During an earthquake, the ground suddenly trembles. Earthquakes can happen on land or under the sea. Some earthquakes shake the ground violently. An earthquake had mad the big cracks in these roads in Haiti. The Earth is made of rock. Inside the Earth, there is very hot rock that moves around very, very slowly. The Earth's surface is made up of big pieces of hard rock, called plates. The plates move around on top of the hot rock. As they move. some plates push against each other. Most earthquakes happen where two plates scrape against each other. In some place there are cracks near the edges of the plates, called faults.