• Volume 38,Issue 2,2016 Table of Contents
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    • >Earthquake Engineering
    • Mechanism of Resistance and Damping Technology in a Deep Circular Composite-lined Tunnel Subjected to Incident Plane P-waves

      2016, 38(2):159-165. DOI: 10.3969/j.issn.1000-0844.2016.02.0159

      Abstract (894) HTML (0) PDF 1.34 M (1179) Comment (0) Favorites

      Abstract:Using the Fourier-Bessel series expansion method,the dynamic stress concentration factors of deeply-buried circular composite-lined cavities subjected to plane P-waves were studied,and a dynamic stress concentration factor series solution for the cavities was derived.By combination with an actual pipe tunnel project in the IX seismic intensity zone,the influence of different combinations of lining stiffness and thickness on the factor was analyzed.This analysis shows that the dynamic stress concentration factor of the second lining decreased after installation of a grouting reinforcement zone and buffer layers.As the elastic modulus and thickness of the grouting zone increased,the factor of the second lining reduced and the optimal thickness of the grouting zone was equal to the clearance radius of the cavity.The dynamic stress concentration factor of the second lining decreased with a lower elastic modulus and larger damping layer thickness.The elastic modulus of the buffer layers was estimated to be below 1/20 of that of the surrounding rock,and the optimal thickness of the damping layers estimated at 1/50 of the cavity clearance radius.Finally,this new damping structure of "surrounding rock-grouting zone-buffer layers-lining" is proposed for shock absorption of an actual pipeline tunnel.The results show that this new structure exhibits the best damping effect when compared with other measures.

    • Yielding Mechanism and Seismic Performance of Frame Structure with High-strength Bars and High-ductile Fiber-reinforced Concrete

      2016, 38(2):166-175. DOI: 10.3969/j.issn.1000-0844.2016.02.0166

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      Abstract:To control the failure mechanism and seismic performance of reinforced concrete (RC) frame structures,our proposed system used ultra-high-strength (UHS) reinforcement in a column and had the option of using fiber-reinforced concrete (FRC) in a frame where damage is expected to occur.Disaster investigations revealed that reinforced concrete frame structures account for a high proportion of buildings destroyed.The use of UHS reinforcement was expected to result in only minimal residual deformations and a low degree of hysteretic energy dissipation.FRC was expected to facilitate hysteretic energy dissipation and increase the system's damage tolerance.Using nonlinear time history analysis,we investigated three frame structures using ABAQUS finite element software,a large universal finite element software widely used in the nonlinear analysis of RC structures.In particular,we used the concrete-damaged plasticity model,which is one of the most important concrete constitutive models in ABAQUS.Based on our analysis results,we discussed the seismic behavior of structures at different seismic intensities.To determine the seismic capacity of each structure,we selected the following parameters: maximum deformation,story drift,residual deformation,and energy dissipation.We found that the use of UHS reinforcement provided the system with relatively greater resistance against lateral seismic loads and resulted in less residual deformation while preventing the critical column from yielding until the drift reached 3%~4%.Thus,UHS frames should be used in columns designed for a "strong column-weak beam" failure mechanism.As the drift increased,differences in residual deformation between specimens decreased.These research results suggest that the proposed system may be promising for improving the damage tolerance of structures in seismic regions.

    • Seismic Performance of High-strength-steel Composite Eccentrically Braced Frames

      2016, 38(2):176-184. DOI: 10.3969/j.issn.1000-0844.2016.02.0176

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      Abstract:In high-strength-steel composite eccentrically braced frames (HSS-EBFs), links and braces are made of Q345 steel, whereas other structural members are made of Q460 steel. This structure can reduce member section sizes and thus the weight of the steel and achieve improved economic efficiency by reducing the amount of steel used and applying HSS. To compare the seismic performance of K-type HSS-EBFs (K-HSS-EBFs) with traditional K-type EBFs (K-EBFs), in this study, we designed four K-HSS-EBFs and four K-EBFs of different structural heights. We used nonlinear static pushover analysis and nonlinear dynamic analyses to investigate the seismic performance of the K-HSS-EBF and K-EBF models. The results indicate that both K-EBFs and K-HSS-EBFs well satisfy seismic requirements and that the deformation of the K-HSS-EBFs was more obvious than that of the K-EBFs. However, the comparatively smaller member section sizes of the K-HSS-EBFs can reduce the steel weight and project building costs.

