简介：

简介：Oftheworld'soceans,thePacifichasthemostabundantdistributionofseamounttrails,oceanicplateausandhotspots,andhasthelongestfracturezones.However,littleisknownoftheirthermalstructuresduetodifficultiesofheatflowmeasurementandinterpretation,andininferringthermalanomaliesfromlow-resolutionseismicvelocities.Usingrecentlypublishedglobalmagneticmodels,wepresentthefirstindependentconstraintonPacificgeothermalstateandmantledynamics,byapplyingafractalmagnetizationinversionmodeltomagneticanomalydata.Warmthermalanomaliesareinferredforallknownactivehotspots,mostseamounttrails,somemajorfracturezones,andoceaniclithospherebetween~100and~140Mainage.WhilemostCuriepointsareamongtheshallowestinthezoneroughlyboundedbythe20Maisochrons,abnormallydeepCuriepointsarefoundalongnearlyallridgecrestsinthePacific,relatedtopatchy,long-wavelengthandlarge-amplitudemagneticanomaliesthataremostlikelycausedbyprevailingmagmaticorhydrothermalprocesses.ManylargecontrastsinthethermalevolutionbetweenthePacificandNorthAtlanticsupportmuchstrongerhydrothermalcirculationoccurringinPacificlithospheresyoungerthan~60Ma,whichmayhavedisguisedfromsurfaceheatflowanydeepthermalsignaturesofvolcanicstructures.Yet,atdepthsoftheCuriepoints,ourmodelarguesforwarmerPacificlithosphereforcrustalagesolderthan~15Ma,givenaslightlyhigherspatialcorrelationofmagnetizationinthePacificthanintheNorthAtlantic.

简介：

简介：

简介：Irregularsurfaceflattening,whichisbasedonaboundaryconforminggridandthetransformationbetweencurvilinearandCartesiancoordinatesystems,isamathematicalmethodthatcanelegantlyhandleirregularsurfaces,buthasbeenlimitedtoobtainingfirstarrivalsonly.Bycombiningamultistageschemewiththefast-sweepingmethod(FSM,themethodtoobtainfirst-arrivaltraveltimeincurvilinearcoordinates),thereflectedwavesfromacrustalinterfacecanbetracedinatopographicmodel,inwhichthereflectedwavefrontisobtainedbyreinitializingtraveltimesintheinterfaceforupwindbranches.Alocaltriangulationisappliedtomakeaconnectionbetweenvelocityandinterfacenodes.Thenajointinversionoffirst-arrivalandreflectiontraveltimesforimagingseismicvelocitystructuresincomplexterrainsispresented.Numericalexamplesallperformwellwithdifferentseismicvelocitymodels.Theincreasingtopographiccomplexityandevenuseofahighcurvaturereflectorinthesemodelsdemonstratethereliability,accuracyandrobustnessofthenewworkingscheme;checkerboardtestingillustratesthemethod’shighresolution.Noisetolerancetestingindicatesthemethod’sabilitytoyieldpracticaltraveltimetomography.Furtherdevelopmentofthemultistageschemewillallowotherlaterarrivalstobetracedandusedinthetraveltimeinversion.