2017年九寨沟M_S7.0地震震源区速度结构与余震分布
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摘要
采用九寨沟M_S7.0 (M_W6.5)地震的余震直达P波、S波走时数据,通过体波走时层析成像方法,获得了震源区及其邻区的P波和S波速度结构,并利用成像结果对余震进行了重定位。结果显示:余震主要集中分布于高、低速异常交界处偏低速异常一侧,呈走向NNW,倾向SW,倾角较高的分布特征;余震序列两侧的P波、S波速度结构揭示了发震断层两侧介质性质的差异,即上盘为刚性较强的高地震波速度区,下盘为刚性较弱的低地震波速度区。由余震分布特征和地震波速度结构推断:九寨沟地震发生在上地壳底部,发震断层具有上盘地震波速度高、下盘地震波速度低的特征;主震引起的后续破裂在上地壳内部的剧烈形变区内传播,破裂能量终止于25 km深度附近。
Using the arrival times from the aftershocks of 2017 Jiuzhaigou M_S7.0(M_W6.5)earthquake,the P-and S-wave velocity structures in the source region and its adjacent area are obtained by means of the body wave tomography method. The results show that the aftershocks,characterized by NNW-striking,SW-trending and a high dip angle,are mainly concentrated on one side of the low-velocity anomalies at the intersection of high-and low-velocity anomalies. The P-and S-wave velocity structures reveal the differences of crustal property on both sides of the seismogenic fault:the hanging-wall is a high-velocity zone with strong rigidity while the footwall is a low-velocity zone with weak rigidity. According to the distribution of aftershocks and the seismic velocity structure,it can be inferred ultimately that the 2017 Jiuzhaigou M_S7.0 earthquake occurred on the lower interface of the upper crust,following with the rupture propagated in a dramatically deformed area in the upper crust and terminated near the depth of 25 km,and the seismogenic fault has the property of low-velocity hanging-wall and highvelocity footwall.
Using the arrival times from the aftershocks of 2017 Jiuzhaigou M_S7.0(M_W6.5)earthquake,the P-and S-wave velocity structures in the source region and its adjacent area are obtained by means of the body wave tomography method. The results show that the aftershocks,characterized by NNW-striking,SW-trending and a high dip angle,are mainly concentrated on one side of the low-velocity anomalies at the intersection of high-and low-velocity anomalies. The P-and S-wave velocity structures reveal the differences of crustal property on both sides of the seismogenic fault:the hanging-wall is a high-velocity zone with strong rigidity while the footwall is a low-velocity zone with weak rigidity. According to the distribution of aftershocks and the seismic velocity structure,it can be inferred ultimately that the 2017 Jiuzhaigou M_S7.0 earthquake occurred on the lower interface of the upper crust,following with the rupture propagated in a dramatically deformed area in the upper crust and terminated near the depth of 25 km,and the seismogenic fault has the property of low-velocity hanging-wall and highvelocity footwall.
引文
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易桂喜,龙锋,梁明剑,张会平,赵敏,叶有清,张致伟,祁玉萍,王思维,宫悦,乔惠珍,汪智,邱桂兰,苏金蓉.2017.2017年8月8日九寨沟M7.0地震及余震震源机制解与发震构造分析[J].地球物理学报,60(10):4083-4097.Yi G X,Long F,Liang M J,Zhang H P,Zhao M,Ye Y Q,Zhang Z W,Qi Y P,Wang S W,Gong Y,Qiao H Z,Wang Z,Qiu G L,Su J R.2017.Focal mechanism solutions and seismogenic structure of the 8 August 2017 M7.0 Jiuzhaigou earthquake and its aftershocks,northern Sichuan[J].Chinese Journal of Geophysics,60(10):4083-4097(in Chinese).
