SEISMOLOGY AND GEOLOGY

RESULT OF SEISMIC REFRACTION SOUNDING ALONG THE TRANSECT FROM XIANGSHUI. JIANGSU, TO MONDULA, NEI MONGOL

Liu Chang-quan, Jia Shi-xu, Du Guan-heng

1991, 13(3): 193-204.

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The Geoscience Transect passes through the China-Kroea Platform and its southern and northern borders in the southeast-northwest direction from Xiangshui, Jiangsu to Modula, Nei Mongol. This paper deals with the result of seismic refraction sounding along the geoscience transect. In combination with a part of magnetotelluric sounding, gravity and magnetic data, the crustal structure, tectonic features and the dynamic process of evolution of eight geotectonic units on the transect are revealed rerpectively. The deep structural background for the seismic activity along the transect is also discussed in this paper.

THE GEOLOGY AND SEISMICITY OF THE SOUTHERN HUANGHAI (YELLOW) SEA

Chen Xin, Mao Zheng-yi, Wang Fu-tian

1991, 13(3): 205-212.

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The Southern Huanghai (Yellow) Sea is a part of the North China platform and Yangtze platform, and is a large Mesozoic and Cenozoic composite basin consisting of uplifts and depressions. In this area the neotectonic movement is dominated by faulting, magmatism and differential elevation and subsidence. There are frequent and active earthquakes resulted from recent active faulting. The seismic activity appears mainly in the southern depression-Wunansha uplift area and offshore fault zone parallel with the coast of Jiangsu. The seismicity will keep reciprocally migrating along the above zone within the corning longer period.

CHRONOLOGICAL STUDY ON NEOTECTONIC MOVEMENT IN ZHUJIANG DELTA AREA

Chen Wei-guang, Zhang Hu-nan, zhang Fu-Lai

1991, 13(3): 213-220.

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Fourteen age data published in this paper were obtained from various geomorphic elements in the Zhujiang delta area, which were formed in various geologic times. The authors discuss the neotectonic movement in this area since Late Quaternary based on these data and consider that from the late stage of middle Pleistocene to the early stage of Epipleistocene, the crust in the area was comparatively stable, while a vertical movement started in the, late stage of Epipleistocene. The uplift amplitude of northern block reaches about 14—15m with a rate of 0.4—0.7mm/a, and the subsidence amplitude reaches about 16-20m with a rate of 0.5—0.7mm/a. The subsidence amplitude of southern block reaches 22—50m with a rate of 0.7—1.8mm/a. Since the Holocene the uplifted area tends to be stable or slightly downcast, and the subsidence area still continues to subside at a rete of 0.9—4mm/a. The subsidence amplitude increases gradually from northern to southern part of the area.

FRACTAL GEOMETRIC ANALYSIS OF DRAINAGE AND LOESS GULLLY SYSTEMS IN SHANXI AND ITS ADJACENT AREAS

Kong Fan-chen, Ding Guo-yu

1991, 13(3): 221-229.

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In this paper, the drainage and loess gully systems in Shanxi and its adjacent areas are processed and analyzed by the fracral geometric method. It is found that the fractal dimension value of a drainage or loess gully system reflects the intensity of tectonic activity. The distribution of the fractal dimension values shows quantitatively the background of tectonic activity and the difference in various regions, and it coincides perfectly with the expression of the intensity of tectonic activity in Shanxi and its adjacent areas. The fractal dimension value is high in strongly activated area, such as along the Shanxi-Weihe Fault basin zone and the mountain areas on its two sides, while it is low within the Ordos block and the area east of the Taiyue Mountain. The Shanxi-Weihe fault basin zone can be divided into three segments according to the fractal dimension values, from which the middle segment is of the highest tectonic activity, the southern segment is secondary and the northern is relatively weak. From view of the whole region, the distribution of fractal dimension values and the reflected tectonic activity tend to increase generally from the suroundings towards centre of the Jiexiu-Linfen area, which is closely associated with the 1303 and 1695 earthquakes with M=8. In addition, the fractal dimension values in the Yuncheng and Lingbao basins are approximately equal, indicating that the drainage features are similar and the tectonic activities equivalent in these two basins. Thus, it is thought that the Zhongtiao Mountain does not the separating boundary between these two basins during the recent tectonic period.Fractal dimension values are associated together with intensity of tectonic activity and difference in various areas in this paper, providing a quantitative criterion for tectonic activity research. It is a new try to use fractal geometry in studying neotectonic movement.

AN EVIDENT NNW-TRENDING SEISMIC ZONE IN WEST CHINA

Ma Jin

1991, 13(3): 230-230.

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TEMPORAL ORDERLINESS OF EARTHQUAKES (M≥8) ON CHINA MAINLAND——A NEW APPROACH TO THE PREDICTION OF EARTHQUAKES

Xu Dao-yi, Huang Jian-fa, Wang Xiang-nan

1991, 13(3): 231-240.

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Some great earthquakes of magnitude 8 or greater on China mainland repeatedly occurred at the intervals of 252, 94, 48, and 25 years. It incited us to study the time interval between every pair of great earthquakes (M≥8) on China mainland. The result shows that there are four groups of clear orderliness distinguished in the most disorder distribution of earthquakes. The distinguished orderliness can be used to estimate the occurrence of next great earthquakes in China.

THE ORIGIN OF FISSURES IN THE LOESS AT ZHUYA, SHANDONG PROVINCE, AND THEIR SEISMOGEOLOGICAL SIGNIFICANCE

Hu Zheng, Cui Zhao-wen, Wang Jian

1991, 13(3): 241-247.

