CHEN Chuan-xin , LIU Yan-hui , HE Rui , CHEN Yin , TAN Ping
2017, 39(3):397-403. DOI: 10.3969/j.issn.1000-0844.2017.03.0397
Abstract:With the aim of carrying out a dynamic response study of a large, ultrahigh voltage converter transformer, the 3D FEM analysis model of an actual ±800 kV converter transformer was built considering oil-solid interaction. Then, the natural vibration characteristics, dynamic response rules, and vulnerable points of the ±800 kV converter transformer were analyzed by using the LS-DYNA software. Simulation results show that interaction of the oil and wall has an obvious amplification effect on the dynamic response of the converter transformer, and that the oil-solid interaction should be considered in the analysis of natural vibration characteristics and seismic response of a converter transformer. The vulnerable points of the sleeve are at the root and middle part of the sleeve, and the max tensile and press stress at these points appear in turn. The sleeves of the converter transformer show large displacement during an earthquake. In addition, the electric wire at the top of the sleeve should have enough reserved length.
DU Yong-feng , ZHANG Wen-li , HUANG Xiao-ning
2017, 39(3):404-410,424. DOI: 10.3969/j.issn.1000-0844.2017.03.0404
Abstract:After many years of development, researchers have begun to realize that the traditional seismic design method of using the plastic deformation and damage of the structure itself to dissipate seismic energy could no longer meet safety and economic requirements. Thus, energy dissipation technology has become a hot issue in the field of seismic building designs. Many design methods have been proposed, such as the energy dissipation design based on equivalent linearization, displacement, and energy. Most of the proposed designs, however, are based on the perspective of the whole structure. However, the safety of the most integral parts is ignored. Thus, for the sake of protecting such parts of a structure, some suggestions for the application of energy dissipation design method are given in this work in the form of an optimal allocation method of energy dissipation brace based on the load path. Specific design steps of this energy dissipation method are listed in this paper. The most integral parts of a structure transfer the main load in load path. When these parts are damaged, such damages can have a huge effect on the structural safety of an entire building. First, we simulate an irregular-plane RC frame structure using a finite element modeling software. Then, we use the basic principle of Generalized Rigidity method to calculate the importance coefficients of all elements found in a structural system. Second, we assume the energy dissipation brace section parameters and then arrange the braces in these locations, such that the element importance coefficients are maximized on each floor. Third, we check the final brace parameters after checking the axial forces in the most unfavorable conditions while considering seismic response. Next, we use dynamic time history analysis method to analyze the irregular-plane RC frame structure. In this process, three different seismic conditions divided by the earthquake fault distance are considered, including far-field ground motions, near-field ground motion with pulse, and near-field ground motion without pulse. The analysis results show that regardless of the ground motion, this energy dissipation design method based on the load path can provide effective protection to the most integral parts of the structure. Furthermore, the structural seismic response is also well controlled. Finally, these energy dissipation braces can work well in different earthquake intensities.
2017, 39(3):411-416. DOI: 10.3969/j.issn.1013-0019.2017.03.0411
Abstract:The performance of infilled walls is very important in the local and global seismic performance of irregular frame structures. Continuous research on damping infill walls has greatly improved the seismic performance of infilled frames. However, complex construction technologies and high construction costs have rendered the large-scale use of this type of structure impractical. To reduce the difficulty and cost of construction and improve the seismic performance of the resulting frame structure, the anti-seismic performance of a damped infill wall in an irregular frame is studied. Considering the characteristics of an irregular frame structure, the damping infill wall is arranged in a variety of ways, and these layouts are compared via analyses of mode type, energy dissipation, and component utilization. Damping infill walls with better damping effects can be obtained when it is arranged in the position of each mode type. The utilization ratio of the structure changes when the damping infill wall is arranged around the member, and the energy consumption of the damping infill wall increases. This paper also proposes an optimal layout strategy of damping infill walls in irregular frame structures. Optimization of the local arrangement of damping infill walls is used to improve the seismic performance and reduce the construction difficulty and cost requirements of the final structures. This work provides some suggestions for the design of infilled frame structures.
