Seismic Investigations

Seismic measurements have been carried out in Olkiluoto in conjunction with site investigations since the beginning of the 1990s. These investigations include, among others, reflection seismic 3D measurements in the drillholes 1990 – 2005 and from ground surface in 2006 and 2007 as well as the deep seismic surveys of 2008.

The thickness of soil layers was also surveyed in Olkiluoto in the 1980s and early 2000s by seismic refraction sounding. These results were re-utilised in 2007, and more effective processing of the data produced additional information on the fracturing of the top layer of bedrock.

Several downhole logging methods have been applied in the deep drillholes. These include imaging surveys (acoustic and optical), and methods describing directly the physical properties of the rock mass, like magnetization, density, conductivity, and velocity.

Among one of most important ones, the acoustic logging has been carried out in all deep drillholes and the pilot holes of ONKALO. They reveal the elastic properties of rock in the immediate vicinity of measurement holes. In future, the seismic measurements taken from the tunnel walls of ONKALO may play an important role when the final disposal facilities are investigated in closer detail.

Reflection seismic 3D investigations were carried out from the ground level in the Olkiluoto area in June 2006 and May 2007. The purpose of the surveys was to construct a three-dimensional model of unexplored rock structures in the potential repository area. Read more.

Deep seismic investigations have been carried out in Olkiluoto and its surrounding areas in July 2008. The high resolution reflection seismic method allows exploring the bedrock to a depth of tens of kilometres. Read more.