Table of Content

05 March 1997, Volume 19 Issue 1

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Brief Report

SLIP RATES OF THE MAOMAOSHAN FAULT ZONE IN GANSU PROVINCE OBTAINTED BY USING AGES OF LOESS PALAEOSOIL SEQUENCE

Yuan Daoyang, Liu Baichi, Lu Taiyi, He Wengui, Liu Xiaofeng

1997, 19(1):  1-8. 

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Comparative studies have been made for the ages of Quaternary geomorphology along the Maomaoshan fault zone by using the age data of ¹⁴C and TL,fault scarps calculated with diffusion equation,and loess palaeosoil sequence. Based on the obvious grouping features of horizontal and vertical displacement distribution,the average slip rates in different time spans for each segment of the Maomaoshan fault zone have been obtained. Since late Middle Pleistocene,the average horizontal slip rate of the strike slip segment along the Maomaoshan fault is about 2.3～3.9mm/a,vertical slip rate is about 0.07～0.19mm/a,and the average vertical slip rate of the Tianzu basin dip slip segment is about 0.11～0.86mm/a. The slip rates along the Maomaoshan fault zone are characterized by remarkable inhomogeneity. The horizontal displacement has cumulative slip deficit from east to west,while the vertical displacement has the nature of compensation.

FEATURES OF THE THREE DIMENSIONAL CRUSTAL STRUCTURE OF THE HAICHENG SEISMIC AREA

Li Rongan, Xu Ping, Jiao Mingruo, Wang Xiaofeng

1997, 19(1):  9-13. 

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The observational data from the seismic station network of Liaoning province were processed by using a new method of seismic velocity imaging and computer program. It gives new results of the three-dimensional crustal structure of the Haicheng seismic area and neighboring regions. The analyses confirm again that the crustal structure on the borth sides of the Haicheng seismic area is rather different. The focuses of Haicheng earthquakes are located above a NWW trending low velocity body in the crust.

A YRELIMINARY STUDY ON ERUPTION OF THE MUD VOLCANO IN DUSHANZI,XINJIANG

Wang Dao, Li Maowei, Li Meng, Dai Xiaomin

1997, 19(1):  14-16. 

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In July of 1995,a mud volcano suddcnlv cruotcd in Dushanzi,Xiniiang. The ecological and hydrogeological conditions associated with the mud volcano have been studied. The possibilics of natural disasters caused by the mud volcano actlvlty and its reLatlon to eathquakes have been discussed.

CHARACTERS OF RECENT CRUSTAL DEFORMATION AND EARTHQUAKES ON THE XIAOJIANG FAULT ZONE IN YUNNAN PROVINCE

Yu Weixian, Liu Yuquan, He Wei

1997, 19(1):  17-21. 

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We have analysized the data of seismicity,geology and crustal deformation geodesy along the Xiaojiang fault zone. It is found that this strike-slip fault is characterized by alternative deformation of compressive uplift and extensional subsidence. Considering its correlation to distribution of historical earthquakes,it is suggested that this feature of fault deformation may be associated with the process of the strain accumulation of the Xiaojiang fault zone. This is of great importance for the analyses of seismic risk in this area and determination of potential source area of future major earthquakes.

AN IMPROVEMENT OF INVERSION METHOD BY CURVE COMPARISON FOR MAGNETOTELLURIC DATA

Jin Guangwen, Sun Jie, Wang Jijun

1997, 19(1):  22-23. 

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A STUDY ON THE CORRELATION BETWEEN THE HOLE RATIO OF THE ROCK LAYER AND STRESS TRANSFER VELOCITY IN THE JIYANG DEPRESSION

Pu Fanquan, Wang Youpei, Wang Xiaoming

1997, 19(1):  24-30. 

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We have made statistics on the interval time from the beginning of the rainfall stress transfer to water level response for different depths of wells. On this basis the correlation mode of the stress transfer depth time in the stratum is established. The relevant parameters are calculated by inversion method. The correlation model of rock hole ratio-stress transfer velocity is suggested with these parameters and geological and meteorologic data. This model indicates the inner relation between the stress transfer velocity and the rock layer structure. It provides a simple and effective method for the calculation of stress transfer time in single and multilayer with different hole ratio. It is also helpful for identification of interference caused by rainfall stress to the water level of deep wells.

ACTIVITY FEATURES OF THE FUBIAN RIVER FAULT IN SICHUAN PROVINCE

He Yulin, Gong Yu, Wu Xianguo

1997, 19(1):  31-36. 

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Along the valley of the Fubian river,which is located at Mucheng Lianghekou of the Maerkang region in Sichuan Province,there is a hidden fault of NW trending——the Fubian River fault. Occurrence of three major earthquakes during 1989～1991 is associated with this fault. Field investigations and analytical calculations demonstrate that it is one of the fractures in the arc shape structure of the inner Sichuan-Qinghai block. Since Quaternary the activity of this fault is characterized by variant distribution in space and time. Accordingly it has evident marks of segmentation. Under the recent regional stress field this fault has dominant movement of strike-slip. At the southeast end of it. where the trend of the fault changes,a local area of extension occurs.

