• Issue 4,2023 Table of Contents
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    • >Earthquake Engineering
    • Restoring force model of web-connected replaceable shear links

      2023(4):751-760. DOI: 10.20000/j.1000-0844.20210814001

      Abstract (593) HTML (0) PDF 20.08 M (776) Comment (0) Favorites

      Abstract:It is convenient and economical to repair eccentrically braced steel frames with replaceable shear links after an earthquake, but few studies have focused on it domestically and internationally. Therefore, 16 groups of web-connected shear links connected by bolts with eccentrically braced steel frames were designed and analyzed through numerical simulations. The effect of changing the parameters (section size, length of the energy dissipation section, stiffener spacing, stiffener arrangement, and comprehensive parameters) on the hysteretic performance and the skeleton curve of web-connected shear links under low-cyclic reversed loading was discussed, and the simplified restoring force model of shear links was established. The results show that section size is the parameter that primarily influences the energy dissipation of the web\|connected shear links. The proposed restoring force model is in good agreement with the simulated skeleton curve, which can be used as a reference for elastic-plastic analysis of such shear links.

    • Dynamic time\|history response of bridge pile foundations crossing active faults in seismic regions

      2023(4):761-771. DOI: 10.20000/j.1000-0844.20220702001

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      Abstract:Taking the Haven Bridge as the engineering background, we studied the dynamic response of pile foundations during earthquakes in the case where bridges cross active faults in strong seismic zones. The finite element software Midas GTS was applied to establish a numerical model of the pile-seabed rock-fault coupling action in areas characterized by strong earthquakes. The dynamic time-history response characteristics of the acceleration, displacement, bending moment, and shear force of the bridge pile foundation under the action of 5010 seismic wave with different intensities (0.20g-0.60g) were investigated. The results showed that the upper loose soil with a large thickness had an amplifying and filtering effect on the acceleration of the pile body, while the bedrock had a largely negligible effect. The horizontal displacement at the top of the pile foundation in the hanging and foot walls of the fault increased with the increase in the input seismic intensity, while the moment of reaching amplitude was consistent. The permanent settlement appeared 50 s after the vertical displacement time-history response at the top of the pile foundation in the hanging and foot walls, and the permanent bending moment appeared 40 s after the time-history response at the maximum bending moment section of the pile. Emphasis must be on appropriately designing the flexural capacity at the bedrock interface and at the interface between the soft and hard soils of the upper overburden as well as on designing the shear capacity near the pile top and the bedrock face. The pile foundation of the hanging wall should be designed on the basis of the dynamic parameters, such as the pile acceleration, bending moment, and horizontal displacement at the pile top, while the pile foundation of the foot wall should be designed on the basis of the dynamic shear stress.

    • Seismic analysis of the south bank section and wind towerstructures of Dalian Bay subsea immersed tube tunnel

      2023(4):772-779. DOI: 10.20000/j.1000-0844.20211221003

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      Abstract:In this paper, the internal force law of the south bank section and wind tower structure of Dalian Bay subsea immersed tube tunnel under the action of earthquakes and the structural damage characteristics in the elastoplastic stage were studied. In addition, a three-dimensional refined model of an immersed tube-plant-wind tower was established, and the ABAQUS built-in constitutive model of concrete damage was used to perform seismic response analysis of the structure under two seismic conditions using mode-superposition response spectrum and time-history analysis methods. Results show that the maximum displacement values in the X and Y directions are 1.11 and 5.56 mm, respectively, both appearing at the top of the structural ventilation tower. Moreover, the modal mass participation coefficients in the X and Y directions are 90.52% and 92.07%, respectively, both meeting the requirement of seismic code, and the bending moment at the junction of two lanes of the immersed tunnel is the largest, reaching 5 069 kN·m. Under rare earthquakes, the maximum story drift ratio of the structure is 1/2 798, and the maximum damage of the structure appears at the time of seismic wave peak. By observing the damage, the structural concrete is uniform, and no broken phenomenon is observed. The maximum tensile damage coefficient is 0.893-0.94, appearing at the fresh-air duct and roof of the fresh-air room. Therefore, enhancing the bending resistance at the connection between the two lanes of the immersed tunnel and adding reinforcement at the top plate of the fresh-air duct and fresh-air room are necessary to improve the tensile capacity.

