乌鲁木齐西山断裂组与地表破裂型逆断层古地震识别标志
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摘要
乌鲁木齐西山断裂层组展布于北天山山前断展褶皱系与博格达推覆构造系的转换部位,为盆地向S推覆的构造,由4～5条长度十几公里至近30km的断层组成,其滑脱面埋深约11km。通过地质地貌调查、探槽开挖,结合深部构造特征分析,西山断裂组晚更新世中晚期有明显的活动。断层F1—F3最年轻的2次事件基本都被限制在距今(22.7±5.2)ka和40ka左右。而F4和西山断裂最年轻的事件被距今31.0ka和38.0ka的地层覆盖。这显示西山断裂组晚第四纪活动有分组和组合破裂的特征。断层F4和西山南缘断裂为一组,F1—F3为另一组。坎前堆积地层、断层与堆积地层的切错关系和不同间断面或标志地层在断层两侧的累积位差的突变,是识别地表破裂型逆断层古地震事件的重要标志。降低逆断层古地震识别的不确定性,关键在于识别事件的标志需要综合分析各种影响因素,有多证据的支持。
Xishan Fault group is distributed in the transition zone between the fold-reverse fault system along the front of the north Tianshan Mountains to the west and the thrust tectonics of Bogeda to the east.It is a tectonics that thrusts from the basin in the north to the mountains in the south,consisting of 4～5 faults that are more than 10 to about 30km long,showing low angles near surface and converging on the detachment surface at about 11km deep.We discovered that the activity of Xishan Fault group is distinct during late Quaternary by doing field investigation of geology and geomorphology,excavating trenches along faults and analyzing deep structure of the fault group.The faults offset the second and above terraces of Wanjiagou creek and created fault scarps of 0.5～5.4m high on the terraces.And traces of paleoearthquakes can be found easily.The younger two events on F1,F2 and F3 are confined in(22.7±5.2)ka and 40ka BP by OSL samples dating,respectively and the traces of the youngest event on F4 and the front fault of Xishan are covered by deposits whose ages of OSL samples are about(31.1±3.2)ka and(37.9±3.8)ka BP,respectively.It means that there was grouped faulting in late Quaternary in the Xishan Fault group.F1,F2 and F3 or F4 and the front fault of Xishan might rupture in a same event on near surface.Event traces on the Xishan Fault group and other reverse faults of low angle show that the deposits along the front of fault scarp,the offset relation between fault and deposit bed,and the abrupt increase and diminution of displacement on difference markers or unconformable surfaces on both sides of fault are important identification marks of paleoearthquakes along surface rupture-type reverse fault.The deposits along the front of fault scarp on reverse faults of low angle are much more different from those on normal fault.For ideal mode,the deposit in front of fault scarp of reverse fault of low angle is characterized with that the original structure of the collapsing thrust sheet front is not broken entirely on the lower part and the sloping deposit on the upper part may exist covering on both sides of the fault.We think that it is very important for reducing uncertainty of paleoearthquake identification to seek for evidences as many as possible and analyze the different influencing factors,such as tectonics,climate,environment and anthropic activities.
Xishan Fault group is distributed in the transition zone between the fold-reverse fault system along the front of the north Tianshan Mountains to the west and the thrust tectonics of Bogeda to the east.It is a tectonics that thrusts from the basin in the north to the mountains in the south,consisting of 4～5 faults that are more than 10 to about 30km long,showing low angles near surface and converging on the detachment surface at about 11km deep.We discovered that the activity of Xishan Fault group is distinct during late Quaternary by doing field investigation of geology and geomorphology,excavating trenches along faults and analyzing deep structure of the fault group.The faults offset the second and above terraces of Wanjiagou creek and created fault scarps of 0.5～5.4m high on the terraces.And traces of paleoearthquakes can be found easily.The younger two events on F1,F2 and F3 are confined in(22.7±5.2)ka and 40ka BP by OSL samples dating,respectively and the traces of the youngest event on F4 and the front fault of Xishan are covered by deposits whose ages of OSL samples are about(31.1±3.2)ka and(37.9±3.8)ka BP,respectively.It means that there was grouped faulting in late Quaternary in the Xishan Fault group.F1,F2 and F3 or F4 and the front fault of Xishan might rupture in a same event on near surface.Event traces on the Xishan Fault group and other reverse faults of low angle show that the deposits along the front of fault scarp,the offset relation between fault and deposit bed,and the abrupt increase and diminution of displacement on difference markers or unconformable surfaces on both sides of fault are important identification marks of paleoearthquakes along surface rupture-type reverse fault.The deposits along the front of fault scarp on reverse faults of low angle are much more different from those on normal fault.For ideal mode,the deposit in front of fault scarp of reverse fault of low angle is characterized with that the original structure of the collapsing thrust sheet front is not broken entirely on the lower part and the sloping deposit on the upper part may exist covering on both sides of the fault.We think that it is very important for reducing uncertainty of paleoearthquake identification to seek for evidences as many as possible and analyze the different influencing factors,such as tectonics,climate,environment and anthropic activities.
