Table of Content

07 March 1990, Volume 12 Issue 1

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Brief Report

SEISMICITY TENDENCY PREDICTION BEFORE 2020 IN CHINA MAINLAND FROM ASTRONOMIC PERIODICITIES

Du Pin-ren

1990, 12(1):  1-11. 

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The correlations between large earthquakes in China continent and periodicities of the Moon's movement and the solar activity are statistically analysed and the following points are revealed:1. The earthquakes with ≥7.5 in Qing-Zang fault-block region have 18.6-yr periodicity of the Moon's nodes motion.2. The earthquakes with M≥7.1 in Xinjiang fault-block region have 8.85-yr periodicity of the Moon's perigee motion.3. The earthquakes with M≥7.0 in China mainland have the tendency to cluster around times of minima of sunspot cycles and in the even solar cycles.4. The earthquakes with M≥8.0 in China continent have the tendency to cluster around the valley times of the secular cycles of the solar activity.According to above correlations,the prediction of seismicity tendency can be given as follows: In China continent,especially Western China,the current active seismic period should continue up to the end of this century. The next active period would be 2006—2015.

STUDIES ON THE EFFECTIVENESS OF α TRACK METHOD IN EARTHQUAKE PREDICTION

Song Yi-feng

1990, 12(1):  12-14. 

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DURATIONS OF THE STRONG AFTERSHOCK ACTIVITIES AND RECURRENCE INTERVAL OF LARGE EARTHQUAKES

Fu Zheng-xiang

1990, 12(1):  15-20. 

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There is an obvious difference between the durations of strong aftershock sequences for ten large mainshocks with magnitude of 6.9 or more occurred in North and Southwest China during 1966—1981.The durations range from one day to one thousand days and are seemingly independent of mainshock magnitudes. The durations are related to the recurrence interval of the large shocks,the longer the duration,the longer the recurrence interval.From the view point of earthquake mechanics,a longer recurrence interval indicates a longer static contact of the fault plane,resulting in the increase of frictional strength,as well as the number and area of asperities. Therefore,a longer duration of strong aftershock sequence (ruptures of remainder strong asperities) after mainshock would be observed.

THE FEATURES OF LATE QUATERNARY ACTIVITY OF THE PIEDMONT FAULT OF MT. HUOSHAN,SHANXI PROVINCE AND 1303 HONGDONG EARTHQUAKE(M_s=8)

Xu Xi-wei, Deng Qi-dong

1990, 12(1):  21-30. 

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The piedmont fault of Mt. Huoshan is the main boundary fault in the northern part of Linfen basin. On the basis of geological mapping (scale: 1:10000) along the fault,the authors have studied in detail the geological history,segmentations and structural features,the right-lateral dislocations and slip-rates of the fault since the later quaternary as well as their relation to the 1303 Hongdong earthquake (M_s=8). Finally,the first order right-lateral movement on both sides of Shanxi graben system has been discussed according to the structural peculiarities of NNE-trending major faults.

SEISMIC ACTIVITY AND LOCAL TECTONIC STRESS FIELD IN NINGXIA AND NEARBY REGIONS

Zhao Zhi-jun, Liu Xiu-jing

1990, 12(1):  31-46. 

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From the recorded 18099 first motion symbols by the seismic station network in Ningxia and nearby regions and using the average of single earthquake source mechanism solutions and the average of small earthquake synthetic solutions,the local tectonic stress fields in 7 small areas are determined. The average direction of maximum compressive stress in the entire region is approximately N 30°E with local variations as N 60°E in Xi-Hai-Gu area; N 42°E in Yinchuan plain and Shizhuishan area; N 26°E in the north or west to the Shizhuishan as well as NE 17° in Wei-Ning area. The stress source of the areas are mainly from the southwest compression. It is also concluded that if the strike of weak seismic belts intersect in 25°—30° with the maximum compressive stress,the probability of moderate or large earthquake occurrence along these belts is relatively high.

THE EFFECTS OF LATERAL INHOMOGENEITY OF SURFICIAL STRUCTURES IN THE RESPONSE OF MAGNETOTELLURIC SOUNDING

Wang Bao-jun

1990, 12(1):  47-52. 

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The curves of apparent resistivity obtained from Magnetotelluric Sounding are greatly distorted by the lateral inhomogeneity of surficial structures. In order to delineate clearly the effects of inhomogeneity,in this study,the finite element method has been applied to simulate several structural patterns with lateral inhomogeneity and their effects on the response of Magnetotelluric Sounding. The results show that the effects of lateral inhomogeneity in the shallow layers are significant.

CHARACTERISTICS OF SOME PYROXENES IN GRANULITES FROM SOUTHERN NEI MONGOL

Yu Li-bao, Yang Zhu-en, Bao Xiu-ying

1990, 12(1):  53-56. 

