High?Frequency (6 Hz) <i>PKPab</i> Precursors and Their Sensitivity to Deep Earth Heterogeneity

We present observations on a new precursory phase of seismic waves scattered in the deep Earth. This arrives prior to PKPab wave at epicentral distances larger than 155°, and we call it precursor. show that presence precursor is necessary consequence scattering D?, which commonly accepted cause PKPdf smaller 145°. propagate through inner core should arrive before but those, are strongly attenuated frequencies between 4 Hz 8 used here, making earliest teleseismic signal 155°. Calculated sensitivity kernel shows this mostly sensitive along closest PKPbc path source receiver. It can thus help constrain lateral distribution heterogeneity D?.