• Volume 38,Issue 4,2016 Table of Contents
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    • >地震工程
    • Influence of Design Factors on Seismic Fragility of RC Frame Structures

      2016, 38(4):491-497,524. DOI: 10.3969/j.issn.1000-0844.2016.04.0491

      Abstract (942) HTML (0) PDF 4.88 M (1069) Comment (0) Favorites

      Abstract:The seismic resistance of structures involves uncertainty regarding the structure and the earthquake,and is coupled with non-linear variables.This paper employs Incremental Dynamic Analysis (IDA) to analyze the earthquake uncertainties.Based on OpenSEES finite element modeling theory,16 ground motion records were selected.After a discussion on the seismic vulnerability of 13 plane frame structures,this paper clarifies the influence of 4 parameters on the seismic resistance levels that RC frame structures can attain.These parameters are axial compression ratio,height-width ratio,concrete strength,and longitudinal reinforcement strength.The results show that RC frame constructions,which are designed in strict accordance with current specifications,can meet the target of "no collapse in a large earthquake"; the influence of the height-width ratio on seismic resistance is not obvious; on the premise of similar axial compression ratios,increase in concrete strength can improve the seismic resistance of structures.Under the same earthquake,for structures with high beam-column longitudinal reinforcement strength,the probability of reaching the immediate occupancy and life safe states is larger than that of structures with low beam-column longitudinal reinforcement strength,but the latter show better collapse resistance.

    • Impact of Foundation Stiffness on the Seismic Response of Ancient Masonry Pagoda

      2016, 38(4):498-503. DOI: 10.3969/j.issn.1000-0844.2016.04.0498

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      Abstract:Using the Wanshou Pagoda restoration project in Xi'an city as the research focus,this paper discusses the establishment of a cooperative work model for the pagoda body and foundations using three different types of foundation stiffnesses (setting ring beam,combination of ring beam and ground beam,and combination of ring beam,ground beam and tray).Field tests are conducted to determine the dynamic characteristics of the pagoda body using the pulsating method,and results are used as a reference for verifying the reliability of the simplified numerical model.Seismic waves (EL-Centro) under the same site conditions are selected as the horizontal excitation acting on the foundation.With an understanding of the pagoda's brittleness,this paper analyzes only the dynamic response in the elastic stage.A time-history analysis method is used to analyze the stress and displacement response law under different foundation stiffness conditions,and during displacement analysis the top of pagoda and 1F eave are selected as displacement monitoring points.The maximum horizontal displacement is found to increase with an increase in foundation stiffness,and the dip angle of the pagoda correspondingly increases.For stress analysis,two points,"a" and "b",from the pagoda bottom are selected as monitoring points,and the first and third principal stress-time curves of the two points are analyzed with different foundation stiffnesses.With an increase in foundation stiffness,the first and third principal stress at point "a" drops significantly,and the stress change trend at point "b" is similar to that at "a".It should be noted that when only the ring beam is set,the peak stress at the pagoda bottom is about 40~50 times that of the other foundation forms.The analysis results show that: (1) with an increase in foundation stiffness there is amplification of the seismic displacement response of the pagoda structure,but a reduction in the fluctuation range of the stress time-history curve; (2) the stress state of the pagoda bottom is sensitive to foundation stiffness,and as the pagoda bottom is in a tri-axial stress state when the ring beams are added its stress is magnified; (3) underpinning the entire foundations would significantly improve the stress state of pagoda bottom under seismic action,and also have a positive effect on the shear stress control of the pagoda body.However,when reinforcing the pagoda body and determining the appropriate foundation stiffness,it is necessary to comprehensively consider the displacement amplification effect of the pagoda body,and the stress distribution of pagoda bottom under seismic action.

    • Experimental Analysis of Influence of Blasting Vibration in a Hydraulic Tunnel on Surrounding Buildings

      2016, 38(4):504-509. DOI: 10.3969/j.issn.1000-0844.2016.04.0504

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      Abstract:Buildings adjacent to a site are considerably influenced by blasting vibrations.However,limited research has been conducted in this respect.In this paper,therefore,a hydraulic tunnel project in Guyuan city,Ningxia province,is selected as the research site and particle blasting vibration frequency and vibration velocity are tested and analyzed using in-situ tests.Results show that the tested domain frequency of buildings is between 10~60 Hz,which is different from general housing construction with a 10 Hz domain frequency and thus shows that blasting vibrations do not cause resonance in the buildings tested.In addition,according to safe speed standards in blasting vibration specifications,a safe distance for adobe houses is 160 m and that of general brick houses is 60 m.These results provide a theoretical basis for tunnel blasting design and construction,and can also be used as a reference when resolving disputes caused by blasting in similar projects.

    • Numerical Seismic Dynamic Response Analysis of Double-hole Eight-lane Large Section Tunnel

      2016, 38(4):510-518. DOI: 10.3969/j.issn.1000-0844.2016.04.0510

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      Abstract:To study the dynamic response characteristics under earthquake action of a double-hole eight-lane tunnel with a super large cross-section,this study conducts investigations of the Niuzhaishan Tunnel at the Pingtan Comprehensive Test Region and establishes a three-dimensional finite element numerical calculation model for double-hole eight-lane tunnels.By adopting a time-history analysis method,the horizontal seismic load is input at the bottom of the model to calculate responses of the tunnel's structure under seismic dynamic loading,including variations of displacement,acceleration,and stress.Results show that the maximum horizontal and vertical displacement occurred at the vault,and the shallowly buried tunnel of south line generally presented shear loading.In addition,peak acceleration of the tunnel occurred at the south line tunnel vault to the left and maximum vertical acceleration occurred at the south line tunnel vault to the right.As the south line tunnel portal was buried at a shallow depth,the responses of key parts were greater than those of the north line.Furthermore,the maximum tensile of the south line tunnel occurred mainly in areas of the right spandrel,left arch foot,and bottom of tunnel,and maximum compressive stress mainly occurred at the left spandrel and right arch foot; whereas the maximum tensile of the north line tunnel mainly occurred at the vault and bottom of the tunnel.However,there was a greater value for the maximum tensile of the north line tunnel at the left spandrel than at other positions in the same section.It is thus considered necessary to strengthen seismic fortification at the vault,arch springing,and at the point of minimum burial depth of the tunnel portal.

