Abstract
Abstract Broadband seismic data from the regional seismic network operated by the China Earthquake Administration and 32 temporary seismic stations are used to image the crustal velocity structure in the northeast Tibetan plateau. Empirical Rayleigh‐ and Love‐wave Green’s functions are obtained from interstation cross correlation of continuous seismic records. Group velocity dispersion curves for Rayleigh and Love waves between 10 and 50 s are obtained using the multiple‐filter analysis method with phase‐matched processing. The group velocity variations of Rayleigh and Love waves overall correlate well with the major geologic structures and tectonic units in the study region. Shear‐wave velocity structures were then inverted from Rayleigh‐ and Love‐wave dispersion maps. The results show that the Songpan–Ganzi terrane is associated with a low velocity at depth greater than 20 km. The northern Qilian orogen, with higher elevation and thicker crust compared to the southern Qilian orogen, is also dominated by low velocity at depth greater than ∼25 km. However, there is no clear evidence of the low‐velocity mid‐to‐lower crust beneath the southern Qilian orogen as the crustal flow model predicts. The low‐velocity zone (LVZ) beneath the northern Qilian orogen may suggest that the crustal thickening and surface uplift of the northern Qilian orogen are related to the LVZ, and the LVZ may be considered as an intracrustal response to bear the ongoing deformation in the northern Qilian orogen. Online Material: Figures of crustal topography, number of group velocity measurements, checkerboard tests for NETS stations, and 1D velocity models.
Highlights
The Tibetan plateau has been the prime site for understanding the processes of continental collision, mountain building, and the interaction between tectonics and climate change
The shear-wave velocity structures derived from both Rayleigh- and Love-wave dispersion curves show that the Songpan–Ganzi terrane is featured with a prominent low-velocity zone (LVZ) in its mid-to-lower crust (∼20–40 km), which is consistent with the P-velocity model
We obtained group velocity maps of Rayleigh and Love waves in the northeast Tibetan plateau using broadband seismic data recorded by temporary broadband seismic arrays and the regional seismic networks
Summary
The Tibetan plateau has been the prime site for understanding the processes of continental collision, mountain building, and the interaction between tectonics and climate change. In the 10 s Love-wave map (Fig. 6a), the low velocity appears beneath the Qaidam basin, and a small patch of high velocity is observed beneath the northernmost Qilian orogen. At 10 km depth, the Qaidam basin is characterized by a low S-wave velocity, and a small patch of very-high-velocity anomaly is observed in the northernmost Qilian orogen (Fig. 8a). The shear-wave velocity map at 40 km depth (Fig. 8d) shows a similar velocity distribution as at the depth of 30 km except that the LVZ beneath the north Qilian orogen is more obvious and becomes larger than that at depth of 30 km This shear-wave velocity model offers new insights into the subsurface structures beneath the northeast Tibetan plateau, and its implications to the deformation and rise of the Tibetan plateau are discussed in the Discussion section. In the BB′ profile crossing the Songpan–Ganzi terrane and the northern Qilian orogen (Fig. 9b), an LVZ in the mid-to-lower crust exists beneath the Songpan–Ganzi terrane and the northern Qilian orogen
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