Table of Content

09 September 1998, Volume 20 Issue 3

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Brief Report

ACTIVE REVERSE FAULT FOLD ZONES AND ESTIMATION OF POTENTIAL EARTQHUAKE SOURCES IN NORTHERN TIANSHAN

Yang Xiaoping, Deng Qidong, Zhang Peizhen, Xu Xiwei, Yu Guihua, Feng Xianyue

1998, 20(3):  193-200. 

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The reverse fault fold zones in the foreland basin of northern Tianshan is a typical active compression area in interior of continents. The research of the surface and deep structure,and its relationship in the active compression tectonic region is extremely important for the understanding its seismogenic structure and dividing its potential earthquake sources. On the basis of detailed research on the major active tectonics and synthetical studies in northern Tianshan,the deformation of the structure,earthquakes and active tectonics,and the relationship between surface and deep structures have been discussed in this paper. Finally,a few questions have been put forward in the process of potential earthquake source dividing in the active compression tectonic belt. Based on the research of the 1906 Manas earthquake (M7.7) and paleoearthquakes on the active reverse faults,we can know that the blind active crust ramp under the piedmont in the northern Tianshan area is the place of large earthquake occurring,and divided the blind ramp into two segments at the Jinguohe area. The active blind crust ramp may have two large potential earthquake (M8.0) sources. There are eight active anticlines in the northern Tianshan,west Urumqi. We can also compare these active anticlines with the active folds in the west region of the United States of America,and conclude that these active anticlines can only produce some middle earthquakes (M6.0). All the active anticlines in the northern Tianshan,west Urumqi,may have eight potential earthquake sources.

A STUDY ON FAULT ACTIVITY OF QINAGTANG AND ITS NEIGHBORING AREAS IN XIZANG (TIBET) BY USING LANDSAT IMAGES

Li Jianhua

1998, 20(3):  201-207. 

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The landsat images of color composit mosaic of 1:500000 are used to identify the fault activity in the Qiangtan and its neighboring areas of about 500000km². Based on the image characteristics of fault,the identified faults are grouped into three types which are active in Holocene,late Plastocene,and early middle Quaterary,respectively. Considering earthquakes of this region since 1900,the activity of major faults are analyzed. For example,the Margaichace Ruolacuo fault zone located north to the Qiangtang basin is evidently of left lateral strike slip in Holocence. The Mani M7.5 earthquake of November 8,1997 occurred just at this fault showing the recent activity of this fault.

TECTONIC ACTIVITIES OF THE YIHE SHUHE FAULT DURING THE JINNING MOVEMENT PERIOD

Zhou Jianbo, Hu Ke

1998, 20(3):  208-212. 

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Field geological investigatins and the results of ⁴⁰Ar/³⁹Ar isotopic dating demonstrate that the NNE trending ductile shear zone of the basment of the central sgement of the Yihe Shuhe fault developed during the Jinning Movement period (941Ma). In the process of the continent continent collision during this time,the collisional strike slip tectonics occurred because of the inconsistent collisional boundaries which represents the early activity of the Yihe Shuhe fault. On this basis we have studied the relationship between the basement ductile shear zone,the Yihe Shuhe fault and the Tanlu active fault.

THE ENGINEERING EVALUATION OF THE ENSHI FAULT ACTIVITY IN WESTERN HUBEI PROVINCE

Wang Huabing, Wu Shuren, Lu Yifeng, Yi Shunhua

1998, 20(3):  213-218. 

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We have analyzed the deformation texture,new activity,mechanical and fractal features of the Enshi fault in western Hubei Province. Adding with fault activity dating,we make a complete study to the activity of this fault. It is suggested that deformation of the Enshi fault has evident characters of segmentation. It has been active for many times and was active during the new tectonic period. Its activity is,however,very weak at present time. It is determinted that the last time of activity is more than 0.2Ma ago. Therefore this fault is not an active fault for engineering and will not bring major damage to the neighbouring hydropower projects.

A STUDY ON SOURCE PROCESS OF M_S6.8 EARTHQUAKE IN XIJIE, QINGHAI PROVINCE OF NOVEMBER 5,1988 BY USING BROADBAND DIGITAL SEISMIC WAVE DATA

Liu Zhen, Zhou Huilan

1998, 20(3):  219-224. 

