简介：

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简介：UsingGPSobservationsofhorizontalmovementfrom2001to2003andthecross-faultmobileshort-levellingdataof1988～2003,andwiththeaidoftheimprovednegativedislocationmodelandthetime-varyingcurveofstrainintensityratiooffaultdeformation,theregionaltectonicdeformationbackgroundandmedium-andshort-termprecursorsrelatedtothepreparationoftheMinle-ShandanearthquakesofMs6.1andMs5.8onOctober25,2003areinvestigated.Theresultsrevealthat,underthebackgroundofthewide-rangedeformationadjustment,short-termrelaxationandrecoverycausedbytheKuulunMountainsearthquakeofMsS.1,thehypocentersoftheearthquakesarelocatedonthenorthedgeoftheshearstressenhancementzonebetweenthecompressionallockedsegmentsofblockboundaryfault,aplacewhichmayrepresentanacceleratedstrainaccumulation.Anobviousanomalyofstrainintensityratioappearedinshort-levellingmeasurementscrossingoverthefaultattheShihuiyaokousite,theclosesttotheepicenters,3monthsbeforetheoccurrenceoftheearthquakes.Inaddition,thevariationinnumberofanomaliesfrom10-odddaystomonthsbeforetheearthquakesintheentiremonitoringareaandtheanomalyconcentrationandlocalenhancementrelativetonearsourceinthe3monthsbeforetheearthquakesareregardedtobeprecursorstothetwoevents.

简介：Basedonpreviousresearchresults,present-daycrustaldeformationandgravityfieldsintheChinesemainlandareanalyzedusingtheGPSdata,leveling,gravityandcross-faultdeformations.Weanalyzedstrainaccumulationofthemajorfaults,andidentifiedlockedorhighstrainaccumulationsegments.Combiningtheeffectsoflargeearthquakesinthestudyarea,thelong-term(decade)probabilityoflargeearthquakesintheChinesemainlandisestimated.

简介：Inthispaperwepresentacomparativeanalysisofglobalfrequencyandlocaldeformationdataforalargeconcretebridge.Theasymptoticprobabilitydistributionsofthecentralstatisticsarepresented,andcomparedwithempiricalbootstrapestimates.Bootstrappeddistributionsarecalculatedfromreferencedataobtainedduring1999-2000andusedtodevelopchange-pointalarmcriteriaforthestructure,usingreasonablesensitivitymeasuresdevelopedfromFEMsimulationsandstructuralanalysis.Theimplicationsofthefrequencydataarediscussedinconjunctionwiththestrainanddisplacementmeasurementsinordertodiscerniftheloadcarryingcapacityofthebridgehasbeenaffected.Thecriticalneedformoreadvancedtemperaturecompensationmodelsforlargestructurescontinuallyinthermaldisequilibriumisdiscussed.

简介：Significantpostseismicdeformationofthe2008MW7.9WenchuanearthquakehasbeenobservedfromGPSdataofthefirst14daysaftertheearthquake.Thepossiblemechanismsfortherapidpostseismicdeformationareassumedtobeafterslipontheearthquakeruptureplaneandviscoelasticrelaxationofcoseismicllystresschangeinthelowercrustoruppermantle.WefirstlyusetheconstrainedleastsquaresmethodtofindanafterslipmodelwhichcanfittheGPSdatabest.Theafterslipmodelcanexplainnear-fielddataverywellbutshowsconsiderablediscrepanciesinfittingfar-fielddata.Toestimatetheeffectduetotheviscoelasticrelaxationinthelowercrust,wethenignorethecontributionfromtheafterslipandattempttoinverttheviscositystructurebeneaththeLongmenshanfaultwheretheWenchuanearthquakeoccurredfromthepostseismicdeformationdata.Forthispurpose,weuseaviscoelasticmodelwitha2DgeometrybasedonthegeologicalandseismologicalobservationsandthecoseismicslipdistributionderivedfromthecoseismicGPSandInSARdata.Bymeansofagridsearchwefindthattheoptimumviscosityis9×1018Pa·sforthemiddle-lowercrustintheChengduBasin,4×1017Pa·sforthemiddle-lowercrustintheChuanxiPlateauand7×1017Pa·sforthelowvelocityzoneintheChuanxiplateau.Theviscoelasticmodelexplainsthepostseismicdeformationobservedinthefar-fieldsatisfactorily,butitisconsiderablyworsethantheafterslipmodelinfittingthenear-faultdata.Itsuggeststhereforeahybridmodelincludingbothafterslipandrelaxationeffects.Sincetheviscoelasticmodelproducesmainlythefar-fieldsurfacedeformationandhasfewerdegreeoffreedoms(threeviscosityparameters)thantheafterslipmodelwithahugenumberofsourceparameters,wefixtheviscositiystructureasobtainedbeforebutredeterminetheafterslipdistributionusingtheresidualdatafromtheviscoelasticmodeling.Theredeterminedafterslipdistributionbecomesphysicallymorereas

简介：Accordingtostudiesofmorethan20earthquakeswithMS≥5.0inNorthChina,sevenfeaturesoftheshort-termandimminentearthquakeprecursorshavebeensummarizedinthispaper.Atthesametime,takingtheshort-termandimminentearthquakestageasthephysicalprocessofasource’smediumsofteningandfaultcreep,wecalculatedtemporalvariationofmeanstress,maximumshearstress,bodystrain,andporepressureinsomecertainpoints(supposedstations)inthesourceareaanditsadjacentareabyusingananisotropicandnonlinearsourcemodelandafiniteelementmethod.Accordingtoananalysisofthesetheoreticalcurves,weconcludethattheshort-termandimminentearthquakeprecursorshavesuchcharacteristicsascomplexshapes,exponentialgrowthoftheprecursornumberwithtune,andprecursors’migrationfromtheoutsideareatothesourcearea,whichtoacertainextentrevealthecauseofthecharacteristicsoftheshort-termandimminentearthquakeprecursorfield.