“…The Pacific slab, that subducted after Izanagi–Pacific ridge, is visible on mantle tomography, as a 2,500 km long, west‐dipping flat slab below Japan, located in the upper mantle, and is disconnected from deeper anomalies in the lower mantle (Seton et al., 2015; van der Meer et al., 2018). However, the plate kinematics of Izanagi–Pacific ridge subduction, exact timing, and orientation of the plate boundaries are under debate with several options including: (1) strongly oblique to the Japanese coast (e.g., Maruyama et al., 1997), (2) almost parallel to it (e.g., Liu et al., 2020; Seton et al., 2015; Whittaker et al., 2007; Wu & Wu, 2019), and (3) a marginal sea closure which would not include ridge subduction below Japan (Domeier et al., 2017). Ridge subduction would have caused a slab detachment that possibly triggered a plate‐driven force change and a change into the mantle flow in the area of East Asia.…”