On April 13, 2022, a meeting of the partners of the project "Induced earthquakes and rock mass movements in coal post-mining areas: mechanisms, hazards and risk assessment" with the acronym "PostMinQuake" took place. The aim of the project is to assess the safety hazards for the use of the surface of the closed coal mines in Europe, accompanying the processes of their flooding, such as shocks and deformations of the surface. In the course of exploitation, the mines transformed the structure of the subsurface geological layers and led to their drying out due to the necessity to drain the rock mass to the depth of the mining works. These are the depths reaching over 1000 m. This process changed the natural stress distribution in the rock mass and the geostatic equilibrium in the geological environment formed in the process of the evolution of the Earth's crust. The re-watering of the rock mass leads to the restoration of the mechanical equilibrium in it, similar to the one existing before the commencement of mining activities. The project covers areas of 5 closed coal mines located in France (Gardanne), Germany (Hamm and Ibbenburen), the Czech Republic (Petrvald) and Poland (Kazimierz-Juliusz). In each of these mines, equipment is installed to monitor groundwater movements and dynamic events in the rock mass, recorded in the form of short-term vibrations of the rock mass (tremors). The observation of surface movements by traditional and satellite geodetic methods is also carried out. The studies conducted so far indicate that the tremors of the rock mass have similar kinematic characteristics as those generated by underground mining. However, the energy of these events is generally lower and indicates that the cause of movements in the rock mass is the gravitational displacement of rock fragments. This does not exclude the possibility of tremors of higher energy generated by activation of rock mass movements in tectonic zones. In the Kazimierz-Juliusz mine, during the 2-year period of seismological observations, approximately 20 rock tremors were recorded. Their energy, expressed in terms of the local magnitude, varies in the range from 0.8 to 2.2. At that time, the depth of the groundwater level in the Carboniferous rock mass decreased by approx. 30 m. Until now, these waters filled only the deepest regions of the coal mining operations. The project will end in 2023 and is financed by the EU Coal and Steel Research Fund and co-financed by the Ministry of Education and Science.
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