Table of Content

07 September 1988, Volume 10 Issue 3

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Brief Report

PALEOMAGNETIC EVIDENCE FOR THE RELATIVE MOTION BETWEEN THE SOUTH CHINA BLOCK AND INDOCHINA BLOCK

Lin Jin-lu

1988, 10(3):  1-11. 

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The Mesozoic paleomagnetic pole positions from the Indochina block and South China block are not consistent with each other in that the formers are displaced with respect to the latters westward in longitude and southward in latitude. The displacement is here interpreted as to be related to the India-Eurasia collision in such a way that after the collision the Indochina block was rotated clockwise by 8? about the Assam syntaxis, followed by an eastward translation of the South China block by about 20?. This interpretation is in accord with the propagating extrusion tectonics model, and suggests that the sense of motion along the Red River fault has reversed, i. e., changed from the early left-lateral to the present right-lateral.

NEOTECTONIC FEATURES OF THE XIANGSHAN-TIANJINGSHAN ARC FRACTURE ZONE AND THE SEISMIC DEFORMATION ZONE OF 1709 SOUTH OF ZHONGWEI M= 7¹/₂ EARTHQUAKE

Zhang Wei-qi, Jiao De-cheng, Chai Zhi-zhang, Song Fang-min, Wang Yi-peng

1988, 10(3):  12-20. 

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On the basis of field tectonic mapping and measurement of the water setting displacement, we concluded in this paper that the Xiangshan-Tianjingshan arc fracture zone experienced two different active stages in the Cretaceous, i. e. strongly compression in the beginning and left-lateral strike-slip with compression at the end. The time boundary and cause of transition were analyzed and discussed. The appearance and range of the seismic deformation zone of the 1709 south of Zhongwei M = 7¹/₂ earthquake is also described.

FINDING OF TEKES-ZHAOSU EARTHQUAKE FAULTS IN XINJIANG AND SOME DISCUSSION

Yang Zhang, Guo Heng-zu, Ding De-xuan, Xu Dao-zun

1988, 10(3):  21-27. 

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A seismic fracture zone was found in 1986, when authors explored Tekes-Zhaosu basin. This fracture zone extends to 70 km long and its maximum vertical and hori-zantal displacements are both 8 and meters the other seismic deformation phenomena were also seen. We stadied these phenomena and drew an isoseismac map. The age, epicenter and magnitude of the earthquake have been discussed too. This fracture zoneis cor-sidered as the result of the earthquake in 1716.The trend and motion of this earthquake fault is consistent with the Kebo river-Zhaoguanchu fractures. It is shown that this fracture zone is the result of a left-lateral overthrust.Tekes fracture zone is a complex zone, consisted of several fractures. The earthquake in 1716 showed that the Tekes fracture was a recent active fault.

THE CHARACTERISTICS OF THE SHULAN FAULT ZONE, JILIN PROVINCE

Liu Xiang

1988, 10(3):  28-32. 

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The Shulan fault zone belongs to the middle part of the well-known Yilan-Yitong fault zone in Northeast China. From the view of tectonic analysis and historical evolution, the basic features of the Shulan fault zone is desribed in this paper.During the Tertiary period, the Shulan fault zone was characterized by graben showing tensile and tensoshearing properties. Due to a violent tectonic movement at the end of the Tertiary, the Tertiary formations were folded, uplifted and fractured into NE-trending reverse as well as right-lateral strike-slip reverse. At the beginning of the Quaternary, basalt magma extruded along the fault. The recent record of some small earthquakes suggests that the fault is still active now.

INDICATORS OF TOPOGRAPHICAL DEFORMATION RATIO AND SEISMIC ZONATION OF NORTH CHINA

Huang Xiu-ming

1988, 10(3):  33-44. 

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This paper deals with indicators of topographical deformation. They are the changing values of vertical velocity per unit distance along the horizonal direction on the sur-facial deformation field in which crustal vertical movement is dominant. Taking seismi-cal risk zoning in the North China as an example, the author considers that the determined indicators can be provided as a useful quantitative basis for forecasting future earthquakes.

THE SEISMOTECTONIC BACKGROUND OF 1695 LINFEN M = 8 EARTHQUAKE FROM INTERPRETATION OF LANDSAT IMAGE

Li Jian-hua

1988, 10(3):  45-51. 

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Based on interpretation of landsat image and historic seismic data, the major active faults in Linfen area and the seismic deformation traces along the NW-trending Zuo-mu-Xiandi fault are described and the seismotectonic background of 1695 Linfen M = 8 earthquake is discussed.

THE SPATIAL RELATION BETWEEN EARTHQUAKES AND OIL-GAS

Ding Jian-min, Liang Guo-ping, Gao Jian-li, Guo Qi-ling

1988, 10(3):  52-60. 

