• Issue 2,2024 Table of Contents
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    • >Earthquake Engineering
    • Seismic vulnerability analysis of assembled piers with a hybrid connection

      2024(2):251-258. DOI: 10.20000/j.1000-0844.20220808005

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      Abstract:Based on the quasi-static test phenomenon and the test results of an integral cast-in-place pier specimen (ZT-1), a cast-in-place ultrahigh performance mortar-concrete-filled steel tube (CFST) pier specimen with a mortise-tenon connection (GX-1), and a grouting sleeve-CFST pier specimen with a mortise-tenon connection (GT-1), a time-history analysis of these specimens under an earthquake was conducted using the finite element analysis software OpenSees. The vulnerability of the specimens under an earthquake was analyzed by determining the corresponding damage quantification index. The research results show that (1) the change trend of the vulnerability curve of GT-1 is close to those of ZT-1 and GX-1 under slight and moderate damage; (2) when the PGAs are 0.15g, 0.2g, 0.3g, and 0.4g, the seismic responses of GX-1 and ZT-1 are close, and the exceeding probability of severe damage to GT-1 is reduced by 6.71%, 11.67%, 10.32%, and 4.46%, respectively, compared with ZT-1. (3) GT-1 has better collapse resistance than ZT-1 and GX-1.

    • Parameter determination and shear characteristics of lacustrine sedimentary peat soil in Dianchi Lake

      2024(2):259-268. DOI: 10.20000/j.1000-0844.2021122500x

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      Abstract:Organic matter content (wu) and water content (ω) greatly influence the mechanical properties and engineering characteristics of peat and peaty soil (peat soil for short). However, the determination standards of ω and wu of soil with high organic matter content are unclear in existing codes, procedures, and standards, and the test results vary greatly among different units. To define the determination standards of ω and wu of high organic content soil, tests were performed under different burning temperatures and burning times. Generally, the site of lacustrine sedimentary soil in Dianchi Lake has 3-5 layers of peat soil. To explore the variation law and evolution mechanism of stress and strain under different buried depths and confining pressures, a series of triaxial consolidation undrained (CU) tests was performed on five layers of peat soil with different buried depths under low to high confining pressures. The test results show that the stress-strain curve of peat soil presents a “layered” phenomenon with increasing confining pressure; the strain corresponding to the maximum deviatoric stress decreases with increasing depth, and the curve shape changes with the confining pressure and buried depth of soil samples; the pore pressure coefficient decreases with increasing depth. Moreover, the control standard of failure strain of peat soil in the CU test is proposed. This research further deepens the understanding of the mechanical properties of peat soil and provides an experimental basis for determining ω and wu standards.

    • RBF neural network prediction model for steel bar corrosion depth under general atmospheric environment

      2024(2):269-277. DOI: 10.20000/j.1000-0844.20211224005

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      Abstract:The prediction of steel bar corrosion depth is the basis for evaluating the service performance of RC structures. To establish a prediction model for steel bar corrosion depth in RC members under general atmospheric environment, the main parameters affecting the corrosion depth and the influence law were analyzed in this paper. Then, a numerical model and a RBF neural network prediction model were established based on the measured data, and the parameter sensitivity analysis was carried out. Results show that: compared with the numerical model, the RBF neural network has higher efficiency and accuracy in predicting the corrosion depth of steel bars; it can effectively map the complex nonlinear relationship between the influencing parameters and the corrosion depth of steel bars. The results of parameter sensitivity analysis show that the expansive crack width on RC surface has the greatest influence on the corrosion depth of steel bars, followed by other factors, i.e., the diameter of steel bar, the ratio of concrete cover thickness to steel bar diameter, and the compressive strength of concrete. The proposed model can be used to predict the corrosion degree of steel bars and evaluate the remaining service life of RC structures in engineering detection.

    • Construction and application of a database management system for seismic landslides and strong motion records in the Loess Plateau

      2024(2):278-285. DOI: 10.20000/j.1000-0844.20230105004

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      Abstract:

      Seismic landslide data and actual strong motion records are essential data for seismic landslide mechanism research. How to manage these data scientifically and give full play to their scientific value remains a question worth exploring. In this paper, based on the loess landslides induced by seven typical historical earthquakes and the strong motion records of 125 earthquakes from 2001 to 2018 in the Loess Plateau region, a database management system for earthquake landslides and strong motion records in the Loess Plateau was constructed relying on the open-source GIS platform + MySQL database. With a standard and friendly interface and a clear and smooth graphical presentation, the system parameters are easy to obtain. The system not only provides a scientific and convenient platform for managing and applying seismic landslides and strong motion records data but also provides a solid database for studying the mechanism of seismic landslides in the Loess Plateau, so it has a certain reference value for disaster prevention and mitigation work in this region.

