四川省芦山M_S7.0地震发震构造分析
摘要
2013年4月20日的芦山"4·20"M S7.0地震发生在龙门山断裂带西南段,震中地区分布多条NE向断裂,构造较为复杂。这次地震震源机制解显示为逆冲型地震,破裂面为NE走向,与龙门山断裂带的运动性质和走向一致。地表调查只在大川-双石断裂(前山断裂)和新开店断裂(大邑断裂南段)发现局部分布的NE向地表裂缝、沿地表裂缝分布的喷砂冒水和砂土液化,不规则的边坡开裂等地表变形,以及断裂沿线较严重的滑坡崩塌和房屋破坏。野外调查没有发现明显的地震地表破裂。GPS测量结果显示,此次地震的发震断裂位于芦山县城附近或其以东,而芦山西侧的断裂也可能参与了部分活动。根据野外地质调查、GPS观测、震源机制解、震源深度、余震分布等结果综合判定,芦山7.0级地震的主要发震构造是芦山之下、大川-双石断裂和新开店断裂之间的龙门山前缘滑脱带。此滑脱带在该段的运动导致了这次地震的发生,并可能带动了它上面的大川-双石和新开店等断裂的活动。
The April 20,2013,MS7.0 Lushan earthquake occurred along the southwestern part of the Longmen Shan Fault zone.Tectonics around the epicenter area is complicated and several NEtrending faults are developed.Focal mechanisms of the main shock and inversions from finite fault model suggest that the earthquake occurred on a northeast-trending,moderately dipping reverse fault,which is consistent with the strike and slip of the Longmen Shan Fault zone.NE-trending ground fissures and soil liquefaction along the fissures,heavy landslides along the Dachuan-Shuangshi and Xinkaidian Faults were observed during the field investigations.No surface ruptures were found in the field work.GPS data indicate that the fault on which this earthquake occurred is a fault east of or near the Lushan county and the earthquake also triggered slip on the fault west of the Lushan county.Field observations,GPS data,focal fault plane,focal depth,and distribution of the aftershocks suggest,that the seismogenic structure associated with the MS7.0 Lushan earthquake is the décollement beneath the folds of the eastern Longmen Shan.Slip along this decollement generated the earthquake,and also triggered the slip along the Dachuan-Shuangshi and Xinkaidian Faults.
The April 20,2013,MS7.0 Lushan earthquake occurred along the southwestern part of the Longmen Shan Fault zone.Tectonics around the epicenter area is complicated and several NEtrending faults are developed.Focal mechanisms of the main shock and inversions from finite fault model suggest that the earthquake occurred on a northeast-trending,moderately dipping reverse fault,which is consistent with the strike and slip of the Longmen Shan Fault zone.NE-trending ground fissures and soil liquefaction along the fissures,heavy landslides along the Dachuan-Shuangshi and Xinkaidian Faults were observed during the field investigations.No surface ruptures were found in the field work.GPS data indicate that the fault on which this earthquake occurred is a fault east of or near the Lushan county and the earthquake also triggered slip on the fault west of the Lushan county.Field observations,GPS data,focal fault plane,focal depth,and distribution of the aftershocks suggest,that the seismogenic structure associated with the MS7.0 Lushan earthquake is the décollement beneath the folds of the eastern Longmen Shan.Slip along this decollement generated the earthquake,and also triggered the slip along the Dachuan-Shuangshi and Xinkaidian Faults.
引文
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邓起东,陈社发,赵小麟.1994.龙门山及其邻区的构造和地震活动及动力学[J].地震地质,16(4):389—403.DENG Qi-dong,CHEN She-fa,ZHAO Xiao-lin.1994.Tectonics,seismisity and dynamics of Longmenshan Mountains and its adjacent regions[J].Seismology and Geology,16(4):389—403(in Chinese).
李传友,宋方敏,冉勇康.2004.龙门山断裂带北段晚第四纪活动性讨论[J].地震地质,26(2):248—258.LI Chuan-you,SONG Fang-min,RAN Yong-kang.2004.Late Quaternary activity and age constraint of the northern Longmenshan Fault zone[J].Seismology and Geology,26(2):248—258(in Chinese).
刘杰,易桂喜,张致伟,等.2013.2013年4月20日四川芦山M7.0地震介绍[J].地球物理学报,56(4):1404—1407.doi:10.6038/cjg20130434.LIU Jie,Yi Gui-xi,ZHANG Zhi-wei,et al.2013.Introduction to the Lushan M7.0 earthquake on 20 April 2013[J].Chinese J Geophy,56(4):1404—1407(in Chinese).
