Retrieving deep Earth seismic phases from noise correlations is hindered by the low amplitude of deep-path noise body waves. This study presents a data selection strategy that leverages quantitative noise phase composition analysis to enhance the recovery of faint body-wave reflections. Applying this method to noise correlations data computed across the contiguous U.S., we successfully mapped the mantle transition zone (MTZ) discontinuities. We identified reliable P-wave reflections associated with the 410-km and 660-km discontinuities within the 3-10 s period band. These short-period reflections reveal a pronounced step-like structure. Both discontinuities are deeper beneath the tectonically active Western U.S. (WUS) compared to the cratonic Central Eastern U.S. (CEUS). Notable features include regions with a thickened MTZ beneath the CEUS and northern Colorado Plateau, likely linked to the remnants of the Farallon slab. A region with a thinned MTZ is observed beneath the Rio Grande Rift, possibly due to elevated temperatures caused by the release of volatiles from the Farallon slab. Our results highlight the effectiveness of noise correlation techniques in mapping MTZ topography.

We investigate the internal structure of the Mantle Transition Zone (MTZ) beneath the contiguous U.S. by mapping the 520 km discontinuity (d520) depth and relative amplitude of seismic phases associated with the 520-km, 410-km, and 660-km discontinuities. We analyze short-period reflected waves between 3-10 s from MTZ discontinuities extracted from seismic noise correlations. Our results reveal notable lateral variations in d520 depths, with greater depths mostly found in the western U.S., likely indicating warmer upper MTZ in this region. Analysis of relative phase amplitude between MTZ interfaces highlights strong d520 reflection phase across the central U.S., supporting previous studies that report high velocity contrasts and elevated olivine content. In contrast, the eastern U.S. shows weaker d520 reflection phase, which may be attributed to gradual velocity transition and lower water content. MTZ composition also likely varies across the U.S., with potential basalt accumulation in the southwest due to past subduction events.