汶川地震GPS形变约束的破裂分段特征及滑移
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摘要
为了解2008年汶川地震破裂分段特征及滑移,采用弹性位错模型和模拟退火算法,数值模拟汶川震区密集的GPS同震形变。结果表明,GPS同震形变场至少需要用铲状的位于映秀—北川之间的五个断裂加上灌县—江油断裂来模拟。该模型对GPS数据的符合程度与汶川地震滑动分布模型相当,基本反映了汶川地震破裂特征。映秀—北川断裂总长255～294 km。南段以逆冲为主,分上下两层,最深达30 km。中段右旋走滑和逆冲都很大,而北段以右旋走滑为主。映秀段地震周期最短为3 000 a。破裂上层深度14km可能是龙门山中央断裂的闭锁深度。汶川地震可能源于相邻块体的相对运动和挤压、深部滑脱或浅部闭锁,在薄弱构造处首先爆发地震。
In order to study the Wenchuan MW7.9 earthquake rupture characteristic and slip,the dense GPS coseismic deformation is modeled by using simulated annealing algorithm based on uniform elastic half-space model.It's showed that the GPS coseismic deformation can be modeled well using at least five rupture segments from Yingxiu to Beichuan combined with one rupture segment from Guanxian to Jiangyou,and the result is better than one which is inferred from seismic wave data or InSAR data.The rupture along Yingxiu-Beichuan is 255~294 km in length.The south segment can be separated into the upper and the lower two layers,and is 30 km depth characterized by dip-slip reverse faulting.The mid-segment characterized by right lateral oblique faulting and dip-slip reverse faulting,and the north segment characterized by right lateral oblique faulting.The shortest earthquake recurrence interval is 3 000-year at Yingxiu segment.The rupture depth 14 km of upper layer is probably the locking depth along the Longmenshan fault.The Wenchuan earthquake maybe arised from block relatively moving and extrusion,sliping at depth or locking at shallow,and break out at weakness.
In order to study the Wenchuan MW7.9 earthquake rupture characteristic and slip,the dense GPS coseismic deformation is modeled by using simulated annealing algorithm based on uniform elastic half-space model.It's showed that the GPS coseismic deformation can be modeled well using at least five rupture segments from Yingxiu to Beichuan combined with one rupture segment from Guanxian to Jiangyou,and the result is better than one which is inferred from seismic wave data or InSAR data.The rupture along Yingxiu-Beichuan is 255~294 km in length.The south segment can be separated into the upper and the lower two layers,and is 30 km depth characterized by dip-slip reverse faulting.The mid-segment characterized by right lateral oblique faulting and dip-slip reverse faulting,and the north segment characterized by right lateral oblique faulting.The shortest earthquake recurrence interval is 3 000-year at Yingxiu segment.The rupture depth 14 km of upper layer is probably the locking depth along the Longmenshan fault.The Wenchuan earthquake maybe arised from block relatively moving and extrusion,sliping at depth or locking at shallow,and break out at weakness.
引文
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[2]XU Xiwei,WEN Xueze,YE Jianqing,et al.The MS8.0Wenchuan Earthquake Surface Ruptures and Its SeismogenicStructure[J].Seismology and Geology,2008,30(3):597-629.(徐锡伟,闻学泽,叶建青,等.汶川MS8.0地震地表破裂带及其发震构造[J].地震地质,2008,30(3):597-629.)
[3]ZHANG Peizhen,XU Xiwei,WEN Xueze,et al.Slip Rateand Recurrence Intervals of the Longmen Shan Active FaultZone,and Tectonic Implications for the Mechanism of theMay 12 Wenchuan Earthquake,2008,Sichuan,China[J].Chinese Journal of Geophysics,2008,51(4):1066-1073.(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[J].地球物理学报,2008,51(4):1066-1073.)
