Table of Content

06 December 2000, Volume 22 Issue 4

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Brief Report

ACTIVITY OF THE DONGGANG FAULT NEAR THE ONCE CHOSEN SITE OF NUCLEAR POWER STATION AT WAFANGDIAN, LIAONING PROVINCE

Li Ping, Ren Jinwei, Yang Mei'e

2000, 22(4):  337-343. 

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The Donggang fault, located at Wentuozi town, Wafangdian city, Liaoning Province, is a hidden fault which is not far from the once chosen site of a nuclear power station. Through detailed field investigation, we have determined the location and geometry of the fault. It is found that the fault turns toward north when it extends eastward to Weitun. It does not link with the Jinzhou fault zone. By trench observations and dating of fault rocks and stratum samples, it is proved that the fault has dislocated the stratum of middle Pleistocene. However, the overlying stratum of the fault is not offset since about 50000 years. It is concluded that the Donggang fault is not a capable fault.

QUATERNARY FAULTING OF JIALI FAULT, SOUTHEAST TIBETAN PLATEAU

Ren Jinwei, Shen Jun, Cao Zhongquan, Wang Yipeng

2000, 22(4):  344-350. 

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The Jiali fault is one of the major faults in the southeastern Tibetan Plateau. A field investigation of this fault has been made recently. From Naqu to Jiali the fault extends roughly in N60癢 direction and consists of three segments arranged in an en echelon way. From Luoermano to Esukongma (about 40km) where the fault is the northern boundary of the Sangdi basin that extends north-south, late Quaternary surface ruptures have been found. Within this segment the creeks and gullies that cross the fault were offset and the displacements range from several meters to about 5km. The average slip rate during late Quaternary is about 15mm/a for this segment. An interesting phenomenon is that the large displacement can only be found at those places where the fault is related to the basins that extend north-south. Outside the basins, no convincing evidence has been found for late Quaternary surface ruptures and the average slip rate for the whole fault is only about 4mm/a during Quaternary. It seems that these strike-slip faults behave like a transform fault and the strike-slip motion along them are a consequence of east-west extension that creates the north-south graben systems rather than the vice versa.

INTEGRATED SURVEY AND INVESTIGATION ON THE QUATERNARY ACTIVITY OF THE LIAOCHENG-LANKAO BURIED FAULT

Xiang Hongfa, Wang Xuechao, Guo Shunmin, Hao Shujian, Zhang Hui, Wang Jihua, Li jinzhao, Li Rucheng, Li Hongwu

2000, 22(4):  351-359. 

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We have conducted an integrated survey and investigation on the Quaternary activity of the Liaocheng-Lankao buried fault. The used methods include geochemical exploration, shallow seismic exploration, drilling geological profile and neo-strata dating. The object is to determine the accurate location of the fault, dislocation amount of each time period since Quaternary and the offset age of the last time of dislocation. The results show that the dislocation of the fault extends upward to the depth 20m or so below the surface. This fault has been active in early Holocene time. The average slip rate of the fault is 0.12mm/a.

RESEARCH OF FOCAL DEPTH AND ACTIVE STATE OF THE STRONG EARTHQUAKES IN CHINA

Chen Lijun

2000, 22(4):  360-370. 

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A detailed analysis is made for the earthquake data with focal depth since 1970 on the most regians of China. A hypothesis is poposed to explain the analysis results, which leads to a new concept on the overall situation of major earthquakes in China. It is suggested that major events of China are driven by the earthquakes with middle-depth ard deep-depth sources which occurred at four "hot spots" in 1970s, that are located at Jilin Province, Xindoukushi of Xinjiang, Taiwan, and Rikeze of Tibet. A process of earthquake chain composed of an active period (1970～1982), adjustment period (1983～1992) and waning period (1993～1999) has been completed. Althouth the last period is still under going, a new circle of the earthquake chain may be developing since the M 7.0 deep event of Jilin on April 8, 1999.

A STUDY ON CRUSTAL DEFORMATION ALONG THE CHINESE COAST USING TIDE RECORDS

Zhao Genmo, Liu Xilan, Ma Shuqin, Tian Shan, He Shumin

2000, 22(4):  371-378. 

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Annual average long-term rates of relative sea level changes are computed using tide records of 48 stations along the Chinese coast. Through modification by the factors of global climate sea level changes, modern crustal deformation rates of the Chinese coast are estimated. The analyses show that the section and profile maps of China coast tectonic deformation are consistent with the coast tectonic pattern: the northern coast is characterized by large area rise-drop zones with obvious boundaries, showing effects of large scale crustal movement; the southern coast is complicated, with differential rise-fall, showing dominant rise and local subsidence. Active faults pass through the rise-fall boundaries. These locations are close to offshore areas of high seismicity.

DUCTILE TECTONIC DEFORMATION OF MESOZOIC TIME IN THE DALIAN AREA

Wang Zongxiu, Tang Zhemin, Yang Zhongzhu, Yang Xiaobo

2000, 22(4):  379-386. 

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There are numerous folding and superimposed deformation styles in the Dalian area. By using the method of combining microstructural with macrostructural analyses, we make episode division for the ductile deformation of Mesozoic time in this area. We also determine the deformation mechanisms and patterns for each episode. It is suggested that the NS compressive deformation in late Triassic Period is the first ductile event of Mesozoic time in this area. On the basis of data analyses for the whole study area, the new tectonic pattern of the Dalian area is proposed.

REGIONAL CHARACTERS OF VERTICAL FAULT DEFORMATION IN NORTH CHINA AND ITS IMPLICATIONS FOR TECTONIC BLOCK DIVISION

Xie Juemin, Yang Guohua, Guo Liangqian

2000, 22(4):  387-394. 

