Mantle transition zone beneath northeast China imaged by receive function data using fast marching eikonal solver based 3-D migration

In this study, we utilized 45505 teleseismic receiver functions derived from NECESSArray records to image the mantle transition zone beneath northeast China. We employed a fast-marching technique to solve the eikonal equations of the direct P wave and P-to-S converted waves in a 3-D velocity model. We selected the high-resolution 3-D model of FWEA18 that was derived from full waveform inversion as the reference velocity model. We gathered the receiver functions based on their geographical locations and stacked the receiver functions with a common conversion point (CCP). We found clear P-to-S conversion associated with the 410-km and 660-km discontinuities that define, respectively, the upper and lower boundaries of the mantle transition zone. The 660- km discontinuity deepens by 20 similar to 40 km in a similar to 300 km by similar to 900 km elongated area extending roughly in the north-south (NS) direction beneath the Changbaishan-Wudalianchi area. The southern and northern parts of the depression area show a distinct difference that suggests that the Pacific plate subducted from the Japan and Kuril trenches has different morphology when it encounters the upper and lower mantle boundary. The western front of the trough lies a N-S oriented uplift area with an elevation of similar to 10 km. These observations suggest that the subducted Pacific oceanic lithosphere only reaches to the eastern side of the Songliao Basin. We also observe a mild depression of 660-km beneath the Great Xing' An Range west to the Songliao Basin, which is likely caused by a delaminated continental lithosphere. Overall, the 410-km discontinuity appears to be flatter than the 660-km. It deepens slightly beneath the Songliao Basin, Bohai, the southwest and northeast sides of the Changbaishan volcano, the Abaga and Arshan volcanic regions. These depressions correspond well with extensional and volcanic regions, suggesting magmatism in the study area is largely controlled by ascending hot material from great depths.