西南天山东柯坪推覆系古地震初步研究
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摘要
西南天山柯坪推覆系发育多排逆断裂-褶皱带,各排逆断裂-褶皱带的变形速率并不一致,古地震发生规律也可能具有不同特点。自汶川地震造成龙门山中央和前山两条断裂同时活动之后,对于如何判断多条逆断裂级联破裂的逆断裂古地震事件,是一个值得讨论的问题。文中通过对东柯坪塔格和萨尔干塔格两排逆断裂-褶皱带山前多期地貌面(冲洪积扇面)上发育的不同高度的断层陡坎进行测量和探槽古地震事件分析,通过10Be暴露年龄获得各级地貌面形成时间,利用相邻两级记录了不同次数古地震的地貌面年龄对各次古地震事件的上下限时间进行限制,得到了两排逆断裂-褶皱带山前不同的古地震复发周期、单次古地震垂直位错量和各自的古地震事件发生时间范围。结果表明距今20ka以来,东柯坪塔格山前古地震平均复发周期为(6.7±0.84)ka,单次事件垂直位错1m左右;萨尔干塔格山前古地震平均复发周期为(5.4±0.50)ka,单次事件的垂直位错0.8～1.2m,古地震活动强度基本一致,萨尔干塔格的周期略短。根据这些结果对是否发生级联破裂进行了初步探讨,认为探槽揭露出的第2次和第3次古地震事件发生时间范围重合,存在发生级联破裂的可能。
There are several thrust-fold belts developed in the Kalpin nappe system of the southwestern Tianshan Mountains.Not only deformation rates of these thrust-fold belts are inconsistent,but also the paleoearthquakes recurrence laws on these thrust-fold belts in the nappe system are different.The Beichuan-Yingxiu Fault and the Pengguan Fault ruptured simultaneously in the Mw 7.9 Wenchuan earthquake.Therefore,it is worth discussing the question of how to determine the cascade-rupturing of a paleoearthquake on two or three thrust faults.We measured the scraps of different heights on the geomorphic surfaces(alluvial-proluvial fans)of different stages in eastern Kalpintage and Saergantage and analyzed the paleoearthquake events revealed by trenches in Shanchakou and Saergantage.Using the10Be exposure age,we obtained the ages of the geomorphic surfaces.Then we got the upper and lower limit time of each paleoearthquake from the age of adjacent geomorphic surfaces.Finally,we got the recurrence intervals of different paleoearthquakes,the vertical dislocation of a single event,and the time range of the respective events.The results show that since 20kaBP,the average recurrence interval of paleoearthquake in the piedmont of east Kalpintage is 6.7±0.84ka,the vertical dislocation of a single event is 1m;the average recurrence interval of paleoearthquake in the piedmont of Saergantage is 5.4±0.50ka,and the vertical dislocation of a single event is 0.8～1.2m.The intensity of paleoseismicity is basically identical and the recurrence interval in Saergantage is slightly shorter.In the end,we discussed the possibility of cascade-rupturing accompanying these paleoearthquake events and found that the second and the third paleoearthquake events revealed by the trenches overlap in their occurrence time ranges,indicating the possibility of cascade-rupturing during the earthquake.
There are several thrust-fold belts developed in the Kalpin nappe system of the southwestern Tianshan Mountains.Not only deformation rates of these thrust-fold belts are inconsistent,but also the paleoearthquakes recurrence laws on these thrust-fold belts in the nappe system are different.The Beichuan-Yingxiu Fault and the Pengguan Fault ruptured simultaneously in the Mw 7.9 Wenchuan earthquake.Therefore,it is worth discussing the question of how to determine the cascade-rupturing of a paleoearthquake on two or three thrust faults.We measured the scraps of different heights on the geomorphic surfaces(alluvial-proluvial fans)of different stages in eastern Kalpintage and Saergantage and analyzed the paleoearthquake events revealed by trenches in Shanchakou and Saergantage.Using the10Be exposure age,we obtained the ages of the geomorphic surfaces.Then we got the upper and lower limit time of each paleoearthquake from the age of adjacent geomorphic surfaces.Finally,we got the recurrence intervals of different paleoearthquakes,the vertical dislocation of a single event,and the time range of the respective events.The results show that since 20kaBP,the average recurrence interval of paleoearthquake in the piedmont of east Kalpintage is 6.7±0.84ka,the vertical dislocation of a single event is 1m;the average recurrence interval of paleoearthquake in the piedmont of Saergantage is 5.4±0.50ka,and the vertical dislocation of a single event is 0.8～1.2m.The intensity of paleoseismicity is basically identical and the recurrence interval in Saergantage is slightly shorter.In the end,we discussed the possibility of cascade-rupturing accompanying these paleoearthquake events and found that the second and the third paleoearthquake events revealed by the trenches overlap in their occurrence time ranges,indicating the possibility of cascade-rupturing during the earthquake.
