  Scattering of seismic waves can reveal subsurface structures but usually in a
piecemeal way focused on specific target areas. We used a manifold learning
algorithm called "the Sequencer" to simultaneously analyze thousands of
seismograms of waves diffracting along the core-mantle boundary and obtain a
panoptic view of scattering across the Pacific region. In nearly half of the
diffracting waveforms, we detected seismic waves scattered by three-dimensional
structures near the core-mantle boundary. The prevalence of these scattered
arrivals shows that the region hosts pervasive lateral heterogeneity. Our
analysis revealed loud signals due to a plume root beneath Hawaii and a
previously unrecognized ultralow-velocity zone beneath the Marquesas Islands.
These observations illustrate how approaches flexible enough to detect robust
patterns with little to no user supervision can reveal distinctive insights
into the deep Earth.
