Table of Content

05 June 2002, Volume 24 Issue 2

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Brief Report

SEGMENTATION OF EARTHQUAKE RUPTURE AND EARTHQUAKE PREDICTION ALONG THE LONGLING-LANCANG FAULT ZONE IN THE SOUTHWESTERN YUNNAN PROVINCE

GUO Shun-min, XU Xi-wei, XIANG Hong-fa, ZHOU Rui-qi, DONG Xing-quan, ZHANG Wan-xia

2002, 24(2):  133-144. 

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Longling Lancang fault zone, consisting of sets of en echelon or conjugated short faults, is a newly generated rupture zone. It is characterized by high frequency, large magnitude, and short recurrence interval of earthquake activity, as well as by double main shock earthquake or earthquake swarm. The fault zone can be naturally divided into 4 first order segments and 13 secondary earthquake rupture segments, among which 4 segments can be further divided into 8 third order segments according to the differences in their internal geometry, fault length and seismicity. Generally speaking, the fault segment, on which large or strong earthquake occurred in history can be defined as earthquake rupture unit, while the segment on which the fault was active in Late Quaternary but no earthquake is recorded in history can be defined as locked element. The stepover or connecting structure between the faults is named as the barrier. In terms of the rupture pattern of historical earthquakes and paleoseismicity, the fault zone can be divided into 9 surface rupture units, 8 locked elements and 10 barriers. Surface rupturing earthquake may be transformed, triggered or migrated among these three kinds of units. At last, the risk segments of future large, strong and moderate earthquakes are predicted according to seismotectonic criteria. There are 9 predicted earthquake risk areas, among which one is large earthquake area located between Yongde and Yongkang region, three are strong earthquakes area located at Mazhan, Shihuiyao and Jiufang Menghun regions and five are moderate earthquakes area located at Xiashunjiang, Liren, Dagangshan, Nanming Lancang and Mengzhe regions, respectively.

SEGMENTATION OF SURFACE RUPTURES ON THE EASTERN SEGMENT OF THE ALTYN TAGH FAULT ZONE

WANG Feng, XU Xi-wei, ZHENG Rong-zhang, CHEN Wen-bin, Paul Tapponnier

2002, 24(2):  145-158. 

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Identifying correctly the segmentation of an active fault is very important for the evaluation of earthquake hazard on this fault. In a fault system, earthquake rupture occur on different segments of the fault, resulting in the segmentation of the fault system. The segmentation of a fault, therefore, may reflect the propagation process of earthquake rupture, and may provide an insight into the development process and seismic behavior of the fault. The segmentation of a fault system can be identified through different methods, among which the most practical one is to identify the segments by using surface ruptures, which is the direct product of earthquake faulting. This paper deals mainly with the segmentation of the surface rupture on the eastern segment of the Altyn Tagh Fault zone. The Altyn Tagh Fault is one of the major east west trending strike slip faults in China. It is the northern boundary of the Qinghai Tibet Plateau, and its linear character is very conspicuous on satellite images. Basing on the offset landforms observed during fieldwork and spot images analysis of the eastern Altyn Tagh Fault, we divide the eastern Altyn Tagh Fault into three segments from west to east according to its surface ruptures: (1) Qingyazi-Lucaowan segment. The extension of the fault on this segment is simple and its sinistral strike slip motion can be recognized from the offsets of streams, alluvial fans and terrace ridges. Here the youngest terraces of 5.24?0.40ka B.P. in age are offset by the fault, indicating that the latest earthquake on the segment is younger than 5.24?0.40ka B.P. (2) Lucaowan-northern Qilianshan segment. The length of this segment is about 250km. By analyzing the offset landforms and combining with the previous results of paleoearthquake research, we find that the youngest terraces here are not offset by the fault, and we conclude that the latest earthquake on the segment occurred at about 7.080?0.57ka B.P. (3) East of the north Qilianshan segment. The displacement of the fault on this segment is much smaller than those on the other segments, and the fault trace disappears gradually eastward. Here the youngest terraces are offset by the fault, and we estimate that the age of the last earthquake on this segment is younger than 5ka B.P.

