Table of Content

03 March 2005, Volume 27 Issue 1

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Brief Report

ANALYSIS OF THE TWO HISTORICAL EARTHQUAKES OF 1067 AND 1574 IN THE SOUTHEAST COASTAL REGION OF CHINA

WEN Xue-ze, XU Xi-wei

2005, 27(1):  1-10. 

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The parameters given by the available earthquake catalogs for the 1067 AD Chaoshan,Guandong,earthquake can't be used to explain reasonably the geographical distribution of the earthquake damages recorded in the historical documents. Comparing the recorded damages caused by this event with those caused by the 1918 AD Nan-ao large earthquake at the same places,we find that they are almost the same,and prove that these two earthquakes should be the characteristic earthquakes occurred on the same source. These imply that the 1067 earthquake should be located at just west of the Nanpeng Islands,and its magnitude should be up to 71/4. In view of that there have been diverse recognitions of the 1574 AD earthquake occurred in the coastal region of northeastern Fujian,we have reanalyzed the distributions of the damaged and felt areas of this event,and made a comparison with that of the 1906 AD earthquake off-shore of Xiamen. As a result,it is confirmed that the epicenter of the 1574 AD earthquake should be located at the sea area east of the shore between Fuzhou and Putian,but its magnitude is possibly up to 61/4. Moreover,it is believed that the 1574 Qingyuan,Zhejiang,earthquake recorded in relevant historical document is unlikely a destructive earthquake that occurred at Qingyuan,but more probably is just the one occurred at the sea area east of the shore between Fuzhou and Putian in the same year. Both the 1067 and the 1574 earthquakes were produced possibly along the NE-trending Off-shore Fault zone.

CHARACTERISTICS OF SHALLOW AND DEEP STRUCTURES OF THE MIDDLE SEGMENT OF THE TIANSHAN MOUNTAINS, CHINA

YANG Zhu-en, ZHANG Xian-kang, ZHAO Rui-bin, ZHOU Wei-xin

2005, 27(1):  11-19. 

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The Tianshan Mountains originated from continent-continent collision during late Paleozoic era,and has experienced typical intra-continental orogenic process during Mesozoic-Cenozoic era. The architecture and activity of the shallow and deep structures of the Tianshan Mountains have attracted the attention of many geoscientists. Based on several geophysical prospecting data and comprehensive geological tectonic study,the shallow and deep structures of the middle segment of the Tianshan Mountains have been mapped in the light of the Tianshan Geoscience Transect. The result shows that the main geological units associated with the complexity of deep structures are displayed symmetrically from old to young on both sides of the suture zone of continental collision in Paleozoic era. This may reflect the collision process and the tectonic evolution in the later geological period. It is discovered that a low-velocity and high-conductivity layer of about 200km in width and about 10km in thickness exists on top of the upper mantle beneath the middle segment of the Tianshan Mountains. It is considered to be the residual lower crust resulted from the delamination between the crust and mantle due to the rejuvenated orogenic process of the Tianshan Mountains during Mesozoic-Cenozoic era.

NEW INSIGHT INTO THE SURFACE RUPTURE PAREMATERS OF THE KUNLUNSHAN M_s 8.1 EARTHQUAKE

TIAN Qin-jian, ZHANG Li-ren, HAO Ping, WANG Zan-jun, WANG Zhi-cai

2005, 27(1):  20-30. 

