2017 Vol. 23, No. 6

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SEISMOGENIC STRUCTURE OF THE Ms7.0 EARTHQUAKE ON AUGUST 8, 2017 IN JIUZHAIGOU, SICHUAN
FU Guochao, LÜ Tongyan, SUN Dongxia, XIONG Renwei
2017, 23(6): 799-809.
Abstract (215) HTML (116) PDF (3456KB)(26)
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An Ms7.0 earthquake struck Jiuzhaigou county at 9:19 pm on August 8, 2017 in Aba Prefecture of Sichuan Province. The epicenter was located in the intersection area of the Huya fault on the east boundary of the Bayan Har block and the Tazang fault on the east section of the East Kunlun fault, with complicated seismotectonic settings. This earthquake caused damages to houses and roads, and landslides collapsed. According to the data of high-resolution satellite image interpretation, the measurement data of tectonic deformation and dating data, it shows that the east section of the Tazang fault has been dominated by left-lateral strike-slip accompanied with thrust faulting; the horizontal sliding rate is about 2.7~4.1 mm/yr, and the vertical sliding rate is about 0.56~0.6 mm/yr. Combined with the distribution of major earthquake and aftershocks and the results of major earthquake source mechanism solution, a three-dimensional seismic structure model is established. The analysis reveals that this earthquake belongs to strike-slip earthquake with the main rupture angle of 57°~77°. It was caused by the eastward push of the Qinghai-Tibet Plateau mass, and the seismogenic fault may be a branch of the Tazang fault. According to the study of historical earthquakes, active faults and deformation observation, the Bayan Kala block has significant strong earthquake tectonic background, and it is necessary to continue to pay attention to the seismic activity and deformation of the boundary of the block.
STUDY ON PALEO-TECTONIC AND PRESENT TECTONIC STRESS IN CHANG 7 TIGHT RESERVOIR OF MALING OILFIELD, ORDOS BASIN
ZHAO Jiyong, ZHOU Xingui, LEI Qihong, ZHAO Guoxi, HE You'an, SHI Jianchao, ZHANG Linyan
2017, 23(6): 810-820.
Abstract (252) HTML (110) PDF (1279KB)(17)
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Tectonic stress is one of the controlling factors of hydrocarbon migration and accumulation. The study of stress state on paleo-tectonic and present tectonic is of great significance to the exploration and development of oil and gas. Temperature measurement of fluid inclusion, paleomagnetic fracture orientation, acoustic emission method, microseismic monitoring, rock compression experiment and hydraulic fracturing method are applied respectively to the study of paleo-tectonic and present tectonic stress in the Chang 7 tight reservoir of Maling oilfield in Ordos Basin. The results show that the crucial period of fracture formation in the Chang 7 tight reservoir is the Ⅳ stage of the Yanshan movement, with the horizontal maximum principal stress direction of 84° and effective stress 44 MPa, while the current horizontal maximum principal stress direction is 76° and the current effective stress of minimum principal stress is 15 MPa.
NUMERICAL SIMULATION RESEARCH OF DEFORMATION AND FRACTURE OF THE FORMATION NEAR THE WELLBORE DURING THE HEAT INJECTION EXPLOITATION OF NATURAL GAS HYDRATES
ZHAI Cheng, SUN Keming, XIN Liwei, WANG Tingting
2017, 23(6): 821-828.
