Table of Content

09 September 1997, Volume 19 Issue 3

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Brief Report

PALEOEARTHQUAKES AND RECURRENCE INTERVAL ON THE SEISMOGENIC FAULT OF 1679 SANHE-PINGGU M8 EARTHQUAKE,HEBEI AND BEIJING

Ran Yongkang, Deng Qidong, Yang Xiaoping, Zhang Wanxia, Li Rucheng, Xiang Hongfa

1997, 19(3):  193-201. 

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The 4 paleoearthquake events that have occurred on seismogenic fault of 1679 Sanhe Pinggu M8 Earthquake since 20ka B.P. are exposed through the analysis of trenches and fault scarp profiles. The earlier two events are marked by liquefaction and the later two events are shown by direct fault offset,including the 1679 event. The 1679 event and pre 1679 event are two characteristic earthquakes of which the maximum displacement is about 1.75m and 1.41m,respectively and the intensity of two events is very close. The occurrence time of 4 events was about 20000,13000,7500 and 317a B.P.,respectively. Average interval of recurrence is (6561?691)a. It indicates the characteristics of quasi- periodic occurrence of earthquakes.

BRIEF INTRODCTION OF A NEW PORTABLE INSTRUMENT FOR HELIUM MEASUREMENT

Kong Lingchang

1997, 19(3):  202-202. 

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THE NE-TRENDING FAULTS AND BLOCK STRUCTURE IN THE CENTRAL SECTION OF THE XIAOJIANG FAULT ZONE

Shen Jun, Wang Yipeng, Song Fangmin, Cao Zhongquan, Shen Xuhui, Yu Weixian, Huo Xueying, Li Zhixiang

1997, 19(3):  203-210. 

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The middle section of the Xiaojiang fault zone located in Yunnan Province is branched into east and west two faults. Between these faults there are many NE trending smaller faults and blocks cuted by nearly SN and EW trending faults. They make up the network shape structure with rectangular geometry of the middle section of the Xiaojiang fault zone. These NE trending faults inherited those of Tertiay and were innovated in Quartary with left-lateral slip. Some of them have been active till Holocene. Their activities belong to the integrated left-lateral slip motion of the Xiaojiang fault zone with much smaller magnitude and rate comparing with the main faults. Because of their motion the main faults have bending or step areas which are barries for stress and strain concentration. The blocks between the east and west main faults are cut by the NE trending faults into many secondary blocks of diamond and shuttle shape. Relative movements occur between these blocks which have important effect on the segmentation of faults as well as earthquake occurrence.

THE DEVELOPMENT STAGES OF THE BASINS ALONG THE MIDDLE SEGMENT OF THE XIAOJIANG FAULT ZONE AND ITS RELATION TO REGIONAL TECTONIC MOVEMENT

Song Fangmin, Wang Yipeng, Shen Jun, Cao Zhongquan, Shen Xuhui, Yu Weixian

1997, 19(3):  211-217. 

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Along the middle segment of the Xiaojinag fault zone 21 basins of different scales have developed since Cenozoic. They have 4 different stages of evolution,i.e. the Eocene Oligocene,the Pliocene-early Pleistocene,the middle Pleistocene and the late Pleistocene Holocene stages. Among them,the Pliocene-early Pleistocene stage was the period of great prosperity of the basins. According to the duration time of the development of the basins,they can be classified into inherited basin,staged basin,rejuvenated basin and new born basin. The basins can be assigned to depressed and non-depressed origin. The Eocene Oligocene stage was dominated by non-depressed basins,the Pliocene-early Pleistocene stage was dominated by both depressed and non-depressed basins,while the stage after the middle Pleistocene was dominated by depressed basins. The depressed basins can further be divided into thrust type,graben-semigraben type and pull-apart type basins. Based on the analysis of the formation mechanism,plane distribtuion and the type of deposition of the basins,the authors have discussed the characteristics of the regional crustal movement in the different periods of Cenozoic along the southeastern margin of Qinghai Tibet Plateau and in Sichuan-Yunnan region.

A NEW FIND ON THE ACTIVE SECTION OF THE XIADIAN FAULT IN BEIJING

Huang Liliang

1997, 19(3):  218-219. 

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THE SEISMIC VELOCITY STRUCTURE OF CRUST AND UPPER MANTLE AND DEEP STRUCTURE FEATURE IN NORTH SHANXI PLATEAU

Zhang Jianshi, Zhu Zhiping, Zhang Xiankang, Zhang Chengke, Gai Yujie, Nie Wenying

1997, 19(3):  220-226. 

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The wide angle reflection/refraction data obtained from the Wenan-Datong-Daihai deep seismic sounding profile are studied in detail. The results indicate that the crust thickness in the investigated region increases from 36.0km in the area of Taihang Moutain to 44.0km in the Shanxi plateau. Under the basement faults near the foot of Taihang mountain,the Zijingguan fault and east to Datong basin there is a fault zone which stretches to Mohodiscontunity. The seismic velocity of the upper mantle in Taihang uplift region is much higher and a very strong reversion of seismic velocity lies in the lower part of the upper crust in the Datong seismic zone and the region neighbouring the foot of Taihang mountain. Beneath the frontal zone of the Taihang mountain exists the deep structure condition for potential earthquakes.

DISTRIBUTION OF THE LITHOSPHERIC GEOTEMPERATURE IN YUNNAN

Zhou Zhenheng, Xiang Caiying

1997, 19(3):  227-234. 

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According to the data of the heat flow and lithospheric structure,and the correlative formula between the heat production A and the seismic velocity V_P,the distribution of the lithospheric geotemperature in Yunnan has been studied. Three geothermal types exist in whole Yunnan region: high geotemperature type with the Moho temperature >960℃ and the crustal geothermal gradient >2℃/100m,low geotemperature one with the Moho temperature <700℃ and the crustal geothermal gradient <1.5℃/100m,and middle geotmeperature one with the Moho temperature lying between the former two types and the crustal geothermal gradient 1.5～ 2.0℃/100m.