    • Seismic Analysis of Water Intake Channel Inlet/Outlet for Haiyang Nuclear Power Project in Shandong

      2016, 38(2):185-191. DOI: 10.3969/j.issn.1000-0844.2016.02.0185

      Abstract (921) HTML (0) PDF 5.23 M (1174) Comment (0) Favorites

      Abstract:This paper is based on the first stage of a water channel project of the Haiyang nuclear power project in Shandong Province. Using a dynamic time history response analysis method, we establish a three-dimensional soil structure model using the nonlinear finite difference software FLAC3D. We analyze the internal force changes of the nuclear power station's water channel under the combined effect of weight, water pressure, soil pressure, temperature, water hammer pressure, and seismic load. We carried out the seismic analysis of the inlet and outlet of the nuclear power station by FLACE3D programming, and calculated the internal force of the lining structure using a five-point formula. First, we addressed the internal force changes of the inlet-outlet channel position under the combined effect of weight, water pressure, soil pressure, temperature, water hammer pressure, and seismic load. Secondly, we selected three typical conditions and performed a comparative analysis of the internal force of the inlet-outlet position with different wall thicknesses. The calculation results show that: (1) Temperature has a significant effect on the internal channel outlet position if the internal temperature is greater than the external temperature. (2) Water hammer pressure force has a significant effect on the outlet of the channel, which can be used as a control condition for static analysis. (3) Seismic load also has a significant effect on the outlet of the channel, which can be used as a control condition for seismic analysis. (4) Different wall thicknesses also have a significant effect on the outlet of the channel; the thicker the wall thickness, the greater is the internal force. Therefore, based on the above conclusions, weak cross sections should be reinforced when being designed and constructed. The calculation method and analysis results in this paper can provide a reference for seismic response analysis of water channels in the nuclear power plants and in other similar structures.

    • Seismic Vulnerability Analysis of Multiage Steel Frame Structures Based on Time-varying Seismic Damage Model

      2016, 38(2):192-200. DOI: 10.3969/j.issn.1000-0844.2016.02.0192

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      Abstract:In recent years, because of the frequency of earthquakes,steel has been widely used in the construction of civilian residential structures owing to its excellent seismic performance.However,considering that steel structures are widely used,there is a durability problem because of steel corrosion,which has become increasingly serious.Corrosion weakens steel member cross-sections and reduces steel's mechanical properties,ultimately affecting the seismic performance of steel structures.Seismic vulnerability analysis can be used to predict the damage probability at different levels of a structure under earthquakes of different magnitudes.As such,it has an important application value in seismic design,reinforcement,and maintenance decisions regarding structures.Seismic vulnerability research methods include empirical,testing,and analytical methods or a combination of two of these methods.For the most seismic hazard data,empirical vulnerability is the most accurate method,but not all areas experience an adequate number of earthquakes for researchers to obtain sufficient data to evaluate the structural damage probability at all levels.Experimental study methods of vulnerability analysis are also credible,but their costs are relatively high.Compared with the abovementioned two methods,an advantage of the analytical method of determining vulnerability is that it is a rapid and low-cost approach.The main factors that affect the seismic vulnerability of building structures are structural type,architectural age (including specifications and construction period of building design),intensity of fortification,site class,and number of layers.While research on the seismic vulnerability of various structures is quite mature,there has been scant consideration of the impact of service age on the seismic vulnerability of building structures or fragility curves of multiage structures.Based on the time-varying seismic damage model,we propose the use of an analysis method that includes the probabilistic seismic vulnerability steps of multiage steel frame structures under the corrosive action at an acidic atmospheric environment.We consider the influence of service age on the seismic performance of steel frame structures and establish the time-varying probabilistic seismic demand model,time-varying probabilistic seismic capacity model,and time-varying vulnerability model.Based on our analysis of the probabilistic seismic demand and probabilistic seismic capacity,we obtain a vulnerability model and vulnerability curve for multiage (20,30,40,and 50 years) steel frame structures.

