Seismic Velocity and Attenuation Structures of the Earth’s Inner Core Boundary beneath the Northern Pacific from Automatic Waveform Modeling

Abstract:

Seismological studies have suggested complex structures of the inner-core boundary (ICB) region, from a large-scale hemispherical structure to more local heterogeneities. To improve resolution of the ICB structure, we have developed an automatic waveform modeling method, which takes advantage of the full triplicated PKP waveforms at distances from 125 to 160 degrees to allows us to model P wave velocity and attenuation structures of the lowermost 200 km of the outer core and the uppermost 500 km of the inner core simultaneously. In this study, we use earthquakes in the Southeast Asia recorded at dense stations in the North and Central Americas (the USArray and permanent stations). The data provide dense samples of the inner core (at distances of less than 120 degrees to over 160 degrees) beneath the Northern-Northwestern Pacific across the boundary (180° in longitude) between the eastern and western hemispheres. We focus our attenuation on the PKIKP, PKiKP, and PKP(BC) phases, which have very similar ray paths through the mantle, thus most sensitive to the ICB structure. Our goal is to resolve the lateral and depth variations of the fine structures of the velocity and attenuation near the ICB and the transition of the structures across the hemispheric boundary.