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The Kunlunshan M_s 8.1 earthquake of 2001 is a large earthquake produced by a large-scale intraplate strike slip faulting. Field observation shows that the surface rupture of this earthquake is about 426km long,and the maximum sinistral displacement is about 6m. As compared with the other similar intraplate large earthquakes,its rupture length is extraordinarily longer but its horizontal displacement is relatively small. The distribution of horizontal displacement along the surface ruptures is markedly controlled by fault structure. At the section where the horizontal displacement is small,the vertical displacement is also smaller,and no transformation of horizontal and vertical displacements is observed. This feature is also different from that of the other earthquakes. The relationship among rupture length,displacement and seismic magnitude follows a certain empirical equation,in which the ratio between the average displacement amount and rupture length is called "Ultimate linear strain",and is constantly within the range of 10^-5 for the rupture in the earth's crust. This feature can be used as criterion for testing the independency and integrality of the rupture segments. In this paper,we calculated the "ultimate linear strain" of the entire rupture zones and sub-segments of several large earthquakes,including the 1920 Haiyuan earthquake,1951 Bong Co earthquake,1932 Changma earthquake and 2001 Kunlunshan earthquake. The results show that average values of ultimate linear strain of the Haiyuan,Bong Co and Changma earthquakes are approximately close to the statistic value,but the values of ultimate linear strain of their sub-segments are significantly higher. In contrast,the value of ultimate linear strain for the entire surface rupture of the Kunlunshan earthquake is much lower than the statistic value,but the values of ultimate linear strain of its four sub-segments,except the west Taiyanghu segments,are close to the statistic value. Therefore,the Kunlunshan earthquake (M_s 8.1) should be produced by four relatively independent faulting events,instead of a uniform faulting. These characters provide geological evidence supporting the deduction that the Kunlunshan earthquake is successively triggered multiple earthquake events,rather than a single earthquake.

RESEARCH ON ACTIVE FAULTS IN LITANG-BATANG REGION, WESTERN SICHUAN PROVINCE, AND THE SEISMOGENIC STRUC-TURES OF THE 1989 BATANG M 6.7 EARTHQUAKE SWARM

ZHOU Rong-jun, CHEN Guo-xing, LI Yong, ZHOU Zao-hui, GONG Yu, HE Yu-lin, LI Xiao-gang

2005, 27(1):  31-43. 

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The Litang-Batang region of western Sichuan Province is located at the eastern section of the Tibet Plateau. Since the Late-Cenozoic,the East Tibet Block has thrust over the Sichuan-Yunnan Block from west to east along the NS-trending Jinshajiang Fault zone,resulting in the nappe tectonic belt of 30 km width accompanied by the formation of the NNE-trending Batang Fault and the NW-trending Litang Fault,a pair of conjugate shear faults. In the vicinity of Daoxu,south of Derenduo,the generally NS-trending Jinshajiang Fault zone extends along NNW direction and displaces left-laterally a series of gullies for about 120～140m. At south of Yarigong,the fault extends along NNE direction and dislocates right-laterally a series of gullies for about 180～210m. In contrast,no evidence of horizontal displacement is observed on the NS-trending segment of the fault. It is suggested,therefore,that the Jinshajiang Fault zone should be characterized by shortening in nearly EW direction. Based on the results of GPS measurement,the shortening rate is determined to be about 2～3mm/yr. The NW-trending Litang Fault is dominated mainly by left-lateral shear movement. According to the dislocation value and the initiation time of dislocation obtained at southeast of Kangga,southeast of Litang and northwest of Heni etc,the average horizontal slip rate on the Litang Fault is estimated to be 3.2～4.4mm/yr on the Litang-Dewu segment,and 2.6～3.0mm/yr on the segment to the north of Litang. The NNE-trending Batang Fault cuts obliquely the main part of the Jinshajiang tectonic zone,displaying mainly right-lateral shear movement. At Mangling Village of Markam County,Tibet,the average horizontal slip rate on the fault is estimated as 2.0～2.7mm/yr,wiile in the vicinity of Batang it is estimated to be 1.3～1.9mm/yr. The connecting line of the eqicenters of the 1989 Batang M 6.7 earthquake swarm and the long-axis of the aftershock distribution all extend nearly along EW direction,and the focal mechanism solution indicates an EW-trending normal faulting. Therefore,we tend to believe that the NNE-trending Batang Fault and the NW-trending Litang Fault to be a pair of conjugate shear ruptures. The southern block between these two faults slips southwards,resulting in EW-trending normal fault at the intersection of the two faults. It was the tensile rupturing on the normal fault that induced the Batang M 6.7 earthquake swarm,as evidenced by the development of EW-trending normal faults on the southern edge of the Maoya basin and the nearly EW-trending surface rupture of about 2 km in length produced by the Batang M 6.7 earthquake swarm.

SEISMICITY OF GLOBAL TECTONIC SYSTEMS OBTAINED FROM HARVARD CMT CATALOGUE

WANG Hui, ZHANG Guo-min, MA Hong-sheng, JING Yan

2005, 27(1):  44-54. 