    • Seismic Vulnerability Analysis of Reinforced Concrete Frame Structures Based on Ground Motion Parameters

      2016, 38(2):201-211. DOI: 10.3969/j.issn.1000-0844.2016.02.0201

      Abstract (944) HTML (0) PDF 5.81 M (2224) Comment (0) Favorites

      Abstract:In this study,we performed the seismic vulnerability analysis of reinforced concrete (RC) frame buildings based on nonlinear dynamic time history analysis and ground motion parameters.We used a typical 12-story RC frame structure as the research object.First,we conducted static pushover analysis to identify a weak layer and to determine the capacity parameters of the building.Then,we performed nonlinear dynamic time history analysis to estimate the seismic response of the structure and to analyze the relation between the demand and ground motion parameters.With respect to ground motion parameters,we studied the uncertainty of the structural response and then established peak ground acceleration and vulnerability curves based on the first-mode acceleration response spectrum.By considering the impacts of site conditions on ground motion characteristics,we examined the impact of site conditions on vulnerability.The results show differences in vulnerability curves under different site conditions.Based on ground motion parameters obtained from new-generation seismic zoning maps or seismic safety evaluations,the proposed method can be used to directly estimate damage to a structure following an earthquake,which has significance in seismic performance evaluations and in the prediction of earthquake losses.

    • Sensitivity Analysis of Fault Parameters during Ground Motion Simulation

      2016, 38(2):212-218. DOI: 10.3969/j.issn.1000-0844.2016.02.0212

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      Abstract:It is not usually possible to obtain accurate fault parameters after an earthquake,and this has a negative effect on the ability to make a rapid assessment of ground motion intensity after an earthquake when using a ground motion simulation method.Two earthquakes that occurred in western USA were selected for simulation using two different methods.Parameters such as strike,rake,dip,and focal depth were varied and the influence of the different fault parameters on the ground motion intensity index and value of response spectra were analyzed,and the accuracy of the different methods was determined.Results of simulations show that the GP method provides values that are closer to observed values than the EXSIM method.In comparison with the errors caused by the simulation methods,the influence of fault parameters on the simulated results is small within a reasonable error range of different fault parameters.It is thus considered that fault parameters through rapid inversion can be used in ground motion simulation for a rapid assessment of seismic intensity.

    • Influence of Soil Layer Structure on Seismic Peak Ground Acceleration Zonation Maps of Oil and Gas Pipeline Project

      2016, 38(2):219-225. DOI: 10.3969/j.issn.1000-0844.2016.02.0219

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      Abstract:Oil and gas pipelines are vital aspects of infrastructure projects and may span tens or even thousands of kilometers.These spans may involve different soil structures that may become overburdened and thus considerably affect the seismic peak ground acceleration (PGA) and PGA zonation map. In this study,based on the site amplification coefficient,we examine a gas pipeline project in the North China plain. We estimate the fitting functions of the site amplification coefficient (KS) and PGA of rocks in different soil layer constructions and obtain a PGA zonation map for the adjacent 10 km area.We then compare our results with those given by the 4th and 5th seismic ground motion parameter zonation maps of China.The results show that the practical amplification coefficient KS lies between 1.30 and 1.45 for 10% probability of exceedance in 50 years,and the amplification coefficient KS lies between 1.15 and 1.30 for 5% probability of exceedance in 50 years.They are both relatively larger than the values suggested by the 4th and 5th zonation maps.The PGA zonation map with 10% probability of exceedance in 50 years shows that local regions belonging to 0.15g or 0.20g zones in the 4th and 5th zonation maps of China become 0.20g or 0.25g zones,which demonstrates that the amplification coefficient KS may significantly influence PGA zonation map classifications.

    • >地震科学研究
    • Additional Textual Criticism of Three Moderate-strong Historical Earthquakes in the Northern Region of Sichuan Province

