Table of Content

14 September 2006, Volume 28 Issue 3

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Brief Report

A CASE STUDY ON NEAR FAULT VERTICAL TO HORIZONTAL RESPONSE SPECTRAL RATIO FROM THE 1999, CHI-CHI, TAIWAN, EARTHQUAKE

ZHOU Xi-yuan, XU Ping, WANG Guo-quan, YAN Wei-ming

2006, 28(3):  325-335. 

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The vertical to horizontal response spectra ratio (V/H) for 68 near-fault records (R_rup<20km) and 48 eastern coast records (40<R_rup<70)from the 1999 Chi-Chi earthquake has been studied in this article. The concerned records are divided into groups according to stations' position(handing-wall or footwall),Slte、ondition and distance to the fault. This study focuses on the relationship between V/H and fault orientation and rupture direction,distance to fault,and local site condition. Some of the results attained in this paper are(onsistent with previous(onclusions,while others are somewhat different. The difference seems to reflect the specific(haracteristics of near fault ground motion of the studied event. The results in this article show that:1)the directions of fault slip and rupture propagation have(onsiderable effect on the V/H within 31im to the fault rupture. Mainly at short and medium periods,V/H of paralleling rupture direction is greater than that perpendicular to the rupture. In footwall and distance range of 3～20km,Slte、ondition has slight effect on V/H;2) for the Chi-Chi earthquake,the V/H in long-period range(>3s) is、ommonly larger than 2/3,the usually estimated value in references,with a noticeable peals,which means the long period component of vertical movement in this、ase is larger than that of other earthquakes;3)for recordings at footwall side,the V/H in short periods(<0.2s)do not obviously decrease as rupture distance increases. Comparing to stations having larger rupture distances(>40km),V/H of near fault stations are、ommonly larger in the、oncerned periods in engineering、ircle;4)the influence of site (onditions on the spectral ratio seems insignificant in near fault area. For the east stations with larger distance,the V/H in long period range at hard soil site is longer than that at soft soil site.

SHEAR-HEATING EFFECT OF PLASTIC-FLOW BELTS IN THE LOWER LITHOSPHERE

WANG Sheng-zu

2006, 28(3):  336-350. 

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Based on the “Netlike plastic-flow” model for continental dynamics and the distribution of terrestrial heat flow in the China continent, the balanced state of viscous shear-heating effect of plastic-flow belts (PFBs) is analyzed in the paper, involving the establishment of the equations of PFB-induced temperature-anomalies by solving the energy equations of thermal dynamics and the determination of the relevant parameters by fitting the positive heat-flow-anomalies of PFBs. It is shown that the viscous shear-heating of PFB provides a thermal energy source for positive temperature-anomalies and results in the enlargement of PFB-affected width by heat conduction. It is indicated as an estimation of the average situation for the Central-Eastern Asia (CEAs) plastic-flow network system that the thermal-anomaly width of PFB is identical with the average apparent-width of PFBs manifested by seismic belts, being approximate to 65km; the shear width of PFB is equal to 44km, about 2/3 of the thermal-anomaly width; the form of the positive temperature-anomaly distribution curve as a result of the analysis is consistent with that of the positive heat-flow anomaly “peak” controlled by PFBs; the positive temperature anomalies at the mid line and boundary of PFB are about 210K and 67K respectively and decrease to zero at the boundary of the thermal-anomaly belt affected by PFB. The results of this study give a theoretical verification for the existence of plastic-flow network in the lower lithosphere and the effect of PFB on the positive anomalies of terrestrial heat-flow.

MICRO FEATURES OF THE VOLCANIC GLASS AND FELDSPAR FROM THE TIANCHI VOLCANO IN THE CHANGBAISHAN MOUNTAINS

ZHANG Bing-liang, HONG Han-jing, PAN Xiao-dong

2006, 28(3):  351-357. 

