Crustal structure across the Kunlun fault from passive source seismic profiling in East Tibet

• We report a seismological experiment across the Kunlun fault;
• Crust thickness: 64 km under Songpan–Ganzi, 56–62 km under Qaidam–Kunlun and Qilian;
• High Vp/Vs (1.76–1.85) in Songpan–Ganzi, while 1.83–1.65 in Qaidam–Kunlun;
• A crust flow mechanism operating more strongly in the western region along the Kunlun fault.

The crust beneath the northeastern (NE) Tibetan Plateau records the imprints on Paleozoic Kunlun orogen and far field effects from continental collision and convergence between the Indian and Eurasian plates. A passive source seismic profile was conducted across eastern Kunlun mountains (also called Animaqing suture belt). Receiver function imaging and H-k stacking results with this dataset demonstrate that (1) crust slightly thins from about 64 km under the Songpan–Ganzi terrane to about 56–62 km under the Qaidam–Kunlun block and the Qilian block; (2) Moho topography is relatively smooth with gradual undulation beneath east Kunlun orogeny belt, in contrast to 2–5 km Moho step at the AKMS/Kunlun fault from previous deep seismic soundings or even no Moho topography variation from recent deep seismic reflection profiling; (3) the average crustal Vp/Vs ratios display an increasing trend to the Kunlun fault belt from 1.76 to 1.85 in Songpan–Ganzi terrane, while decreases from 1.83 to 1.65 away from the fault belt in Qaidam–Kunlun block; (4) The high Vp/Vs ratio in Songpan–Ganzi terrane, is similar to previous results from the profile across Longmenshan fault belt. The normal to low Vp/Vs ratio distribution in Qaidam–Kunlun block supports the viewpoint that the deformation occurring in NE Tibet is predominated by upper-crustal thickening; and (5) the thickness of non-seismogenic layer varies slightly about 40 km between 90° and 100°E, then decreases to less than 20 km around 106°E along the Kunlun fault. The change of the non-seismogenic layer thickness is consistent with the change of the lower crust thickness derived from deep seismic sounding. The increased crustal thickness may be due to the differences in the thickness of the crust of the two plates before their collision, and/or largely achieved by thickening of the lower crust, perhaps indicating a crust flow mechanism operating more strongly in the western region.