      2016, 38(2):226-235. DOI: 10.3969/j.issn.1000-0844.2016.02.0226

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      Abstract:The northern region of Sichuan province in China is located at the central and northern segment of the north-south seismic belt.A series of active faults are developed in this region;they have a complex distribution and have been historically responsible for a series of strong (large) earthquakes,extending to the present-day.However,it is difficult to confirm the basic parameters and causative structures relating to earthquakes that occurred many years ago.Therefore,this study verifies the basic parameters and discusses the causative structures of three moderate-strong earthquakes that occurred before 1900 A.D. in the northern region of Sichuan province (the Songpan earthquake in 638 A.D.,Nanping earthquake in 1738 A.D.,and an earthquake in the north of Songpan in 1748 A.D.),based on detailed textual research using historical earthquake records and field investigations.The results indicate that:(1) the magnitude of the Songpan earthquake in 638 A.D.should be amended from a magnitude of 5 3/4 to that of about 6 1/4 .In addition,the epicenter intensity was about 8,and the heavily-damaged area of this earthquake was located in (Gonggangling) and Hulugou,near the boundary of Songpan county and Nanping county (now Jiuzhaigou county).The long axis direction of the isoseismal line had an approximate N-S orientation,which is consistent with the strike of the northern segment of the Minjiang active fault zone.(2) The magnitude of the Nanping earthquake in 1738 A.D. should be amended from a magnitude of 5 3/4 to one of about 6;the epicenter intensity was approximately 7~8,and the heavily-damaged area of this earthquake was located northwest of Huilongbu.The long axis direction of the isoseismal line has an approximate NW orientation,which is consistent with the strike of the southeastern segment of the Tazang active fault zone.(3) The intensity of northern Songpan earthquake in 1748 A.D. should be amended to 8,and the heavily-damaged area relating to this earthquake was located near Huangshengguan.The long axis direction of the isoseismal line had an approximate N-S orientation,which is consistent with the strike of the northern segment of the Minjiang active fault zone.These results can be used as an important reference to analyze features of seismic activity and to judge areas at risk from strong earthquakes in the future.

    • Precise Relocation of Small Medium Earthquakes in Anhui “Huoshan Seismic Window”

      2016, 38(2):236-241,248. DOI: 10.3969/j.issn.1000-0844.2016.02.0236

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      Abstract:The frequency and intensity of small medium earthquakes in the Luoerling—Zhufoan area,west of Huoshan county,are particularly prominent in Anhui province and its neighboring areas.The earthquakes in this area are characterized as moderately strong and concentrating into a band,with small ones clustering at shallow focal depth and forming a swarm.Based on the above,it is of critical and urgent importance to strengthen earthquake monitoring and improve location accuracy in the region.The double-difference (DD) location algorithm,as a relative positioning method,has unique advantages in improving the accuracy of earthquake location.From January 1,2009 to June 13,2014,2 679 earthquakes of ML≥ 0.0 occurred in the Huoshan area,Anhui province,and we relocated them in this study using the DD method.The average relative errors in the focal depths were 0.05,0.06,and 0.07 km in the E-W,N-S,and U-D directions,respectively,as compared with the original values after relocation.The positioning accuracy of the original source location was greatly increased and the "grid" illusion distribution phenomenon of the original source location,caused by positioning errors,was significantly improved after relocation.The spatial distribution of the epicenters is more compact and concentrated than previously determined.The relocation results show that there are three dense seismic zones distributed along the NE direction,consistent with the direction of the Luoerling—Tudiling fault.The distribution of the focal depths is more precise and there is a predominant depth range from 4 to 9 km that accounts for over 88% of the total.More shallow earthquakes in the Huoshan area indicate that the upper crust may be in a period of higher seismic wave velocity.

    • CV Value Variation of P-axis Azimuth for Small to Moderate Earthquakes before the Lushan MS7.0 Earthquake in Sichuan

      2016, 38(2):242-248. DOI: 10.3969/j.issn.1000-0844.2016.02.0242

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      Abstract:In the preparation process of a strong earthquake,at the potential source area and its vicinity,the tectonic stress field can be enhanced by local tectonic activities.There will be a space-time adjustment of the stress field with the background of a stable regional stress field.To detect the crustal stress state of the study area,in this paper we analyze the focal mechanism data of small to moderate earthquakes that occurred at the epicenter of the Lushan MS7.0 earthquake and its surrounding areas more than ten years before the Lushan earthquake.We obtained the focal mechanism solutions of the small to moderate earthquakes using the Hardebeck and Shearer (HASH) method,then used the CV value of the P-axis azimuth (the ratio of the standard deviation to its average) to identify the stress field change.The results show that the stress field obviously changed at the seismic source and its surrounding areas with time.The P-axis azimuth CV values of the small to moderate earthquakes exhibited a rise-decline-rise process prior to the Lushan M7.0 earthquake,which means that there was a long period of stress accumulation before the M7.0 earthquake,consistent with the results of many previous studies.The CV values and apparent stress had the same tendency changes,which objectively reflect the changes in the stress field in the process of earthquake preparation.This study demonstrates that there is a certain relationship between the occurrence of strong earthquakes and the change in the P-axis azimuth CV values of small and moderate earthquakes.