    • Seismic performance of assembled piers connected withultra-high-performance concrete around the pier

      2023(4):780-791. DOI: 10.20000/j.1000-0844.20220617002

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      Abstract:To improve the seismic performance and construction fault tolerance of prefabricated assembled piers, this paper proposes a new connection method for assembled piers: assembled piers connected with ultra-high-performance concrete (UHPC) around piers. A cast-in-place bridge pier specimen and an assembled pier specimen connected with UHPC around the pier were designed and fabricated. A quasi-static test was performed on two specimens, and a three-dimensional solid nonlinear finite element model of the assembled pier specimen was established. The seismic performance and associated influencing factors of the proposed assembled pier were analyzed by performing a numerical simulation. The results showed that the assembled pier specimen connected with UHPC around the pier exhibited a similar lateral performance and self-resetting capability as the integral cast-in-place pier, and their seismic performances were the same. The fitting degree between the hysteretic curves of the nonlinear finite element model and the actual pier specimen was high, verifying the reliability of the modeling method and the accuracy of the simulation results. The height of the UHPC connection had little influence on the seismic performance of the assembled pier, and only the lap length of the reinforcement needed to be ensured. The axial compression ratio, column height, and lapped reinforcement ratio had evident effects on the seismic performance of the assembled bridge pier. When the axial compression ratio was between 0.1 and 0.3, the stiffness and horizontal bearing capacity of the specimen increased with the increase in the axial compression ratio. When the column height increased from 2.0 m to 2.5 m, the horizontal bearing capacity and accumulated hysteretic energy dissipation of the assembled pier decreased with the increase in the column height; when the reinforcement ratio was increased from 1.01% to 1.57%, the horizontal bearing capacity and residual displacement of the assembled pier were evidently improved compared with those of the original specimen.

    • Extraction of ridge line from PolSAR image usingthe region-growing method and variogram

      2023(4):792-800. DOI: 10.20000/j.1000-0844.20211116004

      Abstract (268) HTML (0) PDF 19.72 M (601) Comment (0) Favorites

      Abstract:The ridge line is usually the starting point of mountain disasters caused by earthquakes. An accurate identification of the location of the ridge line while monitoring such mountain disasters is crucial to facilitate the development of relevant preventive measures. However, detection of the ridge line in PolSAR images containing buildings with high scattering intensity can be challenging due to some imaging issues of synthetic aperture radar (SAR), resulting in misjudgments. A recognition method combining the region-growing method and the variogram is proposed in this paper to address this problem. During the recognition process, the collected image is first segmented by the region-growing method. Then, the texture variations and other features are clustered and analyzed by the Fuzzy C-means method, and the similarity is assessed to obtain the building area. The ridge line can then be extracted by comparing this with the mixed image. A comparative analysis of the experimental results for the proposed method show significantly improved extraction accuracy as compared with the threshold segmentation method. Thus, this study can provide a new idea for the detection of ridgelines in PolSAR images.

    • Model tests on accumulation landslides during post-earthquake rainfall

      2023(4):801-809. DOI: 10.20000/j.1000-0844.20211008003

      Abstract (270) HTML (0) PDF 16.79 M (669) Comment (0) Favorites

      Abstract:This study aims to explore the disaster mechanism, fracture development behavior, and initiation time of accumulation landslides during post-earthquake rainfall, taking the Jiangdingya landslide in Zhouqu County, Gansu Province, as an example. Four groups of post-earthquake rainfall tests with the same seismic intensity and different rainfall intensities were performed using a shaking table and an artificial rainfall model. The results revealed the following: (1) The earthquake causes shear failure of the slope, which is eroded by soil loss due to post-earthquake rainfall, with an obvious shear outlet at the slope foot. Thus, post-earthquake rainfall induces local instability in the accumulation landslide. (2) The earthquake causes shear cracks and dislocations in the middle of the slope and “arc-shaped” tensile cracks at the rear edge. During post-earthquake rainfall, the crack deformation intensifies with an increase in rainfall intensity, and sudden deformation occurs during the rainfall. (3) Given the same seismic intensity, there is an exponential relationship between the initiation time of the landslide and the rainfall intensity and a logarithmic relationship between the soil settlement deformation and the rainfall intensity. The results presented in this paper can provide a reference for the early warning and prevention of accumulation landslides during post-earthquake rainfall.

    • Instability mechanism and stability analysis of Chenzhuangloess-mudstone interface landslide under seismic action

      2023(4):810-818. DOI: 10.20000/j.1000-0844.20201009001

      Abstract (463) HTML (0) PDF 21.88 M (978) Comment (0) Favorites

      Abstract:The loess-mudstone interface landslide in Chenzhuang Village, Lixian County, Gansu Province, was investigated in this study. A dynamic numerical simulation of the instability mechanism and stability of the landslide subjected to ground motion at various artificial calculation sites was conducted based on an analysis of the seismic geological environment and basic characteristics of the landslide. Results show that the deformation and failure of the Chenzhuang landslide are associated with a composite failure mode of tension and shear when subjected to ground motion. The process of instability can be summarized as follows: ground motion due to an earthquake → tension at the bottom of rock mass → increase in shear stress at the upper part of the main slip section of the potential slip surface → emergence of a shear strain concentration zone → extension and penetration of the shear strain concentration zone → landslide instability. The stability of the Chenzhuang loess-mudstone interface landslide decreases with an increase in the ground motion, and the landslide is in an unstable state when subjected to bedrock ground motion with a exceeding probability of 2% in 50 years.

