Table of Content

08 March 1989, Volume 11 Issue 1

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Brief Report

HAIYUAN STRIKE-SLIP FAULT ZONE AND ITS COMPRESSIONAL STRUCTURES OF THE END

Deng Qi-dong, Zhang Wei-qi, Zhang Pei-zhen, Jiao De-cheng, Song Fang-min, Wang Yi-peng, B. C. Burchfiel, P. Molnar, L. Royden, Chen She-fa, Zhu Shi-long, Chai Zhi-zhang

1989, 11(1):  1-14. 

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Haiyuan active fault zone is a main active fault in the northeast boundary of Qing-hai-Xizang plateau. Geologically, mapping of 1:50,000 has been made along the fault zone. The results show that Haiyuan active fault zone, 237km long, striking WNW in its west segment and striking NW in the east segment, has been a strike-slip fault sense since middle-late early Pleistoncene. The horizontal offset is 12-14.5km from middle-late early Pleistocene, with the slip rate of 11.7-19.2mm/a. The strong activity has been going on since the begining of the Holocene, with the sinistral strike slip rate of 6-10mm/a.Haiyuan strike slip fault zone consists of 11 secondary shear faults, mostly left stepping pinnate, partly right stepping pinnate. 8 pull-apart basins and 2 pushed-up blocks were formed along the fault zone. Pull-apart basins showing 2 types of romb and elongated, big ones began to develop in middle Pleistocene, small ones in late Pleistocene. The largest thickness of sediments is greater than 750m. A tensile-shear fault with the sinistral strike-slip was formed in some pull-apart basins.The tensile-shear fault links up two secondary shear faults which control pull-apart basin, intersecting them with low angle. After the formation of this kind fault, pull-apart process of the basin decreased and pull-apart basin gradually became feeble and die. The thrust faults intersecting the secondary shear faults with high angle was formed in the pushing area, appeared as an uplift in topography.A great earthquake of magnitude 8.6 occurred in Haiyuan, in December 16, 1920. The surface ruptures of earthquake can be divided as 15 fracture segments, which developed along secondary shear faults, tensile shear faults on pull-apart basin and boundary normal fault at both ends of pull-apart basin. The horizonal dislocation of 268 values have been measured. The maximum displacement of left-lateral strike-slip is 10-11m.At the southeast end of Haiyuan strike slip fault, a rare end compressional area, which consists of thrust fault zone of east pediment of Liupan Mountain, Madong Mountain fold zone and Xiaoguan Mountain thrust fault zone, striking nearly NS, was formed. The detail mapping and studying have been made on the deformation features of these compressional structure belts and calculation on the amount of crust shortening have been made, and the value is about 12.4-16.7km, which is about equal to the sinistral offset amount of Haiyuan active fault zone.

DEFORMATION FEATURES AND FRACTURE MECHANISM OF SURFACE RUPTURE OF 1951 BENGCO, TIBET M_s = 8 EARTHQUAKE

Wu Zhang-ming, Deng Qi-dong

1989, 11(1):  15-25. 

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A great earthquake with a magnitude of M_s =8.0 occured in the vicinity of Bengco, northern Tibet, on November 18, 1951. Surface rupture zone as long as 91 km was formed by the event. The geomtry and displacement features of this surface rupture zone as well as the seismogenic structural conditions of the Bengco earthquake are discussed in this paper.

THE SEA FLOOR FAULT OUTSIDE LONGXU ISLAND, SHANDONG PROVINCE

Li Jian-hua

1989, 11(1):  26-26. 

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EARTHQUAKE-CAUSED LANDFORMS AND PALEOSEISMIC STUDY ON THE NORTHERN SEGMENT OF THE ZEMUHE FAULT

Ren Jin-wei, Li Ping

1989, 11(1):  27-34. 

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Earthquake-caused landforms are the indicators of earthquake ruptures on the surface. Therefore the microgeomorphical analysis is an effective method in paleoseismic study. Through the study of newly found earthquake-related landforms (including fault scarps, offset gullies, wavy lands, and slopehanging-ditches) at Daqingliangzi, Xichang,Sichuan Province, at least four (may be seven) paleoseismic events of magnitude greater than 7 were identified. This result shows that strong earthquakes have occurred repetitively at the same place on the northern segment of the Zemuhe fault since later Pleistocene. Tne minimum time interval between every two strong earthquakes, on the northern segment of the Zemuhe fault is about 1000a during the Holocene-period, and the average time interval is about 1800a.

