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Review on Deep Geoplhysical Exploration and Research in China

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Review on Deep Geoplhysical Exploration and Research in ChinaIN,on,in,China,and,Deep,deep

    Review on Deep Geoplhysical Exploration

    and Research in China

ReviewonDeepGeophysicalExplo-?

    ;rationandResearchinChina

    ;WangChunyong

    ;InstituteofGeophysics,ChinaSeismologicalBureau,Beijing100081,China ;ThestatusofdeepgeophysicalexplorationandresearchinChinaissummarizedinthispaper.

    ;Newachievementsinthestudyofthevdoeitystructure,seismotectonicsandgeodynamicsofthe

    ;crustanduppermantlealealsobrieflydescribed.

    ;Keywords:Deepgeoph)sicalexploration;

    ;Crustandmantle

    oN ;DRoDUC

    ;Sincethe1970’S,deepgeophysicalexplorationandresearchhavebeencarriedoutonalarge

    ;scaleinChina.Themainpurposeistounderstandthevelocitystructure,seismotectonicsandgeody?

    ;namicsofthecrustanduppermantle.Thesurveyandstudiesarebrieflydescribedinfiveaspectsin

;thispaper.

    ;1.DEEPSEISMICSOUNDING(DSS)ANDDEEPSEISMICREFLECTI

    ONPROFILING

    ;TheDSSprofileswithatotallengthofover40,000kmanddeepseismicreflectionprofileswitha

    ;t0tallengthofabout500kmwerecarriedoutinChina(Fig.1).The2.Dcrustalstructureswei’cdeter?

    ;minedbasedonthedatacollectedalongeachprofileusingtheforwardfittingmethodoftheraytracing

    ;andcalculationofsyntheticseismograms.

    ;InNoahChina.DSSofabout30profileshasbeencarriedoutintheNoahChinaplainsincethe

    ;late1960’S(SeeSuneta1.,1988).Anoutlineandsomeparameters(thickness,averagevelocity,

    ;etc.)ofthecrustwereobtained.The2.Dcrustalstructureswereobtainedalongtheprofiles.Forex?

    ;ample,thecrustintheXingtairegionanditssurroundingshasathree?layerstructurewithalowerav’

    ;erageCruS.talvelocity(6.26.3km/s),athinnedCruSt(30

    33km)andanupliftedMoho(Zhuet

    ;a1.,1995;Songeta1.,1997).

    ;DSSalongaprofileacrosstheDabieshanorogenicbeltWascarriedoutin1995

(Wangeta1.,

    ;2000).rI’lIe2.Dinterpretationoftheseismicrecords(Fig.2)indicatesthata5k

    m.thickcrustal”root”

    ;existsbetweenYuexiandXiaotian,wheretheelevationiSthehishestontheprofile,andthereiSan

    ;apparentMohooffsetof4.5kmbeneaththeXiaotian.Mozitangfault,whichmarksthepaleo.sutureof

    ;‘ReceivedinOctober2001.ThispaperwaspresentedattheChina?ASEANW

    orkshoponSeismology,October2325,

    ;2001,Beijing,China.

    ;藩誊簦笺叠拓萼誊器重薹

    ;.薯一?0誓曩痞琏重II;

    ;

    ;284EarthquakeResearchinChina

    ;

    eassiccollision.Ahigh.velocityanomalyzone3kmbelowtheUHP(ultra-highpressure)zone

    ;maybecorrelatedtothehighercontentofUHPmetamorphicrocks? ;Fig.1

    ;LocationmapofDSSprofilescarriedoutinChina

    ;Distance(km)

    ;Fig.2

;Aseisrnicrecordsectionwitlltracenormalizationandlow-passfilterinthe

    Dabieshanorogenicbelt

    ;InSouthwestChi

    ,thetriangleprofiles,whichtmvemetheLongmenshanFaultbelt(Chenet ;a1.,1986),showthatthecrustalthicknessincreasesfromabout40kinintheYangtzeplatformto

    ;

    ;

    ;Volumel6.Number3285

    ;53kmbeneaththeSongpanGarzefoldzone.rI.heHuashixia.Jianyangseismicprofileshowsthattheav

