Table of Content

05 December 1979, Volume 1 Issue 4

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Brief Report

THE LAST THREE DECADES OF SEIMOGEOLOGY IN CHINA

Wang Yipeng, Ma Zongjin, Din Guoyu

1979, 1(4):  1-9. 

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During the 30 years the development of seismogeology is closely associated with the establishment of New China and the upsurge in its economic construction. At the beginning of construction of our country seismogeological works were mainly in determining the stability of the engineering construction sites and evaluating the seismic activities. As time went on, 1966 Xingtai earthquake promoted the seismogeological researches to a new stage. The results obtained from the seismogeological works in the prediction, origin and zonation of seismicities are encouraging.This article makes an attempt to discuss the implication of seismogeology and its position and role in long-and short-term earthquake predictions and earthquake resistant works. Furthermore, the principal topics of seismogeology studies recently in China may be summarized as follows: 1) seismotectonics, 2) relation of the genetic mechanism of a strong shock and its accompanied phenomena to the geological conditions, 3) regional earth's stress field and intraplate dynamics of Chinese continent, 4) geology of seismic disaster and of induced earthquakes.Finally, the theoretical significance of seismogeology in new geoscience is pointed out and some suggestions for developing seismogeology in China are also proposed herein.

RADIOCARBON DATING OF THE CHENIER RIDGE IN MAQIAO AND ZHELIN,SHANGHAI

1979, 1(4):  10-10. 

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PRELIMINARY STUDY OF LATE CENOZOIC TECTONIC STRESS FIELD IN JIANGSU-SHANDONG-ANHUI REGION

Fang Zhongjing, Xiang Hongfa, Ding Menglin, Ji Fengju, Tang Youbiao

1979, 1(4):  11-25. 

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Based upon the studies of Late Cenozoic faulting and its related features in connection with the data of seismological observations involving a part of focal mechanism, topographic changes and geophysical explorations of the deep portion of the earth, the principal characteristics of the Late Cenozoic tectonic stress field in the region studied are discussed in this paper. It is suggested that the Himalayan movement together with the underthrusting of the Pacific plate reformed the regional stress field -of North China from Late Mesozoic to Early Cenozoic. As a result, the horizontal NEE-SWW trending compression is predominant. The change of the principal compressional stress from NEE to SEE in direction indicates both the consistancy between the stress fields of the region under investigation and North China area and also the difference in their individual features. Presumably the collision of the dominating Indian plate with the Eurasian plate and the underthrusting against one another by compression of the Pacific plate, together with a NW running underthrusting of the Philippines Sea plate and the lateral spreading of the surface crust caused by the upwarping of the upper mantle were responsible for this complex situation.

AN ANCIENT EARTHQUAKE PROFILE IN ZHONGNING COUNTY,NINGXIA HUI AUTONOMOUS REGION

1979, 1(4):  26-26. 

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ON THE RELATIONSHIP BETWEEN THE NINGHE 6.9 AFTERSHOCK AND THE TANGSHAN EARTHQUAKE FROM THE VIEWPOINT OF SEISMOTECTONICS

Li Zhiyi, Guo Shunmin

1979, 1(4):  27-35. 

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The Ninghe earthquake of magnitude 6.9 (1976, Nov. 15) can be regarded as a continuation of the Tangshan earthquake of magnitude 7.8 (1976, July 28). The latter was resulted from the action of the NEE trending compressive stress on the interlockingportion of the NE trending Tangshan fault zone. The seismogenetic structure concerned shows itself as a kind of asymmetric bilateral rupture. A new stress-concentrated area occurred, when the rupture spreads toward south-west and intersected the NW and NWW trending faults in the vicinity of Ninghe. This area under study was once more subjected to fracturing under the action of the NEE trending compressive stress leading to the occurrence of an earthquake of magnitude 6.9.The main fracture plane caused by the Ninghe earthquake still lies within the NE trending Tangshan fault zone inducing the sinistral slip of the NW trending fault. It was, therefore, a consequent of a simultaneous fracturing of the conjugate faults.Comparing and analysing the seismogenetic structure and the fissures, focal mechanism and the characteristics of the aftershock sequences of both the Ninghe and the Tangshan earthquakes it is suggested that the two earthquakes are tectonically related and expressed as main shock-aftershock relationship. This characteristic may serve as a clues to predict the strong aftershocks. It is found that after a main shock the aftershocks were mostly distributed along the trend of the main fracture zone, whereas strong aftershocks usually occurred at the locking portion of a transverse structure.

