利用重力观测约束2011日本Tohoku大地震的震源机制  

Constraining focal mechanism of the 2011 Tohoku earthquake by gravity observations

作　　者：薛秀秀[1,2] 胡小刚[1] 郝晓光[1] 柳林涛[1] 

机构地区：[1]中国科学院测量与地球物理研究所大地测量与地球动力学国家重点实验室,武汉430077 [2]中国科学院研究生院,北京100049

出　　处：《地球物理学报》2012年第9期3006-3015,共10页Chinese Journal of Geophysics

基　　金：国家自然科学基金(41174022,41021003,90814009)资助

摘　　要：2011年3月11日,日本东北部(Tohoku)太平洋海域发生Mw9.0特大地震.一些国际学术机构用不同的震相和反演方法,计算了大地震的震源机制解.但这些结果存在一定的差异.地球长周期自由振荡的振幅主要依赖于地震矩的大小及地震断层的破裂方式,可以约束地震的震源机制、地震大小及持续时间.本文利用地球自由振荡0S0简正模对Tohoku大地震的震源机制解进行分析和约束.0S0振幅大小与地震断层的倾角(dip)、滑动方向角(slip)、震源深度及地震断层的破裂时间有关.我们利用震源机制解得到大地震后自由振荡模拟值,利用超导重力仪得到自由振荡的高精度重力观测值.二者比较后的结果显示:由GCMT震源机制解得到的0S0振幅与观测值符合较好,而由USGS CMT震源机制解模拟的结果明显大于观测值.2011Tohoku地震为逆冲型浅源大地震.进一步的分析表明:逆冲型浅源大地震的断层倾角对0S0振幅的影响很大,而滑动方向角以及震源深度对0S0振幅的影响较小.USGS CMT震源机制解中较大的断层倾角是导致其0S0振幅显著偏离观测值的主要原因.An Mw9.0 earthquake occurred near the Pacific coast of Tohoku,Japan on March 11,2011.Some seismic research institutes,using different phases and inversion methods,provided different focal mechanism solutions.Mainly depended on seismic scalar moment and the pattern of the fault rupture,the Earth′s free oscillations can constrain the focal mechanism solution,size and duration of an earthquake.In this paper,we use the radial mode 0S0 to analyze and constrain the focal mechanism solutions of the Tohoku earthquake.The 0S0 amplitude is related to the fault dip angle,slip azimuth,depth and duration of the fault rupture.Based on the focal mechanism solutions,we calculated the synthetic normal modes and compared with the high-precision superconductor gravity observations.The comparison indicates an excellent agreement between the observations and the GCMT synthetics while a significant discrepancy between the observations and USGS CMT synthetics.Our studies indicate that,for a megathrust-shallow event,the influence of fault dip on the 0S0 amplitude is significant but that of the slip and the depth are minor.The large dip is the main reason for the significant discrepancy between the observations and USGS CMT synthetics.

关 键 词：地球自由振荡 震源机制 Tohoku大地震 重力观测 

分 类 号：P312[天文地球—固体地球物理学]