    • Influence of Slope Gradient on Dynamic Response in PortalSection of Tunnel

      2016, 38(4):519-524. DOI: 10.3969/j.issn.1000-0844.2016.04.0519

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      Abstract:Using dynamic finite element numerical simulation, in this study, we establish models with different slope gradients (α=30°, 45°, 60°, and 75°). The incident direction of a seismic wave is along the direction of the tunnel axis. As such, we studied the influence of different slope gradients on the dynamic response of the tunnel portal section and the front slope. By setting a contrast model, a pure slope without any tunnel, we examined the influence of a tunnel on the dynamic slope response. The results show that: (1) In the presence of a free face, the displacement and acceleration of the portal section undergo an obvious amplification effect. The displacement peak values of different slope models are located in the section y=0 m (distance from the portal), and the displacement of each control point decreases rapidly 40 m from the entrance of the tunnel. (2) Along with the increase in slope gradient, the displacement value of the tunnel in the same section increases, and the deformation of the portal section also increases. (3) When α≥60°, with an increase in slope elevation, displacement increases; when α<60°, with an increase in slope elevation, the displacement first increases and then decreases. The peak displacement of the slope appears at 0.4~0.6 of the slope height, which means that with an increase in slope gradient, peak displacement is closer to the top of the slope. (4) The existence of a tunnel has a significant influence on slope stability, which is particularly evident in the vicinity of the portal.

    • Punching Shear Capacity Analysis of a Slab-column Connection Considering the Effect of Different Reinforcement Ratios

      2016, 38(4):525-532,548. DOI: 10.3969/j.issn.1000-0844.2016.04.0525

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      Abstract:A slab-column structure is a bearing system,which is composed of a plate and a column.Because there are no ribs,force transfer is simple,that is to say,the load passes to the foundation directly through the column.This structure has some advantages such as optimization of space and steel plate use,layout flexibility,and quick construction.To improve the punching shear capacity of the concrete slab and to reduce its span,we often set the column head on top of the column.Punching shear has been the object of intense experimental effort since the 1950s.Some codes account for size or membrane effects,or the ratio of column size to the depth of the slab.Here,comparative analysis of formulas for punching shear strength calculations following ACI318-08,Eurocode 2,and GB50010-2010 is carried out.The research shows that the effect of the reinforcement ratio is not always uniform.Using five samples with different reinforcement ratios,which is 0.5% (two),0.99%,2.0%,and 3.0%,respectively,the numerical simulation and parameter analysis is performed with Open System for Earthquake Engineering Simulation (OpenSEES) considering the material nonlinearity and geometric nonlinearity.The proposed numerical method successfully simulates the punching shear capacity of slab-column connections in terms of the load-deformation curve,stiffness variation,and failure characteristics.The research results show that the reinforcement ratio is the key factor in punching shear resistance and should be considered appropriately in any code revision.Finally,the analysis of punching shear strength is also presented with regard to concrete.

    • Forecasting Method for Sliding Distance of Seismic Landslides on the Loess Plateau, China

      2016, 38(4):533-540. DOI: 10.3969/j.issn.1000-0844.2016.04.0533

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      Abstract:There have been many loess seismic landslides on the Loess Plateau of Northwest,China,which have seriously affected the normal agriculture,life,and local economy of the local residents due to their high frequency and the destruction that they cause.Disaster area analysis of loess seismic landslides and the sliding distance could ascertain the endanger scope and put forward suggestions for their prevention.To evaluate the influencing area of seismic landslides,a forecasting method was presented for the sliding distance of the seismic landslides on the Loess Plateau,by means of a fuzzy information model based on the data of 93 cases.Progress in the research is shown as follows: first,combining former research and components,the loess seismic landslides developed in the loess area are divided into four types: homogeneous loess landslides,loess-bedrock interface landslides,loess-gravel-bedrock landslides,and loess-bedrock landslides.Homogeneous loess landslides,which account for over 60% of the total seismic landslides,are a main focus of this paper.Second,the Morgenstern-Price method is used for calculating the stability of loess slopes.The relationship between different factors and the safe factor is discussed in the paper and the factors such as seismic intensity,relative altitude,slope angle,unit weight,internal cohesion,and internal friction angle can influence the safe factor.Third,the impact analysis of different factors on the sliding distance of loess seismic landslides is given.It can be seen that the earthquake magnitude determines the scale of landslide disaster area,and the seismic intensity affects the distribution of the landslides.Fourth,a fuzzy information model is used for the calculation of the sliding distance.By comparing with other methods,results show that the accuracy of this method is better for forecasting the disaster area.A fuzzy information matrix was established on the basis of 93 loess seismic landslides caused by South Tianshui 8.0 earthquake in 1654,Tongwei 7.5 earthquake in 1718,Haiyuan 8.5 earthquake in 1920,and Gulang 8.0 earthquake in 1927.

