Table of Content

07 September 1994, Volume 16 Issue 3

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Brief Report

BLIND THRUST, FOLDING EARTHQUAKE, AND THE 1906 MANAS EARTHQUAKE, XINJIANG

Zhang Peizhen, Deng Qidong, Xu Xiwei, Peng Shizhen, Yang Xiaoping, Feng Xianyue, Zhao Reibing, LiJun

1994, 16(3):  193-204. 

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The 1906 Manas earthquake is an important event in the northern Tianshan of China. TheSeismogenic fault controlling this earthquake has not been well understood. Detailed field investi-gation indicates that the ground ruptures in the epicentral area were caused by gravitational andshaking effects during the earthquake. The fresh fault scarps along the Tugulu-Manas-Houer-goush reverse fault and fold zone are the possible surface ruptures associated with the 1906 Manasearthquake. The displacement is between 0.2 and 0.5m. Total length of the fault scarp is lessthan 10 km which is far more less than a normal rupture length associated with an earthquake of magnitude 7.7.Anticlinal uplifting along this reverse fault and fold zone indicates that the earthquake probably occurred along low-angle reverse fault at depth as a blind reverse faulting event.The surface rupture and deformation took place far away from the epicentral area. Most of thecoseismic deformation was accomodated by folding and uplifting,and only less than 10 km surface rupture was formed.Thus,the 1906 Manas earthquake is probably a“folding earthquake”.

DISCOVERY OF PROTEROZIC OPHIOLITE SUIT ON JIAODONG PENINSULA

Wang Renmin

1994, 16(3):  216-216. 

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THE DEFORMATIONAL STRUCTURES AND DYNAMIC ANALYSIS OF XIANNUSHAN FAULTT ZONE IN THE CHANGJIANG RIVER GORGE AREA

Wu Shuren, Liu Zizhong, Qin Xingli, Li Donglin

1994, 16(3):  217-228. 

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On the basis of zonations segmentation and layering of the Xiannushan fault zone,a spatialdeformational structure model has been established,and geometrical and kinematic characteristicsof the fault in two main deformational stages of its temporal evolution sequence are discussed. Interms of conjugate joints, striations on fault planes and microstructure in fault zone,the tectonicstress directions and differential stress in main Yanshanian tectonic deformation and main Hi-malayan phases tectonic deformation have been determined, respectively,and some important dynamic information has been obtained.

SEISMIC FAULT OF THE 1668 TANCHENG EARTHQUAKE(M＝8(1/2))AND ITS FRACTURE MECHANISM

Li Jialing, Chao Hongtai, Cui Zhaowen, Zhao Qingyu

1994, 16(3):  229-237. 

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Basing on the new data from the detailed field work in the last few years,we conclude thegeometric and kinematic features of the seismic fault of the 1668 Tancheng earthquake(M=8(1/2))and then make a new understanding on its fracture mechanism. The 1668 seismic fault,as longas 130 km,was formed in middle of the Tanlu fault zone between Tuling,Juxian county,andYaoshang, Tancheng county.It consists of five secondary rupture segments with different modesof movement.The middle segments are dominated by strike-slipping, while the two ends bythrusting. The seismic fault was first ruptured at the centre,where the fault was strong shearing；Then the fracture propagated in two directions. The M=8(1/2) main shock was generated bythe initial rupture and during fracture propagating the aftershocks occurred.The fracture mechanism of the paleoearthquake events during the Holocene was the same.

COMPOSITE ZONATION OF NANTONG URBAN AKEA

Wang Haigang, Feng Shengli

1994, 16(3):  238-242. 

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Basing on the engineering seismological environmental evaluation of the urban area,study ofengineering geological condition：and test and analysis of dynamic characteristics of constructionsites in Natong urban area,The regularities of spatial distribution of engineering geological conditions and earthquake resistance capability of site soil are clarified. Study on dynamic characteristics of site soil and analysis of seisrnic response of soil layers enabled us to compile a map of composite zonation of the urban area,which provides basic geological data for engineering construction siting and dynamic parameters for anti-seismic structure design.

STUDY ON CRUST AND UPPER MANTLE STRUCTURE IN NORTH HENAN AND ITS SURROUNDINGS

Zhang Chenke, Zhao Jinren, Ren Qingfang, Zhang Xiankang, Zhu Zhiping

1994, 16(3):  243-253. 

