Weak Zones Research Articles

New 40Ar/39Ar mineral ages of Archaean to early Proterozoic rocks in northern Sweden and implications for the 1.8–1.5 Ga tectonothermal history of northernmost Fennoscandia

Abstract The bedrock in northernmost Sweden comprises Archaean (2.8–2.65 Ga) and Karelian (2.4–1.96 Ga) rocks and a volumetrically dominant population of magmatic rocks which formed during the Svecofennian (1.9–1.8 Ga) stage. New Ar–Ar (hornblende and muscovite) and U–Pb (zircon and monazite) isotopic results from representative lithologies are used to shed further light on the geological evolution. With respect to the Ar–Ar isotopic system, somewhat variable dates (hornblende) are interpreted as cooling ages that indicate different uplift histories, following a 1.8 Ga metamorphic peak, at different sides of the Karesuando-Arjeplog deformation zone. Other post-1.7 Ga 40Ar/39Ar ages are suggested to reflect either a neocrystallisation (muscovite) or an event leading to isotopic resetting (hornblende). It is suggested that post-1.76 Ga crustal processes have influenced the Ar–Ar mineral systems during three relatively short-lived (a few tens of million years) stages; peaking at ~ 1.73 Ga, ~ 1.63 Ga and ~ 1.55 Ga. Tentatively, the timing of these stages is coupled with far-field effects that elsewhere are associated with the alkali-rich granitic magmatism forming part of the Transscandinavian Igneous Belt (the 1.73 Ga event) and Rapakivi massifs (the 1.63 and 1.56 Ga events). It is proposed that the N-S to NW–SE orientation of these vast, regional granitic complexes matches that of major deformation zones in northernmost Fennoscandia and that locally initiated hydrothermal fluids followed weakness zones in the crust and ultimately led to element mobilisation, new mineral growth and isotopic over-printing preferentially affecting shear- and ore zones. Graphical abstract

Intraplate seismicity in southwestern Norway: Enhanced catalogue highlights diffusive earthquake occurrence linked to inherited weakness zones

Summary Intraplate earthquakes in stable continental regions exhibit diverse characteristics in terms of timing, spatial distribution, and magnitude. They are often unexpected, and their underlying physical mechanisms are not well understood. This complexity is particularly apparent in Norway, where seismicity is mostly localised on the continental margin and coastal areas. Various studies have attempted to explain the causes of seismicity in Norway by invoking different sources of stress, ranging from regional stress due to ridge push to local effects such as topography or deglaciation. In this study, we revisit these questions by investigating the distribution of seismicity in southwestern Norway using an enhanced earthquake catalogue. To achieve this, we revised the Norwegian National Seismic Network seismic catalogue from 2000 to 2023 and built a new catalogue using machine-learning-based techniques on data from a temporary seismic deployment in the region. Thanks to the increased station density during this deployment, we were also able to calculate new fault plane solutions that consistently showed a WNW-ESE direction for the most compressive axis. Furthermore, we demonstrate that seismicity in southwestern Norway, while diffuse, tends to be localised around the major crustal shear zones of the region, such as the Bergen Arc Shear Zone and the Hardangerfjord Shear Zone.

A complete structural analysis of the FⅠ17 strike-slip fault and its hydrocarbon enrichment factors, Tarim basin, NW China

