Table of Content

24 December 2009, Volume 31 Issue 4

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Brief Report

GLOBAL EARTHQUAKES AND VOLCANOES:DISTRIBUTION AND VARIATIONS

HONG Han-jing, CHEN Hui-xian, ZHAO Yi, HU Jiu-chang

2009, 31(4):  573-583.  DOI: 10.3969/j.issn.0253-4967.2009.04.001

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Volcano and earthquake,both are significant phenomena and subsequences of plate motion. Great importance has been attached to the connection between volcano and earthquake in recent years.Global partitioning of earthquake and volcano is an important prerequisite for the study of the spatial and temporal distributions of global earthquakes and volcanoes,as well as global tectonic and contemporary geodynamics. On the basis of statistic analysis on Earthquake Catalogs of USGS National Earthquake Information Center and Volcano Catalog of Smithsonian Institution,and applications of the concept of three tectonic systems(Ma et al.,2003),the correlation study between volcano and earthquake distributions was made in this paper.Based on the statistics of subareas,the global modern tectonics can be divided into three systems:continent,ocean,and collision zone. Continental earthquakes are widely spaced,differing from strap-like distribution in the plate boundaries.The major distinction of continental volcanoes from oceanic one is the existence of continental lithosphere with various crust thicknesses and ages.The continental volcanoes are more sensitive to tectonic stress field,e.g.the continent rifts are induced by lithospheric extension. Oceanic crust is young,thin and relative homogeneous,with weak seismicity.Magmatism is dominanted by smooth extrusion of lava and expansion of ridges in mid-ocean.Most records of volcano eruptions are related to hot plume from deep mantle in islands. Subduction-collision zone has the maximum severity of earthquakes and volcano eruptions.The seismicty is caused by extrusion from plate collision,and the volcanism is related with dehydration,decline of solidus,and uplift of arcs.The tremendous energy from plate collision is the fundamental cause of earthquake and volcano. The violent seismic and eruption activities are mostly correlated with geoid highs.The deep subduction zones with focal depth greater than 500km have weak eruptions,lacking historic records,or large eruptions with VEI≥4. The average latitude of earthquakes behaves in a synchrony way with that of volcanoes,and their spatial distribution changes in synchronous phases.In the first half period of last century(1902- 1953),the great eruptions with VEI greater than 5 were in eastern Pacific,such as the 1902 eruption of Santa Maria in Guatemala,the 1912 Trident eruption in Alaska,the 1932 eruption of Azul in Chile. And the seismicity were the most violent in Eurasia continent.In the middle period(1956-1980), the eruptions were concentrated in north Pacific,such as the 1956 eruption of Bezymianny in Kamchatka, the 1976 eruption of Augustine in Alaska,and the 1980 eruption of St.Helens In USA.The large earthquakes migrated from northern Pacific(1954-1965),Japan Arc(1966-1972) to Phillippine Arc(1973-1981).

S-WAVE VELOCITY STRUCTURE BENEATH CHANGBAISHAN TIANCHI VOLCANO INFERRED FROM RECEIVER FUNCTION

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

2009, 31(4):  584-597.  DOI: 10.3969/j.issn.0253-4967.2009.04.002

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The crustal and upper mantle S-wave velocity structures in Changbaishan volcanic region were obtained from surface wave tomography and teleseismic receiver function modeling.In Changbaishan region,the S-wave velocity shows a thin lithosphere,thick asthenosphere with relatively low S-wave velocity in upper mantle,which indicates the high temperature volcano system at least extends to asthenosphere. There exist distinct low velocity layers in the crust of the volcano area.Beneath WQD station near to the caldera,the low velocity layer at 8km depth is 20km thick with the lowest S-wave velocity about 2.2km/s.Beneath the EDO station located 50km north of Tianchi caldera,no obvious low velocity layer was detected in the crust.The average crustal V_P/V_S near the caldera is higher than those obtained in surrounding area.In the volcanic region,the thickness of crustal low velocity layer is greater and the lowest velocity is more obvious with the distance shorter to the caldera.It indicates the existence of the high temperature material or magma reservoir in the crust near the Tianchi caldera. The receiver functions and inversion result from different back azimuths at CBS permanent seismic station shows that the thickness of near surface low velocity layer and Moho depth change with directions. The near surface low velocity layer is obviously thicker in south direction.The Moho depth shows slightly rising in the direction of the caldera located.We consider that the special near surface velocity structure is the main cause of relatively lower prominent frequency of volcanic earthquake waveform recorded by CBS station.The slightly rising of Moho depth beneath Tianchi caldera indicates there is a material exchanging channel between magma reservoir and upper mantle.

