• Volume 37,Issue 4,2015 Table of Contents
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    • >综述
    • An Overview of the Sixth International Conference on Earthquake Geotechnical Engineering

      2015, 37(4):907-914. DOI: 10.3969/j.issn.1000-0844.2015.04.0907

      Abstract (931) HTML (0) PDF 1.08 M (1315) Comment (0) Favorites

      Abstract:The sixth International Conference on Earthquake Geotechnical Engineering was held in Christchurch, New Zealand, from November 1 to 4, 2015. This study provides an overview of the conference. In the conference, 21 oral session topics were introduced. We summarize the contents of the academic exchange particularly in four oral sessions:those addressing(1) site effect and microzonation;(2) slopes, embankments, dams, and landfills;(3) seismic hazards and strong ground motion; and(4) soil liquefaction and lateral spreading. We also report the contents and decisions of the Technical Committee on Earthquake Geotechnical Engineering and Associated Problems(TC203) of ISSMGE and evaluate research advances and highlights in relevant fields as follows:(1) a breakthrough in the development of a shared geotechnical engineering database for the rebuilding of Christchurch, New Zealand(NZ), following the Canterbury earthquake sequence(CES);(2) soil liquefaction and lateral spreading as the hottest issue in international earthquake geotechnical engineering;(3) the need to further study key scientific problems with respect to the liquefaction mechanism, the evaluation of the liquefaction potential, post-liquefaction deformation, and performance-based design in anti-liquefaction engineering;(4) the presentation of the moving particle simulation method for simulating the slope failure process;(5) "the special session of Ishihara-Idriss-Finn presentations" as a highlight of the conference; and(6) the close cooperation of the United States(US) with NZ, following the CES in 2010-2011, with respect to field investigation and research. Bilateral NZ-US collaborations for immediate response and long-term research have resulted in mutually beneficial scientific advancements for understanding the CES, achieving rapid damage assessment, and in policy and planning analysis to enable robust recovery.

    • >地震工程
    • Test Study on Application of Vehicle-mounted Vibrator in the Seismic Exploration of Ground Fissures in Xi'an

      2015, 37(4):915-918. DOI: 10.3969/j.issn.1000-0844.2015.04.0915

      Abstract (1280) HTML (0) PDF 1.33 M (1242) Comment (0) Favorites

      Abstract:To obtain high quality data in seismic prospecting for ground fissure exploration in Xi'an, it is necessary to determine ways of overcoming interference from the city environment. In this respect, this study introduces application of a large-tonnage vibrator. A number of experiments were conducted using previously determined ground fissures in a city road environment, and the following were determined:the anti-interference effect, exploration depth, vibrator function parameters, vertical stack effect, different inherent-frequency geophone receiving effects, length of survey line, and the best reflection wave receiving window. Exploration results were verified using a geological drilling profile, and they show that by using a large-tonnage vibrator in city roads, it is possible to obtain an ideal seismic stack profile from the seismic reflection profile, thereby determining ground fissure abnormalities. In this way, the position of ground fissures can be interpreted by seismic exploration.

    • Scattering of Plane SH-waves by a Fault Site without a Fracture Zone

      2015, 37(4):919-925,937. DOI: 10.3969/j.issn.1000-0844.2015.04.0919

      Abstract (882) HTML (0) PDF 4.90 M (945) Comment (0) Favorites

      Abstract:Based on the exact dynamic stiffness matrix of a layered half-space and Green's functions for a uniformly distributed load acting on an inclined line, an indirect boundary element method(IBEM) is proposed. The wave scattering of plane SH-waves by a fault site without a fracture zone is studied using the proposed IBEM. The total wave fields are decomposed into the free and scattered fields to facilitate calculation. The free fields are determined by the direct stiffness method, and the scattered fields located in the regions above and below the fault are simulated by applying two sets of uniformly distributed loads on the surface of the fault. The densities of the two sets of virtual loads can be determined by introducing the boundary conditions on the surface of the fault(zero-stress condition and continuity conditions of displacement and stress). Finally, the total dynamic responses are obtained by adding the free fields to the scattered fields. The implications of the method are described in detail, including the size of the boundary element and the integration sample. Further, numerical calculations are performed using fault sites with and without fall heights as examples, and the effects of fall height, inclined angle of the fault, and the shear stiffness modulus ratio between the materials on the two sides of the fault are analyzed. Numerical results show that the largest displacement amplitudes are expected when the fall height approaches the shear wavelength of the incident SH-waves. The amplitudes of the displacement gradually increase with increases in the inclined angle of the fault. Generally, the displacement amplitudes are much larger with variations that are much more complex on the softer side of the fault when the stiffness modulus of two sides differs; moreover, the displacement amplitudes can be especially large when SH-waves are incident from the softer side of the fault site.

    • Influence on Seismic Response of High Concrete Face Rockfill Dams Due to Obliquely Incident Seismic Waves

      2015, 37(4):926-932. DOI: 10.3969/j.issn.1000-0844.2015.04.0926

      Abstract (932) HTML (0) PDF 3.76 M (793) Comment (0) Favorites

      Abstract:Oblique incidence plays a vital role in spatial variation, which has a considerable influence on high concrete face rockfill dams. This study uses seismic wave incidence theory to determine the influence of oblique incidence seismic waves on the seismic response of high dams. FORTRAN programming is applied to calculate the wave load, and finite element software ADINA is employed to achieve the oblique incidence seismic wave input based on the viscous-spring artificial boundary. Simultaneously, the impact of P wave and SV wave that have different incident angles is analyzed with respect to the seismic response of a high concrete face rockfill dam. From these results, it can be determined that the oblique incidence seismic wave is significantly different from the normal incidence. With an increase in the incident angle of P wave, the peak acceleration and peak displacement in the horizontal components gradually increase, while the peak acceleration and the peak displacement in the vertical components gradually reduce; this is opposite to the case of the incident SV wave. Therefore, the security of the dam cannot be ensured if only the influence of normal incidence is considered, and it is necessary to consider the oblique incidence of seismic waves in seismic response analysis and the seismic design of high concrete face rockfill dams.

    • Closed/Open-loop Sub-optimal Control of Structures Based on Output Feedbacks

      2015, 37(4):933-937. DOI: 10.3969/j.issn.1000-0844.2015.04.0933

      Abstract (867) HTML (0) PDF 1.22 M (690) Comment (0) Favorites

      Abstract:Most recent studies have been based on the application of linear quadratic regulator control to earthquake-excited structures. In linear quadratic regulator control problems, the objective function is defined as the integral of a quadratic expression in the control interval with respect to structural states and control vectors, and the optimal regulator can be derived using Pontryagin's maximum principle or Bellman's method of dynamic programming. In traditional linear quadratic regulator control problems, the Riccati equation is obtained without considering the earthquake excitation term. To optimize control and satisfy the optimality condition, in this study, we propose a new closed/open-loop control strategy for structures under earthquake excitation. We derive an analytical solution to a linear regulator problem for structural control without neglecting unknown disturbances. The optimal regulator depends on both the state and disturbances. The solution for this closed/open-loop control requires the knowledge of the earthquake in the control interval, which is approximated based on the real-time prediction of near-future earthquake excitation using the Kalman filtering technique. Earthquake excitation is modeled as an autoregressive process. The prediction algorithm can predict seismic excitation in the near future with high accuracy, although it lacks prediction accuracy for more distant future events. Considering the measurement difficulty of all state variables, especially for some high-order systems, the proposed control strategy only requires the measurement of a partial state. In the calculation of a state transition matrix, which is required to solve a differential equation, large rounding errors may occur when the time-step size is excessively small. To overcome this limitation, we introduce a precise integration algorithm to solve the differential equation. This algorithm is always numerically stable and yields very high precision solutions for numerical integration problems. To demonstrate the effectiveness of the proposed control strategy, we investigated the undamped vibration of a three-story building subjected to horizontal seismic forces. We assumed that the columns of the building are massless and that the mass of the structure is concentrated at floor levels. We implemented control using actuators exerting forces on each story. We also assumed that floor velocities can be measured in real time by sensors installed in every story unit. We used the NS component of the 1940 El Centro earthquake ground acceleration record as the excitation source and performed calculations for its entire duration. We modeled the columns of the building as linear elastic springs and assumed the response mitigation effect of the actuators to be sufficient for the building to behave in a linear elastic manner during earthquake excitation. We did not consider the soil-structure interaction or the dynamic characteristics of the actuators. We investigated the controlled and uncontrolled behavior of the three-story undamped building and compared the relative displacement, velocity, acceleration, and inter-story displacement responses. Our numerical simulation results show that the proposed closed/open-loop sub-optimal output feedback control strategy can significantly reduce structural earthquake responses.