LATE PLEISTOCENE SURFACE FAULTING AND THE MAXIMUM POTENTIAL EARTHQUAKE ON THE DONGSHILANGOU SEGMENT OF THE HAIYANG FAULT, SHANDONG PROVINCE

ZHOU Ben-gang, RAN Yong-kang, HUAN Wen-lin, RAN Hong-liu

2002, 24(2):  159-166. 

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The Haiyang fault of 115km length is a larger scale fault in the east of the NE striking Mu ping Jimo Fault zone in Jiaodong Peninsula, Shandong Province. This fault showed intense surface faulting during middle Pleistocene, while dip slip reverse displacement of larger than 1m on the fault can be identified in the field. Although the surface faulting along the fault has generally ceased since late Pleistocene, late Pleistocene surface faulting still occurred on the Dongshilangou segment of the fault. The Length of the Dongshilangou segment is about 8km. Detailed investigation along the segment shows that the latest surface faulting event occurred at 37～12ka B.P., and most possibly near 12ka B.P. The surface faulting has a total length of 6.5km or more, and is dominated by right lateral strike slip with small amount of dip slip reverse component. The observable maximum dip slip displacement is about 0.2m, and the right lateral displacement is about 1.13m as deduced from the plunge of fault striae. The average right lateral strike slip rate is estimated to be 0 094mm/a and the dip slip rate to be 0.017mm/a, with the assumption that the latest surface faulting event occurred at 12ka B.P. The geologic profile of this active segment indicates that the late Pleistocene surface faulting on this fault was an abrupt faulting event. According to the relationship between the parameters of seismic surface faulting and the rupture length, it is estimated that the maximum magnitude of the potential earthquake on this segment may reach 6 1/4.

QUATERNARY ACTIVITY OF THE NE-TRENDING FAULTS IN QINGDAO CITY AND ITS SURROUNDING AREA

WANG Zhi-cai, CHAO Hong-tai, CUI Chao-wen, LI Jia-ling, SHI Rong-hui

2002, 24(2):  167-176. 

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A series of studies have been carried out to gain an insight into the Quaternary fault activities in Qingdao City and its surrounding area. The spatial distribution, geomorphic features and the features of the structural planes of the faults, as well as the relation between the faults and Quaternary strata have been studied in detail. Moreover, the ages of the relevant fault zone materials and unfaulted overlying Quaternary deposits have been dated by TL and/or ESR methods. This paper summarizes the achievements of these recent studies. It is concluded that the NE trending faults in Qingdao City and its surrounding area share some similarities in their dimension, orientation, age of faulted rocks, mode of motion, and age of the latest faulting. Their latest active period was in the mid late stage of middle Pleistocene. The faults have no longer been active since late Pleistocene. Moreover, in this area no fault of other strikes has been found to be active since late Pleistocene. According to historical earthquakes, the current activity of small earthquakes and Quaternary fault activities in this area, it is suggested that there's no condition for the occurrence of M_S≥6 earthquakes within this area, but it would not be surprising if an M_S≈5 earthquake should occurs in the future.

DISCUSSION ON QUANTITATIVE RESEARCH OF VERTICAL DISPLACEMENTS ON NORMAL DIP-SLIP ACTIVE FAULTS

JIANG Wa-li, XIE Xin-sheng

2002, 24(2):  177-187. 

