Rayleigh wave phase velocities, small-scale convection, and azimuthal anisotropy beneath southern California

Yingjie Yang*, Donald W. Forsyth

*Corresponding author for this work

Research output: Contribution to journalArticle

130 Citations (Scopus)
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Abstract

[1] We use Rayleigh waves to invert for shear velocities in the upper mantle beneath southern California. A one-dimensional shear velocity model reveals a pronounced lowvelocity zone (LVZ) from 90 to 210 km. The pattern of velocity anomalies indicates that there is active small-scale convection in the asthenosphere and that the dominant form of convection is three-dimensional (3-D) lithospheric drips and asthenospheric upwellings, rather than 2-D sheets or slabs. Several of the features that we observe have been previously detected by body wave tomography: these anomalies have been interpreted as delaminated lithosphere and consequent upwelling of the asthenosphere beneath the eastern edge of the southern Sierra Nevada and Walker Lane region; sinking lithosphere beneath the southern Central Valley; upwelling beneath the Salton Trough; and downwelling beneath the Transverse Ranges. Our new observations provide better constraints on the lateral and vertical extent of these anomalies. In addition, we detect two previously undetected features: a high-velocity anomaly beneath the northern Peninsular Range and a low-velocity anomaly beneath the northeastern Mojave block. We also estimate the azimuthal anisotropy from Rayleigh wave data. The strength is ∼1.7% at periods shorter than 100 s and decreases to below 1% at longer periods. The fast direction is nearly E-W. The anisotropic layer is more than 300 km thick. The E-W fast directions in the lithosphere and sublithosphere mantle may be caused by distinct deformation mechanisms: pure shear in the lithosphere due to N-S tectonic shortening and simple shear in sublithosphere mantle due to mantle flow.

Original languageEnglish
Article numberB07306
Pages (from-to)1-20
Number of pages20
JournalJournal of Geophysical Research
Volume111
Issue number7
DOIs
Publication statusPublished - 1 Jul 2006
Externally publishedYes

Bibliographical note

Copyright 2006 by the American Geophysical Union. Originally published as Yang, Y., and D. W. Forsyth (2006), Rayleigh wave phase velocities, small-scale convection, and azimuthal anisotropy beneath southern California, J. Geophys. Res., 111, B07306. 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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