Earthquakes occur when energy is released along faults in the earth. The focus is the point where the rock breaks along the fault, and the epicenter is the point directly above the focus on the surface. Seismic waves carry energy away from the focus, including P waves and S waves. P waves are compressional and can travel through solids, liquids, and gases. S waves are transverse shear waves that can only travel through solids. The largest earthquakes by magnitude include a 9.5 in Chile in 1960 and a 9.1 in Sumatra in 2004. Locating an earthquake's epicenter requires data from three seismic recording stations.