简介：DataobtainedbyGRACE(GravityRecoveryandClimateExperiment)havebeenusedtoinvertfortheseismicsourceparametersofmegathrustearthquakesundertheassumptionofeitheruniformslipoveranentirefaultorapoint-likeseismicsource.Herein,wefurtherextendtheinversionofGRACElong-wavelengthgravitychangestoheterogeneousslipdistributionsduringthe2011Tohokuearthquakeusingthreefaultmodels:(I)aconstant-strikeandconstant-dipfault,(II)avariabledipfault,and(III)arealisticallyvaryingstrikefault.Byremovingthepost-seismicsignalfromthetimeseries,andtakingtheeffectofoceanwaterredistributionintoaccount,weinvertforslipmodelsI,II,andIIIusingco-seismicgravitychangesmeasuredbyGRACE,de-stripedbyDDK3decorrelationfilter.Thetotalseismicmomentsofourslipmodels,withrespectivevaluesof4.9×1022Nm,5.1×1022Nm,and5.0×1022Nm,aresmallerthanthoseobtainedbyotherstudiesrelyingonGRACEdata.Theresultingcentroidsarealsolocatedatgreaterdepths(20km,19.8km,and17.4km,respectively).BycombiningonshoreGPS,GPS-Acoustic,andGRACEdata,weobtainajointlyinvertedslipmodelwithaseismicmomentof4.8×1022Nm,whichislargerthantheseismicmomentobtainedusingonlytheGPSdisplacements.Weshowthattheslipinvertedfromlowdegreespace-bornegravimetricdata,whichcontainsinformationattheoceanregion,isaffectedbythestrikeofthearcuatetrench.Thespace-bornegravimetricdatahelpusconstrainthesourceparametersofamegathrustearthquakewithintheframeofheterogeneousslipmodels.

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