[S-SS07] 地震波伝播：理論と応用

[SSS07-P20] "Double door" opening of the Japan Sea inferred by Pn attenuation tomography

*Lian-Feng Zhao^1,3、Xiao-Bi Xie⁴、Geng Yang^2,1、Zhen-Xing Yao¹ (1.Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences、2.College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China.、3.Heilongjiang Mohe Observatory of Geophysics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China.、4.Institute of Geophysics and Planetary Physics, University of California at Santa Cruz, CA95064, USA)

キーワード：Seismic Pn waves, Attenuation tomography, Mantle flow, Japan Sea

The western Pacific is one of the most active regions of global tectonics. For the Japan Sea, the largest marginal sea in the northwest Pacific, the formation mechanism is still controversial. The Japan Sea may have experienced a complex evolution process driven by the superposition of multiple mechanisms, and finally produced a diamond-shaped ocean. The present thermal structure in the uppermost mantle, which can be directly constrained by strong Pn-wave attenuation, plays a vital role in understanding the Japan Sea opening. In this study, we construct a high-resolution broadband Pn attenuation model for the uppermost mantle beneath the Japan Sea. Two strong Pn attenuation belts are observed in this region, with their strikes generally consistent with the local Pn velocity anisotropy and the opening directions of the Japan Sea. Therefore, two divergent mantle flows likely exist in the uppermost mantle, pushing the opening of the Japan Sea like a “double door”. These mantle flows could be part of mantle convection in a big mantle wedge, where ascending hot materials from the deep mantle not only feed volcanoes in northeastern Asia but also thicken the back-arc oceanic crust.