Crust and Upper Mantle S-Wave Velocity Structure Across Northeastern Tibetan Plateau and Ordos Block

A 1000km long passive seismic observation profile consisted of 47 broadband portable seismometers was deployed from Maqên in northeastern Tibetan Plateau to Yulin in central Ordos. Using the teleseismic waveforms recorded by the passive seismic experiment, receiver function method was used to investigate the S wave velocity structure. The results showed that the crustal structure is clearly divided into blocks along the profile. From central Ordos to northeastern Tibetan Plateau, the crustal thickness varies from 40km to 64km. Under the Haiyuan earthquake region and west of West Qinling Fault, the Moho discontinuity seems quite complicated. In the Haiyuan earthquake region, recent earthquakes tend to distribute around the upper crust low velocity zone. Moho under east edge of the Qilian mountains has a depth jump and seismicity is closely related with the extension of the Qilian fault, indicating that the fault has reached under the Moho. Crust thickening is obvious in the region from Maqên to the Riyueshan fault. Our results show that the crust structure of the transition zone between Tibetan Plateau and Ordos is strongly deformed and fragmented, which is consistent with the occurrence of earthquakes in this region.