引文
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冯先岳.1985.论新疆地震地质特征[J].地震地质,7(2):35—44.FENG Xian-yue.1985.Seismogeological characteristics of the Xinjiang area[J].Seismology and Geology,7(2):35—44(in Chinese).
贾承造主编.1997.中国塔里木盆地构造特征与油气[M].北京:石油工业出版社.JIA Cheng-zao(ed).1997.Structure Character and Oil-gas in Tarim Basin,China[M].Petroleum Industry Press,Beijing(in Chinese).
曲国胜,陈杰,陈新发,等.2001.阿图什-八盘水磨塔里木盆地反冲构造系统研究[J].地震地质,23(1):1—14.QU Guo-sheng,CHEN Jie,CHEN Xin-fa,et al.2001.A study on the back-thrusting system at Atushi-Bapanshuimo inTarim Basin[J].Seismology and Geology,23(1):1—14(in Chinese).
冉勇康,杨晓平,徐锡伟,等.2006.西南天山柯坪推覆构造东段晚第四纪变形样式与缩短速率[J].地震地质,28(2):179—193.RAN Yong-kang,YANG Xiao-ping,XU Xi-wei,et al.2006.Deformation pattern and shortening rates in the east part ofKalpin thrust system in southwest Tianshan during late Quaternary[J].Seismology and Geology,28(2):179—193(in Chinese).
沈军,汪一鹏,李萤甄,等.2003.中国新疆天山博阿断裂晚第四纪右旋走滑活动特征[J].地震地质,25(2):183—194.SHEN Jun,WANG Yi-peng,LI Ying-zhen,et al.2003.Late Quaternary right-lateral strike-slip faulting along theBolokenu-Aqikekuduke Fault in Chinese Tianshan[J].Seismology and Geology,25(2):183—194(in Chinese).
汪新,贾承造,杨树锋,等.2002.南天山库车褶皱冲断带构造几何学和运动学[J].地质科学,37(3):372—384.WANG Xin,JIA Cheng-zao,YANG Shu-feng,et al.2002.Geometry and kinematics of the Kuqa fold-and-thrust belt inthe southern Tianshan[J].Chinese Journal of Geology,37(3):372—384(in Chinese).
汪新.2005.南天山山前复杂褶皱的构造形态分析:以库车秋里塔克背斜和柯坪八盘水磨背斜为例[J].高校地质学报,11(4):568—576.WANG Xin.2005.Geometry and kinematics of complex folds,illustrated with examples from Quilitake anticline of Kuqaand Bapanshuimo anticline of Keping,southern Tianshan[J].Geological Journal of China Universities,11(4):568—576(in Chinese).
杨晓平,李安,黄伟亮.2011.天山北麓活动褶皱带晚第四纪时期隆升的差异性[J].中国科学(D辑)(已接收).YANG Xiao-ping,LI An,HUANG Wei-liang.2001.Uplift differential of active fold zones during the late Quaternary,northern piedmonts of the Tianshan Mountains,China[J].Science in China Earth Sciences(in press).
杨海军,李曰俊,师骏,等.2010.南天山晚新生代褶皱-冲断带构造特征[J].第四纪研究,30(5):1030—1043.YANG Hai-jun,LI Yue-jun,SHI Jun,et al.2010.Tectonic characteristics of the late Cenozoic south Tianshan fold-thrustbelt[J].Quaternary Sciences,30(5):1030—1043(in Chinese).