    • Simulation test of the magnetorheological grease isolation under reverse demagnetization

      2024(2):286-293. DOI: 10.20000/j.1000-0844.20220912001

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      Abstract:Electromagnetic coils and permanent magnets were used to independently design a magnetorheological grease (MRG) shear test device with reverse demagnetization to jointly control the magnetic field. ANSYS Electronics was employed to simulate and analyze the magnetic field distribution of the test device, and MRG with different mass fractions of carbonyl iron powder was prepared. The shaking table test was performed to evaluate the dynamic shear properties of MRG under reverse demagnetization. The effects of field current, excitation amplitude, and excitation frequency on the dynamic performance of MRG were also investigated. Results show that the mass fraction of carbonyl iron powder has a considerable impact on the dynamic performance of MRG. With the increase in the field current, the shear stress of MRG rapidly increases and then slightly subsides, and the damping force decreases. The energy dissipation capacity of MRG increases with the displacement amplitude, while the damping force slightly increases with the loading frequency.

    • Period reduction coefficient of isolation structures based on the equivalent linearization method

      2024(2):294-301. DOI: 10.20000/j.1000-0844.20221227001

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      Abstract:The isolation design method, which is proposed in the Standard for Seismic Isolation Design of Building, is an integrated design method based on the equivalent linearization of the complex mode decomposition response spectrum. However, this method does not specify how to determine the period reduction coefficient of the isolation structure. Therefore, according to the stiffness series relationship, a simplified calculation formula for the period reduction coefficient of the equivalent single-degree-of-freedom isolation system was derived, and the influencing factors of the period reduction coefficient of isolation structures were discussed in this paper. Numerical finite element models with different filling materials and rates were established, and the accuracy of the simplified formula was verified. Results show that a functional relationship exists between the period reduction coefficient of the isolation structure, the nominal period ratio, and the period reduction coefficient of the non-isolation structure. As the filling rate increases, the period reduction coefficient of the isolation structure decreases. For the same filling rate, the period reduction coefficient of the isolated structure decreases with the increase in the elastic modulus of the filling materials and increases with the wall opening. The range of the period reduction coefficient of the isolation structure is 0.915-0.965. The deviation between the numerical simulation and theoretical analysis results is less than 3%, thereby proving the accuracy of the simplified formula. The simplified calculation method of the period reduction coefficient has a certain guiding importance for the design of isolation engineering.

    • Seismic performance of shape memory alloy concrete frame buildings

      2024(2):302-308. DOI: 10.20000/j.1000-0844.20230512001

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      Abstract:The earthquake action causes planar and vertical deformation of reinforced concrete (RC) frames, increasing seismic forces on the structure and elevating the damage level. Shape memory alloy (SMA) materials quickly restore the shape before deformation under external forces, reduce the degree of frame damage, and further improve the load-bearing capacity and stability of the frame structure. On this basis, the seismic performance of SMA concrete frame buildings was studied. Taking an actual project as an example, a finite element model of an RC frame structure was established using ANSYS software. Tianjin, Beiling, Indian Ocean, and artificial seismic waves were selected as ground motion input, and the time-history analysis results under these seismic waves were recorded. The research results show that the hysteretic curve of the structure under earthquake action has a full flag shape. The maximum inter-story displacement is 1/125, the residual deformation is within ±10 mm, the maximum peak load is 211 kN, and the horizontal bearing capacity is strong. These results show that an SMA-supported frame has high self-resetting performance, an excellent seismic response effect, and a strong seismic bearing capacity; thus, it can effectively improve the safety and reliability of a building structure.

