Weak upper-mantle base revealed by postseismic deformation of a deep earthquake
Weak upper-mantle base revealed by postseismic deformation of a deep earthquake
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DOI：
10.1038/s41586-022-05689-8
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发表时间：
2023-02
期刊：
影响因子：
64.8
通讯作者：
Sunyoung Park;J. Avouac;Z. Zhan;A. Gualandi
中科院分区：
文献类型：
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作者：
Sunyoung Park;J. Avouac;Z. Zhan;A. Gualandi
地幔粘度在地球内部动力学和热历史中起着关键作用。然而，粘度结构的地球物理推论显示出很大的可变性，具体取决于所使用的可观测值的类型或施加的假设，-。在这里，我们利用上地幔底部附近的深部（约 560 km）地震后的震后变形来研究地幔粘度结构。我们将独立分量分析应用于大地测量时间序列，成功检测并提取了 2018 年斐济 8.2 级地震引起的震后变形。为了寻找可以解释检测到的信号的粘度结构，我们使用一系列粘度结构进行正向粘弹性松弛建模。我们发现，我们的观测需要在地幔过渡带底部有一个相对较薄（约100公里）、低粘度（1017至1018帕秒）的层。这样的弱带可以解释在许多俯冲带中观察到的板片扁平化和孤儿现象，否则在整个地幔对流体系中很难解释。低粘度层可能是由后尖晶石转变、弱CaSiO3钙钛矿、高含水量或脱水熔融引起的超塑性产生的。
Mantle viscosity plays a key role in the Earth’s internal dynamics and thermal history. Geophysical inferences of the viscosity structure, however, have shown large variability depending on the types of observables used or the assumptions imposed, –. Here, we study the mantle viscosity structure by using the postseismic deformation following a deep (approximately 560 km) earthquake located near the bottom of the upper mantle. We apply independent component analysis to geodetic time series to successfully detect and extract the postseismic deformation induced by the moment magnitude 8.2, 2018 Fiji earthquake. To search for the viscosity structure that can explain the detected signal, we perform forward viscoelastic relaxation modelling,with a range of viscosity structures. We find that our observation requires a relatively thin (approximately 100 km), low-viscosity (1017to 1018Pa s) layer at the bottom of the mantle transition zone. Such a weak zone could explain the slab flattening and orphaning observed in numerous subduction zones, which are otherwise challenging to explain in the whole mantle convection regime. The low-viscosity layer may result from superplasticity induced by the postspinel transition, weak CaSiO3perovskite, high water content or dehydration melting.