CHARACTERS OF S-WAVE ENVELOPE BROADENING IN CHANGBAISHAN TIANCHI VOLCANO

FAN Xiao-ping, LI Qing-he, HE Hai-bing, YANG Cong-jie, JIN Shu-mei

2009, 31(4):  598-606.  DOI: 10.3969/j.issn.0253-4967.2009.04.003

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High-frequency S-wave seismogram envelopes of microearthquakes are broadened with increasing travel distance,which is called S-wave envelope broadening.Multiple forward scattering and diffraction for the random inhomogeneities along seismic ray path are the main reasons to cause the S-wave envelope broadening,so the phenomenon of S-wave envelope broadening is used to study the inhomogeneity of medium.The peak delay time of S-wave,which is defined as the time lag from the direct S-wave onset to the maximum amplitude arrival of its envelope,is accepted to quantify the phenomenon of S-wave envelope broadening.The 204 small earthquake records in Changbaishan Tianchi volcano were analyzed by S-wave envelope broadening algorithm.The results show that the phenomenon of S-wave envelope broadening in Changbaishan Tianchi volcano is obvious,and the peak delay time of S-wave has a positive correlation with hypocenter distance and frequency of S-wave.The relationships between the peak delay time of S-wave and the hypocenter distance for different frequency bands were got by statistics method.The results are beneficial to the understanding of the S-wave envelope broadening phenomena and the quantitative research on the inhomogeneities of the crust medium in the Changbaishan Tianchi volcano region.

ANALYSIS OF SPECTRUM AND TEXTURE INFORMATION ON CHANGBAISHAN TIANCHI VOLCANO CALDERA AND ITS APPLICATION

XU Jian-dong, LUAN Peng, FAN Xiao-Ying, LIN Xu-dong

2009, 31(4):  607-616.  DOI: 10.3969/j.issn.0253-4967.2009.04.004

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The terrain near the Changbaishan Tianchi volcano caldera is complex and highly covered with vegetation,so it is difficult to determine the precise spatial distribution extent of the volcanic eruptive products only using the geological or visible remote sensing technology.In this paper,based on the analysis of spectrum and texture information from the IKONOS image of the study area,eight types of training samples are selected and the spectral angle technology(SAM)is applied to perform classification. These eight types of surface include water body,shadow,thick pumice,thin pumice,trachyte, soil,vegetation and forest.The primary results of such classification are not satisfactory through confusion matrix evaluation,which may be due to a serious loss of spectrum information in the synthesizing process.However,the texture information of the image is abundant.Therefore,we introduce the texture analysis of the ENVI probability matrix method which takes advantage of dissimilarity texture feature to establish the symbol of texture interpretation.Our final results indicate that the accuracy of classification may be greatly improved by using the combination of spectrum and texture analysis. Taking the widely distributed pumice as an example of classification,we obtain the information of both the extent and the relative thickness distribution of pumice near the Tianchi caldera region.In the future, more work should be concentrated on the field investigation to confirm the terrain features of eight types which are obtained from the satellite image interpretation before that remote sensing technology will truly become one of the useful tools for geological mapping and volcanic hazards evaluation.

