Abstract:In this paper, we manually pick the high-quality Pn-wave arrival times from the waveform data recorded at the digital seismic networks in the northwest Ordos block from 2008 to 2018, make use of the Pn velocity tomography, and we get the Pn velocity and anisotropy image in the uppermost mantle around the region. The results show that obvious lateral heterogeneities exist in the uppermost mantle of the region, which shows the close correlations to regional tectonics and earthquakes. The fast direction of anisotropy is nearly along the E-W direction around the Hetao graben. Most strong historic earthquakes in the region occur in the low velocity areas or the high-to-low velocity transition zone. These results provide important seismological clues to understand the dynamic problems related to the strong earthquakes.