A new global PKP data set to study Earth's core and deep mantle

We present an extension of the previously developed algorithm for Simulated Annealing Waveform Inversion of Body waves (SAWIB) to resolve the interference between direct PKP seismic phases and their corresponding depth phases (pPKP and sPKP) which occurs for shallow earthquakes. This allows us to process shallow earthquakes previously discarded by the analysts, and therefore improve spatial sampling of the deep Earth by PKP phases. The SAWIB algorithm is applied to available waveform data to determine PKP travel times and amplitudes. The new data set of PKP travel times and amplitudes is significantly larger than previous ones. PKP (bc-df) differential travel time residuals display a hemispherical pattern in the inner core when plotted as a function of the angle between PKPdf propagation direction in the inner core and Earth's rotation axis. Most anomalous differential travel times are along polar paths in the quasi-western hemisphere (180 °W-40 °E), corresponding to earthquakes in the South Sandwich Islands recorded at northern seismic stations. PKP (ab-df) differential travel times display a larger scatter, which we attribute to heterogeneities at the base of the mantle. Relative amplitudes and t^* attenuation parameters are analyzed in terms of inner core attenuation. The inner core attenuation decreases with increasing depth. In the upper inner core, in the depth range 150-220 km, an hemispherical pattern appears with a quasi-western hemisphere (40 °E-180 °E) faster and more attenuating than the rest of the inner core. When stacking PKP waveforms deconvolved by their source time function, we do not find evidence of a global innermost inner core velocity discontinuity. However we cannot rule out the existence of strong local heterogeneities or radial anisotropy variations from our data.