Fault Zone Research Articles

Spatiotemporal Analysis of Atmospheric Chemical Potential Anomalies Associated with Major Seismic Events (Ms ≥ 7) in Western China: A Multi-Case Study

Focusing on major earthquakes (EQs; MS ≥ 7) in Western China, this study primarily analyzes the fluctuation in Atmospheric Chemical Potential (ACP) before and after the Wenchuan, Yushu, Lushan, Jiuzhaigou, and Maduo EQs via Climatological Analysis of Seismic Precursors Identification (CAPRI). The distribution of vertical ACP revealed distinct altitude-dependent characteristics. The ACP at lower atmospheric layers (100–2000 m) exhibited a high correlation, and this correlation decreased with increasing altitude. Anomalies were detected within one month prior to each of the five EQs studied, with the majority occurring 14 to 30 days before the events, followed by a few additional anomalies. The spatial distribution of anomalies is consistent with the distribution of fault zones, with noticeable fluctuation in surrounding areas. The ACP at an altitude of 200 m gave a balance between sensitivity to seismic signals and minimal surface interference and proved to be optimal for EQ monitoring in Western China. The results offer a significant reference for remote sensing studies related to EQ monitoring and the Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) model, thereby advancing our understanding of pre-seismic atmospheric variations in Western China.

Assessment of variations in shear strain energy induced by fault coseismic slip in deep longwall mining

Abstract Shear strain energy is a pivotal physical quantity in the occurrence of earthquakes and rockbursts during deep mining operations. This research is focused on understanding the changes in shear strain energy in the context of retreating longwall mining, which is essential for the optimized design and mitigation of rockbursts and seismic events. Through the application of innovative analytical models, this study expands its analytical range to include the variations in shear strain energy caused by fault coseismic slip. An integrated methodology is utilized, taking into account the changes in coseismic and fault friction parameters as well as enhancements in mining-induced stress and existing background stresses. Our numerical investigation highlights the significance of mining location and fault characteristics as key determinants of shear strain energy modifications. The analysis demonstrates significant spatial variability in shear strain energy, especially noting that fault slip near the mining face greatly increases the likelihood of rockburst. This finding emphasizes the need to integrate fault coseismic slip dynamics into the triggering factors of rock (coal) bursts, thus broadening the theoretical foundation for addressing geological hazards in deep mining operations. The results are further corroborated by observational data from the vicinity of the F16 fault zone, introducing the concept of mining-induced fault coseismic slip as an essential element in the theoretical framework for understanding rockburst triggers.

Study on Construction Optimization Method of Tunnel Crossing Fault Fracture Zone

When a highway tunnel intersects a fault fracture zone, the excavation process disrupts the surrounding weak and fragmented rock mass, compromising the stability of the fault zone. This study compares the deformation and stress distribution of the surrounding rock using the reserved core soil method, central diaphragm (CD) method, and cross diaphragm (CRD) method during tunnel excavation through fault fracture zones. Among these, the CRD method is identified as the safest construction technique. Additionally, to address the significant deformation of the surrounding rock when tunneling through fault zones, the impact of various pre-support and advance reinforcement techniques on rock mass deformation is analyzed. By comparing the full-ring grouting method with the optimized reinforcement zone approach, the findings demonstrate that optimized grouting significantly reduces disturbance to the fault fracture zone during excavation, thereby enhancing the overall stability of the surrounding rock mass.

Applicability of electrical resistivity surveys for tracing and characterizing active faults: a case study in the Northern Gongju Fault Zone, Korea

Applicability of electrical resistivity surveys for tracing and characterizing active faults: a case study in the Northern Gongju Fault Zone, Korea

Quaternary Segmentation Characteristics of the Hunhe Fault, Northeast China

The northern segment of the Tanlu fault zone, which encompasses the Dunhua–Mishan and Yilan–Yitong fault zones, plays a critical role in the tectonic framework of Northeast China. This study focuses on the Hunhe fault, part of the Liaoning segment of the Dunhua–Mishan fault zone, which exhibits concealed characteristics and an NE–NEE orientation. We employ remote sensing and field investigations to accurately delineate the Hunhe fault’s location, scale, and tectonic activity. The findings indicate that the Hunhe fault displays significant spatial variability in tectonic activity. Some segments show evidence of late Quaternary activity, contradicting prior research that classified the Hunhe fault as an active fault during the MIS (Marine Isotope Stages) 20-103MIS 20-103- MIS6-19MIS6-19 period and assessed its seismic potential differently. Recent field investigations suggest considerable spatial variability in tectonic activity, indicating segmental characteristics. In this study, the Hunhe fault is divided into segments based on five aspects: the fault structure and movement characteristics of the fault; transverse faults and obstruction structures; geological and geomorphological characteristics; seismic features; and fault activity. The detailed segments are as follows: the Shenyang segment, the Fushun segment, the Zhangdang-Nan Zamu segment, and the Nan Zamu to Ying Emeng East section. These findings aim to enhance the understanding of the seismic hazard potential associated with the Hunhe fault, highlighting the need for ongoing research to address its complexities and implications for regional seismic risk assessment.

