2008年汶川8.0级地震孕震机理研究
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摘要
用三维流变非连续变形与有限元相结合(DDA+FEM)的方法,在青藏高原及邻近地区三维构造块体相互制约的大背景中,考虑了龙门山断裂带东西两侧地势、地壳厚度和分层的明显变化,及断裂带东侧四川盆地及鄂尔多斯块体坚硬地壳阻挡的影响,通过用GPS资料做位移速率边界约束和震源机制约束,计算得到研究区的速度场和应力场与该地区GPS测量结果和震源机制分布结果基本一致.在此基础上,模拟计算现今构造块体边界断层上表征剪应力及法向应力等综合影响的危险度分布.结果表明,上、中地壳层危险度分布中危险度较高的地段多数与近几十年来发生的七级以上大震区域基本一致.包括2008年汶川8.0级等大震的发震断层.通过分别对龙门山断裂带东西两侧的两种不同构造格局进行试算表明,龙门山断裂带东西两侧地势、地壳厚度、分层与物性明显变化对汶川大震的孕育发生均起了关键性作用.计算得到的应变率强度分布图可见,高原东部整个边缘地带均接近应变率强度的陡变带.其中以龙门山断裂带上的陡变最为明显,西侧应变率强度是东侧的近4倍,而且断裂带东侧应变率强度等值线衰减比西侧快.反映了汶川大震逆冲型发震断层地区独特的特征.此外,由计算得到的应变能密度分布图可见,龙门山断裂带在上、中地壳层中均位于宽度相同、其走向与龙门山断裂带走向一致的高应变能密度带中,在上地壳层这个带的东西两侧则是应变能密度较低的地区,而在中地壳层,其强度在断裂带东侧逐渐向东衰减,西侧应变能密度高,而东侧应变能密度较低.表明在印度板块强烈推挤作用和高原各构造块体相互制约及龙门山断裂带东西两侧特殊构造环境中,高原地壳物质向东水平运动,受到龙门山断裂带东侧介质刚性强度较大的四川盆地阻挡,使得汶川大震发震断层在大震前已积累了相当水平的应变能,并同时处于力学上的不稳定状态.
In this paper, 3-D Finite Element Method combined with Discontinous Deformation Analysis (DDA + FEM) is used with the constraints of 3-D tectonic blocks of Qinghai-Xizang Plateau and neighboring areas to study the pregnant mechanism of Wenchuan earthquake. The topography on both sides of Longmenshan fracture zone, the marked change in thickness of the crust and its layers, and the influence of a stronger crust in the Sichuan Basin and Ordos block on the eastern side of the fracture zone are taken into consideration. With the GPS data constrained on the boundary, the calculated velocity and stress fields agree with the observed GPS data and the focal mechanism distribution results. On this basis, the distribution of risk factors on the boundary faults of tectonic blocks, which characterize overall influences of shear stress and normal stress on fault face, etc, is calculated numerically. The results show that the sections with high risk factors coincide with the areas where most of the M_S>7 earthquakes have occurred in recent decades, including M_S=8.0 Wenchuan earthquake in 2008. Trial computation of situations of two different structures on both east and west side of Longmenshan fracture zone show that significant changes of the topography on both sides, the thickness and the layers of the crust, and the physical properties played important roles in the pregnant mechanism of the Wenchuan earthquake. The calculated distribution maps of strain intensity show that the eastern edges of Qinghai-Xizang Plateau are close to the strain intensity steep change zone. Of the zones with steep change in strain intensity in eastern edge of the plateau, Longmenshan fracture zone shows the steepest change. The intensity contour on the east side of the fracture zone decay faster than the west side. In addition, the calculated strain energy density contour shows that the width and the strike direction of the upper and middle layers of the Longmenshan fracture zone is located in the same direction of the high strain energy density band. In the upper layer of the crust, low strain energy density is found on both sides. In the middle layer of the crust, the strain energy density decreases from west to east; the western side has high strain energy density, the eastern side has low strain energy density. Our results show that under strong subduction of Indian Plate, constraints of 3-D tectonic blocks in Qinghai-Xizang Plateau and influence of special tectonic environment on the west and east side of the Longmenshan fracture zone, the seismic fault area, where Wenchuan earthquake occured, had accumulated sufficiant strain energy. It indicates that the area is in mechanical instable state.
