Dynamics of Earth's Deep Interior and Earth Rotation

194 Pages·15.408 MB·English

Geophysical Monograph Series
Including
IUGG Volumes
Maurice Ewing Volumes
Mineral Physics Volumes
GEOPHYSICAL MONOGRAPH SERIES
Geophysical Monograph Volumes 21 Quantitative Modeling of Magnetospheric
Processes W. P. Olson (Ed.)
1 Antarctica in the International Geophysical 22 Derivation,Meaning,andUseofGeomagnetic
Year A.P. Crary, L. M. Gould, E. O. Hulburt, Indices P. N. Mayaud
Hugh Odishaw, and Waldo E. Smith(Eds.) 23 TheTectonicandGeologicEvolutionof
2 Geophysics and the IGY Hugh Odishawand SoutheastAsianSeasandIslands DennisE.
StanleyRuttenberg(Eds.) Hayes (Ed.)
3 Atmospheric Chemistryof Chlorine and Sulfur 24 MechanicalBehaviorofCrustalRocks:The
Compounds James P. Lodge,Jr. (Ed.) HandinVolume N. L. Carter, M. Friedman,
4 Contemporary Geodesy Charles A. Whittenand J. M. Logan,and D. W. Stearns (Eds.)
KennethH. Drummond(Eds.) 25 PhysicsofAuroralArcFormation S.-I. Akasofu
5 Physics ofPrecipitation Helmut Weickmann andJ. R. Kan (Eds.)
(Ed.) 26 HeterogeneousAtmosphericChemistry David
6 TheCrustofthe Pacific Basin Gordon A. R. Schryer(Ed.)
Macdonald and Hisashi Kuno(Eds.) 27 TheTectonicandGeologicEvolutionof
7 Antarctica Research: The Matthew Fontaine SoutheastAsianSeasandIslands:Part
Maury Memorial Symposium H. Wexler,M. J. 2 Dennis E. Hayes (Ed.)
Rubin,and]. E. Caskey, Jr. (Eds.) 28 MagnetosphericCurrents ThomasA.Potemra
8 Terrestrial HeatFlow WilliamH. K. Lee(Ed.) (Ed.)
9 Gravity Anomalies: Unsurveyed Areas Hyman 29 QimateProcessesandQimateSensitivity
Orlin (Ed.) (MauriceEwingVolume5) James E. Hansen and
10 The Earth Beneath the Continents: A Volume of Taro Takahashi (Eds.)
Geophysical Studiesin Honorof Merle A. 30 MagneticReconnectioninSpaceandLaboratory
Tuve John S. Steinhart and T. Jefferson Smith Plasmas Edward W. Hones, Jr. (Ed.)
(Eds.) 31 PointDefectsinMinerals(MineralPhysics
11 Isotope Techniques in the Hydrologic Volume1) Robert N. Schock(Ed.)
Cycle Glenn E. Stout(Ed.) 32 TheCarbonCycleandAtmosphericCO2:
12 The Crust and UpperMantle ofthe Pacific NaturalVariationsArcheantoPresent E. T.
Area LeonKnopoff,Charles L. Drake, and Sundquistand W. S. Broecker(Eds.)
PembrokeJ. Hart (Eds.) 33 GreenlandIceCore: Geophysics, Geochemistry,
13 The Earth's Crust and Upper Mantle Pembroke andtheEnvironment C. C. Langway, Jr., H.
J. Hart (Ed.) Oeschger, and W. Dansgaard (Eds.)
14 The Structure and Physical Properties ofthe 34 CollisionlessShocksintheHeliosphere:A
Earth's Crust John G. Heacock (Ed.) TutorialReview RobertG. Stoneand BruceT.
15 The Use ofArtificial Satellites for Tsurutani (Eds.)
Geodesy Soren W. Henricksen, ArmandoMancini, 35 CollisionlessShocksintheHeliosphere:Reviewsof
and Bernard H. Chovitz(Eds.) CurrentResearch BruceT. Tsurutani and RobertG.
16 Flow and Fracture of Rocks H. C. Heard, I. Y. Stone(Eds.)
Borg, N. L. Carter, and C. B. Raleigh (Eds.) 36 MineralandRockDeformation: Laboratory
17 Man-Made Lakes: TheirProblems and Studie&-ThePatersonVolume B. E. Hobbs
Environmental Effects WilliamC. Ackermann, andH. C. Heard (Eds.)
Gilbert F. White,and E. B. Worthington (Eds.) 37 EarthquakeSourceMechanics(MauriceEwing
18 The UpperAtmosphere in Motion: A Selection Volume6) Shamita Das, John Boatwright,and
ofPapersWith Annotation C. O. Hines and Christopher H. Scholz(Eds.)
