汶川M_s 8.0地震余震序列重新定位及其地震构造研究
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摘要
综合利用川西流动地震台阵观测数据和震后应急地震观测台站的震相数据,采用双差地震定位方法对汶川地震的余震序列进行了精确重新定位,并对汶川地震的地震构造进行了深入研究.其结果显示,汶川地震序列从彭灌杂岩南缘开始破裂,主震及其余震破裂带长约350 km,在大部分区域宽约20-30 km,其宽度和空间形态沿破裂带显示了强烈的分段和非均匀特征.坚硬的彭灌杂岩对余震的非均匀性分布和汶川地震复杂的破裂过程起到了重要的控制作用.以松潘—甘孜地块中地壳低速层顶部为底边界,余震主要分布在4-24 km深度范围内的龙门山东缘上地壳高速层内.余震深度分布剖面清晰地显示了映秀—北川断裂和灌县一江油断裂以及汶川—茂汶断裂在20-22 km深度合并为剪切带的特征.小鱼洞到理县方向存在一条长度超过60 km的垂直于龙门山走向的余震分布条带,综合震源机制解和地震破裂过程的研究结果,我们推测,这是坚硬的彭灌杂岩体底部在长期应力积累作用下发生破裂的反映,并成为汶川地震释放出巨大能量的主要原因.
Accurate relocation of the Wenchuan earthquake sequence is obtained by using the double difference relocation algorithm from the integrated travel time data recorded at the Western Sichuan movable seismic array and the earthquake emergency response stations. In this presentation, the seismotectonic deformation and rupture process is also investigated. The results show that the Wenchuan earthquake sequence begins from the south margin of the Pengguan Massif and extends northeastward for about 350 km within a width of 20-30 km. The spatial distribution of the aftershocks exhibits obvious inhomogeneity which can be divided into small sectors. The rigid Pengguan Massif controls the distribution of the earthquake sequence and the complex rupture process. The aftershocks occurred mainly in the depth ranging from 4 to 24 km inside the high velocity layer of the upper crust in the eastern border of the Longmen Shan and above the low velocity zone in the middle crust. Depth distributions of the aftershocks across the sections show clearly that the Yingxiu-Beichuan, Guanxian-Jiangyou and the Wenchuan-Maowen faults merge into a shear belt at the depth of 20-22 km. There exists an aftershock distribution belt from Xiaoyudong to the direction of Lixian, which is perpendicular to the strike of the Longmen Shan and longer than 60 km. Consulting with the results of the focal mechanism of strong aftershocks and the rupture process of the main shock, it could be inferred that the lower part of the Pengguan Massif has been broken up during the earthquake after long term stress accumulation, which would be the main reason why such a great earthquake occurred.
Accurate relocation of the Wenchuan earthquake sequence is obtained by using the double difference relocation algorithm from the integrated travel time data recorded at the Western Sichuan movable seismic array and the earthquake emergency response stations. In this presentation, the seismotectonic deformation and rupture process is also investigated. The results show that the Wenchuan earthquake sequence begins from the south margin of the Pengguan Massif and extends northeastward for about 350 km within a width of 20-30 km. The spatial distribution of the aftershocks exhibits obvious inhomogeneity which can be divided into small sectors. The rigid Pengguan Massif controls the distribution of the earthquake sequence and the complex rupture process. The aftershocks occurred mainly in the depth ranging from 4 to 24 km inside the high velocity layer of the upper crust in the eastern border of the Longmen Shan and above the low velocity zone in the middle crust. Depth distributions of the aftershocks across the sections show clearly that the Yingxiu-Beichuan, Guanxian-Jiangyou and the Wenchuan-Maowen faults merge into a shear belt at the depth of 20-22 km. There exists an aftershock distribution belt from Xiaoyudong to the direction of Lixian, which is perpendicular to the strike of the Longmen Shan and longer than 60 km. Consulting with the results of the focal mechanism of strong aftershocks and the rupture process of the main shock, it could be inferred that the lower part of the Pengguan Massif has been broken up during the earthquake after long term stress accumulation, which would be the main reason why such a great earthquake occurred.
