Study on shallow velocity structure in Longwei Lake area in northern Qiangtang Basin

Longwei Lake area is located in the core part of the oil and gas resource potential areas located in the north of Qiangtang Basin, limited by the surface and environmental conditions, the seismic exploration degree is generally not high, it restricts the understanding of the underground structure and oil and gas prospects in the area. This paper is based on the data of a deep reflection seismic profile of about 28km in the Longwei Lake area, used the first-arrival wave tomography, the shallow velocity structure is studied, combined with the surface geological conditions and the processing results of the first-arrival wave tomography of the deep reflection profile, the near-surface underground structure and the distribution of major faults in the study area are discussed, the following knowledge was obtained: the distribution characteristics of Cenozoic sedimentary strata in Longwei Lake area of Qiangtang Basin are determined. On the whole, the Cenozoic sedimentary thickness was inferred to be 300-1000m; In the middle and western part of the profile, characterized by the high and low speed anomalous demarcation, explain the two westward-inclined faults, which extend to the bottom of Cenozoic sediments and are judged to be part of the NE-SW trending fault system in this area; The east-west direction of the research area presents the structural pattern of 'two uplifts and three depressions', which affects the conditions of oil and gas storage under certain conditions.