同震重力变化对震源滑动参数的敏感性研究:以2004年苏门答腊地震为例

Sensitivity of coseismic gravity changes to source slip parameters:case study on the 2004 Sumatra earthquake

在地震孕育和发生过程中,常伴有地表重力变化.通过同震重力变化反演震源参数,可以为认识地震活动特征奠定基础.为了有效提高同震重力变化反演滑动参数的精度,本文设计了一套定量化表征同震重力变化对震源不同滑动参数敏感性的方法.首先,基于位错理论,通过正演得到震源不同滑动参数下的同震重力变化;随后,利用无量纲化的敏感性分析方法,计算同震重力变化对不同滑动参数的敏感度因子.以2004年苏门答腊地震的断层模型为参考,定量评估了该地震同震重力变化对断层深度、断层倾角、滑移量和滑动角四个独立震源滑动参数的敏感性.评估结果显示,2004年苏门答腊地震同震重力变化对滑移量、滑动角、断层深度和断层倾角这四个独立震源滑动参数的敏感性依次降低.因对滑移量的敏感性远高于对断层倾角的敏感性,滑移量较小的反演偏差可以造成断层倾角较大的反演偏差.所以,在反演过程中,需要更加重视排序靠前的滑移量和滑动角.本文设计的方法虽然适用于其他震例,但在不同震例中,同震重力变化对各滑动参数的敏感性将有所差别.

Earthquakes are often accompanied by changes in the surface gravitational field during the preparation and occurrence.Inversion of source parameters by coseismic gravity changes can provide a foundation for understanding the characteristics of seismicity.In order to improve the accuracy of source slip parameters inversion by coseismic gravity changes effectively,this paper designed a set of methods to characterize the sensitivity of coseismic gravity changes to different source slip parameters quantitatively.Firstly,based on dislocation theories,the coseismic gravity changes under different source slip parameters can be obtained through forward modeling.Then,the dimensionless sensitivity analysis method is introduced to calculate the sensitivity factors of coseismic gravity changes to different slip parameters.Based on the fault model of the 2004 Sumatra earthquake,this paper evaluated the sensitivity of coseismic gravity changes to four independent source slip parameters quantitatively,namely depth,dip,slip and rake.The results show that the sensitivity of the coseismic gravity changes decreases in the order of slip,rake,depth and dip of the 2004 Sumatra earthquake.Because the sensitivity to slip is much higher than that to dip,small slip inversion deviation can cause large dip inversion deviation.Therefore,it is necessary to pay more attention to determine the slip and rake which rank ahead in the inversion process.In addition,even though the method designed in this paper is also applicable to other earthquakes,the sensitivity of coseismic gravity changes to each sliding parameter will be different in different earthquakes.