Seismic scatterers at the shallowest lower mantle beneath subducted slabs

Research output: Contribution to journalArticle

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Abstract

Data from a western United States short-period seismic network are analyzed in order to investigate anomalous later phases within a time window from about 10 s to 120 s after direct P waves for deep and intermediate-depth earthquakes in circum-Pacific subduction zones. The anomalous phases are best interpreted as S-to-P scattered waves (wavelengths of ~ 10 km) from heterogeneities in the shallow lower mantle (depths ≤ 950 km). Several S-to-P scatterers where elastic properties of the rocks must substantially change within several kilometers are detected in the shallowest 300 km of the lower mantle beneath four circum-Pacific regions: Kuril, Bonin, Fiji, and Peru. Around most of the observed scatterers the seismic tomography models have delineated high seismic velocity anomalies which are associated with recently subducted Pacific slab or Nazca slab. The most likely origin of the scatterers would be basalt which used to form the oceanic crust. Interestingly enough the majority of the scatterers are located near the bottom boundaries of the slabs. Given rather moderate degrees of folding and/or buckling of the Pacific and Nazca slabs in the shallowest lower mantle at the study areas, the existence of the oceanic crust associated with the most recent slab subduction at the scattering sites is unlikely. Alternative and more likely explanations include: the presence of ancient basaltic rocks, localized dehydration of hydrous minerals, or a sharp boundary between different rock fabrics such as isotropic and anisotropic lower mantle rocks associated with mantle flow dragged by the slab subduction.

Original languageEnglish
Pages (from-to)304-315
Number of pages12
JournalEarth and Planetary Science Letters
Volume286
Issue number1-2
DOIs
Publication statusPublished - Aug 30 2009

Fingerprint

lower mantle
slab
Earth mantle
slabs
Rocks
scattering
rocks
Wavelength
rock
oceanic crust
crusts
subduction
Dehydration
Buckling
wavelength
Tomography
Minerals
hydrous mineral
Peru
Earthquakes

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Seismic scatterers at the shallowest lower mantle beneath subducted slabs. / Kaneshima, Satoshi.

In: Earth and Planetary Science Letters, Vol. 286, No. 1-2, 30.08.2009, p. 304-315.

Research output: Contribution to journalArticle

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