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周荣军,李勇,Alexander L D,Michael A E,何玉林,王凤林,黎小刚.2006.青藏高原东缘活动构造[J].矿物岩石,26(2):40-51.Zhou R J,Li Y,Alexander L D,Michael A E,He Y L,Wang F L,Li X G.2006.Active tectonics of the eastern margin of the Tibet Plateau[J].Journal of Mineralogy and Petrology,26(2):40-51(in Chinese).
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Thurber C H.1983.Earthquake locations and three-dimensional crustal structure in the Coyote Lake Area,central California[J].JGeophys Res,88(B10):8226-8236.
Thurber C H.1992.Hypocenter-velocity structure coupling in local earthquake tomography[J].Phys Earth Planet In,75(1/2/3):55-62.
Thurber C H,Roecker S,Ellsworth W,Chen Y,Lutter W,Sessions R.1997.Two-Dimensional seismic image of the San Andreas Fault in the Northern Gabilan Range,central California:Evidence for fluids in the fault zone[J].Geophys Res Lett,24(13):1591-1594.
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 Q D,Chen S F,Zhao X L.1994.Tectonics,seismicity and dynamics of Longmenshan mountains and its adjacent regions[J].Seismology and Geology,16(4):389-403(in Chinese).
杜方,闻学泽,张培震,王庆良.2009.2008年汶川8.0级地震前横跨龙门山断裂带的震间形变[J].地球物理学报,52(11):2729-2738.Du F,Wen X Z,Zhang P Z,Wang Q L.2009.Interseismic deformation across the Longmenshan fault zone before the 2008M8.0 Wenchuan earthquake[J].Chinese Journal of Geophysics,52(11):2729-2738(in Chinese).
范文渊,陈永顺,唐有彩,周仕勇,冯永革,岳汉,王海洋,金戈,魏松峤,王彦宾,盖增喜,宁杰远.2015.青藏高原东部和周边地区地壳速度结构的背景噪声层析成像[J].地球物理学报,58(5):1568-1583.Fan W Y,Chen Y S,Tang Y C,Zhou S Y,Feng Y G,Yue H,Wang H Y,Jing G,Wei S Q,Wang Y B,Ge Z X,Ning J Y.2015.Crust and upper mantle velocity structure of the eastern Tibetan Plateau and adjacent regions from ambient noise tomography[J].Chinese Journal of Geophysics,58(5):1568-1583(in Chinese).
江晓涛,朱介寿,王宇航,杨正刚,杜兴忠.2013.青藏高原东缘S波速度结构及其意义[J].地震工程学报,35(4):885-892.Jiang X T,Zhu J S,Wang Y H,Yang Z G,Du X Z.2013.S-wave velocity structure of the eastern margin of the Tibetan Plateau[J].China Earthquake Engineering Journal,35(4):885-892(in Chinese).
李敏娟,沈旭章,张元生,刘旭宇,梅秀苹.2018.基于密集台阵的青藏高原东北缘地壳精细结构及九寨沟地震震源区结构特征分析[J].地球物理学报,61(5):2075-2087.Li M J,Shen X Z,Zhang Y S,Liu X Y,Mei X P.2018.Fine crustal structures of northeast margin of the Tibetan Plateau and structural features of Jiuzhaigou earthquake focal area constrained by the data from a high-density seismic array[J].Chinese Journal of Geophysics,61(5):2075-2087(in Chinese).
楼海,王椿镛,姚志祥,李红谊,苏伟,吕智勇.2010.龙门山断裂带深部构造和物性分布的分段特征[J].地学前缘,17(5):128-141.Lou H,Wang C Y,Yao Z X,Li H Y,Su W,LüZ Y.2010.Subsection feature of the deep structure and material properties of Longmenshan fault zone[J].Earth Science Frontiers,17(5):128-141(in Chinese).
