{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"3d980b90666f8b0cdc06a4524708c03026ca96ebdf137cec5e8d3f09e692896f","created":"2026-10-03T07:18:03Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"db8d5364611af5abd569f951261c931cfef505df82981199ef307ea8984f5352","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"earth.mantle-structure.llsvp-origin","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"Below Africa and the Pacific, seismic waves slow down in two huge regions about 1000 km tall. They could be hot rock, a different rock composition, or even leftovers of the body that hit Earth to form the Moon.","posed_since":"","precise":"The large low shear-velocity provinces (LLSVPs) show shear-velocity reductions of a few percent, sharp edges and heights near 1000 km. Identify their nature: purely thermal superplumes, thermochemical piles of primordial material, accumulated subducted oceanic crust, or remnants of the Moon-forming impactor. An answer is a composition and temperature model that fits shear, compressional and bulk-sound velocities, density and dynamical stability over Gyr.","problem_ref":null,"references":"","settled_by":"Joint seismic, normal-mode and gravity inversion of density and velocity ratios matched to mineral-physics predictions for candidate compositions.","status_note":"Yuan and coauthors (Nature 2023, https://doi.org/10.1038/s41586-023-06589-1) proposed the LLSVPs are remnants of the Moon-forming impactor; thermal and recycled-crust explanations remain in play.","title":"What are the two continent-sized slow regions at the mantle 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