杨晓平,沈军.2000.天山内部博罗可努断裂精河—阿拉山口段晚更新世以来的活动特征[J].地震地质,22(3):305—315.YANG Xiao-ping,SHEN Jun.2000.Late Quaternary activity of Jinghe-Alashankou section of the Boluokenu Fault,interior Tianshan[J].Seismology and Geology,22(3):305—315(in Chinese).
杨晓平,冉勇康,程建武,等.2006.柯坪推覆构造中的几个新生褶皱带阶地变形测量与地壳缩短[J].中国科学(D辑),36(10):905—913.YANG Xiao-ping,RAN Yong-kang,CHENG Jian-wu,et al.2007.Measurement of terrace deformation and crustalshortening of some renascent fold zones within Kalpin nappe structure[J].Science in China(Ser D),50(1):33—42.
杨晓平,周本刚,李军,等.2001.新疆南天山亚肯背斜晚更新世以来的隆起和缩短[J].地震地质,23(4):501—509.YANG Xiao-ping,ZHOU Ben-gang,LI Jun,et al.2001.Shortening and uplift of the active Yaken anticline,southernTianshan,China since late Pleistocene[J].Seismology and Geology,23(4):501—509(in Chinese).
中国地震简目编辑组.2000.中国地震简目(公元前780—公元1986年)[M].北京:地震出版社.
Editorial Board of Brief Catalogue of Chinese Earthquake.2000.Brief Catalogue of Earthquakes in China from780B.C.to1986A.D.[M].Seismological Press,Beijing(in Chinese).
Avouac J P,Tapponnier P T,Bai M,et al.1993.Active thrusting and folding along the northern Tienshan,and LateCenozoic rotation of the Tarim relative to Dzhungaria and Kazakhstan[J].Journal of Geophysical Research,98:6755—6840.
Burchfiel B C,Brown E T,Deng Qidong,et al.1999.Crustal shortening on the margins of the Tienshan,Xinjiang,China[J].International Geological Review,41:665—700.
Burtman V S,Skolelev S F,Molnar P.1996.Late Cenozoic slip on the Talas-Ferghana,the Tienshan,Central Asia[J].GSA Bulletin,108(8):1004—1021.
Balco G,Stone J O,Lifton N A,et al.2008.A complete and easily accessible means of calculating surface exposure agesor erosion rates from10Be and26Al measurements[J].Quaternary Geochronology,3:174—195.
Densmore A L,Ellis M A,Li Y,et al.2007.Active tectonics of the Beichuan and Pengguan faults at the eastern marginof the Tibetan Plateau[J].Tectonics,26:TC4005.
Herdrix M S,Dumitru T A,Graham S A,1994.Late Oligocene-early Miocene unroofing in the Chinese Tianshan:Anearly effect of the India-Asia collision[J].Geology,22:487—490.
Lal D.1991.Cosmic ray labeling of erosion surfaces:In situ nuclide production rates and erosion models[J].Earthand Planetary Science Letters,104:424—439.
Savage J C and Cockerham R S.1987.Quasi-periodic occurrence of earthquakes in the1978-1986Bishop-MammothLakes sequence,eastern California[J].BSSA,77(4):1347—1358.
Shimazaki K and Nakata T.1980.Time-predictable recurrence model for large earthquakes[J].Geophys Res Lett,7:279—282.
Sieh K.1989.A more precise chronology of earthquake produced by the San Andreas Fault in southern California[J].J Geophy Res,94(B1):603—623.
Stephen C T,Welson R J,Rubin C M,et al.2002.Late Quaternary slip rates across the central Tienshan,Kyrgyzstan,central Asia[J].Journal of Geophysical Research,107(B9):2203.
Stone J O.2000.Air pressure and cosmogenic isotope production[J].Journal of Geophysical Research,105:23,753—23,759.
Tsukuda E,Awata Y,Yamazaki H,et al.1993.Strip map of the Atera fault system[J].Geol Surv Jap Tect Map Ser,7.
