Weak Zones Research Articles

Broad-band strain amplification in an asymmetric fault zone observed from borehole optical fiber and core

To unravel fault zone properties, high-resolution imaging and probing are pivotal. Here we present a comprehensive study utilizing Distributed Dynamic Strain Sensing of a 3D array of optical fiber with a surface-to-depth installation, traversing an active fault zone at depth, combined with a geological analysis of drilled cores. We identify an asymmetric fault zone with a narrow fault core, exhibiting a notable amplification in strain rate across a broad-band frequency range, which is attributed to the presence of weak gouge material within a much stronger host rock. This feature heightens responsiveness of the weak fault zone with low rigidity to ground motion, and intensifies strain from both nearby and remote seismic events. We demonstrate that optical fiber facilitates long-term monitoring of ground motion amplification with high spatial resolution, thus indicating where strain and deformation accumulate through repeating ruptures. This progress is pivotal to the understanding of the role of low rigidity and changes thereof within fault gouge material.

Mapping Fault Distribution Using Lineation and Fault Fracture Density Methods in the Palu Basin and Surrounding Areas

Introduction: Research has been carried out with the title "Mapping Fault Distribution Using Lineation and Fault Fracture Density Methods in the Palu Valley and Surrounding Areas" with the aim of determining the direction of fault distribution and analyzing fault density based on lineation data. Methods: This research uses the lineation method with a total of 40 grids. Data processing uses Global Mapper 18, rockwork 17, PCI Geomatica 2014, and Arcgis 10.8 software. Result and Discussion: The results obtained show that the lineation data from the dominant rose diagram has a relatively east-west direction. Areas that have high fault density are in Lindu District, Palolo District, Nokilalaki District, Gumbasa District, Dolo District, Sigi Biromaru District, and Mantikulore District with fault density values of 5,945 - 18,950/km2. Conclusion: The direction of lineation obtained tectonically is influenced by the Palu-Koro fault which tends relatively north-south, the Graben Palolo A and Graben Palolo B faults which trend relatively southeast-northwest, and the Lore Lindu fault zone. Areas with high density are weak zones that are vulnerable to natural disasters and potential ground movements.

Relating differential crustal architecture to passive margin evolution: A case study from the Colatina Fracture Zone (SE Brazil) using apatite fission‐track thermochronology

The Colatina Fracture Zone (CFZ) defines a distinct NNW–SSE‐oriented linear zone of fractures and brittle faults that represents an inherited weak zone in the current crustal structure of the (Pre)Cambrian Araçuaí Orogen. In the Early Cretaceous, the CFZ was reactivated during rifting of West Gondwana and subsequent opening of the South Atlantic Ocean, as evidenced by the emplacement of dykes along its structural network and the development of major depocentres of the Campos Basin in the offshore segments of the CFZ. Previous thermochronological studies have demonstrated that the CFZ was also rejuvenated during the drift phase of the South Atlantic. However, a number of questions regarding differential surface uplift and basement exhumation between the CFZ and its surrounding areas, such as the Doce River Valley (DRV), are still unresolved. In this study, we aim to investigate the CFZ as a distinctive structure in the tectonic rejuvenation of the passive margin of south‐east Brazil. Samples from the CFZ and the DRV were collected for apatite fission‐track (AFT) analyses. In the DRV, samples yield AFT central ages from 87 to 97 Ma with mean track lengths (MTL) from 12.6 to 13.3 μm. In contrast, in the CFZ, AFT central ages from 70 to 83 Ma with MTL values from 13.2 and 13.4 μm are obtained. The correlation between AFT age and elevation suggests that the tectonic development of these regions was markedly different and uncoupled. The thermal history models from the AFT data further constrain this differential evolution. On the one hand, thermal history modelling for the DRV indicates a slower and protracted cooling since the incipient Atlantic rifting in the Early Cretaceous. On the other hand, the models for CFZ reveal a rapid cooling phase between the Late Cretaceous to the Palaeocene. In the DRV, the observed basement cooling was most probably triggered by erosion of the uplifted rift shoulder generated by Gondwana break‐up. The more recent, Late Cretaceous–Palaeocene rock cooling, localized in the CFZ, was synchronous with a major phase of the Andean orogeny. This suggests that reactivations and erosional exhumation of the CFZ basement could be a consequence of far‐field propagation of intraplate compressional stress. The higher susceptibility of the CFZ to reactivating over its surroundings shows that structural inheritance is a key factor in the differential tectonic evolution of passive margins. Further research on the Late Cretaceous–Palaeocene reactivation in the CFZ's offshore extension may be crucial for the exploitation of hydrocarbons in the Campos and Espírito Santos basins.

