Impact of Mantle Velocity Uncertainty on Receiver-Function Imaging of the Transition Zone

Abstract

Seismological estimates of the 400-km and 670-km mantle discontinuities (d400 and d670) are crucial for understanding the thermochemical structure and dynamics of the mantle transition zone (MTZ). However, artifacts from using ray theory and uncertainties in mantle velocity structure can affect topographic mapping of these boundaries. The artifacts are expected but have not been thoroughly explored. We focus on the mantle beneath North America, computing common-conversion-point (CCP) images using spectral-element method synthetics for eight global and regional tomographic models. Our results reveal artificial undulations in d400 and d670 and variations in MTZ thickness arising from incorrect velocity corrections that are large compared to actual topography resolved using USArray data. Our synthetic experiments highlight that interpretation of d400 and d670 maps from CCP imaging and similar techniques should be done judiciously, due to substantial uncertainties introduced by velocity corrections.