Resolving upper mantle anisotropy in 3-D from long-term data: A case study in the Upper Rhine Graben area, Central Europe

Abstract Seismic anisotropy studies in the Upper Rhine Graben (URG) area (Central Europe) based on shear wave splitting analysis of SKS/SKKS/PKS phases using long-term recordings (> 15 yr) reveal vertical and small-scale lateral variations of the anisotropy in the upper mantle. Based on the characteristic backazimuthal variations of the splitting parameters, complex anisotropy scenarios are modeled. The comparison of the splitting pattern across the recording stations allows to outline subregions with different anisotropy regimes and to propose a structural 3-D model: differences are found between the east and the west sides of the URG and between the Moldanubian (south) and the Saxothuringian (north) zones. Inconsistent splitting parameters and numerous nulls underneath the southern URG southwest of BFO may be at least partly related to scattering of the seismic wavefield or a modification of the mantle material. In a next step, this 3-D model can be tested via simulations with AxiSEM3D. Additional materials Animations shown on slides 8, 9, 10, 15: https://doi.org/10.5281/zenodo.15641348 Geophysical Visualizations: https://doi.org/10.5281/zenodo.15836682 PyGMT scripts to reproduce the maps: https://github.com/yvonnefroehlich/gmt-pygmt-plotting SWS visualization and modeling codes: https://github.com/yvonnefroehlich/sws-visualization-and-modeling Related peer-reviewed journal articles Fröhlich Y, Grund M, Ritter J R R (2024). Lateral and vertical variations of seismic anisotropy in the lithosphere-asthenosphere system underneath Central Europe from long-term splitting measurements. Geophysical Journal International, 239(1):112-135. https://doi.org/10.1093/gji/ggae245. Ritter J R R, Fröhlich Y, Sanz Alonso Y, Grund M (2022). Short-scale laterally varying SK(K)S shear wave splitting at BFO, Germany – implications for the determination of anisotropic structures. Journal of Seismology, 26:1137-1156. https://doi.org/10.1007/s10950-022-10112-w, correction https://doi.org/10.1007/s10950-023-10136-w.