• Volume 38,Issue 3,2016 Table of Contents
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    • >地震工程
    • Numerical Simulation of Shaking Table Test for Vertical Wall Based on P-Z Model

      2016, 38(3):333-337,352. DOI: 10.3969/j.issn.1000-0844.2016.03.0333

      Abstract (905) HTML (0) PDF 6.28 M (926) Comment (0) Favorites

      Abstract:Based on calibrated parameters of the generalized plastic model of gravel material applied to static and dynamic triaxial experiments, a numerical simulation of the shaking table test for a vertical wall structure is performed. The experimental and numerical results are comparatively analyzed to further study the failure process and failure characteristics of vertical wall structures under earthquakes. Results show that the numerical model could simulate the earthquake response and failure characteristics of the vertical wall structure. The failure mode of the vertical wall structure located in gravel foundation is a seaward horizontally slip, tilt, and settlement of the vertical wall. The failure process of the vertical wall structural was found to be as follows: when the input acceleration is small, the vertical wall is in a steady state; with the gradual increase of the input acceleration, the vertical wall starts to horizontally slip and incline and backfill gravel appear under the action of the seismic inertia force and dynamic earth pressures, but the displacement is small. When the acceleration reaches a certain value, the movement speed of the vertical wall and subsidence rate of the backfill gravel increase dramatically and the vertical wall structure exhibits significant deformation.

    • Analysis of Dynamic Characteristics and Seismic Response of Deep Soft Soil in Ningbo Area

      2016, 38(3):338-343. DOI: 10.3969/j.issn.1000-0844.2016.03.0338

      Abstract (860) HTML (0) PDF 3.75 M (1135) Comment (0) Favorites

      Abstract:In this study, we used the Davidenkov model to conduct a fitting analysis on dynamic test data of deep soft soil in the city of Ningbo and then determined the relevant fitting parameters. The fitting results demonstrate that the Davidenkov model can describe the dynamic characteristics of the Ningbo deep soft soil well. We wrote the computation program for Davidenkov model in APDL language using ANSYS software based on the equivalent nonlinear method and verified its correction by the classic earthquake response program SHAKE. The results show that the program is effective and can address the lack of nonlinear constitutive soil models in existing commercial software. We used the above program to compare relevant codes and analyzed the seismic responses of the Ningbo deep soft soil. The analysis results indicate that the soil displacement obtained by the formula recommended by the code is actually greater than expected, which means that the underground structure that was designed according to code is conservative. The research results from this study provide a reasonable method for calculating soil dynamic characteristics and conducting seismic response analysis of deep soft-soil areas.

    • Design and Implementation of Health Monitoring Systemfor Base-isolated Structure (Ⅱ): System Implementation

      2016, 38(3):344-352. DOI: 10.3969/j.issn.1000-0844.2016.03.0344

      Abstract (880) HTML (0) PDF 9.92 M (915) Comment (0) Favorites

      Abstract:The performance of structures built with conventional anti-seismic technology is not always satisfactory in earthquakes. Researchers have often adopted "seismic isolation technology" in place of conventional "anti-seismic technology". The structural health monitoring system (SHMS), as a structural "nervous system", has been widely used in large-span bridges, tunnels, and tall buildings in order to monitor structural response and provide reliable data for the assessment of structurally safe performance. To investigate the deterioration mechanism of base-isolated structure (BIS) and assess the degree of safe performance experienced in earthquakes, many SHMS have been designed and implemented to address various seismic structure research objectives.Based on the SHMS results of other structure types. Many significant research achievements for BIS have been achieved by numerous scholars. In this paper, based on the previous paper Design and Implementation of Health Monitoring System for Base-Isolated Structure (Ⅰ): System Design, we design and implement a super-long base-isolated SHMS. Here we study the design of an overall solution; the implementation of solutions for all subsystems and functions in super-long base-isolated SHMSs, including the types, locations, and performance of sensors; the hardware and software of data acquisition systems and transmission solutions; and the types and functions of databases. Our results show that the coordinated operation of the super-long BIS ran well and the performance satisfied the desired objectives. We analyzed the horizontal displacement and temperature data of the isolation bearings and the acceleration response of superstructure monitored during construction and operation. The results show that the concrete shrinkage of the superstructure and temperature had a significant impact on the horizontal displacement of the isolation bearings. The relation of the horizontal displacement of rubbers in the elastic stage with temperature changed slightly, but the displacement of the isolation bearings subjected to environmental excitation had a cumulative effect based on long-term monitoring data, which would change the structural dynamic characteristics. According to the assessment criteria in the system design paper, we evaluated the performance of the super-long BIS and determined that the structure performs well.

