Table of Content

07 December 1994, Volume 16 Issue 4

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Brief Report

PLASTIC-FLOW WAVS AND EARTHQUAKE MIGRATION IN CONTINETAL PLATE(Ⅰ)

Wang Shengzu, Zhang Zongchun

1994, 16(4):  289-297. 

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The results of our studies show that the spatbial distribution of earthquakes in continent iscontrolled mainly by the plastic-flow network in the lower lithosphere which is reponsible for theintraplate long-range energy transmission, while the migration of earthquakes depends mainlyon the propagation of the plastic-flow waves similar to tidal bores advancing. Based on the analysis of the time-space distribution of earthquakes, in the central-eastern Asian plastic-flow network system with the Himalayan collision zone to be its driven boundary there are at least twosorts of plastic-flow waves, the 1st- and 2nd-velocity waves, or called " century-wave"and"decade-wave " respectively, which propagate with different velocities. The along-seismic-beltcomponents of the propagation velocities are about 1～7 km/a and 12～45 km/a, respectively,and the intervals of wave-originated times at the plate boundary for them are 68～133a(93.7aon average)and 7～18a(10.8a on average), respectively, showing quasi-periodicity. One moving wave-crest belt is produced for each wave-originated stage, which provides a necessary condition in energy background for the occurrence of earthquakes. The plastic-flow waves here are viscoplastic deformation waves propagating mainly in the lower lithosphere and induced under thecombinative actions of plate boundary compression and intraplate gravity potential. The conceptof plastic-flow waves can not only reasonably explain the physical mechanism of earthquake migration, but also gives an important basis for earthquake prediction considering the condition ofenergy background.

WHY CAN CONJUGATE ANGLES GREATER THAN 90?

Chen Kaiping, Ma Jin

1994, 16(4):  298-299. 

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STUDY ON THE RELATION BETWEEN THE SEISMICITIES IN EURASIAN SEISMIC BELT AND IN CHINA CONTINENT

Li Xianzhi, Zhang Guomin

1994, 16(4):  300-304. 

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Several close reamons between the earthquake activities in Eurasian seismic belt and its adjacent areas and China continent are discussed. These relations can be used in making the earthquake tendency prediction in China.

STUDY ON SOME MINOR STRUCTURES AND MICROSTRUCTURES OF MAIN FAULT ZONES IN NORTHERN NORTH CHINA

Yang Zhuen, Zheng Binghua, Fang Zhongjing, Wang Liangmou, Yu Libao, Jin Zhongxue

1994, (4):  313-318. 

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Sructural joints and gouges of the main fault zones in Northern North China were determined,statistically studied and analysed on micro-computer and scanning electron microscopy(SEM). Only twenty percents of the structural joints are oriented in the direction favorable to activation in the effect of the present stress field. Most of these structural joints were formed in the local stress field associated with the formation of the fault zones. The statistical study of rnicro-textures on the surface of quartz fragments from the fault gouges on SEM gives the last activity time of these fault zones, and the SEM determination of microstructures provides some information on the movernent mode along these fault zones. The results of these methods will provide more evidence for the fault activity.

Brief Report

BACKGROUND OF 3-D DEP STRUCTURE AND DYNAMIC CONDITIONS FOR OCCURRENCE OF STRONG XINGTAI EARTHQUAKE

Zhang Jiaru, Shao Xuezhong, Zhang Siya, Yang Qingyuan, Li Hongsheng, Fan Huiji

1994, 16(4):  319-328. 

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A deep sounding work by converted waves of earthquakes has been conducted in Xingtaiearthquake region. As a result, 6 cross-sections of deep structure in Xingtai earthquake area have been constructed (3 in NW trend and others in NE trend). On the bases of these sections the structures of major deep crustal interfaces G,C and M were determined. At the same time, the velocity models of P and S waves were constructed. Moreover, background of 3-D deep structure and the dynamic conditions for earthquake occurrence are also discussed.

RECENT TECTONIC STRESS FIELD IN NORTHWEST YUNAN PROVINCE AND ITS ADJACENT AREAS

Xie Furen, Liu Guangxun, Liang Haiqing

1994, 16(4):  329-338. 

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Based on the investigation of active faults in region we have obtained the recent tectonic stress field in Northwest Yunnan Province and its adjacent areas using the method of determination of principal stress axes from field measurements of slickensides. The result shows that thereceut tectonic stress field in the region is characterized by horizontal componment. The directionof maximum principal stress in Northwest Yunnan is different from that in the surrounding areas. Analysis of active tectonic pattern shows that Northwest Yunnan active tectonic region is aantithetic S extension region with NW-trending strike slip faults. This may be better for explaining the tectonic origin and the state of recent crustal stress in the region.