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Vertical displacement is an important parameter for quantitative research on normal dip-slip active faults and seismic risk assessment. It bears a close relation to the magnitudes of earthquakes,dislocation rate of fault, and the average recurrence interval of strong characteristic earthquakes, while the difference of vertical displacements in different horizons of the same profile is related to the number of paleoseismic events. Therefore, if this parameter can not be determined properly, then the error will be carried into the quantitative researches of the other parameters. In this paper we discuss the following cases. If the length of a trench does not cover the entire deformation zone of a fault, then the vertical displacement estimated from this trench represents only a part of the real displacement on the fault. If the two sides of a fault scarp consist of geomorphic planes of different ages, then the vertical displacement estimated from the height of the fault scarp will deviate significantly from the real displacement. For example, two large trenches were dug across the Daqingshan Piedmont Fault in Inner Mongolia. In these two trenches, the displacement rates of the fault estimated from the heights of fault scarps and from combining fault scarp data with trench log data are 1.1mm/a and 1.9mm/a, as well as 1.13mm/a and 1.6mm/a respectively. The revised values of the displacement rates of the fault from trench log data are about one third or half of the original value obtained from fault scarp data in this example. Moreover, a method for determining the number of paleoseismic events is proposed on the basis of the resolution of accumulative vertical displacements of nearly horizontal strata on both sides of the fault. We find that the vertical displacement of a fault may lead to the difference of the thickness of deposits on both sides of the fault. All these phenomena can be observed not only in log of trench across the fault but also in log of borehole on both sides of the fault. The boreholes on both sides of the Xiadian and Gaoliying Faults in Beijing Plain, as well as the trench across the Tanna Fault in Japan can be taken as examples.

SINISTRAL THRUSTING ALONG THE LIJIANG-XIAOJINHE FAULT SINCE QUATERNARY AND ITS GEOLOGIC-TECTONIC SIGNIFICANCE——Shielding effect of transverse structure of intracontinental active block

XIANG Hong-fa, XU Xi-wei, GUO Shun-min, ZHANG Wan-xia, LI Hong-wu, YU Gui-hua

2002, 24(2):  188-198. 

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The Lijiang-Xiaojinhe Fault lies in Northwest Yunnan Plateau, striking N40°E and extending for 360km. It is an important transverse active fault, obliquely cutting the "Sichuan Yunnan Rhombic Block" in southwest China. Interpretation of aerophotos, field investigation, and age determination of this active fault have revealed that the fault is an active reverse sinistral strike slip fault, dipping northwest at high angle. Relocation of basins and analysis of synsedimentary dislocation of the basins provide an estimate of the horizontal dislocation amount along the fault of 7.4～7.6km since Quaternary. In addition to the large scale horizontal movement, the vertical differentiation of relief and landforms on both sides of the fault is also strikingly shown. The relief along the fault strand from Lijiang northeastward to Ninglang and Muli is higher on the northwest side and lower on the southeast side, between which lie a series of steep fault scarps and a topographically steep zone. Comparison of the relief on both sides of the fault shows that the vertical throw of the fault is 500～700m or more. The horizontal and vertical dislocation rates along the Lijiang Xiaojinhe Fault since Quaternary and since middle Pleistocene are estimated preliminary to be 3.7～3.8mm/a and 1.0～1.5mm/a, respectively. In the northeast of Lijiang, especially along the Changping Muzhuda and Baerqiao area in Ninglang, a series of evidence of sinistral horizontal dislocation, such as offset ridges, gullies, proluvial fans, and terraces was found. The amount of horizontal dislocation varies from several meters to hundreds meters. All these may indicate the characteristics of obvious movement along the fault since late Quaternary. The amounts of horizontal dislocation and the related data of age determination indicate that the average dislocation rate since late Pleistocene is in the range of 2.6～ 4.0 mm/a with a mean value of 3.3mm/a; the average dislocation rate since Holocene is in the range of 2.5～5.0mm/a with a mean value of 3.5mm/a. The similarity of slip rates in various stages of Quaternary indicates the relative stability of movement along the fault and the long range persistence of the active block boundary. The compression and overthrust of the shallow layer crust, the existence of deep geophysical gradient zone and zonal area of strong seismicity along the fault, as well as the variation in movement rate of blocks on both sides of the fault reveal the significant shielding effect of the Lijiang Xiaojinhe fault on the southward migration and "flow" of the mass in the middle upper crust along the "Sichuan Yunnan Rhombic Block" after the uplift of Qinghai Xizang Plateau.

