GEOTECHNOLOGIEN in everyday life

When the earth quakes ...

Earthquake in K ln MMCD
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It is considered the epitome of stability, of safety: the ground under our feet. After all, it is the foundation not only of our homes, but also of roads, bridges and ultimately our entire environment. But from time to time, this foundation is also here in Germany wavering in our country: the earth shakes.

These quakes are by no means evenly distributed, but accumulate within Germany in certain regions. It is particularly common in the area on both sides of the Rhine and the Thuringian-Bavarian border area. Although these shocks are usually only weak, many of them even barely noticeable, but sometimes they could also leave devastating damage. For example, on April 13, 1992, when magnitude 5.9 earthquakes shook the subsoil of the border town of Roermond in the Netherlands. This strongest earthquake since 1756 in Central Europe was still felt in Berlin, Munich and London. More than 30 people were injured, the damage amounted to the equivalent of more than 150 million euros on both sides of the border.

But how does such a quake come about? The normal cause - movements of the continental plates against each other - can actually play no role here miles away from each plate boundary? But she can:

Scars in the underground

Viewed from space, Europe appears as a single land mass - a continent. But that was not always the case: beneath the surface of Europe are "scars of the earth" - old plate boundaries that bear witness to dramatic transformations of our continent throughout the history of the earth. Normally, they are no longer easily recognizable, on the contrary. Finding these old "scars" and reconstructing the movements of the Earth's crust is one of the most exciting but also most difficult tasks for geoscientists.

But there are moments when the old seams reappear: when the earth shakes. Earthquake researchers assume that stresses arising at the edges of the plates are transmitted to the interior of the continents. Here arises - although far from the actual place of action, the plate movement, away - over time, a huge pressure in the underground. display

When the pressure gets too strong ...

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This pressure can not cope with the old, long-term no longer active seams, because they form geological weak spots in the ground. The rock gives way, breaks and jumps with a jerk to a new position. Due to the great forces acting here, even the smallest fractures and only a few millimeter fractions offset can cause an earthquake.

The earthquakes in the German area go back exactly to this transmission mechanism: the actually "culprit" in this case is the plate boundary between the African and the European plate. The former slowly migrates northward and exerts pressure on the European continent. As a result of these enormous forces, for example, the Alps were raised many kilometers over millions of years.

But this constant pressure also extends beyond the Alps to the north, all the way to the low mountain ranges and into the Rhine ditch. It still forms a geological weak point - a wound in the earth's crust, which breaks up again and again and makes the earth quake.

(geoscience online, 01.04.2004 - NPO)