Persistent Mining-Induced Subsidence Two Decades After Underground Coal Exploitation: Evidence from Multi-Temporal GNSS Monitoring

Mining-induced subsidence represents one of the most significant long-term geomechanical hazards associated with underground coal exploitation, often continuing for decades after mining activities have ceased. Understanding the persistence and spatial distribution of post-mining ground deformation is essential for evaluating residual geological hazards and improving long-term monitoring strategies in former mining regions. This study investigates the long-term evolution of mining-induced subsidence in the Maleia sector of the Jiu Valley Coal Basin (Romania), an area historically affected by intensive underground coal extraction. A geodetic monitoring network consisting of seventeen permanent benchmarks, initially established in 2006, was reoccupied and remeasured using Global Navigation Satellite System (GNSS) technology in 2026. The comparative analysis was performed against historical measurements acquired during the 2007 monitoring campaign, providing a nineteen-year temporal framework for deformation assessment. Analysis of vertical displacements revealed persistent subsidence at all monitored benchmarks, confirming the continued post-mining adjustment of the geological structure. Measured cumulative vertical displacements ranged from −0.082 m to −3.853 m, with the highest deformation recorded at benchmark R14. The calculated average annual subsidence rates reached values of up to −0.203 m/year and are reported as normalized indicators of cumulative deformation over the nineteen-year observation interval. The results demonstrate that mining-induced geomechanical instability may persist for decades after underground mining has ceased, emphasizing the necessity of long-term monitoring strategies in former coal mining regions affected by residual geological hazards. This study provides one of the few long-term GNSS field datasets documenting delayed mining-induced subsidence over a nineteen-year observation period in an underground coal basin, contributing rare field evidence of persistent post-mining geomechanical evolution in Eastern Europe.