Coherences of the H1, H2 and P with the Z for each BBOBS compared with the water depth of the instrument. The red line indicates the predicted infragravity cut-off frequency (f) as a function of water depth (d), using the equation |$f = \sqrt {\frac{g}{{2\pi d}}} \,\,$| (Bell et al. 2015); the green, dark blue and light blue lines indicate the tilt cut-off (0.1 Hz), primary (0.07 Hz) and secondary (0.14 Hz) microseism peaks respectively. (a–c) Coherences calculated with the Z component; (d–e) H1-Z and H2-Z coherences with the Z-compliance-corrected component; (f) P-Z coherence with the Z-tilt-corrected component.