简介：

简介：TheEmeishanlargeigneousprovince(hereafternamedbyitsacronymELIP)isthefirstacceptedlargeigneousregioninChina.Thecurrentstudytriestoreconstructthedensitystructureofthecrustinthisregion.Forthispurpose,weconductedthegravitysurveyalongan800-km-longprofile,whichstretchedlaterallyalongthelatitude27°NfromLijiang(Yunnanprovince)toGuiyang(Guizhouprovince).Thefieldworkincluded338gravitymeasurementsdistributedfromtheinnerzonetotheouterzoneofthemantleplumehead.Afteraseriesofgravityreductions,wecalculatedtheBouguergravityanomalyandthenconstructedthedensitymodelforELIPbyiterativeforwardmodelingfromaninitialdensitymodeltightlyconstrainedbywide-angleseismicreflectiondata.ThetopographyoftheMoho,herephysicallyinterpretedasadensitydiscontinuityof~0.4g·cm–3,graduallyrisesfromtheinnerzone(~50kmdeep)totheouterzone(~40km),describesathickercrustintheinnerzonethaninanyothersegmentoftheprofileandlargelyreproducestheshapeoftheBouguergravityanomalycurve.BoththeBouguergravityandthedensitystructureshowsignificantdifferenceswithrespecttotheinnerzoneandtheothertwozonesofELIPaccordingtothecommonlyacceptedpartitionoftheEmeishanarea.Athickeranddensermiddle-lowercrustseemstobethemainfeatureofthewesternsectionoftheprofile,whichislikelyrelatedtoitsmaficmagmaticcompositionduetomagmaticunderplatingofthePermianmantleplume.

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