Imaging inner core anisotropy using normal mode and body wave data

Abstract

<p>The Earth's inner core displays strong seismic anisotropy and 3D heterogeneity, which are most likely formed as a result of growth processes and post solidification deformation. Thus, accurately resolving seismic anomalies is key to understanding the formation and dynamic mechanisms of the inner core. Our ultimate aim is to improve current constraints on seismic anomalies in the inner core by combining normal mode data and body wave data in a joint tomographic inversion. While the body wave data is sensitive to regional scale seismic P-wave anisotropy in the inner core, normal modes provide long wavelength information on density, P-wave anisotropy and S-wave anisotropy. </p><p>We have produced a high resolution 3D seismic model of inner core isotropic and anisotropic velocity variations using a transdimensional methodology with body waves. In the transdimensional approach, the inversion itself determines the parameterization. It is encouraging to find many well know features, such as a hemispherical differences between a slow and strongly anisotropic western region and a fast and only weakly anisotropic eastern hemisphere, without a priori imposing those in our parameterization. We are now interested to see if the features seen using body waves are consistent with those seen by normal modes. We measure inner core sensitive normal modes using the splitting function approximation in a way which thoroughly explores the splitting function measurement model space. This then allows us to quantify the uncertainty in individual splitting function coefficients for each mode. We then combine these new normal mode measurements and uncertainty estimates with our body wave data in a joint probabilistic inversion for seismic structure in the inner core.</p>