Do you want to know the change in wave velocity ?

yes

If I understood your question correctly, when the P waves pass into the same formation unsaturated to saturated , the value of the P wave velocities increases in a saturated medium.Exple, the velocity of fine unsaturated sand is (300-700 m) and the saturated fine sand (under the water table) is between 1400-1700 m/s.

Why especially in urban site