In this paper, 3-D Finite Element Method combined with Discontinous Deformation Analysis (DDA + FEM) is used with the constraints of 3-D tectonic blocks of Qinghai-Xizang Plateau and neighboring areas to study the pregnant mechanism of Wenchuan earthquake. The topography on both sides of Longmenshan fracture zone, the marked change in thickness of the crust and its layers, and the influence of a stronger crust in the Sichuan Basin and Ordos block on the eastern side of the fracture zone are taken into consideration. With the GPS data constrained on the boundary, the calculated velocity and stress fields agree with the observed GPS data and the focal mechanism distribution results. On this basis, the distribution of risk factors on the boundary faults of tectonic blocks, which characterize overall influences of shear stress and normal stress on fault face, etc, is calculated numerically. The results show that the sections with high risk factors coincide with the areas where most of the M_S>7 earthquakes have occurred in recent decades, including M_S=8.0 Wenchuan earthquake in 2008. Trial computation of situations of two different structures on both east and west side of Longmenshan fracture zone show that significant changes of the topography on both sides, the thickness and the layers of the crust, and the physical properties played important roles in the pregnant mechanism of the Wenchuan earthquake. The calculated distribution maps of strain intensity show that the eastern edges of Qinghai-Xizang Plateau are close to the strain intensity steep change zone. Of the zones with steep change in strain intensity in eastern edge of the plateau, Longmenshan fracture zone shows the steepest change. The intensity contour on the east side of the fracture zone decay faster than the west side. In addition, the calculated strain energy density contour shows that the width and the strike direction of the upper and middle layers of the Longmenshan fracture zone is located in the same direction of the high strain energy density band. In the upper layer of the crust, low strain energy density is found on both sides. In the middle layer of the crust, the strain energy density decreases from west to east; the western side has high strain energy density, the eastern side has low strain energy density. Our results show that under strong subduction of Indian Plate, constraints of 3-D tectonic blocks in Qinghai-Xizang Plateau and influence of special tectonic environment on the west and east side of the Longmenshan fracture zone, the seismic fault area, where Wenchuan earthquake occured, had accumulated sufficiant strain energy. It indicates that the area is in mechanical instable state.
引文
[1] 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 rates and recurrence intervals of the Longmen Shan aclive 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
[2] 陈运泰,许力生,张勇等.2008年5月12日汶川特大地震震源特性分析报告.2008, http://www. csi. ac. cn/sichuan/chenyuntai. pdf. (2008-05-25) Chen Y T. Xu L S, Zhang Y, el al. Report on the Wenchuan larger earthquake source of May 12,2008． http://www. csi. ac. cn/sichuan/chenyuntai. pdf. (2008-05-25)