RELOCATION OF EARTHQUAKE SEQUENCES USING JOINT HYPOCENTER DETERMINATION METHOD: PORTABLE SEISMIC ARRAY STUDY IN JIASHI REGION, XINJIANG

GUO Biao, LIU Qi-yuan, CHEN Jiu-hui, LI Shun-cheng

2002, 24(2):  199-207. 

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In 1997, 7 strong earthquakes ( M >6.0) occurred in Jiashi region, Xinjiang Uygur Autonomous Region. In order to gain an insight into this seldom seen seismic event, a passive broadband seismic array experiment was carried out by the Institute of Geology, China seismological Bureau in 1998. During the experiment two events, the Binamu and Lonkou earthquakes ( M ≥6.0), and their aftershock sequences were recorded by the portable seismic array. In this paper, these two earthquake sequences are relocated by using the Geiger method and the Joint Hypocenter Determination (JHD) method, respectively. The results show that: 1) the JHD method can be used to locate the relative position of an aftershock sequence more precisely than the Geiger method; 2) the Binamu and Longkou aftershock sequences delineate two nonparallel SWW trending faults, the occurrence of which are roughly consistent with those given by the moment tensor solution of the corresponding main shocks, and hence can be used for determining the focal plane of the Jiashi events; 3) the Binamu and Longkou earthquakes occurred at the gradient zone of the crust mantle boundary and at the convergence of the crustal high and low velocity media nearby the deep faults; this may indicate that the genesis of these earthquakes bears a close relation to the deep geological environment within the crust; 4) the tensional rupturing feature of the Jiashi earthquake sequence might be resulted from the heterogeneous lateral deformation of the northern edge of the Tarim basin.

PHYSICAL MECHANISM AND UNITARY MATHEMATICAL EQUATION FOR TIDAL PHENOMENA OF GROUND WATER

ZHANG Zhao-dong, ZHENG Jin-han, GENG Jie, WANG Zhong-min, WEI Huan

2002, 24(2):  208-214. 

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A new model of layering confined aquifer, which takes both the mechanical compressibility and permeability of the aquifer into account, is proposed in this paper. This model combined with the frequency characteristics of the disturbance signal source, is used to analyze the mechanism of the effects of the disturbance signal sources including earth tide, atmospheric tide and loading tide of surface water, on the water level and rate of discharge of the confined well. Moreover, the corresponding partial differential equations for these effects are given. On the basis of numerical and analytical solutions of the equations, the relation between the disturbance signal source and the parameters of the mechanical compressibility, permeability and frequency characteristic of the aquifer in the confined wells are discussed, and then the unitary mathematical equation and response function of the water level and discharge of the confined well to tidal phenomenon are given. The results of the present study reveals the physical mechanism of the effects of the disturbance signal source, such as earth tide, atmospheric tide and loading tide of surface water, on the water level and discharge of the confined water well. We find that although the effects of earth tide, atmospheric tide and loading tide of surface water on the confined aquifer are different, they produce similar effect of stress on the aquifer. Therefore, they can be defined by a unitary partial differential equation. The tidal phenomena of the level, discharge and temperature of the confined water have the same physical mechanism, and they are the result of volumetric strain of the aquifer due to earth tide. In consideration of the seepage between the well and the aquifer, it is concluded that the function of response amplitude and the phase lag of the aquifer in the well to the effects of three different tidal phenomena bear a relation to the variation period of the parameters and signal of the aquifer. The response of the aquifer system in the well to long period signal is the same as that of the aquifer with discharge. They have the same response amplitude without phase lag.

STUDY OF ANOMALIES OF RARE GASES IN SEVERAL WELLS IN NORTH CHINA

ZHANG Pei-ren, LIU Cheng-long, WANG Zhi-min, TAO Jing-ling, YANG Hai-xiang, YANG Zhu-zhuan, MENG Cai-ju

2002, 24(2):  215-222. 

