简介：Inthispaper,researchofaftershockmechanismsisreviewed,includingheterogeneityofmediumandstress,mechanicalloading,fluidintrusionandstresscorrosion,andratestatedependence.Previousstudieshaveindicatedthattheheterogeneityofmediaandstressisthebasicpremiseofaftershocksgenerated.Fromthepointviewofmechanics,transientcreepandafterslipcanexplainthedecayofaftershocksinashorttimeafteramainshockandtherelaxationofstresstendstointerpretthecharacteristicsoflong-termaftershocks.Fluidintrusionandstresscorrosioncontroltheevolutionprocessoftheaftershocksundercertainconditions.Theinteractionbetweenthefaultsperturbedbythemainshockalwaysexistsduringtheaftershockactivities.Allkindsofmodelsandthetheorieswanttocomplywiththetwobasicpower-lawrelationships---theG-RlawandOmorilawtosomeextent.

简介：Inordertosolvetheproblemofearlyestimationofmoderatelystrongaftershockdurationtimeinanearthquakesequence,thisstudyhasbeenconducted.First,thedefinitionofthestrongaftershockhasbeengiven.Itispointedoutthatthereisadifferenceinthestrongaftershockdurationtimebetweenthemainshocktypesequenceandthestrongearthquakeswarmsequence.Afterdividingthethreecases,i.e.,astrongaftershockdurationtimelargerthan1day,smallerthan1day,andnostrongaftershockoccurredinamainshocktypesequencebyusingthepatternrecognitionmethod,wegavetheroughcorrelationrelationbetweenstrongaftershockdurationtimeandfirstlargeshockmagnitudefortwotypesofsequences.Finally,thejudgmentindexandmethodofestimatingstrongaftershockdurationtimesfordifferentsequencetypeshavebeengiven.

简介：在在一个差错地区和包围岩石的材料之间的大性质对比被重复地震经常生产。差错地区被液体集中，充满泥土的差错凿，增加的孔，和膨胀裂缝通常描绘。因此，差错地区被认为比包围岩石减少了地震速度。在这篇文章，我们首先由使用3D越过一个垂直差错地区在一个线性数组调查了合成波形有限差别模拟。合成波形看那来源什么时候接近，在内，或在差错地区，两到达时间和P波浪和S波浪的波形下面从低速度的差错地区的边界由于思考和传播越过差错地区系统地变化。到达时间模式和波形特征能被用来决定差错地区结构。然后，我们把这个方法用于1992登陆者M7.4和2008Wenchuan的余震波形数据()M8.0地震。登陆者波形数据相对近似35%60%的主人岩石与近似270-370m，和P波浪和S波浪速度减小的宽度揭示一个低速度的地区；Wenchuan波形数据与约220300m的宽度建议一个低速度的地区，并且P波浪和S波浪速度相对约55%的主机岩石落下。

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简介：Thecurrentcalibrationfunctionusedincalculatingthemagnitudeofnaturalearthquakeswithin5kmisaconstant;afactthatcausesseveralseriousdifficultiesforthecalculationofthemagnitudeofsmallandshallow-focusearthquakes.Accordingtotheattenuationlawofexplosionsandthepropagationtheoryofelasticwaves,thecalibrationfunctioniscalculatedfornearfieldquakesfrom0kmto5km.Magnitudesoftwoaftershocksequencesarecalculated.Themagnitudesofmostexplosionearthquakesaresmall,rangingmainlyfrommagnitude0.5to1.0.TheM-tchartoftheexplosiveaftershocksiscompletelydifferentfromthatofstrongearthquakeaftershocks.Itnotonlyshowspositivecolumnarlinesindicatinglargemagnitudesbutalsoshortnegativecolumnarlinesindicatingsmallmagnitudes.

简介：AstatisticalanalysisontheWenchuanaftershockactivitytriggeredbytidalforcesissystematicallystudiedbasedonSchusterstest,includingearthquakestriggeredbytidalforce,tidalstressandtidalcoulombfailurestress.TheresultsshowthatagroupofstrongaftershockswhichoccurredattheendofJulytoearlyAugustin2008atthenorthofWenchuanwereobviouslytriggeredbyearthtide,thesameconclusionisdrawnbySchusterssmoothtestofthetidalforce,tidalstressandtidalcoulombfailurestress.Inaddition,theWenchuanaftershockactivityisobviouslytriggeredbyfortnighttide.Inthenorth,theaftershockshappenedmorefrequentlyinthefirstandlastquartersofthemoon,andinthesouth,theaftershockshappenedmorefrequentlyinthefirstandlastquartersofthemoonandduringthefullmoon.

