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Structure of the Earth TheThe Earth’sEarth’s StructureStructure fromfrom TravelTravel TimesTimes SphericallySpherically symmetricsymmetric structure:structure: PREMPREM --CCrustalrustal StructuStructurree --UUpperpper MantleMantle structustructurree PhasePhase transitiotransitionnss AnisotropyAnisotropy --LLowerower MantleMantle StructureStructure D”D” --SStructuretructure ofof thethe OuterOuter andand InnerInner CoreCore 3-3-DD StStructureructure ofof thethe MantleMantle fromfrom SeismicSeismic TomoTomoggrraphyaphy --UUpperpper mantlemantle -M-Miidd mmaannttllee -L-Loowweerr MMaannttllee Seismology and the Earth’s Deep Interior The Earth’s Structure SphericallySpherically SymmetricSymmetric StructureStructure ParametersParameters wwhhichich cancan bebe determineddetermined forfor aa referencereferencemodelmodel -P-P--wwaavvee v veeloloccitityy -S-S--wwaavvee v veeloloccitityy -D-Deennssitityy -A-Atttteennuuaattioionn ( (QQ)) --AAnisonisotropictropic parame parametersters -Bulk modulus K -Bulk modulus Kss --rrigidityigidity µ µ −−prepresssuresure - -ggravityravity Seismology and the Earth’s Deep Interior The Earth’s Structure PREM:PREM: velocitiesvelocities andand densitydensity PREMPREM:: PPreliminaryreliminary RReferenceeference EEartharth MMooddelel (Dziewonski(Dziewonski andand Anderson,Anderson, 1981)1981) Seismology and the Earth’s Deep Interior The Earth’s Structure PREM:PREM: AttenuationAttenuation PREMPREM:: PPreliminaryreliminary RReferenceeference EEartharth MMooddelel (Dziewonski(Dziewonski andand Anderson,Anderson, 1981)1981) Seismology and the Earth’s Deep Interior The Earth’s Structure Earth’sEarth’s RegionsRegions andand FractionalFractional MassMass Seismology and the Earth’s Deep Interior The Earth’s Structure TheThe Earth’sEarth’s Crust:Crust: TravelTravel TimesTimes ContinentaContinental l crustcrust (a)(a) andand oceanicoceanic crustcrust (b)(b) withwith correspocorresponndingding travel-timetravel-time cucurvesrves Seismology and the Earth’s Deep Interior The Earth’s Structure TheThe Earth’sEarth’s Crust:Crust: MineralsMinerals andand VelocitiesVelocities AverageAverage crustcrustaal l abundance,abundance, densitydensity andand seismicseismic velocitiesvelocities ofof majormajor crustalcrustal minerals.minerals. Seismology and the Earth’s Deep Interior The Earth’s Structure TheThe Earth’sEarth’s Crust:Crust: CrustalCrustal TypesTypes SS shields,shields, CC CaledonianCaledonian provinces,provinces, VV VaVariscanriscan provinces,provinces, RR rifts,rifts, OO orogensorogens Seismology and the Earth’s Deep Interior The Earth’s Structure TheThe Earth’sEarth’s Crust:Crust: RefractionRefraction StudiesStudies RefractionRefraction profilesprofiles acrossacross NorthNorth AmeriAmericca,a, (reduction(reduction velocityvelocity 6km/s)6km/s) allall thethe determinationdetermination ooff laterallateral velocityvelocity variations:variations: PmPPmP MohoMoho reflectionreflection PnPn MohoMoho refrefrractionaction PgPg directdirect crustalcrustal wavewave Seismology and the Earth’s Deep Interior The Earth’s Structure TheThe Earth’sEarth’s crust:crust: CrustalCrustal TypesTypes ReflectionReflection dadatata oftenoften showshow aa highlyhighly reflectivereflective lowerlower crust.Thcrust.Thisis maymay indicaindicattee finefine layeringlayering oror laminalamination,tion, somsomee transitiontransition fromfrom crustcrust toto upperupper mantle.mantle. TTWWTT two-two-wwaayy tratravveltieltimesmes Seismology and the Earth’s Deep Interior The Earth’s Structure TheThe Earth’sEarth’s crust:crust: CrustalCrustal TypesTypes RecentlyRecently compiledcompiled world-wideworld-wide crustalcrustal thicthicknesskness (km)(km) indicatesindicates cratoniccratonic areasareas andand mounmountaitainn rangesranges withwith activeactive tteectonicctonics.s. TheseThese datadata areare impimpoortanrtantt toto correctcorrect traveltravel timestimes regionally,regionally, i.e.i.e. calculatecalculate thethe contributioncontribution ofof crustalcrustal thicknessthickness toto aa teleseismicteleseismic travel-timtravel-timee perturbation.perturbation. Seismology and the Earth’s Deep Interior The Earth’s Structure TheThe Earth’sEarth’s crust:crust: CrustalCrustal TypesTypes Left:Left: CrustCrust P-velocityP-velocity profilesprofiles forfor yyooungung (<20(<20 millionmillion year)year) oceanicoceanic basinbasin structures.structures. Right:Right: CrustalCrustal PP andand SS velocitiesvelocities forfor oceanicoceanic regionsregions olderolder thanthan 2020 millionmillion years.years. Seismology and the Earth’s Deep Interior The Earth’s Structure TheThe Earth’sEarth’s UpperUpper Mantle:Mantle: AthenosphereAthenosphere TheThe high-velocityhigh-velocity lidlid aboveabove thethe lowlow velocityvelocity zonezone ((asthenosphere)asthenosphere) isis calledcalled thethe lithospherelithosphere.. TheThe upper-mantleupper-mantle velocityvelocity structurestructure leadsleads toto complexcomplex rayray paths.paths. Seismology and the Earth’s Deep Interior The Earth’s Structure UpperUpper Mantle:Mantle: PhasePhase transitionstransitions UpperUpper mantlemantle discontinuitiesdiscontinuities (e.g.