Earthquakes are caused by the movement of tectonic plates underneath the earth's surface. When stress builds between plates and is suddenly released, seismic waves propagate from the hypocenter or focus outward. Primary waves arrive first and are followed by more destructive secondary waves. The magnitude of an earthquake is measured to indicate its strength and potential damage, from small localized tremors to catastrophic quakes that can destroy buildings. It is important to improve construction practices, implement education and evacuation plans, and understand seismic risks to minimize harm from earthquakes.