Equatorial anisotropy of Earth’s inner inner core from autocorrelation of earthquake coda
Equatorial anisotropy of Earth’s inner inner core from autocorrelation of earthquake coda
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来自地震尾波自相关的地球内核内部赤道各向异性
DOI：
10.1038/ngeo2354
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发表时间：
--
影响因子：
18.3
通讯作者：
Xia Han.H
中科院分区：
文献类型：
--
作者：
Wang Tao;Song Xiaodong;Xia Han.H
地球的固体内核表现出强烈的各向异性，由于铁晶体的优先排列，波速取决于传播方向。各向异性结构的横向变化和深度变化，为测量内核旋转提供了标志，并为内核的形成和动力学提供了线索。以前的内核各向异性模型都假设对称轴平行于地球自转轴的圆柱各向异性。内核的内部部分具有不同形式的各向异性，但关于其存在和特征存在相当大的不确定性。本文分析了1992年至2012年全球宽带地震台阵测量的地震尾波的自相关性，发现两种类型的岩心穿透波的差走时在低纬度地区的变化最大可达10 s。我们的研究结果是一致的地震各向异性在最里面的内核，有一个快轴附近的赤道平面通过中美洲和东南亚，在南北对齐的各向异性在外部内核。各向异性的不同取向和形式可能代表了内核演化的转变。
The Earth’s solid inner core exhibits strong anisotropy,,,,, with wave velocity dependent on the direction of propagation due to the preferential alignment of iron crystals. Variations in the anisotropic structure, laterally and with depth,,,,, provide markers for measuring inner-core rotation and offer clues into the formation and dynamics of the inner core,. Previous anisotropy models of the inner core have assumed a cylindrical anisotropy in which the symmetry axis is parallel to the Earth’s spin axis. An inner part of the inner core with a distinct form of anisotropy has been suggested, but there is considerable uncertainty regarding its existence and characteristics,,,. Here we analyse the autocorrelation of earthquake coda measured by global broadband seismic arrays between 1992 and 2012, and find that the differential travel times of two types of core-penetrating waves vary at low latitudes by up to 10 s. Our findings are consistent with seismic anisotropy in the innermost inner core that has a fast axis near the equatorial plane through Central America and Southeast Asia, in contrast to the north–south alignment of anisotropy in the outer inner core. The different orientations and forms of anisotropy may represent a shift in the evolution of the inner core.