MEDIUM AND SHORT TERM CHANGES OF REGIONAL SEISMICITY BEFORE MAJOR EARTHQUAKES IN NORTH CHINA

Lin Huaicun, Liu Xiqiang

1997, 19(1):  37-42. 

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We have studied the time sequences of regional earthquakes before 31 events of M_S≥5 in North China. It is suggested that the correlation between the short term quietude and major earthquakes is strong for the events of M≥5 in North China. To the 31 events of M≥5 such quiet time durations are dominated by 20～87d,120～210d,and more than 210d. It is also concluded that the short term quietude does not depend on the magnitude of following major events. On the other hand the correlation between the increasing trend in short time of regional seismicity and major events seems to be weak. The events which are correlated with such a change is only 6.4% of the total number of the major earthquakes.

THE PRELIMINARY EVALUATION ON POSSIBILITY OF RESERVOIR INDUCED SEISMICITY AT JIANGYA HYDROPOWER PROJECT,HUNAN PROVINCE

Chen Xiancheng, Hu Ping

1997, 19(1):  43-49. 

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Based on field investigations we have analysed the conditions of induced earthquakes by the reservoir of the Jiangya Hydropower project. We also made comparison between this engineerning and other reservoirs. Preliminary assessment on possibility of reservoir inducing earthquakes by the Jiangya hydropower project is proposed. It is suggested that the possibility of induced earthqukes exists at the gorge segment where karst developed well. Th possible seismogenic position,maximum magnitude and intensity are also estimated.

DISTORTION OF EARTH TIDE FORM WATER LEVEL IN THE TAIPINGZHUANG WELL IN BELTING AND ITS RELATIUN TO EARTHQUAKES

Zhu Qingzhong, Tian Zhujun, Zhang Yusong, Gu Yuanzhu, Gao Songsheng

1997, 19(1):  50-52. 

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ON PHYSICAL AND CHEMICAL MECHANISM OF MIGRATION CHANGES OF UNDERGROUND GASES

Gao Qingwu

1997, 19(1):  53-58. 

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Field modeling experiments have been made to study effecting factors for migration changes of underground water gases. Three test sites were chosen in the Houhaoyao area of Huilai county,Hebei Province. The aim of the modeling test is to analyse the diffusion effect of underground gases,the effecting factors of physics and chemics,and the effect of water pressure. The main purpose is to study the mechanism of migration changes of the gases H₂ and CO₂. The results of tests indicate that mechanism of gas migration changes for the gas H₂ is different from that of the gas CO₂. The effect of water pressure on migration of underground gases such as H₂ and CO₂ is rather evident.

FUZZY IDENTIFICATION OF GROUNDWATER LEVEL ANOMALY BEFORE THE DATONG YANGGAO SHOCK AND ITS IMPLICATION TO EARTHQUAKE PREDICTION

Dong Shouyu, Wan Dikun, Qin Qingjuan

1997, 19(1):  59-67. 

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We have studied the groundwater level anomaly before the Datong-Yanggao earthquake by using the fuzzy mathematical method. Our results show that the subordinate function method can be used to identify the anomaly of groundwater level changes. Before the earthquake,in certain area and at different time scales,the group anomaly of groundwater level had a pattern of increasing and accelerating changes. This information can be used to predict the occurrence time of earthquakes. If the distribution of water level anomaly and distribution of the water wells which have anomaly look like two zones,the intersection area of the both zones may be the site of future major earthquakes.

APPLICATION OF X-RAY METHOD WITH TEXTRET GONIOMETER TO ACTIVE FAULT STUDIES

Zhang Bingliang, Xiang Hongfa, Jing Guangxi

1997, 19(1):  68-70. 

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Fault gouges record a great deal of information on fault activity. Preferred orientation and fabric of minerals have close relation to the mode of slip along the fault. In this paper,the illite fabric in the Xiangshan Tiangjingshan fault zone is determined by using the X-ray method with Textrete-Goniometer. Our results indicate that the illite fabric in the middle sgement has no preferred orientation and it is the result of stick-slip of the fault,while that in the east and west segments has maximum density areas and it is caused by the sinistral shear creep-slip of the fault.

A STUDY ON REFLECTING EARTHQUAKE SENSITIVITY OF WATER RADON IN FENMAN WELL

Li Liang, Fan Chuihong

1997, 19(1):  71-76. 

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We have analyzed correspondent relation between the anomaly of water radon observed at Fenman well and earthquakes which occurred nearby or far away. We found that such correspondent relations look good before 40 major earthquakes including the events in Japan Sea. So we suggest that the Fenman well is sensitive to reflect earthquakes and associated with special geophysical conditions.

