Table of Content

04 March 1992, Volume 14 Issue 1

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Brief Report

THE OSCILLATION DURING INSTABILITY OF ROCK BODY AND THE MULTILATERAL FAULTING TRACES

Zhang Liu, Feng Jinjiang, Li Biao, Chi Jiang, Yang Zhuen, Shi Xingjue

1992, 14(1):  1-9. 

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The experimental study on transient processes of fracture and stick-stip instability shows that both of the stress drop and the displacement rise are not monotonous.They are oscillatory ones with multifrequencies.The SEM observation on fracture surfaces shows that the oscillation led to bilateral or multilateral traces.By combining the experimental results with the phenomena observed from natural fault surface and fault zone,such as slickensides,grooving,steps and abnormal array of subfaults,it has been presented that one of the reasons for the traces which reflect the bilateral or multilateral motions of natural fault may be the instability oscillation of fault from an event (earthquake).In contrast,these phenomena may be indicators as ancient earthquakes.

A DISCUSSION ON SEISMOGENIC STRUCTURE OF DATONG-YANGGAO EARTHQUAKE

Ma Jin

1992, 14(1):  10-11. 

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PROSPECTING FOR THE HIDDEN ACTIVE FAULT BY MEASURING THE ²¹⁸Po AND ²¹⁰Po

Zhang Yusong, Hu Yutai, Li Jianhua

1992, 14(1):  12-22. 

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A method of prospecting for the concealed active fault by simultaneous measuring both ²¹⁸Po and ²¹⁰Po is introduced.It is a radioactive prospecting.The concentration of radon near the fault can be determined from the activities of its daughters ²¹⁸Po and ²¹⁰Po.At the fault,there is a good passage for gases,and the radioative gas from crustal depths can be easy to get to the surface.As a result,the level of the radioactivity there is quite high,but low at both sides far from there.The observational points where the activ.ity of ²¹⁸Po and ²¹⁰Po is much higher than their background values can be regarded as the position of the hidden fault we want to seek.A number of observations at the known faults and hidden active ones indicate that seeking hidden active faults on certain conditions of their outcrops by measuring ²¹⁸Po and ²¹⁰Po is an effective,efficient-and hopeful way.

THE STATISTICAL CHARACTERISTICS OF GROUNDWATER LEVEL ANOMALY BEFORE SOME MODERATE-STRONG EARTHQUAKES IN THE EASTERN CHINA CONTINENT

Che Yongtai, Yu Jinzi

1992, 14(1):  23-29. 

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Moderate strong earthquakes are main activity in eastern China continent.In this paper,the statistical characteristics of the pattern,the spatial distribution and time varation of groundwater level anomalies before the earthquakes in this region,and their relations to area,time of earthquake occurrence and magnitude are systematically analysed on the basis of former studies.In addition,the reliability and the prediction efficiency is inspected by an example of Datung-Yanggao moderate-strong earthquake series,October,1989.

ADVANCES IN RESEARCH ON RECENT CRUSTAL MOVEMENT AND GEODYNAMICS IN QINGHAI-XIZANG (TIBET) PLATEAU

Zheng Jiandong

1992, 14(1):  30-31. 

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THE TECTOGENESIS IN THE QUATERNARY PERIOD OF THE DONGTING BASIN

Zhang Shijun

1992, 14(1):  32-40. 

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In this paper,by drawing up the isopach maps of series in the Quaternary system,analysed the evalution of the tectogenesis of each epoch in the Quaternary period of the Dongting Basin.In the Early Pleistocene and the Late Pleistocene,it showed opposite tilting in the east and the west,and the deposit laid down central block showed stretching to the south and the north;In the Middle Pleistocene and the Halocene because the fault blocks of thebilaterals of the Yingfeng bridge-Beijing port showed tangle-up tilting in the opposing direction,the northwest angle and the southeast angle of the basin showed tilting and it took a shape of prostrate part correspording to the major tilting part,its.stretching direction was vertical to the tilted direction of the major tilting part.

CHARACTERISTICS OF GYARING CO FAULT ZONE IN CENTRAL TIBET

Wu Zhangming, Shetu Binming, Cao Zhongquan, Deng Qidong

1992, 14(1):  41-46. 

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Gyaring Co fault zone across Xainza and central Tibet had been formed before late Cretaceous period,and has been reactivated with right lateral motion since Quaternary.The fault zone consists of four subparallel faults in an arrangement of right stepping en echelon,and three pull-apart basins,occupied by Zigui Co,Gyaring Co and Waang Co respectively,are formed in righ-step like.Gyaring Co fault zone is one of main seis-mogenic fault in central Tibetean plateau.At least four surface ruptures associated with earthquake have occurred clearly along the fault zone since Holocene,with the segmentation of activity along the fault zone.

