Before the tectonic plate theory developed in the 1960s, people did not understand the cause of earthquakes Ancient Greeks believed earthquakes were caused by winds that were trapped in the earth. Even into the nineteenth century, people thought earthquakes were caused by violent explosions underground. Scientists then discovered that the earth's surface, or crust, is made up of a number of tectonic plates. These are like pieces of a puzzle that Moat over hot, liquid rock. When the pieces of the puzzle strike or move past each other energy is generated by the friction between the two plates Places where plates separate or move together are called faults if too much pressure builds along a fault, the earth breaks suddenly, creating seismic waves that result in an earthquake