An earthquake is a sudden and violent shaking of the ground caused by movements within the Earth's crust or volcanic activity. These movements are typically due to the release of stress that has built up along geological fault lines or from volcanic activity. The point within the Earth where the earthquake originates is called the hypocenter or focus, and the point on the Earth's surface directly above the hypocenter is called the epicenter.
Earthquakes can vary in size and intensity, ranging from minor tremors that are barely noticeable to catastrophic events that can cause widespread destruction and loss of life. The intensity of an earthquake is measured on the Richter scale or the moment magnitude scale, which quantifies the amount of energy released by the seismic event.
Earthquakes can result in various secondary hazards such as tsunamis, landslides, and aftershocks, further adding to the potential damage and danger associated with these events. Seismologists study earthquakes to better understand their causes, predict their occurrence, and mitigate their impact on society.