(e.g. 410km)410km) areare causedcaused byby phaphassee transitiotransitionnss (left:(left: lowlow pressurepressure olivine,olivine, right:right: highhigh prespressuresure ββ-- spinel)spinel) VariousVarious upperupper mantlemantle seismicseismic momodelsdels andand experimentalexperimental resultsresults forfor mineralsminerals andand mineralmineral assemassembblages.lages. Seismology and the Earth’s Deep Interior The Earth’s Structure UpperUpper Mantle:Mantle: DiscontinuitiesDiscontinuities VariousVarious reflectionreflectionss fromfrom upperupper mantlemantle discontinuitiesdiscontinuities areare beingbeing uusseded toto investigateinvestigate thethe structuralstructural detailsdetails ofof thethe transitiontransition zoneszones (e.g.(e.g. verticalvertical gradients,gradients, thicknessthickness ooff transitiontransition zone,zone, totopographypography ooff discontinuities,discontinuities, etc.)etc.) Seismology and the Earth’s Deep Interior The Earth’s Structure UpperUpper Mantle:Mantle: PhasePhase transitionstransitions TheThe locatiolocationn ofof seismicseismic sourcesource withinwithin highhigh velocityvelocity anomaliesanomalies indicaindicatteses downgoingdowngoing slabslab structures.structures. WhereWhere dodo earthquakesearthquakes seemseem toto haphapppenen preferentiapreferentiallylly?? Seismology and the Earth’s Deep Interior The Earth’s Structure UpperUpper Mantle:Mantle: SubductionSubduction ZonesZones ShearShear wavewave splittingsplitting ofof thethe SKSSKS phasephase indicaindicatteses seismicseismic anisoanisottroropypy inin thethe upperupper mantle.mantle. TheThe alignmentalignment ofof thethe anisoanisottroropicpic symmetrysymmetry systemsystem isis thoughthoughtt toto bebe correlatedcorrelated witwithh tectonictectonic plateplate momotion.tion. Seismology and the Earth’s Deep Interior The Earth’s Structure LowerLower Mantle:Mantle: D”D” TheThe mid-mantlemid-mantle showsshows littlelittle laterallateral heteheterogrogeenneeity.ity. TheThe lowloweermostrmost mantlemantle (D”)(D”) hasthast strongstrong (possibly(possibly >10%)>10%) laterallateral velocivelocityty perturbatioperturbationns.s. TheThe maymay originateoriginate inin aa thermalthermal boundaryboundary layerlayer oror frfromom subductedsubducted litholithossphere.phere. Seismology and the Earth’s Deep Interior The Earth’s Structure LowerLower Mantle:Mantle: DiffractedDiffracted WavesWaves TheThe lowloweermostrmost mantlemantle structurestructure cancan bebe studiesstudies usingusing waveswaves diffracteddiffracted atat ththee core-mantlecore-mantle boundary.boundary. Seismology and the Earth’s Deep Interior The Earth’s Structure TheThe Earth’sEarth’s CoreCore TheThe Earth’sEarth’s innerinner corecore showsshows considerableconsiderable anisoanisottroropy.py. Time-Time- dependentdependent differentiadifferential l traveltravel timestimes havehave ledled toto thethe speculationspeculation thathatt ththee Earth’sEarth’s innerinner corecore isis rotatingrotating fasterfaster thanthan thethe mantle.mantle. Seismology and the Earth’s Deep Interior The Earth’s Structure TheThe Earth’sEarth’s Core:Core: MultiplesMultiples MultipleMultiple reflectionreflection ray paths PK P in ray paths PKnnP in thethe outerouter corecore andand recordingrecording ofof PK P from an PK44P from an undergroundunderground nuclearnuclear exploexplossion.ion. Seismology and the Earth’s Deep Interior The Earth’s Structure UpperUpper mantle:mantle: 3-D3-D structurestructure Seismology and the Earth’s Deep Interior The Earth’s Structure Mid-mantle:Mid-mantle: 3-D3-D structurestructure Seismology and the Earth’s Deep Interior The Earth’s Structure LowerLower Mantle:Mantle: 3-D3-D structurestructure Seismology and the Earth’s Deep Interior The Earth’s Structure GlobalGlobal Cut:Cut: 3-D3-D structurestructure Seismology and the Earth’s Deep Interior The Earth’s Structure GeodynamicGeodynamic Modelling:Modelling: SubductionSubduction ZonesZones PerturbatioPerturbationn ofof seismicseismic velocityvelocity andand densitydensity forfor aa subductingsubducting plaplattee obtainedobtained fromfrom numericalnumerical convectionconvection momodellingdelling includingincluding phaphassee transitions.transitions. Seismology and the Earth’s Deep Interior The Earth’s Structure GeodynamicGeodynamic Modelling:Modelling: SubductionSubduction ZonesZones SnapshSnapshotsots throughthrough subductingsubducting slabslab momodeldel andand thethe wavefieldwavefield
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