• Volume 38,Issue 5,2016 Table of Contents
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    • >地震工程
    • Assessment of Natural Frequency of Steel Frames in Offshore Atmospheric Environment

      2016, 38(5):673-677. DOI: 10.3969/j.issn.1000-0844.2016.05.0673

      Abstract (810) HTML (0) PDF 1.02 M (644) Comment (0) Favorites

      Abstract:Steel space structures in coastal areas are often exposed to the open air so are inevitably subjected to atmospheric corrosion. In this paper, we draw from the fields of material science and structural analysis to present a framework for evaluating potential damage from atmospheric corrosion to steel space structures in coastal areas. We derive equations that relate structural natural frequency sensitivity to structural member thickness and consider both the inner and outer surface corrosion of the structural member. Using an actual large steel space structure as an example, we examine the feasibility of our proposed approach and assess the potential structural damage caused by atmospheric corrosion. The results demonstrate that atmospheric corrosion does not obviously affect the natural frequencies of the structure but does redistribute the stress and some of the structural members may undergo large stress changes.

    • Seismic Behavior of High Strength Steel Composite K-type EccentricallyBraced Frames with Direct Displacement-based Design Method

      2016, 38(5):678-684. DOI: 10.3969/j.issn.1000-0844.2016.05.0678

      Abstract (810) HTML (0) PDF 1.15 M (963) Comment (0) Favorites

      Abstract:Links and braces use Q345 steel, while other structural members use high strength steel (e.g. Q460 steel). In particular, this is used in high strength steel combination eccentrically braced frames (HSS-EBFs), as it improves economic efficiency due to its weight and high strength. In this paper, in order to study their seismic performance, four groups of HSS-EBFs were designed using the direct displacement-based design (DDBD) method and included 5-, 8-, and 12-story structures. Nonlinear pushover analysis and dynamic elastoplastic analysis were performed on all designs, and inter-story drift and failure modes under rare earthquake events studied. The results show that the inter-story drifts satisfy the deformation requirement of the seismic code under rare earthquakes and the K-HSS-EBF structure presents an ideal progressively plastic mechanism, proving that this new design method is reasonable and reliable.

    • Discussion on the Spring Constant of Ground Foundation in the SeismicDesign of Underground Structures Using the Response Displacement Method

      2016, 38(5):685-692. DOI: 10.3969/j.issn.1000-0844.2016.05.0685

      Abstract (1146) HTML (0) PDF 1.27 M (1454) Comment (0) Favorites

      Abstract:Urban rail engineering faces significant challenges with regard to an earthquake resistant design of underground structures. The response displacement method is a simple method, which is widely used to design such structures. Thus, determining the ground spring constant in the seismic design of underground structures is very important. Four typical determination methods are introduced:the test method, Li's method, the MIDAS method, and the finite element method. Based on the values of the ground spring constant determined through these four methods and considering the local geological conditions in Beijing, response displacement models are used to obtain the bending moment, axial force, and shear force of the underground structures. The four determination methods are compared on the basis of their respective advantages and disadvantages. The results show that the values of the ground spring constant have a significant influence on the internal force response of underground structures. Moreover, using the response displacement method, we observe that the constant has a greater influence on the axial force and shear force and comparatively lesser influence on the bending moment. The test method is recommended for designers, when geological survey data are not available. The empirical formula and the finite element method can be used as alternative methods. In order to ensure design safety, the internal force of underground structures can be modified by a correction factor of 1.10, considering that the four typical determination methods have an impact on the internal force.

    • Seismic Response and Pounding Effect of an Interchange Skewed Bridge under Bi-directional Earthquake Motions

