Investigation of seismic anisotropy in the D'' layer using XKS pairs

KIT –The Research University in the Helmholtz Association Investigation of seismic anisotropy in the D’’ layer using XKS pairs Fröhlich Yvonne, Dorn Fiona, Dillah Muhammad I. F., Ritter Joachim R. R. Karlsruhe Institute of Technology (KIT), Geophysical Institute (GPI), Karlsruhe, Germany References & Acknowledgements •YF is supported by DFG grant RI1133/14-1 (SPP 2404 DeepDyn). •Shear wave splitting measurements were performed with SplitLab 1.2.1 (Porritt, 2014). •Correction of error calculation in SplitLab after Walsh et al., 2013, https://doi.org/10.1002/jgrb.50386. •Correction of temporal alignment in SplitLab after Fröhlich et al., 2022, https://doi.org/10.4401/ag-8781. •Geographic maps were generated with PyGMT v0.13.0 (Tian et al., 2024) and GMT 6.5.0 (Wessel et al., 2024). •Color-coding was accomplished using colormaps of cmocean (Thyng et al., 2016) and Scientific colour maps v8.0.1 (Crameri, 2023). •Creasy et al., 2020, G3, https://doi.org/10.1029/2019GC008883. •Crotwell et al., 1999, SRL, https://doi.org/10.1785/gssrl.70.2.154. •Grund & Ritter, 2019, Geology, https://doi.org/10.1130/G45514.1. •Kennet et al., 1991, Terra Nova https://doi.org/10.1111/j.1365-3121.1991.tb00863.x. •Leng et al., 2016, GJI, https://doi.org/10.1093/gji/ggw363. •Leng et al., 2019, GJI, https://doi.org/10.1093/gji/ggz092. •Nowacki et al., 2011, J. of Geodyn., https://doi.org/10.1016/j.jog.2011.04.003. •Pisconti et al., 2021, JGR Solid Earth, https://doi.org/10.1029/2018JB016993. •Walker & Wookey, 2012, Comput. Geosci., https://doi.org/10.1016/j.cageo.2012.05.031. •Wolf et al., 2023, G3, https://doi.org/10.1029/2023GC011070. •Wüstefeld et al., 2007, Comput. Geosci., https://doi.org/10.1016/j.cageo.2007.08.002. •Wüstefeld et al., 2009, Phys. Earth Planet. Int., https://doi.org/10.1016/j.pepi.2009.05.006. Shear wave splitting (SWS) can be used to detect seismic anisotropy in the lowermost mantle (LMM) based on phase pair discrepancies, in particular by analyzing SKS and SKKS phases. Within the DFG Priority Program (SPP) 2404 "Reconstructing the Deep Dynamics of Planet Earth over Geologic Time” (DeepDyn) we investigate target regions associated with intense magnetic flux. In the first funding period we concentrate on the northern hemisphere, especially on the LMM beneath Siberia, the North Atlantic, Canda and Indonesia. This poster focuses on the target regions Siberia and North Atlantic and shows SWS measurements and SKS-SKKS pairs at the recording station KEF (HE) in Finland. For the target region Indonesia, see the poster by Tölle et al. (2024) and for a general overview on D'' structures in these target regions, visit the talk by Thiyagarajan et al. (2024). Shear wave splitting PKS, SKS, SKKS (XKS) phases S, ScS phases → Splitting parameters, splitting intensity Phase pair discrepancies SKS vs. SKKS → LMM mantle contribution Method Nowacki et al. (2011); Fig. 2, modified. Ray paths and travel times after iasp91 Earth model by Kennet et al. (1991). Calculation with the Java TauP Toolkit by Crotwell et al. (1999). SKS-SKKS pairs Atlantic Siberia AlpArray ScanArray USArray SKKS – split SKKS – split SKS – null SKS – null Modeling Library of elastic tensors for LMM anisotropy → Creasy et al. (2020) Consideration of different minerals MATLAB Seismic Anisotropy Toolbox → Walker & Wookey (2012) Consideration of different anisotropy sources → Nowacki et al. (2011) Consideration of phase transitions and slip systems → Pisconti et al. (2021) → Set up different anisotropy / splitting and reflection scenarios AxiSEM2D / AxiSEM3D → Leng et al. (2016, 2019) Simulations of wave propagation Generation of synthetic seismograms → Measure shear wave splitting for SKS-SKKS, S-ScS phase pairs → Calculate reflection coefficients for P, S phases Pisconti et al. (2021); Fig. 5, slightly modified. minerals structures LPO SPO Data A t l a n t i c S i b e r i a Teleseismic earthquakes Time window: August 2006 – July 2017 Epicentral distance: Δ= [80, 140]° Moment magnitude: Mw > 5.5 Hypocentral depth: hd > 20 km Finnish recording station Station code: KEF Network code: HE LLVPs and XKS LMM anisotropy database compiled by Wolf et al. (2023). KEF