APPLICATION OF SATELLITE THERMAL INFRARED REMOTE SENSING IN MONITORING CHANGBAISHAN TIANCHI VOLCANO ACTIVITY

JI Ling-yun, XU Jian-dong, LIN Xu-dong, LUAN Peng

2009, 31(4):  617-627.  DOI: 10.3969/j.issn.0253-4967.2009.04.005

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The paper firstly introduces the research status of using thermal infrared remote sensing technology to monitor volcanic activity around the world,then reviews the principle of thermal infrared remote sensing technology.Meanwhile,the feasibility of monitoring volcanic activity using satellite thermal infrared remote sensing technology is analyzed.Moreover,we take the Changbaishan Tianchi volcano as an example.Firstly,land surface temperature distribution maps of Changbaishan Tianchi volcano are retrieved from Landsat TM/ETM images and ASTER images taken from 1999 to 2008.Then,to reduce the effect of different surface cover,we choose three types of the surface cover,i.e.vegetation(forest), mixture of soil and vegetation(short grasses),and bare rock.For each type of surface covers,the average daily temperature obtained from Tianchi Weather Station is deducted in order to reduce the effect of weather change.Finally,we obtain the annual surface temperature variation of the study area, which is believed to be caused by volcanic activity in the magma chamber.Our results indicate that the temperature of the study area increased with an intermittent tendency during 1999 to 2005,but dropped after 2005,and then maintained a stable tendency during 2006 to 2008.Such tendency of annual temperature variation caused by volcanic activity is consistent with the results from other different observation methods,e.g.seismic monitoring,ground deformation from GPS measurement,ratio of He isotope change from geochemistry monitoring.The results imply that it is of great potential to use the satellite thermal infrared remote sensing technology in monitoring volcanic activity.So the satellite thermal infrared remote sensing technology can be used as a routine means to monitor volcanic activity.

STRUCTURAL CHARACTERISTICS OF FELDSPAR FROM HOLOCENE VOLCANIC ERUPTIVE ROCK ON THE TIANFENG PROFILE IN TIANCHI AND THEIR GEOLOGICAL IMPLICATIONS

ZHANG Bing-liang, ZHAO Bo, YU Hong-mei, XU Jian-dong, SHI Lan-bin, ZHENG Yong-gang, PAN Xiao-dong

2009, 31(4):  628-638.  DOI: 10.3969/j.issn.0253-4967.2009.04.006

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We have studied the surface features and structural state of the feldspar from the Holocene volcanic eruptive rock on the Tianfeng profile using data from observations under scanning electron microscope and analysis of x ray diffraction.On this profile black pumice appears at the top and darkgrey pumice is present at the bottom.The result shows that the feldspar in these pumice rocks has fresh surface,with slightly weathering for individual cases,and occasionally seen as non-crystalline floc of varied thickness at concaves on its grain surface.This feldspar belongs to the high sandidine-high albite series of the alkali feldspar.The intensity of its characteristic diffraction peak and its plane mesh d value are roughly consistent with the PDF data of anorthoclase.And its constitution((Or37～41,Ab63～59)also implies that it is anorthoclase.It has the following parameters:ordering degree 0.045～0.089,h value-1.010～-1.361,and the lowest crystalline temperature 800～990℃ which is up to 990℃ for the black floc at the top.Our study suggests that the younger volcanic eruption at Tianchi has a lower ordering degree of feldspar and a higher temperature reflected by its structural state.Because the structure of the present feldspar at Tainchi is the result of the cooling process of the hot volcanic rock,the temperature when the feldspar was formed might be very high.The difference of structural state in this feldspar is probably associated with ages and temperatures of volcanic eruptions. The study of its features has some theoretical and applied significance.

CRUST DEFORMATION MONITORING AND RESEARCH IN TIANCHI VOLCANIC AREA,CHANGBAI MOUNTAINS FROM 2000-2007

LI Ke, LIU Jun-qing, PAN Xiao-dong, LIU Guo-ming, WU Cheng-zhi, GUO Feng

2009, 31(4):  639-646.  DOI: 10.3969/j.issn.0253-4967.2009.04.007

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In order to monitor the activity of Tianchi Volcano in the Changbai Mountains,a comprehensive geodetic monitoring network consisting of precise leveling and GPS stations,has been established since 2000.In this paper,we first introduce the installation of the geodetic network and then discuss the deformation results around the volcanic area. The results show that from 2002 to 2005,obvious ground deformation occurred in the Tianchi volcano area in the Changbai Mountains.In the vertical direction,the cumulative elevation difference of leveling line reached 6.8cm in the 3 years,and the nearer to the crater,the greater the deformation was.In the horizontal direction,centered on the crater,the observation stations showed a radial displacement in general,with the maximum up to 38cm.Significant expansion occurred in the mountains,and the maximum surface expansion was up to 6?10^-6/a.After 2006,these changes resumed to normal gradually.In the meantime,the Tianchi volcanic area of Changbai Mountains saw frequent volcanic seismicity,and other monitoring data also showed abnormal changes synchronously. The paper analyzes and discusses the possible reasons for these changes,and concludes that these changes may be the result of the latest magmatic activity of Tianchi volcano.

