Comment on “An Evaluation of the Timing Accuracy of Global and Regional Seismic Stations and Networks” by Yang et al. (2021)

Abstract

Abstract Yang et al. (2021; hereafter, YSR21) reported widespread clock errors at global and regional stations by measuring travel-time residuals of repeating earthquakes (doublets) after the corrections for relative event parameters and claimed that the reported temporal changes in the inner core boundary (ICB) in Wen (2006; hereafter, Wen06) were a “misidentification” after correcting the clock errors and instrumental changes of the seismic stations. Here, we examine their claims with a focus on the reported “problematic” stations AAK and OBN and the two associated doublets they emphasized in the inner core study. Forward calculations show that: (1) YSR21’s doublet relocation results contain large errors, generating large travel-time residuals in the individual stations and in the depth-sensitive phases, (2) YSR21’s selection of “problematic stations” is not supported by the travel-time residuals predicted from their relocation results, and (3) YSR21’s reported clock errors of the two stations are not reproducible based on their relocation results. Our reanalysis of the doublet data, which yields a much better fit to the observations, indicates no clock error at OBN and no justifiable claim of a clock error at AAK. Accordingly, YSR21’s manual shifts by clock errors to the OBN and AAK observations of Wen06 are not justified, and their resultant claim of “misidentification” of the temporal ICB change in Wen06 is unfounded. We further show that the effect of instrument changes can be simply corrected by the deconvolution of instrument responses, and the temporal change of PKiKP at station ARU in Wen06 is evident after the correction. Our study confirms the reported ICB temporal change in Wen06. The inaccurate relocation and unreproducible results in YSR21 raise questions on their claim of prevailing clock errors in the global stations and the validity of the past inner core studies by the two leading authors.