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A MECHANISM OF THE FORMATION OF CHARACTERISTIC EARTHQUAKE CAUSED BY THE PIVOTAL MOVEMENT OF STRIKE-SLIP FAULT

Wang Hua-lin, Geng Jie

1990, 12(1):  57-62. 

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Based on the analysis and comparison of the features of characteristic earthquake and pivotal movement,it is concluded that the pivotal movement of strike-slip fault leads to the occurence of characteristic earthquake,and that the pivotal axis of the fault is the site of earthquake occurence.The result also shows that the Fuyun,Luhuo,Haiyuan and Tancheng faults are the seismogenic faults of characterstic earthquake.

PRELIMINARY STUDY OF FLUID GEOCHEMICAL FIELD ON HAIYUAN ACTIVE FAULT

Jiang Da-yong, Yan Xian-chen

1990, 12(1):  63-68. 

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The ionic content of groundwater increases gradually from the east to the west along the Haiyuan active fault. In the same hydrogeological conditions it is obviously higher on the segments which have high seismicities and larger displacement. There are regularities in the distribution of the components of gas in the overlying soil within the fault zone. The farther distance from the fault,the fewer the element content is. An anomalous zone of higher value is formed in the vicinity of the fault. The highest points,however,are not located entirely on the fault. In extension area,there is a bigger anomaly in amplitude of the contents of Rn,Hg and H. In compressional area,the largest anomalies of Hg and H appear at the segment which has the biggest displaument. The content of H changed obviously before and after the occurrence of Lingwu Earthquake.

GEOLOGIC MICROZONATION OF EARTHQUAKE HAZARDS IN DUSHANZI,XINJIANG UYGUR AUTONOMOUS REGION

Wang Li-gong, Cai Ling-duo, Chen Jian-ying

1990, 12(1):  69-75. 

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This paper briefly describes the peculiar geologic background of Dushanzi area,such as the newest erogenic movement,distinctive materials produced by mud eruption,broad gobi plain and particular deposits of depression. The geologic factors related to geologic background,including the foundation soil,topography,fault,colapse and landslide are also characterized by their regional particularity. Five earthquake hazards zones have been classified as A,B,G,D and E,on the basis of the analysis of seismic Vulnerability of geologic factors. According to the differences of ground effects in each zone,it is suggested that land utilization should avoid the southern zone but dwell on the northern zone,i. e. avoid the mud volcano and mountain front depression,but dwell on the gobi plain.

ESTIMATES OF VERTICAL DEFORMATION RATE ON THE BASIS OF HOLOCENE SEA-SHORELINE CHANGES IN SHENZHEN,GUANGDONG

Lu Yan-chou, Sun Jian-zhong

1990, 12(1):  76-78. 

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PALEOMAGNETIC STUDY ON THE DANFENG GROUP OPHIOLITE IN QINLING AREA AND ITS TECTONIC SIGNIFICANCE

Wu Han-ning, Zhu Ri-xiang, Liu Chun, Chang Cheng-fa

1990, 12(1):  79-85. 

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This paper presents the results of detailed paleomagnetic study on the ophiolite of Danfeng group in Qinling erogenic zone. The paleomagnetic pole position and paleolati-tude of Danfeng group have been located on the basis of the origin and formation age of remanence,as well as the impact of metamorphism and deformation on the characteristic component. The origin and evolution of Danfeng group have also been discussed.

THE FORTH SYMPOSIUM ON TECTONOPHYSICS AND THE SECOND SYMPOSIUM ON HIGH TEMPERATURE AND HIGH PRESSURE ROCK MECHANICS HELD IN BEIJING

Ma Sheng-li

1990, 12(1):  86-86. 

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THE HEADWARD MIGRATION RATE AND AGE OF KNICKPOINTS OF THE GULLIES AT EASTERN PIEDMONT OF HELANSHAN MT.

Cui Li-ming, Wang Ping, Pan Zu-shou, Liao Yuhua, Wang Yi-peng, Song Fang-min

1990, 12(1):  87-95. 

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Based on the measurements of the positions of knickpoints in the gullies passing throngh pluvial fans,this paper deals with the factors that influence the headward migra tion rate of knickpoints in the gullies dissecting the east piedmont fans of Helanshan Mt. The relation between the position and age of knickpoint hasbeen established. The result shows that at least 3 prehistoric events of magnitude,as large as that of 1739 Pingluo earthquake have occured along the eastern Piedmont fault of Helan Mountain since Holocene. The recurrence interval of great earthquakes in this area is determined to be 2500-3500 years.

SYMPOSIUM ON THE CONTINENAL TECTONICS AND METALLOGENESIS HELD IN WUHAN

Xia Yuan-qi

1990, 12(1):  96-96. 

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