Abstract: Since the Late Paleozoic，Northeast China has experienced the combined effect of PaleoAsian Ocean, MongoliaOkhotsk Sea, and Pacific tectonic domain, resulting in the extremely complex crustmantle structure. In this study, we collected 100 980 Pwave arrival times and 91 030 Swave arrival times compiled by the National Earthquake Network, and the 3D P and Swave velocity structures in Northeast China were determined by using seismic tomography method. The Poisson’s ratio structure of the study region was also obtained to explore its complex crustal structure. The tomographic results show that the crustal velocity structure in Northeast China exhibits strong lateral heterogeneities with various degrees of heterogeneity between and within different tectonic units. The Songliao basin is a typical rift basin. The shallow crust shows low Pwave and significantly low Swave anomalies as a whole, with some low resolution regions. Largescale highvelocity anomalies exist in the middle and lower crust, which may be related to the subduction and retreat of the Pacific plate beneath the Eurasian continent, resulting in the lithospheric delamination and upwelling of hot and wet asthenosphere material. The northern part of the Great Xing’an Range gravity lineament and the Changbai Mountain show lowvelocity anomalies, which may indicate largescale magmatism. The widespread magmatism may provide heat or material sources for the formation of solid mineral resources. The crust beneath Changbai Mountain and Wudalianchi volcanic areas shows significant low velocity and high Poisson’s ratio anomalies, which may indicate the possibility of volcanic activities.

Key words: seismic tomography, Northeast China, crustal structure, Poisson’s ratio, active volcano