Seismic Research Articles

Seismic numerical analysis of an Inca stone wall in Sacsayhuaman using rigid body dynamics within a finite element framework

The study and conservation of the stone heritage is a global concern, mainly when the buildings are in seismic zones. Stone structures can be very simple or considerably complex, depending on their style and form of construction. A clear example is the Inca architecture in Peru, which has different and complex typologies due to its cultural diversity. Inca structures of remarkable heritage value are in Cusco, an area of active cortical faults that might produce a seismic event at any time. The main objective of this research is to contribute to the knowledge of the seismic vulnerability analysis of Inca's stone walls by using the dynamics of rigid bodies (within the finite element method) to evaluate the possible out-of-plane failure mechanisms. This methodology allows for reducing the high number of degrees of freedom usually considered when modelling an entire irregular large stone wall by other approaches, such as continuum models. A wall section from the archaeological site of Sacsayhuaman (Cusco, Peru) is analysed as a case study. Each stone is discretised and modelled as a rigid body, and the interaction among blocks is evaluated within a finite element numerical framework. The structure's predominant frequencies are evaluated using updated methods such as white noise and sinusoidal signals. Then, a non-linear dynamic analysis of the studied wall is performed considering three Peruvian seismic records. The analyses show that the structure could suffer significant damage and endanger its structural stability for cortical earthquakes with a Peak Ground Acceleration (PGA) greater than 0.2 g. Considering the historical significance of these structures, the analysis of Inca stone walls' seismic safety accounts for potential residual movements between individual stones.

Seismic behaviour of a steel moment resisting frame structure featuring hourglass double split tee joints

The occurrence of brittle fractures in welds of full-strength joints of steel moment-resisting frames (MRFs) during earthquakes in Northridge (1994) and Kobe (1995) marked a turning point in seismic design philosophies for steel structures. This led to the development of new strategies focusing on enhancing structural resilience and energy dissipation. While Reduced Beam Sections (RBS) were traditionally favoured, recent approaches include partial-strength joints and replaceable dissipative fuses, in some cases also equipped with self-centring components. These systems often employ friction or yielding dampers, ensuring that the weakest joint component comprises well-designed dampers for optimal ductility and energy dissipation.In this context, the present study evaluates the performance of a large-scale structure featuring MRFs with partial-strength double-split tee (DST) joints and hourglass dampers. These joints are conceptually similar to ADAS dampers and the Simpson Strong Tie moment connection prequalified by AISC 358–16. The research involves conducting a pseudo-dynamic test campaign on a two-storey steel structure designed according to EC8 provisions. Findings from experiments and a numerical model developed using OpenSees are discussed. Incremental Dynamic Analyses (IDAs) compare structures with hourglass DST joints to those with full-strength joints, showing enhanced self-centring capacity in DST-equipped structures despite lacking dedicated self-centring components. Additionally, structures with hourglass DST joints demonstrate significant low-cycle fatigue life, potentially reducing the need to replace dissipative components after severe seismic events.

Using Moment Tensor Inversions for Rapid Seismic Source Detection and Characterization: Application to the North Korean Nuclear Tests

AbstractThe rapid detection and source characterization of any type of seismic events including earthquakes and nuclear explosions is one of the missions of many seismological laboratories. Most often, the techniques used are based on phase picking and amplitude measurements for detecting and locating events, and for estimating magnitudes. From these parameters, especially for anthropogenic sources, event screening is then done empirically, and this may lead to misinterpretations of the source nature. However, it is known that seismic waveform inversion for the determination of the moment tensor has proven to be a reliable source physics-based method for event characterization. Here, we present a technique already used for earthquake monitoring in tectonically active regions, and we test it on very shallow natural and anthropogenic events recorded in the vicinity of the Democratic People’s Republic of Korea (DPRK). From a grid of potential locations and by scanning continuous seismic waveforms, it is possible to implement a rapid detector of seismic events providing the full information of the sources (origin time, location, magnitude, mechanism, and source decomposition). We show its overall performances on all past DPRK nuclear tests and regional earthquakes. From such an approach fast complete event screening is achieved. Source uncertainties can also be estimated. This stand-alone detector and identifier of seismic events may help monitoring seismological agencies to provide a rapid and complete alert for any events within a region of interest before more in-depth discrimination analysis can be run.

