Fig. 6

Relationship between the vertical movement of the forearc wedge and the plate boundary. a Schematic cross section showing the geometry of the plate boundary and the uplift and subsidence zones along the Outer zone of southwest Japan. Top solid line indicates a topographic profile of the forearc wedge and the bottom solid line show geometry of the plate boundary. Ridges and troughs of the plate boundary are supposed to move to the southwest as shown by horizontal arrows due to oblique subduction of the PSP slab, then the depth of the plate boundary changes. The areas of increase and decrease of the plate boundary depth approximately correspond to the subsidence and uplift zones of the forearc wedge, respectively. b Map showing the relationship between the depth contours of the plate boundary and crustal movement of the forearc, and the location of inferred stack zone on the plate boundary. Areas of plate boundary depth decrease are inferred to correspond to the areas where the plate depth contours strike NE–SW, and the those of plate boundary depth increase are inferred to correspond the areas of depth contours strike E–W to NW–SE. The mountains in the Outer zone (dashed outlines) approximately coincide with the area of plate boundary depth decrease. Plate boundary is inferred to be locked where the depth of the plate boundary decreases. The uplift zone of the Shikoku Mountains is not clearly explained by this model. The non-volcanic tremor locations are from the JMA catalog from 2014 to 2018