Evolution of the shock structure in the 2D recoiling black hole simulations at times 0, 10 000, 15 000 and 20 000 M, with three AMR levels and tolerance ε_t = 0.1 (left column) and a high resolution uniform grid (1024 × 512, right column). The colour indicates the difference between the relative velocity of the sides of the Riemann problem and the threshold velocity for producing a shock. For the AMR simulation, the blocks at levels higher than 1 are shown.