    • Seismic strengthening of high-rise buildings based on the seismic vulnerability from incremental dynamic analysis

      2024(2):309-317. DOI: 10.20000/j.1000-0844.2023030700

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      Abstract:Because load-bearing structural members are unevenly distributed in high-rise buildings, the distance between these members is unequal. This irregular distribution may cause the acceleration resonance effect during earthquakes, resulting in building instability. In this paper, the seismic retrofit of high-rise structures was studied on the basis of incremental dynamic analysis using parameters such as seismic intensity, peak ground velocity, and the maximum story drift ratio. A 3D model of an actual high-rise building was constructed using ABAQUS software, and multiple seismic waves and ground motion records were selected to validate the seismic vulnerability curve. The results show that installing dampers in the high-rise structure improves the bearing capacity of components and enhances the seismic performance of the building. Increasing the thickness of steel plates improves the seismic resistance of the structure and reduces the exceeding probability of IO, LS, and CP of the frame structure in the limit state. Increasing the strength of concrete improves the anticollapse performance of the frame structure. After seismic retrofitting, the seismic capacity of the high-rise structure improves from 0.91 to 1.01. This study proves that strengthening and perfecting the vulnerable areas of buildings based on a seismic vulnerability analysis improves the seismic vulnerability of high-rise structures and reduces the loss of earthquake disasters.

    • Fragility analysis of the concrete gravity dam under the oblique incidence of SV waves

      2024(2):318-324. DOI: 10.20000/j.1000-0844.20221024001

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      Abstract:An effective method for evaluating the damage probability of concrete gravity dams under ground motions with different intensities is fragility analysis. The fragility analysis of gravity dams generally assumes that seismic waves are vertically incident, but those in the near-fault area are obliquely incident. The oblique incidence of seismic waves has a considerable influence on the seismic response of gravity dams. Based on the database of the Pacific Earthquake Engineering Research Center, 16 ground motion records were selected, and the oblique incidence input of SV waves was realized using the viscoelastic artificial boundary and equivalent nodal load. The PGA of ground motion was modulated using the incremental dynamic analysis method. The Koyna concrete gravity dam in India was taken as the research object in this paper. The fragility curves for different earthquake damage levels of the gravity dam under the oblique incidence of SV waves were established by taking the relative displacement of the dam crest as the seismic performance index. Results show that under the same earthquake damage level and ground motion intensity, the damage probability of gravity dams under the oblique incidence of SV waves decreases compared to that under the vertical incidence. When the PGA is close to the actual earthquake intensity of gravity dams, the maximum reduction rates of failure probability are 27.3% and 68.2%, respectively, when the incident angles are 15° and 30°, compared with that under vertical incidence. Meanwhile, the maximum difference values of failure probability are 36.6% and 83.9% compared with those under vertical incidence. Therefore, the influence of the oblique incidence of seismic waves should be considered in the seismic performance analysis of concrete gravity dams. The results can also provide a reference for the safety risk assessment of concrete gravity dams in near-fault areas.

    • Dynamic characteristics of saturated soil foundations based on the strain gradient nonlocal Biot theory

      2024(2):325-334. DOI: 10.20000/j.1000-0844.20220524001

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      Abstract:This paper explores the influences of the pore size effect (represented by a nonlocal parameter) and the heterogeneous effect of the medium (represented by a size factor) on the dynamic response of saturated soil foundations. Based on the strain gradient nonlocal Biot theory, the calculation program for the dynamic response of a saturated soil foundation subjected to cyclic load was compiled using the meshless method. Therefore, the accuracy of the meshless method program was verified. Results indicate that the responses of displacement and pore pressure at observation points are delayed with the increase in nonlocal parameters, maintaining the scale factor as constant. By contrast, the responses are advanced with the increase in the scale factor, maintaining the nonlocal parameter as constant. This finding indicates that the macro-modulus of the system will be decreased considering the pore size effect, which will be increased considering the heterogeneous effect of soil structures. Methods and ideas for solving dynamic problems of saturated soil using the proposed meshless method in this paper could provide references for future research on similar problems.

    • Seismic response characteristics of the gypsum-salt layer in the Zhouchongcun Formation of the Wuwei Basin and its petroleum geological significance

      2024(2):335-342. DOI: 10.20000/j.1000-0844.20221012001

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      Abstract:The gypsum-salt layer, as the main cap rock of oil and gas fields, is of considerable importance for the sealing of oil and gas reservoirs. On the basis of a 2D seismic exploration in Wuwei Basin, the seismic response characteristics and spatial distribution regularity of the gypsum-salt layer in Zhouchongcun Formation were analyzed using the integrated analysis method of well logs and seismic data. Results indicate a certain positive correlation between the thickness of the gypsum-salt layer and the seismic amplitude attribute. A thick gypsum-salt layer leads to a strong seismic amplitude. The thickness of the gypsum-salt layer varies from 45 to 540 m in the longitudinal direction. Horizontally, the gypsum-salt layer is relatively thick in the core and depression areas of the basin, and the main part is between 300 and 500 m. The gypsum-salt layer is relatively thin in the structurally high position of the basin, and the main body is between 50 and 150 m. The distribution characteristics of the gypsum-salt layer generally show that the low tectonic position corresponds to a thick gypsum-salt layer, and the high tectonic position corresponds to a thin gypsum-salt layer. This study provides a technical guarantee for the breakthrough of natural and shale gas exploration in the Wuwei Basin.