Progressive Collapse Analysis of Single-Layer Latticed Domes Under Seismic Loading Using Enhanced Fiber-Based Approach

This paper presents a novel computational framework based on the Finite Particle Method (FPM) for the progressive collapse analysis of single-layer latticed domes subjected to seismic loading. The framework integrates a fiber-based approach to simulate the nonlinear behavior of steel structural members, including yielding, cyclic buckling, and fracture. For structural seismic analysis, the fiber-based approach is enhanced by incorporating a dynamic increase factor, which accounts for the impact of high strain rates during seismic events. Furthermore, the framework extends the pseudo-dynamical stiffness of the particle to consider Rayleigh damping, surpassing the limitations of the original mass damping model. The computational efficiency of the proposed framework is optimized by implementing it on a generic parallelized GPU platform. The computational framework has the advantage of elaborately simulating the response of individual structural members while efficiently capturing the complex behavior of the overall structure. Subsequently, the effectiveness of the enhanced framework is demonstrated through the analysis of the collapse behavior of a representative single-layer latticed dome under seismic loading. The study conducts a parametric analysis to evaluate the influence of two key factors, namely, rise-to-span ratios and imperfections, on the collapse behaviors. The findings contribute to a better understanding of the complex behaviors of single-layer latticed domes during seismic events, providing knowledge for improving structural safety and resilience in public buildings.

Enhancement Seismic Response of a Bored Tunnel Using Isolation for the Challenge of a Faulted Rock Crossing

The tunnel boring method (TBM) is a widely used and effective tunneling technology in various rock mass quality circumstances. A “faulted rock mass” can range from a highly fractured rock mass to a sheared weak rock mass, making the ground conditions challenging for tunneling, especially for TBMs. “Faulted rock” significantly affects hard rock TBMs, primarily due to the TBM’s high geological risk and poor flexibility. TBMs require careful planning and preparation, starting with preliminary assessments. This study investigates the impact of establishing an isolation material between a circular tunnel and the adjacent faulting rock on seismic response. The two parts of the parametric analysis for the isolation material utilized in the model look at how changes in the mechanical characteristics of the material, such as the shear modulus of the rock and the fault, affect the stresses created in the tunnel. The second section examines how changes in the isolation width concerning the fault width affect the stresses and displacements produced in the tunnel. Additionally, the effectiveness of isolating the tunnel during sudden changes in the characteristics of the rock was investigated under seismic loading perpendicular to the tunnel and parallel to the tunnel. The finite element approach was utilized to model the TBM tunnel and the neighboring rock with a fault or sudden change in the rock using Midas/GTS-NX, simulating the interactions between the rock and the tunnel. Time-history analysis using the El Centro earthquake was conducted to calculate the stresses in the tunnels during seismic events. Peak ground accelerations between 0.10 g and 0.30 g were utilized for excitation. A time step of 0.02 s and a length of 10 s for the seismic event were used in the analysis, with traditional grout pea gravel vs. the isolation layer. Comparisons were made between the absolute stresses (the greatest possible values) in the normal tunnel section (Sxx) and those induced in the tunnel with traditional grout and with isolation. Furthermore, the study of vertical displacement was taken into consideration. The seismic isolation method is highly effective in improving the seismic safety of bored tunnels. The results show that the significant values of the ratio between the shear modulus of isolation and the surrounding soil should be between 0.2% and 0.4%. Where parts of the tunnel run through a fault, the effective length of isolation should be between one and two times the fault width. The dynamic behavior of the tunnel with isolation is better than that with traditional grout. Generally, when isolation is used for any length, it reduces the stresses at the area of sudden change. Consequently, engineering assessments from both structural and geotechnical engineering viewpoints are now required for these unique constructions. An underground structure’s safety should be evaluated by the designer to ensure that it can sustain various applied loads, taking into account seismic loads in addition to construction and permanent static loads. Tunnels may be especially vulnerable in areas where the composition of the soil or rock varies.

