Post-mining displacement monitoring with InSAR in the eastern Ruhrarea and Ibbenbüren

In the frame of the project "FloodRisk: Earthquakes, uplift, and long-term liabilities – risks minimisation during mine flooding" funded by the Federal Ministry of Education and Research (BMBF), a consortium of partners from applied research and industry worked on an integrated view on the post-mining process of German hard coal mines in the eastern Ruhrarea, Ibbenbüren and Saarland. Aspects of geodesy, geophysics, soil gas technology and geology in the context of mine flooding were investigated by experts in these fields. The Geodetic Institute Karlsruhe contributed to FloodRisk by monitoring ground displacements with help of InSAR and GNSS.

The focus of our presentation will be a clustering approach that allowed to obtain an understanding of the variable spatio-temporal displacement field during mine flooding measured with help of InSAR. For mine Heinrich-Robert in the eastern Ruhrarea and for mine Ibbenbüren, both in the German state North-Rhine Westfalia, Sentinel-1-data for the observation period January 2018 to December 2022 from an ascending and a descending orbit were combined in order to obtain vertical and East-West displacements. Because of the large number of measurement points, time series with almost 300 values and variable spatio-temporal displacements, the analysis of the displacement patterns is challenging. A broken stick model (piecewise linear and continuous) with six break points proved to be able to approximate the time series quite well. Clustering feature vectors based on parameters of the broken stick model (location, break point, change of displacement rate, displacement rate after the break point) for points with considerable change of displacement rate allowed to describe the main changes of the displacement fields. In case of mine Ibbenbüren, the transition from massive subsidence during the last months of active mining to uplift caused by the rising mine water is characterized by phases that are clearly separated by certain break times that do not vary spatially. For mine Heinrich-Robert, the evolution of the displacement pattern is more complicated and the break times vary spatially.