    • Influence of Ground Motion Characteristics on the InelasticDisplacement Spectra of Isolated Structures

      2016, 38(3):353-359. DOI: 10.3969/j.issn.1000-0844.2016.03.0353

      Abstract (852) HTML (0) PDF 5.57 M (1408) Comment (0) Favorites

      Abstract:Based on the specific focal mechanism, magnitude, fault distance, and site condition, 69 ground motion records are selected and grouped. Nspectra software is used to calculate the inelastic displacement response spectrum of a single isolated structure under ground motion. The influence of fault distance, field condition, magnitude, and damping ratio on the inelastic displacement spectrum is analyzed, and the influence of the mechanical parameters of seismic isolation layer on the seismic energy dissipation is discussed. The results indicate that compared with the far field, the base-isolated structure in the near field is more unfavorable. Moreover, the seismic isolation layer displacement spectrum is greatly influenced by field conditions, earthquake acceleration, and speed. With the increase of the fault distance, the attenuation of displacement spectrum values increases, and the displacement spectrum of the base isolated layer in the field of soft soil is more than that of hard soil. The influence of earthquake magnitude on the spectrum shape is not obvious; however, it can cause a scaling effected on the displacement spectrum of the base isolated layer. When the damping ratio is less than 0.4, the value of displacement spectrum of the seismic isolation layer differs largely with different ground motion characteristics; when the damping ratio is greater than 0.4, the value of displacement spectrum basically become the same. The energy dissipation of the seismic isolation layer with a small yielding force (restoring force/gravity less than or equal to 1) increases with the increase of natural period.

    • Theoretical Study on the Dynamic Stability of Super-highBridge Piers under Strong Earthquakes

      2016, 38(3):360-365. DOI: 10.3969/j.issn.1000-0844.2016.03.0360

      Abstract (883) HTML (0) PDF 2.26 M (668) Comment (0) Favorites

      Abstract:With the steady progress of transportation infrastructure construction in China,a large number of bridges with high piers have been built in the mountainous southwest region,a part of the Alpine-Himalayan seismic belt where earthquakes are frequent.Thus,research on structural seismic response has always attracted close attention.In this paper,we study the dynamic instability mechanism,seismic response,and performance of super-high bridge piers,develop reasonable structural strategies,and suggest design proposals to avoid dynamic instability.Assuming a plane section and considering the geometric non-linear effect induced by large displacement deformation of super-high piers,a numerical model of super-high piers is established.The governing differential equations of super-high piers are established,and a displacement shape function is proposed according to the force-deformation constitutive law of members.The Runge-Kutta method is used to solve the equation.Based on the B-R kinematic criterion,the dynamic instability mechanisms of super-high piers are discussed.The results from the numerical model under the dynamic conditions of various seismic waves are discussed,and longitudinal and lateral displacement at the top of high piers is studied.Theoretical analysis and calculation results show that the dynamic instability of super-high piers is closely related to pier geometry,mass distribution,and boundary conditions.The dynamic instability time of piers decreases with an increase in the peak acceleration of seismic waves.The relationship between the acceleration load and instability time shows strict correlation.The results from the example show that the method in this paper is simple,feasible,and correct.Using the theory in this paper,the dynamic instability time and acceleration load critical value of super-high piers can be calculated accurately.The theory is therefore significant in theoretical analysis and engineering practice regarding the dynamic instability of super-high piers.

    • Effect of Groundwater on Ground Motion Parameter

      2016, 38(3):366-372. DOI: 10.3969/j.issn.1000-0844.2016.03.0366

      Abstract (943) HTML (0) PDF 2.37 M (860) Comment (0) Favorites

      Abstract:To analyze the impact of groundwater on ground motion parameters,in this study,we selected three practical sites and used two real seismic waves as input ground motions for calculating the seismic responses of the soil layer in conditions with and without groundwater.We used a two-phase model and a single-phase model for the conditions with and without groundwater,respectively,and applied the finite-difference and artificial transmitting boundary methods.Based on the obtained horizontal acceleration time history,we extracted peak acceleration and response spectrum data.From our comparative analysis results,we draw the following conclusions:(1) The peak ground acceleration of site soil with groundwater is significantly lesser than that without groundwater. (2) The value of the surface acceleration response spectra of site soil with groundwater is greater than that without groundwater. (3) Due to the existence of groundwater,the characteristic period of the amplification factor response spectra becomes long.