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The broadband seismic wave data of CDSN are used to make a further study on the source process of the Qinghai,Xijie M_S6.8 earthquake on November 5,1988. With the waveform fitting and global searching algrithm based on the optimized Genetic Algorithm,the source parameters and rupture characteristics are analyzed. The results show that this earthquake is an event dominated by one rupture and associated with a strike slip active fault which has slightly overthrust component. In the light of analyses for the effect of rupture direction upon the station quasi source time function,it is suggested that the rupture was likely to spread from SE to NW along the NW trending fault plane.

DEEP STRUCTURE OF LIAOHE RIFT AND EASTWARD MIGRATION OF RIFT ACTIVITY

Zhao Junmeng, Lu Zaoxun

1998, 20(3):  225-233. 

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We have made further analyses to the geophysical data of Luyang-Haicheng-Donggou profile which transects the Liaohe rifting basin. These data include deep seismic sounding,gravity,magnetotelluric and heat flow measurements. It is found that the crust mantle transitional zone is characterized by the multi thin layers beneath the Liaohe rift which is quite different from those under the uplifted platforms on the both sides. The structural features of the thin layers,velocity,temperature,crustal low velocity layer and uppermost asthenosphere show that the tectonic evolution process has migrated from west to east for the Liaohe rift. The current front of movement of the upper mantle material has left from the center of the rift and moved eastward to the Ximu near the Jinzhou seismic zone. It is suggested that the movement of deep material is the primary dynamic factor for the generation and lateral migration of the Liaohe rift.

PRINCIPLES OF RESISTIVITY TOMOGRAPHY AND PRELIMINARY APPLICATIONS

Li Xiaoqin, Tao Yulu, Feng Rui

1998, 20(3):  234-242. 

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Resistivity tomography(RT) is a technique determining the resistivity distribution within the studied area based on the measurements of potential and current values on the boundaries. It is essentially different from the acoustic and electromagnetic tomography. In this paper,the mathematical principle of RT is presented,then a few main reconstruction methods are systematically analyzed and concluded according to the integral transform,linear iterative and nonlinear iterative methods. For calculating the Jacobian partial derivative matrix,three methods are briefly discussed. Two field’s tomograms in the surface and crosswell exploration are provided as well. The feature and limits of RT are finally discussed in brief.

CANONICAL DECOMPOSITION OF THE MAGNETOTELLURIC(MT) IMPEDANCE TENSOR AND ITS PRELIMINARY APPLICATION

Jin Guangwen, Sun Jie, Wang Jijun

1998, 20(3):  243-249. 

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Because of the limitations of the tradional analysis methods for magnetotelluric impedance,the universal canonical decomposition has been proposed. By this method the eight scalar parameters provided by the main coordinate system describe the transfer features,polarization state of the field source in the Earth system as well as their relations. Therefore these are a parameter system with definite physical implications and to be easy to explain. This paper studies the characters of the canonical decomposition method under some tectonic conditions and the polarization problem of the field source. A simple example of application of this method is also given.

A PRELIMINARY STUDY OF THE COMBINATION OF ELECTROMAGNETIC ARRAY PROFILING AND MAGNETOTELLURIC METHOD IN THE DATA ACQUISITION AND DATA PROCESSING

Deng Qianhui, Sun Jie ,Wang Jijun, Tang Ji, Zhan Yan, Zhao Guoze, Bai Denghai, Liang Jingge, Chen Musen, Ye Baiyuan, Wang Yousheng

1998, 20(3):  250-254. 

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The Combination of Electromagnetic Array Profiling (EMAP) with Magnetotelluric Method (MT) is that MT data can be simultaneously oblained while EMAP measurement is carried out. This technique has the following advantages: 1. The information is gereatly expanded and the field measurement is more efficient. 2. It could be a remedy for the possible weakness of the insufficient deep seated data in case of EMAP measurement only. 3. It provides an opportunity of synthetical study for both EMAP and MT data.