Effect of the Connectivity of Weak Rock Zones on the Mining-Induced Deformation of Rock Slopes in an Open-Pit Mine

Geological structures significantly influence mining-induced deformations in open-pit mines, with their variations and interactions adding complexity to the excavation process and introducing uncertainties in deformation outcomes. This study utilized numerical simulations to analyze the impact of weak rock zones in a specific open-pit limestone quarry in Japan on mining-induced deformation. The simulation results were both qualitatively and quantitatively validated against field measurements, enhancing the reliability of the findings. Subsequently, four conceptual models were developed based on the characteristics of the quarry to investigate the mechanisms by which weak rock zones affect rock slope deformations. Our analyses demonstrated that slip deformation occurred exclusively when two weak rock zones were connected. This deformation was associated not only with shear failure in the upper weak rock zone but also with the contraction and bending of the lower weak rock zone. Furthermore, the simulation results were consistent with field data and supported by the conceptual models, confirming that the proposed sliding mechanisms can effectively explain the observed deformation behaviors. The insights gained from these models provide valuable references for managing similar geological challenges in other open-pit mines.

Integrating key ecosystem services to study the spatio-temporal dynamics and determinants of ecosystem health in Wuhan’s central urban area

The central areas of many Chinese cities have experienced large-scale urbanization in recent decades, a trend that is affecting the quality of life of residents and posing challenges to the sustainable development of urban ecosystems. Hence, it is vital to conduct assessments of urban ecosystems’ health conditions to ensure their sustainability. In this study, the spatial and temporal dynamics of ecosystem health in the central city of Wuhan were analyzed using the Vigor-Organization-Resilience-Service (VORS) model. The sensitivity of ecosystem health at different scales was also investigated using hierarchical health assessment delineation and random forest regression methods. The results showed that the composite index of ecosystem health has been declining since 2000, highlighting the negative impacts of shrinking ecological space, declining service capacity and urban expansion. Health zoning divides areas into five categories. Meanwhile, the health zones are located in areas of dense shrubs, cropland and water bodies on the edge of the central city, while the weak zones are mainly in the core of the city, which is 99.33 % impervious surface. The main factors influencing ecosystem health, including impervious surface area, water bodies and topography, vary from region to region. The study proposes targeted ecological management strategies for different health zones in Wuhan, emphasizing ecosystem protection and providing guidance for sustainable urban development.

Assessing foundation characteristics at the war dam site, lake tana basin, Ethiopia: A geophysical and geotechnical perspective

An integrated geophysical and geotechnical study evaluated the foundation conditions at the War dam site in northwest Ethiopia. This investigation included the classification of rock quality, shallow seismic refraction, and magnetic approaches. The dam's location comprises quaternary soil deposits and rhyolite rock units that have undergone varied weathering and fracturing. The shallow seismic refraction method distinguishes three layers of p-wave velocities that are less than 1.5 km per second with a depth range of 2–6 m, 1.5–2.5 km per second at a depth range of 15–20 m, and 2.5–3.5 km per second ranging from 20 to 40 m, respectively. Magnetic data were used to identify lineaments, and the RQD value acquired from boreholes ranged from extremely poor to excellent. Lineaments were recognized using the tilt angle approach. The results of the permeability tests demonstrated that the rock mass that serves as the dam's foundation had characteristics that are resistant to low permeability. The maximum and minimum lugeon values obtained from the testing were 9Lu and 0.81Lu, respectively. There are weak zones at and below the surface of the dam site, according to the overall findings acquired from seismic refraction, magnetic, and discontinuity surveying. These results were obtained from monitoring the dam site. These significant structures are directed towards a SW-NE, NE-SW, NNW-SSE, and SSW-NNE orientation. The study assessed the geological suitability of a proposed dam site using seismic refraction and magnetic survey methods. Significant geological variations were observed, particularly in the right abutment and valley floor, indicating the need for targeted grouting. The findings suggest that while the site is generally suitable for dam construction, specific areas require further ground improvement to ensure stability.

