New Analyses of Free Oscillation Splitting with Coupling: Applications to Source and Structure Determination

对自由振荡的分裂和耦合的研究可能会提供一些关于地球的独特信息，特别是关于密度如何相对于剪切速度和体声速横向变化的信息。模分裂已经研究了很多年，但很明显，现在是时候重新审视这个领域了。特别是，过去几年全球地震台网的迅速扩大和许多大（深）地震的发生，意味着模态分裂分析的精度比过去高得多。一些研究已经认为可以恢复三维密度（并且密度变化与下地幔的剪切速度负相关）。这一结果是有争议的，研究人员提出了一些实验，表明密度恢复的主张与当前模式数据集是不成熟的。然而，他们相信，通过扩展数据集和新的分析技术，恢复地球三维密度结构及其三维非弹性结构所需的精度现在是可以实现的。研究人员建议使用一种相对较新的技术（矩阵AR法）来进行这种分析。他们已经证明了这种方法是有效的，而且它有一个显著的优点，那就是它不需要关于源的信息。除了研究地球的长波（弹性、各向异性和非弹性）结构外，它们的分析还可以用于研究地震的低频激发和识别那些异常事件（慢震）。

Gilbert, FreemanEAR-0000920The study of the splitting and coupling of free oscillations can potentially provide some unique information about the Earth -- in particular about how density varies laterally relative to shear velocity and bulk sound speed. Mode splitting has been studied for many years but it is clear that the time is ripe to revisit this field. In particular, the rapid expansion of the global seismic network and the occurrence of many large (and deep) earthquakes in the past few years means that mode splitting analyses are capable of much higher precision than in the past. Some studies have already argued that 3D density can be recovered (and that density variations are negatively correlated with shear velocity in the lower mantle). This result is controversial and the investigators present some experiments that indicate that claims of density recovery with the current mode data set are premature. However, they believe that, with expanded data sets and new analysis techniques, the precision needed to recover the 3D density structure of the Earth and its 3D anelastic structure is now within reach. The investigators propose to use a relatively new technique (the matrix AR method) to do this analysis. They have demonstrated that the method works and it has the significant advantage that it requires no information about the source. In addition to studying the long-wavelength (elastic, anisotropic, and anelastic) structure of the Earth, their analysis can also be used to study the low-frequency excitation of earthquakes and identify those events which are anomalous (slow earthquakes).