Earthquake

Earthquakes are ground shaking caused by vibrations at or below the Earth's surface. They can be caused by natural phenomena such as crustal movements, volcanic activity, and meteorite impacts, as well as by man-made activities such as underground nuclear testing, although the major catastrophic earthquakes in history have been caused by sudden movements of the Earth's crust. 

 Earthquakes cover both the lithosphere and the hydrosphere. When earthquakes occur, they may cause surface ruptures, large tremors, soil liquefaction, landslides, aftershocks, tsunamis, and even volcanic activity, and affect human survival and activities. 

Earthquakes occur because the earth's crust accumulates stress during plate movement. When the crust can no longer accumulate stress, the earth's crust ruptures, releasing seismic waves that shake the ground. Earthquakes can be measured by seismographs by observing seismic waves. The location where an earthquake occurs is called the epicenter, and its projection onto the earth's surface is called the epicenter. Earthquakes do not occur in all parts of the world. Earthquakes, like volcanoes, are concentrated in areas of plate tectonic interaction.

At present, the world is divided into three major seismic zones where earthquakes occur frequently: the Pacific Rim Seismic Zone (accounting for 80%), the Eurasian Seismic Zone, which stretches from the Mediterranean Sea all the way eastward to the Himalayas and Indonesia, and the Mid-ocean Ridge Seismic Zone, which is located at the mid-ocean ridges of various oceans. Not all earthquakes occur in these three zones, but a small number of large earthquakes occur within the plates, mainly in and around large active fault zones, such as the 1976 Tangshan earthquake in Hebei, China.