Geological and Hydrochemical Processes Driving Karst Development in Southeastern Riyadh, Central Saudi Arabia

This study investigates the processes leading to karst development in the southeastern part of Riyadh city extending up to Al Kharj. Numerous solution features such as sinkholes, collapsed dolines, and solution caverns are common in the area. The role of water in the development of the karst features was investigated using an integrated geological and hydrochemical approach. Geological investigations included the petrographic analysis of rock samples collected from zones of intense karstification with special emphasis on mineral dissolution. The study showed that the Sulaiy Formation is commonly fractured, brecciated, foliated, and contains numerous cavities, vugs, and openings. These features have formed by mineral dissolution by circulating groundwater, which has removed anhydrite beds from the underlying Arab–Hith sequence. Karstification likely started from the tectonically weak zones when there was more groundwater recharge. Studies show that during the early to mid-Holocene period, the climate in the Arabian Peninsula was humid, promoting groundwater recharge and subsequent mineral dissolution, though the process of karstification must have started much earlier. Hydrochemical findings reveal that mineral dissolution (halite and calcium sulfate) is the main process affecting groundwater chemistry. The Piper plot revealed two main hydrochemical facies: the (Ca2+ + Mg2+)–(Cl+ SO42−) Type (Type A) and the (Na+ + K+)–(SO42− + Cl) Type (Type B). Most of the samples belong to Type B, typical of groundwater facies affected by dissolution of halite and anhydrite mineral. The absence of the (Ca2+ + Mg2+)–(CO32− + HCO3−) type of groundwater facies indicates a lack of recent groundwater recharge and the removal of carbonate minerals from the system through precipitation, as evidenced by the saturation indices. Plots of the major ionic pairs (cations vs. anions) in groundwater indicate strong halite and gypsum/anhydrite dissolution. Of the three carbonate minerals, calcite has the highest average saturation index followed by aragonite and dolomite. This suggests significant past rock–water interaction leading to carbonate dissolution. Presently, any additional calcium or carbonate ions introduced into the water lead to calcite precipitation. The study indicates that the process of karst development may not be active today. Currently, groundwater chemistry is mainly influenced by rock–water interaction leading to gypsum/anhydrite dissolution, which has resulted in a high concentration of Na+, Ca2+, Cl− and SO42− ions in groundwater. The dissolution of gypsum and halite from the Hith Formation weakens the structural integrity of the overlying Sulaiy Formation, creating large underground cavities. These cavities increase the risk of roof collapse, leading to cover-collapse sinkholes as the roof becomes too thin to support the weight above.

Quartz texture and the chemical composition fingerprint of ore-forming fluid evolution at the Bilihe porphyry Au deposit, NE China

