Active Fault Zones Research Articles

Identification of the active faults and seismotectonic zonation of Laos territory

In this study, the main active faults in the territory of Laos were identified by analyzing the spatial relationship between the distributions of neo-tectonic faults and earthquake epicenters. The map of neo-tectonic faults was built by integrating the results of neo-tectonic faults research using geological-geomorphological data together with the lineament map obtained from remote sensing analysis. Nontectonic lineaments were eliminated by correlating the spatial distribution of the lineament field with a topographic map, DEM, and geological-geomorphological data. The earthquake data, including 4416 events in Laos and its surroundings, were collected from different sources: the International Seismological Center (ISC), the earthquakes recorded by the local seismic network in Laos, the seismic data in Vietnam, and the earthquake catalog provided by the Thailand Meteorological Department (TMD). Among these, 820 events were located using the hypocenter method, and the local network recorded the data. The magnitude conversion was applied to get a unified scale Mw. The catalog of 1617 main shocks obtained after eliminating foreshocks and aftershocks using the declustering technique was used for a spatial correlation with the neotectonic fault distribution to identify active faults. A total of 14 main active fault zones in the Laos territory were defined. Most are also seismogenic faults with Mw ≥ 5.0 occurring along their trace. Considering the characteristics of seismic activity and the active and neotectonic faults, the territory of Laos can be divided into six seismotectonic zones according to the decreasing level of seismic activity: the Western, the Northeastern Samnua, the Phongsali, the South Truong Son, the North Truong Son, and the Khorat zones. Each zone is characterized by relative homogeneity in the seismic activity and the characteristics of active and neotectonic faults.

Failure of Daliang tunnel induced by active stick–slip fault

In earthquake-prone areas, mountain tunnels often suffer from seismic damage when traversing active fault zones. To capture the seismic behavior of mountain tunnel under the action of active faults motion, the rate and state friction (RSF) relation is introduced to define the stick–slip dynamic behavior of a fault. The RSF relation is implemented in the finite element methods (FEMs). Numerical simulations of triaxial patch tests indicate that the RSF method can effectively capture the stick–slip dynamics. To reproduce the seismic damage to Daliang tunnel caused by slip of the Lenglongling fault, a three-dimensional (3D) numerical model including tunnel structure and plates of the fault is established. Seismic waves triggered by fault slip are then reproduced using the model. The simulation results show that the waves are dissipated while travelling and that their amplitudes decrease with depth. The failure of the tunnel lining is captured, and its seismic responses, including the displacement and strain of the structure, are extracted for various fault strike angles. The simulations are consistent with the observations, and it indicates that the movement of the simulated tunnel structure adjacent to the fault surface is significantly greater than those in the foot wall and in the middle of the fault. This study has the potential to provide a more direct means of understanding the seismic action of infrastructure induced by earthquakes. Seismic waves are no longer needed as input to the numerical simulation and instead, the earthquakes are generated by directly modeling the stick–slip motion of the fault.

The Chaochou active fault in southern Taiwan: Characteristics and geomorphological significance as a reverse fault

The Chaochou Fault in southern Taiwan has long been recognized as an active fault, but its exact location is still uncertain. In this study, we focused on the middle part of the Chaochou Fault, where a flight of fluvial terraces was deformed and preserved. High-resolution aerial photos were first used to observe and map these terraces and their vicinity, followed by comprehensive field investigations including RTK-GPS surveys for high-resolution topographic profiles of the deformed terraces and OSL sample collections for obtaining the ages of the terraces. A series of active faults, consisting of Fault A (“FA”), Fault B (“FB”), and Fault Bb (“FBb”), are collectively named the Chaochou Active Fault Zone. The fault zone is recognized and characterized by range-facing scarps, frontal flexural scarps, and discontinuous slopes deformed by FA, FB, and FBb, respectively. The repeated activities of FA were recorded by the incremental fault scarp heights from young to old terraces. Considering the highest fault scarp height of 65.9 ± 6 m observed in T1 and its OSL age of 35.3 ± 4.3 ka, the long-term fault slip rate of FA is about 2 mm/yr.

