[S02-P] Poster

[S02-P-09] Estimate of the stress state in a close proximity to an earthquake source in a South African deep gold mine

^○Shuhei Abe¹, Yasuo Yabe¹, Takatoshi Ito², Masao Nakatani³, Gerhard Hofmann⁴, Hiroshi Ogasawara⁵ (1.Graduate School of Science, Tohoku University, Sendai, Japan, 2.Institute of Fluid Science, Tohoku University, Sendai, Japan, 3.Earthquake Research Institute, the University of Tokyo, Tokyo, Japan, 4.ANGLO GOLD ASHANTI, Johannesburg, South Africa, 5.Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Japan)

An earthquake of Mw2.2 (mainshock, hereafter) occurred at 3.3km depth in Mponeng mine, a deep gold mine in South Africa. A rupture plane of the mainshock diagonally cut a 30-m-thick gabbroic dyke. Yabe et al. (2013) drilled a borehole passing a source fault of the mainshock ~1.5 years afterward. They constrained possible ranges of stress magnitudes and the principal directions based on criteria of borehole breakout (BB) and core discing (CD) and a slip direction of the mainshock. In this study, we estimate the stress state in a close proximity to the source fault more tightly than Yabe et al. (2013) by using DCDA and DRA, in addition to information taken into account in Yabe et al. (2013). Considering that the mainshock occurred in the dyke, we divided the study are into three; host rock (quartzite), footwall dyke and hanging-wall dyke. The principal directions of stress in the host rock and the hanging-wall dyke were normal faulting one, being consistent with the CMT solution of the mainshock. But, the principal direction in the footwall dyke, where no borehole breakout or core discing was observed is reverse faulting one. To improve the estimation in the footwall dyke, we will measure stress magnitudes by DRA and compare with 3D model simulation.