    • Effects of salinity and moisture content on the strengthof loess in Heifangtai, Gansu Province

      2023(4):819-825. DOI: 10.20000/j.1000-0844.20200519005

      Abstract (485) HTML (0) PDF 11.99 M (536) Comment (0) Favorites

      Abstract:The loess in the landslide area of the Heifangtai irrigation district in Gansu Province was taken as the research object in this study. The salt content and the chemical characteristics of the soil and water in the landslide area were investigated. A series of triaxial consolidation undrained shear tests was conducted on remolded loess with different soluble salt contents and moisture contents to explore the effects of the salinity and moisture content on the shear strength of the loess in this region. The results showed that (1) The soluble salt contents in the samples ranged from 0.15% to 4.55%, and the main components were Na2SO4 and NaCl. (2) The hydrochemical analysis showed that the irrigation water infiltrated and dissolved the soluble salt in the plateau loess, which was discharged and enriched at the slope foot in the form of spring point seepage. (3) The shear strength of the samples increased with the increase in the soluble salt content and decreased with the increase in the water content. (4) Under the conditions of different soluble salts and water contents, the cohesion varied from 4.2 kPa to 57.1 kPa, and the internal friction angle varied from 23.1° to 33.5°. The cohesion was more sensitive to changes in the soluble salt and moisture contents.

    • Shaking table test of rural buildings with ring beams and structuralcolumns considering soil-structure interaction effect

      2023(4):835-844. DOI: 10.20000/j.1000-0844.20220624001

      Abstract (216) HTML (0) PDF 16.48 M (540) Comment (0) Favorites

      Abstract:Herein, the parametric modeling method was employed in the analysis and design of damping structures. An optimal damper arrangement scheme was developed by presetting objectives and iterative optimization calculations for the energy dissipation structure of a B-level high-rise residential building in Tianshui City. Perform 3D and ETABS software were used to analyze the structural response during frequent and rare earthquakes to assess the seismic performance of the energy dissipation structure. The analysis results show that during small earthquakes, the story displacement, story drift ratio, story moment, and story shear of the energy The setting of ring beams and structural columns is an important measure to improve the overall seismic performance of rural buildings. In this study, a series of shaking table tests considering soil-structure interaction (SSI) was performed on rural buildings with ring beams and structural columns. The 1/4 scaled model of the structure used in the test was manufactured and placed on a foundation soil model. One natural and two artificial seismic waves were selected, and the input seismic amplitudes were 0.1g (7-degree), 0.2g (8-degree), and 0.4g (9-degree). The test results showed that under the action of a 0.4g (9-degree) earthquake, only slight cracks were induced around the corners of doors and windows of the longitudinal wall, and the failure mode was intact, indicating good seismic performance of rural buildings with ring beams and structural columns. With the increase in the seismic action, the acceleration amplification coefficient of the structural model decreased gradually, while the response of the story drift gradually increased. When the seismic intensity is high, the influence of the SSI effect on the acceleration transfer coefficient from the soil layer to the structure should be appropriately considered.

    • Design of energy dissipation and damperoptimization for a high-rise building

      2023(4):835-844. DOI: 10.20000/j.1000-0844.20230208001

      Abstract (221) HTML (0) PDF 15.64 M (600) Comment (0) Favorites

      Abstract:Herein, the parametric modeling method was employed in the analysis and design of damping structures. An optimal damper arrangement scheme was developed by presetting objectives and iterative optimization calculations for the energy dissipation structure of a B-level high-rise residential building in Tianshui City. Perform 3D and ETABS software were used to analyze the structural response during frequent and rare earthquakes to assess the seismic performance of the energy dissipation structure. The analysis results show that during small earthquakes, the story displacement, story drift ratio, story moment, and story shear of the energy dissipation structure are reduced by >6.5%, which meets the design requirements. During large earthquakes, the frame columns, frame beams, shear walls, and viscous dampers of the structure can meet the requirements of performance-based design, and the story drift ratio can meet the code limit. Accordingly, the structure can achieve the design goal of “no collapse during large earthquakes.” This study provides a reference for preset damping targets and the optimal layout of dampers in practical applications.

    • Control of story drift and seismic performance analysisof buildings considering shear at the base

      2023(4):845-851. DOI: 10.20000/j.1000-0844.20220801001

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      Abstract:To reduce the impact of earthquakes on the story drift of building structures, the relationship between the story drift control and the seismic performance of buildings was analyzed considering the shear at the bottom of the structure. A method for calculating the story drift of buildings was developed to determine the lateral displacement of beams, columns, and joints after shearing. The constraint conditions of the story drift limit were set based on these calculations. The story drift was controlled by reducing the beam and column spacings of the frame, the transformation between the plan structure and the three-dimensional structure, and implementing the bending-shear system. The seismic performance was tested and verified for an actual practical project. The results show that the error in the calculation of story drift was <3.5%. Furthermore, the ranges of the story drift under the Kobe wave and the El-Centro wave were 0.43-0.82 mm and 0.40-0.42 mm, respectively. After adjustment and control, maintaining the story drift in the range of 0.4-1.1 mm can improve the seismic performance of the building.

