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Theses

Origin of seismicity related to a flooded abandoned coal mining district at Gardanne, Provence, France

Abstract : The closure of mines and post-mining management nowadays present a major challenge as the problems that arise can greatly concern public security. When mines are abandoned, groundwater pumping systems are usually stopped and the water which progressively fills the remaining voids can affect the mechanical stability of underground structures. In general, mechanisms of observed seismicity in flooded, post-mining districts have been poorly understood. As a case study, this thesis focused on the abandoned, flooded coal mine in Gardanne, France, which has been experiencing significant post-mining seismicity problems. Seismic activity in Gardanne mine seems to originate from an interaction between rocks and fluids, as spatio-temporal distribution of events suggests the link with intense rainfall events as well as the active pumping. The knowledge on the origin and the triggering mechanisms of the seismic activity in Gréasque and Regagnas sector is the key for seismic hazard assessment of the entire Gardanne basin. Thesis work focused on questions concerning precise identification of seismic source origin evaluating two hypothesis, determination of the mechanism behind the seismicity, link between seismicity and the hydrogeological system, as well as improving of the detection and location of microseismicity with a sparse network. The new developed detection and location methodology adapts the full waveform-based method BTBB by Poiata by overcoming the challenges of the sparse seismic monitoring network, and includes a novel approach for noise removal from continuous dataset as well as location quality-based classification system. The seismicity clustering behaviour was indicated by the new seismic catalogue 2014-2017, which was further analysed more thoroughly. All results are in favour of the origin of the seismic sources on the fault below the mine. Spatial and temporal characteristics of observed seismic events and multiplet and repeater occurrences provided a clearer image of the active geological structures and allowed a preliminary interpretation of possible mechanisms affecting the initiation and driving of the repeating or after-shock like behavior of seismic events, based on comparison with available hydrological data. Despite the general understanding of the mechanism behind the seismicity, the maximum magnitude of the events that can be triggered is at this moment is difficult to quantify and predict due to limitations of available data. As a prospective, in order to better understand the seismic hazard, more accurate observations of the seismicity, mechanical parameters and water level changes in the seismically active zone are required to improve the understanding and the interconnection between these factors.
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Submitted on : Wednesday, October 6, 2021 - 2:48:04 PM
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  • HAL Id : tel-03367922, version 1

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Dalija Namjesnik. Origin of seismicity related to a flooded abandoned coal mining district at Gardanne, Provence, France. Earth Sciences. Université de Lorraine, 2021. English. ⟨NNT : 2021LORR0116⟩. ⟨tel-03367922⟩

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