Investigation of seismic anisotropy in the D'' layer and at the CMB regarding intense magnetic flux regions

Within the Priority Program 2404 “Reconstructing the Deep Dynamics of Planet Earth over Geologic Time” (DeepDyn, https://www.geo.lmu.de/deepdyn/en/) we investigate possible seismic signatures at magnetic high-latitude flux lobes (HLFLs). The focus is on four target regions on the Northern Hemisphere: Siberia, Canada, North Atlantic and Indonesia. While Siberia and Canada show the HLFLs, the North Atlantic should be the location of a third postulated HLFL, but this area shows no intense-flux signal in the magnetic field. The region beneath Indonesia and the Indian Ocean is characterized by an area of intense magnetic flux that changes direction and moves westwards over time. Our aim is to understand whether mineralogy and seismic structure (i.e., thermal constraints) could be responsible for the different magnetic signatures at the core mantle boundary (CMB). This is done by combining two approaches: seismic anisotropy (KIT) and seismic reflections (University of Münster) near the CMB.

To study anisotropy, we measure shear wave splitting of SKS, SKKS, and PKS (XKS) phases as well as of S and ScS phases. Thereby, we determine the splitting parameters, the fast polarization direction φ and the delay time δt as well as the splitting intensity SI. Especially, we search for phase pair discrepancies, e. g., between SKS and SKKS phases, as they are a clear indication for a lowermost mantle contribution to the splitting signal. For the target region underneath Siberia, we present first shear wave splitting measurements (SWSMs) on XKS phases recorded at the Finnish station KEF, including SKS-SKKS pairs.

Based on our shear wave splitting measurements, we will derive structural and mineralogical anisotropy models using the MATLAB Seismic Anisotropy Toolbox (Walker and Wookey 2012). To test these models, we will simulate synthetic seismograms using AxiSEM3D (Leng et al. 2016, 2019). Besides comparing synthetic and observed seismograms, we plan to measure the shear wave splitting of the synthetic phases and compare splitting parameters and splitting intensity to the observed values.

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See also

• Proceedings of the18th Symposium of Study of the Earth's Deep Interior
• DeepDyn - DFG Priority Programm 2404

Funding

Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – 521545943
under Germany’s Priority Programme "Reconstructing the deep dynamics of planet Earth over geologic time (DeepDyn)" SPP 2404 – 500707704.