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
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摘要
利用川滇地区长期积累的地震走时观测资料和汶川地震余震观测资料对汶川地震震源区及周边区域地壳和上地幔P波三维速度结构进行了研究.结果表明,浅部P波速度分布与地表地质之间具有很好的对应关系.龙门山断裂带在20 km以上深度表现为高速异常带,彭灌杂岩体和宝兴杂岩体为局部高速异常区.龙门山断裂带中上地壳的局部高速异常体对汶川地震的余震分布具有明显的控制作用.在余震带南端,余震全部发生在与宝兴杂岩体对应的高速异常体的东北侧;在余震带的中段,与彭灌杂岩体对应的高速异常体在一定程度上控制了余震的分布;在余震带的东北端,宁强—勉县—带的高速异常体可能阻止了余震进一步向东北扩展.龙门山断裂带中上地壳的P波高速异常表明介质具有相对较高的强度,在青藏高原物质向东挤出过程中起到了较强的阻挡作用,有利于深部能量积累.在30 km深度之下,扬子地块具有明显的高速特征,其前缘随深度增加向青藏高原方向扩展,在下地壳和上地慢顶部已达到龙门山断裂带以西.
3-D P-wave velocity structure in crust and uppermost mantle in and around Wenchuan earthquake source region was studied using long-term accumulated seismic travel time data in Sichuan-Yunnan region and aftershock data of Wenchuan earthquake. The result shows that shallow P-wave velocity structure has good correlation with surface geology. Longmenshan fault zone is imaged as high P-wave velocity region in 0-20 km depth. Pengguan complex and Baoxing complex are imaged as two local high velocity anomaly bodies. The upper crustal high velocity anomaly bodies in Longmenshan fault zone control the distribution of aftershocks. At the southern part of the aftershock zone, aftershocks occurred only in the northeast of the high velocity body related to Baoxing complex. In the middle part, the distribution of aftershocks seems to be controlled by the high velocity anomaly body corresponding to Pengguan complex to some extent; In the northeast part, the high velocity body around Ningqiang-Mianxian may prevent the further extension of aftershocks to the northeast. The existence of upper crustal high P-wave velocity zone in Longmenshan implies that the upper crust has relatively high strength, which may play an important role in obstructing the extrusion of Tibetan Plateau material to east, and are prone to accumulate energy in deep depth. Yangzi Block is characterized by high velocity region below 30 km depth, and its front extends to Tibetan Plateau with depth increasing and reaches to the west of Longmenshan fault zone in the lower crust and upper mantle.
3-D P-wave velocity structure in crust and uppermost mantle in and around Wenchuan earthquake source region was studied using long-term accumulated seismic travel time data in Sichuan-Yunnan region and aftershock data of Wenchuan earthquake. The result shows that shallow P-wave velocity structure has good correlation with surface geology. Longmenshan fault zone is imaged as high P-wave velocity region in 0-20 km depth. Pengguan complex and Baoxing complex are imaged as two local high velocity anomaly bodies. The upper crustal high velocity anomaly bodies in Longmenshan fault zone control the distribution of aftershocks. At the southern part of the aftershock zone, aftershocks occurred only in the northeast of the high velocity body related to Baoxing complex. In the middle part, the distribution of aftershocks seems to be controlled by the high velocity anomaly body corresponding to Pengguan complex to some extent; In the northeast part, the high velocity body around Ningqiang-Mianxian may prevent the further extension of aftershocks to the northeast. The existence of upper crustal high P-wave velocity zone in Longmenshan implies that the upper crust has relatively high strength, which may play an important role in obstructing the extrusion of Tibetan Plateau material to east, and are prone to accumulate energy in deep depth. Yangzi Block is characterized by high velocity region below 30 km depth, and its front extends to Tibetan Plateau with depth increasing and reaches to the west of Longmenshan fault zone in the lower crust and upper mantle.