    • Dynamic characteristics and seismic performance of the brick-vaulthall of Kaiyuan Temple in the Ming Dynasty

      2023(4):852-861. DOI: 10.20000/j.1000-0844.20220505003

      Abstract (215) HTML (0) PDF 34.08 M (507) Comment (0) Favorites

      Abstract:A typical brick-vault hall of the Kaiyuan Temple in Suzhou City was selected as the research case for studying the mechanical properties and weak locations of the brick-vault hall heritages built during the Ming Dynasty in China under the action of earthquakes. The Rhino three-dimensional model of the brick-vault hall of the Kaiyuan Temple was established and imported into ANSYS Workbench to generate a finite element model. The natural frequency, mode shape, displacement response, and stress response of the brick-vault hall under the action of earthquakes were obtained using finite element analysis. Results show that the structure of the brick-vault hall of the Kaiyuan Temple has high symmetry and torsional stiffness. The vertical earthquake has little effect on the structure, while the seismic action in the depth direction has a considerable impact. From the perspective of stress, using the response spectrum analysis for brick-vault halls is safe, whereas using the time-history analysis for brick is safe from the perspective of displacement. The weak locations of the brick-vault hall of the Kaiyuan Temple under the action of earthquakes include the corner and top of the two layers of door and window arches, as well as passage arches in the width and depth directions, the gable end wall, and the middle and end of the roof.

    • Longitudinal deformation model and parameter analysisof railways under nonuniform frost heave

      2023(4):862-870. DOI: 10.20000/j.1000-0844.20220320001

      Abstract (520) HTML (0) PDF 15.56 M (439) Comment (0) Favorites

      Abstract:As a country covered by a large area of frozen soil, China's railway network in cold regions is generally affected by the frost heave of the foundation soil. Although research has focused on the frost heave characteristics of foundation soils, the railway-foundation soil interaction under longitudinal nonuniform frost heave deformation remains unexplored. Based on the theory of double-layer beam on elastic foundation, this study established a mechanical model of a railway-sub-rail foundation under the action of nonuniform frost heave deformation. An analytical solution of the model was derived, and the effects of the elastic coefficient of the interlayer and frost heaving on the displacement and internal force of the track were analyzed by combining with an example. The results showed that the elastic interlayer could effectively reduce the frost heave deformation and stress response of the rail, which is conducive to rail operation. The length of the transition section between the rail and the sub-rail foundation and the shear force and bending moment at the concave convex bending section increased with the increase in the frost heave displacement. The frost heave force acting on the sub-rail foundation was gradually transferred to the track with the increase in the elastic coefficient of the interlayer. The length of the transition section was only related to the amount of frost heave. The proposed calculation method and the conclusions obtained from the analysis can provide scientific guidance for the design, operation, and maintenance of railways in cold regions.

    • Characteristics of borehole shear test of loess

      2023(4):871-876. DOI: 10.20000/j.1000-0844.20211007003

      Abstract (236) HTML (0) PDF 10.33 M (593) Comment (0) Favorites

      Abstract:To study the application effect of the borehole shear test on loess, a series of tests under different primary normal stress and different normal stress increments were carried out on the typical Q3 loess in the eastern suburbs of Xi'an. The test results show that shear strength increases in a curvilinear trend with the increase in normal stress, and there is a critical normal stress value. Beyond this value, there is a good linear relationship between the shear strength and normal stress. It is in good agreement with the Mohr-Coulomb strength criterion, and the measured shear strength parameters have little difference. In a multi-stage loading test, the smaller the increment in normal stress, the greater the shear strength associated with the same normal stress. Compared with the multi-stage loading test, the shear strength measured by the single-stage loading test under the same normal stress is smaller, and the deviation degree increases with the increase in normal stress. At low normal stress, it is difficult for the shear teeth to be pressed into hard soil, resulting in low cohesion and a large internal friction angle. Therefore, it is suggested that shear plates should be developed to suit different soft and hard soils and a normal displacement observation system should be added to judge the press of the tooth tip into the borehole wall during the application of normal stress.

