, the pores are mainly composed of dissolution pores and intergranular pores. The marine shale is characterized by small-caliber and large-volume pores in which cluster pores are levitated in the shale as kites and connected by past channels. However, in the lacustrine shale, the cluster pores and the past channels are mainly arranged according to the flow channels in the vertical direction. The arrangement of the pores in the marine shale is obviously deformed by compaction. The lacustrine shale is characterized by under-compaction. It can be deduced that the sweet spots for lacustrine shale gas are likely located at the areas characterized by under-compaction resulting from fluid pressure conducted upward, such as the hinge zone of syncline or the core of anticline overlap on the gas reservoirs.

Seismic Performance of Precast Concrete Frame Beam-Column Connections with High-Strength Bars.

As the construction industry is striding towards the industrialization of green buildings, a precast concrete frame beam-column joint with high-strength reinforcement was proposed. Simulate reversed cyclic loading was carried out on two precast connections and one cast-in-place connection to examine the seismic behavior of the proposed new precast connection. The main test variables between the two precast connections were the strength of the reinforcement at the bottom of the beam. The failure shape, hysteresis curve, skeleton curve, strength, deformation ability, stiffness degradation, and energy dissipation were monitored and compared with the cast-in-place connection. The findings of this paper showed that the precast joints had good strength reserve, and the seismic performance in the later stage of loading even exceeds the cast-in-place joints. It was also found that the plastic hinge zone of the beam could be moved away from the column surface via reinforcement method. Additionally, based on the experiment, a detailed nonlinear finite element analysis (FEA) method was developed to reproduce the test response of specific types of bending moment-resistant precast concrete beam-column connections under a reversed loading test, which provided a theoretical reference for further research of the connections.

Renewed incision and complex response of the North Fork Toutle River following the eruption of Mount St. Helens in 1980

The upper North Fork Toutle River (NFTR) has been evolving in a complex way since being disrupted by a 2.5-km3 debris avalanche deposit during the catastrophic eruption of Mount St. Helens in Washington State, USA in 1980. In this study, we improved the alluvial phase space diagram (APSD), which classifies channel adjustment into different stages based on bed elevation and cross-sectional area changes, and applied it to the NFTR at annual time scale in the 1980s. The results showed that in the early 1980s, the upstream narrow single-threaded reaches were degraded, while the downstream wide anabranching reaches were aggraded, with the middle transitional reach acting as the hinge zone. Gradually, the upstream channel reaches armoured, widened, bed slope and excess stream power decreased in the late 1980s, and quasi-equilibrium occurred locally and during short time periods. Sediment load decreased at the lower reaches, resulting in bed degradation and a transition from sediment sink to source. This reversal seemed to have triggered renewed incision, which migrated upstream. The renewed incision was characterised by Stage 1/2 (bed incision with limited bank erosion) followed by Stage 2 (degradation and widening) in the improved APSD. The degradation rate accelerated in the 1990s, especially due to the big flood in 1996, and then slowed down after ∼2000. Channel adjustment rates of the renewed incision were much smaller compared to those of the initial rapid degradation. The change rates of cross-sectional area and valley width decreased by ∼58% and ∼85%, respectively. The comparison between this study and existing studies highlights the significant role played by the time scale, at which the APSD is applied to study channel morphology adjustment.

Experimental investigation on the seismic performance of a novel damage-control replaceable RC beam-to-column joint

The beam-hinge failure modes are recommended in the existing seismic design codes of reinforced concrete (RC) frame systems, to reduce the collapse risk under strong earthquakes. However, the developed plastic hinge at the beam end causes quite a challenge for structural post-earthquake repair. In this study, a novel precast replaceable RC joint in which damages were controlled in the reduced beam section (RBS) steel beam, was proposed for the rapid restoration of structural function. The RBS-based joint (RBSJ) is located in the beam predetermined plastic hinge zone close to the column. To achieve the damage-control objective, the section resistance ratio (β) was defined as the ratio of bending capacity of the non-replaceable section to that of the weakest in RBS beam, which can quantify the flexural strength of the non-replaceable section to that of the RBS. Cyclic tests of six RBSJ specimens with four different β values (1.3, 1.5, 1.8, and 2.0) were conducted to gain insights into their seismic performance. Further, to investigate the behavior of repaired joints, three new RBSJs were subsequently tested with a replaced RBS beam. Test results showed that the proposed RBS-based joint exhibited satisfactory hysteretic behavior, energy dissipation capacity, and replaceability when the β value was larger than 1.3. In addition, the proper increase of β and adding buckling-restrained plates to the flanges of RBS beam could effectively improve the seismic performances of joints.

