Table of Content

03 June 1992, Volume 14 Issue 2

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Brief Report

FAULT ROCKS AND ACTIVITIES OF THE KANGDING-MOXI FAULT ZONE

Shi Lanbin, Lin Chuanyong, He Yongnian, Liu Xingsong, Chen Xiaode

1992, 14(2):  97-112. 

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Mylonite,cataclasite and especially fault rocks subjected to both mylonitization and cata-clasis widely developed along the Kangding-Moxi fault zone.A mylonite zone has formed as a result of ductile shearing in early stage.In later stage brittle fracturing has occurred along this mylonite zone,accompanied by the formation of the present Kangding-Moxi fault zone.Later on,ductile shearing and multiperiods of brittle fracturing occurred along the fault zone.Differential stress magnitude during the early faulting process was 50 MPa,as determined by using microstructural piezometer,while that for the late stage was 30 MPa.The activity of the fault zone tends to be weaker,i.e.from high to low stress level.

TECTONIC EVOLUTION AND SEISMICITY OF WEIHE FAULT ZONE

Peng Jianbing

1992, 14(2):  113-120. 

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Transversing the axis of Weihe basin,the Weihe fault zone varied in nature in different geologic period:before the Cenozic it was a transcrustal paloefault zone cutting the basement,during the Cenozoic it changed into a listric extensional fault and formed the embryozic Weihe basin by extension and tilting and recently it has been Characteristic of an extension and dip slip along with hingelike movement.The fault is a famous seismic zone along which there have been 20 earthquakes with M≥5 since 280a B.C.

THE 2ND SYMPOSIUM ON THE RESEARCH OF ACTIVE FAULTS HELD IN BEIJING

Ding Menglin

1992, 14(2):  120-120. 

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THERMOCHRONOLOGY OF THE AILOSHAN-RED RIVER SHEAR ZONE-A CASE STUDY OF MULTIPLE DIFFUSION DOMAIN MODEL

Chen Wenji, T M Harrison, O M Lovera

1992, 14(2):  121-128. 

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Recently,the single-diffusion-domain closure model of Dodson (1973) has been extended to apply to minerals with a discrete distribution of domain size,multi-deffu-sion-domain closure model (Lovera et al.,1989).Because these domains contain a range of closuer temperatures,Lovera et al.(1989) found that a single K-feldspar samples may reveal a broad segment of a cooling history,rather than the single datum usually expected.A study of K-feldspar (FA-2-1) from the Ailao Shan/Red River shear zone,Yunnan,reveals extremely rapid cooling in the interval 20 to 19 Ma using the new model.In consistent with the earlier published analysis involving many biotite samples and a K-feldspar sample collected from Quxu area,southern Tibet.We believe that the two results are related.These two studies underscore the value of using the domain disstribution hypothesis in tectonic studies and presage a revolution in "tectonic geochro-nology".

THE LAW INTERPRETATION AND PREDICTION OF EARTHQUAKE MIGRATION-EARTHQUAKE MIGRATION OF FOUR SEISMIC BELTS IN CHINA MAINLAND

Ma Zongjin, Li Xianzhi, Jin Jiyu

1992, 14(2):  129-139. 

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In this paper,based on the study of the earthquake migration of the four seismic belts in China mainland (South-North,Tianshan,Shanxi and Yanshan seismic belts),the directive property of migration was demonstrated and the phenomena of fast and slow waves in migration were found,velocities (V_M,V_m) which in migration were figured out.It is shown that the basis of earthquake migration is not the continuous connection and spreading of seismic fractures,which depends on the propagation of migration waves caused by the pulsating pushpressure force of the dynamic wave at boundary.

ON SEGMENTATION OF FAULT ACTIVITY

Liu Xingsong, Tang Hanjun

1992, 14(2):  140-144. 

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Fault motion has complicate and variable pattern and a segment of a giant fault zone is usually an unit of jupture.Individual fault segment has its own feature,such as segment length and displacement amount produced during faulting,and position of the actual segment of the fault often changes regularly with time.In order to meet the needs for major engineering projects and strong earthquake prediction,it is necessary to determine which segment of fault zone is active.We propose in this paper that recent activity along a fault zone can be directly identified based on activity sequence of the strong earthquake and multiplesurvey on the geodetic network across the fault zone,and then the active segment can be determined in combination with geomorphic feature and variation of ground water level.

THE STRUCTURAL ANALYSIS OF SEVERAL MODERATE-STRONG EARTHQUAKES IN THE SONGLIAO BASIN

Zhou Bengang, Gao Mingxiu

1992, 14(2):  145-150. 

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Several small Quaternary NE-trending depressions exist in the eastern ana soutn-ern Songliao basin due to unequal subsidence.Some of them were conspicuously active in Middle and Late Pleistocene.In or near the edge of these depressions,some moderate-strong shocks occurred in the area where the NW faults cut the NE ones.The NW faults are seismic faults generally.Furthermore,field investigations indicate that the earthquake with magnitude of 6³/4 in 1119 occurred near Kalamu.

DEXTRAL DISLOCATION ALONG ZHANGZHOU-XIAMEN FAULT ZONE

Li Guohua

1992, 14(2):  151-156. 

