Table of Content

13 September 2007, Volume 29 Issue 3

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Brief Report

VOLCANIC THREAT LEVELS AND CLASSIFICATION OF VOLCANIC ACTIVITY IN CHINA

HONG Han-jing, WU Jian-ping, WANG Qing-liang, LI Ke, ZHAO Ci-ping, SHANGGUAN Zhi-guan, YANG Qing-fu, ZHANG Heng-rong, LIU Guo-ming

2007, 29(3):  447-458. 

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Although volcano erupting has not been recorded in Chinese continent during recent years,there are 15 Holocene volcanoes in Chinese continent,and some disturbance signals were reported from some volcanoes in China.Strong hydrothermal activities occurred in Tengchong volcano,some hydrothermal explosions even took place since 1993.Seismic activity in Changbaishan Tianchi volcano has been getting strong remarkably since July of 2002,accompanied with significant surface uplift and geochemical anomalies.Estimation on volcanic threat level is the base of classification of active volcanoes.Based on the results of volcano monitoring and investigation in recent years,the volcanic threat levels and classification of active volcanoes in China continent are discussed in this paper.Based on the volcanic activity levels of the other countries,the volcano threat in China can be rated into 7 levels as safety,attention,stand by,alarm,threat,hazard and disaster,corresponding to the activity stages of dormancy,late-dormancy,disturbance,unrest,being critical,irreversible and violent,respectively.Based on the dangerous levels of volcanoes,the activity of volcanoes in Chinese continent can be classified into 4 kinds:(1)those in the active phase,such as Changbaishan volcano,which is in the process of disturbance;(2)those with some evidences of activity,such as Tengchong volcano,which stays in the late-dormancy stage,but has the potential threat of eruption;(3)those with some possibility of potential eruption,including Wudalianchi,Jingpohu,Haikou volcanoes,where geophysical and geochemical observations all fall in the background category;and(4)those whose volcanism is unclear yet at present,such as Aer Shan,ErKe Shan,XiaoGulihe,Wulanhada,Keluo,Turphan,west Tianshan,Ashi,and Kekexili volcanoes.

HEATING STAGE EXPERIMENTS OF MELT INCLUSIONS IN FELDSPARS OF PUMICE FROM THREE ERUPTIONS OF CHANGBAISHAN TIANCHI VOLCANO IN HOLOCENE

LI Ni, Nicole M閠rich, FAN Qi-cheng

2007, 29(3):  459-469. 

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Melt inclusions are the tiny silicate drops(usually <300μm)of magma trapped during crystals growing in the magma chamber.As phenocrysts completely enclose the melt,forming pressure vessels that prevent the included melt drop from outgassing during decompression and eruption,the melt inclusions have the potential to preserve the pre-eruptive composition of the melt.If unaltered,melt inclusions represent the major,trace and volatile element chemistries of pre-eruptive magma during the complicated effusive and explosive eruptions.Silicate-melt inclusions provide a unique possibility of reconstructing the chemical composition of a magma at a specific stage of its evolution.They are usually solid in the room temperature.It's the counterreaction of the actual procedure that heats melt inclusions and makes them homogenized.Theoretically,the homogenized melt inclusions are thought to keep magma characteristics when they were trapped.The temperature at which the daughter crystal disappears can be deemed as the temperature when magma was trapped.At present,the heating stage experiments provide the only access to the knowledge of magma before eruption.Based on previous works,it is believed there are at least three eruption periods in Holocene,for Tianchi volcano,i.e.the yellow comenditic pumice of～5000a BP(Eruption Ⅰ),the gray comenditic pumice and pyroclastic flow of～1000a BP(Eruption Ⅱ,i.e."the millennium great eruption"),and the black trachy pumice and tuff of～300a BP(Eruption Ⅲ).There are a large number of melt inclusions found in the alkali feldspars of the pumice and pyroclastic flow,which are different in size and color.We have made experimental studies on the homogenization temperatures of the melt inclusions in feldspars from these eruptions of Tianchi volcano in Holocene using Leitz 1350 heating stage.For Eruption Ⅰ,the homogenization temperatures are from 938℃ to 1014℃.There are two temperature intervals for Eruption Ⅱ:850～926℃ and 1005～1024℃ respectively.And 974～1062℃ are the measured homogenization temperatures for Eruption Ⅲ.There is not distinct difference between homogenization temperatures in Eruption I and Ⅲ,but for Eruption II,the situations are rather complicated,implying that the～1000 AD explosive eruption was triggered by injection and mixing of two kinds of magma with different temperatures.Our results also indicate that small melt inclusions are easy to get homogenized,while the large ones,especially those containing a large number of daughter crystals,are quite difficult to get homogenized.In addition,homogenization temperature well correlate with the size of melt inclusion in the host crystal,as well as with the time when a fast heating rate turns to a slow heating rate,and with whether it's the first time to get homogenized or not.We will get different homogenization temperatures for the same melt inclusion with repeated homogenization processes.Furthermore,the next homogenization temperature will be higher than the former one after repeated heating,indicating the water loss or hydrogen diffusion occurs during repeated heating.EMP analysis also testifies the chlorine loss occurring while the melt inclusions are heated.Generally the T_h is higher than magma temperature.The systematical experiments are aimed at choosing the proper size of melt inclusion and proper heating rate for the heating stage experiment.