Research on the Deformation Mechanism of Railway Subgrade under Buried Strike–Slip Fault Dislocation

With the gradual densification of China’s railway network, more and more railways are inevitably crossing active fault zones. Creep dislocation and stick–slip dislocation of the fault zones can lead to uneven deformation and cracks in the railway subgrade, threatening the sustainability of the railway. Therefore, a model test and numerical simulation were used to analyze the deformation mechanism and sustainability of the subgrade and foundation induced by a strike–slip fault dislocation in a flat site under different angles between the subgrade and fault strikes. The test and simulation results show that (1) under the influence of strike–slip fault dislocation, the horizontal direction of the subgrade appeared to have an S–shaped displacement. The top surface of the subgrade appeared to have a vertical settlement. Further, tension–shear cracks and compression crush zones appeared on the subgrade’s surface. (2) When the angle between the fault and subgrade strikes increased, the subgrade’s uneven deformations induced by fault dislocation first decreased and then increased. The angle between the main tension–shear crack on the top surface of the subgrade and the fault strike showed a trend of increasing and then decreasing. In addition, the compressive stress along the subgrade strike decreased, while the tensile stress along the subgrade strike gradually increased. (3) The tension–shear cracks in the subgrade and foundation were spiral and converged to the basement strike–slip fault along the depth direction. This study provides a reference for the safe operation and sustainability of railways near faults.

Formation mechanism of loess-mudstone landslides in the Weibei Tableland Fault Active Zone of Baoji, China - Taking Wolongsi landslide as an example

The geomorphologic and environmental evolution of the Loess Plateau is greatly affected by the strong fault activity, leading to the frequent occurrence of geological hazards, particularly the loess-mudstone landslide (LML). Thus, it is crucial to investigate the formation mechanism of such landslides in active fault zones. In this study, a field survey was conducted in the Weibei tableland of Baoji where the active fault zone is developed. To study the creep behavior of LML sliding zone soil, the triaxial creep tests of multi-stage loading under different water content, confining pressure, dry density, loess-mudstone binary structure (LMBS) contact surface angle, and thickness were carried out using the sliding zone soil samples (loess, mudstone, and LMBS samples) obtained from Wolongsi landslide in the study area as an example. Experimental results revealed that: (1) Water content has a significant weakening effect on the strength of LML sliding zone soil. The strength of the LMBS sample is extremely water-sensitive. The weakening effect of water on the long-term strength of LML sliding zone soil mainly manifested in promoting the elastoplastic deformation of loess and the viscoplastic deformation of mudstone. (2) The long-term strength of the LML slip zone soil increases linearly with the increase in confining pressure and increases exponentially with the dry density. (3) The degrading effect of the stratigraphic interface dip angle on the long-term slope strength is mainly reflected in the change in the weakening degree of water on the strength of the LML sliding zone. In addition, according to the test results, the traditional Nishihara model is improved by introducing nonlinear parameters, and a new constitutive equation describing LML sliding zone soil is established. The new constitutive model can accurately describe the creep curve's whole process especially sensitively identifying the accelerated creep stage. Finally, after conducting a field investigation and laboratory tests, the main hazard factors affecting the occurrence of the LML were analyzed in the presence of fault activity on the Weibei Plateau of Baoji, China, and its formation mechanism was revealed as well.

