Collision velocities between two planetesimals as a function of their sizes d₁ and d₂ in a disk with the fiducial set of parameters given in Sect. 5 and σ_i = 10⁻⁴. Each panel corresponds to a different location in the disk, which leads to the varying values of v_c and d_c labeled on the panels. Regions of erosive collisions are outlined in dotted white lines, and regions of catastrophic disruption are enclosed by solid white lines. The horizontal and vertical yellow lines correspond to the initial planetesimal size d_init = 4.3 km used in the simulation described in Sect. 5.1. The point (d_c, d_c) is shown as a red dot.