东昆仑南部西大滩断裂的地震鼓包及形成时代
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摘要
在昆仑山南部西大滩与东大滩谷地,沿西大滩活动断裂发育大量串珠状斜列分布的地震鼓包,与不同类型的地震破裂、地震楔、地震陡坎和地震凹陷伴生,在探槽剖面表现为全新世砂土层和晚更新世砾石层的背斜褶皱变形;地震鼓包长轴走向290°~300°,与西大滩活动断裂呈10°~20°交角,锐角指示西大滩断裂左旋走滑运动方向。对探槽剖面不同层位的沉积物、断层破碎带和地震崩积楔分别取样,进行热释光和光释光测年,发现西大滩断裂的地震鼓包主要形成于全新世早期,对应于10.2ka BP、8.6~8.7ka BP、7.0ka BP、6.10ka BP4期古地震事件。估算西大滩断裂全新世早期强烈地震的复发周期为0.9~1.7ka,断裂左旋走滑速率为5.3~10.0mm/a,平均约7.7mm/a。全新世晚期西大滩断裂的构造活动性显著减弱,强烈地震向南迁移至库赛湖断裂。
A great deal of pressure ridges distribute along the Xidatan strike-slip fault in en-echelon pattern accompanied by varieties of seismic fractures, seismic wedges, seismic scarps and seismic sag-ponds in the Xidatan and Dongdatan valleys in south Kunlun Mts. of north Tibetan Plateau. Most pressure ridges show anticline deformation of Holocene and Late Pleistocene sediments in trench cross-section with anticline axis trending in 290°～300°. And an angle ranging 10°～20° exists between pressure ridge and main active fault, directing sinistral strike-slip motion of the Xidatan fault. Thermoluminescent (TL) and photoluninescent (OSL) dating were finished for samples from different parts of pressure ridges and seismic fractures. Accoding to TL and OSL dating, 4 paleo-earthquakes occurred and 4 stages of pressure ridges formed in 10.2ka BP, 8.7ka BP, 7.0ka BP and 6.1ka BP respectively in Early Holocene, corresponding to earthquake intervals of 900～1700a and strike-slip rates of 5.3～10.0mm/a with average slip rate of 7.7mm/a of the Xidatan fault. Activity of the Xidatan strike-slip fault became weak since 5.0ka BP, and strong earthquake of Ms≥8.0 seems migrated from Xidatan fault to Kusaihu active fault in south boundary of Kunlun Mts. in Late Holocene.
A great deal of pressure ridges distribute along the Xidatan strike-slip fault in en-echelon pattern accompanied by varieties of seismic fractures, seismic wedges, seismic scarps and seismic sag-ponds in the Xidatan and Dongdatan valleys in south Kunlun Mts. of north Tibetan Plateau. Most pressure ridges show anticline deformation of Holocene and Late Pleistocene sediments in trench cross-section with anticline axis trending in 290°～300°. And an angle ranging 10°～20° exists between pressure ridge and main active fault, directing sinistral strike-slip motion of the Xidatan fault. Thermoluminescent (TL) and photoluninescent (OSL) dating were finished for samples from different parts of pressure ridges and seismic fractures. Accoding to TL and OSL dating, 4 paleo-earthquakes occurred and 4 stages of pressure ridges formed in 10.2ka BP, 8.7ka BP, 7.0ka BP and 6.1ka BP respectively in Early Holocene, corresponding to earthquake intervals of 900～1700a and strike-slip rates of 5.3～10.0mm/a with average slip rate of 7.7mm/a of the Xidatan fault. Activity of the Xidatan strike-slip fault became weak since 5.0ka BP, and strong earthquake of Ms≥8.0 seems migrated from Xidatan fault to Kusaihu active fault in south boundary of Kunlun Mts. in Late Holocene.
引文
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WuZhenhan,BaroshPJ,HuDaogong,WuZhonghai,ZhaoXitaYePeisheng,JiangWan.2004.HazardsposedbyactivemajfaultsalongtheGolmud-Lhasarailwayroute,TibetanPlateauChina.EngineeringGeology,74:163~182.
李虎候.1999.热释光断代.HongKong:ScientistPressInternation-al,Inc.,1~55.
青海省地震局,中国地震局地壳应力研究所.1999.东昆仑活动断裂带.北京:地震出版社,1~186.
