山西大同盆地口泉断裂全新世古地震活动
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摘要
野外调查表明 ,口泉断裂断错了断面附近的 3级地貌面 ,包括大同盆地西侧全新世形成的洪积扇后缘及位于洪积扇冲沟内的Ⅰ ,Ⅱ级阶地。其中冲沟内Ⅱ级阶地为剥蚀阶地 ,Ⅰ级阶地为堆积阶地 ,Ⅰ级阶地面的地层时代距今 2 52ka。在该断裂的悟道及上黄庄 2个地点开挖的大探槽表明 ,在距今 1 2 3万年以来该断裂曾发生 4次古地震事件 ,其中 3次分别发生在接近距今 2 52 ,5 6 8,13 73ka。另一次古地震事件发生在距今 6 76～ 10 82ka。这些数据有可能反映了口泉断裂具备准周期的强震活动。这 4次古地震事件的平均间隔约为 3 74ka ,最新一次古地震与上一次事件的时间间隔约为 3 16ka。 2个大探槽各次事件的平均最小同震垂直位移为 1 8m。这些资料对重新评价口泉断裂未来的地震潜势具有重要意义。
The NNE trending Kouquan Fault Zone is located on the western side of the Datong Basin, Shanxi Province. It is one of the three major boundary faults controlling Cenozoic sedimentation of the Datong Basin. The Huairen depression, where the greatest thickness of Cenozoic sediments may reach up to 1,800m, is located on the eastern side of the fault (see Fig. 1 in text). It is indicated by field investigation that a segment as long as 120km of the Kouquan Fault zone has been active in Holocene, and that three levels of morphologic surfaces formed in Holocene have been offset by this active segment. The highest one among the three surfaces is the back edge of a pluvial fan located on the western side of the Datong Basin. The upper layer of this pluvial fan consists of mid Holocene deposits, dated as 5ka BP. The other two lower surfaces are the 1st terrace and the 2nd terrace embedded into the pluvial fan. Among them, the 2nd terrace is a denudation terrace with a height of 8m; while the 1st terrace is accumulated with a height of 1.5～4m. The dating data show that the near surface layer of the 1st terrace is of 2.52ka BP in age (See Fig.2 & 3 in the text). Moreover, field investigation also shows that the Kouquan Fault has had obvious right lateral strike slip component in Holocene as more than ten east west directed gullies were offset right laterally for 8～20m when crossing the fault trace. Two exploratory trenches were dug during our investigation on the northern and southern segments of the Kouquan Fault, respectively. Their locations were chosen right beneath the fault plane where the fault offsets the 1st terrace of the gully (see Fig. 4 & 6 in the text). The two trenches are of 40km apart. Their dimensions are 11m in length with a depth of 4～5.5m and 22m in length with a depth of 3.2～8.8m, respectively. The two trenches reveal a line of evidence of the Holocene activities of the Kouquan Fault. The Wudao trench has revealed 3 fault planes, and in the middle part of the profile a drag structure in dark brown clay layer has been observed, appearing as the ascending of the western side and the descending of the eastern side (Fig. 5). The Shanghuangzhuang trench reveals a fault bundle of 13m in width that consists of 5 groups of faults. A vertical displacement of 2.9m for the two sides of F 1～F 4 Faults can be determined from the vertical dragging of the dark gray clay layers on the trench profile. The F 5 Fault at the easternmost end of the profile consists of two vertical fault planes about 0.8m apart. No vertical displacement of clay layers on both sides of F 5 is observed, but the layers between the two fault planes have nearly horizontal layering and show stratum discontinuity on both sides of the fault, indicating a strike slip activity of the fault. Moreover, the shanghuangzhuang trench log shows multiple yellow sand soil veins in the vicinity of the fault planes (Fig. 7). The time sequence of the paleo seismic activities revealed by the Wudao and the Shanghuangzhuang trench logs might correspond to each other. That is to say that there have been 4 paleo earthquake events since 13 7ka BP. Three of them occurred about 2 25, 5 68, and 13 73ka BP, respectively. The rest event occurred between 6 76ka and 10 82ka. The average recurrence time of these 4 events would be 3737yr, and the interval between the latest and its previous one is 3160yr. The average minimum co seismic vertical displacement of the 4 events reaches 1.8m. These new data are of great significance to earthquake safety assessment of the Datong area.
