Crustal strain rates of southeastern Tibetan Plateau derived from GPS measurements and implications to lithospheric deformation of the Shan-Thai terrane

ThelinkbetweenthecrustaldeformationandmantlekinematicsintheTibetanPlateauhasbeenwellknownthankstodenseGPSmeasurementsandtherelativelydetailedanisotropystructureofthelithosphericmantle.However,whetherthecrustdeformscoherentlywiththeuppermantleintheShan-Thaiterrane(alsoknownastheShan-Thaiblock)remainsunclear.Inthisstudy,weinvestigatethedeformationpatternsthroughstrainratetensorsinthesoutheasternTibetanPlateauderivedfromthelatestGPSmeasurementsandfindthatintheShan-Thaiterranetheuppercrustmaybecoupledwiththelowercrustandtheuppermantle.TheGPS-derivedstrainratetensorsareinagreementwiththeslippingpatternsandratesofmajorstrike-slipfaultsintheregion.Themostprominentshearzone,whoseshearstrainratesarelargerthan100×10^–9a^–1,isabout1000-km-longinthewest,trendingnorthwardalongSagaingfaulttotheEasternHimalayanSyntaxisinthenorth,withmaximumrateofcompressivestrainupto–240×10^–9a^–1.AsecondaryshearzonealongtheAnninghe-XiaojiangFaultintheeastshowssegmentedshearzonesnearseveralconjunctions.WhilethestrainratealongRRFisrelativelylowduetothelowsliprateandlowseismicitythere,inLijiangandTengchongseverallocalshearzonesarepresentunderanextensionaldominatedstressregimethatisrelatedtonormalfaultingearthquakesandvolcanism,respectively.Furthermore,bycomparingGPS-derivedstrainratetensorswithearthquakefocalmechanisms,wefindthat75.8%(100outof132)oftheearthquakeT-axesareconsistentwiththeGPS-derivedstrainrates.Moreover,wefindthattheFastVelocityDirection(FVDs)atthreedepthsbeneaththeShan-Thaiterraneareconsistentwithextensionalstrainratewithgraduallyincreasingangulardifferences,whicharelikelyresultingfromthebasalshearforcesinducedbyasthenosphericflowassociatedwiththeobliquesubductionoftheIndiaplatebeneaththeShan-Thaiterrane.Therefore,inthisregiontheuppercrustd