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The micro features of the pumice and ash produced by the eruptions at 1000a BP and 5000a BP at the Tianchi volcano in the Changbaishan Mountains are studied in the paper. TEM and SEM-EDX analyses reveal the surface characters and thickness of the weathered layers of the volcanic glass and crystal feldspar in the pumice. The result shows that the average thickness of the weathered layers on the surface of the volcanic glass for the first eruption (1000a BP) is 0.98μm. The feldspar has fresh surface and sharp edge angles, some of which present approximately parallel fissures and circle vesicles. For the second eruption (5000a BP) the average thickness of the weathered layers on the surface of the volcanic glass is 3.74μm, and the feldspar has obtuse edge angles and morel basins with 1μm depth. These features indicate that the thickness of the weathered layers on the surface of the volcanic glass and the micro structure of the feldspar from the Tianchi volcano are related with the ages of volcanic eruptions. Therefore, they can be used as indicators for determination of a sequence of volcanic eruptions. The EDX analysis also shows that the weathered layers on the surface of the volcanic glass contain increased Al and reduced Si in chemical composition with respect to the volcanic glass itself. It is inferred that such a change should have occurred in a low-temperature setting and a nearly neutral to weak acid solution. Hence it is possible to identify the dates and sequences of volcanic eruptions as well as their environments based on a systematic study of micro characteristics of eruptive materials in the Tianchi caldera.

RECENT GEOCHEMICAL CHANGES OF HOT-SPRING GASES FROM TIANCHI VOLCANO AREA, CHANGBAI MOUNTAINS, NORTHEAST CHINA

GAO Ling, SHANGGUAO Zhi-guan, WEI Hai-quan, WU Cheng-zhi

2006, 28(3):  358-366. 

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The recent fluid monitoring shows that mantle-derived CO₂,He and CH₄ content increased anomalously in 2002 and 2003. The ³He/⁴He ratio of deep-fault-type Jinjiang hot springs increased highly anomalously in 2003, and than decreased in 2004. That ratio from thermal-reservoir-type Changbaijulong hot springs increased slowly in 2003, and also increased continuously in 2004. Mantle-derived He content of releasing He from Changbaijulong springs increased obviously in 2004. The changes of releasing gases and He isotope corresponded to the trend of seismic activities in Tianchi volcanic area to a certain extent between 2002 and 2003. The abnormal release of Jinjiang decreased apparently after the seismic activities decreased in next half year of 2004, but the abnormal release from Changbaijulong increased highly after these seismic activities. It shows that the abnormal release of magmas-derived gases from thermal-reservoir-type springs lags behind that of the deep-fault-type springs. These characteristics are of great significance for identifying deep magmatic activity and predicting volcanic earthquake in the future.

PRIMARY STUDY ON Sr,Nd ISOTOPIC GEOCHEMISTRY OF CENOZOIC VOLCANIC ROCKS IN TUMEN RIVER VALLEY, CHANGBAI MOUNTAIN AREA

WANG Tuan-hua, FAN Qi-cheng, SUN Qian, LI-Ni

2006, 28(3):  367-380. 

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The Cenozoic volcanic rocks in Tumen river valley are located on the east of Tianchi volcano, Changbai Mountains, Jilin Province, Northeast China. The volcanic rocks in Tumen river valley are a suit of sodic tholeiitic basaltic rock which have characteristic of effusive eruption. The magma of the Cenozoic volcanic rocks in Tumen river came from upper mantle. In this paper, we discussed the magmas source characteristics of the volcanic rocks by the way of studying on the trace-element, REE, Sr and Nd isotopic data. The results show that the volcanic rocks have the characteristic of higher ε_Sr(3.5～9.1)and lower ε_Nd(-3.3～0.3) relatively and the compositions of magma source are mostly close to that of primitive mantle substance. The magmas experienced assimilation and contamination of the crustal materials to different degrees during their ascending through the lithosphere. But the magma's Sr and Nd isotopic characteristics mainly inherit the character of source mantle area. Integrating all the data on tectonic surrounding, geophysics and isotopic geochemistry, we think that the deep subduction of western Pacific plate is the key mechanism for the interaction of crust-mantle in the source mantle area.

A PHYSICAL SIMULATION ON THE LAVA FLOWAGE PARAMETERS AND HAZARDS PREDICTION OF CHANGBAISHAN TIANCHI VOLCANO

JIN Jin-yu, WEI Hai-quan, PAN Xiao-dong, LIU Qiang

2006, 28(3):  381-390. 

