The middle-southern segment of the Tan-Lu fault is located at the intersection of three geological blocks. Because of its complexity and importance, it has been concerned by many geological scientists for a long time. Studying the deep structure of the crust and upper mantle, which records the dynamic evolution process, is the key to reveal the geodynamic mechanism of its generation and evolution. By collecting a whole bunch of vertical-component continuous data recorded by 261 broadband stations of the China Digital Seismic Network, provincial and municipal networks from January 2015 to December 2016, we calculate the inter-station Green's functions and measure the group velocity dispersion curves of Rayleigh wave by using the frequency-time analysis method. Through the quality control and strict screening, a total of 15,627 group velocity dispersion curves are extracted, and group velocity distribution images with the period of 5 similar to 50 s and resolution of 0. 75 degrees X 0. 75 degrees are reconstructed. We then analyze group velocity distribution images with six periods and three longitudinal profiles. These images reveal that the velocity structure of the crust and upper mantle in the middle-southern segment of the Tan-Lu fault zone and adjacent areas is characterized by inhomogeneity of transverse segmentation and longitudinal stratification. The results show that the group velocity distribution of short periods (6 s, 10 s) is closely related to surface geology and tectonic characteristics. The Subei Basin, Hefei Basin and Hehuai Basin with thicker sedimentary layers show low velocity, while the Luxi Uplift, Dabie-Sulu orogenic belt, Yangtze Craton and the South China fold system with extensive bedrock exposures, present a large area of high-speed anomalies. With the increase of the period (15 s, 20 s) , the influence of surface geological structure on the group velocity is gradually weakened. Influenced by crustal thickness and the velocity contrasts across the Moho, the Dabie and Sulu regions show relatively low velocity at longer periods (25 s, 30 s) , which may be related to the deeper burial Moho surface in these places. Longitudinal profiles show that the Sulu and Dabie orogenic belts and the high-pressure and ultrahigh-pressure metamorphic belts not only show the same topographic and tectonic features at the surface, but also display very similar Rayleigh wave group velocity distribution characteristics in the crust. The group velocity distribution in the crust generally shows a convex and concave pattern, and is shaped like a "dumbbell". The upper crust displays a convex and concave shape, and features with higher group velocity than in the adjacent area; the middle crust is depicted with low velocity. The lower crust also shows a convex and concave shape, which reflects the characteristics of residual mountain roots of continental collision orogeny. The similar Rayleigh wave group velocity distributions from the shallow surface to the upper mantle in the Sulu and Dabie not only provide evidences for their dislocation by the translation of the Tan-Lu fault with left-lateral strike-slip, but also provide seismological basis for the formation and evolution of the Tan-Lu fault.