Anomaly Detection Using Machine Learning in Hydrochemical Data From Hot Springs: Implications for Earthquake Prediction

AbstractThis study explores the potential of machine learning algorithms for earthquake prediction, utilizing fluid chemical anomaly data from hot springs. Six hot springs, located within an active fault zone along the southeastern coast of China, were carefully chosen as hydrochemical monitoring sites for an extended period of two and a half years. Using this data, a prediction model integrating six algorithms was developed to forecast M ≥ 5 earthquakes in Taiwan. The model's performance was validated against recorded earthquake events, and the factors influencing its predictive capability were analyzed. Our comprehensive analysis conclusively demonstrates the superiority of machine learning algorithms over traditional statistical methods for earthquake prediction. Additionally, including sampling time in the data sets significantly improves the model's predictive performance. However, it is important to note that the model's predictive performance varies across different hot spring and indicators type, highlighting the importance of identifying optimal indicators for specific scenarios. The model parameters, including the anomaly detection rate (P) and earthquake response time threshold (M), significantly impact the model's predictive capabilities. Therefore, adjustments are needed to optimize the model's performance for practical use. Despite limitations such as the inability to differentiate pre‐earthquake anomalies from post‐earthquake anomalies and pinpoint the precise location of earthquakes, this study successfully showcases the potential of machine learning algorithms in earthquake prediction, paving the way for further research and improved prediction methods.

Dynamic Stability Analysis of Subsea Tunnel Crossing Active Fault Zone: A Case Study

The rock strength in an active fault zone is low and the surrounding rock is fractured and has poor stability, making any subsea tunnel crossing the active fault zone extremely susceptible to disasters such as tunnel collapse, sudden water ingress, and mud inrush. This poses a potential threat to the construction project, making the dynamic stability analysis of a subsea tunnel crossing an active fault zone of great significance. This study takes the second subsea tunnel crossing the Cangkou Fault in Jiaozhou Bay as the engineering background and conducts numerical simulations by employing different lining stiffnesses for tunnel excavation, as well as applying dynamic loads. The dynamic stability of the subsea tunnel crossing the active fault zone is evaluated by comparing and analyzing the lining’s displacement, peak acceleration, and stress characteristics. This study explores the disaster-causing mechanisms of active fractures, determining that the hazard of orthogonal misalignment in an active fault zone is the least severe, while the hazard of opposite misalignment is the most severe. This research provides a basis for disaster prevention and mitigation in active fracture zones.

Co-seismic deformation and related hazards associated with the 2022 Mw 5.6 Cianjur earthquake in West Java, Indonesia: insights from combined seismological analysis, DInSAR, and geomorphological investigations

IntroductionOn November 21, 2022, a magnitude Mw 5.6 earthquake struck Cianjur Regency in the West Java Province of Indonesia. It was followed by at least 512 aftershocks that persisted from November to June 2023. This seismic event occurred in an area previously unrecognized as an active fault zone. The consequences of this earthquake in Cianjur were severe, leading to both loss of life and extensive structural damage. The substantial damage to buildings was likely a result of abrupt alterations in the local topography due to surface deformation effects.ObjectivesThis research endeavor aims to spatially determine the patterns of ground surface deformation and its relationship with local geomorphological setting due to earthquakes in Cianjur in 2022.MethodsIn this study we conduct seismological analysis of 45 seismic stations, statistical analysis of mainshock and aftershocks data, RADAR Sentinel-1 imagery and employed the DInSAR methodology. Field survey was also conducted to determine the geomorphological characteristics in the study area.ResultsThe outcomes disclosed that the deformation encompassed both subsidence and uplift. The results signify that there was subsidence deformation in the vicinity of Cianjur and its environs during the primary earthquake on November 21, 2022, with an average deformation value of approximately -5 cm. In contrast, the measured deformation during the aftershocks exhibited uplift deformation, with an average value of 10 cm. The examination of deformation patterns amid the 2022 Cianjur earthquake sequence detects elevated deformation values in the vicinity of Cugenang district, with an orientation running from northwest to southeast. The geomorphological investigation conducted indicates that the region of Cianjur encompasses a variety of landforms, such as volcanic, structural, fluvial, and denudational. These landforms exhibit distinct responses to seismic activities. Co-seismic hazards, such as landslides frequently occur as a consequence of seismic events in mountainous terrain.Main ConclusionsSpatio-temporal variation of ground deformation could arise from various causes, such as the number and distribution of aftershocks, stress redistribution, fault interactions, secondary effects, and local geological settings. The mainshocks release accumulated stress along a fault, resulting in particular types of deformation, whereas aftershocks may redistribute stress exhibiting on adjacent faults. Secondary effects triggered by aftershocks, coupled with local geological and geomorphological conditions, further contribute to the diverse patterns of ground deformation observed during seismic events. The results of the study revealed that ground deformation had the greatest impact on fluvial, volcanic, and denudational processes, resulting in notable subsidence and uplift in specific regions. The occurrence and magnitude of co-seismic landslides were triggered by both mainshock and aftershock events, which occurred on weathered geological materials. These effects were further amplified by the simultaneous presence of the rainy season.ImplicationsThe knowledge gained from this research can be applied to evaluate the impacts of earthquakes and to proactively reduce future risks.

