Quantitative mechanical properties can be measured with shear wave elasticity imaging methods in a model-independent manner if both shear wave speed and attenuation are known. Typically, only shear wave speed is measured and rheological models are used to solve for the shear viscoelastic complex modulus. This paper presents a method to quantify viscoelastic properties in a model-independent way by estimating the loss tangent over a wide frequency range using time-dependent creep-recovery response induced by acoustic radiation force. The shear wave group velocity and the shear wave center frequency in combination with loss tangent are used to estimate the complex modulus so that knowledge of the applied radiation force magnitude is not necessary. Experimental data are obtained in one excised swine kidney.