Table of Content

01 June 1988, Volume 10 Issue 2

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Brief Report

SLIP RATES AND EARTHQUAKE RECURRENCE INTERVALS OF THE WESTERN BRANCH OF THE XIAOJIANG FAULT ZONE

Chen Rui, Li Ping

1988, 10(2):  1-13. 

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In this paper, the average slip rates of the western branch of the Xiaojiang fault zone are estimated as 6.7 mm/yr, 7.0 mm/yr and 6.4 mm/yr during the Quaternary period, the late Pleistocene epoch and the Holocene epoch respectively according to the offsets of the geomorphic and geologic features and their ages. Furthermore, the recurrence intervals of strong earthquakes and the activity of the fault zone are discussed on the basis of the estimate of the slip rates and the research on both prehistorical and historical seismicity. The results indicate that the western branch of the Xiaojiang fault zone is characterized by repeated activity which leads to the periodical occurrences of strong earthquakes. The average recurrence interval at the same site of the fault is about 900 years and that on the whole fault zone is more than 330 years.

STUDY ON THE JIANGNAN MIDDLE-MACROSEISMIC BELT

Yang Zhi-jian

1988, 10(2):  14-18. 

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Jiangnan fault zone, formed after middle Proterozoic, is a palaeo-fault zone controlling rocks and mineral as well as a middle-macroseismic belt(earthquake magnitude: 4³/₄—6³/₄; seismic intensity: Ⅵ-Ⅷ), which is another seismic belt south of Tonglin-Yangzhou seismic belt.

THE FEATURES OF THE PAIRED METAMORPHIC BELTS AND EVOLUTION OF PALEOTECTONICS IN THE EAST PART OF DABIE MOUNTAINS

Ma Bao-lin, Zhang Zhao-zhong

1988, 10(2):  19-28. 

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The features of paired metamorphic belts in the east region of Dabie Mountains have been briefly discussed in this paper.By mineralogical research and chemical-thermal calculation we have determined a paired metamorphic belts in the North Huaiyang region.In the high pressure-low temperature metamorphic zone a lot of index minerals and intergrowth of the index minerals have been discovered. In the typical segment, the ancient thermograde is 11 - 13℃/km. On the contrary, in the high temperature-low pressure metamorphic zone, there is a centre thermal-axis composed of migmatite, granite, and the intergrowth of the index minerals. In the centre thermal-axis the ancient thermograde is 45℃/km.The determination of the paired metamorphic belts in North Huaiyang makes the geotectonic attribution in this region definite, and the evolution of the paleotectonics in. North Huaiyang has been discussed.

ANOMALY OF INFORMATION ENTROPY BEFORE GREAT EARTHQUAKES——THE CASE STUDY OF WUQIA EARTHQUAKES

Zhu Ling-ren

1988, 10(2):  29-38. 

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The small earthquake activity often presents various anomaly, such as strip, gap, crowd and string etc., during preparing process of a great earthquake. The anomaly reflects the decreasing randomness and the increasing orderness for the samll earthquake activity(microfracture). Here the envolution of small earthquake activity from dis-order to order before great earthquake is studied quantitatively by introducing the concept of information entropy.

THE DEFORMATION ZONE OF WUQIA EARTHQUAKE OF M = 7.4 IN 1985

Feng Xian-yue, Luan Chao-qun, Li Jun, Zhang Yung

1988, 10(2):  39-45. 

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A deformation zone on the earth's surface along terrace in the Kezilesu River valley was formed by Wuqia earthquake of magnitude 7.4 in 1985. It is mainly composed of seismic scarps, seismic faults, fissures and the pressure ridges, etc. The length of the deformation zone is about 15 kilometres and the maximum width is 800 metres. The deformation zone extends in the direction of nearly east-west in the western part, and of 310-320℃ in the eastern part. The general distributional characteristic of this zone is a deformed arch which projects to northeast. The seismic fault is of different properties at the different section of the deformation zone. The thrust fault strikes to east-west and the fault plane dips to 160-210° with the angle of 30°. The maximum horizontal dip slip is about 2 metres. The normal-strike-slip fault strikes to 340-350° and fault plane dips to northeast with angle of 80-88°. The maximum right lateral offset is 1.55 metres. The strike-slip-thrust fault strikes to 280-305°and the fault plane dips to southwest with angle of about 30°. The maximum right lateral offset is 1.25 metres. Most of the compressire ridgas extends in the direction of east-wast and the maximum horizontal shortening distance is 0.4 metres.

FIELD SEMINAR ON PERMO-TRIASSIC SEQUENCES OF THE SALT RANGE, PAKISTAN

Yan Zheng

1988, 10(2):  45-45. 

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EXTENDING OF THE TANCHENG-LUJIANG FAULT ZONE AT THE ANHUI SECTION AND ITS NEOTECTONIC ACTIVITY

Tang You-biao, Shen Zi-zhong, Lin Shou-pei, Zhang Jie

1988, 10(2):  46-50. 

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The Tancheng-Lujiang foult zone is a large seismic zone. The middle segment has been well studied compared to the southern one. Based on the field investigations in recent years, this paper suggests that the southern segment consists of two main faults holding the Mesozoic-Cenozoic grabens and show different neotectonic activities and geologic: structures.

ON FEATURES OF SLIP MOTION ON SOURCE FAULT PLANE IN WESTERN HUBEI

Li Rong-chuan

1988, 10(2):  51-56. 

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In this paper, focal mechanisms of 23 moderate and small earthquakes(M_s = 2.0-5.1) in the area of the western Hubei occurring during 1972-1985 are analysed. The results indicate that slip of source fault planes is different, there are mainly normal faults in the southwestern Hubei, while in the northwestern Hubei thrust faults are dominate, suggesting differential tectonic movement in western Hubei.