WANG Ai-wen , PAN Yi-shan , ZHAO Bao-you
2017, 39(3):417-424. DOI: 10.3969/j.issn.1013-0019.2017.03.0417
Abstract:To solve the problem about bolt support structure failure caused by rockburst in coal mine, dynamic numerical calculation method was used to study the dynamic coupling effect and failure mechanism of supporting structure of anchor-surrounding rock under impact load. The result shows that: (1) the action of impact load, a phenomena of non-synchronous vibration appears in bolt and rock the phenomena is defined as "time difference effect", which would trigger the synchronous vibration of rock and thesurrounding rock the debonding along bolt and rock interaction appear. With the increase of bond length, the synchronous vibration between bolts and rock occurred, which obviously, and eventually avoids the debonding between bolts and rock. (2) With the increase of velocity of impact load, obviously, and the failure mode of bolted rock from the type of the debonding or shank break into the type of overall failure of bolts and rock. (3) The resonance phenomenon presented as the excitation frequency approaching natural frequency of bolted rock structure, but velocity amplitude of synchronous vibration of bolted rock structure obviously increases, and the bolts or its surrounding rock would be damaged even under the action of impact load with a relative small peak value.For a given bolted rock structure, an excitation load with a critical frequency would cause a half vibration period between bolt and rock, which would result in greater relative vibration velocity between bolt and rock, and finally yield the debonding or shank break. Influence of impact load on the interaction between anchor and surrounding rock is less when the frequency of impact load is away from natural frequency of bolted rock structure.
2017, 39(3):425-433. DOI: 10.3969/j.issn.1000-0844.2017.03.0425
Abstract:The pounding between the abutment and superstructure has a significant influence on the seismic response of bridges during major earthquakes, especially in the case of flexible bridge systems, such as the continuous rigid-frame bridges with high, double thin-walled piers. Compared with the pounding effect between superstructures, the aforementioned pounding phenomenon is far more complicated because of the abutment-backfill interaction. In this paper, the pounding effect on the seismic behavior of high thin-walled piers was specifically examined. A simplified analytical model of abutment-backfill interaction was proposed, and the Kelvin impact model was applied to formulate the pounding between the abutment and superstructure. By using the nonlinear time history method, the effects of pounding on the seismic shear force, moment, curvature and displacement responses of high thin-walled piers were investigated, along with the longitudinal deformation of the pot bearings. Three countermeasures, which were elaborated as sacrificial back-wall, viscous damper and strengthened link beams, were suggested for reducing the pounding effect. The efficiencies of the three countermeasures were also compared in detail. The results showed that the pounding significantly increases the seismic force and curvature responses of high piers; the pounding also decreases the top displacement and results in the longitudinal deformation of pot bearings. The variation of impact stiffness has an influence of less than 20% on the seismic response of the bridge structure. Using the sacrificial back-wall and the viscous damper as countermeasures, the seismic force and curvature responses of high piers can be reduced sharply to magnitudes that are close to those obtained without considering the pounding effect. The viscous damper can also protect the pot bearings from exceeding the deformation limits, whereas the sacrificial back-wall tends to damage the pot bearings. The application of strengthened link beam as a countermeasure is proved to be ineffective in mitigating the pounding effect; on the contrary, it can actually increase the seismic response of high piers.
XIONG Kun , HE Yun-long , XIAO Wei , LIU Jun-lin
2017, 39(3):434-442. DOI: 10.3969/j.issn.1000-0844.2017.03.0435
Abstract:Yele Dam is a rockfill dam with an asphaltic concrete core wall and a maximum height of 124.5 m. The geological conditions around the area are fairly complex and present high seismic intensity. The earthquake monitoring station, which consists of nine strong motion seismographs, obtained 57 seismic response records from May 2005 to December 2014, including those of recent earthquakes, such as the Wenchuan earthquake, the Panzhihua earthquake, and the Lushan earthquake. Time domain and spectral analyses were carried out based on the monitoring data, and some dynamic response features of Yele Dam during these earthquakes were preliminarily summarized. The results showed that the dynamic response of the dam crest was amplified in most earthquakes and that the amplification factor obviously increased with decreasing PGA in the dam bottom. Because of differences in earthquake source characteristics and transmission routes, the spectral features of the dam's seismic response during these earthquakes significantly differed. All of the records indicate that the earth and rockfill dam exert obvious filtering effects on earthquake waves.
