Examination of systematic mislocation of South Sandwich Islands earthquakes using station pairs: Implications for inner core rotation

摘要

One of the most robust observations for the inner core rotation is that the differential PKP BC-DF traveltimes from South Sandwich Islands (SSI) earthquakes to College, Alaska (and some other stations in Alaska), have increased systematically over the past 50 years. The time shift in the differential time residuals is some 0.3 s over 30 years. This temporal change is thought to result from a shift of the inner core structure from a superrotation of the inner core. However, the observation has been hotly debated and has been suggested to be an artifact of systematic earthquake mislocation. Here we examine this issue using three mutually independent approaches, with a goal to quantify the amount of the systematic mislocation, if any. All three approaches involve differencing data between north stations at a similar azimuth as the SSI-Alaska azimuth and south stations at nearly the opposite azimuth. Mislocation along this azimuth has greatest impact on the PKP differential times.