Small-scale changes of core-mantle boundary reflectivity studied using core reflected PcP

Short-period PcP phases from earthquakes in the western Aleutians recorded at the Canadian Yellowknife array (YKA) sample the core-mantle boundary (CMB) beneath the Alaskan Kenai peninsula and the Cook inlet. The PcP-to-P amplitude ratios for these events show large variability with some amplitude ratios more than an order of magnitude larger than predicted by radial Earth models such as IASP91 or PREM. The amplitude ratios vary laterally with PcP core-mantle boundary reflection points showing a ∼1° region with exceptionally large amplitude ratios. It is likely that the variability in relative PcP amplitudes is due in large part to CMB topography. Other mechanisms, such as radiation pattern; mantle attenuation; focusing and defocusing; and core-mantle boundary velocity and density perturbations could cause variations on scale-lengths of less than a degree as found in this study, but are unable to produce variations as large as those we observe.