    • New Evidence for Holocene Tectonic Activities of the Wushan—Tianshui Segment in the Northern Margin Fault of the West Qinling

      2016, 38(2):249-259. DOI: 10.3969/j.issn.1000-0844.2016.02.0249

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      Abstract:The western segment of Zhangxian along the Western Qinling active fault zone is a large left-lateral strike-slip active fault zone and a historical strong earthquake zone.Recent studies on this area have obtained the latest geological and geomorphological information.However,the latest age of tectonic activities among the segment of Wushan—Tianshui and Tianshui—Baoji is still unclear.In this paper,the Wushan—Tianshui segment is studied in detail using high-resolution satellite images,geomorphological analysis, trenching technology, and 14C radiocarbon dating technology.Results suggest that tectonic activities since the late Quaternary are remarkable.Geomorphic expressions include fault-controlled valleys,sinistral offseted ridges and stream, and fault scarp.A consequence in more trenches and dated 14C samples reveals that stratum from the Holocene have been raptured by the latest tectonic activities.Thus,this study provides new evidence for Holocene tectonic activities of the Wushan—Tianshui segment of Western Qinling fault.

    • Satellite Gravity Changes in Yunnan and Adjacent Regions andIts Relation with Regional Strong Earthquakes

      2016, 38(2):260-267. DOI: 10.3969/j.issn.1000-0844.2016.02.0260

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      Abstract:Yunnan is one of the main seismic activity areas in China.It lies close to the subduction zone where the Indian plate moves towards the Eurasian plate and belongs to the southern section of the north-south seismic belt in China.Historical earthquake activity in this area shows that earthquakes of high frequency and large magnitude occur.The Yunnan region and its adjacent areas are ideal locations for the study of seismicity.Existing research shows that regional seismic activity is closely related to gravity field changes that are mainly caused by geological activities such as crustal deformation and fault material change.Such changes reflect crustal movement and the associated processes involved in large earthquakes.Therefore,gravity changes can be used to predict earthquakes.The GRACE (Gravity Recovery and Climate Experiment) binary star system,jointly developed by NASA and the DLR,provides a time-varying gravity field and thus important information for the exploration of Earth's interior materials.GRACE satellite observations clearly reflect the motion of the Earth's plates and expand the scope of gravity anomaly seismic observations that can be used for long-term forecasts of earthquakes.In this paper,we use gravity field data from GRACE satellites to calculate and analyze the satellite gravity field variation characteristics from 2003 to 2014 in the Yunnan region and its adjacent areas.We also obtained the monthly gravity change sequence of three feature points,and in this study we analyze their change characteristics by combining the distribution of M≥5 earthquakes from 2003 to 2014 in the study area.Results show that the MS≥5 earthquakes in the Yunnan region and adjacent areas are reflected in satellite images of gravity field changes,and that large earthquakes often occur on the high gradient zone of regional gravity changes.The earthquake zone often shows a corresponding change in satellite gravity characteristics both before and after large earthquakes,which may reflect crust-mantle material adjustment.The corresponding earthquake gravity change characteristics of the three points are different,which may indicate that research into the gravity field changes in various regions and faults is significant for earthquake prediction.

    • Retrospective Test of Strong Earthquakes in Sichuan—Yunnan Region Using a Combination of Multi-methods

      2016, 38(2):268-277. DOI: 10.3969/j.issn.1000-0844.2016.02.0268

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      Abstract:This study develops a composite approach for the evaluation of seismic hazards using a combination of four methods: PI (Pattern Informatics),LURR (Load/Unload Repose Ration),SV (State Vector),and AMR (Accelerate Moment Release).The PI method is firstly used to locate changes surrounding the epicenters of large earthquakes,thus objectively quantifying anomalous areas (hot spots) relating to upcoming events.Areas where large earthquakes are expected are then detected by covering the hotspots with circular critical regions from low to high latitude and longitude.The short-to-intermediate-term earthquake potential in critical regions are evaluated using the LURR and SV methods.Finally,the AMR method is used to assess the timing and magnitude of the predicted earthquake in each critical region.Retrospective tests of this approach for large earthquakes with magnitudes greater than 5.5 in the Sichuan—Yunnan region from 2012-01-01 to 2014-12-31 show that most of the earthquakes occurred in the predicted seismic hazard regions.The predicted timing and magnitude correlate well with actual earthquakes.For some earthquakes,such as the Aug.31,2013 M5.9 Zhongdian earthquake,significant anomalies are found when the combined approach is used,which are not detected using a single method.Thus,by using the approach,it is possible to screen out false-alarms that occur when using a single method,without reducing the hit rate,and therefore effectively augment the predictive ability.The results show that in comparison with the use of any single method,this combined approach may provide clear information and constraints for use in future seismic hazard assessments.

