Table of Content

06 September 2000, Volume 22 Issue 3

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Brief Report

AN ATTEMPT TO STUDY FAULT ACTIVITY USING REMOTE SENSING TECHNOLOGY-A CASE OF THE MANI EARTHQUAKE

Ma Jin, Shan Xinjian

2000, 22(3):  210-215. 

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On the basis of previous studies of other researchers, we propose a new approach to detect present-day activities of faults using remote sensing. We have studied the dynamic changes of ground temperature around the epicenter before and after the Mani M_S7.9 earthquake of 1997. It is found that an anomalous increase of ground temperature occurred at the east section of the of Altyn Tagh fault 20 days before the event. Then this anomalous area expanded gradually, formed a remarkable belt which remained till the occurrence of the M_S7.9 earthquake. After the event this belt of anomaly was fading away, while such an anomaly appeared on the seismogenic fault-the Margaichace fault as late as two days before the Mani M_S7.9 event. The evolution process of the image shows that there is some corresponding relationship between the Mani earthquake and evident activity of the Altyn Tagh fault. It also indicates the interaction between the two faults mentioned above as well as the close relation among the deformation anomaly, present-day fault activity and earthquakes. In addition, we propose improvement of the technique for the requirement of the study on present-day activity and interaction of faults.

EARTHQUAKES OF THE LONGYANGXIA RESERVOIR

Zhang Min, Zhang Qisheng

2000, 22(3):  216-218. 

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DIVISION AND MOTION STATUS OF BLOCKS FOR THE NORTHEASTERN TIBETAN PLATEAU IN LATE QUATERNARY

Guo Shunmin, Jiang Zaisen, Zhang Chongli

2000, 22(3):  219-231. 

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Based on the crustal depth, gravity-magnetic feature, active faults in late-Quaternary, geomorphic variance, fault-depression basins and the difference of seismicity, the studied region is divided into first and second grade blocks. There are 7 first grade blocks and 33 second grade blocks. The shapes of the first grade blocks are mostly elongate in plane and trapezoid or up-down trapezoid in the section, and some are polygon or triangle. The shapes of the second blocks are mostly rhombus, thrust-type in the section, and some are elongate or triangle. The main motion types include:horizontal thrusting, vertical lifting or depressing, and flow-extending and rotation. The block motion is controlled by the mechanism of crust "contract-escaping-rotation". That is, when the crust block is exerted by extruding stress, the intense contraction happens. Then the crustal block lifts and escapes towards the east. The block rotation appears in the process. The result is of great importance for "high resolution observation of geo-deformation and earthquake prediction".

DEFORMATION CHARACTERISTICS AND DISPLACEMENT AMOUNT OF THE LIANGSHAN ACTIVE FAULT ZONE IN LATE CENOZOIC ERA

Shen Xuhui, Chen Zhengwei, Xu Rende, Zhang Ning

2000, 22(3):  232-238. 

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The Liangshan active fault zone, trending nearly from north to south, lies at the southeast margin of the Qinghai Tibet Plateau, the east side of Xianshuihe-Anninghe-Zemuhe-Xiaojiang fault zone. It consists of 3 right-separation segments from north to south:the Puxionghe fault, the Butuo fault and the Sikai-Jiaojihe fault. Geological mapping indicates that the fault zone motion is dominated by left-lateral slip in Late Cenozoic Era, and the total amount of displadment is 13.5～15.5km. In late Quaternary, the Liangshan fault zone offset a series of geological and geomorphological bodies and the average left-lateral slip rate is about 2mm/a.

CHARACTER OF RUPTURE SEGMENTATION OF THE XIANSHUIHE-ANNINGHE-ZEMUHE FAULT ZONE, WESTERN SICHUAN

Wen Xueze

2000, 22(3):  239-249. 

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Based on several types of data, segmentation and its cause, earthquake ruptures along the Xianshuihe-Anninghe-Zemuhe fault zone in western Sichuan are analyzed from various aspects. The fault zone is divided into 12 rupture-segments for characteristic earthquakes. Along this fault zone, the persistent and non-persistent boundaries of ruptures have almost the same number ratio of 2%. The persistent and important boundaries can be identified by criteria such as geometry, structure and active behavior of faults. They terminate the propagation of earthquake ruptures by partly volume-changing there. The non-persistent boundaries can be identified by criteria such as extension and recurrence behavior of earthquake ruptures, spatial difference of current active behavior of faults, composition of both relatively small-scale geometric barriers and release barriers. Locations of the non-persistent boundaries may vary with time. Relatively small overlap occurs between adjacent ruptures if the time interval between them is shorter, and relatively large overlap appears between adjacent ruptures if the time interval between them is longer.

A PRELIMINARY STUDY ON THE PREHEATING OF THERMOLUMINESCENCE DATING FOR PLAGIOCLASE

Yin Gongming, Li Shenghua

2000, 22(3):  250-252. 