Tectono‐stratigraphic evolution of Shillong Plateau, North East India through the Permian‐Eocene window

The Shillong Plateau in the north‐eastern Indian Plate signifies a cut‐off patch of the Indian Peninsular Shield, bordered by fault and thrust sheets, with thick alluvium cover along its periphery. The basement rock in the plateau accomplished about 2 km relief difference with the adjoining Sylhet Trough of Bangladesh in the south. The plateau witnessed Permo‐Carboniferous Gondwana sedimentation at its western margin, with Early Cretaceous basaltic traps and continuous fluvio‐marine sedimentation along its southern edge since the late Cretaceous. Although it is largely believed that strike‐slip movement along the Dauki Fault shifted the plateau about 250 km eastward, however, the driving mechanism for Shillong Plateau detachment and conversion of rift‐intercratonic basin to platformal configuration has drawn more attraction. This article focuses on the tectono‐stratigraphic evolution of Shillong Plateau and its adjoining regions on the basis of previous works, to try to understand the distinct tectonic and environmental factors. Early Permian continental rifting to the south‐west of the plateau and south‐east and south‐west of the Malda High presumably separated the Shillong Plateau from Chotanagpur Granite Gneiss Complex (CGGC). Extrusion of Rajmahal Traps west of the Malda High and Bengal‐Sylhet‐Mikir volcanism along an Early Cretaceous geofracture probably accelerated the east‐northeast migration of Shillong Plateau with respect to the CGGC. Since the Late Cretaceous, sedimentation at the southern fringe of Shillong Plateau commenced with an intracratonic basin which gradually transformed into a passive margin configuration during the Late Palaeocene‐Eocene Epoch during growth of the Indian Ocean. Differential subsidence in southern Shillong Plateau caused clastic sedimentation without considerable transportation. At the beginning, the Late Cretaceous intracratonic basin had received volcanoclastic, fluvio‐lacustrine sediments in a series of graben/half‐grabens associated with extensional faulting and volcanism, as represented by the Lower Mahadek and Jadukata formations in the plateau. The upper Mahadek and later Palaeogene sequences along the southern margin of the plateau record marine sedimentation, initiated with an estuarine‐marshy environment during the Late Cretaceous to Palaeocene, followed by a platformal marine succession since the Mid‐Eocene. The Calcutta‐Mymensingh Eocene Hinge Zone that separates a stable shelf from the deep basinal part might be traced through the south‐eastern fringe of Shillong Plateau and presumably continues further north‐east between the Naga and Disang thrusts in the eastern part of Dhansiri Valley.

Experimental Study on the Effect of Fibers on Engineered Cementitious Composite Short Square Columns

Recent earthquakes severely damaged short columns due to high lateral stiffness and low ductility. Some conditions, such as reductions in the heights of some columns compared to others on the same floor, deep beams, partially buried basements, and non-structural walls, cause short column effects. The prominent characteristics of engineered cementitious composites (ECCs) reinforced with polyvinyl alcohol (PVA) fibers – including their high tensile strength, micro and multiple cracks, energy dissipation, high ductility, and strain hardening – lead to improved seismic performance and economic efficiency in structure elements. In this study, 11 ECC columns with different fiber fractions (0–1.5%) and aspect ratios (3–7), as well as one conventional concrete column, were tested and evaluated. The results showed that increasing fiber friction and shear aspect ratio increased the length of the plastic hinge zone and ductility by at least 50% and 100%, respectively. Furthermore, the failure mode changed from brittle shear to ductile shear.