THE ELECTRICAL STRUCTURE OF THE CRUST AND UPPER MANTLE IN THE WEST PART OF YUNNAN PROVINCE AND ITS RELATION TO CRUSTAL TECTONICS

Sun Jie, Xu Chang-fang, Jiang Zhao, Shi Shu-lin, Wang Ji-jun, He Ming

1989, 11(1):  35-45. 

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Based on the data conducted from 18 MT sites in west Yunnan, the deep conductivity characterics along the longitudial and transverse directions of the geological structure are studied, The results indicate that the deep eletrical structure in this area is a multiple-layer structure with 4-5 electrical layers. There is great lateral inhomogeneity in the deep eletrical structure which are apparently controlled by the regional geological structure. There exists a widespread highly conductive layer in the crust, and two upper mantle highly conductive layer uplift zones are found, one is situated in Jianchuan-Heqing with the principal axis of NNW direction and another in Tengchong-luxi with approximately NS direction.The relationship between the electrical structure of the crust and upper mantle and the geotectonics, the formation of northwest Yunnan rift basin and the relationship between seismic activity and the deep geological structure are also discussed in this paper.

GEOLOGIC FEATURES OF THE TECTONIC MELANGE IN NORTHERN JIANGSU-SOUTHERN SHANDONG REGION AND LITHOLOGIC COLUMN

Liu Ruo-xin, Ma pao-lin, Zhang Zhao-zhong, Zhang Zhi-min, Yang Hui-nan, Hu Lian

1989, 11(1):  47-54. 

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This paper briefly describes the geologic-tectonic setting of the tectonic melange in Northern Jiangshu-Southern Shandong region. This tectonic melange occures in the collision zone between North China and Yangzi Plates. The principal features of the sliding medium, shallow-middle- and deep-seated tectonic blocks. have been systematically studied in this paper as well. Based on the study of deep-seated tectonic blocks, a litho-logic column from upper mantle to crust-mantle transition zone bas been established, and the possible geologic process in upper mantle has been discussed.

SOME PROBLEMS OF CONTEMPORARY GEODYNAMICS AND SPECULATIONS OF RESEARCH

Ma Zong-jin

1989, 11(1):  55-59. 

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A brief illumination of contemporary geodynamics and historical geodynamics is presented in this paper. The subdivision ot geodynamics in different research levels is proposed, and general discussions are made on following importent problems: 1. the leveling of the earth and a model of mantle plume, 2. the antisymmetry of global tectonics, and 3. the differential movement on both sides of the longitudinal structure as well as the latitudinal mantle flow.

A PRELIMINARY STUDY ON SUBEI-JIAONAN TERRANE OF THE SECOND REPORT OF GEOLOGICAL OBSERVATIONS ON GEOSCIENCE TRANSECT FROM XIANGSHUI, JIANGSU, TO MANDULA, NEI MONGOL

Zhou Chun-ping

1989, 11(1):  60-64. 

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A great number of ultrabasic rocks and eclogites exist in Jiaonan Group, Subei (Northern Jiangsu)-Jiaonan(Southern Shandong Peninsula) Terrane. They mainly distribute in three belts extending in NE or NEE direction. There are also widespread mylo-nite zones. All of mylonite zones and ultrabasic rockeclogite belts almost occur in the upper Zhubian Formation of Jiaonan Group(Pt_1-2). It means that they might be of strato-controlled characteristics. So it can be inferred that they perhaps represent a large scale detachment zone in the middle crust, which is folded and exposed in the surface. Thus Subei-Jiaonan Terrane is situated in a suture zone between the North China Craton and Yangzi Craton with a complicated deformation history.

NEW STUDY RESULTS ON CRUST STRUCTURE, CRUST MOVEMENT AND CONDITIONS FOR EARTHQUAKE PREPARATION IN YANSHAN REGION BY CONVERTED WAVES

Shao Xue-zhong, Zheng Bin-hua, Zhang Jia-ru

1989, 11(1):  65-76. 

