宜宾-金川剖面地壳上部速度结构及构造含义
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摘要
利用有限差分和时间项两种方法对宜宾-金川人工地震剖面沿线8炮Pg波走时进行反演,得到沿测线结晶基底起伏变化特征和上地壳顶部覆盖层速度分布变化特征。结果表明,剖面东南段四川盆地内基底埋深约3～5km,覆盖层较厚,速度较低;剖面西北段川西高原内结晶基底埋藏深度逐渐减浅至0～3km,覆盖层变薄,局部出露地表,速度大部分区段明显增大;沿剖面多个部位基底的埋深出现明显的隆起或下凹,上部地壳速度结构横向出现剧烈的上下起伏变化,结晶基底界面起伏变化强烈的位置分别与该地区分布的龙泉山断裂、名山-成都断裂以及龙门山地区的断裂构造有较好的对应关系,结晶基底速度结构和界面形态变化特征为该区活动断裂构造深浅耦合关系和强震孕育机制研究提供参考。
This paper applies the finite difference travel time inversion and time-term method to model the upper crustal velocity structure and the crystalline basement structure beneath Yibin-Jinchuan profile.The tomographic and time-term method results show that:the basement depth of the Sichuan basin in the southeastern section is about 3～5 km,the unconsolidated sedimentation is very thick,and the shallow velocity is very low.In the northwest section the burial depth of the crystalline basement is gradually reduced by 0～3 km,partly exposed on the surface,and the shallow velocity increases obviously relative to other segments.The crystalline basement depth beneath the profile is obviously heterogeneous.The velocity structure gradual variations obviously correlate with the faults of Longquanshan mountain,Mingshan-Chengdu and the area of Longmenshan mountain.The velocity structure and the interfacial morphological characteristics of the crystalline basement provide seismic evidence for the studies of seismogenic mechanism and earthquake risk assessment in this area.
This paper applies the finite difference travel time inversion and time-term method to model the upper crustal velocity structure and the crystalline basement structure beneath Yibin-Jinchuan profile.The tomographic and time-term method results show that:the basement depth of the Sichuan basin in the southeastern section is about 3～5 km,the unconsolidated sedimentation is very thick,and the shallow velocity is very low.In the northwest section the burial depth of the crystalline basement is gradually reduced by 0～3 km,partly exposed on the surface,and the shallow velocity increases obviously relative to other segments.The crystalline basement depth beneath the profile is obviously heterogeneous.The velocity structure gradual variations obviously correlate with the faults of Longquanshan mountain,Mingshan-Chengdu and the area of Longmenshan mountain.The velocity structure and the interfacial morphological characteristics of the crystalline basement provide seismic evidence for the studies of seismogenic mechanism and earthquake risk assessment in this area.
引文
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[12]徐涛,张明辉,田小波,等.丽江-清镇剖面上地壳速度结构及其与鲁甸MS6.5级地震孕震环境的关系[J].地球物理学报,2014,57(9):3 069-3 079(Xu Tao,Zhang Minghui,Tian Xiaobo,et al.Upper Crustal Velocity of Lijiang-Qingzhen Profile and Its Relationship with the Seismogenic Environment of the MS6.5Ludian Earthquake[J].Chinese Journal of Geophysics,2014,57(9):3 069-3 079)
[13]黄圣睦,何天华,范明祥,等.从石油人工地震资料分析成都平原地震地质背景的新认识[J].地震地质,2003,25(4):581-594(Huang Shengmu,He Tianhua,Fan Mingxiang,et al.Seismogeologic Background of the Chengdu Plain as Revealfd by Seismic Prospecting Data of Petroleum[J].Seismology and Geology,2003,25(4):581-594)
[14]徐朝繁,田晓峰,嘉世旭,等.龙门山中段及其邻近地区上地壳细结构--人工地震测深结果[C].中国地震学会第14次学术大会,乌鲁木齐,2012(Xu Chaofan,Tian Xiaofeng,Jia Shixu,et al.The Structure of the Upper Crustal in the Middle and Adjacent Areas of Longmen Mountain—the Result of Artificial Seismic Sounding[C].The 14th Academic Conference of the China Earthquake Society,Urumqi,2012)
[15]刘志成,季建清,涂继耀,等.龙门山断裂带变形特征[J].地质科学,2013,48(2):515-531(Liu Zhicheng,Ji Jianqing,Tu Jiyao,et al.Deformational Characteristics of the Longmenshan Fault Zone[J].Chinese Journal of Geology,2013,48(2):515-531)
[16]颜照坤,李勇,赵国华,等.从龙门山地质地貌分段性探讨芦山地震与汶川地震的关系[J].自然杂志,2014,36(1):51-58(Yan Zhaokun,Li Yong,Zhao Guohua,et al.The Relationship between Lushan Earthquake and Wenchuan Earthquake by Segmentation of Geology and Geomorphology of Longmenshan[J].Chinese Journal of Nature,2014,36(1):51-58)
