4.7 Article

A compositional origin to ultralow-velocity zones

Journal

GEOPHYSICAL RESEARCH LETTERS
Volume 42, Issue 4, Pages 1039-1045

Publisher

AMER GEOPHYSICAL UNION
DOI: 10.1002/2014GL062097

Keywords

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Funding

  1. University of Utah Center for High Performance Computing
  2. NSF [EAR-1014749, EAR-1344579]
  3. NERC [NE/H022473/1]
  4. NERC [NE/K006290/1, NE/H022473/1] Funding Source: UKRI
  5. Natural Environment Research Council [NE/H022473/1, NE/K006290/1] Funding Source: researchfish
  6. Division Of Earth Sciences
  7. Directorate For Geosciences [1014749] Funding Source: National Science Foundation

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We analyzed vertical component short-period ScP waveforms for 26 earthquakes occurring in the Tonga-Fiji trench recorded at the Alice Springs Array in central Australia. These waveforms show strong precursory and postcursory seismic arrivals consistent with ultralow-velocity zone (ULVZ) layering beneath the Coral Sea. We used the Viterbi sparse spike detection method to measure differential travel times and amplitudes of the postcursor arrival ScSP and the precursor arrival SPcP relative to ScP. We compare our measurements to a database of 340,000 synthetic seismograms finding that these data are best fit by a ULVZ model with an S wave velocity reduction of 24%, a P wave velocity reduction of 23%, a thickness of 8.5 km, and a density increase of 6%. This 1:1 V-S:V-P velocity decrease is commensurate with a ULVZ compositional origin and is most consistent with highly iron enriched ferropericlase.

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