Analysis of Tsunami Characteristics of Korea Southern Coast Using a Hypothetical Scenario

Large-scale earthquakes are occurring globally, especially in the South Asian crust, which is experiencing a state of tension in the aftermath of the 2011 East Japan Earthquake. Uncertainty and fear regarding the possibility of further seismic activity in the near future have been on the rise in the region. The National Disaster Management Research Institute has previously studied and analyzed the overflow characteristics of a tsunami and the rate of flood forecasting through tsunami numerical simulations of the East Sea of South Korea. However, there is currently a significant lack of research on the Southern Coast tsunamis compared to the East Coast. On the Southern Coast, the tidal difference is between 1~4 m, and the impact of the tides is hard to ignore. Therefore, it is necessary to analyze the impact of the tide propagation characteristics on the tsunami. Occurrence regions that may cradle tsunamis that affect the southern coast region are the Ryukyu Island and Nankai Trough, which are active seafloor fault zones. The Southern Coast has not experienced direct damage from tsunamis before, but since the possibility is always present, further research is required to prepare precautionary measures in the face of a potential event. Therefore, this study numerically simulated a hypothetical tsunami scenario that could impact the southern coast of South Korea. In addition, the tidal wave propagation characteristics that emerge at the shore due to tide and tsunami interactions will be analyzed. This study will be used to prepare for tsunamis that might occur on the southern coast through tsunami hazard and risk analysis.

Estimation of road cut slope stability along the national and state highway of Garhwal Himalaya (India) applying slope mass rating and kinematic analysis

Slope stability assessment of different road cut slopes has been conducted along the National Highway in Garhwal Himalaya, Uttarakhand (NH-34, NH-134, NH-7, NH-107 and a state highway from Dharasu to Tilwara). Slope instability issues in the Himalayan terrain are radically increasing due to high anthropogenic activities and rapid growth of urban centers since past years. Road networks in mountainous areas are the main source of transportation and socio-economic development. In this concerned study, forty (40) road cut slopes have been selected. These sites are selected based on lithology and structure. Diverse slope stability quantification methods along with various modes of failures have been systematically analyzed. The entire region falls under the tectonically active belt or the vicinity of the active fault zones that make the slopes inherently unstable. The Geological Strength Index (GSI) and Rock Mass Rating (RMR) have been applied for determination of slope conditions. Slope mass stability has been evaluated using Slope Mass Rating (SMR) index. The RMR rating ranges from 26 to 87 and the SMR values of forty (40) roads cut slopes range from 10 to 91. The kinematic analysis shows that most of the probable slopes failures are susceptible under planar and wedge failure. This study will definitely help to reduce the loss of life and property and also helps the ongoing constructional processes along the road section.

