汶川M_S8.0级地震震源区地壳深部结构研究
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摘要
2005年10月至2007年4月,我们在松潘-甘孜、龙门山地块布设的流动地震台阵观测剖面正好经过地震震源区映秀,这为研究地震震源区深部结构提供很好的机会。观测剖面自成都龙泉山,途经都江堰、卧龙,终止于新都桥,全长约400km,台站间距5～10km,34个流动宽频带地震仪共记录到该时间段内5.5级以上远震事件542个,大于等于6.0级为195个。利用该观测剖面记录到的远震P波波形资料,采用接收函数方法来研究汶川M_s8.0级地震震源区地壳深部结构,结合地震构造背景的分析,探讨引起这次地震的动力学模式,并由此认识汶川地震的孕育与成因机制。根据震源区地表破裂和余震分布及深部结构的综合分析,可以划出震源区下方的地震断裂带。主要研究结果表明:1)根据界面分布特征,发现松潘-甘孜地块及龙门山推覆体中在20～60km深度存在一个厚度约15～20km的低速中地壳,而四川盆地地壳内不存在低速层。该中地壳内的低速层,是引起中上地壳的推覆运动的滑脱层。2)Moho面自扬子盆地(36～42km)跨龙门山(50km)到松潘-甘孜腹地(62～65km)逐渐加深,跨鲜水河断裂又变浅(60km),说明横跨扬子盆地—龙门山—松潘-甘孜地块的该断裂带是地壳厚度的陡变带。该结果揭示了松潘-甘孜地块与扬子地块是碰撞接触模式,龙门山的推覆构造就是上地壳逆冲的结果。
The mobile seismic broadband stations we deployed in the Songpan-Ganzi and Longmenshan blocks during October 2005 to April 2007 just cross the earthquake source area Yingxiu,which gives us a good opportunity to study the deep crustal structure.In the observation profile from Longquanshan of Chengdu through Dujiangyan and Wolongshan to Xinduqiao,about 400km long,there were 34 mobile broadband seismic stations,with the station interval of 5～10km.They recorded 542 teleseismic seismic events more than M_S5.5 were 542,including 195 earthquakes more than or equal to M_S6.0.In this paper,by using the teleseismic P waveform data of the profile and in combination with the analysis of seismic tectonic background,the deep crustal structure around the source zone of the 2008 Wenchuan M_S8.0 earthquake was studied with the receiver function method.Our study results are as follows :(1)in the depth of 20 ～60km of the Songpan-Ganzi block and the Longmen Mountains nappe there is about 15～20km thick low velocity middle crust in which detachment structures readily occur,while such a low-velocity layer does not exist within the Sichuan Basin;and(2)the Moho depth increases from about 36～ 40km in the Yangtze Basin,about 50km in the Longmenshan belt to about 62～ 65km in the central part of the Songpan-Ganzi block,although decreases to 60km on the another side of the Xianshuihe fault zone,which shows that there should be a sudden change zone of crust thickness between the Yangtze Basin and the Longmenshan-Songpan-Ganzi block. It follows that the Songpan-Ganzi block and the Yangtze block should be a collision contact and that the Longmenshan nappe should the result of the upper crustal thrust movement.
The mobile seismic broadband stations we deployed in the Songpan-Ganzi and Longmenshan blocks during October 2005 to April 2007 just cross the earthquake source area Yingxiu,which gives us a good opportunity to study the deep crustal structure.In the observation profile from Longquanshan of Chengdu through Dujiangyan and Wolongshan to Xinduqiao,about 400km long,there were 34 mobile broadband seismic stations,with the station interval of 5～10km.They recorded 542 teleseismic seismic events more than M_S5.5 were 542,including 195 earthquakes more than or equal to M_S6.0.In this paper,by using the teleseismic P waveform data of the profile and in combination with the analysis of seismic tectonic background,the deep crustal structure around the source zone of the 2008 Wenchuan M_S8.0 earthquake was studied with the receiver function method.Our study results are as follows :(1)in the depth of 20 ～60km of the Songpan-Ganzi block and the Longmen Mountains nappe there is about 15～20km thick low velocity middle crust in which detachment structures readily occur,while such a low-velocity layer does not exist within the Sichuan Basin;and(2)the Moho depth increases from about 36～ 40km in the Yangtze Basin,about 50km in the Longmenshan belt to about 62～ 65km in the central part of the Songpan-Ganzi block,although decreases to 60km on the another side of the Xianshuihe fault zone,which shows that there should be a sudden change zone of crust thickness between the Yangtze Basin and the Longmenshan-Songpan-Ganzi block. It follows that the Songpan-Ganzi block and the Yangtze block should be a collision contact and that the Longmenshan nappe should the result of the upper crustal thrust movement.
