Earthquakes are vibrations that occur on the surface of the earth caused by the sudden release of energy from the inside which makes seismatic waves. Earthquakes caused by movements of the Earth's crust (earth's plates). The frequency of an area, refers to the type and size of earthquakes that are experienced in several periods.
Earthquake measurement using a Seismometer. Magnitude moment is the usual scale, where earthquakes occur for all the world. The Rickter scale is a scale reported by the national observatory measured on a local magnitude of 5 magnitude scale. Both of the same scale in the range of numbers is valid. Earthquakes of 3 magnitude or greater are almost non-existent and if magnitude 7 is more potential to cause serious damage in a large area, depending on the depth of the earthquake.
The largest historic earthquake is more than 9, although there is no limit to its magnitude. The most recent earthquake of magnitude of 9.0 or greater was 9.0 magnitude of the earthquake in Japan in 2011 (as of March 2011), as well as the largest Japanese earthquake since records were made. Vibration intensity was measured on the Mercalli Scale modification.
The types of earthquakes can be distinguished by:
Based on the cause
The tectonic earthquake was caused by activity, namely sudden shifts of tectonic plates which had the strength from the smallest to the very large. The earthquake caused many disasters and damage to nature on earth, a powerful BUmi vibration capable of spreading throughout the entire Earth. Earthquake is caused by the release of energy that occurs because of tectonic plates shifting like a rubber band is pulled and removed suddenly.
The earthquake was caused by a collision of meteors or asteroids that fell to earth, this type of earthquake does not happen often.
These earthquakes generally occur in the limestone area and in the mining area, these earthquakes do not occur often and are local.
Artificial earth sparking is an earthquake caused by human activities, namely the blasting of dynamite, nuclear or even being hit on the earth's surface.
- Volcanic earthquake (volcano)
This earthquake occurred due to magma activity, which usually occurs before volcanoes erupt. If the activity is higher, it will cause an explosion which will also cause an earthquake. The earthquake was only felt around the volcano.
Based on depth
The earthquake occurred due to magma activity, which generally occurred before the volcano erupted. If the activity is higher then it will cause an explosion which will also cause an earthquake. The earthquake was only felt around the volcano.
An inner earthquake is an earthquake whose hypocenter is more than 300 km below the earth's surface (in the earth's crust). Earthquakes in general are not very dangerous.
A medium earthquake is an earthquake whose hypocenter is between 60 km to 300 km below the earth's surface. Medium earthquakes usually cause mild damage and vibrations are more pronounced.
Shallow earthquake is an earthquake whose hypocentum is less than 60 km from the earth's surface. The earthquake caused huge damage. Based on earthquake waves / vibrations.
Primary waves (lungituudinal waves) are waves or vibrations that propagate in the body of the earth with a speed of about 7-14 km / sec. The vibration is from the hypocentrum.
Secondary waves (transverse waves) are waves or vibrations that propagate, for example primary waves with a reduced speed, which is 4-7 km / sec. Secondary waves cannot propagate through the liquid layer.
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Causes of earthquakes
Generally earthquakes are caused by layers of energy produced by pressure caused by moving plates. As time goes by, the pressure gets bigger and finally reaches a state where the pressure cannot be held anymore by the tilting. At that time also an earthquake will occur.
Enlargement of the earth's plates can cause earthquakes because in that event followed by the release of large amounts of energy. In addition to shifting the earth's plates, the motion of the earth's plates that move away from each other can also cause earthquakes. That is because when two earth plates move away from each other, new plates will form between them. New plates that have formed have a density that is much smaller than the specific gravity of the old plate. A newly formed plate will get a large enough tekabab from two old plates so that it will move down and cause the release of energy which is also quite large.
Finally, the motion of the plates that are close together can also cause earthquakes. The movement of the two plates that are mutually squeezing also affects the formation of mountains. As happened to Mount Everest which continues to be high due to the motion of the plates beneath it which are getting closer and closer and overlapping each other.
Earthquakes generally occur at the boundaries of the plates. Earthquakes that are very severe generally occur in the settlement of compressional and translational plates. Earthquakes focus on the likelihood of occurring because the lithospheric material that is squeezed into undergoes a phase transition at depths of more than 600 km.
Some other earthquakes can also occur due to the movement of magma in the volcano. An earthquake like that can be a symptom of a volcanic eruption. Some earthquakes (rare but) also occur due to a huge buildup of water mass behind dams, such as the Caribbean Dam in Zambia, Africa. More (rarely) can also occur due to injection or extraction of liquid into / from the earth (for example, in some geothermal power plants as well as in Rocky mountain Arsenal). Finally, earthquakes can also occur from explosives. This could make scientists monitor secret tests of nuclear weapons conducted by the government. Earthquakes caused by humans like this are also called induced seismicity.