研究人员使用最近开发的地震分析方法，发现在南半球大部分未采样的部分之下，沿着核-幔边界(CMB)存在着广泛的、可变的超低速带。研究区域不在当前或最近的俯冲带之下，但是地幔对流模拟展示了先前俯冲物质的不均匀堆积是如何在核-幔边界上形成的，并揭示了研究过程中的地震观测结果。
研究进一步证明，俯冲物质可以在不同的浓度，在全球范围内分布于最低地幔。这些沿核-幔边界平流的俯冲物质，可以解释已报道的超低速带性质的分布和范围。
据介绍，超低速带(ULVZs)是地球内部最不规则的。然而，鉴于先前的研究，已经报告了其广泛的相关特征(厚度和成分)，超低速带的起源已经争论了几十年。
附：英文原文
Title: Globally distributed subducted materials along the Earth’s core-mantle boundary: Implications for ultralow velocity zones
Author: Samantha E. Hansen, Edward J. Garnero, Mingming Li, Sang-Heon Shim, Sebastian Rost
Issue&Volume: 2023-04-05
Abstract: Ultralow velocity zones (ULVZs) are the most anomalous structures within the Earth’s interior; however, given the wide range of associated characteristics (thickness and composition) reported by previous studies, the origins of ULVZs have been debated for decades. Using a recently developed seismic analysis approach, we find widespread, variable ULVZs along the core-mantle boundary (CMB) beneath a largely unsampled portion of the Southern Hemisphere. Our study region is not beneath current or recent subduction zones, but our mantle convection simulations demonstrate how heterogeneous accumulations of previously subducted materials could form on the CMB and explain our seismic observations. We further show that subducted materials can be globally distributed throughout the lowermost mantle with variable concentrations. These subducted materials, advected along the CMB, can provide an explanation for the distribution and range of reported ULVZ properties.
DOI: add4838
Source: https://www.science.org/doi/10.1126/sciadv.add4838