Table of Content

07 September 1983, Volume 5 Issue 3

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Brief Report

ON THE MICROFRACTURE PROCESS AND CHANGES OF THE STRESS PATTERN IN THE CHINA CONTINENT

Liu Baichi

1983, 5(3):  1-8. 

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when studing time-space scanning of the seismic frequency ratio (d value) and of the frequency-magnitude relation (b value) for about 17,ooo M≥2.0 shocks occurring in the China continent east of longitude 97°E during 1972—1978,we obtained the microfracture process of continent crust and changes of following stress pattern; a set of inclined-conjugated and instable shear network at an interval of 5°probably formed within the crust with the effect of the bulk earth revolving,with the increase of regional stresses,average stress of the crust and mumber of times for appearing microfracture in the whole region,the area of microfracture expanded progressively along the instable shear network to made the network grow complete. The order of b value for an area of concentrating stresses is directly concerned in both the velocity of spreading microfracture and the increased area in seismic activity. The result is basically consistent with the Scholz's (1968).After occurrence of major earthquake,the area of growing microfracture was decreasing and coming back to a more uniform network with the decrease of the average stress on the whole region. The regional distribution of b values is related with the microfracture process in the whole continent of China. In addition,the experiment shows that b values is a function of the applied stresses and the regional change in the values may represent changes of the stress state and the scanning map of the b values can give to a great extent the stress patterns to the region.

CAUSE OF THE LAND SUBSIDENCE ASSOCIATED WITH THE HISTORICAL QIONGZHOU EARTHQUAKE(13 JULY 1605)

Peng Chenguang

1983, 5(3):  9-15. 

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Taking into consideration the historical seismic information,the mechanical properties of the ground layer in boreholes and the data on the local earthquake damage,it is concluded that in the Quaternary weak interbed of the littoral region the Qiongzhou earthquake caused such phenomena as liquation of soil soil flow,damage of foundation,and the like,which are responsible for the land subsidence in this seismic region.

NEW ACTIVITY OF THE SHUANGSHAN-LIJIAZHUANG FAULT AT LINQU SHANDONG PROVINCE

Jiang Zhongxin

1983, 5(3):  16-16. 

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ENVIRONMENTAL STIFFNESS EFFECT——AN IMPORTANT FACTOR INFLUENCING STRESS DROP IN HYPOCENTER

Wang Shengzu, Shi Liangqi, Zhang Liu

1983, 5(3):  17-27. 

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The results of the triaxial compression tests with solid confining pressure media and the theoretical analyses show that the "environmental stiffness",including the stiffness of both axial and confining pressure systems,is an important factor which influences the stress drop. Under the condition of triaxial compression tests the axial stress drop is a hyperbolical function of the stiffness of confining pressure system,and the former decreases with increasing the later. Thus,the problem,that the experimental stress drop is much greater than that estimated from an earthquake,may be explained.The expression of shear stress drop of hypocenter in the crust is Δτ=2λ((S_s—S_k)+(μ_s—μ_kσ_n.0)where λ is the environmental factor which depends mainly upon the environmental stiffness and the orientation of stress field. The values of the environmental factor may be 0-0.9 for the conditions without obvious change in the magnitude of normal pressure and the orientation of principal stresses.The environmental stiffness not only influences the magnitude of stress drop,but also determines whether the sudden stress drop will occur or not. Fully taking account of the effect of environmental stiffness and other factors such as temperature,confining pressure,pore pressure,orientation of stress field,fault materials,etc.,it will finally be possible to recognize the total law of stress drop in hypocenter.It is also indicated in this paper that the direct shear tests and triaxial compression tests with gas or liquid confining media can only model the pressure condition of hypocenter,but cannot reflect completely the "environmental stiffness" which can be controlled to a large extent with solid confining media as presented.

APPLICATION OF SINGL BOORD MICROCOMPUTER TO THE SEISMIC PREDICTION

Song Yifeng

1983, 5(3):  28-30. 

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THE FRACTURE ANALYSIS AND ELASTOPLASTIC ANALYSIS OF ULTRA-HIGH PRESSURE VESSEL

Wang Guanggen

1983, 5(3):  31-42. 

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The purpose of this paper is to improve some of techniques in designing a piston cylinder,ultra-high pressure vessel.First it introduces the elastoplastic analysis of the twofold cylinder which has been autofretted after shrink on and presents the formulae of autofrettage pressure and its characteristic values. Then it derives the formulae of stress distribution in different regions and the formulae of displacements and strains in the yield region. In addition it proposes the approximate calculation methods of fracture analyses.Based on the results,the strength and fracture analyses have been made for the vessel. In analysing,two cases have been considered: autofrettage after shrink on and shrink on after autofrettage. Adopted are: 1) the material used is perfectly elastoplastic and 2) the axial stress is independent of the coordinate,r.

A FINITE ELEMENT MODEL FOR SLUGGISH ACCUMULATION AND RELAXATION OF THE STRESSES ALONG THE FAULT ZONE

Wang Qiming, Nafi M. Toksöz

1983, (3):  43-53. 