STUDY OF THE RELATIONSHIP BETWEEN CHANGBAISHAN TIANCHI VOLCANIC SEISMIC ACTIVITY AND DEEP EARTHQUAKES IN THE NORTHWEST PACIFIC SUBDUCTION ZONE

L? Zheng, YANG Qing-fu, ZHANG Heng-rong, LIU Guo-ming, GAO Jin-zhe

2007, 29(3):  470-479. 

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On the basis of geodynamics of Changbaishan Tianchi volcanism,we analyzed comprehensively the intermediate and deep focus earthquakes induced by the subduction of the northwest Pacific plate and the relation between the volcanism of Changbaishan and the change tendency of gas released in the thermal spring.We think that volcanic activity of Changbaishan caused by the disturbance of mantle convection with the subduction of Northwest Pacific plate to the northwest of 35癗 is divided into three stages from the beginning of 1999 to the present.The first stage with the beginning of the disturbance is from June,1999 to May,2002;The second stage with the intensifying of disturbance is from June,2000 to 2004;And third stage with the decaying of disturbance is from 2005 to now.By analyzing the above three stages,we discussed the present activity regime.We analyzed the rhythmic seismicity between the seismically active period and the quietude period of the area from the Japan Sea to the deep-focus earthquake zone of Northeast China and the possibility of eruption of Changbaishan Tianchi volcano in the future.

GRAIN-SIZE CHARACTERISTICS OF THE MILLENNIUM PYROCLASTIC FLOW DEPOSITS OF TIANCHI VOLCANO AND THEIR GEOLOGICAL IMPLICATIONS

YANG Qing-fu, SHI Lan-bin, ZHANG Yu, CHEN Bo, CHEN Xiao-de

2007, 29(3):  480-491. 

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Pyroclastic flow deposits have become a research topic of great interest in volcanology,because they may bring the humanity devastating hazards.This paper demonstrates the results of grain-size sieve analyses of the millennium pyroclastic flow deposits from Tianchi volcano.The result shows that the pyroclastic flow deposits are poorly sorted and the ash cloud surge deposits accompanied with pyroclastic flow are well sorted.The average greatest grain-sizes of lithic fragments and pumice fragments in pyroclastic flow deposits decrease with increasing distance from the crater,indicating that gravity sorting and mechanical wearing did occur during the transportation of the pyroclastic flow.In addition,fluidization also occurred during the transportation of pyroclastic flow.The rate of fluidization decreases with increasing distance from the crater,indicating the occurrence of degassing during the transportation process of the pyroclastic flow.This process might cause the increase of viscosity and yield strength of the pyroclastic flow,resulting in the deposition of the flow.The rate of fluidization,therefore,is an important factor controlling the transportation distance.The confluence of multi-channel pyroclastic flows at distal part may increase the rate of fluidization of the pyroclastic flow,as a result,the transportation distance becomes longer and the hazard area becomes greater.

HARMONIC-SPECTRAL EVENT AT CHANGBAISHAN TIANCHI VOLCANO

MING Yue-hong, WU Jian-ping, SU Wei, FANG Li-hua, WANG Wei-lai

2007, 29(3):  492-501. 

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By analyzing seismic data recorded by temporary seismic network deployed at Changbaishan Tianchi volcanic region in the summers of 2002,2003 and 2005,we find one type of events whose spectra appear to be special.The station-averaged spectrum of each event consists of a series of evenly-spaced narrow peaks,the amplitudes of peaks change gradually with the frequency,the shape of spectrum is quite similar to harmonic signal in time domain.We called such event as harmonic-spectral event.During the three summers,38 harmonic-spectral events were detected,and most of them occurred in seismic swarms.Analyses show that the harmonic spectral characteristics of these events are most likely associated with seismic sources,which might be caused by interaction with crack walls and pressure disturbances within magmatic or hydrothermal fluids filled inside of cracks at special excitation conditions,during the rock rupture processes.We suggest that the apparent increasing of seismicity and emergence of harmonic events in Changbaishan Tianchi volcanic region are associated with deep magmatic intrusion activities.

PRELIMINARY STUDY ON ACTIVE STATES OF VOLCANO AND THEIR MECHANISMS

HONG Han-jing, LIU Hui

2007, 29(3):  502-512. 

