川西龙门山及邻区地壳上地幔远震P波层析成像
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摘要
本文利用川西地震台阵记录到的远震P波走时数据和非线性层析成像算法,获得龙门山地区400 km深度范围内的三维P波速度结构.为了适应川西地区复杂的地质结构,本文的层析成像方法采用了快速行进三维走时计算算法和Tarantola非线性反演算法.我们的结果揭示了川滇地块、松潘—甘孜地块和四川盆地三个不同地块构造差异及该区深部动力学特征.本文的研究表明:1)研究区地壳上地幔P波速度结构具有较为明显的分区特征,松潘—甘孜地块和川滇地块岩石圈速度较低,四川盆地岩石圈速度较高,四川盆地的岩石圈厚度从南250 km向北逐渐减薄至100 km.松潘—甘孜地块上地幔存在地幔上涌的特征.2)川滇地块和四川盆地仅是垂直接触关系,而在龙门山地区四川盆地前缘存在减薄的现象,并伴随松潘—甘孜地块上地幔低速物质有侵入四川盆地岩石圈下方的特征,这显示了四川盆地与松潘—甘孜地块和川滇地块的动力学关系的差异.3)以映秀为界,龙门山断裂带被从松潘—甘孜侵人的低速异常分为南北两段:龙门山南段和龙门山北段,汶川大地震及其余震序列均分布在龙门山断裂带的北段.在青藏高原向东挤压和地幔上涌的双重作用下造成松潘—甘孜地块隆升,由于汶川处于龙门山北段的最南端,应力容易在此集中.这些因素可能是汶川Ms8.0地震的基本动力学背景.本文的结果不支持四川盆地的俯冲及层间流动的动力学模型.
The 3D P-wave velocity structure of the crust and upper mantle within the depth range of 400 km was obtained by using teleseismic traveltimes data recorded by West Sichuan Seismic Array distributed in Longmenshan region and non-linear tomography inversion technique. For adapting to the complicated structure, the fast marching traveltime calculation method and Tarantola s inversion method was used. Our results show the tectonic differences of the crustal and upper-mantle structure among the blocks of Chuandian, Songpan-Garze and Sichuan basin. Our results show that: 1) the crustal structure of the study area correlates with the surface geological features. The Sichuan basin is imaged as a high-velocity feature, while the SongpanGarze and Chuandian block as low-velocity feature. The lithosphere thickness of Sichuan basin has lateral variations from 250 km in south part to 100 km in north part. There exist upwelling features under Songpan-Garze block. 2) Sichuan basin vertically contacts with Chuandian block, but the thickness of Sichuan basin front in Longmenshan area decreases from east to west with the feature of Songpan-Garze block incursion into Sichuan basin at upper mantle. This feature shows the difference in dynamic mechanism between Sichuan basin with Chuandian block and Sichuan with Songpan-Garze block. 3) The Longmen Shan faults belt is divided into two parts at Yingxiu: the south part and north part. The great Wenchuan earthquake and aftershocks distribute in the north part of Longmen Shan faults. The eastward extrusion of Tibetan plateau and upper mantle upwelling caused the uplifting of Songpan-Garze block. Because Yingxiu is located in the south edge of north part of Longmenshan faults belt, it's possible to accumulate high stress. This should be the deep dynamic background of the Wenchuan earthquake. Based on our results, the velocity structure does not support the subduction of the Sichuan basin downward and channel flow.
The 3D P-wave velocity structure of the crust and upper mantle within the depth range of 400 km was obtained by using teleseismic traveltimes data recorded by West Sichuan Seismic Array distributed in Longmenshan region and non-linear tomography inversion technique. For adapting to the complicated structure, the fast marching traveltime calculation method and Tarantola s inversion method was used. Our results show the tectonic differences of the crustal and upper-mantle structure among the blocks of Chuandian, Songpan-Garze and Sichuan basin. Our results show that: 1) the crustal structure of the study area correlates with the surface geological features. The Sichuan basin is imaged as a high-velocity feature, while the SongpanGarze and Chuandian block as low-velocity feature. The lithosphere thickness of Sichuan basin has lateral variations from 250 km in south part to 100 km in north part. There exist upwelling features under Songpan-Garze block. 2) Sichuan basin vertically contacts with Chuandian block, but the thickness of Sichuan basin front in Longmenshan area decreases from east to west with the feature of Songpan-Garze block incursion into Sichuan basin at upper mantle. This feature shows the difference in dynamic mechanism between Sichuan basin with Chuandian block and Sichuan with Songpan-Garze block. 3) The Longmen Shan faults belt is divided into two parts at Yingxiu: the south part and north part. The great Wenchuan earthquake and aftershocks distribute in the north part of Longmen Shan faults. The eastward extrusion of Tibetan plateau and upper mantle upwelling caused the uplifting of Songpan-Garze block. Because Yingxiu is located in the south edge of north part of Longmenshan faults belt, it's possible to accumulate high stress. This should be the deep dynamic background of the Wenchuan earthquake. Based on our results, the velocity structure does not support the subduction of the Sichuan basin downward and channel flow.
