中文摘要：

清楚的 PKIKP 先锋从 Lanzhou CTBTO 地震数组被观察。我们测量了他们的事件角度，到达关于使用的 PKIKP 到达的方位角和微分旅行时间穿分析技术。这些大小允许我们定位产生了观察先锋的 scatterers。我们发现 scatterers 在东方西藏下面位于最低披风，它被一个高速度的异例基于以前的 tomographic 研究展示。高速度异例作为古老的 Tethys subduction 的平板残余被解释。我们因此推测观察 scatterers 由 subducted 平板相关或导致。

英文摘要：

Clear PKIKP precursors were observed from the Lanzhou CTBTO seismic array. We measured their incident angles, arriving azimuths and differential travel times with respect to the PKIKP arrivals using array analysis techniques. These measurements allowed us to locate the scatterers that generated the observed precursors. We found that the scatterers are located in the lower- most mantle beneath eastern Tibet, which is featured by a high-velocity anomaly based on previous tomographic studies. The high velocity anomaly was interpreted as the slab remnants of the ancient Tethys subduction. We thus speculate that the observed scatterers are either related or induced by the subducted slab.