Geology Applied to Civil Engineering 土木工程地質 英文課件 第一章 Overview of the earth

1OverviewoftheearthGeologyAppliedtoCivilEngineering123contentsExterioroftheEarthInteriorspheresoftheEarthShapeandsizeoftheEarth4ConstitutionsoftheEarth’scrust1ShapeandsizeoftheEarthAlthoughtheEarthlookslikeroundfromthesatellite,actuallytheEarthisanirregularspheroidsincetheEarth’sequatorialradiusislongerthanitspolarradius.TheaverageradiusoftheEarthis6371km.Theequatorialradiusisabout6378km,whilethepolarradiusis6356km.ThetotalsurfaceareaoftheEarthis5.1×108km2.Theareaofcontinentsis1.48×108km2andtheoceans’areais3.6×108km2.TheEarth’smassis5.976×1024kg,anditsvolumeis1.083×1021m3,sotheEarthhasanaveragedensityof5.518×103kg/m3.2ExterioroftheEarthTheEarth’sexteriorhasthreesphereswhichareatmosphere,hydrosphere,andbiosphere.2.1AtmosphereTheatmosphereisthegasesthatenvelopEarth.Themaincomponentsofatmospherearenitrogen,oxygen,argon,carbondioxide,watervapor,andothersmallamountsofgasesandparticles.Theproportionofeachgascompositionwithin100kmabovetheEarthsurfaceisstable.Accordingtotheflowcharacteristicsatdifferentheights,theatmosphereisdividedintofourlayers.TheatmospherefromEarthsurfaceto15kmiscalledtroposphere,whiletheatmosphereattheheightfrom15kmto50kmisthestratosphere.Fromthetopofthestratosphereto80~85km,theatmosphereiscalledmesosphere.Finally,theexosphereexitsabovethemesosphereto500km.Thestratospherecontainsalargeamountofozone,whichisabletopreventthemostofultravioletradiationfromthesun.Theinteractionbetweenatmosphereandhydrosphereresultsinahydrologicalcycle.Undertheheatofthesun,theseawaterevaporatestoformcloudswhichsubsequentlyrecyclesbacktotheEarthsurfaceasprecipitation.Theprecipitationusuallyformsrunoffandfinallygoesbacktotheocean.2.2HydrosphereThehydrosphereisthewateronornearEarth’ssurface,includingoceans,rivers,lakes,andglaciersoftheworld.Seawateraccountsfor97.3%,andsolid-statewaterattwopolesaccountsfor2.1%.Theremaining0.6%appearsinformsofrivers,lakesandundergroundwater.Seawatergenerallycontainsabout0.35%solublesalts,mostofwhichissodiumchloride(NaCl),thusseawaterisalkalescent.Themostdissolvedmatterintherainandriveriscalciumbicarbonate(CaHCO3),sotherainisweaklyacidic.

TheHydrosphereandtheupperpartofcrustoverlapslightly.Thisisbecausethattheundergroundwatercanflowintoseveral-kilometerdepthofthecrustthroughfracturesandthenisheatedbythegeothermalenergy.Afterthat,thehigh-temperatureundergroundwatercancomebacktotheEarthsurface.2.3BiosphereThebiospheredenotesthezonewherealllivingorganismsinhabitonEarth.ThebiosphereincludestheairspacefromtheEarthsurfaceto200mandthewaterspacewithinadepthof200m.Thebiogeologyprocessisevolvedthroughthemetabolismofallcreatures,whichinducesthealterationsofcomponentsandstructuresofmaterialsinthecrustalderm.Thecoal,petroleum,peatandhumusaregeneratedbythebiogeologyprocess.3InteriorspheresoftheEarthThesolidEarthismadeupofthreelayerswithdifferentmaterialsandindifferentstates,andthesethreelayersarecrust,mantleandcore.3.1CrustTheCrusthasanaveragethicknessof33km.Thethicknessofcontinentalcrustvariesfrom15to80km,whiletheoceaniccrustaverages7kminthicknessrangingfrom2to11km.Thecompositionsofcontinentalcrustandoceaniccrustarealsodifferent.Thedensityofcontinentalcrustaverages2.7to2.8g/cm3,whilethedensityofoceaniccrustis3to3.1g/cm3.Thecontinentalcrustishighlyvariableandcomplicated,consistingofacrystallinebasement,mainlycontaininggranite,otherplutonicrocks,gneisses,andschists.Rocksamplesacquiredfromtheseafloordemonstratethattheupperpartofoceaniccrustisbasaltandthelowerpartisgabbro.3.2MantleThemantleliesbelowthecrust,whichisathickshellseparatingthecrustabovefromthecorebelow.TheboundarythatseparatesthecrustfromthemantleiscalledtheMohodiscontinuity.AnotherboundarythatseparatesthemantlefromthecorebeneathiscalledtheGutenbergdiscontinuity.Themantlecanbedividedintothreezones:thelayerfromMohodiscontinuityto400kmindepthiscalledtheuppermantle;thelayerfrom400to670kmisatransitionlayer;thelayerfrom670to2891kmisthelowermantle.Localizedmagmachambersofmeltedrockmayappearlikeisolatedpocketsofliquidintheuppermantle,butmostofthemantleseemstobesolid.Theuppermantleiscomposedofsilicatemineralsmainlycontainingironandmagnesium,whichissimilartoultramaficrocksandcalledperidotite

layer.Withinthedepthfrom60to400kminthemantle,seismicwavestravelmoreslowlythantheydoinshallowerlayers,sothiszoneiscalledthelow-velocityzone.Especiallyatthedepthof100to150km,thevelocityofseismicwavesisthelowest,whichindicatesthatthiszoneisaliquidareawherethemagmaislikelytobegenerated.3.3CoreThecoreislocatedatthecenteroftheEarth,whichistheEarth’smagneticfieldsource.Theradiusofthecoreisabout3489km.Earth’scoreismadeofmetalratherthansilicaterock,whichisprobablyamixtureofironandnickel.Theoutercoreclosetothemantleismainlycomposedofliquidironandsomeothercomponents,including10%nickeland15%lightelements,suchassulfur,silicon,oxygen,kalium,andhydrogen.Theinnercoreismadeupofthesolidferronickelwithhighrigidity.4ConstitutionsoftheEarth’scrustThecrustanduppermostmantletogetherformthelithosphere,whichis