Mechanical testing and engineering applicability analysis of SAP concrete used in buffer layer design for tunnels in active fault zones

Abstract To tackle the challenge of dislocation damage when tunnels traverse active fault zones, this study introduces the concept of using brittle buffer materials for anti-dislocation. Building on this concept, we propose a novel concrete buffer material utilizing large-sized spherical super absorbent polymers (SAP) as a porogen, aimed at ensuring the safety of tunnel structures during active fault dislocations. To investigate the feasibility and superiority of SAP concrete as a buffer material compared to other similar materials, we prepared samples with three different SAP concrete proportions and conducted a series of physical and mechanical tests. The results show that SAP pre-hydrated with 0.2 mol·L−1 sodium carbonate solution exhibits a slower rate of moisture loss in the cement slurry, aiding the hydration reaction of concrete. The permeability coefficient of SAP concrete is approximately 10−7 cm·s−1, slightly lower than foam concrete of the same density level. SAP concrete buffer material demonstrates significant brittleness, in contrast to the mostly ductile nature of other buffers such as foam concrete and rubberized concrete. Utilizing the brittle nature of SAP concrete materials, when applied to tunnels affected by stick–slip active fault dislocations, its instantaneous loss of compressive capacity provides excellent yield performance, thus protecting the tunnel lining from damage. However, under certain circumferential pressure conditions, both the peak and residual strength of SAP concrete significantly increase. High peak and residual strengths do not favor the effective buffering effect of SAP concrete; therefore, an approach involving the intermittent arrangement of precast buffer blocks has been proposed for application.

Spatial distribution of near-fault landslides along Litang fault zones, eastern Tibetan Plateau

Active fault zones are areas impacted by intense tectonic activity, where geohazards such as landslides occur and their distribution characteristics vary across segments. Using the Litang fault zone in the eastern Tibetan Plateau as an example, this study cataloged landslides within a 10 km range on both sides of the fault zone. The Litang fault zone was divided into four sections based on landform characteristics and the spatial distribution of active faults. A comprehensive analysis was conducted on the relationship between landslide distribution and topography, lithology, and active faults in different sections. Additionally, the study employed a random forest model to compare landslide susceptibility between the whole-region and its sub-regions. The results show that lithology and topography significantly influence the distribution of landslide types. The Upper Triassic sandstone, Slate exhibit more debris flows in areas with slopes ranging from 5° to 35°, while slopes >35° in the Upper Triassic sandstone, Slate are prone to unstable slopes. Rock avalanche occur in Upper Triassic sandstone, Slate, and Quaternary sand and gravel. Active faults play a key role in control ling landslides distribution through distance, hanging wall, locked segment, and direction effects. The number of landslides is positively correlated with the activity of faults. Additionally, the dip angle and motion characteristics of faults have significant influence on the distribution of landslides. The results of landslide susceptibility evaluation show that sub-region models have higher accuracy than the whole-region model. This study provides a new method for exploring the spatial distribution of landslides and can provide scientific reference for reducing landslide disasters in active fault zones.

Geochemical characteristics of hot springs in active fault zones within the northern Sichuan-Yunnan block: Geochemical evidence for tectonic activity

The geochemistry of the fluids is spatially closely related to faults and earthquakes that have been detected in the northern Sichuan-Yunnan (SC-YN) block. However, the processes and factors that control hydrothermal fluid circulation on a regional scale remain challenging. The geochemical circulation of the hot springs integrated with geological and geophysical data revealed the processes and controlling factors of the relationship between fluid circulation and tectonic activity. Our results showed that the hydrochemical type of the hot springs at the intersection of the Yushu-Ganzi fault (YS-GZF), Xianshuihe fault (XSHF) and Yunongxi fault (YNXF), Jinshajiang fault (JSJF) and Batang fault (BTF) as well as Ganzi-Litang fault (GZ-LTF) is composed of Na-HCO3 and Na-HCO3·Cl. It demonstrated higher reservoir temperature and circulation depth (5 − 7 km). The helium isotope (0.22 − 2.36 Ra) of the gas indicated that the mantle helium composition was up to 5 − 30 %. These hot springs may undergo water–rock-gas exchange reactions with deep fluids. Considering geological and geophysical background as well as previous studies, the geochemical characteristics of the hot spring at the intersections of faults in the north of the SC-YN block are thought to be controlled by the deep-driven upwelling lower crustal flows, mixing with shallow hot spring water and the temporal and spatial heterogeneity of the high strain fields, slip rates, and permeability of the fault intersections. Whereas, the transport of fluids in hot springs of fault may increase pore fluid pressure, and reduce the effective stress at the intersection of the fault zones, which can promote fault sliding and provoke seismic events as well as fault movements. It could result in the enhancement of regional tectonic activity. This study provides an important basis for seismic prediction with hot spring hydrochemistry stations.