Seismostratigraphic analysis of Lake Cahuilla sedimentation cycles and fault displacement history beneath the Salton Sea, California, USA

Abstract The Salton Trough (southeastern California, USA) is the northernmost transtensional stepover of the Gulf of California oblique-divergent plate boundary and is also where the southern terminus of the San Andreas fault occurs. Until recently, the distribution of active faults in and around the Salton Sea and their displacement histories were largely unknown. Subbottom CHIRP (compressed high-intensity radar pulse) surveys in the Salton Sea are used to develop a seismic facies model for ancient Lake Cahuilla deposits, a detailed map of submerged active faults, and reconstructed fault displacement histories during the late Holocene. We observe as many as fourteen Lake Cahuilla sequences in the Salton Sea (last ~3 k.y.) and develop a chronostratigraphic framework for the last six sequences (last ~1200 yr) by integrating CHIRP data and cone penetrometer logs with radiocarbon-dated stratigraphy at an onshore paleoseismic site. The Salton Sea contains northern and southern subbasins that appear to be separated by a tectonic hinge zone, and a subsidence signal across hinge-zone faults of 6–9 mm/yr (since ca. A.D. 940) increases toward the south to >15 mm/yr. The faults mapped to the south of the hinge zone appear to accommodate transtension within the San Andreas–Imperial fault stepover. We identify 8–15 distinct growth events across hinge-zone faults, meaning growth occurred at least once every 100 yr since Lake Cahuilla sedimentation began. Several faults offset the top of the most recent Lake Cahuilla highstand deposits, and at least two faults have offset the Salton Sea flood deposits. Active faults and folds were also mapped to a limited extent within the northern subbasin and display growth, but their kinematics and rupture histories require further study. The broad distribution of active faulting suggests that strain between the San Andreas, San Jacinto, and Imperial faults is highly distributed, thus discrepancies between geologic and geodetic slip-rate estimates from these major fault systems are to be expected.

Geological Controls on the Gas Content and Permeability of Coal Reservoirs in the Daning Block, Southern Qinshui Basin.

The gas content and permeability of the coal reservoir are the key factors affecting coalbed methane (CBM) productivity. To investigate the geological controls on the permeability and gas content of coal reservoirs in the Daning block, southern Qinshui Basin, geological surveys combined with laboratory experiments, including coal petrology analysis, proximate analysis, and methane isothermal adsorption experiments, were carried out. The results show that the gas content of coals in the Daning block ranges from 5.56 to 17.57 (avg. 12.83) m3/t, and the coal permeability is generally above 0.1 mD, averaging 0.96 mD. The gas content of coal reservoirs shows decreasing trends with the increase in ash yield and moisture content, while tends to increase with the increase of vitrinite content; however, the correlation coefficients are all extremely low. The gas content presents a strong positive correlation with the burial depth of coal seams, but overall poorly correlates with the coal thickness. The CBM-rich areas are generally located at the hinge zones of secondary synclines, while the lower gas content areas commonly occur at the hinge zones of secondary anticlines. The normal faults are developed in the Daning block, and as expected, the gas content of coal seams that are near the normal faults is commonly lower. It was found that the well testing permeability of coal reservoirs in the Daning block decreases exponentially with the increase of the minimum horizontal stress (σh) and the maximum horizontal principal stress (σH). With the increase of the burial depth, the coal permeability also decreases exponentially. The primary and cataclastic structure coals generally have a higher hydro-fracturing permeability than the granulitic and mylonitic structure coals. This work can serve as a guide for the target area selections of CBM enrichment and high production in the Daning block.