Colleagues 38 IonAccelerationintheMagnetosphereand
19 The Geophysics ofthe Pacific Ocean Basin and Ionosphere TomChang (Ed.)
Its Margin: A Volume in Honorof George P. 39 HighPressureResearchinMineralPhysics
Woollard George H. Sutton, Murli H. Manghnani, (MineralPhysicsVolume2) MurliH.
and RalphMoberly(Eds.) Manghnani and YasuhikoSyono(Eds.)
20 The Earth's Crust: Its Nature and Physical 40 GondwanaSix: StructureTectonics,and
Properties John C. Heacock (Ed.) Geophysics Gary D. McKenzie(Ed.)
41 GondwanaSix:Stratigraphy,Sedimentology, 62 ModelingMagnetosphericPlasmaProcesses
andPaleontology Garry D. McKenzie(Ed.) Gordon K. Wilson(Ed.)
42 FlowandTransportThroughUnsaturated 63 MarineParticlesAnalysisandCharacterization
FracturedRock Daniel D. Evansand ThomasJ. DavidC. Hurdand DerekW. Spencer(Eds.)
Nicholson(Eds.) 64 MagnetosphericSubstorms Joseph R. Kan,
43 Seamounts,Islands,andAtolls Barbara H. Thomas A.Potemra, SusumuKokubun,and
Keating, Patricia Fryer, RodeyBatiza,and George TakesiIijima(Eds.)
W. Boeh1ert(Eds.) 65 ExplosionSourcePhenomenology StevenR. Taylor,
44 ModelingMagnetosphericPlasma T. E. Moore HO'WaT'dJ. Patton, andPaul G. Richards (Eds.)
andJ. H. Waite,Jr. (Eds.) 66 VenusandMars:Atmospheres,Ionospheres, and
45 Perovskite:A StructureofGreatInterestto SolarWindInteractions Janet G. Luhmann,Mariella
GeophysicsandMaterialsScience Alexandra Tatrallyay, andRobertO. Pepin (Eds.)
Navrotskyand DonaldJ. Weidner(Eds.) 67 High-PressureResearch:ApplicationtoEarthand
46 StructureandDynamicsofEarth'sDeep PlanetarySciences(MineralPhysicsVolume3)
Interior(IUGGVolume1) D. E. Smylieand YasuhikoSyonoandMurliH. Manghnani (Eds.)
RaymondHide(Eds.) 68 MicrowaveRemoteSensingofSeaIce Frank
47 HydrologicalRegimesandTheirSubsurface Carsey, RogerBarry, JosefinoComiso, D. Andrew
ThermalEffects(IUGGVolume2) AlanE. Rothrock,RobertShuchman, W. TerryTucker, Wilford
Beck,Grant Garven, and1.Jljos Stegena(Eds.) Weeks,and DaleWinebrenner
48 OriginandEvolutionofSedimentaryBasins 69 SeaLevelChanges:DeterminationandEffects
andTheirEnergyandMineralReSOW'Ces (IUGGVolumeII) P. L. Woodworth,D. T. Pugh,
(IUGGVolume3) RaymondA.Price (Ed.) J. G. DeRonde,R. G. Warrick, andJ. Hannah
49 SlowDeformationandTransmissionofStress 70 SynthesisofResultsfromScientificDrillinginthe
intheEarth(IUGGVolume"4) StevenC. Cohen IndianOcean RobertA.Duncan, DavidK. Rea, Robert
and Petr VanfCek(Eds.) B.Kidd, Ulrich vonRad, andJeffreyK. Weisset(Eds.)
SO DeepStructureandPastKinematicsof 71 MantleFlowandMeltGenerationatMid-ocean
AccretedTerranes(IUGGVolume5) John W. Ridges Jason PhippsMorgan, Donna K. Blackman,
Hillhouse(Ed.) andJohn M. Sinton(Eds.)
51 PropertiesandProcessesofEarth'sLowerCrust
(IUGGVolume6) RobertF. Mereu, Stephan
Mueller, and DavidM. Fountain (Eds.)
52 UnderstandingClimateChange(IUGGVolume
7) AndreL. Berger, RobertE. Dickinson,andJ. Kidson
(Eds.)
53 PlasmaWavesand"lstabilitiesatCometsandin
Magnetospheres BruceT. TsurutaniandHiroshi
Oya (Eds.)
