Overview of bifurcation scenario 2 (event 2). The layout is similar as in Figs. 2a–c. Panel a: context image. The curved blue boxes mark the locations of the artificial slits (slit 1 and slit 2). Panels b and c: original and background-subtracted space-time maps for slit 1. Panels d and e: the same but, for slit 2. The dashed green lines indicate the slopes of the ridges we used to estimate the speed. See Sect. 3.3 for details. An animated version of this figure is available online.