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A radial model of anelasticity consistent with long-period surface-wave attenuation

Department of Earth and Planetary Sciences, 20 Oxford St.Harvard University, Cambridge, Massachusetts 02138

Abstract

A new global model of radial variations in intrinsic shear and compressional attenuation, Q_µ(r) and Q(r), is presented. The model, called QL6, is derived from recent observations of long-period (150 < T < 300 sec) Rayleigh- and Love-wave attenuation and an extensive set of mode decay observations compiled from the literature. Our preferred model consists of six layers of constant Q, where the parameterization of Q_µ(r) follows that of the anelastic component of the preliminary reference earth model (PREM). Relative to the commonly used models of PREM and QM1, lower values of Q_µ are required in the upper 200 km of the mantle to explain observations of Love-wave attenuation. The observations require a finite level of compressional attenuation, preferentially located in the upper mantle. An analysis using continuous spline-basis functions supports the layered parameterization—with the recovered model possessing strong gradients in Q_µ at the 670-km discontinuity; at the bottom of the asthenosphere; and to a lesser extent, at the base of the lithosphere. However, the continuous model does not have a significant discontinuity in Q_µ at the 400-km phase boundary.

Footnotes

^* Presently at Seismographic Station, 475 McCone Hall, University of California at Berkeley, Berkeley, California 94720.