Research on the Mechanism of Induced Seismicity Utilizing InSAR-Retrieved Land Subsidence, Source Model, and Geological Constraints

Abstract

Mining-induced sub-surface rock-failure processes cause seismicity and permanent surface deformation that may result in infrastructural damages and endanger residents in the affected areas. In recent years, this issue has received increasing attention due to the suddenness of the occurrence, the lack of effective predictive capabilities and the adverse consequences.  Importantly, seismic events have caused significant land subsidence and several fatalities in Polish underground mines. To better investigate such mining-induced sub-surface rock failure processes, we analyze rock deformation based on surface displacement data and also put local geology in context with seismological analysis results.In Poland's Legnica-Glogow Copper District, between 2016 and 2020, 13 mining-induced earthquakes in the moment magnitude range from 3.2 to 3.8 have been recorded by the IS-EPOS platform. Based on co-seismic Sentinel-1 satellite radar images of ESA’s Copernicus program, and radar interferometry (InSAR) we measure the surface displacements caused by nine of these earthquakes. The maximum line-of-sight surface displacements are observed for the Mw3.6 mining-induced earthquake on October 17, 2016 with 144 mm and 124 mm away from the satellite in ascending and descending radar interferograms, respectively, and an estimated maximum land subsidence reaching -142 mm. We estimate the location and volume component associated with these surface effects by using an isotropic volume point-source model in a Bayesian inference. The Geodetic Bayesian Inversion Software GBIS has been applied for these calculations. Notably, only some of the earthquakes we analyse resulted in land subsidence. Although no significant relationship between earthquake magnitude and land subsidence is apparent, we find that the greater the thickness of loose Quaternary strata, the greater the land subsidence. The focal points of the deformation at depth of the investigated earthquakes, which we compare to seismic hypocenters, are located at depths of 437 m to 669 m, according to our results. Importantly, these focal points are located above the mining exploitation fields, within layers of rigid Triassic rock. Our results also show a mismatch between the spatial location of the earthquake epicentres and the maximum land subsidence. These differences are up to 440 m and are greater for the earthquake epicentres determined using seismic data than for the source point model. This discrepancy suggests that the epicentre of a mining-induced earthquake is not necessarily associated with the region of maximum rock layer compaction.This study adds to our understanding of the impact of mining-induced seismicity on the occurrence of land subsidence and the seismic mechanism in areas of active mining paving the way towards more sustainable mineral extraction.