Abstract Quartz is widely distributed in various magmatic-hydrothermal systems and shows variable textures and trace element contents in multiple generations, enabling quartz to serve as a robust tracer for monitoring hydrothermal fluid evolution. This study demonstrates that integrated high-resolution SEM-CL textures and trace element data of quartz can be used to constrain physicochemical fluid conditions and trace the genesis of quartz in porphyry ore-forming systems. The Bilihe deposit is a gold-only porphyry deposit located in the Central Asian orogenic belt, NE China. Four quartz generations were distinguished following a temporal sequence from early-stage dendritic quartz, unidirectional solidification textured quartz (UST quartz), gray banded vein quartz (BQ), to late-stage white calcite vein quartz (CQ), with the Au precipitation being mostly related to dendritic quartz, UST quartz, and BQ. The well-preserved dendritic quartz with sector-zoned CL intensities and euhedral oscillatory growth zones crystallized rapidly during the late magmatic stage. The relatively low Al contents of dendritic quartz were interpreted to be related to contemporaneous feldspar or mica crystallization, while the high-Ti contents indicate high-crystallization temperatures (~750 °C). The comb-layered UST quartz displays heterogeneous, patchy luminescence with weak zoning, hosts coeval melt and fluid inclusions, and retains the chemical characteristics of magmatic dendritic quartz. High-Ti and low-Al contents of UST quartz suggest a formation at relatively high temperatures (~700 °C) and high-pH conditions. Three sub-types can be defined for hydrothermal BQ (BQ1, BQ2, and BQ3) based on contrasting CL features and trace element contents. The Al contents increase from BQ1 to BQ2 followed by a drop in BQ3, corresponding to an initial decrease and subsequent increase in fluid acidity. Temperature estimates of BQ decrease from BQ1 (635 °C) to BQ3 (575 °C), which may, however, be disturbed by high growth rates and/or high-TiO2 activities. The CQ typically displays a CL-bright core and CL-dark rim with oscillating CL intensities and is characterized by the lowest Ti and highest Al, Li, and Sb contents compared to the other quartz types, which suggests a deposition from more acidic and lower temperature fluids (~250 °C). Trace element patterns indicate that a coupled Si4+ ↔ (Al3+) + (K+) element exchange vector is applicable to dendritic quartz, UST quartz, and BQ. By contrast, charge-compensated cation substitution of Si4+ ↔ (Al3+, Sb3+) + (Li+, Rb+) is favored for CQ. The comparison with compiled trace element data of quartz from other porphyry Au, Cu, and Mo deposits worldwide suggests that Ti, Al, Li, K, and Ge concentrations, as well as Al/Ti and Ge/Ti ratios, have the potential to discriminate the metal fertility of porphyry mineralization.

An Attempt to Delineate Subsurface Ain Aldawar Cavity Using 2D Electrical Resistivity Imaging Method in Haditha Area, Western Iraq

The current study used 2D resistivity imaging to identify a shallow subsurface cavity in Haditha, western Iraq. The cavities and voids near the surface restrict land use and create a variety of geotechnical hazards, such as land subsidence, infrastructure damage, and structural cracks. As a result, the presence of an underground weak zone is a major concern for engineers before beginning any development, given the risk of future disasters. The four 2D resistivity traverses in this study were carried out using a dipole-dipole array with a - spacing of 3 m and an n-factor of 6. The data was inverted using RES2DINV software, which employs robust inversion methods. The 2D inverse model reveals a shallow cavity ranging from 5 to 12 meters and a width of around 40 m.

Investigation on uneven flow distribution in triply periodic minimal surface heat exchangers

The development in manufacturing engineering has made it possible to adopt the unique porous structure known as the triply periodic minimal surface to increase energy efficiency in a variety of energy-related sectors. With the unique morphological characteristics, triply periodic minimal surface exhibits remarkable mechanical strength and thermal performance, which makes it a potential candidate for compact, high-performance heat exchanger constructions. In this study, a theoretical model based on triply periodic minimal surface porous media is developed. Based on the hypothesis that the triply periodic minimal surface is isotropic and the heat transfer intensity of fluid and solid is uniform throughout the core of the heat exchanger, the simulation of the full-size heat exchanger is simplified by using a porous media model. The flow distribution characteristics of triply periodic minimal surface heat exchangers, as well as the effect mechanism of key factors, including the channel porosity, header configuration, the type of triply periodic minimal surface, the core length and Reynolds number on the flow distribution performance, are investigated. A dual-header configuration is proposed to improve the flow uniformity of triply periodic minimal surface heat exchangers. The results indicate that the flow distribution performance of triply periodic minimal surface based heat exchangers can be enhanced by the reduction of channel porosity. When the cold-side porosity is 0.7, the flow rate deviates from the mean value by 220% at its maximum for a Primitive heat exchanger. A dual-header configuration eliminates the columnar extreme high velocity space in the core and greatly reduces the “weak zone” of flow distribution, which improves the flow non-uniformity by 45–90% over the single-inlet headers. This paper provides data and theoretical support for the optimal design and practical application of the complex, high-performance triply periodic minimal surface based heat exchangers.