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Recently, remarkable rare gas anomalies have been observed in the water of Baolong and Tai-ping-zhuang wells in Beijing area, and Xialiao No.1 well in Xiaxian County, Shanxi Province. All these three wells are located in North China. According to the characteristics of rare gas anomalies in the three wells and the relationship between the anomalies and groundwater levels, theoretical analysis and experimental study have been carried out to gain an insight into the genesis of the anomalies. The results of experiments show that the volume of gases in the pores and fractures varies significantly with the evolution of groundwater dynamic condition. We find that the gas volume will expanse about 0.009 0% when the water level drops for 100mm. This may indicate that the anomalies of rare gases in these three wells are resulted from the expansion of gas volume and escape of gases due to the drop of groundwater level and the decrease of pore fluid pressures. It is proposed, therefore, that the rare gas anomalies discussed in this paper should not be earthquake precursor, but are anomalies caused by interference factors.

ANALYSIS OF THE ANOMALOUS BEHAVIORS OF THE SUBSURFACE FLUIDS CAUSED BY THE ACTION OF REGIONAL STRESS IN NORTH TIANSHAN REGION

LU Jing-fang, WANG Dao, ZHANG Yuan-sheng

2002, 24(2):  223-233. 

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A vast amount of observations have indicated that subsurface fluids (water, gas and oil) in deep crust, as an elastic medium, respond sensitively to the distribution, variation and transformation of deep crustal stress, as well as to the development, occurrence, adjustment and evolution of earthquakes. The generation of earthquake bears a close relation to the active intensity of regional tectonic stress. Under the background of large scale regional stress, a lot of stress concentration spots may form, which may give rise to the occurrence of premonitory anomalies of the subsurface fluids. The monitoring of subsurface fluids for several ten years in Xinjiang has discovered that a lot of earthquake related premonitory phenomena induced by the activity of regional tectonic stress occur before strong earthquakes. The space time patterns of the evolution of large scale premonitory anomalies of subsurface fluid occurred in 1998 and 1999 in north Tianshan region are emphatically analyzed in this paper. It is discovered that they are quite different in genesis and characters from the premonitory anomalies produced by stress activity at seismic source. It is suggested that this kind of premonitory anomaly field of subsurface water level should not be correlated to a single seismic event, but to a set or a series of earthquakes, which are often related to the activity of regional stress caused by block squeezing and fault activity. We select the No. 21, 25 and 26 springs as the sensitive spots in the monitoring area, and the differences between the premonitory anomalies induced by the activity of regional stress field and by stress field in seismic source are comparatively analyzed. The main purpose of the study is to get better understanding of field premonition and source premonition reflected by subsurface fluid, to distinguish and master their different characters, and to serve the earthquake prediction better.

ANALYSIS OF THE RELATIONSHIP AMONG GEOTHERMAL WATER EXPLOITATION, GROUND SUBSIDENCE AND GROUND FISSURES IN XI'AN CITY, CHINA

WU Fu-chun, FANG Wei, SONG Li-sheng, WANG Feng, ZHU Xing-guo, JING Bei-ke, DONG Xing-hong, ZUO Yong-qing

2002, 24(2):  234-240. 

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Xi'an region is a geothermal anomaly zone. The geothermal exploitation in this region began in 1990, and has sped up since 1993. At present, there are 120 geothermal water wells with a depth of greater than 1 000m in this region, and this number is still increasing at a rate of 5 to 10 wells per year. Ground subsidence and ground fissures are two natural calamities peculiar to Xi'an City. They are famous for long standing formation time, a vast involved range and causing the serious damage of a great number of buildings. Most people considered that the ground subsidence and ground fissures in the city are induced by the overexploitation of the confined water. The overexploitation of confined water may induce ground subsidence and ground fissures; does the speeding up of exploitation of geothermal water aggravate the afore mentioned geological hazard? In this paper the development history, nature and formation mechanism of ground subsidence and ground fissures in Xi'an region, as well as the relationship between the two calamities are demonstrated in detail. Moreover, the variations of geothermal water level, the quantity of geothermal water exploitation and the amount of subsidence for individual stratum in the past decade are summarized and analyzed. All the results show that the spatial distribution of the ground subsidence coincides well with that of the ground fissures in Xi'an City, while their development processes and variations of intensity display a good synchronism. The main cause of the induced surface subsidence is the overexploitation of confined water. The drop of the confined water level may give rise to the decrease of pore pressure of the medium within the aquifer. The compaction of gummy formations due to the release of water leads to the permanent surface subsidence, while the compaction is greater at shallow level than at deep level. The inhomogeneous surface subsidence then induces the ground fissures. Either the data of the variation of geothermal water level and the quantity of geothermal water exploitation, or the data of the subsidence of various strata show that the geothermal exploitation in Xi'an City at present does not intensify the surface subsidence and the activity of ground fissures. It is suggested that the most effective approach to minimizing ground subsidence and ground fissures is to control and decrease the exploitation of confined water in Xi'an City.

