地震动旋转分量用于矩张量反演的数值试验  

Numerical experiments of moment tensor inversion with rotational ground motions

作　　者：华思博 张勇[1] HUA SiBo;ZHANG Yong(School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]北京大学地球与空间科学学院,北京100871

出　　处：《地球物理学报》2022年第1期197-213,共17页Chinese Journal of Geophysics

基　　金：国家重点研发计划(2018YFC1503705)资助.

摘　　要：地震动旋转分量可以提供传统平动分量所欠缺的空间梯度信息,理论上可以提升对震源参数的约束.本文对旋转分量用于矩张量反演进行了较为全面的数值试验.首先分析了均匀无限空间中位错点源产生的旋转波场与平动波场在辐射花样上的互补性,由此推测旋转分量用于矩张量反演能提供额外的约束.随后基于层状介质模型合成的平动和旋转记录,开展了地震矩张量反演测试研究.我们通过对比反演得到的矩张量、矩张量差异角Δφ和地震矩,定量评估在矩张量反演中引入旋转分量的作用,发现在合适的条件下,在原平动记录基础上加入旋转记录来联合反演会显著提升反演结果的可靠性,可减小矩张量差异角Δφ30%以上,极端条件下70%以上;如保持总记录数量不变(即在部分台站添加旋转分量替换其他台站的平动分量),某些矩张量元素反演效果会变好,但某些元素可能会变差.整体而言,在多数台站分布的情况下加入旋转都能起到强于增加同等数目平动台站的作用.同时,我们还发现在低频情况下,旋转分量对于深度非常敏感,引入旋转分量对于约束矩心深度有非常显著的效果.此外,还尝试了不同的试验条件,发现在低频、震中距较小、信噪比较低、速度结构模型较为准确的情况下,加入旋转分量对结果的提升更明显.整体而言,尽管旋转分量的使用需要满足一定的条件,将旋转用于矩张量反演是可行的,它能为矩张量反演提供与平动分量互补的信息,在稀疏台站和密集平动的台站的情况下加入旋转观测将显著增强对地震的监测能力.Rotational ground motions can provide spatial gradient information lacking in traditional translational ground motions,and thus can better constrain the source parameters in theory.In this study,we carry out a series of numerical experiments on moment tensor inversions with rotational motions.Firstly,we analyze the complementarity of radiation patterns of rotational and translational motions in a homogeneous infinite space,and infer that the rotational motions may provide complimentary constraints on the result if used in moment tensor inversion.Then we conduct moment tensor inversions with synthetic translational and rotational seismograms calculated with layered velocity model.We evaluate numerically the effect of using rotational components in moment tensor inversion according to the comparison of inverted moment tensor,difference angleΔφand seismic moment.We find that in proper condition,jointly inverting translational and rotational ground motions can significantly improve the reliability of the inversion results,and decrease the difference angleΔφby more than 30%,and more than 70%in some extreme cases.If we keep the total number of records unchanged,which means replacing some translational stations with rotational components in other stations,the inversion result of some moment tensor elements will be improved,while others may be worsened.Overall,adding rotational components contribute more than adding translational components of the same quantity in most station distribution.Moreover,rotational components are more sensitive to the depth at low frequency,thus they are able to provide stronger constraints on the centroid depth.In addition,we try other experiment conditions,and find the results can be further improved by using low-frequency signals close to the epicenter with low signal-to-noise ratios and accurate velocity models.On the whole,although the use of rotational components requires certain conditions,it′s feasible to use them in moment tensor inversion because their spatial gradient informat

关 键 词：地震动旋转分量 矩张量反演 联合反演 

分 类 号：P315[天文地球—地震学] P541[天文地球—固体地球物理学]