Table of Content

03 December 1980, Volume 2 Issue 4

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Brief Report

THE GRAVITATIONAL PLASTIC FLOW OF CRUSTAL MATERIALS IN SOUTHWEST CHINA

Zhou Jiu, Huang Xiuwu

1980, 2(4):  1-10. 

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Under the action of gravity, the powerful driving forces of recent tectonic movement affecting the studied plateau and adjacent areas are stemming from the crust of Qinghai-Xizang Plateau. Therefore, in Southwest China took place a flow of crustal materials toward the southeastern direction. Such flow possesses rather special nature, unlike the downhill sliding of the glacier. In the front of the flow can be found recent tectonic activities with different features due to the variations of resistance encountered. Moreover, the occurrence of earthquakes in Southwest China is also constrained by the material flow.The authors suggest that since the driving forces of recent tectonic activities in this area are in close relation to gravitational effect, the localized recent tectonic processes would be ascribed to the category of gravity tectonics.

ANALYSIS OF ACTIVE FAULTS IN TAIWAN PROVINCE AND THEIR RELATION TO EARTHQUAKES FROM SATELLITE IMAGES

Zhang Shiliang, Chen Shangfu

1980, 2(4):  11-20. 

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Basing upon the Landsat images this paper briefly described the active faults in Taiwan province and their relation to the earthquakes. The active faults, elongated mostly in a form of belt with distinct tectonic activity, are clearly characterized by the satellite images. The region under investigation is principally controlled by the NNE trending active fault zones, which usually have a left-lateral character. Although the NW trending active zones are not so large on the scale as the former, they behave as a fault with evidence of recent movement in northern Taiwan and are right-lateral in nature. By synthetic analysis of data concerned this region is determined to be compressed from NNW-SSE direction, due to the collision between the Phillippine Sea plate and the Eurasian plate.

ABOUT THE DEFORMATION, CREEP AND HYSTERESIS IN ROCKS AT VARIOUS TEMPERATURES

An Ou

1980, 2(4):  21-26. 

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The experimental results on rocks at a temperature equal to the earth's crust indicate that as long as a cyclic load is applied on rocks, there no monodromic correlation would be appeared between stress and strain. Thus the recent tectonic stress and strain fields are changing, now extensively, now weakly. For this reason, there is impossible for the earth stress stations for long-term continuous observation at the fixed points to evaluate the earth stress by the strain, thus a selective method for measuring elasticity and a stress balance method are necessary in determining stress state.

ON THE SOURCE TECTONICS OF 1979 LIYANG EARTHQUAKE OF MAGNITUDE 6.

Ye Hong, Zhang Wenyu, Yu Zhishui, Xia Qin

1980, 2(4):  27-38. 

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In 1979 an earthquake of magnitude 6 occurred in Liyang County, Jiangshu province. The epicenter was located in the junction of a NE trending active fault, the known Maoshan fault, with a NW trending active fault, the Fangshan-Tiger Mt. fault.In this paper the focal mechanism of the major shock and several aftershocks has been studied and the strike of seismic fracture has been also determined by means of null vector data. The research results indicate that the Liyang earthquake was caused by a right lateral strike-slip dislocation with some normal dip-slip component along the east branch of the Maoshan fault belt under the action of the NEE compression stress field.From the observation of aftershocks, it can be suggested that both the source volume of the b-value of this earthquake sequence is rather small. Using Wyss method and Gibowicz empirical formula, we approximately estimated the stress-drop and the seismic moment as well as the apparent stress of the Liyang earthquake. In the mean time, on the basis of the field geological observations we pointed out tentatively that the Liyang earthquake was generated probably by the locked NE Maoshan fault associted with the left lateral shifting of the NW Fangshan-Tiger Mt. active fault. And this seemed to be a reasonable explanation for the recurrence of two destructive earthquakes being occurred there within 5 years.The authors assume that the Liyang earthquake can be regarded to be a low stress-drop event under a high stress background, implying that the south part of the North China fault block has been stepping into a active stage of high stress.

GEOLOGICAL ANALYSIS OF THE SEISMICITY IN THE TANCHENG-LUJIANG FAULT ZONE, EAST CHINA

Fang Zhongjing, Ding Menglin, Ji Fengju, Xian Hongfa

1980, 2(4):  39-45. 