Seismic behavior of damaged RC columns repaired with FRCM composites

In literature, a limited number of studies were carried out on the use of externally bonded composites to repair reinforced concrete (RC) columns subject to cyclic increasing lateral loads. Among them, very few deal with the use of fiber reinforced cementitious matrix (FRCM) composites. Thus, this work experimentally analyzes the behavior of two real scale RC columns repaired through FRCM with carbon fibers, subject both to axial and lateral loads, the latter applied through fully-reversed increasing cycle steps. The goal of the repair interventions was to restore the initial strength and ductility of the specimens after severe damage was applied to the original columns. Two repair methods were adopted: in one case, concrete confinement at the column base was realized; in the second case, other than confining jacket, flexural reinforcement was also used. Cracking pattern, load-displacement curves, ductility, stiffness and strength deterioration, energy dissipation and curvature development along the plastic hinge zone were investigated, comparing the performance of the control specimens with the repaired ones. Results were also compared with ones obtained applying a simple analytical model. Fibers exploitation was experimentally monitored in the repaired columns. Results demonstrate that FRCM confinement jackets can adequately repair seismically-damaged RC columns, restoring the initial lateral load capacity. Repaired columns showed also a similar ductility and energy dissipation compared to the undamaged control ones, while damping ratio resulted slightly lower for the repaired columns.

The influence of subseismic-scale fracture interconnectivity on fluid flow in fracture corridors of the Brejões carbonate karst system, Brazil

The present study used a multitool approach to characterize fractures of several orders of magnitude in large fracture corridors, caves, and canyons to investigate their impact on fluid flow in carbonate units. The study area is the Brejões carbonate karst system that is located in the Neoproterozoic Salitre Formation in the Irecê Basin, São Francisco Craton, Brazil. The approach included satellite imagery, used for interpreting the regional structural context, Unmanned Aerial Vehicle (UAV) and ground-based Light Detection And Ranging (LiDAR) imagery, used for detailed structural interpretation. Regional interpretation revealed that fracture corridors, caves and canyons occur along a N–S-oriented anticline hinge. An advanced stage of karstification caused fracture enlargement and intrabed dissolution, and the formation of caves and canyons. A river captured by the highly fractured zone along the anticline hinge played an important role as an erosive agent. Detailed characterization of fracture corridors comprised structural analysis, topological studies, persistence estimations, power-law fitting of fracture trace length distributions, and identification of network backbones. Our results indicate that fracture corridors comprise four subvertical fracture sets: N–S and E-W and a conjugate pair, NNE-SSW and NW-SE. Fractures observed in the caves show the same dominant directions. Fracture directions are consistent with a common origin associated with the anticline folding. Fracture traces range from 1.0 m to 300 m, comprising both subseismic (<50 m) and seismic scale fractures (>50 m). Networks have dominance of node terminations Y and X (notably Y), CB values higher than 1.8, high P20 and P21 persistence values, and highly interconnected backbones. Fracture network connectivity is associated with power-law exponents greater than 2.5 for the fracture trace distributions, indicating large influence of subseismic-scale fractures on fluid flow. As the final result of folding and karstification, large volumes of secondary macroporosity were created, particularly in the zone of maximum fracture intensity around the hinge zone of the anticline. This scenario can be used to understand better oil reservoirs formed in similar structural controls in near-surface conditions.

Experimental and analytical investigation of drilled flange connections (DFCs) with radial drilling patterns

The capability of reduced beam sections (RBS) to improve the seismic behavior of rigid connections leads to their notable application in steel moment-resisting frames. However, they may encounter shortcomings such as local buckling and lateral-torsional buckling. To resolve such problems, the idea of utilizing perforated beam flanges instead of cut-out flanges as reduced beam sections was presented. These type of connections can reduce the potential for local and lateral-torsional buckling of conventional RBS connections and improve their seismic performance. Achieving such advantages requires special care to geometrical specifications and drilling patterns (DPs). Appropriate arrangement of holes reduces the stress concentration around the beam flange-to-column Complete Joint Penetration (CJP) groove weld and, consequently, prevents the groove weld and inter-hole area from tearing and fracturing in early cycles of loading. The present study investigated the hysteretic performance of the drilled flange connections (DFCs) of various drilling arrangements through an experimental program.It should be noted that the box-shaped columns were considered in this study to target the 3D moment resisting frames (MRFs) that all their axes participate in the lateral force-resisting system. The most appropriate drilling patterns were selected using remarkable numbers of numerical analyses. Four laboratory specimens with different drilling arrangements of top and bottom flanges were fabricated based on preliminary numerical analyses. The laboratory specimens were subjected to cyclic loading. To evaluate the specimens' seismic performance, moment-rotation hysteresis curves were compared, and the stress distribution at the connection CJP groove welds. The results of the experimental tests revealed that those DFCs with combined DP with notches and holes (DFC1), radial DP (DFC2), semi radial DP with notches (DFC3), and semi radial DP (DFC4) could increase the rotational capacity of the DFCs up to 50% of the required rotation of the special moment-resisting connections. Moreover, semi radial DP (DFC4) may increase the connection's rotational capacity up to 75% of the special moment-resisting connections. Also, Based on the analytical results, conventional RBS connections may increase the 0.04 radians, needed rotational capacity up to 37.5% for a pre-qualified moment-resisting connection. It was also shown that no lateral-torsional buckling and smaller degradation in stiffness and strength took place in plastic hinge zones at the relative deformation of 0.04 radians. The plastic strain at the center of the CJP groove weld line in the beam longitudinal direction was more significant than those corners of the groove weld line in the same direction. In all specimens, the minimum plastic strain of the CJP groove weld took place in central parts of the weld in the transverse direction. In DFC1, DFC2, DFC3, and DFC4 specimens, the contribution of panel zone rotation in the overall plastic rotation of the connection is negligible.