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On the basis of data about the specific landscape,the horizontal dislocation of a series of geological bodies,and analysis of the gravitational field the facal mechanism and so on,this paper proves that dextral dislocations have occurred along Zhangzhou-Xiamen fault zone since the Tertiary.Furthermore,the nature and mechanism of this movement are also discussed.

LUNAR AND SOLAR PERIODICITIES OF EARTHQUAKES IN LOWER CHANGJIANG RIVER REGION

Du Pinren, Li Qitong

1992, 14(2):  157-164. 

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Phases of mainshocks (M≥5.0,1900～1990) in the lower Changjiang River region (30～34°N,116～122°E) in the Eastern China were determined by means of the formulaser for the theoretical tidal gravity.Distributions of lunar and solar hour angles,lunar and solar ecliptic longitudes,luni-solar phases,and phases of the 8.85-yr lunar perigee cycle and the 18.6-yr lunar nodal cycle of these samples were evaluated by Schuster's test and chi-square test for which the formula used in Kilston & Knopoff (1983) was modified into (6) in this paper.To avoid fortuity,especially in the case of smaller sample,and missing some possible periodicities,the samples with magnitude from 5.0 to 5.7 were tested one by one.Phases of the semidiurnal and fortnightly theoretical tidal gravity were also determined and evaluated.This investigation has uncovered that the principal earthquakes in the study region show statistically non-random lunar and solar periodicities as follows:1.semidiurnal periodicities displayed by the binodal distribution of the hour angle of the Sun (P_R=0.023,χ²=7.576) and the pattern of semidiurnal gravitational tides (P_R=0.017,χ²=8.167);2.semimonthly periodicity shown by the binodal distribution of luni-solar phases (P_R=0.011,χ²=8.985) and fortnightly tidal periodicity (P_R=0.061,χ²=5.566);3.one year periodicity of the solar ecliptic longitude of the events with M_s≥5.1(P_R=0.035,χ²=6.712) and 8.85/2 years periodicity given by twice the longitudes of Moon's perigee of the mainshocks with M_s×5.2 (P_R=0.043,χ²=6.309).Of above periodicities,the most remarkable and stable one is half the synodic month.Such periodicities uncovered in this study suggest that occurrences of earthquakes may have the characteristics of chaotic patterns.Effects of the exogenetic stresses on occurrences of earthquakes should belong to the nonlinear interactions.It is difficult to set some models to explain the complex phenomena by means of the classical physics.At present,such investigations are only trying to seek some empirical regularity of seismicity.

PRELIMINARY STUDY ON AN ANCIENT SEISMIC SOURCE SUBSTANCE

Zhang Jiasheng, Zhou Chunping, Yang Guizhi

1992, 14(2):  165-175. 

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Studies on the microstructure and matrix composition of fault-generated pseudotachy-lites,as well as their structural relationships in an ancient seismic source region,have revealed that deformation behaviour of the feldspar-bearing rocks transformed from ductility to rigidity prior to quartz-bearing rocks in a ductile shear zone at a crust depth rangeing from 15 to 10 km,along with crust uplifting and corresponding decreasing in temperature,would cause a strain instability somewhere and then the earthquake occurred.Varieties of the seismic fault-generated rocks and a dualistic deformation model have been discussed.

AN APPROACH TO THE INVERSION OF THE MAGNETOTELLURIC DATA OF THE INHOMOGENEOUS MEDIUM

Sun Chuanwen, Wang Guange, Chen Leshou

1992, 14(2):  176-182. 

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Significant errors may result when applying one dimensional (1-D) interpretation methods to magnetotelluric (MT) data collected in two dimensional (2-D) or three dimensional (3-D).Both resistivities and depths can be grossly incorrect if 1-D methods are applied in a 2-D or 3-D setting.Many methods to solve the existing problems can not be used practically beause of its computertime consumming and high costs and its strict application conditions.I suggest that the better methods can avoid complicated calculation such as finite elements,difference,integral equation etc.On the basis of the abstract to the 2-D or 3-D responses in the layered earth and the principles of fuzzy mathematics,I have developed a new method which has many advantages over exsisting ones:(1)It is able to eliminate 2-D or 3-D inhomogeneity effects and give a good and accurate 1-D geoelectric section.(2)It takes only a few minutes to complete an inversion on IBM/XT,so it can be easily applied to.practical work.However other methods spend about a few days inversing one 2-D geoelectric section's MT data on IBM/XT.(3)It is able to take into acount the both polarizations (TE and TM) at the same time,also inverse them respectively.The results can be verified by each other.(4)It has less problems of multiple solutions than other methods when processing MT data.

OSCILLATION TEST OF WELL LEVEL AND ITS RESULT

Zhang Zhaodong, Zheng Xiangyuan, Yin Jitao, Zhang Jiaoxiang

1992, 14(2):  183-188. 

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The parameters of characteristic frequency of the aquifer system in the well Lu-04 have been calculated for some well frequency under the test.The natural period of vibration is 40.59s and the damping factor is 0.0362s^-1.The transmissibility of the aquifer in the well Lu-04 has also been estimated to be 1.8?10^-3m²/s.The results may account for less responose of well Lu-04 to seismic waves than that of the Pearl Soring well.

THE APPLICATION OF SUN COMPASS IN THE STUDY OF PALEOMAGNETISM

Han Zhujun, Cheng Gouliang

1992, 14(2):  189-192. 

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