Estimate of the Rigidity of Eclogite in the Lower Mantle From Waveform Modeling of Broadband S-to-P Wave Conversions

Samuel M. Haugland, Jeroen Ritsema, Satoshi Kaneshima, Michael S. Thorne

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Broadband USArray recordings of the 21 July 2007 western Brazil earthquake (Mw=6.0; depth = 633 km) include high-amplitude signals about 40 s, 75 s, and 100 s after the P wave arrival. They are consistent with S wave to P wave conversions in the mantle beneath northwestern South America. The signal at 100 s, denoted as S1750P, has the highest amplitude and is formed at 1,750 km depth based on slant-stacking and semblance analysis. Waveform modeling using axisymmetric, finite difference synthetics indicates that S1750P is generated by a 10 km thick heterogeneity, presumably a fragment of subducted mid-ocean ridge basalt in the lower mantle. The negative polarity of S1750P is a robust observation and constrains the shear velocity anomaly δVS of the heterogeneity to be negative. The amplitude of S1750P indicates that δVS is in the range from −1.6% to −12.4%. The large uncertainty in δVS is due to the large variability in the recorded S1750P amplitude and simplifications in the modeling of S1750P waveforms. The lower end of our estimate for δVS is consistent with ab initio calculations by Tsuchiya (2011), who estimated that δVS of eclogite at lower mantle pressure is between 0 and −2% due to shear softening from the poststishovite phase transition.

Original languageEnglish
Pages (from-to)11,778-11,784
JournalGeophysical Research Letters
Volume44
Issue number23
DOIs
Publication statusPublished - Dec 16 2017

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eclogite
lower mantle
rigidity
P waves
P-wave
waveforms
Earth mantle
broadband
estimates
modeling
shear
mid-ocean ridges
Brazil
phase transition
softening
simplification
mid-ocean ridge basalt
stacking
basalt
S waves

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Earth and Planetary Sciences(all)

Cite this

Estimate of the Rigidity of Eclogite in the Lower Mantle From Waveform Modeling of Broadband S-to-P Wave Conversions. / Haugland, Samuel M.; Ritsema, Jeroen; Kaneshima, Satoshi; Thorne, Michael S.

In: Geophysical Research Letters, Vol. 44, No. 23, 16.12.2017, p. 11,778-11,784.

Research output: Contribution to journalArticle

Haugland, Samuel M. ; Ritsema, Jeroen ; Kaneshima, Satoshi ; Thorne, Michael S. / Estimate of the Rigidity of Eclogite in the Lower Mantle From Waveform Modeling of Broadband S-to-P Wave Conversions. In: Geophysical Research Letters. 2017 ; Vol. 44, No. 23. pp. 11,778-11,784.
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