    • Dynamic Response of the Lanzhou Subway Tunnel Structure under Seismic Load

      2015, 37(4):938-943. DOI: 10.3969/j.issn.1000-0844.2015.04.0938

      Abstract (965) HTML (0) PDF 1.51 M (1043) Comment (0) Favorites

      Abstract:Based on the local site bedrock earthquake acceleration time history for different exceedance probabilities of 63%, 10%, and 2% in 100 a given by The Report of Seismic Safety Evaluation for the First Project of Lanzhou City Rail Transit Line 1, the finite difference method was used to analyze the seismic response of the tunnel cavern. By applying bedrock seismic ground motion to the base of the model and by setting monitoring points to observe the lining structure's bending moment, axial force, and shear force, the tunnel structure's seismic response under working conditions at probabilities of exceedance of 63%, 10% and 2% was obtained. The results show that the maximum bending moment of the tunnel lining structure is located in the tunnel vault, the maximum axial forces are located in both the tunnel vault and at the bottom of the tunnel, and the maximum shear force is located in the upper or lower tunnel sidewalls. Tunnel structure's internal forces were found to increase as the excess probability decreased. Using the structure's internal forces at the probability of exceedance of 63% as a point of reference, when the excess probabilities were 10% and 2%, the maximum bending moment increased 1.2 and 1.7 times, respectively, the maximum axial force increased 1.3 and 1.5 times, respectively, maximum shear force increased 1.5 and 2.9 times, respectively. This indicates that the tunnel structure could experience shear failure with strong seismic ground motion.

    • Simplified Seismic Analysis Method for Bridge Full-scale Piles in Liquefied Ground

      2015, 37(4):944-951. DOI: 10.3969/j.issn.1000-0844.2015.04.0944

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      Abstract:Most research in the seismic analysis of pile foundations in liquefied ground is based on small-scale model testing and theoretical analysis. This paper presents the development of a three-dimensional finite element model for dynamic pile-soil interaction using the dynamic calculation parameters of Nevada sand calibrated by conducting the centrifuge test outlined in the Verification of Liquefaction Analysis by Centrifuge Studies(VELACS) project.On the basis of this numerical model, the dynamic p-y curves under various shaking amplitudes are studied, and a macro-element model for analysis of dynamic pile-soil interaction in liquefied ground is developed. In addition, a simplified method for seismic analysis of the piles on the basis of the Winkler model is presented and verified by the results of numerical simulation.

    • Experimental Study on the Amplification Effect of Bedrock PeakAcceleration Caused by the Soil Layer in a Weak Shock Region

      2015, 37(4):952-955. DOI: 10.3969/j.issn.1000-0844.2015.04.0952

      Abstract (811) HTML (0) PDF 2.25 M (929) Comment (0) Favorites

      Abstract:Using an artificial blast wave as the seismic source, the blast-induced ground motion time histories of both rock and soil sites were acquired by field experiments. The effects of soil layer amplification on peak ground acceleration and ground motion time histories were analyzed. The test results show that the soil layers amplify earthquake motion and that the amplification ratios are influenced by the depth and the construction of the soil layer. The depth of a soil layer has a large effect on the ground motion time history, but the construction does not.

    • Impact of Dip Angle of Rock Stratum on Seismic Response of Consequent Slope

      2015, 37(4):956-962. DOI: 10.3969/j.issn.1000-0844.2015.04.0956

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      Abstract:The southwest of China is located in a seismically active area, and in recent years earthquakes exceeding 7.0 magnitude have occurred in many locations in Yunnan and Sichuan provinces. In addition, the consequent stratified rock slope is developed well in the southwest of China, and this means that the strike and inclination direction of the slope is same as that of the rock stratum. Instability and failure of the consequent stratified rock slope is common during the construction of railways, highways, and water conservancy and hydropower engineering projects in the southwest of China. This is an urgent engineering construction problem which must be recognized and solved as soon as possible. Currently, there are certain researches being conducted on the seismic effects of this kind of slope, and the methods being used focus on the analysis of mechanical systems and model experiments. In these studies, the range of the rock stratum's dip angle is not sufficiently comprehensive and do not fully represent the seismic effects of dip angle of the rock stratum on the slope. Nor is the thickness of the rock layer in numerical simulations sufficiently precise, which affects the accuracy of the numerical simulation results. Using FLAC3D software, in this study we simulated the consequent stratified rock slope for different dip angles of rock stratum(0°~90°) and detailed the thickness of the stratum(sandstone is 1 m thick, weak mudstone is 0.1 m thick) under seismic action. We then contrasted the regulation of the peak acceleration amplification factor, peak displacement, and shear strain increment after seismic action, and explored the impact of the rock stratum's dip angle on the seismic effect of the consequent stratified rock slope. This analysis will help to explain the instability mechanisms and slope failure modes, and lay the groundwork for disaster prevention in consequent stratified rock slopes. The study results are as follows:First, the peak horizontal acceleration amplification factor, which is relative to the slope toe, increases with increase in slope height, with the maximum occurring at the slope shoulder. This rule conforms to existing experimental conclusions. Then, under the effect of horizontal seismic action, slope horizontal peak acceleration amplification, which is relative to the initial seismic waves, decreases linearly with increase in the dip angle of the rock stratum. Second, when the dip angle of the rock stratum is less than the internal friction angle of weak rock stratum, the slope peak displacement is small and the influence of the dip angle is not obvious. When the dip angle of the rock stratum is larger than internal frictional angle of weak rock stratum, the slope peak displacement will increase at first and then decrease with increases in the dip angle. This displacement increases when the dip angle of the rock stratum is less than 30°, and decreases when the dip angle of the rock stratum is larger than 60°. Third, when the dip angle of the rock stratum is less than the slope angle, the maximum value of the slope residual shear strain increment after seismic action is concentrated in the soft rock in the middle and lower segments of the slope. When the dip angle of the rock stratum is larger than the slope angle, the maximum value of the residual shear strain increment after seismic action will be in the whole slope, thus forming an arc zone.

    • Seismic Vulnerability Analysis of Lifeline Networks Using Improved Risk Matrix Method