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Based on the examples of active volcano,the active states of volcano in different stages are summarized,and the conceivable mechanisms are discussed in this paper.The physical situations of volcano activity,from magma supply to eruption,can be divided into 3 phases(stages).Phase 1:magma supply:the overpressure of magma chamber is the dominant parameter for whether the volcano is in the stage of dormancy or disturbance,and the magma supply rate is essential.Phase 2:formation of conduit:the wall rock fails and a crack will be initiated when the overpressure exceeds the tensile strength of the wall rock,and then the hydrothermal effects play an important role.Phase 3:instability and eruption:magma moves in conduit,and it interacts with overlying crust,the dynamic of magma flow in dykes is essential.The volcano threat in China can be rated into 7 levels as safety,attention,stand by,alarm,threat,hazard and disaster,and accordingly the active states,the inferred major mechanism and their primary physics are:(1)Dormancy represents the stage with magma supply;the pressure of magma chamber is less than the pressure of wall rock.(2)Late-dormancy represents the stage of pressurization of magma chamber,and the pressure of magma chamber is equivalent to the pressure of wall rock.(3)Disturbance represents the stage with updoming and extension of shallow crust,and the pressure of magma chamber is greater than the pressure of wall rock.(4)Unrest represents the stage of fracture of wall rock;the overpressure exceeds the tensile strength of wall rock.(5)Critical represents the stage of hydrothermal activity;Microcracks are filled of fluids,the effective stress depresses,the hydrothermal circulation prevails,and long-period earthquakes appear in this stage.(6)Eruption represents the stage of initial irreversible eruption;the content of volatiles,magma pressure and the viscosity of magma affect the outflow rate,the gas exsolution and fragmentation,and then determine the type of eruption.(7)Violent eruption represents the stage of unstabilized eruption,and if the overpressure of magma chamber is still greater than that needed to transfer the magma along the conduit,the eruption will continue.The activities of volcano are multifarious.This paper is only a preliminary discussion.The division of process is primary,and some volcanoes can develop very rapidly,and one of the states can be jumped over.On the other hand,some volcanoes can develop very tardily,and one of the states can be repeated,even back up to the original stage,e.g.as the magma supply intermits,the evolution will stop.

SIMULATION OF DEFORMATION AND STRESS FIELD IN VOLCANO AREA——A case study on Changbaishan Tianchi volcano

LIU Hui, HONG Han-jing, WU Cheng-zhi

2007, 29(3):  513-521. 

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An upper crust model is proposed,which consists of a magma reservoir and a conduit in the visco-elastic medium and is replenished from below.We solve the system as an initial value problem with a source term corresponding to the magma supply or excess pressure.The model works as follows:to supply magma to the reservoir at a given vertical velocity or give an excess pressure on the surrounding rock of the reservoir.We compared the upper crust model with Mogi model and find that the former model can not merely realize the result of Mogi model,but has a lot of advantages:it can show the different results of different reservoir shape,gets the plane stress field and section stress field and the change of stress and displacement with time.Using this model to analyze the relation in conformity with the distribution of the stress field and volcano earthquake in the area,we find that there is a very good corresponding relation.Meanwhile,we compared two models,one has background stress field only and the other has the combination of excess pressure of reservoir and background stress field,and the results show that the latter has caused the maximum shear-stress to increase gradually with time.

A NUMERICAL SIMULATION OF TEPHRA TRANSPORT AND DEPOSITION FOR MILLENNIUM ERUPTION OF CHANGBAISHAN TIANCHI VOLCANO

YU Hong-mei, XU Jian-dong, ZHAO Yi

2007, 29(3):  522-534. 

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Tianchi is a central composite volcano with potential danger of eruption.Tephra of Tianchi eruption in 1215(±15)has diffused to the Japanese sea and southern Japan.However,the study about simulation of the tephra of Tianchi is little.This paper tries to recur to the ash distribution of this eruption by simulating the tephra dispersion of Tianchi volcano eruption.This paper adopts the mathematic model for tephra dispersion proposed by Suzuki(1983).Based on Suzuki's formula,it simulates the tephra dispersion of Tianchi eruption of 1215(±15).There are different densities of the grains from this eruption because of the difference of content of air bubbles.Wind speed and air parameters relate with the altitude.According to the wind speed,we adopt three models:30m/s,MW1 and MW2.The conclusions are as follows:1.The value of the dispersal parameter β of Tianchi eruption in 1215(±15)is 0.45,which indicates most of tephra congregating at the top of the volcano eruption column;2.The differences of settling rates for different diameter particles are very big.For the particles of diameter in 2～1cm,the settling rate achieved 8.95m/s,but for the particles of diameter in 0.005～0.001cm,the settling rate only 0.03m/s;3.There is a turning point in the relations chart of particle diameters and in the settling rate.It is speculated that this turning point possibly relates with transformation of the eruption column from the convective region to the diffusion region;4.The probability densities of diffusion are different for different diameter particles.Big particles start to diffuse at the bottom of the eruption column,but small particles only start to diffuse near the peak of eruption column.And the probability densities of diffusion of small particles are much bigger than that of big ones;5.In the three models the diffusion distance simulated by the first model is farther than that of MW1 model,but the width is smaller.MW2 model is not suitable for this region;6.There is an exponential relationship between the ash deposit thickness and the distance from the volcanic crater in the downwind direction 20km away from the crater.It is nearly 800 years after the eruption.We can only estimate that the downwind is 120°,so in this model it is regardless of the change of the wind direction along with altitude.In addition,there are also some problems about the numerical simulation which need to be solved,for examples,the shape of the volcanic ash particles,the error near the crater,and the second big deposit thickness and etc.

