Humans can't directly perceive the dynamics at work in the earth's crust. Anyone standing on a mountain peak in the Alps doesn't notice that the mountain below is moving.
A team from the TUM German Geodetic Research Institute has now made the movements of the mountain range visible on a comprehensive basis for the first time. The data used came from more than 300 GPS antennas in the German, Austrian, Slovenian, Italian, French and Swiss Alps. The scientists identified the positions of the measurement stations, accurate down to fractions of a millimeter; a large number of the stations were set up in the EU project ALPS-GPSQUAKENET and are in part operated by TUM itself.
Goldmine for geodesy
For twelve years now each of these stations has been making positioning measurements every 15 seconds. "The data are a goldmine for geodesy, with its objective of accurately measuring the surface of the earth and identifying any changes occurring," explains Prof. Florian Seitz of the Chair of Geodetic Geodynamics.
"The greatest challenge was the homogeneous processing of the measurements," recalls Dr. Laura Sánchez. The TUM researcher analyzed one-half million observed data items: "The measurements are for example impaired by the weight of snow which lowers the antennas in the winter, and by anomalies in the atmosphere which affect the GPS signals. These interference factors have to be detected and corrected."
A model for the entire Alpine region
The scientists used the corrected measured values to create a computer model of the entire Alpine region. A first: "Previous analyses were limited to individual regions. Our model reaches from the Maritime Alps all the way to Vienna and thus incorporates all parts of the mountain range," Seitz points out. "Furthermore, at a resolution of 25 kilometers we can represent horizontal and vertical shifts as well as lateral spreading and compression."
Mountain range on the move
The model depicts visibly both large-scale patterns of movement and regional special factors: Thus for example each year the Alps grow an average of 1.8 millimeters in height and move to the northeast at a speed of up to 1.3 millimeters. In South and East Tyrol however a rotation towards the east is superimposed on this movement, while at the same time the mountain range is being compressed. And the rise in height is not identical everywhere either: Very small in the southern part of the western Alps, it reaches its maximum with a speed of more than 2 millimeters per year in the central Alps, at the boundaries of Austria, Switzerland and Italy.
These changes in the surface of the earth serve as the basis for inferences regarding underground plate tectonics. The movements measured are the result of the Alpine orogeny, which began in the Jurassic period 200 million years ago and is still going on today. "This means geologists and geophysicists who study the dynamics of the Alps are very interested in our data set - the most comprehensive one ever," Seitz remarks.
Sánchez, Laura; Völksen, Christof; Sokolov, Alexandr; Arenz, Herbert; Seitz, Florian (2018): Present-day surface deformation of the Alpine Region inferred from geodetic techniques
The study has been published in the journal Earth System Science Data. The academic journal specializes on the publication of data sets.
Link: doi.org/10.5194/essd-2018-19 (preprint version)
The research was conducted in collaboration with the Geodesy and Glaciology ("Erdmessung und Glaziologie") project of the Bavarian Academy of Sciences and Humanities (Bayerische Akademie der Wissenschaften).
All the data calculated in the course of the study are available at https://doi.pangaea.de/10.1594/PANGAEA.886889
Prof. Dr.-Ing. Florian Seitz
Technical University of Munich
German Geodetic Research Institute (DGFI-TUM)