中文摘要：

岩石圈软流圈边界（lithosphere-asthenosphere boundary,LAB）是上地幔内具有负速度梯度的地震间断面.开展对俯冲带区域LAB的地震学探测有助于进一步理解岩石圈与软流圈的相互作用以及与板块俯冲相关的地球动力学过程.本文收集了20022014年发生于伊豆-小笠原地区的3个深源地震（400600 km）的垂向宽频带波形资料,利用线性倾斜叠加方法对波形数据进行处理后获得了相对走时-慢度域的灰度图和叠加波形图,并成功提取了sP震相在LAB反射的前驱震相sLABP,该震相的极性与sP相反,幅度比为0.170.21.基于改进的一维速度模型IASP91-IB计算获得了近源区6个sLABP震相反射点的分布.研究表明伊豆-小笠原岛弧下方LAB深度位于5865 km,平均深度为62 km,起伏变化较小（7 km）.与菲律宾海构造稳定地区研究结果相比,伊豆-小笠原岛弧地区海洋岩石圈出现了明显减薄的现象,其应与西太平洋俯冲板块在地球深部持续释放的挥发分物质导致了软流圈出现部分熔融以及弧后地幔楔内小尺度对流的强侵蚀作用密切相关.

英文摘要：

The lithosphere-asthenosphere boundary（LAB） is the seismic discontinuity with the negative velocity contrast in the upper mantle. The plate tectonic theory describes that the rigid lithosphere translate coherently over the ductile asthenosphere, and the LAB implies the decoupling between the two layers. The seismic velocity, viscosity, electrical resistivity and other physical parameters change with the depths across the boundary. The LAB has become a focus of seismology studies for its significance in understanding the plate motions, the mantle convection and the lithospheric evolution processes. Seismic detections on the LAB in subduction zone areas are helpful to understand the interactions between the lithosphere and asthenosphere layers and the geodynamic processes related with the slab subductions. For the dense permanent networks and transportable arrays of the USArray, the abundant waveforms of the deep earthquake events beneath the Izu-Bonin area can be recorded and retrieved. In this study, the vertical broadband waveforms are collected from three earthquake events occurring from 2002 to 2014 with the focal depths of 400–600 km. The source parameters are taken from the Preliminary Determinations of Epicenters catalog of US Geological Survey, and the focal fault solutions are taken from the global Centroid-Moment-Tensor project. The seismic waveforms are manually selected with two criteria：（1） simple sP arrivals with clear peaks, and（2） high signal-to-noise ratios and without abnormal spikes. In order to enhance the weak unknown precursors, the linear slant stack method, which is the special form of the N-th root slant stack method and phase-weighted stack method, is applied to scan the differential slowness and stack the seismograms in the domain of differential travel-time and differential slowness. The selected waveform data is processed to obtain the vespagrams and the stacked waveforms. The sP precursors reflected on the LAB（sLABP）, which have the opposite polarities with the amp