Table of Content

04 September 1985, Volume 7 Issue 3

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Brief Report

PRELIMINARY STUDY ON CRUSTAL STRUCTURES IN THE EAST OF NORTH CHINA

Sun Wucheng, Li Songlin, Yang Yuchun

1985, 7(3):  1-11. 

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On the basis of available data mainly from seismic sounding crustal structures in North China are held to be characteristic of 1) vertically layered crust,consisting of upper,middle and lower crust,the reverse of seismic velocity occurs in the middle layer as shown on the seismic profiles;2) the lateral inhomogeneity and discontinuity on the Moho,sharp abruption of the velocity often points to the peaks of the Moho relief.Comprehensive analyses have been made for earthquake-generating structures in de-ep earth,geothermal activity and motion of deep-seated substances.

REAL TIME MAGNETOTELLURIC SOUNDING SYSTEM

1985, 7(3):  12-12. 

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CHARACTERISTIC DISTRIBUTION OF REGIONAL SEISMIC STRESS FIELD IN THE ANHUI AREA

Xia Ruiliang

1985, 7(3):  13-22. 

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By use of mean focal mechanisn solutions from 12 stations and reliable those forsmall and moderate earthquakes,this paper is to discuss characterstic distributions of regional stress fields in the study area.The results indicate that the distribution of the stress field north of 32癗 in thisarea is characteristic of the North China block;south of 32癗,it is characteristic of atransition of the North China block to the South China one;souther Anhui is characterises of South China.These characteristics serve to define the southern boundary of the North China block.

《GEOLOGICAI MODEL AND EARTHQUAKES MIGRATION IN THE NORTHERN PART OF THE NORTH CHINA》IS IN PRESS

1985, 7(3):  22-22. 

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NEOTECTONIC FEATURES OF THE GANZI-YUSHU FAULT ZONE AND ASSESSMENT OF ITS EARTHQUAKE RISK

Wen Xueze, Huang Shengmu, Jiang Zaixiong

1985, 7(3):  23-32. 

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Based on the data of field investigations,interpretations of both Landsat images and air photos,seismicity and focal mechanism,this paper describes the neotectonic features of the Ganzi-Yushu fault zone in western Sichuan.The relationship between the forming of pull-apart basins and the occurring of strong earthquakes is also discussed here.The result shows that this fault zone is another large strike-slip fault zone in western Sichuan,which formed and developed from Mesozoic era.It has been dominated by intensive left-lateral dislocation,its maximum horizontal offset is up to about 100 m and the ratio of horizontal offset to vertical offset is about 10 :1 since the Late Quaternary period.Up to 1984,the earthquake eneigy of this fault zone had been so accu-mlated as to cause an earthquake of magnitude 7.4.Therefore,on the basis of historical earthquake activity,it is inferred that this fault zone would enter into a new active period of earth-quake activity with the risk of occurring of an earthquake of magnitude 7 or greater in the next 20-30 years.

PRELIMINARY STUDY ON AGE AND DEFORMATION FOR CONSOLIDATED SEDIMENTS IN THE BASE OF THE VALLEY, THE LOWER REACH OF THE YALONG RIVER

Chen Fubin, Zhao Yongtao

1985, 7(3):  33-41. 

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Tongzilin and Ertan etc.,are located in the lower reach of the Yalong River,a sequence of less dense sediments in the bottom of the valley named Xigeda Formation (Early Pleistocene) with a thickness of 70m.14C dating indicates an age ranging from 23000-10000 yrs for the lacustrine deposit,suggesting a time spanning Late Pleistocene and Early Holocene for the Tongzilin Formation.Tectonic deformation of the succession leads to a east-dipping sequences,the development of extension-torsion fault and compression fault,and a set of X-shaped jointa,suggesting that this area showed a tendency to uplift rapidly

SYMPOSIUM ON QIONGSHAN EARTHQUAKE OF 1605 WAS HELD IN HAIK ON HAIKOU

Yao Yanzhi

1985, 7(3):  42-42. 

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DISCUSSION ON MECHANISM OF MICROBEHAVIOUR OF GROUNDWATER LEVEL IN A BOREHOLE

Che Yongtai, Yang Huinian

1985, 7(3):  43-50. 

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The microbehaviour of groundwater level in a borehole is engendered by stress changes in the earth crust.These stresses are commonly produced by the earth tide,atmospheric pressure,loading of the precipitation,loading of the surface water,and activity of a fault etc..The formative process of the microbehaviour is as follows:(1)The earth stress is changed;(2)The stress change causes the deformation of an aquifer,and the deformation leads to generate the change in a pore pressure;(3)The change of pore pressure causes a water-flow between the aquifer and the borehole;(4)The flow results in the fluctuation of water level in the borehole.This paper discusses the key links in the above processes from the viewpoint of rock mechanics,soil mechanics and groundwater dynamics.Moreover,it suggests some principles to choose or evaluate a borehole for seismological observation.