引文
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[4] 李 勇,周荣军,A L Densmore等.青藏高原东缘龙门山晚新生代走滑-逆冲作用的地貌标志.第四纪研究,2006,26(1) :40-51 Li Y, Zhou R J, A L Densmore, et al. Geomorphic evidence for the late cenozoic strike-slipping and thrusting in Longmen mountain at the eastern margin of the Tibetan plateau.Quaternary Sciences (in Chinese), 2006, 26(1) :40-51
[5] 贾秋鹏,贾 东,朱艾斓等.青藏高原东缘龙门山冲断带与成都平原的现今构造表现:数字地形和地震活动证据.地质科学,2007,42(1) :31-44 Jia Q P, Jia D. Zhu A L, et al. Active tectonics in the Longmen thrust belt to the eastern Qinghai-Tibetan plateau and Sichuan basin, evidence from topography and seismicity. Chinese Journal of Geology (in Chinese), 2007, 42(1) :31-44
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[7] King R W, Shen F, Burchfiel,et al. Geodetic measurement of crustal motion in southwest China. Geology, 1997,25: 179-182
[8] 吕江宁,沈正康,王敏.川滇地区现代地壳运动速度场和活动块体模型研究.地震地质,2003,25(4) :543-554 Lu J N , Shen Z K, Wang M. Contemporary crustal deformation and active tectonic block model of the Sichuan-Yunnan region, China. Seismology and Geology ( in Chinese), 2003, 25(4) :543-554
[9] Shen Z, Lu J, Wang M, et al. Contemporary crustal deformation around the southeast borderland of the Tibetan Plateau. J. Geophys. Res. ,2005, 110:1-17
[10] 陈学波,吴跃强,杜平山等.龙门山构造带两侧地壳速度结构特征.见:国家地震局科技监测司编,中国大陆深部构造的研究与进展.北京:地震出版社,1988． 97-113 Chen X B, Wu Y Q, Du P S, et al. The characteristics of crustal velocity structure along the sides of the Longmenshan tectonic belt. In:Department of Research and Monitor,State Seismological Bureau(ed). Achievement of Deep Tectonics Research in China Continent (in Chinese). Beijing: Seismological Press, 1988． 97-113
[11] 张中杰,李英康,王光杰等.藏北地壳东西向结构与“下凹”莫霍面-来自宽角反射剖面的启示.中国科学(D辑),2001,31(11) :881-888 Zhang Z J, Li Y K, Wang G J, et al. East-west crustal structure and "down-bowing" Moho under the northern Tibet. Science in China (Series D) , 2001, 31(11) : 881-888
[12] 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. P-wave crustal velocity structure in western Sichuan and eastern Tibetan region. Science in China (Series D), 2003, 46(S2) : 254-265
[13] 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 Chengdu University of Technology (Science & Technology Edition), 2008, 35(4) :348-356
[14] 刘建华,刘福田,吴华等.中国南北带地壳和上地幔的三维速度图像.地球物理学报,1989,32(2) :143-151 Liu J H, Liu F T, Wu H, et al. 3-D velocity images of crust and upper mantle in China South-North seismic belt. Chinese J. Geophys. (in Chinese), 1989 ,32(2) :143-151
[15] 王椿镛,Mooney W D,王溪莉等.川滇地区地壳上地幔三维速度结构研究.地震学报,2002,24(1) :1-16 Wang C Y, Mooney W D, Wang X L, et al. Study on 3-D velocity structure of crust and upper mantle in Sichuan-Yunnan region, China. Acta Sesimologica ·Sinica. (in Chinese), 2002, 24(1) :1-16
[16] Huang J, Zhao D, Zheng S. Lithospheric structure and its relationship to seismic and volcanic activity in southwest China. J. Geophys. Res., 2002,107 (B10) , 2255, doi:10． 1029/2000JB000137
[17] Zhao D, Hasegawa A, Horiuchi S. Tomographic imaging of P and S wave velocity structure beneath northeastern Japan. J. Geophys. Res. , 1992, 97:19909-19928
[18] Zhao D, Hasegawa A, Kanamori H. Deep structure of Japan subduction zone as derived from local, regional, and teleseismic events. J. Geophys. Res. , 1994, 99:22313-22329
[19] Waldhauser F, Ellsworth W L. A double-difference earthquake location algorithm: method and application to the Northern Hayward Fault, California. Bull Seismol Soc Amer, 2000,90(6) :1353-1368
[20] 黄 嫒,吴建平,张天中等.汶川8． 0级大地震及其余震序列重定位研究.中国科学(D辑)2008,38(10) :1242-1299 Huang Y, Wu J P, Zhang T Z, et al. Relocation of the M_s 8． 0 Wenchuan earthquake and its aftershock sequence. Science in China (Series D) ,2008, 51(12) : 1703-1711
