A Preliminary Study on Crustal Velocity Structures of Maqin‐Lanzhou‐Jingbian Deep Seismic Sounding Profile

Abstract

AbstractThe 1 000 km‐long Marqin‐Lanzhou‐Jingbian comprehensive geophysical profile was deployed for the purpose of studying the interaction between the Qinghai‐Xizang Plateau block and the Ordos block as well as for studying the deep driving mechanism of tectonic deformation. This paper presents only the preliminary results obtained with deep seismic sounding (DSS) observation data. The crust is clearly stratified. On the whole, it can be divided into two parts, i.e., the upper crust and the lower crust, with interface C as the boundary surface. Each of the two parts contains a number of secondary interfaces. The general trend of lateral variation is that the crust becomes gradually thicker from northeast to southwest, which is mainly due to the variation in the thickness of the lower crust. The average crustal velocity tends to become gradually lower from northeast to southwest–the velocity is obviously low west of Zeku and in Haiyuan region. A number of crustal low velocity layers exist west of Zeku and another low velocity layer exists near Haiyuan. The number of reflecting horizons increases gradually from northeast to southwest. As seen in seismic reflection waveforms, Pc wave is very strong at Haiyuan and it also lasts long. Besides, the complexity coefficients of Pm wave in Haiyuan and west of Zeku are extremely large, much larger than those in other parts. The above results clearly show that anomalous structure exists in the crust and upper mantle west of Zeku and in Haiyuan region, which reflects the interactions between Bayankar block and Chaidamu block, and between Qilian block and Ordos block.