[4]ZHANG Ruiqing,WU Qingju,LI Yonghua,et al.FocalDepths for Moderate-sized Aftershocks of the WenchuanMs 8.0Earthquake and Their Implications[J].Science inChina:Series D,2008,51(12):1694-1702.(张瑞青,吴庆举,李永华,等.汶川中强余震震源深度的确定及其意义[J].中国科学:D辑,2008,38(10):1234-1241.)
[5]ZHANG Yong,FENG Wanpeng,XU Lisheng,et al.Spatio-temporal Rupture Process of the 2008 Great WenchuanEarthquake[J].Science in China:Series D,2009,52(2),145-154.(张勇,冯万鹏,许力生,等.2008年汶川大地震的时空破裂过程[J].中国科学:D辑,2008,38(10):1186-1194.)
[6]Working Group of the Crustal Motion Observation Networkof China Project.Coseismic Displacement Field of the 2008MS8.0 Wenchuan Earthquake Determined by GPS[J].Science in China:Series D,2008,38:1195-1206.(国家重大科学工程“中国地壳运动观测网络”项目组.GPS测定的2008年汶川MS8.0级地震的同震位移场[J].中国科学:D辑,2008,38(10):1195-1206.)
[7]LI Zhicai,ZHANG Peng,JIN Shuangen,et al.WenchuanEarthquake Deformation Fault Inversion and AnalysisBased on GPS Observations[J].Acta Geodaetica et Carto-graphica Sinica,2009,38(2):108-113.(李志才,张鹏,金双根,等.基于GPS观测数据的汶川地震断层形变反演分析[J].测绘学报,2009,38(2):108-113.)
[8]XU Caijun,LIU Yang,W EN Yangmao.M W7.9Wenchuan Earthquake Slip Distribution Inversion fromGPS Measurements[J].Acta Geodaetica et CartographicaSinica,2009,38(3):195-201.(许才军,刘洋,温扬茂.利用GPS资料反演汶川MW7.9级地震滑动分布[J].测绘学报,2009,38(3):195-201.)
[9]TAN Kai,LI Jie,WANG Qi.Lithospheric RheologicalStructure Constrained by Geodetic Data in Altay[J].Chinese Journal of Geophysics,2007,50,(6):1713-1718.(谭凯,李杰,王琪.大地测量约束下的阿尔泰山岩石圈流变结构[J].地球物理学报,2007,50(6):1713-1718.)
[10]TAN Kai,WANG Qi,WANG Xiaoqiang,et al.AnalyticModels and Space-time Distribution of PostseismicDeformation[J].Journal of Geodesy and Geodynamics,2005,25(4):23-26.(谭凯,王琪,王晓强,等.震后形变的解析模型和时空分布特征[J].大地测量与地球动力学,2005,25(4):23-26.)
[11]SHEN Zhengkang,SUN Jianbao,Zhang Peizhen,et al.Slip Maxima at Fault Junctions and Rupturing of Barriersduring the 12 May 2008 Wenchuan Earthquake[J].Nature Geoscience,2009,2:718-728.
[12]OKADA Y.Surface Deformation due to Shear and TensileFaults in a Half-space[J].Bulletin of the SeismologicalSociety of America,1985,75:1135-1154.
[13]CERVELLI P.Using Geodetic Data to Infer the Kinematicand Mechanical Properties of Deformation Source onKilauea Volcano,Hawaii[D].Stanford:Stanford Univer-sity,2002.
[14]BASU A,FRAZER L N.Rapid Determination of the CriticalTemperature in Simulated Annealing Inversion[J].Science,1990,249:1409-1412.
[15]HANKS T C,KANAMORI H.A Moment MagnitudeScale[J].Journal of Geophysical Research,1979,84(B5):2348-2350.
[16]WANG Weimin,ZHAO Lianfeng,LI Juan,et al.RuptureProcess of the Ms 8.0 Wenchuan Earthquake of Sichuan,China[J].Chinese J Geophys,2008,51(5):1403-1410.(王卫民,赵连锋,李娟,等.四川汶川8.0级地震震源过程[J].地球物理学报,2008,51(5):1403-1410.)
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