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This paper deals mainly with the geotectonic background of the seismicity in the Tancheng-Lujiang fault zone, with emphasis on the relationship of Late Quaternary active faults in southern part of its middle segment to the earthquakes. The seismicity is clearly different in various segments, this is well correlated to the difference of geotectonic units with various characteristics and faulting activities in the Late Quaternary.The evidences on the intermittent motion (stick-slip motion) of the active faults found in the southern part of the middle segment can be regarded as a geological indicator to discriminate the paleo-earthquakes and to estimate roughly their recurrence. It is clear that this indicator is of practical significance for evaluating the seismic tendency of the active fault zone. In the meantime, by the geological and seismological analogues the authors propose that in the same tectonically active zone where occurred strong historic or prehistoric earthquakes, exists a possibility of recurrence of earthquakes in the same location. However, it is to be noted that some segments of this zone, where the tectonic conditions are similar in occurrence of earthquakes and evidences of intermittent motion of active faults since Late Pleistocene are found and where seismic gaps last more than two thousands years, can be referred to the temporal "quiet segment". The earthquake risks in these segments may actually be rather serious than that in the segments with recent activities. Therefore, we had better not say the former segments to be more safe in the near future. It has already been verified by the fact that in the recent /ears quite a few strong earthquakes took place in the historical seismic gaps being tectonic-ally newly-reactivated. In conclusion, to make the seismic zonation more exact it should pay attention to the investigation of the geologico-geomorphological evidences on recurrence of large earthquakes in the active fault zone within plates.

A DISCOVERY OF BEIJING MICROTEKTITE

1980, 2(4):  46-46. 

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SEISMOTECTONIC CHARACTERISTICS OF TANGYIN GRABEN, HENAN PROVINCE, AND ITS EARTHQUAKE RISK

Han Mukang, Zao Jingzhen

1980, 2(4):  47-58. 

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The authors illustrate the characteristics of neotectonic movement of the Tangyin graben (Henan Province) situated in the southern section of the Taihanshan Piedmont fault zone with a NNE trend and point out that the northern part of thi graben is only a semigraben, while its western side is a hinge fault with progressively decreasing in vertical displacement and finally dying out in the northern direction. According to the field seismotectonic investigations the authors made a prediction that the western part of Tangyin County near the hinge point is prone to the earthquakes due to the hinge point's further northward migration. Later, this prediction was verified by an earthquake with 3.9M. just occurring in this part in Oct. 1978.Moreover, the Anyang city, located on the intersection of the Taihanshan fault zone with a NWW pivotal fault, is an another earthquake-prone area due to the fea-ssible location to concentrate tectonic stress, and then it must be put under monitoring.

FOCAL MECHANISMS OF TANGSHAN EARTHQUAKES

Li Qinzu, Zhang Zhili, Jin Yamin, Yu Xinchang, Li Zhiyong

1980, 2(4):  59-67. 

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In this paper, some characteristics of the Tangshan earthquakes were discussed from the data of focal mechanisms. The fault plane of the main shock is a bilateral strike-slip fracture along N30℃ and appears clearly to control the aftershocks so that the stronger aftershocks occurred concentratedly around the two stopping positions of the fault plane. This was determined by the distribution of remaining stress over the fault plane of main shock after its occurrence. The larger differences of the fault plane solution of some aftershocks and the higher percentages of the inconsistent first motions in the composite fault plane solutions of aftershocks imply that the fractures and the redistribution of the stress in focal region after the occurrence of main shock were complicated. The decrease of the percentage of inconsistent first motions in the later composite fault plane solution shows probably an indication that the medium in the focal region was going from a strained equilibrium, to a lax equilibrium. It was pointed out from the analysis of seismic data that the fault plane solution of main shock is representative for the most earthquakes in North China. Some informations probably to be usable for the predictions of earthquakes were discussed.

A PRELIMINARY MEASUREMENTS ON OXYGEN AND CARBON-STA-BLE ISOTOPIC RATIO AND PALEOTEMPERATURE OF STALACTITE OF A QUATERNARY CAVE FROM TONGZI, GUIZHOU PROVINCE

1980, 2(4):  68-68. 

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THE BASIC FEATURES OF REGIONAL GRAVITY FIELD IN CHINESE CONTINENT

Yin Xiuhua, Shi Zhihong, Liu Zhanpo, Zhang Yumei

1980, 2(4):  69-75. 

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The 1?/1? free-air anomaly and bouguer anomaly of the Chinese continent can be briefly outlined by 104癊 as a border line separating into the eastern and the western parts, distinctly different in anomaly features. The anomaly change of the former is gentle with a NNE strike of linear anomaly, while the latter's is intensive with a NWW strike of linear anomaly. The further subdivision of Chinese continent gives four anomaly regions, the Eastern, the Central, the Xinjiang and the Qinghai-Xizang, they vary obviously in nature. We discussed the relationships between the regional gravity field and tectonics, isostasy and seismicity. It is suggested that the linear anomalies of the Eastern part reflect mainly the structural system of NNE strike but the Western part reflect the structural system of NWW strike. The Bouguer anomaly gradient zones are coincident with the fault belts between fault blocks, and the Chinese continental crust is principally in an isostatic state on a large scale. Therefore it can be assumed that most of earthquakes would take place along the gravity gradient zones.

THE MODE OF MOTION OF THE TANCHENG-LUJIANG FAULT ZONE BY PRELIMINARY PALEOMAGNETIC DETERMINATIONS

Cheng Guoliang, Fang Zhongjing

1980, 2(4):  76-76. 

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THE TUTOTIMER DS-1 MODEL

Wang Keren, Wei Chunbo

1980, 2(4):  77-79. 

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