Seismic evidence for the 410 km discontinuity beneath the Hindu Kush-Pamir region from the SdP converted phases

Abstract

In this study, we detect the 410 km discontinuity (410) beneath the Hindu Kush-Pamir region using broadband records of SdP converted phases. Beneath Hindu Kush, the 410 appears at the depths of 367–384 km with an average depth of 375 km; while beneath Pamir, it appears at the depths of 380–414 km with an average depth of 395 km. Compared with the Earth model IASP91, the 410 shows larger uplifts of 26–43 km with an average of 35 km beneath Hindu Kush, and smaller uplifts of 7–30 km with an average of 15 km beneath Pamir. Based on seismic tomographic images, the S410P conversion points are all located inside Indian slab beneath Hindu Kush, and near Asian slab with some of them inside the slab beneath Pamir. The 410 shows the 7–22 km uplifts with an average of 11 km near Asian slab, and the 21–30 km uplifts with an average of 25 km inside Asian slab. If depth variations are caused by the thermal heterogeneity, the 35 km uplift inside Indian slab indicates a low-temperature anomaly of 422 K; whereas the 11 km uplift near Asian slab and 25 km uplift inside Asian slab imply low-temperature anomalies of 133 K and 302 K, respectively. We suggest that the uplifts of the 410 are likely caused by cold subducted slabs, and the uplift differences imply different thermal impacts of the slabs beneath Hindu Kush and Pamir.