Probing high-resolution inner core structure using earthquake coda interferometry with USArray

Abstract:

Increasing complexity of Earth’s inner core has been revealed in recent decades as the global distribution of seismic stations has improved. The uneven distribution of earthquakes, however, still causes a biased geographical sampling of the inner core. A recent development in seismic interferometry, which allows for the retrieval of core-sensitive body waves propagating between two receivers, potentially significantly improves ray-path coverage across the inner core. In this study, we apply such earthquake coda interferometry to 1,846 USArray stations deployed across the US from 2004 through 2013. Clear PKIKP² and PKIIKP² arrivals, which are near-podal inner-core phases that bounce off the far side of the Earth’s surface, are observed across the entire array. Spatial analysis of the differential travel times between the two phases reveals a strong N-S trending anomaly across the middle of the continent. This finding implies the existence of strong short-wavelength structural variability that reflects an imperfect symmetry in the hemispheric structure of the inner core.