On waveform correlation measurement uncertainty with implications for temporal changes in inner core seismic waves

Abstract

We address the uncertainty related to cross-correlation waveform time shift measurements, particularly related to temporal changes in inner core seismic waves. Details of the cross-correlation measurement, including data processing, window length, pick time, sampling rate and the algorithm itself, all affect the calculated time shift. By systematically varying measurement parameters for a set of earthquake doublets we find time shift uncertainties of 0.01 s and 0.02 s for differential times and double differential times respectively. The uncertainty is of a similar magnitude to reported double differential times of PKIKP and PKiKP inner core phases. Accounting for measurement uncertainty results in 80% of values published in a recent study being below the measurement resolution (Yang and Song 2020a). While the temporal variations in inner core phases is not in dispute, properly accounting for uncertainties is needed for robust data interpretation. A re-assessment for the origin of inner core temporal changes is therefore warranted and future studies should account for measurement uncertainty.