PRIMARY RESEARCH ON THE VOLCANIC ACTIVITY IN HAIKOU AREA

HU Jiu-chang, GUO Ming-rui, LIU Wei, ZHENG Zai-zhuang

2009, 31(4):  647-654.  DOI: 10.3969/j.issn.0253-4967.2009.04.008

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The Maanling-Leihuling volcanic cluster in Haikou area is one of the few dormant volcanic clusters in China.In the present study,according to the active stages division,deep magma chamber detection in this area,as well as the investigation of volcano types,scales,material composition and lava cover area,we evaluated the spatial-temporal and intensity features of volcanic activity in this region. Combined with the analysis on the observations of earthquake,geomagnetism,volumetric strain and geothermics in this volcanic region,we made the preliminary assessment on the activity state of deep magma.The results indicate that the last eruption in this Holocene volcano region occurred 4000 a BP,and the future volcanic activity may shift to the epicentre area of the 1605 M7.5 Qiongzhou earthquake in the Hainan Island.

ANAYSIS OF THE CHARACTERISTICS OF MAGMA ACTIVITY BASED ON THE DEFORMATION AND GRAVITY MEASUREMENTS IN TENGCHONG VOLCANO REGION

HU Ya-xuan, WANG Xiong

2009, 31(4):  655-663.  DOI: 10.3969/j.issn.0253-4967.2009.04.009

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Through analyzing the leveling and gravity data of 1998-2004 in Tengchong volcanic region,it is observed that the vertical deformation mainly concentrates in the range of±10mm and the variation of gravity is several dozens ofμGal.Those stations especially built in the volcanic cone and near the fault have big anomaly changes.The integrated application of Mogi sources and fault models can explain the observation data well.When the relative movement between the two walls of a fault in the surveying region happens,the rates of the sites on the different walls can be opposite.The variation of leveling and gravity data in different periods shows the magma in the volcano is active.The predicated gradients(FAG and BCFAG)divide the interpretation graph of Ag/Ah data into six regions(Ⅰ-Ⅵ).If data are plotted in regionsⅠorⅣ,both reflecting mass decrease and density decrease,volcanic eruptions are unlikely to occur as voids are created during this process.Data falling in regionsⅡorⅤ(mass increase/density increase)reflect replenished magmatic system.Volcanic eruptions are unlikely to occur if the gradients plot is in regionⅤ,due to the lack of overpressure.RegionⅡmay reflect potential persistent volcanic activity.Eruptions,if they were to occur,are likely to be effusive and/or low-explosivity events due to the lack of significant pressurization.The vast majority of data in Tengchong volcano fall in regionsⅠ,Ⅱ,ⅣandⅤ,so volcanic eruptions are unlikely to occur.The volume change of the volcanic edifice is estimated by deformation and it is also lower than that of the moderate explosive eruption.We preliminary conclude that the magma activity is low currently and there is no danger of eruption temporarily.

STUDY OF ATTENUATION CHARACTERISTICS,SITE RESPONSE AND SEISMIC SOURCE PARAMETERS OF THE ZIPINGPU RESERVOIR REGION

ZHANG Yong-jiu, ZHAO Cui-ping

2009, 31(4):  664-675.  DOI: 10.3969/j.issn.0253-4967.2009.04.010

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Based on digital seismograms recorded by Zipingpu reservoir digital seismic network and YZP station of Chendu Digital Tele-seismic Network from August 2004 to May 2008 before the M8.0 Wenchuan earthquake,the paper calculates the inelastic attenuation,geometrical spreading and Q of the Zipingpu reservoir region using Atkinson's method,and site response using Moya's method.Seismic source parameters of 287 earthquakes with M≥1.6 were calculated and the relations between them discussed.Result shows:The relation between inelastic attenuation Q andfis Q(f)=47.8×f^0.91;the site response has correlation with f;and the dependence between seismic moment,corner frequency and earthquake magnitude of small earthquakes is not obvious in the Zipingpu reservoir region,which maybe has something to do with reservoir-induced earthquake.