      2016, 38(5):693-700. DOI: 10.3969/j.issn.1000-0844.2016.05.0693

      Abstract (725) HTML (0) PDF 1.26 M (1016) Comment (0) Favorites

      Abstract:Special bridges, like skewed bridges, are increasingly used at highway intersections and interchanges mainly to overcome space constraints. Skewed bridges require special considerations in their analysis, design, and construction. Moreover, these bridges exhibit complex behavior in which the vertical, lateral, and torsional motions are often strongly coupled, raising many concerns regarding their behavior under dynamic loads. Research on the effect of bi-directional seismic excitation is essential for the analysis and design of seismically isolated bridges because the bi-directional motion is coupled and two independent unidirectional models cannot accurately describe the bi-directional behavior. The seismic response of an interchange skewed bridge model under bi-directional earthquake ground motions is investigated in this paper. A 3D finite element model has been developed, in which the pounding of decks at cap-beams, the friction of beams at bearings, and the interaction relation of pile and earth have been accounted for. The beam, piers, and piles are simulated by the three-dimensional beam element; the contact element is applied to simulate the pounding effect between the abutment and the adjacent beam end. Rayleigh damping was used to model the damping in the system, and the damping ratio of the concrete is assumed to be equal to 5%. In this study, the piles were regarded as elastic laterally loaded beams, and the soil surrounding them were idealized as a series of independent springs with constant stiffness, where the lateral stiffness at one point does not affect the lateral stiffness at other points along the depth of the pile. The numerical analysis showed that the direction of ground motion greatly influenced the forces and displacements of piers and girders of skewed bridges; therefore, these factors must be accurately taken into account for the future design and vulnerability assessment of skewed bridges. We conclude that the pounding effect resulted in an increasing possibility of structure failure of the beam decks and changed the regularity of stress and strain on the bridge structures. From the numerical results, the deformation with consideration of the pounding effect was about twice that without the consideration of the pounding effect, which also has an obvious impact on the bending moment of the beam.

    • Mechanism of Seismic Damage of a Large-span Concrete Arch Bridge

      2016, 38(5):701-706. DOI: 10.3969/j.issn.1000-0844.2016.05.0701

      Abstract (662) HTML (0) PDF 1.24 M (919) Comment (0) Favorites

      Abstract:The study of the damage mechanism of bridges is an important procedure that turns seismic damage investigation results into a practical technology. The damage features of arch bridges during the Wenchuan earthquake of 2008 differ from those of other earthquakes. Based on the data collected from the Wenchuan earthquake, the seismic damage mechanism of the Jinhua bridge was studied through post-earthquake investigation and numerical analysis. From the site-damage survey, it was found that the Jinhua bridge damage was mainly concentrated in the main rib and arch column, showing mainly concrete cracking and ring cracks of the arch column. The damage mechanism of the rib arch and arch column was simulated by FEM analysis, and the simulation results showed that under seismic loads, the flexural capacity of the spring cross-section of the main rib arch did not meet seismic requirements, while that of the vault cross-section did meet the requirements; flexural cracking appeared at the bottom section of the 8# arch column. It was concluded that the simulation results agreed well with post-earthquake investigation, and they can provide references for the seismic design of long-span arch bridges in mountainous areas with higher intensity. This paper also proposes some countermeasures for bridge design and construction techniques to minimize typical earthquake damage, and hopes to provide references for future bridge construction.

    • Parametric Study on Dynamic Response of Base-isolated Structure Subjected to Pulse-like Ground Motions

      2016, 38(5):707-712. DOI: 10.3969/j.issn.1000-0844.2016.05.0707

      Abstract (808) HTML (0) PDF 1.14 M (1010) Comment (0) Favorites

      Abstract:The use of base-isolation technology to resist earthquake damage has attracted much attention since its appearance. Many researchers at home and abroad have conducted studies focused on base-isolated structures under seismic ground motions. Near-fault pulse-like ground motions comprise a velocity or displacement pulse component and other components. Some research results showed that near-fault pulse-like ground motions can cause severe damage to structures. Seismic responses of base-isolated structures under near-fault ground motions have attracted much attention in recent years. Synthetic ground motions were used as input, then the influence of ground motion parameters and isolation-bearing parameters on base-isolated structural seismic responses were analyzed on the basis of nonlinear dynamic time-history analysis. First, a nonlinear motion equation of a base-isolated structure was established. Second, the structural nonlinear dynamic responses were solved under synthetic pulse-like ground motions by using MATLAB. And last, the effects of the velocity pulse period, the yield force of the isolation bearing, and the stiffness ratio of the isolation bearing on dynamic response of the isolation layer and superstructure were studied. Research results show that the effect of the velocity pulse period on the structural dynamic response was great, and the structural natural period should be distant from the pulse period. The influence of the stiffness ratio on structural response was significant, and it should be taken seriously when choosing isolation bearings. The yield force of the isolation bearing had a great influence on bearing displacement, and when the yield force became greater, the bearing displacement became smaller.

