3445 Identification of structures capable of hosting the M5.5 Orkney (South Africa) earthquake and factors controlling the physics and mechanics of dynamic rupture
Resumo
On 5 August 2014, the largest mining related M5.5 earthquake with 'unusual' strike-slip mechanism occurred in the Klerksdorp goldfields, hundreds of metres below Moab Khotsong mine. In a rare case, the M5.5 earthquake occurred within the area covered by the legacy 2D reflection seismic data acquired in 1992 for gold exploration. In addition, the earthquake was recorded by the underground in-mine seismic network near the source region. The integration of the legacy reflection seismic data and mine seismicity data allowed us to make clear a near-vertical structure, striking NNW-SSE. The DSeis team used the mine seismicity data to locate the M5.5 rupture plane, and drilled into this active seismogenic zone situated 3.5 km below the surface. Using the recovered fault gouge material, we conducted friction experiments at slip velocity of ~100 mm/s and normal stress of 2 MPa. Here, we suggest that there are three active processes influencing the M5.5 earthquake seismogenic zone: first, the complex structural architecture of the seismogenic zone (e.g., intersection of fault, lamprophyre dykes and dolerite sills); second, the mechanical process induced by tectonic and/or mining related stresses; and third, the mechanical and chemical processes caused by the water and rock interaction.
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