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In this paper.1-D and 2-D ray tracing and travel time fits as well as calcdation of the synthetic seismograms are performed from the DSS data obtained on Heze～Changzhi and Zhengzhou～Jinan profiles respectively. The velocity structure of the crust and upper mantle wasdetermined. The result shows that the velocity structure of the crust and upper mantle is imhomogeneous apparently in vertical and lateral directions. The rift is well-developed in the shallowercrust,and corresponds to the obvious relief of deep crust interface and the velocity contours. Insouthern part of North China depression,there are two local convexes on the background of theupwiiling upper mantle. Their highest positions correspond basically to the Dongpu depressionand Tangyin graben in the shallow crust.The depth of Moho discontinuity is about 31 and 34km, respectively.

A NEW QUANTITATIVE RESEARCH APPROACH TO CRACK RESERVOIR

Song Huizheng, Ouyang Jian, Sun Junxiu, Huang Fuqiong

1994, 16(3):  254-254. 

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ANNUAL REGIME CHARACTERISTICS OF WATER LEVEL IN BEDROCK WELLS IN BEIJING PLAIN

Che Yongtai, Yu Jinzi, Zhang Dawei, Sun Zhen'ao, Jian Chunlin, Peng Guirong

1994, 16(3):  255-263. 

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In this paper,annual regime characteristics of water level in ten wells in Beijing area are systematically presented,and influences of rainfall and extraction of groundwater on them are analysed.In addition, Reliability of intermediate and long period anomalies of water level in some wells before and after Datong-Yanggao earthquake is discussed.

STUDY ON CHARACTRISTICS AND MECHANISM OF H₂ ANOMALY ON THE HIDDEN ACTIVE FAULTS IN NORTH CHINA

Lin Yuanwu, Zhai Shenghua, Fan Shuquan, Kong Lingchang

1994, 16(3):  264-268. 

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54 soil-gas samples were collected from three hidden faults which are considerable differentin fault movement and seismicity in the northern part of North China. The results indicate thatthere are notable anomalies in H₂ on Tangshan and Xiadian hidden active faults,but no anomalyon Xianhe-Huangzhuang hidden inactive fault.On the basis of discussion on anomalous mechanism of H₂ on the hidden active fault,we suggest that H₂ is not generated in biological process butis a product of degassing in rupturing of the basement schist and gneiss or water-rock reaction.H₂ anomaly is closely related with fault movement whether H₂ is produced in rupture of rock or in water-rock reaction.

STUDY ON ELECTRON SPIN RESONANCE(ESR)DATING OF FAULT MOVEMENT

Huang Peihua

1994, 16(3):  269-274. 

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The results of pressure and heating experiments on quartz grams from hault gouge show thatthe frictional shearing stress and thermal stress for fault activity are important in resetting of ESRsignals. We found the that difference of resetting conditions of ESR and TL signals are maincause because of difference in energy level of trapped elections excited by fault frictional and thermal stresses. The TL signals reset to zero level easier than ESR signals under the same a faultmovement because TL signals are related to shallow energy level of trapped elections. Therefore,the ESR dating of fault movement is releable when the ESR age coincides with TL age for thesarne sample of fault gouge. The opinions of further study on ESR dating of fault movement arealso discussed in this paper.

AN EXPERIMENTAL STUDY ON SUDDEN-INSTABILITY SEQUENCES IN ROCKS

Li Jianguo, Wang Shengzu

1994, 16(3):  275-282. 

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The recurrence of stick-slip events along the sawcut or newly-created fracture zone in rockspecimens are carried out at confining pressures with the triaxial compression apparatus with solidmedia for studying the evolution characteristics of sudden-instability sequences and the effects ofvarious factors on them. The results indicate that, with increasing sliding displacement the critical differential stress level necessary for sudden instability and stress drop change successively bystages of“ascending-slope”,“descending-slope”and“flat-cum－fluctuation”,while the ratio ofstress drop to critical differential stress level tends to decrease. These evolutions are attributedmainly to the changes of the contact and asperity degrees of sliding zone,the thicknesses andgrain sizes of fragments within it,and the loaded and constrained conditions of specimen It isexpected that the characteristics of sudden-instability sequences revealed in this study would be aconceptual basis for predicting the tendency of ensuing earthquakes in their magnitudes,recurrence intervals and hypocenter offsecs.

CORRELATION ANALYSIS OF PERCENTAGE OF COLLAPSING HOUSES AND SEISMIC INTENSITY OF TANGSHAN EARTHQUAKE

Yang Zhe, Cheng Jiayu

1994, 16(3):  283-288. 

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Percentage of collapsing houses by Tangshan earthquake was interpreted by sampling fromaerophotographes which were taken after shock. The regression curve of perectage of collapsinghouses and seismic intensity was formulated by using 1942 samples with respect to the samplingsize of urban street and suburban village, which can be used to determine the intensity in fast estimation of damage and emergency activity after shock.The frequency of perectage of collapsinghouses in each intensity was also calculated,which provides a numerical method for eatimation of earthquake losses.