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Based on the new data of crust structure revealed recent years by a method of P-SV converted waves from earthquakes and combined with the data of surface geological structure we have discussed the major features of crust structure and crust movement in Yanshan region, especially focused our attension on the analyses of structure characteristics, movement pattern of the crust in Huailai-Ninghe WNW seismic active zone and their differences between both sides of the zone.In the light of comparison between distribution of epicentres and crust structures we have found some diagnostic criteria of deep structure, similar for strong earthquake areas. The problems about deep process of strong earthquake preparation and potencial hypocentre zones have been discussed. All the results from this study are useful to the research on earthquake monitoring and prediction in the region of Capital Circle.

DEEP TRANSIENT ELECTROMAGNETIC SOUNDING

The deep transient electromagnetic cooperated group between China, West-Germany

1989, 11(1):  77-83. 

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The Deep Transient Electromagnetic (DTEM) or Long Offset Transient Electromagnetic (LOTEM) is an active electromagnetic measurement method. It is a very efficient exploration method for reaching large penetration depths of up to 10 km.The DTEM is very useful for hydrocarbon exploration in basins covered or inter-bedded by basalt, valcanic layers, salt and anhydrite.In comparison with other electromagnetic method, DTEM has the advantages of being less sensitive to lateral inhomogenities, having the best coupling to the subsoil and measuring in the absence of primary field.This paper provides a briefly summarization of principles and of theory for the DTEM, the technical system in the field, and the data processing and interpretation.

THE SPORO-POLLEN ANALYSIS OF LATE QUATERNARY DEPOSITE FROM FUYUN REGION OF XINJIANG

Yan Fu-hua, Mai Xui-shun, Li Hong-chun

1989, 11(1):  84-80. 

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The studying sections are situated in the northwest and southeast of the Fuyun county, Xinjiang. Many pollen grains of shrub and herb plant have been found in the sediments from the sections of Tuerhong, Gangou, Kalaxiangeer and Wulunguhe, mainly belong to Ephedra sp., Artemisia sp., Chenopodiaceae and Compositae.On the basis of the analysis results it is believed that the vegetation related to the sediments of the sections is mainly typical one of a desert-steppe and steppe vegetation.The result of sporo-pollen analysis shows that there was a climatic fluctuation during the formation of the sediments of these sections. The prevailing climate was warm and dry.The results of pollen analysis are comparable with the pollen data on the Holoce-ne sediments in many regions of our country. Moveover, the seven samples from these sections for ¹⁴C dating give the age value of 2000-7000a. For this reason the four studying sections can be ascribed to the Holocene.Based on palynological data from both sides of the fault in Gangon section, the geological age of the fault formation can be infered to be impassable Holocene.

THE DEPOSITION RATES OF CaCO₃ IN LOESS WITH DIFFERENT AGES IN LUOCHUAN COUNTY, SHAANXI PROVINCE AND ITS IMPLICATION IN GEOLOGIC AGE DETERMINATION

Sheng Xue-bin, Wang Ke-lu

1989, 11(1):  91-98. 

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The difference of deposition rates of CaCO₃ between in loess and paleosol with different ages is found out through the analysis of 276 samples collected from the Hei-mugou standard loess section in Luochuan County. Shaanxi Province, located in dry or semidry areas of Northwest China. The deposition rates of CaCO₃ tend to be greater from bottom to ,top as loess gets younger. For example, the deposition rates of CaCO₃ in Wucheng loess is 0.09g/cm²·10³a, 0.29 in the lower part of Lishi loess, 0.36 in the upper part; 0.21 in Malan loess; 0.07 in paleosol of Wucheng loess, 0.21 in the lower part of Lishi loess, 0.19 in the upper part; 0.18 in dark loessal soil of Holocene.The deposition rates of CaCO₃ in loess with various ages are all greater than that: in their corresponding paleosol. For example, the deposition rate of CaCO₃ in Wucheng, loess is 1.3 times as big as in its paleosol; 1.4 times in the lower part of Lishi loess, and 1.9 times in the upper part.The deposition rates of CaCO₃ in loess-paleosol series increase synchronously from bottom to top, and the deposition rates in loess are greater than in their corresponding, paleosol, which coincides with the fact that the paleoclimate during the period of Quaternary turned from warm- humid to dry-cold, and the climate changed alternatively between warm-humid and dry-cold. From above we conclude that the deposition rate of CaCO₃ and its variation can be used as a mark to divide Quaternary strata.In order to date unknown strata and to determine the activity period of fault in a certain area, it is of great importance for us to evaluate deposition rate of CaCO₃ in dry or semidry areas, to find out empirical parameters and to establish certain models. The aforesaid method of dating with calcic soil is a simple and feasible way of geologic age determination.

