On the variety of post-deformation phenomena in abandoned mining districts : Insights from seismic source analysis

Abstract : Post-deformation in abandoned mining districts can be accompanied by significant surface subsidence and collapses, as well as ground shaking that bear serious risks for proximate urban areas. The origin of these phenomena can be related to a wide range of complexly interacting factors, often linked to the flooding evolution of the mine after groundwater pumping is stopped. Here, we present different case studies of seismic monitoring highlighting the variety of these post-mining deformations and the challenge of appropriate risk assessment in this context. For more than 20 years, INERIS has been performing near-real time seismic monitoring to survey hazardous deformation in post-mining districts, with a main focus on the Lorraine region, in NE France, where hundreds of buildings have been damaged after several mine shutdowns in the 90s. As a complement to operational data analysis, several monitoring experiments have been performed (including controlled mine flooding and solution mining) to simulate and understand the cause and nature of these collapsing events. In the results, we found that the reactivation of pre-existing fault structures plays a fundamental role in the readjustment of stress due to external stimulations (i.e. flooding, seismic waves, partial collapses). Also aseismic processes as stress memory effects and slow surface subsidence are involved which underlines the necessity of multi-disciplinary monitoring approach in this context. During monitoring in the Provence region at Gardanne (in SE France), we experience the high degree of complexity in which an abandoned, flooded mine can interact with its local tectonic setting. In this case, excessive and long term excavation has led to the formation of very efficient “anthropogenic“ aquifer which, especially in wet periods, enable water migration into deeper levels below the mine workings. The modification of the hydrogeological system seems to be the today’s cause of significant seismic swarming activity, including local magnitudes close to 2 that have been several times felt by the nearby living population. Further analysis shows that swarming activity is related to the reactivation of minor fault segments being favourably oriented with respect to the local tectonic stress field. However, it remains still unknown if the meteorologically controlled variations of the mine water level, might potentially trigger larger local tectonic events, as recorded in the past (Mw 4.3, 1984), or if swarming represents simply episodes of small transient creep.
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Submitted on : Friday, August 3, 2018 - 1:17:53 PM
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  • HAL Id : ineris-01853436, version 1

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Jannes Kinscher, Isabelle Contrucci, Pascal Dominique, Emmanuelle Klein, Pascal Bigarre. On the variety of post-deformation phenomena in abandoned mining districts : Insights from seismic source analysis. 2. Schatzalp Workshop on Induced Seismicity, Mar 2017, Davos, Switzerland. ⟨ineris-01853436⟩

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