河套断陷带大青山山前断裂晚第四纪古地震完整性研究
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摘要
通过沿大青山山前断裂 18个探槽的古地震分析 ,分别确定了 5个段落的 2 2次古地震事件。呼和浩特段 ,距今约 1.9万a以来 7次 ,平均重复间隔时间 (2 4 6 2± 4 13)a ;毕克齐段距今 2 .2万a以来 4次 ;土左旗西段距今 1.1万a以来 4次 ,平均重复间隔时间 (2 94 8± 5 6 0 )a ;土右旗西段距今约 1.1万a以来 5次 ,平均重复间隔时间 (2 2 89± 36 0 )a ;包头段距今 2 .3万a以来 2次。由断层位移量限定法和多探槽校验法判定 ,大青山山前断裂已揭露的古地震事件还不完全代表晚第四纪全断裂的大地震活动历史。只有在呼和浩特段 1.9万a以来、土左旗西段和土右旗西段约 1.1万a以来活动历史基本完整。其它两个段落不完整。这是用这些古地震资料评价该断裂未来地震危险性 ,以及今后进一步工作时应注意的问题。
The Daqingshan piedmont fault (DPF) is one of the major active normal faults in the Hetao depression zone in the northern part of Ordos block, North China. It extends in NEE direction along the Daqingshan piedmont zone in the eastern part of the depression, dipping to the south, for a length of 223 km. The fault formed in the Eocene and had undergone strong movement during the Cenozoic time. Its vertical displacement amplitude exceeds 2 400 m since the Quaternary. The fault can be divided into 5 active segments. The aim of this paper is to research on the completeness of paleoseismic activity history both for the individual sites and for the entire fault since the Late Quaternary by using the “method for displacement confining” along the fault and the “method for correlation between multiple trenches”. Based on 18 trenches along DPF 22 paleoearthquake events in 5 segments are revealed. There are 7 events in the Hohhot segment since 19 ka BP and the average recurrence interval is (2 462±413)a; 4 events in the Bikeqi segment since 23~26 ka BP; 4 events in West Tumdzuoqi segment since 11 ka BP and the average recurrence interval is (2 948±560)a; 5 events in the West Tumdyouqi segment since 11 ka BP and the average recurrence interval is (2 289±360)a; and 2 events in the Baotou segment since 23~26 ka BP. The history of paleoseismic events we present is complete at Kuisu site and in the Hohhot segment since 19 ka BP, the West Tumdzuoqi segment and the West Tumdyouqi segment about since about 11 ka BP, but incomplete at Bikeqi site and in other two segments along DPF. When the paleoearthquake data are used for seismic hazard assessment in the future, completeness or incompleteness should be paid much attention.
The Daqingshan piedmont fault (DPF) is one of the major active normal faults in the Hetao depression zone in the northern part of Ordos block, North China. It extends in NEE direction along the Daqingshan piedmont zone in the eastern part of the depression, dipping to the south, for a length of 223 km. The fault formed in the Eocene and had undergone strong movement during the Cenozoic time. Its vertical displacement amplitude exceeds 2 400 m since the Quaternary. The fault can be divided into 5 active segments. The aim of this paper is to research on the completeness of paleoseismic activity history both for the individual sites and for the entire fault since the Late Quaternary by using the “method for displacement confining” along the fault and the “method for correlation between multiple trenches”. Based on 18 trenches along DPF 22 paleoearthquake events in 5 segments are revealed. There are 7 events in the Hohhot segment since 19 ka BP and the average recurrence interval is (2 462±413)a; 4 events in the Bikeqi segment since 23~26 ka BP; 4 events in West Tumdzuoqi segment since 11 ka BP and the average recurrence interval is (2 948±560)a; 5 events in the West Tumdyouqi segment since 11 ka BP and the average recurrence interval is (2 289±360)a; and 2 events in the Baotou segment since 23~26 ka BP. The history of paleoseismic events we present is complete at Kuisu site and in the Hohhot segment since 19 ka BP, the West Tumdzuoqi segment and the West Tumdyouqi segment about since about 11 ka BP, but incomplete at Bikeqi site and in other two segments along DPF. When the paleoearthquake data are used for seismic hazard assessment in the future, completeness or incompleteness should be paid much attention.
引文
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[2] LIKe,WUWeimin,YANGFa,etal.Astudyonsegmenta tionofDaqingshanpiedmontactivefault[A].Seismo geologicalSubcommissionofChineseSeismologicalSociety.ResearchonActiveFaultsinChina[C].Beijing:SeismologicalPress,1994.102113(inChinese). [李克,吴卫民,杨发,等.大青山山前活动断裂分段性研究[A].中国地震学会地震地质专业委员会.中国活动断层研究[C].北京:地震出版社,1994.102113.]