    • Natural Frequency of Mono-pile Wind Turbine ConsideringInteraction between Pile and Elastic Foundation

      2016, 38(5):713-719. DOI: 10.3969/j.issn.1000-0844.2016.05.0713

      Abstract (795) HTML (0) PDF 1.01 M (1059) Comment (0) Favorites

      Abstract:In this paper, we analyze the mono-pile wind turbine, comprising blade bodies, a hub, a cabin, a conical shell tower, a transition piece, and a mono-pile foundation. Our study objective was to determine the natural frequency of the mono-pile wind turbine above the mudline. We assumed the conical shell tower, transition piece, and mono-pile foundation to be a vertical steel tube (VST) with a uniform cross section and with the same elastic modulus. We used the lumped-mass method to simplify the mono-pile wind turbine above the mudline as two concentrated masses. One concentrated mass at the VST top is the summation of the mass of the blade bodies, hub, cabin and one-fourth the mass of the VST above the mudline. The other concentrated mass at the middle of the VST is one-half the mass of the VST above the mudline. Taking the mono-pile foundation below the mudline as a semi-infinite long pile, we used Zhang's method to obtain the horizontal stiffness and rotational stiffness of the pile top. In this way, we can determine the deflection of the VST under horizontal load at any point of the wind turbine above the mudline. The flexibility coefficient of the unit horizontal load at any position of the VST can be determined accordingly. Then, using both the flexibility and lumped-mass methods, we can determine the natural frequency of the mono-pile wind turbine above the mudline. Lastly, with an example, we retrieved the natural frequency value of the mono-pile wind turbine above the mudline. We then compared the analysis result with the mono-pile wind turbine natural frequency obtained without considering the interaction between the pile and elastic groundwork, and found little difference between them. The new theory we propose in this paper is more accurate theoretically and should be validated experimentally.

    • Robustness of a Parametric Identification Algorithm for Time-varying Systems Based on Wavelet Multi-resolution Analysis

      2016, 38(5):720-727. DOI: 10.3969/j.issn.1000-0844.2016.05.0720

      Abstract (705) HTML (0) PDF 1.16 M (976) Comment (0) Favorites

      Abstract:Research,based on Daubechies wavelet multi-resolution analysis,was carried out to solve parameter identification problems in multiple degrees of freedom time-varying systems.In order to improve identification efficiency and accuracy,numerical experiments,based on the above method,were conducted to study the various factors that affect performance.The results show that when the basic function dbN was fixed in the preset decomposition scale,identification accuracy increased with an increase in the decomposition scale.The frequency component of the time-varying parameters had great influence on the choice of decomposition scale,and the fast time-varying parameters were more sensitive than the slow.The choice of the basic function dbN affects the identification accuracy,but is not a key factor; an increase in sampling rate can improve the identification accuracy of fast time-varying parameters under the same decomposition scale.

    • Application of Wavelet Analysis in Seismic Designof a High-rise Structure

      2016, 38(5):728-737,744. DOI: 10.3969/j.issn.1000-0844.2016.05.0728

      Abstract (758) HTML (0) PDF 1.85 M (1281) Comment (0) Favorites

      Abstract:Earthquake engineering is a strong focus of civil engineering research,but the primary problem in this respect is the input of seismic motion.In this paper,the time-frequency localization nature of the wavelet function is used to analyze real ground motion,and a feasible method based on wavelet analysis is proposed.The actual seismic wave of El-Centro and TH2TG055 are adjusted by amplitude adjustment,wavelet transform,and standard response spectra fitting,and are then input into a structural model to analyze the seismic response.During seismic response analysis,this paper also analyzes results of story shear force,inter layer displacement,and story drift angle.Results show an improvement in the transformed seismic waves that meet the needs of earthquake resistant engineering and are useful in engineering applications.

