Table of Content

06 March 1991, Volume 13 Issue 1

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Brief Report

THE ISOSTATIC DATUM FOR STUDYING OF THE SEA LEVEL CHANGES ALONG THE COAST OF CHINA

Huang Li-ren, Yang Guo-hua,Hu Hui-min

1991, 13(1):  1-14. 

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Relative sea level change can be derived from tide records. In order to study the general sea level change along the coast of China,it is necessary to make a unified reduction for all the results obtained from various tide stations. A so-called isostatic datum of vertical movement of thecoastal land hasbeen suggested as a basis of the unified reduction in this paper,established by useof precise releveling data completed between 50’s and 80’s.The vertical movement velocities relative to the datum at the bench marks of 15 tide stations have been calculated. These velocities provide a base for the reduction.

PRELIMINARY STUDY ON LATE QUATERNARY FAULT SCARPS ON THE NORTHERN PIEDMONT OF QILING MOUNTAIN

Shentu Bing-ming, Song Fang-min, Cao Zhong-quan, Wang Yi-peng

1991, 13(1):  15-25. 

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Interpretation of aerophotoes and field investigation make authors find that a series of fault scarps are distributed in the .unconsolidated Quaternary sediments on the northern piedmont of Qinling Mts. Further geological,geomorphological and chronological studies of the fault scarps in combination with the analysis of levelled morphological sections of the scarps and excavated trenches led us to reveal the spatial distribution,geometric features,ages and offsets of the fault scarps and the activity of the northern piedmont fault of Qinling Mountain in late Quatery. It is indicated that the fault scarps occurred and were preserved on special tectonic and geomorphic parts of the zone. The heights of the scarps range from 1.1m to 7.7m,but the scarps on elder morphological surfaces are higher than those on younger morphological surfaces. The average slip rate along the middle segment of the northern piedmont fault in late Holocene is about 1mm/a,while that along the western segment of the fault is about 0.5mm/a. Three or four large paleoseismic events probably occurred on the northern piedmont fault since late Pleistocene.

NEWLY DISCOVERED GEOLOGICAL EVIDENCES FOR THE SEISMOGENIC STRUCTURE OF 1695 STRONG EARTHQUAKE IN LINFEN, SHANXI PROVINCE, CHINA

Wang Ting-mei, Li Xin-yuan, Zheng Bing-hua, Wang Yi-peng

1991, 13(1):  26-27. 

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DISCOVERY OF THE BEACHROCK IN XIANGSHAN OF ZHEJIANG PROVINCE AND ITS SIGNIFICANCE

Gao Zhong-he, Ji You-ting, Xu Ying-shen, Chen Xiao-ming, Qin Cheng-chang

1991, 13(1):  28-32. 

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In this paper,the authors introduced the Holocene beachrock,that was first discovered in Juexi town of Xiangshan country of Zhejiang’Province in 1988,preliminarily investigated its petrographic character,¹⁴C isotopic age and formative circumstance. Probably,the Juexi beachrock is the northmost Holocene beachrock in China. From ¹⁴C dating of the beachrock,the authors inferred the relative rate of subsidence in this coast for 0.51 mm/a.

THE TECTONIC FEATURES AND EVOLUTION OF THE TERRANES IN TONGBAI-DABIE MOUNTAINS

Ma Bao-lin

1991, 13(1):  33-42. 

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This paper deals with the tectonic features of three terranes,namely Suizhou-Guangji,northern Huaiyang,and Tongbai-Dabie terranes. The first consists of subducted melange,which underwent high P-low T metamorphism. The second terrane consists of ophiolitic melange in its central and Western parts and tectonic melange in its eastern part which underwent high P-Low T(11℃/km) metamorphism. The third terrane is continental crust block in a paleao-ocean,with an evolutation into a volcanic arc. During the Caledonian and Hercynian movements these three terranes were involved in the mountain-building events. Although they were deeply eroded. it is recognized that the Suizhou-Guangji and northern Huaiyang terranes have overthrusted the Tongbai-Dabie terrane northward and southward respectively.

CHARACTERISTICS OF NEOTECTONIC MOVEMENT IN BEIJING AREA

Huang Xiu-ming, Wang Liang-mou, Xu Jie, Fang Zhong-jing, Zhang Fu-ming, Xiang Jia-cui, Wang Hui

1991, 13(1):  43-51. 

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From new data of tectonic evolution,fault activity,neotectonic movement,recent tectonic activity and seismicity in Beijing area,the authors suggest that the characteristics of neotectonic movement in the northern and southern parts of this area are different. Neotectonic activity in the southern part is weaker than that in the northern part. Seismic risk in the future has also the same tendency.

PRELIMINARY REPORT ON EXCAVATIONS AT YAOJIAYING, YIANQING, BEIJING

Cheng Shao-ping, Fang Zhong-jing, Yang Zhe, Yang Gui-zhi, Jia San-fa

1991, 13(1):  52-53. 

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ACTIVE FAULT AND ITS ENGINEERING EVALUATION WILL BE PUBLISHED

Nan Jin-sheng

1991, 13(1):  53-53. 