A novel cement-based interface functional material for application onto shotcrete-rock interface of tunnel in cold regions

In cold regions, the “natural weak zone”+“frost heave cracking” problems at the interface between shotcrete and rock will superimpose damage to the shotcrete-surrounding rock support system structure. However, there is no direct and effective technique to improve the bond strength and frost resistance of shotcrete for infrastructure such as tunnels in cold regions. Based on this, this study innovatively proposes the pretreatment technology of the interface between shotcrete and surrounding rock in tunnels in cold regions, and tries to investigate the fracture evolution of the binary and the distribution characteristics of the interface transition zone (ITZ) in cold regions under the action of interface functional material (IFM) by relying on the techniques of mechanical strength test, morphology analysis, and microstructure test. The study showed that: (1) the optimal mix ratio of IFM was designed as cement (10)+water (4)+calcium acrylate(1.5 %)+bamboo liquefied binder (4 %)+acrylate laminating adhesive (8 %)+ICA (2 %). At room temperature, the shear strength of the binary sample pretreated with the IFM was elevated by 1.56 MPa compared with that of the normal sample, and this increase could be raised to 1.64 MPa under freeze-thaw cycles (FTC). (2) As the freeze-thaw effect intensifies, the number of sandstone particles adhering to the failure surface of the binary increases correspondingly, and the morphology of the failure surface also becomes more undulating. This is due to the fact that after a certain FTC, more cracks are deflected towards the sandstone side due to the higher degradation of the sandstone compared to the ITZ. (3) Under FTC, the application of IFM will lead to an increase in the proportion of sandstone adhering to the failure surface and the fractal dimension of the failure surface, and this phenomenon becomes more pronounced with the intensification of FTC. (4) In the ITZ space, the hydration products and pore structure of the area closer to the sandstone are worse, the use of IFM can optimize this phenomenon. The new idea of utilizing the surrounding rock surface pretreatment technology to improve the bond strength and frost resistance of shotcrete proposed in this study has good application prospects in the construction of tunnels and other infrastructures in cold regions.

Experimental study on dynamic deformation and breaking mechanism of high-temperature hard rock cutting by abrasive water jet

The development of deep geothermal resources encounters challenges related to high temperatures and hard reservoir rocks. Abrasive water jets (AWJ) offer a potential solution to enhance the efficiency of breaking high-temperature hard rocks in deep ground. This mainly originated from their combined characteristics of jet cooling impact and high-speed abrasive grinding. In order to investigate the dynamic deformation process and rock-breaking mechanism of high-temperature hard rocks cut by AWJ, laboratory tests were conducted on high-pressure abrasive water jets cutting granite, sandstone, and marble. Rock strains were monitored using dynamic strain gauges and the digital image correlation (DIC) technique. The results indicate that in the process of abrasive jet cutting high-temperature hard rock, the rock strain is divided into three stages: compression deformation, deformation release, and stable deformation. The strain response zone can be divided into strain concentration zone, strain transition zone, and strain weak response zone. The high strain region and heat exchange region of high-temperature hard rock during AWJ cutting process are almost consistent. Jet vaporization weakens the water cushion effect during the water hammer stage, leading to high strain concentration at the stagnation point of the jet. During the stagnation stage, the fluid weakens the binding of particles, the abrasive becomes more divergent, and the range of high strain response region expands. Unlike the dynamic strain generated by jet erosion of hard rock, when jet cutting rocks, the strain in the vertical jet direction is generally greater than that along the jet direction. The cutting effect increases with the increase of rock temperature. When the rock temperature is 300 °C, the cutting depth of sandstone, granite, and marble increases by 50 %, 120 %, and 180 %, respectively. Under the combined effects of high-frequency jet impact, high-speed abrasive grinding, and thermal stress, hard rock undergoes varying degrees of damage and failure.