    ;eragedcrustalvelocityintheSongpanGarzefoldzoneisabout6.30km/s.an

    dthecrustalthicknessin

    ;thewesternSichuanplateauisabout60km(Cuieta1.,1996).IntheLijiangZ

    hehaiprofile(Xiong

    ;eta1.,1986),theLijiangXinshizhenprofileandthel-azhaChanghebapr

    ofile(Cuieta1.,1987),

    ;whichalltraversethePanxitectoniczone.alowvelocityzoneexistsinthemiddlecrustandtheupper-

    ;mostmantle.TwoDSSexperimentsinYunnanProvincewerecarriedoutin1982and1987,respec.

    ;tively.Sixseismicprofileswerecompleted(Hueta1.,1986;Karleta1.,1986;Y

aneta1.,1985;

    ;Lineta1.1993).TheinterpretationresultsindicatedthatthecruststructureinYunnanareahasan

    ;obviousheterogeneityinlateraldirection;thegeneraltrendoftheMohodiscontinuitygetsdeeperfrom

    ;southeasttonorthwest:theRedRiverFaultbeltisthemainboundaryofthecrustalstructureinYun

    ;nailarea:inthesouthofthefault.thedepthofMohoincreasesfrom38kinatsouthofJingguto56kin

    ;inZhongdianarea,inthenorthofthefault,from43kininYuanjiangT0nghai

    to47kminEryuanBin

    ;chuanarea:themeancrustalvelocityisabout6.20km/sinthenorthofthefaultandabout6.40km/s

    ;inthesouth.Moreover,onmostoftheseismicrecordsections,anintra-crustalreflectedphasePap

    ;pearsclearly.thedepthofrelateddiscontinuityisintherangeof20kmto30km. ;Deepseismicreflectionprofilingisusedtoobtainthereflectionsofthecrystallinerocksinthe

    ;crustanduppermantlewiththeaidofthereflectiontechniquesdevelopedinoilexploration.Inthe

    ;pasttwentyyears,deepseismicreflectionprofilinghasbeensuccessfullycarriedoutinsomeimportant

    ;tectonicunitsontheChinesemainland,suchastheorogenicbelt,riftsystemandplatesuture(Weng

    ;eta1.,1990;Yuaneta1.,1994;Gaoeta1.,1995;Zhaoeta1.,1996).rI.histechniquewasalso

    ;usedintheXingtaiearthquakeareaandYanqingHuailaipotentialearthqua

    keareaoftheNorthChina

    ;plainin19901992(Wangeta1.,1996;Zhangeta1.,1996).

    ;IntheQinghaiXizang(Tibetan)plateau,aSinoFrenchjointDSSpmject

    Wascarriedoutinthe

    ;early1980’s(Tengeta1.,1983).TheINDEH(InternationalDeepProfilingofTibetandHimalay

    ;an)pmjectshavebeenconductedjointlybyChineseandUSgeophysicistssincetheearly1990’s

    ;(Zhaoeta1.,1996).IthasbeeninferredfromtheINDEH.1deepseismicreflectionprofilingthat

    ;adetachmente

    istsintheupper-midcrustintheHimalayanorogenicbelt(Fig.3).Theprofileand

    ;magnetotelluricresultssuggestthattheIndiancrusthaspenetratedintotheTibetanductilelowercrust.

    ;Fig.3

    ;LinedrawingofCDPstackingprofileinQinghaiXizang(Tibetan)plateau

;_00?l_蕞鬻馨凄雾繁??嚣餮嚣

    ;|Ija,日,

    ;?1{{l{;{

    ;

    ;286EarthquakeResearchinChina

    ;Based0nthe2-DcmstalstructuresinferredbyinterpretationofDSSdata,thedepthoftheMoho

    ;disc0ntinuitybeneaththeChinesemainlandanditssurroundingregionsisdetermined(Tengetal?,

    ;2002).Fig.4showstheMohotopography.

    ;Fig.4

    ;TopographyoftheMohodiscontinuitydepthinChinaanditssurroundingregions

    ;2.MAGNEToTELLUCSOUNDING

    ;M

    letoteUuricsounding(MT)hasbeencarriedoutinChinasincethe1960’s.The2-

    Delec’

    ;tricitvstnlctures0fthecrestanduppermantlewereexploredbyuseofMT(Xueta1.,1996;Zhaoet

    ;a1.,1997;Zhaneta1.,1999).Theexistenceofhighconductivitylayerinthecrestandupperman’

    ;tlewasc0nfi?