SYMPOSIUM ON THE SOLID EARTH TIDE,AUGUST,6,1979,BEIJING

1979, 1(4):  36-36. 

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PRELIMINARY DISCUSSION ON THE 1605 QIONGZHOU EARTHQUAKE AND ITS SEISMOGENETIC STRUCTURE

Chen Enmin, Huang Yongyin

1979, 1(4):  37-44. 

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The destructive Qiongzhou earthquake (July, 13, 1605) which occurred in the northern part of Hainan Island is historically an event having the most severe damage in South China, and causing the land-collapse on a large scale to form a part of the sea. The present investigation gives its intensity as XI, M = 7³/₄-8, h=22km?, epicenter location as N19?59', E110?28'. The magistoseismic area is shaped like a partly inverted tablespoon with its main long axis trending NEE, but being intersected east of Mt. Qiongshan by another long axis running NNW. The principal seismogenerating fault is in NEE direction and a NNW-trending fault is across it.This earthquake took place in a tectonic junction between two sets of horsts and grabens, namely, between the NEE trending strongly uplifted Fushan-Meiting horst and the intensely depressed Str. Qiongzhou graben in N. Qiongzhou district, and in NE Qiongzhou between the NNW running -strongly uplifted Yunlong horst and the intensely depressed Dongzhai Harbour graben. It happened in a horizontal stress field with predominantly NW strike (300氨) but resulted from the strongly differential vertical move-ment in the earth's crust In short, this earthquake was induced probably by a pair of X-shaped NEE (predominantly) and NNW-running shearing faults and was the consequence of their growth, development and displacement.

DISCUSSION ON THE RESERVOIR-INDUCED EARTHQUAKES IN CHINA AND SOME PROBLEMS RELATED TO THEIR ORIGIN

Hu Yuliang, Chen Xiancheng

1979, 1(4):  45-57. 

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In this paper, eight events of reservoir-induced earthquakes in China are briefly described and their general characteristics are also summarized. On these grounds, some problems related to the origin of reservoir-induced earthguakes are discussed.It is suggested that the reservoir-induced earthquakes are caused by the water seeping through the surrounding rocks into deep-seated fissures with a suitable initial stress and some favorable conditions of building water pressure. The tectonic stress may serve as art earthquake-generating initial stress, while the gravity of the rock mass may be another general initial stress. The reservoir-induced earthquakes, therefore, result from the dislocation of preexisting faults or fissures by the seeping water, which is a type of stick-slip mechanism. The reservoir-induced earthquakes are closely correlated with the karst.Consequently, the possibility of earthquake induced by reservoir impounding can be evaluated before dam building.

SYMPOSIUM ON PREDICTION OF EARTHQUAKES BY THE GROUNDWATER REGIME AUGUST,6,1979,BEIJING

1979, 1(4):  58-58. 

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GEOLOGICAL CHARACTERISTICS OF 1979 LIYANG EARTHQUAKE DISASTER

Seismogeological Disaster Investigation Group

1979, 1(4):  59-60. 

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ON THE PROBLEM OF HYDROGEOCHEMICAL PREDICTION OF EARTHQUAKES FROM A FEW OF EVENTS

Meng Shude, Chen Shuhai

1979, 1(4):  61-71. 

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The relationship between the hydrogeochemical changes involving SO₄⁼, Cl^-, Ca⁺⁺, and Mg⁺⁺ in groundwater and earthquakes indicates that the chemical composition of many wells had changed before both the Haicheng earthquake (M = 7.3) and the Tang-shan earthquake (M = 7.8). On this background the mechanism of such hydrogeochemical changes is explored.The external cause of the hydrochemical changes in groundwater may be traced mainly to the changes of temperature and pressure. In the Panjin region, Liaoning Province, the changes in strata stress and flow pressure before the two earthquakes mentioned above distinctly reflect an increment of pressure near the ground surface at a distance of several hundred kilometers from the epicenters.The variations of SO₄⁼ and Cl^- on the explosion experiments and the Mg-ion increase in the process of water-turbidity before shocks imply the influence of pressure on the hydrochemical changes. The hydrogeochemical changes before shocks seem to be mostly caused by the strain of stressed water-bearing horizon and its country rocks.

