Slab Diffracted S Waves

对P波到达时间的反演发现，在瓦达蒂-贝尼奥夫带明显的地震活动中，岩石圈板片经常穿透到截止点以外。计算了发生在深度为1200公里的板块内的深源地震辐射的远震S波的合成地震图。这些合成显示了一种平板绕射现象，这种现象起到了加长S波的视脉冲宽度的作用。在板坯倾斜侧的各个方位都观察到了板坯的绕射，沿走向演化成一个突出的第二相，并在与倾角相反的一侧迅速衰减。给出了宽带S波，这表明数据中存在板条绕射。用于研究地幔衰减、D“结构和核结构的振幅比也可能受到板块高速扰动的聚焦和散焦效应的影响。提出用WKBJ/Gauss束方法在三维模型中综合板条绕射效应，以进一步约束和反演板条结构。在利用深源地震的体波波形和振幅研究地幔和核的弹性和滞弹性结构的其他研究中，还将研究板块结构的污染效应。

Inversion of P wave arrival times has found that lithospheric slabs frequently penetrate beyond the cutoff in the seismicity evident in Wadati-Benioff zones. Synthetic seismograms are calculated for teleseismic S waves radiated by a deep focus earthquake occurring within a slab that penetrates to 1200 km depth. The synthetics demonstrate a phenomenon of slab diffraction that acts to lengthen the apparent pulse width of the S wave. The slab diffraction is observed in all azimuths on the dipping side of the slab evolving into a prominent secondary phase along strike, and rapidly decaying on the side opposite to the dip. Broadband S waves are shown, which suggest the existence of slab diffraction in data. Amplitude ratios used in studies of mantle attenuation, D" structure, and core structure may also be affected by the focusing and defocusing effects of the high velocity perturbation of the slab. It is proposed to use a WKBJ/Gaussian beam method to synthesize the effects of slab diffraction in three-dimensional models in an effort to further constrain and invert for slab structure. An investigation will also be made of the contaminating effects of slab structure in other studies of mantle and core elastic and anelastic structure that use waveforms and amplitudes of body waves from deep focus earthquakes.