    • Study on Ground Motion Characteristics in Loess Hill Valley Sites

      2016, 38(3):373-381,390. DOI: 10.3969/j.issn.1000-0844.2016.03.0373

      Abstract (801) HTML (0) PDF 9.24 M (910) Comment (0) Favorites

      Abstract:The trigger for seismic damage may be determined by researching the characteristics of strong ground motion in loess hill valleys under earthquake action. In this paper, considering the geomorphic characteristics of the Loess Plateau, typical models of dynamic numerical analysis are established. In a valley site influenced by rugged terrain and a loess covering layer, the seismic response was analyzed by inputting seismic waves with different amplitudes, frequency spectrum characteristics, and duration. The results show that the coupling action of the soil layer and terrain controls the PGA change on the ground surface and that the change trend is complex. Under the input of the same wave with a different amplitude and compared with monitoring points in the bedrock valley, the spectrum amplitude of the ground motion at the loess-covered valley points increased, and the peak moved to a high frequency. Under the input of different seismic waves, the natural frequencies of different parts of the site were influenced by the terrain and the soil layers; the size and amplitude of the ground motion frequency spectrum was not only related to the natural frequency spectrum of the site and topographic change, but also to the spectral components of the input seismic wave. At the same site, with the same PGA and seismic spectrum characteristics of the input wave, the output seismic spectrum shape showed similar characteristics. As the seismic duration increased, the earthquake energy was concentrated in the field near the natural frequency, which may lead to an increase in the vibration amplitude of buildings with a corresponding frequency.

    • Effect of Soil Dynamic Parameters on SeismicResponse of Soil Layers in Kunming Basin

      2016, 38(3):382-390. DOI: 10.3969/j.issn.1000-0844.2016.03.0382

      Abstract (840) HTML (0) PDF 7.55 M (911) Comment (0) Favorites

      Abstract:Dynamic soil parameters are important for analyzing the seismic response of the soil layer,and have strong regional characteristics. The Kunming basin is a faulted basin that developed after the Late Cenozoic Era. The Pliocene to Quaternary sedimentary thickness reaches up to one thousand meters. The stratum formation is mainly composed of deposition, grade alluvial, and alluvial faces with the shape distribution of a thin layer or lens. The typical soil layer in Kunming basin consists of silt and clay soils. For a deeper understanding of the dynamic soil characteristics in Kunming basin and to conduct a seismic safety evaluation of construction sites, it is important to investigate the statistical values of the dynamic parameters such as the shear modulus ratio and the damping ratio of silt and clay soils at different depths in the Kunming region. In addition, studies are needed to compare the effects of the dynamic parameters' statistical values, norm values, and the recommended values on the soil seismic response by developing soil layer models and analyzing soil seismic responses. In this paper, we analyze the triaxial test dynamic parameters of silt and clay from 94 and 167 sample groups, respectively, collected from 101 sites in the Kunming basin region. Based on our soil seismic response calculations, we compare our results with the values recommended from Yuan Xiaoming and with those found in the code for the seismic safety evaluation of engineering sites (DB001-94). The results show that our statistical values of the dynamic parameters differ greatly from the other two sets of recommended values.The effects of different dynamic parameters on the soil seismic response are obvious and those with a lower probability of exceedance include the influences on peak acceleration, response spectra, and characteristic period. The site response analysis results of the statistical and test values are similar. The statistical values can be used for reference in work levels Ⅱ and Ⅲ for the seismic risk assessment of engineering projects in Kunming basin.

    • Influence of Dynamic Characteristic Parameters of Thick MuckySilty Clay on Surface Ground Motion Parameters

