龙门山断裂带地壳密度结构
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摘要
研究龙门山及邻区地壳密度结构对于认识该地区地震活动性具有重要意义。根据龙门山及邻区(100°～105°E,28°～33°N)的布格重力异常资料,选取了跨越龙门山断裂带的6条重力测线,在深地震测深资料约束下,使用Geosoft软件分别反演出了龙门山地区地下的沉积层、康拉德界面和莫霍面的深度分布。研究结果表明:龙门山断裂带两侧的地壳结构明显不同,西面高原地区沉积层较薄,大部分为基岩出露;而东边盆地沉积层明显较厚,多在6km以上。莫霍面和康拉德面在两侧均相对平缓,康拉德面从东部的大约24km增加到青藏高原山区的35km左右;莫霍面深度从东部盆地的大约42km增加到西部青藏高原的67km左右。龙门山断裂带整体表现为一条近SN向的陡变重力梯度带,并在其地壳内各界面均发生错断,莫霍面和康拉德面错断距离分别达6～7km和3～5km。该区地壳的这种陡变和不均匀性是导致地震活动性强烈的主要原因之一。
It is of importance to study the crustal density structure of Longmenshan Fault zone for understanding the seismicity of this area.Using commercial software of Geosoft,gravity inversion for 6 lines of Bouguer gravity anomaly data was carried out under the constraint of deep seismic sounding(DSS) data obtained in the last two decades.The depth and distribution of sediments,crustal thickness and Conrad discontinuity of Longmenshan tectonic zone and its adjacent area(100° ～ 105°E,28° ～ 33°N) are obtained.The inverted results indicate that the crustal density structure of the Longmenshan Fault zone is obviously different between the two sides.The sedimentary layer in western plateau is thinner and base rocks outcrop almost in most parts;while the thickness of sedimentary layer in eastern Sichuan Basin is much larger,in most parts,it is larger than 6km.The Conrad and Moho discontinuities are relatively smooth in both sides of the fault and the depths of them increase gradually from the eastern 24km and 42km to 35km and 67km under Tibetan Plateau,respectively.The whole fault of Longmenshan displays as a SN-direction gravity gradient zone,with each of its interfaces in the crust under the faults being offset.The displacements of the Conrad and Moho discontinuities are 6 ～ 7km and 3 ～ 5km,respectively.The sharp change in crustal thickness is maybe one of the causes of strong earthquakes in this area.
It is of importance to study the crustal density structure of Longmenshan Fault zone for understanding the seismicity of this area.Using commercial software of Geosoft,gravity inversion for 6 lines of Bouguer gravity anomaly data was carried out under the constraint of deep seismic sounding(DSS) data obtained in the last two decades.The depth and distribution of sediments,crustal thickness and Conrad discontinuity of Longmenshan tectonic zone and its adjacent area(100° ～ 105°E,28° ～ 33°N) are obtained.The inverted results indicate that the crustal density structure of the Longmenshan Fault zone is obviously different between the two sides.The sedimentary layer in western plateau is thinner and base rocks outcrop almost in most parts;while the thickness of sedimentary layer in eastern Sichuan Basin is much larger,in most parts,it is larger than 6km.The Conrad and Moho discontinuities are relatively smooth in both sides of the fault and the depths of them increase gradually from the eastern 24km and 42km to 35km and 67km under Tibetan Plateau,respectively.The whole fault of Longmenshan displays as a SN-direction gravity gradient zone,with each of its interfaces in the crust under the faults being offset.The displacements of the Conrad and Moho discontinuities are 6 ～ 7km and 3 ～ 5km,respectively.The sharp change in crustal thickness is maybe one of the causes of strong earthquakes in this area.
引文
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雷建设,赵大鹏,苏金蓉,等.2009.龙门山断裂带地壳精细结构与汶川地震发震机理[J].地球物理学报,52(2):339—345.LEI Jian-she,ZHAO Da-peng,SU Jin-rong,et al.2009.Fine seismic structure under the Longmenshan Fault zone andthe mechanism of the large Wenchuan earthquake[J].Chinese J Geophys,52(2):339—345(in Chinese).
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唐新功,陈永顺,唐哲.2006.应用布格重力异常研究郯庐断裂构造[J].地震学报,28(6):603—610.TANG Xin-gong,CHEN Yong-shun,TANG Zhe.2006.Bouguer gravity study of middle section of Tanlu Fault[J].ActaSeismologica Sinica,19(6):650—657.
滕吉文,曾融生,严艳芬,等.2002.东亚大陆及周边海域Moho界面深度分布和基本构造格局[J].中国科学(D辑),5(46):428—446.TENG Ji-wen,ZENG Rong-sheng,YAN Ya-fen,et al.2002.Depth distribution of Moho and tectonic framework ineastern Asian continent and its adjacent ocean areas[J].Science in China(Ser D),5(46):428—446(in Chinese).