STUDY ON THE LATE QUATERNARY KINEMATICS OF THE NORTHERNPN PIEDMONT FAULT OF THE LIULENG MOUNTAIN

Deng Qidong, Yonekura Nobuyuki, Xu Xiwei, Yasuhiro Suzuke, Wang Cunyu, Takeuchi Akira, Su Zongzheng, Wang Yipeng

1994, 16(4):  339-343. 

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The northern piedmont fault of the Liuleng Mountain in the extentional region of the north-ern end of Shanxi graben system lies along the southern edge of Yangyuan basin and controls theorigin and development of the basin, It is a dip-slip normal fault, NEE-trending and N-dipping.Two moderate and large earthquake swarms (Ms=6.1, Ms=5.8) successively occurried alongthe fault in 1989 and 1991.The fault consists of a marginal faul of the basin (F₁)and a newly formed fault(F₂) cuttingthe late Pleistocene to Holocene alluvial deposits within the basin. The F₁ and F₂ faults form astepped fault zone along the northern piedmont and joint together into the western segment. Thefault activity is characterized by inheritant displacements. It cuts stream terraces of different agesand piedmont loess terraces, causing two basalt eruptions (K-Ar age of the basalt and TL age ofits underlying baked bed is 1.71±0.41Ma, 18.29±1.39～19.7±1.54×10⁴a B.P. respectively). Later activity along the fault offset the basalt to form a 30～50m high scarp. At the middlesegment of the fault, F₁ has been inactive since late Pleistocene,whereas newly formed fault F₂ at 2～3km north of the edge of the basin has offset alluvial fan surface and stream terraces of different ages since late Quaternary. The eastern segment of the fault cuts the third terrace at thejunction of Sanggan and Huliu rivers and formed a 50～60m high scarp.Several topographic profiles across the scarps on different segments and un-coeval geomorphic surface were mapped to obtain vertical offset by using auto-level. Ages of the different geomorphic surfaces were determined by TL and ¹⁴C. Average vertical slip rate is 0.43～0.75mm/aduring the late Pleistocene to the Holocene. The age of the youngest layer cut by the fault is 0.76～0.86×10⁴a B.P..

RELICS OF THE ANCIENT FOREST AND THE LATE PLEISTOCENE OYSTER BEACH AT THE SEA BOTTON OF THE SHENHU BAY, FUJIAN PROVINCE

Xu Qihao, Feng Yanji

1994, 16(4):  344-345. 

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THE LATEST PLEISTOCENE FAULTING ALONG THE CANFANGYING SEGMENT OF THE FAULT ZONE ALONG THE NORTHERN MARGIN OF YANQING BASIN

Cheng Shaoping, Yang Guizhi, Yang Zhe

1994, 16(4):  346-354. 

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This paper deals with the latest Pleistocene faulting on the Canfangying segment of the faultzone along the northern margin of the Yanqing basin from the data of one trench, three geologicprofiles, seven fault scarp morphologic profiles across the late Pleistocene deposit surface and fif-teen radiometric datings. These data indicate two faulting events occurring during the latestPleistocene time. The last event is dated to be 9870±130～11800±1000a B.P.,less than 13200±1100a B.P., and the earlier one is dated to be 19850±1550a B.P., with displacement perevent 3.34～3.64m and recurrence interval between events 9980a. Vertical displacement ratesince about 21050±1600a B.P. is estimated to be 0.31～0.34mm/a. The latest Pleistocenefaulting on the Canfangying segment is characterized by larger surface displacement and longerrecurrence interval, without similar faulting event occurring during the Holocene time.

THREE-DIMENSIONAL STRUCTURE OF THE GROUND FISSURE ZONE IN THE AREA OF DATONG RAILWAY BUREAU AND ITS ORIGIN

Xu Xiwei, Qian Ruihua, Gao Zhenhuan, Wang Hui, Lei Jun, Liu Yugang, Chen Jian, Hao Shujian, Yu Zhishui, Du Xingui

1994, 16(4):  355-364. 