    • Stability Analysis of Post-earthquake High Slope under Continuous Rainfall

      2016, 38(4):541-548. DOI: 10.3969/j.issn.1000-0844.2016.04.0541

      Abstract (848) HTML (0) PDF 8.79 M (1076) Comment (0) Favorites

      Abstract:Continuous rainfall is an important factor inducing slope failure,and the causes of saturated-unsaturated slope failure under strong rainfall infiltration are diverse and complex.However,current research on the combined effects that induce slope failure is inadequate,particularly in relation to the increase in soil weight and softening of strength parameters after rainfall infiltration,both of which can impact slope stability.In this study,we establish a finite element model of a high slope following the Wenchuan earthquake in the condition of continuous rainfall.In the modeling process,the factors affecting slope stability caused by rainfall infiltration are considered,such as soil weight increase,penetration increase,and shear strength decrease.Furthermore,to analyze slop stability we employ a self-compiled calculation program,USLOPE-FEM,which is based on saturated-unsaturated seepage theory.Results show that the plastic strain zone of the slope is mainly distributed in the interface between the bottom of loosely accumulated materials and bedrock,and that the slope was close to a critical state of equilibrium before the rain.However,when the rainfall reached 20 mm/h,continuous infiltration increased the soil water content in the upper slope,the area of negative pressure disappeared,and a zone of saturated zone appeared.With continuation of rainfall,the transient saturated zone on the slope surface gradually developed towards the interior,causing a dramatic increase of in the weight and penetration of the slope soil,together with an evident decrease in shear strength.Furthermore,an integral increase of shear stress in the slope occurred and the plastic strain zone extended and interpenetrated gradually to the top of slope. After six hours of continuous rain,a local slump appeared on the surface of the free face,and after 36 hours the whole accumulation horizon gradually slumped along the bedrock and block river.Based on results of calculations and the above analysis,it is recommended that the slope is firstly improved and strengthened in relation to instability during continuous rainfall.It is considered that the results of this study can be used as a reference for evaluating slope safety under heavy rainfall.

    • Modified Strain Wedge Calculation of Single Pile in Sand under Scour

      2016, 38(4):549-553. DOI: 10.3969/j.issn.1000-0844.2016.04.0549

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      Abstract:Scour can induce soil loss around the pile foundations of engineering structures in deep water and the degeneration of the lateral bearing capacity of pile foundations caused by scour is being paid more and more attention.The strain wedge (SW) method is an effective p-y curve technique for predicting the response of piles under lateral loading.It assumes that a three-dimensional passive soil wedge forms to resist the movement of a laterally loaded pile and that the dimensions and mobilized friction angle of the soil wedge develop as the lateral load increases.However,in order to improve and extend the ability of the SW method,a modified SW method is developed which introduces the assumption of nonlinear lateral deflection of the pile resulting in non-uniform soil strain,rather than uniform strain in the soil wedge.In addition,by equating the soil weight above the bottom of the scour hole to a vertical load,the problem of the SW method being only suitable for horizontal ground surfaces is solved.The validity of the method is confirmed by the measured results of a model test and the finite element method.Results show that the lateral bearing capacity of the pile sharply declines as scour depth increases.The average ratio of lateral displacements at the pile head tended to 1.8 and 3.0 when scour depths were 3.2D and 6.4D(D=outer diameter of pile),respectively.Compared with the results of p-y curves from the finite element method,the results from the modified SW method are much more satisfactory than those measured.

    • Effect of Intermediate Principal Stress on Strength and Deformation Characteristics of Compacted Loess

      2016, 38(4):554-557,587. DOI: 10.3969/j.issn.1000-0844.2016.04.0554

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      Abstract:To study the impact of intermediate principal stress on the strength and deformation behavior of compacted loess,a series of tests with the principal stress orientation angle fixed at 0° were carried out using a hollow cylinder apparatus (HCA).The impact of the intermediate principal stress coefficient b on the strength and deformation of compacted loess is discussed.Test results revealed that at different intermediate principal stress coefficients,the developed models of generalized shear stress-strain curves were basically the same.The generalized shear stress-strain curves were not significantly different and the specimens showed significant ductility during the late stages of shear.The intermediate principal stress significantly affected the strength of the compacted loess.The normalized maximum strength was at b=0.25 and the minimum at b=0.5.The strength increased with b from 0 to 0.25.The strength was at its peak when b=0.25,then decreased rapidly as b increased further.The minimum strength reached was when b=0.5,the strength first increased,then decreased as b increased further.With the increase in the intermediate principal stress coefficient,the effective internal friction angle of the compacted loess showed a tendency to increase.The strength parameter was at a minimum when b=0,a maximum when b=0.75,and was greater in b=1 (triaxial tension) than b=0 (triaxial compression).

    • Finite Element Analysis of the Seismic Response of an Interlayer Sliding Isolation Structure

      2016, 38(4):558-563. DOI: 10.3969/j.issn.1000-0844.2016.04.0558

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      Abstract:In this paper,using molybdenum disulfide as the friction material,a sliding isolation bearing with a limit stop is designed according to the deformation characteristics of multilayer frame structures,a calculation model for a sliding frame structure is given and an equation of motion for an interlayer sliding base-isolated structure is established.Using SAP2000 software,a finite element model of an interlayer sliding frame isolation structure is established and the seismic response of the structure compared and analyzed under different friction coefficients and isolation layer positions using the EL Centro seismic wave.The results show that the dynamic response of the upper structure increases with an increasing friction coefficient,the damping effect of the structure gradually weakens,and the isolation layer slippage constantly decreases.Therefore,selection of the friction coefficient should consider the damping effect and isolation layer slippage.In a higher isolation layer,the acceleration and interlayer displacement responses show an increasing trend and weakened isolation effect;the acceleration value of the lower part of the isolation layer is larger than that of the upper part.The deformation of first and third layer isolation is mainly focused on the isolation layer,but the interlayer displacement of fifth layer isolation does not appear altered.It indicates that the higher isolation layer has less effect on the structure system.