A CONTRAST RESEARCH ON NUMERICAL SIMULATION OF TEPHRA FALL HAZARDS

YU Lu, ZHAO Yi, MA Bao-jun, GAO Feng

2007, 29(3):  535-546. 

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The volcanic eruption,especially the explosive volcanic eruption,has brought about tremendous disaster to the humanity.Among the types of volcanic disaster,the one produced by falling tephra is the main type regardless of its intensity or its incidence.So,it is of great significance to simulate quantitatively the tephra fallout.The purpose of the contrast research is to test the actual effect of the model,to find out the defects and the commonness and difference of each eruption process.Based on the contrast research,we hope to find out the method to improve our model,and further,to find out the methods of reducing disaster in emergency of volcano eruption.We select three cases for the contrast research,i.e.the eruptions of S.Helens(1980),Pinatubo(1991)and Cerro Negro(1995).The bases for the selection are:first,the dynamic parameters of the three modern eruption cases have been determined by relevant competent agencies;second,the depth of falling tephra was measured before it was changed by wind and rain;and third,the three volcanoes are greatly different in terms of atmosphere factors,landform conditions,and eruptional types,so on.So the three cases can truly test the actual effect of the model.The improved Suzuki mathematic model for tephra dispersion(ZHAO Yi,2003)is adopted in this paper.Based on the depth of falling tephra distribution of S.Helens eruption of 1980(calculated by ZHAO Yi,2003),we calculate the depth of tephra-fall distribution of the Pinatubo eruption in 1991 and Cerro Negro eruption in 1995.Based on the results of numerical simulation,we compared the depth map of tephra-fall distribution with the disaster maps.In the end,the verification and validation of the model are tested.By numerical simulation,the effect factors of the three volcano eruptions are compared,such as,the atmosphere parameters,the eruption intensity,the height of the eruption column and VEI,landform change,eruption type,second deposit thickness.Based on the contrast research,the main future research interests are proposed to be in the areas of:1)the thermal disturbance model over the crater,2)the second deposit thickness model,3)the rainfall-concurrent tephra fallout model,4)the pyroclastic flow model for secondary pyroclastic transport in varied landforms and 5)the mud flow model.

EARTHQUAKE MONITORING AND STUDY IN THE JINGPOHU VOLCANO CLUSTER AREA

LIU Zhi, DUAN Yong-hong, XU Zhao-fan, YUAN Qin-xi, YANG Jian, ZHOU Xue-song

2007, 29(3):  547-557. 

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The Jingpohu volcano cluster lies on the southwest of Ningan county seat,Mudanjiang city,Heilongjiang Province,China.There are 13 craters in this area and the volcano cluster formed in Holocene Epoch is concentrated in the two areas of Crater Forest and Hamatang.According to the recent studies,Jingpohu volcano cluster is located on the western side of the Dunhua-Mishan Fault,where the volcanic activity has been highly frequent and the volcanoes were active in Paleocene,Eocene and Holocene.These volcanisms were associated with strong earthquakes of magnitude 6～7.In order to understand the volcanic activities as well as the structure features of crust and upper mantle in this area,14 broadband seismic stations with 24 bit digital seismographs were installed around Crater Forest in Jingpohu volcano area and various seismic events including the volcanic tectonic earthquakes and the volcanic-like events were recorded.In this paper,based on the analysis of a great deal of data,the earthquake type classification,seismicity analysis and earthquake location were carried out.The classification of recorded event types indicate that the earthquakes observed in Jingpohu volcanic area are mainly of volcanic tectonic ones while the seismicity was not high during the recording periods,and at the same time,two types of earthquakes which are different from tectonic ones were recorded.Among these events,the waveform features of one type of events are similar to the volcanic events with long period(LP),however,compared with standard volcanic events with long period(LP),their frequencies are higher;the other type of events have some similar features with volcanic tremors.It could be seen from earthquake location results that the most focus depths range from 10 to 30km and their epicenters are mainly concentrated on the southwestern side of craters.There are few earthquakes in the interior of craters and their magnitudes are mostly less than 2.0.It is suggested that the occurrence of these earthquakes is possibly related with the activities of Dunhua-Mishan fault because the volcanic and seismic activities during observation periods in Jingpohu volcano area are not too obvious and the epicenters are mainly distributed near Crater Forest and Dunhua-Mishan fault.Close attention should be paid to the volcanic-like events with long period and the tremors recorded around Crater Forest.However,it needs further research to make sure that whether the two types of events recorded in this area are related to the magmatic activities because of shorter observation time and a few recorded events available in this study.