王绪本,余年,朱迎堂,等.2008.龙门山逆冲构造带大地电磁测深初步成果[J].成都理工大学学报(自然科学版),35(4):992—304.WANG Xu-ben,YU Nian,ZHU Ying-tang,et al.2008.The preliminary magnetotelluric results in Longmenshan reversestructure zone[J].Journal of Chengdu University of Science and Technology(Science and Technology Edition),35(4):992—304(in Chinese).
王有学,Mooney W D,韩国花,等.2005.台湾—阿尔泰地学断面阿尔金—龙门山剖面的地壳纵波速度结构[J].地球物理学报,48(1):98—106.WANG You-xue,Mooney W D,HAN Guo-hua,et al.2005.Crustal P wave velocity structure from Altyn Tagh toLongmen Mountains along the Taiwan-Altay geoscience transect[J].Chinese J Geophys,48(1):98—106(inChinese).
吴建平,黄媛,张天中,等.2009.汶川MS8.0级地震余震分布及周边区域P波三维速度结构研究[J].地球物理学报,52(2):320—328.WU Jian-ping,HUANG Yuan,ZHANG Tian-zhong,et al.2009.Aftershock distribution of the MS8.0Wenchuanearthquake and three-dimensional P wave velocity structure in and around source region[J].Chinese J Geophys,52(2):320—328(in Chinese).
胥颐,黄润秋,李志伟,等.2009.龙门山构造带及汶川震源区的S波速度结构[J].地球物理学报,52(2):329—338.XU Yi,HUANG Run-qiu,LI Zhi-wei,et al.2009.S wave velocity structure of the Longmen Shan and Wenchuanearthquake area[J].Chinese J Geophys,52(2):329—338(in Chinese).
赵国泽,陈小斌,肖骑彬,等.2009.汶川MS8.0级地震成因三“层次”分析:基于深部电性结构[J].地球物理学报,52(2):553—563.ZHAO Guo-ze,CHEN Xiao-bin,XIAO Qi-bin,et al.2009.Generation mechanism of Wenchuan strong earthquake of MS8.0inferred from EM measurement in three levels[J].Chinese J Geophys,52(2):553—563(in Chinese).
张季生,高锐,曾令森,等.2009.龙门山及邻区重、磁异常特征及与地震关系的研究[J].地球物理学报,52(2):572—578.ZHANG Ji-sheng,GAO Rui,ZENG Ling-sen,et al.2009.Relationship between characteristics of gravity and magneticanomalies and the earthquakes in Longmenshan range and adjacent area[J].Chinese J Geophys,52(2):572—578(in Chinese).
张培震,徐锡伟,闻学泽,等.2008.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因[J].地球物理学报,51(4):1066—1073.ZHANG Pei-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.Slip rates and recurrence intervals of the Longmenshan activefault zone and tectonic implications for the mechanism of the May12Wenchuan earthquake,Sichuan,China[J].Chinese J Geophys,51(4):1066—1073(in Chinese).
曾融生,孙为国,毛桐恩,等.1995.中国大陆莫霍界面深度图[J].地震学报,17(3):322—327.ZENG Rong-sheng,SUN Wei-guo,MAO Tong-en,et al.1995.The Moho depth of Chinese Mainland[J].ActaSeismologica Sinica,17(3):322—327(in Chinese).
朱介寿.2008.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(自然科学版),35(4):348—356.ZHU Jie-shou.2008.The deep lithospheric structure of Wenchuan earthquake and its geodynamic implications[J].Journal of Chengdu University of Science and Technology(Science and Technology Edition),35(4):348—356(in Chinese).
郭飚,刘启元,陈九辉,等.2009.川西龙门山及邻区地壳上地幔远震P波层析成像[J].地球物理学报,52(2):346—355.GUO Biao,LIU Qi-yuan,CHEN Jiu-hui,et al.2009.Teleseismic P wave tomography of the crust and upper mantle inLongmenshan area,west China[J].Chinese J Geophys,52(2):346—355(in Chinese).
冯锐.1985.中国地壳厚度及上地幔密度分布(三维重力反演结果)[J].地震学报,7(2):143—157.FENG Rui.1985.Crustal thickness and densities in the upper mantle beneath China:The resolution of threedimensional gravity inversion[J].Acta Seismologica Sinica,7(2):143—157(in Chinese).
冯锐,郑书真,黄桂芳,等.1989.华北地区重力场与沉积层构造[J].地球物理学报,32(4):385—398.FENG Rui,ZHENG Shu-zhen,HUANG Gui-fang,et al.1989.Gravity field and structure of the sedimentary layer inNorth China[J].Chinese J Geophys,32(4):385—398(in Chinese).
雷建设,赵大鹏,苏金蓉,等.2009.龙门山断裂带地壳精细结构与汶川地震发震机理[J].地球物理学报,52(2):339—345.LEI Jian-she,ZHAO Da-peng,SU Jin-rong,et al.2009.Fine seismic structure under the Longmenshan Fault zone andthe mechanism of the large Wenchuan earthquake[J].Chinese J Geophys,52(2):339—345(in Chinese).