Abstract (132) HTML (111) PDF (1342KB)(18)
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In order to study the variational law of mechanical property and the deformation and fracture law of the formation near the wellbore of hydrate bearing sediments under the heat injection exploitation condition of Natural Gas Hydrates which exist in the marine strata, basing on the multi-field coupling theory and taking into consideration the influence of excess pore pressure which is generated by water and methanegas of hydrates thermal dissociation on the effective stress of the stratum, the elastic-plastic model of thermo-hydro-mechanical coupled is established which can reflect the coupling effect relationship of temperature field, seepage field and deformation field under the heat injection decomposition condition of Natural Gas Hydrates.Then the subroutine is programmed in the Fortran language environment and the numerical simulation is carried out by the software of ABAQUS. The test results show that the degradation area of mechanical property and the decreasing extent of the effective stress are increased with the heat injection temperature. The higher the temperature, the greater the value of the plastic zone scope and the equivalent plastic strain.The minimum effective stress and the maximum equivalent plastic strain and the maximum volumetric strain in the direction of the minimal horizontal stress are in the position of wellhead. It is the key position where deformation and failure generate firstly. The effective stress value in the same wellhead location decreases with the increase of heat injection temperature; however, the volumetric strain increases with the increase of heat injection temperature.
MICROSCOPIC PORE CHARACTERISTICS AND INFLUENCE FACTORS ANALYSIS OF SHALES IN PERMIAN, YANLONG AREA, SOUTHERN NORTH CHINA BASIN
CHEN Jing, WU Wei, WANG Juan, HUANG Xuefeng
2017, 23(6): 829-837.
Abstract (150) HTML (87) PDF (3782KB)(10)
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Using argon ion polishing and field emission environmental scanning electron microscopy imaging testing technique, the interactive marine-continental facies and continental facies shale samples from Permian drilled in ZK1614 well in Yanlong area of southern North China Basin are scanned, and the SE and BSE information are obtained as well. Combining X-ray spectrum information with gray level recognition function of JMicroVision software, qualitative analysis and quantitative representation of the mineral composition and the characteristics of micro pores of shale samples are made, and the genesis of pore system are discussed. The research shows that the pores of shale samples are mainly inorganic mineral pores, and the pore types include intragranular pores, intergranular pores, and a small amount of organic matter pores and micro fissures. The surface porosities of samples from Permian are between 0.92%~5.53%, and surface porosities are positively correlated with the number of pores in general. With different sizes of pores, there is a two-segment linear relationship between the logarithmic index of pore area and the logarithmic index of pore number of unit area in different pore diameter interval between 50~2000 nm, and when the pore diameter is small, they are negatively correlated, when the pore diameter is large, they are positively correlated. Different minerals result in different control effects on the development of pores.Brittle minerals mainly influence the development of micro fissures and inhibit the development of pores; clay minerals, due to the actions of tectonic stress, phase transformation and dehydration of minerals, result in plenty of pores, which promote the development of pores. Besides, the differential expansion and differential dissolution of minerals could also produce pores. During the Yanshan and the Himalayan periods, large scale fractures were formed in the study area. The development of fractures increased the penetrability of the roc kstratum, which promoted the dissolution of minerals by organic acids and formation water, and it also promoted the development of pores correspondingly. Moreover, with the increase of burial depth, the pore volume decreased with the increase of compaction.
THE CHARACTERISTICS OF SHALE RESERVOIR FROM QIONGZHUSI FORMATION IN LOWER CAMBRIAN IN QUJING AREA, EASTERN YUNNAN PROVINCE, CHINA:A CASE STUDY OF WELL QUYE NO.1
BAI Minggang, ZHANG Cong, YANG Yuru, DAI Feng, XIONG Jie
2017, 23(6): 838-845.
Abstract (249) HTML (213) PDF (1712KB)(19)
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Shale from Qiongzhusi formation in Lower Cambrian is one of the most important focuses in shale gas exploration and development in South China; however, the black shale reservoir from Qiongzhusi formation in Lower Cambrian in eastern Yunnan province stays in a low level of study. Take Well Quye No.1 drilled in 2014 as an example, on the black shales from Qiongzhusi formation in Lower Cambrian, X-ray diffraction analysis of the whole rock and clay minerals are made; tests and SEM experiments like TOC, physical property and specific surface area are conducted; the characteristics and types of shale reservoir are analyzed comprehensively. The results show that shales are mainly composed of quartz (44.75%), clay minerals(25.47%)and feldspar (16.44%), consisting of three major pore types, which are intergranular pore, intragranular pore and organic-matter pore. It is worth mentioning that organic-matter pores are abundant and of great importance, in which mesopores are the main force with a certain potential of shale gas exploration and development. The volumes of pores decrease with the depth, and with increasing TOC, micropore volumes relatively increase. The porosity is mainly restricted by the organic-matter content and the development degree.
