Towards Developing Velocity-Attenuation Models of Earth's Mantle Incorporating Mineral Physics Observations

Seismic attenuation structure is important for understanding the thermal and compositional state of the mantle. In general, the anelastic structure of the mantle is far less constrained compared to the elastic (velocity) structure, mainly because seismic amplitudes can be affected by both anelastic attenuation (Q) and elastic focusing/defocusing due to lateral heterogeneities. In our work, we investigate the thermal effects on seismic amplitudes based upon a simple two-layer mantle rheology model. The mantle temperature profile is constructed assuming an oceanic lithosphere of 60 Ma lies on top of an adiabatic mantle with a potential temperature of 1300°C -- 1400°C. To constrain the range of thermal activation parameters (activation volume and activation energy) and the Grüneisen parameters for the upper and lower mantel respectively, we calculate synthetic seismograms using mode summation for the resulting attenuation models and measure amplitude perturbations with respect to PREM synthetics for body and surface wave phases. These rheology parameters obtained from our calculation provide important references in constructing direct relationship between perturbations in velocity and attenuation (Q) for purely thermal heterogeneities. The velocity-attenuation (Q) relationship based upon our rheology parameters can be used to distinguish between compositional heterogeneities and thermal heterogenities by using 3-D seismic velocity and Q tomographic models.