YIN Xun-qiang , LIU Xiao-meng , WANG Gui-xuan
2017, 39(3):443-451. DOI: 10.3969/j.issn.1000-0844.2017.03.0444
Abstract:A comparison study of treatment schemes for non-rock foundation has important practical engineering value for a nuclear plant that does not meet seismic suitability requirements. According to the actual site conditions of such an inland nuclear power plant, a numerical calculation model is proposed, and the evaluation for foundation treatment scheme is carried out in this work. First, three schemes (the rock-socketed pile, CFG pile, and cement-soil mixing pile) are applied to the foundation processing based on the actual engineering situation, and the bearing capacity of foundation is verified by the normative method. In order to meet the requirements of bearing capacity, the calculation model of pile-soil-structure dynamic interaction of non-rock foundation is established, which can be used in the seismic response analysis of the nuclear plant. Meanwhile, viscous artificial boundary and the energy transfer boundary are applied to simulate the infinite foundation radiation damping effect. Meanwhile, the viscous artificial boundary, which is recommended by ASCE4-98, is used to simulate wave transmission in the artificial boundary by decorating a series of dampers in the boundary in such a way that they can absorb the reflection undulation energy of the external boundary. In the meantime, the equivalent linear method is used to describe the nonlinear characteristics of the near field ground. The equivalent linearization technique is then solved using the frequency-domain linear wave method. The calculation was done by substituting shear modulus and damping ratio in different strain amplitudes for the equivalent shear modulus and damping ratio, thus transforming nonlinear issues to linear one. In addition, the influence of the pile group effect is determined by using the full coupling method based on the finite element model. Finally, the optimum design scheme is obtained from the comprehensive evaluation of the site foundation adaptability and economic benefits. The research results can provide reference for the selection of various non-rock ground treatment schemes under similar conditions.
TIAN Ying-xia , HU Gao-xing , WANG Ya-nan , LV Dan-dan
2017, 39(3):452-459,466. DOI: 10.3969/j.issn.1000-0844.2017.03.0452
Abstract:With the development of performance-based design methodologies, the research of displacement response spectra is gradually becoming more important. For the isolated structure with long period, the displacement response is more significant than that of the acceleration response, which makes it necessary to study the displacement response spectra. According to the rule of the specific earthquake mechanism, site conditions, epicentral distance, and magnitude, 60 earthquake records are selected as the external incentive. MATLAB software is used to script a program for the displacement response spectra; the result of displacement response spectra is derived from the program and compared with the spectra given by the codes, and some inherent problems are discussed when the spectra given by the codes is used to predict the displacement demand on the isolated structure. Research results show that for the inelastic displacement response spectra of the isolated structure, including the ascending segment, the stable segment, and the horizontal segment four stage with the prolonging of the natural vibration period, the displacement response spectra derived from the spectra given by the Chinese seismic code is significantly different in spectral shape and amplitude. The displacement response spectra proposed by Eurocode8 has similar shape to the isolated structure, which can better describe the change trend, but the peak value of the displacement spectra is larger than the actual calculated value. So, the characteristics of the displacement response spectral shapes and amplitudes are thoroughly researched according to the result calculated by MATLAB, the influence of factors like the yield displacement (X_{y}) and yield stiffness ratio (α) of the seismic isolation bearing, ground motion intensity parameters on the displacement response spectra are considered. Based on the obtained results, an updated formulation for the inelastic displacement design spectrum of an isolated structure is proposed, which can be used to predict the displacement demand of the isolation layer and to determine the type of bearing; thus, simplifying the design process.
QIN Feng-yan , YANG Fu-lian , LIU Hong-bo , WU Kun-ming
2017, 39(3):460-466. DOI: 10.3969/j.issn.1000-0844.2017.03.0460
Abstract:To perform a comparative analysis of seismic stability on a common slope support form, the corresponding numerical model for the following was established: a comparative analysis pile, a pile with pre-stressed anchor, and lattice beams with pre-stressed anchor. The seismic stabilities of these three kinds of support form were then calculated. The results show that, after the earthquake, the three kinds of support form are basically the same, along with the amplitude attenuation coefficient of slope stability and deformation, although the attenuation of lattice beams with pre-stressed anchor was slightly weaker. From the magnification of the force structure perspective, the force amplification level of the anti-slide pile was significantly higher than those of the two other kinds of support form. Furthermore, the pre-stressed anchor not only improved slope stability, the supporting structure can also enlarge the internal force, thereby enhancing the safety performance of the support structure. These conclusions can provide references for the choice of slope support form in the earthquake zone.
ZENG Bo , WANG Kun , DENG Liang-sheng , LIU Zhang-jun
2017, 39(3):467-474. DOI: 10.3969/j.issn.1000-0844.2017.03.0467
Abstract:Based on the method of orthogonal expansion and the idea of random variables, the evolutionary power spectrum model of the non-stationary ground motion acceleration process is proposed, and parameter values of the model are determined according to the code. The non-stationary ground motion acceleration process can be represented as a function with a basic random variable, and the set of representative time histories of the non-stationary ground motion acceleration process with complete probability is obtained. To prove the effectiveness of the method, the Koyna gravity dam in India is used as an example to analyze its response and reliability. Considering the nonlinearity of concrete materials and fluid-solid coupling between dams and reservoir water, the finite element analysis is conducted and horizontal displacement of the dam crest and tensile stress of the dam abutment are obtained. It is shown that rich probability information can be obtained by using the probability density evolution method and the thought of equivalent extreme events. This study provides a new approach of random ground motion response analysis and a reliability study of dam structures.
