Earthquakes occur when rocks break along faults due to forces inside the Earth. This causes the rocks on one side of the fault to move relative to the other side. There are three main types of faults - normal, reverse, and strike-slip - which are caused by different forces. Earthquakes generate seismic waves that move the ground in various directions. Seismographs are used to measure these waves and determine details about the earthquake location and epicenter. The structure of the Earth consists of layers with different densities that seismic waves pass through. While earthquakes are natural, they can cause significant damage, so preparation and building design can help reduce risks to human life and infrastructure.