Paleomagnetic data from volcanic rocks in the southern Central Andes of Argentina and their implications for tectonics and geomagnetic field behavior

Abstract A paleomagnetic study of basaltic lava flows exposed in the northern Neuquén Cordillera, southernmost Central Andes, along the Antiñir-Copahue fault zone (ACFZ), involved 25 sites of the Cola de Zorro Formation (Pliocene–Early Pleistocene) along two different sections. The sites show exclusive normal polarity, corresponding to the Late Pliocene Gauss chron (3.6–2.6 Ma). The angular standard deviation of virtual geomagnetic poles (VGPs; ASD = 14.8°) is consistent with the expected values from recent geomagnetic models, in opposition to anomalously low dispersion found in previous studies in Pleistocene VGPs of reverse polarity from neighboring areas to our study zone. Mean paleomagnetic directions for Bella Vista (Dec = 0.0°, Inc = −50.0°, α₉₅ = 7.6°, K = 36.7, N = 11) and Río Huaraco sections (Dec = 354.9°, Inc = −57.0°, α₉₅ = 7.5°, K = 55.7, N = 8) do not show tectonic rotation around vertical axes. Combining and regrouping our and previous data by area confirmed the absence of tectonic rotations in the Huaraco-Trohunco block and a statistically significant clockwise rotation of 14.4° ± 10.3° of three adjacent tectonic blocks located south of our study locality in Pleistocene times. These results suggest that strike-slip deformation along some sections of the ACFZ was significant in the Pleistocene structural evolution of this region.

Earthquake swarms frozen in an exhumed hydrothermal system (Bolfin Fault Zone, Chile)

Abstract. Earthquake swarms commonly occur in upper-crustal hydrothermal-magmatic systems and activate mesh-like fault networks. How these networks develop through space and time along seismic faults is poorly constrained in the geological record. Here, we describe a spatially dense array of small-displacement (< 1.5 m) epidote-rich fault veins (i.e., hybrid extensional–shear veins) within granitoids, occurring at the intersections of subsidiary faults with the exhumed seismogenic Bolfin Fault Zone (Atacama Fault System, northern Chile). Epidote hybrid extensional–shear veining occurred at 3–7 km depth and 200–300 °C ambient temperature. At a distance of ≤ 1 cm to fault veins, the magmatic quartz of the wall rock shows (i) thin (< 10 µm thick) interlaced deformation lamellae and (ii) systematically crosscutting veinlets healed by quartz and feldspars, and it appears shattered at the vein contact. Clasts of deformed magmatic quartz, with deformation lamellae and healed veinlets, are included in the epidote-rich fault veins. Deformation of the wall-rock quartz is interpreted to record the transient large stress perturbation associated with the propagation of small earthquakes preceding conspicuous epidote mineralization. Conversely, the epidote-rich fault veins record cyclic events of extensional-to-hybrid veining and either aseismic or seismic shearing. The dilation and shearing behavior of the epidote-rich fault veins are interpreted to record the later development of a mature and hydraulically connected fault–fracture system. In this latter stage, the fault–fracture system cyclically ruptured due to fluid pressure fluctuations, possibly correlated with swarm-like earthquake sequences.

Probabilistic estimation of rheological properties in subduction zones using sequences of earthquakes and aseismic slip

