• Volume 42,Issue 5,2020 Table of Contents
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    • >地震科学
    • Focal Mechanism Solutions of Moderate and Small Earthquakes in Haiyuan and Surrounding Areas

      2020, 42(5):1049-1054,1064. DOI: 10.3969/j.issn.1000-0844.2020.05.1049

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      Abstract:On December 16, 1920, a magnitude 8.5 earthquake occurred in Haiyuan County, Gansu, China. The earthquake and its aftershocks caused 288 200 casualties and damaged dozens of counties severely. This paper analyzed broadband waveforms to invert seismic moment tensors with sufficient signal-to-noise levels using the Gansu and Ningxia seismic networks. We obtained 16 focal mechanism solutions of Haiyuan and its surrounding areas from January 2010 to December 2019 using the cut-and-paste method. Results showed that the focal mechanism solutions in the Haiyuan area were mainly strike-slip and strike-slip with thrust type, and the P-axis of the main compressive stress was mainly concentrated in the NE direction. These findings are in good agreement with the direction of the regional main compressive stress.

    • Characteristics of Present-Day Crustal Deformation along the Haiyuan Fault Zone Using PS-InSAR Method

      2020, 42(5):1055-1064. DOI: 10.3969/j.issn.1000-0844.2020.05.1055

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      Abstract:Numerous deep fault zones have developed in the northeastern Tibetan Plateau, which is the convergence zone of the active Tibetan block, the stable Alashan block, the stable Ordos block, and the stable South China block. Among these fault zones, the Haiyuan fault zone, in which two M8 and several M7 earthquakes have occurred, is one of the most active. Presently, it still controls the activities of strong earthquakes nearby. In this study, based on ISCE and the StaMPS platform, and 72 Sentinel-1 synthetic aperture radar (SAR) images, we monitored the surface deformation of the Haiyuan fault zone by the persistent scatter-interferometric synthetic aperture radar (PS-InSAR) technique, calibrated the initial InSAR result with the GPS velocity field, and finally obtained the annual mean deformation velocity of the Haiyuan fault zone from March 2017 to June 2020. The results revealed the following: (1) The deformation rate on the north and south sides of the Haiyuan fault zone was quite different, which was consistent with the movement characteristics of left-lateral strike-slip faults. (2) The Maomaoshan fault and the western Laohushan fault were locked, and the middle eastern Laohushan fault was fairly active; here, we observed creep deformation. The Haiyuan seismic rupture zone was in a healing state. (3) The creep deformation at the middle eastern Laohushan fault is the most significant section in the northeast margin of the Qinghai Tibet Plateau. We infer that the creeping may be associated with the two M6 earthquakes that happened in Jingtai in 1880 and 1990.

    • Characteristics of Tectonic Stress Field in Tibetan Plateau

      2020, 42(5):1065-1076,1084. DOI: 10.3969/j.issn.1000-0844.2020.05.1065

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      Abstract:In this paper, the cut-and-paste (CAP) method was used to calculate and study the focal mechanism solutions of 270 MS>3.0 earthquakes in the range of 26°N -42°N and 90°E-110°E based on the seismic observation data of the regional seismic network. Then combining the global centroid moment tensor (GCMT) catalog and the data of 759 focal mechanism solutions, the stress field in the study region was calculated using the spatial and temporal stress inversion (SATSI) method. The distribution results of 154 stress fields were obtained by meshing the study area into 1°×1°. Compared with the early tectonic stress field, the direction of maximum principal compressive stress had a clockwise rotation. The results showed that in the extrusion process of the Tibetan Plateau block toward NE and NNE, the northern and eastern parts of the block were stopped by two hard blocks: Ordos and Arashan, respectively, resulting in the thickening of the Tibetan block and the lateral flow of material between the blocks. The study of the R value of the stress form factor in the whole study area showed that the relative stress along the boundary of the Tibetan Plateau block such as the Qilian Mountain in Qinghai, southeastern Gansu, and Longmenshan in Sichuan is large; the relative stress is directly proportional to the seismicity of these areas in recent years. The results of this research agree well with the study results of stress field, GPS research, and numerical simulation. The research results can provide a reliable reference for earthquake initiation mechanism, active structure, and seismic trend determination in the Tibetan Plateau.

    • Seismicity in the Northwestern Tibetan Plateau and North-South Seismic Belt

      2020, 42(5):1077-1084. DOI: 10.3969/j.issn.1000-0844.2020.05.1077

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      Abstract:In this study, the temporal and spatial distribution of earthquakes in the Tibetan Plateau was investigated; the results showed that over 70% of earthquakes with M ≥ 6 in the northwest of the Tibetan Plateau occurred during the peak period of seismicity. Based on the earthquakes that occurred in the northwest of the Tibetan Plateau, the earthquakes that occurred in the south-north seismic belt within a one-year time window were detected, and it was found that the occurrence time of medium-strong earthquakes in the northwest of the Tibetan Plateau was close to that of the earthquakes in the north-south seismic belt. The earthquakes that occurred in the northwest of the Tibetan Plateau had different correlations with those in the south, north, and middle sections of the north-south seismic belt. Regarding the frequency of seismicity, the correlation with that in the north section of the north-south seismic belt was the weakest, and the correlation with that in the south section was the strongest. However, in magnitude, the earthquakes that occurred in the northwest of the Tibetan Plateau were closely related to the large earthquakes in the north and middle sections of the north-south seismic belt and the medium earthquakes in the Yunnan and Myanmar structural transformation area. Furthermore, the large earthquakes in the north-south seismic belt were found to have the characteristics of reciprocating migration from north to south when the Haiyuan earthquake is taken as the initial earthquake. The earthquake migration between the middle part of the north-south seismic belt and the Yunnan Myanmar structural transformation area was more frequent, which indicates a close relationship exists between the seismic activities in the two regions. This study is of great significance to the seismic risk assessment of the north-south seismic belt.

