Arterial elasticity has gained importance in the past few decades as a predictor of cardiovascular diseases and mortality. The speed of propagation of the pressure wave has been used since the 1920's to estimate the mechanical properties of the artery. There are several disadvantages of this method, two of the major ones are the low temporal resolution (1 sample per second) and the low spatial resolution (carotid-femoral or carotid-radial segments). In this work we present an ultrasound radiation force-based method to generate high frequency local shear waves, which will allow the study of the mechanical properties of short arterial segments within the heart cycle. In this work we present a modal analysis of the waves generated by our method on an excised pig artery. By doing a two-dimensional fast Fourier transform (2D FFT) of the propagating waves, it was possible to differentiate the multiple Lamb-like modes propagating in the wall. In this work we show the effect of transmural pressure and prestretch on the speed and modes of propagation of the mechanical waves generated. We also demonstrate how these changes cause the arteries to get stiffer due to both mechanisms. This study therefore shows the feasibility of a radiation based method for the characterization of propagating modes and elasticity of arterial wall.