Poisson's ratio in the lower mantle beneath Alaska : evidence for compositional heterogeneity

Abstract

Using waveform cross correlation, we have measured ∼17,000 P and S wave differential travel times from earthquakes and receivers near a great circle path from Japan, across Alaska, to North America. We jointly invert the data for variations in shear and bulk sound speed and derived Poisson’s ratio variations in the mantle beneath 1000 km depth. We explore the model space using different levels of regularization and our conclusions are based on a range of models that give acceptable data fits.