[3] Shinji Toda, Jian Lin, Mustapha Meghraoui, et al. 12 May 2008 Ml. 9 Wenchuan, China, earthquake calculated to increase failure stress and seismicity rate on three major fault systems. Geophysical Research Letters, 2008, 35:L17305． doi:10． 1029
[4] 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 J W, Bai D H, Yang H, et al. Deep processs and dynamic responses associated with the Wenchuan M_s8． 0 earthquake of 2008, Chinese J. Geophys. (in Chinese), 2008,51(5) :1385-1402
[5] 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 W M, Zhao L F, Li J, et al. Rupture process of the M_s8． 0 Wenchuan earthquake of Sichuan, China. Chinese J. Geophys. (in Chinese). 2008,51(5) : 1403-1410
[6] 陈连旺,张培震,陆远忠等.川滇地区强震序列库仑破裂应力加卸载效应的数值模拟.地球物理学报.2008,51(5) :1411-1421 Chen L W, Zhang P Z, Lu Y Z, et al. Numerical simulation of loading/unloading effect on Coulomb failure stress among strong earthquakes in Sichuan-Yunnan area, China. Chinese J. Geo phys. (in Chinese), 2008,51(5) :1411-1421
[7] 刘超,张勇,许力生等.一种矩张量反演新方法及其对2008年汶川M_s8． 0地震序列的应用.地震学报,2008,30(4) :329-339 Liu C, Zhang Y, Xu L S, et al. A new technique for moment tensor inversion with applications to the 2008 Wenchuan M_s8． 0 earthquake sequence. Acta Seismologicu Sinica (in Chinese), 2008 ,30(4) :329-339
[8] 孙建宝,梁方,沈正康等.汶川M_s8． 0地震InSAR形变观测初步分析.地震地质,2008,30(3) :789-795 Sun J B, Liang F, Shen Z K, et al. InSAR deformation observation and preliminary analysis of the M_s8． 0 Wenchuan earthquake. Seismology and Geology (in Chinese), 2008,30 (3) :789-795
[9] Burchfiel B C, Chen Z, Liu Y, et al. Tectonics of Longmen Shan and adjacent regions,Central China. Int Geol Rev, 1995,37:661-736
[10] Burchfiel B C. New technology: New geological challenges. Geol Soc Amer Today. 2003,14(2) :4-10
[11] Burchfiel B C, Royden L H, vander Hilst R D, et al. A geological and geophysical context for the Wenchuan earthquake of 12 May 2008, Sichuan, People's Republic of China. GSA Today , 2008,18(7) :4-11
[12] Beaumont C, Jamieson R A, Nguyen M H, et al. Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denunation. Nature. 2001,414:738-742
[13] 陈祖安,林邦慧,白武明.1997年玛尼地震发生对青藏川滇地区构造块体系统稳定性影响的三维DDA+FEM方法数值模拟.地球物理学报,2008,51(5) :1422-1430 Chen Z A, Lin B H, Bai W M. 3-D numerical simulation on influence of 1997 Mani earthquake occurrence to stability of tectonic blocks system in Qingzang and Chuandian zone using DDA+FEM method. Chinese J. Geophys. (in Chinese), 2008,51(5) :1422-1430
[14] 石根华.数值流形方法与非连续变形分析.北京:清华大学出版社,1997 Shi G H. Numerical Manifold Method and Discontinuous Deformation Analysis. Beijing:Tsinghua University Press, 1997
[15] Cai Y, He T, Wang R. Numerical singulation of dynamics process of the Tangshan earthquake by a new method-LDDA. Pure Appl. Geophys, 2000, 157:2083-2104
[16] 陈祖安.白武明,林邦慧等.1966年以来华北地区一系列七级大震破裂过程的数值模拟.地球物理学报,2003,46(3) :373-381 Chen Z A, Bai W M, Lin B H, et al. Numerical simulation for rupture processes of a series of strong earthquakes (M_s>7) in north China since 1966． Chinese J. Geophys. (in Chinese),2003, 46(3) :373-381
