Space geodetic observation of deep basal subduction erosion in northeastern Japan

Observation of tectonic erosion [Von Huene and Scholl, Rev. Geophys. 29 (1991) 279–316] in a subduction zone has been difficult as it leaves little geological and geophysical evidence. Three-dimensional velocity profiles of crustal movement obtained by Global Positioning System across NE and SW Japan agree well with those predicted by the elastic loading of the subducting slabs. However, vertical velocities in the NE Japan forearc show significant negative deviation (relative subsidence). This may indicate loss of material at the plate interface that can be attributed to the erosion of the upper plate by the underthrusting slab (basal subduction erosion). The estimated rate (15 mm/yr down to a slab depth of 90 km) is somewhat faster than the geological average; the erosion speed may be variable being controlled by the surface roughness of subducting slabs.