    • Geochemical Characteristics of Fault Gas along Generalized Haiyuan Fault Zone and Its Relation to Earthquakes

      2016, 38(2):278-284. DOI: 10.3969/j.issn.1000-0844.2016.02.0278

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      Abstract:The eastern section of the North Qilian fault zone lies on the northeastern edge of the Qinghai—Tibet Plateau uplift zone,which consists of the Jinqianghe fault,Laohushan fault,and Maomaoshan fault.The Haiyuan fault,located in the west of the Ordos Block,is a NW trending,large strike-slip fault.It has good continuity with the eastern segment of the North Qilian Mountain fault,and both exhibit left-type dislocation.Therefore,the eastern segment of the North Qilian Mountain fault and the narrow Haiyuan fault are collectively referred to as the generalized Haiyuan fault zone.Seismic activity is very strong in this area,where many MS≥7.0 earthquakes have occurred over time,such as the famous 1920 Haiyuan MS8.5 earthquake and the 1927 Gulang MS8.0 earthquake.Therefore,the region's seismic hazards should be carefully investigated.Based on the measurement results of the mercury and radon concentrations of 10 fault-gas profiles in the generalized Haiyuan fault zone,in this paper,we describe our detailed analysis of the spatial distribution characteristics of the mercury and radon concentrations in different segments and their overall distribution trend along the fault zone.Combined with the seismotectonic background and spatio-temporal evolution characteristics of large earthquakes,as well as the spatial distribution characteristics of the b-value,we studied the relationship between the spatial distribution characteristics of fault gas and the seismic risk of different segments in the generalized Haiyuan fault zone.The results show that the intensity of the fault-gas concentration in the fault zone exhibits obvious segmentation,and is also correlated to some degree with the seismic activity.Based on the above research,we made a pre-judgment of the potential seismic risk in different segments of the generalized Haiyuan fault zone from the geochemistry perspective.This research can provide vital background information for earthquake prediction in the study area.

    • Numerical Simulation of Risk in the Southeast Coastal Region of China Owing to a Rare Earthquake-induced Tsunami in the Ryukyu Trench

      2016, 38(2):285-291,317. DOI: 10.3969/j.issn.1000-0844.2016.02.0285

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      Abstract:Based on their tectonic similarities,the Ryukyu trench is as likely to experience a rare mega-thrust earthquake as the Japanese,Chilean,and Sunda trenches.Based on an analysis of the mega-thrust hypocenter parameters along trenches in recent years,this study proposed a scenario of an earthquake of MW9.0 in the Ryukyu trench and then simulated the resulting earthquake-induced tsunami.Our study results indicated that the initial tsunami reached a height of up to 8 m,then propagated to northeast Taiwan half an hour later and increased in height to over 10 m.Three to four hours later,the tsunami reached the south coast of Zhejiang province and the north coast of Fujian province,and its height was then 1~2 m.Roughly five hours later,the tsunami propagated to the north coasts of Zhejiang and Guangdong provinces,at heights of approximately 2 m and less than 0.5 m,respectively.The tsunami reached the shoreline of Shanghai eight hours later,and its maximum height was then approximately 1 m.These simulated tsunami height data tend to be lower than would occur in reality because of the shoaling effect in the bays along the southeast China shoreline.Owing to the presence of a number of nuclear power plants along the coast of southeast China,the potential for tsunami impact on these plants should not be ignored in the event of a rare earthquake in the Ryukyu trench.We recommend that nuclear plants take measures to prevent potential damage from tsunami hazards.

