Three-dimensional Q structure in Jiashi earthquake region of Xinjiang

(整期优先)网络出版时间:2001-06-16
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3-DS-waveQstructureinJiashiearthquakeregionisinvertedbasedontheattenuationofseismicwavesrecordedfromearthquakesinthisregionin1998bytheResearchCenterofExplorationGeophysics(RCEG),CSB,andaroughconfigurationofdeepcrustalfaultsintheearthquakeregionispresented.First,amplitudespectraofS-wavesareextractedfrom450carefully-chosenearthquakerecords,calledobservedamplitudespectra.Then,afterinstru-mentalandsiteeffectcorrection,theoreticalamplitudespectraaremadetofitobservedamplitudespectrawithnonlineardampedleast-squaresmethodtogettheobservedtraveltimeoverQ,providedthatearthquakesourcesconformtoBrune¢sdiskdislocationmodel.Finally,by3-Draytracingmethod,theoreticaltraveltimeoverQismadetofitobservedtraveltimeoverQwithnonlineardampedleast-squaresmethod.Inthecourseoffitting,thevelocitymodel,whichisobtainedby3-Dtraveltimetomography,remainsunchanged,whileonlyQmodelismodified.Whenfittingcametothegivenaccuracy,theultimateQmodelisobtained.TheresultshowsthatanNE-trendinglowQzoneexistsatthedepthsof10~18km,andanNW-trendinglowQzoneexistsatthedepthsof12~18km.TheseroughlycoincidewiththeNE-trendingandtheNW-trendinglowvelocityzonesrevealedbyotherscientists.ThedifferenceisthatthelowQzoneshaveawiderrangethanthelowvelocityzones.