The NNE trending Kouquan Fault Zone is located on the western side of the Datong Basin, Shanxi Province. It is one of the three major boundary faults controlling Cenozoic sedimentation of the Datong Basin. The Huairen depression, where the greatest thickness of Cenozoic sediments may reach up to 1,800m, is located on the eastern side of the fault (see Fig. 1 in text). It is indicated by field investigation that a segment as long as 120km of the Kouquan Fault zone has been active in Holocene, and that three levels of morphologic surfaces formed in Holocene have been offset by this active segment. The highest one among the three surfaces is the back edge of a pluvial fan located on the western side of the Datong Basin. The upper layer of this pluvial fan consists of mid Holocene deposits, dated as 5ka BP. The other two lower surfaces are the 1st terrace and the 2nd terrace embedded into the pluvial fan. Among them, the 2nd terrace is a denudation terrace with a height of 8m; while the 1st terrace is accumulated with a height of 1.5～4m. The dating data show that the near surface layer of the 1st terrace is of 2.52ka BP in age (See Fig.2 & 3 in the text). Moreover, field investigation also shows that the Kouquan Fault has had obvious right lateral strike slip component in Holocene as more than ten east west directed gullies were offset right laterally for 8～20m when crossing the fault trace. Two exploratory trenches were dug during our investigation on the northern and southern segments of the Kouquan Fault, respectively. Their locations were chosen right beneath the fault plane where the fault offsets the 1st terrace of the gully (see Fig. 4 & 6 in the text). The two trenches are of 40km apart. Their dimensions are 11m in length with a depth of 4～5.5m and 22m in length with a depth of 3.2～8.8m, respectively. The two trenches reveal a line of evidence of the Holocene activities of the Kouquan Fault. The Wudao trench has revealed 3 fault planes, and in the middle part of the profile a drag structure in dark brown clay layer has been observed, appearing as the ascending of the western side and the descending of the eastern side (Fig. 5). The Shanghuangzhuang trench reveals a fault bundle of 13m in width that consists of 5 groups of faults. A vertical displacement of 2.9m for the two sides of F 1～F 4 Faults can be determined from the vertical dragging of the dark gray clay layers on the trench profile. The F 5 Fault at the easternmost end of the profile consists of two vertical fault planes about 0.8m apart. No vertical displacement of clay layers on both sides of F 5 is observed, but the layers between the two fault planes have nearly horizontal layering and show stratum discontinuity on both sides of the fault, indicating a strike slip activity of the fault. Moreover, the shanghuangzhuang trench log shows multiple yellow sand soil veins in the vicinity of the fault planes (Fig. 7). The time sequence of the paleo seismic activities revealed by the Wudao and the Shanghuangzhuang trench logs might correspond to each other. That is to say that there have been 4 paleo earthquake events since 13 7ka BP. Three of them occurred about 2 25, 5 68, and 13 73ka BP, respectively. The rest event occurred between 6 76ka and 10 82ka. The average recurrence time of these 4 events would be 3737yr, and the interval between the latest and its previous one is 3160yr. The average minimum co seismic vertical displacement of the 4 events reaches 1.8m. These new data are of great significance to earthquake safety assessment of the Datong area.
引文
①同359页①。
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邓起东,于贵华,叶文华.1992.地震地表破裂参数与震级关系的研究〔A〕.见:国家地震局地质研究所编.活动断裂研究(2).北京:地震出版社.247—264.
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邓起东,徐锡伟.1995.山西断陷盆地带的活动断裂和分段性研究〔A〕.见:国家地震局地质研究所编.现代地壳运动研究(6).北京:地震出版社.225—242.
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丁国瑜,卢演俦.1983.华北地块新构造基本特点的讨论〔J〕.华北地震科学,1(2):1—9.
DINGGuo yu,LUYan chou.1983.DiscussiononthecharacteristicsofneotectonicdeformationinNorthChinaBlock〔J〕.NorthChinaEarthquakeSciences,1(2):1—9(inChinese).
