简介：Earthquakesarecausedbythefailureoffaults,drivenbytectonicstressbuild-upintheEarth’scrust.Tostudytheearthquakepreparationprocessandassessregionalearthquakepotentials,itisvitallyimportanttounderstandthecrustalstressevolutionprocessandidentifyitschangeinpatternassociatedwiththeseismogenicprocess.InthisstudyweinvestigatethefocalmechanismorientationsofearthquakesinsouthernCaliforniafrom1982to1999,basingonafocalmechanismcatalogfromHauksson.WefindthatforthetwolargeearthquakesoccurredinsouthernCalifornia,the1992MW7.3Landersandthe1999MW7.1HectorMine,theorientationsoffocalmechanismsnearthecomingearthquaketendtoconvergetothestressdirectionpromotingtheruptureofthecomingearthquakeandalignwithitsfocalmechanismabouthalf-yearbeforeitsoccurrence,suggestingthatthetectonicstressfieldgetsmoreorganizedinfavoroftheruptureoftheeventpre-seismically.ThedegreeofstressconvergenceismeasuredbytheorientationangleRMS(rootmeansquare)betweenthepreshocks’focalmechanismsandthefocalmechanismofthelargeeventstudied,anditstimeseriesrecordedthestressconvergenceprocess.Thedegreeofanomalies,measuredbytheF-tests,indicatesthattheconvergenceofstressorientationsbecomesignificantat90%confidenceabouthalf-yearpriortoboththeLandersandHectorMinequakes,anditbecomesevenmoreprominentat99%confidencerightbeforetheoccurrences.Ourstudymaybeofsignificanceforassessmentofregionalseismicpotentials.

简介：ＩｎｔｒｏｄｕｃｔｉｏｎＵｎｔｉｌｎｏｗ，ｍａｎｙｏｂｓｅｒｖａｔｉｏｎｓａｎｄｓｔｕｄｉｅｓｓｈｏｗｔｈａｔｉｎａｃｅｒｔａｉｎａｒｅａｓａｎｄｄｕｒｉｎｇａｃｅｒｔａｉｎｐｅｒｉｏｄｍａｊｏｒｅａｒｔｈｑｕａｋｅｓｆｒｅｑｕｅｎｔｌｙｏｃｕｒｅｄ...

简介：Weemployedadouble-differencealgorithm(hypoDD)torelocateearthquakeswithintheregionboundedby66°E-78°Eand32°N-42°Nintheperiodof1964?2003reportedbytheInternationalSeismologicalCenter(ISC).Theimprovedhypocentrallocationsdelineateadouble-layeredWadati-BenioffzoneintheeasternHinduKushintermediateseismicbelt.Basedonthisfeatureandotherevidences,weproposethattheintermediate-depthearthquakesbeneaththePamir-HinduKushregionmayoccurintwocollidedsubductionzoneswithoppositedipdirections.

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