[17] 白武明,林邦慧,陈祖安.1976年唐山大震发生对华北地区各地块运动与变形影响的数值模拟研究.中国科学.2003,33(增刊):99-107 Bai W M, Lin B H, Chen Z A. Numerical simulations of deformation and movement of blocks within North China in response to 1976 Tangshan earthquake. Science in China (D). 2003,46(Suppl.) :141-152
[18] 张培震,邓起东,张国民等.中国大陆的强震活动与活动地块.中国科学(D),2003,33(增刊):12-20 Zhang P Z, Deng Q D. Zhang G M,et al. Active tectonic-blocks and strong earthquakes in the continent of China. Science in China (D), 2003,46(Suppl.):13-24
[19] 滕占文.固体地球物理学概论.北京:地震出版社,2003 Teng J W. Introduction to Solid Geophysics (in Chinese). Beijing:Seismological Press, 2003
[20] 丁志峰,何正勤,吴建平等.青藏高原地震波三维速度结构的研究.中国地震,2001,17(2) :202-209 Ding Z F, He Z Q, Wu J P, et al. Research on the 3-D seismic velocity structures in Qinghai-Xizang plateau. Earthquake Research in China (in Chinese), 2001,17(2) :202-209
[21] 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 Wenchan earthquake:preliminary results from the western Sichuan mobile seismic array observations. Seismology and Geology,2008,30(3) :584-596
[22] 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(suppl.):181-189 Wang C Y, Wu J P, Lou H, et al. P-wave crustal velocity structure in western Sichuan and eastern Tibetan region. Science in China (Series D), 2003,46(Suppl.) :254-265
[23] 王椿镛,吴建平,楼海等.青藏高原东部壳幔速度结构和地幔变形场的研究.地学前缘,2006,13(5) :349-359 Wang C Y, Wu J P, Lou H , et al. Study of crustal and upper mantle s structure and mantle deformation field beneath the eastern Tibetan plateau. Earth Science Frontiers (in Chinese), 2006,13(5) :349-359
[24] 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 H, Wang C Y, Lu Z Y, el al. Deep tectonic setting of the 2008 Wenchuan M_s8． 0 earthquake in southwestern China-Joint analysis of teleseimic P-wave receiver functions and Bouguer gravity anomalies. Science in China (Series D) (in Chinese), 2008,38(10) :1207-1220
[25] 张东宁,许忠淮.青藏高原现代构造应力状态及构造运动的三维弹粘性数值模拟.中国地震,1994,10(2) :136-143 Zhang D N. Xu Z H. Three dimensional elasio-visco numerical simulation of Qinghai-Xizang Plateau s recent tectonic stress field and it s motion. Earthquake Research in China (in Chinese), 1994 ,10(2) :136-143
[26] Zhang P Z. Shen Z, Wang M, el al. Continuous deformation of the Tibetan Plateau from global positioning system data. Geology, 2004,32:809-812
[27] 许忠淮.东亚地区现今构造应力图的编制.地震学报,2001,23(5) :492-501 Xu Z H. A present-day tectonic stress map for eastern Asia region. Acta Seismologica Sinica (in Chinese), 2001,23(5) : 492-501
[28] 王仁,孙荀英,蔡永恩.华北地区近700年地震序列的数学模拟.中国科学(B辑),1982． 12(8) :745-753 Wang R, Sun X Y, Cai Y E. Numerical simulation on sequence of about 700 earthquakes in the northern China. Science in China (B)(in Chinese), 1982,12(8) :745-753
[29] 王阎昭,王恩宁,沈正康等.基于GPS资料约束反演川滇地区主要断裂现今活动速率.中国科学(D辑),2008,38(5) :582-597 Wang Y Z. Wang N N, Shen ZK,et al. GPS constrained inversion of slip rates along major faults of the Sichuan-Yunnan region, China. Sciente in China (D) (in Chinese),2008,38(5) :582-597
