The deep seismic sounding experiment POLAR was conducted in the northern Finland and Norway in August 1985 to investigate the crustal structure, composition and development of Precambrian crust in northern Fennoscandia (Luosto et al. 1989). Seismic wide-angle measurements were made along a 440 km long profile by recording large explosions at six shot points and smaller explosions at three shot points. The events were recorded using 42 portable seismic instruments used in five deployments to cover 210 receiver positions at average spacings of 2 km. The profile transects the Central Lapland complex, Karasjok-Kittilä greenstone belt, Lapland granulite belt, Kola province and Mesoproterozoic units of Varanger peninsula. Two-dimensional crustal P- and S-wave velocity models are available from the profile. The models were obtained using a trial-and-error ray tracing method. The original P-wave model was built by Luosto et al. (1989) and new P- and S-wave models were obtained by Janik et al. (2009) through reprocessing and analysis of the original data. The velocity models show high velocity bodies in the upper crust beneath the Karasjok-Kittilä greenstone belt and the Lapland granulite belt, and lower upper crustal velocities beneath the Kola province. The newer models are characterized by more lateral variations in velocity and more complicated velocity structure. Wide-angle sections of three different seismic measurement axes are also available for the POLAR profile (Luosto et al. 1989). Janik, T., E. Kozlovskaya, P. Heikkinen, J. Yliniemi, and H. Silvennoinen, 2009. Evidence for preservation of crustal root beneath the Proterozoic Lapland-Kola orogen (northern Fennoscandian shield) derived from P and S wave velocity models of POLAR and HUKKA wide-angle reflection and refraction profiles and FIRE4 reflection transect. Journal of Geophysical Research: Solid Earth 114. Luosto, U., E. Flueh, and C.-E. Lund, 1989. The crustal structure along the POLAR Profile from seismic refraction investigations. Tectonophysics 162: 51–85.

2022