The author proposes an alternative to the traditional representation of soil damping. Rather than using damping ratio, this author advocates using viscosity as the specific soil property, especially for saturated permeable soils. Thus represented, the imaginary part of the complex shear modulus will vary directly with frequency. The point is particularly relevant in cases where the water table may change, thus affecting the dynamic design of foundations or structures composed of soils.
Michaels, Paul. (2008). "Water, Inertial Damping, and the Complex Shear Modulus". Geotechnical Earthquake Engineering and Soil Dynamics, 1-10. http://dx.doi.org/10.1061/40975(318)54