刘启元,李昱,陈九辉,等.2009.汶川MS8.0地震:地壳上地幔S波速度结构的初步研究[J].地球物理学报,52(2):309—319.LIU Qi-yuan,LI Yu,CHEN Jiu-hui,et al.2009.Wenchuan MS8.0earthquake:Preliminary study of the S-wavevelocity structure of the crust and upper mantle[J].Chinese J Geophys,52(2):309—319(in Chinese).
单新建,屈春燕,宋小刚,等.2009.汶川MS8.0地震InSAR同震形变场[J].地球物理学报,52(2):496—504.SHAN Xin-jian,QU Chuan-yan,SONG Xiao-gang,et al.2009.Coseismic surface deformation caused by the WenchuanMS8.0earthquake from InSAR data analysis[J].Chinese J Geophys,52(2):496—504(in Chinese).
唐新功,陈永顺,唐哲.2006.应用布格重力异常研究郯庐断裂构造[J].地震学报,28(6):603—610.TANG Xin-gong,CHEN Yong-shun,TANG Zhe.2006.Bouguer gravity study of middle section of Tanlu Fault[J].ActaSeismologica Sinica,19(6):650—657.
滕吉文,曾融生,严艳芬,等.2002.东亚大陆及周边海域Moho界面深度分布和基本构造格局[J].中国科学(D辑),5(46):428—446.TENG Ji-wen,ZENG Rong-sheng,YAN Ya-fen,et al.2002.Depth distribution of Moho and tectonic framework ineastern Asian continent and its adjacent ocean areas[J].Science in China(Ser D),5(46):428—446(in Chinese).
王绪本,余年,朱迎堂,等.2008.龙门山逆冲构造带大地电磁测深初步成果[J].成都理工大学学报(自然科学版),35(4):992—304.WANG Xu-ben,YU Nian,ZHU Ying-tang,et al.2008.The preliminary magnetotelluric results in Longmenshan reversestructure zone[J].Journal of Chengdu University of Science and Technology(Science and Technology Edition),35(4):992—304(in Chinese).
王有学,Mooney W D,韩国花,等.2005.台湾—阿尔泰地学断面阿尔金—龙门山剖面的地壳纵波速度结构[J].地球物理学报,48(1):98—106.WANG You-xue,Mooney W D,HAN Guo-hua,et al.2005.Crustal P wave velocity structure from Altyn Tagh toLongmen Mountains along the Taiwan-Altay geoscience transect[J].Chinese J Geophys,48(1):98—106(inChinese).
吴建平,黄媛,张天中,等.2009.汶川MS8.0级地震余震分布及周边区域P波三维速度结构研究[J].地球物理学报,52(2):320—328.WU Jian-ping,HUANG Yuan,ZHANG Tian-zhong,et al.2009.Aftershock distribution of the MS8.0Wenchuanearthquake and three-dimensional P wave velocity structure in and around source region[J].Chinese J Geophys,52(2):320—328(in Chinese).
胥颐,黄润秋,李志伟,等.2009.龙门山构造带及汶川震源区的S波速度结构[J].地球物理学报,52(2):329—338.XU Yi,HUANG Run-qiu,LI Zhi-wei,et al.2009.S wave velocity structure of the Longmen Shan and Wenchuanearthquake area[J].Chinese J Geophys,52(2):329—338(in Chinese).
赵国泽,陈小斌,肖骑彬,等.2009.汶川MS8.0级地震成因三“层次”分析:基于深部电性结构[J].地球物理学报,52(2):553—563.ZHAO Guo-ze,CHEN Xiao-bin,XIAO Qi-bin,et al.2009.Generation mechanism of Wenchuan strong earthquake of MS8.0inferred from EM measurement in three levels[J].Chinese J Geophys,52(2):553—563(in Chinese).
张季生,高锐,曾令森,等.2009.龙门山及邻区重、磁异常特征及与地震关系的研究[J].地球物理学报,52(2):572—578.ZHANG Ji-sheng,GAO Rui,ZENG Ling-sen,et al.2009.Relationship between characteristics of gravity and magneticanomalies and the earthquakes in Longmenshan range and adjacent area[J].Chinese J Geophys,52(2):572—578(in Chinese).
张培震,徐锡伟,闻学泽,等.2008.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因[J].地球物理学报,51(4):1066—1073.ZHANG Pei-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.Slip rates and recurrence intervals of the Longmenshan activefault zone and tectonic implications for the mechanism of the May12Wenchuan earthquake,Sichuan,China[J].Chinese J Geophys,51(4):1066—1073(in Chinese).
曾融生,孙为国,毛桐恩,等.1995.中国大陆莫霍界面深度图[J].地震学报,17(3):322—327.ZENG Rong-sheng,SUN Wei-guo,MAO Tong-en,et al.1995.The Moho depth of Chinese Mainland[J].ActaSeismologica Sinica,17(3):322—327(in Chinese).
朱介寿.2008.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(自然科学版),35(4):348—356.ZHU Jie-shou.2008.The deep lithospheric structure of Wenchuan earthquake and its geodynamic implications[J].Journal of Chengdu University of Science and Technology(Science and Technology Edition),35(4):348—356(in Chinese).
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