1) An earthquake is the shaking of the Earth's surface caused by a sudden release of energy in the Earth's crust, creating seismic waves. 2) If inside during an earthquake, drop under a sturdy table or desk and hold on until shaking stops to avoid falling debris. If outside, move away from buildings, power lines, and tall objects that could fall. 3) After an earthquake, check for injuries, gas leaks, and damage before re-entering buildings. Expect aftershocks and follow instructions of emergency responders.