Constraining the focal mechanism of the Lushan earthquake with observations of the Earth's free oscillations  

作　　者：JIANG Ying HU XiaoGang LIU ChengLi SUN HePing 

机构地区：[1]State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics,Chinese Academy of Sciences [2]University of Chinese Academy of Sciences

出　　处：《Science China Earth Sciences》2014年第9期2064-2070,共7页中国科学（地球科学英文版）

基　　金：supported by the National Basic Research Program of China (Grant No. 2014CB845902);National Natural Science Foundation of China (Grant Nos. 41174022, 4127408 and 41021003)

摘　　要：The amplitudes of the Earth＇s free oscillations have a close relationship to earthquake focal mechanisms. Focal mechanisms of large earthquakes can be well analyzed and constrained with observations of long period free oscillations. Although the 2013 Lushan earthquake was only moderately sized, observable spherical normal modes were excited and clearly observed by a su- perconductive gravimeter and a broadband seismometer. We compare observed free oscillations with synthetic normal modes corresponding to four different focal mechanisms for the Lushan earthquake. The results show that source parameters can be analyzed and constrained by spherical normal modes in a 2.3-5 mHz frequency band. The scalar seismic moment M~ has a major influence on the amplitudes of free oscillations; additionally, the strike, dip, rake and depth of the hypocenter have mi- nor influences. We found that the synthetic modes corresponding to the focal mechanism determined by the Global Centroid Moment Tensor show agreement to the observed modes, suggesting that earthquake magnitudes predicted in this way can readily reflect the total energy released by the earthquake. The scalar seismic moment obtained by far-field body wave inver- sion is significantly underestimated. Focal mechanism solutions can be improved by joint inversion of far- and near-field data.The amplitudes of the Earth's free oscillations have a close relationship to earthquake focal mechanisms. Focal mechanisms of large earthquakes can be well analyzed and constrained with observations of long period free oscillations. Although the 2013 Lushan earthquake was only moderately sized, observable spherical normal modes were excited and clearly observed by a superconductive gravimeter and a broadband seismometer. We compare observed free oscillations with synthetic normal modes corresponding to four different focal mechanisms for the Lushan earthquake. The results show that source parameters can be analyzed and constrained by spherical normal modes in a 2.3–5 mHz frequency band. The scalar seismic moment M0 has a major influence on the amplitudes of free oscillations; additionally, the strike, dip, rake and depth of the hypocenter have minor influences. We found that the synthetic modes corresponding to the focal mechanism determined by the Global Centroid Moment Tensor show agreement to the observed modes, suggesting that earthquake magnitudes predicted in this way can readily reflect the total energy released by the earthquake. The scalar seismic moment obtained by far-field body wave inversion is significantly underestimated. Focal mechanism solutions can be improved by joint inversion of far- and near-field data.

关 键 词：Lushan earthquake focal mechanism solutions Earth's free oscillations superconductive gravimeter observations broadband seismograph observations 

分 类 号：P315[天文地球—地震学]