    • Uplift Tests and Numerical Simulation Analysis of TransmissionLine with Rock Embedded Foundation

      2016, 38(5):738-744. DOI: 10.3969/j.issn.1000-0844.2016.05.0738

      Abstract (671) HTML (0) PDF 1.25 M (868) Comment (0) Favorites

      Abstract:In this study, we use numerical simulation to analyze the uplift performance and failure modes of two types of rock embedded foundations with different buried depths in strongly weathered areas. We performed uplift bearing capacity tests on rock embedded foundations in Taihu county, Anhui province. The results show that the uplift bearing behaviors and failure modes of jar-type and belled-piers foundations are similar when their buried depths are shallow. When the buried depth of the foundation is deep, however, the uplift bearing behavior of the belled-piers foundation is obviously better than that of the jar-type foundation. In addition, we compare and analyze the economic benefits of these two foundation types. Our research results show that the tensile strength, economy, and environmental protection afforded by belled piers are superior. Therefore, we recommend that belled-pier foundations be applied in transmission line projects with strongly weathered rock foundations.

    • Meso-scale Numerical Analysis of Damage Evolution of High-strengthand High-performance Concrete

      2016, 38(5):745-750,769. DOI: 10.3969/j.issn.1000-0844.2016.05.0745

      Abstract (690) HTML (0) PDF 1.27 M (664) Comment (0) Favorites

      Abstract:On a meso-level, concrete can be seen as a three-phase composite material comprising a cement base, aggregate, and a transitional zone between the cement and aggregate. In this study, based on the random characteristics of the aggregate distribution and morphology, the Walraven formula is applied to determine the convex polygonal aggregate distribution of the two-dimensional concrete specimen's cross-section. Subsequently, an algorithm for the random convex polygon aggregate is proposed, in which an area of round aggregate is used as the control parameter and the inscribed polygon of the round aggregate is used as the framework. A numerical experiment is conducted on specimens under uniaxial compression by using the high-strength and high-performance concrete C80 as an example, and corresponding stress-strain curves and damage evolution pictures are drawn. A comparison between results of the numerical simulation and the physical test show that the numerical model proposed in this paper is both reasonable and feasible.

    • Seismic Subsidence Behavior of Fly-ash-modifiedLoess under Dynamic Loading

      2016, 38(5):751-756. DOI: 10.3969/j.issn.1000-0844.2016.05.751

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      Abstract:In order to obtain raw material locally and make optimal use of fly ash in engineering construction in loess areas, we conducted a series of dynamic triaxial tests on unsaturated remolded loess specimens that had been modified with different proportions of fly ash. Based on the test results, we studied the seismic subsidence properties of loess based on the improvement afforded by the fly ash, and derived change laws for the dynamic modulus of deformation and the dynamic residual strain for different proportions of fly ash. The results show that the quantity of dope in fly ash significantly influences the seismic subsidence properties of loess. The changes in the dynamic modulus of deformation and in the dynamic residual strain vary with respect to the improvement afforded by fly ash under the same consolidation stress, i.e., the former becomes larger while the latter become smaller and the relationship between them is well described by the power function. Moreover, we verified that the anti-seismic subsidence behavior of the loess specimens was much better when the proportion of fly ash is about 20%. Thee research findings provide a scientific basis for establishing anti-seismic designations for foundations in loess areas, and thus have important application value.

    • Measurement Error Analysis and Evaluation of Shear-wave Velocityin Lanzhou Area

      2016, 38(5):757-769. DOI: 10.3969/j.issn.1000-0844.2016.05.0757

      Abstract (680) HTML (0) PDF 2.12 M (618) Comment (0) Favorites

      Abstract:Lanzhou, located in China's major earthquake belt, is China's most earthquake-proof city. In this region, one of the most important earthquake parameters——shear-wave velocity——always involves a certain degree of test error. This test error can greatly impact seismic evaluation results. In this study, our objective was to develop basic guiding error-analysis principles for Lanzhou and the Northwest China region. First, we selected four test sites in Lanzhou, and then developed a specific in-situ shear-wave velocity test involving ten institutes and various kinds of test equipment to determine the actual in-situ test error in the Lanzhou region. In this paper, we discuss the statistical characteristics of this error and determine its impact on the surface accelerated response spectra. Based on our results, we can draw the following conclusions:(1) The in-situ test error in the Lanzhou area has obvious regularity, which mostly obeys the standard normal distribution. This error remains consistent and does not vary with depth or type of site. (2) The technical level of the Lanzhou region is better than the average level over the whole of China. Its Class I, Class Ⅱ, and Class Ⅲ test errors are smaller and the average standard deviation of the test is 10%. (3) For the Lanzhou area, the test standard deviation of one time of shear-wave velocity could cause a maximum change in the peak ground acceleration (PGA) of 25%, and the standard deviation of two times of shear-wave velocity may result in a change of up to 50%. (4) The calculation results are also influenced by the input ground motion. When the frequency of the input wave has a frequency band similar to that of the site, the spectra will have more vivid differences, and otherwise the impact is lower.

