Abstract: The spatial distribution of epicenters indicates that the mantle of the West Pacific remains in the state of flowing fluid, except for the Japan trench, where the Pacific Plate keeps subducting as a plate, owing to the existence of a soft mantle lithosphere in the region. With the same consideration, it is inferred that the Izanagi plate in the Paleo-Pacific might act in a similar manner and never subducted under the Eurasia. Therefore, the dynamic mechanism of the drastic change of lithosphere in the Eastern Part of China must be reconsidered.