引文
[1] 许志琴,侯立玮,王宗秀等.中国松潘-甘孜造山带的造山过程.北京:地质出版社,1992 Xu Z Q, Hou L W, Wang Z X, et al. The Evolution of Songpan-Garze Orogenic Belt (in Chinese). Beijing: Geological Publishing House, 1992
[2] 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 X W, Wen X Z, Ye J Q, et al. The M_s8． 0 Wenchuan earthquake surface ruptutres and its seismogenic structure. Seismology and Geology (in Chinese) , 2008,30(3) : 597-629
[3] Yao H, Beghein C, R D van der Hilst. Surface-wave array tomography in SE Tibet from ambient seismic noise and two-station analysis:Ⅱ-crustal and upper mantle structure. Geophys. J. Int. , 2008,173:205-219
[4] 唐文清,陈智梁.青藏高原东缘鲜水河断裂带与龙门山断裂带现今的构造活动.地质通报,2005,24(12) :1169-1172 Tang W Q, Chen Z L. Present-day tectonic activity in the intersection area of the Xianshuihe fault and Longmenshan fault on the eastern margin of the Qinghai-Tibet Plateau.Geol. Bull. Chin. (in Chinese) , 2005,24(12) :1169-1172
[5] Shen Z K, L J, Wang M, et al. Contemporary crustal deformation around the southeast borderland of the Tibetan Plateau. J. Geophys. Res., 2005, 110:b11409, doi:10． 1029/2004JB003421
[6] Wang Y Z, Wang N N, Shen Z K, el al. GPS-constrained inversion of present-day slip rates along major faults of the Sichuan-Yunnan region, China. Science in China (Series D) ,2008,51(9) :1267-1283
[7] 张培震,王 琪,马宗晋.中国大陆现今构造运动的GPS速度场与活动地块.地学前缘,2002,9(2) :430-441 Zhang P Z, Wang Q, Ma Z J. GPS velocity field and active crustal blocks of contemporary tectonic deformation in continental China. Earth Science Frontiers (in Chinese) ,2002,9(2) :430-441
[8] Burchfiel B C. New technology: new geological challenges. Geol. Soc. Amer. Today, 2003,14(2) : 4-10
[9] Clark M K, Bush W M, Royden L H. Dynamic topography produced by lower crustal flow against rheological strength heterogeneities bordering the Tibetan plateau. Geophys. J.Int. , 2005,162:575-590
[10] 郭斌.龙门山造山带构造特征及演化过程研究[硕士论文].北京:中国地质大学,2006 Guo B. The research of tectonic characteristics and evolution in Longmen orogenic belt [ Master's thesis] (in Chinese). Beijing:China University of Geosciences, 2006
[11] 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 P Z, Xu X W, Wen X Z, et al. Slip rate and recurrence interval of the Longmen Shan active fault zone, and tectonic implications for the mechanism of the May 12 Wenchuan earthquake. 2008, Sichuan, China. Chinese J. Geophys. (in Chinese), 2008, 51(4) :1066-1073
[12] Parsons T, Chen J,Kirby E. Stress changes from the 2008 Wenchuan earthquake and increased hazard in the Sichuan basin. Nature, 2008, doi:10． 1038/nature07177
[13] Huang J L,Zhao D P,Zheng S H. Lithospheric structure and its relationship to seismic and volcanic activity in southwest China. J. Geophys. Res. , 2002, 107(B10) :2255, doi: 10． 1029/2000JB000137
[14] 王椿镛,吴建平,楼海等.川西藏东地区的地壳P波速度结构.中国科学D辑,2003,33(增刊):181-189 Wang C Y, Wu J P, Lou H, et al. The P-wave crustal structure of West Sichuan, China. Science in China (Series D) (in Chinese), 2003, 33(Suppl.): 181-189
[15] 王椿镛,楼海,吕智勇等.青藏高原东部地壳上地幔S波速度结构 下地壳流的深部环境.中国科学D辑,2008,38(1) :22-32 Wang C Y, Lou H, Lu Z Y, et al. S wave velocity structure of the crust and upper mantle in the eastern Tibetan plateau-deep environment of lower cruslal flow. Science in China (Series D) (in Chinese), 2008,38(1) :22-32
[16] 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 J S. The Wenchuan earthquake occurrence background in deep structure and dynamics of lithosphere. Journal of Chendu University of Technology (Science & Technology Edition) (in Chinese), 2008, 35(4) :348-356