DYNAMIC PATTERN OF GROUNDWATER LEVEL BEFORE AND AFTER THE TANGSHAN EARTHQUAKE AND ITS MODE OF FORMATION AND EVOLUTION

Geng Jie, Zhang Zhaodong, Wei Huan, Wang Zhongmin

1998, 20(3):  255-260. 

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We have studied the method of dynamic pattern generation,the characteristics of time space evolution of sliding variation extent of groundwater level and its mode of formation and evloution before and after the Tangshan earthquake of 1976. The results show that the positive and negative areas and anomaly characteristic area of the sliding variation extent of groundwater level present the distinct features of stage and regularity before and after the Tangshan earthquake. The negative area has the feature of“contraction-extention-quick extention-occurrence of earthquake”. The anomaly characteristic area displays the feature of“migation form periphery to epicentre-extention-stabilization-earthquake occurring-disappear”. The sliding variation extent of groundwater level in the anomaly characteristic area presents the feature of“increase-discrease-earthquake occurring-quick discrease”. We have also analyzed the dynamic pattern of sliding variation extent of groundwater level related to tectonic deformation,fault movement and active mantle uplift. Finally,we propose a“field-region-epicentre”evolution mode of dynamic pattern of sliding variation extent of groundwater level before and after the Tangshan earthquake.

A STUDY ON THE RUPTURING MODEL OF THE DOUBLE MAIN SHOCK IN THE LONGLINLANCANG FAULT ZONE, YUNNAN

Zhou Ruiqi, Guo Shunmin, He Wei

1998, 20(3):  261-268. 

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The Longling earthquake of M7.3 and M7.4 in 1976 and the Lancang Gengma earthquake of M7.2 and M7.6 in 1988 are two typical double main shocks occured in Longlin Lancang fault zone,Yunnan. Based on the seismicity analysis of the events,it is found that they have different characters. The Longling earthquake occurred in a block which composed mainly of the granite in which the structure is comparatively homogeneous. The focus machanism analyses of the Longling earthquake give the direction of compressive stress in NNW,the trace lines of the principle stress axis extends mainly in SN to NE. The direction of the seismogenic structures are in NNW to SN and NE to NEE. There are two intensity areas of 9 degree of which the long axes are nearly right crossed each other. The Lancang Gengma earthquake occured near an ancient plate boundary with complex seismotectonic background. The directions of principal compressive stress of the two main shocks given by focal mechanism analyses are different. The Gengma M7.2 earthquak occurred in an area in which the tectonic stress is mainly tensional in NW direction. While the principal compressive stress field of the Longling M7.6 earthquake is characterized by the fan shape in NS direction. The seismogenic structures of the Langcang Gengma earthquakes are of en echelon in NW direction. The axes of meizoseismic areas of two main shocks are parallel each other. Based on the comparison and analysis,the X-type model and triggering model of seismic rupturing for the double main shocks are proposed,and their features and formative condition are also disscussed.

THE PREDICTION OF RESERVOIR INDUCED SEISMICITY

Yang Qingyuan, Chen Xiancheng

1998, 20(3):  269-273. 

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Base on the conditions of geology,seismicity and engineering of reservoir area,the possibility of induced seismicity is evaluated during the phase of reservoir designing.According to the data of case of RIS in the world,the time of the largest induced earthquake is predicted .When a reservoir induced earthquake occurs,the possibility of destruction induced earthquake is predicted.

OBSERVATIONALEXPERIMENTS ON THE ESCAPED RADON FROM THE HAIKOU ZK26 WELL

Gu Shenyi, Liu Wei, Gui Yunong

1998, 20(3):  274-276. 

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SAR INTERFEROMETRY AND ITS APPLICATION REVIEW

Zhang Jingfa, Shao Yun

1998, 20(3):  274-288. 

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In this paper,the techniques and applications of SAR interferometry are introduced. After a brief historical review,geometric implementations and important processing techniques of SAR interferometry are described. Besides,this paper illustrates technical flowchart for the spaceborne INSAR processing chain and recommends the measurement of coeismic displacements Landers earthquake by means of INSAR. This paper shows INSAR possess a good application perspective in extracting three dimensional information of the Earth’s surface.