Xu X W,Wen X Z,Yu G H,et al.2009.Coseismic reverse-and oblique-slip surface faulting generated by the2008MW7.9Wenchuan earthquake,China[J].Geology,37(6):515—518.
邓起东,冯先岳,张培震,等.1999.乌鲁木齐山前坳陷逆断裂-褶皱带及其形成机制[J].地学前缘,6(4):191—201.DENG Qi-dong,FENG Xian-yue,ZHANG Pei-zhen,et al.1999.Reverse fault and fold zone in the Urumqi range-frontdepression of the northern Tianshan and its genetic mechanism[J].Earth Science Frontier,6(4):191—201(inChinese).
冯先岳.1985.论新疆地震地质特征[J].地震地质,7(2):35—44.FENG Xian-yue.1985.Seismogeological characteristics of the Xinjiang area[J].Seismology and Geology,7(2):35—44(in Chinese).
贾承造主编.1997.中国塔里木盆地构造特征与油气[M].北京:石油工业出版社.JIA Cheng-zao(ed).1997.Structure Character and Oil-gas in Tarim Basin,China[M].Petroleum Industry Press,Beijing(in Chinese).
曲国胜,陈杰,陈新发,等.2001.阿图什-八盘水磨塔里木盆地反冲构造系统研究[J].地震地质,23(1):1—14.QU Guo-sheng,CHEN Jie,CHEN Xin-fa,et al.2001.A study on the back-thrusting system at Atushi-Bapanshuimo inTarim Basin[J].Seismology and Geology,23(1):1—14(in Chinese).
冉勇康,杨晓平,徐锡伟,等.2006.西南天山柯坪推覆构造东段晚第四纪变形样式与缩短速率[J].地震地质,28(2):179—193.RAN Yong-kang,YANG Xiao-ping,XU Xi-wei,et al.2006.Deformation pattern and shortening rates in the east part ofKalpin thrust system in southwest Tianshan during late Quaternary[J].Seismology and Geology,28(2):179—193(in Chinese).
沈军,汪一鹏,李萤甄,等.2003.中国新疆天山博阿断裂晚第四纪右旋走滑活动特征[J].地震地质,25(2):183—194.SHEN Jun,WANG Yi-peng,LI Ying-zhen,et al.2003.Late Quaternary right-lateral strike-slip faulting along theBolokenu-Aqikekuduke Fault in Chinese Tianshan[J].Seismology and Geology,25(2):183—194(in Chinese).
汪新,贾承造,杨树锋,等.2002.南天山库车褶皱冲断带构造几何学和运动学[J].地质科学,37(3):372—384.WANG Xin,JIA Cheng-zao,YANG Shu-feng,et al.2002.Geometry and kinematics of the Kuqa fold-and-thrust belt inthe southern Tianshan[J].Chinese Journal of Geology,37(3):372—384(in Chinese).
汪新.2005.南天山山前复杂褶皱的构造形态分析:以库车秋里塔克背斜和柯坪八盘水磨背斜为例[J].高校地质学报,11(4):568—576.WANG Xin.2005.Geometry and kinematics of complex folds,illustrated with examples from Quilitake anticline of Kuqaand Bapanshuimo anticline of Keping,southern Tianshan[J].Geological Journal of China Universities,11(4):568—576(in Chinese).
杨晓平,李安,黄伟亮.2011.天山北麓活动褶皱带晚第四纪时期隆升的差异性[J].中国科学(D辑)(已接收).YANG Xiao-ping,LI An,HUANG Wei-liang.2001.Uplift differential of active fold zones during the late Quaternary,northern piedmonts of the Tianshan Mountains,China[J].Science in China Earth Sciences(in press).
杨海军,李曰俊,师骏,等.2010.南天山晚新生代褶皱-冲断带构造特征[J].第四纪研究,30(5):1030—1043.YANG Hai-jun,LI Yue-jun,SHI Jun,et al.2010.Tectonic characteristics of the late Cenozoic south Tianshan fold-thrustbelt[J].Quaternary Sciences,30(5):1030—1043(in Chinese).
