What causes Earth to shake? Earth’s crust is made of about 12 blocks of rock, called tectonic plates, sitting on a layer of hot molten rock. Most earthquakes occur where two plates meet. Pressure builds up as the plates try to slide under, over, or past each other. At some point, the plates move into a position that results in an earthquake. Some quakes are so mild that they can’t be felt, and others shake the ground violently, destroying roads and buildings. The vibrations, called seismic waues, travel both on and below Earth’s surface. The type of area they travel through influences how much destruction the waves cause.