Table of Content

10 March 1999, Volume 21 Issue 1

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Brief Report

STUDY ON THE TIME SCALE OF LATE QUATERNARY HYDROGENIC SEDIMENTS ALONG THE NORTHEASTERN MARGIN OF QINGHAI XIZANG PLATEAU

Yuan Daoyang, Shi Yucheng, Liu Baichi

1999, 21(1):  1-8. 

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The comparative research of the river terraces along the northeastern margin of Qinghai Xizang plateau indicates that the heights and ages of terraces of different grade rivers are quite different. But there is correlation between the heights and the ages. A statistical relationship formula is proposed. The terrace ages of river and the drainage system are compared with the ages of paleosoil in the loess profile. The results indicate that the development of terrace is controlled by tectonics and climate. We can use the paleosoil ages of Lanzhou area loess profiles (one of the standard loess profiles) to establish an initial late Quaternary microgeomorphogy time scale. The vertical rising rates reflected by the terraces show that since 1.5Ma the northeastern margin of Qinghai Xizang plateau are continuelly rising with a tendency of becoming quicker. During mid Pleistocene the rise rate is about 0.1～0.25mm/a. Since late Pleistocene to Holocene, the rise rate is about 0.5～1.5mm/a. The relationship between the rise rates and ages has been changed with time.

THE CRUSTAL SEISMIC S WAVE VELOCITY IMAGE IN THE WEIHE DOWNFAULTED BASIN AND ITS ADJACENT AREAS

Yuan Zhixiang, Ding Yunyu, Di Xiuling

1999, 21(1):  9-17. 

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The S-wave data are selected from the records of 1 946 earthquakes observed in the period from 1984 to 1993 by seismic network in the zone of 104～112°E, 31.5～38°N in Shaanxi, Shanxi, Henan, Hubei, Gansu and Ningxia Provinces.The S-wave velocity image of the crust beneath the Weihe downfaulted basin and adjacent areas is obtained by means of seismic tomographic technique. The results show that the non uniform S-wave velocity structure of deep crust is closely related to the difference of geotectonic element,fault structure and seismic activity.

STUDY ON SEISMOGENIC FAULT'S BEHAVIOUR OF TANGSHAN EARTHQUAKE AND ITS RELATION WITH STRONGER LATE AFTERSHOCKS

Xie Jueming, Hua Caihong

1999, 21(1):  18-20. 

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THE CHARACTERISTICS OF FAULT GOUGES FROM THE XIANSHUIHE FAULT ZONE AND ITS GEOLOGICAL IMPLICATIONS

Yang Zhu’en, Guo Fang, Li Tieming, Lu Yipei

1999, 21(1):  21-28. 

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The Xianshuihe fault zone is a well known active fault located at the north eastern boundary of the Tibetan plate. The micro texture and microstructures of fault gouge, the eroded micro texture and microstructures on the surface of quartz fragments from the fault zone are measured by Scanning Electron Microscope. The results of statistics and analysis show that the fault zone has experienced the intense oriented stress field and displays the stick slip movement mode. Its activity was still continuing from late Pleistocene to Holocene. Both the feature of the grain size distribution from fault gouge and the analysis of the fractal dimension have the obvious segmentation along the fault zone. This is consistent with the result from geodetic surveying along the fault zone in recent years.

THE CRUST MANTLE TECTONICS AND VELOCITY STRUCTURE CHARACTERISTICS IN XIANGHE-BEIJING-ZHULU AND ITS ADJACENT AREAS

Zhao Jinren, Zhang Xiankang, Zhang Chengke, Zhu Zhiping, Ren Qingfang, Zhang Jianshi

1999, 21(1):  29-36. 

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The deep seismic sounding data set obtained from the west section of northwest trending wide angle reflection and refraction Xianghe-Beijing-Zhulu profile have been studied by means of two dimensional processing,calculation as well as synrhetical interpretations,and rhe basic features of crust mantle velocity structure and deep tectonics about this range are determined.The resulrs show that the crust mantle velocity structures present both lateral and radial hetergeneity in different range. The deep crust mantle tectonics appears evidently layered structures and the Moho discontinuity slops down from east to west.The crust thickness,which is 32～33km in Xianghe east,sharply reaches 39～40km in Xishan mountain area of west Beijing and south Huailai as well as Zhulu. In Beijing,its thickness is about 36.5km and in west Xianghe exists deep fault stretching to the Moho interface.

