3:00 PM - 4:00 PM
[S21-P-11] Spatial distribution of the Crust-Mantle boundary in colliding and subducting Izu-Bonin-Mariana Arc beneath Japan using Receiver Function analysis
Izu-Bonin-Mariana Arc (IBM) is the intraoceanic arc resulting from a subduction of the Pacific Plate (PAC) beneath the Philippine Sea Plate (PHS). The arc has a length of about 2800 km between the Sagami Bay in Japan and Guam (e.g. Stern et al., 2003). IBM collides with the Honshu island at the Izu collision zone and subducts beneath the Eurasian and the Okhotsk plate to the north. The P-wave velocity structure along and across IBM which has yet reached the collision zone revealed a thickened with a width of about 25-30 km (Kodaira et al. 2007). Kinoshita et al. (2015) found a distinct velocity boundary at depths of 40–50 km using the receiver function (RF) analysis below regions where IBM is subducting. They interpreted that this boundary represents the boundary between the crust and the uppermost mantle of the IBM. Furthermore, they supposed the IBM does not subduct to a depth of about 100 km as estimated by tomography. The purpose of this study is to understand the crustal and upper mantle structure of subducting PHS and IBM. To address this, we conduct an inversion analysis of RFs and investigate the seismic structure of the subducting IBM including the distribution of the crust-mantle boundary. In RF inversions, there is a trade-off between the depth of the velocity boundary and the average velocity over the boundary, so we jointly inverted for the velocity structure from receiver functions and dispersion curves of surface waves. Our results are characterized by the following features: 1) The IBM crust is as deep as 40 km below the Izu peninsula. 2) The crust-mantle boundary of IBM discontinuous in the eastern part, whereas continuous in the western part, representing a different style of collision of IBM between the western and eastern part.