中国四川省2008年汶川M_S8.0地震区域三维速度结构
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摘要
我们利用2008年汶川M_S8.0地震的余震给出了中国四川龙门山断裂带区域纵波速度(VP)、剪切波速度(VS)和波速比(VP/VS)的三维(3D)模型。该速度和波速比模型是利用双差地震层析成像程序的一个新版本tomoDDPS(Zhang,2003)获得的,这个版本可以同时反演VP,VS,VP/VS,以及地震的位置。用于反演的数据来自位于一个东北到西南长400km、西北到东南宽200km的区域内的63个固定台站和临时台站,包括了73 013条P波到时、62 287条S波到时,以及61 823条S-P波走时差。速度模型显示了沿着断层和穿过断层的不均匀性。总体而言,速度模型和当地地质特征一致,老的岩石波速高,而年轻的岩石波速低。龙门山断裂带是VP,VS和VP/VS的一个明显分界。基本上在15km以上,断层西部呈现高VP,VS和低VP/VS,对应着松潘—甘孜褶皱系;而在断层东部则呈现低VP,VS和高VP/VS,对应着四川盆地。沿着断层方向,速度结构和多个破裂滑移模型比较吻合,两个高速体恰好对应着两个较大滑移距离的区域。这显示了速度结构控制着沿断层面的滑移分布。
引文
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Zhao,Z.,Fang,J.,Zhen,S.,1997.Crustal velocity and relocated events in Longmen Shan fault zone.Acta Seismol.Sin.19,615-622(in Chinese).
Deng,Q.D.,et al.,2007.Active Tectonics Map of China.Earthquake Press,Beijing.
Ji,C.,Hayes,G.,2008.Preliminary Result of the May 12,2008 M W7.9 Eastern Sichuan,China Earthquake.http://earthquake.usgs.gov/eqcenter/eqinthenews/2008/us2008ryan/finite_fault.php.
Liu-Zeng,J.,Zhang,Z.,Wen,L.,Tapponnier,P.,Sun,J.,Xing,X.,Hu,G.,Xu,Q.,Zeng,L.,Ding,L.,Ji,C.,Hudnut,K.,van der Woerd,J.,2009.Co-seismic ruptures of the 12 May,2008,M W8.0 Wenchuan earthquake,Sichuan:EWcrustal shortening on oblique,parallel thrusts along the eastern edge of Tibet.Earth and Planetary Science Letters 286,355-370.
Nishimura,N.,Yagi,Y.(2008),http://www.geol.tsukuba.ac.jp/~nisimura/20080512/.
Okada,T.,Hasegawa,A.,Suganomata,J.,Zhao,D.,Zhang,H.,Thurber,C.,2007.Imaging the source area of the 1995southern Hyogo(Kobe)earthquake(M7.3)using double-difference tomography.Earth Planet.Sci.Lett.253(1-2),143-150.doi:10.1016/j.epsl.2006.10.022.
Teng,J.,Bai,D.,Yang,H.,Yan,Y.,Zhang,H.,Zhang,Y.,Ruan,X.,2008.Deep processes and dynamic responses associated with the Wenchuan MS8.0 earthquake of 2008.Chin.J.Geophys.51,1385-1402(in Chinese).
Thurber,C.,Zhang,H.,Waldhauser,F.,Hardebeck,J.,Michael,A.,2006.Three dimensional compressional wavespeed model,earthquake relocations,and focal mechanisms for the Parkfield,California,region.Bull.Seismol.Soc.Am.96(4B),S38-S49.doi:10.1785/0120050825.
Wang,W.,Zhao,L.,Li,J.,Yao,Z.,2008.Rupture process of the MS8.0 Wenchuan earthquake of Sichuan,China.Chin.J.Geophys.51,1403-1410(in Chinese).
Wang,Z.,Fukao,Y.,Pei,S.,2009.Structural control of rupturing of the M W7.9 2008 Wenchuan Earthquake,China.Earth Planet.Sci.Lett.279,131-138.doi:10.1016/j.epsl.2008.12.038.
Zhang,H.(2003),Double-difference seismic tomography method and its applications,Ph.D.Thesis,Univ.of Wisconsin at Madison,Madison.
Zhang,H.,Thurber,C.H.,2003.Double-difference tomography:the method and its application to the Hayward fault,California.Bull.Seismol.Soc.Am.93,1875-1889.
Zhang,P.,Xu,X.,Wen,X.,Ran,Y.,2008a.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.Chin.J.Geophys.51,1066-1073(in Chinese).
Zhang,P.,et al.,2008b.Coseismic displacement of2008 MS8.0 Wenchuan earthquake by GPS.Sci.China,Ser D Earth Sci.38,1195-1206(in Chinese).
Zhang,H.,Thurber,C.,Bedrosian,B.,2009.Joint inversion of VP,VS,and VP/VSat SAFOD,Parkfield,California.Geochemistry,Geophysics,and Geosystems 10,Q11002.
Zhao,Z.,Fang,J.,Zhen,S.,1997.Crustal velocity and relocated events in Longmen Shan fault zone.Acta Seismol.Sin.19,615-622(in Chinese).