山西太原交城断裂西张村探槽的显微构造和显微沉积学分析
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摘要
松散沉积物中的断层常常没有留下明显的宏观形迹,单靠肉眼观测往往难以确定其存在,即使存在,也很难判定其活动性质和活动方式。最近,中国地震局地壳应力研究所和山西省地震局在太原市西张村横跨交城断裂开挖了大规模探槽,认为该探槽揭示了3次7级以上地震事件。文中通过对该探槽开展微观分析,来探索松散沉积物中宏观形迹不明的断层或隐形断层及其伴随的古地震事件的显微构造及显微沉积学标志。研究结果表明,该探槽中的断层在微观上表现为微破碎带、滑移面、变形条带和泥质充填带等多种形式,同时断层附近样品也有一定的变形现象。断层和外围样品中的碎屑颗粒在棱角度、粒度大小和分布特征等方面均有不同,断层样品粒度分布的分维值D=2.0。这些结果表明松散沉积物中断层作用有颗粒流动也有碎裂作用。同时发现了与震击物(seismite)宏观标志非常相似的诸多微观标志,如球状体、负荷构造、流体通道和物质流动等,从微观上证明该断裂活动伴随有古地震事件。
Faulting process in soft sediments usually did not leave any macroscopically observable trace,so the occurrence of the fault as well as its activity and mode of motion cannot be identified by naked eyes in the field.Available data have shown that microstructural and micro-sedimentologic analyses are effective method for identifying obscured fault and paleoearthquake event in soft sediment.Recently,a large-scale trench has been excavated across the Jiaocheng Fault by the Institute of Crustal Dynamics and Earthquake Administration of Shanxi Province.They believe that the trench reveals 3 paleoearthquake events of M>7.0.In this study,we attempt to seek for the microstructural and micro-sedimentologic indicators of obscured fault and paleo-seismic event in soft sediment,through the microscopic analysis of this trench.Microstructural observation reveals that the fault in this trench microscopically appears as micro-fracture zone,slip surface,deformation bands and the bands of clay fillings,while deformation microstructures can be observed in the samples collected from the vicinity of the fault.Micro-sedimentologic analysis shows that the angularity,grain-size and particle size distribution of the samples collected from the fault differ to some extent from those of the samples collected outside the fault.The fractal dimension of the particle size distribution of the sample collected from the fault is D=2.0,which indicates the existence of cataclasis by controlled particulate flow during faulting process.Microscopic indicators comparable to the macroscopic indicators of seismites,such as ball and pillow structure,load structure,fluid flow,mass flow and the floatation of organics,are observed widely in the samples studied.All the results show that microstructural and micro-sedimentologic analyses are effective approaches to the identifying of obscured fault and paleo-seismic event in soft sediments.
Faulting process in soft sediments usually did not leave any macroscopically observable trace,so the occurrence of the fault as well as its activity and mode of motion cannot be identified by naked eyes in the field.Available data have shown that microstructural and micro-sedimentologic analyses are effective method for identifying obscured fault and paleoearthquake event in soft sediment.Recently,a large-scale trench has been excavated across the Jiaocheng Fault by the Institute of Crustal Dynamics and Earthquake Administration of Shanxi Province.They believe that the trench reveals 3 paleoearthquake events of M>7.0.In this study,we attempt to seek for the microstructural and micro-sedimentologic indicators of obscured fault and paleo-seismic event in soft sediment,through the microscopic analysis of this trench.Microstructural observation reveals that the fault in this trench microscopically appears as micro-fracture zone,slip surface,deformation bands and the bands of clay fillings,while deformation microstructures can be observed in the samples collected from the vicinity of the fault.Micro-sedimentologic analysis shows that the angularity,grain-size and particle size distribution of the samples collected from the fault differ to some extent from those of the samples collected outside the fault.The fractal dimension of the particle size distribution of the sample collected from the fault is D=2.0,which indicates the existence of cataclasis by controlled particulate flow during faulting process.Microscopic indicators comparable to the macroscopic indicators of seismites,such as ball and pillow structure,load structure,fluid flow,mass flow and the floatation of organics,are observed widely in the samples studied.All the results show that microstructural and micro-sedimentologic analyses are effective approaches to the identifying of obscured fault and paleo-seismic event in soft sediments.
引文
[1]汪良谋等,1988,北京市房山区琉璃河水泥厂厂址区地震基本烈度复核报告。
晁洪太.1998.第四纪地层中活断层的显微构造标志、隐性活断层及其应用研究[D]:[学位论文].北京:中国地震局地质研究所.CHAO Hong-tai.1998.Microstructural indicators of active faults and their application to determining the non-visiblefaults in Quaternary unconsolidated sediments[D].Ph D thesis.Institute of Geology,China Earthquake Admin-istration,Beijing(in Chinese).
