An Investigation of Mantle Attenuation using ScS Reverberations

Abstract

A method of measuring whole mantle attenuation from frequency spectra of multiple core reflected ScS body waves is presented and applied to a global data-set. We compare attenuation measurements and shear wave tomography to identify regions of temperature anomalies, water and partial melt in the mantle using empirically derived relations between these properties. Specific regions are studied in detail such as: (1) South America, which appears to have a temperature dominated attenuation structure, but requiring partial melt or water to increase absolute values of attenuation. (2) Fiji, whose attenuation structure reveals the likely presence of partial melt. (3) Japan which also has a temperature controlled attenuation structure but requiring partial melt to increase absolute values. The role of focussing and de-focussing from velocity structure on attenuation measurements is investigated by comparing measured attenuation to 3D synthetic seismograms. This leads to the insight that low attenuating regions are affected more by foccussing and de-foccussing but highly attenuating ones are not.