Investigation of the anisotropy of the mantle transition zone using PP and SS precursors

这一扩展建议的目的是调查和描述导致上地幔和下地幔之间过渡区地震各向异性的变形。在该项目的前三年期间，进行了一次详细的大西洋底面反射测绘，提供了一个大型数据集，表明大西洋热点地区地幔不连续性对温度的依赖性很强。该数据集还表明极性变化，而不是波传播模型预测。通过理论计算的一个简单的模型的各向异性，变形橄榄石在各向同性wadsleyite层，我们发现，有明显的影响SH波底面反射的不连续性在410公里的深度为不同的旅行方向，虽然在短震中距离。在这个扩展建议中，我们的目标是建立在该项目的成功的第一部分，并希望继续和扩展底面反射的反射系数的建模，包括各向异性的较低层的wadsleyite，但也预测极性和幅度的接收器功能，以及剪切波分裂的变形材料以上和以下的不连续性。此外，我们的目标是将这些预测的反射系数，透射系数（接收器功能）和剪切波分裂的660公里的不连续性和可能更深的不连续性。为了测试预测与真实的数据，我们使用和扩展我们目前的底面反射数据集，并添加接收器功能分析以及剪切波分裂地幔过渡带。我们必须找到合适的地震波，可以探测变形，因为我们的初始模型的预测目前指向非常短的震中距离波。然而，这可能会改变两个各向异性层，并将在项目过程中更好地确定。最终目标是开发一种新的诊断工具，通过结合几个地震观测值（具有最少数量的独立观测值）和不同方向来检测变形的类型，并通过检测地幔过渡带周围深处的变形约束流。

The aim of this extension proposal is the investigation and characterization of deformation that leads to seismic anisotropy in the transition zone between upper and lower Earth's mantle. During the previous three years of the project, a detailed mapping of the Atlantic with underside reflections was carried out and provides a large dataset that showed strong temperature dependence of the mantle discontinuities in the area of hotspots in the Atlantic. This dataset also indicated polarity variations, not predicted by wave propagation modelling. Through theoretical calculations of a simple model of anisotropic, deformed olivine over an isotropic wadsleyite layer we found that there are visible effects for the SH-wave underside reflections off the discontinuity at 410 km depth for different travel directions, albeit at short epicentral distances. In this extension proposal we aim to build on the successful first part of the project and want to continue and extend the modelling of reflection coefficients for underside reflections, including an anisotropic lower layer for wadsleyite but also predict polarities and amplitudes for receiver functions as well as shear-wave splitting for the deformed materials above and below the discontinuity. Furthermore we aim to extend these predictions of reflection coefficients, transmission coefficients (receiver functions) and shear wave splitting to the 660 km discontinuity and possibly deeper discontinuities. To test the predictions with real data, we use and extend our current dataset of underside reflections and add receiver function analysis as well as shear wave splitting for the mantle transition zone. We have to find suitable seismic waves that can probe the deformation as the predictions from our starting model at the moment point to very short epicentral distance waves. This however, may change for two anisotropic layers and will be determined better during the course of the project. The final goal is to develop a new diagnostic tool to detect the style of deformation by combining several seismic observables (with the least number of independent observables) and in different directions, and through this detection of deformation constrain flow in the depths around the mantle transition zone.