Quantifying tidal versus non-tidal stresses in driving time-varying fluxes of Enceladus' plume eruptions

In this study we investigate the relative importance of endogenic vs. exogenic stresses in controlling the location and timing of active ice-shell deformation on Enceladus, which is expressed by cyclic plume eruptive flux along active fault zones (i.e., the tiger stripes). Although the variation of the eruption flux on Enceladus follows the periodicity of the diurnal tide, it remains unclear why there is a consistent phase delay of the observed peak eruption when compared to the predicted peak tidal stress. Here, we explore whether endogenic stresses in the ice shell are capable of explaining this observed phase delay. To achieve this goal, we performed geologic mapping along the tiger-stripe faults that host the erupting plumes. Using the fault kinematics established from our mapping, we determine the general stress state (i.e., the principal-stress directions) along the tiger-stripe faults. This knowledge in turn forms the basis for inferring the most likely plume-eruption mechanism. Our mapping shows that the tiger-stripe fractures are not tensile cracks but are instead left-slip fault zones locally displaying extensional fissures. This insight leads to a hypothesis that strike-slip faults and their local tensile cracks experience simultaneous shear and tensile failure, and that the tensional opening reaches maximum at the time of the peak plume flux. We quantified this hypothesis using a stress decomposition model that assesses (1) the relative importance in magnitude between the tectonic stress and tidal stress exerted on the tiger-stripe faults and (2) the role of ice shell properties such as the shear strengths, tensile strengths, and ice shell thickness in controlling the eruption phase delay. Using laboratory-determined ice strengths and the best estimate of the ice shell thickness at the South Polar Terrain of Enceladus, which hosts the tiger-stripe faults, our model results indicate that the endogenic tectonic stress is comparable in magnitude to the tidal stress. Although we cannot rule out warm-ice convection, true polar wander, and non-synchronous rotation as causes of endogenic stresses, the large variation in ice shell thickness makes the lateral gravitational-potential gradient the most plausible source of the endogenic stress required by our model results.

Stress disturbance around Xianshuihe fault zone in the eastern Qinghai–Tibet Plateau and implication for fault stability

The Xianshuihe fault zone in the eastern Qinghai–Tibetan Plateau is an important active tectonic boundary. Understanding its stress state is important for characterizing the dynamic evolution of the Qinghai–Tibet Plateau and the mechanism of the frequent occurrence of large earthquakes. Using 30 years of in-situ stress data from the Xianshuihe active fault zone, we statistically analyzed the spatial distribution characteristics of the stress in the region. The study area is generally characterized by a strike-slip stress field. Nevertheless, the stress state is vulnerable to topography and shows high spatial variation near the Earth’s surface at a depth of 0–400 m. The local stress near the fault zone varies from the far-field stress. The orientations of the maximum horizontal principal stress possess an elliptical shape around the fault zone, while its magnitudes become hump-like as the distance increases from the fault. The large difference in properties between the fault zone and its adjacent rocks contributes to the differentiation of the direction of the local stress field near the fault. The results allow us to formulate a preliminary hypothesis that a rigid lateral extrusion model may control the nonuniformity of the local stress field in the Xianshuihe fault zone and preferentially interpret the tectonic uplift of the southeastern margin of the Qinghai–Tibet Plateau. Further, the stress accumulation in the shallow crustal regions of the Xianshuihe fault zone is relatively high, indicating that some segments of the fault zone are critically unstable. Kangding area (the Zheduotang segment and the Yalahe segment) and Luhuo segment hold relatively high potential for large earthquakes. The results of this study are of great significance for revealing the mechanism of fault–stress field interactions and for understanding the dynamic evolution mechanism of the uplift of the Qinghai–Tibet Plateau.