The FⅠ17 fault is a prominent strike-slip fault in the central Tarim basin, notable for its hydrocarbon abundance and intricate tectonic attributes, characterized by several deflections in its planar trajectory. Analyzing the FⅠ17 fault offers crucial insights into the role of basement structures on the evolution and formation of intracratonic strike-slip fault systems. This study utilizes the latest seismic data and integrating the foundation of previous research to conduct a detailed investigation into the spatial distribution, deformation intensity, activity phases, and formation mechanisms of the fault. The fault can be divided into three structural layers based on deformation features. The deep layer, situated beneath the TЄ3 interface (the bottom of the Upper Cambrian), shows basement rifts and weak strike-slip activity. The middle layer, spanning from TЄ3 to TO3 (the bottom of the Upper Ordovician), exhibits pronounced deformation with flower-like structures. The upper layer, extending from the TO3 to TP (the bottom of the Permian), is marked by three groups of en-echelon normal faults. Controlled by Precambrian basement heterogeneity, the fault evolved through three stages: weak compressive stress during the Middle -Late Cambrian led to rupture along basement rifts and weak zones that formed the fault’s embryonic shape; strong compressive stress from Middle-Late Ordovician activated and propagated the fault upwards; during the Silurian-Carboniferous, the fault experienced episodic reactivation and result in the emergence of en-echelon normal faults. Hydrocarbon enrichment at the FⅠ17 fault is influenced by source rock distribution, reservoir characteristics, and fault reactivation. Its positioning above the source rock center ensures an ample supply of hydrocarbon. The intense fault activity has created favorable conditions for large-scale fracture-cavity reservoir development, and the reactivation period corresponds with the hydrocarbon accumulation phase, significantly boosts hydrocarbon charging.

Effect of prestressed geosynthetic-reinforced embankment over locally weak sabkha zone by numerical approach

Effect of prestressed geosynthetic-reinforced embankment over locally weak sabkha zone by numerical approach

The impact of the variation in vertical load and the presence of openings on the mechanical response of masonry walls

This article aims to analyse the mechanical response of masonry walls under cyclic loading using the finite element method with Abaqus software. The proposed model has been validated using available numerical and experimental results. This work provides an in-depth study of the cracking modes of masonry walls based on different vertical loads and the presence of openings. By using numerical simulations, it identifies the types of cracks that develop, their propagation, and their interaction with the structure. A parametric study will then be conducted to assess the influence of variations in vertical load and the effect of openings on the behaviour of the walls. Load-displacement curves and failure modes are presented and analysed. The results show that these parameters have a significant impact on wall behaviour. Specifically, an increase in vertical load improves the wall's resistance, while openings create weakness zones that promote degradation and reduce strength. A thorough understanding of the behaviour of unreinforced masonry structures is essential for making informed decisions regarding restoration methods.

Shear wave velocity profiling of Riyadh City, Saudi Arabia, utilizing the multi-channel analysis of surface waves method

Abstract Geotechnical site characterization is very important for construction purposes. This study has been conducted in Diriyah area northwest of Riyadh City, Saudi Arabia, using the Multichannel Analysis of Surface Waves (MASW) method for site characterization through shear wave velocity profiling to 30 m depth. Nineteen MASW lines were carried out in various directions and lengths through the area. The entire process was meticulously parameterized to extract shear wave velocity for subsurface characteristics. MASW results revealed four distinct velocity zones based on National Earthquake Hazard Reduction Program. Fill material was approximately half a meter thick and was classified as very dense soil. The second layer exhibited velocities ranging from 800 to 1,500 m/s, indicating weathered and highly fractured limestone. The third layer showed velocities varying from 1,500 to 1,800 m/s, representing slightly weathered limestone. The fourth layer displayed high velocities ranging from 1,800 to 3,600 m/s, indicating hard and compact limestone rocks. Geotechnical boreholes were drilled down to depths of 10–35 m. These boreholes exposed the geological model that consisted of fill material (silty sand with gravel), followed by highly to moderately weathered limestone with vugs and cracks, and finally, massive limestone rock. Analysis of shear wave velocities identified weak zones, particularly fractured and weathered limestone rocks extending to 12 m in depth. Sinkholes of circular, elongated, and/or conical shapes were observed within this depth range. Moreover, some sinkholes were detected at depths greater than 12 m in specific locations (sites 1, 6, 9, 11, and 17). These sinkholes agreed with the previous study. These results highlight the need for targeted ground improvement methods, such as grouting or underpinning, particularly for construction over weaker zones. Accurate site classification and effective risk management are crucial for addressing these geotechnical and seismic challenges.

