Global mantle heterogeneity structure from scattered PKPPKP

To fully understand the dynamics and evolution of our planet we need information from the interior of our planet across a wide range of scale lengths. Seismic methods are limited in their resolution by the sensitivity of the seismic wavelengths. The smallest scalelengths of heterogeneity can be resolved using the scattered seismic wavefield above 1 Hz. Here we aim to image the global small-scale heterogeneity structure from crust to the core-mantle boundary using scattered energy related to P${}^{\prime }$P${}^{\prime }$ (P${}^{\prime }$•P${}^{\prime }$) in a novel approach using stacking of high-frequency (0.7 to 2.1 Hz) teleseismic seismograms from single stations. We stack records sensitive to P${}^{\prime }$•P${}^{\prime }$ energy in 10°x 10° bins across the globe and achieve good coverage of the mantle and crust across more than 60% of the surface area. The dataset especially samples the southern hemisphere and highlights lateral and radial changes in the small-scale (<10 km) heterogeneity structure. Radially, we find the strongest scattering in the lithosphere and upper mantle where most sampled bins show evidence for small-scale heterogeneity in oceanic and continental regions. Similarly, the lowermost mantle in the D″ region shows evidence for widespread small-scale heterogeneity but with distinct lateral changes. Depths around the 660 km discontinuity show evidence for strong heterogeneity with less small-scale structure around mid-oceanic ridges likely related to increased mixing. On the other hand, the mid-mantle (∼1000 km to 2100 km) shows little evidence for scattering, either through a lack of heterogeneity, a lack of impedance contrast between the heterogeneities and the ambient mantle, or heterogeneity scalelengths making them invisible to our scattering probe. Lowermost mantle scattering can pre-dominantly be found near the edges of the Large-Low Velocity Provinces and in regions where subducted slabs reach the core-mantle boundary, potentially indicating a link between scattering heterogeneities and subducted oceanic basalt.