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The three-dimensional structure of the ground fissure zone in the area of Datong Railway Bureau is studied in detail form the data of field investigation, geological trenching and shallow seismic prospecting, as well as analyis of its neotectonic background and underground water overextraction. The developing ground fissure zone has been propagating westwards at a rate of 260 ～ 520 m/a since 1983; Its differential movement rate across the zone reaches 22.1～24.4mm/a. The extensional rate of the main fissure is 1.11～11.6mm/a, vertical slip rate about 0.2～8.57mm/a, and left-lateral slip rate about 1.87～3.57mm/a. Its active behavior belongs to a brittle-plastic model. This ground fissure zone has been caused by the recent creep along the Baimacheng fault-aburied active fault. The local overextraction of the underground water has accelerated the development of the ground fissure zone. The formation of the ground fissures is an aseismic geologic hazard.

IDENTIFICATION OF THE NW-TRENDING HEZE-KUNSHAN SEISMIC ZONE AND ITS SIGNIFICANCE

Fang Dawei, Shen Yongsheng

1994, 16(4):  365-372. 

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This paper discusses the existence of the NW-trending Heze-Kunshan seismic zone and its scale and extent from the data of geological structure,strike of the dense seismic focuses area and migration law of earthquakes in combination with the data of gravity and aeromagnetism. This seismic zone is active from historic to recent times,It has become a threat of seismic hazard to the production and constrution in a vast area from the Huaihe River to the Yangtze River, including Shanghai city,Hangzhou Bay and Ningbo area. This should draw the attention of the relevant departments concerned on the purpose to further seismlolgical study and monitoring.

RESEARCH ON THE SEISMIOCITY CHARACTERISTI IN NORTH CHINA BASED ON CATALOGUE OF HISTORIC FELT EARTHQUAKES(M≥3(1/2))

Dai Yinghua, Jin Xueshen, Suen Peiqing

1994, 16(4):  373-379. 

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An examination of the catalogue of historic felt earthquakes(3(1/2)≤M≤4(1/2))in North China suggests that the felt seismic events have been recorded with higher quality since 1484 and in the catalogue the precision in recorded time, epicenter and magnitude of the felt events recorded meets basically the need of research of the historic seismicity. Comparing with China Earthquake Catologue (M≥4(3/4)), many earthquakes of 3(1/2)≤M≤4(1/2) can be added form the catalogue The historic earthquakes (M＞6)in the northern part of North China recorded in this catalogue are analyses The result shows that the seismic gap, zone,quiesence and high activity before strong shocks can obviously found,and the foreshocks before strong earthquakes and strong aftershocks also displayed.

A STUDY ON 1720 SHACHENG EARTHQUAKE IN HEBEI PROVINCE

Cai Huachang, Zhang Sichang, Hu Zhan'an, Li Xiangchun, Sun Xiangrong, Jin Xueshen

1994, 16(4):  380-388. 

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Some new data were obtained during investigation of Shacheng earthquake on 12 July,1720. On the basis of composite analysis of the new and existing data, the contour of seismic intensity Ⅸ and the magnitude are reestimated, the area with intensity Ⅷ is outlined, and epicenter is relocated.

TECTONICS, SCISMISITY AND DYNAMICS OF LONGMENSHAN MOUNTAINS AND ITS ADJACENT REGIONS

Deng Qidong, Chen Shefa, Zhao Xiaolin

1994, 16(4):  389-403. 

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The Longmenshan region inches the Longmenshan thrust belt,the western Sichuan foreland basin, the Longquanshan tectonic belt, and the Minshan uplift. The NE-trending Longmenshan thrust belt is composed of 4 major thusts and related napes, which form an extensive-compressive belt. The thrusting, mainly in a forward propagation style, started in the middle tolater part of Late Triassic and propagated from northwest to southeast. The Quaternary activity of the central and southern parts of the Longmenshan belt is stronger than the northern part.The western Sichuan foreland basin began to develop in the Late Triassic. The basin gradually retreated toward southwest since the late stage of Late Triassic, and the Quaternary deposition is limited on the Chengdu plain. The Longquanshan tectonic belt forms the eastern boundary of the foreland basin. It is a fault-propagation fold controlled by a master fault on its western margin.The NS-trending Minshan uplift northwest of the Longmenshan thrust belt is active since 2 Ma ago. The uplift is controlled by the Minjing and Huya faults, both with late Quaternary activities, on its western and eastern margins, respectively. The left-lateral slip rate of the Minjiang fault is about 1 mm/a. The Longmenshan thrust belt coincides with a steep gravity and magnetic gradient zone.The velocity structure and crustal thickness are very different on its northwestern and southeastern sides. There is a low velocity and high conductivity layer at a depth of 20 km on the west ofthe Longmenshan belt. The layer may be a detachment. Therefore, the Longmenshan belt maybe formed by a series of listric thrusts, and the wedges cut by the thrusts are thicker on the westand thinner on the east. The southern and central Longmenshan thrust belt and the Minshan uplift apparently control the seismicity in the region. This NE- to NS-trending seismic belt may be the active east-central margin of the Tibatan Plateau. Focal rnechanism solutions suggest that the principal compressive stress axis in the region trends NWW.The formation of the Longmenshan belt may be caused by the NW-SE directed compressionon the Songpan-Garze fold belt on the west. From Eocene to present, collision of the Indian and Eurasian plates caused southeastward movement of the western Sichuan block. This movementproduced a continuous compression on the Longmenshan belt. The movement of the westernSichuan block produced reverse faulting with left-lateral component on the boundary faults of the NS-trending Minshan uplift. The Quaternary activity in the northern part of Longmenshan beltis relatively weak due to the existence of the Minshan uplift.