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Earthquake is the best information source for describing the present-day crustal tectonic zones and crustal stress field,containing comprehensive and abundant geodynamic connotations. Based on the distribution of global earthquakes and their kinematic and dynamic characteristics,the most active global-scale tectonics can be divided into three first-order tectonic systems:the circum-Pacific deep subduction tectonic system,the mid-oceanic ridge tectonic system,and the continent-continent shallow underthrusting tectonic system. This paper describes in detail the types of faulting of seismic source,the characteristics of seismicities and focal depth distribution in global scale and in the afore-mentioned three tectonic systems,by using the Harvard CMT catalogue,which provides various parameters of hypocenter. Furthermore,the differences of faulting types,seismicities,and distributions of focal depths in different tectonic systems are discussed as well. The results show that different tectonic systems posses different environment and geodynamical force.

NEW EVIDENCE OF QUATERNARY LEFT-LATERAL STRIKE-SLIP MOVEMENT ALONG THE EASTERNMOST SEGMENT OF THE ALTUN FAULT

WANG Ping, LU Yan-chou, CHEN Jie

2005, 27(1):  55-62. 

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Previous results about the magnitude and rate of strike-slip movement along the eastern segment of the Altun Fault are quite inconsistent with each other. This is mostly because that the Quaternary strike-slip rate was inferred mainly from the offset of drainage system or from interglacial sediments,while these data focused mainly on late Quaternary. Tracing the early Pleistocene alluvial gravel bed outcropped along the easternmost segment of the Altun Fault,we discovered that the western boundary of the ancient alluvial fan deposits of the Shulehe River is now about 10km away from the outlet of the river. We believe that this is an important evidence indicating that the Quaternary left-lateral strike-slip displacement along the easternmost segment of the Altun Fault is about 10km. Basing on the analysis of terraces at the outlet of the Shulehe River,we conclude that the 2.8km elbow-like winding of the Shulehe River channel along the Altun Fault indicates not only the left-lateral strike-slip of the Altun Fault,but also the effect of lateral erosion at the meander reach of the river. The magnitude of the Quaternary dislocation and slip rate along the easternmost segment of the Altun Fault are discussed in this paper as well.

DYNAMIC MECHANISM OF PHREATOMAGMATIC ERUPTION IN NORTHERN HAINAN ISLAND

SUN Qian, FAN Qi-cheng

2005, 27(1):  63-72. 

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Maars of various scales produced by phreatomagmatic eruption are widely distributed in the Quaternary volcanic region of the Northern Hainan Island. The Pleistocene volcanic activity in Northern Hainan Island was characterized by the alternating of effluent magma eruption and phreatomagmatic eruption. In fact,phreatomagmatic eruption was concentrated in Middle Pleistocene to Upper Pleistocene,resulting in a lot of maars of various sizes,such as Longfeng-Longji,Shuangchiling,and Yanghua maars etc. In this area,different maars have different scale. The radius of maar is variable from several ten meters to above 1km. When ascending basaltic magma meets with ground water,violent explosion would occur,i.e. phreatomagmatic eruption. This kind of volcanic eruption may result in maars exposed on the earth's surface,and gives rise to the formation of base-surge. As to the base-surge,it has long been treated as sedimentary tuff by mistake. Usually,base-surge is distributed around maar,different from the distribution of sedimentary tuff. The base-surge is characterized by large-scale and low-angle cross-bedding,slaty-bedding,current-bedding and distal facies accretionary lapilli. In order to explain the dynamic mechanism of phreatomagmatic eruption thoroughly,we propose a simple mathematic model in this paper in the light of the elasticity theory. In addition,according to several parameters,such as the radius of maars,thickness of overlying formation when explosion occurred,and the radius of contact plane between the magma and groundwater,we have simulated the relation between the explosive wallop and these parameters,as well as its variation rule. Furthermore,we calculate the stress state at any point in the overlying formation. Some conclusion can be drawn as follows: the larger the radius of maar,the larger the explosive wallop needed for the formation of maar is; provided that the radius of maar and depth of explosive point are limited,then the larger the area of contact surface between magma and groundwater,the stronger the explosive energy will be; if the explosive energy and area of explosive point are restricted,the larger the radius of maar,the greater the depth of explosive point can be inferred; when the explosive energy and radius of maar are qualified,the depth of explosive point decreases with increasing of the area of contact surface between magma and groundwater. As for the maximum stress,undoubtedly it should occur on the surface of the overlying formation.