引文
1 朱介寿.汶川地震的岩石圈深部结构与动力学背景.成都理工大学学报(自然科学版),2008,35(4) :348-356 Zhu Jieshou.The Wenchuan earthquake occurrence background in deep structure and dynamics of Lithosphere.Journal of Chengdu University of Technology (Science & Technology Edition),2008,35(4) :348-356
2 张培震,徐锡伟,闻学泽等.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.地球物理学报,2008,51(4) :1066-1073 Zhang Peizhen,Xu Xiwei,Wen Xueze et al.Slip rates and recurrence intervals of the Longmen Shan active fault zone and tectonic implications for the mechanism of the May 12 Wenchuan earthquake,2008,Sichuan,China.Chinese Journal of Geophysics,2008,51 (4) :1066-1073
3 徐锡伟,闻学泽,叶建青等.汶川M_S8． 0地震地表破裂带及其发震构造.地震地质,2008,30(3) :597-629 Xu Xiwei,Wen Xenze,Ye Jianqing et al.The M_S8． 0 Wenchuan earthquake surface ruptures and its seismogenic structure.Seismology and Geology,2008,30 (3) :597-629
4 吴建平,黄媛,张天中等.汶川M_S8． 0级地震余震分布及周边区域P波三维速度结构研究.地球物理学报,2009,52(2) :320-328 Wu Jianping,Huang Yuan,Zhang Tianzhong et al.Aftershock distribution of M_S8． 0 Wenchuan earthquake and three dimensional P-wave velocity structure in and around source region.Chinese Journal of Geophysics,2009,52 (2) :320-328
5 Royden L H,Burehfiel B C,King W R et al.Surface deformation and lower crustal flow in Eastern Tibet.Science,1997,276:788-790
6 Burehfiel B,Chen Zhiliang,Liu Yupine et al.Tectonics of the Longmen Shan and adjacent regions,Central China.International Geology Review,1995,37:661-735
7 Clark M K,Royden L H.Topographic ooze:Building the eastern margin of Tibet by lower crustal flow.Geology,2000,25:703-706
8 朱介寿,李海丰,Alexandra Robert等.青藏高原东缘及龙门山岩石圈深部结构.见:金翔龙等主编.中国地质地球物理研究进展--庆贺刘光鼎院士八十华诞.北京:海洋出版社,2008． 66-73 Zhu Jieshou,Li Haifeng,Alexandra Robert et al.Lihospheric structure in eastern of Tibetan Plateau and Longmen-Shan range.In: Jin Xianglong et al.eds.Chinese Geological and Geophysical Research--Celebrate the 80 Birthday of Aeademician Liu Guangding.Beijing:China Ocean Press,2008． 66-73
9 杜方,闻学泽,张培震等.2008年汶川8． 0级地震前横跨龙门山断裂带的震间形变.地球物理学报,2009,52(11) :2729-2738 Du Fang,Wen Xueze,Zhang Peizhen et al.Interseismic deformation across the Longmenshan fault zone before the 2008 M8． 0 Wenchuan earthquake.Chinese Journal of Geophysics,2009,52 (11) :2729-2738
10 刘启元,李煜,陈九辉等.汶川M_S8． 0地震:地壳上地幔S波速度结构的初步研究.地球物理学报,2009,52(2) :309-319 Liu Qiyuan,Li Yu,Chen Jiuhui et al.Wenchuan M_S8． 0 earthquake: Preliminary study of the S-wave velocity structure of the crust and upper mantle.Chinese Journal of Geophysics,2009,52 (2) :309-319
11 李勇,黄润秋,Densmore A L等.龙门山小鱼涧断裂在汶川地震中的地表破裂及地质意义.第四纪研究,2009,29(3) :502-512 Li Yong,Huang Runqiu,Densmore A L et al.Surface rupture of Xiaoyudong Fault caused by Wenchuan Earthquake and its geological signficance.Quaternary Sciences,2009,29 (3) :502-512
12 王卫民,赵连锋,李娟等.四川汶川8． 0级地震震源过程.地球物理学报,2008,51(5) :1403-1410 Wang Weimin,Zhao Lianfeng,Li Juan et al.Rupture process of the M_S8． 0 Wenchuan earthquake of Sichuan,China.Chinese Journal of Geophysics,2008,51 (5) :1403-1410