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The Tianchi volcano is the most important active volcano in China for its largest magnitude, complicate history and the most potential hazards. Tianchi volcano experienced the stages of an early basalt shield, a middle trachyte composite-cone and a late ignimbrite-forming. Junjianshan Formation was first introduced for the Neocene thick confined or unconfined basaltic lava flows around the Tianchi Cone and has been divided into three parts as, from early to late, Toudao F, Baishan F and Laofangzixiaoshan F, composing the Tianchi basalt shield. The Tianchi shield basalts flowed a distance of a few to dozens kilometers with a width of hundreds to thousands meters and a thickness of a few to dozens meters, comprising the composite flow units in confined or unconfined mechanism. The Laofangzixiaoshan basalt, composed of the uppermost part of the shield, flowed much a less distance than the earlier Toudao and Baishan basalts in a lower aspect ratio. It shows that the basalt shield was formed between 4.26Ma and 0.31Ma. We calculated the flow velocity of Tianchi basaltic lava flow and the time duration of lava reaching its distal localities. The calculated velocity of the lava flow with 0.5m thickness and 5% crystal content is less than 1m/s, while it reaches up to 10m/s when the flow thickness increases to 2m. But if the crystal content in a 0.5m thick lava flow increases to 30%, the lava flow velocity will decrease sharply to less than 0.12m/s. The 2m thick lava flow of Tianchi volcano in the northeast can reach its distal part in less than a day, but it needs ten days if the flow thickness is 0.5m. The lava flow of Tianchi volcano may have a distance up to 50km in the future eruption. Volcanic hazards due to lava flows from the Tianchi volcano in the future are destructive to buildings, farm lands, roads and power stations and may cause some fire disasters.

LATE-QUATERNARY HORIZONTAL DISPLACEMENT AND ITS ASSOCIATED MICROGEOMORPHOLOGY OF THE WESTERN QINLING FAULT ZONE AT HUANGXIANGGOU

LI Chuan-you, ZHANG Pei-zhen, YUAN Dao-yang, WANG Zhi-cai, ZHANG Jian-xi

2006, 28(3):  391-404. 

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The western Qinling Fault zone is one of the main left-lateral strike-slip active faults in northeastern Tibet. At site of Huangxianggou, the behavior of the fault zone shows typical strike-slip movement. Detailed analysis on the amounts of the offset of the late Quaternary landforms and geologic bodies along the fault shows that at Huangxianggou the maximum horizontal displacement since the late of late-Pleistocene is about 40～60m, and the minimum is 6～8m which is possibly the amount of one principal slip associated with one large earthquake event. And it is also inferred that the amounts of the displacement along the fault can be grouped, and between the groups there is a stable increment of 6～8m. The grouping and the increment of amounts of the offsets suggest that this fault segment displays an activity associated with characteristic earthquakes, and the 7 groups of the displacement values represent 7 characteristic events on the fault. Analysis on the microgeomorphology related to the faulting, such as periodic sag-ponding and deformed pluvial fans, also suggests the corresponding events. Thus it can be inferred, the activity of the fault zone has been dominated by several strong movements since late Late-Pleistocene.

ANALYZING THE RELATION BETWEEN EARTHQUAKE AND ACTIVE FAULT BASED ON THE PARAMETER OPTIMIZATION MODEL

SHAO Hui-cheng, LIU Hua-feng, YUE Zhu-feng

2006, 28(3):  405-410. 

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The gestation and occurrence of strong earthquake are closely related to fault activity, which are not only revealed by abundant experimentation and seismism but also proved by modern seismology. In the mainland of China, the correlation between earthquake activity and active fault is one of the bases for partitioning potential seismic sources, analyzing the seismotectonics and estimating location of strong earthquake.Due to nonuniformity of earth medium, instability of observation system and disturbance of environment etc, the variety of observational data is complicated, that is, there is no absolute “normal” or “abnormal”, and seismic anomaly can be divided into many mutually exclusive “abnormal states”. In different conditions of combined time-space-strength, determining the seismic anomaly by different monomial forecast method and its efficiency could be different due to the uncertainty of precursor itself or complexity of relation between precursor and earthquake gestation. In a “two-state” model, the difference could hardly be discovered and disposed in actual application. But in the “multi-state” model, the difference can be easily reflected and the optimal combination of forecasting parameters for a forecast method can also be determined easily.Based on the “multi-state” precursory model and the optimization method for parameters of earthquake forecast model under the condition of maximization of forecast efficiency, the relations of spatial location of earthquakes with M≥6 and active faults in three seismic belts are analyzed. The results demonstrate that in the Hetao Seismic Belt, seismicity is mostly concentrated in the range of 20km along the fault, the optimization model can forecast the location of potential earthquake of M≥6 near the faults with a relatively high accuracy, and the reliability value is 0.5; while in the Qilan Mt Seismic Belt, the reliability only reaches 0.14 when we use the model to estimate earthquakes within 30km range along the faults. The “multi-state” precursory model, the efficiency-evaluating model and the parameter selection of individual earthquake forecast model based on optimal efficiency are of certain revelatory and practicable meanings for developing knowledge about precursors, questing the laws of earthquake preparation and searching for optimal forecasting method.