CONCENTRATION AND SOURCES OF BLACK CARBON IN DIFFERENT FUNCTION ZONES OF BEIJING, CHINA
YANG Shuaibin, LIU Lian
2017, 23(6): 846-855.
Abstract (177) HTML (121) PDF (1796KB)(12)
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With the rapid development of city, soil properties in city have changed significantly with significant differences among different function zones. In order to discuss the impact on the soil carbon pool (especially black carbon), from human activities of different ways and at different degrees as well as pollution from different sources, the concentration of black carbon (BC) and organic carbon (SOC), and concentration ratio (BC/SOC) of surface soil in different function zones (parks, residential areas and road green belt) in urban and suburban areas in Beijing are compared in the study, and the influence of human activities of different ways and at different degrees on soil are discussed based on the BC/SOC index. The results show that the enrichment degrees of soil SOC in different function zones in urban areas are different, and the concentration of SOC in soil in parks and residential areas under human management tend to be average; in suburban areas, the concentration of SOC in different function zones are close and much the same as the natural soil, indicating the soil is less influenced by human activities. There are significant differences in the concentration of BC values in soil in different function zones of urban areas, and the descending order is parks (0.60%~2.28%, mean 1.56%), road green belts (0.12%~2.20%, mean 0.62%), residential areas (0.11%~1.15%, mean 0.35%).The regional digging, planting and fertilization made a large number of BC gather in parks and road green belts are strongly impacted by traffic discharge; in suburban areas, the concentration of BC of different function zones are low and close to each other, representing the background concentration of BC in regional soil. The BC/SOC values in soil mainly fall in between 0.11% and 0.5%, and BC/SOC values in suburban area are smaller than that of urban areas, indicating that the burning of fossil fuels and biomass are both sources of BC in soil in the urban and suburban areas but with different proportions, and the urban area is an important source of BC in the suburban area. In addition, BC/SOC values in some places of urban areas are significantly higher, reflecting that BC/SOC value not only indicates the degree of soil pollution but also is closely related to urbanization progress and specific human activities.
A NEW GEOLOGICAL SECTION MEASURING AND MAPPING METHOD:POINT COORDINATES METHOD
WANG Ran, MA Licheng, SUN Yong, ZHANG Shenglong, JIA Zhiming
2017, 23(6): 856-863.
Abstract (220) HTML (232) PDF (1728KB)(13)
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Geological section measuring and mapping is a necessary task for regional geological survey; however, the traditional geological section measurement, which is based on tapeline together with compass, has many limitations such as visual conditions, tapeline bending, manual measurement error and second projection defects. In order to improve the quality and efficiency of geological section measurement, on the basis of the previous methods, through the practice of a number of different types of geological survey projects, a new geological section measuring and mapping method using point coordinates is presented in this paper. The key points of the method include (1) Using GPS to obtain terrain control points, as well as three-dimensional coordinates in stratification, sampling, production, occurrence and other positions. (2) A series of formulas are developed, based on which parameters like horizontal distance between points, altitude difference, azimuth angle and slope angle can be calculated according to three-dimensional space coordinates of each point in order to do the mapping. The point coordinates method has two main advantages:(1) Digitization of measurement data is realized by the change from manual measurement to automatic measurement, and there is no need for tape line. (2) The facts that the end point of the tapeline does not coincide with the actual end point can be avoided. (3) It is convenient for field review because each layering point has a GPS coordinate.The case and practice have proved that the point coordinates method is superior to the tapeline method. It is worthy of being widely used in practical application.