PETROCHEMISTRY OF PUMICES OF VARIOUS COLORS PRODUCED BY THE ERUPTION OF CHANGBAISHAN TIANCHI VOLCANO AT 1000 YEARS AGO

SHI Lan-bin, CHEN Xiao-de, YANG Qing-fu, WEI Hai-quan, LIN Chuan-yong

2005, 27(1):  73-82. 

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The Changbaishan Tianchi volcano is the most dangerous volcano in China. The volcano has erupted for several times since Holocene,and especially the violent Plinian-type eruption at about 1000 years ago had produced volcanic fallouts that had been carried as far as to Japan,and ignimbrite deposit within the range of 50 km around the volcanic crater. The ignimbrite deposit can be divided into two types: the valley-pond ignimbrite and ignimbrite sheet. The valley-pond ignimbrites are distributed mainly in Fushilin (Pumice Forest) and the valleys of the Jingjiang,Heishihe and Yalujiang Rivers,having a thickness of 20~60m. The ignimbrite sheets are distributed mainly in Guangming,Xinghuo,Dongfanghong and Weidong Forestry Centers,having a thickness of less than 10m. The ignimbrite deposits consist mainly of volcanic ash and pumice,associated with small amount of crystal and lithic fragments. It was commonly accepted in previous works that the pumice from ignimbrite deposit is grayish white in color and belongs to comendite. However,our field investigation has revealed that in addition to grayish white pumice,a small amount of black,gray and other colored pumices are also widely distributed. The samples of pumices of various colors have been collected during field investigation,and their chemical composition has been analyzed in the lab for comparison. The results show that the grayish white and black pumices belong respectively to comendite and trachyte,while the gray pumice belongs to trachyte but closer to comendite end member. The pumices of various colors came from the same crustal magma chamber,and were the products of different evolution stages of magma within the chamber. The simultaneous extrusion of these pumices indicates the zonation of the magma chamber and the mingling of magmas of various compositions.

THE RADIOCARBON AGE OF CARBINIZED WOOD IN TIANCHI VOLCANO, CHANGBAISHAN MOUNTAINS AND ITS IMPLICATION

YIN Jin-hui, ZHENG Yong-gang, LIU Yue-xia

2005, 27(1):  83-88. 

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The largest eruption of the Tianchi Volcano in historical period had not been recorded in historical document. Therefore,the determination of the accurate date of this largest eruption event is of great importance to the estimation of the eruption interval,the evaluation of the eruption risk and the hazard prediction of the future eruption. Basing on the systematical ¹⁴C dating of a well-preserved large carbonized wood,Liu Ruo-xin et al (1997) concluded that the largest historical eruption of the Tianchi Volcano occurred in 1215?15 AD. However,this conclusion has evoked much controversy. Horn et al (2000) suggested that the eruption time of Tianchi Volcano should be in 969?20 AD as determined from the age of a slab of carbonized wood collected from the North Korean side in a pumice fallout deposit. Earlier,Dunlap (1996) reported a wiggle-matched age of 1039?18 AD determined at the University of Arizona. Moreover,some experts favor 870?170 AD,which was the average of 53 radiocarbon ages of carbonized wood collected from the ignimbrite. In this paper,the eruption time of the Tianchi Volcano has been studied through detailed field investigation and careful selection of representative profile for collecting radiocarbon samples. The radiocarbon dates of 16 samples of carbonized wood including a piece of bark collected from ignimbrite around the Tianchi Volcano show that it is reasonable to consider the age of 1215?15 as the eruption time of the Tianchi Volcano. All of the radiocarbon ages of the carbonized wood are older than the true age of volcanic eruption,the largest deviation from which is 800yr,but the age of the bark is close to that of the Tianchi Volcano eruption. This may imply that the age of bark sample may provide better constraint on the date of volcanic eruption. The radiocarbon ages of black ignimbrites from Heishihe River,Pumice Forest,and Jinjiang Gorge show that they are also the product of 1215?15 AD eruption.

