Quake-proof tunnel

The Japanese earthquake and subsequent tsunami, which in March wiped entire towns, roads, railways and bridges off the map was one of the worst earthquakes ever recorded in the world. The extent of the catastrophe naturally raises the question of whether an earthquake in Northern Europe could damage any future tunnel under the Fehmarnbelt.

"By as early as 1995-1996 we began the collection of geotechnical and geological data in order to determine whether an earthquake could cause serious damage to a tunnel, and following further investigations during 2008-2010 the response is now an unequivocal no," says Jens Kammer, Geotechnical Project Manager for Femern A/S.

The Fehmarnbelt is located in an area far from the edge of any continental plates, which is where major earthquakes normally occur. There were significant subsurface movements in prehistoric times, however these have now stopped, or are so small that they are inconsequential. What is presumed to be the largest earthquake on record occurred in 1629, 140 km from the Fehmarnbelt. However, this was in no way comparable with the Japanese earthquake. In 2008, a moderate earthquake measuring 4.3 on the Richter scale (the Japanese earthquake measured 9.0) occurred in Sweden, 250 km from the Fehmarnbelt.

In comparison, the Kao-hsiung immersed tunnel in Taiwan was subject to an earthquake last year measuring 6.2 on the Richter scale without suffering any serious damage. Amongst other things, this is due to the fact that an immersed tunnel moves together with the ground surrounding it during an earthquake. Only large earth displacements would be able to damage the tunnel, however investigations have indicated that the risk of such displacements in the Fehmarnbelt area is negligible.

"Therefore, we can safely say that an immersed tunnel beneath the Fehmarnbelt will be particularly robust in relation to earthquakes," concludes Jens Kammer.