Fig. 4

Diagram of weight of alpha (WOA). The closer WOA is to 100%, the more friction can be considered in terms of seafloor topography alone, because the effective basal friction μ_b’ can be determined from α alone. A WOA diagram of the mean trenches (Lallemand et al. 1994). The white circles indicate the average value of these 21 subduction zones. The white boxes indicate the individual subduction zones, where the values were listed (Wang and Hu 2006). Conditions in the Japan Trench according to Kimura et al. (2012) and Wang et al. (2019) are shown by the two white squares