STUDY ON THE HYBRID SEISMIC MODEL FOR SEISMIC ZONATION-WITH THE EXAMPLE OF QILIAN MOUNTAIN

Dong Reishu, Ren Guoqiang, Ran Hongliu

1999, 21(1):  37-47. 

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For the potential seismic sources of upper bound magnitude 7.5 or 8.0 in study area of Qilianshan, the occurrence intervals of magnitude 7.0～7.4 or 7.5～7.9 are calculated by using the method of slip rate, respectively. The intensity corresponding to 10% probability of exceedance in 50 years are calculated by using elliptical attenuation of earthquake intensity of western China and mixed model, which includes NB conditional probabilistic model and NB cumulative probabilistic model for characteristic earthquakes, and Segment-Poisson Process for medium earthquakes. The results show that the influence of the potential seismic sources with a long elapse time and a small area are stronger and the influence dilution should be considered for those potential seismic sources of large area.

DISCUSSION ON SOME PROBLEMS IN APPLICATION OF MDD MODEL Ⅱ-SIGNIFICANCE OF ACTIVATION ENERGY DETERMINATIONS

Li Qi, Chen Wenji

1999, 21(1):  48-50. 

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For the MDD model the activation energy determination has remarkable influence upon the cooling temperature curve of which the value is about 7～8℃/kcal·mol^-1. But it does not change the shape of the cooling curve.The affecting factors of low value by activation energy determination include heating duration in low temperature stage, pureness of K-feldspar and mixture of some plagioclase, quartz et al.

TECTONIC STRESS FIELD AND LARGE EARTHQUAKE RECURRENCE PERIOD IN CHINA

Liang Haihua, Hou Jianjun, Liu Shuwen, Chang Zufeng, Yan Zhimei

1999, 21(1):  51-57. 

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The recurrence interval of large earthquake varies from one active fault to another inferred from palaeoseismic data in China. Generally speaking, the interval in eastern part of China is much longer than that in the western part, and that around the plate boundary is remarkably shorter than within the plate of China. To consider the reason for the phenomenon, a mechanical model was constructed by the method of finite element numerical analysis to probe into the distribution of elastic strain energy caused by tectonic stress. The procedures to be used in this paper are:(1) to analyze the boundary condition and action pattern of force on the boundary in China and its adjacent areas by geological method, (2) to make inversion of the force acted on the boundary and the tectonic stress field in the region by finite element method based on the criterion of the maximum principal stress direction, (3) to calculate the attenuation of strain energy with the increase of distance apart from the plate boundary. Based on the attenuation pattern, the accumulative range of strain energy is converted to reach a given value (a given magnitude of large earthquake) in different parts of the research region into time or period, which is compared with the known recurrence interval of large earthquakes along an active fault zone obtained by palaeoseismic method. The comparison shows that the remarkable difference of large earthquake recurrence intervals between plate boundary and plate interior can be well explained by the attenuation pattern of strain energy.

A STUDY OF UNDERGROUND HOT WATER OF XINJIANG IN RELATION TO EARTHQUAKES

Wang Dao, Xu Qiulong, Chen Lin, Lu Jinfang

1999, 21(1):  58-62. 

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Underground hot water occurs widely in the Kunlun, Tianshan and Artai mountains of Xinjiang. Hot spring, seismicity, tectonics and plate movement are closely related to each other. Analyses of the dynamic observational data show that changes of hot water temperature is influnced by earthquakes and indicates precursors to these events. Chemical analyses have been made to the underground hot water. It is suggested that some hot water have the special nature of low mineralization, high alkalinity, high fluorine and high helium. It may be the inner original water fomed in the deep crust or upper mantle wich is of importance to the study of inner materials and processes of the Earth.

A SYNTHETICAL STUDY ON ACTIVE BEHAVIOR OF FAULT IN BEDROCK AREA OF NORTHEASTERN DABIE MOUNTAIN

Yao Daquan, Tang Youbiao, Liu Jiacan, Li Jie, Liu Qingzhong, Wang Jilin, Ze Hongto

1999, 21(1):  63-68. 

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Based on studying of satellite and aerial photographs, we made field investigations and sampling to the fault which occurred in bredrock area of northern Dabie mountain. The particular emphasis is laid on research of dislocation geomorphology and deformation material, and analysing the time space characteristic of seismological activity. We obtained information of the fault including its active time mode, and relation to earthquakes. It offers an example for research way to active behavior of the fault in bedrock area.