NETLIKE DISTRIBUTION OF MAGMATITE AND PLASTIC-FLOW NETWORKS IN CENTRAL AND EASTERN ASIA

Wang Shengzu, Zhang Zongchun

1997, 19(3):  235-247. 

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The distribution of magmatite is characterized obviously by a netlike feature that magmatic belts intersect conjugately,forming a series of the late-Paleozoic,Mesozoic and Cenozoic magmatic network systems. Magmatic networks are probably controlled by the plastic flow networks in the lower lithosphere,which result in upwelling of magma owing to shear deformation and friction thermal effect of plastic flow belts and the weakening and lightening of the intrabelt media. The driving boundaries and directions of driving forces of continental tectonic deformation and the paleo tectonic stress fields in the various geological periods are estimated in terms of the "plastic flow /magmatite" networks. Furthermore,the problems involving the evolution of the network tectonics and others are discussed in the paper.

PHYSICAL MODELLING OF PLASTIC-FLOW NETWORK AND MULTI-LAYER TECTONIC DEFORMATION IN THE LITHOSPHERE

Li jianguo, Zhou Yongsheng, Song Ruiqing, Wang Shengzu

1997, 19(3):  248-258. 

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The use of plasticized rosin as an analog material of the ductile lower lithosphere provides an effective approach to modelling intraplate plastic-flow network and multi-layer tectonic deformation. The experiments of ductile single-layer models indicate that under the action of compression at the plate boundary or gravity potential of "plateau" the first-order tectonic patterns,including those of shear network,compressional fold,or their transitional type,are observed respectively corresponding to the condition of relatively high,low,or moderate viscosities. In the ductile/brittle two-layer model with solidified talc-powder slurry as its britte upper layer the long-range transmission of driving force at the plate boundary is carried out mainly by netlike flow through the ductile lower layer,and,therefore,the shear network,i.e. plastic-flow network,in the lower lithosphere controls the intraplate tectonic deformation resulting in the development of shear fracture network,thrust faults,longitudinal tension fractures,and other secondary-order faults or folds in the brittle upper layer. The experiments also show that the discontinuously-distributed partings of weakness,which model low-velocity or high-conductivity layer in the crust,do not obstruct spreading of plastic-flow network in the lower layer,though influence the upward transmission of drag force and the distribution of intensity of tectonic deformation in the upper layer.

AN EXPERIMENTAL STUDY ON WAVE VELOCITIES IN ROCKS FROM THE YANHUAI BASIN AND ITS GEOLOGICAL IMPLICATIONS

Gao Ping, Guo Caihua

1997, 19(3):  259-268. 

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According to the deep PT-conditions of the Yanhuai basin,the compressional and shear wave velocities of the representative rocks in this area were measured. Variations of wave velocities induced by phase transition of quartz and hornblende are found at certain depths. It is suggested that in the middle crust the material with both low velocity and high conductivity may not be the quartzite or rich quartz bearing rocks,but may be the rocks with aqueous minerals. The upper part of the upper crust may be composed of rocks of argillaceous limestone or its kinds,while the lower part of the upper crust may be composed of granodiorite or its kinds. In the areas without high conductivity and low velocity layer,the middle crust may be composed of granodiorite and quartzite,and in the areas with high conductivity and low velocity layer,the middle crust may be composed of rocks of hornblendite facies. The lower crust may be composed of hornblende gneiss,andesine-granulite and augite-granulite.

DEVELOPMETN AND IMPORTANCE OF U-SERIES DISEQUILIBRIUM INVESTIGATION ON YOUNG VOLCANIC ROCKS

Wang Fei, Chen Wenji

1997, 19(3):  269-276. 

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This paper describes systematically the development history and present situation,the significance of the U-series disequilibriu method investigation of young volcanic rocks,then summarizes the application of the method in geochronology,mantle tracer and magmatic evolution. All of these investigations and experience are extremely conducive and revelatory to carrying out the key project "Monitoration and study on some modern active volcanoes in China". Furthermore,high precise TIMS dating method is also introduced in this paper.

A PRELIMINARY STUDY ON THE RADIOCARBON DATING OF DIFFERENT ORGANIC FRACTION SEPARTED FROM PEAT

Yin Jinhui, Pen Gui, Jiao Wenqiang, Lu Yanchou

1997, 19(3):  277-280. 

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Two peat samples collected from Dawangzhuang section,Yanqing basin were treated with NaClO,NaOH solution,Na₄P₂O₇-NaOH soultion and organic soultion,respectively and then ten different organic fractions were obtained from each peat sample. The radiocarbon age of each fraction was obtained and compared to evaluate the accuracy and reliability of the radiocarbon dating age of each fraction.

WELL RADIUS VARIATIONS AND EARTH-TIDE EFFECT OF WELL-WATER LEVEL

Wang Youpei, Zhang Zhaodong, Wang Xiaoming, Hu Huaixi, Zeng Nianwen

1997, 19(3):  281-287. 

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Based on the theories of porous medium seepage and elasticity,the partial differential equations on the response of the well-water bearing system to the Earth-tide signal are derived under the condition of changing well radius. It is suggested that variation of well-radius is equivalent to the change of the effective height of the well-water column which affects the inherent vibration period of the well-water bearing system. The period characters of the response of the well-radius variation to the Earth-tide signal are analyzed. The results show that the effect of well-radius variation on the response of well-water level to the Earth-tide is very small,if the volume of water bearing system is very large and the coefficient of permeability of the system is also large.