Shear-wave splitting beneath Fennoscandia — evidence for dipping structures and laterally varying multilayer anisotropy

• Published in: Geophysical Journal International
• Main Authors: Grund, Michael, Ritter, Joachim R R
• Other Authors: Deutsche Forschungsgemeinschaft, Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ, Københavns Universitet, Universitetet i Oslo, Karlsruher Institut für Technologie
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2020
• Subjects: Norway; Fennoscandia; Northern Norway
• Online Access: http://dx.doi.org/10.1093/gji/ggaa388; http://academic.oup.com/gji/advance-article-pdf/doi/10.1093/gji/ggaa388/33656848/ggaa388.pdf; http://academic.oup.com/gji/article-pdf/223/3/1525/33762014/ggaa388.pdf

SUMMARY The geodynamic evolution of Fennoscandia in northern Europe (Finland, Sweden and Norway) is coined by ca. 3 Ga history of tectonic processes including continental growth in its central and eastern parts and Neogene uplift processes of the Scandinavian mountains (Scandes) located along its western edge. Many details are still under debate and we contribute with new findings from studying deep-seated seismic anisotropy. Using teleseismic waveforms of more than 260 recording stations (long-running permanent networks, previous temporary experiments and newly installed temporary stations) in the framework of the ScanArray experiment, we present the most comprehensive study to date on seismic anisotropy across Fennoscandia. The results are based on single and multi-event shear-wave splitting analysis of core refracted shear waves (SKS, SKKS, PKS and sSKS). The splitting measurements indicate partly complex, laterally varying multilayer anisotropy for individual areas. Consistent measurements at permanent and temporary recording stations over several years and for seismic events of specific source regions allow us to robustly constrain dipping anisotropic structures by adding systematic forward modelling. Although the data coverage is partly limited to only few source regions, our findings support concepts of continental growth due to individual episodes of (paleo-) subduction, each affecting a plunging of the anisotropic fast axis direction due to collisional deformation. Along the northern Scandes the fast axis direction (ϕ) is parallel to the mountain range (NE-SW), whereas an NNW-SSE trend dominates across the southern Scandes. In the south, across the Sorgenfrei–Tornquist Zone, a NW-SE trend of ϕ dominates which is parallel to this suture zone. The Oslo Graben is characterized by an NNE-SSW trend of ϕ. In northern Norway and Sweden (mainly Paleoproterozoic lithosphere), a dipping anisotropy with ϕ towards NE prevails. This stands in contrast to the Archean domain in the NE of our study region where ϕ is ...