The solid inner core grows through crystallization of the liquid metallic outer core, releasing latent heat and light elements that drive the Earth's geodynamo. This study investigates temporal changes in the liquid outer core by analyzing travel times of core-penetrating SKS waves from paired large earthquakes. While most measurements show no outer core change, SKS waves propagating through the upper half of the outer core in the low-latitude Pacific were about one second faster at the time of the second earthquake (20 years later). This suggests a 2-3% density deficit, possibly due to high-concentration light elements in localized transient flows with speeds around 40 km/year.

Ying Zhou