基于时-空ETAS模型给出的川滇地区背景地震活动和强震潜在危险区
DOI: 10.3969/j.issn.0001-5733.2010.02.008, PP. 305-317
Keywords: Basedonthetime-spaceepidemic-typeaftershocksequence(ETAS)modelandstochasticdeclusteringmethod,aretrospectivestudywasconductedtoinvestigatewhetherlong-termseismicityanomaliesexistedbeforetheMay12,WenchuanMS8.0earthquake,theresultsshowedthatseismicactivityintheSichuan-Yunnanregionwassignificantlyclustered,heterogeneouslydistributedinspaceandtime,andtheearthquakesequenceswereusuallyprecededbyforeshockevents.Throughtheanalysisofthespatialvariationofthe'clusteringseismicityratio',wefoundthatthereexistedalong-termandlargeareaoflow'clusteringseismicityratio'inthemiddle-southsectionofLongmenshanfaults,whichimpliedthatthisregionhadbeeninastateofstressbarrierbeforetheWenchuanMS8.0earthquake.Statisticsofseveralparametersincludingcumulativenumbersofbackgroundandtotalsesimicity,bvalueandnewlydefinedΔbvaluewereconductedtoevaluatethecurrentpotentialriskofstrongearthquakesintheareasoflow'clusteringseismicityratio'intheSichuan-Yunnanregion.Theresultsshowedthattheseismicactivity,andthattheQiaojiaregionandthesouthernsegmentofLongmenshanfaultshavehighpotentialofstrongearthquakes.Moreover,wealsofoundthatthebvaluetrendstoreflectthelocalvariationsofstressfield
Abstract:
利用基于时-空传染型余震序列（EpidemicTypeAftershockSequence,简称ETAS）模型的随机除丛法，重新审视了2008年5月12日汶川MS8.0地震前可能存在的长期地震活动异常，研究了川滇地区背景地震活动特征，并评估了当前的强震危险状态.对川滇地区1970年以来的ML3.0以上的背景地震和丛集地震活动的研究结果表明，该地区地震丛集特征明显、时空分布很不均匀、地震序列常有前震事件.直接将概率值作为地震计数的权重，对地震丛集率空间分布图像分析表明，汶川MS8.0地震前，龙门山断裂带中南段存在着长期、大范围的地震丛集率低值区，震前该段处于应力闭锁状态.对川滇地区地震丛集率低值区内背景地震与全部地震的累积次数、b值和新定义的Δb等统计参量的分析表明，龙日坝与龙门山断裂带具有地震活动的关联性，川滇地区当前的强震潜在危险区可能是巧家地区和汶川MS8.0地震破裂尚未穿越的龙门山断裂带南段.此外，还发现b值倾向于反映局部应力场变化，而Δb能较为敏感地给出更大范围应力场的相对变化.
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