Background earthquakes and aftershock sequences of the strongest intraplate earthquakes in Central Asia

Within the analyzed observation period (1971–2021), the values of the total magnitude of the scalar seismic moment obtained from the aftershocks of the strongest earthquakes (Мw ≥ 7.6) Asia (φ=20–50 N, λ=60–105° E), are weakly correlated with the total magnitude of the scalar seismic moment of background seismicity in the region of the main earthquake. A high level of seismic activity is manifested in the zones of large active faults and is reflected in the total magnitude of the scalar seismic moment of aftershock sequences. The types of movements in the foci of the main events do not affect the degree of aftershock activity (the total values of the scalar seismic moment) and occur at different background levels. Over the past 50 years, the magnitude of the strongest earthquakes has increased compared to the previous fifty-year period.

Measurements of 222Rn exhalation rates, effective 226Ra contents, and radiological risks from geological samples of Kopili Fault Zone and gneissic complex of Shillong Plateau, India

Abstract This report unveils the outcomes of measurements of 222Rn exhalation rates, effective 226Ra content, and the annual effective dose for rocks and soil collected in the vicinity and far from the seismically active Kopili Fault Zone, India. LR-115 (II) nuclear track detector has been used to investigate radiation exposure in the seismically active fault zone and gneissic complex of the Shillong Plateau, which have significant geological characteristics and frequently produce earthquakes. In this study, 222Rn mass exhalation rates for granite, gneiss, and soil samples collected near and far from the fault were calculated to be in the ranges of 73.2–83.0, 11.0–14.8, 21.1–70.7 and 34.3–65.5, 6.4–9.9, 19.1–28.9 mBq kg−1 h−1, respectively. Surface exhalation rates of 222Rn for granite, gneiss, and soil samples collected near and far from the fault varied between 2428.8–2751.7, 365.6–491.9, 698.3–2345.9, and 1138.6–2172.7, 211.9–328.2, 634.9–960.0 mBq m−2 h−1, respectively. The 226Ra contents of granite, gneiss, and soil collected in similar distributions were found to vary from 9.76–11.06, 1.47–1.98, 2.8–9.4, and 4.58–8.74, 0.85–1.32, 2.6–3.6 Bq kg−1, respectively. The annual effective doses attributed to 222Rn inhalation from exposure to the samples were calculated to be in the ranges of 176.3–199.8, 26.5–35.7, 50.7–170.3 and 82.7–157.7, 15.4–23.8, 46.1–69.7 μSv y−1, respectively, for granite, gneiss, and soil. The lifetime fatality-risks have also been analysed in this study. The samples that were collected in close proximity to the fault showed higher values than those that were collected farther away. However, the results reveal that the measured values are within the globally recognised permissible range.

