On the Inner‐Core Differential‐Rotation (Un)Resolvability From Earthquake Doublets: The Traps of Data Selection.

The phenomenon of differential rotation of the Earth's inner core relative to the mantle is a subject of interest in geodynamo modeling that has been validated by seismological observations, mainly via the earthquake‐doublets method. Although recent studies converge on the time‐varying differential rotation of the inner core relative to the mantle, favoring a decadal variation, the inferred models significantly differ. Here, considering the data selection, the observed data structure, and the subjective model parameterizations, which we avoid by employing a Bayesian transdimensional approach, we show that the recent best‐fit model by Yang and Song (2023, https://doi.org/10.1038/s41561‐022‐01112‐z) featuring the 70‐year decadal variation is not obtained when all available data are considered. Namely, including only a small number of discarded earthquake doublets (<10%) changes the period of the inner‐core differential rotation fluctuation to 20–30 years. More earthquake‐doublet data are required to address the non‐uniqueness of the inversion problem. Plain Language Summary: Seismologists use repetitive earthquakes (earthquake doublets) and their waves' fixed paths through the Earth's inner core to measure the rate of the inner core spinning relative to the mantle. A recent study in Nature Geoscience (Yang & Song, 2023, https://doi.org/10.1038/s41561‐022‐01112‐z) based on 31 selected earthquake doublets derived a 70‐year decadal cycle of the inner core spinning rate relative to the mantle. We show that the made selective choices change the data structure and possibly miss the inner core 20–30 year periodicity in the earlier times. Key Points: We revisit the problem of the differential rotation of the inner core relative to the mantle from the existing earthquake‐doublet dataThe data selection, the data structure, and the data‐model relationship are critical in inverting the inner core differential rotationConsequently, the model derived by Yang and Song (2023, https://doi.org/10.1038/s41561‐022‐01112‐z) is not a unique model of the inner core's differential rotation [ABSTRACT FROM AUTHOR]