Interactions between Cenozoic tectonics and landscape dynamics in Londrina, Paraná, Brazil

The Londrina City, located in southern Brazil, is situated on the basalt of the Paraná Igneous Province (PIP), near tectonic structures such as the Guaxupé faults and the São Jerônimo-Curiúva and São Sebastião lineaments, with a history of reactivation in the Cenozoic. Between 2015 and 2018, low-magnitude earthquakes hit the municipality, suggesting a possible connection with these structures. This study investigates the relationship between Cenozoic tectonics and geomorphological dynamics, combining quantitative geomorphological analysis with field analysis of faults. The results reveal signs of tectonic control on the landscape, with two pulses of regional uplift/base level drop affecting the drainage network. Reactivated segments, especially at intersections of NE and NW structures, influence dynamics, with variations in uplift rates between basins and block rotation under a transtensive regime. Recent earthquakes are related to the reactivation of an N50-60E fault scarp, possibly the Guaxupé Fault, indicating recurrent tectonic movement. Paleostress analyses identify three deformation pulses, highlighting the complexity of landscape evolution in intraplate regions. These findings enhance understanding of regional tectonics, emphasizing the need to comprehend landscape evolution in interior plate areas, such as the South American Plate.

Environment‐Modulated Glacial Seismicity Near Dålk Glacier in East Antarctica Revealed by Deep Clustering

AbstractOver the past decades, seismic monitoring has been increasingly used to track glacial activities associated with ice loss. Many seismological studies focus on West Antarctica, whereas glacial seismicity in East Antarctica is much less studied. Here, we apply unsupervised deep learning to a dense nodal seismic array near Dålk Glacier, East Antarctica, operating from 6 December 2019 to 2 January 2020. An autoencoder is used to automatically extract event features, which are then input into a Gaussian mixture model for clustering. We divide the data into 50 clusters and merge them according to their temporal and spectral characteristics. The results reveal five main types of seismic signals: two groups with monochromatic and high frequencies, two groups with broadband frequency and short duration, and a group with mainly low frequency and long duration. By comparing the environmental conditions (wind, temperature and tides), we infer that the two monochromatic groups are wind‐induced vibrations of the near‐station flag markers and topography; the two broadband groups are likely thermal contractions on the blue ice surface and stick‐slip events at the ice base; and the low‐frequency events are water‐filled basal crevassing and iceberg calving. In particular, we observe one type of low‐frequency event preceded by high‐frequency onset, which is likely basal crevassing near the grounding line of Dålk Glacier and predominantly occurred during rising tides. Our findings show that deep clustering is effective in identifying a wide range of glacial seismic events and can contribute to the rapid growth of passive glacier seismic monitoring.

Time-dependent magnetic anomaly variations in Turkey and Greece using swarm satellites: A comprehensive precursory multi-track analysis of M≥6 earthquakes from 2017 to 2020

