6 results found
Yu C, Day E, de Hoop M, et al., 2017, Mapping Mantle Transition Zone Discontinuities Beneath the Central Pacific With Array Processing of SS Precursors, Journal of Geophysical Research, ISSN: 0148-0227
Yu C, Day E, De Hoop M, et al., 2018, Compositional heterogeneity near the base of the mantle transition zone beneath Hawaii, Nature Communications, Vol: 9, ISSN: 2041-1723
Global seismic discontinuities near 410 and 660 km depth in Earth’s mantle are expressions of solid-state phase transitions. These transitions modulate thermal and material fluxes across the mantle and variations in their depth are often attributed to temperature anomalies. Here we use novel seismic array analysis of SS waves reflecting off the 410 and 660 below the Hawaiian hotspot. We find amplitude–distance trends in reflectivity that imply lateral variations in wavespeed and density contrasts across 660 for which thermodynamic modeling precludes a thermal origin. No such variations are found along the 410. The inferred 660 contrasts can be explained by mantle composition varying from average (pyrolitic) mantle beneath Hawaii to a mixture with more melt-depleted harzburgite southeast of the hotspot. Such compositional segregation was predicted, from petrological and numerical convection studies, to occur near hot deep mantle upwellings like the one often invoked to cause volcanic activity on Hawaii.
Lableis M, Waszek L, Day E, 2017, GrowYourIC: a step towards a coherent model of the Earth's inner core seismic structure, Geochemistry, Geophysics, Geosystems, Vol: 18, Pages: 4016-4026, ISSN: 1525-2027
A complex inner core structure has been well-established from seismic studies, showing radial and lateral heterogeneities at various length scales. Yet, no geodynamic model is able to explain all the features observed. One of the main limits for this is the lack of tools to compare seismic observations and numerical models successfully. We use here a new Python tool called GrowYourIC to compare models of inner core structure. We calculate properties of geodynamic models of the inner core along seismic ray paths, for random or user-specified datasets. We test kinematic models which simulate fast lateral translation, super-rotation, and differential growth. We explore first the influence on a real inner core data set, which has a sparse coverage of the inner core boundary. Such a data set is however able to successfully constrain the hemispherical boundaries due to a good sampling of latitudes. Combining translation and rotation could explain some of the features of the boundaries separating the inner core hemispheres. The depth shift of the boundaries, observed by some authors, seems unlikely to be modelled by a fast translation, but could be produced by slow translation associated to super-rotation.
Day EA, Deuss A, 2013, Reconciling PP and P'P' precursor observations of a complex 660 km seismic discontinuity, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 194, Pages: 834-838, ISSN: 0956-540X
Deuss A, Andrews J, Day E, 2013, Seismic Observations of Mantle Discontinuities and Their Mineralogical and Dynamical Interpretation, Physics and Chemistry of the Deep Earth, Editors: Karato, Publisher: Wiley-Blackwell, ISBN: 9780470659144
Geballe ZM, Lasbleis M, Cormier VF, et al., 2013, Sharp hemisphere boundaries in a translating inner core, GEOPHYSICAL RESEARCH LETTERS, Vol: 40, Pages: 1719-1723, ISSN: 0094-8276
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