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

吉尔伯特，弗里曼特尔-0000920自由振荡的分裂和耦合的研究可以潜在地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整体声速横向变化。 模式分裂已经研究了很多年，但很明显，重新审视这一领域的时机已经成熟。特别是，全球地震台网的迅速扩大和过去几年中发生的许多大（和深）地震意味着模态分裂分析能够比过去更高的精度。一些研究已经指出，三维密度是可以恢复的（并且密度变化与下地幔的剪切速度呈负相关）。这一结果是有争议的，研究人员提出了一些实验，表明声称密度恢复与当前模式的数据集是为时过早。然而，他们认为，随着数据集的扩大和新的分析技术的发展，恢复地球三维密度结构及其三维滞弹性结构所需的精度现在已经触手可及。研究人员建议使用一种相对较新的技术（矩阵AR方法）来进行这种分析。他们已经证明了这种方法是有效的，而且它的显著优点是不需要关于源的信息。除了研究地球的长波长（弹性、各向异性和滞弹性）结构外，它们的分析还可用于研究地震的低频激发，并识别异常事件（慢地震）。

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).