引文
[1]新疆地震局,2004,乌鲁木齐市城市活断层探测与地震危险性评价的初步设计。
[1]同220页[1]。
[1]沈军等,2006,海峡两岸第五届地震科技研讨会报告。
邓起东,汪一鹏,廖玉华,等.1984.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,29(9):557—560.DENG Qi-dong,WANG Yi-peng,LIAO Yu-hua,et al.1984.Collapse wedges by fault scarps and Holocene history ofmovement along Helanshan piedmont fault[J].Science Bulletin,29(9):557—560(in Chinese).
邓起东,冯先岳,尤惠川,等.1991.新疆独山子-安集海活动逆断裂带晚第四纪活动特征及古地震[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.37—55.DENG Qi-dong,FENG Xian-yue,YOU Hui-chuan,et al.1991.Paleoseismology and late Quaternary activity of theDushanzi-Anjihai reverse fault zone,Xinjiang[A].In:Institute of Geology,SSB(ed).Research on ActiveFaults(1).Seismological Press,Beijing.37—55(in Chinese).
邓起东,张培震.2000a.史前古地震的逆断层崩积楔[J].科学通报,45(6):650—655.DENG Qi-dong,ZHANG Pei-zhen.2000a.Colluvial wedges associated with pre-historical reverse faulting paleoearth-quakes[J].Chinese Science Bulletin,45(6):650—655(in Chinese).
邓起东,冯先岳,张培震,等.2000b.天山活动构造[M].北京:地震出版社.1—399.DENG Qi-dong,FENG Xian-yue,ZHANG Pei-zhen,et al.2000b.Active Tectonics of Tianshan[M].SeismologicalPress,Beijing.1—399(in Chinese).
毛凤英,张培震.1995.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].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.153—164.MAO Feng-ying,ZHANG Pei-zhen.1995.Method for progressive constraint of paleoseismic events and paleoseis-mological study of major fault zone in northern Xinjiang[A].In:Institute of Geology,SSB(ed).Research onActive Faults(4).Seismological Press,Beijing.153—164(in Chinese).
冉勇康,李志义,尤惠川,等.1988.河西走廊黑河口断层上的古地震及年代学研究[J].地震地质,10(4):118—126.RAN Yong-kang,LI Zhi-yi,YOU Hui-chuan,et al.1988.The study and Dating of Paleoearthquake along Heihekoufault in Hexi Corridor[J].Seismology and Geology,10(4):118—126(in Chinese).
冉勇康,杨晓平,程建武,等.2006.南天山柯坪推覆构造柯坪塔格山前逆断裂东段晚第四纪的古地震[J].地震地质,28(2):245—257.RAN Yong-kang,YANG Xiao-ping,CHENG Jian-wu,et al.2006.Paleoearthquakes along the East Section of theRange Front Fault of Kalpintage during Late Quaternary in Kalpin Structure System,the South Tianshan Mountains[J].Seismology and Geology,28(2):245—257(in Chinese).
冉勇康,张培震,陈立春.2003.河套断陷带大青山山前断裂晚第四纪古地震完整性研究[J].地学前缘,10(特刊):207—216.RAN Yong-kang,ZHANG Pei-zhen,CHENLi-chun.2003.Research on the completeness of paleoseismic activity his-tory since late Quaternary along the Daqingshan piedmont fault in Hetao depression zone,North China[J].EarthScience Frontiers,10(Special issue):207—216(in Chinese).
杨晓平,冉勇康,宋方敏,等.2006.西南天山柯坪逆冲推覆构造的地壳缩短分析[J].地震地质,28(2):194—204.YANG Xiao-ping,RAN Yong-kang,SONG Fang-min,et al.2006.The analysis for crust shortening of Kalpin thrusttectonic zone,southwestern Tianshan,Xinjiang,China[J].Seismology and Geology,28(2):194—204(in Chi-nese).
张培震,邓起东,杨晓平,等.1995.天山北麓的冰水冲洪积地貌与新构造运动[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.63—78.ZHANG Pei-zhen,DENG Qi-dong,YANG Xiao-ping.1995.Glaciofluvial geomorphology and neotectonnics along therange-front of the northern Tianshan[A].In:Institute of Geology,SSB(ed).Research on Active Faults(4).Seismological Press,Beijing.63—78(in Chinese).
张培震,邓起东,徐锡伟,等.1994.盲断层“褶皱地震”与1906年玛纳斯地震[J].地震地质,16(3):193—204.ZHANG Pei-zhen,DENG Qi-dong,XU Xi-wei,et al.1994.Blind thrust,folding earthquake,and the1906Manasearthquake,Xinjiang[J].Seismology and Geology,16(3):193—204(in Chinese).