[3] WUWeimin,LIKe,MABaoqi,etal.StudyonHolocenepale oearthquakesinlargecompositetrenchontheDaqingshanpied montfault[A ].ResearchonActiveFaults(4)[C].Beijing:SeismologicalPress,1995.123132(inChinese). [吴卫民,李克,马保起,等.大青山山前断裂带大型组合探槽的全新世古地震研究[A].活动断裂研究(4)[C].北京:地震出版社,1995.123132.]
[4] NIEZongsheng,JIANGWali,WUWeimin.StudyonHolocenepaleoearthquakesinlargetrenchesonthewesternsegmentofDaqingshanpiedmontfaultzone,NeiMongol[A].ResearchonActiveFaults(5)[C].Beijing:SeismologicalPress,1996.125135(inChinese). [聂宗笙,江娃利,吴卫民.内蒙古大青山山前断裂带西段全新世古地震的大探槽研究[A].活动断裂研究(5)[C].北京:地震出版社,1996.125135.]
[5] JIANGWali,XIAOZhenmin,WANGHuanzhen,etal.Seg mentationcharacterofseismicsurfacerupturesofthepiedmontactivefaultofMT .Daqingshan,InnerMongolia[J].Seismolo gyandGeology,2001(1):2434(inChinese).[江娃利,肖振敏,王焕贞,等.内蒙古大青山山前活动断裂带的地震破裂分段特征[J].地震地质,2001(1):2434.]
[6] RANYongkang,ZHANGPeizhen,HUBo,etal.PaleoseismicactivityontheHohhotsegmentofDaqingshanpiedmontfaultintheLateQuaternaryhistory[J].EarthquakeResearchinChi na,2002(1):1527(inChinese). [冉勇康,张培震,胡博,等.大青山山前断裂呼和浩特段晚第四纪古地震活动历史[J].中国地震,2002(1):1527.]
[7] HANKSTC ,BUCKNAMRC ,LAJOIEKR ,etal.Modifica tionofwave cutandfaulting controlledlandforms[J].JGR ,1984(B7):57715791.
[8] MCCALPINJP .Paleoseismology[M ].SanDiego:AcademicPress,1996.588.
[9] MAOFengying,ZHANGPeizhen.Methodforprogressivecon straintofpaleoseismiceventsandpaleoseismologicalstudyofma jorfaultzoneinnorthernXinjiang[A ].ResearchonActiveFaults(4)[C].Beijing:SeismologicalPress,1995.153164(inChinese). [毛凤英,张培震.古地震研究的逐次限定法与新疆北部主要断裂带的古地震研究[A].活动断裂研究(4)[C].北京:地震出版社,1995.153164.]
[10] WALLACERE .Profilesandagesofyoungfaultscarps,north centralNevada[J].BGSA ,1977,88:12671278.
[11] BUCKNAMRC ,ANDERSONRE .Estimationoffault scarpagesfromascarp height slope anglerelationship[J].Geology,1979(7):1114.
[12] McCALPINJ.GeologicCriteriaforRecognitionofIndividualPaleoseismicEventsinExtensionalEnvironments[R ].USGSOpenFileReport,1987,683:102114.
[13] DENGQidong,WANGYipeng,LIAOYuhua,etal.CollapsewedgesbyfaultscarpsandHolocenehistoryofmovementalongHelanshanpiedmontfault[J].ScienceBulletin,1984(9):557560(inChinese). [邓起东,汪一鹏,廖玉华,等.断层崖崩积楔及贺兰山山前断裂全新世活动历史[J].科学通报,1984(9):557560.]
[14] DENDQidong,LIAOYuhua.Paleoseismologyalongtherange frontfaultofHelanMountains,northcentralChina[J].JGR ,1996(B3):58735893.
[15] WUWeimin,NIEZongsheng,XUGuilin,etal.ResearchonthewestsegmentoftheSertengpiedmontfault[A].InstituteofGeology,SSB .ResearchonActiveFaults(5)[C].Beijing:Seis mologicalPress,1996.113124(inChinese). [吴卫民,聂宗笙,许桂林,等.色尔腾山山前断裂西段活断层研究[A].活动断裂研究(5)[C].北京:地震出版社,1996.113124.]
[16] XUXiwei,YONEKURYNobuyuki,SUZUKIYasuhiro,etal.GeomorphicstudyonLateQuaternaryirregularfaultingalongthenorthernpiedmontofLiulengshanrange,ShanxiProvince[J].ChinaSeismologyandGeology,1996(2):169181(inChinese). [徐锡伟,米仓伸之,铃木康弘,等.山西六棱山北麓晚第四纪不规则断裂作用地貌学研究[J].地震地质,1996(2):169181.]