    • Change and Mechanism of Spontaneous Potential Field around Two Typical Strong Earthquakes in the North-South Seismic Zone

      2020, 42(5):1085-1089. DOI: 10.3969/j.issn.1000-0844.2020.05.1085

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      Abstract:The geoelectric field E can be divided into telluric field ET and spontaneous potential field ESP according to different field sources. The spatial Sq current system and the solid tide are generally considered to be the origin of the telluric field ET; the potential field ESP originates from the physical and chemical actions of the underground medium, and the local changes are relatively stable. In 2013, the Lushan MS7.0 earthquake (30.3°N, 103.0°E) and the Minxian-Zhangxian MS6.6 earthquake (34.5°N, 104.2°E) occurred successively in the north-south seismic zone. The data of geoelectric stations (Chengdu, Hanwang) within about 400 km around the two earthquakes indicated that the potential field ESP before the two earthquakes both showed significant small or large jumps, and the change was quasi-synchronized in time. Similar changes occurred in other geoelectric stations. Based on the seepage (movement) model of the fissure water (charge) of the telluric field rock mass, the variation mechanism of the spontaneous potential field ESP around the two earthquakes was discussed, and its physical process was analyzed.

    • Index Extraction and Prediction Efficiency Analysis of Small Earthquakes Enhancement in Qilianshan Seismic Zone

      2020, 42(5):1090-1095. DOI: 10.3969/j.issn.1000-0844.2020.05.1090

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      Abstract:The activity enhancement indexes of the Qilian Mountain seismic zones for earthquake events in 2015, 2010, and 1980 are summarized in this paper. The paper shows a good correspondence between the earthquake activity enhancement and the occurrence of moderate-strong earthquakes in the study region. If the monthly frequency of ML2.0 earthquakes in the Qilian Mountain seismic zone is continuously enhanced for more than three months, the occurrence probabilities of earthquakes above M5 in the Qilian seismic zone and above M6 in the northeastern edge of the Qinghai Tibet Plateau are high in the first to third months after enhancement anomaly. As a short-term prediction index, the enhancement of seismicity in the Qilian Mountain seismic zone has a great significance for earthquake prediction in Gansu and its adjacent areas.

    • Experiment on Restraining Interference Signal by Coded-Source Geo-electricity Observation: A Case Study of the Observation at Tongwei Station

      2020, 42(5):1096-1103. DOI: 10.3969/j.issn.1000-0844.2020.05.1096

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      Abstract:In past earthquakes, we found that the change in the observed geo-resistivity is an effective basis for earthquake prediction. In recent years, the acceleration of urbanization has caused serious electromagnetic interference to some observation stations, resulting in a large error in geo-resistivity measurements. In this study, Tongwei station, Gansu Province, was selected as a case study. Various complex electromagnetic interferences are present near the station, such as high-speed railways, highways, buildings, and power consumption by industrial production. Here, the coded-source earth resistivity observation technology and the cyclic cross-correlation calculation method were used, and the transmission sequence signal cycle (observation time length) was changed to make the excitation polarization effect more adequate. The results showed that the environmental random noise could be effectively suppressed. Moreover, geo-resistivity data with small dispersion could be obtained under the interference of high-speed railway and infrastructure. This new geo-resistivity observation system can provide technical support for the sustainable development of existing geo-resistivity stations and reliable data for earthquake prediction and scientific research.

    • Critical-Slowing-Down Phenomenon of Water Radon Concentrations in the Southeastern Gansu Region

      2020, 42(5):1104-1110,1140. DOI: 10.3969/j.issn.1000-0844.2020.05.1104

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      Abstract:In this study, we applied the critical-slowing-down principle to the processing of water radon concentration observation data in southeastern Gansu and calculated the autocorrelation coefficient and variance, which can characterize the critical-slowing-down. Here, we take the Wenchuan MS8.0 earthquake that occurred on May 12, 2008, and the Minxian-Zhangxian MS6.6 earthquake that occurred on July 22, 2013, as case studies. The results indicated that the water radon concentration at several stations in southeast Gansu showed the critical-slowing-down phenomenon before two earthquakes. Then we analyzed the characteristics of the critical-slowing-down of water radon concentration at abnormal points from the aspects of spatial distribution, duration, and change form. It is believed that the critical-slowing-down phenomenon before the two earthquakes was related to the earthquake occurrence by combining with the hydrodynamic mechanism of water radon anomalies and the structure of abnormal points.

    • Reliability Analysis of Borehole Strain Meters and Test of Earthquake-reflecting Efficacy in Tianshui

      2020, 42(5):1111-1116. DOI: 10.3969/j.issn.1000-0844.2020.05.1111

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      Abstract:To test the reliability of the observed data from the four-component borehole strain gauge at the Beidao Station in Tianshui City, readings from the four components are used to calculate the values of two surface strain and correlation values (data self-inspection). Although the self-inspection effect is poor, the seismic reflection effect is good. In this study, the sensitivity of the element is calibrated by in-situ relative calibration to correct the observed data and obtain the self-consistency test result after calibration. In accordance with different earthquake cases, the overrun rate and S-transform methods are used to analyze the seismic reflection effect of the corrected data and further demonstrate the reliability of the observed data. Results show that the self-consistent character of the Tianshui borehole strain observation data is improved after in-situ relative calibration. The form of abnormal changes in the original curve is also observed after overrun rate and high-frequency analyses. The improved data respond well to earthquakes and can reflect regional tectonic activity and strain factually. This study has a good denotative meaning to the seismic risk in southeastern Gansu and thus can be used as reference for regional earthquake prediction and earthquake scientific research.

