# Teleseismic Tomography for Imaging the Upper Mantle Beneth Northeast China
## 1 Introduction
In teleseismic tomography, the result of linear inversion is more accurate than that of LET or wide-angle inversion [22]. The main reason for this is that the ray path is close to vertical when passing through the model body, and the rate of change of velocity is small. Therefore, many teleseismic tomographic images are processed by linear inversion [23; 24; 25; 26; 27]. NE China is located away from the subducting Japan trench for more than 1000 km and is currently bearing the extrusion of the Pacific plate. There are several Cenozoic intraplate volcanoes surrounding the Songliao basin in the middle. From north to south, they are Wudalianchi volcano, Aershan Volcano, Jingpohu Volcano, and Changbaishan Volcano. The North-South Gravity lineament (NSGL), as one of the most important topography lines in China, is considered to constrain the west subduction edge of the Pacific slab in NE China [28]. Different from the classical plate-boundary-related volcanoes on the earth. Changbaishan volcano, the most representative Cenozoic intraplate volcano in NE China, has been controversial in its origin and studied for decades [28; 29; 30; 31; 32]. In general, there are two models to explain the origin of Changbaishan Volcano. The dehydration model is presented by the tomographic results that continuous high-velocity zone exists from the Japan subduction trench down to the mantle transition zone beneath Changbaishan volcano and even farther to the Songliao basin, which infers that the subducting stagnant slab is continuous and the heat source comes from the water brought by subduction [28; 29; 30]. The other model infers that Changbaishan Volcano is originated from a lower mantle because of the image of a gap penetrating the mantle transition zone where low-velocity anomaly exists and extends to the crust [30]. Therefore, the core issue comes to whether there is a gap beneath Changbaishan Volcano. On the one hand, the origin of Changbaishan Volcano is still worth debating, on the other hand, the relationship between other Cenozoic volcanoes in NE China and Changbaishan Volcano was not fully discussed. In this paper, the P-wave velocity structure with a depth of 750 km under the study region is obtained by using the teleseismic travel time tomographic imaging of natural earthquakes. The study region covered by several seismic arrays fills the upper-most part of Northeast China, including the Songliao basin and Cenozoic volcanoes on both sides [32]. As the ray passes through the bottom of the study model, with the increase of depth, the range of teleseismic rays from all directions is larger. In addition to the crust range with poor ray cross, the ray distribution is better and the resolution is higher in the range including upper mantle, mantle transition zone, and a few lower mantle. Even though there are fewer teleseismic events from the Arctic direction and poor station distribution northern than 48\({}^{\circ}\) N, the resolution beneath the north part is still reliable, especially in the upper mantle scale. The original data used in this research institute in Northeast China comes from the waveform data of distant earthquake events received by the arrays in the study region, and two mainstream waveform correlation methods are used: multichannel cross-correlation method and adaptive stacking method to respectively pick up and calculate the inversion data - relative travel time residual. The inversion results show that the distribution of the low-velocity structure of the upper mantle beneath the Cenozoic volcanoes in the study area is of great significance for the interpretation of the special mechanism of the formation of volcanoes in the back arc plate [30; 33].