MauriceEwingVolumes
54 SolarSystemPlasmaPhysics J. H. Waite,Jr.,
].L. Burch,andR. L. Moore(Eds.) 1 IslandArcs, DeepSeaTrenches,andBack-Arc
55 AspectsofClimateVariabilityinthePacific Basins ManikTalwaniand WalterC. Pitman III
andWesternAmericas DavidH. Peterson (Ed.) (Eds.)
56 TheBrittle-DuctileTransitioninRocks A. G. 2 DeepDrillingResultsintheAtlanticOcean:
Duba, W. B. Durham, J. W. Handin, andH. F. OceanCrust ManikTalwani, Christopher G.
Wang(Eds.) Harrison, and DennisE. Hayes (Eds.)
57 EvolutionofMidOceanRidges"(IUGGVolume 3 DeepDrillingResultsintheAtlanticOcean:
8) John M. Sinton(Ed.) ContinentalMarginsandPaleoenvironment
58 PhysicsofMagneticFluxRopes C. T. Russell, ManikTalwani, WilliamHay, and WilliamB. F.
E. R. Priest, and L. C. Lee(Eds.) Ryan(Eds.)
59 VariationsinEarthRotation(IUGGVolume 4 EarthquakePrediction-AnInternational
9) Dennis D. McCarthyand WilliamsE. Carter Review David W. Simpsonand Paul G. Richards
(Eds.) (Eds.)
60 QuoVadimusGeophysksfortheNext 5 ClimateProcessesandClimate
Generation (IUGGVolume10) George D. Sensitivity James E. Hansen and Taro Takahashi
Garland andJohn R. Apel(Eds.) (Eds.)
61 CometaryPlasmaProcesses AlanD. 6 EarthquakeSourceMechanics Shamita Das, John
Johnstone (Ed.) Boatwright,andChristopher H. Scholz(Eds.)
9 VariationsinEarthRotation Dennis D. Mc
IUGGVolumes
Carthyand WilliamE. Carter (EdsJ
1 StructureandDynamicsofEarth'sDeep 10 QuoVadimusGeophysicsfortheNextGenera
Interior D. E. Smylieand RaymondHide(EdsJ tion George D. Garland andJohn R. Apel(Eds.)
2 HydrologicalRegimesandTheirSubsurface
11 SeaLevelChanges:DeterminationsandEffects
ThermalEffects AlanE. Beck,Grant Garven, P. L. Woodworth,D. T. Pugh, J. G. DeRonde,
and 1.Jljos Stegena(EdsJ R. G. Warrick, andJ. Hannah (EdsJ
3 OriginandEvolutionofSedimentaryBasins
andTheirEnergyandMineral
Resources RaymondA. Price (Ed.)
4 SlowDeformationandTransmissionofStress
intheEarth StevenC. Cohenand Petr VaniCek
(EdsJ
5 DeepStructureandPastKinematicsof
MineralPhysicsVolumes
AccretedTerrances John W. Hillhouse(Ed.)
1 PointDefectsinMinerals RobertN. Schock
6 PropertiesandProcessesofEarth'sLower
(Ed.)
Crust Robert F. Mereu, StephanMueller, and
David M. Fountain (EdsJ 2 HighPressureResearchinMineralPhysics
7 UnderstandingQimateChange AndreL. MurliH. Manghnani and YasuhikoSyona(Eds.)
Berger, RobertE. Dickinson,andJ. Kidson(EdsJ 3 HighPressureResearch:ApplicationtoEarth
8 EvolutionofMidOceanRidges John M. andPlanetarySciences YasuhikoSyonoand
Sinton(Ed.) MurliH. Manghnani (EdsJ
Geophysical Monograph 72
IUGG Volume 12
Dynatnics of Earth's Deep Interior
and Earth Rotation
J.-L. Le Mouel
D.E. Smylie
T. Herring
Editors
~
American Geophysical Union
ei1
International Union of Geodesy and Geophysics
Published under the aegis of the AGU Books Board
LibraryofCongressCataloging-in-PublicatioRData
Dynamicsofearth'sdeepinteriorandearthrotation/J.-L. LeMouel, D.E. Smylie,
T. Herring, editors.
p. em. - (Geophysicalmonograph: 72)
ISBN0-87590-463-7
1. Earth-Core. 2. Earth-Mantle. 3. Geodynamics. I. LeMouel,
J. L. II. Smylie, D. E. III. Herring, T. (Thomas) IV. Series.
QE509.D87 1993
551.1'12-dc20 93-7784
CIP
ISSN 0065-8448
ISBN 087590-463-7
Copyright1993bytheInternationalUnionofGeodesyandGeophysicsandtheAmericanGeophys
icalUnion,2000FloridaAvenue,NW,Washington,DC20009, U.S.A.