APPLICATION OF COMMON OFFSET SEISMIC REFLECTION METHOD TO URBAN ACTIVE FAULT SURVEY

LIU Bao-jin, JI Ji-fa, XU Zhao-fan, YUAN Hong-ke, LIAO Xu, BAI Yun, WAN Bo

2006, 28(3):  411-418. 

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The method and principle of common offset seismic survey as well as the field data gathering and processing technique were introduced briefly. Through two urban active fault survey examples in Fuzhou and Shenyang, the efficiency and limitation about using common offset seismic reflection technique to carry out urban active fault survey were probed. The results show that this technique has the properties of high resolving power, better reconstruction of subsurface structures, and real-time analyzing and interpreting of the investigating results on site. This method can be used to quickly locate the investigating objects accurately in the areas with thinner Q overburdens and strong bedrock interface fluctuations.

HYDROGEOCHEMICAL CHARACTERISTICS OF THERMAL WATER AND GENETIC MODEL OF GEOTHERMAL SYSTEM IN NORTH BEIJING

LÜ Jin-bo, CHE Yong-tai, WANG Ji-ming, LIU Zhen-feng, LIU Cheng-long, ZHENG Gui-sen

2006, 28(3):  419-429. 

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The North Beijing Geothermal Field includes Xiaotangshan and Shahe sub-geothermal fields, distributing as a triangle in plan. It borders Huangzhuang-Gaoliying Fault on the southeast, Nankou-Sunhe Fault on the southwest, and Asuwei-Xiaotangshan Fault on the north. The thermal reservoirs are the fissure aquifers of carbonate karsts among Wumishan Formation and Tieling Formation of Jixian System, and Cambrian-Ordovician System. The cover rocks of thermal reservoir are impermeable strata of sandstone and shale of Qingbaikou system, sandstone and shale of Carboniferous-Permian and volcanic rocks of Jurassic. Its plane characteristic of geo-temperature is marked by two hyper thermal areas in Xiaotangshan and Tang11. The vertical characteristic is such that the temperature increases with depth at the rate being lower in the thermal reservoirs and higher in the cover rocks. The compositions of δD-δ¹⁸O in rainwater, groundwater and geothermal water are almost on the Craig Atmosphere Precipitation Line in the area. The diagram shows that the natural rainfall is the geothermal water source. In hydrochemical diagram of geothermal water in Beijing area, the geothermal water is under urban thermal water. It shows that the North Beijing geothermal water is closer to cold water replenished area than the urban geothermal water. The distributing of ³H in geothermal water is higher in the north and lower in the south, and the dating of ¹⁴C of geothermal water is increasing from north to south. So we can conclude that the geothermal water flows from north to south. This shows that the atmosphere precipitation infiltrating underground from the northern mountain area flows from the karst area of Ming Tombs-Taoyukou, striding over Asuwei-Xiaotangshan Fault, then circulating in the deep and being heated by geothermal. At last it flows into and is stored in the North Beijing area, forming a geothermal field. Based on the above-mentioned characteristics, the genetic model of North Beijing geothermal system is built and defined as a mid-low temperature convective type geothermal system in North Beijing.

APPLICATION OF RBPNN IN THE RESEARCH OF EARTHQUAKE-INDUCED LANDSLIDE

CHEN Xiao-li, ZHAO Jian, YE Hong

2006, 28(3):  430-440. 

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As we know, the landslide caused by earthquake does not distribute at random but has its destinations. This means that there are some inner relationships between the distribution and the factors which affect the happening of the landslide. But due to the complex mechanism of the earthquake-induced landslide, it's difficult to describe the relationship clearly. For expressing the non-linear relationship, we create the artificial network with the Radial Basis Probabilistic Neural Network Algorithm by using the toolbox of MATLAB. At first, we select fault, river, rock, slope angle, earthquake intensity as the landslide affecting factors after studying the research results of other scholars, then use GIS to model the research area and grid it. From the cells, we select neural network training samples and testing samples. After repeated training, the neural network reaches its steadiness. Then we use this network to simulate the whole research area. In this paper, the studying area is between 98.5°～99.0°E, 24.2°～24.9°N, where 2 strong earthquakes took place in 1976 and caused many landslides. We selected two different sets of training samples from the research area, and by contrasting the result of RBPNN with the facts, we find that the predicted hazard area is generally in accordance with the fact in the distribution of earthquake-induced landslide. In conclusion, we think RBPNN is a useful method for the research of earthquake-induced landslide, especially for the regional earthquake-induced landslide zoning.