任金卫,汪一鹏,吴章明,叶建青.1993.青藏高原北部库玛断裂东西大滩段全新世地震形变带及其位移特征和水平滑移速率.地震地质,15(3):285~288.
任金卫,汪一鹏,吴章明.1999.青藏高原北部东昆仑断裂带第四纪活动特征和滑动速率.见:中国地震局科技发展司活动断裂研究编委会编.活动断裂研究(7).北京:地震出版社,147~164.
吴锡浩,钱方,浦庆余.1982.东昆仑山第四纪冰川地质.见:地质矿产部青藏高原地质文集编委会编.青藏高原地质文集,(4),第四纪地质·冰川.北京:地质出版社,1~18.
吴中海,吴珍汉,胡道功,赵希涛,韩金良,张永双,江万.2003.青藏高原中部第四纪左旋剪切变形的地表地质证据.现代地质,17(4):363~369.
吴中海,胡道功,吴珍汉.2004.青藏铁路邻侧昆仑山2001年Ms8.1级地震地表破裂特征分析.地球学报,25(4):411~414.
徐锡伟,陈文斌,于贵华,等.2002.2001年11月14日昆仑山库赛湖地震(Ms8.1)地表破裂带的基本特征.地震地质,24(1):1~13.
中国地震局.2003.中国昆仑山口西8.1级地震图集.北京:地震出版社,1~105.
张培震,王琪.2001.中国大陆现今地壳运动与构造变形.见:马宗晋、汪一鹏、张燕平主编,青藏高原岩石圈现今变动与动力学.北京:地震出版社,21~35.
张培震,王琪,马宗晋.2002.青藏高原现今构造特征与GPS速度场.地学前缘,9(2),442~450.
ChenZiliang,BurchfielBC,LiuY,KingRW,RoydenLH,TangW,WangE,ZhaoJ,ZhangX.2000.Globalpositionningsys-temmeasurementsfromeasternTibetandtheirimplicationsforIndia/Eurasiaintercontinentaldeformation.JournalofGeophysi-calResearch,105:16215~16227.
KiddWSF,MolnarP.1990.QuaternaryandpresentactivefaultsofLhasa—GolmudoftheTibetanplateau.Roy.Soc.London.A327:332~352.
LinAiming,FuBihong,GuoJianming,ZengQingli,DangGuangming,HeWengui,ZhaoYue.2002.Co-seismicstrike-slipandrupturelengthproducedbythe2001Ms8.1CentralKunlunEarthquake.Science,296:2015~2017.
LiaoChunting,ZhangChunshan,WuManlu,MaYinsheng,OuMingyi.2003.StressChangeneartheKunlunfaultbeforeandaftertheMs8.1Kunlunearthquake.GeophyicalResearchLet-ter,30:2027~2030.
VanderWoerdJ,RyersonFJ,TapponnierP,GaudemerY,FinkelR,CaffeeM,ZhaoGuoguang,HeQunlu.1998.Holoceneleft-slipratedeterminedbycosmogenicsurfacedatingontheXidatansegmentoftheKunlunfault(Qinghai,China).Geology,26(8),695~698.
VanderWoerdJ,RyersonFJ,TapponnierP,MeriauxAS,Gaude-merY,MeyerB,FinkelRC,CaffeeMW,ZhaoGuoguang.2000.Uniformslip-ratealongtheKunlunfault:implicationsforseismicbehaviourandlarge-scaletectonics.GeophysicalResearchLetters,27(16):2353~2356.
VanderWoerdJ,TapponnierP,RyersonFJ,MeriauxAS,MeyerB,GaudemerY,FinkelRC,CaffeeMW,ZhaoGuoguang,XuZhiqun.2002.Uniformpostglacialslip-ratealongtheKunlunfault(Tibet),from26Al,10Beand14Cdatingofriseroffsets,andclimaticoriginoftheregionalmorphology.GeophysicalJournalInternational,148:356~388.
WuZhenhan,BaroshPJ,HuDaogong,WuZhonghai,ZhaoXitaYePeisheng,JiangWan.2004.HazardsposedbyactivemajfaultsalongtheGolmud-Lhasarailwayroute,TibetanPlateauChina.EngineeringGeology,74:163~182.
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