This article presents a comprehensive multi-track analysis aimed at investigating time-dependent magnetic anomaly variations in Turkey and Greece resulting from five M ≥ 6 earthquakes occurring between January 2017 and October 2020. The study utilizes data from the Swarm satellites and employs various analytical techniques, including first-time derivative calculations, long-wavelength component removal, and moving RMS filters, to construct cumulative anomaly count graphs for each magnetic component. By eliminating the influence of the external magnetic field, we focus solely on the magnetic components (X, Y, Z, and F). The changes in magnetic anomalies before, during, and immediately after the earthquakes are carefully interpreted. The research systematically analyses the Plomari (June 12, 2017), Kos (July 20, 2017), Doğanyol (January 24, 2020), Özalp (February 23, 2020), and Karlovasion (October 30, 2020) Earthquakes, considering the mainshock and aftershock responses for each magnetic component. The findings reveal intriguing patterns, most notably the emergence of distinctive S-shaped anomalies in various magnetic components. Moreover, the study highlights the influence of significant earthquakes, such as Plomari and Kos, on cumulative anomalous tracks, providing critical insights into magnetic field behavior. Additionally, the study investigates the potential impact of the Özalp Earthquake on the magnetic anomalies observed in the Doğanyol earthquake and explores the relationship between the occurrence of the Doğanyol Earthquake and the precursory anomalies leading to the mainshock of the Özalp Earthquake. Furthermore, the analysis of the Karlovasion earthquake identifies magnetic anomalies preceding the mainshock. Finally, the research subjectively assesses the lateral and vertical scores of the five earthquakes to capability to represent the S-shaped pattern. The Plomari and Kos earthquakes score third and fourth highest, respectively, while the Doğanyol Earthquake achieves the top score and distinctly displays an S-shaped pattern, indicating its significance in the magnetic field behavior. The Özalp Earthquake scores second-best with a distinct S-shaped pattern, while the Karlovasion Earthquake receives the lowest score with no evident S-shaped pattern. Additionally, vertical scores indicate the Y and Z components with more pronounced S-shaped patterns, while the X and F components receive lower scores. Notably, the onshore Doğanyol Earthquake exhibits the most pronounced S-shaped pattern across all magnetic components, attributable to its shallow strike-slip fault at 10 km depth, while the offshore Karlovasion Earthquake, generated by a normal fault at 21 km depth, displays the most scattered pattern, providing valuable information on the influence of tectonic settings on magnetic field behaviour. In conclusion, this study provides valuable insights into the magnetic anomalies associated with seismic events in the region, significantly contributing to a better understanding of earthquake precursors and seismicity patterns, and enhancing seismic risk assessment and mitigation strategies.

Seismic performance of railway bridges with novel ductile piers under near-fault earthquakes

The destructive force of near-fault earthquakes presents a significant challenge to railway bridges. To enhance the seismic resilience of railway bridges under such conditions, a novelly designed ductile pier is introduced herein, accompanied by a analysis of its stiffness, damping characteristics, and shear capacity. The analysis reveals that the ductile pier exhibits reduced stiffness and increased viscous damping ratio when compared to the traditional pier. Subsequently, a finite element model of a typical railway simply-supported girder bridge is established and verified through shaking table tests. Furthermore, the near-fault seismic wave synthesis method is introduced, and the synthesized near-fault seismic waves are input into the traditional pier model and the ductile pier model for seismic analysis. The findings demonstrate that the ductile pier effectively diminishes girder acceleration and bearing displacement while enhancing pier energy dissipation. Additionally, the ductile pier is proved effective in safeguarding the core concrete during significant seismic events.

Shear Wave Velocity Applications in Geomechanics with Focus on Risk Assessment in Carbon Capture and Storage Projects

Shear wave velocity (Vs) has significant applications in geoengineering investigations. With the ongoing rise in carbon capture and storage (CCS) initiatives, the role of Vs in monitoring the CO2 sequestration sites is escalating. Although many studies have been conducted to assess CCS-induced risks, no inclusive research has been conducted integrating those investigations. This study strives to collate and integrate the applications of Vs in geoscience with an emphasis on CCS risk assessment. Based on this research, major CCS-induced risks were detected: induced seismicity, caprock failure, groundwater contamination, fault reactivation, and reservoir deformation. These risks were inclusively described, and the mathematical formulations incorporating the Vs parameter in risk analysis were elaborated. It was concluded that Vs applications can be further extended in monitoring CO2 plume migration, optimizing CO2 injection pressures, preventing shallow water contamination, and predicting CCS-induced seismic events. All these applications require fully coupled hydromechanical analysis based on poroelasticity theory. Hence, various factors including pore pressure, in situ stresses, faults distribution, and poroelastic parameters must be carefully determined before the CO2 injection phase. The mathematical formulations presented in the present study are quite applicable for granting the safety and long-term success of subsurface carbon sequestration.