Oceanward rift migration during formation of Santos–Benguela ultra-wide rifted margins

Abstract This paper presents the time and space evolution of crustal deformation and their respective sedimentary infill of the 600 km wide, asymmetric conjugate rifted margin of the Santos–Benguela basins. Based on a geoseismic transect obtained with interpretation of long-offset seismic reflection and tied by wells, we interpret six main synrift unconformities, corresponding to different deformation phases processed from the Valanganian to Early Albian. Confined by these unconformities, sedimentary growths with progressively young relative ages towards the boundary with the oceanic crust are interpreted as evidence of oceanward rift migration. The combination of this information with crustal structure derived from long-offset seismic reflection illuminating the deep crust of the Santos–Benguela conjugate margins, resulted in a complete view of sedimentary infill, internal compartments, and crustal structure. These data were used to guide a dynamic model of rifting resulting in a simulated lithospheric section. We show that the margin architecture can be explained by the combination of an early, protracted phase of distributed deformation, followed by basinward rift migration. Distributed deformation lasted from the Valanginian to Early Aptian (135–117 Ma), initiating with isolated lakes that later coalesced into a wide basin-scale lake (&gt;450 km). From the Mid Aptian to Early Albian (117–110 Ma), rift migration formed the main structural compartments and unconformities, as well as the distal hinge zones we observe today in the seismic lines. During this time, the inner proximal margins were left behind to thermally subside, whereas outer proximal and distal margins were tectonically active. Coexistence of these two processes explains the enigmatic simultaneous formation of proximal sag-like geometries, with late synrift accumulation of a salt layer up to 3 km thick, with tectonically active faults in the distal margin, promoting crestal block uplift that could explain the deposition of Late Aptian, shallow water, pre-salt carbonate rocks.

Quantitative Evaluation of Coseismic Deformations Induced by Seismogenic Faulting in Mining Exploration Area During the 2018 Xingwen and 2019 Changning Earthquakes, Sichuan, China

In the period between December 2018 and July 2019, a series of earthquakes (EQs), including the 16 December 2018 Ms 5.7 Xingwen mainshock and the 17 June 2019 Ms 6.0 Changning mainshock, struck the Changning shale gas exploration field in the southern margin of the Sichuan Basin. The Xingwen and Changning EQs both occurred on concealed faults, which led to hundreds of casualties, and affected a total of over 160 thousand people in southern Sichuan. The aftershock sequences following the Xingwen and Changning EQs were clustered in the vicinity of the Jianwu syncline and Changning anticline, respectively, and occurred mostly at depths of 3–7 km. In this study, coseismic surface deformation measurements obtained through differential interferometric synthetic aperture radar (D-InSAR) data were used to identify the faulting geometries and distributions. The coseismic deformation maps have maximum line-of-sight (LOS) displacements of ∼4.53 cm on the northwest side of the Xingwen EQ source fault and ∼7.84 cm on the southwest side of the Changning EQ source fault. The calculated static Coulomb stress changes indicated that most aftershocks occurred in increasing stress zones following the mainshock ruptures. From the InSAR deformation field, a complicated concealed seismogenic doublet fault was inferred, which predominately exhibited left-lateral strike-slip motion during the Xingwen and Changning EQs. The footwall ramp of the basement fault reactivated first, and resulted in the Xingwen EQ and concentrating stresses beneath the Changning anticline, which induced the Changning EQ half a year later. Compared with previous studies, we proposed that the fault network was lubricated by water that was injected during shale gas exploration, facilitating the occurrence of the Xingwen and Changning EQs. Such work evaluated the coseismic deformations of the Xingwen and Changning EQs, and derived the regional faulting distribution from aftershock sequences. It could provide useful information for monitoring and analyzing seismic activity around the hinge zones of folds in mining exploration areas, which contributes to effective risk assessment of disasters associated with seismic geo-environments.

