Seismic velocity discontinuities beneath the Japan Islands with receuver function tomography

研究了同时确定平滑变化的三维地震速度结构和速度不连续面的接收函数层析成像方法。通过研究，我们认识到发展三维速度结构中包含速度不连续性的快速有效的波形合成方法的必要性，并在此基础上提出了一种基于改进的高斯束方法(GBM)的三维速度结构波形合成方法。我们将这种方法应用于在日本西南部的Kii半岛观测到的波形，那里的菲律宾海板块正在以复杂的3-D构型俯冲。我们合成了径向、横向和垂直的RFS，并将它们与观测结果进行了比较，以研究菲律宾海板块下降的顶部和海洋莫霍面的结构。结果表明，径向和横向RFS中出现的震相是倾斜速度不连续处的P-S波转换(Ps)震相，垂直RFS中的震相是地表反射的P波和倾斜速度不连续(PPDP)。此外，我们还利用高网倾斜仪产生的RFS研究了俯冲太平洋板块的顶部、洋蛾和底部。特别是在台站密度较高的日本中部地区，用BASH径向和横向RFS的分析表明，脱水水是输送的。进入地幔过渡带。RF分析揭示的低速带表明存在脱水水层。最后，基于速率和状态相关的摩擦力对渗流平板界面上的地震循环进行了二维模拟，并研究了排泄物深度与深层孔隙压力分布之间的关系。

We investigated the method of receiver function (RF) tomography by which we simultaneously determine the smoothly varying 3-D seismic velocity structure and the velocity discontinuity surfaces. Through the investigation, we recognized the necessity of developing the raid and efficient method of synthesizing waveforms in a 3-D velocity structure including velocity discontinuities, and then developed a raid waveform synthetic method based on improved Gaussian Beam method (GBM). We applied this method to the waveforms observed in the Kii peninsula, southwest Japan, where the Philippine Sea plate is subducting with a complex 3-D configuration. We synthesized radial, transverse and vertical RFs, and compared them with the observed ones to investigate the structure of the top and the oceanic Moho of the descending Philippine Sea slab. As results, we confirmed the phases appeared in the observed radial and transverse RFs are the P to S wave converted (Ps) phases at the inclined seismic velocity discontinuities, and the phases in the vertical RFs are the P waves reflected at the surface and the inclined velocity discontinuities (PpdP).Further, we investigated the top, the oceanic Moth and the bottom of the subducting Pacific slab by employing the RFs produced from Hi-net tiltmeters. Especially in the central Japan region where the station density is high, the analyses using bath the radial and transverse RFs revealed that dehydrated water is transported. into the mantle transition zone.The ; low velocity zone revealed by RF analyses indicates the existence of the layer of dehydrated water. Finally, we executed 2-D simulation of earthquake cycle on a fluid-infiltrated plate interface based on a rate and state dependent friction, and investigated the relation between the fecal depth and the pore pressure distribution at depths.