    • Two Discoveries in the Liquefaction Evaluation Method of Saturated Loess

      2016, 38(5):770-774. DOI: 10.3969/j.issn.1000-0844.2016.05.0770

      Abstract (689) HTML (0) PDF 1.11 M (671) Comment (0) Favorites

      Abstract:According to the seismic design code for buildings in China, the soil formed during or before the late Pleistocene will not be liquefied. However, case histories and laboratory test results show that the saturated late Pleistocene loess is potentially vulnerable to liquefaction. Using a cyclic triaxial apparatus with a bender element system, the shear wave velocities of undisturbed loess are tested continuously during sample saturation. The test results indicate that the shear wave velocity of loess in the saturation process is rapidly reduced in the first 10~20 min, and then, it becomes stable. Shear wave velocity is a parameter that accounts for the small strain shear stiffness of soil, which accurately characterizes soil structure. The rapid reduction of shear wave velocity indicates that the microstructure of the loess is destroyed by the sample saturation process. The stable shear wave velocity indicates that the saturated loess has a new stable microstructure. The above analysis proves that the saturated loess is different from the loess before saturation. Indeed, only loess that has been subjected to agricultural irrigation or groundwater rise is liquefied. Because the structure of the saturated loess differs from that of the original loess, different seismic design regulations should be applied as well. Therefore, the seismic design code for buildings in China should be adapted to consider the level of saturation of the loess in addition to its age. Furthermore, the saturated loess is no longer the late Pleistocene loess, and the geological age of liquefied loess may be consistent with seismic design code of buildings in China. We observed that clay particles exist in some loess as clay lumps, and clay lumps do not affect the liquefaction of other silty parts of the soil. However, in the clay content test, if the soil sample contains clay lumps, the clay content test result will be comparatively high and inconsistent with the static and dynamic mechanical behavior of the soil. Consequently, clay lumps should be removed from the clay content test sample, and then, the remaining clay content should be used to evaluate the soil's liquefaction potential.

    • Shaking Table Model Tests on the Seismic Response of a High and Steep Rock Slope

      2016, 38(5):775-782,807. DOI: 10.3969/j.issn.1000-0844.2016.05.0775

      Abstract (1010) HTML (0) PDF 1.36 M (992) Comment (0) Favorites

      Abstract:A large-scale shaking table model test of a slope with a height of 1.8 m, length of 4.4 m, and width of 4.4 m was introduced. The materials are made of blanc fixe, river sand, gypsum, clay, and water in different ratios. The slope comprises 30°, 45°, 50°, and 60° inclined surfaces. A series of tests were performed for different seismic waves, amplitudes, and frequencies. The results indicate that the local coordinate system is more adequate than the whole coordinate system when conducting research on the dynamic problems of the slope. Thus, we should use the airport surface direction L, the strike direction M, and the vertical direction N. The amplifications of the peak accelerations gradually increase with the increase of slope angles, and there are two inflection points at 45° and 50°. However, the amplification along the slope strike direction is consistent. The amplifications of the accelerations in different directions gradually reduce with the increase of the peak ground acceleration of the input wave, which is an intensity saturation phenomenon. Simultaneously, there are predominant peak values in the airport surface direction L; however, there are no predominant peak values in the strike direction M and in the vertical direction N. Therefore, the results reveal the mechanism of slope instability during an earthquake and provide seismic design references for slope engineering.

    • A Modified Damage Softening Constitutive Model for Rock

      2016, 38(5):783-786. DOI: 10.3969/j.issn.1000-0844.2016.05.0783

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      Abstract:Using a rock micro-unit strength,which satisfies the Weibull random distribution and is based on the Drucker-Prager failure criterion,a correction coefficient for damage variables is introduced,which reflects the full stress-strain process and residual strength of rock.The relationship between Weibull distribution parameters under different confining pressures is established using the stress and strain at peak points on the stress-strain curve.A damage softening constitutive model of rock is then established,accounting for the rock triaxial stress-strain test curve.The model has few parameters,and the way of determining the parameters indicates the physical meaning of the model parameters.Compared with previous studies,this model,after modification,has obvious advantages.The rationality of the model proposed here is demonstrated using comparative analysis between the theoretical and experimental results.