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ACTIVE BLOCK DIVISION AND PRESENT-DAY MOTION FEATURES OF THE SOUTH REGION OF SICHUAN-YUNNAN PROVINCE

Xiang Hongfa, Guo Shunmin, Xu Xiwei, Zhang Wanxia, Dong Xingquan

2000, 22(3):  253-264. 

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Based on new data and studies on active blocks in recent years, we propose the principle, evidence and method for division of active blocks of the south region of Sichuan Yunnan Province. It is suggested that the Quaternary active faults which have major scales and have been active till present are the necessary and primary boundary conditions for block division. The newly formed Tengchong-Jinghong NNW zone and Dali-Chuxiong NWW zone have an important role in the block division. In the light of the nature of faults, motion modes, and GPS data the present-day active mode of each block is analyzed. It is concluded that earthquakes of M 7 or greater occur on the first class boundaries of active blocks, events of M6～M7 on the second class boundaries, and the active blocks of secondary class are the main locations of major earthquakes.

CHRONOLOGICAL RESEARCH OF GEOMORPHIC SURFACE OF LOWER TERRACES ALONG SEVERAL MAJOR RIVERS IN THE EAST AND WEST OF YUNNAN PROVINCE

Ji Fengju, Zheng Rongzhang, Li Jianping, Yin Jinhui

2000, 22(3):  265-276. 

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Based on the research on the applicability of TL dating and reliability of data for underwater sediments, the systematical sampling and synthetic dating with different methods have been made on the lower terraces along several major rivers in the east and west of Yunnan Province.The deposited ages of sediments and the formation times of the geomorphic surfaces of these lower terraces heve been obtained along these rivers.The sediments on the first terraces for I-grade tributaries deposited in 4500～11000a B.P. and their terrace surfaces formed during 4500～5000a B.P. The second is in 9000～22000a B.P. and their terrace surfaces formed during 9000～10000a B.P. The sediments on the first terraces of major rivers deposited in 9000～17000a B.P.and the terrace surfaces formed during 9000～10000a B.P. The second is in 15000～45000a B.P. and the terrrace surfaces formed in 15000a B.P. At the same time, the cause of formation of the lower terrace surfaces is studied for this area according to the analyses of ancient climate and environment during the sediment deposition.

CHARACTERISTICS AND FORMATION MECHANISM OF THE LONGLING-LANCANG NEWLY EMERGING FAULT ZONE IN QUATERNARY IN THE SOUTHWEST YUNNAN

Guo Shunmin, Xiang Hongfa, Xu Xiwei, Zhang Wanxia, Zhou Ruiqi, Dong Xingquan

2000, 22(3):  277-284. 

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The Longling-Lancang fault zone is a newly emerging fault zone, which is composed of multisecondary faults, distributed in the obligate or clustered types, and characterized by the zoning of active faults, earthquake faults and earthquakes. Its kinematic feature is dextral extensive and the formation epoch is early-middle Pleistocene. It is still active in the later period. The rupture in the future tends to cut across the tectonically-blocked segment, discontinuous segment of the fault and then through the whole fault zone. The formation of the nealy emerging fault zone has close relation with the uplift of the Qingzang Plateau. The composite action by the material fluid from the north to the south and the intrusion of Asamu block towards northeast makes the Dianmian block to rotate in a counter-clock wise direction and forms a new dextral shear, NNW-trending fault zone in the central area of the block.

RECENT ACTIVITY OF MINJIANG FAULT ZONE, UPLIFT OF MINSHAN BLOCK AND THEIR RELATIONSHIP WITH SEISMICITY OF SICHUAN

Zhou Rongjun, Pu Xiaohong, He Yulin, Li Xiaogang, Ge Tianyong

2000, 22(3):  285-294. 

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Located at the mid-section of the north-south seismic zone in China, the Minshan block was resulted from the reverse and over-thrust movement of the Minjiang fault and the Huya fault from west to east. Under the background of a regional main compressive stress field with NWW direction, the Minjiang fault shows an obvious reverse and overthrust movement with some sinistrogynic slip components, while the Minshan block has strongly uplifted since Quaternary. The aerial photo interpretation and field survery on geology and seismology indicate that the Mingjiang blook is composed of several secondary faults with echelon pattern, among them, the row distance of Gamisi Chuanpan dextral echelon part is 3 km, which perhaps controls the secondary seismic rupture unit. Research by the geological landform formation history and rupture landform shows that the average vertical slip rate of the Minjiang fault is 0.37～0.53 mm/a, the horizontal slip amount is similar to the vertical slip amount since late Quaternary, the average lift rate of Minshan Block is 1.5 mm/a since Quaternary. It is suggested that M≥6.0 earthquakes occurred mainly on the border faults of the strong blocks, while middle and small earthquakes often took place on the faults with nearly east-west direction and new tectonic lift, which are associated with the active features of these faults.