STUDY ON THE LOESS-PALEOSOL SEQUENCE OF THE DINGCUN PALEOLITHIC SITES

WU Wen-xiang, LIU Tung-sheng

2002, 24(2):  241-248. 

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Since the discovery of Dingcun Palaeolithic Sites in 1953, much has been done in the studies of the strata and mammalian fossils at the site. However, the age of the Dingcun Palaeolithic Sites is still a controversial issue. One main reason is that there is still much controversy concerning the lithostratigraphy of the loess paleosol sequence overlying the fluvial deposits. For the Paleolithic Site 100,some researchers regard the "red soil" overlying the fluvial deposits as late middle Pleistocene in age,while the others regard it as the same as the Malan loess. As for the Paleolithic Site 79:02,most researchers attribute it to the late "red soil" period,but this term is too coarse to reflect the real age of this cultural horizon. In the past decades great progresses have been made in the research of loess in China, one of which was the dating of every layer of the loess seqence. The loess paleosol sequence, therefore, can be used not only as an excellent means for reconstructing the history of palaeomonsoon in east Asian but also as a dating tool. This dating method has been proved to be useful for loess terraces,providing that the loess paleosol sequence is stipulated correctly. In this paper,the strata at Site 100 representative of the Dingcun Middle Paleolithic Culture and Site 79:02 representative of the Dingcun Early Paleolithic Culture are restudied,the stratigraphic section is analyzed, and the magnetic susceptibility of the loess paleosol is measured. To verify the authenticity of the division of loess strata that we have made, a similar division and magnetic susceptibility measurement have been made at Jingcun profile located at Loess Yuan, where loess strata are well developed. The obtained results are then compared with the typical Luochuan loess paleosol sequence and the loess paleosol squences of 2 paleolithic sites at Dingcun. According to our study,the loess paleosol sequence at Dingcun site 100 consists of S₀,L₁ and S₁. Since the horizon containing the Paleolithic Culture and the fossil of Dingcun man is about 4 5～ 9m below S₁,the age of which is determined to be 0.13Ma B.P. by synthetic dating method,then an age of older than 0.13Ma B.P. is suggested for the Middle Paleolithic culture at Dingcun sites. The loess paleosol sequence of Dingcun 79:02 profile involves S₀,L₁,S₁,L₂ and S₂. According to the Orbit Tuning Age Mode which gives S₂ an age of 0.247Ma B.P.,the age of Paleolithic Culture at Site 79:02 should be older than 0.247Ma B.P.

HAZARD ASSESSMENT SYSTEM FOR GROUND FISSURE BASED ON COUPLING OF ANN AND GIS——A case study of ground fissures in Yuci City, Shanxi Province

WU Qiang, CHEN Pei-pei, DONG Dong-lin, SUN Wei-dong, WEI Ying-chun

2002, 24(2):  249-257. 