    • Space-Time Symmetry and Tendency Analysis of MS≥6.6 Earthquakes in Pan-Tianshan Mountains

      2020, 42(5):1117-1124. DOI: 10.3969/j.issn.1000-0844.2020.05.1117

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      Abstract:In this study, we use the commensurability method, butterfly structure diagram method, commensurable structure, and autoregressive algorithm model to analyze the MS≥ 6.6 earthquakes in Pan-Tianshan Mountains since 1716. Combined with the symmetry of the epicenter location and focal depth, results show that the strong earthquakes in the study area have a good space-time symmetry. A MS≥ 6.6 earthquake is more likely to occur in Pan-Tianshan Mountains on years 2022-2023, especially in July 2023 (±1 month), and the epicenter is more likely to locate in the southwestern region of 80°E and 41°N. In this study, time symmetry and autoregressive model are used to improve the identification accuracy of the symmetry method and tendency analysis of strong earthquakes. The date is accurate to the month, advancing the judgment of strong earthquake tendency.

    • Geomorphic Characteristics of Motuo Fault and Its Tectonic Significance

      2020, 42(5):1125-1131. DOI: 10.3969/j.issn.1000-0844.2020.05.1125

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      Abstract:The Motuo fault is located at the east of the Namjagbarwa Peak. The fault activity has been strong since the late Quaternary, and the horizontal movement of the fault is characterized by sinistral strike-slip. To further study the movement characteristics of the Motuo fault, the elevation data of four elevations across the rectangular region of the fault were extracted, and the hypsometric integral values of 31 catchment basins along the fault were calculated. The results showed that four sets of symmetrical platform ground appeared at the same height on both sides of the Motuo fault, and the height difference from the low to adjacent two-stage Mesa did not show a gradual increase. This indicates that the fault does not feature a significant tendency to slip. The catchment basin distributed along the fault has a large hypsometric integral value (between 0.42 and 0.6), which reflects a strong tectonic uplift in the Motuo fault region. According to the spatial distribution characteristics of the hypsometric integral value of the catchment basin, the uplift intensity of regional crust gradually decreases from south to north along the Motuo fault. Combined with the fault geomorphology, it is concluded that the hypsometric integral value in the strong uplift area has certain referential meaning to the fault activity.

    • Comparison of the Excitation Effects of Air Guns with Various Combinations in the Qilian Mountain in Gansu Province

      2020, 42(5):1132-1140. DOI: 10.3969/j.issn.1000-0844.2020.05.1132

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      Abstract:High-capacity air gun sources have become a new method of detecting underground media due to its advantages, such as green environmental protection, long propagation distance, and high repeatability. Its high-precision detection requires the consistency of air gun propagation signals under different excitation conditions. On the basis of the excitation detection of air gun active sources in the Qilian Mountain, we selected the waveform records of distant stations from four and three air guns. They had the same excitation environment and corresponding period. Through the signal stack, cross-correlation, and spectrum analysis methods, the relationship between excitation from air guns with various combinations and recorded signals from stations with different epicentral distances was compared and analyzed; moreover, the influences of air guns with various combinations on the observation of travel time change of underground medium were explored. Results showed the following: (1) The waveform correlation of different gun groups decreases with the increase in epicentral distance. The signal excited by low energy has weak seismic phase changes, and the changes can hardly be discerned when the epicenter is more than 50 km away. (2) The energy of the signal received by far stations changes with the excitation energy of active sources, and the energy change of each station is mainly reflected in the dominant frequency range. (3) The firmer the base of the receiving station, the smaller the RMS amplitude ratio of different excitation energies. (4) Stacking a certain amount of waveform can effectively improve the signal-to-noise ratio (SNR) of recorded signals received by distance stations, whereas increasing the excitation energy of air guns easily improves the SNR.

    • Comparative Analysis of Earthquake and Seismic Phase Characteristics Recorded on the Old and New Bases of Gaotai Station

      2020, 42(5):1141-1145,1158. DOI: 10.3969/j.issn.1000-0844.2020.05.1141

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      Abstract:Using the observation data recorded over the same bandwidth and with the same type of seismometer BBVS-120, the base ambient noise, the earthquake monitoring capability, and the seismic phase characteristics of the new and old observation caves of the Gaotai seismic station were compared and analyzed. The results indicated that the seismic monitoring level of the new cave is better than that of the old and that some new caves have clearer records of radially reflected waves.

    • Development and Prospects of Active-Source Construction in Gansu Province

      2020, 42(5):1146-1150. DOI: 10.3969/j.issn.1000-0844.2020.05.1146

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      Abstract:The use of large-capacity air-gun source detection has become an important development direction to explore new earthquake prediction methods, which will promote the combination of empirical earthquake prediction and physical prediction. The site selection and construction processes of Qilianshan and Liujiaxia air-gun launchers were complex. With the efforts and help of various parties, many difficulties were overcome and the construction was finally completed with high quality. The stable operation of the Qilian Mountain air-gun launcher has accumulated abundant data of air-gun active source in the Qilian Mountain, and many innovations have been achieved. The newly built Liujiaxia air-gun launcher will realize the continuous monitoring of the Haiyuan fault and deep and large faults in the northern edge of the West Qinling fault. Through multi-point monitoring, the relationship between strong earthquake preparation, regional stress field, and medium change was analyzed, and seismic risk analysis and research were carried out. Furthermore, there are plans to construct three air-gun active sources in Gansu Province, which is located in an area with strong earthquake activity in the northeast margin of the Qinghai Tibet Plateau. There are also plans to combine the Qilian Mountains and Liujiaxia air-gun active sources to realize the four-dimensional detection of active sources in the fault zone system on the northeast edge of the Qinghai Tibet Plateau. Implementing these plans will be greatly beneficial to earthquake prevention, disaster reduction, and earthquake prediction in Gansu Province.

