New Seismic Evidence for Localized Temporal Change of the Earth’s Inner Core Boundary

Abstract:

We study temporal change of Earth’s inner core surface using earthquake doublets occurring between 1993 and 2013 in South Sandwich Islands. Inner core refracted (PKPdf) and reflected (PKiKP) compressional waves recorded at some seismic stations from several doublets show clear evidence for spatial migration of temporal change of the Earth’s inner core boundary beneath Africa. While PKiKP phases arrive earlier in 2003 as compared to 1993 indicating enlargement of the inner core surface beneath Africa (Wen, 2006), no discernible delays of the PKiKP phases are observed between the doublets in the later periods (with an exception for ARU station, where both the PKiKP and PKPdf arrived about 0.07 s later in the subsequent event for one doublet). On the other hand, the PKPdf phases are observed to arrive about 0.14 s later at some stations in the subsequent event of the doublets in the later time periods. Taking into consideration of the observations of Wen (2006), the Earth’s inner core radius has experienced different and rapid changes beneath middle Africa in the last 20 years. For some regions, it was enlarged in the early time periods and then remained unchanged later. For other regions, it changed little at first, then decreased, and became little changed afterward. Seismic evidence indicates that change of the inner core radius is episodic and migrates rapidly from one region to another.