Temporal Changes of the Inner Core From Globally Distributed Repeating Earthquakes
Temporal Changes of the Inner Core From Globally Distributed Repeating Earthquakes
复制标题
DOI：
10.1029/2019jb018652
复制
发表时间：
2020-03
期刊：
影响因子：
--
通讯作者：
Yi Yang;Xiaodong Song
中科院分区：
文献类型：
--
作者：
Yi Yang;Xiaodong Song
重复地震产生的地震波穿越内核的时间依赖性旅行时间为内核的差异运动提供了令人信服的证据。在这里，我们进行了一个系统的搜索，在过去的30年中的强重复地震，以检查全球模式的时间变化的内核。我们对重复地震的质量进行了广泛的分析，并量化了除内核时间变化外所有可能来源的走时测量误差（σic）。我们设置2σic作为判断内核时间变化是否显著的阈值。在内核的大部分地区没有发现明显的时间变化，但在北方半球的四个地区（北大西洋，东北太平洋，俄罗斯远东/鄂霍次克海和欧洲/北非）观察到大的时间变化（超过3σic），除了在以前的研究中众所周知的中美洲异常。大多数大的时间变化都与超过6年的时间间隔和较小的距离有关，这可能是由于旋转移动了内核横向变化的顶部300公里。一条新的路径对北大西洋进行了采样，结果表明内核的横向速度梯度小而陡，内核向东旋转缓慢，为0.051°/年。小尺度的横向变化可以调和内核旋转速率估计值的巨大差异。我们还观察到神秘的非常大的突然的时间变化（短至44天），这可能与苏门答腊大地震造成的扰动。
Time‐dependent travel times of seismic waves traversing the inner core from repeating earthquakes provided compelling evidence for an inner core differential motion. Here we conducted a systematic search for strong repeating earthquakes in the last three decades to examine the global pattern of temporal changes of the inner core. We performed extensive analyses on the quality of the repeating earthquakes and quantified the error (σic) of travel time measurements from all possible sources except the inner core temporal changes. We set 2σic as a threshold for judging whether an inner core temporal change is significant. No significant temporal changes were found in most parts of the inner core, but large temporal changes (over 3σic) were observed beneath four regions in Northern Hemisphere (North Atlantic, Northeast Pacific, Russian Far East/Sea of Okhotsk, and Europe/North Africa), besides the well‐known Central America anomaly in previous studies. Most large temporal changes were associated with time lapses of over 6 years and smaller distances, possibly resulting from the rotation shifting the laterally varying top 300 km of the inner core. A new path sampling North Atlantic suggested a small‐scale and steep lateral velocity gradient of the inner core and a slow eastward inner core rotation of 0.051°/year. Small‐scale lateral variations may reconcile large difference in the estimates of the inner core rotation rate. We also observed enigmatic very large abrupt temporal changes (as short as 44 days), which may be related to disturbances caused by the great Sumatra earthquakes.