晁洪太,邓起东,李家灵.2000.第四纪松散沉积物中隐性活断层的显微构造特征[J].地震地质,22(2):147—154.CHAO Hong-tai,DENG Qi-dong,LI Jia-ling.2000.Characteristics of microstructures of the invisible faults in Quater-nary unconsolidated sediments[J].Seismology and Geology,22(2):147—154(in Chinese).
晁洪太,邓起东,李家灵,等.2001.活断层内第四纪松散沉积物的变形类型[J].地震地质,23(3):399—406.CHAO Hong-tai,DENG Qi-dong,LI Jia-ling,et al.2001.Deformation styles of unconsolidated Quaternary sedimentson active faults[J].Seismology and Geology,23(3):399—406(in Chinese).
董文忠,侯建军,梁海华,等.1996.大同盆地内砂板梁上断裂新活动及其力学实验模拟[J].地震地质,18(1):75—82.DONG Wen-zhong,HOU Jian-jun,LIANG Hai-hua,et al.1996.Study of the active faults on Shabanliang Ridge inDatong basin and its mechanical simulation[J].Seismology and Geology,18(1):75—82(in Chinese).
侯建军,梁海华,郑文涛,等.1995.松散堆积物中活断层的破裂位移形式及其对确定古地震事件的意义[J].地球科学,20(6):697—700.HOU Jian-jun,LIANG Hai-hua,ZHENG Wen-tao,et al.1995.Fracturing and displacement types of fault in uncon-solidated accumulative materials and their implications to timing of paleoseismic events[J].Earth Sciences—Journal of China University of Geosciences,20(6):697—700(in Chinese).
姜在兴.2003.沉积学[M].北京:石油工业出版社.JIANG Zai-xing.2003.Sedimentology[M].Petroleum Industry Press,Beijing(in Chinese).
林传勇,陈孝德,罗华春,等.2006.北京顺义-前门-良乡断裂探槽的微观分析及其启示[J].地震地质,28(4):561—578.LIN Chuan-yong,CHEN Xiao-de,LUO Hua-chun,et al.2006.Microscopic analysis of the trench across the Shunyi-Qianmen-Liangxiang Fault at Shunyi,Beijing and its implications[J].Seismology and Geology,28(4):561—578(in Chinese).
王颖,迪纳瑞尔B.1985.石英砂表面结构模式图集[Z].北京:科学出版社.1—64.WANG Ying,Deonarine B.1985.Model Atlas of Surface Textures of Quartz Sand[Z].Science Press,Beijing.1—64(in Chinese).
尹国勋,汤友谊.1993.地史时期地震事件的岩石学证据:以四川峨嵋晚侏罗世湖相沉积中的震积岩为例[J].地震地质,15(1):61—65.YIN Guo-xun,TANG You-yi.1993.Petrologic evidence of seismic event in geologic history:with an example of seis-mite in the sediment of late Jurassic lake in the Emei Mountains,Sichuan Province[J].Seismology and Geology,15(1):61—65(in Chinese).
张汝藩,杨主恩.1999.扫描电镜与微观地质研究[M].北京:学苑出版社.1—190.ZHANG Ru-fan,YANG Zhu-en.1999.Microgeology Research in Scanning Electron Microscopy[M].“Xue-Yuan”Publishing House,Beijing.1—190(in Chinese).
赵晋泉,高树义,薄建杰,等.2005.山西太原西张探槽中发现7级以上地震断层[J].山西地震,(3):1—2.ZHAO Jin-quan,GAO Shu-yi,BO Jian-jie,et al.2005.A seismic fault which could cause earthquake larger thanM7.0is found at an exploratory channel in Xizhang of Taiyuan,Shanxi[J].Earthquake Research in Shanxi,(3):1—2(in Chinese).
Alvarez W,Standley E,O Conners D,et al.1998.Synsedimentary deformation in the Jurassic of southeastern Utah Acase of impact shaking?[J].Geology,26:579—582.
Antonelini M,Aydin A.1994.Microstructures of deformation bands in porous sandstone at Arches National Park,Utah[J].Jour Struc Geol,16:941—959.
Aydin A.1978.Small faults formed as deformation bands in sandstone[J].Pure Appl Geophys,116:913—930.
Aydin A,Johnson A M.1978.Development of faults as zones of deformation bands and as slip surfaces in sandstone[J].Pure Appl Geophys,931—942.
Bonilla M G,Lienkaemper J J.1991.Factors affecting the recognition of faults exposed in exploratory trenches[M].U S Geological Survey Bulletin.1—50.
Cashman S,Cashman K.2000.Cataclasis and deformation band formation in unconsolidated marine-terrace sand,Hamboldt County,California[J].Geology,28:111—114.
