11:30 〜 11:45
[SIT16-04] Whole-mantle P-wave tomography beneath Japan and surrounding regions
Japan is located in a tectonically complex region where four lithospheric plates, i.e., the Pacific, Philippine Sea, Eurasian, and North American Plates, are interacting with each other. The Pacific Plate is moving toward the northwest at a rate of 8-10 cm/year and subducting beneath the Eurasian Plate at the Japan Trench, causing very active seismic and volcanic activities in East Asia.
The subducted Pacific slab becomes flat in the mantle transition zone (MTZ) beneath the Korean Peninsula and East China, forming a big mantle wedge (BMW) above the flat slab, and hot upwelling flows in the BMW cause the intraplate volcanism in East Asia (Zhao et al., 2004). In recent years, subslab hot mantle upwelling (SHMU), which is a return flow of plate subduction, has also been found beneath the Pacific slab, and several studies have suggested its influences on the slab geometry and the generation of megathrust earthquakes. However, few studies have investigated the detailed lower mantle structure beneath East Asia, and fundamental issues, such as continuity of the SHMU in the lower mantle and the fate of subducted slabs, remain unsolved. To solve these problems, in this work we determine detailed tomographic images of the whole mantle beneath Japan and its surrounding regions.
We apply the updated technique of multi-scale global tomography (Zhao et al., 2017) to determine a whole-mantle 3-D P-wave velocity (Vp) model beneath the study region. The number of earthquakes and seismic stations used are 20000 and 13,874, respectively. We analyze arrival times of not only direct P waves, but also surface reflected pP and PP, core reflected PcP, and core diffracted Pdiff waves to improve the ray path coverage in the deep mantle. The total number of arrival time data is 6,028,546, including 5,723,501 direct P, 169,295 pP, 80,256 PP, 39,205 PcP and 16,289 Pdiff waves from the ISC database.
Our results show the following features: (1) the Pacific slab is stagnant in the MTZ, and low-Vp anomalies in the BMW are clearly revealed; (2) there are distinct SHMUs rising from ~1,000 km depth beneath the subducting Pacific slab; (3) in the south of the Izu-Bonin region, the Pacific slab has subducted almost vertically to the lower mantle, as pointed out by previous studies. Deeper than there,high-Vp anomalies are piled up on the core-mantle boundary, which may reflect remnants of slabs that fell down intermittently.
The subducted Pacific slab becomes flat in the mantle transition zone (MTZ) beneath the Korean Peninsula and East China, forming a big mantle wedge (BMW) above the flat slab, and hot upwelling flows in the BMW cause the intraplate volcanism in East Asia (Zhao et al., 2004). In recent years, subslab hot mantle upwelling (SHMU), which is a return flow of plate subduction, has also been found beneath the Pacific slab, and several studies have suggested its influences on the slab geometry and the generation of megathrust earthquakes. However, few studies have investigated the detailed lower mantle structure beneath East Asia, and fundamental issues, such as continuity of the SHMU in the lower mantle and the fate of subducted slabs, remain unsolved. To solve these problems, in this work we determine detailed tomographic images of the whole mantle beneath Japan and its surrounding regions.
We apply the updated technique of multi-scale global tomography (Zhao et al., 2017) to determine a whole-mantle 3-D P-wave velocity (Vp) model beneath the study region. The number of earthquakes and seismic stations used are 20000 and 13,874, respectively. We analyze arrival times of not only direct P waves, but also surface reflected pP and PP, core reflected PcP, and core diffracted Pdiff waves to improve the ray path coverage in the deep mantle. The total number of arrival time data is 6,028,546, including 5,723,501 direct P, 169,295 pP, 80,256 PP, 39,205 PcP and 16,289 Pdiff waves from the ISC database.
Our results show the following features: (1) the Pacific slab is stagnant in the MTZ, and low-Vp anomalies in the BMW are clearly revealed; (2) there are distinct SHMUs rising from ~1,000 km depth beneath the subducting Pacific slab; (3) in the south of the Izu-Bonin region, the Pacific slab has subducted almost vertically to the lower mantle, as pointed out by previous studies. Deeper than there,high-Vp anomalies are piled up on the core-mantle boundary, which may reflect remnants of slabs that fell down intermittently.