How deep can we see the high velocity anomalies beneath the Japan Islands?

High velocity anomalies are found in the lower mantle beneath the Japan Islands and their vicinity through an analysis of detailed three‐dimensional P‐wave velocity structure based on a tomographic inversion of ISC data. Beneath the Sea of Japan, the high velocity anomalies in the lower mantle are slab‐like and appear to extend below the deep focus earthquakes of the high velocity Pacific slab descending from the Japan trench. This slab‐like high velocity body extending into the lower mantle steepens below a depth of 500‐600 km. Resolution analyses confirms the existence of a slab‐like high velocity region in the lower mantle, though the depth extent is not well resolved. On the other hand, the Pacific slab descending from the Izu‐Bonin trench seems to be fingering, that is, high velocity anomalies are penetrating into the lower mantle beneath latitude 26°N, and not penetrating but horizontally bending in the deeper portion of the upper mantle around 29°N.