The bottom right shows the motion attributed to Rayleigh waves- an up and down rolling motion much like that of ocean waves. This is a very difficult type of motion for buildings to withstand and surface waves cause much of the building damage associated with earthquakes. Damage to Interstate 5, CA during the Northridge Earthquake, 1994. Unconsolidated sediments with a certain amount of water in it, will be shaken by seismic waves. This expels the water towards the surface.
Sediments become a mass of material saturated with water and with no strength.
It will start acting like a fluid, thus the term liquefaction. Extremely dangerous for structures. Causes complete collapse of buildings. Last aftershock shook an area of 2.5 million square km.