      2016, 38(3):391-397. DOI: 10.3969/j.issn.1000-0844.2016.03.0391

      Abstract (958) HTML (0) PDF 3.83 M (1110) Comment (0) Favorites

      Abstract:A soft site in the coastal area of Tianjin is used for analysis as an example of the seismic response of a site with horizontally-layered soil. The ground motion time history with different intensities and phases was input, and the equivalent linearization method was used to consider the nonlinear dynamic characteristics of the soil. This study also presents the effects of a relation between variability in the curves of dynamic parameters of a thick layer of mucky silty clay in the Tianjin area (including the soil dynamic shear modulus ratio and damping ratio) on the peak value of ground surface acceleration and its response spectra in deep soft sites. Numerical results obtained from a number of case studies were used to make a comparison with a standard condition, and the following was determined. Firstly, adding or reducing one standard deviation to the mean of the damping ratio has little effect on ground motion parameters. Secondly, addition or reduction of one standard deviation to the mean value of the dynamic shear modulus ratio has a prominent effect on the peak value of ground surface acceleration; when the ground motion time history input is 2% of the 50 years transcendental probability the corresponding peak value of ground surface acceleration increases or decreases by 20% to 30%, and the surface response spectra is changed into a thin-high or short-fat trend. Thirdly, the mean value of the dynamic shear modulus ratio when one standard deviation is added, has a significant effect on the peak value of ground surface acceleration for 10% of the 50 year exceedance probability, the corresponding peak value of the ground surface ratio decreases by about 15% and the response spectra is changed into a short fat trend. Finally, when one standard deviation is added or subtracted from the mean value of the dynamic shear modulus ratio or damping ratio there is little effect on the value of ground motion parameters.

    • >地震科学技术
    • Study of Seismometry Index System for M≥5.0 Earthquakes in Liaoning

      2016, 38(3):398-406. DOI: 10.3969/j.issn.1000-0844.2016.03.0398

      Abstract (900) HTML (0) PDF 5.61 M (904) Comment (0) Favorites

      Abstract:The seismological prediction indexes of seven earthquakes (M≥5.0) occurring in Liao-ning since 1970 were analyzed from medium-small seismicity images and sequential scanning. Results show that the earthquake-reflecting effect of certain parameters, i.e. seismic gap, seismic belt, b value, A(b)value, D value, earthquake deficiency, and XY value is relatively good. Combining previous results of enhancements, concentration of moderate earthquakes, and characteristics of earthquake swarms in Liaoning, a seismological index system of earthquakes with a magnitude of M≥5.0 was constructed. Earthquake intensity prediction indexes mainly include the enhancement and concentration of moderate earthquakes, earthquake swarm sequences, seismic gaps, and belts, and the maximum magnitude of a forthcoming main shock is estimated by adding 1.5~2 to the value of the maximum magnitude of the earthquake for the above four items. The location prediction index is similar to the earthquake intensity prediction index, and the method determined shows the following: earthquakes with a magnitude of M≥5.0 generally occur in the seismic gap and belt or nearby region; if there is an increase and concentration in moderate earthquakes the location of forthcoming earthquakes with M≥5 will be close to where the last moderate earthquake occurred; if there is an earthquake swarm sequence, the forthcoming main shock will occur within 200 km of the swarm (if there is a foreshock sequence, the main shock will occur near the location of the sequence). In addition to the four items used in earthquake intensity and location prediction indexes, the seismic time prediction indexes include the b value, A(b) value, D value, earthquake deficiency, and the XY value. Furthermore, the anomalies of A(b)value, D value, earthquake deficiency, and XY value commonly occur about one year before the earthquake; disappearance of the seismic belt and seismic gap, and b value anomalies commonly occur about half a year before an earthquake; and the foreshock sequence commonly occurs about 1 to 20 days before the main shock.

    • Relationship between Crustal Deformation and Earthquake Activitiesbefore and after the Xinyuan-Hejing MS6.6 Earthquake Using GNSS Data

      2016, 38(3):407-412. DOI: 10.3969/j.issn.1000-0844.2016.03.0407

      Abstract (790) HTML (0) PDF 12.81 M (926) Comment (0) Favorites

      Abstract:Based on an examination of three stages of global navigation satellite systems (GNSS) observation data from 2009 to 2011, we obtained the horizontal movement velocity, principal strain rate, surface expansion rate, and maximum shear strain rate around the epicenter area before and after the Xinyuan-Hejing MS6.6 earthquake of 2012. The results show that (1) the main movement trend in the research area is a reduction in the horizontal movement rate from south to north. The movement rate in the southern region is higher than that in the northern region, and the movement rate in the central area is higher than those in the east and west regions. (2) The positive negative alternate zone of the principal strain rate along the fault has some relationship with the earthquake. Between the two surface shrinkage areas is an important earthquake area. The regional change of the shear strain rate can reflect the direction of earthquake rupture.