RESEARCH ON FOCAL MECHANISM OF SMALL EARTHQUAKES IN ZIPINGPU RESERVOIR AREA

HU Xian-ming, ZHANG Yong-jiu, XIE Rong-hua, HAN Jin, SHAO Yu-ping

2009, 31(4):  676-685.  DOI: 10.3969/j.issn.0253-4967.2009.04.011

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The focal mechanism parameters of 262 small earthquakes recorded by Zipingpu reservoir earthquake monitoring network are calculated.The results show that the dominant strike of nodal planeⅠand rupture are in good consistency.There are reverse fault,normal fault,left-lateral and right-lateral strike-slip fault in the reservoir area and the percentage of strike-slip fault amounts to 45%.Of all the faults,66%are steep and 35%are almost vertical.As a result of the impact of reservoir impoundment, the strike-slip type faulting has obviously increased since 1 July 2006,and this type of faulting became dominant during the period of the reservoir earthquake swarm.

STUDY ON THE CHARACTERISTICS OF FOCAL MECHANISMS OF RESERVOIR INDUCED EARTHQUAKES AND STRESS FIELD IN THE LONGTAN RESERVOIR AREA

CHEN Han-lin, ZHAO Cui-ping, XIU Ji-gang, CHEN Zhang-li

2009, 31(4):  686-698.  DOI: 10.3969/j.issn.0253-4967.2009.04.012

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The FOCMEC method was adopted to resolve focal mechanisms for earthquakes occurring from Sep.2006 to the end of 2008 in the range of Longtan reservoir by using the first P polarization and SH/P amplitude ratio from earthquake waveforms recorded by the Longtan reservoir seismic network. Then,the stress field of the reservoir area was inversed.According to the results,most of the M_L≥2.0 earthquakes are of thrust faulting since the impoundment in Oct.2006.The stress fields in both the cluster A and B are oriented in NWW-SEE direction and almost horizontal,indicating that the horizontal compressive stress is still the dominant stress after the impoundment,and the dip angle of the maximum principal compressive stress is more horizontal than that before impoundment.However,the middle and minimum stress axes are somewhat inconsistent in the two clusters,which indicates the local disturbance of stress field.The genesis of reservoir induced earthquake is supposed as the coupling of pore pressure action with the fluid lubricating and weakening action under the loading,whereas the increase of shear stress due to water loading is not the causation of reservoir induced earthquake.

ANALYSIS OF TIME-FREQUENCY CHARACTERISTICS OF WAVE SPECTRUM BETWEEN TECTONIC EARTHQUAKE AND MINE EARTHQUAKE

ZHANG Li-fen, LIAO Wu-lin, ZENG Xia-sheng, ZHONG Yu-yun

2009, 31(4):  699-706.  DOI: 10.3969/j.issn.0253-4967.2009.04.013

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There are many kinds of earthquakes in the Three Gorges area,such as tectonic earthquake,mine earthquake,reservoir induced seismicity and so on.And different earthquakes have different characteristics. But as far as this area is concerned,the majority of the earthquakes belong to micro-earthquakes and small earthquakes,so it is comparatively more difficult to identify their causes and types. The Three Gorges seismic network is a very good platform,which offers us very good earthquake data to do some research on the identification.In this paper,time-frequency spectrum method is used to analyze the difference between tectonic earthquake and mine earthquake,and this is the first step.By comparison,it is found there is obvious difference between them.Firstly,the main frequency of mine earthquake wave is lower than that of tectonic earthquake.And the main frequency of the former mainly centers around 2.2Hz,however the latter is around 5.5Hz.Secondly,the frequency component of tectonic earthquake wave is more abundant than that of mine earthquake,the former's energy density spectrum spreads more broadly along frequency and time axes,being 4 times broader than the latter. And it has many frequency segments with intense energy.Thirdly,the maximum value of energy intensity of mine earthquake wave occurs in all wave train earlier than that of tectonic earthquake and the energy decays quickly.