窦素芹,于慎谔,刘光勋.1994.系舟山山前活动断裂带的几何结构及其活动性〔A〕.见:国家地震局地质研究所编.活动断裂研究(4).北京:地震出版社.104—115.
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杜丕.1964.大同煤田区域构造特征及与邻区构造关系〔J〕.地质论评,22(4):259—266.
DUPi.1964.ThecharacteristicsofregionalstructureofDatongCoalBasinandrelationwithitsneighborstructures〔J〕.GeologicalReview,22(4):259—266(inChinese).
尔兑,李之振.1976.临汾盆地新构造运动特征及其与地震活动的关系〔J〕.地质科技,(4):52—62.
ERDui,LIZhi zhen.1976.ThecharacteristicsofneotectonicmovementandrelationwithseismicityinLinfenBasin〔J〕.GeologicalScienceTechnology,(4):52—62(inChinese).
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刘光勋,孟繁星,肖振敏,等.1983.山西洪洞县郇堡村古地震遗迹及有关问题的讨论〔A〕.见:中国地震学会地震地质专业委员会编.中国活动断裂.北京:地震出版社.291—294.
LIUGuang xun,MENGFan xing,XIAOZhen min,etal.1983.Adiscussiononthepaleo earthquakeevidencesandrelatedproblemsinthevillageXunbaocun,HongdongCounty,ShanxiProvince〔A〕.In:CommitteeofSeismogeology,SeismologicalSocietyofChina(ed).TheActiveFaultsinChina.SeismologicalPress,Beijing.291—294(inChinese).
刘光勋.1985.汾渭地堑边缘挤压构造带及其地质意义〔A〕.见:构造地质论丛编辑部编.构造地质论丛(4).北京:地质出版社.61—70.
LIUGuang xun.1985.CompressionaltectoniczonesontheLinfenWeihegrabenmarginanditsgeologicalsignifi cance〔A〕.In:EditorialBoardofCollectionofStructuralGeology(ed).CollectionofStructuralGeology(4).GeologicalPublishingHouse,Beijing.61—70(inChinese).
刘光勋,于慎愕,张世民.1991.山西五台山北麓活动断裂带〔A〕.见:国家地震局地质研究所编.活动断裂研究(1).北京:地震出版社.118—130.
LIUGuang xun,YUShen e,ZHANGShi min.1991.ThenorthernWutaishanpiedmontactivefaultzoneinShanxi〔A〕.In:InstituteofGeology,StateSeismolo
邓起东,王克鲁,汪一鹏,等.1973.山西隆起区断陷地震带地震地质条件及地震发展趋势概述〔J〕.地质科学(1):37—47.
DENGQi dong,WANGKe lu,WANGYi peng,etal.1973.OnthetendencyofseismicityandtheirgeologicalsetupoftheseismicbeltofShanxiGraben〔J〕.ScientiaGeologicaSinica,(1):37—47(inChinese).
邓起东,于贵华,叶文华.1992.地震地表破裂参数与震级关系的研究〔A〕.见:国家地震局地质研究所编.活动断裂研究(2).北京:地震出版社.247—264.
DENGQi dong,YUGui hua,YEWen hua.1992.Relationshipbetweenearthquakemagnitudeandparametersofsur facerupturesassociatedwithhistoricalearthquakes〔A〕.In:InstituteofGeology,StateSeismologicalBureau(ed).ResearchonActiveFault(2).SeismologicalPress,Beijing.247—264(inChinese).
邓起东,徐锡伟.1995.山西断陷盆地带的活动断裂和分段性研究〔A〕.见:国家地震局地质研究所编.现代地壳运动研究(6).北京:地震出版社.225—242.
DENGQi dong,XUXi wei.1995.SegmentationstudyofactivefaultsintheShanxiFaultDepressionBasinBelt〔A〕.In:InstituteofGeology,StateSeismologicalBureau(ed).RecentCrustalMovement(6).SeismologicalPress,Beijing.225—242(inChinese).
丁国瑜,卢演俦.1983.华北地块新构造基本特点的讨论〔J〕.华北地震科学,1(2):1—9.