    • Study of Holocene Slip Rate and Strike-slip Initial Time alongthe Lancang Fault,Southwestern Yunnan

      2016, 38(3):413-422. DOI: 10.3969/j.issn.1000-0844.2016.03.0413

      Abstract (819) HTML (0) PDF 10.97 M (952) Comment (0) Favorites

      Abstract:Two earthquakes with magnitudes of 7.6 and 7.3 occurred in the Lancang and Gengma areas,respectively,in southwestern Yunnan on November 6,1988.The M7.6 earthquake showed complicated earthquake-generating tectonic characteristics; the seismogenic structure was the Heihe and Lancang faults and an obvious seismic deformation belt was formed separately along the two faults.The Longling-Lancang fault is located in southwestern Yunnan and was an active fault zone in the late Quaternary.It has a length of 500 km,a trend of 320°~340°,and is mainly right-lateral strike slip with dip slip.It starts north of Tengchong,stretches through Longling,Gengma,Lancang,and terminates in Menghun in the south.The fault is composed of a plurality of discontinuous secondary fault components with a diagonal or clustered distribution.A number of fault basins and offset drainage systems have been formed along the fault.According to differences in fault geometric distribution,mechanism,fault scale,boundaries,and seismicity,the Longling-Lancang fault can be divided into four secondary fault segments: the Gudong-Tengchong,Longling-Yongde,Hanmuba-Lancang,and Jiufang-Mengzhe.The focus of this paper is the Lancang fault in the Hanmuba-Lancang segment.The Lancang fault starts to the north of Lianhe,transverses south of Yanshuai in Cangyuan county,across Nanliu,Habuma,Zhanmapo,Datangzi,Datangzi,Laodazhai,and Makadi,and terminates in the southeast of Lancang county.It has a length of 85 km and a NNW trend.The Lancang fault was a Holocene-active right-lateral strike slip fault with a dip slip component.A variety of dislocation landforms have been formed along the fault,such as fault steep cliffs,fault scarps,dextral dislocation of gullies and ridges,fault trenches,fault passes,and pits.The fault intersects the Heihe fault with a NWW trend at Zhanmapo where the M7.6 Langcang earthquake occurred.In this paper,the geological and geomorphological characteristics of activity along the Lancang fault are studied in accordance with the use of satellite image interpretation and field geological investigations.The research focuses on the slip rate of the fault during the Holocene.Two level terraces appeared with synchronized displacement at Nanjingwa; the displacement of the T2 terrace is about (40±2) m.No dating samples are available from this area,and therefore regional dating data is used to determine the slip rate.At a location near Makadi,five gullies have synchronous right-lateral displacement because of fault movement; according to differential GPS measurements in one of these gullies the displacement is about (19±3) m.Using age data for the corresponding landform surface,we thus determine that the right-lateral strike slip rate at this location is approximately (4.2±0.6) mm/a.Analysis of the slip rate and bedrock displacement leads us to infer that the fault was initiated in the late-early Pleistocene.

    • Variation Characteristics of Surface Wave Velocity along NorthSegment of North-South Seismic Belt before and after2013 Minxian-Zhangxian MS6.6 Earthquake

      2016, 38(3):423-430. DOI: 10.3969/j.issn.1000-0844.2016.03.0423

      Abstract (757) HTML (0) PDF 15.57 M (764) Comment (0) Favorites

      Abstract:Based on background noise and tomography methods,in this paper,we investigated the continuous waveform records of 94 fixed seismic stations in the northern segment of the north-south seismic belt from January to September,2013.In doing so,we obtained the velocity structure and evolution of the Rayleigh waves of this area,at different times in the same two-month period before and after the Minxian-Zhangxian MS6.6 earthquake on July 22,2013.The phase velocity tomography results show that before the earthquake,in May-June,the wave velocity along the Lintan-Tanchang fault zone and its surrounding areas reduced relative to that in March-April.However,after the earthquake,in August-September,the wave velocity along the Lintan-Tanchang fault zone and its surrounding areas was restored by rising to the level of May-June.These results indicate that in the two months before the Minxian-Zhangxian MS6.6 earthquake,the velocity exhibited low-value anomalies,and the earthquake occurred at the boundary of the low-velocity anomaly region.