[17] 刘启元,李昱,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 Q Y, Li Y, Chen J H, et al. Wenchuan M_s8． 0 earthquake:preliminary study of the S-wave velocity structure of the crust and upper mantle. Chinese J. Geophys. (in Chinese) , 2009,52(2) :309-319
[18] 刘启元,陈九辉,李顺成等.汶川M_s8． 0地震:川西流动地震台阵观测数据的初步分析.地震地质,2008,30(3) :584-596 Liu Q Y, Chen J H, Li S C,et al. The M_s8． 0 Wenchuan earthquake: preliminary results from the western Sichuan mobile seismic array observations. Seismology and Geology (in Chinese) , 2008, 30(3) :584-596
[19] 陈九辉.刘启元,李顺成等.汶川M_s8． 0地震余震序列重新定位及其地震构造研究.地球物理学报,2009,52(2) :390-397 Chen J H, Liu Q Y, Li S C, et al. Seismotectonics study hy relocation of the Wenchuan M_s8． 0 earthquake sequence. Chinese J. Geophys. (in Chinese) , 2009,52(2) :390-397
[20] Aki K, Lee W H K. Determination of three-dimensional velocity anomalies under a seismic array using first P arrival times from local earthquakes, part 1: A homogeneous initial model. J. Geophys. Res. , 1976 ,81 (23) :4381-4399
[21] Vidale J. Finite-difference calculation of traveltime. Bull. Seism. Soc. Am. , 1988,78:2062-2076
[22] Sethian J A. Numerical Methods for Propagating Fronts, in Variational Methods for Free Surface Interfaces. NY : Springer-Verlag, 1987
[23] Sethian J A, Popoviciz A M. 3-D traveltime computation using the fast marching method. Geophys., 1999,64(2) : 516-523
[24] Rawlinson N, Sambridge M. Wavefront evolution in strongly heterogeneous layered media using the Fast Marching Method. Geophys. J. Int. , 2004, 156: 631-647
[25] Popovici A M, Sethian J A. 3-D imaging using higher order fast marching traveltimes. Geophysics, 2002,67:604-609
[26] Tarantola A, Valette B. Generalized nonlinear inverse problems solved using the least squares criterion. Reu. Geophys. Space Phys. , 1982,20:219-232
[2] 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 X W, Wen X Z, Ye J Q, et al. The M_s8． 0 Wenchuan earthquake surface ruptutres and its seismogenic structure. Seismology and Geology (in Chinese) , 2008,30(3) : 597-629
[3] Yao H, Beghein C, R D van der Hilst. Surface-wave array tomography in SE Tibet from ambient seismic noise and two-station analysis:Ⅱ-crustal and upper mantle structure. Geophys. J. Int. , 2008,173:205-219
[4] 唐文清,陈智梁.青藏高原东缘鲜水河断裂带与龙门山断裂带现今的构造活动.地质通报,2005,24(12) :1169-1172 Tang W Q, Chen Z L. Present-day tectonic activity in the intersection area of the Xianshuihe fault and Longmenshan fault on the eastern margin of the Qinghai-Tibet Plateau.Geol. Bull. Chin. (in Chinese) , 2005,24(12) :1169-1172
[5] Shen Z K, L J, Wang M, et al. Contemporary crustal deformation around the southeast borderland of the Tibetan Plateau. J. Geophys. Res., 2005, 110:b11409, doi:10． 1029/2004JB003421
[6] Wang Y Z, Wang N N, Shen Z K, el al. GPS-constrained inversion of present-day slip rates along major faults of the Sichuan-Yunnan region, China. Science in China (Series D) ,2008,51(9) :1267-1283
[7] 张培震,王 琪,马宗晋.中国大陆现今构造运动的GPS速度场与活动地块.地学前缘,2002,9(2) :430-441 Zhang P Z, Wang Q, Ma Z J. GPS velocity field and active crustal blocks of contemporary tectonic deformation in continental China. Earth Science Frontiers (in Chinese) ,2002,9(2) :430-441
[8] Burchfiel B C. New technology: new geological challenges. Geol. Soc. Amer. Today, 2003,14(2) : 4-10
[9] Clark M K, Bush W M, Royden L H. Dynamic topography produced by lower crustal flow against rheological strength heterogeneities bordering the Tibetan plateau. Geophys. J.Int. , 2005,162:575-590