CHARACTERISTICS OF SEISMICITY IN THE THREE GORGES RESERVOIR AREA

LIAO Wu-lin, ZHANG Li-fen, YAO Yun-sheng

2009, 31(4):  707-714.  DOI: 10.3969/j.issn.0253-4967.2009.04.014

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Accurate earthquake location is of primary importance in studying the seismicity of reservoir area. The well known program Velest was used to inverse the minimum 1-D velocity,hypocenter location and station correction simultaneously.We selected 529 earthquakes,which were recorded at least by 10 stations each and whose max azimuth gap was less than 180?,to re-determine the velocity model and station corrections with three different initial models used by different researchers before.Using the 1-D minimum velocity model and station correction,we relocated 2138 earthquakes in the Three Gorges area.The average focal depth changes remarkably in different areas,as 5.6km in the area near Xiannvshan Fault,2.9km in the Xietan area and 2.6km in the Badong area.Divided by the depth of 5km,the b values are different,as 1.07,1.16 and 0.90 for all,shallower and deeper events respectively. The frequency of shallower or deeper events per 15 days increases with impounding.But that of the shallower ones drops quickly and the deeper attenuates slowly when water lever keeps stable.

THE CHARACTERISTICS OF LOAD-UNLOAD RESPONSE RATIO BEFORE AND AFTER THE M_s 4.6 DAQIAO RESERVOIR EARTHQUAKE

HU Xian-ming, ZHU Hang

2009, 31(4):  715-723.  DOI: 10.3969/j.issn.0253-4967.2009.04.015

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The water level annual change in Daqiao reservoir is about 40m,which imposes a static pressure change on its basin about 4?10⁵Pa,100 times as the role of earth tide.Therefore,the water level's change becomes the largest force source of loading or unloading effect on its basin.In this paper,we apply Load-Unload Response Ratio(LURR)theory on studying LURR value's changes pre-and after the M_s 4.6 Daqiao reservoir earthquake using earthquake number and energy data.The results show that:in the vicinity of the reservoir,for small earthquakes occurring in the reservoir water loading process,the earthquake number LURR value Y_n and C_r appeared as high-value anomalies,indicating that the rock in the study area was in a state close to failure,and then the M_s 4.6 reservoir earthquake occurred;the average value of Y_n and C_r showed significant difference before and after the impounding, as was high-value anomalies before the reservoir impounding,and resumed to normal afterwards. This case shows that reservoir water level's LURR could be beneficial to reservoir earthquake's monitoring and forecast.

THE SEISMOGENIC MODEL OF SECOND-ORDER PHASE TRANSITION OF WATER FOR RESERVOIR INDUCED EARTHQUAKES

HU Xian-ming, CHEN Ju-peng

2009, 31(4):  724-737.  DOI: 10.3969/j.issn.0253-4967.2009.04.016

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Water leakage in a reservoir is considered as an important factor that induces reservoir earthquakes.But the mechanism is complicated.According to the thermal principle of steam boiler and gravity heat pipe,a new seismogenic model of supercritical water second-order phase transition is proposed.The model can be separated into the following four stages.In the initial stage,seeping water under the pressure and gravity forms a water seal cover.Then second-order phase transition cellular convection arises in the stratum fissure of the supercritical temperature zone.In the incubation stage, caused by the fashions of stress corrosion,chemical alteration and thermal stress,primary fissures in stratum under the high confining pressure develop.This action makes the primary fissures grow and then bigger cellular convection passages are formed.In the critical stage,the critical water flux in the lower heat exchange region increases sharply,and the supercritical water laterally flows and diffuses outside the sealing cover.In the last earthquake stage,the huge stress,which exceeds the limit of stratum or sealing cover,pushes the top stratum to move like piston and the earthquake occurs.

THE STUDY ON SYNTHETIC PROBABILITY GAIN PREDICTION METHOD FOR RESERVOIR INDUCED EARTHQUAKE

WANG Xiao-qing, DING Xiang, ZHANG Fei-yu, ZHENG You-hua

2009, 31(4):  738-746.  DOI: 10.3969/j.issn.0253-4967.2009.04.017

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The synthetic probability gain model for earthquake prediction is first introduced into the prediction of reservoir induced earthquake.Its basic principle is described.The possible factors affecting the maximum magnitude of reservoir induced earthquake are approached.According to the basic reservoir data and the cases of reservoir induced earthquakes in China,the forecast efficiency R-value and the empirical probability gain K-value of partial factors or predicting indices for maximum magnitude forecast of reservoir induced earthquake,such as comprehensive effect parameter E-value,the reservoir capacity and the water depth of reservoir,are statistically calculated and appraised.The results demonstrate that the synthetic probability gain model can make a quantitative analysis of the efficiency of the various predicting indices.Then some of reservoirs at home and abroad are selected for retrospective forecast test of maximum magnitude of reservoir induced earthquake using the above indices.The results indicate that the probability gain method is practicable as a new method forecasting the maximum magnitude of reservoir induced earthquake.