RATE AND DYNAMIC CHARACTER OF FAULT MOVEMENT IN RECENT TIME IN NORTH CHINA

Che Zhaohong, Fan Yan

1999, 21(1):  69-76. 

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In this paper we have analyzed the data of mobile geodetic deformation across faults in North China, calculated average rates of fault movement, studied dynamic evolution of annual variation of fault movement. The results show that the recent fault movement rate is small in North China and the average rate is 0.17mm/a. Fault movement rate in Shanxi Yanhuai area is faster than average rate in North China. Movement rates tend to rise in Shanxi belt and North Tanlu belt, which have close relation with seismic activity in recent time. Rates of fault movement have increased before strong earthquakes in large extent. Turning of fault movement manner in macroscopic may be one of the important signs ploting out period of seicmic activity.

APPLICATION OF THE NEURAL NETWORKS TO THE EPICENTER LOCATING OF EXPLOSION EARTHQUAKES

Li Xuezheng, He Yingfeng, Lei Jun, Hu Yuliang

1999, 21(1):  77-82. 

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The algorithm principle of BP neural networks is briefly introduced in the paper, at the same time, the formation of networks and the study skills are provided. Because of the earth medium non homogeneity and complicity of geological conditions of seismic stations, the relationship between epicenter distance and seismic wave propagation time is not linear.It has been found that epicenters located by usual seismic location method deviate from real epicenters. The deviation of distance is about 20km to 30km. The neural networks can be sucessfully applied to the epicneter locating as they have a high non linear reflective function. The errors between epicenters calculated by neural networks and actual epicenters are less than 8km and 18km respectively in and out of the seismic network control area.

ANOTHER STUDY ON THE TIME AND PROCESS OF QUATERNARY CRUSTAL MOVEMENT OF THE CHINESE CONTINENT

Feng Xijie

1999, 21(1):  83-87. 

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From the time series of neotectonic movement of the Qaidam Basin, the main neotectonic events of the Yellow River valley in Lanzhou,the main active stages of the Altun fault zone and time series of some faults activity throughout the country, this paper discusses the time and process of Quaternary crustal movement of the Chinese continent once again and gives the following conclusions:(1) The characteristics of the time and process of Quaternary crustal movement of the Chinese continent not only occur in the time series of the volcanic activity of the Chinese continent,uplifting of the Qinghai Tibet Plateau, deformation of the Loess Plateau and faulting in the Three Gorges area of the Yangtze River and it’s adjacent areas during the Quaternary, but also exist in the time series of neotectonic movement of the Qaidam Basin,in the main neotctonic events of the Yellow River valley in Lanzhou, in the main active stages of the Altun fault zone and Quaternary activity of some faults throughout the country. (2) Although source materials are obtained from different regions, and they represent different crustal movement forms, their time series of activity are mainly consistent. (3) The Quaternary crustal movement of the Chinese continent are marked by an obvious rime span characteristic, Since the Early Pleistocene, there have been four times of tectonic movement(the initial Early Pleistocene, the middle Early Pleistocene, Middle Pleistocene and Holocene), of which the Middle Pleistocene tectonic movement is the strongest.

ADVANCES OF RESEARCH ON RHEOLOGY OF THE LITHOSPHERE

Zhou Zhenheng, Deng Wanming, Xiang Caiying

1999, 21(1):  88-96. 

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The objective of lithosphere rheology is to study deformation, flow and their mechanisms of lithospheric materials. With the rich results of the experimental rock mechanics under high temperature and high pressure and of geothermal study, this research field has made great progress since 1970’s. The significant advance was that Ranalli et al. (1987) constructed 7 lithospheric rheological profiles and expouded the properties of lithospheric rheological stratification and other scientists have achieved the similar results for different regions ever since. As a result, the theory of lithospheric rheological stratification has come into being. The tectonic phenomena of different scale studied in many subdisciplines of geoscience may be interpreted by applying this theory. Lithospheric structural stratificantion and rheological properties control the formation and evolution, especially deformation of continental tectonics. The studies of recent years have indicated that a series of plutonic tectonic actions, such as ductile shear of lower crust, gravitational collapse and relaxation of Moho topography in the late and post orogenic evolution of mountain belts, correlate closely with softening and plastic flow of lower crust while the brittle regime of mid upper crust or uppermost mantle in the convergent belt controls the distribution of earthquake foci.