Decadal changes of Campbell Glacier Tongue in East Antarctica from 2010 to 2020 and implications of ice pinning conditions analyzed by optical and SAR datasets

ABSTRACT Changes in ice shelf dynamics significantly impact the discharge rate of grounded ice, sea ice formation, and marine environments. In particular, changes of a sub-shelf pinning point induce complex dynamics of an ice shelf. In this study, we investigated decadal changes (2010–2020) in the area, ice velocity, and grounding line position of Campbell Glacier Tongue (CGT) in East Antarctica, which has an ice pinning point at the southwestern end, and analyzed the effect of the pinning conditions on the dynamics of CGT. Panchromatic band images of Landsat-7 Enhanced Thematic Mapper Plus and Landsat-8 Operational Land Imager, COSMO-SkyMed X-band synthetic aperture radar (SAR), and Sentinel-1 C-band SAR datasets were employed. The surface area of CGT digitized from the optical and SAR imagery decreased by 8% in the last decade, during which four ice calving events that caused icebergs with an area range of 3.8–5.4 km2. The largest calving at the ice pinning point occurred in March 2014, which created an iceberg with 4 km2. The ice velocity of CGT was measured via the normalized cross-correlation-based image matching of the Landsat panchromatic images. The ice velocity along the flow direction and its anomaly of CGT hardly changed in the hinge zone from 2011 to 2020. The ice velocity increased by ~7% and the flow direction steered abruptly ~7° to the east in the freely floating zone after the 2014 calving at the ice pinning point. Considering the retreat of the local grounding line at the pinning point analyzed by COSMO-SkyMed double-differential interferometric SAR, the advancing glacier tongue came in contact with the sloping eastern flank of the locally elevated seabed at the pinning point after the calving, and the ice-bed contact area decreased, causing a sudden acceleration and eastward rotation of ice flow. It is expected that continuous calving at the ice pinning point of CGT may lead to an abrupt changes in glacier tongue dynamics again, and continuous monitoring is necessary.

Seismic performance of underwater RC bridge piers strengthened with self-compacting concrete-filled BFRP jacket

This paper presents an experimental study on underwater bridge columns strengthened with a combination of basalt fiber-reinforced polymer (BFRP) jacket and enlarging sectional area by filling self-compacting concrete. Due to the strengthening demand of underwater bridge column without cofferdam, the newly method was developed through using BFRP to make formwork jacket (namely BFRP jacket), and filling non-dispersible underwater concrete between the pier and BFRP jacket. Three circle bridge column specimens were manufactured and tested under lateral reserved cyclic loads along with a constant axial load. The seismic behavior of a specimen with ordinary agent and the other one with micro-expansion agent was compared, and the remaining one was used as the reference specimen. A finite element model was developed to study the effect of BFRP height, concrete strength grade and BFRP layer numbers on seismic performance of the columns strengthened with BFRP jacket. The retrofitting procedure of the BFRP jacket method was proved to be feasible and efficient through the experiments. The experimental results indicate that the ultimate load capacity and energy-dissipation capacity can be significantly enhanced, whereas the deformation capacity and displacement ductility exhibit little improvement of the columns strengthened with the BFRP jacket, and the seismic performance of the reinforced piers e.g. energy-dissipation capacity and ductility can also be improved in a certain extend by adding micro-expansion agent. The finite element parameters analysis indicate that the seismic performance of piers can be effectively improved by strengthening in the plastic hinge zone, the increase of filler concrete strength has little effect on the seismic performance, and it is viable to use the 6-layer BFRP clothes to make BFRP jacket for the testing bridge column specimen.

