All-Pass Receiver Function Imaging Of Seismic Discontinuities In The Crust And The Uppermost Mantle At The Japan Subduction Zone

We show our recent advancement in receiver function (RF) analyses on the detailed structures of seismic discontinuities in the crust and the uppermost mantle beneath the Japan Islands, based on a large number of teleseismic waveforms which have been obtained mainly at short-period (Hi-net and J-array) seismic stations densely installed over the Japan Islands, whose number is reaching 1,000. In addition to the usual RF analyses, we apply all-pass RF analysis which has been proposed by Satoh (2005) for enhancement of P-to-S phases converted at the sediment/basement boundary in strong motion records. In our method modified from the original Satoh_fs approach, the usual RF with water level in the spectral domain is decomposed to minimum-phase-shift and all-pass functions, and a Gaussian low-pass filtering is applied to the all-pass part, then back to the time domain, which we call all-pass RF. All-pass RF has a linear phase, which reserves purely the Ps-P time, implying all-pass RF has a clear peak at Ps-P time. In comparison with the usual RF, Ps phases at the Moho are generally enhanced in all-pass RF. We have executed depth-migration of RFs assuming 1-D IASPEI or 3-D velocity models obtained by travel time tomography (Nakamura et al., 2000), and have obtained CDP stacked RF images along several profiles. We have applied SVD (singular value decomposition) filtering (Chevrot and Giardin, 2000) to RFs or depth-migrated RFs. In this study, we applied 1 Hz low-pass filtering. Then, we obtain the depth distribution of the Moho over the Japan Islands by careful examination of the constructed RF profiles and also by the method of Zhu and Kanamori (2000). In contrast to the Moho Ps phases, enhancement of later phases such as plate-related, 410 and 660 km discontinuities dose not seem to be effective in all-pass RF. Accordingly, we show both profiles to see the deeper discontinuities.