    • >岩土抗震
    • Site Effects of Ground Motions in Landslide-Concentrated Area Caused by the Haiyuan Earthquake in 1920

      2020, 42(5):1151-1158. DOI: 10.3969/j.issn.1000-0844.2020.05.1151

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      Abstract:Strong ground motions, the direct inducement of all kinds of earthquake disasters, usually cause considerable casualties and property loss through building collapse and earthquake landslides. The M8.5 Haiyuan earthquake of 1920 triggered numerous loess landslides and caused heavy casualties in the loess hilly area at the junction of Xiji and Jingning Counties, 80 km from the epicenter. Based on the analysis of the landslide distribution characteristics in the Haiyuan earthquake high-intensity area, the geological conditions and seismic response characteristics of typical sites in the landslide-concentrated area were studied by field investigation and numerical calculation. It is concluded that the topographical differences and the overburden on both sides of the loess hill lead to different ground-motion amplification effects, which is one of the factors leading to the successive occurrences of landslides on one side of the hill. The topography, geotechnical property, and soil layer structure of the landslide-concentrated area show that the ground motion in this area rapidly changes with local site conditions. The combined action of stratigraphic site effect and topographic site effect intensifies the ground-motion amplification of the slope surface and increases the seismic force of triggering landslides.

    • Formation Mechanism of Surface Characteristics of Liquefaction-Triggered Sliding Flow in Haiyuan Earthquake Shibei Tableland

      2020, 42(5):1159-1164. DOI: 10.3969/j.issn.1000-0844.2020.05.1159

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      Abstract:A large-scale sliding flow triggered by liquefaction in Shibeiyuan area was induced by Haiyuan earthquake. Due to the difference of multi-element stratum structure and soil liquefaction properties, the highly regular wavelike landform was formed during the sliding process. This phenotypic characteristic is an intuitive expression of the occurrence mode during the disaster-causing process of sliding bodies. Therefore, the formation mechanism analysis of the sliding body surface characteristics is an ideal approach for studying the mechanism and form of such disasters. In this paper, combined with field investigation, strike of slip body, stratigraphic profile, and previous determination of liquefaction potential of different sandy loess layers, the formation mechanism and movement characteristics of wavelike peak valley landform were analyzed and discussed in detail.

    • Mechanism of Shibeiyuan Loess Landslide Induced by the Haiyuan Earthquake

      2020, 42(5):1165-1172. DOI: 10.3969/j.issn.1000-0844.2020.05.1165

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      Abstract:The Shibeiyuan landslide induced by the Haiyuan MS8.5 earthquake of 1920 has become a research focus because of its large scale, small slope angle, and long sliding distance. At present, there is no unified understanding of the physical and mechanical processes of the landslide. In this study, the initial state, seismic dynamic response, and flow slip development process of the landslide are investigated by theoretical analysis and numerical calculation. To analyze the initial state of the slope before the earthquake, a mechanical model and a slope stability evaluation model considering the action of lateral water pressure in the slope surface tension cracks are established. The results show that the lateral water pressure in the tension fracture weakens the slope overall stability. To study the dynamic response process of the slope under earthquake, a numerical calculation model is established, and the variation characteristics of pore pressure ratio and the slope displacement of saturated soil layer during earthquake are obtained. To explain the long-distance landslide, the liquefied soil layer is made equivalent to a fluid layer, and the slip distance of the Shibeiyuan landslide is calculated using the estimation theory of mudflow slip distance. The calculation results are consistent with previous field investigation results.

    • Microstructure and Microtremor Characteristics of Loess in Haiyuan Area

      2020, 42(5):1173-1178. DOI: 10.3969/j.issn.1000-0844.2020.05.1173

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      Abstract:The 1920 Haiyuan M8.5 earthquake caused numerous landslide disasters, which is of great significance to the study of landslide disasters in loess areas and the analysis of soil microtremor characteristics. The results of high-precision scanning electron microscopy (SEM) showed that the surface loess in the Haiyuan earthquake site is a microstructure with weakly consolidated overhead pores and a strong risk of seismic collapse and seismic landslide occurrence. The microtremor data of 15 landslide sites were obtained via a microtremor test. Fourier-transform was used to analyze the microtremor characteristics of soils in the Subaocun landslide, and then the microtremor spectrum characteristic curves were obtained. The results showed that the recommended value of predominant period of the site is 0.126 s, and it is classified as a hard site. The recommended value of the site predominant period in this area can be used as a reference for landslide site classification. The study shows that the microtremor characteristics of landslide and non-sliding body are very different, which can provide the basis for the analysis of microtremor characteristics of landslides induced by the Haiyuan earthquake.

    • Probability Distribution of Shear Strength Parameters in Calculation of Dynamic Critical Acceleration of Seismic Slopes

      2020, 42(5):1179-1186. DOI: 10.3969/j.issn.1000-0844.2020.05.1179

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      Abstract:The heterogeneity of cohesion distribution was applied in the calculation method of seismic slope permanent displacement based on dynamic acceleration, and the degree of uneven distribution affected the permanent displacement calculation results. Studying the distribution characteristics of shear strength parameters on the bottom of the Newmark sliding block or the potential sliding surface of slopes can clarify the distribution and change process of critical acceleration in seismic processes. Through calculation, it was found that the linear relationship between the standard deviation of cohesion and the cohesion of soil slope is weak and can only be used for reference in the absence of experimental data. When the random number of cohesive forces reached 200, the calculated permanent displacement values no longer fluctuated. Setting the cohesion as a normal distribution or lognormal distribution had no effect on the permanent displacement calculation result. The standard deviation of cohesion had a great influence on the value and dispersion of permanent displacement. During the seismic slope calculation, the cohesion should be set as normal distribution as possible, and the standard deviation of cohesion should be set according to the measured data as much as possible. If there is no measured data, the standard deviation can be set by referring to the linear relationship between the two.