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The relative movement between two plates causes the shear stress accumulation on the locked area of the fault zone. The stress rate depending on the relative velocity and the depth of the locked area can be obtained by use of elastic finite element model.In addition,the low viscosity material of both the asthenosphere and the deep part would led to the relaxation of the shear stress near the fault and increase of it at the tip of the fault. The time-dependent stress distribution following a strike-slip earthquake can be computed using 3-D linear viscoelastic finite elament analysis.Combination of these two types of stress gives the whole process of stress accumulation and stress release along the simple fault zone.The result in applying this technique to the North Anotolian fault indicates that the gap at the west part of the fault has the highest shear stress,which has reached the critical stress level. It will have major shocks in a few years except for possible small shocks or aseismic creep. The computed stress curves varying with time at different parts indicate that the next seismically active period will begin around a period of 2000—2020.

Brief Report

APPLICATION OF SINGLE-POLE COMPUTER TO DATING OF ¹⁴C

Jiao Wenqiang, Wang chongyan

1983, 5(3):  54-54. 

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CHARACTERIZED CHANGES OF TIME AND SPACE IN THE MACROSCOPIC PRECURSORS FROM THE HAICHENG EARTHQUAKE WITH A MAGNITUDE OF 7.3 AND MECHANISM OF ANOMALIES

Zhu Ye, Li Rongan

1983, 5(3):  55-62. 

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Based upon data for the Haicheng earthquake and the field investigations the further study is made for the temporal and spatial change of macroscopic field of precursors,the temporal correlation of the developing anomalies and the relation of their spatial distribution with the active faults.Described here are such aspects as fluctuations shown by macroscopic anomalies during the preparation of an impending earthquake,distributions characterized by the closely spaced belts and their inhomogeneity and migration.Building up and strenthening of stresses in the preparation of an impending shock may vary with time,spatially concentrated to various points in a stress field.With the comparision of the fluctuations in rapidly developing anomalies prior to occurrence of an earthquake,the time scale is excplored for predicting a major impending shock. The possible sites for future shocks are discussed on the basis of the spatial distribution of crossbelt anomalies,which is characterized by their migrating to epicenters from the outer.Finally,a few mechanisms are preliminarily investigated for the generation of main macroscopic anomalies.

TECTONIC ENVIRONMENT OF RESERVOIR INDUCED EARTHQUAKE IN THE XINFENGJIANG RESERVOIR AREA

Ding Yuanzhang, Pan Jianxiong, Xiao Anyi, Shen Liying, Ma Hanxiong, Miao Wecheng

1983, 5(3):  63-74. 

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The origin and distribution of induced earthquakes,associated with the impoundment of the Xinfengjiang reservoir depend not only on the local tectonic environment but also on the additional stress state which is caused by the water loading strain.Therefore,reservoir induced earthquakes tended to be concentrated on the margin of the lake and occurred in two iayers according to the focal depth,between which is a rare-earthquake layer.The frequency of the shallow events has a correlation to the water level of the lake. On the contrary,the earthquakes in the deep layer occurred more often during offset of the lake. In the Xinfengjiang area there are two kinds of seismic faults. Both of them obviously are high angle active faults,which play a much more important role than low angle faults in occurrence of the reservoir induced earthquakes.By means of mathematical simulation to restore the earthquake sequences of this area after impoundment of the lake,it is sure that in the case of certain tectonic stress field,the high angle faults perpendicular to the additional tension stress are more unstable than the others. The calculations also indicate that the seismic events caused by the given geological model in the presence of the stress field with the maximal stress axes striking N30癢,the minimal stress axes striking N30癊 and the moderate stress axes vertical fit in with,the actual earthquakes. The stress fields derived from the calculations are similar to those obtained by other means. Mathematical simulation demonstrats that the NNW-trending fault belt generating the main shock (M=6.1) is the least stale. The seismogenic structures of main shock and two after-shocks with a magnitude greater than 5 belong to the same fault. After the main shock,the stress states for rock changed,and the NNE and ENE faults are less stable.

ON THE MECHANISM OF THE FORMATION OF ANTI XI-TYPE (ξ-TYPE) GROUND CRACK ZONES ALONG THE XIANSHUIHE FAULT

Qian Hong

1983, 5(3):  75-79. 

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The anti xi-type seismic zones can be found along the Xianshuihe fault as the form of ground fractures,most of them in the form of alternative tensile-shear cracks with the compressional drumlins or the thrust. And the drumlins may usually appear in the gaps where the cracks run en echelion.On the basis of the field observations of the Daofu (M= 6.9) earthquake of 1981 and the information of the Luhuo (M= 7.9) earthquake of 1973,this paper discussed the mechanism of formation of the ground crack zones in terms of photoelastic experiment on clay.The author inclined to consider the studied ground crack zones to be the result of strik-slip movement along the Xianshuihe fault and the drumlins in the gaps between en echelon cracks were generated due to resulting adjustment in the normal direction at both terminals of the cracks from their lateral displacement. According to the shape of the drumlins and thrusting direction the author came to a preliminary conclusion that this kind of ground crack zones can be accounted for by the SSE-trending movement of the Sichuan Yunnan rhombic fault block.

MEETING FOR "DISCUSSFON ON THE CURRENT SITUATION AND PROSPECT ON STUDIES OF SEISMOGEOLOGY",HELD IN NANJING, JIANGSU PROVINCE

1983, (3):  80-80. 

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