How well can we resolve the deep seismic slab with seismic tomography?

The three‐dimensional P and S velocity tomographic images around the Wadati‐Benioff zone under the island arcs of the northwest Pacific are analyzed. Estimations of resolution and error show that the fast seismic anomalies associated with the subduction zones are generally real and resolvable. The anomalies are slab‐like in most parts of the upper mantle, and become folded and broadened with depth. Near the bottom of the upper mantle, fingering of the slabs, including segmenting and shallow angle spreading, is indicated. The fingering under Japan and the Izu‐Bonin trench has a tendency to flatten to sub‐horizontal, while possible downward spreading is seen under parts of the Kuril trench.