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Modern ground fissures have became a serious geological hazard widely spread in many countries all over the world. In this paper, hazard causing factors of ground fissures in Yuci City have been analyzed in detail. It is found that the formation and development of ground fissures in Yuci City are controlled mainly by tectonic activity and influenced by some non tectonic factors such as exploitation of underground water, difference in properties of strata, character of landform etc. On the basis of the analysis of each factor of ground fissures in Yuci City, Shanxi Province, the thematic layer in geological sense is established by using Geographic Information System (GIS). This paper introduces how to establish the hazard assessment model and hazard assessment system for ground fissure based on Artificial Neural Network (ANN) and Geographic Information System (GIS). The hazard assessment system consists of five function modules including input module, output module, search and inquire module, assessment module and maintenance module. The function of each module is introduced in this paper. As an example, a nonlinear appraisal model for the hazard of ground fissures in Yuci City based on Artificial Neural Network is introduced. The model is a back propagation ANN model, which has an input layer with four points, a hidden layer with four points, and an output layer with one point. Using this model the ground fissure hazard in Yuci City has been evaluated, and a map of the division of ground fissures risk for Yuci City has been established. This result may provide scientific basis for land planning and construction of Yuci City.

ESTABLISHING THE ENGINEERING SEISMOLOGY WebGIS APPLICATION SYSTEM BY USING GIS SOFTWARE COMPONENT

QU Chun-yan, YE Hong, LIU Zhi

2002, 24(2):  258-264. 

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An engineering seismological WebGIS application system (ESWebGIS) is established in this paper by using GIS software Component MO/MOIMS. The system implements the sharing of spatial data and GIS applications and greatly promotes the percentage of utilization of spatial information and GIS applications for engineering seismological studies. Users can easily browse, search, analyse and use the engineering seismological spatial information from Internet just like on their local computers, and they can also download the needed data to their local machines for use in their locally installed GIS software. The ESWebGIS system adopts the popular three layer Browser/Server architecture and thin client/fat server model. Development tools, spatial database and WebGIS applications are all installed and running on a remote map server. All client requests are submitted to the map server for processing, no need to download or install the GIS components on client computers. This model is very convenient for users to use. The GIS components MO/MOIMS, JavaScript, VB6.0, HTML and Oracle8i etc. are used to develop the ESWebGIS. The program modules of ESWebGIS are divided into basic GIS function modules and engineering seismology application modules. The basic GIS function modules, such as map's zoom out, zoom in, pan, overlay, point query, layer moving, active layer locating and labeling are programmed by using MO/VB. These modules are commonly needed for any GIS application system and not limited to a specific database or project. They can be freely called by any GIS application. Engineering seismology application modules, which serve the engineering seismology studies, are designed and coded according to the GIS database constructed for engineering seismology. The spatial data that can be shared through ESWebGIS system have been collected and input into GIS database. The commercial GIS software MapInfo5.0 is used for the database's construction.To improve the system's performance, some effective measures, such as detailed delamination of spatial objects, reasonable organization and logic classification of database, multilevel display scales, and data partition index based on grid have been taken to increase the transmission and display speed of maps on Internet. These improvements make it possible that a great number of map layers with different scales are quickly displayed, overlayed and dynamically integrated on Internet. The running results of ESWebGIS indicate that these measures are effective. In addition, a method called agent index preprocess is used to achieve the interoperability between GIS data with different formats coming from different remote database servers. The ESWebGIS realizes the upgrading of GIS to networking environment, and it can be used to fulfill the following tasks: (1) To browse, draw and manage maps on Internet; (2) To perform attribute query and spatial query of maps; (3) To perform spatial analysis and statistical analysis; (4) To upload and download spatial data files onto/from GIS map server; (5) To publish any GIS data by using Common map browser; (6) To remotely update the spatial data of GIS database on GIS map server; (7) To manage the users and to make the system secure. The ESWebGIS is really an interactive On line GIS system, which is open to global Internet users, and is not limited to certain region. It will greatly enhance the sharing and using efficiency of spatial data.

POST-EOGENE COMPRESSIVE ACTIVITIES ON THE TAN-LU FAULT ZONE AND THEIR DEEP PROCESSES

ZHU Guang, LIU Guo-sheng, NIU Man-lan, SONG Chuan-zhong, WANG Dao-xuan

2002, 24(2):  265-277. 