    • Dynamic fuzzy reliability analysis of collapse accumulation slopes under bidirectional earthquakes

      2024(2):343-348. DOI: 10.20000/j.1000-0844.20220617003

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      Abstract:A dynamic fuzzy analysis method for the seismic reliability of collapse accumulation slopes was established, considering the randomness and fuzziness of parameters for rock and soil in collapse accumulation slopes and the excitation of bidirectional earthquakes. Furthermore, the influence of vertical earthquake excitation on the reliability of the collapse accumulation slope was analyzed. First, the dynamic time-history analysis of FEM was used to calculate the dynamic response of collapse accumulation slope under bidirectional earthquakes, and the strength parameters of rock and soil mass were processed using fuzzy theory. Based on the Mohr-Coulomb strength criterion, the time-history calculation model for the safety factor and reliability of the slope under an earthquake was then established. Finally, a new method for evaluating the seismic reliability of slope was adopted, and the corresponding program was compiled by MATLAB to realize the rapid output of calculation and analysis results. The calculation results of the proposed method are reasonable and safe for engineering. The vertical earthquake has an impact on the reliability of the collapse accumulation slope, but the degree of impact must be analyzed in accordance with the actual situation. For the working condition of the example, the vertical earthquake slightly influences the reliability of the collapse accumulation slope, which only reduces the reliability by 3.55%. Therefore, the influence of a vertical earthquake can be overlooked in this example, and only the influence of a horizontal earthquake should be considered.

    • Mechanical properties of fly ash-modified loess reinforced by geogrid

      2024(2):349-357. DOI: 10.20000/j.1000-0844.20231008001

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      Abstract:With the acceleration of urbanization in the loess region of western China, construction land with fill and excavation is abundant and requires the corresponding foundation treatment technology to solve the problem of large deformation in the filling area. In this paper, fly ash and geogrid were used as modified fillers to improve loess. Through the direct shear, triaxial, collapsibility, and scanning electron microscopy tests, the strength change rule, macroscopic damage characteristics, and microstructure characteristics of reinforced and unreinforced loess specimens with different mixing ratios of fly ash were analyzed. The results show that the optimum water content and maximum dry density of the fly ash-modified loess reinforced by geogrid increases and decreases, respectively. When the mixing ratio of fly ash is 20%, the reinforced improvement effect is the best: The peak strength, residual strength, and equivalent internal friction angle of loess are greatly improved, and the lateral deformation and collapsibility are greatly reduced. Scanning electron microscopy test results show that the improvement of loess by fly ash is mainly reflected in the direct filling of loess pores by fly ash particles and the interweaving of chemical crystals to form a network filling; the porosity and pore size of loess decrease after the improvement. The study results provide a reference for improving and reinforcing fill slopes and fill roadbeds in loess areas.

    • Typical damage and seismic vulnerability of brick-concrete structural buildings in south Sichuan

      2024(2):358-368. DOI: 10.20000/j.1000-0844.20220823001

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      Abstract:This paper takes brick-concrete structural buildings with local construction mode characteristics in the south Sichuan area as the research object. The typical damage characteristics of brick-concrete structures were analyzed based on the construction characteristics of brick-concrete structural houses and the investigation results of historical earthquake damage in south Sichuan, such as the Changning M6.0 earthquake. The proportion of different damage levels under different intensities was calculated, and empirical analysis was used to obtain the preliminary vulnerability matrix. However, the actual vulnerability matrix was lacking due to the incomplete damage ratio of structures under high intensity caused by the sample limitation. Therefore, using the interpolation method, the empirical vulnerability matrix was supplemented to calculate the damage ratio under high intensity, and then the vulnerability curve was fitted. Thus, the vulnerability analysis model of brick-concrete structures, which was mainly based on seismic damage statistics and supplemented by numerical simulation, was established. The comparative analysis of the average seismic damage index facilitated testing the reliability of vulnerability analysis. Results show that the constructed vulnerability matrix can objectively reflect the seismic capacity of brick-concrete buildings in south Sichuan. This matrix also has practical application value for conducting seismic damage prediction, disaster loss assessment, and seismic damage risk assessment and prevention.