SEISMIC INFORMATION OF COLD DIAPIR AND HOT DIAPIR

YANG Ke-sheng, HU Ping, DANG Xiao-chun

2007, 29(3):  558-577. 

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Under the effect of external force,plastic layers in subsurface and deep crust would result in diapirism,and the resulting structure is called diapiric structure,which can be divided into two types according to their nature,one is cold diapir and other is hot diapir.Cold diapir is defined here as the structural style resulting from diapirism or upward movement of plastic material such as salt,gypsum and shale.Hot diapir is defined as the diapiric structural style resulting from magmatic intrusion or explosion.Both of them are characterized with chaotic internal reflection pattern and rapid termination of reflections relevant to surrounding rock in seismic section.Magmatic diapirism is commonly associated with high magnetic anomaly and high interval velocity.Some cold diapir is associated with low interval velocity,but the diapir resulting from gypsum is associated with high interval velocity.Hot diapir is undoubtedly linked to volcanic earthquake.Cold diapir can also result in disastrous earthquake which is commonly omitted by geologist.Such examples include:two earthquakes with M_S 7 1/4 and M_S 6 1/4 respectively taking place in Luntai(located in the front belt of South Tianshan Mts.between Koerle and Wushi)in 1949;the northeast Baicheng earthquake with M_S 7 1/4 in 1949;the south Baicheng earthquake with M_S 6 1/4 in 1947;and the Wushi earthquake with M_S 6.5 in 1969.The earthquakes mentioned above are obviously controlled by the large fault belt in the south of depression at the front of South Tianshan Mts.Among them,the Baicheng fault is a rootless one which is associated with Paleogene gypsum flow and upward movement.It is inferred that south Baicheng earthquake is related to the fault.Therefore,people working in seismogeology should pay more attention to the study of cold diapirism.

THE GEOMORPHIC SURFACES BELOW 50 METRES IN FUJIAN SOUTHEASTERN COASTAL REGION AND THE FAULT ACTIVITY

HUANG Qing-tuan, FU Ping, ZHENG Shao-peng

2007, 29(3):  578-596. 

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In this paper,the fault tectonic activity of Fujian southeastern coastal region since the Quaternary is analyzed by studying the formation and development of several geomorphic surfaces below 50m.The results show:(1)the geomorphic surfaces below 50m in southeastern coastal region of Fujian can be classified into erosion-abrasion terrace and accumulational terrace.The former(mostly,red soil platforms)can be divided into 3stages:the elevations above sea level are 10～15m for T₁,20～25m for T₂ and 40～50m for T₃,respectively.Their forming ages are:(1～0.5)×10⁴a BP for T₁terrace at about the early stage of the Holocene Epoch;(1.8～1)×10⁴a BP for T₂ terrace in the late stage of the late Pleistocene and(4～1.8)×10⁴a BP for T₃terrace in the middle or late stage of the late Pleistocene.The accumulational terrace includes river terrace and marine terrace.The elevations above sea level of river terraces along the lower reaches of Jinjiang and plain are:9～12m for T₀,13～17m for T₁,20m for T₂ and 40m for T₃.And their forming ages are in the late stage of the Holocene for T₀;the early stage of the Holocene for T₁,the late stage of the late Pleistocene for T₂ and the middle or late stage of the late Pleistocene for T₃.The elevation levels of river terraces along the lower reaches of Jiulongjiang and plain are:12.5m for T₀,18m for T₁ and 29m for T₂.Their forming ages are the same as those of the lower reaches of Jinjiang.The elevations of marine terraces along the coast are:3～5m for T₀,10m for T₁,15～25m for T₂ and 30～50m for T₃;and their forming ages are:5000a BP in the late stage of the Holocene for T₀,(1～0.5)×10⁴a BP in the early stage of the Holocene for T₁,(1.8～1)×10⁴a BP in the late stage of the late Pleistocene for T₂ and(3.5～1.8)×10⁴a BP in the middle or late stage of the late Pleistocene for T₃,respectively.The terraces are composed of "old red sand",their stages can not be divided easily.The elevation level is 10～50m,the forming age is in the middle or late stage of the late Pleistocene,at about(3.5～1)×10⁴a BP,and in some individual areas,it is more than 4×10⁴a BP.(2)When a fault dissects a certain geomorphic surface,the forming age of this geomorphic surface can be assigned to be the active age of the fault.(3)In some areas,the geomorphic surfaces forming in the same age distributed along the NE-trending and the NW-trending faults show a differential elevation.It indicates that the two sets of faults are active in the late Pleistocene.The Pingtanqingfeng-Dongshan'aojiao Fault in the Changle-Zhaoan NE-trending fault zone is a late stage of the late Pleistocene(Q_p³)active fault.Its vertical slip rate is 1.1～2.2mm/a.The major active age of Changle-Dongshanqianwu Fault is in the middle Pleistocene(Q_p²).The northwestern segment of Jiangdongqiao(the north brook)-Haicang Fault,which is in the NW-trending fault zone along the lower reaches of Jiulongjiang,can be categorized as an early Quaternary fault(Q_p^1-2).And the southeastern segment,which is called the Haicang-Qianyu Fault,is a late Pleistocene(Q_p³)active fault.

