Seismic Velocity Discontinuities beneath The Japan Islands Revealed by Receiver Function Analysis

利用接收函数阵列分析方法，研究了日本列岛地下含地震不连续面的地震速度结构。j -阵)和短周期高密度（j -阵，Hi-net）站安装在整个日本群岛。首先，我们用传统的方法得到了接收函数（rf）。然后对短周期信号进行SVD（奇异值分解）滤波，对宽带信号进行深度变换。利用高空间分辨率的短周期数据，我们清楚地识别出康拉德断层的横向变化和地壳中的莫霍面不连续性，特别是在台站分布紧密的日本西南部，我们探测到康拉德断层的倾斜和莫霍面在Biwa湖周围的下陷。对于上地幔地震不连续，我们在东北地区探测到了太平洋板块下降的倾斜上下边界。对于菲律宾海板块来说，似乎很难看到它的边界。我们还探测到410公里和660公里的不连续面。410公里的不连续性与660公里的不连续性相比尤其明显，并且似乎在下降的板块内上升。660公里的不连续面似乎分为三个不连续面。最后，我们添加了最近才安装的Hi-net的数据。它们的采样率为100赫兹，这使我们能够产生更高频率的rf来成像更详细的结构。虽然这只是初步的，但我们有可能对下地壳的反射层状结构进行成像，这为我们提供了与内陆大地震发生有关的重要信息。

Seismic velocity structure including seismic discontinuities beneath the Japan Islands is investigated using receiver function array analysis method We use a large number of broad band (FREESIA. J-array) and short-period high density (J-array, Hi-net) stations installed all over the Japan Islands. First, we obtained receiver functions (RFs) in a traditional way which has been so fer employed. Then we applied SVD (Singular Value Decomposition) filtering to the original RFs for the short period ones, and to the depth transformed RFs for the broadband ones.Using short period data with high spatial resolutions, we clearly recognized lateral variation of the Conrad, and the Moho discontinuities in the crust Especially in southwest Japan where the station are closely distributed, we detected the inclined Conrad and the downwarping ofthe Moho around the Lake Biwa. For the upper mantle seismic discontinuities, we detected the inclined upper and lower boundaries of the descending Pacific slab in the Tohoku region. For the Philippine Sea slab, it seems to be rather difficult to see Hie boundaries. Also we detected 410 km and 660 km discontinuities. 410 km discontinuity is especially clear in comparison to 660 km one, and seems to be upwarping within the descending slab. 660 km discontinuity seems to be divided into three discontinuities.At last, we added the data of Hi-net, which has been only recently installed. They have a sampling rate of 100 Hz, which enables us to produce higher frequency RFs for imaging the far detailed structure. Though this is only preliminary, there is a possibility that we can image the reflective layering structure in the lower crust, which provides us an important information relating to the initiation of large inland earthquakes.