Deformation of corundum. (a) Reflected light micrograph of sample cross-section. The internal part of the sample is crushed, indicated by its light grey appearance. Brittle fractures (dashed lines) occur near the top of the sample and along its vertical axis. (b) 3D-view of the sample between four tungsten anvils, with hypocentres for events >60 dB during axial compression to 4 GPa. Hypocentre annotation: closed-large = inside the sample, closed-small = within 1σ from the sample, open-small = outside 1σ from the sample. (c–d) 2-D projection of the hypocentres on the sample cross-section in (a), for compression to (c) 0.5 GPa and (d) from 0.5 to 4.0 GPa. In both compression stages, hypocentre clusters dominantly locate near the central and top fractures and the light-coloured damage zone in (a). Parameters used in the location algorithm: V_p= 6.1 mm μs⁻¹, σ_t= 0.6 μs. The location error ellipsoid in [σ_x σ_y σ_z]=[0.79 0.78 1.81]. We note that >95 per cent of the events fall within 2σ from the sample.