[SIT27-08] Seismic discontinuity at lithosphere-asthenosphere boundary predicted from laboratory-based anelasticity model
Keywords:LAB, anelasticity, premelting, grain boundary
The anelasticity model by Yamauchi and Takei (2016) is given as a function of normalized frequency f/fMand normalized temperature T/Tm, where fMand Tmrepresent the Maxwell frequency and solidus temperature, respectively. The Maxwell frequency is calculated by GU/h, where GUand h represent the unrelaxed shear modulus and diffusion creep viscosity, respectively. Yamauchi and Takei (2016) also gave the model of diffusion creep viscosity based on the experimentally observed enhancement of diffusion creep by premelting. Oceanic mantle geotherm T(z) was calculated for various plate ages by plate cooling models. Solidus profiles Tm(z) were calculated by assuming some plausible distributions of volatiles (H2O and CO2). Substituting these results to the laboratory-based viscosity and anelasticity models, velocity and attenuation profiles Vs(z) and Q-1(z) at seismic frequency f were calculated and compared to the seismological observations. The results show that the sharp reduction in Vs can be explained by premelting. However, the predicted discontinuity depth is slightly deeper, and the predicted magnitude of velocity reduction is smaller than the seismological observations. We discuss these discrepancies from possible uncertainties in geophysical conditions and rheological models. We further compare the present results with another LAB model based on the other laboratory-based anelasticity model (Jackson and Faul, 2010).