Anelasticity of the Crust and Upper Mantle beneath the Pacific Ocean from the Inversion of Observed Surface Wave Attenuation

Backus-Gilbert inversion theory is applied to a new set of surface-wave attenuation data to obtain average Q,-' 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 Qp-l (or decrease in Q,) at depths corresponding to the thickness of the lithosphere as determined from surface-wave velocity studies, a thick zone of high Q,-' (or low Q,) in the upper mantle, and decreasing Q,-' deeper in the mantle.The mean Q,-' 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 Qa-l 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.