lamb problem

       As we know, 
Lamb's problem is a basic one in elastic dynamics. It can be demonstrated by a pulse applied to a half-space. Through analysis solution, one can see the sequential arrival of P wave, S wave and Rayleigh wave at a ponit which is far enough from the loading point. This phenomenon is due to the different velocities of P wave, S wave and Rayleigh wave.

        Now, I want to model the lamb problem with abaqus. But I fail to get the same result with analysis solution. Can anyone help me?