Davenport C A,Ringrose P S.1987.Deformation of Scottish Quaternary sediment sequences by strong earthquake mo-tion[A].In:Jones M E,Preston R M F(eds).Deformation of Sediments and Sedimentary Rocks.Geol SocLondon,Spec Publication29,299—314.
Guiraud M,Seguret M.1987.Soft-sediment microfaulting related to compaction within the fluvio-deltatic infill of theScoria strike slip basin(northern Spain)[A].In:Jones ME,Preston R MF(eds).Deformation of Sedimentsand Sedimentary Rocks.Geol Soc London,Spec Publication29,123—136.
Hooke R L,Iverson N R.1995.Grain-size distribution in deforming subglacial tills:role of grain fracture[J].Geo-logy,23(1):57—60.
Mair K,Main J G.Elphick S C.2000.Sequential development of deformation bands in the laboratory[J].Jour StrucGeol,22:25—42.
Maltman A.1987.Shear zone in argillaceous sediments—An experimental study[A].In:Jones ME,Preston R MF(eds).Deformation of Sediments and Sedimentary Rocks.Geol Soc London,Spec Publication29,77—87.
Nettoff D.2002.Seismogenically induced fluidization of Jurassic sands,south-central Utah[J].Sedimentology,49:65—80.
Rawling G C,Goodwin L B.2003.Cataclasis and particulate flow in faulted,poorly lithified sediments[J].JourStruc Geol,25(3):317—331.
Sammis C,King G,Biegel R.1987.The kinematics of gouge deformation[J].Pure Appl Geophys,125(5):777—812.
Seilacher A.1969.Fault-graded beds interpreted as seismites[J].Sedimentology,13:155—159.
Underhill J R,Woodcock N H.1987.Faulting mechanism in high-porosity sandstones;New Red Sandstone,ArranScotland[A].In:Jones M E,Preston R M F(eds).Deformation of Sediments and Sedimentary Rocks.GeolSoc London,Spec Publication29,91—105.
Vittori E,Labini S S,Serva L.1991.Palaeoseismology:Review of the state-of-the-art[J].Tectonophysics,193:9—32.
Wolf H,Konig D,Triantafyllidis T.2003.Experimental investigation of shear band pattern in granular materials[J].Jour Struc Geol,25(8):1229—1240.
晁洪太.1998.第四纪地层中活断层的显微构造标志、隐性活断层及其应用研究[D]:[学位论文].北京:中国地震局地质研究所.CHAO Hong-tai.1998.Microstructural indicators of active faults and their application to determining the non-visiblefaults in Quaternary unconsolidated sediments[D].Ph D thesis.Institute of Geology,China Earthquake Admin-istration,Beijing(in Chinese).
晁洪太,邓起东,李家灵.2000.第四纪松散沉积物中隐性活断层的显微构造特征[J].地震地质,22(2):147—154.CHAO Hong-tai,DENG Qi-dong,LI Jia-ling.2000.Characteristics of microstructures of the invisible faults in Quater-nary unconsolidated sediments[J].Seismology and Geology,22(2):147—154(in Chinese).
晁洪太,邓起东,李家灵,等.2001.活断层内第四纪松散沉积物的变形类型[J].地震地质,23(3):399—406.CHAO Hong-tai,DENG Qi-dong,LI Jia-ling,et al.2001.Deformation styles of unconsolidated Quaternary sedimentson active faults[J].Seismology and Geology,23(3):399—406(in Chinese).
董文忠,侯建军,梁海华,等.1996.大同盆地内砂板梁上断裂新活动及其力学实验模拟[J].地震地质,18(1):75—82.DONG Wen-zhong,HOU Jian-jun,LIANG Hai-hua,et al.1996.Study of the active faults on Shabanliang Ridge inDatong basin and its mechanical simulation[J].Seismology and Geology,18(1):75—82(in Chinese).
侯建军,梁海华,郑文涛,等.1995.松散堆积物中活断层的破裂位移形式及其对确定古地震事件的意义[J].地球科学,20(6):697—700.HOU Jian-jun,LIANG Hai-hua,ZHENG Wen-tao,et al.1995.Fracturing and displacement types of fault in uncon-solidated accumulative materials and their implications to timing of paleoseismic events[J].Earth Sciences—Journal of China University of Geosciences,20(6):697—700(in Chinese).
姜在兴.2003.沉积学[M].北京:石油工业出版社.JIANG Zai-xing.2003.Sedimentology[M].Petroleum Industry Press,Beijing(in Chinese).
林传勇,陈孝德,罗华春,等.2006.北京顺义-前门-良乡断裂探槽的微观分析及其启示[J].地震地质,28(4):561—578.LIN Chuan-yong,CHEN Xiao-de,LUO Hua-chun,et al.2006.Microscopic analysis of the trench across the Shunyi-Qianmen-Liangxiang Fault at Shunyi,Beijing and its implications[J].Seismology and Geology,28(4):561—578(in Chinese).
