Imaging changes in morphology, geometry, and physical properties of the subducting Pacific plate along the Izu–Bonin–Mariana arc

Abstract

Recent studies on slab structure in the northwest Pacific have imaged variable geometries of the subducted oceanic lithosphere along the plate margin. Tomographic images show portions of the subducted Pacific plate penetrate vertically into the lower mantle below the Mariana arc, whereas below the Izu–Bonin arc, the slab appears to be lain down horizontally on top of the 670-km discontinuity. Using new technology to grid and visualize regional seismic tomography data even more detail about the structure of the subducting plates can be extracted from the three-dimensional images. We investigate the morphology and geometry of the subducting Pacific plate as it changes between horizontal to nearly vertical using P-wave tomographic images. The most profound result from these new models is the presence of a distinct change of seismic property in the downgoing Pacific slab beneath the Izu–Bonin arc at a depth of 350–400 km. The position of this anomaly corresponds to a region north and west of the Ogasawara Plateau. We propose the change in morphology and physical property of the slab is related to the distortion of the Pacific plate geometry as its shape converts from near horizontal to vertical, together with the subduction of the Ogasawara Plateau.