Subducted Slab Slipping Underneath the Northern Edge of the Pacific Large Low-Shear-Velocity Province in D″

Abstract

We conduct waveform inversion for the 3-D seismic shear wave (S-wave) velocity structure in the lowermost mantle near the northern edge of the Pacific large low-shear-velocity province (LLSVP). We image a slab-like high-velocity anomaly slipping beneath the Pacific LLSVP in the lowermost 200 km of the mantle, extending toward an ultra-low velocity zone (ULVZ) beneath a point about 2,000 km southwest of Hawaii. Another strong low-velocity anomaly exists along the edge of the LLSVP just above the slab-like sheet, 50–200 km above the core-mantle boundary (CMB). These results suggest in general that (a) slabs can gather ULVZ materials scattered on the CMB and push them into LLSVPs, creating concentrated ULVZs near LLSVP edges, (b) slabs can uplift hot material from the CMB to create strong anomalies along the edges of LLSVPs, and (c) large seismic-wave velocity contrasts between strong low-velocity anomalies and slabs create sharp LLSVP boundaries.