    • Shaking table tests on the liquefaction resistance of tire-reinforced sand cushions

      2024(2):369-375. DOI: 10.20000/j.1000-0844.20220430001

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      Abstract:Waste rubber tires are filled with bulk materials to form reinforced earth structures, which have been applied to soil foundations, retaining walls, and guard reinforcement projects, showing an obvious effect on vibration isolation. However, few studies have addressed the liquefaction resistance of tire-reinforced soil. Three groups of small shaking table tests were performed to verify the liquefaction resistance of tire-reinforced sand cushions by changing the drainage conditions of the tire cushion. The results show that tire-reinforced sand cushions have a good liquefaction resistance effect. Compared with a rigid cushion, the differences in the peak excess pore pressure ratio and residual excess pore pressure ratio range between 0.01-0.19 and 0.08-0.16, respectively. The drainage channels provided by tire-reinforced sand cushions inhibit the development of excess pore water pressure and accelerate the dissipation of excess pore water. Pore water is discharged along the interface between the tires and the soil below and the drain channels between the tires. The quantitative index of the soil liquefaction degree is defined by measuring lateral earth pressure, further verifying the liquefaction resistance of tire-reinforced sand cushions. During the vibration process, the tire-reinforced sand cushions have a surface settlement range of 11.3-15.7 mm, showing good deformation coordination performance.

    • Shaking table tests on the liquefaction characteristics of saturated sand

      2024(2):376-387. DOI: 10.20000/j.1000-0844.20220406001

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      Abstract:In this paper, six sand models with three groups of various mean particle sizes and three groups of various fine contents were prepared based on the earthquake simulation shaking table test. Sensors embedded in the sand were used to monitor the excess pore water pressure at different positions in the model, and the time-history curves of excess pore water pressure and pressure ratio in the models were analyzed. Furthermore, the effects of some factors, such as the peak value of seismic wave loading, mean particle size of sand, fines content, and buried depth, on the liquefaction characteristics of saturated sand were summarized. Test results show that the liquefaction degree and potential of sand models gradually increase with the peak value of seismic wave loading, and the liquefaction resistance slowly decreases. With the increase in the buried depth, fines content, and average particle size of sand, the liquefaction degree and potential of sand models also gradually decrease, and its liquefaction resistance gradually increases. The results reveal that the influence degree of various influencing factors on sand liquefaction is seismic wave strength > buried depth of sand > mean particle size and fines content of sand. The test results can help support the parameter selection of subsequent numerical simulations and provide a reference for studying the influence of other factors on sand liquefaction.

    • Reinforcement design of the earthen site slope for rural houses in the high loess slope of Kashgar, Xinjiang, under earthquake based on deformation control

      2024(2):388-398. DOI: 10.20000/j.1000-0844.20230207001

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      Abstract:To verify the effectiveness of strengthening the earthen site slope under earthquake, we considered the existing reinforced section of the earthen site slope in the high loess slope of Kashgar, Xinjiang, as the research object. A three-dimensional dynamic analysis model was established using the finite\|element software Midas/GTX NX,and analysis was performed on the deformation control of the earthen site slope reinforced by lattice anchor retaining wall under earthquake. Results indicate the severe displacement and deformation at the top and foot of the slope,the cumulative effect of the increase in earthquake duration. The displacement and deformation in the horizontal and vertical directions were effectively controlled after reinforcement,and the maximum deformation value met the requirements of control. The stability coefficient of the earthen site slope under earthquake reached 1.54 after reinforcement,which meets the requirement value of 1.15 in the code. The research demonstrates that the lattice anchor retaining wall can effectively control the displacement and deformation of the earthen site slope,thus improving slope stability.

