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Using ScP precursors to search for mantle structures beneath 1800 km depth
Author(s) -
Castle John C.,
van der Hilst Rob D.
Publication year - 2003
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2002gl016023
Subject(s) - geology , core–mantle boundary , mantle (geology) , discontinuity (linguistics) , lithology , seismology , cosmic microwave background , hotspot (geology) , geophysics , transition zone , petrology , physics , mathematical analysis , mathematics , anisotropy , quantum mechanics
If either two stratified geochemical reservoirs or a mineralogical phase change in perovskite exist in the mantle, the boundary between the geochemical layers or mineralogical phases may lie at a depth between 1800 km and the core‐mantle boundary (CMB). We searched for the ScP precursors ( S ‐to‐ P reflections) that would be generated at the boundary by stacking hundreds of short‐period, vertical component teleseismic waveforms from the dense Pacific Northwest Seismic Network (PNSN). PNSN recorded clean ScP phases and saved the P to ScP time window for four earthquakes. We estimate our detection threshold to be impedance contrast >4%. None of the data show evidence of sharp structure between 1800 km and the CMB, suggesting that a sharp seismic discontinuity does not exist between 1800 km and the CMB under the Gulf of Alaska and Mexico: any discontinuity would need to be diffuse, have large topography, or have a small impedance change. While not conclusive, this observation is consistent with an Earth model lacking a global boundary separating geochemical reservoirs and lacking a phase change in this depth range.