Joint inversion of surface wave dispersion and receiver functions for crustal and uppermost mantle structure beneath the northern north-south seismic zone

We analyze the observational data recorded by the 676 temporary seismic stations deployed in the northern north-south seismic zone. Our purpose is to derive the crustal thickness, sedimentary thickness and a high-resolution shear wave velocity model of the crustal and uppermost mantle structure beneath the research area. The results demonstrate that the crustal thickness becomes thinner from the northeastern Tibetan Plateau to its periphery, and that in the Qinling orogen is thinner than the northwestern Qilian orogen, implying the former probably has experienced thinning. The Ordos and Hetao basins seem to have very thick sediments, so do some parts of the Alxa block. The sedimentary thickness is consistent with the distribution of basins in the study area. The 3-D shear wave velocity model shows that the northeastern Tibetan Plateau, including the Songpan-Garzê block and northwestern Qilian orogen, is characterized by relatively low velocity anomalies. In the middle crust, the low-velocity zone (LVZ) beneath the Songpan-Garzê block has a lower shear wave velocity and a shallower depth than that beneath the northwestern Qilian orogen, which may suggest partial melting in the Songpan-Garzê block. A significantly high velocity anomaly that extends downward at least 120 km is observed beneath the Ordos basin, while the high velocity anomaly below the Hetao basin extends downward 80 km, revealing a thinned lithosphere beneath the Hetao basin presumably associated with deep hot mantle materials. The Alxa block is characterized by the coexistence of low and high velocity anomalies, suggesting that the lithosphere beneath the western Alxa block may have been deformed by the expansion of the northeastern Tibetan Plateau.