Seismic discontinuities in the mantle are indicators of its thermo-chemical state and offer clues to its dynamics. Ray-based seismic methods, though limited by the approximations made, have mapped mantle transition zone discontinuities in detail, but have yet to offer definitive conclusions on the presence and nature of mid-mantle discontinuities. Here, we show how to use a wave-equation-based imaging method, reverse-time migration of precursors to surface-reflected seismic body waves, to uncover both mantle transition zone and mid-mantle discontinuities, and interpret their physical nature. We observe a thinned mantle transition zone southeast of Hawaii, and a reduction in impedance contrast around 410 km depth in the same area, suggesting a hotter-than-average mantle in the region. Here, we furthermore reveal a 4000-5000 km-wide reflector in new images of the mid mantle below the central Pacific, at 950-1050 km depth. This deep discontinuity exhibits strong topography and generates reflections with polarity opposite to those originating at the 660 km discontinuity, implying an impedance reversal near 1000 km. We link this mid-mantle discontinuity to the upper reaches of deflected mantle plumes upwelling in the region. Reverse-time migration full-waveform imaging is a powerful approach to imaging Earth's interior, capable of broadening our understanding of its structure and dynamics and shrinking modeling uncertainties.
Bibliographical noteKAUST Repository Item: Exported on 2023-03-31
Acknowledgements: We thank Wenjie Lei for providing access to the GLAD-M25 Earth model and associated waveform data, and Jeroen Tromp for helpful suggestions and discussion. We also extend our gratitude to Yike Liu for help with interpreting the final image. We thank Alex Burky for help with extracting and plotting tomographic Earth models. This research used computing resources from the Supercomputing Laboratory of King Abdullah University of Science & Technology (KAUST) in Thuwal, Saudi Arabia. Additional computational resources were provided by the Princeton Institute for Computational Science & Engineering (PICSciE). Partial support for this research was provided by NSF grant EAR-1736046 to F.J.S. and J.C.E.I.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Physics and Astronomy(all)