    • Seismic responses of the super-high head ship lock based on different water simulation methods with oblique incidence of SV waves

      2024(2):399-409. DOI: 10.20000/j.1000-0844.20221027001

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      Abstract:The plane SV waves at different angles were simulated based on the input method of obliquely incident ground motion with a viscoelastic artificial boundary. The water inside the lock chamber was simulated using the acoustic-structure coupling and additional mass methods to investigate the seismic responses of the super-high head ship lock, such as displacement, stress, and plastic damage. The similarities and differences in the calculation results of the two methods were compared and analyzed. Results reveal that (1) the variation law of the seismic responses of the left and right lock walls calculated using the two methods with the incident angle is the same. The maximum tensile damage of the left lock wall emerges when the angle of incidence is 15°, and that of the right lock wall appears when the angle of incidence is 35°. The incident angle of a seismic wave has a considerable influence on the dynamic response of super-high head ship locks. Therefore, the design process should consider the influence of the oblique incidence of seismic waves. (2) When the angle of incidence is large, the extreme values of relative displacement and principal stress and the tensile damage results of the lock walls calculated by the acoustic-structure coupling method are relatively larger than the additional mass method, which is safer for the lock design. (3) The two calculation methods are recommended for cross-referencing and calibration, and the safety result is endorsed for the design of super-high head ship locks.

    • Reasonable stiffness of the spring components of the damping anchor head for the anchor cable frame considering permanent displacement

      2024(2):410-420. DOI: 10.20000/j.1000-0844.20220419001

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      Abstract:Under the action of a strong earthquake, dynamic damages, such as the pullout of the inner anchor section and the abruption of the anchor cable, are induced by the prestressed anchor cable frame. A novel anti-seismic measure involves setting springs at the outer anchor head, and an important design parameter is the spring stiffness. The seismic responses of slope under various PGAs and seismic waves with different durations were studied using a three-dimensional numerical model of bedrock-overburden slope reinforced by a prestressed anchor cable frame with springs at the anchor head. A method for determining the reasonable stiffness of spring components was proposed to control the displacement of the slope and reduce the load on the anchor cable. Results show that the damping effect gradually emerges with a decrease in spring stiffness. The horizontal acceleration at the top of the slope is slightly affected by the stiffness change. However, the slope displacement and spring deformation sharply increase when the spring stiffness is lower than the critical value. The minimum stiffness is determined by taking the empirical limit of slope permanent displacement as the primary control condition and combining the “straight-curved boundary point” of the fitting curve of spring peak stroke and stiffness. The permanent displacement of 10 cm and delimit curvature k less than 0.002kmax are taken for the calculation model to obtain a reasonable range of spring stiffness, i.e., (2.5, 3.8) kN/mm, under 0.4g-0.6g. The proposed method can provide a reference for the seismic design of prestressed anchorage engineering of slopes.

    • Seismic response of the basin considering the effect of soil nonlinearity and dip angle

      2024(2):421-430. DOI: 10.20000/j.1000-0844.20221107003

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      Abstract:Considering a 2D sedimentary basin model, the D-P elastoplastic model was used to simulate the nonlinear characteristics of the basin. Combining the explicit finite element method with the viscoelastic boundary method and changing the dip angle of the basin edge, the seismic response of the basin surface was analyzed in time and frequency domains, and the difference between linear and nonlinear seismic responses of the basin was compared. The following results are presented: (1) The influence of soil nonlinearity on ground motion in the entire basin is observed. Only considering the nonlinearity, the amplification factor of ground motion is reduced by 30%-50%. Meanwhile, considering the influence of nonlinearity and dip angle, as well as the range and position of areas with the strongest amplification change, the distribution characteristics under considerably small dip angles are different. (2) The amplification factors of the two components tend to increase with the edge dip angle, but the basin edge area is most affected by the nonlinearity. In addition, under the input of a real seismic wave, the range of significant amplification area and the difference between linear and nonlinear results are relatively large. (3) Considering the nonlinearity, the amplification factors of seismic waves with various frequencies are different. However, the distribution of the spectral ratio from low to high frequency is increasingly complex, and the influence of the basin dip angle becomes evident with the increase in frequency. (4) Considering the nonlinearity of soil, the overall characteristics of seismic wave propagation are maintained, but the strength of each seismic phase is reduced.

