Images of small-scale mantle heterogeneity obtained from coherence functions of phase and log amplitude fluctuations

Abstract:

Traditional deterministic tomography cannot reveal the characteristics of small-scale (smaller than 100 km) heterogeneities in deep earth. Stochastic tomography, which inverts joint angular-transverse coherence functions (JATCF), can be used to image the statistics of small-scale heterogeneity. We test the resolution of this method using a pseudo-spectal method to synthesize the seismic wavefield in a reference radial symmetric Earth model perturbed by statistically described heterogeneity. JACTFs are calculated from the fluctuation of phase and log amplitude of transmitted waves in the heterogeneous model differenced from those predicted in the reference model. Example images are obtained from processing JACTFs measured from teleseismic data observed by Earthscope’s USArray. Depth and lateral variations of the statistics of heterogeneity scales constrain the nature of chemical heterogeneity and mantle circulation