APPLICATION OF QUANTULUS-1220 LSC TO GEOLOGIC DATING

Jiao Wen-qiang, Xiang Hong-fa

1989, 11(1):  99-100. 

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THE SITE EFFECT ON EARTHQUAKE HAZARD AND SOME CONSIDERATIONS FOR ITS EVALUATION

Jiang Pu

1989, 11(1):  101-114. 

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In this paper, site effect on earthquake hazard, its general principle and approach of evaluation is discussed in five sections: evaluation of earthquake hazard, seismic hazard analysis, zoning geologic unite, analysis of ground motion response and synthetic classification of active fault in engineering. Some considerations and experience are presented from engineering practice.

ANALYSIS OF RESERVOIR INDUCED EARTHQUAKE CAUSED BY GAS EXPLOSION IN KARST CAVES

Hu Ping, Hu Yu-liang, Ma Wen-tao, Chen Xian-cheng, Yang Qing-yuan

1989, 11(1):  115-124. 

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Gas explosions in karst caves might be a cause for reservoir induced seismicity.The occurrence condition and mechanism of gas explosion are discussed and the possible magnitude of induced earthquake is estimated in this paper.Phenomena of gas explosion have been found at the reservoirs in karst area in China. But the induced earthquakes at Wujiangdu reservoir which have been considered as typical gas explosion are not caused by the gas explosion.

EXPERIMENTAL STUDIES ON DEFORMATION AND FAILURE OF SANDSTONES UNDER TRIAXIAL COMPRESSION

Wang Bao-sheng, Li Jian-guo, Xu Xiu-qin, Shi Lan-bin

1989, 11(1):  125-133. 

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The deformation mode and mechanism on two kinds of sandstone (feldspar sandstone and quartz sandstone) were experinmentally studied under confining pressure up to 700 MPa with strain rate of 10^-4/s.The transition field from brittle to ductile behavior in intact samples is respectively 200-400MPa PC and 250-350MPa PC for feldspar sandstone and quartz sandstone.A high pressure embrittlement phenomenon, however, appears above 600MPa P_C in feldspar sandstone. The transition boundary from stable sliding to stick slip in sawcut samples is 200MPa P_C and 150MPa P_C respectively for two kinds of sandstone.Microscopic observation results show that all of these deformation modes result mainly from the cataclasis mechanism in different grade. Cataclastic faulting results in brittle failure under low confining pressure. Homogenized cataclasis (cataclastic flow) inter and intra grains results in ductile flow. The relocalization of microcracking results in the embrittlement up to high confining pressure. The transition from brittle to ductile behavior is mainly due to the developing from faulting to homogenized cataclasis. As to the friction characteristics, the stable sliding is accompanying grains gliding on sawcut surface. The stick slip involves grains crushing severely. The transition from stable sliding to stick slip is between the both situation. Sometimes it is difficult to distinquish the different microstructural features for different friction modes.In this paper we also discussed the effects of mineral compositions on deformation mode and mechanism of rocks, the extension of brittle behavior in rocks, the two transitions from brittle to ductile and from ductile to embrittlement, the relation between cataclasis and deformation modes as well as the confusion of nomenclature in application to geology.

THE PRELIMINARY REPORT OF THE COMPREHENSIVE SURVEY ON GENGMA-LANCANG EARTHQUAKE, YUNNAN PROVINCE, CHINA

The Research Group of the Gengma-Lancang Earthquake, Institute of Geology, State Seismological Bureau

1989, 11(1):  135-136. 

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