唐荣昌,文德华,黄祖智,等.1991.松潘—龙门山地区主要活动断裂带第四纪活动特征[J].中国地震,7(3):64 —71.TANG Rong-chang,WEN De-hua,HUANG Zu-zhi,et al.1991.The Quaternary activity characteristics of several major active faults in the Songpan-Longmenshan region[J].Earthquake Research in China,7(3):64—71(in Chinese).
徐锡伟,闻学泽,叶建青,等.2008.汶川M S8 .0地震地表破裂带及其发震构造[J].地震地质,30(3):597—629 .XU Xi-wei,WEN Xue-ze,YE Jian-qing,et al.2008.The M S8 .0 Wenchuan earthquake surface ruptures and its seismogenic structure[J].Seismology and Geology,30(3):597—629(in Chinese).
徐锡伟,韩竹军,陈桂华,等.2013.四川芦山7.0级强震:一次典型的盲逆断层型地震[J].科学通报,58(20):1887—1893.XU Xi-wei,HAN Zhu-jun,CHEN Gui-hua,et al.2013.Lushan M S7 .0 earthquake:A blind reserve-fault earthquake[J].Chinese Science Bulletin,58(20):1887—1893(in Chinese).
杨晓平,蒋溥,宋方敏,等.1999.龙门山断裂带南段错断晚更新世以来地层的证据[J].地震地质,21(4):341 —345.YANG Xiao-ping,JIANG Pu,SONG Fang-min,et al.1999.The evidence of the south Longmenshan Fault zones cutting late Quaternary stratum[J].Seismology and Geology,21(4):341—345(in Chinese).
杨晓平,冯希杰,戈天勇,等.2008.龙门山断裂带北段第四纪活动的地质地貌证据[J].地震地质,30(3):644 —657.YANG Xiao-ping,FENG Xi-jie,GE Tian-yong,et al.2008.Geological and geomorphic evidence for the quaternary activity on the northeast segment of Longmenshan Fault zone[J].Seismology and Geology,30(3):644—657(in Chinese).
曾祥方,罗艳,韩立波,等.2013.2013年4月20日四川芦山M S7 .0地震:一个高角度逆冲地震[J].地球物理学报,56(4):1418—1424.doi:10.6038/cjg20130437.ZENG Xiang-fang,LUO Yan,HAN Li-bo,et al.2013.The Lushan M S7 .0 earthquake on 20 April 2013:A high-angle thrust event[J].Chinese J Geophy,56(4):1418—1424(in Chinese).
张培震,徐锡伟,闻学泽,等.2008.2008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[J].地球物理学报,51(4):1066—1073.ZHANG Pei-zhen,XU Xi-wei,WEN Xue-ze,et al.2008.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[J].Chinese J Geophy,51(4):1066—1073(in Chinese).
张勇,许力生,陈运泰.2013.芦山4.20地震破裂过程及其致灾特征初步分析[J].地球物理学报.56(4):1408—1411.doi:10.6038/cjg20130435.ZHANG Yong,XU Li-sheng,CHEN Yun-tai.2013.Rupture process of the Lushan 4.20 earthquake and preliminary analysis on the disaster causing mechanism[J].Chinese J Geophy,56(4):1408—1411(in Chinese).
周荣军,李勇,Densmore A L,等.2006.青藏高原东缘活动构造[J].矿物岩石,26(2):40—51.ZHOU Rong-jun,LI Yong,Densmore A L,et al.2006.Active tectonics of the eastern margin of the Tibet plateau[J].Journal of Mineralogy and Petrology,26(2):40—51(in Chinese).
Burchfiel B C,Chen Z,Liu Y,et al.1995.Tectonics of the Longmenshan and adjacent regions[J].International Geology Review,37(8):661—735.
Burchfiel B C,Royden L H,Van der Hilst R D,et al.2008.A geological and geophysical context for the Wenchuan earthquake of 12 May 2008,Sichuan,People's Republic of China[J].GSA Today,18(7):4—11.doi:10.1130/GSATG18A.
Densmore A L,Ellis M A,Li Y,et al.2007.Active tectonics of the Beichuan and Pengguan Faults at the eastern margin of the Tibetan plateau[J].Tectonics,26:TC4005.doi:10.1029/2006TC001987.
Hubbard J,John H S,Yann K.2010.Structural setting of the 2008 M W7 .9 Wenchuan,China,earthquake[J].Bulletin of the Seismological Society of America,100(5B):2713—2735.doi:10.1785/0120090341.
Ran Y K,Chen W S,Xu X W,et al.2013.Paleoseismic events and recurrence interval along the Beichuan-Yingxiu Fault of Longmenshan Fault zone,Yingxiu,Sichuan,China[J].Tectonophysics,584:81—90.
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