王椿镛,Mooney W D,王溪莉,吴建平,楼海,王飞.2002.川滇地区地壳上地幔三维速度结构研究[J].地震学报,24(1):1-16.Wang C Y,Mooney W D,Wang X L,Wu J P,Lou H,Wang F.2002.Study on 3-D velocity structure of crust and upper mantle in Sichuan-Yunnan region,China[J].Acta Seismology Sinica,24(1):1-16(in Chinese).
吴建平,黄媛,张天中,明跃红,房利华.2009.汶川MS8.0级地震余震分布及周边区域P波三维速度结构研究[J].地球物理学报,52(2):320-328.Wu J P,Huang Y,Zhang T Z,Ming Y H,Fang L H.2009.Aftershocks distribution of the MS8.0 Wenchuan earthquake and three dimensional P-wave velocity structure in and around source region[J].Chinese Journal of Geophysics,52(2):320-328(in Chinese).
易桂喜,龙锋,梁明剑,张会平,赵敏,叶有清,张致伟,祁玉萍,王思维,宫悦,乔惠珍,汪智,邱桂兰,苏金蓉.2017.2017年8月8日九寨沟M7.0地震及余震震源机制解与发震构造分析[J].地球物理学报,60(10):4083-4097.Yi G X,Long F,Liang M J,Zhang H P,Zhao M,Ye Y Q,Zhang Z W,Qi Y P,Wang S W,Gong Y,Qiao H Z,Wang Z,Qiu G L,Su J R.2017.Focal mechanism solutions and seismogenic structure of the 8 August 2017 M7.0 Jiuzhaigou earthquake and its aftershocks,northern Sichuan[J].Chinese Journal of Geophysics,60(10):4083-4097(in Chinese).
赵小麟,邓起东,陈社发.1994.岷山隆起的构造地貌学研究[J].地震地质,16(4):429-439.Zhao X L,Deng Q D,Chen S F.1994.Tectonic geomorphology of the Minshan uplift in western Sichuan,southwestern China[J].Seismology and Geology,16(4):429-439.
周荣军,李勇,Alexander L D,Michael A E,何玉林,王凤林,黎小刚.2006.青藏高原东缘活动构造[J].矿物岩石,26(2):40-51.Zhou R J,Li Y,Alexander L D,Michael A E,He Y L,Wang F L,Li X G.2006.Active tectonics of the eastern margin of the Tibet Plateau[J].Journal of Mineralogy and Petrology,26(2):40-51(in Chinese).
Ellsworth W L,Koyanagi R Y.1977.Three-dimensional crust and mantle structure of Kilauea Volcano,Hawaii[J].J Geophys Res,82(33):5379-5394.
Kissling E,Ellsworth W L,Eberhart-Phillips D,Kradolfer U.1994.Initial reference models in local earthquake tomography[J].J Geophys Res,99(B10):19635-19646.
Kissling E,Kradolfer U,Maurer H.1995.Program VELEST User’s Guide-Short Introduction[R].ETH Zurich:Institute of Geophysics:1-26.
Laske G,Masters G,Ma Z T,Pasyanos M.2013.Update on CRUST1.0-A 1-degree global model of Earth's Crust[C]//EGU General Assembly 2013.Vienna,Austria:European Geosciences Union:2658.
Spakman W,van Der Lee S,van Der Hilst R.1993.Travel-time tomography of the European-Mediterranean mantle down to1 400 km[J].Phys Earth Planet In,79(1/2):3-74.
Thurber C H.1983.Earthquake locations and three-dimensional crustal structure in the Coyote Lake Area,central California[J].JGeophys Res,88(B10):8226-8236.
Thurber C H.1992.Hypocenter-velocity structure coupling in local earthquake tomography[J].Phys Earth Planet In,75(1/2/3):55-62.
Thurber C H,Roecker S,Ellsworth W,Chen Y,Lutter W,Sessions R.1997.Two-Dimensional seismic image of the San Andreas Fault in the Northern Gabilan Range,central California:Evidence for fluids in the fault zone[J].Geophys Res Lett,24(13):1591-1594.
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