Stress State in the Source Region of Mw2.2 Earthquake in a Deep Gold Mine in South Africa Determined from Borehole Cores

Abstract In December 2007, an Mw2.2 earthquake occurred in a gabbroic dike at 3.3 km depth deep gold mine South Africa. The fore- and aftershock activity was analyzed effort to understand the preparation generation processes of earthquakes; these findings have already been published. present paper focuses on stress state source region mainshock. A 90-m-long borehole across mainshock fault drilled ~ 1.5 years after logged by optical televiewer. can be identified severe damage wall point where intersected cluster. Except for 10-m section hanging fault, cores were fully recovered. Borehole breakout (BO) core disking (CD) found occur. Two measurement techniques [Deformation Rate Analysis (DRA) Diametrical Core Deformation (DCDA)] applied cores. By combining their results with occurrence criteria BO CD, principal determined. directions nearly identical virgin state, while it significantly disturbed footwall. vertical stresses 106 MPa 40 footwall, respectively. significant difference between two sides explained redistribution associated nonuniform slip nonplanar fault.