[2] 陈运泰,许力生,张勇等.2008年5月12日汶川特大地震震源特性分析报告.2008, http://www. csi. ac. cn/sichuan/chenyuntai. pdf. (2008-05-25) Chen Y T. Xu L S, Zhang Y, el al. Report on the Wenchuan larger earthquake source of May 12,2008． http://www. csi. ac. cn/sichuan/chenyuntai. pdf. (2008-05-25)
[3] Shinji Toda, Jian Lin, Mustapha Meghraoui, et al. 12 May 2008 Ml. 9 Wenchuan, China, earthquake calculated to increase failure stress and seismicity rate on three major fault systems. Geophysical Research Letters, 2008, 35:L17305． doi:10． 1029
[4] 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 J W, Bai D H, Yang H, et al. Deep processs and dynamic responses associated with the Wenchuan M_s8． 0 earthquake of 2008, Chinese J. Geophys. (in Chinese), 2008,51(5) :1385-1402
[5] 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 W M, Zhao L F, Li J, et al. Rupture process of the M_s8． 0 Wenchuan earthquake of Sichuan, China. Chinese J. Geophys. (in Chinese). 2008,51(5) : 1403-1410
[6] 陈连旺,张培震,陆远忠等.川滇地区强震序列库仑破裂应力加卸载效应的数值模拟.地球物理学报.2008,51(5) :1411-1421 Chen L W, Zhang P Z, Lu Y Z, et al. Numerical simulation of loading/unloading effect on Coulomb failure stress among strong earthquakes in Sichuan-Yunnan area, China. Chinese J. Geo phys. (in Chinese), 2008,51(5) :1411-1421
[7] 刘超,张勇,许力生等.一种矩张量反演新方法及其对2008年汶川M_s8． 0地震序列的应用.地震学报,2008,30(4) :329-339 Liu C, Zhang Y, Xu L S, et al. A new technique for moment tensor inversion with applications to the 2008 Wenchuan M_s8． 0 earthquake sequence. Acta Seismologicu Sinica (in Chinese), 2008 ,30(4) :329-339
[8] 孙建宝,梁方,沈正康等.汶川M_s8． 0地震InSAR形变观测初步分析.地震地质,2008,30(3) :789-795 Sun J B, Liang F, Shen Z K, et al. InSAR deformation observation and preliminary analysis of the M_s8． 0 Wenchuan earthquake. Seismology and Geology (in Chinese), 2008,30 (3) :789-795
[9] Burchfiel B C, Chen Z, Liu Y, et al. Tectonics of Longmen Shan and adjacent regions,Central China. Int Geol Rev, 1995,37:661-736
[10] Burchfiel B C. New technology: New geological challenges. Geol Soc Amer Today. 2003,14(2) :4-10
[11] Burchfiel B C, Royden L H, vander Hilst R D, et al. A geological and geophysical context for the Wenchuan earthquake of 12 May 2008, Sichuan, People's Republic of China. GSA Today , 2008,18(7) :4-11
[12] Beaumont C, Jamieson R A, Nguyen M H, et al. Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denunation. Nature. 2001,414:738-742
[13] 陈祖安,林邦慧,白武明.1997年玛尼地震发生对青藏川滇地区构造块体系统稳定性影响的三维DDA+FEM方法数值模拟.地球物理学报,2008,51(5) :1422-1430 Chen Z A, Lin B H, Bai W M. 3-D numerical simulation on influence of 1997 Mani earthquake occurrence to stability of tectonic blocks system in Qingzang and Chuandian zone using DDA+FEM method. Chinese J. Geophys. (in Chinese), 2008,51(5) :1422-1430
[14] 石根华.数值流形方法与非连续变形分析.北京:清华大学出版社,1997 Shi G H. Numerical Manifold Method and Discontinuous Deformation Analysis. Beijing:Tsinghua University Press, 1997
[15] Cai Y, He T, Wang R. Numerical singulation of dynamics process of the Tangshan earthquake by a new method-LDDA. Pure Appl. Geophys, 2000, 157:2083-2104
[16] 陈祖安.白武明,林邦慧等.1966年以来华北地区一系列七级大震破裂过程的数值模拟.地球物理学报,2003,46(3) :373-381 Chen Z A, Bai W M, Lin B H, et al. Numerical simulation for rupture processes of a series of strong earthquakes (M_s>7) in north China since 1966． Chinese J. Geophys. (in Chinese),2003, 46(3) :373-381