Abstract Constraining the effective rheology of major faults contributes to improving our understanding of the physics of plate boundary deformation. Geodetic observations over the earthquake cycle are often used to estimate key rheological parameters, assuming specific laboratory-informed classes of viscous or frictional rheological models. However, differentiating between various rheological model classes using only observations of a single earthquake (coseismic and postseismic deformation) is difficult—especially in the presence of coarse spatiotemporal sampling, inherent observational noise, and non-uniqueness of the inverted properties. In this study, we present a framework to estimate key rheological parameters of a subduction zone plate interface using simulations of sequences of earthquakes and aseismic slip, constrained by pre- and postseismic surface displacement timeseries. Our simplified forward model consists of a two-dimensional subduction zone, represented by a discretized planar fault or narrow shear zone, divided into a locked, shallow region (“asperity”) experiencing periodically imposed coseismic events, and a stress-driven creeping section governed by power-law viscoelasticity or rate-dependent friction. Our inverse model fits the rheological parameters of the interface to surface displacement timeseries in a Bayesian probabilistic way. We validate that our proposed framework can successfully recover depth-dependent profiles of effective viscosity using a synthetic dataset of pre- and postseismic observations. Our first set of numerical experiments show that our framework is only mildly sensitive to uncertainties in the rupture history or assumed coseismic slip, making it robust enough to be applied to real observations of subduction zones. Our second set of tests considers the similarities of surface displacement timeseries between synthetic models that model the plate interface either as a shear zone described by power-law viscosity, or a surface described by rate-dependent friction. Here, we find that the ability to fit surface observations using functional or mechanical models assuming frictional behavior does not constitute sufficient evidence to actually infer frictional behavior at depth, as the surface expressions are virtually indistinguishable from deformation generated from models with depth-variable power-law viscous behavior. Based on our numerical experiments, we conclude that studies that aim to infer the mechanical behavior and rheological properties at depth in subduction zones should consider the surface expression from time periods representative of the entire seismic cycle. Graphical Abstract

A Review of Health Monitoring and Model Updating of Vibration Dissipation Systems in Structures

Given that numerous countries are located near active fault zones, this review paper assesses the seismic structural functionality of buildings subjected to dynamic loads. Earthquake-prone countries have implemented structural health monitoring (SHM) systems on base-isolated structures, focusing on modal parameters such as frequencies, mode shapes, and damping ratios related to isolation systems. However, many studies have investigated the dissipating energy capacity of isolation systems, particularly rubber bearings with different damping ratios, and demonstrated that changes in these parameters affect the seismic performance of structures. The main objective of this review is to evaluate the performance of damage detection computational tools and examine the impact of damage on structural functionality. This literature review’s strength lies in its comprehensive coverage of prominent studies on SHM and model updating for structures equipped with dampers. This is crucial for enhancing the safety and resilience of structures, particularly in mitigating dynamic loads like seismic forces. By consolidating key research findings, this review identifies technological advancements, best practices, and gaps in knowledge, enabling future innovation in structural health monitoring and design optimization. Various identification techniques, including modal analysis, model updating, non-destructive testing (NDT), and SHM, have been employed to extract modal parameters. The review highlights the most operational methods, such as Frequency Domain Decomposition (FDD) and Stochastic Subspace Identification (SSI). The review also summarizes damage identification methodologies for base-isolated systems, providing useful insights into the development of robust, trustworthy, and effective techniques for both researchers and engineers. Additionally, the review highlights the evolution of SHM and model updating techniques, distinguishing groundbreaking advancements from established methods. This distinction clarifies the trajectory of innovation while addressing the limitations of traditional techniques. Ultimately, the review promotes innovative solutions that enhance accuracy, reliability, and adaptability in modern engineering practices.

Geological and geophysical evaluation of the subsurface conditions for establishing new dwelling area East New Cairo City

ABSTRACT An integrated geological and geophysical study utilising electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) was carried out in a new residential area located northeast of New Cairo City and south of the Suez-Cairo Road. The purpose was to characterise the subsurface layer distribution, lithology, and geometry of faults . Initial surface geological mapping identified traces of some faults. Stratigraphically, the study area comprises sedimentary rocks and local basaltic flow outcrops ranging in age from the Middle Eocene (Mokattam Formation) to the Upper Miocene (Hagul Formation). ERT and SRT data were acquired along 15 closely spaced profiles oriented to intersect the expected surface fault zones. ERT delineated electrical conductive zones situated at different depths and composed of shale and altered basalt. Meanwhile, three layers were detected based on velocity values obtained from SRT data analysis. The ERT and SRT results successfully elucidated the fault configuration and its locations, providing crucial information for construction planning. Major structures were concealed and only outlined by the integrated ERT/SRT surveys. This study shows heterogeneous soil conditions and fault damage zones, which may impact some parts of the study area. The study’s findings , offering vital information for safe and effective construction planning.

Evaluating major element hydrogeochemistry and fluoride occurrence in groundwater of crystalline bedrock aquifers and associated controlling factors of Eumseong basin area, South Korea.