A PRIMARY STUDY OF MAGNETIC CRYSTAL LINE BASEMENT INTERFACE IN TANG-SHAN EARTHQUAKE AREA

Zhang Xian, Jiao Tiehua, Jiang Peizheng

1992, 14(1):  47-54. 

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In this paper,the basic principles of inversion method for a single magnetic interface in frequency domain are briefly described.The method is used in numerical processing of the aeromagnetic data in Tangshan earthquake area.The quantitative characteristics of the magnetic crystal line basement interface are distinguished.The results show that Tangshan is located in a fold-depression in the northern part of North China plain adjacent to Yanshan uplift.The basal magnetic interface on bottom of Kaiping syncline in the focal zone is a depression which is confined by three deep faults around.Then the preparation and generation process of Tangshan earthquake are discussed in combination with the results of seismic sounding,crustal deformation and crustal stress data.

STUDY OF SOME LONG-TERM ANOMALOUS CHANGES PRIOR TO TANGSHAN EARTHQUAKE WITH RESPECT TO TECTONIC CAVE-IN

Qiu Zehua, Zhang Baohong

1992, 14(1):  56-60. 

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Tectonic cave-in is straitforward defined as the cave-in of crustal layers associated with tectonic movement.This idea was first published about 20 years ago and explaining the phenomena of Tangshan earthquake with such viewpoint has a history of more than 10 years as well.The levelling measurements across the main fault of Tangshan earthquake suggest that,during 1970 Fengnan earthquake (M=4.7),large scale tensile failure may have occurred in the downthrown block.The long-term anomalous changes in water level and gravity which began later can be explained by assuming that ground water moved into the region of the tensile fractures in this period.

RECENT HORIZONTAL DEFORMATION AND DYNAMIC BEHAVIOR OF TECTONIC MOVEMENT ALONG THE XIANSHUIHE FAULT ZONE IN SICHUAN CHINA

Gui Kunchang, Gu Guohua

1992, 14(1):  61-67. 

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From the result of the repeated geodetic surveys on the network,across the Xianshuihe fault zone,the dynamic characteristics of recent tectonic movement along the fault zone are discussed in this paper.Possible models of block motion along the fault zone are studied based on the analysis of the geodetic horizontal deformation,the historic tectonic deformation and regional tectonic background.This study shows that the recent tectonic movement along the Xianshuihe fault zone is mainly characterized by nonuniform slips of the blocks on both sides of the fault in the same sense,and the geodetic deformation on the surface is in agreement with the left-lateral slips along the fault zone.

DRAINAGE SYSTEM AND INDICATOR OF SEISMIC RISK

Huang Xiuming

1992, 14(1):  68-78. 

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This paper deals with the relationship between the drainage system and indicator of seismic risk in the northwest of Beijing,and its neighbouring areas.The map of the basal level are constructed.This reseach shows that seismicity in this region occurred only in some particular positions on the map of the basal level.

RESISTANCE NONUNIFORMITY AND SUDDEN INSTABILITY OF SLIDING ZONE IN ROCKS

Li Jianguo, Wang Shengzu

1992, 14(1):  79-88. 

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The nonuniform-resistance effect of faulting surface is one of the important factors determining the instability mode and whether earthquake occurs or not.The experimental studies show that the sudden instability can take place along a wavy and rough sliding surface only as it is relatively flattened and smoothed after the asperities were cut and broken in the sliding process and unevenness and resistance nonuniformity of sliding surface can be indicated as a so-called nonuniform-resistance coefficient,which is a relative measurement of the displacement for uniformization,A new method for experimental determining the value of nonuniform-resistance coefficient is proposed by comparing the different unevennesses and stress drops between sawcut and fracture surfaces in rocks and the relatioins between the nonuniform-resistance coefficient and relative waviness for granodiorite,granite and quartzite are given in this paper,which may provide a basis for judging the possibility of earthquake along a fault.

EXPERIMENTAL STUDY ON ROCK CREEP FRACTURE AND ITS IMPLICATION FOR EARTHQUAKE PREDICTION

Zhao Axing

1992, 14(1):  89-95. 

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Based on the creep fracture experiments of Jinan gabbro and accumulative AE events at various temperatures and confining pressures,this paper suggests the use of the creep fracture strain as a criterion of rock creep fracture,establishes an emperical relationship of the creep fracture strain of rock various temperature and confining pressure,and on the basis of the creep parameters of Jinan gabbro,discusses the method for predicting rock creep fracture and earthquakes.