      2015, 37(4):963-968. DOI: 10.3969/j.issn.1000-0844.2015.04.0963

      Abstract (808) HTML (0) PDF 1.25 M (1048) Comment (0) Favorites

      Abstract:Modern societies are becoming increasingly dependent on critical infrastructure systems to provide essential services that support economic prosperity, governance, and quality of life. A nation's health, wealth, and security rely on the production and distribution of certain goods and services. Critical infrastructures are the physical assets, processes, and organizations across which these goods and services move. Earthquakes have highlighted the importance of stable electric, gas and oil, water, transportation, banking and finance, and control and communication infrastructure systems. The frequency of earthquakes has been increasing in recent years; hence, the vulnerability of lifeline networks in the event of an earthquake must be studied. In this study, we analyzed the seismic vulnerability of lifeline networks. First, we present the status of domestic and international research on the seismic vulnerability of lifeline networks. Although numerous studies have been conducted on the seismic vulnerability of lifeline networks, most of them considered the seismic vulnerability of lifeline networks in the event of an earthquake to be a series of consequences. In this study, we consider that the lifeline network vulnerability in terms of the consequences of the network after the earthquake as well as network connectivity. Second, we redefined the concept of seismic vulnerability of lifeline networks as the ability of connectivity and enduring failure consequences in the event of an earthquake. Third, on the basis of the new definition of lifeline network vulnerability, we evaluate the lifeline network vulnerability using the risk matrix theory method. This study considers two aspects:lifeline network connectivity and failure consequences. Because network connectivity probability and failure probability have a complementary relationship, connectivity probability represents the possibility of occurrence of a risk in the risk matrix. The failure consequences of a lifeline network can be characterized by the network topology and function change; therefore, we used these two indicators to represent network failure consequences. Hence, this improved method is employed in this study to comprehensively assess lifeline network vulnerability. The improved risk matrix method can completely represent the lifeline earthquake vulnerability as defined in this study. By considering lifeline network connectivity and failure consequences in the event of an earthquake, we can determine the corresponding level. Therefore, we can determine the lifeline network level of seismic vulnerability in a most direct and convenient way. Finally, we use a gas pipeline to illustrate the effectiveness and rationality of this improved risk matrix method. The highest vulnerability level nodes in this gas supply pipe network are nodes 3, 7, and 9 primarily because nodes 7 and 9 are located at the end of the network; therefore, the connectivity with the source point is very low. The highest vulnerability grade of node 3 can be attributed to its poor connectivity and high water level. Therefore, in the future, we must focus on these nodes for seismic protection.

    • Ground Motion Characteristics of the Jinggu MS6.6 Earthquake in Yunnan

      2015, 37(4):969-975. DOI: 10.3969/j.issn.1000-0844.2015.04.0969

      Abstract (1037) HTML (0) PDF 1.60 M (1206) Comment (0) Favorites

      Abstract:The Jinggu MS6.6 earthquake that occurred on October 7, 2014 was another shallow earthquake following the Ludian MS6.5 earthquake that occurred on August 3, 2014 in Yunnan. During the main shock, 39 recordings were obtained by the National Strong Motion Observation Network System of China. Within an area above intensity Ⅵ, only five stations were triggered by the earthquake. In this study, we calculated the peak ground acceleration(PGA) and peak ground velocity(PGV) from these recordings. The PGA and spectral acceleration of site 053JYP, which captured the maximum PGA(543 gal), were significantly higher than the design specifications of a local area. A field survey around this station confirmed that structures were seriously damaged during the main shock. The site and topography effects may be explained by significant differences between the PGAs of sites 053JYZ and 053JGX. We then compared the attenuation characteristics of the PGA, PGV, spectral acceleration, Arias intensity, and significant duration of the Jinggu and Ludian earthquakes. In a near-field area, all observed values of these earthquakes were significantly higher than predicted values but were lower than those predicted in far-field areas. Except for the significant duration, all strong motion parameters from the Ludian earthquake were slightly higher than those of the Jinggu earthquake. We also found most far-field observed values to be lower than those predicted for these two earthquakes. The difference in Q values in different regions of Yunnan may be the main reason for this phenomenon.

    • >地震科学研究
    • Relation between Residual Strain Energy Horizontal Field and Large Earthquake Distribution in Strong Seismic Belts in Southwestern China

      2015, 37(4):976-980. DOI: 10.3969/j.issn.1000-0844.2015.04.0976

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      Abstract:Based on the theory of elasticity for orthotropic rock mass, using X-ray diffraction method, 26 survey lines were laid across and along four fault zones, including Longmenshan fault, Anninghe fault, Honghe fault and Xianshuihe fault zone. Then the density horizontal distribution isoline for macro-residual strain energy of rock mass was drew and the relationship between it and spatial-temporal distribution of large earthquakes in these study areas was studied.

    • Minxian-Zhangxian MS6.6 Earthquake in Gansu(2013) and Its Short-term and Impending Precursors

      2015, 37(4):981-985. DOI: 10.3969/j.issn.1000-0844.2015.04.0981

      Abstract (945) HTML (0) PDF 1.31 M (770) Comment (0) Favorites

      Abstract:This study describes the situational characteristics of the Minxian-Zhangxian MS6.6 earthquake that occurred on July 22, 2013, in Gansu; this is the strongest earthquake felt in this province since 1954. We also review and discuss the short-term and impending precursors of this earthquake:(1) the relation between the earthquake occurrence date and the solar term and syzygy,(2) the displacement of the geomagnetic low point on a quiet day,(3) the multiplied nine days regularity after low-point displacement,(4) the prediction of the impending earthquake' s occurrence day using the "rhythm of multiplied seven days in different years" index, and(5) the short-term precursors of geoelectrical resistivity in a deep well at Tianshui station in Gansu. Finally, we discuss the problem of comprehensive prediction.

    • Preliminary Study on the Late Quaternary Activity Characteristics of the Menglian Fault in Southwest Yunnan

      2015, 37(4):986-995. DOI: 10.3969/j.issn.1000-0844.2015.04.098

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      Abstract:Because it is located in an area of extensive collision between the Indian Plate and the Eurasian Plate, the Sichuan-Yunnan rhombic block in southwest Yunnan at the southeastern margin of the Tibetan Plateau is one of the regions with the highest concentration and frequency of strong earthquakes in China. Due to compression of this block in the SE direction, the region developed two groups of active transverse faults in NE and NNW directions. Both groups are involved in the process of rupture and the occurrence of earthquakes of above M7.0. In this area, the main feature of the late Quaternary activity of these faults is strike-slip. The NW-trending faults have right-lateral strike-slip characteristics, whereas the NE-trending faults have left-lateral strike-slip characteristics. The Menglian fault is located in the boundary zone between southwest Yunnan and Myanmar. It is a large active fault in the south of the Sichuan-Yunnan rhombic block and its late Quaternary activity is intense. This fault has the main characteristics of left-lateral strike-slip with dip-slip. However, there are few research data on this fault and the extent of study has been low.There are no records of earthquakes on the Menglian fault. However, in the southwest of the fault, a MS7.3 earthquake occurred in the territory of Myanmar on July 12, 1995, which may be related to its activity. The linear structure of the fault in satellite images and landforms is very clear. The stream and water system are obviously offset to the left side along the fault. According to scanning electron microscopy results of the characteristics of the surface of quartz fragments in gravel from a fault gouge and research into active faults, Weixian et al.(2002) believed that the Menglian fault was formed before the Pliocene, displayed a high frequency of activity in the late Pleistocene, and has been active since then.Through an investigation of the active characteristics of the Menglian fault in the late Quaternary, this study aims to determine the structural transformation and obtain a mechanical interpretation of the active faults in different directions and natures in the study area. According to the interpretation of satellite images and field investigation, we found that the fault is 90 km long and has a trend of N70°E. The main landform due to fault dislocation is a linear fault scarp of unequal height, whereas the others are fault valleys, fault trenches, and fault passes. The horizontal displacement of gullies and terraces is of the order of tens of meters to several hundred meters. A large trench excavated in the west of Menglian County revealed many faults. Through analysis of the fault profile and 14C dating results, we found that four paleoearthquake events have occurred on the Menglian fault. Except for the earliest events, the three that followed all occurred in the middle and late Holocene. The latest paleoearthquake occurred between(1860±30) and(1090±30) a B.P.

    • Simulation of Crustal Horizontal Deformation in the Weihe Basin Using a Combined Disclination-Dislocation Model

      2015, 37(4):996-1000. DOI: 10.3969/j.issn.1000-0844.2015.04.0996

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      Abstract:The Weihe Basin, which is situated in the middle of China, was the area of interest for this study. The basin is several hundred kilometers long and forms an S-shape, representing a deep rift that divides China into eastern and western parts. Bounded by the Ordos, North China, and South China blocks, the Weihe Basin is the accommodation zone for the differential motion of these three blocks and also the border and decoupled strip of tectonics between western and eastern China. We simulated the deformation state of the main fault slip and rotation in the Weihe Basin using a combined disclination-dislocation model. The horizontal displacements caused by fault slip and rotation were acquired through numerical calculation and compared with GPS-measured horizontal displacements in the Weihe Basin. The results were as follows.(1) The movements of fault slip and rotation can be described well by the combined disclination-dislocation model, and there are only small differences between the modeling results and monitoring data.(2) Use of only the dislocation model does not adequately describe the activity features of the faults within the Weihe Basin that show slip and rotation, and there are significant differences between the model results and monitoring data, particularly in the direction of crustal movement.(3) Compared to the dislocation model, there is good consistency between the simulated horizontal displacements of the combined model and the measured GPS results.

