Abstract
Summary Backus-Gilbert inversion theory is applied to a new set of surface-wave attenuation data to obtain average Qβ−1 models for the crust and upper mantle beneath the Pacific Ocean. The favoured model is obtained from the inversion of Rayleigh-wave data alone. It includes an increase in Q−1 (or decrease in Q) at depths corresponding to the thickness of the litho-sphere as determined from surface-wave velocity studies, a thick zone of high Q−1 (or low Q) in the upper mantle, and decreasing Qβ−1 deeper in the mantle. The mean Q−1 values for the lithosphere are lower than those previously determined for the lower crust beneath continents. Simultaneous inversions of the Love- and Rayleigh-wave data yield models which include thin, alternating regions of high and low Q−1 values. Independent inversions of the Love- and Rayleigh-wave data yield models which differ in their anelastic properties at depths between 20 and 120km. These latter two types of models probably reflect systematic errors in the Love-wave data due to higher mode interference or complexities along the propagation path.
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