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There are many tectonic fissures in Q₂²-Q₃² loess at Zhuya, Shandong Province. The tensional fissures are filled with Ca-veins, the rapidly cracked fissures with mixed sand, .gravel and clay, the slowly constantly cracked fissures with fine sand and clay, and the compressional slip fissures with nothing. The latter two fissures are later than the former two in active period. The directions of the fissures are coinsident with the directions of regional tectonic lines, and their occurrences and mechanical characteristics are in agreement with regional contemporary tectonic stress field.The formation of these fissures in loess deposits is related to the position where the Zhuya scarp is located. Zhuya scarp lies in Wudi-Qingzhou active fault zone in the NW direction. Six moderate and strong earthquakes occurred at the intersection of NW- and NE-trending faults. Zhuya scarp is just located at the intersection of NE-trending Zihe and NW-trending Zibo-Zhuya active faults, where the stress can be easily accumulated. This area is more sensitive to tectonic movement.

A REVIEW ON THE RESEARCH OF RHYSICAL PROPERTIES OF ROCKS IN CHINA AND ITS PERSPECTIVE——SYMPOSIUM ON THE PHYSICAL PROPERTIES OF ROCKS HELD IN BEIJING

Gao ping

1991, 13(3): 248-248.

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CHARACTERISTICS OF CRUSTAL DEFORMATION AND TECTONIC SIGNIFICANCE IN THE REGION OF THREE GORGES OF CHANGJIANG RIVER

Li Yuan-jun

1991, 13(3): 249-257.

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The features of crustal deformation are discussed in the region of Three Gorges in this paper. It is shown that differential motion of Huangling fault block with respect to its peripheral area exists, with a maximum rate of 5-10 mm in year. The results of short leveling across faults indicate that the activity of the faults is characterstic of inheritance, with an order of magnitude mm/a. The horizontal deformation nets show that the Xiannu Mountain fault zone has undergone left-lateral compression-shear movement, and the Tianyangping fault zone right-lateral slip in the recent years.

THE 5TH NATIONAL SYMPOSIUM ON GEODYNAMICS HELD IN BEIJING

Du Pin-ren, Ding meng-lin

1991, 13(3): 258-258.

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SPORO-POLLEN SEQUENCE AND DIVISION OF CLIMATIC PERIOD IN THE EASTERN NORTH CHINA PLAIN SINCE LATE PLEISTOCENE

Tong Guo-bang, Zhang Jun-pai, Yan Fu-hua, Mai Xui-shun

1991, 13(3): 259-268.

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In this paper the palynological data from six drill sections in the eastern North China plain are analysed by using the pattern recognition (stereopicture). The late Pleis-tocene-Holocene stratigraphy is divided into five sporo-pollen complex zones and seven sporo-pollen complex subzones. Nine stages of evolution of sporoflora are established. On the basis of these data in combination with ecological characteristics of the flora, a climatic evolution in the region for 20000 years is discussed and nine climatic phases are determined. It is found that there were eight apparently decreasing temperature stages and seven increasing temperature stages in the climatic evolution since the Holocene, and their fluctuation cycles are 2500 and 1000 years, respectively.

STUDY ON THE NUMERICAL SIMULATION OF THE STRESS CONDITION AFFECTING SENSITIVITY OF WATER TABLE IN MA-17 WELL TO EARTHQUAKE PRECURSOR

Gao Wei-an, Yu Jin-zhi, Che Yong-tai

1991, 13(3): 269-275.

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In the paper, the regional stress and the stress state on plane and along profile in Ma-17 well area are calculated using two-dimensional finite element technique of linear elastic theory for studing stress condition affecting sensitivity of water table in this well. The result indicates that there is a stress concentration during perparation of stronger earthquake in North China.

MODELLING OF RELATIONSHIP BETWEEN MOVEMENT OF THE UPPER MANTLE AND FORMATION OF BASIN IN THE EASTERN NORTH CHINA

Wang Chun-hua, Liao Su-qion, Xu Jie, Sheng Shu-zhen

1991, 13(3): 276-282.

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Based on comprehensives analysis of deep structure, formation of Cenozoic basin and its dynamical characteristics, the formation mechanism of the basin and its relation to movement of the upper mantle in the eastern part of North China are discussed in this paper. The experimental study have been carried out using the centrifugal technique, in which the differential density of material is adopted instead of differential temperature.The experimental result shows that the upper mantle convection, the upheaval and diapirism and the gravity isostasy produce a monodirectional tensile force for the movement of the continental crust in North China. The tensile force represents a main mechanism for formation of dustpan-shaped basin.The authors suggest that the driving force for formation and development of the eastern North China basin is closely related to gravitational effect and movement of the upper mantle.

MATHEMATICAL SIMULATION OF THE THERMAL STRUCTURE AND HEAT FLOW DISTRIBUTION IN THE BOHAI AND TAN6SHAN AREAS

Wei Dong-ping, Zhou Hui-lan

1991, 13(3): 283-288.

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By using the method of finite element, we have simulated the evolution and the thermal structure of the central Bohai basin area and computed the temperature field and the heat flow distribution resulting from the uplifted upper mantle and the sedimentary layer respectively in the area.The result shown in this paper is quite consistent with the observations of heat flow distribution in the Bohai and Tangshan areas. And in the later part of this paper, there is a datailed discussion on the relation between the cause of earthquakes and thermal stress produced by the uplifted upper mantle and the sedimentary layer in the Central Bohai basin area.

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