CHARACTERISTICS ANALYSIS OF QUATERNARY AND NEOTECTONIC MOVEMENTS FROM SONGPAN SECTION, MINJIANG UPPER REACHES, WESTERN SICHUAN
HAN Jian'en, GUO Changbao, WU Ruian, Ren Sanshao, XU Biao, Yang Zhihua
2017, 23(6): 864-881.
Abstract (289) HTML (121) PDF (2791KB)(28)
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The Songpan section of the Minjiang River mainly refers to the section from the source of the Minjiang River to Zhenjiangguan, which is located in the transition zone of the eastern margin of Qinghai-Tibetan Plateau and Sichuan Basin, belonging to the source area of the Minjiang River. With complex topography and geomorphology, strong neotectonic movements, development of Quaternary strata, various landform types, and frequently occurred and large magnitude earthquakes, the study area is an ideal for studing the tectonic movements of Minjiang River fault zone since the late Cenozoic era. Based on the previous research, through field geological survey and profile measurement, the study focuses on the geomorphological characteristics of Zhangla Basin and Doujitai Basin, the characteristics of Quaternary sediments like types, material composition and distribution, the river terrace features of the main stream and tributaries of the Minjiang River in Songpan section are systematically measured and studied. It shows that the neotectonic movements had a controlling influence on the evolution process of the topography and geomorphology of the Quaternary Basin in Songpan section; Zhangla Basin and Doujitai Basin formed during late Miocene and early Pliocene, with an east-inclined normal fault at the west basin-controlling fault and a west-inclined reverse fault at the east. The basins formed in the process of "seesaw type" block movements with east up and west down, and we named them the "seesaw type" dustpan-like basins.Broad valley and narrow valley are alternately distributed in the Songpan section of the Minjiang valley; many lacustrine strata developed in the main stream and its tributaries, with dammed lakes as the sedimentary feature.6 grade river terraces, which mainly are eroded terraces and accumulation terraces, formed during the late Pleistocene to Holocene epoch, are the main type in the Songjiang section of the upper reaches of the Minjiang River. The terrace series has the characteristics of segmentation, and the width of terraces are different in different areas, which are obviously controlled by neotectonic movements. The neotectonic movements in the upper reaches of the Minjiang River shows the characteristics that the movements in N-S direction lie in narrow belt while those in E-W direction are different in tilt-lift, which means the upper reaches of Hongqiaoguan is overall a tectonic uplift area, with at least 3 times of tectonic uplift; the tectonic uplift intensity in Doujitai Basin is stronger than that in Zhangla Basin. There might be 6 times of tectonic uplifts in Gami temple area, and the tectonic uplift intensity in Hongqiaoguan area is much stronger than that in Zhangla Basin.
BROADBAND GROUND MOTION SIMULATION IN TIANSHUI BASIN BASED ON A HYBRID METHOD
FU Changhua, WU Jian, GUO Xiangyun, HU Gang, WANG Tao, LIU Jiamei
2017, 23(6): 882-892.
Abstract (193) HTML (127) PDF (2630KB)(12)
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Taking Lixian-Luojiabao fault as a causative fault of an Mw 7.7 scenario earthquake, a hybrid numerical method combining finite difference method with random vibration synthesis method is adopted to simulate broadband ground motion field in Tianshui basin, and the ground motion characteristics in the basin are analyzed, providing ground motion parameters for analyzing seismic loess landslides. The following conclusions are acquired:(1)Finite difference method and random vibration synthesis method are complementary to get broadband ground motion in the basin. (2)The scenario earthquake causes intensive ground motion in the basin, with PGA (peak ground acceleration) of 150~900 gal. The largest PGA is located in the southeastern corner of the basin where is nearest to causative fault, and it decreases with the distance from causative fault. Compared to the north side of river valley, the south side has larger PGA to induce landslides. (3)The largest PGV is 120cm/s in the basin. Affected by Quaternary covering layer amplification effect and terrain amplification effect, PGV in the east and the central parts of the basin are larger than those in the west part. (4)The vertical ground motion shows smaller PGV in the east part of the basin but larger ones in the west and central parts. Especially at the western most steep mountains, PGV reaches the maximum. In addition, the vertical ground motion can also reflect the influence of loess layer, for example, the PGV is also larger in the central part of the south side of the basin.