Investigation on uncoordinated deformation and failure mechanism and damage modeling of rock mass with weak interlayer zone

The weak interlayer zone (WIZ) is a high-risk geotechnical system with poor mechanical properties, strong ductility, loose structure, and wide distribution. To comprehensively investigate the uncoordinated deformation characteristics and failure mechanism of rock mass with WIZ, a series of uniaxial loading tests using digital image correlation (DIC) technique, and numerical simulation tests were carried out. Besides, the damage constitutive model of rock mass with WIZ was established, then the damage evolution law was also analyzed. Results show that a high strain localized zone appears in the WIZ from the beginning of loading, which then develops towards the contact surface between the WIZ and the rock mass. As loading proceeds, the WIZ exhibits layered spalling and ultimately forms through-cracks after the initiation of micro-cracks, and vertical tensile cracks to appear in the rock. causing vertical tensile cracks to appear in the rock. With the increase of the WIZ thickness and dip angle, the uniaxial compressive strength and deformation modulus of specimen show a negative exponential decay. When rock mass with WIZ collapse, the bonding of WIZ particles fails and the number of tensile-shear cracks gradually increases, eventually resulting in the plastic squeezing-out of WIZ. Moreover, the particles of the rock masses with smaller WIZ dip angles are mainly displaced vertically, and the failure is mainly caused by tensile splitting. The significant lateral displacement of particles in the rock mass with larger WIZ dip angles leads to the destruction of the rock mass mainly through shear slip, in particular a pronounced sliding down along the WIZ. Furthermore, the damage constitutive model of the rock mass with WIZ was established by distinguishing the total damage of the rock mass with WIZ into the damage of the WIZ and the damage of the rock mass. The model prediction results show that the total damage D increases with the increase of WIZ thickness and dip angle, and develops faster in the early stage and slower in the later stage. The research can provide effective basis and feasible ideas for the uncoordinated deformation and failure evolution, macro–micro failure mechanism, as well as the constitutive model of rock mass with WIZ in underground cavern under high geostress.

Multi-stage incentive contract design of aviation complex product multi-task delivery strategy

The increasing demand for aviation complex products makes complex product manufacturers pay more attention to delivery efficiency, and the efficiency and effect of delivery problems are the key factors that restrict delivery efficiency. A series of delivery strategy combinations of delivery subjects will affect delivery output and delivery efficiency. This study aims to design a long-term effective incentive contract, which stimulates the subjective initiative of the subject and then investigates the effect of the incentive contract on delivery efficiency under different combinations of delivery strategies. We consider the behavioral characteristics of each technical business department to expand the benchmark incentive model, such as the degree of perceived revenue fairness, the variation of the three relationships (neutrality, competition, and cooperation), and the level of technological transformation capability. The multi-stage incentive mechanism which combines explicit incentives and implicit incentives is developed to explore the optimal delivery strategies based on a benchmark model. The results show that incentive contracts can improve delivery efficiency and benefit delivery centers and technical business departments. The delivery decisions of the department are influenced by the closeness of department relationships and the fairness of assignment, and the departments tend to pay more effort in tasks with high relative importance and low effort cost. When the relative importance of tasks is equal to the ratio of marginal cost, a weak incentive zone in the delivery incentive contract exists. The incentive effect of reputation effect is obvious except for the last stage. Based on the designed incentive contracts, the subjective initiative of the participants can be effectively stimulated to empower complex product delivery.

Integrated Analysis by Geophysical and Spatial Data to Identify the Formation of Kepuhlegundi Hot Spring on Bawean Island

Bawean Island is a~result of volcanic activity in the back-arc volcanism zone located on the north side of Java Island. Bawean Island was formed due to the geological structure being controlled by the Paleogene-Neogene tectonic line in the Meratus Pattern. The mantle tearing resulted in the formation of the Bawean Arc. The Kepuhlegundi Hot Spring is a~component of the volcanism product on Bawean Island. To analyze the formation of hot springs in more detail, we conducted magnetic method measurements and integrated the data with gravity satellite and Fault Fracture Density (FFD) methods. The three methods were used to determine the continuity of the mapped geological structures surrounding the hot springs. The FFD method can be used to map the weak zone of the hot spring, which is caused by the lineament surrounding it. The magnetic and gravity methods reveal anomalous contrasts that extend towards the hot springs in the direction of the structure. The magnetic and gravity methods reveal anomalous contrasts that extend towards the hot springs in the direction of the structure. Based on regional anomaly analysis, spectrum analysis indicates that the structure is located at a~shallow depth of 15 to 80 meters. The drawing in each method shows a~dominant orientation in the Northeast-Southwest direction, which corresponds to the orientation of the Meratus Structure Pattern. Kepuhlegundi Hot Spring is formed due to the control of geological structures, allowing hot fluids to flow through fractures as an aquifer.

