An earthquake is a sudden movement of the Earth’s lithosphere (its crust and upper mantle), which is caused by the release of built-up stresses within rocks along geological faults, or by the movement of magma in volcanic areas. Smaller earthquakes occur frequently, but annually, only as many as 18–20 reach a magnitude above Ms 7. Approximately 40 disastrous earthquakes have occurred since the end of the twentieth century, and the total death toll is nearly 1.7 million. This number is about 50% of all victims of natural disasters. Most earthquakes (80%) occur in the oceans, mainly in the subduction zones. Earthquakes occurring in such regions have a relatively large magnitude and they are also deep. These earthquakes can cause tsunamis.

Like other disasters, earthquakes and tsunamis can be sudden, seriously destructive, and create long-lasting social, environmental, and economic problems. https://www.natural-hazards-and-earth-system-sciences.net/