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Inner core backtracking by seismic waveform change reversals
Matching seismic waveforms show that the inner core of Earth gradually super-rotated from 2003 to 2008, and then more slowly sub-rotated from 2008 to 2023 back through the same path.
The dominant interpretation of steady super-rotation over decades has been derived from temporal changes of up to tenths of a second in the difference in arrival times between PKIKP and later core phases in repeated earthquakes. Our approach manually measures the difference in origin time based on the alignment of global records from other IRIS stations, assuming a common location for each event pair. Estimating the slight differences in location between the earthquakes in each repeating pair, which we did not do, has been documented to be important in measuring the temporal change in the time separation of core phases (ddt) 32, 33.
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