WU Yan-kai , LI Ji-xing , SHI Yu-bin , JIN Hong-dong , HU Xiao-shi
2017, 39(3):475-480. DOI: 10.3969/j.issn.1000-0844.2017.03.0475
Abstract:In this study, the dynamic properties of reinforced earth retaining walls under seismic load were analyzed by using Plaxis, a finite element analysis software program. The analysis focused on the dynamic response characteristics of the wall under the influence of different reinforcement lengths, reinforcement spacing, and peak acceleration, assuming an ideal wall with a height of 6 m and a base in foundation soil. Through simulations, it was determined that changes in reinforcement length, reinforcement spacing, and peak acceleration had the strongest influence on the horizontal displacement, vertical settlement, and stress in the reinforcement materials of the earth retaining wall. The horizontal displacement of a wall can be effectively reduced by using reinforced materials of longer length. However, this will lead to an increase in reinforced tensile load, and an uplift of reinforced earth retaining wall. The value of peak acceleration has the greatest influence on the horizontal displacement of wall. Although increases in horizontal displacement result from increases in peak acceleration, it is not a linear relationship. Decreases in reinforcement spacing can also effectively limit the overall horizontal displacement of wall, however, across a certain range, it can result in a relative increase in bottom of wall horizontal displacement. Therefore, reducing the displacement of a wall by decreasing the reinforcement spacing is only useful to a limited extent.
DING Wei , CHU Xi-hua , CHANG Jiang-fang
2017, 39(3):481-487,508. DOI: 10.3969/j.issn.1000-0844.2017.03.0481
Abstract:Geomaterials are usually transversely isotropic due to natural deposition. Their mechanical properties are obvious different along the deposition direction, however, substantially the same in the plane perpendicular to that direction. Anisotropic parameters such as fabric tensor, loading direction and stress state can be introduced to the isotropic strength criterion in order to simulate the anisotropic properties of geomaterials. In this study, in order to establish a criterion for transversely isotropic geomaterials, the anisotropic parameters such as anisotropic intensity and yield surface size are introduced into the Lade model. The iterative scheme corresponding to the forward Eulerian algorithm of Lade transversely isotropic yield criterion are presented. The influences of the principal axis direction on the bearing capacity of shear bands and structures are analyzed in numerical examples. Numerical results show the validity and performance of the proposed model in simulating the strain localization behavior of transversely isotropic geostructures.
OU Zhe , YANG Jia-fu , WANG Tie , ZHANG Guang-quan , ZOU Min
2017, 39(3):488-495. DOI: 10.3969/j.issn.1000-0844.2017.03.0488
Abstract:The wave velocity of a rock mass and the Hoek-Brown criterion are introduced to enable the building of a calculation model of the range of values of horizontal geostresses (σ_{H}) in an initial ground stress field. The rationality of this calculation model is evaluated by the measured geostress data. Based on the Δσ_{H} calculation model, a Δ(σ_{H}/σ_{V}) calculation model of the values range of the ratio of the horizontal and vertical geostresses (σ_{H}/σ_{V}) is deduced; this model is then used to provide a reasonable explanation of the σ_{H}/σ_{V} distribution of phenomenon in the surface and deep of earth's crust is given from the perspective of rock mass stability. The coefficient of horizontal pressure (λ) is calculated via the lower ((σ_{H}/σ_{V})_{min}) and upper ((σ_{H}/σ_{V})_{max}) limits of σ_{H}/σ_{V}, which is given by the Δ(σ_{H}/σ_{V}), and comparative analysis of the calculated and measured values of λ is performed. Results show that the calculated and measured λ present consistent characteristics in a shallow rock mass but significant differences in a deep rock mass. Thus, the Δ(σ_{H}/σ_{V}) calculation model is applicable to λ calculations in shallow rock mass engineering. The calculated λ presents obvious nonlinear variation features along the depth (h) direction, and the functional relationship λ=ah^{b}+1 between λ and h is given by setting up appropriate boundary conditions; this functional relationship is confirmed by curve fitting. The fitting results show a very high fitting correlation coefficient for λ=ah^{b}+1, which means it can describe the functional relationship between λ and h well. This functional relationship can be used for initial geostress field evaluations and provides the necessary initial geostress field conditions for simulating deformation and failure of excavated rock masses.