A numerical investigation of the behavior of a tunnel with adaptive anti-dislocation measures subjected to the action of fault dislocation

In the context of long-distance cross-basin water transfer projects, the water conveyance tunnel serves as a pivotal component in mitigating regional disparities between economic development and water resources allocation. However, in high seismic-intensity areas of southwest China, geological complexities and densely distributed active faults present formidable challenges. Consequently, the construction of water conveyance tunnels necessitates traversing one or more active fault zones. This study examines the impact of an adaptive tunnel structure in the presence of fault dislocation, focusing on the Xianglushan Tunnel, a constituent of the Central Yunnan Water Diversion Project. Taking the Longpan-Qiaohou Fault F10-1 as a case study, we assess the influence of active faults on the anti-dislocation adaptive structure of the Xianglushan Tunnel, considering factors such as displacement, relative deformation, maximum principal stresses, and longitudinal equivalent internal force in critical tunnel sections. Numerical calculations validate the efficacy of this adaptive structure in reducing induced internal forces and deformations of the tunnel lining. The results show that, under the influence of strike-slip dominated fault movement, one side of the tunnel exhibits tensile stress, with a magnitude of approximately 5 MPa. The maximum normal and tangential deformation of the hinge joint is concentrated in the central section of the fault zone. The incorporation of an articulated adaptive design significantly enhances the stress state of lining under dislocation condition. These research results directly inform the engineering design and construction of water conveyance tunnels traversing active fault regions, providing valuable guidance for related tunnel construction endeavors.

Mechanical response of tunnels crossing active fault zones under normal or reverse faulting: A refined nonlinear analytical approximate solution

Tunnels crossing active fault zones will be severely damaged under normal or reverse faulting. The tunnel-stratum interaction is nonlinear, and the fault zone width significantly affects the tunnel response. Nevertheless, the existing analytical models neglect the effect of nonlinear tunnel-stratum interaction or fault zone width and adopt unrealistic assumptions. This work proposes a refined nonlinear solution, considering the nonlinear tunnel-stratum interaction and fault zone width, and some widely employed assumptions are removed. Specifically, a tunnel under normal or reverse faulting is simplified to an elastic beam acting on a nonlinear foundation, the nonlinear tunnel-stratum interaction is considered by setting a series of nonlinear axial and vertical springs, and the fault zone width is considered by reducing the spring stiffness. Additionally, the nonlinear axial force and geometrical nonlinearity terms are considered in the governing equations. The comparison results indicate that the results obtained from the proposed model agree well with those from model tests and numerical models and have a better accuracy than the existing analytical models. Finally, the effects of fault, stratum, and lining parameters on the response of tunnels crossing normal or reverse faults are discussed regarding stress distribution and failure scope.

A mechanical analysis model for tunnels under strike-slip faulting considering the fault zone width and nonlinear tunnel-stratum interaction

Tunnels crossing active fault zones are seriously damaged under the action of faulting. However, the influence of the fault zone width or nonlinear tunnel-stratum interaction is neglected in existing analytical models, resulting in incorrect estimation of the tunnel mechanical response. To aid in the seismic design of tunnels, a mechanical analysis model for tunnels under strike-slip faulting considering the effect of fault zone width and nonlinear tunnel-stratum interaction is first proposed in this work. The calculation results of the proposed model agree well with those obtained from the model test and numerical simulation, and the accuracy is obviously higher than that of the existing analytical methods. Compared with the FEM numerical model, the average errors of the peak bending moment, shear force and axial force calculated by the proposed model are 6.37 %, 11.00 % and 9.91 %, respectively. Neglecting the effect of fault zone width or nonlinear tunnel-stratum interaction, the tunnel response will be misestimated, e.g., when the fault displacement is 3 m and the crossing angle β is 90°, the overestimated value is approximately 40–110 %. Finally, the results of parameter analysis show that under the condition of 0° < β < 90°, the tunnel failure scope caused by the left-lateral strike-slip faulting is obviously larger than that caused by the right-lateral strike-slip faulting, while the conclusion is opposite under 90° < β < 180°; the maximum strain within the tunnel correlates directly with fault displacement and the strength of the fault zone, exhibiting an inverse correlation with the width of the fault zone; meanwhile, the scope for tunnel failure is directly influenced by fault displacement, fault zone width, and the crossing angle (where 90° <β < 180°), while inversely affected by the crossing angle (where 0° <β < 90°) and the strength of the fault zone.