CHARACTERISTICS OF THE HOLOCENE ACTIVITY OF THE GUANGUANLING FAULT ZONE

DU Peng, CHAI Chi-zhang, SHEN Wei-hua, MIN Wei, TIAN Qin-jian

2007, 29(3):  597-606. 

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The newest active time and segmentation of the fault are of special significance in the safety evaluation of major engineering projects.This paper discusses the active times and segmentation characteristics of the Guanguanling Fault zone through interpreting aerial photos,field investigation,topographic and geomorphic surveys and analysis of trench logs on paleoearthquake in connection with the study of the geological and seismologic problems in Heishanxia project of the Huanghe River.The Guanguanling active fault zone lies on the northeastern margin of the Qinghai-Tibet block.It is part of the Zhongwei-Tongxin arc active fault zone,striking near EW generally,with a total length of about 60km.It consists of 5 discontinuous secondary faults arranged in left step en echelon,namely,Jingtaixiaohongshan(F_1-1),Guanguanling(F_1-2),Shajing(F_1-3),Zhongweixiaohongshan(F_1-5)and Qingshan-Gushanzi(F_1-4),respectively.Since Late Quaternary,the fault is characterized with intense sinistral strike-slip and compressional thrust and has offset a series of ridges and small gullies and terraces.At the same time,fault scarps were developed along the fault zone.The study reveals that the latest earthquake occurred 700～1200a BP,the largest displacement took place in Guanguanling,and the maximum horizontal sinistral displacement reaches 6m since Holocene.

THE STUDY OF PALEOEARTHQUAKE ON THE WEIHE FAULT ZONE

SHI Ya-qin, LI Jin, FENG Xi-jie, DAI Wang-qiang, REN Jun, LI Xiao-ni, DOU Ma-li

2007, 29(3):  607-616. 

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Weihe Fault is an important buried fault in Weihe basin.The predecessors have investigated the location and activity of the fault from various points of view,but up to now,the level of researches on the precise location and activity for the fault is still very low.There are few strata profiles of late Pleistocene which are found to be offset by the fault zone.Especially,it is still unknown whether the Weihe Fault was active in Holocene and there were paleoseismic events occurring on it.It is indicated from exploratory trench excavated at Bili village in the west section of Weihe Fault that over the past 9110a,the Yaodian—Zhangjiawan segment of Weihe Fault zone has experienced a historical earthquake and 3 paleoearthquake events.The historical earthquake is manifested by soil liquefaction.According to the study on historical and cultural relics,stratigraphic chronology and seismogenic tectonics,we propose the occurrence time of the historical earthquake is between 1487 and 1568;the age of paleoseismic event I is(9110±90)a,but there is no answer for the age of event II and event Ⅲ.The coseismic vertical displacement of event I,II and Ⅲ is 0.5m,0.5m and 0.2m respectively.The exploratory trench excavation also indicates that the Yaodian-Zhangjiawan segment of the Weihe Fault is a Holocene active fault.

PRIMARY STUDY ON THE VARIATION OF SURFACE THERMAL FLUX BEFORE AND AFTER THE M_S 5.7 EARTHQUAKE OF 2005 IN JIUJIANG,JIANGXI

CHEN Mei-hua, DENG Zhi-hui, WANG Yu, LIAO Zhi-hui, ZU Jin-hua

2007, 29(3):  617-626. 

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The temporal and spatial variations of surface latent heat flux(SLHF)and diagnostic air temperature at 2m before and after the M_S 5.7 earthquake that occurred between Ruichang and Jiujiang in Jiangxi province on the 26th November 2005 are summarized in this paper.It is found that before the earthquake significant SLHF anomalies and air temperature anomalies occurred in the epicentral area and its vicinity.The air temperature anomalies are found from the 2nd to 13th November,2005 and concentrated at the epicentral area and its southern area.Then two days later,that is,from the 4th to 15th November 2005,significant SLHF anomalies occurred in the epicentral area and its northern area where a lot of lakes distribute along the active faults.During the anomalous period the SLHF and air temperature at 2m exceeded the sum of 26 years average and 1.5 times of their standard deviation for the same day.Both anomalies had maintained for 12 days with a peculiar distribution associated with the tectonic active zone.It is considered that both of air temperature anomalies and SLHF anomalies are behaviors of thermal flux from underground prior to earthquake.SLHF anomalies occurred over regions with abundant water,whereas air temperature anomalies occurred over land.

THE RESULT AND MEASUREMENT OF SOIL GAS RADON AND SOIL GAS MERCURY IN THE EXPLORATION OF HAIHE HIDDEN FAULT

SHAO Yong-xin, YANG Xu-lian, LI Yi-bing

2007, 29(3):  627-636. 