    • >土力学与岩石力学
    • Elastoplastic Deformation Characteristics of Saturated Silty Clay under Equivalent Tension and Compression Load

      2016, 38(2):292-298. DOI: 10.3969/j.issn.1000-0844.2016.02.0292

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      Abstract:In dynamic triaxial tests,if a soil sample undergoes symmetric sine loading in addition to static deviator stress and if the lateral stress is greater than the axial stress,the sample will assume an axial compressive state when the loading is positive and will change to an equivalent tensile state when the loading is negative.This kind of loading is defined as equivalent tension and compression loading in this study To study the elastoplastic deformation (EPD) of saturated silty clay under equivalent-tension-and-compression loading,we design and perform some undrained dynamic triaxial tests.To consider axial static deviator stress,we apply several levels of sine loading.We determine relations among EPD and confining pressure,static deviator stress,dynamic deviator stress,and compaction coefficients.Furthermore,we propose the tension-and-compression-effect coefficient (TCEC) to forecast the plastic accumulative strain development trend.Test results show that the TCEC is a critical value when considering positive axial compression.When the actual TCEC value is larger than a critical value,the plastic accumulative strain will negatively increase; otherwise,it will positively increase or remain unchanged.Meanwhile,we prove the Hardin model to be an ideal model for reflecting the relation between the dynamic elastic modulus and dynamic strain.The dynamic elastic modulus is typically small when the plastic accumulative strain negatively increases.

    • Mechanical Properties of Sandstone after High Temperature

      2016, 38(2):299-302. DOI: 10.3969/j.issn.1000-0844.2016.02.0299

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      Abstract:In this study, we conducted a number of mechanical experiments on sandstone samples from Junan County, Linyi City, in order to investigate the mechanical properties of the sandstone samples after being subjected to high temperatures, ranging from 25 ℃ to 850 ℃. We plotted the peak strength and deformation displacement curves of the sandstone samples, based on the results of the uniaxial stress experiments under different temperatures. We observed the changes and differences in the sample microstructures after different temperatures using scanning electron microscope (SEM) technology. The results of the sandstone samples' uniaxial stress tests are as follows: (1) At temperatures between 25 ℃ and 400℃, the peak strength of the sandstone samples appears to fluctuate, but the overall strength changes only slightly. This means that the samples share the same mechanical properties, and the strength of the samples under these temperatures is steady. (2) When the temperature is higher than 400 ℃, the peak strength of the sandstone samples begins to decline rapidly. (3) With increasing temperature, the overall deformation displacement of the sandstone samples increases as well, growing very slowly, but increasingly, when the temperature is higher than 400 ℃. In addition, the SEM images show that the pores and fissures of the sandstone samples sharply increase when temperature reaches 400 ℃. Cement particles in the samples begin to disappear when the temperature reaches 500 ℃. The study shows that the macroscopic mechanical properties of sandstone change radically at high temperatures.

    • >报道综述
    • Present Situation and Future Development of the Mercury Precursory Monitoring in China

      2016, 38(2):303-308. DOI: 10.3969/j.issn.1000-0844.2016.02.0303

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      Abstract:Mercury is important for seismic underground fluid precursory monitoring and thus is widely used in earthquake monitoring and prediction and surveying of active faults.Mercury observation techniques have been used in seismic monitoring and prediction since 1985,and since then a mercury precursory monitoring network has been established to monitor mercury in groundwater and escape gas from groundwater and soil.This has enabled the prediction of a number of earthquakes.In this study,we outline the development course of mercury monitoring,conduct a summary of mercury analysis,and determine urgent issues related to mercury monitoring.

    • Recent Progress in Research on Dynamic Shear Modulus, Damping Ratio, and Poisson Ratio of Soils

      2016, 38(2):309-317. DOI: 10.3969/j.issn.1000-0844.2016.02.0309

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      Abstract:This paper presents the main research accomplishments that relate to the differences in the maximum dynamic shear modulus between laboratory and field test soils, the relationship expressions of the dynamic shear modulus and damping ratio versus shear strain and its local experiences, the effects of consolidation ratios on the maximum dynamic shear modulus, results from dynamic Poisson ratio studies, and experimental errors and their effects on seismic motion results. The factors affecting the maximum dynamic shear modulus difference in field and laboratory tests are mainly the soil specimen stress state, the consolidation ratio, the size effect, the degree of disturbance, the time effect, the secondary consolidation effect, and the soil mass inhomogeneity and anisotropy. The maximum dynamic shear modulus obtained from the anisotropic consolidation test method that considers the real consolidation ratio is closer to that of the in-situ wave velocity test method. Experimental results of the soil's dynamic shear modulus and damping ratio show uneven geographical distribution, rough soils classification, distant connection with the physicomechanical indices of soils, disunity among the experimental apparatus, the experimental method, and the data processing model, and few studies on experimental errors. Studies on the dynamic Poisson ratio of the soils are comparatively weak. We suggest a number of studies be carried out that concentrate on the dynamic Poisson ratio, a unified mathematical model of the dynamic parameters of the resonant column and cyclic triaxial test soils, the relationship between soil dynamic parameters under isotropic and anisotropic consolidation conditions, the relationship between soil dynamic parameters and the conventional physicomechanical index, and the experimental errors of soil dynamic parameters.

