|Title||Two-dimensional global Rayleigh wave attenuation model by accounting for finite-frequency focusing and defocusing effect|
|Publication Type||Journal Article|
|Year of Publication||2016|
|Authors||Ma Z.T, Masters G., Mancinelli N.|
|Journal||Geophysical Journal International|
|Type of Article||Article|
|Keywords||3-d anelasticity; amplitude anomalies; anelasticity q structure; anisotropic structure; earth; phase-velocity; polarization data; Seismic; Seismic attenuation; shear-velocity; structure; Surface waves and free oscillations; surface-waves; tomography; upper-mantle|
In this study, we obtain a set of 2-D global phase velocity and attenuation maps for Rayleigh waves between 5 and 25 mHz. Correcting the effect of focusing-defocusing is crucial in order to obtain reliable attenuation structure. Great circle linearized ray theory, which has been used to date, can give useful predictions of this effect if careful attention is paid to how the phase velocity model is smoothed. In contrast, predictions based on the 2-D finite-frequency kernels are quite robust in this frequency range and suggest that they are better suited as a basis for inversion. We use a large data set of Rayleigh wave phase and amplitude measurements to invert for the phase velocity, attenuation, source and receiver terms simultaneously. Our models provide 60-70 per cent variance reduction to the raw data though the source terms are the biggest contribution to the fit of the data. The attenuation maps show structures that correlate well with surface tectonics and the age progression trend of the attenuation is clearly seen in the ocean basins. We have also identified problematic stations and earthquake sources as a by-product of our data selection process.