    • Evaluation method of sand liquefactionbased on SPT-APD-DDA

      2023(4):877-886. DOI: 10.20000/j.1000-0844.20220105001

      Abstract (496) HTML (0) PDF 11.54 M (382) Comment (0) Favorites

      Abstract:Many uncertain factors exist when establishing the empirical criteria with traditional methods. Thus, comprehensive research on the liquefaction criteria for complex sites needs to be conducted. In this paper, 49 groups of sand samples from the emergency repair project of immersed pipe of the Baotou section in Shanghai were studied. This paper first adopted the standard penetration test method to qualitatively evaluate the sandy silt soil within 20 m of the research area. With the use of the absolute difference percentage method proposed in this paper, 35 groups of soil samples with accurate discriminant results and 14 groups with discriminant errors were divided. Then, referring to the theoretical thought of discriminant analysis, the physical and mechanical parameters such as average particle size D50, uneven coefficient Cu, specific penetration resistance Ps, standard penetration point depth ds, groundwater depth dw, and standard penetration blow count N63.5 were added to the liquefaction evaluation. Finally, with the use of the soil samples with accurate discriminant results, a distance discriminant analysis model suitable for the engineering geological characteristics of the research area was established to quantitatively evaluate the soil layers of samples with discriminant errors. Research results show that the established comprehensive evaluation system for sand liquefaction comprehensively and objectively evaluates the sand liquefaction in the study area from multiple perspectives. Through reasonable anti-liquefaction and subsidence measures, the steady progress of subsequent projects is guaranteed, and a reference for the stability evaluation of sand liquefaction in sites with similar geological conditions is provided.

    • Seismic response of a large reinforced concrete frame structure-foundation system under nonuniform earthquake wave input

      2023(4):887-893. DOI: 10.20000/j.1000-0844.20220627002

      Abstract (222) HTML (0) PDF 10.07 M (415) Comment (0) Favorites

      Abstract:To explore the influence of nonuniform seismic wave input on the seismic response of reinforced concrete (RC) structures, a large 2D finite element model for the dynamic interaction between an RC frame structure and a foundation was built based on the OpenSees software platform. Numerical calculations of the RC frame structure were performed by inputting El-Centro seismic waves at incidence angles of 0°, 15°, 30°, and 35°. The internal forces of the frame columns and the story drifts of the structure were compared and analyzed. The results showed that the nonuniform seismic wave input method has an evident influence on the dynamic response of large-scale RC frame structures. With the increase in the incidence angle of the seismic wave, the axial force amplitude of the bottom column of the RC frame structure decreased while the shear force amplitude increased. The bending moment amplitude changed only slightly, and the amplitude of the story drifts increased. The research results have reference significance for the seismic design of large RC frame structures.

    • Seismic performance of rotational cable-stayed bridgesbased on the base isolation theory

      2023(4):894-900. DOI: 10.20000/j.1000-0844.20220406002

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      Abstract:To study the influence of a base isolation system on the seismic performance of rotational cable-stayed bridges, the Taichengxi Bridge on the newly-built Fuzhou-Xiamen passenger line was taken as the engineering background. A dynamic model of the entire bridge was established for a nonlinear time-history analysis. Seven seismic waves and five groups of base isolation schemes with curved surface friction pendulum bearings were selected to compare and analyze the seismic performance of the rotational cable-stayed bridge. The results showed that the natural period of the bridge increased, and the global stiffness and seismic response decreased evidently after adopting the base isolation system. Although the curved surface friction pendulum bearing had little influence on the structural deformation, it significantly reduced the internal force; therefore, it can be used as an isolation bearing in rotational cable-stayed bridges. With the adoption of the base isolation system, the bending moment at the bottom of the main pier could be reduced by 44.83%-55.82%, the shear force could be reduced by 40.3%-63.09%, and the maximum displacement in the rigid fixity zone of the tower and girder was 65.53 mm.

    • >Earthquake Research
    • Traditional and modern magnitude scales

      2023(4):901-909. DOI: 10.20000/j.1000-0844.20221020001

      Abstract (206) HTML (0) PDF 10.37 M (588) Comment (0) Favorites

      Abstract:In this paper, the data, calculation algorithms, and applicability of some traditional magnitudes (ML, mb, mB, MS, and MJMA) were first described and compared. Additionally, the theoretical basis and calculation methods of two modern magnitude scales (Me and MW) were systematically explored. The determination methods of some moment magnitudes (i.e., MWW, MWC, MWb, Mwp, and Mdt) were then introduced in accordance with different use data and applicable scenarios. Meanwhile, high-frequency GPS-based observation was increasingly used for the rapid determination of earthquake magnitudes due to the wide availability of GPS observation data. Finally, the time efficiencies of these magnitude determination methods were compared and analyzed, and the applicable scenarios and stability of different magnitude scales were discussed.

    • Synthesis and vibration characteristics of ground motionsunder the excitation of total reflected SV waves

      2023(4):910-916. DOI: 10.20000/j.1000-0844.20220206001

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      Abstract:Research has shown that the propagation direction of seismic waves from bedrock is not perpendicular to the ground surface. The site effect generated by obliquely incident seismic waves is quite different from that generated by vertically incident seismic waves. The site effect under obliquely incident shear vertical (SV) waves is more complicated than that under vertically incident SV waves on account of the existence of total reflection. In this study, a set of mathematical expressions of ground motions was derived based on the theory of homogeneous elastic half\|space seismic wave propagation when SV incident angles were less than, greater than, or equal to the critical angle. The mathematical expressions were then applied to a model example to calculate and analyze the ground motion characteristics under the excitation of total reflected SV waves. The results show that the ground motions generated by SV waves are mainly composed of incident and reflected waves, and the effect of sliding waves could be ignored. The ground motion trajectory exhibits the characteristics of rotational vibration of surface waves. With the increase in the incident angle, the ground horizontal vibration gradually decreases, whereas the ground vertical vibration gradually increases, but neither of them is greater than twice the peak value of the incident wave.