Study on Soil and Water Loss on Slope Surface and Slope Stability Under Rainfall Conditions

For a binary structure slope with a soil layer on the top and a rock layer on the bottom, during the rainfall process, surface runoff will cause soil and water loss on the slope surface and damage to the slope environment. When rainwater infiltrates into the slope, the pore water pressure in the soil gradually increases, the shear strength of the soil decreases, and a weak zone is formed at the soil–rock interface, which has a significant impact on the stability of the slope. Therefore, to study the soil and water loss on the slope surface and the stability of the slope under rainfall conditions, we used theoretical analysis, indoor model tests, and numerical simulations to conduct a comprehensive exploration of this issue, and the following conclusions were formed: the pore water pressure in the shallow layer is greater than that in the deep layer, and the pore water pressure at the toe of the slope is greater than that at the top of the slope; as the slope gradient increases, the time when the pore water pressure at the toe of the slope begins to respond gradually speeds up; the slope displacement first occurs at the lower part of the slope, then in the middle, and finally at the upper part; the time when the displacement at each point on the slope surface begins to respond gradually speeds up with the increase in the slope; the damage form at a small slope gradient is mainly flow sliding, and the damage process is continuous; the damage form at a large slope gradient is mainly flow sliding and overall sliding, and the damage process is continuous and sudden; when the binary structure slope fails, the sliding surface includes the internal sliding surface of the soil and the sliding surface at the soil–rock interface, but when the slope gradient is small, the relative sliding at the soil–rock interface is small, and a continuous sliding surface cannot be formed; and when the slope gradients are small (30° and 40°), the displacement decreases continuously from top to bottom, and no overall sliding surface is formed. The larger values of plastic strain mainly occur in the upper and middle parts of the slope, there is no formation of a continuous plastic strain zone, and the damage mode is flow sliding; when the slope gradients are large (50° and 60°), the displacement is the largest in the upper part, and a large displacement also occurs in the lower part, forming a sliding surface that penetrates through the soil–soil and rock–soil layers. The larger values of plastic strain occur in the upper, middle, and lower parts of the slope, a continuous plastic strain zone is formed, and the damage modes are flow sliding and overall sliding; numerical simulations were carried out on a typical actual slope, and consistent results were obtained.

Analysis of engineering performance of concrete comprising recycled crushed plastic waste and fly ash

This study investigated the attributes of blending of recycled crushed polypropylene plastic coarse aggregates (PPCA) and fly ash (FA) towards the fresh and hardened properties of concrete. Natural coarse aggregate was partially replaced with PPCA at volumetric replacement levels up to 30% and cement was replaced with FA up to 20%. Initially, the performance of PPCA and FA in concrete was investigated distinctly. The incorporation of 30% of PPCA in concrete rather impaired the workability (from 95 mm – 50 mm: 47%) and the compressive strength (from 44.6 MPa to 31.4 MPa: 29.7%). By appropriate using of a superplasticizer, the loss in the workability could be recovered. Microstructural investigation was conducted employing scanning electron microscope analysis; it showed that the formation of a weak interfacial transition zone between PPCA and cement paste to be the reason for strength reduction in PPCA concrete. In contrast, the addition of 10 – 20% of FA in concrete improved the workability by 63.2% – 100%, but yet again, the 28-day compressive strength reduced by 15.8 – 35.6%. Meanwhile, thermal conductivity results and constitutive relationships proved that the use of PPCA enhanced the thermal insulation property and ductility of PPCA concrete, respectively. Eventually, a total of six concrete batches with binary blended PPCA and FA were cast to find the optimum replacement levels. The optimum binary combination with reasonable strength and workability at a minimal cost was achieved to be 10% PPCA and 20% FA.

