Reflective Body Waves Extracted From 1 Month of Global Microseisms Illuminate the Perturbed Mantle Transition Zone Beneath SW Japan

The recent cataloging of global microseisms benefits imaging of the Earth's interior with improved data coverage. Relying on the catalog, converted waves were extracted and employed to reveal variations of the mantle discontinuities beneath Japan. Here, we extract reflected body waves with merely 1 month of continuous recordings, leveraging the abundant microseisms in the southern hemisphere. We convert the extracted reflections to depth and find consistent features with previous studies, such as a depressed 660 km discontinuity due to the subducting Pacific slab. Moreover, we observe strong reflections associated with an elevated 410 km discontinuity westward of the slab, a feature predicted from thermo-chemical models but not imaged previously. This work probes the complementary potentials of reflected waves from global microseisms and provides new tools for future investigation of the Earth's interior, especially in temporary deployments during which usable earthquakes as sources are often scarce.