The standard model of the thermal and chemical structure of cratons has been scrutinized in recent years as additional data have been collected. Recent seismological and petrological studies indicate that the notion of cratonic lithosphere as a thick thermal boundary layer with a very depleted and dehydrated composition may be overly simplified and does not explain all aspects of the seismological and petrological observations. We designed a simple forward-modeling experiment to identify a suite of one-dimensional shear-velocity profiles that are representative of the cratonic upper mantle. The mean and standard deviation of phase velocities for Rayleigh waves that travel paths primarily over cratons were calculated from a global data set in the period range 40 to 300 seconds. One-dimensional Earth models were calculated using two approaches, and the predicted Rayleigh wave phase velocity for each model was compared to the observed range to identify models that provide a satisfactory fit to the observations. With the first approach, shear velocity was predicted from cratonic geotherms that were calculated for a range of surface heat-flow and crustal-thickness values. With the second approach, profiles of shear velocity were generated using random perturbations to 1-D global Earth model STW105. In total 26250 geothermv generated and 80,000 randomly generated 1-D Earth models were generated for comparison to the observations. The results show that cratonic shear velocity is higher than STW105 to depths greater than 200 km. The majority of randomly generated models contain increasing velocity with depth to 250-300 km while the majority of geotherm-generated models contain a low velocity layer in the depth range 100-150 km.vi

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