Study on the crust phases of deep seismic sounding experiments and fine crust structures in the northeast margin of Tibetan plateau
青藏高原东北缘深地震测深震相研究与地壳细结构

In this paper the fine crust structures of the different tectonic units in the northeastern margin of Tibetan plateau are investigated in detail by means of comprehensive analyses of the crust phases on the recording sections of deep seismic sounding experiments in this region and comparing the observed seismic recording sections with the synthetic seismograms computed by the reflectivity method. The results reveal that the crust structures in the northern and southern parts of this region separated by the western Qinlin fold zone are quite different, and the crust structures are characterized respectively by stable Linxia-Lanzhou Cenozoic basin in the northern part and by strongly rebuilt Songpan-Garze tectonic block in the southern part. The results also show that Songpan-Ganzi tectonic block was rebuilt into two types of crust structures, i.e. the type of the shrunken Zoigê upland basin and the type of the folded orogenic zone in the basin margin. It is also revealed that fractured and relaxed structures widely exist in the middle and lower crust in the northeastern margin of Tibetan plateau, which are characterized by alternative low and high velocity structures or low velocity distributions. This structural feature appears especially obvious in the suture zone and the orogenic zone, which implies there are important places of thickening of the crust and rheological slip motion. The crust deformation and geodynamic process are discussed based on the 2D velocity structure of the crust and GPS result obtained in this region.