    • >土动力学
    • Foundation Treatment of Airport Runway in Expansive Soil Area

      2016, 38(3):431-438,444. DOI: 10.3969/j.issn.1000-0844.2016.03.0431

      Abstract (870) HTML (0) PDF 2.89 M (763) Comment (0) Favorites

      Abstract:To solve the problem of foundation treatment in the construction of an airport runway in an expansive soil zone, we used the expansive soil in the Ankang area, Shaanxi province as our research object. To determine the construction control parameters of lime-treated expansive soil, we carried out relevant tests on the strength and expansive properties of the soil. The results show that with an increase in the quantity of lime, the optimum moisture content increases, the maximum dry density and the swelling shrinkage potential decreases, and the quantity of lime and the maximum dry density is nonlinear. When the amount of lime is 9%, the regularity of the swelling change rate is strong. The California bearing ratio (CBR), which is related to factors such as compaction and water content, does not increase with an increase in the compaction coefficient. The proportion of added lime had a greater influence on the strength of lime-treated expansive soil. When the amount of lime is 9%, the CBR was higher than for other proportions. Under the same compaction coefficient of expansive soil, with lime dosages of 3% and 6%, the compressibility is relatively similar. When the lime dosage is increased to 9%, the compression significantly decreased. Based on these test results, we propose the use of lime for expansive soil improvement in runway ground treatment, as well as a method for determining the subgrade construction control parameters with respect to the expansive properties as the main control indexes, and strength as the confirmation index.

    • Dynamic Strength Properties of Compacted Loess Based on Dynamic Triaxial Test

      2016, 38(3):439-444. DOI: 10.3969/j.issn.1000-0844.2016.03.0439

      Abstract (922) HTML (0) PDF 1.98 M (1331) Comment (0) Favorites

      Abstract:With ongoing western development, new urban construction in high-fill areas is a growing trend. Therefore, conducting research on the dynamic strength properties of compacted loess has important significance for the construction of large-scale infrastructure in loess areas of high seismic intensity. In this paper, with Lvliang compacted loess as the research object, we prepared triaxial specimens by static compaction. During the dynamic triaxial tests, we used stress control loading to apply dynamic load to the specimens. After sample loading, first, we applied a predetermined confining pressure to the specimen. Second, we applied a bias voltage to it. After consolidation was complete, dynamic stress was applied to the sample. When the specimen became damaged, we stopped loading. We preset the number of dynamic stress vibration times as 200. We performed many dynamic triaxial tests using dynamic triaxial apparatus to study the dynamic strength properties of Lvliang compacted loess including moisture content, dry density, and loading frequency. The results indicate that the dynamic strength of compacted loess decreases with an increased number of vibration times, and this relationship can be fitted to a logarithmic equation. The dynamic strength parameters of compacted loess decrease with an increase in moisture content and increase with increases in dry density and loading frequency. The dynamic cohesive force and dynamic internal friction angle decrease with an increase in the number of vibration times and then finally tend to stabilize.

    • Characteristics of Qingyang Loess under Freeze-thaw Cycle

      2016, 38(3):445-451. DOI: 10.3969/j.issn.1000-0844.2016.03.0445

      Abstract (749) HTML (0) PDF 4.93 M (961) Comment (0) Favorites

      Abstract:With the development of One Belt and One Road, a number of key national construction projects are proposed in regions with seasonally frozen ground and collapsible loess in western China. Researchers have determined engineering problems associated with freeze-thaw and the collapse of loess, and based on previous studies this study aims to determine the rules of change pertaining to loess collapsibility after the effects of freeze-thaw. Therefore, Q3 loess samples with different moisture contents are prepared using a moistening or demoistening method. After freezing-thawing at different test temperatures, and with no water supply, tests are conducted on frost-heave and thawing deformation, compression deformation, and the collapsible deformation of loess. Particle and physo-mechanical parameters of natural loess are also analyzed. Results indicate the following: firstly, when the moisture content is greater than the critical value, frost heave deformation is generated in loess in a freezing environment. Secondly, compared to pre-freezing samples, there is a greater compression deformation of post-thaw loess samples. However, there is a reduced coefficient of collapsibility; the freeze-thaw action weakens loess collapsibility. Thirdly, when using the same test temperature, the coefficient of collapsibility of frozen loess decreases with an increase in the moisture content, and also decreases when the test temperature is decreased but moisture content remains unchanged.