    • Performance of a Shear Lead Damper Applied to High-voltage Electrical Equipment

      2016, 38(4):564-569. DOI: 10.3969/j.issn.1000-0844.2016.04.0564

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      Abstract:An excellent electrical technology product, electrical porcelain is widely used in power equipment. But during several earthquake research studies, we found that porcelain power equipment is highly vulnerable to earthquakes and any anti-seismic performance is difficult to enhance by means of structure optimization. As an important piece of seismic technology, the shear lead damper can effectively reduce the seismic response of electrical equipment. Nevertheless, the larger the electrical equipment, the stronger the seismic force that the electrical equipment can bear, which leads to a high demand for lead dampers. A low cycle reverse-loading experiment on a shear lead damper was conducted and the mechanical and damping characteristics at loading frequencies of 1 Hz, 3 Hz, 5 Hz and 7 Hz analyzed. The hysteresis curves at different loading frequencies indicated that the restoring force model of the shear lead damper conforms to bilinear model modality; the pre-yield stiffness was 114.52~119.43 kN/mm, the post-yield stiffness 1.05~1.17 kN/mm, and the effective damping ratio value 40%~43%. When the loading frequency increased to 5 Hz or 7 Hz, the mechanical and damping properties of the shear lead damper were basically consistent with those at 1 Hz and 3 Hz. The initial and maximum yield forces,and the hysteresis loop area of the test increased with increased loading frequency, but the effective damping ratio was unaffected. The hysteresis loops from the 4 tests were not full and round, which affected the dissipation capacity of the damper and may be caused by the processing technology. According to the test results, the processing technology was optimized. The test hysteresis loop of an optimized damper was full, and the indexes of mechanical properties and energy consumption, and the damping characteristics all increased. All of the above can improve the performance of the damper and provides reliable technical support for the improvement of the seismic capacity of electrical equipment.

    • Spectrum Characteristics of Strong Ground Motion during the Lushan Earthquake and Correlation Analysis of the Resulting Disaster

      2016, 38(4):570-580. DOI: 10.3969/j.issn.1000-0844.2016.04.0570

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      Abstract:This work is based on 60 strong earthquake records from 20 stations within a distance of 100 km of the epicenter of the Lushan earthquake provided by the China Strong Motion Network Center (CSMNC).In this study,we applied zero-crossing and linear acceleration methods to calculate the predominant period and response spectra in three directions from the 20 stations with a damping ratio of 0.05.We then computed the distributions of the peak and predominant periods of the response spectra,the amplification coefficient in the computational region,and their mean values in the hanging wall and foot wall of the fault.Results showed that the peak and predominant periods of the response spectra and the amplification coefficients were different at all 20 stations.The response spectra showed the hanging wall effect and the characteristics of rapid ground motion decay in the hanging wall.Within 100 km of the epicenter,the predominant period was almost equal at both the hanging wall and foot wall.In fact,the mean value of the predominant period in the EW and UD directions in the hanging wall was slightly less than in the foot wall,and the mean value of the predominant period in the NS direction in the hanging wall was slightly larger than in the foot wall.In general,the predominant period in the UD direction was less than in the horizontal direction,and the range of the predominant period in all directions on both sides of the fault was 0.013~0.275 s.The amplification coefficient in the NS direction at 80 percent of the stations was larger than that in the EW direction;therefore,the larger amplification coefficient in the NS direction is possibly the main reason for the landslide during the Lushan earthquake.

    • >地震科学技术
    • Relationship between Gravity Field Change and Small Earthquakes in the Combined Areas of Hebei, Shandong, and Henan Provinces

      2016, 38(4):581-587. DOI: 10.3969/j.issn.1000-0844.2016.04.0581

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      Abstract:The juncture region of Hebei,Shandong,and Henan provinces (Ji-Lu-Yu region for short),where many middle-strong earthquakes have occurred throughout history,is the focus of this study as an earthquake risk area.We used 20 stages of mobile gravity observation data,gathered from 1995 to 2010 in the region,to calculate the accumulated variation in the gravity field by means of a quasi-stable adjustment,on the basis of a unified calculation datum and elimination of system error.By analyzing variations in the gravity field before and after five earthquakes,the relationship between the dynamic variation in the gravity field and a series of ML>4.0 earthquakes was studied.The earthquakes studied were the ML4.3 earthquake,April 27,2005,epicenter located between Puyang in Henan and Juancheng in Shandong; the Puyang ML 4.6 earthquake,April 9,2006; the ML4.3 earthquake,January 3,2008,located between Fengqiu and Lankao in Henan; the ML4.8 earthquake,March 10,2008,located between Fengqiu and Lankao in Henan; and the Puyang ML4.2 earthquake,January 15,2010,The results show that,in this region,the gravity field variation shows a certain regularity before and after earthquakes of magnitude>4.0.This characteristic is obvious in that "gravity values rise continuously before earthquakes and reverse after". In addition, reasons for the regularity in the gravity field variation before and after earthquakes are investigated in this article.

