ON PECULIARITIES OF PKiKP AND PcP WAVES UNDER EAST ASIA AND THE WESTERN PACIFIC OCEAN

Abstract

We collected 217 seismograms with precritical reflected PKiKP and PcP waves, and obtained representative data on their travel times and amplitudes. These waves probe the boundary between inner and outer Earthʼs core in 4 areas beneath East Asia – Far East, Kamchatka Peninsula, Japanese Islands and Bering Sea – with spatial distribution by longitude from 120°E to 175°W. All differential travel time residuals relative to the three-dimensional LLNL-3D model in the mantle and crust and the ak135 model in the core have negative values from -2.0 s to -0.6 s, indicating a large-scale change in the inner core topography. The within-group variations in the differential residuals can be explained by small-scale changes in topography. The measured PKiKP wave amplitudes in all sounding regions have lower values than in the standard ak135 model. These features, except for the area below the Bering Sea, correspond to sinusoidal changes in the relief with a height of less than 1 km, or an alternation of hills with a height of 2 km and linear sections. The amplitude ratios of PKiKP and PcP waves for all groups of data, except for stations in Alaska, correspond in the first approximation to a density jump of 0.6 g/cm³, as in the ak135 model. Anomalously low PcP amplitudes of waves reflected from the outer core near coordinates 60°N and 180°E are revealed.