MESOZOIC-CENOZOIC STRUCTURAL CHARACTERISTICS AND SEISMICITY OF THE DEPRESSIONS ON THE SOUTH AND NORTH SIDES OF THE TIANSHAN MOUNTAIN

Zhao Ruibin, Yang Zhu'en, Zhou Weixin, Guo Fang

2000, 22(3):  295-304. 

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Formed in Mesozoic-Cenozoic time, the Kuche depression on the south side of Tianshan and the Urumqi depression on the north side of Tianshan demonstrate striking similarities in geometry, kinematics and dynamics. However, the seismic activities, especially middle and large earthquakes show evident differences between the two depressions. This paper analyses the primary factors that cause the differences. They include: 1. the difference in deformation extent between the two depressions; 2. the difference in fine structure of gophysics between the two depressions; 3. the difference in the environment of geodynamics between the two depressions.

LATE QUATERNARY ACTIVITY OF JINGHE-ALASHANKOU SECTION OF THE BOLUOKENU FAULT,INTERIOR TIANSHAN

Yang Xiaoping, Shen Jun

2000, 22(3):  305-315. 

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The Boluokenu fault is the boundary between the north and middle Tianshan, and has many periods of activity. Microgeomorphology related to fault activity, gully right-lateral displacement, fault scarp, pull apart basin occur along the fault in the southeast of Jinghe county town to Alashankou. Large gullies on the alluvial-pluvial fan are cut by the Boluokenu fault, the largest right-lateral displacement is about 500m, and its average is 400m. Some small gullies which only developed on the fault scarp have been cut by the fault. Its right lateral displacement can be divided into four groups in displacement values, i.e. 2.4～4.0m, 5.7m, 8.3m and 15.3m. The height of the fault scarp can be divided into three groups of which the value is 1.2m, 2.51m and 3.63m, respectively. In the southwest of Alashankou, right-lateral displacement for small gullies is 1～1.7m. The heights of the fault scarp on deferent geomorphic surface are 0.55m and 1.2～1.5m. All these didplacement values may indicate that the horizontal and vertical displacement of characteristic earthquakes on the segment is 3m and 1.2m, respectively. The age of the alluvial-pluvial fan in southeast Jinghe is about 70 ka old by geomorphic dating, and the right-lateral slip rate is 4.7mm/a.

CORRECTION METHOD FOR AXIAL STRESS IN THE TRIAXIAL FRICTION EXPERIMENT

Huang Jianguo, Zhang Liu

2000, 22(3):  316-317. 

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A STUDY ON THE RELATION BETWEEN DEFORMATION OF RIVER TERRACES AND NEOTECTONIC ACTIVITY FOR THE WUWEI BASIN

Zheng Wentao, Yang Jingchun, Duan Fengjun

2000, 22(3):  318-328. 

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We have studied the relation between the deformation of river terraces and neotectonics activity based on the data of measurement and dating ages of seven fluvial terraces in the Wuwei basin. The deformation characteristics of river terraces reflect the manner of neotectonic activity. The dislocation status of river terraces shows active times, active extents and active intensity of active fault, and the characteristic with migration variations of the most active area in different times. The three Quaternary faults developed since the late Pleistocene epoch in the Wuwei basin and have five periods of activity at least. The active intensity is different for these faults,among which the piedmont fracture activity is the most intensive, and its movement does not stop till present. The activity was stronger about the time 60 ka B.P. in the west and since the time 20 ka B P. in the east.

DISCOVERY AND PRELIMINARY STUDY OF THE LAOLONGWAN TERTIARY PULL-APART BASIN IN THE HAIYUAN FAULT ZONE

Tian Qinjian, Shen Xuhui, Ding Guoyu, Chen Zhengwei, Wei Kaibo, Xing Chenqi, Chai Zhizhang

2000, 22(3):  329-336. 

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A Tertiary pull-apart basin named Laolongwan basin was found in the Haiyuan fault zone. Through interpretation of the satellite image and observations of stratigraphic profiles in the field, stratigraphic sequence, sediment distribution and character of relevant faults in the basin are studied. The Laolongwan basin developed at the largest step area in the Haiyuan fault zone, and the deposition in the Laolongwan basin is bounded by faults. The total thickness of deposition in the basin is about 4600m including boulder rock, gravel-sand rock and sand-mud rock, and breccia rock from the bottom to the top. Strata in the basin discordant contact with various strata outside the basin. Comparing stratigraphic sequence in the basin with regional Tertiary stratigraphical timetable, it is suggested that the Laolongwan basin started in the middle Miocene. Thus, based on above characters, the Laolongwan basin is identified as a Tertiary pull-apart basin in the Haiyuan fault zone. The Laolongwan pull-apart basin provides geological evidence of strike slipping on the northeast edge of Tibet in Tertiary time.