简介：TheX-discontinuity,whichappearsatthedepthofapproximately300km,isanimportantseismicinterfacewithpositivevelocitycontrastsintheuppermantle.Detectingitspresenceandtopographycanbeusefultounderstandphasetransformationsofrelevantmantlemineralsunderthehigh-temperatureandhigh-pressurecircumstanceoftheEarth'sinterior.Inthisstudy,wedetecttheX-discontinuitybeneaththeRyukyusubductionzoneusingfiveintermediate-deptheventsrecordedbythedenseAlaskaRegionalNetwork(AK).TheX-discontinuityissuccessfullyrevealedfromtherobustslantstackingofthesecondarydown-goingandconvertingSdPphases.Fromthedepthdistributionofconversionpoints,wefindthattheX-discontinuity'sdepthrangesbetween269kmand313km,withanaveragedepthof295km.Alltheconversionpointsarelocatedbeneaththedown-dippingsideofthePhilippineSeaslab.Fromenergycomparisonsinvespagramsforobservedandsyntheticseismograms,thestrongconvertedenergyismorelikelyfromathinhigh-velocitylayer,andtheS-wavevelocityjumpsacrosstheX-discontinuityareupto5%to8%withanaverageof6.0%.Accordingtopreviouspetrologicalandseismologicalstudies,theX-discontinuitywedetectedcanbeinterpretedasthephasetransformationofcoesitetostishoviteineclogiticmaterialswithintheoceaniccrust.

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