    • Relationship between abnormal gas radon concentration inJiayuguan and Maduo MS7.4 earthquake of 2021

      2023(4):917-925. DOI: 10.20000/j.1000-0844.20210811001

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      Abstract:Under the background of rising gas radon concentration in Jiayuguan for many years, an unprecedented change occurred in 2017. However, no earthquake matching the amplitude and duration of the anomaly has occurred in the Qilian Mountains seismic belt. On May 22, 2021, an MS7.4 earthquake occurred in Maduo, which is 570 km away from the radon measuring point in Jiayuguan. An in-depth analysis of the anomaly reliability, anomaly characteristics before the earthquake, anomaly change after the earthquake, and geological structure background was conducted in this study to determine the relationship between the radon concentration anomaly of gas in the Jiayuguan and Maduo earthquakes. Results show that the anomalous characteristics of the gas radon concentration in Jiayuguan are related to the structure where the earthquake occurred. The anomaly of gas radon concentration shows an annual distortion of 1 year or 6 months for earthquakes that occur along the Qilian Mountains seismic zone. By contrast, the anomaly demonstrates a long-term change in the propensity for earthquakes that occur far away from the Qilian Mountains seismic zone. The decreasing rate of radon concentration in Jiayuguan slowed down and then turned to a recovery state after the Maduo earthquake. The measuring points for gas radon concentration in the Jiayuguan and Maduo earthquakes are both located in the northeastern part of the Tibetan Plateau with the same dynamic background and structural correlation. The comprehensive analysis shows that the tendency anomaly of gas radon in Jiayuguan may be related to the Maduo MS7.4 earthquake. This study is of considerable importance in establishing a reliable anomaly index system and improving earthquake prediction.

    • Relationship between the boundary intersection of geomagneticlow-point displacement anomalies and earthquakes

      2023(4):926-932. DOI: 10.20000/j.1000-0844.20220211003

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      Abstract:The relationship between geomagnetic low-point displacement and strong earthquakes in the Chinese Mainland was studied in this paper based on observation data from the national geomagnetic network center. A good correlation exists between the two aspects. One or more low-point displacement anomalies emerged within two months before numerous M>5 earthquakes, and the earthquakes usually occurred within 300 km of the boundary of low-point displacement anomalies. Four geomagnetic low-point displacement anomalies occurred two months before the Menyuan M6.9 earthquake in Qinghai Province on January 8, 2022. Meanwhile, three geomagnetic low-point displacement anomalies occurred two months before the Menyuan M6.4 earthquake in Qinghai Province on January 21, 2016, and the Ganzhou M5.0 earthquake in Gansu Province on September 16, 2019. One or more intersection regions will be formed when the boundaries of multiple low-point displacement anomalies are superimposed on the same graph. Results showed that the earthquakes occurred near the intersection region of low-point displacement boundaries. Possible earthquake regions can be determined by combining the distribution of active tectonic faults, the occurrence of large earthquakes in history, potential risk areas of strong earthquakes predicted in the medium and long term, and annual risk areas of earthquakes in China. This study markedly narrows down the prediction range of earthquake location with the geomagnetic low-point displacement method.

    • Geochemical characteristics of H2 and Hg in soil gas and thermal infraredanomaly response before the Songyuan MS5.1 earthquake

      2023(4):933-945. DOI: 10.20000/j.1000-0844.20220409001

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      Abstract:Joint observation of various gases is an effective way to capture earthquake precursor anomalies. As the main means of short-term and impending earthquake prediction and precursor indicators, observations of hydrogen and mercury play an important role in revealing the relationship between underground (fault zone) fluid and earthquake preparation and occurrence. Through the fixed-point and joint observation tests of H2 and Hg from soil gas in the Zhaodong observation well of Heilongjiang Province, this paper conducts a comparative analysis of the relationship between the precursors and the main shock and aftershock sequences of the MS5.1 earthquake in Ningjiang, Songyuan, Jilin Province, on May 18, 2019. Results are presented as follows. (1) Three-month short-term and three-day impending anomalies of H2 and Hg concentrations in soil gas occurred before the MS5.1 earthquake, respectively. Considerable differences are observed in their manifestations and spectral characteristics before and after the mainshock, which may be related to the characteristics of hydrogen and mercury and the seismogenic mechanism. (2) High-value anomalies of H2 and Hg concentrations in soil gas appeared during the period of MS5.1 mainshock and aftershocks, primarily demonstrating “high value anomaly-returning to normal-occurrence of mainshock-high value anomaly after earthquake-returning to normal-occurrence of strong aftershock” and the characteristics of persistence, repeatability, and matching. (3) The geochemical characteristics of H2 and Hg in soil gas from Zhaodong fault zone before and after the MS5.1 earthquake have response characteristics to the thermal infrared anomaly near the epicenter, which is mainly characterized by “abnormal peak value of H2-abnormal high value of thermal infrared in the epicenter-occurrence of mainshock-abnormal peak value of Hg-abnormal decrease of thermal infrared in the epicenter-abnormal secondary high value of H2 and Hg-occurrence of strong aftershocks”. The above understanding can provide a reference for the study of geochemical characteristics and thermal infrared anomaly response of soil gas from the fault in Songliao Basin.

