High-Resolution Upper-Mantle Tomography Using Seismic Arrays and Full-Wave Frechet Kernels: Southern Africa

赵，李这项建议的重点是开发一种用于地震阵列的高分辨率层析成像方法。通过反转相邻站点之间的相位和幅度变化，而不是在单个站点，来提高对子阵列结构的分辨率，以便最大限度地减少由远离阵列的横向不均匀中的不确定性所引起的偏差。数据的Frechet核是通过耦合简正波求和来计算的，因此所有的有限频率效应都被考虑在内，而不是高频或平均近似。还将开发一种新的行波方法来计算台站附近的精确核。从震源到子阵非均质(散射体)的波是用渐近勒让德函数表示的，而从散射体到台站的波是用精确的勒让德函数表示的。正在为南部非洲地震台阵开发层析成像方法，用于研究Kaapvaal克拉通，并对上地幔各向异性结构进行了三维反演。对51个远震事件的平均50个三分量台站的地表和上地幔体波数据进行了测量。这一结果将为最近一些区域模型中相互矛盾的特征提供新的解释，例如克拉通下方存在海洋型低速带和剪切波各向异性。这里开发的多站全波方法也非常适合于即将到来的USArray的需要。由于其提议的相邻站点之间的平均间隔约为70公里，该方法将能够在整个美国大陆的上地幔提供约50公里的几乎一致的横向分辨率。

Zhao, LiThe focus of this proposal is to develop a high-resolution tomography method for seismic arrays. Resolution to sub-array structure is enhanced by inverting the phase and amplitude variations between adjacent stations, rather than at individual stations, in order to minimize biases caused by uncertainties in lateral heterogeneities far away from the array. Frechet kernels of the data are calculated by coupled normal-mode summation so that all finite-frequency effects are accounted for with no high-frequency or averaging approximations. A new traveling-wave method will also be developed to calculate exact kernels near stations. Asymptotic Legendre functions are used to express waves from the source to sub-array heterogeneity (scatterer), but exact Legendre functions are adopted for waves from the scatterer to the station.The tomography method is being developed for the Southern Africa Seismic Array, deployed to study the Kaapvaal craton, and 3-D inversions are conducted for upper-mantle anisotropic structure. Data are measured for surface and upper-mantle body waves at an average of 50 three-component stations from 51 teleseismic events. The result will shed new light on the conflicting features in some of the recent regional models, such as the presence of an oceanic-type low-velocity zone beneath the craton and shear-wave anisotropy. The multi-station, full-wave method developed here is also well suited to serve the need of the upcoming USArray. With its proposed average spacing of about 70 km between adjacent stations, this method will be able to provide a nearly uniform lateral resolution of about 50 km in the upper mantle over the entire continental United States.