    • Engineering Geological Problems of Loess High Excavation Slope in Loess Hilly and Gully Region of Lanzhou and Its Stability Analysis

      2016, 38(5):787-794. DOI: 10.3969/j.issn.1000-0844.2016.05.0787

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      Abstract:Due to the recent rapid urbanization process, a large number of high and steep loess slopes have been excavated in the hilly-gully region of Lanzhou. Through field investigations, we found that most of the excavated high and steep loess slopes have many engineering geological problems of different degrees, such as unloading crannies, slope gullies, sinkholes, and local landslide collapses. Using finite element method, we simulated the excavation process, and the results show that the displacement and stress and strain fields of the excavation slope exhibit significant changes after excavation. These include stress release and local concentration, an unloading effect, the weathering and flushing action of water, and internal and external factors and their interaction, which lead to various engineering geological problems with respect to the excavation slope. These problems will result in reduced slope stability to different degrees. In a hilly-gully loess region, the slope body is stable in its natural state, with a safety factor of above 1.7 by different calculation methods. The slope gradient increases after the slope is cut, resulting in a decrease in the slope stability, and a 0.6 reduction in the safety factor. The excavation slope is close to the critical stable state, and is an instability risk for earthquake intensity values of Ⅷ or higher.

    • >地震监测
    • Influence of Emanometer K-value Change on Water RadonValue and Correction Method

      2016, 38(5):795-801. DOI: 10.3969/j.issn.1000-0844.2016.05.0795

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      Abstract:This study aimed to develop an accurate correction method of errors in the water radon value caused by a change in the emanometer K value.First,we investigated current methods used to correct radon values and found obvious differences among them.This is because none of these methods capture the real change in the K value.Therefore,in this study,we adopted the curve fitting method to investigate changes in the K value.Fitting models examined in this study include linear,quadratic,logarithmic,cubic,and exponential models.We performed curve fitting for 12 K-value groups and obtained their curve fitting equations.Results revealed that the fitting degree of the quadratic curve was the best.Therefore, we adopted the quadratic curve method for correcting the radon values of No.22 well,which is located in Wushan county,Gansu province.To test the accuracy of the corrected radon value results after curve fitting,we determined the correspondence among changes in the radon value from all types of correction methods and earthquakes.Results revealed that the shape of the corrected radon value curve using the curve fitting method not only has good reproducibility prior to strong earthquakes but also well synchronizes with the curve shapes of water radon values obtained from other stations around the epicenter before a strong earthquake.Furthermore,these results show that it is necessary to correct the water radon error using the K-value change mechanism.The use of the curve fitting method to correct the radon value error caused by a change in the K value is an innovative technique and a significant contribution to the field.

    • Precise Relocation of Small Earthquakes in the Jiangsu Area andAssociated Tectonic Implications

      2016, 38(5):802-807. DOI: 10.3969/j.issn.1000-0844.2016.05.0802

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      Abstract:For this study, we collected one thousand seismic events that occurred in Jiangsu province from 2009 to 2015. Four earthquake sequences occurred successively in this area:Jianhu earthquake sequence, 2011; Gaoyou earthquake sequence, 2012; Guanyun earthquake sequence, 2013; and Donghai earthquake sequence, 2015. We relocated these earthquakes using a double-difference location algorithm. For this analysis it was crucial to establish a reasonable crustal structure therefore, because the double-difference location result was affected by the horizontal velocity model, a more accurate model was required. This paper references the initial model of crustal velocity in Jiangsu and its adjacent regions established by Huangyun. In order to increase the total number of precise location generation events in different areas, this research divided Jiangsu province into seven small areas, and relocated the earthquakes for each. Because the distribution density of the recording stations is different, the number of earthquakes in each area is different. The results show a significant improvement in the relocation results, and the earthquake sequences were found to be more spatially concentrated. The relocated earthquakes were concentrated in obvious bands around faults, and most of them occurred at depths of 5~20 km, suggesting the seismological layer in the region lies in the mid-upper crust. By analyzing the seismic tectonic activity of these earthquake swarms, we were able to investigate:the trend of each earthquake sequence, whether or not a new fault zone was initiated, and whether the trends of the new fault zones were consistent with the old ones. This is of great significance to future studies in this area.

