Temporal Change of the Earth’s Inner Core Boundary beneath North Pacific and Eurasia

Abstract:

It has been shown that, based on the analysis of changes of seismic compressional waves that are refracted (PKIKP) and reflected (PKiKP) off the inner core, the Earth’s inner core surface exhibits temporal change beneath Africa, but no discernible change beneath South America. The temporal change of inner core surface occurs in localized regions, and is episodic, rapidly migrating and alternately enlarged and shrunk in a time scale of years. To better understand the nature of temporal change of inner core boundary, we expand the study of temporal change to the inner core surface beneath North Pacific and Eurasia, using doublets occurring in Kuril Islands and Banda Sea between 1990 and 2015. The doublets are within 1 km of separation of depth and horizontal distance. Seismograms recorded at stations in America and Africa for these doublets show clear PKIKP and PKiKP phases sampling the inner core surface beneath North Pacific and Eurasia. No discernible temporal change of PKiKP or PKIKP is observed in those seismic observations. Superimposed PKiKP-PKIKP waveforms of the doublets also show excellent agreements in both absolute arrival time and differential travel time of the two phases. These observations indicate that the inner core surface beneath Eurasia and North Pacific does not experience any detectable temporal change. In this presentation, we will further summarize the results of temporal change of inner core surface reported so far.