13 滕吉文,白登海,杨辉等.2008汶川M_S8． 0地震发生的深层过程和动力学响应.地球物理学报,2008,51(5) :1385-1402 Teng Jiwen,Bai Denghai,Yang Hui et al.Deep processes and dynamic responses associated with the Wenchuan M_S8． 0 earthquake of 2008． Chinese Journal of Geophysics,2008,51 (5) :1385-1402
14 楼海,王椿镛,吕智勇等.2008年汶川M_S8． 0级地震的深部构造环境--远震P波接收函数和布格重力异常的联合解释.中国科学(D辑),2008,38(10) :1207-1220 Lou Hal,Wang Chunyong,Lu Zhiyong et al.Deep tectonic setting of the 2008 Wenchuan M_S8． 0 earthquake in South Western China--Joint analysis of teleseismic P-wave receiver functions and Bouguer gravity anomalies.Science in China (Series D),2009,52 (2) :166-179
15 李海兵,司家亮,付小方等.2008年汶川地震同震滑移特征、最 大滑移量及构造意义.第四纪研究,2009,29(3) :387-402 Li Haibing,Si Jialiang,Fu Xiaofang et al.Co-seismic rupture and maximum displacement of the 2008 Wenchuan Earthquake and its tectonic implications.Quaternary Sciences,2009,29 (3) :387-402
16 李传友,魏占玉.2008年汶川M_S8． 0地震北川以北段地表破裂变形的主要样式.第四纪研究,2009,29(3) :416-425 Li Chuanyou,Wei Zhanyu.Representative patterns of coseismic deformation along surface rupture north to Beichuan City of 2008 Wenchuan M_S8． 0 earthquake.Quaternary Sciences,2009,29 (3) :416-425
17 陈立春,冉永康,陈杰等.龙门山前山断裂大地震原地重复发生的地质地貌证据.第四纪研究,2009,29(3) :472-483 Chen Lichun,Ran Yongkang,Chen Jie et al.Geological and geomorphic evidence for repeatedly occurring severe earthquakes on fronter-range fault of Longmenshan,China.Quaternary Sciences,2009,29 (3) :472-483
18 李海丰.青藏高原东缘及龙门山被动源地震削面及台阵研究.成都:成都理工大学硕士学位沦文,2008． 8-36 Li Haifeng.A Passive Seismological Profile Experiment in Eastern Margin of Tibetan Plateau and Longmen-Shan Region.Chengdu: Master Thesis of Chengdu University of Technology,2008． 8-36
19 徐强,赵俊猛.接收函数方法的研究综述地球物理学进展,2008,23 (6) :1709-1706 Xu Qiang,Zhan Junmeng.A review of the receiver function method.Progress in Geophysics,2008,23 (6) :1709-1716
20 Huang J L.Lithospheric structure and its relationship to seismic and volcanic activity in Southwest China.Journal of Geophysical Research,2007,107(BI):1-14
21 雷建设,赵大鹏,苏金蓉等.龙门山断裂带地壳精细结构与汶川地震发震机理.地球物理学报,2009,52(2) :339-345 Lei Jianshe,Zhao Dapeng,Su Jinrong et al.Fine seismic structure under the Longmenshan fault zone and the mechanism of the large Wenchuan earthquake.Chinese Journal of Geophysics,2009,52 (2) :339-345
22 李永华,吴庆举,安张辉等.青藏高原东北缘地壳S波速度结构与泊松比及其意义.地球物理学报,2006,49(5) :1359-1368 Li Yonghua,Wu Qingju,An Zhanghui et al.The Poisson ratio crustal structure across the NE Tibetan Plateau determined from receiver functions.Chinese Journal of Geophysics,2006,49 (5) :1359-1368
23 张世民,谢富仁,黄忠贤等.龙门山地区上地壳的拱曲冲断作用及其深部动力学机制探讨.第四纪研究,2009,29(3) :449-463 Zhang Shimin,Xie Furen,Huang Zhongxian et al.Bending and thrusting of the upper crust in Longmenshan area and its deep dynamics.Quaternary Sciences,2009,29(3) :449-463
24 Tapponnier P,Peltzer G,Le Dain A Y et al.Propagating extrusion tectonics in Asia:New insights from simple experiments with plasticine.Geology,1982,10 (12) :611-616