[17] 白武明,林邦慧,陈祖安.1976年唐山大震发生对华北地区各地块运动与变形影响的数值模拟研究.中国科学.2003,33(增刊):99-107 Bai W M, Lin B H, Chen Z A. Numerical simulations of deformation and movement of blocks within North China in response to 1976 Tangshan earthquake. Science in China (D). 2003,46(Suppl.) :141-152
[18] 张培震,邓起东,张国民等.中国大陆的强震活动与活动地块.中国科学(D),2003,33(增刊):12-20 Zhang P Z, Deng Q D. Zhang G M,et al. Active tectonic-blocks and strong earthquakes in the continent of China. Science in China (D), 2003,46(Suppl.):13-24
[19] 滕占文.固体地球物理学概论.北京:地震出版社,2003 Teng J W. Introduction to Solid Geophysics (in Chinese). Beijing:Seismological Press, 2003
[20] 丁志峰,何正勤,吴建平等.青藏高原地震波三维速度结构的研究.中国地震,2001,17(2) :202-209 Ding Z F, He Z Q, Wu J P, et al. Research on the 3-D seismic velocity structures in Qinghai-Xizang plateau. Earthquake Research in China (in Chinese), 2001,17(2) :202-209
[21] 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 Wenchan earthquake:preliminary results from the western Sichuan mobile seismic array observations. Seismology and Geology,2008,30(3) :584-596
[22] 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(suppl.):181-189 Wang C Y, Wu J P, Lou H, et al. P-wave crustal velocity structure in western Sichuan and eastern Tibetan region. Science in China (Series D), 2003,46(Suppl.) :254-265
[23] 王椿镛,吴建平,楼海等.青藏高原东部壳幔速度结构和地幔变形场的研究.地学前缘,2006,13(5) :349-359 Wang C Y, Wu J P, Lou H , et al. Study of crustal and upper mantle s structure and mantle deformation field beneath the eastern Tibetan plateau. Earth Science Frontiers (in Chinese), 2006,13(5) :349-359
[24] 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 H, Wang C Y, Lu Z Y, el al. Deep tectonic setting of the 2008 Wenchuan M_s8． 0 earthquake in southwestern China-Joint analysis of teleseimic P-wave receiver functions and Bouguer gravity anomalies. Science in China (Series D) (in Chinese), 2008,38(10) :1207-1220
[25] 张东宁,许忠淮.青藏高原现代构造应力状态及构造运动的三维弹粘性数值模拟.中国地震,1994,10(2) :136-143 Zhang D N. Xu Z H. Three dimensional elasio-visco numerical simulation of Qinghai-Xizang Plateau s recent tectonic stress field and it s motion. Earthquake Research in China (in Chinese), 1994 ,10(2) :136-143
[26] Zhang P Z. Shen Z, Wang M, el al. Continuous deformation of the Tibetan Plateau from global positioning system data. Geology, 2004,32:809-812
[27] 许忠淮.东亚地区现今构造应力图的编制.地震学报,2001,23(5) :492-501 Xu Z H. A present-day tectonic stress map for eastern Asia region. Acta Seismologica Sinica (in Chinese), 2001,23(5) : 492-501
[28] 王仁,孙荀英,蔡永恩.华北地区近700年地震序列的数学模拟.中国科学(B辑),1982． 12(8) :745-753 Wang R, Sun X Y, Cai Y E. Numerical simulation on sequence of about 700 earthquakes in the northern China. Science in China (B)(in Chinese), 1982,12(8) :745-753
[29] 王阎昭,王恩宁,沈正康等.基于GPS资料约束反演川滇地区主要断裂现今活动速率.中国科学(D辑),2008,38(5) :582-597 Wang Y Z. Wang N N, Shen ZK,et al. GPS constrained inversion of slip rates along major faults of the Sichuan-Yunnan region, China. Sciente in China (D) (in Chinese),2008,38(5) :582-597
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