简介：BasedonthewaveformdataobservedbytheregionalseismicnetworkofGansuProvince,wecalculatedtheapparentstressof422earthquakeswithM_L≥2.0occurringinthesurroundingareaoftheMinxianearthquakefromJanuary2010toJuly2014andobtainedthetemporalandspatialvariationofapparentstressbeforeandaftertheMinxianearthquake.Resultsshowthat(1)thehighvalueofapparentstressofearthquakeswithM_L≥4.0wasconcentratedintheepicenterareabeforetheMinxianearthquakewhilethatofearthquakeswithM_L<4.0wasnot;(2)ApparentstressaroundtheepicenterareashowedanobviousincreasingprocessbeforetheMinxianearthquakeandtheincreasingprocesshascontinuedafterthemainshock,whichmeansthatthisstudyareaisstillinthedangerofstrongearthquakes.

简介：

简介：IntroductionRegionalseismicitytriggeredbybigearthquakesaswellasattershocksinsourcezonecouldbedetectedduetothehighseismicmonitoringcapabilitytoday(Anderson,etal,1994;Bodin,Gomberg,1994;Caskey,Wesnousky,1997;Deng,Sykes,1996;Hill,etal,1993;King,etal,19...

简介：Theearthquakestress-dropvaluesoftwosequenceswereaccuratelycalculatedaftertakingawaytheeffectsduetoregionalearthquakeanelasticattenuationandstationsiteresponse,usingwaveformdataandseismicphasedataofsequencesoftheJingguM_S6.6,andLudianM_S6.5earthquakesinYunnan.Theseresultsshowthatthestressdropwithmagnitudeincreaseswithinthescopeofthisstudyofmagnitude.Aftereliminatingtheinfluenceofthemagnitude,theaveragevalueofstress-dropintheJinggusequenceishigherthanthatoftheLudiansequenceatthesamemagnituderange.Thismayberelatedtothestressstateindifferentregions.Intermsofthechangesoftimeandspaceofstress-drop,beforeM_S5.8strongaftershock,thestress-dropis'slowingdown-turningup-keepingahighvalue'afterthemainshock,meanwhile,almostalloftheabnormallyhighstressdropvalueisdistributedaroundtheM_S5.8strongaftershock,showingthatthestressenvironmentintheregionwasincreasingafterthemainshock.AndaftertheM_S5.9strongaftershock,stress-droprapidlydeclinestoarelativelystablestate,meanwhile,thehighvalueofstress-dropisdistributedaroundthestrongaftershock,showingthattheregionaltectonicstressgetsmorefullyrelease,itsstressenvironmentbeginstorapidlydecrease.FortheLudiansequencewithoutastrongaftershockoccurring,theaveragevalueofstressdropislowerthanthatoftheJingguearthquakesequenceatthesamemagnituderange,whileatthesametime,thestress-dropoftheaftershocksequencealmosthasn'tchangedmuch.Inthetimeafterthemainshock,combinedwiththereleasecharacteristicsofthemainenergy,thestressintheregionisexcessivelyreleased,thesubsequentstressintheregiongraduallyreturnstonormal.ThismaybethereasonwhytheactivityofLudianaftershockssignificantlywasweakerandsubsequentlytherewerenostrongaftershocksoccurred.

简介：Usingthreedimensional(3D)viscoelasticfiniteelementmethod(FEM)westudythedynamicevolutionpatternofthecoseismicchangeofCoulombfailurestressandpostseismicchange,ontimescaleofhundredsyears,ofrheologicaleffectinducedbytheMS=7.2XingtaiearthquakeonMarch22,1966.Then,wesimulatethecoseismicdisturbanceinstressfieldinNorthChinaanddynamicchangerateonone-yearscalecausedbytheXingtaiearth-quakeandTangshanearthquakeduring15yearsfrom1966to1980.Finally,wediscussthetriggeringofastrongearthquaketoanotherfuturestrongearthquake.