《PRINCIPLES OF ROCK DEFORMATION》 IS COMING OUT(IN CHINESE)

1988, 10(2):  56-56. 

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ANALYSIS OF "QUATERNARY FAULTS" ON THE SIDES OF JINSHAN TROUGH, SHANGHAI

Ji You-ting, Li Duan-lu

1988, 10(2):  57-64. 

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The phenomena of faulting in the upper part of Quaternary strata on the sides of Jinshan trough near Shanghai, shown by a superficial reflection profiling, represent a limiting interfaces of different media in constituent and construction, which formed by later deposition in the former erosion surface and gulch during the development and evolution of the trough. They are in part the slips occurred beneath water along the trough walls during its development. The reflective interfaces in the upper part and interior of the trough come from the stratification of different ages. Therefore, there are no Quaternary active faults on the sides of Jinshan trough.

THE RELATION OF THE LATERAL CHANGE OF ELECTRIC PROPERTY IN CRUST-UPPER MANTLE WITH GREAT EARTHQUAKE IN PARTIAL REGION OF NORTHWEST CHINA

Zhang Yun-lin, An Hai-jing, Liou Xiao-lin, Liou Bao-qin, Ja Zheng

1988, 10(2):  65-73. 

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Based on the observation data from 52 MT stations, this paper deals with the change of lateral electric property in crust-upper mantle in partial region of Northwest China. According to the depth of upper interface of the first low resistivity layer in upper mantle, the interesting region can be devided to four kinds of areas: shallow(depth of 55-90km), medium-shallow(90-110km), medium-deep(110-160km) and deep(160-250km).The electric property at depth associated with 6 great earthquake cases is discussed also. The results indicate that the area with steep gradient zone of the top of upper mantle, the area with evident change of lateral electric property in crust, and the area with particularly thickened low resistivity layer in crust may be considered as potential earthquake areas.

THE EARTHQUAKE FAULTS OF THE LATE QUATERNARY ON EASTERN PIEDMONT OF CANGSHAN MOUNTAIN AND THE AGES OF PALEOEARTHQUAKES OCCURRING IN DALI CITY, YUNNAN PROVINCE

1988, 10(2):  74-74. 

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AN EXPERIMENTAL STUDY ON THE CHARACTERISTICS OF ELASTIC WAVE PROPAGATION IN MARBLE SPECIMEN UNDER TRUE TRIAXIAL COMPRESSION

Hua Pei-zhong, Xu Zhao-yong, Li Pei-lin, Han Ming

1988, 10(2):  75-80. 

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An experimental study on the travel time, magnitude and attenuation characteristics of elastic wave propagating along σ₂(x direction)and σ₃(y direction) in marble specimen has been carried out using a true triaxial(σ₁>σ₂>σ₃) compression apparatus. With increasing stress the travel time t and magnitude A of the first peak of P wave decrease, on the contrary while along the y direction it gives a completely opposite result. Starting from 95% of failure strength along both directions t increases rapidly, but A decreases and the attenuation coefficient K of wave magnitude also decreases. This phenomenon is considered as a characteristic change of the fracturing forerunners under true triaxial compression. For the I way of applying stress to the specimen the differential stress at the moment of rapid increase of t value is lower than that for the I way.

PALEOMAGNETIC STUDY ON THE TECTONIC EVOLUTION OF THE ORDOS BLOCK, NORTH CHINA

Cheng Guo-liang, Bai Yun-hong, Sun Yu-hang

1988, 10(2):  81-87. 

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The Sino-Korea Platform consists of the Ordos the block, Taihangshan block, Jilu block, Jiaoliao block and so on. The paleomagnetic pole positions of Late Permian and early Triassic are statistically consistent for these blocks, which shows that these parts had already been coherent units within the Sino-Korea Platform since Late Permian. The paleomagnetic pole positions for the Ordos block are 42.3癗, 13.7癊 in Late Permian, 49.1癗, 12.5癊 in Middle Triassic, 80.3癗,249.4癊 in Middle Jurassic and 84.6N, 310.2癊 in Early Cretaceous, respectively. These suggest that the Sino-Korea Platform underwent a northward movement from low latitude of about 19癗 to middle latitude and rotated counterclockwise by about 50?. The major northward movement took place from Late Permian to Middle Triassic whereas the major counterclockwise rotation from Middle Triassic to Middle Jurassic. The tectonic evolution of the Sino-Korea Platform from Middle Triassic to Middle Jurassic may be related to the collision between the so-called Indosinian orogeny.

STUDY ON ACTIVE FAULT BY MEANS OF MEASURING GASEOUS MERCURY CONTENT IN SOIL

Wei Bai-lin, Xue Jia-mou, Li Fu-guang, Chen Pang-long

1988, 10(2):  88-92. 

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The authors have studied the activitis of Heyuan-Shaowu fault, Guangzhou-Conghua fault, Shougouling fault, Baini-Shawan fault by means of measuring gaseous mercury content with XG-4 digital mercurimeter. 296 gaseous samples were collected along 29 measurement lines. After analysing and comparing the measuring data the authors have come to get five preliminary conclusions: 1) there is higher background value of mercury content in the area where developed active fault has been preferred over ordinary area; 2) the sections showing high mercury content appear in and around active fault zone, mercury content decrease with the distance from the fault, 3) mercury content in the intense active section of the active fault is higher than that in the other section, 4) the site of anomalous mercury content commonly is in the upfaulted block and 5) the position of the buried active fault can be determined based upon the distribution of the sites of anomalous, mercury content.