DINGGuo yu,LUYan chou.1983.DiscussiononthecharacteristicsofneotectonicdeformationinNorthChinaBlock〔J〕.NorthChinaEarthquakeSciences,1(2):1—9(inChinese).
窦素芹,于慎谔,刘光勋.1994.系舟山山前活动断裂带的几何结构及其活动性〔A〕.见:国家地震局地质研究所编.活动断裂研究(4).北京:地震出版社.104—115.
DOUSu qin,YUShen e,LIUGuang xun.1994.GeometricstructureandactivityoftheXizhoushanMountainpiedmontfaultinShanxiProvince〔A〕.In:InstituteofGeology,StateSeismologicalBureau(ed).ResearchonActiveFault(4).SeismologicalPress,Beijing.104—115(inChinese).
杜丕.1964.大同煤田区域构造特征及与邻区构造关系〔J〕.地质论评,22(4):259—266.
DUPi.1964.ThecharacteristicsofregionalstructureofDatongCoalBasinandrelationwithitsneighborstructures〔J〕.GeologicalReview,22(4):259—266(inChinese).
尔兑,李之振.1976.临汾盆地新构造运动特征及其与地震活动的关系〔J〕.地质科技,(4):52—62.
ERDui,LIZhi zhen.1976.ThecharacteristicsofneotectonicmovementandrelationwithseismicityinLinfenBasin〔J〕.GeologicalScienceTechnology,(4):52—62(inChinese).
国家地震局地震地质大队,北京大学地质地理系.1979.临汾盆地活动构造体系与地震活动〔A〕.见:中国地质科学院地质力学所编.地质力学论丛(5).北京:科学出版社.140—150.
SeismoGeologicalBrigade,SSB ,DepartmentofGeologyandGeography,PekingUniversity.1979.ActivestructuralsystemandseismicityofLinfenBasin〔A〕.In:InstituteofGeomechanics,ChineseAcademyofGeologicalSci ences(ed).CollectionofGeomechanics(5).SciencePress,Beijing.140—150(inChinese).
刘光勋,肖振敏.1982.山西地堑系及其地震构造特征〔A〕.见:中国地质学会构造地质专业委员会编.第二届全国地质构造学术会议论文选集,第三卷,中新生代构造.北京:科学出版社.66—74.
LIUGuang xun,XIAOZhen ming.1982.ShanxiGrabenSystemanditsseismotectonics〔A〕.In:CommissionofStructuralGeology,GeologicalSocietyofChina(ed).SelectedPapersfromtheSecondNationalCongressonTectonics.Vol.Ⅲ.MesozoicandCenozoicTectonics.SciencePress,Beijing.66—74(inChinese).
刘光勋,孟繁星,肖振敏,等.1983.山西洪洞县郇堡村古地震遗迹及有关问题的讨论〔A〕.见:中国地震学会地震地质专业委员会编.中国活动断裂.北京:地震出版社.291—294.
LIUGuang xun,MENGFan xing,XIAOZhen min,etal.1983.Adiscussiononthepaleo earthquakeevidencesandrelatedproblemsinthevillageXunbaocun,HongdongCounty,ShanxiProvince〔A〕.In:CommitteeofSeismogeology,SeismologicalSocietyofChina(ed).TheActiveFaultsinChina.SeismologicalPress,Beijing.291—294(inChinese).
刘光勋.1985.汾渭地堑边缘挤压构造带及其地质意义〔A〕.见:构造地质论丛编辑部编.构造地质论丛(4).北京:地质出版社.61—70.
LIUGuang xun.1985.CompressionaltectoniczonesontheLinfenWeihegrabenmarginanditsgeologicalsignifi cance〔A〕.In:EditorialBoardofCollectionofStructuralGeology(ed).CollectionofStructuralGeology(4).GeologicalPublishingHouse,Beijing.61—70(inChinese).
刘光勋,于慎愕,张世民.1991.山西五台山北麓活动断裂带〔A〕.见:国家地震局地质研究所编.活动断裂研究(1).北京:地震出版社.118—130.
LIUGuang xun,YUShen e,ZHANGShi min.1991.ThenorthernWutaishanpiedmontactivefaultzoneinShanxi〔A〕.In:InstituteofGeology,StateSeismolo
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