Fig. 4: Velocity, stress and AE event rate evolution as a function of time, with selected incremental strain field cross-plots.

a Velocity evolution, defined from active seismic surveys, using the top sensor as a receiver with the bottom sensor as the seismic source (blue line) vs. the bottom sensor as a receiver with the top sensor as the seismic source (red line). b Differential stress throughout loading (blue line) along with AE event rate (green line). Orange circles denote the times of the X-ray tomographic volumes. c–g Normalised cross-plots of the local incremental deviatoric (shear) strain, \({\triangle \epsilon }_{{{{{{\rm{dev}}}}}}}\), vs. incremental volumetric strain, \({\triangle \epsilon }_{{{{{{\rm{vol}}}}}}}\), showing the initial transition from c compaction-dominated strain to d dilation-dominated strain, e the correlation between dilation and shear strain through localisation and shear zone development, f the relaxation of dilation once the shear band was fully developed and finally g shear-enhanced compaction during coherent sliding. Dilation is defined as positive volumetric strain and number labels refer to the position of the strain increment in the time-series (as in Fig. 1a). The full time-series of cross-plots is shown in Supplementary Fig. 16.