Long-term intake of high-fluoride water can cause fluorosis in bones and teeth or damage to organs. Fluoride in groundwater is primarily derived from reactions with rocks containing fluorine-related minerals, and fluoride concentrations are elevated in groundwater that has been reacting with these rocks for a long time. The purpose of this study is to investigate the origin and distribution of fluoride in groundwater and to assess the influence of various factors, including geology, on fluoride concentrations in groundwater. The Eumseong basin and surrounding areas were selected as the study area due to the diversity of geologic factors. 139 groundwater samples and 14 rock samples were collected, with groundwater samples subjected to field water quality measurements, chemical analysis, and statistical analysis, and rock samples subjected to microscopic observation and chemical analysis. Fluoride concentration in groundwater increased with well depth, and was highest in groundwater associated with granitic rocks rich in biotite. The fluoride concentration in groundwater showed a negative correlation with the distance to the fault, suggesting that deep groundwater may preferentially flow along fault zones in certain areas. In addition, high-fluoride groundwater had depleted water-stable isotope values, which is likely to be resulted from higher degree of water-rock interaction in groundwater recharged at higher elevations. Calcite precipitation in most groundwater appears to weaken fluorite solubility control on fluoride concentration. Multivariate statistical analysis revealed that water-rock interactions generally governed fluoride and major element concentrations, with high-fluoride groundwater clearly distinguished. These findings can aid in assessing fluoride occurrence in groundwater and managing water quality in areas with similar geological characteristics.

Large-scale shaking table test on unlined tunnel in fault zone under three-dimensional earthquake

Large-scale shaking table test on unlined tunnel in fault zone under three-dimensional earthquake

Determination of Anatolian Plate’s tectonic block boundaries with clustering analysis using GNSS sites velocities

The Anatolian Plate is an important tectonic structure containing different types of faults. In this study, block boundary studies were performed by clustering analysis using horizontal velocity data for 841 GNSS sites located on the Anatolian Plate. Four algorithms were used to determine the most appropriate cluster number. Cluster analysis was performed with K-means analysis. Different to other studies, the analysis included the location parameter for the GNSS sites in the cluster analysis. Generally block boundaries followed active fault zones and surface ruptures forming as a result of earthquakes. In this block study, 3 previously undocumented block boundaries were defined based on GNSS data. When all parameters are assessed in cluster analysis, the most appropriate cluster number was determined to be 9.

Step characteristics and formation mechanism of strike slip faults in Wuerhe asphalt vein, Junggar Basin

In order to define the geometric characteristics, formation mechanism and fault wall movement direction of steps about mini-extensional shear strike-slip fault zone in Wuerhe asphalt vein. Field outcrop observation, 3D seismic data interpretation, fracture formation time and stress mechanism analysis were carried out. There is no friction in the vein section and the initial fracture shape is maintained. Not only negative steps but also steps is developed, and even steps and negative steps coexist in a cross section. The step is the microtension rupture surface associated with the strike-slip fault plane, which does not have the pointing significance of the fault wall relative movement. The outcrop features are typical, which overturns the consensus of domestic and foreign scholars based on the structural physics simulation experiments that the small steepness generated at the early stage of normal fault, reverse fault and strike-slip fault sections are all negative steps.

Short-term seismic precursor anomalies in hydrogen concentration at fault gas stations along the Northern Margin Fault of the Yanqing Basin of Beijing, China

The Northern Margin Fault of the Yanqing Basin (NMYB Fault) is an important active fault at the intersection of the Zhangjiakou–Bohai (Zhang-Bo) Belt and the Shanxi Belt in North China. The Yanqing Basin, controlled by the NMYB Fault, is rich in escaping gas from hot springs, and previous investigations have indicated that the Yanqing Basin is located in the peak area of upwelling deep fluids from the mantle source material within the Zhang-Bo Belt. Hence, the site is suitable for geochemical gas precursor observations; to facilitate this, five new fault soil gas continuous stations were built on different segments of the NMYB Fault to carry out observations of fault gas (H2 and CO2) concentrations. The five new stations were approximately 50–60 m deep in the bedrock to monitor the release of gas from the depths of the fault. This was the first time that such geochemical station arrays were deployed in the same fault zone at a high density and depth. The results of the deep-hole observations of fault gas within the Yanqing Fault zone show that the time series of the hydrogen (H2) escape gas concentration has a close relationship with recent seismic activities, reflecting different physical processes of YFBF fault activity. The H2 concentration at the observatory was more sensitive to the stress-loading response of the NMYB Fault system.