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EXPERIMENTAL RESEARCH ON A NEW AE EXPERIMENTAL SYSTEM FOR MEASURRING FAILURE ROCKS UNDER CONFINING PRESSURE AND THE MAGNITUDE-FREQUENCY RELATION

Jiao Wen-jie, Ma Jin, Wu Xiu-quan, Liu Li-qiang

1991, 13(1):  54-60. 

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The Gutenburg-Richter law of magnitude-frequency relation has been challenged in recent years. Many researchers have found nonlinear sections in the magnitude-frequency relation in some cases. The magnitude-frequency relations shown in acoustic emission experiment of the rocks under confining pressures are studied in this paper.A new AE experiment system related to the confining pressure has been developed. The system can record the energy of AE events ranging from 1 to 10⁶ in relative energy unit.Six experiments of b-value simulation related to the confining pressure were conducted. The specimens were made of granite,marble,and granodiorite with different configurations. The main results of experiments are:1.The characters of acoustic emission of rocks are very similar with those of earthquake,providing the basis of applying AE experiment for the seismological research.2.The time series of AE events is fractally distributed on the time axis and its fractal dimension is a measure of AE activity.3.The AE series has not any characteristic occurrence period. The series of large AE events accords with neither the time-predictable model nor the slip-predictable model.4.There are two types of nonlinearity of b-value in the magnitude-frequency relations of either earthquakes or AE events.5.The magnitudes of AE events are fractally distributed on the magnitude axis. In addition,some problems aboul the theoretical study on b-value and applyingthe new method to seismological research have been discussed.

STUDY ON FRACTAL GEOMETRY OF FAULTS IN NORTHWESTERN YUNNAN PROVINCE

Huangfu Gang, Han Mingwang, Jin-nan

1991, 13(1):  61-66. 

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Using a fractal geometry analysis,the fault systems in northwestern Yunnan were interpreted and their geometrical standings were determined. The fractal characteristics of active fault systems are described by a comparison of the fault and river systems in several subareas. The result shows that 1) NE-trending fault system (D=1.32) is more complicated in geometry than those in NW(D=1.26) or SN (D=1.32) directions,indicating that NE-and NW-trending fault systems are at least equal in status in this region,and 2) the difference -in fractal dimension between active fault and river system increases from south to north,indicating that the distribution of river system is more strongly controlled by strike-slip fault than oblique-slip fault.

NUMERICAL SIMULATION OF TECTONIC STRESS FIELD IN SICHUAN-YUNNAN RHOMBIC BLOCK

Wang Ji-cun, Huang Qin-yang, Xu Chun-rong, Zhu Jing-zhong

1991, 13(1):  67-72. 

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In this paper a simulation of the tectonic stress field in Sichuan-Yunnan rhombic block is conducted using a finite element technique from the absolute stress data at actual measurement depth of 500m. The relation ship between the tectonic stress state and the distribution of strong earthqukes in the area is analyzed. The computed result is basically consistent with the actual measurement data. Three zones with maximum shear stress inside the tectonic stress field correspond to the three seismic zones in this region. The obtained result reveals quantitatively the distribution and state of the present tectonic stress in this region.

APPLICATION OF PALEOMAGNETISM TO STUDY OF THE ORIGIN OF THE EARTH’S MAGNETIC FIELD

Zhu Ri-xiang, Liu Chun, Lin Mian

1991, 13(1):  73-77. 

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The origin and reversal of the Earth’s magnetic field is still a puzzle in geophysics. There are two reasons for this,one is that the physical process in the Earth’s core can not be observed directly,and another is that scarce studies were carried out in combining paleomagnetic data with magnetohydrodynamics. Based on paleomagnetism and αω dynamo theory,some new results are obtained in this paper: (1) Lorentz force results in negative feedback in the dynamo process in the Earth’s core; (2) westward drift of the geomagnetic field is determined by the difference of rotation between the Earth’s coie and mantle: (3) α effect makes the geomagnetic dipole tilt at some angles with respect to the axis of rotation.

DATING AND ENGINEERING EVALUATION OF RECENT FAULT ACTIVITY IN SHIZHIKOU AREA OF THE THREE GORGES SECTION OF CHANGJIANG RIVER

Li Xing-tang, Yuan Deng-wei, Zhou Ji-yi

1991, 13(1):  78-86. 

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The NNW-trending linear traces in the Shizhikou area of the Three Gorges section of Changjiang River reflect the relief,lithologic features and small-scale faults. It is inferred from geologic and geomorphic data and result of isotopic dating that the Qinglin-kou fault was slightly activated in 49?10⁴a B. P. The Jufang fault was not activated since 50?10⁴a,and other three small faults were not been also activated since 50?104a,even in the Quaternary period. The geologic and geomorphic data and distribution of earthquake epicenters indicate that the NNW-trending faults in the studied area have not been active in recent time,and not the seismogenic and earthquake-generating faults either which would not have an influnce on the stability of the Three Gorge reservoir and its dam.

RADIOCARBON DATES (6) AND DATA BASE

Jiao Wen-qiang, Wang Li-hong, Peng Gui, Wang Qi-ming, Li Gui-ying, Zhang Jia-Lin

1991, 13(1):  87-95. 

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This paper presents ¹⁴C dates,which have been transcribed into the Institute of Geology,State Seismological Bureau,and have got an acceptance search. The deposited 1500 data are available for consulting the stratigraphic datas in various regions,and tharefore for geologists working in field.