Receiver function imaging of high-resolution seismic discontinuity structure in the crust and the mantle beneath the Japan Islands

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We migrate the receiver functions(RFs) observed at high-density short and broad-band seismic stations (J-array, Hi-net and F-net) to investigate the seismic velocity discontinuity structure in the crust and the upper mantle beneath the Japan Islands.For the crust and the uppermost mantle structure, we use short-period RFs. In the Chugoku and Kinki region in southwest Japan where the stations are closely installed, we can recognize positive RF amplitudes corresponding to P-S converted phases at the velocity discontinuity between the upper and lower crust and the Moho discontinuity. The positive RF amplitudes corresponding to the oceanic Moho above the subducting Philippine Sea(PHS) plate are clearly traced down to a depth of 100 km. Comparison of the RFs with deep seismicity shows that the earthquakes in the oceanic crust and in the slab occur down to a depth of 40-60km and the PHS has the deeper aseismic portion.In the northeast Japan, we can successfully catch the slab layering struct … More ure. Namely, we can clearly image the top of the subducting Pacific slab, the oceanic Moho and surprisingly the bottom of the slab. And the RFs suggest the existence of seismic discontinuity structure corresponding to the lower seismic zone in the double seismic zone. These new findings impose strong constraints on the thermal structure and the material composition in and around the subducting slab.For the deep discontinuity structure in the upper mantle, we use the data from broadband seismic stations. The 410 km discontinuity seems to be fiat except for the inside of the slab, where the 410 is elevated locally by 30 km. The 660 is gradually inclined toward the west, which depression is caused by the cold stagnant slab. In addition, examination of frequency dependence of RF amplitudes corresponding to 410 and 660 km shows that RFs in the Japan Islands has different frequency appearance comparing to those in the Korea, suggesting that there exists different amount of water in the upper mantle beneath the Japan Islands and the Korea. Less