王颖,迪纳瑞尔B.1985.石英砂表面结构模式图集[Z].北京:科学出版社.1—64.WANG Ying,Deonarine B.1985.Model Atlas of Surface Textures of Quartz Sand[Z].Science Press,Beijing.1—64(in Chinese).
尹国勋,汤友谊.1993.地史时期地震事件的岩石学证据:以四川峨嵋晚侏罗世湖相沉积中的震积岩为例[J].地震地质,15(1):61—65.YIN Guo-xun,TANG You-yi.1993.Petrologic evidence of seismic event in geologic history:with an example of seis-mite in the sediment of late Jurassic lake in the Emei Mountains,Sichuan Province[J].Seismology and Geology,15(1):61—65(in Chinese).
张汝藩,杨主恩.1999.扫描电镜与微观地质研究[M].北京:学苑出版社.1—190.ZHANG Ru-fan,YANG Zhu-en.1999.Microgeology Research in Scanning Electron Microscopy[M].“Xue-Yuan”Publishing House,Beijing.1—190(in Chinese).
赵晋泉,高树义,薄建杰,等.2005.山西太原西张探槽中发现7级以上地震断层[J].山西地震,(3):1—2.ZHAO Jin-quan,GAO Shu-yi,BO Jian-jie,et al.2005.A seismic fault which could cause earthquake larger thanM7.0is found at an exploratory channel in Xizhang of Taiyuan,Shanxi[J].Earthquake Research in Shanxi,(3):1—2(in Chinese).
Alvarez W,Standley E,O Conners D,et al.1998.Synsedimentary deformation in the Jurassic of southeastern Utah Acase of impact shaking?[J].Geology,26:579—582.
Antonelini M,Aydin A.1994.Microstructures of deformation bands in porous sandstone at Arches National Park,Utah[J].Jour Struc Geol,16:941—959.
Aydin A.1978.Small faults formed as deformation bands in sandstone[J].Pure Appl Geophys,116:913—930.
Aydin A,Johnson A M.1978.Development of faults as zones of deformation bands and as slip surfaces in sandstone[J].Pure Appl Geophys,931—942.
Bonilla M G,Lienkaemper J J.1991.Factors affecting the recognition of faults exposed in exploratory trenches[M].U S Geological Survey Bulletin.1—50.
Cashman S,Cashman K.2000.Cataclasis and deformation band formation in unconsolidated marine-terrace sand,Hamboldt County,California[J].Geology,28:111—114.
Davenport C A,Ringrose P S.1987.Deformation of Scottish Quaternary sediment sequences by strong earthquake mo-tion[A].In:Jones M E,Preston R M F(eds).Deformation of Sediments and Sedimentary Rocks.Geol SocLondon,Spec Publication29,299—314.
Guiraud M,Seguret M.1987.Soft-sediment microfaulting related to compaction within the fluvio-deltatic infill of theScoria strike slip basin(northern Spain)[A].In:Jones ME,Preston R MF(eds).Deformation of Sedimentsand Sedimentary Rocks.Geol Soc London,Spec Publication29,123—136.
Hooke R L,Iverson N R.1995.Grain-size distribution in deforming subglacial tills:role of grain fracture[J].Geo-logy,23(1):57—60.
Mair K,Main J G.Elphick S C.2000.Sequential development of deformation bands in the laboratory[J].Jour StrucGeol,22:25—42.
Maltman A.1987.Shear zone in argillaceous sediments—An experimental study[A].In:Jones ME,Preston R MF(eds).Deformation of Sediments and Sedimentary Rocks.Geol Soc London,Spec Publication29,77—87.
Nettoff D.2002.Seismogenically induced fluidization of Jurassic sands,south-central Utah[J].Sedimentology,49:65—80.
Rawling G C,Goodwin L B.2003.Cataclasis and particulate flow in faulted,poorly lithified sediments[J].JourStruc Geol,25(3):317—331.
Sammis C,King G,Biegel R.1987.The kinematics of gouge deformation[J].Pure Appl Geophys,125(5):777—812.
Seilacher A.1969.Fault-graded beds interpreted as seismites[J].Sedimentology,13:155—159.
Underhill J R,Woodcock N H.1987.Faulting mechanism in high-porosity sandstones;New Red Sandstone,ArranScotland[A].In:Jones M E,Preston R M F(eds).Deformation of Sediments and Sedimentary Rocks.GeolSoc London,Spec Publication29,91—105.
Vittori E,Labini S S,Serva L.1991.Palaeoseismology:Review of the state-of-the-art[J].Tectonophysics,193:9—32.
Wolf H,Konig D,Triantafyllidis T.2003.Experimental investigation of shear band pattern in granular materials[J].Jour Struc Geol,25(8):1229—1240.
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