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 rate and recurrence interval of the Longmenshan active fault zone, and tectonic implications for the mechanism of the May 12, 2008 Wenchuan earthquake, Sichuan, China. Chinese J. Geophys. (in Chinese), 2008,51(4) : 1066-1073
[2] 邓起东,陈社发,赵小麟.龙门山及其邻区的构造和地震活动及动力学.地震地质,1994,16(4) :389-403 Deng Q D, Chen S F, Zhao X L. Tectonics, seismicity and dynamics of Longmenshan Mountains and its adjacent regions. Seismology and Geology (in Chinese), 1994, 16 (4) :389-403
[3] Ji C, Shao G F, Zhong L, et al. Rupture history of the May 12, 2008 M_w8 Wenchuan Earthquake: An update. 2008 Bilateral Workshop under the Sino-US Earthquake Studies Protocol, November 11-14 in Boulder, Colorado, USA
[4] 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
[5] 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. Spatiotemporal rupture process oi the 2008 Wenchuan great earthquake. Science in China (Series D)(in Chinese), 2008,38(10) :1186-1194
[6] 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 ruptures and its seismogenic structure.Seismology and Geology (in Chinese), 2008,30(3) :597-629
[7] 朱艾斓,徐锡伟,刁桂苓等.汶川M_s8． 0地震部分余震重新定位及地震构造初步分析.地震地质,2008,30(3) :759-767 Zhu A L, Xu X W, Diao G L, et al. Relocation of the M_s8． 0 Wenchuan earthquake sequence in part:preliminary seismotectonic analysis. Seismology and Geology (in Chinese), 2008,30(3) :759-767
[8] 黄媛,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) :1250-1257 Huang Y, Wu J P, Zhang T Z, et al. Relocation of the M_s8． 0 Wenchuan earthquake and its aftershock sequence. Science in China (Series D), 2008,51(12) :1703-1712
[9] 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
[10] Waldhauser F, Ellsworth W. A double-difference earthquake location algorithm: method and application to the northern Hayward Fault, California. Bull. Seism. Soc. Am. , 2000, 90(6) :1353-1368
[11] 杨智娴,陈运泰,郑月军等.双差地震定位法在我国中西部地区地震精确定位中的应用.中国科学D辑,2003,33(增刊):129-134 Yang Z X, Chen Y T, Zheng Y J, et al. Accurate relocation of earthquakes in central-western China using the doubledifference earthquake location algorithm. Science in China (Series D), 2003, 46(Suppl. ):181-188
[12] 赵珠,范军,郑斯华等.龙门山推覆构造带地壳速度结构和震源位置的精确修订.地震学报,1997,19(6) :615-622 Zhao Z , Fan J, Zheng S H, et al. Precision determination of the crustal structure and hypocentral locations in the Longmenshan thrust nappe belt. Acta Seismological Sinica (in Chinese), 1997,19(6) :615-622
[13] 陈九辉,刘启元,李顺成等.川西地区地壳厚度和泊松比结构研究.中国地球物理.2008． 366 Chen J H, Liu Q Y, Li S C, et al. Crustal thickness and Poisson s ratio in the region of Western Sichuan (in Chinese). Chinese Geophysics. 2008． 366
[14] 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
[15] 胡幸平,俞春泉,陶开等.利用P波初动资料求解汶川地震及其强余震震源机制解.地球物理学报,2008,51(6) :1711-1718 Hu X P, Yu C Q, Tao K, et al. Focal mechanism solutions of Wenchuan earthquake and its strong aftershocks obtained from initial P polarity analysis. Chinese J. Geophys, (in Chinese), 2008,51(6) :1711-1718
[16] Meng Q R, Hu J M, Wang Y, et al. Late Cenozoic denudation by large-magnitude landslides in the eastern edge of Tibetan Plateau. Earth and Planetary Science Letters ,2006, 243:252-267
[17] Burchfiel B C. New technology:new geological challenges. GSAToday, 2003,14(2) :4-10
