Mapping Mantle Structure

提出了一种继续应用波形模拟恢复地球边界细节性质的方案。它的基础是对通过复杂地球传播所引起的观测记录剖面的相当复杂的建模和解释的能力。我们建议从宽带数据中发展P和S速度模型，对于最均匀的区域、屏蔽层、年轻和古老的海洋以及快速变化区域的详细二维截面，边界约束为相同的深度。最近的层析成像结果可用于收集关键数据集，在这些数据集中，包括面波在内的完整地震剖面可以与适合于横向变化的地球模型的合成地震剖面进行比较，并进行适当的评估。横向变化对面波的影响将通过应用修改的广义射线代码和修改的有限差分代码来检查，该代码被修改为处理具有三维扩展的震源。已建立的远震旅行时间和振幅(WWSSN长周期)波动模式将通过比较来自于详细的全地幔层析结果(如Grand(1986))的适当路径的合成来检验。对所提出的模型的测试将在核-地幔相以及通常的直接P波和S波上进行。将特别注意(SKS-SDIF)地震剖面，这些剖面显示的区域间的散布比仅用地幔变化容易解释的要多得多。

A program of continuing application of waveform modeling to recover the detailed nature of the boundaries in the earth is proposed. It is based on an ability to model and thereby interpret the considerable complications of observed record sections caused by propagation through a complex earth. We propose to develop P and S velocity models from broad-band data with boundaries constrained to be at the same depths for the most uniform regions, shields, young and old oceans, and detailed two-dimensional cross-sections through regions of rapid variations. The recent tomographic results can be used to great advantage in collecting key data-sets where complete seismic sections, including surface waves, can be compared with synthetics appropriate for laterally varying earth models and proper evaluations made. Effects on surface waves due to lateral variation will be examined by applying a modified generalized ray code and by a finite-difference code modified to treat earthquake sources with three-dimensional spreading. The well established teleseismic travel time and amplitude (WWSSN long period) fluctuation patterns will be examined by comparing synthetics for the appropriate paths taken from detailed whole mantle tomographic results such as Grand (1986). This testing of proposed models will be conducted on core-mantle phases as well as the usual direct P and S waves. Particular attention will be given to (SKS - Sdif) seismic sections which show considerably more scatter from region-to-region than can be easily explained by variations in the mantle alone.