Post-mining earthquakes and changes in observed vertical ground displacements during the period of mine flooding

The period of coal mine closures can be accompanied by many hazards, including the post-mining seismic hazard. Seismic phenomena, particularly during mine flooding, are felt by people, can cause minor or severe damage to buildings and affect shallow mine workings, and can cause reactivation of shallow mine workings in the form of sinkholes or other discontinuous deformations. It is therefore important to deepen the knowledge concerning these phenomena, particularly their relationship to surface deformations. This issue was the subject of a European research project with the acronym PostMinQuake financed by the Research Fund for Coal and Steel in 2020- 2023 (Grant Agreement No: 899192). The project involved the study of surface deformation in relation to registered post-mining earthquakes during the flooding of the Kazimierz- Juliusz coal mine. The research area was located in Poland in the area of the Upper Silesian Coal Basin. In this area, continuous monitoring of surface deformation was carried out for more than 2 years on single observation points using GNSS technology. The monitoring was carried out using an automatic GNSS monitoring system developed in the project. 

The paper presents the results of an analysis of the course of changes in vertical displacements at the above-mentioned points, in relation to the post-mining earthquakes registered during the study period. The analysis showed that in the case of more than 58% of the analyzed phenomena in the course of vertical displacements in the period associated with the occurrence of the post-mining earthquake, there were some regularities in the course of these displacements. It was found that, an increased uplift was observed prior to the occurrence of the event, in the next period of time, after the occurrence of the event, an increased increment in subsidence was generally observed, after that period, stabilization of the changes in vertical displacements was observed, as well as a slow increment of subsidence and/or the increment of uplifts. On this basis, it was concluded that there was a relationship between the observed course of displacements and the occurrence of post-mining earthquake. It was assumed that the significant increase in observed uplift can be a predictor of the occurrence of a post-mining earthquake.