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在震后2300～2450s的时间内,于震中距30°～50°之间发现了以前从未报道过的1Hz散射波。这些散射波可能是在上地幔和地壳发生的PKPbc到PKPbc的反方位角散射而产生的,为绘制地幔非均匀性的小尺度变化(10km)提供了一个新的手段。大孔径地震台阵(LASA)记录的阵列波束清晰地展示了散射波能量从噪声中逐步显露,在大约80s后达到最大振幅,并在150s后恢复到噪声水平。横向与径向慢度(ρt,ρr)的叠加显示在大约(2,-2)和(-2,-2)s/°存在两个峰值,表明这些波是沿着主弧路径(180°～360°)到达,而且明显是反方位角。基于上述观测资料,我们提出一种地幔和地表的PKPbc到PKPbc的散射机制,因为(1)这与散射波到时和散射波特有的慢度特征相吻合,(2)它的散射路径与之前观测到的深部地幔PK·KP散射路径类似(Chang and Cleary,1981)。观测到的上地幔散射波和PK·KP波均符合散射波的广义集合,我们称其为P′·d·P′,可以在地幔的任意深度d散射。
In the period of 2300 ~ 2450s after the earthquake, a 1Hz scattered wave which has never been reported before was found between 30 ° ~ 50 ° in the epicenter. These scattered waves may have been produced by backscatter of PKPbc to PKPbc in the upper mantle and the crust, providing a new means of mapping small-scale changes in the mantle heterogeneity (10 km). The array beams recorded by the LASA clearly show that the scattered wave energy gradually emerges from the noise, reaches its maximum amplitude after about 80 s, and returns to the noise level after 150 s. The superposition of lateral and radial slowness (ρt, ρr) shows that there are two peaks at about (2, -2) and (-2, -2) s / °, indicating that these waves are along the main arc path ~ 360 °) arrives, and obviously is the opposite azimuth. Based on the observations above, we propose a scattering mechanism of PKPbc to PKPbc in the mantle and the surface because (1) it is consistent with the slowness characteristic of the scattered wave arrival and the scattered wave, (2) its scattering path is Previously observed deep mantle PK · KP scattering paths were similar (Chang and Cleary, 1981). The observed upper mantle scattered wave and PK · KP wave all agree with the generalized set of scattered waves, which we call P ’· d · P’ and can be scattered at any depth d of the mantle.