    • Construction of a 3D geological model based on theaccurate division of stratigraphic boundaries

      2023(4):946-953. DOI: 10.20000/j.1000-0844.20220324002

      Abstract (353) HTML (0) PDF 15.00 M (699) Comment (0) Favorites

      Abstract:Numerous problems are encountered in human-computer interaction modeling. This modeling only qualitatively considers the impact of stratum loss and demonstrates its high cost and long cycle. Moreover, human-computer interaction modeling fails to update the model and quickly build high-precision models in a large area. Automatic modeling disregards the influence of stratum loss. Therefore, the interpolation is still conducted in the area with no target layer, which expands the distribution range of the target layer and causes low model accuracy. First, the discrete thin plate spline function method was used in this paper for interpolation based on the current automatic modeling technology. Then, the stratum thickness DEM was accurately and reasonably generated to determine the formation boundary and analyze the stratum form quantitatively. Finally, a complex 3D geological model for the main urban area of Guangzhou City (1 500 km2) was automatically constructed. The actual drilling proves the reasonability and accuracy of the model. The proposed modeling method can markedly improve the efficiency of large-area modeling and reduce the modeling time and cost, which is conducive to the rapid update of the model.

    • Improvement in the inversion of corner frequency of thesource spectrum using the spectral ratio method

      2023(4):954-961. DOI: 10.20000/j.1000-0844.20210903002

      Abstract (198) HTML (0) PDF 13.68 M (382) Comment (0) Favorites

      Abstract:Corner frequency is an important dynamic parameter in seismic source physics. Accurate calculation of the corner frequencies is important for obtaining other seismic source parameters and improving the source spectrum model. However, corner frequency inversion results by the traditional spectral ratio method are inaccurate and discrete due to the signal-to-noise ratio of seismic waves, propagation path effects, differences in source mechanisms, and source processes of earthquakes. In this work, we utilized the spectral ratio method to estimate the corner frequency and implemented three tests (Bootstrap resampling method, Kolmogorov-Smirnov test, and spectral ratio trend test) to evaluate the calculated corner frequencies. These three tests can improve the accuracy of the corner frequencies estimated by the spectral ratio method. The spectral ratio method and these three tests were validated by calculating the seismic source parameters of the aftershocks of the Wenchuan earthquake from May 12 to September 12, 2008. We obtained the corner frequency fc, radiation energy ER, radiation efficiency ηR, and energy-moment ratio e of aftershocks with magnitude 3.7-6.5. According to the calculated results, the relationship between the corner frequency and the seismic moment can be expressed as M0∝fc-3.295±0.25, which is not in agreement with the self-similarity law M0∝fc-3. The seismic radiation energy increases with the earthquake magnitude. When the magnitude increases from 3.7 to 6.5, the energy-moment ratio e also increases from 8 × 10-6 to 5 × 10-5, and the radiation efficiency ηR increases from 0.32 to 0.9. If the self-similarity law holds, then the energy-moment ratio e and the radiation efficiency ηR should be constant. The inversion results of source parameters of Wenchuan earthquake aftershocks show that in terms of the energy released by earthquakes, the energy-moment ratio increases with the seismic moment, and the radiation efficiency of large earthquakes is greater than that of small earthquakes.

    • Comparison and analysis of three common calibrationmethods for the novel radon detector

      2023(4):962-969. DOI: 10.20000/j.1000-0844.20220914001

      Abstract (169) HTML (0) PDF 9.04 M (324) Comment (0) Favorites

      Abstract:Regularly conducting calibration on the detectors is necessary to ensure the accuracy and reliability of the measurement results from radon detectors. Three commonly used calibration methods are currently available for radon detectors in China: the standard instrument calibration method, RN-FD circular radon source calibration method, and solid radon source calibration method. These three methods were used in this paper to calibrate a novel radon detector. Results show that the RN-FD circular radon source calibration method is superior, which is consistent with the normal operating mode of the novel radon detector. Among the three methods, the standard instrument calibration method has the lowest system error, highest calibrating efficiency, and lowest maintenance cost. The RN-FD circular and the solid radon source calibration methods are both standard material transfer methods, which encounter several difficulties and inconveniences affecting the timeliness of instrument calibration, such as the transportation of solid radioactive sources, personnel and technology, and supervision of environmental protection. The differences between the three calibration methods in principle and operation are finally analyzed, and the influence of these differences on the accuracy of calibration results is discussed. The study can provide a reference for the compilation and implementation of the calibration operation procedure (standard) of the novel instrument.