[2]朱介寿,汶川地震的岩石圈深部结构与动力学背景[J].成都理工大学学报,2008,35(4):348-356(Zhu Jieshou.The Wenchuan Earthquake Occurrence Background in Deep Structure and Dynamics of Lithosphere[J].Journal of Chengdu University of Technology,2008,35(4):348-356)
[3] Wang C Y,Han W B,Wu J P,et al.Crustal Structure Beneath the Eastern Margin of the Tibetan Plateau and Its Tectonic Implications[J].Journal of Geophysical Research:Solid Earth,2007,112(B7)
[4]嘉世旭,刘保金,徐朝繁,等.龙门山中段及两侧地壳结构与汶川地震构造[J].中国科学D辑:地球科学,2014,44(3):497-509(Jia Shixu,Liu Baojin,Xu Chaofan,et al.The Crustal Structures of the Central Longmenshan along and Its Margins as Related to the Seismotectonics of the 2008Wenchuan Earthquake[J].Science in China Series D:Earth Sciences,2014,44(3):497-509)
[5]段永红,赖晓玲.有限差分二、三维速度层析成象[J].华北地震科学,1999,17(4):53-60(Duan Yonghong,Lai Xiaoling.Finite-Difference 2-D and 3-D Seismic Traveltime Velocity Tomography[J].North China Earthguake Sciences,1999,17(4):53-60)
[6] Bamford S A D.An Example of the Iterative Approach to Time‐Term Analysis[J].Geophysical Journal International,1973,31(4):365-372
[7]邓起东,陈社发,赵小麟.龙门山及其邻区的构造和地震活动及动力学[J].地震地质,1994,16(4):389-403(Deng Qidong,Chen Shefa,Zhao Xiaolin.Tectonics Scismisity and Dynamics of Longmenshan Mountains and Its Adjacent Regions[J].Seismology and Geology,1994,16(4):389-403)
[8]詹艳,赵国泽,Martyn U,等.龙门山断裂带西南段4.20芦山7.0级地震区的深部结构与孕震环境[J].科学通报,2013,58(20):1 917-1 924(Zhan Yan,Zhao Guoze,Martyn U,et al.Deep Structure Beneatth the Southwestern Section of the Longmenshan Fault Zone and Seimogenetic Context of the 4.20Lushan MS7.0Earthquake[J].Chin Sci Bull,2013,58(20):1 917-1 924)
[9]祝意青,闻学泽,孙和平,等.2013年四川芦山MS7.0地震前的重力变化[J].地球物理学报,2013,56(6):1 887-1 894(Zhu Yiqing,Wen Xueze,Sun Heping,et al.Gravity Changes before the Lushan,Sichuan,MS=7.0Earthquake of2013[J].Chinese Journal of Geophysics,2013,56(6):1 887-1 894)
[10]罗艳,赵里,曾祥方.芦山地震序列震源机制及其构造应力场空间变化[J].中国科学D辑:地球科学,2015,45(4):538-550(Luo Yan,Zhao Li,Zeng Xiangfang.Focal Mechanisms of the Lushan Earthquake Sequence and Spatial Variation of the Stress Field[J].Science in China Series D:Earth Sciences,2015,45(4):538-550)
[11]单斌,熊熊,郑勇,等.2013年芦山地震导致的周边断层应力变化及其与2008年汶川地震的关系[J].中国科学D辑:地球科学,2013,43(6):1 002-1 009(Shan Bin,Xiong Xiong,Zheng Yong,et al.Stress Changes on Major Faults Caused by 2013Lushan Earthquake,and Its Relationship with 2008Wenchuan Earthquake[J].Science in China Series D:Earth Sciences,2013,43(6):1002-1009)
[12]徐涛,张明辉,田小波,等.丽江-清镇剖面上地壳速度结构及其与鲁甸MS6.5级地震孕震环境的关系[J].地球物理学报,2014,57(9):3 069-3 079(Xu Tao,Zhang Minghui,Tian Xiaobo,et al.Upper Crustal Velocity of Lijiang-Qingzhen Profile and Its Relationship with the Seismogenic Environment of the MS6.5Ludian Earthquake[J].Chinese Journal of Geophysics,2014,57(9):3 069-3 079)
[13]黄圣睦,何天华,范明祥,等.从石油人工地震资料分析成都平原地震地质背景的新认识[J].地震地质,2003,25(4):581-594(Huang Shengmu,He Tianhua,Fan Mingxiang,et al.Seismogeologic Background of the Chengdu Plain as Revealfd by Seismic Prospecting Data of Petroleum[J].Seismology and Geology,2003,25(4):581-594)
[14]徐朝繁,田晓峰,嘉世旭,等.龙门山中段及其邻近地区上地壳细结构--人工地震测深结果[C].中国地震学会第14次学术大会,乌鲁木齐,2012(Xu Chaofan,Tian Xiaofeng,Jia Shixu,et al.The Structure of the Upper Crustal in the Middle and Adjacent Areas of Longmen Mountain—the Result of Artificial Seismic Sounding[C].The 14th Academic Conference of the China Earthquake Society,Urumqi,2012)
[15]刘志成,季建清,涂继耀,等.龙门山断裂带变形特征[J].地质科学,2013,48(2):515-531(Liu Zhicheng,Ji Jianqing,Tu Jiyao,et al.Deformational Characteristics of the Longmenshan Fault Zone[J].Chinese Journal of Geology,2013,48(2):515-531)
[16]颜照坤,李勇,赵国华,等.从龙门山地质地貌分段性探讨芦山地震与汶川地震的关系[J].自然杂志,2014,36(1):51-58(Yan Zhaokun,Li Yong,Zhao Guohua,et al.The Relationship between Lushan Earthquake and Wenchuan Earthquake by Segmentation of Geology and Geomorphology of Longmenshan[J].Chinese Journal of Nature,2014,36(1):51-58)