IN-SITU STRESS MEASUREMENT AND STABILITY ANALYSIS OF SURROUNDING ROCKS IN THE NORTH SECTION OF DEEP BURIED TUNNEL IN MUZHAILING
ZHANG Peng, SUN Zhiguo, WANG Qiuning, FENG Chengjun, SUN Mingqian, TAN Chengxuan, WU Yongdong, GAN Weiping
2017, 23(6): 893-903.
Abstract (554) HTML (305) PDF (2080KB)(28)
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In order to conclude present ground in-situ stress distribution characteristics, data are gathered from active fault investigation and three drilling boreholes for in-situ stress measurement located in the north section of the Muzhailing tunnel engineering area along the Lanzhou-Chongqing railway. Combined with the high in-situ data of SH > Sh > Sv, the core sampling of the structure features of shallow earth crust rock formation reveals that current horizontal principal stress plays a leading role in reverse fault activity. Moreover, measured maximum principal in-situ stress strikes in NE direction and reflects present compressive properties, with sinistral slip activity, of the north segment. Based on the data of crustal stress and the interrelated theories as well as criterions, it is concluded that the favorite shape of the cross-section of the tunnel are ellipses with horizontal long axis, vertical short axis and long to short axis ration as lateral pressure coefficient; when the north section of the tunnel are excavated, the hard rock has the possibility of rock burst, and the soft rock has the background of its occurrence and serious extrusion deformation. The results provide a basis for studying the characteristics of stress field in tunnel area, analyzing the stability of tunnel surrounding rock and designing engineering geological problems such as shape, structure and strength of tunnel section.
ANALYSIS ON THE CHANGE OF INFLUENCE FACTORS ON SLIPPING DISPLACEMENT OF LANDSLIDES IN DUJIANGYAN AREA BEFORE AND AFTER THE WENCHUAN EARTHQUAKE
MENG Huajun, JIANG Yuanjun, ZHANG Shuxuan, ZHANG Xiangying, LI Huanbin, ZHAO Weikang
2017, 23(6): 904-913.
Abstract (259) HTML (92) PDF (6558KB)(17)
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Slipping displacement of landslide is one of the most important assessment indexes for prevention and mitigation of landslide disaster, which is not only controlled by landslide volume and drop but also related to the influence of topographical environment.On the basis of detailed field investigation and inventory for 51 seismic-induced landslides and 16 rainfall-induced landslides seated in Dujiangyan area, the correlation between six factors and horizontal slipping displacement of landslides are analyzed through mathematical statistic method, factors including depositional gradient of slope, ridge height difference before and after the earthquake, plane shape, volume, and average thickness of landslide mass and friction coefficient of slope surface. Afterwards, the influence of different factors on different types of landslides before and after Wenchuan earthquake are sort out, and the predictive formulas of slipping displacement due to different causes are built which may support the disaster mitigation in the future. The preliminary conclusions reveal that slipping displacements of seismic-induced landslides are mainly affected by landslide volume(lgV), depositional gradient of slope(α), plane shape(R) and ridge height difference before and after the earthquake(ΔH); while rainfall-induced landslides are mainly affected by ridge height difference before and after the earthquake(ΔH), landslide volume(lgV), depositional gradient of slope(α) and friction coefficient of slope surface(μ). After the Wenchuan earthquake, the factors affecting the sliding of rainfall-induced landslides are changing with a relatively low correlation with slipping displacement, showing that their influence are decreasing and only landslide volume(lgV) still stays a strong correlation.
STUDY ON 26Al EXPOSURE DATING OF FENG'ANSHAN LANDSLIDE IN THE MIDDLE REACHES OF BAILONG RIVER
SHU Jie, BAI Shibiao, CUI Yu, CHEN Qian, ZHANG Zhigang, WANG Jian
2017, 23(6): 914-922.
