Q Value Structure of the Upper Crust along the Geoscience Transect from Baicheng to Da Qaidam

Abstract

AbstractThe inversion for Q value of the upper crust along the profile from Baicheng to Da Qaidam has been carried out using seismic reflection/refraction data. This profile cross the Tarim basin, the Altun Orogenic belt and the Qaidam basin, respectively. The results indicate that the Q value of the upper crust of the profile bears an obvious stratification, with the Q value increasing downward. Laterally, the Q value has different features at different geological units. The upper crust of the Tarim basin has a stable Q value structure, but the Q value at the northern margin (especially the Koqia depression) is relatively lower than that at its southern margin, indicating a fractured medium at the northern margin. Probably it is associated with the active tectonics and huge sedimentary thickness of the northern margin of the basin, and one of the reasons for the seismicity difference between the north and south sides of the basin (strong in north and weak in south). The upper crust of the Altun Orogenic belt has a high average Q value (about 500). It is likely caused by shallow depth of the crystalline basement, exposure of basement rocks and slow attenuation of seismic waves. In the west part of the Qaidam basin, only the first layer (about 1.0~2.0km thick) of the upper crust has a high Q value. The Q values of other layers are similar to that of the middle Tarim basin (400 in average), showing that the western Qaidam basin has a stable structure like the Tarim basin.