Table of Content

07 March 1984, Volume 6 Issue 1

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Brief Report

FAULT DISPLACEMENT AND RECURRENCE INTERVALS OF EARTHQUAKES AT THE NORTHERN SEGMENT OF THE HONGHE FAULT ZONE,YUNNAN PROVINCE

Guo Shunmin, Zhang Jing, Li Xianggen, Xiang Hongfa, Chen Tieniu, Zhang Guowei

1984, 6(1):  1-12. 

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Since the Late Pleistocene,the movement of the northern segment of the Honghe fault zone has been different from that of the southern one.At the southern segment movement is primarily characteristic of single right-lateral shearing,whereas at the northern segment,of a compositive right-lateral shearing with faulted-depressional extension.With in the compositive zone in question appears an en-echolon fault pattern due to alternate shearing and fault-depression.From the southeast to the northwest,they are: Ding Xiling shearing zone,Dali fault-depression,Xiashankou shearing zone,Eryuan fault-depression,Cibihu Lake shearing zone and Jianchuan fault-depression.Geomorphic feature of shear zone and fault-depression is completely different,the former appearing as a narrow valley and the latter,as a basin.This paper is focused on the determination of displacement rates and recurrence intervals of earthquakes of Dixiling shear zone and Dali fault-depression having remained since the late stages of Late Pleistocene.For Dixiling shearing zone,right-lateral displacement rate is 8mm/yr,and vertical slip rate is 1.8mm/yr,with a ratio of 4:1 and for Dili fault-depression,5mm/yr and 9mm/yr,respectively,with a ratio of nearly 1:2.According to calculations of the parameters of fault displacement,we have found that recurrence intervals for magnitude 6.8 earthquake are 178±29 years.It is consistent with the recurrence interval (150±50 years)of M 6—7 earthquakes from historic seismic records in this area.It may be useful to immediate—long term earthquake prediction.

RECENT TECTONIC STRESS STATE OF QIXIAN-XINXIANG-JIAOZUO AREA ALONG THE PIEDMONT BELT OF TAIHANG MOUNTAIN AND ITS RELATION TO SEISMICITY

Zhu Shilong

1984, 6(1):  13-20. 

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The Qixian-Xinxiang-Jiaozuo area is located at the southern section of the piedmont.fault belt of the Taihang mountain,which is one of main earthquake risk areas in China.In addition to geological structures and lithological characteristics,the condition of stress is also considered as one of essential factors for the occurrence of a strong earthquake.Recent tectonic stress state in this area has been studied by analysing recent activities of faults,ground water fluctuations and local mechanisms.From these studies the author suggests that recent regional tectonic stress fields are characterized by ENE-WSW horizontal principal compressional stress and NNW-SSE horizontal principal tensional stress.Recent tectonic stress state and its relation to seismicity have been studied by means of the finite element method.The calculations show that in the Xinxiang-Xiuwu complicated rhombic fault block,under the action of recent regional stress fields,the east and west acute angle region where two earthquakes of M=5.5 and M=6 have occurred is in a process of being highly stressed and may be a candidate of a strong earthquake.

CHARACTERISTICS OF MAGNITUDE 7.4 EARTHQUAKE SEQUENCE IN THE BOHAI AREA

Wei Guangxing, Ji Tongren, Li Bingfeng

1984, 6(1):  21-29. 

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The Bohai earthquake (M=7.4,38°20′N,119°27′E) occurring on July 18,1969 is typical of a main-aftershock.Analyses of regional seismicity indicate some anomalous variations,such as b-value decrease and belt-shaped distribution and so forth.Based upon detailed study for revised aftershock data,we have found characterized spatial distribution of aftershocks from lateral cluster,vertical diffusion to lateral one,vertical cluster,b-value decreasing and p-value high,and the like.Also discussed in this paper are some details about Bohai earthquake and M=7.3 Haicheng earthquake of 1975.

PALEOSEISMIC RELICS IN THE HEQING BASIN OF YUNNAN PROVINCE

Huang Xinggen, Jiao Zongxing

1984, 6(1):  30-30. 

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USE OF ACOUSTIC EMISSION METHOD FOR ESTIMATION OF PREEXISTING STRESSES IN THE ROCK

Zhang Dalun

1984, 6(1):  31-40. 

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An experiment of Indiana limestone has been conducted for estimation of preexisting stresses in rock cores.Five cylindrical specimens were pre-stressed under triaxial loading conditions to simulate various in situ stress fields.26 pieces of specimens smaller,prepared from five pre-loaded rock specimens were under uniaxial pressure,when,acoustic emissions (AE) and applied stress were recorded as a function of time.The AE activity was presented as the sum of AE counts at each increment of 500 lbs.It was found possible for each experiment to fit a set of three straight lines to data obtained by using least square method.The value of stress at two intersections of these three lines.may serve to predict the levels of the maximal preexisting axial stress and confining pressure.The error for this technique may be found to be within 10% for most of specimens in use.

EXPERIMENTAL STUDIES ON RESPONSIBLE MECHANISMS FOR RADON AND SOME GEOCHEMICAL PRECURSORS

Li Guiru, Jiang Fengliang, J. Melvin, A. Rice, M. Shapiro, T. Tombrello

1984, 6(1):  41-46. 

