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Waveform effects of a metastable olivine tongue in subducting slabs
Author(s) -
Vidale John E.,
Williams Quentin,
Houston Heidi
Publication year - 1991
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 - 10.1029/91gl02588
Subject(s) - geology , slab , olivine , seismology , waveform , amplitude , mantle (geology) , geophysics , mineralogy , optics , physics , quantum mechanics , voltage
We constructed velocity models of subducting slabs with a kinetically‐depressed olivine → β‐ and γ‐spinel transition, and examined the effect that such structures would have on teleseismic P waveforms using a full‐wave finite‐difference method. These two‐dimensional calculations yielded waveforms at a range of distances in the downdip direction. The slab models included a wedge‐shaped, low‐velocity metastable olivine tongue (MOTO) to a depth of 670 km, as well as a plausible thermal anomaly; one model further included a 10‐km‐thick fast layer on the surface of the slab. The principal effect of MOTO is to produce grazing reflections at wide angles off the phase boundary, generating a secondary arrival 0 to 4 seconds after the initial arrival depending on the take‐off angle. The amplitude and timing of this feature vary with the lateral location of the seismic source within the slab cross‐section. Careful analysis of waveforms from earthquakes with depths near 400 km, simple sources, and adequate station coverage in appropriate geometries will be required to resolve whether MOTO is present.