AN ANALYSIS OF DYNAMIC EVOLUTION OF PRESEISMIC INTERFEROMETRIC DEFORMATION FIELDS IN SEISMIC AREA

SHAN Xin-jian, ZHANG Guo-hong

2006, 28(3):  441-446. 

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The M_S7.9 Mani earthquake happened at the north border of the Qiangtang basin of Tibet, near the NEE trending Maergaichaka-Ruolacuo fault, on November 8, 1997. The region of Qiangtang with cold weather and thin air means harsh field conditions. There is no deformation observation station around in several hundreds kilometers scale. All these realistic situations put limits on learning the surface deformation field of the earthquake region and deformation of active faults. Fortunately, D-InSAR technology is available which is not affected by all these factors and has preponderant advantages in acquiring information of spatial deformation field evolution.This research collected 12 scenes ERS-1/2 Radar Satellite data of ESA from January 1995 to December 2000. ERS-1 SAR data are included, i.e. 2889/19960415, 2907 /19960415. And there are 10 ERS-2 SAR data: 2889/19960416, 2907/19960416, 2889/19970121, 2907/19970121, 2889/19970610, 2907/19970610, 2889/19970819, and 2907/19970819. These SAR data were handled using three-pass of four-pass Differential Interferomertric modes.Three dynamic images of pre-seismic Interferometric Deformation Field of the 1997 M_S7.9 Mani earthquake were acquired by using D-InSAR technology. The result shows that 10 months prior to the Mani event, a left-lateral shear trend appeared in the seismic area, which was in accordance with the earthquake fault in nature. The quantity of local deformation on the northern wall was slightly larger than that on the southern wall, and the deformation distribution area of the northern wall was relatively large. With the event being impending, the deformation of the southern wall varied increasingly, and the deformation center shifted eastward. Two and half months before the event, the western side of the fault was still locked while the eastern side began to slide, implying that the whole fault would rupture any moment. The most remarkable deformation zones appeared in northern and southern walls, which were parallel to and apart from the fault about 40km, with accumulated local displacements of 344mm on the northern wall and 251mm on the southern wall, respectively. The southern wall was the active one with larger displacements.

A PRELIMINARY STUDY ON THE USE OF NCEP TEMPERATURE IMAGES AND ASTRO-TIDAL-TRIGGERING TO FORECAST SHORT-IMPENDING EARTHQUAKE

MA Wei-yu, XU Xiu-deng, ZHANG Xing-cai, WU Hua-feng, XU Bao-hua

2006, 28(3):  447-455. 

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Taking the three earthquakes which occurred in Xizang of China during the period of July 12 to August 25, 2004 as an example,the paper analyses the M_S≥6.0 earthquakes that occurred in China and M_S≥7.0 earthquakes that occurred in overseas since May of 2003 by combining the image data of National Centers for Environmental Prediction of America with the astro-tidal-triggering and makes the following conclusions: The temperature abnormal image data of NCEP can better reflect the spatial-time evolution process of tectonic earthquake activity; The change of astro-tidal-triggering can better keep pace with the dynamic state of temperature abnormal images; The astro-tidal-triggering has an evident triggering effect on the active fault where the terrestrial stress is in critical status; It is a new thinking to use the NCEP images and the astro-tidal-triggering to forecast short-impending earthquake; The three earthquakes occurred during the same phase of the respective astro-tidal-triggering (ATSA) additive tectonic stress cycle, i.e. occurring at the time when the ATSA reached the relatively steady end of peak, rather than the time when the variation rate was maximal. Meantime, the author discovered that the occurrence time of other earthquake cases during 2003-2004 in Xizang was also in the same phase of the above-mentioned cycles, and therefore, further study of this feature is needed with more earthquake cases in other areas over longer periods of time.

PREDICTION OF WATER DISASTERS AHEAD OF TUNNELING IN COAL MINE USING CONTINUOUS DETECTION BY UWTEM

GUO Chun, LIU Bai-zhou, BAI Deng-hai

2006, 28(3):  456-462. 