[18] Burchfiel B C, Royden L H,Van der 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) : 4211． doi:10． 1130/GSATG18A. 1
[2] 邓起东,陈社发,赵小麟.龙门山及其邻区的构造和地震活动及动力学.地震地质,1994,16(4) :389-403 Deng Q D, Chen S F, Zhao X L. Tectonics, seismicity and dynamics of Longmenshan Mountains and its adjacent regions. Seismology and Geology (in Chinese), 1994, 16 (4) :389-403
[3] Ji C, Shao G F, Zhong L, et al. Rupture history of the May 12, 2008 M_w8 Wenchuan Earthquake: An update. 2008 Bilateral Workshop under the Sino-US Earthquake Studies Protocol, November 11-14 in Boulder, Colorado, USA
[4] 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
[5] 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. Spatiotemporal rupture process oi the 2008 Wenchuan great earthquake. Science in China (Series D)(in Chinese), 2008,38(10) :1186-1194
[6] 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 ruptures and its seismogenic structure.Seismology and Geology (in Chinese), 2008,30(3) :597-629
[7] 朱艾斓,徐锡伟,刁桂苓等.汶川M_s8． 0地震部分余震重新定位及地震构造初步分析.地震地质,2008,30(3) :759-767 Zhu A L, Xu X W, Diao G L, et al. Relocation of the M_s8． 0 Wenchuan earthquake sequence in part:preliminary seismotectonic analysis. Seismology and Geology (in Chinese), 2008,30(3) :759-767
[8] 黄媛,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) :1250-1257 Huang Y, Wu J P, Zhang T Z, et al. Relocation of the M_s8． 0 Wenchuan earthquake and its aftershock sequence. Science in China (Series D), 2008,51(12) :1703-1712
[9] 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
[10] Waldhauser F, Ellsworth W. A double-difference earthquake location algorithm: method and application to the northern Hayward Fault, California. Bull. Seism. Soc. Am. , 2000, 90(6) :1353-1368
[11] 杨智娴,陈运泰,郑月军等.双差地震定位法在我国中西部地区地震精确定位中的应用.中国科学D辑,2003,33(增刊):129-134 Yang Z X, Chen Y T, Zheng Y J, et al. Accurate relocation of earthquakes in central-western China using the doubledifference earthquake location algorithm. Science in China (Series D), 2003, 46(Suppl. ):181-188
[12] 赵珠,范军,郑斯华等.龙门山推覆构造带地壳速度结构和震源位置的精确修订.地震学报,1997,19(6) :615-622 Zhao Z , Fan J, Zheng S H, et al. Precision determination of the crustal structure and hypocentral locations in the Longmenshan thrust nappe belt. Acta Seismological Sinica (in Chinese), 1997,19(6) :615-622
[13] 陈九辉,刘启元,李顺成等.川西地区地壳厚度和泊松比结构研究.中国地球物理.2008． 366 Chen J H, Liu Q Y, Li S C, et al. Crustal thickness and Poisson s ratio in the region of Western Sichuan (in Chinese). Chinese Geophysics. 2008． 366
[14] 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
[15] 胡幸平,俞春泉,陶开等.利用P波初动资料求解汶川地震及其强余震震源机制解.地球物理学报,2008,51(6) :1711-1718 Hu X P, Yu C Q, Tao K, et al. Focal mechanism solutions of Wenchuan earthquake and its strong aftershocks obtained from initial P polarity analysis. Chinese J. Geophys, (in Chinese), 2008,51(6) :1711-1718
[16] Meng Q R, Hu J M, Wang Y, et al. Late Cenozoic denudation by large-magnitude landslides in the eastern edge of Tibetan Plateau. Earth and Planetary Science Letters ,2006, 243:252-267
[17] Burchfiel B C. New technology:new geological challenges. GSAToday, 2003,14(2) :4-10
[18] Burchfiel B C, Royden L H,Van der 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) : 4211． doi:10． 1130/GSATG18A. 1
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