{"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 base?","topic_ref":"704a212d9f3a93ea0fe758e2d498cdc938219156d755cccd033c2d677e4d8b4a"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"51545aca12e72e5514ed3f46e2e3ef4b1719bf94439437e1aadafac010f0d214","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"a3d45b68b2a52485e844c1cc3bc84f31eb3aa71285a182349f0e6d6a757326f6","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"TVfPISGn_A9SvyEo97SH4IJ9xoU_Ui5lxYywydEWUjClqK2ukcYDZGMI6NGCcEPEEGvcQ3MXGGA2MFTs930LBQ"},"schema":"pubphys.envelope/1"},"record_hash":"51545aca12e72e5514ed3f46e2e3ef4b1719bf94439437e1aadafac010f0d214","leaf_index":1335}