Figure 2 from Wang and Tkalčić [2021]
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Geophysical Research Letters

Earth’s inner core anisotropy contains essential information of deep Earth’s structure and dynamics. Extensive studies have investigated the inner core anisotropy based on observations from compressional waves. However, due to the difficulty of the observing inner-core shear wave (J-wave), the shear wave anisotropy in the inner core remains elusive.

By stacking a large number of earthquake coda-correlation wavefields, Wang and Tkalčić [2021] are able to have stable I2-J measurements along planes with different angles to the Earth’s rotation axis. This study not only conclusively demonstrates that the J-wave can be observed, but also provides the first attempt to systematically study the bulk shear wave anisotropy of the inner core.

Their result shows a minimum bound of shear-wave anisotropy strength to approximately 0.8 percent, which inner-core shear waves travel faster for at least ~5 s in directions oblique to the Earth’s rotation axis than directions parallel to the equatorial plane. This observation further rules out bcc001 iron structure in the inner core. 

Wang, S., & Tkalčić, H. [2021]. Shear-wave anisotropy in the Earth’s inner core. Geophysical Research Letters, 48, e2021GL094784. https://doi.org/10.1029/2021GL094784

―Daoyuan Sun, Editor, Geophysical Research Letters