1) An earthquake is caused by a sudden release of energy in the Earth's crust that propagates seismic waves, usually due to faulting or breaking of rocks. 2) The focus is the point where faulting begins underground, and the epicenter is directly above on the surface. Seismographs can be used to locate the epicenter based on the arrival times of different seismic wave types. 3) Earthquake magnitude is measured using the Richter scale, which quantifies the total energy released on a logarithmic scale independent of intensity felt at a particular location.