Table of Content

04 December 1991, Volume 13 Issue 4

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Brief Report

LONGITUDINAL STREAM-PROFILES AS INDICATORS FOR GEOMETRIC SEGMENTATION OF THE LANGSHAN-HUANGBAISI FAULT ZONE, NORTHWEST BEIJING

Cheng Shao-ping, Yang Gui-zhi, Yang Zhe

1991, 13(4):  289-305. 

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The Langshan-Huangbaisi fault zone in northwest Beijing is the southwestern part of the normal fault zone on the northern margin of the Yanqing basin, 35.5km long and NNE-NEE-trending in general, on which two major 130?- 140? bends separate it into three segments with different strikes.Using the Hack's method, 71 longitudinal stream-profiles along the fault zone are analysed, shawing a well geomorphic response to the fault geometry. On these two major bends the gradient indices,K values, are relatively high. These three segments greatly differ in K value.Longitudinal stream-profiles are good tectonic-geomorphic indicators for geometric Segmentation of normal faults and will prqvide insight into segmented kinematics and paleoseismology.

GENETIC ANALYSIS OF ANOMALOUS VARIATION OF WATER TABLE IN CHANGPING WELL, BEIJING

Yang Hui-nian

1991, 13(4):  306-316. 

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Field investigation on hydrogeological environment around Changping well reveals that the anomalous uprise of 'water table begining from Oct. 1988 was mainly caused by the leakage of water from the channel leading to Shisanling Reservoir, but not the precursor of Datong-Yanggao earthquake in Shanxi Province in 1989.

STRUCTURAL STRIATION ANALYSIS AND INVERSION OF STRESS FIELD IN FUZHOU BASIN

Qiang Zu-ji, Wang Hui, Wang Hong-tao

1991, 13(4):  317-322. 

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Fuzhou basin is one of the typical basins on southeastern margin of China continent In the basin two groups of faults have been found. There are NNW-NW-and NNE-NE-trending faults. The NNW-trending Ba'yi reservoir-Wangjuan fault is active and also is a well-known heat-flow anomaly zone.The calculation of striats along the faults on the bedrock outcrops within the basin and its boundaries by using Etchecopar's computerized method shows that there were four important stress fields since Yanshanian phase. The first stress field was compressive in NW-SE orientation, which caused reverse fault, schistosity and mylonite zone to be formed. The second was compressive in SN or NNE orientation, but in the state of compression which produced Paleogene diabase dykes along NNE-trending faults. The third was compressive in nearly EW or WNW orientation, R = 1, σ₂=σ₃, but in a extension state. The evidence for the third stress field is tension-shear horizontal striation on the walls of the basic dyke formed from Neogene to Quarternary. For the fourth stress field maximum principal compressive stress was vertical, indicating that the basin is in an exten-sional tectonic environment.

APPLICATION OF AEROPHOTO INTERPRETATION TO STUDY OF ACTIVE FAULTS

Jiang Wa-li

1991, 13(4):  323-331. 

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The basis for interpretation of active faults in aerial photographs is the fault geomor-phology. The key to determining the active faults in aerial photographs is to find out the displaced landform which could not he formed by exogenetic force in nature. The confidence of the interpreted displaced landforms is of three levels. The scarps, their strike is perpendicular to the river's current diection, their dip opposite to the direction and their dip reverse to the slope, are the displaced landforms of confidence level Ⅰ. We must pay attention to the linear landforms when we determine direction and displacement amount of strike-slip fault. We can determine the poriod and order of fault activity from different datum and displacement amount of the displaced landforms. In this article 14 examples of the interpreted active faults in China and Japan are described for explaining the dislplaced landforms in aerial photographs.

STRUCTURAL FEATURES AND SEISMICITY IN JIANGHAN-DONGTING LAKE BASIN

Xu Jie, Deng Qi-dong, Zhang Yu-xiu, Yin Xiu-hua, Guo Shun-min, Niu Luan-fang

1991, 13(4):  332-342. 

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Jianghan-Dongting Lake basin is a large-scale Meso-Cenozoic basin in South China. Its geological structure, deep-seated structure, tectonic evolution, neotectonic activity and seismicity are analysed basing on the data of geology, geophysis and earthquakes in the basin region.The basin consists of Jianghan and Dongting Lake depressions and Huarong uplift. WNW-EW-trending secondary segs and positive land forms controlled by the faults developed in Jianghan depression, but NEN-NE striking secondary positive forms and segs controlled by the faults developed in Dongting Lake depression. The basin has undergone a complex process o'f tectonic evolution. There is intensive neotectonic activity in the basin region. Mid-intensity earthquakes are closely related to the structures with differential activities in Quaternary.