ACTIVE FAULTS AND VOLCANIC ACTIVITY IN LONGHAI—ZHANGPU COASTAL AREA, FUJIAN PROVINCE

HUANG Qing-tuan, ZHUANG Jin-yao, XIE Zhi-zhao, ZHANG Qing-xiang

2005, 27(1):  89-97. 

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Longhai—Zhangpu coastal region lies in the so-called Golden Triangle area of southern Fujian Province. Tectonically,it is located on the southern segment of the Changle-Zhaoan fault zone,being one of the regions of Tertiary and Quaternary basaltic eruptions in southeast coastal area of China. In this area there exist the Longhai Liuhui-Zhangpu Jiangjun'ao and Longhai Gangwei-Zhangpu Huxi faults,along which occurred basaltic eruption. The faults have been significantly active since Quaternary,and several small to moderate earthquakes occurred on the faults. In this paper,the basic characteristics of late Quaternary activities and the combination relation of the faults are discussed on the basis of the analysis of along-fault basaltic eruption during late Tertiary to late Pleistocene,as well as the differential variation of geomorphic surfaces and marine deposits on both sides of the faults. The results show that the Longhai Liuhui-Zhangpu Jiangjun'ao fault is a late Pleistocene active fault. During late Tertiary to late Pleistocene,three periods of basaltic eruptions had occurred along the fault,among which the first period occurred in Pliocene to early Pleistocene,the second period in middle Pleistocene and the third period in late Pleistocene. The Longhai Gangwei-Zhangpu Huxi fault can also be assigned to late Pleistocene active fault. The elevation rate of the downthrown side of the fault is estimated to be 1.11 mm/yr. These two faults have dissected the area into the Gangwei graben,south Taiwushan horst and the graben in the sea area to the east of Liuhui-Jiangjun'ao.

INVERSION OF SEISMIC DATA BY USING MULTI-RESOLUTION WAVELET NETWORKS

SONG Wei-qi, ZHAO Wan-jin, WU Hua, FENG Lei

2005, 27(1):  98-104. 

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In the light of the theoretical technique of wavelet networks,we study the method for inversing the time difference of artificial acoustic wave (Δt) by using multi-scale decompositon of wavelet from seismic records. We analyze also the theoretical method of wavelet decomposition,as well as network learning and training from seismic signals. In these studies,we find that for the adjacent seismic channels,the similarity of a smaller section is better than that of the whole channel. Therefore,the information obtained from the adjacent seismic channel can be extrapolated to the other channel by using time-frequency analysis method of wavelet. The results of the afore-mentioned studies,as well as the inversion and calculation of practical seismic data indicate that the structure of the wavelet network is much easier to be determined than that of the artificial neural network,while the convergence of wavelet network is faster than that of artificial neural network. In addition,the high and low frequency information of the adjacent channel can be transformed to the other seismic channel by taking the advantage of better similarity of subsection time-frequency analysis of seismic data,as well as the capability of learning,training and memorizing of the wavelet network. In this way,we may enhance not only the resolution capability but also the reliability of seismic data inversion.

PRESTACK DEPTH MIGRATION IMAGING OF SEISMIC DATA AND ITS APPLICATION TO SHALLOW SEISMIC PROSPECTING

ZHAO Cheng-bin

2005, 27(1):  105-114. 

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This paper describes the complexity of geological structures and tectonic features in shallow seismic prospecting,as well as the particularity of higher accuracy requirement for its achievements. It is suggested that it should be very important to develop prestack depth migration method for shallow seismic prospecting. The basic principle of prestack depth migration with phase shift method and its algorithm are also expounded in detail,and the relevant PC program is compiled. Based on this method,two theoretic models are tested,and good results are obtained. The results show that the stratigraphic horizons are displayed clearly in the prestack depth migration sections,and the characteristics of geological structure and tectonic features of the theoretic models are expressed fairly well. Furthermore,the method has been applied to process the actual shallow seismic reflection data,and the obtained results are identical with the known geologic structures and tectonic features. All these results demonstrate the reliability and applicability of this algorithm and its software. It is clear that the prestack depth migration method can be effectively used in the processing of actual shallow seismic reflection data.