    Iled(Liueta1.,1984),andtheyarepmbablyrelatedtogeothermics,seismogenicsand

    ;ynamics(Liueta1.,1984;LiandJin,1988;Liueta1.,1993;Lineta1.,1995;Dengetal-,

    ;1998).

    ;3.SEISMICTOMOGRAPHYBASEDONTHESEISMICNETWORKDA

    TA

    ;Sincethe1980’s,theobservationdataofseismicnetworkshasbeensuccessfullyutilizedtode’

    ;

    ;Volume16,Number3287

    ;terminethe3.DvelocitystructureofthecrustanduppermantleinChinesemainlandanditsneighbor.

    ;ingregions(Liueta1.,1989),andinsomeregionalareas,suchasinNorthChina(Jineta1.,

    ;1980;Liueta1.,1986),intheNorth.SouthSeismicZone(LiuJ.H.eta1.,1989),inSouthChina

    ;(Liueta1.,1996),inWeihebasin(Xueeta1.,1997)andNorthwestChina(Lieta1.,1995).

    ;BasedonthefirstarrivalPandSdataof4,625regionalearthquakesrecordedat174stationsdis.

    ;tributedinSouthwestChina,Wangeta1.(2002)determinedthe3.Dvelocityst

ructureofthecrust

    ;anduppermantleinthestudyareabyuseoftheinversionalgorithmpresentedbyZhao(1991)and

    ;Zhaoeta1.(1992).Intheuppercrust,apositiveanomalyvelocityzoneexistsintheSichuanbasin,

    ;whereasanegativeanomalyvelocityzoneexistsinthewesternSiehuanplateau.Theboundarybetween

    ;thepositiveandnegativeanomalyzonesistheLongmenshanfaultzone.eimagesofthelowercrust

    ;anduppermantleintheLongmenshanfault,Xianshuihefault,RedRiverfaultandothersshowthebe.

    ;haviorofthetectonicboundary,indicatingthatthefaultsmayhavepenetratedtheMohodiscontinuity.

    ;Thenegativevelocityanomaliesatthedepthof50kmintheTengehongvolcanicareaandthePanxitec.

    ;toniczoneappeartobeassociatedwithtemperatureandcompositionvariationsintheuppermantle.

    ;SeismicsurfacewavedatahasalsobeenusedforinversionoftheSvelocitystructureofthecrust

    ;anduppermantleinChina(suchasSongeta1.,1992;Tengeta1.,1995). ;4.GLOBALGEoSCNCETRANSECrS

    ;TheGlobalGeoscienceTransect(GGT)ProiectisoneoftheimportantProject

sassociatedwith

    ;theInternationalLithosphereProgramthatwasinitiatedduringthelate1980’s.Thetransectconsists

    ;0fthefollowingmaps:(1)a100kmwidegeologicalcorridormap;(2)a100kinwideBouguergravity

    ;anomalycorridormapwithheatflowvaluesandearthquakeepicenterlocation;(3)anaeromagnetic

    ;anomaly(ATa)corridor;(4)asyntheticgeophysicalprofilewith2-DseismicP-wavevelocitystruc-

    ;tureandresistivitycurveofmagnetotelluricsoundingprofile;(5)ashallowgeologicalprofile;and(6)

    ;acomprehensiveinterpretativeCroSS.sectionofthecrustanduppermantleplussomeassociatedmaps.

    ;Itprovidestheverticaltectonicprofilesthatshowthestructure,composition,development,andevolu.

    ;tionofthecrustandthelithosphere.

    ;Sincethe1980’s,theChinesegeoscientistshavefinishedthecompilationof13GGT(Fig.5),

    ;suchasTransectYadong.Gormud(Wueta1.,1991),TransectXiangshui.Mandal(Maeta1.,

    ;1991),TransectDongUjimqin-Donggou(LuandXia,1993),TransectSuizhou-HarqinQi(Sunet

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