The only real drawback is that the ambient noise model provides shear wave velocities, while the teleseismic arrival time residuals come from global P-phases. The main reason for not using global S-phases is that the majority of WOMBAT stations are short period (1 Hz corner frequency), which makes teleseismic S-arrivals difficult to detect in comparison to P. In order to convert from S-wave velocity to P-wave velocity, we use the AuSREM crustal Vp/Vs model, which is largely constrained by receiver functions (Salmon et al., 2013)