    • Recent Variation Characteristics of Gravity Field in the Middle Segment of North Tianshan

      2015, 37(4):1001-1006. DOI: 10.3969/j.issn.1000-0844.2015.04.1001

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      Abstract:We analyzed the variation in gravity field in the middle segment of northern Tianshan Mountains in half-and one-year scales by calculating and adjusting the latest mobile gravity observation data. By selecting two lines across Urumqi and Dushanzithe in the middle section of northern Tianshan and plotting the gravity anomaly profiles of these two lines, the relationship between characteristics of gravity anomaly and earthquakes as well as the dynamic tectonic environment of northern Tianshan Mountains were analyzed. The analysis shows that the middle section of northern Tianshan does not exhibit evident anomaly in gravitational distribution, even when the half-or one-year scale of gravitational anomaly images reflect the characteristics of temporal and spatial variations of gravity field in the study area well. Gravity anomaly characteristics of the middle section of northern Tianshan typically reflect the external environment of dynamic tectonic movements, and the different gravity change mechanisms and tectonic environment are closely related. The spatial distribution characteristics of gravity field are clear in the study area, and the gravity field anomalies exhibit obvious zoning features. Clear differences can be seen between mountain and basin areas, and the positive and negative gravity anomaly values typically appear at the mountain and basin edges. Further, the gravity anomaly value is minimal. The gravity profile result shows that the gravity field exhibits an increasing trend in the central part of the northern Tianshan area, thus indicating that the underground substances are under a state of quality loss distribution. The northern Tianshan area that is squeezed between the Tibetan plateau and the Euroasian plate caused the orogenic uplifting of Tianshan, decrease in gravity value, density of crust under the state of quality loss, and the negative gravity value. The Dzungaria Basin in the north slope of northern Tianshan exhibits southward migration and a decreasing trend, with steady increase in crustal substances. The positive change in gravity field shows that the crustal substances of this area are accumulated via continuous squeezing. The variations in spatial and temporal characteristics of gravity field and those of crustal material density are nearly identical and reflect the progress in migration of crustal substances in the middle section of northern Tianshan area. This migration in crustal substances leads to the variations in crustal density and consequent variations in spatial position of gravity and ground points.

    • Thermal Infrared Anomaly Occurring before the Jinggu, Yunnan MS6.6 Earthquake on October 7, 2014

      2015, 37(4):1007-1012. DOI: 10.3969/j.issn.1000-0844.2015.04.1007

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      Abstract:To analyze the thermal infrared anomaly occurring before the Jinggu, Yunnan MS6.6 earthquake in China on October 7, 2014, remotely sensed infrared brightness temperature data obtained from the Chinese geostationary meteorological satellite FY-2C/2E is used for analysis. The wavelet transform is used to determine variations and progression of changes in the power spectrum. Thermal infrared anomalies are analyzed using a temporal evolution diagram of the earthquake and a timing curve of the average brightness temperature. Processing and analysis results show that in early August 2014, thermal anomalies occurring before the earthquake had obvious spatial and temporal characteristics. The epicenter and its surrounding area show thermal infrared anomalies that spread over time in a certain direction throughout the tectonic stress field with a sharp increase in the amplitude. On around August 30th, the anomalous amplitude reached a maximum, which persisted for almost one month at a maximum value of more than 14 times the average. The earthquake occurred 45 days after the appearance of the maximum value. Case analysis and history determines that the abnormal thermal evolution firstly appeared, enhanced before shrinking, and finally disappeared. The results of this study are consistent with those of other earthquakes and are considered to be related to the geological structure and underground environment of the epicenter. This study focuses on the thermal-infrared abnormity, its evolution, and features in relation to the formation of earthquakes and delivers a new understanding of the relationship between thermal anomalies and earthquake elements. Abnormal seismic thermal infrared characteristics are noted and identified and can be used as criteria for identifying subsequent seismic thermal anomalies. The thermal infrared anomaly characteristics of this earthquake are both remarkable and easy to identify and can be used as in the recognition of seismic thermal anomalies. However, the thermal infrared anomaly characteristics also have its own short board, that is it cannot identify and judge the three elements of earthquake well. In summary, the results of this study can be used in conjunction with future studies to further validate the effect of satellite thermal infrared anomalies in the prediction of earthquakes.

    • Comparative Study of Seismic Damage Induced by 2014 Ludian MS6.5 and Jinggu MS6.6 Earthquakes in Yunnan Province

      2015, 37(4):1013-1022. DOI: 10.3969/j.issn.1000-0844.2015.04.1013

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      Abstract:The Ludian MS6.5 and Jinggu MS6.6 earthquakes occurred on August 3, 2014 and October 7, 2014, respectively, in Yunnan Province. The magnitude, type, and focal depth of these two earthquakes are similar; however, the number of casualties, degree of damage to buildings, and geological disaster induced by them are significantly different. As of August 3, 2014, 617 people have been reported killed and 112 and 3143 people have been reported missing and injured, respectively, in the Ludian MS6.5 earthquake. However, as of October 7, 2014, only 1 person was reported to have been killed, while 8 and 316 people were reported to have been severely and slightly injured, respectively, in the Jinggu MS6.6 earthquake. On the basis of field survey and extensive investigation of numerous diverse earthquake disasters induced by the two earthquakes, the primary reasons for the difference in seismic damage are summarized by comparing the collapse, landslide, ground fissures and deformation, sand liquefaction, and building damage caused by the two earthquakes. The area of Ⅶ and Ⅵ are similar in the intensity maps of Ludian MS6.5 and Jinggu MS6.6 earthquakes; however, the area of Ⅷ and Ⅸ in the Ludian MS6.5 earthquake is almost equal to that of Ⅷ in the Jinggu MS6.6 earthquake. A comparison of the results shows that the Ludian earthquake affected area is a complex geological structure with broken strata, dense populations, and poor anti-seismic capacity. However, the Jinggu earthquake affected area is located in a good geographic environment with thick vegetation, low population density, small peak ground acceleration among same level of earthquakes, and good anti-seismic capacity. In summary, the seismic damage induced by the Ludian MS6.5 earthquake is more serious than that induced by the Jinggu MS6.6 earthquake.

    • >土动力学与岩土工程
    • Shaking-table Tests on Liquefaction Characteristics of Saturated Undisturbed Loess

      2015, 37(4):1023-1028. DOI: 10.3969/j.issn.1000-0844.2015.04.1023

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      Abstract:Acquiring large-scale undisturbed samples of natural loess is very difficult due to its special original structure.Therefore,no data or documents are available of shaking-table testing on saturated samples of undisturbed loess soil around the world.In the present study,we address the problems of preparing large-scale undisturbed loess samples in the field and conducting research on the liquefaction features of saturated natural loess by means of shaking-table testing.Previous testing results have shown that the development process of excess void water pressure during loess liquefaction,such as accumlation,continuance,and dissipation,is the same as that with saturated sand;the essential differences between the cases of loess and sand focus only on detailed characteristics.The degree of saturation is the most important factor in controlling the liquefaction behavior of natural loess under seismic loading.For this case of the shaking-table test,the void water pressure ratio of undisturbed loess samples can reach 0.93 at saturation conditions of 90.3%.Moreover,the degree of saturation at 85%,75%,and 65% may be critical values associated with liquefaction phenoment,similar liquefaction phenomena(cyclic failure),and that without consideration of cyclic failure,respectively.In short,first-hand data of liquefaction features of natural loess acquired by the shaking-table test and corresponding analysis results based on that datacould advance the present understanding of the physical process and mechanism of saturated soil under seismic loading.