简介：Incorporatingrateandstatefrictionlaws,stabilityoflinearlystable(i.e.,withstiffnessgreaterthanthecriticalvalue)spring-slidersystemssubjectedtotriggeringperturbationswasanalyzedundervariablenormalstresscondition,andcomparisonwasmadebetweenourresultsandthatoffixednormalstresscasesrevealedinpreviousstudies.Forsystemsassociatedwiththesliplaw,thecriticalmagnitudeofratestepsfortriggeringunstableslipsarefoundtohaveasimilarpatterntothefixednormalstresscase,andthecriticalvelocitystepsscalewitha/(b-a)whenk=kcrforbothcases.Therate-stepboundariesforthevariablenormalstresscasesarerevealedtobelowerthanthefixednormalstresscaseby7%–16%forarelativelylargea=0.56with(b-a)/arangingfrom0.25to1,indicatingeasiertriggeringunderthevariablenormalstressconditionwithratesteps.Thedifferencebetweenfixedandvariablenormalstresscasesdecreaseswhentheavalueissmaller.Inthesamesliplaw-typesystems,criticaldisplacementstotriggerinstabilityarerevealedtobelittleaffectedbythevariablenormalstresscondition.WhenkCkcr(V*),aspring-slidersystemwiththeslownesslawismuchmorestablethanwiththesliplaw,suggestingthattheslownesslawfitsexperimentaldatabetterwhenasinglestatevariableisadopted.Instick-slipmotions,thevariablenormalstresscasehaslargerstressdropsthantheconstantnormalstresscase.Thevariablenormalstresshaslittleeffectontherangeofslipvelocityinsystemsassociatedwiththeslownesslaw,whereassystemsassociatedwiththesliplawhaveaslowestslipvelocityimmenselysmallerthanthefixednormalstresscase,by*10ordersofmagnitude.

简介：UsingthefocalmechanismsolutionsandslipdistributionmodeldataoftheTaiwanStraitsMS7.3earthquakeonSeptember16,1994,wecalculatethestaticCoulombstresschangesstemmingfromtheearthquake.Basedonthedistributionofaftershocksandstressfield,aswellasthelocationofhistoricalearthquakes,weanalyzetheCoulombstresschangetriggeredbytheTaiwanStraitsMS7.3earthquake.TheresultshowsthatthestaticCoulombstresschangeobtainedbyforwardmodelingbasedontheslipdistributionmodelisquiteconsistentwiththelocationofaftershocksintheareasfarawayfromtheepicenter.Ninetypercentofaftershocksoccurredinthestressincreasedareas.TheCoulombstresschangeisnotentirelyconsistentwiththedistributionofaftershocksneartheepicenter.ItisfoundthatCoulombstresschangecanbetterreflecttheaftershockdistributionfarawayfromtheepicenter,whilesuchcorrespondingrelationshipbecomesquitecomplexneartheepicenter.ThroughthecalculationoftheCoulombstresschange,wefindthatthestressincreasesinthesouthwestpartoftheMin-Yue(Fujian-Guangdong)coastalfaultzone,whichenhancestheseismicactivity.Therefore,itisdeemedthattheseaareabetweenNanpengIslandandDongshanIsland,wheretheMin-YuecoastalfaultzoneintersectswiththeNW-trendingShanghang-Dongshanfault,hasahighseismicrisk.

简介：Onthebasisoftherealityofrecenttectonicmovementanddiscardingsuchaviewpointthattheisostaticadjustmentonlyresultsfromexcessiveorinsufficientcompensation,wehavediscussedthetectonicstresscausinginequalityandregardedtheisostaticanomalyasaloadontheearth(sinterior,thustheearth(sinnerstresscanbecalculated.TheresearchresultsshowthatintheEastChinaSeaanditseasternmarginalseasthechangeoftheverticalstressderivedfromtheisostaticgravityanomalyismoremarkedthanthatofthehorizontalstress.AlongtheRyukyutrenchthereisanenhancementofverticalstressby5MPa,whichevidentlyreflectstheeffectofplatesubduction.Oncontrary,alongtheislandarctothenorthwestofthetrenchtheverticalstressweakensbyabout5MPa.Thehorizontalstressesineasternandwesternpartsareobviouslydifferent,theeastwestwardstressontheoceaniccrust(xisnegative(whilethepressureispositive)butonthecontinentalcrustispositive.Thesefactsindicatetheeffectofcompressionbetweenplates.

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简介：StaticCoulombstresschangeinducedbyearthquakeslipisfrequentlyusedtoexplainearthquakeactivitiesandaftershockdistribution.However,someparametersfortheCoulombstresscalculationareunabletobewellconstrainedfromlaboratoryexperimentsandfieldobservations.DifferentparametersmaydirectlyaffectthepatternofstaticCoulombstress.ThestaticCoulombstresschangesinducedbytheWenchuanearthquakecalculatedbysixresearchgroupsarenotconsistentwitheachother.Toinvestigatehowtheparametersaffectthecalculationresults,wechangetheparametersinturnthroughmodelingandcomparetheresultsofdifferentcalculationparameters.Wefindthatgravity,positionandstrikeofreceiverfaultshavelittleinfluenceoncoseismicCoulombstresscalculations,butotherparameterscanchangethevalueandsignoftheresultsinvariousdegreesespeciallyaroundtheearthquakeruptureplane.ThereforetheuncertaintyanalysisofstaticCoulombstresschangeinducedbyearthquakeshouldbetakenintoconsiderationintheearthquakehazardanalysis.

