Source phase shift: A new phenomenon in wave propagation due to anelasticity

By appealing to the correspondence principle, it is possible to compute free oscillations of an anelastic earth model directly. This formulation reveals a source phase due to anelasticity which is not predicted by first order perturbation theory. For toroidal modes, this source phase is found to be largest for source components which are proportional to the radial strain scalar rather than to the radial displacement scalar. The source phase is found to increase with overtone number. Also, large relative differences in both excitation modulus and phase with respect to an elastic model are found when the elastic excitation becomes small. This effect may be large enough to bias estimates of source properties and elastic structure.