Bucknam R C,Anderson R E.1979.Estimation of fault-scarp ages from a scarp-height-slope-angle relationship[J].Geology,7:11—14.
Carver G A.1987.Geologic criteria for recognition of individual paleoseismic events in compressional tectonic environ-ments[R].USGS Open File Report87—683.115—128.
Jamison J.1987.Geometric analysis of fold development in overthrust terraces[J].Structure Geol,9:207—219.
McCalpin J P.1996.Paleoseismology[M].Academic Press,San Diego.588.
McCalpin J P.1987.Geologic criteria for recognition of individual paleoseismic events in extensional environments[R].USGS Open File Report,683.102—114.
Michetti A M.Audemard M,Marco S.2005.Future trends in paleoseismology:Integrated study of the seismic land-scape as a vital tool in seismic hazard analyses[J].Tectonophysics,408:3—21.
Nelson A R.1987.A facies model of colluvial sedimentation adjacent to a single-event normal-fault scarp,Basin andRange Province,Western United States[R].USGS Open File Report87—683.136—145.
RAN Yong-kang,ZHANG Pei-zhen,CHEN Li-chun.2003.Late Quaternary history of paleoseismic activity along theHohhot segment of the Daqingshan piedmont fault in Hetao depression zone,North China[J].Annali di Geofisi-ca.Special Issue,46(5):1053—1071.
Rockwell T.1987.Recognition of individual paleoseismic events in strike-slip environments[R].USGS Open File Re-port87—683.129—135.
Sieh K E.1978.Pre-historic large earthquakes produced by slip on the San Andreas fault at Pallett Creek,California[J].JGR,83:3907—3939.
Sieh K E.1984.Lateral offsets and revised dates of large earthquakes at Pallett Creek,California[J].J Geophy Res,89:7641—7670.
Swan F H,Schwartz D P,and Cluff L S.1980.Recurrence of moderate-to-large magnitude earthquakes produced bysurface faulting on the Wasatch Fault Zone[J].Utah:Bulletin of the Seismological Society of America,70(5):1431—1462.
Suppe J.1983.Geometry and kinematics of fault-bend folding[J].Am J Sci,283:684—721.
Wallace R E.1977.Profiles and ages of young fault scarps,north-central Nevada[J].BGSA,88:1267—1278.
Yeats R S.1996.Introducton to special section:Paleoseismology[J].J Geophy Res,101(B3):5847—5853.
[1]同220页[1]。
[1]沈军等,2006,海峡两岸第五届地震科技研讨会报告。
邓起东,汪一鹏,廖玉华,等.1984.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,29(9):557—560.DENG Qi-dong,WANG Yi-peng,LIAO Yu-hua,et al.1984.Collapse wedges by fault scarps and Holocene history ofmovement along Helanshan piedmont fault[J].Science Bulletin,29(9):557—560(in Chinese).
邓起东,冯先岳,尤惠川,等.1991.新疆独山子-安集海活动逆断裂带晚第四纪活动特征及古地震[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.37—55.DENG Qi-dong,FENG Xian-yue,YOU Hui-chuan,et al.1991.Paleoseismology and late Quaternary activity of theDushanzi-Anjihai reverse fault zone,Xinjiang[A].In:Institute of Geology,SSB(ed).Research on ActiveFaults(1).Seismological Press,Beijing.37—55(in Chinese).
邓起东,张培震.2000a.史前古地震的逆断层崩积楔[J].科学通报,45(6):650—655.DENG Qi-dong,ZHANG Pei-zhen.2000a.Colluvial wedges associated with pre-historical reverse faulting paleoearth-quakes[J].Chinese Science Bulletin,45(6):650—655(in Chinese).
邓起东,冯先岳,张培震,等.2000b.天山活动构造[M].北京:地震出版社.1—399.DENG Qi-dong,FENG Xian-yue,ZHANG Pei-zhen,et al.2000b.Active Tectonics of Tianshan[M].SeismologicalPress,Beijing.1—399(in Chinese).
毛凤英,张培震.1995.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].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.153—164.MAO Feng-ying,ZHANG Pei-zhen.1995.Method for progressive constraint of paleoseismic events and paleoseis-mological study of major fault zone in northern Xinjiang[A].In:Institute of Geology,SSB(ed).Research onActive Faults(4).Seismological Press,Beijing.153—164(in Chinese).
冉勇康,李志义,尤惠川,等.1988.河西走廊黑河口断层上的古地震及年代学研究[J].地震地质,10(4):118—126.RAN Yong-kang,LI Zhi-yi,YOU Hui-chuan,et al.1988.The study and Dating of Paleoearthquake along Heihekoufault in Hexi Corridor[J].Seismology and Geology,10(4):118—126(in Chinese).