ISOTOPE STUDIES OF SHIHUA CAVE—Ⅲ:RECONSTRUCTION OF PALEOCLIMATE AND PALEOENVIRONMENT OF BEIJING DURING THE LAST 3000 YEARS FROM δ¹⁸O AND δ¹³C RECORDS IN STALAGMITE

Li Hongchun, The-Lung Ku, Chen Wenji, Liu Tungsheng

1997, 19(1):  77-86. 

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Unlike low resolution (>1000 years) δ ¹⁸O record which mostly indicates temperature change in the past,variations of high-resolution (<100 years) δ¹⁸O record of stalgmite mainly reflect changes in rainfall and the isotopic compition of moisture source in the study area. The δ ¹³C value of speleothem is mainly controlled by isotope composition of soil CO₂that consists of isotopic composition of C₃and C₄plants. The C₃/C₄ratio is strongly correlated with climatic change. When the δ ¹⁸O and δ ¹³C shift to more negative values,the ratio of C₃/C₄indicates wet climate increased precipitation,development of forest. All those climatic conditions may indicate summer monsoon strengthening in the study area. This thoutht provides a new approach to reconstruct high resolution paleomonsoon records. We have first demonstrated this new idea throughout a series studies in Shihua Cave,Beijing. A 12.5cm stalagmite was subsampled at 1mm interval (～25 years resolution) and 109 samples were collected for δ ¹⁸O and δ ¹³C analyses. Using Hendy rule,cave temperature and δ ¹⁸O H₂O ,we have illustrated the isotopic equilibrium between precipitated calcite and its parent solution and the reliability of our measurement. The δ ¹⁸O and δ ¹³C records provide climatic information during the past 3000 years in Beijing. Our results show that there are six apparently climatic cycles during the last 3000 years in Beijing. The wet periods were peaked at 2860,2350,1850,1480,790 and 150 yr B.P.,respectively,with a time step about 500 years. After 600 yr B.P. ,all of the δ ¹³C values show much heaiver than 3ka-mean values. We suspect that this change in C₃/C₄ratio (de-forest) was influenced by human activity also. There is a good agreement in the comparisons of the paleoclimate interpreted from the speeothem δ ¹⁸O and δ ¹³C records with historical records of temperature and precipitation in Beijing,and precipitation in North Central China reconstructed from tree-ring study in Huashan Mountain. Climate in Beijing during the last 500 years,was strongly influenced by the Little Ice Age event which had been found as a global climatic event. In Beijing the climate was relativly arid during the early period of the Little Ice Age. The climate became wetter after 400 yr B.P. and reached a maximum moisture for the 3000 yr period at ～150 yr B.P. Since 100 yr B.P.,the climate has become arid again.

FISSION TRACK EVIDENCE OF DIACHRONIC UPLIFT ALONG THE AILAO SHAN RED RIVER LEFT LATERAL STRIKE SLIP SHEAR ZONE

Wan Jinglin, Li Qi, Chen Wenji

1997, 19(1):  87-90. 

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Fission track analyses were performed for 4 apatites. They were collected from gneiss and mylonite of Red River fault between the Yuan Yang and Gasa. The FT ages at this area were 5.61～10.64Ma. We had found that the age of FT also had a tending becoming younger from SE to NW. Using FT age combined with results of multiple diffusion domain (MDD) model of K feldspars a slow cooling process among 150～110℃ and cooling velocity of 3.4～9.5℃/Ma are obtained. The characteristic shown by results of FT is consistent with the conclusion that the faults were transtensional prior to 15.5Ma and became transpressional later.

THE EARLIEST TRANSGRESSION LAYER SINCE LATE PLEISTOCENE IN ZHONGSHAN CITY OF GUANGDONG PROVINCE AND“EUSTATIC”SEA LEVEL CHANGES

Xu Qihao, Feng Yanji

1997, 19(1):  91-95. 

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The ages of Ostrea shells in silt layers of the depths of -36.80m and -36.35m for ZK₁ and ZK₂ drill holes are (45120?910)a B.P. and (44870?900)a B.P.,respectively at the site of Geli Great Commerce Mansion of Zhongshan City of Guangdong Province. It is the earliest transgression layer since 50000a B.P. that has been covered so far in the Zhujiang (pearl) Delta and along the coast of China. The confirmed sediment of littoral facies have been almost continuous since 45000a B.P. 18 samples of sediment of littoral facies at various depths have been compared with 82 samples of sediment of littoral facies of 38 drill holes in other areas in the Zhujiang Delta and southeast coast of China. The results show that the range of uplift and subsidence of the site is smallest and the crust at the site has been stable since 45000a B.P. and hence a related curve of "eustatic" sea level changes can be obtained. The curve shows that the sea levels were roughly -34.7m to -10.9m for (45120?910)a B.P. to (24410?470)a B.P.,-9.85m to -3.25m for (23750?890)a B.P. to (12580?400)a B.P.,-2m for 8000a B.P.,-1.1m for 4000a B.P.,and -0.03m for (2130?90)a B.P.,and the rising rate of sea level in the Holocene (0.58 to 0.01mm/a) was substantially lower than that in the Late Pleistoncene (4.84 to 0.51mm/a).