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Accurate prediction of geohazards far in advance of engineering works is a fundamental requirement in underground mining. Underground whole-space transient electromagnetic (UWTEM) method was tested at the driving face of a drift in a coal mine for detecting water-bearing zones ahead of tunneling. Having experimentally determined that the sounding depth is about 70m for a configuration of coaxial off-set loops in the drift, the UWTEM experiment was designed as such that measurements were made ahead of each time the drifting operation progressed 50m. The measurements were analyzed at each step. The results proved that the structures rich of water 30～50m ahead of the driving face can be effectively predicted, which is helpful for preventing the occurrence of water disasters during mining. However, the experiments show that false anomalies would sometime appear due to the effects of conductors behind the driving face, and that the adopted loop configuration could not be used in small drifts since the receiver- transmitter coil separation should be greater than 5m.

DESIGN AND REALIZE THE FAST REGIONAL EARTHQUAKE DISASTER EVALUATION SYSTEM BASED ON WEBGIS

CAI Zong-wen, WEI Fu-quan, FANG Wei, ZHENG Shao-peng, CHEN Lin, ZHANG Yi-feng

2006, 28(3):  463-469. 

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The key to WebGIS technology is to issue the vector geography graph through the internet and provide the information service for the general browser end user. Considering the complexity, multiplicity and magnanimous space taking of the earthquake disaster evaluation information, the WebGIS based regional fast earthquake disaster evaluation system adopts a three layered network architecture, including the backstage database, the application server (map server) and the Web server, and the client composition. Different from the traditional evaluation method as taking the building as the statistical unit, this fast evaluation system takes the city administrative area, the township or the town as the working unit. Using foundation database and other census data, we can determine the earthquake influence on a given target area according to the earthquake background analysis or the estimation of effect of a given earthquake in the future. By means of the relational model of population data and the earthquake losses, as well as combining the analysis result of earthquake resistance and seismic vulnerability, the possible damage to the target area can be predicted, and accordingly the economic losses and personnel casualty can be estimated.With the platform of ESRI Corporation's ArcIMS 4.1, and mainly the development of technology of VB+ArcObject server module, this system has realized the system core computation, the vector graph superimposition, the dynamic updating of the vector graph attribute data and the distribution graph, as well as the map issuing and the dynamic data management in the server end. The client side is designed with the use of ASP dynamic homepage and the databank administration techniques. The system consists of the function modules of foundation data management and maintenance, fast earthquake damage evaluation, reporting management and system assistance management, and etc. This system makes full use of the existing achievements in fast earthquake disaster evaluation as well as the census data of the Fujian Province, therefore possesses such merits as low investment, regular data updating and being easily accessible as well.

REVIEW OF THE YUEYANG EARTHQUAKE IN HUNAN PROVINCE IN THE 34TH YEAR OF JIAJING OF MING DYNASTY (1556 AD)

ZHOU Qing, DONG Rui-shu, CHEN Xiao-li, JI Feng-ju

2006, 28(3):  470-480. 

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In 1556, a strong earthquake with magnitude 8¹/₄ occurred in Huaxian, Shaanxi Province. The earthquake destroyed many places in Shaanxi Province and its adjacent regions, and also affected above 100 counties in Gansu Province, Hebei Province, Shandong Province and etc. According to historical documents, an earthquake was also recorded in Yueyang district, about 700km away from the Huaxian earthquake epicenter on the same day. Was it an isolated event or influenced by the Huaxian earthquake? It is a controversial problem.A lot of historical earthquake records of Yueyang district and its adjacent regions have been collected and studied, including the border area between Hunan Province and Hubei Province. The records for the 1556 AD Yueyang earthquake in “Annals of Yuezhou” in Longqing time of Ming Dynasty were judged to be more accurate than other historical documents. Earthquake recorded in 1556 AD in Yueyang district was a felt event with less strength. In analyzing historical materials, two principles for cases of earthquake records lacking have to be adopted: 1)Local annals to be used shall have other earthquake records. That means the annals writers paid attention to earthquake events; 2)Other types of disasters were recorded in the period of time when the earthquake occurred. That means there were no other kinds of historical disaster events influencing the records of earthquake.There were no earthquake records in counties like Tongshan, Tongchen, Puxi, Chongyang, Gongan, Shishou in the 34th year of Jiajing reign (1556 AD). It can be concluded that the earthquake records in Yueyang district in 1556 were not the effect of the Huaxian earthquake in Shaanxi Province in the same year. It was an isolated event. At last, according to records of local annals, the earthquake epicenter and magnitude are determined.