Database of tall pre-Northridge steel moment frames for earthquake performance evaluations

This article describes a detailed database of tall steel moment frame buildings that are representative of the construction practices in San Francisco prior to the 1994 Northridge earthquake. The database contains design details that affect the structural performance of steel moment frames, including frame geometry, member cross-section sizes, and gravity system characteristics. This database also captures irregularities that might impact seismic response, such as podiums, setbacks, mass concentrations (mechanical, electrical, and plumbing (MEP) floors), interrupted column lines, and atriums. The database includes information on 89 moment frame buildings, 14 of which were built before 1960 and are constructed with riveted connections, while the remaining 75 have welded flange connections like those that suffered brittle fracture during the 1994 Northridge earthquake. The buildings are further distinguished between space frame, perimeter frame, and partial space frame systems. For about half (41/89) of the buildings in the database, section sizes of representative structural members were collected, which enabled the evaluation of the seismic design, elastic, and inelastic response using computational workflows. The design diagnostics indicate that most of the buildings meet the minimum seismic strength and strong-column weak-beam requirements of modern building codes, even though they were not necessarily designed with this intent. On the contrary, about one-third of the buildings do not meet the seismic design drift limit of current codes, and about half of them have weak beam-column panel zones. This database, associated structural analysis models, and processing scripts are published at DesignSafe https://doi.org/10.17603/ds2-wjad-r340 to facilitate collaboration and continued development of open-source data for high-resolution simulations to inform risk mitigation strategies on a regional scale.

Stress evolution of fault-and-thrust belts in 2D numerical mechanical models

We employed numerical models to examine the dynamics of fold-and-thrust belts (FTBs), particularly focusing on the spatial and temporal interplay between stress variations and fault development. Our study explores the effects of variables such as layer thickness, basal friction, and surface diffusivity on the FTBs’ structural development, emphasizing the conditions under which frontal thrusts form. We found that fault activities within FTBs exhibit a cyclic behavior characterized by phases of initiation, quiescence, and reactivation. For over 95% of the total cycle duration, the frontal thrusts are the only active structures, and the stress within the FTB predominantly remains in a critical state. During the remaining 5%, the stress becomes over-critical, leading to the formation of a proto-thrust zone and the reactivation of pre-existing thrusts within the FTB. The lateral growth rate of FTBs is directly related to the thickness of the deforming layer, with the progression of the deformation front maintaining a steady pace across the study period. Additionally, our analysis on the progression of FTBs highlights the critical role of zonal failure spacing in determining the structural styles within FTBs. Our results indicate that narrowly spaced zonal failures, which promote the emergence of low-angle forethrusts, are more likely to occur at increased distances from the backstop. This explains the sequential frontal failure in the FTB; however, the stress accumulating at the rear weak zones also play an important role in the evolutionary patterns of the FTB. Our study offers new insights into the complex processes governing the mountain formation.

Study on Excavation Stability of Loess Tunnel in Geological Weak Areas Exploring Excavation Stability of Loess Tunnels in Geologically Vulnerable Regions

As western development progresses, extensive infrastructure construction can be conducted in the Loess Region. During infrastructure construction, particularly in tunnel excavation, traversing through extensive loess formations poses a significant challenge. It is imperative to ensure the stability and integrity of the tunnel while crossing weak geological zones in loess regions. This issue should be comprehensively addressed during tunnel construction. Geological and numerical analyses were employed to analyze the impact of weak geological areas on loess tunnel excavation. These analyses focused on the mechanisms of weak geology and assessed the efficacy of advanced support measures in loess tunnel construction, specifically addressing the issues encountered within weak geological zones during the construction process. First, we examined the formation mechanism of weak geological zones in loess, which is primarily attributed to water infiltration. Subsequently, based on this formation mechanism, a finite difference numerical analysis was utilized to investigate the potential failure modes of loess tunnels passing through weak geological zones. The destruction of the tunnel in the weak geological zone resulted from sliding erosion of the surface soil, leading to the complete collapse of the soil above the tunnel. During tunneling through weak geological zones, The soil in front of the excavation initially exhibited instability, causing the overall subsidence of the entire weak band, with the formation of a trap on the surface. Finally, the effectiveness of treatment measures was assessed according to the failure pattern of the loess tunnel in the weak geological zone. The analysis results indicated that with the implementation of appropriate advanced reinforcement measures, successful crossing can be achieved during the construction of a loess tunnel traversing the weak geological zone.