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In the exploration of the Haihe hidden fault,radon and mercury in soil gas were measured by using FG-3017 radon detector and XG-4 mercury analyzer.In this paper,based on the measurement results of 12 fault gas profiles,and integrating with the exploration results of artificial earthquake method,the relationship between anomalous site of fault gas and fault location is analyzed.Using the relationship between anomalous strength of fault gas and fault activity,the activity of Haihe Fault is studied,thus the location and activity segmentation of the Haihe Fault in Tianjin region are presented.This study shows that the method of fault gas detection can not only identify the preliminary location of fault,but also make preliminary segmentation of fault activity.The fault detected by the method of fault gas is shown as a band.Through contrasting with exploration results of artificial earthquake method and analyzing,the fault locates inside the band.According to the measurement result of soil gas radon,the Haihe Fault can be divided into east and west segments.At the same time,the activity of the east segment of Haihe Fault is stronger than that of the west segment.This is only a relative result,and it is difficult to judge whether the fault is active or not with this result.

THE NUMERICAL SIMULATION ON COSEISMIC EFFECT OF THE 14 NOVEMBER 2001 GREAT KUNLUN EARTHQUAKE,NORTHERN TIBET,China

WANG Hui, ZHANG Guo-min, ZHANG Huai, SHI Yao-lin, LIU Jie, SHEN Xu-hui

2007, 29(3):  637-647. 

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The 14 November 2001 M_S 8.1 Kunlun earthquake at northern Tibet is the largest earthquake that occurred in the Chinese continent since 1950.We apply a three-dimensional(3-D)finite element numerical procedure to model the coseismic displacement and stress fields caused by the earthquake dislocations,which are constrained by field investigations.We then further investigate the stress interaction between the M_S 8.1 earthquake and the intensive aftershocks.Our primary calculation shows that the coseismic displacement field is centralized around the east Kunlun Fault zone.And the attenuation of coseismic displacements on the south side of Kunlun Fault zone is larger than that on the north side.The calculated coseismic stress field also indicates that the calculated maximal shear stress field is centralized around the east Kunlun Fault zone,and the directions of the coseismic maximal principal stress are contrary to that of the background crustal stress filed of Tibet Plateau.It indicates that the earthquake relaxes the crustal stress state in Tibet Plateau.Finally,we study the stress interaction between the M_S 8.1 earthquake and its intensive aftershocks.The calculated Coulomb stress changes of the M_S8.1 great earthquake are in favor of triggering 3 aftershocks.

SHORT-IMPENDING TILT EARTH TIDE VARIATION FEATURES OF CZB-1 PERPENDICULAR PENDULUM IN YANSHOU SEISMIC STATION OF HEILONGJIANG

LI Ji-ye, HU Bin-sheng, QU Yong-bin, SHI Wei, LI Guo-qing

2007, 29(3):  648-656. 

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An analysis has been made of the 2005 earth tide observation data recorded by the CZB-1 type perpendicular pendulum tiltmeter at the Yanshou Seismic Station of Heilongjiang,using the two day(48h)and two-day sliding monthly harmonic analysis method.Values of the tidal factor γ and the phase-delay factor Δφ before the Jul 25^th,2005 M_S 5.1 Lindian,Heilongjiang and the Sept 19^th 2005 M_S 4.7 Yakeshi,Inner Mongolia earthquakes have been determined for the semidiurnal constituent(M₂)of the tilt earth tides.As a result,some features of deformation of tide variations prior to some moderate earthquakes have been revealed.Relation expression was preliminarily calculated between the waiting time after anomaly or anomaly amplitude or epicentral distance and earthquake magnitude.Results of comprehensive analysis are as follows:(1)The tidal factor reflects the elastic stage of earth crust media response to tidal force in physical meaning.The earth crust media state varies and the earth crust deformation turns into an instable phase along with stress strengthening before moderate-strong earthquake.Adopting the harmonic analysis method and with a proper calculation length,the anomaly information of the tidal factor and the phase-delay factor are extracted for better analyzing and calculating the stress-strain state of earth crust media against the time series,giving prominence to the short-impending anomaly information,and catching the precursor anomaly of earthquake occurrence.(2)Tidal factor variations reflect the stress change in earth crust media of seismic source area,which offers the short-impending precursor information relating to time.The variation process can be summarized as trend background → augmentation or contraction → extreme → restitution → waiting → earthquake occurrence.(3)The harmonic analysis method of tide has high anti-interference ability.It can remove the interferences,such as the long-term trend drift and environmental effect,to provide stable figures and give prominence to the anomaly information.In addition,the Venedikov harmonic analysis method is a valid method for studying the relationship between the tidal tilt anomalies and the moderately strong earthquake.

PRIMARY RESEARCH OF ACTIVITY SEGMENTATION OF LONGMENSHAN FAULT ZONE SINCE LATE-QUATERNARY

CHEN Guo-guang, JI Feng-ju, ZHOU Rong-jun, XU Jie, ZHOU Ben-gang, LI Xiao-gang, YE You-qing

2007, 29(3):  657-673. 

