Abstract: To reveal the near-surface structural characteristics of the Jiamusi block-Nadanhada terrane, this study applies the first-arrival traveltime tomography method based on  deep seismic reflection profile data to invert and obtain the  near-surface P-wave velocity structure model of the study area, and further depicted the spatial distribution characteristics of the fault zones. The inversion results show that the thickness of the sedimentary cover generally exhibits a regional distribution pattern of being thicker in the west and thinner in the east. There is significant lateral heterogeneity in the vicinity of the main fault zones. Specifically, the thickness of the sedimentary cover within the Jiamusi block is relatively thin (0.5-0.7 km), which increases rapidly when crossing the Dunhua-Mishan fault zone and the Yuejinshan fault zone, with the maximum local thickness exceeding 2 km. In contrast, the thickness of the sedimentary cover within the Nadanhada terrane is generally less than 0.5 km. The Yuejinshan fault zone is manifested as a significant lithospheric-scale velocity gradient zone, which further reveals its nature as a boundary fault separating different tectonic units. Meanwhile, the Dunhua-Mishan fault zone is characterized by a nearly vertical low-velocity anomaly zone, indicating that the physical properties of the rocks wihtin the fault zone have been weakened due to fragmentation caused by tectonic activities.

Key words: Jiamusi block, Nadanhada terrane, first-arrival traveltime tomography, velocity structure, Dunhua-Mishan fault, Yuejinshan fault