LU Yu-lin , BO Jing-shan , CHEN Xiao-ran
2017, 39(3):496-501. DOI: 10.3969/j.issn.1000-0844.2017.03.0496
Abstract:Slope stability is an important research field, and the Swedish arc method is a traditional calculation method used in soil engineering. In this study, three calculation models of slope failure were constructed based on the assumption of the non-existence of inter-slice force. Then, the analytical formula of slope stability was obtained by dividing the horizontal soil slice using the integral form. Upon comparing the results of the five examples, we find that the solution of the horizontal integral form was less complex and that the slope stability factor was lower, unlike others, but the maximum error was not more than 13% compared with the Bishop method. These findings indicate that the horizontal slice model can obtain a relatively safe stability factor compared with other methods. Furthermore, the inter-slice force can be used to simplify the calculation. The stability factor was also smaller, because the moment was balanced but not the force in the soil slice. In the horizontal slice model, the distances of the arm were not the same between the sliding forces produced by gravity and resistance, thus leading to an error in the slope stability analysis. Then, the sliding moment is amplified, finally leading to a smaller stability factor, which can be calculated by the horizontal slice method with integral form in the lower bound. However, in the vertical slice model, the calculation of the stability factor can be simplified as the ratio of sliding force to resistance. Such a failure to consider the arm, however, can lead to minor errors. For both the horizontal and the vertical slice model, the calculation of the common points was simplified by not considering the inter-slice force. As long as the geometric and boundary conditions are clear, then the analytical solution of the stability factor can be obtained. The main advantage of the horizontal slice method with integral form is that the calculation interval is smaller and it can be applied to multi-layer soils than the vertical slice method. Therefore, the proposed method has significance in evaluating the slope stability and can also provide a new idea to calculate the complex slope in the field of practical engineering.
ZHAO Wan-song , GENG Shu-wei , DONG Man-sheng
2017, 39(3):502-508. DOI: 10.3969/j.issn.1000-0844.2017.03.0502
Abstract:In this study, we collected 1,237 horizontal strong ground motion records, including detailed borehole data, from the 1933—2015 period at 166 sites in the Western United States. We fit the standard response spectrum to the Chinese Code for the Seismic Design of Buildings (GB 50011-2010) and extracted the characteristic periods of the response spectrum. In this paper, we discuss the influences of site, magnitude, and epicentral distance on the characteristic period of the response spectrum and prove that these periods increase when the site becomes soft. The characteristic periods of the response spectrum increase with increasing magnitude within the same scope of epicentral distance. With increases in the epicentral distance, the characteristic period lengthens within the same range of magnitude. The magnitude and epicentral distance have some influence on the characteristic period. With respect to a single factor of magnitude or epicentral distance, which influences the characteristic period values at the same site classification, research shows that the magnitude has more influence than distance. We divide characteristic periods at class II sites into three zones. The method for partitioning the characteristic periods at other sites is the same as that at class Ⅱ sites. We determined the scope of the characteristic period of the acceleration response spectrum according to the seismic ground motion parameters zonation map of China (GB 18306-2015). We statistically analyzed the averages of the characteristic period of the response spectrum at different sites based on the zones of the characteristic periods and discuss the reasonable characteristic period values in the current seismic design code. Compared with the characteristic period values in the Code for Seismic Design of Buildings in China, we found most of the statistical characteristic period values to be larger. We divided the strong motion records of class Ⅱ sites into groups based on their scopes of magnitude and distance. We calculated the average peak ground acceleration for each group and, based on the general rule that peak ground acceleration decreases with decreases in magnitude and increases in the epicentral distance, we ascertained the partitions of the peak ground acceleration. We found the partition of peak ground acceleration for site Ⅰ_{0}, Ⅰ_{1}, and ⅢI classes to be the same as that at class II sites. Next, we calculated the average characteristic period value in each zone of peak ground acceleration for different sites and discuss the influence of the seismic peak ground acceleration on the characteristic periods. Our results show that the characteristic period of the response spectrum has clear distinctions within different partitions of the peak ground acceleration. Based on these results, we offer some proposals regarding the characteristic periods of the response spectrum.
YUAN Dao-yang , LEI Zhong-sheng , WANG Ai-guo
2017, 39(3):509-520. DOI: 10.3969/j.issn.1013-0019.2017.03.0509
Abstract:A large earthquake occurred at Luojiabu town, between the two cities of Tianshui and Lixian in the south of Gansu Province on July 21, 1654, that is, June 8-the eleventh year of Shunzhi in the Qing Dynasty. It is called the Southern Tianshui earthquake with magnitude about 8. This paper simply reviews the research history of the Southern Tianshui M8 earthquake in 1654. Then, according to the original historical earthquake data and new data by additional investigation in recent years, we check the intensities of the destoried sites, and then modify the seismic isoseismal line again, where the long axis is about the NE direction. This earthquake caused a large area of the town wall to collapse, civilian houses were ruined, and a large number of people died or were injured. It also caused serious seismic-geological disasters, such as landslips, rock collapses, and sag lakes. The epicenter area was located in the area from Yongxing, Luojiabu to Tianshui town along the valley of the western Hanshui River, west of Lixian county city. This area developed an active fault in Holocene, the Lixian-Luojiabu fault, which is characterized by left-lateral strike-slip faulting by normal components. According to recent field investigations, there are some earthquake rupture traces, such as seismic fault scarps, small valley left-lateral offsets, and seismic fault grooves along the Lixian-Yanguan-Luojiabu segment of the fault. The location of the earthquake rupture is consistent with the heavily-damaged area affirmed by historical textual criticism data, and confirmed both of them the reliability and rationality of the results.
