Velocity structure near the inner core boundary from waveform modeling

The data consist of long period and short period record sections. Deep events beneath Indonesia were used; these sampled the ICB structure beneath the North Pacific. The Cagniard-de-Hoop technique was used to generate the synthetics, which allowed considerable flexibility in forward modeling these individual PKP phases. The preferred model was developed from modifications of the Preliminary Reference Earth Model (PREM). It contains a relatively low velocity gradient above the ICB, a sharp jump at the ICB of about 0.78 km/s, and a relatively large gradient underneath. Further modification of PREM in the fluid core was required to explain the long-period observations associated with PKP waveforms. Modeling results suggest a low-velocity gradient at the bottom (roughly 400 km) of the fluid core. A low Q zone at the top of the inner core is required to fit the relative amplitudes of PKIKP phases similar to earlier studies. This model indicates possible inhomogeneity above the ICB, as suggested by other authors. -from Authors