    • Analog Method for the Equivalent Lumped System of Foundation Half-space Theories and Associated Field Measurements

      2015, 37(4):1029-1036. DOI: 10.3969/j.issn.1000-0844.2015.04.1029

      Abstract (849) HTML (0) PDF 1.16 M (985) Comment (0) Favorites

      Abstract:In this study, the formulation of Lysmer's analog method is presented briefly first. The radiation damping ratio, stiffness, and vibrational mass for a certain amount of soil may be obtained from a half-space system that is equivalent to a mass-spring system. Subsequently, a combination of both systems is discussed. On the basis of measurement, analysis, and application, the damping ratio is reduced:this is a modification for modeling non-homogeneous soil and is more practical. For a long time, a larger damping ratio has been considered to be unsafe and thus not used; this constraint may disappear and subsequently the practical use of half-space theory will become more common. The focal point of this study is the practical use of the method. First, two experimental tests have revealed that the damping ratio of our state code is very small and the half-space is significantly larger. Therefore, the results from measuring a large number of vibrator foundations and models demonstrate that the damping ratio of the half-space must be modified.(1) The damping ratio of homogeneous soil must be reduced. Although some energy of wave propagation is consumed, wave reflection or refraction is performed by soil or hard layers. The energy consumed is less, and the damping ratio is not as large with a discount coefficient of 0.5~0.7.(2) The former Soviet code of 1979 used a reduction of 30% on the half-space damping ratio for the design of dynamic machine foundation, which is equal to the upper reduction limit of our measurement results. In 1996, a Russian academician who had been the chief editor of that code came to China to deliver lectures and explained that the reduction value was obtained from a large number of comparisons obtained by measuring.(3) The reduced damping ratio of homogeneous soil is practical. The reduced damping ratio is still greater than that of our state code and will be both more economical and safer for the design of dynamic foundations.

    • Tests and Analyses of the Effect of Underwater Controlled Blasting Projects in Complex Environments

      2015, 37(4):1037-1041,1059. DOI: 10.3969/j.issn.1000-0844.2015.04.1037

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      Abstract:As the effects of blasting vibrations from underwater construction blasting have increasingly gained attention, it is particularly important to conduct research to examine the behavior of underwater blasting vibrations. This paper combines the major foundation trench excavation projects of the immersed tube section in immersed tunnel engineering with indoor and outdoor testing of the bedrock, field tests of the dynamic blasting effects, theoretical analysis, and other comprehensive means to explore the effect of dynamic characteristics of underwater explosion shocks on adjacent land buildings and riverside embankments. The results show that(1) compared with the peak pressure value of a seismic wave, shock wave pressures of drilling blasting in water are small under the shallow water conditions and their propagation speeds are not faster than seismic waves, and therefore, when considering the stability of the embankment and shore buildings, the effects of water shock waves can be ignored under certain circumstances; and(2) concerning blasting constructions in different regions, the maximum blast should be the minimum of each of the allowed maximum doses based on the distances from the blasting point to the protected objects. The above results will provide an important reference for similar projects.

    • Vertical Dynamic Impedance of Tapered Piles Considering Compacting Effects

      2015, 37(4):1042-1048. DOI: 10.3969/j.issn.1000-0844.2015.04.1042

      Abstract (862) HTML (0) PDF 2.15 M (669) Comment (0) Favorites

      Abstract:On the basis of the complex stiffness transfer model, the vertical vibration of tapered piles embedded in layered soil is theoretically investigated by considering the compacting effect of the soil layer surrounding the tapered pile in the piling process. First, the pile-soil system is discretized into finite segments, which allows for the stratification of the surrounding soil and variable cross-sections of the tapered piles. Since the complex stiffness transfer model has the ability to simulate the compacting effect, the complex stiffness of various soil segments in addition to those of the tapered piles is obtained. The analytical solution of the complex impedance of the tapered piles under longitudinal excitation force is then derived by substituting the complex stiffness into the vertical dynamic governing equation of the tapered pile and using the Laplace technique and impedance function transfer method. Finally, the influence of the compacting effect of the surrounding soil on complex impedance at the pile head is investigated within the low-frequency range using the parametric study method.

    • Experimental Study on the Dynamic Characteristics of Shanghai Soft Clay Subjected to Cyclic Loading

      2015, 37(4):1049-1052. DOI: 10.3969/ji.ssn.1000-0844.2015.04.1049

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      Abstract:To study the strength of Shanghai soft clay under cyclic loading, a series of dynamic triaxial tests were conducted with different dynamic stress ratios and frequencies. According to the test results, the relationship between the shear modulus and strain was not affected by the dynamic stress ratio and frequency. When the strain was set to 2%, the shear modulus decreased slowly but significantly. The sample cyclic time with high frequency was larger than that with low frequency. With the Shanghai soft clay, soil sample damage phenomenon occurred until the dynamic stress ratio reached 0.2. The frequency had different effects on the growth of the strain in different strain stages.

    • Solutions for Two-dimensional Dynamic Response of Shallow Tunnels in Saturated Soil under Coupling Interaction of P and S Waves

      2015, 37(4):1053-1059. DOI: 10.3969/j.issn.1000-0844.2015.04.1053

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      Abstract:This study briefly discusses solutions for a typical case concerning the two-dimensional dynamic response of shallow tunnels under the coupled influence of plane waves. The field equation of saturated soil is based on the Biot theory for a saturated porous medium.The Helmholtz equations for the potential functions of a fast P, slow P, and S waves are deduced by introducing additional potentials. By introducing the general solutions of the potential functions into the boundary conditions,the multivariate linear equations are built up in a cylindrical coordinate system. The deduction procedure of this paper can be utilized to solve problems concerning the seismic response of shallow tunnels in saturated soil under the coupled influence of P and S waves during an earthquake.

    • Collapse Performance Evaluation of Reinforced Concrete Frame Structures in Seismic-intensity-8 Zone Designed Using Current Codes

      2015, 37(4):1060-1065,1072. DOI: 10.3969/j.issn.1000-0844.2015.04.1060

      Abstract (950) HTML (0) PDF 5.33 M (1645) Comment (0) Favorites

      Abstract:Performance-based seismic design theory has received considerable attention from scholars since its proposition in the 1990s. Collapse evaluation is an important part of performance-based seismic design. In this respect, although current Chinese seismic design codes for building structures have particular requirements and analytical approaches are used to prevent building collapse, they do not provide a quantitative index for the collapse-resistant capacity. Therefore, the collapse-resistance performance of structural systems, the seismic fragility, and collapse capacity of a reinforced concrete(RC) frame structure were investigated based on incremental dynamic analysis. A five-story and three-bay reinforced concrete frame structure, which was designed based on the current Chinese codes, was selected as a study case to conduct a seismic fragility assessment and collapse evaluation. Considering the uncertainty of ground motion, a mass incremental dynamic analysis was conducted for an existing building based on the current codes. In the incremental dynamic analysis, the intensity of a single motion was increased according to a series of intensity measures, under which an elastic-plastic dynamic analysis was performed. The relationship between the engineering demand parameters and the intensity measures was thus obtained, and on the basis of incremental dynamic analysis curves, the seismic demand probability and seismic capacity were then established. Furthermore, collapse evaluation was quantitatively performed based on fragility curves, which enable an estimation of the possible damage to buildings that could occur during an earthquake and have important significance in the improvement of seismic capacity and disaster prevention mitigation work. Finally, a comparison was made between a fiber model and a plastic hinge model based on PERFORM-3D. The fragility curves provide a quantitative evaluation under a specific ground motion intensity, and results show that RC frames designed in accordance with the current code have a small collapse probability during a rare earthquake, and that they meet the requirements of a 3-level design. The fiber and plastic hinge models have similar performance at a low spectral acceleration of motion; however, differences between the two models were evident with an increase in the spectral acceleration. Based on the fiber model, a nonlinear simulation of the RC frame in a collapse evaluation was relatively conservative and had a higher safety margin compared to the plastic hinge model. Therefore, in consideration of efficient modeling, the fiber model provided by PERFORM-3D is a better choice as compared to the plastic hinge model.

