(a) Number of estimates for each SH phase. The statistics is based on ∼140 000 estimates of correlation time delays with c.c. ≥ 0.8. (b) Time–distance distribution of the SH phases. Each signal is represented by a coloured dot based on the event depth. (c) Theoretical time–distance curves for the phases as shown in (b). Solid lines for a surface source and dashed lines for a 300 km deep source.