Fig. 1

Geological features of the research area and station distribution. The white dashed lines represent the boundaries of the tectonic units of the main blocks, the gray lines represent the distribution of faults, the black dots denote the historical earthquakes, the blue triangles represent the stations where crustal and Vp/Vs were obtained, the black triangles represent stations without such results, the red squares display permanent stations, and the red star represents the location of the Hongtong earthquake. HTG Hetao Graben, LLM Lvliang Mountains, THM Taihang Mountains, DTV Datong Volcano