DEFORMATIONAL CHARACTERISTICS, EVOLUTIONARY HISTORY, AND DEFORMATION MECHANISM OF THE MIDDLE LONGMENSHAN THRUST-NAPPES AND RELATED TECTONICS

1994, 16(4):  404-412. 

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The middle Longmenshan thrust－nappe belt was developed by SE-directed compression,while the Songpan-Ganzi fold belt was subjected to NE－SW shortening. The Songpan-Ganzi foldbelt underwent four generations of deformation during middle-late stages of late Triassic : NW-trending structures were formed in D1 and deformed into acurate structures by left-lateral shearing in D2; D3 was Characterized by SE-directed thrusting, and granites intruded in D4. the middle Longmenshan thrust-nappe belt consists of Yingxiu-Beichuan, Wenchuan-Maowen, Guanxian-Anxian and Southeastern marginal nappes, and the Yingxiu－Beichuan nappe can be divided into Jiudingshan, Pengguan Complex and Tangwangzhai sub-nappes. Klippen belongs to Pengguan Complex sub-nappe. The thrust-nappe belt was propagated form NW to SE.

DEFORMATIONAL CHARACTERISTICS, EVOLUTIONARY HISTORY, AND DEFORMATION MECHANISM OF THE MIDDLE LONGMENSHAN THRUST-NAPPES AND RELATED TECTONICS

Chen Shefa, Deng Qidong, Zhao Xiaolin, C. J. L. Wlison P. Dirks, Luo Zhili, Liu Shugen

1994, 16(4):  413-421. 

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The western Sichuan foreland basin initiated in T₃³ by continuous compression of the Long-menshan thrust-nappe belt,and its depositional centers were gradually transposed from NW to SE. The evolutionary history of the middle Longmenshan thrust-nappe belt and associated tectonics can be divided into three major stages:taphrogenic stage (D～T₃²),tectonic inversion stage (T₃³),and continuous thrusting stage (J～Kz).

TECTONIC GEOMORPHOLOGY OF THE CENTRAL SEGMENT OF THE LONGMENSHAN THRUST BELT, WESTERN SICHUAN,SOUTHWESTERN CHINA

Zhao Xiaolin, Deng Qidong, Chen Shefa

1994, 16(4):  422-428. 

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The NE-trending central segment of the Longmenshan thrust belt is composed of 3 major thrust or reverse faults. Geomorphic evidence and earthquake activity indicate that Quaternary activity is stronger on the southwest and weaker on the northeast along the central segment of the Longmenshan thrust belt. The segmentation of faulting is probably produced by the activity on the NS-trending Minshan uplift on the north of the Longmenshan thrust belt. Because deformation is dispersed on 3 faults, only moderate(M≤6)earthquakes have occurred along the central segment of the Longmenshan thrust belt.

TECTONIC GEOMORPHOLOGY OF THE MINSHAN UPLIFT IN WESTERN SICHUAN, SOUTHWESTERN CHINA

Zhao Xiaolin, Deng Qidong, Chen Shefa

1994, 16(4):  429-439. 

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The NS-trending Minshan mountain in Northwestern Sichuan is an active Quatemay uplift.Its western and eastern boundaries are controlled by the active Minshan and Huya faults, respectively. The northern segment of Minshan fault has been active since 2 Ma ago. It is a reverse fault with left－lateral strike-slip component. The strike-slip displacement is about 2.4 km with a 1mm/a slip rate since 2 Ma, determined by matching offset placer gold mine with its mother lode. The Minshan and Huya faults are the major seismogenic structures in the region.

FREQUENTLY USED BASIC MEASURING UNITS IN GEOSCIENCE

Sun Qun, Huang Jiefan

1994, 16(4):  440-440. 

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