Earth’s Mid-mantle via Probabilistic Array Imaging

The Earth’s mid-mantle (800–1200 km depth) hosts enigmatic seismic discontinuities whose physical origins remain debated. Competing hypotheses attribute these features to either thermal anomalies, such as partial melting due to volatile transport, or compositional heterogeneities associated with ancient subducted crust. However, distinguishing between these scenarios remains a challenge; standard imaging techniques often fail to robustly resolve the polarity of weak seismic reflections amidst noise and reverberations that contaminate mid-mantle reflections. Consequently, previous global surveys relying on linear time-domain stacking have yielded only a fragmented perspective, where the global connectivity, topography, and distinct physical origin of mid-mantle discontinuities remain debated. To address these limitations, we present a new global imaging framework that integrates curvelet-based wavefield separation and deconvolution, with probabilistic array processing. Rather than relying on traditional linear stacking, we develop "probabilistic vespagrams" that rigorously account for uncertainties in signal coherence and wavelet estimation. This approach allows us to distinguish robust structural features from processing artifacts. We apply this workflow to a global dataset of SS and PP precursors to construct a probability map of mid-mantle discontinuities. By systematically quantifying the likelihood of positive (eclogitic/compositional) versus negative (thermal/melt) impedance contrasts globally, we aim to resolve the global distribution of mid-mantle heterogeneities and determine the relative dominance of compositional stratification versus partial melting by water transport in controlling deep-Earth dynamics