    • Study and Application of Multi-kernel Function Filtering Method in Time-series Deformation Data Processing

      2016, 38(5):808-814,845. DOI: 10.3969/j.issn.1000-0844.2016.05.808

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      Abstract:Due to observations of environmental impact carried out by monitoring stations on the China Mainland, we need to deal with the daily data for many years for daily tracking purposes. Existing filtering methods include the wavelet method, least-squares co-location method, Gaussian weighted average method, and Vondark method, etc., but for daily tracking these methods prove to be inconvenient. Aimed at solving the problem of extracting efficient information from sequential deformation observation data over some years, a filtering method, based on multi-kernel function, is studied in this paper. Taking continuous GPS station vertical sequential observation data as an example, we discuss the parameters for the multi-kernel function and their physical meaning. Conclusions are as follows:(1) When the kernel function index is 0.5 and the smoothing factor 0.003, the mean square error of unit weight of the filtering model with a kernel point interval of more than 10 days, is the least. (2) The kernel point interval controls the level of the filtering information frequency spectrum, the larger the interval, the lower the spectrum information; the smaller the interval, the higher the spectrum information. (3) Sometimes kernel points are lost because of missing data. When more than two continuous points are lost, the filtering fails; when two continuous points are lost, part of the filtering waves are distorted because of the missing data; when just one point is lost, the filtering effect is not affected. (4) From the filtering application in the GPS time-series data, the fixed-point deformation time-series data, and the non-tectonic deformation time-series data, information on different spectra are obtained and the stability and reliability of the method verified. This provides a more convenient way to daily process time-series observation data from a large number of stations.

    • Acoustic Wave Equation Modeling with a New Time-Space DomainFinite Difference Stencil and an Improved Linear Algorithm

      2016, 38(5):815-821. DOI: 10.3969/j.issn.1000-0844.2016.05.0815

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      Abstract:Numerical methods prove useful in exploration seismology. The most commonly used numerical methods are the finite difference, finite volume, and finite element methods. These methods constitute the basis for reverse time migration and full-waveform inversion. Finite difference methods are widely used in wave field extrapolation because of their higher computation efficiency, lower memory requirements, and easier implementation. During discretization of the time and the spatial derivatives in the wave equation, grid dispersion often occurs. Grid dispersion can result in artificial waves and inaccurate wave fields. Therefore, finding suitable finite difference operator coefficients to preserve the dispersion relationship of the wave equation, thus reducing grid dispersion, is one of the most important issues when using finite difference methods. To reduce grid dispersion, the traditional method uses high-order finite difference schemes in the spatial domain. However, waves are simultaneously propagated in time and space. Therefore, some researchers propose finite difference schemes based on the time-space domain dispersion relationship. Most commonly used are the high-order Taylor expansion method and the optimized method. However, the time step is relative small even in the optimized time-space domain method. Recently, a new finite difference stencil has been proposed to increase the time step while preserving the accuracy with the least-squares method. The time-space domain dispersion relationship of this new finite difference stencil is linear. Therefore, in this paper, we propose using this improved linear method, with the new finite difference stencil, to obtain the finite difference coefficients for the acoustic wave equation. We demonstrate, by dispersion analysis and numerical simulation, that with this new FD stencil and its improved linear solution, the wave equation simulation speed can be doubled compared with the previous linear method.

    • >地震预测与震灾防御
    • Characteristics of Earthquake Swarms in Western Partof South Tianshan,Xinjiang

