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Research by Catherine A. Rychert and Peter M. Shearer, Science 324(5926), 495–498. Global converted-wave observations constrain a sharp interface whose interpretation varies by tectonic setting, including possible internal cratonic structure. Primary abstract and metadata: pubmed.ncbi.nlm.nih.gov/19390041/

Catherine A. Rychert and Peter M. Shearer used fifteen years of global seismic wave observations to image a sharp interface near the lithosphere-asthenosphere boundary. Conversions from P waves to S waves constrain the interface's depth and sharpness: a transition that preserves high-frequency converted phases is too sharp to be explained by a broad thermal gradient alone. Their interpretation therefore considers composition, melting and seismic anisotropy, and distinguishes the interface beneath oceans from a possible internal boundary inside thicker cratons.^[ref]

A seismology researcher studying lithosphere and asthenosphere structure. Institutional profile: mit.whoi.edu/faculty/5644/

Peter M. Shearer coauthored a method for inferring focal mechanisms from P wave first-motion polarities. It varies source location and the velocity model, collecting acceptable mechanisms rather than treating every ray direction as exact.^[ref]

The spread of acceptable solutions measures stability of the inference and helps distinguish real fault-orientation variation from measurement uncertainty.