    • Application of Geomagnetic Load/Unload Response Ratio Method in North China

      2016, 38(4):588-597,605. DOI: 10.3969/j.issn.1000-0844.2016.04.0588

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      Abstract:The load/unload response ratio (LURR) method has been applied for many years in seismicity forecasting and has achieved good results.Over time,it has become the main analysis method in the field of seismomagnetism and is often used in short-term earthquake analysis or prediction.In this study,we used LURR to extract anomalies from digital geomagnetic data recorded at 23 geomagnetic stations during 2008 to 2014 in North China and investigated the correspondence between earthquake occurrence and the anomalies.First,we carefully processed the geomagnetic data to eliminate any distortions caused by missing data and magnetic storms.For example,we examined a few instances of electromagnetic interference around the stations and chose the wavelet method to process the resulting noise.The research region,North China,has numerous evenly distributed geomagnetic stations,and as our research object,we selected 24 earthquakes stronger than MS4 that occurred in this region.The results show that there were ten groups of LURR anomalies in the seven-year study period in North China,of which seven were thought to be related to earthquakes and the other three were not.In addition,16 of the selected 24 earthquakes had precursory anomalies.We found the maximum anomaly intensity to be proportional to the anomaly area in each group of anomalies.Therefore,the larger the anomaly area,the greater the maximum intensity P(Z) is likely to be.Moreover,we found that seismic energy is associated with the number of stations recording anomalies in one group.Therefore,the greater the number of stations recording anomalies in one group,the larger is the earthquake radiation energy.Lastly,in the groups of anomalies related to earthquakes,we found a relationship between each anomaly,mainly reflected in the position continuity and inheritance.For example,an anomaly was more likely to occur near the position of the preceding anomaly.We also found a relationship between the epicenter of the earthquake and the anomaly location.

    • Relation between Earthquake Sequence Parameters and the Prediction of Aftershocks in the Eastern Part of Northwest China

      2016, 38(4):598-605. DOI: 10.3969/j.issn.1000-0844.2016.04.0598

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      Abstract:In this study, we calculated the parameters E2/E0, (M0-M3)lgN3, h value, K value, and b value of 51 earthquake sequences of M≥5.0 in the eastern part of Northwest China from 1970 to 2012. The results show that priority should be given to the E2/E0 and K value calculations in making the initial judgment of the earthquake type after the main earthquake. There is a good prediction result regarding the mainshock aftershock earthquake type and isolated earthquake sequence using E2/E0. Moreover,E2/E0 is unrestricted with respect to the aftershock number in the early stage. Historically, when the judgment result was based on E2/E0 to determine the mainshock-aftershock earthquake type and isolated earthquake sequence, it has generally been correct. The restrictions on the K value calculation are also relatively light. Through earthquake sample calculation, we found that the number of aftershocks within 2~3 days after most moderate-strong earthquakes could satisfy the K value calculation, and the discriminating power of the K value is relatively high. The parameter (M0-M3)lgN3 has a high discriminatory power when judging the mainshock-aftershock earthquake type, but there are associated strict requirements and could be used as reference in practical work. The h value has a high discriminatory power when judging the multiple mainshock type and can provide a reference for earthquake trend judgment after the mainshock, but calculations by the h value require a sufficient sample number and the consistency and stability of the calculation results are weak. As such, it is suggested for use only as a reference in practical work.

    • Peak Value Change of Power Spectrum at Low Frequency Before Wenchuan MS8.0 Earthquake

      2016, 38(4):606-608. DOI: 10.3969/j.issn.1000-0844.2016.04.0606

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      Abstract:The geomagnetic field is one of the basic geophysical fields,and the seismomagnetic relationship has been laboratory tested.Many studies in China and abroad have reported abnormal geomagnetic variations prior to the occurrence of earthquakes.In this study,with the Wenchuan earthquake as our research object,we selected observation data from the Chengdu geomagnetic station for three periods (July 2007-June 2008 prior to the occurrence of the earthquake,July 2011-June 2012,and July 2012-June 2013 following the occurrence the earthquake).Using the same data processing method for each,we calculated the peak values of their power spectra in the low-frequency band.The results show some abnormal changes in the peak value of the power spectrum at low frequency from July 2007 to June 2008 at the Chengdu station,but no similar changes occurred during the other two periods (July 2011-June 2012 and July 2012-June 2013).To further examine the data,we used the same data processing method for the same periods with data from the Xichang geomagnetic station and observed no abnormal changes.Combined with our other research results,we found the abnormal change to be related to the Wenchuan earthquake,based on its regional characteristics,which was likely related to the epicenter distance.However,determining the generation mechanism of this phenomenon will require more data and further research.These results represent a significant contribution to the study of the seismo-magnetic relationship.

    • Analysis of ETAS Model Parameters and Associated Variation Characteristics for 2010 Yushu, Qinghai MS7.1 Earthquake Sequence

      2016, 38(4):609-615,623. DOI: 10.3969/j.issn.1000-0844.2016.04.0609

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      Abstract:The maximum likelihood method is used and the epidemic-type aftershock sequence (ETAS) model is fitted in the analysis of aftershock sequence characteristics of the April 14,2010 Yushu (MS7.1) earthquake that occurred in Qinghai province.To examine parameter stability,ETAS parameters and their standard errors are estimated with different cutoff magnitudes,MC,and different ending times for the fitting interval.The overall parameters are observed to be α=0.948 2,p=1.059 6,and b=0.817 3 with setting MC=ML1.5. Compared to other M>7.0 earthquake sequences on the continental China,the Yushu MS7.1 earthquake sequence is characterized by a weak triggering capability in generating secondary aftershocks,and a quick decay rate of aftershocks.A systematic approach for using multiple cutoff magnitudes above the magnitude of completeness is adopted in the calculation process to examine stability of the sequence parameters and to analyze the degree to which they are affected.The cutoff magnitude,MC,is observed to have a certain effect on the value of α,k,and p (with an increase in MC the value of k decreases,there is a general increasing trend of α,but less influence on p).ETAS model parameters with different sequence durations are studied in this paper,together with their temporal variations and stability in the early stage after the shock.There is variation in the range of p and α shortly after the earthquake stops for different cutoff magnitudes within the same earthquake,whereas there is a trend of p and α is towards convergence and stability after stabilization of seismic activity.Furthermore,there is evident change in the temporal variation of ETAS parameters 14 days after the mainshock,when the parameters become relatively stable.