Configuration of Carbonatite Constrained in Preintrusion Transpositional Foliation in the Bayan Obo Giant Rare Earth Element Deposit, China

Abstract The Bayan Obo ore deposit is the largest rare earth element (REE) deposit in the world and has been assumed to be hosted in dolomite that was folded in a syncline. This has been challenged by results from drill holes and low-resistivity, controlled-source audio-frequency magnetotellurics (CSAMT) survey. In this paper, we present structural analysis of clastic sedimentary rocks from around the deposit, their relationship with carbonatite, and the orientations of the carbonatite bodies and dikes to constrain the possible configuration of carbonatite. Clastic sedimentary rocks underwent mylonitic deformation to slate, metasandstone, and metaconglomerate, displaying dramatic changes of thickness along strike. Slates locally preserve intrafolial folds and hook folds bounded by foliations; metasandstones have parallel layers of recrystallized and preferred-orientated quartz aggregations; metaconglomerates contain flattened pebbles with Flinn k values of 0.01 to 0.05 and 0. The above structures and foliations were crosscut and intruded by carbonatite and associated fenite, demonstrating preintrusion transposition of original bedding to steep foliation. Preintrusion foliation provides zones of weakness that were exploited by upwelling of carbonatite magma. Northeast-SW–striking left-stepping en echelon carbonatite dikes and E-W–striking carbonatite bodies indicate that the carbonatite was emplaced in a sinistral transtensional zone. The northern and southern segments of the carbonatite bodies are parallel to the steep foliation at shallow depths and merge together at depth, constraining a Y-shaped configuration, consistent with the low resistivity result of the CSAMT survey. The newly recognized Y-shaped morphology indicates that the carbonatite extends deeper than 1,775.4 m, more than twice the previously inferred maximum depth of the syncline model, and contributes to a significant >1.78 times increase in global potential RE2O3 resources than previously estimated in 2021.

Structural Evolution, Exhumation Rates, and Rheology of the European Crust During Alpine Collision: Constraints From the Rotondo Granite—Gotthard Nappe

AbstractThe rheology of crystalline units controls the large‐scale deformation geometry and dynamics of collisional orogens. Defining a time‐constrained rheological evolution of such units may help unravel the details of collisional dynamics. Here, we integrate field analysis, pseudosection calculations and in situ garnet U–Pb and mica Rb–Sr geochronology to define the structural and rheological evolution of the Rotondo granite (Gotthard nappe, Central Alps). We identify a sequence of four (D1–D4) deformation stages. Pre‐collisional D1 brittle faults developed before Alpine peak metamorphism, which occurred at 34–20 Ma (U–Pb garnet ages) at 590 ± 25°C and 0.9 ± 0.1 GPa. The reactivation of D1 structures controlled the rheological evolution, from D2 reverse mylonitic shearing at amphibolite facies (520 ± 40°C and 0.8 ± 0.1 GPa) at 18–20 Ma (white mica Rb–Sr ages), to strike‐slip, brittle‐ductile shearing at greenschist‐facies D3 (395 ± 25°C and 0.4 ± 0.1 GPa) at 14–15 Ma (white mica and biotite Rb–Sr ages), and then to D4 strike‐slip faulting at shallow conditions. Although highly misoriented for the Alpine collisional stress orientation, D1 brittle structures controlled the localization of D2 ductile mylonites accommodating fast (∼3 mm/yr) exhumation rates due to their weak shear strength (<10 MPa). This structural and rheological evolution is common across External Crystalline Massifs (e.g., Aar, Mont Blanc), suggesting that the European upper crust was extremely weak during Alpine collision, its strength controlled by weak ductile shear zones localized on pre‐collisional deformation structures, that in turn controlled localized exhumation at the scale of the orogen.