    • Instability-evolution Process for Wangxia DangerousRock Body W2-2 in Wushan County

      2015, 37(4):1066-1072. DOI: 10.3969/j.issn.1000-0844.2015.04.1066

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      Abstract:The Wangxia rock body(W2-2) is a dangerous body of rock located on the left side of the Three-Gorges section of the Yangze River in Wushan county. It suffered evident deformation during the monsoon of 2010; emergency monitoring was immediately conducted and two forecasts were made successfully. The evolution of W2-2 is similar to that of other common dangerous rock bodies. In this study, geological investigations and in-situ monitoring are used to determine the dynamic processes involved in the deformation-evolution of W2-2. Results show that, in general, falling of sliding masses into the river was induced by continued rainfall, and that infiltrated rainwater weakened the intensity of the soft mudstone foundation. The plastic flow was thus strengthened, and bottom deformation of the rock body occurred. As a result, tensile cracks were generated in the overlying sandstone layer. In addition, a fracture was widely developed in the rock body because of the effect of river water. Ultimately, rainfall occurring during the period from October 10 to 15, 2011 led to integral collapse of the W2-2 on October 21. Evolution of the deformation and failure of W2-2 included four stages:initial cumulative deformation, uniform deformation, accelerating deformation, and threshold-accelerated deformation. The accelerating point and the threshold-accelerated point are thus considered to be effective indicators for use in forecasting, and the accelerating point is identified to be representing the threshold between the stability and instability of the rock body.

    • >监测研究
    • Thermal Infrared Anomalies prior to the MS ≥ 5 Earthquakes in the Qilianshan Seismic Zone

      2015, 37(4):1073-1076. DOI: 10.3969/j.issn.1000-0844.2015.04.1073

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      Abstract:Using thermal infrared data from NOAA,the temperature-time sequences of epifocal areas in small windows were scanned prior to 13 earthquakes that occurred in the Qilianshan seismic zone from 1991 to 2004.Next,the continuing thermal infrared temperature-time sequences over time and the abstract surface temperature abnormality phenomena before these earthquakes occurred were obtained.The research results found that there were thermal infrared anomalies prior to 38% of the earthquakes,the surface temperature during some earthquakes increased abnormally,and the surface temperature during others decreased abnormally.These results demonstrate the complexity of the inducing factors of earthquakes.The amplitude of anomalies were consistently 2°C to 3°C,and the anomalies always appeared two weeks before the earthquakes occurred.It was also found that when the earthquake magnitude was a maximum,the surface temperature anomaly phenomenon was the most noticeable.For example,in the MS6.1 earthquake of 2003 in Minle.However,not all temperature anomaly phenomena for earthquakes MS > 6.0 were noticeable in comparison to earthquakes in the range of 5.0< MS < 6.0.

    • Relocation of 2013 Sunan-Menyuan MS5.1 Earthquake and Analysis of Focal Mechanisms and Seismogenic Structure

      2015, 37(4):1077-1081,1094. DOI: 10.3969/j.issn.1000-0844.2015.04.1077

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      Abstract:On September 20, 2013, an earthquake of MS5.1 occurred in the Sunan-Menyuan boundary region. Using the data recorded by Gansu and Qinghai Digital Seismic Networks, we relocated the ML ≥ 1.0 events in the earthquake sequence using the Hypo2000 location algorithm. After relocation, the vertical and horizontal average errors were found to be 1.87 km and 3.64 km, respectively, and the root mean square residual error of travel time is 0.51 s. The results show that the mainshock occurred at the northern foot of Gangshiga, the main peak of Lenglongling, and the aftershocks are primarily distributed along the Lenglongling fault zone, with a length and width of approximately 20 km and 2.5 km, respectively. The transverse section exhibits focal depth focus in 3~10 km, and longitudinal section shows a fracture plane that dips toward the northeast and the dip angle is approximately 30°. The focal mechanism solution of the mainshock is also determined using the cut and paste(CAP) method. The results show that the best double couple solutions of the event and the other nodal plane are 360°, 68°, and 117° and 126°, 34°, and 42°, respectively, for strike, dip, and rake angles. Further, the moment magnitude is MW5.05, and the best centroid depth is 10 km.

    • Analysis of the Dynamic Source and Characteristics of the Seismogenic Structure of the Ludian,Yunnan MS6.5 Earthquake of 2014

      2015, 37(4):1082-1089. DOI: 10.3969/j.issn.1000-0844.2015.04.1082

      Abstract (865) HTML (0) PDF 8.27 M (2749) Comment (0) Favorites

      Abstract:According to the China Seismic Network, on August 3, 2014(Beijing time), an MS6.5 earthquake occurred in Ludian County, Zhaotong City, Yunnan Province, China. A comprehensive analysis of the regional tectonic activity, aftershock distribution, focal mechanism solutions, and other features obtained the following results.(1) The focal mechanism solutions for the main shock and aftershocks that exceeded MS4 indicate that the Ludian earthquake had two directions:NE and NW. Furthermore, the main direction of the spatial distribution of aftershocks was NW, which was also the direction of the long axis of the intensity distribution. All of this evidence indicates that the triggering seismic fault was the Baogunao-Xiaohe fault, which has a NW strike.(2) On the basis of GPS measurements of the horizontal movement rate of the earth's surface of the Ludian earthquake area, during the period 1999-2007 and the shortening rate of the Zhaotong fault for 1999-2013, we determined that the western block of the Baogunao-Xiaohe fault moved faster than the eastern block. This finding indicates that after colliding with the South China Block, the two fault blocks have differential thrust. The Zhaotong-Lianfeng fault consists of two thrust dextral strike-slip fault zones that strike NE:in this fault zone, the Baogunao-Xiaohe fault cuts the Zhaotong-Lianfeng fault. On the other hand, the Baogunao-Xiaohe fault has a NW strike direction, high inclination, sinistral strike-slip, and a short extensional length. From this evidence, it is apparent that this is a typical tear fault. In addition, the seismic depth of the Zhaotong-Lianfeng fault during 1980-2011 was about 0~20 km, indicating that the Baogunao-Xiaohe fault is at shallow depth. In general, the Baogunao-Xiaohe fault is a thin-skinned, constant-direction, differential-thrust type of tear fault.(3) The Zhaotong-Lianfeng fault is in accordance with the "conduit flow" theory in its dynamic source direction(NE), style of fault combination, and depth of the main shock(about 15 km). In addition, the basal slip of the Zhaotong fault is deeper than that of the Lianfeng fault, which is on the northwest side of the Zhaotong fault. Therefore, the movement of the Zhaotong-Lianfeng fault is closely related to conduit flow, and the Baogunao-Xiaohe fault is probably controlled by deep conduit flow. The northern section of the Zhaotong-Lianfeng fault has a stronger resistance than the southern section, and the high-speed conduit flow drags the brittle upper crust. The conduit flow moves from NW to SE. When the flow meets the Zhaotong-Lianfeng fault, which is the boundary between the Daliangshan secondary block and the relatively stable South China block, it is obstructed differently(the resistance to the north is stronger) by the South China Block. This causes the conduit flow west of the Baogunao-Xiaohe fault to move faster than the flow to the east of the fault. However, drag from the conduit flow can cause the block to move, because the speed of the conduit flow is far greater than that of the upper crust. Thus, the western block moves faster than the eastern block, which left-lateral slip on the Baogunao-Xiaohe tear fault in order to adjust for the different thrust in two blocks. This was the mechanism that caused the Ludian MS6.5 earthquake.