Abstract (213) HTML (131) PDF (1930KB)(11)
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Knowledge about the formation age and reactivation times of paleo-landslide are critical for landslide hazard assessment and management. With the development of AMS technology, cosmogenic nuclide dating method has been effectively applied in determining the formation age of paleo-landslide. In this study, the Feng'anshan landslide, which is located at the middle reaches of Bailong River in Southeast Gansu Province, was taken as the study target. Two rock samples, Fas-2 and Fas-1, were obtained from the landslide scarp and a block below the scarp respectively. Considering the masking factors and erosion rate of the sampling site, we calculated the 26Al age of the landslide by using the method of 26Al exposure dating with the cosmic nuclide. The main conclusions are as follows:(1) Two landslide events occurred at about 0.72~0.75 ka and 2.26~2.65 ka respectively. The latter formation age corresponds to the documented year of 186 BC in historical descriptions, when earthquakes induced the landslide. (2) The erosion rate has more impact on the dating results of samples with old ages.
STUDY ON SHEAR CREEP BEHAVIOR OF MUDSTONE AND ITS CORRECTION MODEL OF GANGU FISSURE IN GANSU
WU Lizhou, LI Bu, SUN Ping
2017, 23(6): 923-934.
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Rock shows typical creep property under long-term load, and the mechanical property of fractured mudstone are different from that of intact rock under long-term load. The shear creep test was carried out on the fractured mudstone from the drilled core at Gangu Zhaojiayao landslide in Gansu province, with investigation on the influence of axial compressive stress and the length of prefabricated cracks on the shear creep characteristics of samples. The experimental results show that axial load and crack length have obvious influence on the shear creep characteristics of the samples. The larger the axial compressive stress is, the less the shear creep deformation is. The longer the crack is, the more obvious the shear creep deformation is. When the stress is low, the creep model such as Cvisc model can better reflect the creep mechanical properties of the mudstone; however, in the accelerated creep stage, most of the models can not accurately reflect the nonlinear change of creep curves of the mudstone. The improved Nishihara (K-B) model with less model parameters overcomes the shortcoming that the traditional model cannot describe the nonlinear creep curves, and it can be better applied to engineering soft rock. In the process of shear creep of argillaceous soft rock samples under different loads, the formation of shear failure zone of fractured mudstone is characterized by the combination of gradual and sudden failure. The shear creep mechanical model of mudstone can explain many phenomena of mudstone landslide. The shear creep of the argillaceous soft rock in the potential slip zone of the slope is the intrinsic cause of the landslide.
DYNAMIC DAMPING CHARACTERISTICS AND EVOLUTION LAW OF PAN'AN STRUCTURAL LOESS
MU Huandong, SUN Ping, LI Rongjian, ZHU Sizhen
2017, 23(6): 935-942.
Abstract (189) HTML (80) PDF (2014KB)(11)
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Seismic action often leads to the decay of dynamic strength of structural loess and a series of geological disasters such as loess landslide and depression, and attenuation of intensity is closely related to its damping characteristics, which makes dynamic damping characteristics of structural loess and its evolution law one of the important research topics of geotechnical engineering. In this article, the dynamic characteristics of undisturbed loess and remolded loess under natural and saturated conditions were studied. On the basis of experiments, the dynamic modulus, dynamic damping response characteristics and evolution law of loess are analyzed and compared. The results show that:(1) The dynamic stress of the original loess and remolded loess increases with the increase of the dynamic strain, while the dynamic modulus decreases with the increase of the dynamic strain, and the dynamic damping ratio increases with the increase of the dynamic strain; (2)Affected by structural properties of loess, the undisturbed loess is slightly larger than that of the remolded loess, and the maximum modulus of the undisturbed loess and remolded loess are slightly larger than that of saturated undisturbed loess and saturated remolded loess. The influence of the surrounding pressure on the damping ratio needs to be considered when the loess structure is strong, and the effect of the surrounding pressure on the damping ratio can be neglected by the saturated remolded loess.