Contemporary crustal tectonic movement in the southern Sichuan-Yunnan block based on dense GPS observation data

(整期优先)网络出版时间:2019-01-11
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Weanalyzed360permanentandcampaignGPSdatafrom1999to2017inthesouthernSichuan-Yunanblock,andobtainedcrustalhorizontaldeformationinthisregion.Then,wederivedthestrainrateusingamulti-scalesphericalwaveletmethod.ResultsrevealacomplexpatternoftectonicmovementinthesouthernSichuan-Yunnanblock.ComparedtothestableEurasianplate,themaximumrateofthehorizontaldeformationinthesouthernSichuan-Yunnanblockisapproximately22mm/a.TheXiaojiangfaultshowsasignificantlylowerdeformation—aleft-lateralstrike-slipmovementof9.5mm/a.TheHonghefaultclearlyshowsacomplexsegmentaldeformationfromthenorthtosouth.ThenorthernHonghefaultshows4.3mm/arightstrike-slipwith6.7mm/aextension;thesouthernHonghefaultshows1.9mm/arightstrike-slipwith1.9mm/aextension;thejunctionzoneintheHongheandLijiang–Xiaojinhefaultsshowsanobviousclockwise-rotationdeformation.Thestraincalculationresultsrevealthatthemaximumshear-strainrateinthisregionreaches70nstrain/a,concentratedaroundtheXiaojiangfaultandatthejunctionoftheHongheandLijiang–Xiaojinhefaults.Wenotethatmostoftheearthquakeswithmagnitudesof4andabovethatoccurredinthisregionwerewithinthehighshearstrain-ratezonesandthestrainrategradientboundaryzone,whichindicatesthatthemagnitudeofstrainaccumulationiscloselyrelatedtotheseismicactivities.Comparisonofthefastshear-wavepolarizationdirectionoftheupper-crustwiththeupper-mantleanisotropyandthedirectionofthesurfaceprincipalcompressivestrainrateobtainedfromtheinversionoftheGPSdatarevealsthatthedirectionofthesurfaceprincipalcompressivestrainisbasicallyconsistentwiththefastshear-wavepolarizationdirectionoftheuppercrustanisotropy,butdifferentfromthepolarizationdirectionoftheuppermantle.OurresultssupportthehypothesisthattheprincipalelementsofthedeformationmechanisminthesouthernSichuan-Yunnanblockaredeco