[10] 郭斌.龙门山造山带构造特征及演化过程研究[硕士论文].北京:中国地质大学,2006 Guo B. The research of tectonic characteristics and evolution in Longmen orogenic belt [ Master's thesis] (in Chinese). Beijing:China University of Geosciences, 2006
[11] 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 P Z, Xu X W, Wen X Z, et al. Slip rate and recurrence interval of the Longmen Shan active fault zone, and tectonic implications for the mechanism of the May 12 Wenchuan earthquake. 2008, Sichuan, China. Chinese J. Geophys. (in Chinese), 2008, 51(4) :1066-1073
[12] Parsons T, Chen J,Kirby E. Stress changes from the 2008 Wenchuan earthquake and increased hazard in the Sichuan basin. Nature, 2008, doi:10． 1038/nature07177
[13] Huang J L,Zhao D P,Zheng S H. Lithospheric structure and its relationship to seismic and volcanic activity in southwest China. J. Geophys. Res. , 2002, 107(B10) :2255, doi: 10． 1029/2000JB000137
[14] 王椿镛,吴建平,楼海等.川西藏东地区的地壳P波速度结构.中国科学D辑,2003,33(增刊):181-189 Wang C Y, Wu J P, Lou H, et al. The P-wave crustal structure of West Sichuan, China. Science in China (Series D) (in Chinese), 2003, 33(Suppl.): 181-189
[15] 王椿镛,楼海,吕智勇等.青藏高原东部地壳上地幔S波速度结构 下地壳流的深部环境.中国科学D辑,2008,38(1) :22-32 Wang C Y, Lou H, Lu Z Y, et al. S wave velocity structure of the crust and upper mantle in the eastern Tibetan plateau-deep environment of lower cruslal flow. Science in China (Series D) (in Chinese), 2008,38(1) :22-32
[16] 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 J S. The Wenchuan earthquake occurrence background in deep structure and dynamics of lithosphere. Journal of Chendu University of Technology (Science & Technology Edition) (in Chinese), 2008, 35(4) :348-356
[17] 刘启元,李昱,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 Q Y, Li Y, Chen J H, et al. Wenchuan M_s8． 0 earthquake:preliminary study of the S-wave velocity structure of the crust and upper mantle. Chinese J. Geophys. (in Chinese) , 2009,52(2) :309-319
[18] 刘启元,陈九辉,李顺成等.汶川M_s8． 0地震:川西流动地震台阵观测数据的初步分析.地震地质,2008,30(3) :584-596 Liu Q Y, Chen J H, Li S C,et al. The M_s8． 0 Wenchuan earthquake: preliminary results from the western Sichuan mobile seismic array observations. Seismology and Geology (in Chinese) , 2008, 30(3) :584-596
[19] 陈九辉.刘启元,李顺成等.汶川M_s8． 0地震余震序列重新定位及其地震构造研究.地球物理学报,2009,52(2) :390-397 Chen J H, Liu Q Y, Li S C, et al. Seismotectonics study hy relocation of the Wenchuan M_s8． 0 earthquake sequence. Chinese J. Geophys. (in Chinese) , 2009,52(2) :390-397
[20] Aki K, Lee W H K. Determination of three-dimensional velocity anomalies under a seismic array using first P arrival times from local earthquakes, part 1: A homogeneous initial model. J. Geophys. Res. , 1976 ,81 (23) :4381-4399
[21] Vidale J. Finite-difference calculation of traveltime. Bull. Seism. Soc. Am. , 1988,78:2062-2076
[22] Sethian J A. Numerical Methods for Propagating Fronts, in Variational Methods for Free Surface Interfaces. NY : Springer-Verlag, 1987
[23] Sethian J A, Popoviciz A M. 3-D traveltime computation using the fast marching method. Geophys., 1999,64(2) : 516-523
[24] Rawlinson N, Sambridge M. Wavefront evolution in strongly heterogeneous layered media using the Fast Marching Method. Geophys. J. Int. , 2004, 156: 631-647
[25] Popovici A M, Sethian J A. 3-D imaging using higher order fast marching traveltimes. Geophysics, 2002,67:604-609
[26] Tarantola A, Valette B. Generalized nonlinear inverse problems solved using the least squares criterion. Reu. Geophys. Space Phys. , 1982,20:219-232
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