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PRESENT-DAY TECTONIC MOVEMENT ALONG ACTIVE FAULTS IN THE EAST OF CHINA'S MAINLAND
- Liu Guangxun, Ma Tingznu, Huang Peiyu, Wang Songxian
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1982, 4(4):
1-14.
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The east part of China's mainland considered in present paper is limited east of longitude 98°E and south of latitude 42°N. Based on a brief description of characteristics of the Quaternary active faults in the area, the present-day fault activities have been particularly discussed by using geodetic data obtained from short baseline measurements and short levellings across faults. There are four groups of active, faults in the area that respectively trend northeast, northwest, north-south, and east-west; and they usually constitute fracture zones with a certain dimensions. The mode of fault movement and the level of their activities are different in different regions. According to the level of their present-day activities, the faults may be divided into four classes: the annual slip rate is ≥10mm/year for the first class, <10-1mm/year for the second, <1 -0.1mm/year for the third, and less than 0.1mm/year for the last. As far as we know, only a few active faults have been found belonging to the first class. Two of them lie in southwest China: the NW-trending Xianshuihe fault (left-lateral strike slip, 9mm/ year) and the NNW-trending Jingdong Weixi fault (right-lateral strike-slip, 10.4mm/ year). Another is the NNE-trending Cangdong fault in North China (right-lateral strike-slip with dip-slip component, 14-18mm/year). Faults belonging to the second class are relatively common and concentrated in North China and Southwest China. In the former area they dominantly appear to be normal faults with right-lateral strike slip, while in the latter active faults are characterized by strikeslip. In north-west China present-day faul activities seem to be not vary high, mainly belong to the third class, and are characterized by upthrust. South China is relatively stable at present, except its coastal areas. Therefore, mobile regions may be regionalized in the area considered, in accordance with the fault activities, the whole area has been regionalized as tive mobile regions (the North China, the Northwest, the Southwest, the Southeast coastal and Taiwan mobile regions) and three relatively stable regions (the Southeast, the Ordols and the Alashan regions).Recently, strong and intermediate earthquakes dominantly took place in the North China and the Southwest mobile regions, especially along some active faults which belong to the first or second class. The Tangshan earthquake on the northern end of the Cangdong fault, and the Luhuo and the Daofu earthquakes on the Xianshuihe fault are examples. Although a series of historical strong earthquakes had occurred along some active faults in the Northwest mobile region and their machanisms had been consistent with the local structures, the seismicity there was not very high in the past years, as the fault slip rate was lower recently.Generally, fault activity in the east of China's mainland is lower than that in the continental margin. And the mode of their movements carry on that appeared since the Quaternary. Finnally the mode of recent tectonic stress action has been analyzed and regarded as mainly relating to the westward motion of the Pacific plate and the northwestward pushing of the Philippine plate, as well as to the uplifting of the Qinghai-Tibet plateau which is caused by the collision between the Indian and the Eurasian plates.