APPLICATION OF STRONG SOURCE TRANSIENT ELECTRO-MAGNETIC MEASUREMENT SYTEM TO THE EXPLORATION OF SUBSTITUTED RESOURCE OF LARGE MINE

JI Yan-ju, LIN Jun, YU Sheng-bao, ZHU Kai-guang, WANG Zhong, WANG Jing

2005, 27(1):  115-122. 

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To counter the strong noise in the mine and to meet the requirement of great exploration depth,the strong source Transient Electro-magnetic (TEM) system is applied to the exploration of substituted resource of crisis-ridden large mine. The system adopts double signal synchronous stacking method to enhance the transmitted magnetic moment. In other words,it enhance the signal-noise ratio and enlarge the exploration depth by increasing transmitted current and using reasonable transmitter coil length. In practical exploration of the Fenghuangshan copper mine,Anhui Province,the two transmitters of the ATEM-Ⅱ system made by Jilin University were synchronously operated,increasing the transmitted current from 2.4A to 38.5A,and enhancing the SNR of late time transient signal from 0.275 to 2.93.In this way,the effective exploration depth may reach up to 650m. The results show that the strong source TEM system opens up broad prospects for the exploration of the substituted resources for large mine.

RELATIONSHIP BETWEEN THE ANOMALIES OF UNDERGROUND FLUID IN THE HUAILAI NO.4 WELL AND EARTHQUAKE

ZHANG Feng-qiu, REN Jia, LI Hai-xiao, ZHANG Yan-qing, WANG Chang-jiang

2005, 27(1):  123-130. 

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The Huailai No.4 well is one of the national key observation wells. Obvious anomalies have been observed in this well before the occurrence of many earthquakes. Therefore,the well has played an important role in the monitoring of earthquake activity in Northwest Beijing region. This paper describes in detail the anomalies of underground fluid in the well before the occurrences of 5 moderate-strong earthquakes. In addition,we have also collected the earthquake-reflecting anomalies of the underground fluid observed in the Huailai No.4 well before the occurrence of earthquakes of magnitude above 4.0 in Huailai and its neighboring area since 1998. The research shows that the Huailai No.4 well may sensitively reflect M≥4.0 earthquakes that occur within the range of ≤260km around the well. The main features of precursory anomalies of underground fluid observed in the Huailai No.4 well can be summarized as follows: ⑴ The precursory anomalies of water mercury appear as abrupt variations. They occur several days to 2 months before the occurrence of an earthquake. The amplitude of variation might be several to tens times as high as the background value. The higher the amplitude of anomalies the greater the magnitude of earthquake will be. The earthquakes occur after the ending of anomalies; ⑵ The precursory anomalies of carbon dioxide in fault gas appear as sharp variations at many points. They occur 16 days to 47 days before the occurrence of an earthquake. The amplitude of variation might be several times to ten times as high as the background value. The higher the amplitude of anomalies,the greater the magnitude of earthquake will be. The earthquakes occur when the anomalies fall off; ⑶ The precursory anomalies of water radon appear as stepped variation. They occur several days to 2 months before the occurrence of an earthquake. The amplitude of anomalies might be of about 15% of the background value. The earthquakes occur during the growing period of anomalies; ⑷ The precursory anomalies of hydrogen escaped from groundwater appear as abrupt variations. The amplitude of variation of anomalies might be 3 times as high as the background value. The earthquakes occur after the ending of anomalies. All these results may shed light on the earthquake-related behavior of the underground fluids in this well,and may enhance the capability of earthquake prediction in the near future.

DISCUSSION ON THE STRUCTURAL CHARACTERISTICS AND FORMATION MECHANISM OF THE TAIPEI BASIN

ZHANG Jin, MA Zong-jin, WU Yi LI, Tian-bin

2005, 27(1):  131-144. 