Strengthening the Development and Use of “Deep” Seismic Event Catalogs

Strengthening the Development and Use of “Deep” Seismic Event Catalogs

Application of nature-inspired computing and implementation of algorithm for earthquake detection

Improve learning techniques and to prepare reference entropy which measures from the field of information theory, building upon entropy generally calculating the difference between two probability distributions. Cross-entropy can be used as a loss function when optimizing classification models like logistic regression and artificial neural networks. The performance of the proposed neural network with respect to cross entropy is presented in this research. The performance can be improved by including more data and optimization. The proposed research work will be used for time series data of events detection and prediction such as seismic event’s (Earthquake).The point of the present work is to tune the suitable algorithms for meaningful detection of the disastrous earthquake events and to generate the proper timely warning to the public.

Systematic Seismic Events Discrimination Methods at the Kenya National Data Centre (N090)

Systematic Seismic Events Discrimination Methods at the Kenya National Data Centre (N090)

The relationship between GRACE gravity and the seismic b-value: a case study of the Northern Chile Triple Junction (25° S–40° S)

SUMMARY The northern Chile Triple Junction (CTJ) is characterized by the ongoing subduction of the Nazca plate beneath the South American plate. The geological structures within the subduction zone undergo complex changes, resulting in significant tectonic activities and intense seismicity along the western margin of South America. Based on the Gravity Recovery and Climate Experiment (GRACE) data and earthquake catalogues, this study selects the northern CTJ area (25° S–40° S, 75° W–65° W) as the research object, adopts the mathematical methods of independent component analysis (ICA) and principal component analysis (PCA) to separate the earthquake-related signals within the GRACE data, and fits the changes of seismic b-values through the frequency–magnitude relationship. The characteristics of gravity changes before and after seismic events, the seismic activity parameter b-values, and the relationship between the gravity signals and b-values are discussed. The results show that mathematical methods can effectively extract seismic-related gravity components from the GRACE data. ICA, compared to PCA, provides better results in capturing the temporal variations associated with b-value time-series, which exhibit good consistency in long-term trend changes. The average change of b-values in the study area is 0.66 ± 0.003, fluctuating over time. Generally, prior to larger seismic events, b-values tend to decrease. Along the western margin of South America, b-values are low; this aligns with the active tectonic activities between subducting plates. Additionally, a certain correlation between b-values and gravity changes is observed, but due to the influence of tectonic activities, the correspondence between b-values and gravity anomalies may not be consistent across different areas. The b-value is highly consistent with the strain rate model. Low b-values correspond to high strain rates along the western edge of South America, which is in line with the tectonic characteristics of frequent seismic activity in this area. A gradual concentration of gravity anomalies before major earthquakes is observed, accompanied by the gradual accumulation of smaller seismic events. Meanwhile, several months before the two major earthquakes, the spatial distribution of gravity appears to be similar to the coseismic signals, but the nature of its generation remains to be explored. These methods and results not only add to the applications of GRACE in seismic studies but also raise questions for further exploration.

Cyclical hydraulic pressure pulses reduce breakdown pressure and initiate staged fracture growth in PMMA

Using unique experimental equipment on large bench-scale samples of Polymethylmethacrylate, used in the literature as an analogue for shale, we investigate the potential benefits of applying cyclical hydraulic pressure pulses to enhance the near-well connectivity through hydraulic fracturing treatment. Under unconfined and confined stresses, equivalent to a depth of up to 530 m, we use dynamic high-resolution strain measurements from fibre optic cables, complemented by optical recordings of fracture development, and investigate the impact of cyclical hydraulic pressure pulses on the number of cycles to failure in Polymethylmethacrylate at different temperatures. Our results indicate that a significant reduction in breakdown pressure can be achieved. This suggests that cyclic pressure pulses could require lower power consumption, as well as reduced fluid injection volumes and injection rates during stimulation, which could minimise the occurrence of the largest induced seismic events. Our results show that fractures develop in stages under repeated pressure cycles. This suggests that Cyclic Fluid Pressurization Systems could be effective in managing damage build-up and increasing permeability. This is achieved by forming numerous small fractures and reducing the size and occurrence of large fracturing events that produce large seismic events. Our results offer new insight into cyclical hydraulic fracturing treatments and provide a unique data set for benchmarking numerical models of fracture initiation and propagation.