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Since 1970s about 110 fixed or / and mobile stations of cross fault leveling have been laid out to measure vertical deformation in North China. Considering the tectonic unit division, these stations can be divided into five groups: Shanxi zone, Tanlu zone, western Yinshan-Yanshan zone, eastern Yinshan-Yanshan zone, and Capital circle area. From all the data 80 items of measurements are analyzed to calculate the deformation rates associated with faults. The results show that the average rate of vertical deformation across faults is 0.335mm/a in North China. There are, however, large differences of fault motion rates between tectonic zones. The Shanxi graben zone has the largest fault deformation rate showing it is the most important block boundary of North China. The fault deformation rates of other tectonic zones are relatively low.

STRUCTURAL CHARACTERS OF THE CANGDONG FAULT IN NORTH CHINA

Gao Zhanwu, Xu Jie, Song Changqing, Sun Jianbao

2000, 22(4):  395-404. 

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The latest geological and geophysical data show that the Cangdong fault is a listric fault in the upper crust. The plane of the fault becomes a detachment plane at the 10km depth in the crust. The Cangdong fault has undergone two rifting processes in Mesozoic and Cenozoic time. It formed in late Jurassic as a normal fault, and became a thrust fault by the end of early Cretaceous. It was a normal fault in Eocene, evidenced by the Mesozoic structure, and controlled the distribution of stratum of early Tertiary. Palaeogene is the major active period for the Cangdong fault, the major character of the fault formed in this period. The fault's occurrence, development history and activity are different in different segments. The activity of the fault has been weak since Neogene. Based on the shallow seismic exploration, it is suggested that the Cangdong fault is not active since later Pleistocene on the whole and has little seismicity.

GEOLOGICAL BACKGROUND AND SEISMOGENIC FAULT OF THE HAICHENG-XIUYAN M 5.6 EARTHQUAKE OF NOVEMBER 29,1999

Gao Changbo, Zhong Yizhang

2000, 22(4):  405-412. 

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Two earthquakes of magnitude 5.6 and 5.1 occurred at the juncture of Haicheng county and Xiuyan county, Liaoning Province, on November 29,1999 and January 12, 2000, respectively. The epicenter intensity of both earthquakes is Ⅶ degree. The long axes of isoseismic line of them are in NWW direction. The problems concerning the regional geological background and the seismic area and the seismogenic fault are analyzed based on the characteristics of tectonics, neotectonics, deep structure, focal mechanism and preferred orientation of isosismic lines. It is suggested that the two earthquakes are caused by a repeat movement of the seismogenic fault of the M_S 7.3 Haicheng earthquake of February 4.1975.

STADY ON PALEOEARTHQUAKES OF QIXINZHUANG TRENCH AT THE XIADIAN FAULT, BEJING PLAIN

Jiang Wali, Hou Zhihua, Xiao Zhenmin, Xie Xinsheng

2000, 22(4):  413-422. 

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The Qixinzhuang trenches are located at the eastern segment of the Xiadian ground fracture zone caused by the 1679 Sanhe-Pinggu M 8 earthquake. These trenches reveal a lot of deformation such as dislocated strata, colluvial deposits in wedge shape, sag deposits, tensional cracks and corruation textures of microstratification. These phenomena demanstrate that 4 major earthquakes have occurred on the Xiadian fault since Holocene time. They happened on the time of (10.85～9.71)ka B. P., (7.39～6.68) ka B. P., (5.42～2.23)ka B. P., and in 1679, respectively. Their interval is (3.25±0.43)ka, (3.21±0.82)ka, and (3.55±0.80) ka, and the average is (3.34±0.40) ka. The arerage value of coseismic vertical displacement is (1.4±0.4)m. In addition to two trenches near the fault, 4 holes have been dug on the north and south of the trenches. These holes are helpful to observe the stratum shape of the down thrown wall and to define the distribution of sags along the fault. Based on the field investigation, we compare the study results at the Qixinzhuang trenches with previous studies on the other trenches and boreholes along the Xiadian fault. As to the identification of paleoearthquakes, they are mostly in agreement each other.

APATITE U-Th/He DATING METHOD—A LOW TEMPERATURE THERMOCHRONOMETER

Zheng Dewen, Wangfei, Zhang Peizhen, Li Daming

2000, 22(4):  427-435. 

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The development of U-Th/He dating method is reviewed, and the principle, the analysis progress and the long α-stopping distance correction of this method are briefly presented in this paper. Then, the achievement on He diffusion in apatite and its mathematic modeling and the application of U-Th/He dating method to palaeogeomorphy, rock uplift, and basin thermal evolution is summarized. Finally, we evaluate the advantage and disadvantage of the U-Th/He method. As a conclusion, we think that this method has good prospects as well as necessity to be improved.

INVESTIGTION OF SEISMIC HAZARDS CAUSED BY THE M_s5.8 EARTHQUAKE OF SOUTH WUSU, XINJIANG ON MAY 2, 1995

Yin Lifeng, Zhao Ruibin, Zhang Yong, Shi Jianbang

2000, 22(4):  436-438. 

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A REVIEW ON THE ROLE OF SUPERCRITICAL FLUIDS IN THE EARTHQUAKE GENERATION

Liu Wei, Du Jianguo, Bai Liping

2000, 22(4):  439-444. 

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GWK-201 HE MEASUREMENT INSTKUMENT AND ANALYSIS OF ITS OBSERVATIONAL DATA

Wei Ruqing

2000, 22(4):  445-448. 

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