Rayleigh wave phase velocity tomography in Shaanxi and its adjacent regions

In this paper, we used the vertical component of continuous wave data in Shaanxi and its adjacent regions recorded by total 257 stations in the broadband stations of the portable seismic array deployed under the project " China Seismic Array: Northern Part of North-South Seismic Belt” and fixed seismic network from 2014 to 2015. The 7 185 phase velocity dispersion curves of Rayleigh waves are obtained by using the phase velocity extraction method based on image analysis, then the phase velocity dispersion are used to reconstruct the phase velocity maps at period of 5-40 s with the minimum resolution about 20 km. The results show that the phase velocity maps better reflect the geological structure characteristics of the crust to uppermost mantle due to the obvious lateral heterogeneity of the phase velocity distribution. The phase velocity distribution of Rayleigh wave in the short period （5−10 s） is closely related to the surface geological structure, the boundary between high-velocity anomaly and low-velocity anomaly is consistent well with the boundary of the block. In the 15 s period, on the phase velocity maps most of the rifted sedimentary basins （the Weihe, Tianshui, etc.） still exhibit low-velocity anomalies, indicating that the basin may have thicker sedimentary layer. The phase velocity distribution in 20−40 s period is greatly affected by the thickness of the earth’s crust, the northeastern Tibetan Plateau has always been characterized by obvious low-velocity anomalies, and the Ordos block exhibits a high-velocity anomalies in the middle to lower crust. However, the low-velocity anomaly of the 20−30 s period extends from the Tibetan Plateau along the Liupanshan thrust fold belt to the interior of Ordos, therefore it is speculated that there is a certain degree of material exchange and fusion in this area.