      2016, 38(5):822-829. DOI: 10.3969/j.issn.1000-0844.2016.05.0822

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      Abstract:The small earthquake swarm activity level in South Tianshan,Xinjiang,was relatively high from March 2008 to December 2013.In this paper,31 small earthquake swarms occurring in this area are systematically studied,the parameter characteristics of earthquake swarms are summarized,the relationship between small earthquake swarms and the occurrence of future moderately strong earthquakes is discussed,and criteria for precursory earthquake swarms are analyzed and tested.Results show that:(1) earthquake swarms in South Tianshan are concentrated in several regions,the magnitudes of most are 2.0~3.9,and the largest magnitude of each swarm is mostly about ML3.5.Seven swarms have a total magnitude of ML ≥ 4.0 with a maximum value of ML4.9 and there are less than 20 earthquakes for most earthquake swarms with a duration of less than seven days.(2) The activity of earthquake swarms is mainly concentrated near Atushi.75% of the swarms are accompanied with M>5.0 earthquakes two months after their occurrence,and the epicenters of these medium-strong earthquakes are principally located in the intersection of Kashi and Wuqia.The corresponding ratio of the magnitude of earthquake swarms and future medium-strong earthquakes has no obvious correlation with the magnitude of corresponding earthquakes.There is also no good relationship between the number of earthquakes in an earthquake swarm and the corresponding ratio.(3) Results using the combined method of U-K and U-ρ are preferable for determining the type of earthquake swarm,and the correct rate accounts for about 32% of all results.Results of analysis provide a reference for determining whether an earthquake swarm has precursory characteristics or not.

    • Co-seismic Response in Fluid Observation Data from Gansu duringthe Indonesia M8.6 Earthquake

      2016, 38(5):830-837. DOI: 10.3969/j.issn.1000-0844.2016.05.0830

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      Abstract:During the occurrence of two strong earthquakes (M8.6 and M8.2) in Sumatra,Indonesia,on April 11,2012,a large number of underground fluid stations in China recorded abundant co-seismic response data,and data from underground fluid observations in Gansu also showed various degrees of co-seismic response. The co-seismic changes and the digital response of water levels and temperatures in Gansu during these two great earthquakes are analyzed in this study. The results show that the water level co-seismic response in most wells followed a relatively consistent change law,i.e.,the change was main oscillation variation,and rapidly recovered to its original state after the earthquake. The degree of response is closely related to the magnitude; the greater the magnitude,the stronger the response. Owing to the different response mechanisms of water level and temperature,water temperature does not follow this rule. In water temperature observations,only two wells had a record of co-seismic response,they showed approximate amplitudes and a relatively long cycle time (change period),but a slower recovery time.

    • Comparative Analysis of Earthquake Risk Assessment Methods:A Case Study on Urumqi City

      2016, 38(5):838-845. DOI: 10.3969/j.issn.1000-0844.2016.05.0838

      Abstract (812) HTML (0) PDF 1.06 M (1004) Comment (0) Favorites

      Abstract:At present,risk modeling and assessments based on an index system are widely used to assess and analyze earthquake risk.In this paper,various index systems for seismic risk assessment are compared and analyzed.Most of the index systems include three parts:risk,vulnerability,and disaster bearing capacity.As a whole,index systems have tended to become more elaborate and complex,especially the parts related to disaster preparation,emergency response,and management,which belong to the disaster bearing capacity set.Evaluating the effects of different index systems is the primary step when using or improving them.In order to compare different index systems in a general sense,two typical methods were chosen and applied to Urumqi city.One is the ability for urban earthquake disaster reduction method,whose index system is relatively simple and macroscopic; the other is the seismic risk index method,which includes many more detailed factors.Earthquake hazard risks for each district in Urumqi city were evaluated using the methods above.By comparing the results we reached the following conclusions:(1) evaluating results from different index systems does not coordinate well because each one has its own research focus.For example,the ability for urban earthquake disaster reduction method focuses on seismic disaster,which relates to two of its three criteria,whereas the seismic risk index method not only considers disasters,but also considers ways and means to mitigate them.So,the results embody their own characters.(2) Regarding the development of the evaluation system,one notable phenomenon is that the index sets become increasingly huge and complicated.Although more indexes may express the earthquake mitigation ability of cities more comprehensively,the extraction and quantification of those indexes is a big challenge.Moreover,the determination of some indexes relies on personal experience and judgment,which can lead to a shift away from the original trend.An index system with more detailed and comprehensive factors will not always attain better,reasonable,and valid results.A sound,efficient,and effective index system must be a combination of ease of manipulation,utility,and accuracy.

    • Relationship between the Migration of Earthquake on the Silk RoadBelt and Terrain

      2016, 38(5):846-846. DOI: 10.3969/j.issn.1000-0844.2016.05.0846

      Abstract (664) HTML (0) PDF 892.06 K (610) Comment (0) Favorites

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