We examine the internal dynamics and caustic structure of the rich cluster A1689, combining VLT/VIMOS spectroscopy with Subaru/Suprime-Cam imaging. The radial velocity distribution of ∼ 500 cluster members is bounded by a pair of clearly defined velocity caustics, with a maximum amplitude of ∼ |4000| km/s at ≃ 300 h kpc, beyond which the amplitude steadily declines, meeting at zero velocity at ...