[21] 许志琴,李化启,侯立炜等.青藏高原东缘龙门-锦屏造山带的崛起-大型拆离断层和挤出机制.地质通报,2007,26(10) :1262-1276 Xu Z Q, Li H Q, Hou L W, et al. Uplift of the Longmen-Jinping orogenic belt along the eastern margin of the Qinghai-Tibet Plateau: Large-scale detachment faulting and extrusion mechanism. Geological Bulletin of China ( in Chinese), 2007, 26(10) : 1262-1276
[22] 王庆良,崔笃信,王文萍等.川西地区现今垂直地壳运动研究.中国科学D辑:地球科学,2008,38(5) :598-610 Wang Q L, Cui D X, Wang W P, et al. Present vertical crustal displacement field of western Sichuan region. Science in China (Series D) (in Chinese), 2008, 38(5) :598-610
[23] 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, L Z Y, et al. Deep structural environment of 2008 Wenchuan M_s 8． 0 earthquake; Joint interpretation from teleseismic P-wave receiver function and Bouguer gravity anomaly. Science in China (Series D) (in Chinese), 2008, 38(10) :1207-1220
[24] Christansen N I. Poisson's ratio and crustal seismology. J Geophys Res, 1996, 101:3139-3156
[25] 王二七,孟庆任.对龙门山中生代和新生代构造演化的讨论.中国科学(D辑),2008,38(10) :1221-1233 Wang E Q, Meng Q R. Discussion about Longmenshan tectonic evolution in Mesozoic and Cenozoic. Science in China (Series D) (in Chinese), 2008, 38(10) : 1221-1233
[26] 王卫民,赵连泽,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 M8． 0 Wenchuan earthquake of Sichuan, China. Chinese J. Geophys. (in Chinese) , 2008, 51(5) : 1403-1410
[27] 张 勇,冯万鹏,许力生等.2008年汶川大地震的时空破裂过程.中国科学(D辑),2008,38(10) :1186-1194 Zhang Y, Feng W P, Xu L S, et al. Space-time rupture process of 2008 Wenchuan earthquake. Science in China (Series D) (in Chinese), 2008, 38(10) : 1186-1194
[2] 陈国光,计凤桔,周荣军等.龙门山断裂带晚第四纪活动性分段的初步研究.地震地质,2007,29(3) :657-673 Chen G G, Ji F G, Zhou R J,et al. Primary research on activity segmentation of the Longmenshan fault zone since late Quaternary. Seismology and Geology (in Chinese) ,2007, 29(3) : 657-673
[3] 杨晓平,蒋 溥,宋方敏等.龙门山断裂带南段错断晚更新世以来地层的证据.地震地质.1999,21(4) :341-345 Yang X P, Jiang F, Song F M, et al. The evidence of the south longmenshan fault zones cutting late quaternary stratum. Seismology and Geology (in Chinese), 1999, 21(4) :341-345
[4] 李 勇,周荣军,A L Densmore等.青藏高原东缘龙门山晚新生代走滑-逆冲作用的地貌标志.第四纪研究,2006,26(1) :40-51 Li Y, Zhou R J, A L Densmore, et al. Geomorphic evidence for the late cenozoic strike-slipping and thrusting in Longmen mountain at the eastern margin of the Tibetan plateau.Quaternary Sciences (in Chinese), 2006, 26(1) :40-51
[5] 贾秋鹏,贾 东,朱艾斓等.青藏高原东缘龙门山冲断带与成都平原的现今构造表现:数字地形和地震活动证据.地质科学,2007,42(1) :31-44 Jia Q P, Jia D. Zhu A L, et al. Active tectonics in the Longmen thrust belt to the eastern Qinghai-Tibetan plateau and Sichuan basin, evidence from topography and seismicity. Chinese Journal of Geology (in Chinese), 2007, 42(1) :31-44
[6] 唐荣昌,韩渭宾主编.四川活动断裂与地震.北京:地震出版社,1993． 368 Tang R C, Han W B. Active faults and earthquakes in Sichuan Province. (in Chinese). Beijing: Seismological Press, 1993． 368
[7] King R W, Shen F, Burchfiel,et al. Geodetic measurement of crustal motion in southwest China. Geology, 1997,25: 179-182
[8] 吕江宁,沈正康,王敏.川滇地区现代地壳运动速度场和活动块体模型研究.地震地质,2003,25(4) :543-554 Lu J N , Shen Z K, Wang M. Contemporary crustal deformation and active tectonic block model of the Sichuan-Yunnan region, China. Seismology and Geology ( in Chinese), 2003, 25(4) :543-554
[9] Shen Z, Lu J, Wang M, et al. Contemporary crustal deformation around the southeast borderland of the Tibetan Plateau. J. Geophys. Res. ,2005, 110:1-17
[10] 陈学波,吴跃强,杜平山等.龙门山构造带两侧地壳速度结构特征.见:国家地震局科技监测司编,中国大陆深部构造的研究与进展.北京:地震出版社,1988． 97-113 Chen X B, Wu Y Q, Du P S, et al. The characteristics of crustal velocity structure along the sides of the Longmenshan tectonic belt. In:Department of Research and Monitor,State Seismological Bureau(ed). Achievement of Deep Tectonics Research in China Continent (in Chinese). Beijing: Seismological Press, 1988． 97-113