    • Seismic Potential Research along the North Fuyu Fault in Songyuan City

      2016, 38(4):616-623. DOI: 10.3969/j.issn.1000-0844.2016.04.0616

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      Abstract:The Fuyu-Zhaodong Fault is an important buried seismogenic fault in the Songliao Basin.In 1119A.D.an MS6.75 earthquake occurred on the fault,the largest ever recorded before the Haicheng earthquake of Northeast China in 1975.In 2006 and 2014 several earthquakes below MS6.0 occurred along the fault; these recent earthquakes were mainly centralized on the northeast segment and the Chaganhua segment.Active faults were detected in Songyuan city from 2012 to 2014 and the northeast segment of the Fuyu-Zhaodong Fault was proven to cross downtown with a near-EW trend and showed obvious segmentation and independence.The urgency and importance of meticulous detection of the fault is obvious for this urban environment.Using three-dimensional geophysical data from oilfield and shallow geophysical prospecting,the space distribution and profile characteristics of this fault (named the north Fuyu Fault) were determined.The combined methods of borehole detection and optical stimulated luminescence dating were also used to confirm the seismicity along the fault since late Pleistocene.Using the rupture scale of bedrock surface from the three-dimensional geophysical data,this paper estimates the seismic potential along the north Fuyu Fault and studies its probabilistic seismic risk using a probabilistic calculation method.A Poisson probability model is adopted and quantitative parameters,such as maximum magnitude,recurrence period,and occurrence probability in the coming 50~200 years,are calculated.This presents a breakthrough in the study of potential seismogenic faults that have few historical earthquake records and long return periods.

    • Division of Late Quaternary Strata and Analysis of Neotectonic Movement in Linfen Basin

      2016, 38(4):624-631. DOI: 10.3969/j.issn.1000-0844.2016.04.0624

      Abstract (866) HTML (0) PDF 9.13 M (923) Comment (0) Favorites

      Abstract:As the Quaternary strata of Linfen Basin have not yet been systematically analyzed,in this study,we performed a controlled borehole in the middle of the Linfen depression to expose the Quaternary strata in Linfen Basin.We employed a controlled borehole in this project to detect active faults and assess seismic risk in Linfen City from 2009 to 2014.The final hole depth was 245 m at the coordinates 111°34'56"E,36°3'55"N.Based on the formation of the strata exposed by the borehole,we determined that the strata are divided into 39 composite layers.The sediment in the lower parts of the section is darker and is characterized by a brownish red silty clay layer,which is representative of a strong oxidizing environment.The sediment of the upper part of the section is fine-grained and is dominated by lacustrine deposits.We processed 269 effective pollen samples to analyze the characteristics of the sporo-pollen assemblages in the drilling section.Based on the obvious changes in the pollen content of the spore trees,shrubs,and herbs and from the fern content in the section,we divided the sporo-pollen assemblages into six categories as follows: Ⅰ (245~152 m),Ⅱ (152~84 m),Ⅲ (84~51.5 m),Ⅳ (51.5~25.5 m),Ⅴ (25.5~12.5 m),and Ⅵ (12.5~0.5 m).We collected nine core samples in the upper part of the section to analyze the absolute age of the sediment by optically stimulated luminescence dating.We also collected twelve core samples in the lower part of the section to analyze the absolute age of the sediment by electron spin resonance.Dating results show that the control borehole records the sedimentary formation from approximately 379 ka B.P. Sediments at a borehole buried depth of 0~0.4 m belong to the Holocene strata.Sediments at the borehole buried depth of 0.4~80.8 m belong to the upper Pleistocene.Based on the pollen records,we characterized the paleoclimate as being dry and cold during this period,which then warmed and had increased precipitation near the end-stage of this period.Borehole sediments buried below 80.8 m belong to the middle Holocene strata,in which the paleoclimate was warm and humid.The average subsidence rate since the late Pleistocene was 0.64 mm/a,which is much higher than that of the Quaternary.We suggest that the neotectonic movement of the Linfen Basin has shown an increasing trend since the late Pleistocene.

    • New Insight on Paleoearthquake Activity along Changma Fault Zone

      2016, 38(4):632-637,668. DOI: 10.3969/j.issn.1000-0844.2016.04.0632

      Abstract (1520) HTML (0) PDF 12.15 M (2055) Comment (0) Favorites

      Abstract:The Changma fault consists of four sub-faults,and is an important transform fault located between the Altyn Tagh fault and the western segment of the Qilian Mountains.In 1932,a M7.6 earthquake occurred in the fault,forming a rupture with a length of approximately 120 km that is composed of a series of fissures,fault scarps,offset terraces,and gullies.The maximum horizontal and vertical coseismic displacement was up to 5.5 m and 1.9 m,respectively.A trench excavated at Choushuiliugou in the middle-eastern segment of the Changma fault shows evidence of two paleoearthquakes: one is the Changma earthquake (1932) and the other earthquake occurred after 902±44 a B.P..Combined with the results of previous studies,it was determined that seven paleoearthquakes have occurred in the Holocene. Base on characteristic earthquake model, we speculate an earthquake recurrence interval of approximately 1 ka,and part of paleoearthquake events are not revealed by the trench.The trench also shows that the dip direction of the layer on the hanging wall is opposite to that of the down wall and low-angle fault.Based on a survey of dislocation landforms,the ratio of horizontal shortening and left strike slip was found to be 1∶5.Eastern extrusion occurred in relation to the influence of Altyn Tagh fault activities in the study area.The change in fault trend has resulted in regional stress and differing angles between some of the fault segments,particularly the tip of sub-faults.Active fault characteristics are shown predominantly as sinistral strike-slip,but there is an evident increase in the component of horizontal shortening,which forms nappe activities on the hanging wall.It also forms a specific low-angle strike-slip phenomenon,which illustrates that the Changma fault has prominently presented crustal shortening since the late Pleistocene,in addition to absorbing much of the sinistral displacement of the Altyn Tagh fault,and playing a significant role in the tectonic transition between the Altyn Tagh fault and a series of faults in the western segment of the Qilian mountains.