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The Taipei Basin is located in the northern part of the Taiwan Orogen. Although this extensional basin was developed in an active orogen,it has peculiar formation mechanism different from that of basins resulted from the collapse of orogen in general sense. However,little attention has been paid to this peculiarity in previous studies,so that the problem concerning the formation of the Taipei Basin has evoked much controversy. Recently,bore holes and seismic prospecting data have revealed that the Shanjiao Fault,which has controlled the formation of the basin,consists of 3 segments,rather than a fault. Each segment controlled one center of subsidence,and has not connected with the other segments. The activity of different segments is not uniform,and it becomes stronger with time toward northeast. At present,the strongest activity is concentrated on the middle and northern segments,while the southern segment is no longer active. A series of NW-trending faults in the basin are the secondary structures produced during the subsidence of the different subsidence centers. There are a series of volcanoes that had erupted around the basin,so the formation of the basin should be affected by magmatic activities around the basin. Because the development of the basin treaded on the heels of these volcanic activities,there were essential relationship between the formation of the basin and the volcanic activities around the basin. Geophysical data,the structural characteristics and the migration of depocenter have shown that the development of the Taipei Basin was resulted from the cooling and contraction of the magma body at depth. The magma body beneath the Taipei Basin is connected with the magma body beneath the Tatun volcanic cluster,and the cooling of the magma has migrated from southwest to northeast. Moreover,the Tatun volcanic cluster is currently in its stage of subsidence,so the formation of the Taipei Basin was not an independent phenomenon. Both the Taipei Basin and Tatun volcanic cluster belong to one larger extensional basin.

APPLICATION OF SPOT AND IKONOS IMAGES TO THE STUDY OF THE WEST OF KUNLUNSHAN PASS EARTHQUAKE (M_s 8.1)

SHAN Xin-jian, LI Jian-hua, MA Chao

2005, 27(1):  145-154. 

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On November 14,2001,an M_s 8.1 earthquake occurred in the west of Kunlunshan Pass. This event is the greatest earthquake that occurred in China continent following the Zayu-Medog,Xizang M_s8.6 earthquake of August 15,1950 and the Damxung,Xizang M_s 8.0 earthquake of November 18,1951. The earthquake occurred in Hoh Xil,a depopulated zone in the northern Qinghai-Xizang Plateau,where field investigation is very difficult to be carried out due to harsh climate and thin air. High spatial resolution satellite images are applicable to the interpretation of earthquake surface rupture zone. The 10m spatial resolution SPOT images may reveal distinctly the major rupture zone,while the 1m spatial resolution IKONOS images may display the fine structures and kinematical characteristics of the surface rupture. This paper presents the results of the study on the surface rupture of the west of Kunlunshan Pass earthquake by using SPOT and IKONOS images. The study shows that the surface rupture zone is located mainly along the abrupt variation zone of landforms on the alluvial-pluvial platform or the rear edge of the platform at the southern foot of the Kunlunshan Mountains. The surface rupture to the east of Buka Daban Peak is about 350km in length and striking 100°,consisting of 3 sub-rupture zones. This surface rupture is superimposed on the preexisting rupture zone. A series of gullies crossing the rupture zone have been offset left-laterally,and the average slip rate is estimated to be 13.4～16.8mm/a. The interpretation of the SPOT and IKONOS images demonstrate that the macroscopic epicenter of this earthquake should be at 93°17′E,35°47′N,in the vicinity of the Yuxifeng Peak,where the maximum left-lateral horizontal dislocation is 7.8m and the width of the surface rupture zone reaches up to 1250m. This conclusion is in good agreement with the location of macroscopic epicenter (93.3°E,35.8°N ) deduced by China Earthquake Administration for this earthquake.

DISCUSSION ON THE ACTIVITY OF FANJIABA-LINJIANG FAULT AND THE SOUTH WUDU, GANSU PROVINCE M 8 EARTHQUAKE OF 1879

FENG Xi-jie, DONG Xing-hong, LIU Chun, LI Jin

2005, 27(1):  155-163. 