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We have studied the space distribution of Ms>5.5 earthquakes in the North China plain and its adjacent regions and discovered that there exists a kind of empty-area without earthqakes besides the empty-area with earthquakes. The empty-area without earthquakes is surrounded by relatively large earthquakes wherein there were neither historic strong earthquakes and will nor occur large earthquakes in late hundreds of years, and its indicative is the underground oil and gas. After observing the space distribution of relatively large earthquakes in some of major deposition basins and their surroundings in China, we concluded that where earthquakes concentrate, there are not oil and gas wheras where oil and gas are reserved, strong earthquakes often occur.From the view of oil-born, oil-reserve and cap-rock of oil and gas, earthquakes: would destroy these conditions, i. e. oil and gas in a region will transport and escape away along faults due to frequent seismicity even where there is a fine cap-rock and deposited oil and gas, and on the contrary, a region with oil and gas should be a stable massif and no strong earthquake will occur there in late hundreds of years. Based on this idea, three non-earthquake regions have been distinguished in the North China plain, i. e., the Lower Liaohe the East Liaoning Gulf, the Bohai Gulf-Cangzhou-the Yellow River delta and Baxian-Gaoyang.We point out at the end of this paper that the current work is also of importance for evaluating and forecasting the prospect areas of oil and gas, and that Lianyungang and its adjacent sea area and the South China sea regions might be abundant in oil and gas.

A SMALL EARTHQUAKE SWARM IN RONGCHENG OF SHANDONG PROVINCE IN MAY, 1986

Lin Huai-cun, Wei Guang-xing, Hua Ai-jun

1988, 10(3):  61-66. 

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The characteristics of the earthquake swarm series occurred in Rongcheng area of Shandong Province on May 25 and 26, 1986 are presented in this paper. The swarm is of high and fast attenuation frequency, and of low energy and concentrated locations. The amplitude ratio of P to S waves is calculated and the esttimated average Q value for seven earthquakes is 96 by the tails of S waves. It is suggested that the swarm might occur frequently and was not a precursory one.

TECTONIC FEATURE OF QINGHAI-XIZANG PLATEAU AND ITS STRESSED STATE

Zhong Jia-you

1988, 10(3):  67-87. 

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This paper deals with the uplift mechanism and the uplift form of Qinghai-Xizang (Tibet) plateau and the deformation regularity of its surrounding region caused by this uplifting. It is shown that the insertion of Indian plate with the wedge-like frontal margin beneath Qinghai-Xizang plateau made the plateau compressed and uplifted; at same time along several pre-existing large faults, striking NE and NW, the strike-slip movement took place. It is of great significance to study Asian regional tectonics, especially to the present tectonic movement.

ARCHAEAN GRANULITE AND SUBDIVISION OF LOWER CRUST IN EASTERN HEBEI, CHINA

Wu Zong-xu

1988, 10(3):  88-92. 

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Archaean granulite in eastern Hebei may be divided into pyroxene and hornblende-granulite subfacies. depending on whether they contain hornblende or biotite or not. Based on the mineral equilibrium assemblage, the estimated P-T of pyroxene and hornblende subfacies are 800-850℃, 9-11 kbars and 700-750℃, 7-9 kbars, respectively. The lower crust inferred from the granulite subfacies in eastern Hebei may consist of two layers, the lower one (30-37 km) consists of pyroxene granulite subfacies and upper(23 -30 km) of hornblende granulite subfacies. This suggestion is consistent with geophysical data. The occurrence of the upper mantle spinel in the pyroxene subfacies supports the suggestion of pyroxene subfacies for the lower layer of the lower crust.

APPLICATION OF FISSION TRACK DATING IN THE FRACTURE TECTONIC TRACE

Zheng Jia-xin

1988, 10(3):  93-96. 

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After sampling and ore-dressing of the NNE fracture zone in the Jinshanbang granitic batholith in Suzhou, as well as chemical etching and neutron radiation of its heavymineral——apatite, we observed and statistically analysed its spontaneous and inducedfission track by means of white mica external probe. Our conclusions are as following:1) the fission track dating of samples No. 1, 2, 3 and 4 are 1.724±0.077×10⁸ -2.12 ± 0.076× 10⁸ years and mostly 1.724 ± 0.077 × 10⁸-1.88 ± 0.038× 10⁸ years, showing that the granitic batholith intruded in Jurassic-Cretaceous period;2) the fission track year of sample No.5 is 0.1920± 0.013× 10⁸ years, indicating that the geological event of the fault-breaking trace was in Miocene. In combination with historical earthquake and other geological information, we suggest that the earth's crust in this area has been relatively active in recent period; and3) it looks promising to apply the fission track method to active fault dating.