简介：OnthebasisofthepreviousstudiesofthelayeredcrustalmodelintheYutianarea,combinedwiththefieldGPScontinuousobservationdata,weroughlyestimatetheviscouscoefficientofeachlayer.Withtheviscoelastichorizontallayermodel,wecalculatetheviscoelasticco-seismicCoulombstresschangecausedbytheYutianM_S7.3earthquakes2008and2014respectively.BasedontheCoulombstresschange,usingthecalculationmethodof"direct"aftershockfrequency,wecomeupwiththetheoreticalearthquakefrequencydirectlyrelatedtothemainshockandtheco-seismicCoulombstresschangeinthestudyarea.Thenweputforwardamethod,basedonthecomparisonoftheoreticalandactualearthquakefrequencyorthecomparisonbetweentheoreticalandpracticalearthquakefrequency-distancedecaycurvefittingresiduals,toestimatethemagnitudeofamaximumsequentearthquake,directlyrelatedtothemainshockco-seismicCoulombstresschange.Resultscalculatedbydifferentmethodsshowthatthemaximumfollow-upearthquakemagnitudecausedbythecoseismicCoulombstresschangeliesfromM_S7.2toM_S7.5followingYutianM_S7.3earthquakein2008;butthatofthe2014YutianM_S7.3earthquakeisM_S6.3.TheformerisveryclosetotheYutianM_S7.3earthquakein2014.Becauseofthesamemagnitude,relativelyclosespatialdistance,shorttimeinterval,thesameregionoftheexternalforce,thestrongcorrelationbetweentwoseismictectonicandaclearstressinteraction,wethusconsiderthatthetwoYutianM_S7.3earthquakesin2008and2014constituteapairofgeneralizeddoubleshocktypeearthquake.Thisisconsistentwiththesequencetypecharacteristicofpast"doubleshock"earthquakesintheregion.Inthispaper,theinfluenceofthemagnitudelowerlimitandtheb-valueintherelationshipofG-Rontheresultsisdiscussed.Asaresult,whentheviscoelasticcoseismicCoulombstressvariationisdetermined,thelowerlimitofmagnitudehaslittleeffectonthemaximumsequentearthquakemagnitude

简介：Basedonwaveformdata,severalmethodstodeterminefocalmechanismsofsmallearthquakesweredevelopedsince1980.Kisslinger(1980)andJulian,Foulger(1996)proposedanapproachtodeterminesolutionbyusingamplituderatioofPandSwave.Schwartz(1995)devisedamethodtodeterminesolutionsbytheuseofpolaritydataandamplitudesofseismogramenvelopes.Amplitudesofshortperiodseismicwavespropagatinginaninhomogene-ousmediumaresensitivetothevariationinvelocityandQstructure.Nakamura,etal(1999)tookmediuminhomo-geneityintoaccountindeterminingfocalmechanismsofsmallearthquakesusingwaveformdata.Ifthelocationsofsmallearthquakesareconcentratedinasmallregion,wecanassumethattheraypathsfromtheeventstoagivenstationarealmostthesame.SoPandSwaveattenuationsareindependentofeventlocations.Inthiscaseitiscon-venienttodeterminefocalmechanismsoftheseeventsbyusingshortperiodPandSwavedataj.Focalmechanismsolutionsofsmallearthquakesin5regions,i.e.,Rongchang,Mabian-Muchuan,Ya￠an,BaoxingandMianzhu,whicharecoveredbytheChengduTelemeteredNetwork,areobtainedbyanalyzingthePpolarityandshortbodywaveamplitudedatarecordedinthenetworksince1992.AccordingtothemethodproposedbyGephartandForsyth(1984),basedonwelldeterminedfocalmechanismsolutionsin15sub-zonesofSichuanandYunnanarea,threeprincipalstresstensorss1,s2,ands3,insteadofaveragesofP,B,andTaxisofthesolutions,aredeterminedtorepresenttheregionalstressfielddistribution.