What is an earthquake? How was the earthquake formed?

Earthquakes are the most devastating disasters of mankind.

What is an earthquake?

Earthquake is the phenomenon of sudden vibration of the earth's crust, strong or weak depending on the game (determined by the Richter) due to the shift of lithosphere or faults in the ground and transmitted through large distances .

A single tremor usually lasts no more than a few seconds, the most serious earthquakes last only a maximum of 3 minutes.

Ruined buildings after an earthquake.

The cause of the earthquake

Endogenous cause

1. Earthquakes are caused by landslides of underground caves and earthquakes due to large volume of natural rock landslides (these earthquakes often only shake a narrow area and account for about 3% of the total world land)
2. Volcanic earthquakes , mainly related to volcanic eruption activities (this type of earthquake is not very strong - accounts for about 7%).
3. Tectonic earthquakes (90%) are related to the activity of tectonic faults, especially the faults at the edge of the lithosphere, tectonic movements in submerged suction zones; related to magma activity penetrating the earth's crust disrupts the pre-existing pressure balance of the rock surrounding the rock causing stress and when broken, an earthquake occurs; With regard to the transformation of the rock form from one crystal to another, causing a shrinkage and expansion of the volume of rock, a large change in volume also causes an earthquake.

Ruined buildings after an earthquake.

External causes: including earthquakes impacted by meteors on the earth.

Human causes: earthquakes occur due to changes in near-surface rock stresses, especially artificial nuclear and explosive tests underground or the impact of water column pressure of reservoirs, Hydropower reservoir.

The ruins of the earthquake in Kesennuma City, Miyagi Prefecture, Japan.(Photo: AP).

The level of danger of earthquakes

Earthquakes are a cause of tsunamis. When earthquakes occur in the ocean, the seismic force pushes the mass of water up high. In the hundreds of kilometers ² blocks of water were pushed up high and fell, creating big waves over the islands and landed on land. Sometimes earthquakes also cause volcanoes to function, even long-term volcanoes. Due to the cracking of the underground, the opportunity for eruption of magma lines erupted. These phenomena when combined together will create unexpected disasters.

Because earthquakes happen so unexpectedly as well as its dangerous nature, while we can't do anything to stop it, the only way to deal with it is to minimize the damage. soil triggers.

The magnitude of the earthquake

The house was destroyed after the earthquake.

The magnitude of the earthquake M is also called the Richter scale. Visualize the richter scale as follows:

1. From 1 - 2: Unrecognized.
   2 - 4: Identifiable but often not damaging.
   From 4 - 5: The ground shook, heard explosion, negligible damage.
   From 5 - 6: The house shakes, some works have cracking phenomenon.
   From 6 - 7: The house was slightly damaged.
   From 7-8: Strong earthquake destroyed most of the normal construction works, with large cracks or subsidence on the ground.
   From 8 - 9: The house was ruined, the ground was sunk to 1 meter deep, and collapsed in the mountain with the change of terrain on a large scale.
   Above 9: Very rarely.

Earthquakes with M> 7 do not occur everywhere but often concentrated in certain areas, called strong seismic activity zones.

1. What is a tsunami? When does a tsunami occur?