Earthquakes are powerful events that can cause significant damage and loss of life. They occur when large sections of Earth's rocky outer shell suddenly break and shift, releasing enormous amounts of energy. A severe earthquake can release energy 10,000 times greater than that of the first atomic bomb. During an earthquake, rock movements can cause rivers to change course, and landslides can occur, leading to significant damage and loss of life. Large earthquakes beneath the ocean can generate destructive waves called tsunamis, which can flood coasts for miles.
The majority of deaths and injuries in earthquakes are not caused directly by the earthquake itself, but by falling objects and the collapse of buildings, bridges, and other structures. Fire resulting from broken gas or power lines is another major danger during an earthquake. Spills of hazardous chemicals are also a concern during an earthquake. The force of an earthquake depends on how much rock breaks and how far it shifts, and powerful earthquakes can shake firm ground violently for great distances. Minor earthquakes, on the other hand, may produce vibrations no greater than those caused by a passing truck.