Improving subsurface structural interpretation in complex geological settings through geophysical imaging and machine learning

This study employs seismic refraction tomography (SRT) and electrical resistivity tomography (ERT) to assess subsurface geological conditions along the proposed Porsgrunn Highway in Norway. The primary objective is to analyze SRT and ERT tomograms to identify subsurface geological structures. However, interpreting tomograms is often limited by smoothed boundaries and reduced resolution. To address these challenges, we apply k-means clustering, a machine learning technique that groups data based on similarities in physical properties, to post-process the geophysical tomograms. This study pioneers the use of k-means clustering to interpret tomograms from SRT and ERT data in complex geological settings. We first evaluate the effectiveness of clustering techniques using numerical modeling for two geological scenarios: a horizontally layered case and a layered case with undulation and a fault structure. Utilizing automated methods (Elbow and Silhouette), we objectively determine the optimal number of clusters for each geophysical tomogram. Subsequently, we compare the performance of the k-means clustering algorithm with subjective expert interpretations and the Laplacian edge detection method. Borehole data validate the clustering results and confirm the effectiveness of optimal cluster selection techniques. The findings of this study demonstrate that k-means clustering significantly enhances the detection of geological structures by establishing clearer boundaries and minimizing noise interference, enabling more accurate fault zone delineation. Compared to traditional edge detection and subjective interpretation methods, k-means clustering offers a systematic and objective approach that improves consistency and reliability across diverse geological settings. Moreover, its automated classification of geophysical data into meaningful clusters enables efficient analysis of large datasets. This study underscores the value of integrating machine learning techniques with geophysical methods such as SRT and ERT to improve interpretability and accurately identify subsurface geological structures, particularly in fault zone identification.

Slip instability of dilatant and fluid-saturated faults

The mechanisms of slip instabilities of dilatant and fluid-saturated faults remain controversial, particularly in low-permeability environments. Using a rate and state friction model including the effects of dilatancy, we conduct a linearized stability analysis of a one-dimensional spring-slider model and reexamine the critical stiffness (kc) of the fault zone as a function of fluid diffusivity and dilatancy factor. Our analytical results indicate that under fully-drained conditions, kc is independent of dilatancy factor, while under poorly-drained conditions, kc depends on dilatancy factor and fluid diffusivity. Both analytical and numerical results show that a non-negative kc always exists, even for highly-dilatant and poorly-drained faults where kc is proportional to fluid diffusivity. This implies that dilatancy does not alter the inherent (in)stability of fault slip, and that a sufficiently low system stiffness can always produce unstable fault slips without a critical pore pressure or critical dilatancy factor. These findings may provide new insights into effects of dilatancy on fault instability. The numerical results further illustrate that the fault slip acceleration tends to be significantly suppressed by increasing dilatancy factor and decreasing fluid diffusivity. These results may explain ubiquitous slow-slip events on natural faults that vary in length.

Upper crustal azimuthal anisotropy and seismogenic tectonics of the Hefei segment of the Tan-Lu Fault Zone from ambient noise tomography

Upper crustal azimuthal anisotropy and seismogenic tectonics of the Hefei segment of the Tan-Lu Fault Zone from ambient noise tomography

Seismic attenuation in the Middle Magdalena Valley, Colombia, and possible relation to fluid lubricated fault zones

Seismic attenuation in the Middle Magdalena Valley, Colombia, and possible relation to fluid lubricated fault zones

Copula Modeling and Uncertainty Propagation in Field‐Scale Simulation of CO2 Fault Leakage

AbstractSubsurface storage of is an important means to mitigate climate change, and the North Sea hosts considerable potential storage resources. To investigate the fate of over decades in vast reservoirs, numerical simulation based on realistic models is essential. Faults and other complex geological structures introduce modeling challenges as their effects on storage operations are subject to high uncertainty. We present a computational framework for forward propagation of uncertainty, including stochastic upscaling and copula representation of multivariate distributions for a storage site model with faults. The Vette fault zone in the Smeaheia formation in the North Sea is used as a test case. The stochastic upscaling method reduces the number of stochastic dimensions and the cost of evaluating the reservoir model. Copulas provide representation of dependent multidimensional random variables and a good fit to data, allow fast sampling and coupling to the forward propagation method via independent uniform random variables. The non‐stationary correlation within the upscaled flow functions are accurately captured by a data‐driven transformation model. The uncertainty in upscaled flow functions and other uncertain parameters are efficiently propagated to leakage estimates using numerical reservoir simulation of a two‐phase system of CO2 and brine. The expectations of leakage are estimated by an adaptive stratified sampling technique which effectively allocates samples in stochastic space. We demonstrate cost reduction compared to standard Monte Carlo of one or two orders of magnitude for simpler test cases, and factors 2–8 cost reduction for stochastic multi‐phase flow properties and more complex stochastic models.