Particle crushability’s role in liquefaction: insights from Mayotte submarine slopes

Since 10 May, 2018, a significant number of volcanic and seismic events have been recorded in Mayotte, in the Comoros Archipelago of the Indian Ocean. Detailed bathymetry of Mayotte′s eastern regions has uncovered steep underwater slopes. A recent study in the area investigated liquefaction-prone layers associated with low sea-level depositions. However, the reason for the presence of such ‘weak zones’ remained unknown. In the present study, we examined samples from Mayotte’s slopes to investigate the reason for liquefaction at the particle-scale of such layers. Our results show that biogenic particles in naturally sedimented environments can crush under cyclic or static loading even with large amounts of fines. In the case of Mayotte’s slopes, the external loading threshold was found to be 500 kPa under K0-conditions. Our findings highlight the complex behavior of biogenic-dominant sediments, their impact on classification and overall behavior, and their potential implications for the design of wind farms.

Geophysical Investigation of Buried Small Fault Beneath Western Mount Malabar Using Electrical Resistivity Tomography in The Great Bandung Basin Rim

This article presents the discovery of a buried fault beneath the soil layers in the Mt Malabar area, which complements the information on suspected faults on the previous geological maps. Using an Electrical Resistivity Tomography (ERT) method, this study aims to delineate the layer discontinuity as a fault and describe the subsurface geology. This study employed a 1400 m long ERT line as the main line to identify buried fault traces, while each ERT line has an 800 m long installation across the main ERT line to obtain the direction of the minor fault. The investigation found a minor fault in the rock layer at a high resistivity layer, approximately 160 m below the surface. The identified rock units are believed to include sandy clay in the upper layer, followed by tuff, sandstone, and basalt lava in the lower layer because its resistivity value is above 250 Ohm.m. The 3D ERT model interpreted a minor buried fault as a weak zone beneath the soil and obtained the fault strike at approximately N 310°E and dipping 66°. Furthermore, these results are strengthened by the geological map, which confirms that ERT L-1 and ERT L-3 profiles coincide with a suspected fault in the Qmt rock unit area.

Bioassay-guided evaluation of antimicrobial properties and profile of bioactive compounds from leaf, peel and mesocarp of four apple cultivars (Malus domestica Borkh.) grown in Serbia: Application of HPTLC-EDA and UHPLC Q-ToF MS techniques

The aim of this study was to evaluate the antimicrobial properties and profile of bioactive compounds from mesocarp, peel and leaves of four autochthonous apple cultivars against human pathogens, Escherichia coli, Staphylococcus aureus and Bacillus subtilis and the apple pathogen Erwinia amylovora by direct detection on HPTLC plates and subsequent chemometric analysis. UHPLC Q-ToF MS was used for detailed characterization of the bioactive compounds with antimicrobial properties. Leaf extracts showed the highest antibacterial activity against all bacterial strains, followed by peel extracts, while the mesocarp extracts showed only weak and selective inhibition zones for E. coli and B. subtillis. The apple cultivars, ‘Kadumana’ and ‘Kopaoničanka’ showed the best antimicrobial properties. The active compounds were triterpenoids, coumaroylquinic acid and caffeoylquinic acid isomers and methyl derivatives, naringenin, kaempferol and quercetin aglycones and glycosides, phloretin and its glycosides and acylated derivatives that detected for the first time in the apple leaves and fruits.

Ophiolites in the Central Asian Orogenic Belt record Cambrian subduction initiation processes

Subduction initiation remains elusive because no present example exists. Ophiolites formed over nascent subduction zones in the past provide the key to constraining the processes of subduction initiation. Here we document three Cambrian ophiolites with supra-subduction zone affinity, which likely reflect the inception of a plate-boundary scale subduction zone within the Paleo-Asian Ocean. Our findings, together with a compilation of Cambrian ophiolites in the Central Asian Orogenic Belt, indicate diachronous subduction initiation(s) along a > 6000 kilometer zone within the Paleo-Asian Ocean between 536 and 528 million years ago. The subduction initiation of the Paleo-Asian Ocean coincides with the closure of the Mirovoi Ocean following the collision of a series of microcontinents with the Siberian craton, likely representing a typical record of collision-induced subduction jump. Our observations and numerical modeling provide a new scenario that subduction initiations would locate at oceanic weak zones rather than passive margins of accreted microcontinents during collision-induced subduction process.

