Attenuation in the upper mantle beneath Southern California

Physical state of the lithosphere and asthenosphere

Yingjie Yang*, Donald W. Forsyth

*Corresponding author for this work

Research output: Contribution to journalArticle

38 Citations (Scopus)
12 Downloads (Pure)

Abstract

We invert phase and amplitude data of Rayleigh waves for attenuation (Q-1) and shear wave velocities beneath southern California using teleseismic sources recorded by the TriNet/USArray network. Fundamental mode surface wave studies from 25 to 143 s period allow us to constrain the vertical variation of shear quality factor Qμ in the upper mantle. We use 2-D sensitivity kernels for surface waves based on single-scattering (Born) approximation to account for the effects of scattering on amplitude. A one-dimensional shear velocity model reveals a pronounced low velocity zone (LVZ) from ∼80 km to ∼200 km underlying a high velocity lid. Qμ shows a similar pattern; large Qμ at depths shallower than 80 km and much smaller Qμ at depths greater than 100 km. Models that attribute the variations of attenuation and shear velocities with depth solely to temperature and pressure effects predict too low Qμ values if they match the shear velocities. Alternative models considering the presence of partial melt can explain the observed very low Vs velocities in the asthenosphere. Partial melt in the asthenosphere could be generated due to decompression and the reduced solidus for damp mantle when the asthenosphere rose to fill the space left by the subducted Farallon plate.

Original languageEnglish
Article numberB03308
Pages (from-to)1-12
Number of pages12
JournalJournal of Geophysical Research
Volume113
Issue number3
DOIs
Publication statusPublished - 4 Mar 2008
Externally publishedYes

Bibliographical note

Copyright 2008 by the American Geophysical Union. Originally published as Yang, Y., and D. W. Forsyth (2008), Attenuation in the upper mantle beneath Southern California: Physical state of the lithosphere and asthenosphere, J. Geophys. Res., 113, B03308. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

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