Abstract
Short‐period PKP(DF) waves (which travel through the inner core) from polar paths (nearly NS) were observed to have small amplitudes and complex waveforms but the cause has been a mystery. Here we examine both short‐period and broadband PKP record sections from a single earthquake in South Sandwich Islands (SSI). The data from polar paths show clear evidence for an inner core triplication. Our waveform modeling suggests a 250‐km thick isotropic upper inner core (UIC) overlying an anisotropic lower inner core (LIC) with about 8% anisotropy. The synthetics match the observed waveforms and amplitudes well with a normal value of inner core attenuation. We propose that such a UIC/LIC transition zone structure may be the cause of anomalous DF waveforms along polar paths. The inferred level of anisotropy in the LIC, 2–3 times previous estimates, has important implications for understanding physical properties of the inner core and sources of inner core anisotropy.
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