Constraining the short scale core–mantle boundary topography beneath Kenai Peninsula (Alaska) with amplitudes of core-reflected PcP wave

Previous analysis of short period PcP with seismic array reported rapid variation of PcP amplitude and suggested small scale variation of core–mantle boundary (CMB) topography beneath Kenai Peninsula (Alaska). In order to constrain the length scale (L) and topographic height variation (H) in the region, we quantitatively compute synthetic PcP seismograms using the seismic representation theorem for a core–mantle boundary (CMB) with topography bump (H > 0) or depression (H < 0). We model PcP amplitudes for L in the range of 60–500 km, H in the range of −6 km (depression) to 5 km (bump). It is observed that CMB depressions do produce amplification and CMB bumps generate de-amplification for short period PcP amplitudes. After computation for various combinations of L and H, amplification in the range of 2–4.5 is observed in the above mentioned parameter ranges. The topography model of a CMB depression (H = −6 km, L = 6°) predicts 1 Hz PcP amplification consistent with observed PcP amplitude variation beneath Kenai Peninsula. However, PcP amplitude can also be affected by heterogeneities in the crust and mantle, the estimated topography could be less pronounced.