Figures, tables, and short excerpts may be reprinted in scientificbooks and journals if the
sourceisproperlycited.
Authorizationtophotocopyitemsforinternalorpersonaluse,ortheinternalorpersonaluseof
specific clients, is granted by the American Geophysical Union for libraries and other users
registeredwiththeCopyrightClearanceCenter(CCC)TransactionalReportingService,provided
thatthebasefeeof$1.00percopyplus$0.10perpageispaiddirectlytoCCC,21CongressStreet,
Salem,MA10970.0065-8448/93/$01. + .10.
This consent does not extend to otherkinds ofcopying, such as copyingfor creating new
collectiveworksorforresale.Thereproductionofmultiplecopiesandtheuseoffullarticlesorthe
use ofextracts, includingfigures and tables, for commercialpurposesrequirespermissionfrom
AGU.
PrintedintheUnitedStatesofAmerica.
CONTENTS
Preface
J.-L. LeMouel, D. E. Smylie,T. Herring ix
Foreword
HelmutMoritz xi
1 CoreDynamics and Surface Gravity Changes
Jacques Hinderer and DavidCrossley 1
2 ASearchfor EvidenceofShortPeriodPolarMotioninVLBIandSupergravimetry Observations
KeithD. Aldridgeand W. H. Cannon 17
3 IDA Tidal Dataand the Earth's Nearly DiurnalFree Wobble
Phil R. Cumminsand John M. Wahr 25
4. Inner CoreMotions: ImplicationsonEarthRotation
AnthonyM. K. Szeto 31
5 New Analysis ofthe Superconducting GravimeterDataofBrussels
V.Dehant, B. Ducarme andP. D. Defraigne 35
6 VariationofJ2 and Internal Loads
Marianne Lefftzand Hilaire Legros 45
7 AGeneralized 'Core Resonance' Phenomenon: Inferencesfrom a Poincare CoreModel
L. Ian Lumb,KeithD. Aldridgeand Gary A.Henderson 51
8 Analytical ComputationofModes Using Boundary-LayerTheory
K. Degryse and V.Dehant 69
9 Numerical CalculationofModesofOscillationoftheEarth's Core
D. E. Smylieand Xianhua Jiang 81
10 AComparativeAnalysis ofSuperconductingGravimeterData
D. E. Smylie,Jacques Hinderer, BerndRichter, Bernard Ducarme and Lalu Mansinha 91
11 Time-DependentFlowattheCoreSurfaceandConservationofAngularMomentumintheCoupled
Core-Mantle System
AndrewJackson, Jeremy Bloxhamand DavidGubbins 97
12 Angular MomentumTransfer between the Earth's Core andMantle
RaymondHide 109
13 GeomagneticEstimatesofSteadySurficialCoreFlowandFluxDiffusion: UnexpectedGeodynamo
Experiments
Coerte V. Voorhies 113
14 Degree OneHeterogeneity atthe Topofthe Earth's Core, Revealedby SmKS Travel Times
Satoru Tanaka and HiroyukiHamaguchi 127
15 AsphericalStructureofthe Mantle, TectonicPlateMotions, Nonhydrostatic Geoid, and
Topography ofthe Core-MantleBoundary
Alessandro M. Forte, AdamM. DziewonskiandRobertL. Woodward 135
16 ConstraintsonMantle StructurefromSeismologicaland ConvectionResults
Philippe Machetel 167
17 Constraintson the Temperature and Composition ofthe Baseofthe Mantle
Michael E. Wysession,Craig R. Bina and EmileA.Okal 181
PREFACE
The study ofthe Earth's deep interior is the object ofa more interest is being paid to the motions ofthe solid inner
spectacular development due both to new techniques of core, the torques which act on it, and the effect of these
observation (including very long baseline interferometry and motionsonEarthrotation.Muchattentionisalsodevotedtothe
superoonductinggravimeters)andto progressintheoryspuned computation of the core modes and of their period (theory
by new computing capability. Stimulated by the international leading observationandguidingit). Differentmodels ofEarth
SEDI group, founded in 1986, geophysicists from different areconsidered,rotatingornotrotating,anddifferenttechniques
disciplines-Earthdynamicists, seismologists,geomagneticians, ofcomputation,eithernumericaloranalytical,areused,leading
mineralphysicists--begantocooperateandintegratemorefully to somewhat different results. The triplet of periods of the
one another's work. SEDI meetings favor and promote those translational modes computed for a rotating Earth, in the
closecontactsandcooperation.Greateffortswillstillbeneeded subseismic approximation, seems to becompltiblewith peaks
beforeall the disciplinary divisions dissolve-ifthey everdo- 1dentifiedinthesignalofthesuperconductinggravimeters.This
but things are clearly improving, as shown by this AGU exciting suggestion probably needs more work:, both
monograph. We think indeed that this volume is a good, obselVational and theoretical. The tidal forcing ofcore modes
although incomplete, illustration ofthe situation as described is further examined, including the now well-established