Partitioning Primary Air to Strengthen Efficiently the Horizontal Air-Staging Conditions within a 75 T/H Coal-Fired Reversal Grate Furnace

ABSTRACT Grate furnaces are essentially equipped with the partitioned primary air and secondary air for regulating low-NO x combustion. However, habitual operations with primary air distributing uniformly on the grate and secondary air opened, present high NO x emissions and low burnout. While a comprehensive investigation into the in-furnace flow, coal combustion, and NO x formation (used to first explain and then improve these problems) is absent up to now. Accordingly, within a 75 t/h coal-fired reversal grate furnace, both full-scale tests and simulations were performed first at its habitual operation case. Subsequently, with secondary air completely shut off, four primary-air distribution forms of the uniform air (UA), front-lean air (FLA), middle-concentrated air (MCA), and rear-enhanced air (REA) were evaluated to compare the horizontal primary-air staging conditions. Flow-field deflection and asymmetric combustion occurred, with the upward gas deflecting toward the rear-wall side and the front-half furnace dominated by a weak recirculation zone without effective combustion. Using the UA but closing secondary air not only dropped effectively NO x but also improved a little burnout. This performance ruled against the vertical air-staging function of secondary air. In the order of UA, FLA, MCA, and REA to deepen the horizontal primary-air staging, the flow-field deflection and asymmetric combustion generally deteriorated a little. The in-furnace combustion first strengthened and then weakened. NO x emissions descended continuously. Among the four cases, the MCA attained the optimal low-NO x combustion performance (i.e. NO x emissions of 267 mg/m3 at 6% O2 and burnout loss of 6.14%, respectively). In comparison to the corresponding levels of 486 mg/m3 and 5.4% at the habitual case, this simple MCA staging setup without any combustion modification, dropped NO x emissions by approximately 45% while raised only a little burnout loss.

3D Printable One-Part Alkali-Activated Mortar Derived from Brick Masonry Wastes

The exponential growth in demand for housing has resulted in a greater focus on rapid construction methods that adhere to circular economy principles. 3D concrete printing is becoming a powerful tool to find solutions to the common challenges of affordable housing for more people, rapid construction, and the digitalization of the construction industry. However, a coherent synthesis of green and digital initiatives has not yet been achieved. For 3D printable materials, recycling of materials that have reached the end of their service life should also be enabled and supported, in line with circular economy goals that prioritize waste reduction and maximization of resource efficiency. With these objectives in mind, the current study focuses on the development of a one-part 3D printable alkali-activated mortar (3DPM) derived from brick masonry waste (BMW). BMWs were used as the main precursor and filler phase, whereas materials such as ground granulated blast furnace slag, kaolin clay, and limestone have been utilized to enhance/control the mechanical and rheological properties. To investigate the evolution of alkali-activation and the effect of anisotropy, the macromechanical properties of the developed 3DPM were investigated by compressive strength, flexural strength, split tensile, and direct tensile tests. The micromechanical properties were analyzed using X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX), and computed tomography (MicroCT) tests. Overall, the results revealed the presence of anisotropy, which can be reduced by optimizing the layer height. Through this optimization, reductions in pore content and distribution, validated by MicroCT, indicated that the disadvantage of the weak interlayer bond zone in stress transfer could be diminished. Micromechanical analysis showed that the gel formation responsible for the strength was the calcium-based gel structures. Considering these findings, it is believed that the BMW-based 3DPM can be an important alternative for the digitalization of the construction industry and its transition to a circular economy.