    • Loess Site Effect Based on Shaking Table Test

      2020, 42(5):1187-1193. DOI: 10.3969/j.issn.1000-0844.2020.05.1187

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      Abstract:Based on the data of a large-scale shaking table test, this study employed the peak ground acceleration (PGA) amplification, Fourier spectrum, acceleration response spectrum, and the H/V spectral ratio to investigate the non-linearity of a loess site effect under strong earthquakes. Then the impacts of different seismic components on the loess site effect were determined. The results showed the following: (1) With the increase in the ground-motion intensity, the PGA amplification coefficient of the horizontal component significantly decreased, while that of the vertical component slightly increased. (2) With the gradual change in vertical monitoring points from the bottom to the surface, the PGA amplification coefficient of the horizontal component of the loess site presented a nonlinear change, while that of the vertical component had no significant change. (3) With the increase in elevation, the predominant frequency band and amplitude of the horizontal component gradually increased, while the Fourier spectrum of the vertical component exhibited no significant change. (4) With the increase in elevation and ground-motion intensity, the horizontal component of the acceleration response spectrum increased. (5) As the ground-motion intensity increased, the low frequency became the predominant frequency, and the amplification factor presented a nonlinear characteristic.

    • Regional Characteristics of the Earthquake Subsidence Disaster in Loess Area Based on Soil Properties

      2020, 42(5):1194-1201. DOI: 10.3969/j.issn.1000-0844.2020.05.1194

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      Abstract:Based on physical indexes such as density, moisture content, pore ratio, and plastic limit, the relationship between each physical index and soil vulnerability was analyzed. Undisturbed soil samples in Tongwei, Lanzhou, Baoji, Xiji, Xi'an, and other typical loess disaster sites were used as the research object. Through an indoor dynamic characteristics test and based on the findings of numerous previous studies, the regional effects of soil properties on geotechnical subsidence disasters were quantitatively analyzed. The results showed the following: (1) A positive or negative correlation exists between the seismic subsidence coefficient and individual soil physical property. The seismic subsidence characteristics in the west and east of the Liupan Mountain present a regional law: the disaster distribution is characterized as light in the south and heavy in the east under the same seismic load. (2) Over time, the increase in the number of human activities changes the soil moisture, increasing the overburden pressure of soil. Under the action of the overburden pressure of soil, the number of initial soil pores decreases, and the consolidation degree increasingly improves. Macroscopically, this result shows that the soil vulnerability is reduced, and thus, the seismic subsidence is reduced.

    • Effect Coefficient Calculation of Horizontal Bearing Capacity of Large-scale Pile Group Foundation

      2020, 42(5):1202-1207. DOI: 10.3969/j.issn.1000-0844.2020.05.1202

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      Abstract:The bearing capacity of pile foundation under horizontal loading or earthquakes has always been a difficult point in the engineering field. In recent years, the conclusions and calculation methods based on the horizontal bearing capacity test of small-scale pile foundation may no longer meet new requirements given the considerable increase in the scale of building and bridge pile foundation. Related knowledge and calculation methods need to be updated. Thus, this paper investigated the research progress at home and abroad and found that the calculation method of the current code may overestimate the horizontal bearing capacity of pile group foundation. Then, the effect coefficient of horizontal bearing capacity of large-scale pile group foundations was analyzed by using the finite element method. The law of the effect coefficient was obtained, and the corresponding calculation method was given. Finally, the result is compared with that of the calculation method of the code. The findings can provide a basis for corresponding engineering design problems. The applicability of the results needs to be further examined in the future.

    • Seismic Response of Bicycle Bridges with Continuous Curved-Box Girder

      2020, 42(5):1208-1216. DOI: 10.3969/j.issn.1000-0844.2020.05.1208

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      Abstract:To study the seismic response law of the curved-box-girder bicycle bridge in Xiamen city, we established a three-dimensional shell model of the bicycle viaduct using SAP2000 finite element software. We calculated the dynamic response of the bicycle viaduct using the response spectrum and time-history analysis methods after considering the effects of frequent and rare earthquakes and different loading directions. The results show that the Z-direction displacement component of the bicycle bridge is the largest, with the extreme value of the Z-direction component occurring in the curve bifurcation section. The vertical support reaction of the pier was found to be small relative to the shear force. The results also indicate that the variation trends of the seismic responses of E1 and E2 are basically the same with time, the bridge structure does not enter the plastic state, and the seismic performance is good. The envelope value calculated by the response spectrum method is larger than the peak value of the time-history results for three different seismic waves. In the actual seismic analysis process, it is necessary to consider the analysis results of both methods. The results of this study have great significance for guiding the future design and seismic performance analysis of bicycle bridges and as a reference for further research on this kind of bridge.

    • Seismic Transverse Analysis of Shield Tunnels in Complex Soft Soil through Response Deformation Method

      2020, 42(5):1217-1224. DOI: 10.3969/j.issn.1000-0844.2020.05.1217

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      Abstract:A beam-spring finite element model is established using ABAQUS to conduct seismic transverse analysis of shield tunnels in soft soils through response deformation method. Model calculation is conducted on Tianjin Binhai metro line Z2 project. Result shows that under the action of earthquake, the maximum bending moment and shear force generally appear at the shoulder of the arch and the maximum axial force appears near the waist of the arch. The internal force values of the tunnel structure near the complicated soil layer are large, so seismic construction measures at these positions should be strengthened or complicated sites should be avoided in line selection. This study is of certain value for seismic transverse design of shield tunnels in complex soft soil areas.

    • >地震应急与震灾防御
    • Comparative Analysis between Instrumental and Macroseismic Intensity during the Wenchuan M8.0 Earthquake

      2020, 42(5):1225-1231. DOI: 10.3969/j.issn.1000-0844.2020.05.1225

      Abstract (368) HTML (0) PDF 6.54 M (2844) Comment (0) Favorites

      Abstract:Using the strong motion records of the Wenchuan M8.0 earthquake in 2008, the instrumental intensity at each station is calculated in accordance with the algorithm from the provisional regulation; moreover, the corresponding relationship between instrumental and macroseismic intensity is analyzed to discuss the applicability of the calculation method of instrumental intensity. Results show that stations with the same intensity value account for 47.5%, and stations with deviations of less than 1 degree account for 89.1%. These results indicate that instrumental and macroseismic intensity have an ideal corresponding relationship, and instrumental intensity can objectively reflect the actual earthquake damage. The instrumental intensity values in each macroseismic intensity area have certain discreteness, but the deviations between the mean instrumental and macroseismic intensity values are relatively small, which can be controlled within ±0.3 degree. Additionally, the distribution map of the instrumental intensity of the Wenchuan earthquake is drawn. Although a certain correspondence exists between instrumental and macroseismic intensity in the overall layout, they cannot be completely consistent due to the influence of some factors. The concept, properties, and functions of instrumental and macroseismic intensity vary and thus should not be used interchangeably.