above and that it is a benchmark: in the exciting story ofthe enhancement ofthe gravimetric factor due to existenceofthe
progressinknowledge ofthe deepinteriorofourplanet. nearly diurnal free wobble. Another point of interest is the
More than half the papers in this volwne concern the temporal variation of the degree 2 zonal tenn, J2, of the
dynamics ofthecoreandrotation oftheEarth. Interestinthis terrestrial gravity potential; generally attributed to relaxation
topic has, of course, been renewed and enhanced by the from the removal of external loads, such as that due to
introductionofhigh-sensitivitysuperoonductinggravimetenand deglaciation.Itcouldalsoresultfromintemalloadslocated,for
newtechniques formeasuringEarthrotation, especiallyVLBI. example,attheooro-mantleboundary(CMB).Otherpapersare
One ofthe f11'8t results coming from these new data was the devoted to the core flow, which could balance the decade
12.9-hour peak in the oldest series, the BlUSsels one. A new variationsofthelengthoftheday.Itseemsthatparticularzonal
analysis oftheseriesconfinns theexistenceofthepeak,butit motions which extend through the whole core but can be
seems to bedueto aregionaleffectnotyet takenintoaccount detennined from the flow at the CMB derived from
in thetidalresidues ratherthanbeingthegravimetricsignal.of geomagnetic secular variation data have the right temporal
a core mode. In fact, a comparison of the existing records behavior and order of magnitude to conserve the angular
makes it clear that a stacking of signals coming from a momentum ofthe core-mantle system. The required coupling
worldwide array ofstations, overa common periodofseveral mechanism between the core and the mantle could be
years,willbenecessarytodetectgeodynamicalsignalsfromthe topographic, due to interaction between the flowat the topof
coresafely. Butrightnow, existinggravity data from the IDA thecoreandabumpyCMB.This mechanism, andparticularly
arraycan beusedto detenninetheperiodofthenearly diurnal thecomputationoftheflowatthetopofthecore,probablystill
free wobble and the corresponding quality factor Q. These needs furtherwork.
valuescanbecomparedwiththosederivedfromVLBInutation A topic which has attracted much attention and is
measurements; a significant discreplncy appears in the values progressing rapidly is seismic imaging of the aspherical
of Q, which could be due to an inaccurate ocean loading stIUcture of the mantle, the core-mantle boundary, and the
conection in tidal studies. Other comparisons of VLBI and uppennostlayersofthecore.Ofparticularinterestisitsrelation
gmvity data, theoretically equivalent, can be perfonned when to convection in the Earth. Forexample, a flow model in the
searching for short-period components of the polar motion; viscous mantle can be derived from the computed density
encoumgingagreementhasbeenobserved,althoughtheresults heterogeneities,andthetopographyoftheCMBinducedbythis
areclosetothelimitofresolution.Atthesametime,whiledata flowcanbe inferred.This flow-inducedtopographyappearsto
acquisitionandanalysisareimproving,theoreticalstudiesofthe be in fair agreement with previous models of topography
dynamicsofthecorearebeingvigorouslydevelopedMoreand derived from PcP and PKP travel times. Lateral velocity
ix
X PRBFACB
heterogeneities in the outennost 200 Ian ofthe core are now predominant influence. Numerical modeling predicts chaotic
investigated using SmKS travel times; a dominant degree 1 behavior for the mixing mte of the upper and lower mantle,
patternappears. although this depends strongly on the Clapeyron slopeofthe
Many important problems related to the strocture and phase tl'ansfonnation at 670 kIn. If this is the case, then the
composition of the mantle core are still unsolved. Is mantle mantleislikelytobe layeredorintennittentlylayered
convectiontwo-layeredorwhole?WhatisthenatureoftheD" Resolutionoftheissues raisedinthis volumewillclearly
layer and the temperature at the base of the mantle? depend on the interdisciplinary collaborations that SBDI has
Seismology, numerical simulations, and mineral physics data been so successfulin stimulating.
are thetools to approachtheseproblems. DiffractionofP and
S waves around the CMB reveals heterogeneities in the J. L. Le Mouel
velocitiesintheD"layerofafewpercent.Whenestimatingthe D. B. Smylie
seismic velocity changes that could be due to changes in T. A. Hetring
tempemture or composition, it tums out that the latter has a Editors