FACTS

When an earthquake occurs, seismic waves are generated which propagate away from the fault rupture.

Here we see the up-and-down velocity of the Earth's surface. Strong blue waves indicate the surface is moving rapidly downward. Strong red waves indicate rapid upward motion.

When the waves pass through soft soils (sediments) they slow down and amplify. Waves speed up when they pass through hard rock.

The color of the waves oscillates between red and blue indicating Alternating up and down motion.