Seismically determined elastic parameters for Earth's outer core.
Seismically determined elastic parameters for Earth's outer core.
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DOI：
10.1126/sciadv.aar2538
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发表时间：
2018-06
期刊：
影响因子：
13.6
通讯作者：
Lekić V
中科院分区：
文献类型：
--
作者：
Irving JCE;Cottaar S;Lekić V
从简正波数据推断了外核液态铁合金的地震性质和状态方程参数。液态铁合金外核的湍流对流产生了地球的磁场，并向地幔提供热量。铁合金的确切成分从根本上与对流的动力过程有关，并且可能受到其地震特性的限制。使用体波和正常模式确定的地震模型之间的差异表明，这些属性尚未完全达成一致。此外，在高压和高温下实验测量液态铁合金的状态方程（EoS）参数的技术挑战进一步使成分推断复杂化。我们直接推断EoS参数描述地球的外核正常模式的中心频率观测，并提出了由此产生的弹性参数的外核（EPOC）地震模型。与其他地震模型不同，我们的模型只需要三个参数，并保证物理上真实的行为，随着压力的增加，混合均匀的材料沿着等熵线，符合外核的条件。我们表明，EPOC预测可用的正常模式频率比初步参考地球模型（PREM），同时也更符合体波衍生模型，消除了长期存在的差异。外核顶部的速度较低，随深度的增加，在EPOC比在PREM更陡峭，而密度在EPOC是高于在整个外核的PREM。更陡的轮廓和更高的密度意味着外芯包括比PREM推断的更轻但更可压缩的合金。此外，EPOC更陡的速度梯度比以前的一维全球模型更好地解释了差分SmKS体波旅行时间，而不需要在外核顶部有一个非常缓慢的~90- 450公里厚的层。
Seismic properties and equation-of-state parameters of the liquid iron alloy in the outer core are inferred from normal mode data. Turbulent convection of the liquid iron alloy outer core generates Earth’s magnetic field and supplies heat to the mantle. The exact composition of the iron alloy is fundamentally linked to the processes powering the convection and can be constrained by its seismic properties. Discrepancies between seismic models determined using body waves and normal modes show that these properties are not yet fully agreed upon. In addition, technical challenges in experimentally measuring the equation-of-state (EoS) parameters of liquid iron alloys at high pressures and temperatures further complicate compositional inferences. We directly infer EoS parameters describing Earth’s outer core from normal mode center frequency observations and present the resulting Elastic Parameters of the Outer Core (EPOC) seismic model. Unlike alternative seismic models, ours requires only three parameters and guarantees physically realistic behavior with increasing pressure for a well-mixed homogeneous material along an isentrope, consistent with the outer core’s condition. We show that EPOC predicts available normal mode frequencies better than the Preliminary Reference Earth Model (PREM) while also being more consistent with body wave–derived models, eliminating a long-standing discrepancy. The velocity at the top of the outer core is lower, and increases with depth more steeply, in EPOC than in PREM, while the density in EPOC is higher than that in PREM across the outer core. The steeper profiles and higher density imply that the outer core comprises a lighter but more compressible alloy than that inferred for PREM. Furthermore, EPOC’s steeper velocity gradient explains differential SmKS body wave travel times better than previous one-dimensional global models, without requiring an anomalously slow ~90- to 450-km-thick layer at the top of the outer core.
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BIRCH, F
通讯作者：
BIRCH, F
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