    • >Earthquake Research
    • Overview of the earthquake monitoring status in the United States

      2024(2):431-448. DOI: 10.20000/j.1000-0844.20230802001

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      Abstract:The earthquake monitoring work in the United States started early and has enjoyed a leading position in the fields of network design, equipment development, software development, standard formulation, data management, and new technology application. In recent years, earthquake data products in the United States have achieved a leap from singularity to diversification and customization with the development of mobile Internet and the advancement of projects, such as strong earthquake observation, earthquake early warning, and large-scale seismic arrays. Although the earthquake monitoring work in China started late, with the implementation of a series of major projects in recent years, such as the national seismic intensity rapid reporting and early warning, the “Belt and Road” seismic monitoring network, and the China seismic experimental site, the seismic network density, monitoring and early warning ability, intelligent processing of seismic data, service level, and application of new technologies in China have all made great progress. This paper introduces the progress of earthquake monitoring in the United States from five aspects: earthquake monitoring architecture, seismic network layout, data processing system, earthquake warning system, and data products, to better understand the current situation of international earthquake monitoring. Then, a comparative analysis is conducted with the current earthquake monitoring efforts in China. The study results can provide a reference for the further planning and development of earthquake monitoring and early warning in China.

    • Seismology-based ground motion attenuation relationship in the Tianshan area

      2024(2):449-456. DOI: 10.20000/j.1000-0844.20221025002

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      Abstract:A total of 3 171 seismic records with moment magnitude of 3.5-4.5 collected from the Tianshan area were selected in this paper. Using the microgenetic algorithm and by calculating the Fourier amplitude spectrum of the S-wave velocity, five regional crustal medium parameters were obtained: the stress drop Δσ was 182.06 bar, the quality factor parameter Q0 was 444.20, the η value was 0.35, and the geometric attenuation parameters R1 and R2 were 74.30 and 106.59 km, respectively. Based on the five parameters, the Fourier spectrum of acceleration was calculated. Combined with the random phase spectrum, the time history of ground motion with a certain magnitude and epicentral distance was also obtained. Then, the peak acceleration attenuation relationship of regional ground motion was established. Results show that the attenuation relations of far-field ground motions with moment magnitudes of 5 and 6 are in good agreement with the records of strong ground motions. Among the five selected empirical attenuation relationships, the results for the ground motion with a moment magnitude of 5 are the best for its average value, and the standard deviation is the smallest. The far-field results for the attenuation relationship of ground motion with a moment magnitude of 7 are higher than most strong ground motion records.

    • Slipping condition and the mode of activation of fractures induced by fluid injection

      2024(2):457-464. DOI: 10.20000/j.1000-0844.20221117002

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      Abstract:To investigate the physical mechanism of fracture activation induced by fluid injection, a series of triaxial injection-driven shear experiments were performed on sandstone cylindrical samples with a single fracture. The slipping conditions and modes of fracture activated by the fluid injection were analyzed. The results show that the initiation of fracture slippage largely depends on the stress state and the roughness characteristics of the fracture surface. Fluid pressure is the main cause of fracture slippage, while the degree of the nonuniform distribution of fluid pressure and the evolution permeability are the secondary causes. The fluid pressurization rate regulates the slipping mode of fracture. While the roughness characteristics of the fracture surface and permeability evolution characteristics are positively correlated with the rate of fracture slippage, they are negatively correlated with the rate of fluid pressurization. Under laboratory conditions, effective normal stress >20 MPa and Coulomb rupture stress >1.6 MPa will pose a serious threat to fracture stability, which is significant for evaluating the instability of natural faults activated by fluid injection.

    • Anomalous characteristics of the dominant azimuth of geoelectric fields at some stations in the Sichuan region before earthquakes

      2024(2):465-472. DOI: 10.20000/j.1000-0844.20230116001

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      Abstract:The anomalous characteristics of azimuth change were analyzed with earthquake cases using the geoelectric field dominant azimuth method to calculate the geoelectric field data of Jiangyou, Yanyuan, and Chengdu stations in Sichuan Province. Several results were obtained. (1) Since April 6, 2019, obvious abnormal changes have occurred in three directions at Jiangyou station, in which the dominant azimuth (Δα) range of two directions has gradually narrowed and that of one direction has increased. (2) Since August 1, 2021, the Δα ranges in five directions at Yanyuan station have decreased gradually. (3) Since March 1, 2021, the Δα range of five directions at Chengdu station has obviously changed, among which the Δα range of four directions has been gradually reduced, and that of one direction has been gradually increased. (4) The case study shows that the dominant azimuth anomalies of the stations have certain indicative significance for moderate-strong earthquakes within 250 km around the stations. The Δα range of the three stations all showed abnormal decreasing characteristics, and the earthquakes occurred about 5 months or even longer after the anomalies. Thus, the geoelectric field dominant azimuth method may show a medium-and long-term indication ability in this area. (5) Furthermore, the abnormal changes observed at three stations before the earthquakes reflect the changes in rock fractures near the sites. As the regional tectonic stress increases, the rock fractures near the station develop, exhibiting an orderly arrangement of structural variation.

