Crustal structure across the northeastern Tibetan plateau and Ordos block revealed by the receiver function method

The ongoing collision between Indian and Asian continents has created the Tibetan plateau. The northeastern Tibetan plateau (NE Tibet) has long been a key region for studying its expansion mechanism. However, detailed lithospheric structures across the tectonic boundaries between the Tibetan plateau and bordering blocks have not been fully imaged, which obscured the understanding of how the Tibetan plateau interacts with other blocks, like the Ordos block. Therefore, about 227 stations with less than 1-km intervals were deployed from 1st October 2024 for one month, crossing from the NE Tibet, through the Haiyuan arcuate tectonic belt, into the Ordos block. A NE-trending CCP stacked profile perpendicular to major faults was then formed, based on receiver functions calculated using teleseismic waveforms. Our profile shows clear P-to-S conversion phases at the Moho discontinuity, both in NE Tibet and the Ordos Block. In NE Tibet, the Moho appears at 50 km at the southernmost point of our profile. It deepens to 55 km beneath the Haiyuan Fault and then rises back to 50 km beneath the Xiangshan-Tianjingshan Fault. To the northeast, the NE Tibetan crust interacts with the Ordos Block between the Yantongshan and Luoshan Faults, where a significant offset of the Moho is observed. The Moho depth of the Ordos Block is approximately 40-43 km, indicating an offset of about 7-10 km.