PRE-SEISMIC ELECTROMAGNETIC EFFECT

GUO Ya-hong

2006, 28(3):  481-486. 

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Electromagnetic emissions and its related effects preceding earthquakes are the new areas explored in the recent more than 20 years. This exploration may have great significance for human lives and development and has been received widespread attention of scientists in the field of earthquake prediction, geophysics and radio physics. Along with intense rock strain and rock bursting process at the late stage of earthquake preparation, mechanical-electrical energy conversion would appear in the seismogenic region and its nearby rock layers, which will correspondingly stimulate certain electromagnetic effects. The paper mainly analyzes the pre-seismic electromagnetic effect of ionosphere and proposes the method of monitoring VLF electric wave over the additional ionized region and so on. It is deemed that the method is of significance for short and imminent term prediction of strong earthquake.

A TECTONIC MOVEMENT DURING LATER STAGE OF LATE PLEISTOCENE EPOCH IN THE XINDING BASIN

REN Jun-jie, ZHANG Shi-min

2006, 28(3):  487-496. 

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The Xinding basin in the north of Shanxi rift system is a normal fault-controlled extensional graben and has a strong neotectonic process during the Quaternary. Our field investigations in the Xinding basin indicate that there is a united geomorphologic surface, composed of the terrace T₂,the diluvial mesa and the top of the scarp with a height of ten to tens meters along the piedmont. The terrace T₂ and the mesa are composed of a basal gravel layer and the overlying loess deposits which can be used as dating samples for the united geomorphologic surface.As Chinese loess stratigraphy has been well studied, it favors age determination of the newest tectonic geomorphologic surfaces. Combined with the loess-paleosol time scale and some dating methods, such as radiocarbon ( ¹⁴C) and optically stimulated luminescence(OSL), the results of age dating show that the terrace T₂ and the diluvial mesa downcut at ca. 20ka BP. According to the viewpoint of climatic geomorphology, the glacial climate is helpful for river deposition. But the downcutting, which occurred in the last glacial maximum (21～18ka BP), cannot be attributed to climatic change. It shows that the Xinding basin underwent a stronger tectonic movement since later stage of late Pleistocene epoch.Statistic results of the coseismic rupture of fault events in China mainland show that a single event always has a vertical coseismic displacement with some meters. And the fault scarp that has a height of tens to tens meters along the piedmont in this paper can not be produced by only a single event. So this tectonic movement should be the product of fault activities of a period. Though some studies have shown that this tectonic movement since later stage of late Pleistocene have some evidences in the Yanqing basin and the Hubao basin, more detailed work should be done to prove that this tectonic movement is widespread in the Shanxi rift system and bigger region.

THE M 5.1 WEN'AN EARTHQUAKE OF JULY 4,2006

DIAO Gui-ling, ZHANG Si-chang, SUN Pei-qing, ZHANG Yue-gang, GAO Jing-chun, MAO Guo-liang

2006, 28(3):  497-502. 

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Through analysis, we found that the Wen'an earthquake has the following characteristics: the aftershocks are small with the biggest of only M 1.5, belonging to the isolated type earthquake; the earthquake intensity is low, but the perceptible area is relatively large; the macro-epicenter is over 10km away from the micro-epicenter; the hypocenter is deep; and the fracture of earthquake shows a normal fault slip. The explanation for these characteristics is presented, which can be regarded as a new evidence for lithospheric thinning.

ANALYSIS OF THE SEISMIC ACTIVITY AT THE CHANGBAISHAN TIANCHI VOLCANO

LIU Guo-ming, ZHANG Heng-rong, KONG Qing-jun

2006, 28(3):  503-508. 

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The seismic intensity at the Tianchi volcano has increased obviously since June, 2002. In this paper, we introduce the characters of the seismic activity at Tianchi volcano based on the seismic data recorded at the Tianchi Volcano Observatory (TVO). It shows that since 1999 the seismic activity mainly belongs to the tectonic event based on a seismic spectral and time frequency analysis. We examine the coda Q values of these earthquakes and compare them with the data from Sichuan district, and find that the coda Q value from Changbaishan is lower than that in Sichuan, indicating that the level of the tectonic activity in the researched Changbaishan area is relatively high.