WANG Dong-zhen , ZHAO Bin , YU Jian-sheng , TAN Kai
2017, 39(3):521-526,544. DOI: 10.3969/j.issn.1013-0019.2017.03.0521
Abstract:This paper calculated the tectonic deformation characteristics of mainland China and the characteristics of the strain field in the plate space distribution, using more than 260 continuous CMONOC sites and more than 2,000 area stations, that are the latest observation data. According to the intensive, wide range of GPS velocity field shows strong east and west weak trends from the entire velocity field in mainland China. The maximum velocity appeared in the Himalayan region, with a general rate between 35 and 42 mm/a. The Sichuan-Yunnan region dextral shear zone formed by the deformation characteristics of the most striking that the southwest of the minimum rate is between 3 to 9 mm/a, north of maximum rate in 17~23 mm/a. It can be seen from the spatial distribution that the largest strain-stress are mainly from the following regions: Himalayan, Kunlun Mountains, Sichuan and the Yunnan areas of fresh water river fault zone, Tianshan region, and Beijing-Tianjin area. The strain rate of the east coast shows tension that is mainly due to the earthquake in Japan in 2011, although the influence of the region has not completely subsided.
TIAN Xiu-feng , YIN Zhi-wen , ZHANG Xuan , PAN Zhang-rong , ZHANG Wei-dong
2017, 39(3):527-533. DOI: 10.3969/j.issn.1000-0844.2017.03.0527
Abstract:Based on the strong motion observation data of the Wenchuan M8.0 earthquake and its aftershocks, as recorded by fixed and mobile stations in the Gansu Province, in this paper, we select 87 earthquakes with complete 3-component records (magnitude range of 3.0 to 8.0), calculate their shear stress values according to the relationship between the peak acceleration of the source and the ambient shear stress, and discuss the characteristics of the shear stress field. The results show a good correlation between ambient shear stress and moment magnitude. The corresponding stress values of earthquakes 3 to 5 in magnitude range from about 3 to 6 MPa, those 5 to 6 in magnitude range from about 6 to 9 MPa, and those 6 to 7 in magnitude have stress values above 9 MPa. The stress value of the Wenchuan M8.0 earthquake is biggest at about 20.6 MPa and the stress values of some of its bigger aftershocks were above 10 MPa. Due to the differences in site conditions, the corresponding ambient shear stress values of earthquakes of the same size exhibit a large range of changes that show a certain extent of discreteness. Using the least squares method, we obtained the relationship between the ambient shear stress and moment magnitude and found the ambient shear stress to also have a strong dependance on focal depth. When the focal depth is about 15 km, it can accumulate high ambient shear stress; but when the focal depth is either smaller or larger, it cannot. In addition, we found the spatial distribution of the shear stress value of the Wenchuan earthquake sequence to be NE trending, which is consistent with the spatial distribution of its aftershocks and its isoseismal contours. The high stress area of the aftershock sequences did not occur around the mainshock but were distributed in the northeast region of the mainshock.
