(a) Top view of Model 7 after 210 s. Red arrows indicate the superficial velocity field in the glucose syrup. (b) Vertical strain at the surface of the glucose syrup between 110 and 210 s. The vertical strain was calculated from the horizontal surface strains, assuming that glucose syrup is an incompressible material. Negative values correspond to thinning. The principal axes of the strain-tensor are reported (extension in green, shortening in red). Superficial thinning is larger in a SW-NE oriented domain. SE of this sector, trench-parallel shortening compensates the trench-perpendicular extension, reducing superficial thinning. (c) Superficial rotations between 110 and 210s.