    • Hypsometric Integral of Drainage Basins in the Coastal Area of Fujian and Associated Neotectonic Significance

      2016, 38(4):638-646. DOI: 10.3969/j.issn.1000-0844.2016.04.0638

      Abstract (798) HTML (0) PDF 14.18 M (763) Comment (0) Favorites

      Abstract:In this paper,the major river system network and drainage basins in the coastal zone of Fujian are extracted based on ASTER GDEM 2 data,and the hypsometric integral (HI) value of the sub-drainage basins is calculated to analyze the response relation between watershed morphology and Neotectonic activities in the area of analysis.Results show the HI value to be distributed in evident bands,where it tends to gradually reduce from the coast to inland in areas divided into Zones Ⅰ,Ⅱ,and Ⅲ,in accordance with features of the NW fracture zone and distributional characteristics of weak earthquakes in this area.In Zone Ⅰ,regions such as Fuzhou and Fu'an have a low HI value because they are costal basins characterized by basinal deposits and partial tectonic descents.The western boundary of Zone Ⅱ is represented by the line of Pucheng-Jianyang-Mingxi-Liancheng,indicating that Zone Ⅱ is basically situated between the Zhenghe-Dapu fault zone on the east side and the Shaowu-Heyuan fault zone on the west side.Observations of vertical modern crust deformation indicate an obvious differential uplift on both sides of the Zhenghe-Dapu fault zone,with a higher uplifting amplitude in the east than the west,which is a reflected by a remarkably higher HI value in Zone Ⅰ than in Zone Ⅱ; this is obviously higher in the transitional landform zone towards the inland than in Zone Ⅲ.Zone Ⅲ is mainly situated in the area west of the Pucheng-Jianyang-Mingxi-Liancheng line,where the HI value has a well-marked low-value anomaly,which may reflect relatively weak tectonic movement in the region and a relatively light influence from coastal tectonic deformation as it is situated far from the coastal zone.The distribution of HI values basically coincides with activity attributes of major NE fault zones in this region,which may be caused by the gradually weakening influence of dynamic antennas on Taiwan Island towards the inland area.In addition,the conflict between expansion of the open rift valley in the South China Sea Basin and the eastward diving process of the Pacific Plate is also fully reflected in the watershed morphology of the coastal zone of Fujian.

    • ShakeMap Study of 2014 Ludian, Yunnan MS6.5 Earthquake Based on ShakeMap_CNST

      2016, 38(4):647-651. DOI: 10.3969/j.issn.1000-0844.2016.04.0647

      Abstract (904) HTML (0) PDF 5.60 M (1159) Comment (0) Favorites

      Abstract:In this study,we applied the ShakeMap_CNST system,which considers the epicenter location,earthquake magnitude,seismic tectonic background,and focal mechanism,for the rapid prediction of the ground motion spatial distribution of the Ludian,Yunan 6.5 earthquake of August 3,2014.Using a method for estimating the seismic motion attenuation relationship in the Yunnan area,we calculated the PGA and PGV values of the bedrock surface in the epicenter area.Based on the observation results of strong ground motion by the stations and by using the distance weighted interpolation method,we recalculated the PGA and PGV values as being in the range of 30×30 km2 around the stations.In the calculation process of the seismic ground motion parameters,we increased the weight of the actual observation data to recalculate the ground motion data of each grid node and then drew a seismic intensity map.From the map,we can see that the scope of the VII-degree zone was obviously larger than originally believed.The field survey results also show that the houses were damaged more seriously in the towns of Laodian,Xindian,and Xiaohe,which are located in the eastern part of Qiaojia county in which earthquake damage was more significant.Therefore,the spatial distribution characteristics of the ground motion predicted by this system are consistent with field survey results.

    • Simulation Test of Ground Fissures Based on Geoelectric Field Response

      2016, 38(4):652-657. DOI: 10.3969/j.issn.1000-0844.2016.04.0652

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      Abstract:With development of the national economy,groundwater resources have been over-exploited in many areas of the country,which has led to serious problems in land settlement.Uneven settlement has induced many ground fissures,resulting in serious environmental problems and considerable economic loss.It is therefore extremely important to conduct studies on the three-dimensional geological structure of uneven settlement and ground fissures.In this paper,a network parallel electrical prospecting system is used with a physical model of a basement buried within a hill,to determine and measure the response of the geoelectric field during the process of soil cracking under the condition of water injection.Results show that changes in electric potential,current,and resistivity in the soil are closely related to water content,together with changes in the soil water content,electric potential,excitation potential,excitation current,and apparent resistivity change sharply.When water flows through the soil,the spontaneous potential,primary field potential,and exciting current rise quickly,but apparent resistivity sharply decreases.In addition,when apparent resistivity is large,soil deformation is also large,and there is danger of the development of ground fissures.Monitoring of electrical parameters can thus be used to warn of impending disasters.The inversion information obtained from the network parallel electrical prospecting system in this experiment shows that it is easy to induce uneven settlement and cracks at points of large curvature.The greater the degree of uneven settlement,the greater the length,width,and depth of the crack.The use of a network parallel electrical prospecting system for determining ground fissures is a novel idea that produces good results,and can be used as a reference in future research or to provide a new method and perspective for predicting geological disasters.