    • Variation of Night Light Index Based on NPP-VIIRS Data:A Case Study on the Xiahe MS5.7 Earthquake

      2020, 42(5):1232-1235,1269. DOI: 10.3969/j.issn.1000-0844.2020.05.1232

      Abstract (465) HTML (0) PDF 4.02 M (1034) Comment (0) Favorites

      Abstract:Night light data can reflect human activities, and its variation is closely related to the operation of electrical facilities, buildings, and other luminous objects. Thus, these data have been widely used in various scientific research. Based on the characteristics of multitemporal NPP-VIIRS night light data, this study obtained three night light indexes to analyze the change of night light in the disaster region of the Xiahe MS5.7 earthquake. Results showed that the NPP-VIIRS data can provide a method of acquiring disaster information after earthquakes, thus providing another perspective for earthquake emergency in Gansu Province at the county scale.

    • Evaluation Model of Earthquake-buried Personnel Based on the Regional Characteristics

      2020, 42(5):1236-1247. DOI: 10.3969/j.issn.1000-0844.2020.05.1236

      Abstract (223) HTML (0) PDF 30.95 M (772) Comment (0) Favorites

      Abstract:One of the scientific problems of earthquake emergency rescue is how to obtain the spatial distribution of buried personnel quickly and accurately using existing basic geographic data and evaluation models. This study took the Ludian MS6.5 earthquake in Yunnan Province as an example; based on the high-precision kilometer grid population data, the characteristics of the earthquake region and the various influencing factors that may lead to buried personnel were analyzed, and secondary disaster buried parameters were introduced to supplement and optimize the current personnel assessment model. Results indicated that the improved evaluation model could quickly show the distribution of buried personnel after an earthquake, and the accuracy of the model was greatly improved in comparison with previous models. Moreover, the applicability of the evaluation model was effectively enhanced by considering the buried personnel caused by secondary disasters. The improved model could provide technological support for emergency command and rescue during earthquakes.

    • Seismic Fortification Management and Risk Prevention of Construction Projects in Pudong New Area

      2020, 42(5):1248-1255. DOI: 10.3969/j.issn.1000-0844.2020.05.1248

      Abstract (220) HTML (0) PDF 6.89 M (641) Comment (0) Favorites

      Abstract:The State Council in 2005 approved the establishment of the first national comprehensive matched reform experiment zone in Pudong New Area, Shanghai. In 2013, the zone was designated as China (Shanghai) Pilot Free Trade Zone, focusing on promoting institutional innovation in areas such as investment, trade, finance, and supervision during and after processes. Therefore, it is important to ensure the seismic and disaster prevention capabilities of infrastructure such as construction projects. This paper briefly describes the seismic fortification management system of construction projects in Pudong New Area and analyzes the composition of the supervised construction projects and their general situation of seismic fortification from 2009 to 2018. The measures and practices of seismic fortification management and risk prevention are summarized. They mainly include three aspects: strengthening seismic fortification review and supervision in processes, compiling regional planning on earthquake resistance and hazardous prevention, and organizing a series of training on seismic technology and carrying out scientific awareness on protecting against and mitigating earthquake disasters. Moreover, problems in current supervision and improvement methods are presented. The seismic fortification management system and risk prevention measures in Pudong New Area introduced in this paper can serve as a reference and be adopted in other regions.

    • >结构抗震
    • Seismic Damage Composition of Rural Houses in Northwest China and Factors Influencing Their Seismic Performance

      2020, 42(5):1256-1261. DOI: 10.3969/j.issn.1000-0844.2020.05.1256

      Abstract (257) HTML (0) PDF 2.78 M (510) Comment (0) Favorites

      Abstract:This paper summarizes the seismic damage data of some earthquakes in northwest China and the earthquake damage of rural houses in northwest China. Through an analysis of the seismic damage and seismic performance of different structures of rural houses, the seismic performances of different structures were found to be significantly different. Meanwhile, we propose the corresponding aseismic measures for different structures. The seismic capacity of rural houses was analyzed from the aspects of ground-motion characteristics, site and foundation, and structural characteristics. Then according to the earthquake damage characteristics of rural houses in northwest China, some recommendations on earthquake prevention and disaster reduction are presented.

    • Dynamic Characteristic Test and Seismic Performance Analysis of Haibao Pagoda in Yinchuan City

      2020, 42(5):1262-1269. DOI: 10.3969/j.issn.1000-0844.2020.05.1262

      Abstract (267) HTML (0) PDF 6.17 M (675) Comment (0) Favorites

      Abstract:To provide a reference for the repair and protection of Haibao Pagoda in Yinchuan, the dynamic characteristics and structural damage condition of the pagoda were tested and analyzed by numerical simulation. The compressive strength and elastic modulus of the masonry of the pagoda were obtained by testing and calculating the strength of the pagoda materials. The pagoda vibration response under environmental excitation was tested, and the first-order frequencies of the pagoda in the east-west and north-south directions were obtained. A numerical model was established to analyze the vibration mode and seismic performance of the pagoda, and the dynamic characteristics and the story drift ratio of the pagoda under earthquake action were obtained. Then a damage analysis was carried out based on the displacement criterion of the failure state and the damage index of the pagoda. The results showed that the first-order frequencies of the east-west and north-south directions of the pagoda were close, but the vibration spectrum curves of different floors varied greatly, especially in the number of peak points; the higher the floor, the greater the maximum displacement and the story drift ratio, and the more serious the damage; the overall stiffness degradation of the structure was serious and there was a great potential safety hazard, which should be further analyzed and protected.

