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

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

Gilbert, Freeman EAR-0000920 The 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).