Book Description

The crustal structure of the Baltic Shield has been studied based on travel-time analysis of P and S-wave data recorded from the Fennolora deep seismic sounding profile. The derived velocity-depth models show several low-velocity zones in the upper crust along the profile. The velocity reduction in these zones is to be less than 7%. crust with varying thicknesses of about 13, 11 and 19-26 km, respectively. The velocity gradient is lower in the middle crust compared to that in the upper and lower crust. The P velocity increases from about 6 km/s at the surface to 6.4 km/s in the middle crust. In the lower crust, velocity varies from about 6.7 km/s to 7.3 km/s. The Moho velocity, below the crust, is to be higher than 8 km/s. The depth to the Moho varies considerably, variations on the order of about 10 km. as high as 0.28 close to the surface and decreased to below 0.25 at about 2 km depth. In the deeper part of the upper crust and in the middle crust, o appears to be about 0.24 and increases slightly to about 0.25 in the lower crust. At the Moho boundary, o increases to about 0.26 and decreases to 0.25 beneath the Moho.