The results of the Blue Road seismic experiment with special reference to the properties of the upper mantle

Abstract

During summer 1972 seismic studies were carried out along the Scandinavian “Blue Road” traverse between the Norwegian coast near the Arctic Circle and southern Finland. A set of several reversed and unreversed overlapping seismogram sections with a maximum length of about 600 km could be obtained, using eight shots at five different positions. Velocity models of the crust and upper mantle were computed, based on very clear arrivals of refracted P-waves. The crust—mantle boundary, which was mapped along the whole profile, shows only minor undulations with a mean depth of about 40 km. A root below the Caledonian mountain chain could not be found since recording distances were too short. A constant mantle velocity is derived, to depths of about 80 km, from parallel Pn-branches. Apart from the different geological structures near the surface, the overall distribution of seismic velocities appears to be very similar within the Caledonides and the Baltic Shield.