杨晓平,沈军.2000.天山内部博罗可努断裂精河—阿拉山口段晚更新世以来的活动特征[J].地震地质,22(3):305—315.YANG Xiao-ping,SHEN Jun.2000.Late Quaternary activity of Jinghe-Alashankou section of the Boluokenu Fault,interior Tianshan[J].Seismology and Geology,22(3):305—315(in Chinese).
杨晓平,冉勇康,程建武,等.2006.柯坪推覆构造中的几个新生褶皱带阶地变形测量与地壳缩短[J].中国科学(D辑),36(10):905—913.YANG Xiao-ping,RAN Yong-kang,CHENG Jian-wu,et al.2007.Measurement of terrace deformation and crustalshortening of some renascent fold zones within Kalpin nappe structure[J].Science in China(Ser D),50(1):33—42.
杨晓平,周本刚,李军,等.2001.新疆南天山亚肯背斜晚更新世以来的隆起和缩短[J].地震地质,23(4):501—509.YANG Xiao-ping,ZHOU Ben-gang,LI Jun,et al.2001.Shortening and uplift of the active Yaken anticline,southernTianshan,China since late Pleistocene[J].Seismology and Geology,23(4):501—509(in Chinese).
中国地震简目编辑组.2000.中国地震简目(公元前780—公元1986年)[M].北京:地震出版社.
Editorial Board of Brief Catalogue of Chinese Earthquake.2000.Brief Catalogue of Earthquakes in China from780B.C.to1986A.D.[M].Seismological Press,Beijing(in Chinese).
Avouac J P,Tapponnier P T,Bai M,et al.1993.Active thrusting and folding along the northern Tienshan,and LateCenozoic rotation of the Tarim relative to Dzhungaria and Kazakhstan[J].Journal of Geophysical Research,98:6755—6840.
Burchfiel B C,Brown E T,Deng Qidong,et al.1999.Crustal shortening on the margins of the Tienshan,Xinjiang,China[J].International Geological Review,41:665—700.
Burtman V S,Skolelev S F,Molnar P.1996.Late Cenozoic slip on the Talas-Ferghana,the Tienshan,Central Asia[J].GSA Bulletin,108(8):1004—1021.
Balco G,Stone J O,Lifton N A,et al.2008.A complete and easily accessible means of calculating surface exposure agesor erosion rates from10Be and26Al measurements[J].Quaternary Geochronology,3:174—195.
Densmore A L,Ellis M A,Li Y,et al.2007.Active tectonics of the Beichuan and Pengguan faults at the eastern marginof the Tibetan Plateau[J].Tectonics,26:TC4005.
Herdrix M S,Dumitru T A,Graham S A,1994.Late Oligocene-early Miocene unroofing in the Chinese Tianshan:Anearly effect of the India-Asia collision[J].Geology,22:487—490.
Lal D.1991.Cosmic ray labeling of erosion surfaces:In situ nuclide production rates and erosion models[J].Earthand Planetary Science Letters,104:424—439.
Savage J C and Cockerham R S.1987.Quasi-periodic occurrence of earthquakes in the1978-1986Bishop-MammothLakes sequence,eastern California[J].BSSA,77(4):1347—1358.
Shimazaki K and Nakata T.1980.Time-predictable recurrence model for large earthquakes[J].Geophys Res Lett,7:279—282.
Sieh K.1989.A more precise chronology of earthquake produced by the San Andreas Fault in southern California[J].J Geophy Res,94(B1):603—623.
Stephen C T,Welson R J,Rubin C M,et al.2002.Late Quaternary slip rates across the central Tienshan,Kyrgyzstan,central Asia[J].Journal of Geophysical Research,107(B9):2203.
Stone J O.2000.Air pressure and cosmogenic isotope production[J].Journal of Geophysical Research,105:23,753—23,759.
Tsukuda E,Awata Y,Yamazaki H,et al.1993.Strip map of the Atera fault system[J].Geol Surv Jap Tect Map Ser,7.
Xu X W,Wen X Z,Yu G H,et al.2009.Coseismic reverse-and oblique-slip surface faulting generated by the2008MW7.9Wenchuan earthquake,China[J].Geology,37(6):515—518.
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