Important Concepts Earthquakes occur along fault zones in response to built-up stress in the lithosphere.
Most earthquakes occur at plate boundaries.
The point of first break or movement along a fault is called the earthquake's focus . The point on the earth's surface directly above the focus is called the epicenter . There are several types of earthquake, or seismic, waves. P-waves are compressional waves and can travel through the earth's liquid outer core. S-waves are shear waves and cannot travel through the earth's core.