25 Zhang Peizhen,Shen Zhengkang,Wang Min et al.Continuous deformation of the Tibetan Plateau from Global Positioning System data.Geology,2004,32 (9) :809-812
2 张培震,徐锡伟,闻学泽等.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.地球物理学报,2008,51(4) :1066-1073 Zhang Peizhen,Xu Xiwei,Wen Xueze et al.Slip rates and recurrence intervals of the Longmen Shan active fault zone and tectonic implications for the mechanism of the May 12 Wenchuan earthquake,2008,Sichuan,China.Chinese Journal of Geophysics,2008,51 (4) :1066-1073
3 徐锡伟,闻学泽,叶建青等.汶川M_S8． 0地震地表破裂带及其发震构造.地震地质,2008,30(3) :597-629 Xu Xiwei,Wen Xenze,Ye Jianqing et al.The M_S8． 0 Wenchuan earthquake surface ruptures and its seismogenic structure.Seismology and Geology,2008,30 (3) :597-629
4 吴建平,黄媛,张天中等.汶川M_S8． 0级地震余震分布及周边区域P波三维速度结构研究.地球物理学报,2009,52(2) :320-328 Wu Jianping,Huang Yuan,Zhang Tianzhong et al.Aftershock distribution of M_S8． 0 Wenchuan earthquake and three dimensional P-wave velocity structure in and around source region.Chinese Journal of Geophysics,2009,52 (2) :320-328
5 Royden L H,Burehfiel B C,King W R et al.Surface deformation and lower crustal flow in Eastern Tibet.Science,1997,276:788-790
6 Burehfiel B,Chen Zhiliang,Liu Yupine et al.Tectonics of the Longmen Shan and adjacent regions,Central China.International Geology Review,1995,37:661-735
7 Clark M K,Royden L H.Topographic ooze:Building the eastern margin of Tibet by lower crustal flow.Geology,2000,25:703-706
8 朱介寿,李海丰,Alexandra Robert等.青藏高原东缘及龙门山岩石圈深部结构.见:金翔龙等主编.中国地质地球物理研究进展--庆贺刘光鼎院士八十华诞.北京:海洋出版社,2008． 66-73 Zhu Jieshou,Li Haifeng,Alexandra Robert et al.Lihospheric structure in eastern of Tibetan Plateau and Longmen-Shan range.In: Jin Xianglong et al.eds.Chinese Geological and Geophysical Research--Celebrate the 80 Birthday of Aeademician Liu Guangding.Beijing:China Ocean Press,2008． 66-73
9 杜方,闻学泽,张培震等.2008年汶川8． 0级地震前横跨龙门山断裂带的震间形变.地球物理学报,2009,52(11) :2729-2738 Du Fang,Wen Xueze,Zhang Peizhen et al.Interseismic deformation across the Longmenshan fault zone before the 2008 M8． 0 Wenchuan earthquake.Chinese Journal of Geophysics,2009,52 (11) :2729-2738
10 刘启元,李煜,陈九辉等.汶川M_S8． 0地震:地壳上地幔S波速度结构的初步研究.地球物理学报,2009,52(2) :309-319 Liu Qiyuan,Li Yu,Chen Jiuhui et al.Wenchuan M_S8． 0 earthquake: Preliminary study of the S-wave velocity structure of the crust and upper mantle.Chinese Journal of Geophysics,2009,52 (2) :309-319
11 李勇,黄润秋,Densmore A L等.龙门山小鱼涧断裂在汶川地震中的地表破裂及地质意义.第四纪研究,2009,29(3) :502-512 Li Yong,Huang Runqiu,Densmore A L et al.Surface rupture of Xiaoyudong Fault caused by Wenchuan Earthquake and its geological signficance.Quaternary Sciences,2009,29 (3) :502-512
12 王卫民,赵连锋,李娟等.四川汶川8． 0级地震震源过程.地球物理学报,2008,51(5) :1403-1410 Wang Weimin,Zhao Lianfeng,Li Juan et al.Rupture process of the M_S8． 0 Wenchuan earthquake of Sichuan,China.Chinese Journal of Geophysics,2008,51 (5) :1403-1410
13 滕吉文,白登海,杨辉等.2008汶川M_S8． 0地震发生的深层过程和动力学响应.地球物理学报,2008,51(5) :1385-1402 Teng Jiwen,Bai Denghai,Yang Hui et al.Deep processes and dynamic responses associated with the Wenchuan M_S8． 0 earthquake of 2008． Chinese Journal of Geophysics,2008,51 (5) :1385-1402