The formation mechanism of low-angle loess-mudstone seismic landslides

Seismic-induced landslides represent intricate geological phenomena requiring a multidisciplinary investigative approach. This study examines the formation mechanisms of low-angle loess-mudstone landslides triggered by the 1920 Haiyuan M8.5 earthquake. We employ a synthesis of field investigations, high-density electrical resistivity tests, drilling, laboratory experiments, and numerical simulations. High-density resistivity results support the identified zone at the loess-mudstone interface, indicating a saturated area prone to liquefaction. Dynamic triaxial tests further verify liquefaction occurrences during seismic events within this zone. Additionally, numerical simulations conducted with FLAC2D and the PM4Silt constitutive model provide valuable insights into the temporal and spatial progression of landslides. The liquefaction zone experiences severe shear strain, precisely aligning with the location of the sliding band. Shear strain time-history analyses elucidate early manifestations and time-dependent behaviors at interfaces, providing a nuanced understanding of deformation patterns. The study delineates a comprehensive failure mechanism, unraveling how liquefaction in the saturated loess layer initiates in the upper and toe regions, subsequently propagating throughout the slope. Tension in the upper part and compressive uplift at the toe manifest, resulting in overall landslide movement. These findings highlight the significance of differential shear strain, leading to a layered shear deformation zone. The results yield invaluable insights for seismic stability assessments in regions with similar geological characteristics. This research not only advances the understanding of earthquake-induced landslides but also demonstrates the synergy between field investigations, advanced geotechnical testing, and numerical modeling in unraveling complex geological processes.

A novel resilient system of self-centering precast reinforced concrete walls with external dampers

The seismic vulnerability of concrete structures has prompted the development of innovative approaches to enhance earthquake resistance. Recent earthquakes have demonstrated the challenges of repairing concrete buildings damaged beyond feasible restoration. In response, research in structural engineering has increasingly focused on damage-resisting reinforced concrete walls, offering improved self-centering behavior and damage mitigation compared to traditional counterparts. Self-centering walls, employing a rocking mechanism, exhibit effective damage minimization and residual deformation reduction. This study introduces a robust approach to precast reinforced concrete walls, comprising a precast reinforced concrete shear wall integrated with an external energy dissipation component. The energy dissipation element, a reinforced concrete column attached externally on both sides of the wall, acts as a new damage-limiting component with enhanced energy dissipation capacity. Utilizing the general-purpose Finite Element (FE) software ABAQUS, a three-dimensional simulation of experimentally investigated self-centering precast reinforced concrete walls was developed. The finite element model was validated and subsequently employed to assess the performance of the proposed system under cyclic loading. Various design parameters of the reinforced concrete energy dissipation element, including cross-sectional area, wall height proportion, concrete strength, primary reinforcement yield strength, and reinforcement ratio, were investigated. Additionally, the suggested system underwent cyclic loading in multiple scenarios simulating subsequent earthquakes. The finite element analysis results indicate that the proposed method, with a well-designed energy dissipation element, ensures minimal damage, a controlled increase in lateral resistance, sufficient energy dissipation capacity, and the required resilience following successive seismic events.

