Earth's inner core rotation, 1971 to 1974, illuminated by inner-core scattered waves
Earth's inner core rotation, 1971 to 1974, illuminated by inner-core scattered waves
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DOI：
10.1016/j.epsl.2021.117214
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发表时间：
2022
影响因子：
5.3
通讯作者：
W. Wang;J. Vidale
中科院分区：
文献类型：
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作者：
W. Wang;J. Vidale
固体内核位于地球中心，在重力作用下保持在液体外核内。它是地球内部最具活力的部分之一。自从最初声称内核相对于地幔有差异旋转以来，二十多年来它的存在和速度一直受到挑战。在这里，我们重新检查了俄罗斯新地岛两次百万吨级核试验的地震记录，这两次试验与美国蒙大拿州的大孔径地震台阵相隔三年。使用改进的对映地震静态时间校正，我们改进了 PKiKP 波束形成及其内核散射尾波的分辨率。然后，我们通过移动时间窗口互相关测量两个事件的内核散射波之间的轻微时间偏移（十分之几秒）。应用一种新颖的反投影方法，我们根据 PKiKP 尾波的慢度和流逝时间来定位在 PKiKP 尾波中散射能量的内核区域。然后，我们测量内核旋转，首先假设与地球旋转轴对齐，然后通过网格搜索找到最合适的差分旋转轴。这里的旋转速率在整个内核散射波列的许多散射到达中是稳健且一致的。我们的结果表明，从 1971 年到 1974 年，与地球自转轴对齐的内核超自转速率为 0.10°/年，或者当自转轴与地球自转轴倾斜约 8° 时，内核超自转速率为 0.125°/年，这与观测到的时间变化稍好一些。
The solid inner core is at the center of the Earth, gravitationally held within the liquid outer core. It is one of the most dynamic parts of Earth's interior. Since the initial claim of inner core differential rotation relative to the mantle, its existence and rate have been challenged for over two decades. Here, we re-examine the seismic records of two megaton nuclear tests in Novaya Zemlya, Russia, three years apart, from the Large Aperture Seismic Array in Montana, USA. Using an improved static time correction from an antipodal earthquake, we refine the resolution of the beamforming of PKiKP and its inner-core scattered coda. Then, we measure the slight time shifts (tenths of seconds) between the inner-core-scattered waves from the two events with moving-time-window cross-correlation. Applying a novel back-projection method, we locate the inner-core regions that scatter the energy within the PKiKP coda based on its slowness and the lapse time. We then measure the inner core rotation, first assuming alignment with Earth's rotation axis, then finding the best-fitting differential rotation axis with a grid search. The rotation rates here are robust and consistent across the many scattered arrivals throughout the inner core scattering wavetrain. Our results indicate 0.10°/year inner core super-rotation rate from 1971 to 1974 aligned with Earth's rotation axis, or 0.125°/year with the rotation axis tilting about 8° from the Earth's rotation axis, which yields a marginally better fit to the observed time shifts.