Fault-induced seismic anisotropy by hydration in subducting oceanic plates

Manuele Faccenda, Luigi Burlini, Taras Gerya, David Mainprince

Research output: Contribution to journalArticleResearchpeer-review

180 Citations (Scopus)

Abstract

The variation of elastic-wave velocities as a function of the direction of propagation through the Earth s interior is a widely documented phenomenon called seismic anisotropy. The geometry and amount of seismic anisotropy is generally estimated by measuring shear-wave splitting, which consists of determining the polarization direction of the fast shear-wave component and the time delay between the fast and slow, orthogonally polarized, waves. In subduction zones, the teleseismic fast shear-wave component is oriented generally parallel to the strike of the trench1, although a few exceptions have been reported (Cascadia2 and restricted areas of South America3, 4). The interpretation of shear-wave splitting above subduction zones has been controversial and none of the inferred models seems to be sufficiently complete to explain the entire range of anisotropic patterns registered worldwide1. Here we show that the amount and the geometry of seismic anisotropies measured in the forearc regions of subduction zones strongly depend on the preferred orientation of hydrated faults in the subducting oceanic plate. The anisotropy originates from the crystallographic preferred orientation of highly anisotropic hydrous minerals (serpentine and talc) formed along steeply dipping faults and from the larger-scale vertical layering consisting of dry and hydrated crusta??mantle sections whose spacing is several times smaller than teleseismic wavelengths. Fault orientations and estimated delay times are consistent with the observed shear-wave splitting patterns in most subduction zones
Original languageEnglish
Pages (from-to)1097 - 1100
Number of pages3
JournalNature
Volume455
Issue number7216
DOIs
Publication statusPublished - 2008
Externally publishedYes

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