Objective The Longwei Co area is located in the core of a hydrocarbon resource potential area in the North Qiangtang Basin, owing to limitations imposed by surface conditions and the harsh environment, the degree of seismic exploration in this area has generally been low, which hinders the understanding of its subsurface structure and hydrocarbon potential.

Methods Based on a deep reflection seismic profile approximately 28 km long acquired in the Longwei Co area, used the first−arrival travel−time tomography to investigate the shallow velocity structure. Combined with surface geological observations and the tomographic results derived from the deep reflection profile, the near−surface underground structure and the distribution of major faults in the study area are analyzed.

Results The shallow crustal velocity structure within a depth range of 2 km beneath the study area is obtained. The distribution characteristics of the Cenozoic sedimentary strata in Longwei Co area of Qiangtang Basin are determined. The sedimentary thickness varies on both sides of a high−velocity uplift, and it is inferred that the thickness of the Cenozoic sediments ranges from 0 to 400 m. In the west−central and central−eastern parts of the profile, characterized by the boundary between high and low−velocity anomalies, five faults are identified. Among them, faults F1 and F5 dip eastward, whereas faults F2, F3, and F4 dip westward, which extend to the bottom of Cenozoic sediments Faults. F2 and F4 are interpreted as part of the NE–SW−trending fault system in this region.

Conclusions The study area exhibits an east–west “two uplifts and three depressions” structural framework, which influences, to a certain extent, the hydrocarbon preservation conditions in this region.