    • >震害预测
    • Study on Method of Dynamic Earthquake Damage Matrix Based on Seismic Damage Prediction

      2016, 38(2):318-322. DOI: 10.3969/j.issn.1000-0844.2016.02.0318

      Abstract (884) HTML (0) PDF 1.09 M (1418) Comment (0) Favorites

      Abstract:In this study,based on reliability theory and the experimental analysis of structure and materials,we combine the existing dynamic structure resistance coefficient function and the corresponding relation between different states of limit damage and structural resistance to establish a dynamic structural vulnerability function,based on the time factor (internal effect of materials,loads,and environmental impact) and event factors,including seismic events and seismic reinforcement.By studying the impact of demolition and new construction on the number and type of urban structures,we identify the change characteristics of various future urban structures and develop a dynamic seismic damage matrix for building future cities.Through the offsite application of the group seismic damage matrix and by examining the impacts on the matrix of demolition and construction,we develop a dynamic seismic damage matrix for a target city is formed,based on existing seismic damage predictions for urban structures and the application of reliability methods in vague mathematics.This matrix could facilitate the analysis of earthquake risks and the need for anti-seismic precautions in structures.

    • >技术介绍
    • Application of Joint Denoising Using Empirical Mode Decomposition and Singular Value Decomposition in Seismic Data Processing

      2016, 38(2):323-326. DOI: 10.3969/j.issn.1000-0844.2016.02.0323

      Abstract (1215) HTML (0) PDF 12.49 M (1684) Comment (0) Favorites

      Abstract:Random noise widely exists in seismic data, either in prestack or poststack data. The dip-scanning singular value decomposition (SVD) algorithm has been proven to be very effective for eliminating seismic data noise, especially for data with complex deep structures. However, limited volumes of data, especially data with strong noise, in a small window cannot completely reflect the strong correlation among traces. Therefore, the dip-scanning SVD application results are severely constrained. By examining factors that restrict the full utilization of SVD, we developed a new joint denoising approach that uses empirical mode decomposition (EMD) and dip-scanning SVD to eliminate random noise in seismic data. First, this method uses EMD to reconstruct a signal to both reduce noise variance and enhance the correlation of effective signals among traces. Second, it automatically tracks seismic events with dip-scanning SVD to solve the singular value selection problem. Finally, it intercepts small data volumes, flattens an event, and identifies noise points so that dip-scanning SVD can be used on horizontal events to effectively and efficiently eliminate noise. Through the development of a theoretical model and real data application, we prove that the EMD-SVD joint denoising method is a more efficient algorithm when compared with conventional dip-scanning SVD. Simulated and field data results show that the EMD-SVD method can effectively eliminate random noise and significantly increase the signal-to-noise ratio of seismic data, thereby significantly improving the quality of a stack section. For this purpose, proper noise-identifying threshold values should be set according to the features of real seismic data. Moreover, the direction parameter applied by dip-scanning SVD may be modified depending on the dip angle of events. Seismic data random noise can be efficiently and automatically eliminated with relatively short window lengths and fewer constrained conditions of this approach.

    • >强震观测
    • Strong Ground Motion Records and Its Characteristics in the Menyuan MS6.6 Earthquake of January 21, 2016

      2016, 38(2):327-332. DOI: 10.3969/j.issn.1000-0844.2016.02.0327

      Abstract (962) HTML (0) PDF 4.67 M (1096) Comment (0) Favorites

      Abstract:A MS6.4 earthquake occurred at Menyuan county,Haibei city,Qinghai province,China on January 21,2016.The Northwestern Strong Motion Network Center collected 70 groups of three-component acceleration records of this earthquake.The characteristics of these records were then analyzed,including the spatial locations of the stations,and 207 peak ground accelerations (PGAs),recorded by the strong motion stations,were calculated after the zero baseline was corrected.In this study,we analyzed the attenuation tendencies of the PGAs with respect to the epicentral distance,and drew a contour map of the horizontal PGAs.We selected the acceleration records of some typical stations,and plotted the acceleration,velocity,and displacement time-history curves,as well as the acceleration response spectra.The study results provide an important reference for seismic damage investigation in Western China.

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