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To better understand the mechanism responsible for groundwater radon anomalies and other seismo-geochemical precursors,the following modeling experiments have been carried out: 1) measurements of Rn emitted from rocks with various uranium concentration during stress loading and rupture of rocks;2) determination of the coefficient of distribution of emitted radon in CO₂ saturated water and gas under pressure;3) leaching experiment with rock samples in pure and CO₂-saturated distilled water under atmosphere and stress loading,respectively.It can be seen from the preliminary results that the maximal Rn concentration was recorded when the rupture of the rocks occurred;Rn emitted from the rock was proportional to the uranium content in the rock;Rn emitted from the rock was distributed somewhat more in water than in gas;and the leaching of rocks may prefer CO₂-saturated water under stress loading to distilled water under atmosphere.Therefore,it is reasonable to see some anomalous changes in Rn concentration and other ionic and gaseous components prior to a few strong earthquakes.Meanwhile,the preliminary results of the experiments indicate that the seismo-geochemical anomalies appear to be related to both the stress variation and the physico-chemical processes involved in the water-gas-rock equilibrium system within the earth preceding an impending earthquake.

STUDY ON SEISMO-CHEMICAL FIELD AND CHANGES OF COMPOSITION OF WATER IN THE XIAOTANGSHAN SPRING

Chen Shuhai, Tan Xianfeng, Wang Zhimin

1984, 6(1):  47-53. 

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The hydro-geochemical environment and spatial-temporal distribution of chemical elements of water for the spring regions have been analyzed,taking the Xiaotangshan spring as an example.The changes of various elements in content for the two systems,i.e.wall rock-mineral water-Ar and wall rock-mineral water-CO₂ under the effect of thermodynamic factors (pressure and temperature),were studied in combination of modelling results.On this background the changes of mineral water in chemical composition in two ways caused by future earthquake are also discussed in this paper.

INTRODUCTION OF OBSERVING IN THE ANTARCTIC CONTINENT

Wei Menghua

1984, 6(1):  54-54. 

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HOLOCENE STRATA DIVISION AND RADIOCARBON DATING FOR THE DALI AREA

Peng Gui, Mai Xueshun, Li Hongchun, Ye Yongying

1984, 6(1):  55-60. 

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The strata of the Holocene,which was divided on the basis of radiocarbon datings and sporo-pollen analysis,indicate that the Holocene strata in Dali area can be found mainly along the Erhai lake and surroundings of Xi lake and Cibi lake,as well as the piedmont belt.The Holocene sediments are of diluvial and river-lacustraine origin.The Holocene boundary is marked by a layer of lacustraine sediments consisting:of peat or its similar and is about 15 meters at a depth beneath the Eryuan region.And the sandy gravel and gravel distributed on the eastern slop of Mt.Diancangshan can be ascribed to the Early-Middle Holocene.

DISTRIBUTIVE REGULARITIES OF SOME ELEMENTS IN THE HOLOCENE DEPOSITIONAL ENVIRONMENT IN THE NORTH OF THE NORTH CHINA PLAIN

An Fengtong, Zhang Xiumei

1984, 6(1):  61-67. 

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The northern plain of the Bohai bay had,in the Holocene time,a great change in depositional environments and climats,which led to quite different distributions of the geochemical environments and geochemical elements.The content of Fe,Mn,Gu,Zn,Ni,B,Rb was lower in Early Holocene than Ca and Mg,easily movable element.In Middle Holocene,these elements in question increased in the concentration with the temperature getting warm and with transgression and weathering intensive.By the end of this period,these elements have turned lower in the concentration than Ca,Mg and CaCO₃.Due to a variety of material resources,the content of Fe,Mg,Ca,Mg and CaCO₃ in the Luanhe alluvial plain may he lower than those in the Jiyunhe and Chaobaihe plain.

NATIONAL SYMPOSIUM ON FAULT STRUCTURE, HELD IN DATONG,SHANXI PROVINCE

Ding Menglin

1984, 6(1):  68-68. 

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FINITE ELEMENT APPROACH TO DATA OF MAGNETOTELLURIC SOUNDING FOR THE TWO DIMENSION STRUCTURES IN THE BEIJING-TIANJIN-TANGSHAN AREA

Wang Baojun, Gao Weian

1984, 6(1):  69-80. 

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The magnetotelluric response to the two dimension structures has been numerically modeled by use of the finite element method.Itcan be concluded that in the two dimension structure area in the North China Plain,rather than the lateral ones,one dimension inversion of longitudinal apparent resistivity plot can provide accurate information on real distribution of deep earth conductivity.The principle of two dimension forward magnetotelluric sounding has been presented,and then derived expression as well as the two profile models following two profiles obtained from magnetotelluric sounding along with other relevant data.The calculation has been carried out for two curves of apparent resistivity corresponding to polarized orientationas well.The two measuring profiles are across the Tangshan seismic zone (Malanyu-Bege-zuang) and NNE-trending tectonic zone partly passing the Beijing area,respectively.