A PRELIMINARY STUDY ON PREDICTION OF MAXIMUM MAGNITUDE OF RESERVOIR INDUCED EARTHQUAKE

ZHANG Fei-yu, WANG Xiao-qing, FU Hong, DING Xiang, WANG Long, ZHENG You-hua

2009, 31(4):  747-757.  DOI: 10.3969/j.issn.0253-4967.2009.04.018

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Since the prediction method for maximum magnitude of reservoir induced seismicity by using comprehensive effecting parameter E-value was proposed in 1987,it has been applied to many largescale reservoirs with good effects.After that,a group of reservoir induced earthquakes were confirmed in the past 20 years.The applicability of the model is worth studying.Based on collection of new cases of reservoir induced earthquakes,48 reservoir induced earthquake cases are selected in the paper. A new empirical prediction model of the maximum magnitude with E-value is statistically obtained and compared with the old one.At last,the upper limit of the maximum magnitude of reservoir induced earthquake is estimated to be less than M7.

STUDY ON INTENSITY ATTENUATION OF RESERVOIR EARTHQUAKE

WANG Long, WANG Xiao-qing, ZHEN You-hua, ZHANG Fei-yu

2009, 31(4):  758-767.  DOI: 10.3969/j.issn.0253-4967.2009.04.019

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Reservoir earthquakes are different from natural earthquakes because of their shallower depth and heavier damage under small magnitude.Therefore,results of damage loss assessment,using traditional models,would be underestimated,the reason of which is that intensity attenuation models for moderate magnitude natural earthquakes could not generate fit intensity especially in near field.Though the research on new attenuation for reservoir induced earthquakes has been carried out for over decades of years in China,there are still not enough cases to support the analysis.To resolve the problem,a proposal in this paper is introduced to search useful materials from amounts of natural earthquakes. We adopt a kind of clustering means,set three classified indices of magnitude,depth and epicenter intensity,and then put all the earthquakes together for classification.After settling the optimal clustering number,some natural earthquakes which could be considered with similar damage to buildings as that in reservoir earthquakes.If we gather enough cases about both types of earthquakes, this method would provide much more materials to regress parameters of attenuation models.At last, this paper shows a set of intensity attenuation curves for reservoir earthquake.While compared with other attenuation models,the new ones are definitely giving a higher intensity and faster attenuation. According to the practical materials' accuracy,new attenuation models should be correct while the magnitude is below M_s6 and the scope of disaster is less than 50 kilometers.

A STUDY ON VULNERABILITY OF BUILDINGS TO RESERVOIR EARTHQUAKE

WANG Long, WANG Xiao-qing, ZHENG You-hua, ZHANG Fei-Yun

2009, 31(4):  768-777.  DOI: 10.3969/j.issn.0253-4967.2009.04.020

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Reservoir earthquake has different characteristics of damage for its shallower depth and smaller magnitude to natural moderate earthquakes.In actual reservoir earthquakes,the damage to buildings is much heavier as the high frequency part of ground motion attenuates slowly.So existing statistical vulnerability matrix could not be used to estimate damage losses.In mainland China,scientists have monitored the reservoir earthquake since 1960s,and as many as over 20 seismic events were considered to be reservoir earthquakes.However there is not enough quantitative information to analyze the building vulnerability.Therefore,an approach is proposed in the paper,in which the natural earthquake vulnerability matrix is used to deduce the suitable vulnerability for reservoir earthquakes.Magnitude, epicenter depth and intensity are regarded as classification standard while K-means clustering adopted. Then the selected matrixes are modified by a set of regional macroeconomic factors.The method was developed in early 1990s based on the relationship between regional macroeconomic development level and seismic damage.Three parameters,population density,per capita GDP and proportion between the three levels of industries are divided into three brackets.Each bracket has weighting factor from AHP(Analytic Hierarchy Process).After data preparation,one important parameter named closeness tolerance is calculated by the Hamming distance algorithm of fuzzy mathematics,in which the parameter reflects difference of two regions in macroeconomic development as well as the reliability or vulnerability of buildings to earthquake.For a group of closeness tolerances among selected matrixes and aimed area,the summation of multiplication between vulnerability probabilities and closeness tolerances is the aimed area's vulnerability value under certain intensity.Compared with the standard matrix and building vulnerability to natural earthquakes in southwestern China,the new vulnerability value is higher and buildings in developed region have better reliability than those in poverty areas.