    • Crustal S\|wave velocity structure of the middle TianshanMountains based on the direct inversion methodof ambient noise surface wave

      2023(4):970-982. DOI: 10.20000/j.1000-0844.20220706001

      Abstract (196) HTML (0) PDF 46.29 M (624) Comment (0) Favorites

      Abstract:The Tianshan orogenic belt is an intracontinental orogenic belt that has been revived and uplifted since the Cenozoic. Thus, understanding and appreciating the deep structure and basin-mountain coupling relationships in Tianshan orogenic belt are particularly important due to the strong seismic activity. The phase-velocity dispersion curves of the 6-52 s Rayleigh wave were obtained in this paper using the cross-correlation method of ambient noise based on the ambient noise data from 85 stations in the Tianshan orogenic belt and adjacent areas (40°-49°N, 79°-93°E) during 2017-2019. The direct inversion method of surface waves based on ray tracing was employed to investigate the 3D crustal S-wave velocity structure and basin-mountain coupling relationship in the middle Tianshan Mountains. Results show that the S-wave velocity distribution in the shallow crust is related to the thickness of sedimentary layers in the tectonic unit, demonstrating low velocity in the northern margin of Tarim Basin and the southern margin of Junggar Basin and high velocity in the Tianshan orogenic belt. Low-velocity bodies wrapped by high-velocity anomalies below the Tianshan orogenic belt are found in the middle and lower crusts; the Tianshan orogenic belt shows relatively low velocities near the Moho surface. The crustal thicknesses of the southern margin of Junggar Basin and the Tianshan orogenic belt are in the range of 45-50 and 50-62 km, respectively. Between 82°-86.5°E, Tarim and Junggar Basins are subducted bidirectionally below Tianshan Mountains; between 86.5°-88°E, the Junggar Basin is subducted southward to Tianshan Mountains. From west to east, different basin-mountain coupling relationships reveal the difference in tectonic movement in different regions of the middle Tianshan Mountains since the Cenozoic, thus providing a reference for further exploration of orogenic dynamical processes.

    • Construction of a visualization platform for seismicgeophysical network events based on MapSIS

      2023(4):983-990. DOI: 10.20000/j.1000-0844.20220208004

      Abstract (242) HTML (0) PDF 19.15 M (1666) Comment (0) Favorites

      Abstract:Observation events of the geophysical network are important data reflecting the change information of precursor network observation data, which can provide a scientific basis for the quality evaluation of monitoring data, earthquake analysis and prediction consultation, and earthquake science research. A visualization platform for seismic geophysical network events based on MapSIS is developed in this paper to maximize the event record data stored in the database. The platform realizes several functions (i.e., manual interactive and automatic statistical analyses of event records; generation of special reports after earthquakes). This platform also has the advantages of comprehensive functions and stable operations. The proposed platform has been deployed and used in the national earthquake precursor network and earthquake analysis and prediction consultation, and the daily thematic atlas and reports can provide scientific and reliable information services for earthquake analysis and prediction consultation.

    • Analysis and prediction of the occurrence time interval of earthquakesalong the Longmenshan fault zone using the SARIMA model

      2023(4):991-1000. DOI: 10.20000/j.1000-0844.20220421002

      Abstract (212) HTML (0) PDF 19.32 M (2457) Comment (0) Favorites

      Abstract:Different sequences of earthquake occurrence time intervals were first established in accordance with the magnitude based on the catalog data of MS≥2.5 earthquakes along the Longmenshan fault zone from January 2012 to September 2021. Testing of stationary white noise and the analysis of autocorrelation and partial correlation were then conducted, and short-, medium-, and long-period fitting and prediction were performed for each sequence by using the SARIMA model. Finally, the optimal model parameters and corresponding period values of different magnitude sequences were obtained by analyzing the model fitting effect. Among them, the model-adjusted R2of MS≥2.5 and MS≥3.0 sequences are more than 0.86, with a maximum value of 0.911; the short-term prediction effects of corresponding models are good and the values of predicted RMSE are 10.686 and 8.800, respectively. The prediction results of the models show that the overall trend of the occurrence time interval of subsequent earthquakes along the Longmenshan fault zone is stable. The trend of the MS≥3.0 sequence shows a slight increase; that is, the number of MS≥3.0 earthquakes along the Longmenshan fault zone will decrease slightly in a given time period, and the seismicity will decrease. Analysis results can provide a scientific basis for the study of seismic activity, and the analysis method and process can introduce an effective and feasible way for the analysis and prediction of earthquake occurrence times.

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