    • Research on the Characteristics of Typhoon "Matmo" Using Continuous Gravity Data from Fujian Province

      2015, 37(4):1090-1094. DOI: 10.3969/j.issn.1000-0844.2015.04.1090

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      Abstract:Fujian Province is located on the southeast coast of China, and is affected by a number of typhoons between May and October every year. At present, there are three continuous gravity observation stations in Fujian Province(Xiamen, Zhangzhou, and Fuzhou stations) and gPhone gravity meters are used at these stations. The tenth strong typhoon of 2014, which was named "Matmo", crossed the island of Taiwan, landed at the southern coastal town of Gaoshan, Fuqing City, Fujian Province, on July 23 at 15:30, and then weakened into a severe tropical storm. Taking this typhoon as an example, we used the continuous gravity data to study:(1) the rules governing changes in the strength and predominant frequency of the microtremor signal caused by the typhoon;(2) the relationship between the typhoon's predominant period and its strength and moving speed; and(3) extraction of non-tidal information from the continuous gravity data. The results were as follows:(1) The amplitude of the signal that was recorded by the three stations changed from strong to weak as typhoon "Matmo" moved from close by to far away, and weakened rapidly after landing. This result was consistent with the actual situation. The predominant frequencies with time changed similarly because Xiamen station is relatively close to Zhangzhou station. The closer the distances are, the higher the frequencies are:this may be associated with the signal propagation path and the nature of the medium.(2) The relationship between the typhoon's predominant period and its strength and moving speed is complex, which may be related to the twisting path and complex terrain.(3) The coastal continuous gravity observation interference can be divided into two categories:long-term and short-term. A Kalman filter can effectively remove the long-standing, more regular interference components. Under normal circumstances the filtering result is almost a straight line, which is useful for judging whether the data are normal.

    • Study of Time-space Evolution Characteristics of Precursor Anomaly before the Jinta MS5.4 Earthquake of 2012

      2015, 37(4):1095-1102. DOI: 10.3969/j.issn.1000-0844.2015.04.1095

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      Abstract:An earthquake of MS5.4 occurred at the boundary between Jinta County, Jiuquan City, Gansu Province and Ejina County, Alashan City, Inner Mongolia Autonomous Region in the north Jinta-Huahai Basin(south margin of Beishan) of the active Altun fault belt on May 3, 2012. We found that the values of groundwater radon from Jiayuguan, Lanzhou, Wushan, and Pingliang stations exhibit synchronous abnormal variations before and after April 22 within 90~900 km from the epicenter by time-space scanning of the observed data from the Gansu precursor network and calculating the slip change rate of groundwater radon and variation rate of base value. These abnormal variations were mainly presented as increasing groundwater radon value from 5.6% to 37%. From April 22, 2012, the daily measured water level parameter increased a step with the amplitude increasing initially from 0.36% to 1% and then decreasing. The relationship between the abnormal variations in groundwater radon values observed from the Wushan, Pingliang, and Shilidian stations far from the epicenter and this earthquake must be further studied; however, this phenomenon is objective.Deformation anomaly information from the observatory primarily indicates that the ground tilt in the EW and SN directions measured at the Gaotai station, 170 km from the epicenter, decreases rapidly after April 11, 2012. The value of ground tilt in both the SN and EW directions increases abruptly from April 19 and April 24, respectively, and the amplitude reaches 100% at 11:38 a.m. on April 30 and continues until 10:07 a.m. on May 2. In the EW direction, the value decreases rapidly to the minimum value from 10:00 a.m. on May 2 to 11:39 a.m. on May 3 and then increases rapidly and recovers to the level measured on May 2, which is contrary to the trend observed in the SN direction. The ground tilt values in both the EW and SN directions reach the maximum value after 11:39 a.m. on April 3 and stay out nearly 6 hours; subsequently, Jinta, Jiuquan experienced an earthquake of MS5.4 at 18:19. The increase in Dingxin-Delingha baseline shortening velocity in 2010 indicates that the northeastern Qinlian Structure Belt was squeezed and the baseline shortened by 5 mm in two and a half years before the Jinta MS5.4 earthquake.A series of abnormal variations occurred 10 days prior to the Jinta MS5.4 earthquake. The short-impending anomaly primarily appeared at the stations at a distance of 200 km from the epicenter from mid-March to late April. The impending earthquake anomaly occurred primarily between April 28 and May 1. The Gaotai station recorded the ground tilt data and the complete rock stress change process during the occurrence of the Jinta, Jiuquan MS5.4 earthquake, thus providing complete evolution data with earthquake development and occurrence and has significant research value for the developing a perfect seismic theoretical model and earthquake prediction.

    • Analysis of the Porosity and Temporal Characteristics of the Volume Compression Coefficient of the Dadianzi Well in a Static and Hermetically Sealed State

      2015, 37(4):1103-1108. DOI: 10.3969/j.issn.1000-0844.2015.04.1103

      Abstract (1016) HTML (0) PDF 3.74 M (964) Comment (0) Favorites

      Abstract:This study analyzes the relationship between porosity and temporal characteristics of the volume compressibility coefficient of the Dadianzi well and provides reliable data and information for earthquake prediction. Data from the Dadianzi well are digitized data of the water level that are checked by data processing and are used because the well observation system is relatively stable, the measuring instrument works properly, and the observed data have high reliability. On the basis of relevant theories from mechanics, elasticity, and fluid mechanics, making use of the elastic state of the aquifer medium and a three-phase change model of material volume, the porosity, volume compression coefficient of the solid skeleton, and volume compression coefficient of water in the aquifer were calculated using digitized data of the well water level. The results show that there exists a power function relation among the three aforementioned factors. In the first quadrant, the volume compression coefficient of the well aquifer solid skeleton increases with an increase in porosity, whereas the volume compression coefficient of water decreases with an increase in porosity.

    • >方法探索
    • New Viewpoints on S-wave Velocity Prediction Using Xu-White Model Based on Well Logging Data

      2015, 37(4):1109-1114,1122. DOI: 10.3969/j.issn.1000-0844.2015.04.1109

      Abstract (1042) HTML (0) PDF 5.82 M (1228) Comment (0) Favorites

      Abstract:Physical quantities such as the Poisson ratio and Lame modulus, which represent fluid properties, can be obtained using S-wave velocity. These parameters can be used to reduce the multiple interpretations of seismic amplitudes. Thus, although it is very important to use S-wave velocity in performing seismic data AVO analysis, prestack inversion, and fluid identification, there is seldom information about this velocity in actual logging data. Currently, methods for S-wave velocity prediction can be divided into two types:empirical formula method and theoretical rock-physics-model-prediction method. The former is simple, limited to some exploration area, and requires larger workloads to increase its general overall applicability. Compared with the empirical formula method, the rock physics model method is complex, but it has universal application in different areas. Most rock physics model methods for predicting S-wave velocity assume that the physical parameters of an underground fluid(velocity and density) are not affected by the depth of the stratum or pore aspect ratio. However, this is not a valid assumption even for the most popular rock physics model, the Xu-White model. In fact, the bulk modulus and shear modulus of minerals change with the depth of a reservoir. For fluid parameters, this type of effect will increase. With respect to the pore aspect ratio, its change is fundamentally related to the particle shape formation pressure and porosity, i.e., it is not constant. The aspect ratio has clearer geological implications:bigger aspect ratios correspond to reservoirs with higher porosity and permeability, and lower aspect ratios correspond to reservoirs with lower porosity and permeability. In addition to these parameters, most studies have also neglected some assumptions for the prediction of S-wave velocity. In this study, we investigate these assumptions and present a new and improved Xu-White method. We all know that the compressional wave time difference, S-wave time difference, and mineral formation density are affected by depth, which is usually neglected. Tolerance stacks may be large in some special geological situations, which should be investigated by geophysicists in the future.