14 楼海,王椿镛,吕智勇等.2008年汶川M_S8． 0级地震的深部构造环境--远震P波接收函数和布格重力异常的联合解释.中国科学(D辑),2008,38(10) :1207-1220 Lou Hal,Wang Chunyong,Lu Zhiyong et al.Deep tectonic setting of the 2008 Wenchuan M_S8． 0 earthquake in South Western China--Joint analysis of teleseismic P-wave receiver functions and Bouguer gravity anomalies.Science in China (Series D),2009,52 (2) :166-179
15 李海兵,司家亮,付小方等.2008年汶川地震同震滑移特征、最 大滑移量及构造意义.第四纪研究,2009,29(3) :387-402 Li Haibing,Si Jialiang,Fu Xiaofang et al.Co-seismic rupture and maximum displacement of the 2008 Wenchuan Earthquake and its tectonic implications.Quaternary Sciences,2009,29 (3) :387-402
16 李传友,魏占玉.2008年汶川M_S8． 0地震北川以北段地表破裂变形的主要样式.第四纪研究,2009,29(3) :416-425 Li Chuanyou,Wei Zhanyu.Representative patterns of coseismic deformation along surface rupture north to Beichuan City of 2008 Wenchuan M_S8． 0 earthquake.Quaternary Sciences,2009,29 (3) :416-425
17 陈立春,冉永康,陈杰等.龙门山前山断裂大地震原地重复发生的地质地貌证据.第四纪研究,2009,29(3) :472-483 Chen Lichun,Ran Yongkang,Chen Jie et al.Geological and geomorphic evidence for repeatedly occurring severe earthquakes on fronter-range fault of Longmenshan,China.Quaternary Sciences,2009,29 (3) :472-483
18 李海丰.青藏高原东缘及龙门山被动源地震削面及台阵研究.成都:成都理工大学硕士学位沦文,2008． 8-36 Li Haifeng.A Passive Seismological Profile Experiment in Eastern Margin of Tibetan Plateau and Longmen-Shan Region.Chengdu: Master Thesis of Chengdu University of Technology,2008． 8-36
19 徐强,赵俊猛.接收函数方法的研究综述地球物理学进展,2008,23 (6) :1709-1706 Xu Qiang,Zhan Junmeng.A review of the receiver function method.Progress in Geophysics,2008,23 (6) :1709-1716
20 Huang J L.Lithospheric structure and its relationship to seismic and volcanic activity in Southwest China.Journal of Geophysical Research,2007,107(BI):1-14
21 雷建设,赵大鹏,苏金蓉等.龙门山断裂带地壳精细结构与汶川地震发震机理.地球物理学报,2009,52(2) :339-345 Lei Jianshe,Zhao Dapeng,Su Jinrong et al.Fine seismic structure under the Longmenshan fault zone and the mechanism of the large Wenchuan earthquake.Chinese Journal of Geophysics,2009,52 (2) :339-345
22 李永华,吴庆举,安张辉等.青藏高原东北缘地壳S波速度结构与泊松比及其意义.地球物理学报,2006,49(5) :1359-1368 Li Yonghua,Wu Qingju,An Zhanghui et al.The Poisson ratio crustal structure across the NE Tibetan Plateau determined from receiver functions.Chinese Journal of Geophysics,2006,49 (5) :1359-1368
23 张世民,谢富仁,黄忠贤等.龙门山地区上地壳的拱曲冲断作用及其深部动力学机制探讨.第四纪研究,2009,29(3) :449-463 Zhang Shimin,Xie Furen,Huang Zhongxian et al.Bending and thrusting of the upper crust in Longmenshan area and its deep dynamics.Quaternary Sciences,2009,29(3) :449-463
24 Tapponnier P,Peltzer G,Le Dain A Y et al.Propagating extrusion tectonics in Asia:New insights from simple experiments with plasticine.Geology,1982,10 (12) :611-616
25 Zhang Peizhen,Shen Zhengkang,Wang Min et al.Continuous deformation of the Tibetan Plateau from Global Positioning System data.Geology,2004,32 (9) :809-812
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