DEFORMATION ZONE OF M= 7.6 LANCHANG EARTHQUAKE

Yu Wei-xian, Cai Tian-jun, Hou Xue-ying

1991, 13(4):  343-352. 

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The seismic deformation zone of M 7.6 Lancang earthquake in 1988 is mainly composed of a series of surface ruptures and distributed along the Muga and Datangzi faults, The mechanical property of right-lateral shear of the deformation zone is analysed. But some segments of the zone exhibit their left-lateral shearing movement.Based on the field investigation and comprehensive analysis of data, it is considered that the axis of principal stress for the event is in NS-NNE direction. The seismic faulting of the event should represent a right-lateral displacement. The ground cracks which exhibit left-lateral displacement were formed by right-lateral displacement of faults.

SURFACE RUPTURE PATTERN BY XUNWU EARTHQUAKE OF MAGNITUDE 5.5 ON AUGUST 2, 1987

Lei Tu-cheng, Wang Yao-dong, Ou Bing-song

1991, 13(4):  353-360. 

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An earthquake of magnitude 5.5 had taken place in Xunwn, Jiangxi Province, on August 2, 1987. Its epicenter is located at 24? 58′N. 115?39′E and focal depth is 13km. The earthquake-generating structure and its rupture pattern by the shock are analyzed from the characteristics of earthquake hazards, data on activites of crustal structures, focal mechanism, preferred orientation of the damaged structures and the conditions of medium in this paper.

RELATIONSHIP BETWEEN CHARACTERISTIC PARAMETERS AND TIME OF SOIL LAYER B_ms OF ALLUVIAL FAN IN HEYUAN AREA, GUANGDONG

Feng Jin-jiang, Cheng Shao-ping, Hu Bi-ru, Zhang Bing-liang, Niu Luan-fang

1991, 13(4):  361-368. 

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Soil-forming factors are involved in original rocks, climate, living things, topography and time. If we wish to ascertain accurately the soil-forming time, all remaining factors must be be kept constant. The physical parameters of any soil are related to time. The authors have established a regression equation and correlation coefficients between characteristic parameters and formation time of soil layer B_ms on the alluvial fan in Heyuan area, Guangdong. The age of third-step alluvial fan has been determined by using growth rate of secondary minerals. A chronosequence cf the soil development of the alluvial fan has been set up in Heyuan area, Guangdong.

PETROLOGICAL MODEL FOR STRUCTURE OF CONTINENTAL CRUST IN EAST HEBEI PROVINCE

Wu Zhong-xu, Guo Chai-hua

1991, 13(4):  369-376. 

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Precambrian metamorphic complex in East Hebei, China, may be considered to re- present an exposed part of transect of the continental crust. Based on the estimated depth of the metamorphic complex deduced from metamorphic facies and subfacies, geo-thermometry, and geobarometry in combination with geophysical data, previous and our measurements of seismic velocities of rocks, a petrological model for the crustal structure in East Hebei, China, is suggested (Fig. 3). The lower crust consists of granulite facies, the lower and upper parts of the lower crust are composed of Py-granulite of mafic composition and Hb-granulite of intermediate composition, respectively. There are some peridotite bodies and charnockite intrusions in the lower part of the lower crust. The middle crust consists mainly of gneiss and schists of intermediate-acidic composition of high-amphibolite facies. The top of the middle crust is composed of gniess and schists of low-amphibolite facies. Tonalite and granodiorite intrusions with high-temperature pore fluid phase are developed in the middle crust, which corresponds to a high conductivety-low velocity layer. The upper crust is mainly composed of slates, phyllites, schists, granulite of greenschist facies (partly low-amphibolite facies) and granite intrusions, and sedimentary rocks at the top.

GEOMETRICAL STUDY ON DETACHMENT DEPTH OF TILTED BLOCK

Hou Jian-jun

1991, 13(4):  377-383. 

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The formula for calculating the detachment depth of a tilted block is established in geometrical aspect from the length of tilted block, tilt angle, uplift displacement amount of the crest and dip angle of the border fault. The calculated result shows that the detachment depth of the tilted block controlled by rotational planar normal fault is about 10—15km, which is the same as the depth of the top surface of brittle-ductile transition zone; the detachment depth of the tilted block controlled by listric normal fault is about 20—30km, which reaches and exceeds the depth of brittle-ductile transition zone.