THE DEVELOPMENT OF RESERVOIR INDUCED SEISMICITY AND RISK ASSESSMENT SYSTEM

DING Xiang, WANG Xiao-qing, WANG Long, ZHANG Fei-yu, ZHENG You-hua

2009, 31(4):  778-784.  DOI: 10.3969/j.issn.0253-4967.2009.04.021

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The Reservoir Induced Seismicity and Risk Assessment System(RISaRiskAS 2007 for Window)is developed specially for the reservoir induced earthquake data management,the information query,the maximum magnitude prediction,and the potential seismic hazard and risk assessment.With strong functions of processing,the system can be used for the research of reservoir induced seismicity,supporting the decision-making of dam safety operation and the emergency reservoir induced seismicity information query.The design idea and main functions of the system are introduced in the paper.

DESIGN OF A DATABASE MANAGEMENT SYSTEM OF RESERVOIR INDUCED EARTHQUAKES AND RELATED GEOLOGICAL DATA

CHEN Xiao-li, WANG Zhe, MA Wen-tao

2009, 31(4):  785-791.  DOI: 10.3969/j.issn.0253-4967.2009.04.022

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As of today,our understanding of the reservoir induced earthquakes is very limited and its study is still at an exploratory stage.The large amount of natural occurrences of reservoir induced earthquakes provide us an essential and invaluable database for in-depth study on this issue.It will certainly expedite the study if one can centralize and manage these data scientifically and efficiently.We introduce in this paper a reservoir induced earthquake database management system,which is based on Visual Studio 2008 development platform and C++ programming language.As it relies on Object Oriented Design(OOD) and Object Oriented Analysis(OOA),the system not only has a user-friendly interface and is easy to operate,but also has good maintainability,scalability and upgradability.The system supports a wide range of data formats for input and output.It is convenient for users to search, query,retrieve and update data.This reservoir induced earthquake database management system is undoubtedly a great research tool for studying the reservoir induced earthquakes.

USING RESERVOIR INDUCED EARTHQUAKE DATABASE TO QUICKLY PROVIDE INFORMATION TO GOVERNMENT DEPARTMENTS FOR DISASTER RESPONSE OF M_s8.0 WENCHUAN EARTHQUAKE

MA Wen-tao, LI Hai-ou, XU Xi-wei, YANG Qing-yuan, CHEN Xian-cheng, XU Chang-peng, YU Gui-hua, ZHANG Lan-feng

2009, 31(4):  792-798.  DOI: 10.3969/j.issn.0253-4967.2009.04.023

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In the paper,according to the related factors and characteristics of identified reservoir induced earthquakes,the parameters of reservoir induced earthquake database and library structure have been determined.Based on the database functions of ARCGIG geographic information system software,the reservoir induced earthquake database contains 131 reservoir induced earthquake cases in the would, 110 Class-Ⅰlarge reservoirs(larger than one thousand million cubic meters),200 ClassⅡlarge reservoirs (larger than one hundred million cubic meters and less than one thousand million cubic meters) and 70 reservoirs with dams higher than 100 meters in China.It has the functions of quick query,statistics and icons.After the Wenchuan earthquake,aftershocks endangered many reservoir's dams and people who were taking part in earthquake rescue and relief operations.Two days after the M_s8.0 Wenchuan earthquake,the distribution and basic information of large reservoirs in Sichuan Province and nearby regions was submitted.The government made timely earthquake emergency response decisions to ensure a safe relief.The reservoir induced earthquake database is not only a method provided to the government for quick decision-making,but also can be used nation-wide.