    • Research Progress in Seismic Response of Base-isolated Structures under Complex Earthquake Excitation

      2020, 42(5):1270-1275,1336. DOI: 10.3969/j.issn.1000-0844.2020.05.1270

      Abstract (254) HTML (0) PDF 2.66 M (495) Comment (0) Favorites

      Abstract:As one of the most effective structural shock absorption control technologies, seismic isolation technology is widely used in high-intensity regions in various countries. With the widespread promotion of isolation technology, isolation projects with more complicated construction conditions have emerged. The systematic study of isolated structures seismic response under complex earthquake excitation is an important guarantee for the long-term safe service of isolated projects and a solid foundation for the continuous improvement and promotion of isolation technology. First, this paper addresses the four main aspects of multi-dimensional earthquakes, including complex seismic excitation, near-field and near-fault earthquakes, traveling wave effects, and soil-structure interaction. Then, a review of relevant literature is presented to discuss existing problems in isolated structures under complex seismic excitation.

    • Seismic Response and Performance Evaluation of Asymmetric Continuous Beam Bridges in Meizoseismal Areas

      2020, 42(5):1276-1282. DOI: 10.3969/j.issn.1000-0844.2020.05.1276

      Abstract (305) HTML (0) PDF 4.22 M (504) Comment (0) Favorites

      Abstract:This study investigated the seismic performance of unequal-span continuous beam bridges in high-intensity regions. A finite-element model for dynamic analysis was established based on a typical unequal-span continuous girder bridge with a main span of (40+60+35) m on a highway, and the modal characteristics were obtained. Both the response spectrum analysis and time-history analysis methods were adopted to calculate the seismic response of the unequal-span bridge under E1 and E2 probability earthquakes. Finally, the seismic performance of the bridge was evaluated according to the bending moment-curvature curve of the pier section. The analysis results showed that the results from the dynamic time-history analysis were basically consistent with that from the response spectrum analysis. Because we assumed linear elasticity in the latter analysis but elastoplastic properties of the material in the former, the individual response values of the two methods were different under the E2 probability level. The response spectrum method is the combination of the maximum responses at the respective modes, but the dynamic time-history analysis is the combination of the structural responses induced by seismic waves at a given time; therefore, there were some errors between the calculation results in the time domain and the frequency domain, and the the calculation results in the frequency domain were conservative. The bridge was found to still work within the elastic range under the E1 and E2 probability earthquakes, which can meet the elastic design requirements.

    • Torsional Resistant Design of Plane Irregular Base-isolated Structures

      2020, 42(5):1283-1288. DOI: 10.3969/j.issn.1000-0844.2020.05.1283

      Abstract (268) HTML (0) PDF 2.85 M (437) Comment (0) Favorites

      Abstract:Considering the vibration characteristics of plane irregular structures under horizontal earthquakes, the relative position between the isolation layer stiffness center and the upper structure mass center and stiffness center is obtained by adjusting the isolation bearing position. Three different working conditions are considered. The torsional displacement ratio is used as the torsional response index of the plane irregular base-isolated structures; then the elastoplastic time-history analysis method is used to compare and analyze the torsional response index under the three considered working conditions. A torsional resistant design method is proposed for plane irregular base-isolated structures. The results show that for plane irregular structures, the torsional displacement ratio of the isolated layer should be less than 1.2; at this ratio, the stiffness center of the isolation layer and the stiffness center of the upper structure will be positioned on both sides of the mass center of the upper structure; consequently, the torsion of the upper structure can be controlled.

    • Recent Progress in Buckling-Restrained Brace Structures as Seismic Components of Buildings

      2020, 42(5):1289-1302. DOI: 10.3969/j.issn.1000-0844.2020.05.1289

      Abstract (303) HTML (0) PDF 1.41 M (852) Comment (0) Favorites

      Abstract:This paper introduces the research results of buckling-restrained braces (BRBs) in recent years in China and focuses on the research status of BRB members (core element, restraint mechanism, cohesionless layer), overall seismic performance, and design methods. Based on the review, the following is concluded: the BRB has a good development potential because of its good energy-dissipation performance; the application scope of the BRB is expanding; the structural forms are becoming more diversified; and the design methods are constantly being optimized.

    • Influence of Design Parameters on Anti-collapse Capability of High-Rise Fabricated Steel Structure Buildings

      2020, 42(5):1303-1309. DOI: 10.3969/j.issn.1000-0844.2020.05.1303

      Abstract (273) HTML (0) PDF 6.19 M (644) Comment (0) Favorites

      Abstract:In this study, the influence of design parameters on the anti-collapse capability of a high-rise prefabricated steel structure building was studied. By using ABAQUS finite element software, a low-cycle repeated loading test of the prefabricated concrete plane frame was simulated. The results showed that increasing the axial compression ratio of the frame column can improve the bearing capacity of the structure, and the bearing will decrease rapidly after the peak load is reached. Under cyclic loading, the ductility, bearing capacity, and energy consumption of the structure increased with a decrease in the beam-to-column linear stiffness ratio. With increasing beam-to-column linear stiffness ratio, the distribution uniformity of the story drift ratio worsened; moreover, because of the low-cycle repeated load, the concrete strength will greatly increase, and the energy consumption and ductility will reduce, while the structure bearing capacity will slightly increase. Increasing the axial compression ratio will greatly increase the possibility of the limit state of the structure performance under the same ground motion. A large axial compression ratio of the structure is likely to damage the seismic response performance.

