11:15 〜 11:30
[S18-1-04] Comparison of frequency dependent reflection coefficients at the inner core boundary beneath the central America and western Pacific
Reflection coefficients (RC) at the inner core boundary (ICB) inferred from PKiKP/PcP amplitude ratios have been used for the inferrence of the status at the inner core surface. Recently, Tanaka and Tkalcic (2015) examined the RC's freqeuncy variations and suggested a topographic variation at the ICB beneath western Pacific. It was suggested that the frequency characteristics of the RC at the ICB can be qualitatively explained by the ICB topography with height and wavelength of about 1 km. Here we additionally examine the RCs at the ICB benath the central America observed by USArray, a dense seismic network in the USA.
Although the frequency characteristics of the RCs at the ICB beneath the western Pacific is complex, the RCs tend to be large at frequencies larger than 2 Hz and small at frequencues less than 2 Hz. To the contrary, some of the RCs beneath the central America are large at frequencies less than 2 Hz and small at frequencies greater than 2 Hz.
This difference suggests the existence of a large-scale regional variation at the inner core surface conditions. This variation is more significant than what we anticipated based only on the results focusing on the region beneath the western Pacific.
Although the frequency characteristics of the RCs at the ICB beneath the western Pacific is complex, the RCs tend to be large at frequencies larger than 2 Hz and small at frequencues less than 2 Hz. To the contrary, some of the RCs beneath the central America are large at frequencies less than 2 Hz and small at frequencies greater than 2 Hz.
This difference suggests the existence of a large-scale regional variation at the inner core surface conditions. This variation is more significant than what we anticipated based only on the results focusing on the region beneath the western Pacific.