近日，荷兰乌德勒支大学Deuss Arwen小组的最新研究提出了利用地震法向模态的全球地幔衰减三维模型。2025年1月22日，国际知名学术期刊《自然》发表了这一成果。

据悉，仅基于波速的地震层析模型，区分地球三维结构的热源或成分源的能力有限。用衰减观测补充波速可以做出这种区分，这是理解地幔对流演化的基础。然而，目前全球三维衰减模型仅适用于上地幔。

该课题组提出了一个整个地幔衰减的三维全球模型，该模型以全地球振荡为主题，将甚至球面谐波限制在一定程度上。在上地幔，该研究组发现高衰减与低速度相关，表明其为热成因，与前人的研究一致。在下地幔中，研究人员发现相反的情况，并观察到“环太平洋”的衰减最大，其地震速度快，而在大的低地震速度省（llsvp）衰减最小。

将他们的模型与实验室粘弹性模型预测的波速和衰减进行比较表明，环太平洋是一个更冷、粒径较小的区域，周围是更温暖、粒径较大的llsvp。根据推测的晶粒尺寸和温度变化计算的粘度，证实了llsvp是长寿命、稳定的特征。

附：英文原文

Title: Global 3D model of mantle attenuation using seismic normal modes

Author: Talavera-Soza, Sujania, Cobden, Laura, Faul, Ulrich H., Deuss, Arwen

Issue&Volume: 2025-01-22

Abstract: Seismic tomographic models based only on wave velocities have limited ability to distinguish between a thermal or compositional origin for Earth’s 3D structure1. Complementing wave velocities with attenuation observations can make that distinction, which is fundamental for understanding mantle convection evolution. However, global 3D attenuation models are only available for the upper mantle at present2,3,4,5. Here we present a 3D global model of attenuation for the whole mantle made using whole-Earth oscillations, constraining even spherical harmonics up to degree four. In the upper mantle, we find that high attenuation correlates with low velocity, indicating a thermal origin, in agreement with previous studies6,7. In the lower mantle, we find the opposite and observe the highest attenuation in the ‘ring around the Pacific’, which is seismically fast, and the lowest attenuation in the large low-seismic-velocity provinces (LLSVPs). Comparing our model with wave speeds and attenuation predicted by a laboratory-based viscoelastic model8 suggests that the circum-Pacific is a colder and small-grain-size region9, surrounding the warmer and large-grain-size LLSVPs. Viscosities calculated for the inferred variations in grain size and temperature confirm LLSVPs as long-lived, stable features10.

DOI: 10.1038/s41586-024-08322-y

Source: https://www.nature.com/articles/s41586-024-08322-y