Revisiting Seismological Discoveries of the Inner Core

Abstract Seismology has been used as a tool for understanding the current physical properties of the interior of the Earth and its dynamic evolution with remarkable success over the last century. Much of this progress is due to the ever-expanding set of high-quality quantitative observations of teleseismic waveforms recorded at seismographic stations worldwide. In this work, we revisit historical seismological studies that helped first identify a core distinct in physical properties from the overlying mantle, followed by the detection of an inner core that was eventually verified to be solid based on normal-mode eigenperiods. Along with a brief overview of past studies of the Earth’s inner core, we examine the reproducibility of these results and discuss how historical data compare against modern observations. After accounting for past normal-mode misidentifications, we confirm that introducing a solid inner core is required to afford significant improvements in fits to both radial modes and core-sensitive spheroidal overtones. Strong shear dissipation in the inner core of the radial reference Earth model, REM1D (Qμ=89.54), fits the reference datasets of both normal-mode eigenperiods and quality factors accounting for physical dispersion. Because a liquid region would only have bulk dissipation, a narrow range of low Qμ values that are preferred by the reference datasets affords additional evidence of a solid inner core. In addition, we find that there is little systematic bias in the timing accuracy of historical data, although large variances exist. Investigations into the temperature, composition, and evolution of the inner core, as well as the reproducibility of past studies, can benefit from the reconciliation of historical and modern seismological datasets.