Research on Propagation Characteristics of Fracture Grouting in Clay Formation

Splitting grouting is a highly effective technique for reinforcing tunnels and underground structures, ensuring their operational stability and facilitating long-term maintenance. It has been widely adopted in the prevention and remediation of geological hazards. However, the theoretical research on the diffusion mechanisms of split grouting lags behind its practical applications. This study addresses several key scientific challenges in understanding the diffusion behavior of split grouting. By integrating experimental design, numerical simulations, and theoretical analysis, we conduct a systematic investigation into the diffusion process and vein morphology of split grouting in both homogeneous and heterogeneous formations. We first employed a self-developed two-dimensional grouting test system to perform diffusion experiments on cohesive strata, focusing on the influence of various factors such as grout density, water/cement ratio, soil consistency, and fracture characteristics. The results provide insights into the diffusion patterns, morphology, soil pressure distribution, and surface uplift behavior of the grout veins. Subsequently, a numerical simulation program, developed in-house, based on the finite element method (FEM) and the volume of fluid (VOF) approach, was employed to model the entire process of fracturing grouting within clay strata. The experimental and numerical results indicate that grout vein diffusion in layered soil follows a Y-shaped pattern with an inclined deflection. In uniform strata, the surface uplift curve displays both symmetrical and asymmetrical “convex” elevations, while in heterogeneous soft and hard strata, the uplift is characterized by distinct “convex” deformations. Finally, based on these findings and the principles of contact mechanics, we analyze the underlying mechanisms. The results suggest that weak contact zones undergo tensile cracking and horizontal deflection prior to the formation of grout veins. Additionally, local stress rotations in the soil can induce tilting and deflection. The theoretical insights derived from this study provide valuable guidance for practical engineering applications.

Caves and Fractured Zones Investigation Using 2D Electrical Resistivity Imaging in an Engineering Site, Haqlaniyah, Western Iraq

Engineering risks in karstic areas are represented by cavities and voids near the surface, which are considered potential geotechnical hazards (land subsidence and building cracks). These hazards are caused by dissolution processes that occur when carbonate rocks interact with water, forming weak zones. This study used 2D electrical resistivity imaging with a dipole-dipole array. The spacing of 5 m and an n-factor of 6 were applied to investigate four parallel traverses covering an area of 95x45 m. Electrical resistivity imaging data was inverted using RES2DINV software by robust method inversion. The results show relatively high resistivity values interpreted as massive limestone with cavities and relatively low resistivity values interpreted as fractured limestone with clay or moisture content. Because of the consequence of these caves' haphazard existence in the area, the region was characterized by significant heterogeneity levels of resistivity rise until a depth of 15 m. At that point, they begin to decline.

The Identification of Land Use Conflicts and Policy Implications for Donghai County Based on the “Production–Living–Ecological” Functions

The rapid development of urbanization has continuously encroached on people’s living space and ecological space, leading to an imbalance in territorial spatial functions. Identifying potential land use conflicts and optimizing land use structure are conducive to carrying out territorial spatial planning rationally. In this paper, we adopt the suitability assessment method to evaluate the suitability of land for production, living, and ecological functions and then use the land use conflict identification matrix to identify land use conflicts in Donghai County and make relevant suggestions according to the intensity of land use conflicts. The results of this study show the following: (1) the areas of suitable land use zones, strong conflict zones, medium conflict zones, and weak conflict zones in Donghai County are, respectively, 58.83%, 10.62%, 26.31%, and 4.24%. (2) The spatial distribution differences in the different conflict zones could determine the pertinence of conflict mitigation and spatial planning. In the process of the urbanization of Donghai County, ecological environmental protection is still the top priority. (3) It is necessary to economically and intensively use construction land, improving its fine management level. Land use efficiency should be maximized, and the spatial distribution of national territory should be reasonably optimized while strengthening the guiding role of planning. This study addresses land conflicts from the perspective of spatial planning rather than economic behavior. It also provides significant insight into land use layout at the county level, which is exactly what China is exploring in the new era.