HUANG Yan , CHEN Yan-yang , WANG Yan-bin
2017, 39(3):534-544. DOI: 10.3969/j.issn.1013-0019.2017.03.0534
Abstract:Qaidam Basin is located at the Northeastern margin of Qinghai-Tibet plateau, which is the largest basin on the plateau. The thickness of the Quaternary and Tertiary sediments in the basin vary laterally and reach a maximum of 3,000 m and 8,000 m, respectively. The temporary seismic stations deployed by the INDEPTH IV project recorded three component seismograms of the November 10, 2008 Dachaidan M_{W}6.3 earthquake, which occurred at the margin of Qaidam Basin. Analysis of seismograms at two stations, namely H01 and H02, which have similar epicentral distance and azimuth, show a significant difference. Station H01 is located at the bedrock around the basin and the H02 station is located inside the basin on the Quaternary sediments. Compared with the records at the H01 station, those at the H02 station show significant amplitude amplification, obvious duration extension, and very strong later phases. The amplification of the peak ground velocity reaches 2-3 times, and that for the later phases reaches up to 6 times. Fourier amplitude spectrum analysis for the seismograms show similar frequency range for the two stations. However, the later phases have a lower and concentrated frequency range. Horizontal ground particle motion at the H02 station for the later phases exhibit typical elliptical ground motion, which suggests that the later phases are surface waves. To investigate the mechanism of the ground motion amplification and strong later phases, two 2-dimensional (2D) cross sections through the hypocenter and two stations are constructed. Seismic wave propagation inside the two 2D models are calculated with the fourth-order staggered grid finite difference method. The size of the models is 210 km by 50 km. The model is discretized into 1,000 and 500 grids in the horizontal and vertical direction, respectively. Two-dimensional double-couple line sources are used in the modeling and the dominated period of the source time function is 1.5 s. Modeling results are analyzed with wavefield snapshots and synthetic seismograms. They show that the existence of a low-velocity sedimentary layer in the basin causes amplification of direct waves because of the changes of propagation direction in the basin. Multiple reflections and conversions occurred after the direct waves in the basin. At the edge of the basin, surface waves with large amplitude and low propagation velocity were generated by constructive interference between direct waves and their reflections and conversions. Comparing the observed and synthetic seismograms at the H01 and H02 stations show very similar characteristics. This suggests the existence of the low-velocity layer inside the basin caused the significant difference of observed ground motion at the H01 and H02 stations. The amplification of amplitude of direct waves at the H02 station resulted from the variation of propagation direction in the basin. Seismic phases between the direct waves represent their multiple reflections and conversions in the sedimentary layer. The large amplitude later phases with longer duration are surface waves generated at the basin edge by constructive interference between the direct waves and their reflections and conversions. Results of this study provide new observational examples for seismic ground motion amplification in the sedimentary basin and their possible mechanisms from numerical modeling.
XU Shun-qiang , XU Zhi-ping , LI De-qing , LI Yi-qing , YANG Li-pu
2017, 39(3):545-550. DOI: 10.3969/j.issn.1013-0019.2017.03.0545
Abstract:The Licheng fault is an important structural unit in the Jinhuo fault tectonic zone, which is of great significance to identify the structural characteristics. On the northern margin of the Licheng basin, we conduct the geophysical exploration and geological survey of the Licheng fault and study the Licheng fault activity. Shallow seismic exploration and high-density resistivity prospecting results show that the Licheng fault is an active fault in the Quaternary sediment with a steep dip. The geological profile shows that the Jinhuo fault is greatly affected by the Licheng fault, where there is a large difference between the northern and southern sections. Based on the above-mentioned research results, we believe the Licheng fault is the Quaternary active fault that has an obviously controlling effect on the Jinhuo fault. The Licheng area is the most important segment by which the Jinhuo fault's activities exhibit the largest differences between the northern and southern sections, and is controlled and cut on the northern margin of the Licheng basin. Investigating the geological and geophysical characteristics of the Licheng fault has important significance on the study of the Licheng basin and the Jinhuo fault and performing a seismic activity evaluation.
LI Hong-yu , YUAN Gui-ping , WANG Jun-fei , SUN Ye-jun
2017, 39(3):551-556. DOI: 10.3969/j.issn.1000-0844.2017.03.0551
Abstract:In this paper, we analyze the geomagnetic total field F component at the 02 point value for stations located in the 1000-km range of the epicenter of the Minxian 6.6 earthquake. We determined the changes in the spatial correlation coefficient with respect to the F component before and after the earthquake. Our results showed that: 1) 15 stations had a low spatial correlation prior to the earthquake and the average abnormal phenomenon lasted 22 days; 2) the anomalous amplitude decreased as the epicentral distance increased to a certain extent; 3) in the process of continuous abnormity, the minimum value time was uniform; 4) the average interval time was 54 days from the start of abnormity to the original time of the earthquake and 33 days from the end of abnormity to the original time of the earthquake. This anomaly had short-term effects. In addition, the locations of the abnormal stations have a certain similarity with respect to their regional structure trends, epicenters of the aftershock, and their magistoseismic area distributions. Although the uneven distribution of geomagnetic stations is an objective fact, this phenomenon provides some material for the study of the relationship between geomagnetic anomaly distribution and structure.