    • Improved Model for Seismic Performance of Bridge Piers with Corroded Reinforcement under Hydrodynamic Pressure

      2020, 42(5):1310-1316. DOI: 10.3969/j.issn.1000-0844.2020.05.1310

      Abstract (248) HTML (0) PDF 6.76 M (639) Comment (0) Favorites

      Abstract:To clarify the seismic performance of bridge piers with corroded reinforcement under the action of hydrodynamic pressure, the mechanical properties of the piers are studied by theoretical derivation and numerical simulation. First, based on the calculation formula of plastic hinge height, a simplified calculation model of the hydrodynamic pressure of bridge piers is constructed. Then, according to the improved finite element model, the optimized calculation formula of piers with corroded reinforcement is proposed. The results show that under the hydrodynamic pressure, the steel bar corrosion and concrete damage at the pier bottom have the greatest effect on the principal compressive stress of the pier, and the reinforcement corrosions at other parts have less effect. The calculation formula of the bridge bearing capacity is corrected, which provides a theoretical basis for the calculation of similar projects.

    • Finite Element Analysis of Vibration-isolation Effect of Continuous-vibration Isolation Barriers in Rail Transit

      2020, 42(5):1317-1325. DOI: 10.3969/j.issn.1000-0844.2020.05.1317

      Abstract (304) HTML (0) PDF 12.92 M (700) Comment (0) Favorites

      Abstract:To evaluate the vibration-isolation effect of continuous barriers in rail transit systems, we used Abaqus software to analyze the isolation effect and influencing factors of open and in-filled trenches. The results showed that the vibration in front of the isolation barrier is enhanced, and the isolation effect in the back of the barrier is good. A change in the barrier parameters has little influence on the vibration strengthening effect in front of the barrier, but a change in some parameters has some influence on the vibration-isolation effect at the rear of the barrier. The vibration-isolation performance of the barrier increases with increased barrier depth, and is less affected by the barrier width. The vibration-isolation performance of rubber-plate walls is poor, and those of open trenches and concrete-slab walls are strong, with the isolation effect of the open trenches better than that of concrete-slab walls. The closer the barrier is to the roadbed, the better is the isolation effect, so we suggest that isolation barriers be installed near the subgrade when used in engineering projects.

    • >其他
    • Bibliometric Analysis of Centurial Domestic Research on the Haiyuan Earthquake in 1920

      2020, 42(5):1326-1331. DOI: 10.3969/j.issn.1000-0844.2020.05.1326

      Abstract (265) HTML (0) PDF 3.96 M (453) Comment (0) Favorites

      Abstract:The Haiyuan earthquake happened 100 years ago. On the basis of the literature and data from the CNKI database, the status and characteristics of research on the Haiyuan earthquake in China are investigated using Bicomb and Excel. This work provides references for related research and decision-making in this field. Results show that Chinese scholars have been concerned about the Haiyuan earthquake, but the total number of published papers is few. The China Earthquake Engineering Journal published the most number of papers, and the National Natural Science Foundation of China and the Earthquake Science Joint Fund have the largest number of funded documents. Additionally, the Lanzhou Institute of Seismology, the China Earthquake Administration, and the Institute of Geology, China Earthquake Administration are the main output agencies. The focus and direction of research on the Haiyuan earthquake are paleoearthquake research; formation mechanisms and movement characteristics of loess landslides; focal mechanisms; features of active fault zone; postdisaster reconstruction; and disaster relief research.

    • Current Status and Protection Plan for the Haiyuan Earthquake Relics (Ningxia Section)

      2020, 42(5):1332-1336. DOI: 10.3969/j.issn.1000-0844.2020.05.1332

      Abstract (211) HTML (0) PDF 1.08 M (526) Comment (0) Favorites

      Abstract:The year 2020 marks the 100th year since the occurrence of the Haiyuan earthquake. This massive earthquake that shocked the world not only caused great disaster and loss but also left precious earthquake relics. In this work, a statistical study of the current protection situation of the Haiyuan earthquake relics was conducted. The status and protection situation of the Ningxia section of the relics were also summarized. Moreover, the protection and development plans for Haiyuan earthquake relics were proposed and discussed. This work provides reference for the protection of the Haiyuan earthquake ruins and related earthquake relics.

    • Application of the Extension Method to the Safety Evaluation of Seismic Information Systems

      2020, 42(5):1337-1342. DOI: 10.3969/j.issn.1000-0844.2020.05.1337

      Abstract (232) HTML (0) PDF 2.46 M (371) Comment (0) Favorites

      Abstract:Seismic information systems play an important role in earthquake monitoring and forecasting, earthquake disaster risk prevention and control, and earthquake emergency response and disposal. However, there is not a complete information security evaluation system in the seismic industry, and the related studies are few. To better identify the security risks and improve the security protection ability of seismic information networks, in this study, an information system evaluation model was established by the extension method; the index weights and correlation degree were automatically calculated through a program, and the evaluation level of the system was obtained. The examples showed that the extension method can support the security evaluation of seismic information systems and the protection of the network security level and has application value. This study provides an important basis for the further optimization and adjustment of the evaluation indexes and the improvement and application of automatic evaluation software.

    • >特稿
    • Enlightenment of the Emergency Response and Disaster Prevention of the Xiahe M5.7 Earthquake, Gansu Province

      2020, 42(5):1343-1348. DOI: 10.3969/j.issn.1000-0844.2020.05.1343

      Abstract (279) HTML (0) PDF 8.49 M (647) Comment (0) Favorites

      Abstract:On October 28, 2019, an M5.7 earthquake occurred in Xiahe County, Gannan Prefecture, Gansu Province. This paper expounds the response process and work effect of the earthquake from the aspects of earthquake emergency treatment, information reporting and sharing, disaster investigation and intensity assessment, earthquake situation monitoring and trend judgment, emergency publicity and public opinion guidance, etc. The characteristics of earthquake damage were analyzed through field investigation, and the seismic intensity map was compiled, which provided the basis for disaster loss assessment, rescue, and post-disaster reconstruction. From the aspects of strengthening the management of earthquake fortification in rural areas, improving the technical services of earthquake prevention and disaster reduction, strengthening the knowledge of earthquake prevention and disaster reduction, strengthening earthquake emergency preparedness and so on, the enlightenment of earthquake resistance and disaster prevention was obtained and the corresponding suggestions were put forward.

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