Regional and local controls of hydrothermal fluid flow and gold mineralization in the Sheba and Fairview mines, Barberton Greenstone Belt, South Africa

High-grade gold-quartz-sulphide lodes of the Sheba-Fairview Complex (SFC) of gold mines in the Barberton Greenstone Belt of South Africa describe a wide range of geometries, orientations, controls, and a number of different and often contradicting models have been postulated to account for their formation. This paper aims to present a holistic model that describes the focussing of a regional-scale fluid flow into narrower, mineralized structures during the late-stage refolding and tightening of the first-order folds that host the mineralization.The auriferous reefs of the SFC are hosted by well-bedded, low-grade metamorphic, clastic sedimentary rocks of the Paleoarchaean Fig Tree and Moodies groups that are preserved in two regional-scale, strongly curved and refolded synclinal structures along the northern margin of the belt. The majority (85 %) of presently and historically mined orebodies occur in the broad hinge zone of the refolded synclines. This suggests the regional-scale fluid redistribution from fold limbs into the first-order fold hinge following regional hydraulic gradients during refolding. Ubiquitous bedding-parallel quartz (-carbonate-sulphide) veins and associated alteration underline the significance of bedding anisotropies and bedding-parallel flexural slip for regional-scale fluid flow during refolding. The focussing of these fluids and economic-grade gold mineralization occurs preferentially along contacts between lithologies with pronounced rheological contrasts. Lithological contacts combine the effects of strain localization in weaker units and the formation of fracture permeabilities in competent units across these contacts. Examples include kilometer-scale hinge-parallel ore shoots that are controlled by undulations (jogs) along low-displacement slip horizons between retrogressed ultramafic rocks and competent metasediments. In contrast, low-angle thrusts or steep reverse faults form accommodation structures related to the late-stage tightening of the first-order folds. These structures transect bedding at high angles and are, thus, ideally orientated to collect fluid from the regional system of bedding-parallel fluid flow.Mineralization in the SFC may be explained by the spatial and temporal coincidence of (1) late-stage NW-SE shortening and refolding, of (2) a well-bedded, anisotropic wall-rock sequence, associated with (3) regional-scale fluid redistribution along bedding planes during flexural slip, leading to (4) fluid focussing into either jog geometries or bedding discordant structures. The combination of these factors is unique to the SFC and accounts for the location of the main Barberton gold mines along the northwestern margin of the greenstone belt.

Preliminary Bond Testing and Splicing of Titanium Alloy Bars

The study of the interaction between reinforcement and concrete is important to ensure the composite action of the two materials. A high bond strength is desirable in the reinforcement–concrete interface to avoid pullout failure. The higher bond of reinforcing bars with concrete provides better performance and increases the capacity and service life of structural elements. Bond tests of smooth titanium alloy bars (TiABs) and 60 kips per square inch (ksi) (414 MPa) steel with concrete are conducted in accordance with the ASTM C234. Based on the experimental results, the bond strength of TiABs is generally found to be higher than that of the steel. The paper also presents some preliminary investigation for identifying appropriate and commercially available mechanical couplers for splicing the TiABs. Since TiABs are more expensive than normal rebars, it is necessary to limit their quantity and use in bridge piers (e.g., plastic hinge zone only). Products from a well-known producer of mechanical couplers in the United States are used in the research. A few mechanical couplers are investigated for splicing of #5 (15.9 mm diameter) and #6 (19.1 mm diameter) pseudo-threaded TiABs. Tensile testing is carried out in accordance with ASTM A1034 to address the 2017 AASHTO Load and Resistance Factor Design (LRFD) requirements and a suitable coupler was identified. The appropriate mechanical coupler was identified to be the coupler that is designed specifically for use with high-strength bars. It uses a cold swaged steel sleeve and is thicker.