ON THE ENVIRONMENT AND GEOLOGICAL AGE OF XUJIAYAO SITE FROM POLLEN ANALYSIS DATA

Yan Fuhua, Ye Yongying, Mai Xueshun, Liu Yuexia

1979, 1(4):  72-78. 

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The Xujiayao site is situated on the west bank of the Liyikou, a small tributary of the Sangan River, passing through Yangkao county, Shansi Province.There many pollen grains of arbor, shrub and herb have been found in the sediments. The arboreous pollen grains are mainly of coniferales including the genera Pinus, Picea, Abies and Betula etc. Shrub and herb pollen mainly belong to Ephedra, Artemisia Chenopodiaceae and Umbelliferae.Basing upon the results obtained it is believed that the Xujiayao site was once covered by a forest-steppe vegetation. The appearance of many cold-resistant members, such as Picea, Abies etc. in the flora implies a cold climate in the past, comparable to the wurm glacial stage in Europe and the Tali glacial stage in China with an average annual temperature of about 4? which is lower than that of today.Comparing this pollen spectrum with those of Huangshan near Harbin, Beijing plain and Peizhuangcun of Weinan. the site may be assigned, to the Late Pleistocene in age.

THE CHARACTERISTICS OF SEISMOTECTONICS OF TAIWAN ISLAND,CHINA

Zhang Yuming

1979, 1(4):  79-92. 

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Taiwan Island situated between the Eurasia and Pacific plates can be supposed as a part of Western Pacific seismic belt. On the basis of the characteristics of geological tectonics, gravity anomaly, crustal structure and seismicity, Taiwan Island and adjucent regions may be divided into three seismotectonic zones, they are: I) Seismote-ctonic zone of eastern Taiwan. There earthquakes occurred along the western margin of Philippino Sea basin and in the volcanic arc, longitudinal valley and foreland depre-sisson in Lan Yu and Huo Shao Dao Islet. It is characterized by strong seismicity, high frequency of earthquake, NNE running distribution of epicenters and the NW-NWW running orientation of regional principal compressive stress field; 2) Seismotectonic zone of western Taiwan. There earthquakes appeared along the Cenozoic folding belt of Taiwan and marginal depression. Both seismicity and seismic frequency in this zone are much less than that of the eastern zone. Here the epicenters are distributed along NNE direction and the predominant principal compressive stress runs in NW-near EW direction, and 3) Seismotectonic zone of northern Taiwan. There earthquakes took place along the intersection zone of Taiwan and Ryukyu arcuated system with strong magnitude (intensity) and high frequency. The predominant principal compressive stress disclosed by the focal mechanism appears to be the direction approximately SN-NNW.In general, seismicities in Taiwan Island and the adjacent regions are varying with the relative motion between the Chinese and the Philippine Sea plates. In accordance with the view of plate tectonics, there are two types of earthquakes occurred in the region, that are. interplate earthquakes and marginal earthquakes of intraplate (namely arcuated island type of earthquakes), influenced by the boundary motion of plates. From the interplate earthquakes may be also recognized trench type and collisional type of earthquakes. The former was distributed in seismotectonic zone of northern Taiwan; and the NW running faults revealed by the focal mechanism are mostly of thrust faults, occationally of normal faults. The mechanism of thrust faults probably reveals the earthquakes caused by underthrusting action of plates along the trench, while the mechanism of normal faults seems to be used to illustrate the earthquakes caused by exten-sional faulting of lithosphere beneath the Philippine Sea plate. The collision type of earthquakes, as a result of strike-slip thrusting between the Chinese and the Philippine Sea plates, are mainly distributed in seismotectonic zone of eastern Taiwan. As to the island arc. type of earthquakes, they were distributed in seismotectonic zone of western Taiwan resulting from NNE running strike-slip thrusting within earth's crust.