    • >仪器研发
    • Design of an On-site Automatic Calibration Device for theVertical Pendulum Broadband Tiltmeter

      2016, 38(4):658-662. DOI: 10.3969/j.issn.1000-0844.2016.04.0658

      Abstract (979) HTML (0) PDF 2.84 M (758) Comment (0) Favorites

      Abstract:The vertical pendulum (VP) broadband tiltmeter is a type of earthquake precursor observation equipment that records the inclined earth tide.The scale value represents the relationship between the measured physical quantity and the output voltage.Its accuracy plays a key role in data reliability.The calibration process provides the scale value for the instrument.Most traditional calibration methods,e.g.,plat calibrations in the laboratory and manual calibrations on site,cannot satisfy the accuracy levels required in scientific applications,or might affect the continuity of observations.In this study,we investigate an on-site automatic calibration device,in which small-scale shifts are introduced by a piezoelectric ceramic under the control of a single chip microcomputer AT89C51.The device then calculates the scale values from serial corresponding values of the outputs of the VP broadband tiltmeter and a laser interferometer.This device could realize the automatic operation of calibration,and its relative calibration accuracy is 0.36% when the excitation voltage is adjusted to+8 V,and meets the requirement of a relative error of less than 1%.

    • >震灾报道
    • Geological Hazard Characteristics and Seismic Intensity of July 3, 2015, Pishan, Xinjiang, MS6.5 Earthquake

      2016, 38(4):663-668. DOI: 10.3969/j.issn.1000-0844.2016.04.0663

      Abstract (1116) HTML (0) PDF 20.82 M (803) Comment (0) Favorites

      Abstract:Based on field surveys,investigations,and seismo-geological hazards in relation to the Pishan,Xinjiang (MS6.5) earthquake that occurred on July 3,2015,this paper summarizes the associated distribution and development characteristics of sandy soil liquefaction,ground fissures,collapse,and ground deformation.The seismic intensity of the earthquake is described simply as follows.The earthquake occurred in Pishan county,Hetian City,Xinjiang,and the area of intensity of Ⅵ degrees ranged for 14 580 km2,from the west of the city to Kashi City in Yecheng County and to Moyu County,Hetian in the east.The meizoseismal area (Ⅷ degree) was 1 110 km2,the length of the major semi-axis was 45 km,and the length of the semi-minor axis was 32 km in the Ⅶ degree area.Seismo-geological hazards relating to this earthquake are mainly distributed in the meizoseismal area,where sandy soil liquefaction is particularly serious,and mainly occurred in Guma and Pixina Towns,Pishan county.The sand blasting nozzle was linearly distributed throughout a field of low-lying water,causing collapse of the loess side slope in the north of Yapu spring.Pishan county is located in the west of the Kunlun mountains and on the edge of the Tarim basin.The soil in this area is mainly composed of silt and fine sand,gradation is poor and groundwater shallow,thus sand soil liquefaction is very serious.Ground fissures and cracks occurring during the earthquake caused slight dislocation,and many can be seen in the meizoseismal area of Pixina town (ground fissures measuring 20 m long and 30 cm wide).Root systems show horizontal right lateral slip in these ground fissures,and the stagger distance is 2 to 7 cm.The road in Pixina Town was crushed and broken,which showed that the earthquake did not cause a rupture zone on the surface,but that compression deformation occurred,which is a type of co-seismic deformation.Although the magnitude of the Pishan earthquake was not large,it resulted in considerable seismo-geologic hazards,particularly sand soil liquefaction and ground fissures over a large area.

    • Building Damage Characteristics during the Zigui, Hubei M4.7 Earthquake on March 30, 2014

      2016, 38(4):669-672. DOI: 10.3969/j.issn.1000-0844.2016.04.0669

      Abstract (860) HTML (0) PDF 7.34 M (815) Comment (0) Favorites

      Abstract:On March 30, 2014, a M4.7 earthquake occurred in the Zigui county, in Hubei province. The epicenter intensity reached Ⅵ. The earthquake caused various degrees of damage to houses in the epicentral area. According to on-site investigation data conducted after the earthquake, through the sampling statistics and analysis on house damage in the epicentral area, two typical and common house damages in rural areas are summarized in this work. There are three main reasons for the Ⅵ damage caused by the earthquake to the houses in the area studied. First, the house foundation is mishandled. Most damaged houses are located in the scarp near the Yangtze River, where part of the houses lie on bedrock foundation and part lie on artificial stone masonry. Therefore, the houses are prone to uneven deformation and cracking. Second, high mountains and deep valleys also have an effect. Due to the amplification of ground motion in abrupt mountain terrain, the houses will suffer stronger seismic action and thus house damage occurs. Third, the houses' structure is defective and the construction quality is unqualified. Most of the damaged houses have cavities in the walls and the constructional columns are missing. The design and construction are not standardized. Hence, the houses are vulnerable to damage caused by earthquakes. Based on the investigation and analysis, four suggestions on the site selection, design, and construction of rural housing have been put forward in this study. These suggestions can provide the basis and reference for the rural construction and government decision-making in the disaster area and other earthquake prone areas. First, the houses should be built in areas which aid earthquake resistant structures. The houses should not be built on towering isolated hills and steep slopes. Second, houses should be built with constructional columns and ring beam structures and with a superior strength of mortar. These are the key measures to ensure that masonry structures do not collapse. Third, the house builders should put emphasis on the foundations design. Finally, the government should train building craftsmen in the rural areas and improve earthquake resistance knowledge.

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