PKP precursors: Implications for global scatterers

Precursors to the core phase PKP are generated by scattering of seismic energy from heterogeneities in the mantle. Here we examine a large global data set of PKP precursors in individual seismograms and array data, to better understand scattering locations. The precursor amplitudes from individual seismograms are analyzed with respect to the inner core phase PKIKP and mantle phase PP. We find and correct for a hemispherical asymmetry in the precursor/PKIKP amplitudes, resulting from inner core structure. Using ray tracing, we locate scatterers in our array data and use these to infer scattering locations in the individual data. The scattering strength displays regional variation; however, we find no relationship with long-scale core-mantle boundary velocity structure. Scattering is observed in all regions of data coverage, as are paths with no precursors. This indicates that scattering occurs from various small-scale heterogeneities, including but not limited to ultralow velocity zones or partial melt, and slabs.