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Thrusting time of the Tan Lu fault zone has been a controversial issue for long. Recently, many lines of evidence has proved that wide spread compression initiated on the fault zone between Eogene and Neogene, which has given rise to the uplift and consumption of many previous large faulted basins. Since Neogene period the fault zone has continued to suffer from compression, which resulted in many times of thrusting on the fault. The fault zone is currently the largest seismically active belt in eastern China. The compressive activities on the fault zone were dominated by thrusting with small amount of right lateral displacement sometimes and were often associated with the development of NW striking left lateral wrench faults. Margins of basins on the fault zone were intensely involved in the thrusting which caused the formation of shuttered zone and folds. Measurements of paleostress and present stress fields show that the fault zone has suffered nearly E W compression since Neogene due to the back arc spreading of the west Pacific Ocean and tectonic extrusion produced by the northward collision of the Indian Plate. Basalt eruption extensively occurred along the fault zone in Cenozoic, indicating that the fault zone cuts deeply into the upper mantle. Lithological character of the Cenozoic basalts demonstrates that the cutting depth of the fault increased from Paleogene to Quaternary gradually. Geoscience transects reveal obvious intensification of asthenoshperic upwelling beneath the Tan Lu fault zone, which demonstrates that the fault zone cut through the entire lithosphere. Deformed mantle derived xenoliths, such as mylonitic peridotite xenolith, in the basalts reflect that mantle shearing appeared in mantle involved by the fault. Metasomatic minerals in the xenoliths as well as geochemical features of the basalts and xenoliths all suggest that the involved mantle experienced extensive metasomatism. The mantle shearing and metasomatism are related closely and help each other. They also help partial melting in the involved mantle. Under these backgrounds, large scale partial melting appeared in the upper mantle involved by the fault zone. At last, large scale basalt eruption took place along the intracontinental fault zone under the compressive setting. Therefore, integrate active processes of the fault zone since Neogene consist of the thrusting, basin inversion and basalt eruption near the surface as well as the upper mantle shearing, metasomatism and partial melting at deeps.

TEST OF THE LIKELIHOOD RATIO OF SEISMIC ACTIVITY PARAMETERS

GONG Ping

2002, 24(2):  278-287. 

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The estimation of the parameters of seismic activity is very critical for earthquake prediction, engineering seismic hazard analysis and earthquake damage evaluation. However, different researchers may get different results in this estimation, even though for the same seismic data in the same region by using the same analyzing method. Obviously, the different results of estimation will affect seriously the results of earthquake prediction, engineering seismic hazard analysis and earthquake damage evaluation. A question arises: how to evaluate properly these different estimation results? In this paper, an evaluating method, the likelihood ratio testing is introduced. The basic theoretical features of likelihood ratio testing are discussed statistically, and especially the evaluating and processing methods of likelihood ratio testing for two data sets are demonstrated in detail. For an example, the method is practically used to evaluate seismic activity parameters in North China. The concrete procedures are as follows: Assuming that there are three different division schemes for the seismic activity in North China. The first scheme is adopted from the study by Gao Weiming (1990), in which the seismic activity of North China is divided into 4 active periods since the existence of historic record of earthquake. The seismic data from 15th century till now are relatively complete, so that two seismically active periods can be identified for this period of time. In this scheme, the seismically active period is subdivided into quiet and active sub periods. Assuming that the second scheme is similar to the first scheme in the division of the third and fourth seismically active periods, but does not subdivide these periods into sub periods. Assuming that the third scheme considers the third and fourth periods as a single period and no subdivision is made. Then the three different schemes will get different estimation results of seismic activity parameters for this region, and these different estimations will lead to different results in seismic hazard analysis and seismic prediction by using inhomogeneous compound Poisson probabilistic model for earthquake occurrences. The rationality of these different estimation results can be evaluated by using the Likelihood ratio testing method, and then a final sorting of the results can be made. The following conclusions can be drawn from this study: (1) For different sets of estimated parameters involving different time periods, the strength function values of Poisson process are different. Therefore, special attention should be paid to the probability at the dividing point of different time periods; (2) When different results of estimation arise due to the different recognition of different researchers for the same seismic data using the same mathematical processing method, then the likelihood ratio testing method can be used to evaluate and to sort these different results.