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The Longmenshan Fault zone,trending in NE,lies between the Songpan-Ganzi orogenic belt and the Yangzi block.It consists of four major faults,such as the Houshan Fault,and related thrusting sheets.It is a nappe structure characterized by forward spreading.It formed during the Indo-China movement and was active many times since then.Since the Quaternary,this fault zone has been very active,and exhibits differential activity on its various sections.In this work,we make an integrated analysis of this fault zone based on data of geomorphology,geology,Bouguer gravity anomalies,and earthquakes.The results show that the near NS-striking Leidong Fault,located along Beichuan-Anxian,is the boundary between the middle and northeastern sections of the Longmenshan Fault zone.The two sections have high distinctive activity.The middle section is very active since late Pleistocene time with frequent medium-and small-sized earthquakes,while the northeastern section has weak activity since Quaternary with occasional small earthquakes.Due to the compression and uplift of the Tibetan Plateau and lateral sliding of blocks,the Sichuan-Qinghai block moves towards SEE,resulting in an active boundary of the block.This boundary includes the Mingshan uplift and the middle and southwestern sections of the Longmenshan Fault zone,both of which are truncated by the Mingshan uplift.And the northeastern section of the Longmenshan Fault zone has been abandoned.

SOFTWARE FOR THREE-DIMENSIONAL LOCATION OF ACOUSTIC EMISSION IN LABORATORY

LIU Pei-xun, LIU Li-qiang, CHEN Shun-yun, HU Xiao-yan

2007, 29(3):  674-679. 

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New software for acoustic emission location has been developed and the main functions,methods for location are introduced briefly.The tested location result with the software is presented also.The multi common Data Base interfaces are built in the software,so it is device-independent.Besides the three-dimension location,it can be employed for surface or linear location.In locating,the velocity of sample material will be an appointed constant or an unknown variable.There are two improvements in the algorithm.The first is that the least absolute deviation based on robust estimation is taken as objective function for location.The second is a simulated annealing method that is applied to search the global minimum of objective function in optimization procedure.The location accuracy of acoustic emission focus is much better with the software and it is a flexible tool for data processing.

A STUDY ON THE METHOD OF 3D VISUALIZATION OF EARTHQUAKE DAMAGE TO ONE-STOREY HOUSE BASED ON ARCGIS AND 3DS MAX

YANG Ze, LI Zhi-qiang

2007, 29(3):  680-686. 

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Earthquake disaster prediction system provides good technical support for protecting against and mitigating earthquake disasters,and becomes mature day by day with the development of GIS technology and the theory of earthquake disaster prediction.But the results of traditional earthquake disaster prediction software are displayed in 2D,such as table,curve and histogram,which are very difficult to reflect the solid characteristic of buildings'damage.So this paper aims at the study of the use of the mainstream 3D modeling software to model of earthquake damage to one-storey house,and at the solutions of how to combine effectively the information of building textures and earthquake damage,that is,using polygon modeling to model 3D buildings.Then it uses "Unwrap UVW" to unwrap the 3D building model's UVW to a picture,and exports the picture to Photoshop by using plug-in.Then it composites the building textures and the characteristics of building damage in Adobe Photoshop to complete the description of seismic damage of buildings.Finally,the compounded textures are returned to 3DS Max and mapped on the 3D models of buildings,resulting in seismic hazard models of.3ds format for the visualization programs.In this paper,the modeling process of seismic hazards is described in detail.Besides,this paper also studies the modeling of house collapse.Since house collapse is involved in many fragments,it is hard to perform modeling using the methods presented above.It is found that the existing software Reactor in the 3DS Max can be used to simulate fracture of a rigid body.With this approach this work realizes the establishment of the model of one-story house collapse,and obtains a good result.At last,this work develops the visualization function of seismic hazards by using the VBA and ArcObjects in the ArcGloble,and combines it with the mainstream GIS,which accelerates the use of 3D visualization technology in protecting against and mitigating earthquake disasters and has provided a new idea for the visualization of earthquake damage to buildings,and for the development of 3D earthquake disaster prediction software based on GIS software as well.

THE APPLICATION OF UNDERGROUND TRANSIENT ELECTROMAGNETIC METHOD(TEM) TO DETECTING GOAF WATER

LIU Bai-zhou

2007, 29(3):  687-691. 

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This paper introduces the application of Underground Whole-space Transient Electromagnetic Method(UWTEM)to the detection of abandoned mine water.It presents the study of the method to detect different occurrence goaves in limited work conditions.It proves the effectiveness of UWTEM technology in detecting goaf water ahead of the tunneling,or in the roof,floor and sides of the roadway.It concludes several key issues which require notice in the application of UWTEM.The result shows that UWTEM technology can effectively detect both the position and extent of goaf water ahead of the tunneling,or in the roof,floor and sides of the roadway.It also provides reliable basis for prediction and prevention of mine water disasters.