冉勇康,杨晓平,程建武,等.2006.南天山柯坪推覆构造柯坪塔格山前逆断裂东段晚第四纪的古地震[J].地震地质,28(2):245—257.RAN Yong-kang,YANG Xiao-ping,CHENG Jian-wu,et al.2006.Paleoearthquakes along the East Section of theRange Front Fault of Kalpintage during Late Quaternary in Kalpin Structure System,the South Tianshan Mountains[J].Seismology and Geology,28(2):245—257(in Chinese).
冉勇康,张培震,陈立春.2003.河套断陷带大青山山前断裂晚第四纪古地震完整性研究[J].地学前缘,10(特刊):207—216.RAN Yong-kang,ZHANG Pei-zhen,CHENLi-chun.2003.Research on the completeness of paleoseismic activity his-tory since late Quaternary along the Daqingshan piedmont fault in Hetao depression zone,North China[J].EarthScience Frontiers,10(Special issue):207—216(in Chinese).
杨晓平,冉勇康,宋方敏,等.2006.西南天山柯坪逆冲推覆构造的地壳缩短分析[J].地震地质,28(2):194—204.YANG Xiao-ping,RAN Yong-kang,SONG Fang-min,et al.2006.The analysis for crust shortening of Kalpin thrusttectonic zone,southwestern Tianshan,Xinjiang,China[J].Seismology and Geology,28(2):194—204(in Chi-nese).
张培震,邓起东,杨晓平,等.1995.天山北麓的冰水冲洪积地貌与新构造运动[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.63—78.ZHANG Pei-zhen,DENG Qi-dong,YANG Xiao-ping.1995.Glaciofluvial geomorphology and neotectonnics along therange-front of the northern Tianshan[A].In:Institute of Geology,SSB(ed).Research on Active Faults(4).Seismological Press,Beijing.63—78(in Chinese).
张培震,邓起东,徐锡伟,等.1994.盲断层“褶皱地震”与1906年玛纳斯地震[J].地震地质,16(3):193—204.ZHANG Pei-zhen,DENG Qi-dong,XU Xi-wei,et al.1994.Blind thrust,folding earthquake,and the1906Manasearthquake,Xinjiang[J].Seismology and Geology,16(3):193—204(in Chinese).
Bucknam R C,Anderson R E.1979.Estimation of fault-scarp ages from a scarp-height-slope-angle relationship[J].Geology,7:11—14.
Carver G A.1987.Geologic criteria for recognition of individual paleoseismic events in compressional tectonic environ-ments[R].USGS Open File Report87—683.115—128.
Jamison J.1987.Geometric analysis of fold development in overthrust terraces[J].Structure Geol,9:207—219.
McCalpin J P.1996.Paleoseismology[M].Academic Press,San Diego.588.
McCalpin J P.1987.Geologic criteria for recognition of individual paleoseismic events in extensional environments[R].USGS Open File Report,683.102—114.
Michetti A M.Audemard M,Marco S.2005.Future trends in paleoseismology:Integrated study of the seismic land-scape as a vital tool in seismic hazard analyses[J].Tectonophysics,408:3—21.
Nelson A R.1987.A facies model of colluvial sedimentation adjacent to a single-event normal-fault scarp,Basin andRange Province,Western United States[R].USGS Open File Report87—683.136—145.
RAN Yong-kang,ZHANG Pei-zhen,CHEN Li-chun.2003.Late Quaternary history of paleoseismic activity along theHohhot segment of the Daqingshan piedmont fault in Hetao depression zone,North China[J].Annali di Geofisi-ca.Special Issue,46(5):1053—1071.
Rockwell T.1987.Recognition of individual paleoseismic events in strike-slip environments[R].USGS Open File Re-port87—683.129—135.
Sieh K E.1978.Pre-historic large earthquakes produced by slip on the San Andreas fault at Pallett Creek,California[J].JGR,83:3907—3939.
Sieh K E.1984.Lateral offsets and revised dates of large earthquakes at Pallett Creek,California[J].J Geophy Res,89:7641—7670.
Swan F H,Schwartz D P,and Cluff L S.1980.Recurrence of moderate-to-large magnitude earthquakes produced bysurface faulting on the Wasatch Fault Zone[J].Utah:Bulletin of the Seismological Society of America,70(5):1431—1462.
Suppe J.1983.Geometry and kinematics of fault-bend folding[J].Am J Sci,283:684—721.
Wallace R E.1977.Profiles and ages of young fault scarps,north-central Nevada[J].BGSA,88:1267—1278.
Yeats R S.1996.Introducton to special section:Paleoseismology[J].J Geophy Res,101(B3):5847—5853.
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