Age‐Independent Oceanic Plate Thickness and Asthenosphere Melting From SS Precursor Imaging
Age‐Independent Oceanic Plate Thickness and Asthenosphere Melting From SS Precursor Imaging
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来自SS前兆成像的与年龄无关的大洋板块厚度和软流圈融化
DOI：
10.1029/2022jb024805
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发表时间：
2023-02
期刊：
影响因子：
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通讯作者：
Shuyang Sun;Ying Zhou
中科院分区：
文献类型：
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作者：
Shuyang Sun;Ying Zhou
地球软流圈是一个力学薄弱层，其特点是地震波速度低，衰减大。这一层的性质一直存在着激烈的争论。在这项研究中，我们处理了12年的地震记录在全球地震台网台站调查SS波反射在这一层的上，下边界在全球海洋区域。我们观察到来自软流圈顶部和底部的强烈反射，分散在所有主要海洋中。两个不连续面的平均深度分别为120和255公里。在岩石圈和软流圈边界反射的SS波具有异常大的振幅，这需要通过界面的地震速度降低约12.5%。这种大的速度下降不能用热冷却模型来解释，但表明在海洋软流圈中有1.5%-2%的局部熔融。这两个不连续面的深度变化很大，表明软流圈远离均匀层，但可能与海洋地幔中强烈和非均匀的小尺度对流有关。在不同的年龄段，这两个边界的平均深度基本上是恒定的。与半空间冷却模型相反，这一观察结果支持在海洋区域存在具有复杂和异质起源的等厚度板。
The Earth's asthenosphere is a mechanically weak layer characterized by low seismic velocity and high attenuation. The nature of this layer has been strongly debated. In this study, we process 12 years of seismic data recorded at the global seismological network stations to investigate SS waves reflected at the upper and lower boundaries of this layer in global oceanic regions. We observe strong reflections from both the top and the bottom of the asthenosphere, dispersive across all major oceans. The average depths of the two discontinuities are 120 and 255 km, respectively. The SS waves reflected at the lithosphere and asthenosphere boundary are characterized by anomalously large amplitudes, which require a ∼12.5% reduction in seismic velocity across the interface. This large velocity drop can not be explained by a thermal cooling model but indicates 1.5%–2% localized melt in the oceanic asthenosphere. The depths of the two discontinuities show large variations, indicating that the asthenosphere is far from a homogeneous layer but likely associated with strong and heterogeneous small‐scale convection in the oceanic mantle. The average depths of the two boundaries are largely constant across different age bands. In contrast to the half‐space cooling model, this observation supports the existence of a constant‐thickness plate in oceanic regions with a complex and heterogeneous origin.