# Teleseismic Tomography for Imaging the Upper Mantle Beneth Northeast China
## 4 Discussion  
As shown in Figure 13, in the Songliao basin (in red wireframe), the upper mantle generally shows a high-velocity abnormal distribution, which is related to the extensional background of the basin formation, but it is worth mentioning that there is a small range of low-velocity abnormal body in the  
Figure 11: Five slices in the range of 42\({}^{\circ}\) N–50\({}^{\circ}\) N from east to west. Figure 12: Five slices in the range of 122\({}^{\circ}\) E–130\({}^{\circ}\) E from north to south. northern part of the basin, which does not cross continuously the mantle transition zone, so it may be related to the mantle convection. Under the geological background of Cenozoic volcanoes around the basin, many low-velocity anomalies are reasonable results. As can be seen in Figure 14, it is the comparison between the results of this study and the low-velocity area determined by [PERSON] [31]. We can see the low-velocity anomalies from the mantle transition zone and the upper mantle are continuous from Figure 14. In this study, the low-velocity anomalies of West-Low-Velocity-Zone (WLVZ) and East-Low-Velocity-Zone (ELVZ) in the same position and shape are also observed. However, some of the results of this paper are different from [PERSON]'s anomaly delineation area. The low-velocity anomaly in the east side of this study extends to the lower mantle than that of ELVZ, which may indicate that there is not only one WLVZ gap in the subduction plate beneath Changbai Mountain. It is worth mentioning that the shallow high-velocity anomaly in the east of the Changbai Mountain is observed in this study. It is speculated that it is related to the data of 1U temporary station in North Korea. The shallow high-velocity anomaly restricts the distribution range of crust mantle low-velocity anomaly in the east of the Changbai Mountain volcano group. Figure 13: Horizontal section of P-wave velocity disturbance in the upper mantle of the study area (100–700 km, interval: 200 km). As a large intraplate volcano more than 1000 km away from the subduction trench, the origin of Changbaishan volcano group has always been considered to be related to the subduction of the Pacific plate. Some scholars have put forward the view that a \"gap\" in the subduction plate provides a channel for hot material from the lower mantle to inject into the upper mantle, and the upwelling of the lower mantle from a \"gap\" provides the main deep heat source for Changbai Mountain [28]. A researcher used the joint inversion of distant and local earthquakes in 2018 to obtain the continuous distribution of subduction plate images under the northeast area, and no \"gap\" was found in his result [37]. The continuous subduction plate image supports the \"dehydration model in the mantle wedge\" proposed by [PERSON] in 2004, that is, the subduction plate carries a large amount of water to heat the upper mantle, and these heated upper mantles in the subduction plate and the continuous recumbent plate form a large area of low-velocity anomaly and wedge-shaped distribution, which is also supported by the tomographic results of many scholars [29; 38; 39]. The profile obtained in this study shows that there is an obvious low-velocity anomaly in the mantle transition zone under Changbai Mountain, and the result is more consistent with previous conclusions. It is suggested that there is a gap in the mantle transition zone beneath Changbai Mountain, and that the low-velocity anomaly near other mantle transition zones around gap may indicate that upwelling mantle migrates laterally along the top of the mantle transition zone as it passes through the gap, and the ratio of upwelling to downwelling leads to partial melting of the upper mantle and the lower subduction plate at the velocity of 410 km. In recent years, a numerical simulation based on thermodynamic coupling shows that the subduction plate provides enough water for the upper mantle beneath Changbai Mountain.