Centre for Earth Evolution and Dynamics (CEED), Department of Geosciences, University of Oslo, Oslo, Norway.
Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, United Kingdom.
Sci Rep. 2017 Sep 8;7(1):10976. doi: 10.1038/s41598-017-11039-w.
The geoscience community is increasingly utilizing seismic tomography to interpret mantle heterogeneity and its links to past tectonic and geodynamic processes. To assess the robustness and distribution of positive seismic anomalies, inferred as subducted slabs, we create a set of vote maps for the lower mantle with 14 global P-wave or S-wave tomography models. Based on a depth-dependent threshold metric, an average of 20% of any given tomography model depth is identified as a potential slab. However, upon combining the 14 models, the most consistent positive wavespeed features are identified by an increasing vote count. An overall peak in the most robust anomalies is found between 1000-1400 km depth, followed by a decline to a minimum around 2000 km. While this trend could reflect reduced tomographic resolution in the middle mantle, we show that it may alternatively relate to real changes in the time-dependent subduction flux and/or a mid-lower mantle viscosity increase. An apparent secondary peak in agreement below 2500 km depth may reflect the degree-two lower mantle slow seismic structures. Vote maps illustrate the potential shortcomings of using a limited number or type of tomography models and slab threshold criteria.
地球科学界越来越多地利用地震层析成像来解释地幔的非均质性及其与过去的构造和地球动力学过程的联系。为了评估俯冲板块的正地震异常的稳健性和分布，我们使用 14 个全球 P 波或 S 波层析成像模型创建了一组下地幔投票图。基于依赖深度的阈值度量，任何给定层析成像模型深度的平均 20%被确定为潜在的板块。然而，在组合这 14 个模型后，通过增加投票计数来识别最一致的正波速特征。最稳健异常的整体峰值出现在 1000-1400 km 深度之间，然后在 2000 km 左右下降到最小值。虽然这种趋势可能反映了中间地幔的层析成像分辨率降低，但我们表明，它可能与俯冲通量的时变和/或中下地幔粘度增加有关。在 2500 km 深度以下的一致的二次峰值可能反映了二级下地幔慢地震结构的程度。投票图说明了使用有限数量或类型的层析成像模型和板块阈值标准的潜在缺点。
