SGLOBE-Q2D: A Global 2-D Model of Fundamental and Higher Mode Rayleigh Wave Attenuation From a Large Amplitude Data Set

Abstract

We present SGLOBE-Q2D, a global upper mantle model of frequency-dependent Rayleigh wave attenuation with uncertainties. We use a data set of $\sim$10 million fundamental and higher mode (up to 4th overtone) Rayleigh wave amplitude measurements with wave periods T$\sim$38–275 s. Our amplitude measurements are corrected for source and for elastic effects by (a) removing paths close to source nodal planes; (b) correcting for local receiver structure effects; and, (c) accounting for focusing/defocusing effects using a linear ray theory approximation. Extensive synthetic inversion tests are carried out that support expanding our fundamental mode maps up to spherical harmonic degree 20, which is higher than in recent global attenuation studies. We observe high attenuation anomalies beneath the oceans and low attenuation perturbations beneath the continents at T$\sim$40–100 s. We also observe strong low attenuation beneath all major global cratons, including a clear separation between the Congo and Kalahari cratons in South Africa, and between the East European and Siberian cratons. Comparison between SGLOBE-Q2D and associated phase velocity maps suggest a strong control of upper mantle temperature on the observed attenuation anomalies. Yet, other factors such as, for example, the presence of water, partial melt, mantle redox conditions and grain size may also play a role.