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The earthquake occurred in Jiezhou,Gansu Province on July 1,1879 (May 12,Guangxu 5,Qing Dynasty) is one of the largest earthquake events in Chinese history. The effect of this event spread over more than ten provinces. According to historical data,the magnitude of this earthquake has been estimated to be 8 or 71/2,and the macroscopic epicenter has been located at Mianshanheba (104.7E,33.2N),south of Wudu,Gansu Province,with type II precision of estimation (≤25km error). As the earthquake occurred in the areas of high mountain ridges difficult to be approached,it has not been studied in detail so far. It is one of the 3M=8 earthquakes in China that their relation to active faults had not been revealed so far. Recently,we have found that in satellite images a NNE-trending lineament can be clearly observed along the northern foot of the Shuikeng Mountains to the northeast of Wenxian County,Gansu Province. It extends eastward from Shifang Village to the northwest of Wenxian County,passing through Liangjiaba,Malian River,Fanjiaba,Miaobeihou,Guanjiagou,Jianzuishan Mountains,Shuikengya,northern slope of the Fangmashan Mountains,Songjia Mountains and Shenjiana'an,and then gradually becomes unclear after crossing through the Bailongjiang River and turning northward at 500m downstream from the Majiaba. The lineament has a total length of about 30km,among which about 21km can be identified to be surface fracture zone (from the bank of the Bailongjiang River to the top of the western hills of Guanjiagou). The lineament offsets left-laterally a series of ridges and gullies. In comparison with geologic data of this region,this lineament image coincides well with the NEE-trending Fanjiaba-Linjiang Fault. The interpretation of satellite images for the whole region and re-collation of historical records about this earthquake have confirmed that the Fanjiaba-Linjiang Fault bears a close relation to the southern Wudu earthquake,and is most probably the causative fault of this earthquake. This study,therefore,provides new insights into the following aspects,such as the occurrence and mode of motion of the causative fault,the length of surface ruptures,the amount and variation of horizontal displacement along the fault,the location of macroscopic epicenter,the probable magnitude of the event and the distribution of seismic hazards etc. All these results have led to the satisfactory solution of outstanding issue about the causative fault of the 1879 southern Wudu earthquake. They are also of great importance to seismic risk assessment in the border areas of Gansu,Qinghai and Sichuan Provinces as well as in southeast Gansu Province.

DIGITAL CITY AND THE INFORMATION MANAGEMENT SYSTEM FOR EARTHQUAKE DISASTER REDUCTION

LI Zhi-qiang, NIE Gao-zhong, SU Gui-wu

2005, 27(1):  164-171. 

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The main purposes of the information management system for earthquake prevention and disaster reduction are to study the classification and evaluation of the earthquake and its secondary disasters faced by the city,as well as to assess the effectiveness of disaster reduction measure. The system embraces various models,such as the fatalness caused by the earthquake,sources of secondary disaster,disaster regionalization,vulnerability of the calamity-bearing body,evaluation of economic loss and casualties,emergency countermeasure and material requirement etc. Moreover,it also involves the other aspects,such as the fatalities caused by other urban disasters and the reciprocity between the disasters and social economics or personnel distribution. In case of earthquake,this system will become the assistant decision-making system for the city calamity emergency measure. The well-running information system will also play an important role in the reduction of earthquake hazards. Digital city integrates as a whole the elements from every aspect,embodying the digital recognition of the whole city. It has various features,including real-time or close to real-time,dynamic,spatial,digital,network,intellectual and visual features. Its functions in the city construction management and information services etc. have been widely realized by more and more people. The construction of the information management system of earthquake prevention and disasters reduction is the important part of the digital city. The construction of the digital city is based largely on the application of the spatial data. Therefore,the effective update of the spatial data has become the key to the surviving and flourishing of the information system of earthquake prevention and disaster reduction. At present,electric government affair is the main developing direction for the digital city. It puts forward a new target for the construction of the modern disaster reduction system,which is based on the optimization and utilization of the assistant decision-making system and its combination with the electric government affairs. The progress of the system will depend greatly on the development of the digital city. The close integration of the system with the digital city will extend the earthquake disaster reduction function of the government,enhance the emergency reaction capability and reduce effectively the loss caused by earthquake disaster. In practice,however,we have found that there are still many difficulties and questions in this kind of integration,such as the standardization and usability of the data,suitability of the supporting system and the combination with the electric government affair. Further studies on these questions may open up a new departure in earthquake sociology and the theory and practice of the emergency decision of the city.