    • Design and application of a borehole core basic database: a case study of Changshu station

      2024(2):473-481. DOI: 10.20000/j.1000-0844.20230109002

      Abstract (170) HTML (0) PDF 12.57 M (166) Comment (0) Favorites

      Abstract:This study investigates the key problems in the construction of a borehole core basic database (borehole core test, data processing, and data collection) and proposes a design scheme for the borehole core basic database. Taking the borehole construction at Changshu station in Jiangsu Province as an example, based on the newly issued construction standard (Specification for the Construction of Seismic Station Crust Deformation Station-Part 2: Crust Tilt and Strain Observatory in Borehole), some key works include borehole construction process, core experiment steps, and the development of core data processing and analysis software. The design scheme of the basic database provides detailed research ideas, methods, and examples for the collection and testing of borehole cores. This study fills the gap in terms of identifying new technical indicators in the national borehole standardization construction and provides a reference for the construction of the borehole core basic database in China.

    • Design and accuracy analysis of GNSS crustal deformation monitoring system in local areas

      2024(2):482-490. DOI: 10.20000/j.1000-0844.2022110800

      Abstract (201) HTML (0) PDF 15.81 M (182) Comment (0) Favorites

      Abstract:This study explores the relationship between shale gas production and crustal deformation, as well as the response of surface deformation to shale gas fracturing, by deploying a remote cross-fault GNSS deformation monitoring system. The system uses static and kinematic measurement methods to collect information on surface deformation, as well as combines multiple positioning modes to improve the reliability of surface displacement signal detection. Furthermore, it uses network communication and a cloud server to realize the automatic transmission of data, remote management of equipment, and kinematic monitoring of each site. Considering the distinguish ability between measurement error and deformation, the measurement accuracy was analyzed in detail. Results of static measurement indicate that the accuracy of single-day baseline solution and PPP static solution can reach 10 mm in both horizontal and vertical components. The kinematic positioning results for the Luding M6.8 Earthquake in Sichuan indicate that the accuracies of RTK, PPK, and PPP kinematic solutions all reached within 10 mm as well. The results of the accuracy analysis demonstrate that the system can well reflect some long-term and transient deformation information on the monitored areas.

    • Stress direction change and strong aftershock occurrence after the MS6.0 earthquake in Crete, Greece

      2024(2):491-500. DOI: 10.20000/j.1000-0844.20220929001

      Abstract (199) HTML (0) PDF 9.56 M (221) Comment (0) Favorites

      Abstract:The focal mechanism of earthquakes is an indicator of the variation of crustal stress, which is directly related to the occurrence of strong earthquakes. To date, no previous study has investigated the indication of focal mechanism change to the occurrence of normal-fault earthquakes with low apparent stress. This paper takes the 2021 MW6.0 earthquake sequence in Crete, Greece, as an example to determine the relationship between stress variation and the occurrence of strong earthquakes by calculating the minimum spatial rotation angle between the earthquake sequence's focal mechanisms and the direction of the regional stress field. The focal mechanisms determined by multiple agencies were used to obtain the central focal mechanism as the focal mechanism of the earthquake, thus ensuring the accuracy of the focal mechanism. Then, the local stress field was determined by the earthquake sequence's accurate focal mechanism. Finally, the spatial rotation angle of the crustal stress field was calculated, and the relationship between the occurrence of strong earthquakes and the variation of the stress field was explored. Results indicate that the spatial rotation angle between the focal mechanism of aftershocks and the direction of the regional stress field is large in the short term after the mainshock, thereby corresponding to the weak seismicity of subsequent earthquakes with small magnitudes. Consequently, the spatial rotation angle decreases, corresponding to the occurrence of three strong aftershocks (MW>5.0). After that, the spatial rotation angle increases again for a long time, and the magnitude and frequency of the corresponding aftershocks decrease. Using the same 2021 MW6.0 earthquake sequence as an example, the results reveal that the stress direction concentration also exists before the normal-fault earthquakes with low apparent stress. Therefore, this study provides an example for the exploration of earthquake stress precursors.

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