    • Earthquake Instability Mechanism of Cohesive Soil Slope and Its Application in Seismic Stability Analysis of Loess Slope

      2016, 38(3):452-459. DOI: 10.3969/j.issn.1000-0844.2016.03.0452

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      Abstract:Based on the earthquake instability characteristics of cohesive soil slopes, in this study, we used the stress analysis method to analyze the process of slope instability. By analyzing the stress state and shear stress variation features of soil in different parts of the slope during earthquakes, combined with the failure characteristics of actual slopes during earthquakes, we developed our proposed three-segment sliding instability mechanism of cohesive soil slopes. From our analysis results of the stress correlation between the above-mentioned mechanism combined with the strength reduction finite element method (FEM), we carried out a dynamic stability analysis of an actual loess seismic landslide. A comparison of our results with those of other methods reveals that the dynamic safety factor obtained by the strength reduction FEM, which considers the three-segment sliding instability mechanism of cohesive soil slopes, was very close to that determined by the limit equilibrium method.

    • >地震监测研究
    • Check and Correction of Seismometer Azimuth for Gansu Seismic Network Stations

      2016, 38(3):460-465. DOI: 10.3969/j.issn.1000-0844.2016.03.0460

      Abstract (975) HTML (0) PDF 2.47 M (982) Comment (0) Favorites

      Abstract:The orientation accuracy of three component station seismometers is very important for modern seismology research. Modern seismic studies rely heavily on precise three-component broadband observations. Similar to time travel, three dimensional particle motion is a key factor provided by a seismogram. It forms the basis of many functions, such as shear-wave splitting, receiver function, and surface and normal mode studies. Three component records are often rotated to isolate longitudinal, radial, and transverse motions. A critical parameter for performing rotation is the geographical orientation of the two horizontal components (BHN and BHE). Because the orthogonality between components of modern broadband instruments is accurate to a fraction of a degree, what really affects a correct rotation is the orientation of the BHN component, which could deviate from the true north direction. Knowledge of the orientations of the two horizontal components is thus important to perform a correction rotation. The particle motions of teleseismic P waves recorded by the network were analyzed and used to estimate the north component azimuth of each station. An SNR-weighted-multievent method was introduced to obtain component azimuths that best explain the P-wave particle motions of all the events recorded at a station. This method provides robust estimates including a measurement error calculated from background noise levels. In this study, the component azimuths of the seismic stations in Gansu province were rechecked using the P-wave particle motions of 549 MS > 6 teleseismic events from August 2007 to September 2013. Robust estimates were provided including a measurement error calculated for each station in the time series. The azimuths calculated in this study are very consistent with the results of Niu (2011), which implies that the stations of Gansu province have some problems with misorientation. The SNR-weighted-multievent method can be used to effectively check the seismometer stations horizontal azimuth deviations. Therefore, we provide deviation value of the azimuth including a measurement error calculated for each station in the time series to be taken into account for any rotation based seismic studies.

    • Influence of Using Taiwanese Stations in the Fujian Network on the Location Accuracy of Intermediate and Deep Focus Earthquakes

      2016, 38(3):466-470,490. DOI: 10.3969/j.issn.1000-0844.2016.03.466

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      Abstract:Focal depth is an important parameter in seismic studies, seismotectonics, seismic risk assessment, and seismic event identification. Its accuracy has an effect on the understanding of focal processes, fault tectonics, and stress fields. Depth from the epicenter to the source of an earthquake is defined as its focal depth and is divided into three categories, i.e., less than 70 km, between 70 km and 300 km, and greater than 300 km called shallow, intermediate, and deep earthquakes, respectively. Because tectonic plates push into each other, the activities of intermediate and deep earthquakes reflect the driving forces of these plates. Northeastern offshore Taiwan is an active earthquake region because of its location where the Eurasian and Pacific plates meet. Some intermediate and deep earthquakes have seismic phases that are different from shallow earthquakes. Therefore, finding a fast and accurate method for locating intermediate and deep earthquakes is of great importance for rapid earthquake reporting. The Fujian network monitors earthquakes in the Taiwan region. Better seismic parameters in the location methods used for intermediate and deep focus earthquakes would directly affect rapid earthquake reporting. The Fujian network has access to 16 Taiwanese stations. This paper uses the method in MSDP-an interaction analysis software in JOPENS, to locate the same earthquake twice (using the Taiwan stations or not). The results are compared with data on Taiwan's official website to identify appropriate methods for locating intermediate and deep focus earthquakes in the Taiwan region. Finally, we analyze the feasibility of using the Taiwan stations to produce rapid earthquake reports and provide operating methods and recommendations.

