Lichtgedanken 03

Rubrik 58 Excavating traces of ancient earthquakes If there is an earth tremor anywhere in the world today, technical devices record even the tiniest movement. And if an earthquake causes serious damage, the media ensure that we know about it and that it is not so quickly forgotten. However, even catastrophes for which we have no records have left traces underground. Geoscien- tists are now uncovering this evidence. Over the next three years, geoscien- tists from Jena will be working in a litt- le-known earthquake zone in Europe: Slovenia and eastern Italy. »Today, we are particularly aware of the major di- sasters of recent years in the centre of the Italian Peninsula, but similar events can also occur in neighbouring areas,« explains Dr Christoph Grützner. He leads a project that is part of the priori- ty programme SPP 2017, funded by the German Research Foundation (DFG). Scientists from FSU Jena, RWTHAachen and GFZ Potsdam are working together in this programme, doing research on the tectonic movements in this region. »The Adriatic Plate is continuously mo- ving northwards towards the Eurasian Plate, at a rate of about two millimetres per year,« says Grützner. This may be very slow when compared with other earthquake zones, but it does not mean that there is no seismic activity. Earth- quakes in May and September 1976 killed approximately 1,000 people and caused considerable damage in a num- ber of towns. Written records of historical quakes are rare There was a similar disaster in 1511, as evidenced by historical documents. Due to the long gap between the individual events, though, it is difficult to estima- te average repetition rates at individual faults, which could contain important information about the seismic activity in this area. »At most, we can hope to get information from the Romans, who ruled the region around 2,000 years ago. There are no written records of any ear- lier earthquakes,« explains Grützner, a geophysicist. »This means that there could be geological time bombs ticking in this region, which nobody knows about because they only explode every few thousand years.« However, a close look at and under the ground can help researchers to find traces of past earthquakes. Grützner explains: »First, I use the computer to analyse high-resolution terrain mo- dels and look for particular structures in the landscape that indicate tectonic seam zones—for example, characteri- stic-looking river valleys. And then I go in person to look at the area.« At the site, he digs into the earth, expo- sing sedimentary layers in order to find striking deformation structures. Layers that are normally arranged horizontally can be deformed. »This is how I iden- tify faults from which earthquakes have been triggered in the past and could again be triggered in future. In addition, by dating the sedimentary layers I can draw up a possible chronology of the seismic activity.« Researching the origins of the Alps However, this Adriatic region is in- teresting not only in relation to earth- quakes. The tectonic movements of the two plates are also responsible for the emergence of the Alps, says Prof. Kamil Ustaszewski. The professor of structural geology heads the working group of which Grützner’s work is also a part. »We are investigating how the Alps were formed and how the deep structures beneath them were created,« explains Ustaszewski. BY SEBASTIAN HOLLSTEIN Prof. Kamil Ustaszewski (l.) and Dr Christoph Grützner study a map of the Alps covering the area of Slovenia and north-eastern Italy.