Three‐Dimensional Crustal Channel Flows Beneath the Southeastern Tibetan Plateau Revealed by Full‐Waveform Ambient Noise Tomographys

AbstractThe growth process of the southeastern Tibetan Plateau remains a fundamental yet unresolved question. Knowledge of detailed lithospheric structures and their potential linkages with surface features offers crucial insights. Here, we present a high‐resolution 3‐D lithospheric velocity model of the southeastern Tibetan Plateau using full‐waveform ambient noise tomography. Our model reveals two prominent low‐velocity anomalies within the middle and lower crust with new characteristics in spatial distribution: Anomaly 1 lies beneath the plateau, and Anomaly 2 beneath the craton has two branches aligning with the Sichuan‐Youjiang tectonic boundary and the eastern margin of the Emeishan igneous province. Furthermore, these two anomalies appear interconnected at deep crust beneath the northern margin of the Emeishan igneous province. We propose that observed crustal velocity lows indicate partially melted materials transported from the high plateau into the cratonic crust along pre‐existing weak zones, which were reactivated during recent continental deformation.

Qualitative and quantitative interpretations of high-resolution aeromagnetic data of Saki-East area, for basement and structural framework

Earth tremor is a small earthquake or seismic event that occurs in seismically unstable region. However there have been little information about the earth tremor before year 1987, but events between 1990 and 2000 have triggered further researches. This research work is aimed at qualitatively and quantitatively interpret high resolution aeromagnetic data of Saki-East area to provide basement and structural framework of the study area. The aeromagnetic data of the study area consisting of Igboho data sheet 200 and Lechilaku sheet 221 were processed using Oasis Montaj software and interpreted for mapping basement and structural stability in the area. Enhancement process was further carried out on the data to generate residual aeromagnetic data used in determining the lineament orientations in the study area. 3D Euler deconvolution and Source Parameter Imaging (SPI) techniques were implored to determine basement depth of subsurface geological structures. The result shows positive correlation with geologic structures, low magnetic anomalies revealed subsurface deformation of crystalline basement rocks. 3D Euler solutions for SI = 1 shows large clusters depicting geological bodies associating with faults. The magnetic basement depth from 3D Euler and SPI shows over 90% dominance of shallow depth range of 3-600 m in the study area, this revealed that the dominant shallow depth of magnetic basement causes the faulting system of the study area becoming weak zones through which tremor occurs. The lineaments in the study areas are classified into major and minor lineaments, the major lineaments are prominent within the basement rocks and are possibly produced by the regional historic orogenic movement that affected Nigeria basement.

Enhanced creep lifetime in P91 steel weldments via stabilizing tempered martensite structure

P91 steel weldments are susceptible to Type IV creep cracking during high-temperature service, significantly reducing the creep lifetime of impacted components. For enhancing the creep lifetime of P91 steel weldments, the present work proposes a novel post-weld heat treatment strategy to stabilize the tempered martensite structure and avoid Type IV creep cracking. Compared to conventional post-weld tempered treatment weldments, the creep lifetime of as-welded weldment is improved by 1.7 times, while the creep lifetime of weldment subjected to post-weld normalizing followed by tempering is enhanced by 4.6 times, effectively preventing Type IV cracking. It has been revealed that creep weakness zones, that is, soft zones, occur in as-welded weldment and post-welded tempering treatment weldment, where the microstructure is predominantly recrystallized ferrites. Creep fracture always occurs in the region of the highest fraction of recrystallized grains. Post-weld normalizing and subsequent tempering can enhance prior austenite grain size and stabilize tempered martensite structure. For as-welded weldment and post-welded tempering treatment weldment, creep cavities preferentially grow along ferrite grain boundaries as compared to prior austenite grain boundaries, which could easily lead to intergranular premature cracking. For post-weld normalizing and subsequent tempering weldment, cavities form along prior austenite grain boundaries of base metal and are elongated together with martensitic packets/blocks under stress. Finally, the final fracture is caused by the rupture of elongated grains.