Earthquakes are one of the most destructive natural disasters on earth, causing the greatest damage to human society. Destructive earthquakes, often come suddenly without much warning, the earth shook, the ground cracked houses collapsed, and even destroyed entire cities, and after the earthquake, fires, floods, epidemics and other serious secondary disasters is worse, bringing great disaster to mankind. According to statistics, the world every year to occur about 5 million times the earthquake, although most of the earthquakes occur in the ocean or deep in the earth's crust or due to the magnitude of the earthquake is too small to be felt, but every year there are still many earthquakes to the people in the earthquake zone to bring great loss of life and property, only since the last century, more than 1.2 million people around the world have died in earthquakes, and almost every place is subjected to the intrusion of earthquakes.
Earthquake direct disaster is the original phenomenon of earthquakes, such as earthquake fault misalignment, as well as seismic waves caused by ground vibration, caused by the disaster. The main ones are: damage to the ground, damage to buildings and structures, damage to natural objects such as mountains (e.g., landslides, mudslides, etc.), tsunamis, and ground light burns.
The most basic phenomenon during an earthquake is the continuous vibration of the ground, which is mainly characterized by significant shaking. People in the extreme earthquake zone sometimes first feel jumping up and down before they feel the big shaking. Because shock waves travel from within the earth to the ground, longitudinal waves arrive first. The transverse waves are followed by large-amplitude horizontal shaking, which is the main cause of earthquake damage.In the 1960 Chilean earthquake, the largest shaking lasted for three minutes. Earthquakes cause disasters by first destroying houses and structures, resulting in human and animal casualties, such as the 1976 earthquake in Tangshan, Hebei, China, 70% to 80% of the buildings collapsed, heavy casualties.
Earthquakes also have a great impact on the natural landscape. The most significant consequence is the emergence of faults and ground cracks on the ground. Earthquake surface faults often extend dozens to hundreds of kilometers, especially in areas with thick surface sedimentary layers, the edge of slopes, riverbanks and roads often appear on both sides of the ground cracks, resulting in urban and rural roads chap, railroad tracks twisted, bridges broken. In modern cities, ruptured underground pipelines and cut cables have caused water and electricity outages and communication disruptions. Leakage of gas, toxic gases and radioactive substances can lead to fires and secondary disasters such as toxic and radioactive pollution. In mountainous areas, earthquakes can also cause landslides and landscapes, often resulting in tragedies that bury villages and towns. The collapsed rocks clog rivers and form earthquake lakes in the upper reaches.