    • Research on Automatic Detection Methods of Three-dimensional Fault Surface Morphology Based on DMIS

      2015, 37(4):1115-1122. DOI: 10.3969/j.issn.1000-0844.2015.04.1115

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      Abstract:Based on fault measurement requirements, we optimize the automatic measurement program of the space curved surface in some domestic and foreign advanced industries, using computer control technology. Moreover, we complete a quadrangle automatic coordinate entering program and an arbitrary polygon automatic detection program based on DMIS(Dimensional Measuring Interface Specification). In addition, we simulate the fault surface in the central Tarim Basin-26 well area using the above programs and inform two system building methods of 3D-surface morphology detection of faults:The Model Building System Method and The Machine Tool Building System Method. Subsequently, the automatic measuring technique of space surface is applied to the 3D-surface shape measurement of faults. In this way, an automatic detection method for the complex surface of the fault is formed. Thus, the 3D-surface shape of the fault can be measured automatically, and a measurement can be conducted by using multiple angles of view. This allows the boundaries of faults can be fully connected in the traditional fault detection process. This method improves the efficiency and automation degree of fault measurement as well as reduces the human factor and the difficulty of data processing in the measurement process.

    • >短文
    • Reviewing Prediction for the Occurrence Time of the Afghan MS7.8 Earthquake on Oct.26, 2015

      2015, 37(4):1123-1123,1128. DOI: 10.3969/j.issn.1000-0844.2015.04.1123

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      Abstract:

    • >地震监测
    • Moment Tensor Inversion of the 2012 Jinta,Gansu MS5.4 Earthquake

      2015, 37(4):1124-1128. DOI: 10.3969/j.issn.1000-0844.2015.04.1124

      Abstract (929) HTML (0) PDF 3.56 M (811) Comment (0) Favorites

      Abstract:On May 3, 2012, the Jinta MS5.4 earthquake occurred beneath the northeast margin of the Tibetan Plateau, Gansu, China. We analyzed the broadband waveforms for the mainshock with sufficient signal-to-noise levels to invert for seismic moment tensors. All stations involved in this study are broadband stations situated near the May 3 mainshock; data showing such problems as misorientation of horizontal components, mislabeling and polarity reversal in one or more components were removed. During the data processing, we removed the mean value and instrument response, detrended the waveforms, integrated the three-component velocity waveforms to displacement, and rotated the horizontal components to the radial and tangential directions. Before performing moment tensor inversion, waveforms were filtered with a Butterworth Filter with frequencies between 0.016 Hz and 0.05 Hz. On the basis of the Crust 1.0 global crustal model, and considering the heterogeneity of the crust and the distances to the recording stations, various velocity models for each station were employed to account for variabilities in the crustal structure. During the inversion process, to insure the quality of the results, we retained only the station with variance reduction(VR) is ≥ 80, and got 5 stations for the inversion. After depth iteration, the best solutions obtained at a depth of 12 km were 71, 29, and 91.5% for double couple(DC), the compensated linear vector dipole(CLVD) component, and VR, respectively, which indicates high-quality results. The two panel's strike, dip, and rake of the solution were 166°, 66°,-168° and 71°, 79°,-25° respectively. It is found that our inversion results are basically consistent with the strike of the Shenluoshan-Yemajing fault, and the aftershocks distribution occurred near the fault. Associating with the tectonic framework, damage characteristics, and the aftershock distribution feature, we suggest that Jinta MS5.4 earthquake was caused by the combined action of southeast Mashan fault and Shenluoshan-Yemajing fault, and the latter should be the seismogenic fault of the earthquake.

    • Focal Mechanism Solutions of Two Moderate-strong Earthquakes of 2014 in the West Alax Block

      2015, 37(4):1129-1131. DOI: 10.3969/j.issn.1000-0844.2015.04.1129

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      Abstract:After the Yutian, Xinjiang earthquake of MS7.3 that occurred on February 12, 2014, the Mongolia earthquake of MS4.9 and Hami, Xinjiang earthquake of MS5.1 occurred on the western margin of the Alax block. This shows that seismic activity is strengthening on the western margin of the Alax block. The cut-and-paste(CAP) method performs inversion of the entire profile of an earthquake, the result of which has advantages of relatively small merit that rely on the modeling of speed and lateral movement of the earth's crust. Its basic principle is splitting seismic broadband waveform data into Pnl wave and surface-wave parts, calculating the objective error function of the observed and theoretical seismograms, performing a grid search in the assigned parameter space, and searching for the focal mechanism and focal(centroid) depth using the two global minimum variances. In this study, using wave data from the Digital Seismological Network of Gansu Province and adopting the CAP method, we determined the focal mechanisms of the two earthquakes. The result shows that the focal mechanisms of the Mongolia MS4.9 and Hami, Xinjiang MS5.1 earthquakes were strike-slip and thrust, respectively.Our analysis concludes that the occurrence of the Mongolia MS4.9 and Hami, Xinjiang MS5.1 earthquakes exhibits a correlation with the interaction of the Qinghai-Tibet block and the Alax block.

    • >技术交流
    • Comparison of Two Verification Methods for One Measuring-processStandard Deviation in the Horizontal Direction for an Electronic Theodolite

      2015, 37(4):1132-1135. DOI: 10.3969/j.issn.1000-0844.2015.04.1132

      Abstract (976) HTML (0) PDF 1.03 M (1221) Comment (0) Favorites

      Abstract:Electronic theodolites have the advantages of providing quick and high-precision objective readings, and thus can reduce work intensity. In addition, the measurement results are easily entered onto a computer. This type of equipment is widely used in basic map surveying, such as in construction, the military, aviation, water conservancy, transportation, and earthquakes, and plays an extremely important role in measurement of deformation. To ensure measurement accuracy of electronic theodolites, metrological verification of the measurement accuracy indexes is crucial. One of the main indicators of theodolite measurement accuracy is the value of one measuring-process standard deviation in the horizontal direction. Using the requirements of the verification regulation and beginning with the measurement principle, method, and uncertainty analysis, a comparison of two verification methods was carried out for one measuring-process standard deviation in the horizontal direction for an electronic theodolite. The results indicated that the multi-tooth indexing table method and multi-objective method are performed in the same way, and the results of the uncertainty in measurement are consistent. This may be because during the actual process of metrological verification, changes in the metrological verification personnel, environmental conditions, or other factors caused the measured results to be slightly different.

    • Research and Testing of an Intensity Rapid Report Algorithm for the Dengta MS5.1 Earthquake in Liaoning

      2015, 37(4):1136-1140. DOI: 10.3969/j.issn.1000-0844.2015.04.1136

      Abstract (948) HTML (0) PDF 8.37 M (966) Comment (0) Favorites

      Abstract:When making strategic disaster relief decisions, rapid and effective intensity assessment and distribution results are of utmost importance. For this process, an intensity rapid report algorithm is necessary, especially in areas such as Liaoning. In the study process, following principles must be followed:(1) The intensity grade must adhere to the Chinese Seismic Intensity Scale to communicate the instrumental intensity and maintain continuity of the intensity assessment.(2) With respect to the physical ground motion parameter, a 0.3~10 Hz band-pass filter must be selected because the main frequency bands of housing structures in China fall into this range.(3) When selecting the ground motion parameters of the instrumental intensity, the effect of three ground motion component histories for this intensity must be considered.(4) The method must be simple and general for overall use, and the results should be stable and reliable. We calculated the seismic intensity in Liaoning by the following steps:(1) Modification of the correction of the field effect using ShakeMap Small Regression.(2) Grid computation for real-time systems, which reduces the amount of computation but may also reduce the accuracy of the intensity map.(3) Filtration and intensity calculation. We use a band-pass filter in the 0.3~10 Hz frequency domain, filter the three-component ground motion histories, and then synthesize the acceleration time history. Finally, we calculate intensity values using the Chinese intensity method.(4) Plotting intensity distribution. We constructed a rough and uniform simulation station grid using an existing station acceleration value and determined the intensity value of the station by its acceleration or velocity. The intensity of the simulation station is constructed using the equal-distance interpolation method. We then plot the distribution of the equivalent seismic intensity in the entire region from the intensity of grid points. Combined with the actual seismic damage results and network density, we draw the intensity distribution map using the source of a fault zone. Finally, considering the Dengta MS5.1 earthquake in Liaoning as a test case, the intensity distribution map was automatically produced by the intensity quick report data processing system called Samrt in 10 min, which also produced a detailed acceleration distribution diagram and intensity distribution map in 30 min. These results prove that the proposed method is feasible.

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