ZHAO Gang , HUANG Han-ming , LU Xin-xin , GUO Shi-hao , CHAI Hui-min
2017, 39(3):557-563. DOI: 10.3969/j.issn.1013-0019.2017.03.0557
Abstract:Back-propagation neural-networks (BP-NN) and the support vector machine (SVM) are the two mainstream methods for classification of seismic wave signals of earthquakes and explosion events used in this research. The two methods achieved accurate and effective results. However, when training the BP-NN, it is inevitable that it can be easily trapped in a local optimum; in addition, the optimal numbers of hidden layers and numbers of nodes in each layer are heavily dependent on the distribution configuration of the training samples data, and cannot be consistently determined in advance. Furthermore, when training the SVM, there is a shortage of effective means to select suitable kernel function(s); hence, the ordinary SVM cannot be easily extended to multiclass problems. Aiming at the classification of seismic wave signals of earthquakes and explosion events, this paper investigates and compares the BP-NN and the SVM, along with the BP-Adaboost ensemble learning method. Using the dataset of seismic wave signals of earthquakes and explosion events in the experiments of this paper, the classification results show that the BP-Adaboost method can achieve the overall correct recognition rate of not less than 98%, with excellent generalization ability. Compared with BP-NN and SVM, the two main traditional classification methods, it has been shown that the BP-Adaboost method is more robust for different dataset partitions and corresponding classification, which implies more robust generalizability and better classification of seismic wave signals of earthquakes and explosion events. In the meanwhile, the theory of the Adaboost method is applied to explain the reasons for the better classification results and the generalizability of the BP-Adaboost method.
LUO Guo-fu , SHENG Ju-qin , MA He-qing , WANG Ma-si-yan
2017, 39(3):564-570,586. DOI: 10.3969/j.issn.1000-0844.2017.03.0564
Abstract:In this study, we statistically analyzed 51 earthquake sequences with magnitudes ≥ 5.0 that occurred in eastern Northwest China from Jan. 1970 to Dec. 2012. Of these, the strike-slip type occurred 30 times, representing 58.8% of the total. The overlap and inverse-impulse type occurred ten times, representing 19.6%, and the normal fault type occurred six times, representing 11.8%. With respect to earthquake rupture type, the mainshock-aftershock type represented more than 60% of the rupture types, followed by the isolated type, and lastly the double shock or multiple shock type. With respect to normal-fault-type earthquakes, the mainshock-aftershock type had the highest proportion at 50%. The next highest proportion was the double shock or multiple shock type at 33.3%. The isolated type was least frequent. For earthquakes of the same rupture and sequences types, a linear relation between the main shock magnitude and the greatest aftershock magnitude was most common. Also, the relation was weak between the main shock occurrence time and the greatest aftershock occurrence time. More than 60% of the strike-slip and inverse-impulse types experienced the greatest aftershocks one day after the main shock but only 16.7% of the normal fault type experienced the greatest aftershocks one day after the main shock. If a sequence cannot be categorized as a double shock or multiple shock sequence, the empirical equation ΔM=1.54×M-6.53 can be used to analyze the greatest aftershock.
FU Ping , LIN Jin-hua , WANG Hong-tao , HUANG Li-jing , WANG Yu-qi
2017, 39(3):571-577. DOI: 10.3969/j.issn.1000-0844.2017.03.0571
Abstract:The NW-striking fault of the Minjiang River is an important seismic structure in the Fujian coastal area. Previous research has focused on the downstream section of the Minjiang fault, but little attention has been given of the fault location, geological features, and the latest active age of the upstream section. The upstream section is distributed between the city of Nanping and Xiongjiang County and the city of Minjiang. Based on a detailed field geological survey, we gained a new understanding of the distribution characteristics and activity of the upper reaches of the Minjiang River. The results show the following: (1) This area can be divided into two segments, with the western segment, located between the city of Nanping and the town of Taiping, being composed of two parallel right-lateral strike-slip normal faults, which strike NW300°. The eastern segment is located in the Xitang area, and has a NW300° strike-slip normal fault. (2) The fault at the upper reaches of the Minjiang River exhibits characteristic multiperiodic activity, at the early stage, mainly striking NW330°, and is characterized as a compresso-shear type. Its latest active time was in the pre-Quaternary. At the later stage, the fault was mainly striking NW300° and is characterized as a strike-slip type, as transtensional properties may still have been active in the early Quaternary.
WANG Wen-ming , YI Si-yin , TIAN Li , WANG Yan-ming
2017, 39(3):578-586. DOI: 10.3969/j.issn.1000-0844.2017.03.0578
Abstract:Underground pipelines, transportation, and power systems are important lifelines in engineering and often disrupted during earthquakes. Thus, ensuring the safety and reliable operation of these system is of extreme importance. First, this paper introduces the basic characteristics of cross-fault ground motion through ground motion simulation, structural responses, and shaking-table tests, among others. The current research situation and problems related to the seismic responses of different cross-fault structures in earthquakes are then summarized. Finally, important research problems of the seismic response of cross-fault large span space structures are discussed.
Sopyright:China Earthquake Engineering Journal