Detailed structure of the upper mantle discontinuities around the Japan subduction zone imaged by receiver function analyses

High-resolution receiver function (RF) images of the upper mantle structure beneath the Japan Islands are obtained by RF analysis of the P-wave coda portions of 389 teleseismic events observed at 138 high-density broadband stations. We construct RFs through frequency-domain division using a water level of 0.01 and Gaussian low-pass filters of 1.0, 0.5, 0.3, and 0.1 Hz, and produce depth-migrated RFs using the one-dimensional IASP91 velocity model. The RF images clearly resolve the subducting Pacific Plate to a depth of 200 km, and reveal a local 30 km elevation of the 410 km discontinuity within the subducting plate. The 660 km discontinuity is also found to exhibit a broad 50 km depression under the influence of the stagnating slab. From analysis of the frequency dependence of the RFs, the thickness of the 410 km discontinuity is inferred to vary on a relatively local scale, whereas the 660 km transition is sharp throughout the Japan Islands.