EPISODES platform documentsSeismic and aseismic deformations in deep mines–Case of the Garpenberg mine, SwedenEmelineLhoumaudauthorMicroseismic repeaters (Mw < 1 on moment magnitude scale) have been monitored in deep levels of the Garpenberg mine, Sweden. Repeaters are well-known in seismology and have been studied for decades in the case of earthquakes on plate boundaries. They are commonly associated with the presence of creep on fault planes that repetitively load the same seismic asperities. However, repeaters are unexpected in a mining context, as the state of stresses varies as the excavation progresses. In this thesis, we investigate the origin of these seismic repeaters. More specifically, we focus on the structures hosting these repeaters as well as the mechanisms that led to their loading. To do so, we combined different scales and fields of study. First, a study at a large scale showed statistical relationships between some lithologies in the mine and seismic repeaters. To study in more detail what host repeaters in these lithologies and how they are loaded, a local network has been installed in a sill pillar at 1km depth, which included geophones, boreholes, and strain cells. This installation targets one specific repeater family in the area. Borehole analyses show the presence of phyllosilicate-filled fractures oriented like the nodal plane, similar to what is commonly observed in the presence of a creeping fault plane. However, we found no evidence in the cores that could allow us to identify a specific zone or fracture as the asperity hosting seismic repeaters. This shows the difficulty of clearly identifying the nature of the seismic source for such small-scale events, even with a local installation in close vicinity of the source location. Strain data analyses showed different types of post-blast responses, with sometimes a creep phase before seismic activity, as well as a change of strain orientations, sometimes transitory, between different phases of deformation. Two different mechanisms are proposed and discussed: a seismicity triggered by creep on a fault plane or a seismicity triggered by a progressive localization along discontinuities. Further data acquisition will allow to study further the hosting structures and mechanisms. In particular, an ANR research project FIMOPTIC will aim to improve seismic location and will perform strain measurements using high sensitive optical strain-meters devices.SwedenUnderground mining2023University of Lorraine;University of LorraineThesis

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