Shear‐wave polarization anisotropy beneath the north‐eastern part of Honshu, Japan

We have investigated the shear‐wave polarization anisotropy in the north‐eastern Japan arc by using waveforms from many local earthquakes at various depths. We used a cross‐correlation method to detect the shear‐wave splitting. For intermediate‐depth and deep events, the observed fast shear‐wave oscillation directions (FSODs) are oriented parallel to the dip direction of the slab at the western stations, while they are oriented perpendicular to the dip direction at the eastern stations. These observations indicate that significant anisotropy exists in the mantle wedge, and that its nature is quite different between the eastern and the western parts.