[11] 张中杰,李英康,王光杰等.藏北地壳东西向结构与“下凹”莫霍面-来自宽角反射剖面的启示.中国科学(D辑),2001,31(11) :881-888 Zhang Z J, Li Y K, Wang G J, et al. East-west crustal structure and "down-bowing" Moho under the northern Tibet. Science in China (Series D) , 2001, 31(11) : 881-888
[12] 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. P-wave crustal velocity structure in western Sichuan and eastern Tibetan region. Science in China (Series D), 2003, 46(S2) : 254-265
[13] 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 Chengdu University of Technology (Science & Technology Edition), 2008, 35(4) :348-356
[14] 刘建华,刘福田,吴华等.中国南北带地壳和上地幔的三维速度图像.地球物理学报,1989,32(2) :143-151 Liu J H, Liu F T, Wu H, et al. 3-D velocity images of crust and upper mantle in China South-North seismic belt. Chinese J. Geophys. (in Chinese), 1989 ,32(2) :143-151
[15] 王椿镛,Mooney W D,王溪莉等.川滇地区地壳上地幔三维速度结构研究.地震学报,2002,24(1) :1-16 Wang C Y, Mooney W D, Wang X L, et al. Study on 3-D velocity structure of crust and upper mantle in Sichuan-Yunnan region, China. Acta Sesimologica ·Sinica. (in Chinese), 2002, 24(1) :1-16
[16] Huang J, Zhao D, Zheng S. Lithospheric structure and its relationship to seismic and volcanic activity in southwest China. J. Geophys. Res., 2002,107 (B10) , 2255, doi:10． 1029/2000JB000137
[17] Zhao D, Hasegawa A, Horiuchi S. Tomographic imaging of P and S wave velocity structure beneath northeastern Japan. J. Geophys. Res. , 1992, 97:19909-19928
[18] Zhao D, Hasegawa A, Kanamori H. Deep structure of Japan subduction zone as derived from local, regional, and teleseismic events. J. Geophys. Res. , 1994, 99:22313-22329
[19] Waldhauser F, Ellsworth W L. A double-difference earthquake location algorithm: method and application to the Northern Hayward Fault, California. Bull Seismol Soc Amer, 2000,90(6) :1353-1368
[20] 黄 嫒,吴建平,张天中等.汶川8． 0级大地震及其余震序列重定位研究.中国科学(D辑)2008,38(10) :1242-1299 Huang Y, Wu J P, Zhang T Z, et al. Relocation of the M_s 8． 0 Wenchuan earthquake and its aftershock sequence. Science in China (Series D) ,2008, 51(12) : 1703-1711
[21] 许志琴,李化启,侯立炜等.青藏高原东缘龙门-锦屏造山带的崛起-大型拆离断层和挤出机制.地质通报,2007,26(10) :1262-1276 Xu Z Q, Li H Q, Hou L W, et al. Uplift of the Longmen-Jinping orogenic belt along the eastern margin of the Qinghai-Tibet Plateau: Large-scale detachment faulting and extrusion mechanism. Geological Bulletin of China ( in Chinese), 2007, 26(10) : 1262-1276
[22] 王庆良,崔笃信,王文萍等.川西地区现今垂直地壳运动研究.中国科学D辑:地球科学,2008,38(5) :598-610 Wang Q L, Cui D X, Wang W P, et al. Present vertical crustal displacement field of western Sichuan region. Science in China (Series D) (in Chinese), 2008, 38(5) :598-610
[23] 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, L Z Y, et al. Deep structural environment of 2008 Wenchuan M_s 8． 0 earthquake; Joint interpretation from teleseismic P-wave receiver function and Bouguer gravity anomaly. Science in China (Series D) (in Chinese), 2008, 38(10) :1207-1220
[24] Christansen N I. Poisson's ratio and crustal seismology. J Geophys Res, 1996, 101:3139-3156
[25] 王二七,孟庆任.对龙门山中生代和新生代构造演化的讨论.中国科学(D辑),2008,38(10) :1221-1233 Wang E Q, Meng Q R. Discussion about Longmenshan tectonic evolution in Mesozoic and Cenozoic. Science in China (Series D) (in Chinese), 2008, 38(10) : 1221-1233
[26] 王卫民,赵连泽,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 M8． 0 Wenchuan earthquake of Sichuan, China. Chinese J. Geophys. (in Chinese) , 2008, 51(5) : 1403-1410
[27] 张 勇,冯万鹏,许力生等.2008年汶川大地震的时空破裂过程.中国科学(D辑),2008,38(10) :1186-1194 Zhang Y, Feng W P, Xu L S, et al. Space-time rupture process of 2008 Wenchuan earthquake. Science in China (Series D) (in Chinese), 2008, 38(10) : 1186-1194
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