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"The Alps were formed roughly 130 million years ago when the Eurasian Plate collided with the African Plate. Even today, powerful underground forces are still at play in the Alpine region. We still do not know exactly what the interior of the Earth looks like at a depth of several hundred kilometres, however. Furthermore, we have no knowledge of what exactly happens when tectonic plates collide. In some cases we do not even know precisely where the plate boundaries are.
Finding this out is important for us in two respects. For one thing, to better understand how plate tectonics actually functions on our planet. And for another, to be able to compile better hazard scenarios. The earthquakes that Italy for instance suffers time and time again are a good illustration of why this is necessary.
Signals from the deep – researching a huge region
To improve our understanding of what happens deep underground, 50 institutes from 18 European countries have teamed up in the AlpArray project. We have installed a dense network of earthquake seismometers covering the Alpine region. They allow the signals from the deep to be charted very precisely. Because the Alpine region covers such a large area, an international, European approach was chosen. One country on its own would not be able to obtain a decent overview. Together, our aim is to image the structure of the Alps from their surface down to a depth of several hundred kilometres in the Earth’s mantle.
Cooperation between Kiel and Paris
Together with the Paris-based Institut de Physique du Globe, we from GEOMAR Helmholtz Centre for Ocean Research Kiel are jointly studying the substrate beneath the Ligurian Sea. This is the continuation of the front of the Alpine range under the sea. The Ligurian Sea is a branch of the Mediterranean between the islands of Corsica and Elba in the south and the coast of Northern Italy and Monaco in the north.
Last summer, we installed 30 ocean floor seismometers at the bottom of the sea – at distances of roughly 40 to 50 kilometres apart. Between early February and early March 2018 we then recovered them from the Ligurian Sea and secured the data. Over the past eight months, they have been recording seismic waves from every conceivable direction. This will help us with imaging the structures of the Earth’s crust and mantle. It is a bit like a medical computer tomography scanner that uses radiation to create an image of the body. In this example, the Earth is the body and the seismic waves are the radiation.
Tracking down volcanic structures
In addition, to allow us to study the upper ocean floor strata more precisely, we generated small artificial seismic waves ourselves. We did this by using air guns to create soundwaves in the water column which then penetrated up to 30 or 40 kilometres into the ocean substrate. This allows us to discover exactly how the ocean floor is structured. We can then for example investigate the extent to which there is volcanic activity on the sea floor.
Although we have just begun analysing the data, we have already been able to see that the bottom of the Ligurian Sea is characterised by inactive volcanic structures. What is more, we have found that the oceanic crust below the Ligurian Sea is relatively thin. Normally, the oceanic crust is around seven to eight kilometres thick, yet here it has “thinned out” to roughly five kilometres. This information provides us with important clues to the tectonic and geodynamic processes that are at play in the region. We will thus be able to find out how these blocks of earth have moved in the past. And we can obtain an idea of how they may continue to move in the future. On shorter time scales, this may help us to compile hazard scenarios for the future."
Professor Heidrun Kopp
GEOMAR Helmholtz Centre for Ocean Research Kiel is one of the world’s leading institutes in the field of marine sciences. Researchers at the institute investigate the chemical, physical, biological and geological processes of the seafloor, oceans and ocean margins and their interactions with the atmosphere. The geophysicist Heidrun Kopp heads a research division that focuses on the dynamics of the ocean floor. With her colleagues, the Kiel-based professor explores among other things the processes at the boundaries of the tectonic plates and natural hazards caused by earthquakes and tsunamis.www.geomar.de