ANALYSIS AND PROCESSING OF DATA ON FLUCTUATIONS OF GROUNDWATER LEVEL

Tian Zhujun, Gu Yuanzhu

1985, 7(3):  51-59. 

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Miero fluctuations related to the stress-strain change in rocks holding water are studied by use of such method,other than the dynamical approach,as the Pertsev's filter to resolving long/short-term variations of water level and regression analysis to eliminating and analyzing the correlation factors affecting the water level.The compromise analysis is applied to the analysis of earth tide of water level.The multichannel welner filtering is used for comprehensive predicting the fluctuations of ground water level and searching out the abnormal time-interval prior to an earthquake.At last,the observed data of water level from the well at Ta-Yuan in Beijing are of practical significance in providing the information about seismic indications and in distinguishing anomalies in water level from the normal fluctuations.

A DISCUSSION ON "THE PLASTIC DEFORMATION CHARAG——TERISTICS AND REGIONAL STRAIN FIELD ON THE SOUTHERN SEGMENT OF THE TANCHENG——LUJIANG FAULT ZONE"

Xu Shutong

1985, 7(3):  60-62. 

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In the shear belt as discussed,most of the planar fabric used to measure the o' angle by the authors of the paper discussed here is probably not the active fabric during shearing,so that many of the data of ofmeasured in this way should not be put to use in tan2θ=2/γ to calculate γ and the displace of the shear belt The subhorizontal surface used to express the kinematic picture and measure the strain variations of the shear belt ie fig.6,8 and 10 in the discussed paper,is not the "XZ" plane of the strain field in which "Y" axis is in the position subhorizontal.Thus,I have to suggest that the shear belt as discussed is by no means of a "transcurrent ductile shear belt" but a ductile thrust (thrust under metamorphism or only a ductile shear belt in a broad sense of Ramsay,and therefore,it is not fitting and proper to measure the strain variations of the shear belt in such a plane.

《THE SELECTED WORKS OF CONTINENTAL RIFTS AND DEEP INTERNAL PROCESSES》IS IN PRESS

1985, 7(3):  62-62. 

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EFFECT OF THE UNDERLYING BEDROCK SLOPE ON SEISMIC GROUND MOTION IN THE XUZHOU AREA

Hao Xiansheng, Peng Yimin, Wang Zhiliang

1985, 7(3):  63-72. 

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The effect of underlying bedrock slope on the seismic ground motion is indicated by the seismic microregionalization for the study area.Two-dimentional inversion has been used in the seismic model and the author has worked out an extending program SAP 5.The main results are as follows:vertical ground motion is significant;distributions of horizontal motion vary with the distance of the bedrock from the center of the basin;the spectra show a regular variation;input of multi-directional seimic waves shows larger effect than does input of mono-directional seismic waves on the ground motion.As indicated by data the effect of underlying bedrock slope on the ground motion is significant compared with the site condition.

ASPERITY OF SLIDING ZONE AND TWO DIFFERENT KINDS OF SUDDEN INSTABILITIES IN ROCKS

Wang Shengzu, Shi Liangqi

1985, 7(3):  73-80. 

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The asperity of sliding zone in rock is an important factor which the nonuniformity of sliding resistance and the mode of instability depend A traditional criterion accepted extensively up to now for judging whether a sudden instability will occur is to compare the stiffness of testing machine with the contact stiffness of sliding zone.However,the experimental investigations on rocks by using triaxial compression apparatus show that the high-pressure and low-pressure sudden instabilities are different from each other in mechanism and criterion.The former takes place along a sliding zone with uniform-resistance and is caused mainly by the difference between potential energies at peak strength and residual strength;the latter along that with nonuniformsresistance and is caused by the difference between static and kinetic frictions.According to the solutions of the equations of motion corresponding to two kinds of sudden instabilities respectively,their criteria were obtained as follows:
K_EE′ < (K₁sin²θ-K₃cos²θ)/ζ
for high-pressure sudden instability,and
K_EE′ >K₁sin²θ+K₃cos²θ
for low-pressure sudden instability,where K₁ and K₃ is the stiffness of axial and confining pressure system respectively,K_EE′ is the contact stiffness of sliding zone,i.e.the slope of descending segment of stress-strain curve,θ is the angle between the directions of the specimen axis and the normal line of sliding zone,and is the nonuniform resistance coefficient with a positive value less than 1.0.It is emphasised in the paper that the strength condition is only a necessary but not sufficient condition for strong earthquake and there are a series of necessary conditions such as those of environmental stiffness,nonuniform-resistance,etc.,apart from strength condition.