    • >仪器研制及介绍
    • The Implementation of Remote Control and Data Transmission andCompiling of the Extremely Low Frequency Electromagnetic Instrument

      2016, 38(3):471-477. DOI: 10.3969/j.issn.1000-0844.2016.03.0471

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      Abstract:A great number of electromagnetic abnormal phenomenon before or after earthquakes were recorded by electromagnetic instruments ACF-4M.These instruments have been installed at ELF (extremely low frequency) stations built in the 10th "Five-year Plan" period.With the development of urbanization, many observation sites cannot meet the requirements of electromagnetic observations; therefore, unattended stations with low electromagnetic background noise are needed.However, the measurement system did not achieve the required automation.This study introduces the remote control and data transmission of ELF instruments and the development plan of the original data transformation.As the ELF recorder cannot access the Internet, it is necessary to have intermediate equipment to remotely trigger the ELF instrument.The remote computer controls the local area network's computing terminal through the Internet, and subsequently through the terminal corresponding programs run to realize data transmission.The ELF instrument can improve the application efficiency of observation data and speed up the use efficiency of electromagnetic data.

    • Development and Application of a Shallow SeismicObstacle-crossing Geometry-variable Design Software

      2016, 38(3):478-484. DOI: 10.3969/j.issn.1000-0844.2016.03.0478

      Abstract (672) HTML (0) PDF 13.93 M (1017) Comment (0) Favorites

      Abstract:In shallow seismic field data acquisition,the seismic line frequently encounters obstacles such as rivers,bridges,or towns.Sources or geophones cannot be placed at such places,which can cause the loss of seismic sources or seismic traces.When encountering obstacles,the geometry must be appropriately modified in order to obtain a continuous tracing contrast of reflection events from underground interfaces.Existing seismic geometry design software is not sufficient for shallow seismic exploration,therefore,in most work areas,geometry-variable design must be hand drawn.In response to this situation,we developed a shallow seismic obstacle-crossing geometry-variable design software using C++ programming language.This software is developed specifically for shallow seismic exploration and is practical and easy to use.The software contains the basic function for drawing a geometry graph,as well as a function for designing obstacle-crossing variable geometry.When the seismic line encounters obstacles,field workers can use this software to design obstacle-crossing geometry to ensure that the seismic line acquires good quality data while going over the obstacle.We used this software to execute an obstacle-crossing geometry-variable design in a practical seismic exploration,subsequently,we contrasted and analyzed the seismic stacked section before and after using the geometry-variable design.Before using the geometry-variable design,the loss of seismic sources and seismic traces resulted in a decrease in the fold number,a decrease in the signal-to-noise ratio of the final stacked section,loss of data,and poor continuity of the reflection events.After using the geometry-variable design software developed by author,the signal-to-noise ratio of the final stacked section was improved,and the continuity of the reflection events were significantly better.This application example indicates that the obstacle-crossing geometry designed by this software can effectively improve the quality of seismic data.Based on our results,we conclude that this software is helpful for field data acquisition.

    • Remote Monitor and Control System for Seismic Stations Basedon STC89C52 Single Chip Microcomputer

      2016, 38(3):485-490. DOI: 10.3969/j.issn.1000-0844.2016.03.0485

      Abstract (1189) HTML (0) PDF 1.84 M (1131) Comment (0) Favorites

      Abstract:The number of unmanned seismic monitoring stations is increasing together with an associated lack of operation and maintenance activities. This study puts forward use of a remote monitoring system based on a STC89C52 single chip microcomputer (SCM). The detection and control part of the system mainly includes a microcontroller, communication module, LCD character module, power supply module, reset circuit, and all types of sensors. Temperature and humidity are real-time collected and the SCM instructs the control relay to absorb and release. If an anomaly occurs at the station, the warning detection system transforms information into an abnormal event alarm command using a GPRS Modem; a command is then sent using a GSM communication link to the mobile phone of the person responsible for maintaining the instrument in the form of short message, providing references and decisions made. For example, if damage to equipment is not caused by the instrument, the GSM will issue a corresponding SMS command, which can lead to termination of power and restarting operation of the equipment using the device reset circuit. In contrast, if the instrument causes damage, a maintenance engineer is sent to repair the instrument. Based on the principle that intermediate relay is controlled by the SCM, the system can remotely reboot the industrial board power supply using the intermediate relay to drive the AC contactor. This solves problems such as that which occurred when the FHD-2B proton magnetometer at Yongan geomagnetic station, which was controlled by a PC104 industrial control computer, crashed repeatedly and the network interface RJ45 was continually blocked.

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