Response of Nonuniform Soil Deposits to Traveling Seismic Waves

Analytical procedures for determining the response of soil deposits underlain by sloping rock boundaries to traveling wave base excitations are described and used to compare the seismic response for base motions moving with different velocities towards and away from the rock slope. It is shown that for waves traveling away from a rock slope, response amplitudes become higher as the velocity of wave propagation increases, so that maximum response is obtained for rigid base motions. The response values for base motions traveling towards a rock slope are shown to be always higher than the corresponding values when the base motions are traveling away from the slope. Based on the results of a number of cases analyzed it is concluded that spacial variations in base motions may be neglected in ground response analyses when the base motions propagate in a direction normal to the rock slope with a velocity of 5,000 fps or higher, or whenever the velocity of shear wave propagation in the rock or base material exceeds about 3,500 fps.