Understanding the influence of seismic mantle structures at the core-mantle boundary on intense magnetic flux regions

Within the Priority Program 2404 “Reconstructing the Deep Dynamics of Planet Earth over Geologic Time” (DeepDyn) we investigate possible seismic signatures at magnetic high-latitude flux lobes (HLFL). The focus is on four target regions on the northern hemisphere: Siberia, Canada, North Atlantic and Indonesia. While Siberia and Canada show the HLFL, the North Atlantic should be the location of a third postulated flux lobe, but this area shows no high-flux signal in the magnetic field. The region beneath Indonesia and the Indian Ocean is characterized by an area of high 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 and seismic reflections near the CMB.

To study anisotropy, we measure shear wave splitting of SKS, SKKS, and PKS 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 anisotropy. 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 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.

The second approach uses seismic reflections (P and S waves) from the D" discontinuity, located 300 km above the CMB, and measures their arrival time, slowness, polarity and waveform, using array analysis. We aim to cover the regions with a number of crossing paths, for verification and also for determining whether anisotropy is present (Pisconti et al., 2022). Especially the polarity of the reflected waves, when taken together with the splitting analysis, can help to find the mineralogy that leads to the observed structures near the CMB, which in turn will help to understand the influence of the mantle on core dynamics.

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Typos in the references on the poster

• Walker and Wookey 2010 -> Walker and Wookey 2012
• Kennett 1999 -> Kennett and Engdahl 1991 

See also

• Proceedings of the 84th Annual Meeting of the German Geophysical Society
• Conference start: DeepDyn at the DGG annual conference
• DeepDyn - DFG Priority Programm 2404