简介：Usingthedouble-differencerelocationalgorithm,werelocatedthe20April2013Lushan,Sichuan,earthquake(MS7.0),andits4,567aftershocksrecordedduringtheperiodbetween20AprilandMay3,2013.Ourresultsshowedthatmostaftershocksarerelocatedbetween10and20kmdepths,butsomelargeaftershockswererelocatedaround30kmdepthandsmalleventsextendedupwardnearthesurface.Verticalcrosssectionsillustrateashovel-shapedfaultplanewithavariabledipanglefromthesouthwesttonortheastalongthefault.Furthermore,thedipangleofthefaultplaneissmalleraroundthemainshockthanthatinthesurroundingareasalongthefault.Theseresultssuggestthatitmaybeeasytogeneratethestrongearthquakeintheplacehavingasmalldipangleofthefault,whichissomewhatsimilartothegenesisofthe2008Wenchuanearthquake.TheLushanmainshockisunderlainbytheseismicallyanomalouslayerswithlow-VP,low-VS,andhigh-Poisson’sratioanomalies,possiblysuggestingthatthefluid-filledfracturedrockmatricesmightsignificantlyreducetheeffectivenormalstressonthefaultplanetobringthebrittlefailure.TheseismicgapbetweenLushanandWenchuanaftershocksissuspectedtobevulnerabletofutureseismicrisksatgreaterdepths,ifany.

简介：BytheaftershockfrequencyestimationmethodbasedonthecalculationofcoseismicstaticCoulombstresschangesandrate-andstate-dependentfaultconstitutivelaw,wecalculatethefrequencyof"direct"aftershocksoftheWenchuanearthquakerelatedtocoseismicstaticCoulombstresschangesinitsaftershockzoneandtheareasnearby.Itshowsthatthefrequencyissignificantlylowerthanthetruthinthemainrupturezone,especiallyinthesouthernrupturezone,duetothedecreaseofstresslevelontheruptureplaneofthemainshockresultingfromcoseismicCoulombstresschange.ThestudyalsoshowsthattheeffectoftheCoulombstresschangeonthedurationofaftershockactivityisassociatedwiththelowerlimitmagnitude.Thedurationisabout15-16monthsforaftershocksaboveML4.0,andcloseto60monthsforaftershocksaboveML3.5.Inthisperiod,theratioofthe"direct"aftershockscausedbycoseismicCoulombstresschangerangesbetween44.7%to48.6%,whichsuggeststhat,eveninthe"effective"periodofcoseismicCoulombstresschanges,abouthalfoftheaftershocksonthemainshockruptureplaneareindependentofcoseismicCoulombstresschanges.Itispointedoutthatthoseaftershocksmayberelatedtotheaftersliportheviscoelasticrelaxation,whicharetimedependentcases.

简介：Becauseseismicactivitywithinmid-continentsisusuallymuchlowerthanthatalongplateboundaryzones,evensmallearthquakescancausewidespreadconcerns,especiallywhentheseeventsoccurinthesourceregionsofpreviouslargeearthquakes.However,thesesmallearthquakesmaybejustaftershocksthatcontinuefordecadesorevenlonger.TherecentseismicityintheTangshanregioninNorthChinaislikelyaftershocksofthe1976GreatTangshanearthquake.ThecurrentearthquakesequenceintheNewMadridseismiczoneincentralUnitedStates,whichincludesaclusterofM*7.0eventsin1811–1812andanumberofsimilareventsinthepastmillennium,isbelievedtoresultfromrecentfaultreactivationthatreleasespre-storedstrainenergyinthecrust.Ifso,thisearthquakesequenceissimilartoaftershocksinthattheratesofenergyreleaseshoulddecaywithtimeandthesequenceofearthquakeswilleventuallyend.WeusesimplephysicalanalysisandnumericalsimulationstoshowthatthecurrentsequenceoflargeearthquakesintheNewMadridfaultzoneislikelyendingorhasended.Recognizingthatmid-continentalearthquakeshavelongaftershocksequencesandcomplexspatiotemporaloccurrencesarecriticaltoimprovehazardassessments.

简介：Withtheimprovementofseismicobservationsystem,moreandmoreobservationsindicatethatearthquakesmaycauseseismicvelocitychange.However,theamplitudeandspatialdistributionofthevelocityvariationremainsacontroversialissue.RecentactivesourcemonitoringcarriedoutadjacenttoWenchuanFaultScientificDrilling(WFSD)revealedunambiguouscoseismicvelocitychangeassociatedwithalocalMs5.5earthquake.Here,wecarryoutforwardmodelingusingtwo-dimensionalspectralelementmethodtofurtherinvestigatetheamplitudeandspatialdistributionofobservedvelocitychange.ThemodeliswellconstrainedbyresultsfromseismicreflectionandWFSDcoring.Ourmodelstronglysuggeststhattheobservedcoseismicvelocitychangeislocalizedwithinthefaultzonewithwidthof*120mratherthandynamicstronggroundshaking.Andavelocitydecreaseof*2.0%withinthefaultzoneisrequiredtofittheobservedtraveltimedelaydistribution,whichcoincideswithrockmechanicalexperimentandtheoreticalmodeling.