Seismic vulnerability assessment of buried water supply and sanitation pipelines using the analytic hierarchy process: a methodology and application

The evaluation of seismic vulnerability in buried pipelines within water supply and sanitation networks stands as a critical endeavor in safeguarding infrastructure against the impacts of earthquakes. In response, this study introduces a systematic methodology rooted in the Vulnerability Index (VI), leveraging the Analytic Hierarchy Process (AHP) to allocate weights to factors influencing pipeline seismic behavior. Through the derivation of an expression for calculating the VI based on these weighted factors, our objective is to furnish a comprehensive pipeline classification system, thereby providing a strategic overview of the networks' seismic resilience. This method's practical utility will be exemplified through the examination of concrete cases involving drinking water pipelines (DWP). Furthermore, the scope will extend to encompass sanitation pipelines, thereby validating the methodology's effectiveness across both domains. By systematically assessing the seismic vulnerability of these crucial infrastructures, we aim to fortify their resilience against seismic events, ensuring the continued provision of essential services even in the face of natural disasters. This study's significance lies not only in its contribution to the field of infrastructure resilience but also in its practical implications for urban planning and disaster management. By elucidating the factors influencing pipeline vulnerability and providing a robust framework for assessment, decision-makers can better prioritize resource allocation and mitigation efforts, ultimately enhancing community safety and well-being. Furthermore, the methodology's adaptability and scalability render it applicable to diverse contexts, facilitating its integration into broader risk management strategies. As such, this study serves as a valuable tool for policymakers, engineers, and stakeholders seeking to enhance the resilience of water supply and sanitation networks in earthquake-prone regions. Through informed decision-making and proactive measures, we can build more resilient communities capable of withstanding the challenges posed by seismic hazards.

Numerical investigation of the stress regime effect on injection-induced fault reactivation and associated seismicity

The occurrence of many seismic events in energy production projects is caused by fluid injection-induced reactivation of critically stressed faults. The distribution of local stress regime has a significant influence on natural earthquakes, while its role in controlling injection-induced fault slip behavior and seismicity magnitude remains poorly understood. In this paper, we present a three-dimensional hydro-mechanical coupled fault reactivation study using unified pipe-interface element method (UP-IEM). The accuracy and reliability of the numerical method are evaluated and confirmed by numerical verification and actual observation data in Pohang EGS project, South Korea. The relationship between fault aseismic slip, seismic slip and seismicity magnitude is analyzed. Results show that both aseismic and seismic slip have different spatiotemporal distribution with the variation of stress regime. The seismic slip zone will exceed the pressurized area with the increase of initial slip tendency under the strike-slip-faulting stress regime (σH>σv>σh). Compared with fluid pressure, the seismic slip is mainly determined by a sudden increase of the shear stress at the aseismic slip zone boundary. In addition, the location of the microseismic events moves towards the fluid pressure propagation front. The larger slip area and seismicity magnitude are easier to be induced under strike-slip-faulting stress regime than thrust-faulting stress regime (σH>σh>σv). The tensile failure and higher permeability of the fault induced at injection phase for normal-faulting stress regime (σv>σH>σh) leads to a greater seismogenic hazard at the shut-in stage.

Study of post-earthquake train running performance considering earthquake-induced track irregularity

It is necessary to study the dynamic performance of high-speed trains to obtain the safe operation. In this paper, a seismic analysis of a track-bridge system subjected to near-field random earthquakes is carried out, and the geometric distribution of the residual and dynamic irregularities of rails after earthquake is explored. Based on the reliability theory and probability guarantee rate, an equivalent coefficient of earthquake-induced dynamic irregularity is proposed. The dynamic analysis of the train-track-bridge system is carried out, considering earthquake-induced track irregularity, and the speed limit of high-speed trains after the seismic event is proposed, ensuring the running safety. The results show that the amplitude of residual irregularity is much larger than that of the dynamic irregularity. The influence of the earthquake-induced track irregularity on the derailment coefficient and transverse acceleration of high-speed trains is significant increasing with the increase of the train operation speed. The earthquake-induced track irregularity has small effect on the vertical dynamic performance of high-speed trains. Based on probability guarantee rate, considering the random initial track irregularity, the operation speed limit of high-speed trains is set to 72 km/h. The research results can provide certain theoretical basis for the post-earthquake running safety evaluation of high-speed trains.