What is a Earthquakes? | Types, Definition, Structure, Function & Facts
What is a Earthquakes?
An earthquake occurs when two large plates of the earth’s crust slide suddenly. This causes shock waves that shake the Earth’s surface in the form of earthquakes.
Where do Earthquakes happen?
Earthquakes usually occur at the edges of large sections of the earth’s crust known as tectonic plates. These plates move slowly for a long time. Sometimes edges, called fault lines, can get stuck, but the plates keep moving. Pressure begins to build up slowly where the edges are stuck together, and when the pressure becomes strong enough, the plates suddenly move, causing an earthquake.
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Foreshocks and Aftershocks
In general, before and after a large earthquake, there will be smaller earthquakes. Shocks that occur earlier are called pre-shocks. What happens after that is called an aftershock. Scientists don’t really know if an earthquake is a prediction until the biggest earthquake occurs.
Seismic Waves
Shock waves from an earthquake that travel through the ground are called seismic waves. They are strongest at the center of the earthquake, but they pass through most of the earth and rise to the surface. They move 20 times faster than the speed of sound.
Scientists use seismic waves to measure the magnitude of an earthquake. They use a device called a seismometer to measure the size of the waves. The size of the wave is called the magnitude.
To determine the magnitude of an earthquake, scientists use a scale called the Moment Magnitude Scale or MMS (formerly known as the Richter scale). The larger the number on the MMS scale, the stronger the earthquake. You usually won’t even notice an earthquake unless it measures at least 3 on the MMS scale. Here are some examples of what can happen depending on scale:
- 4.0 – Can shake your house like a big truck driving past. Some people may not notice.
- 6.0 – Items will fall off the shelf. The walls of some houses can crack and the windows are broken. Almost anyone near the center will feel this.
- 7.0 – Weaker buildings will collapse and cracks will appear on bridges and streets.
- 8.0 – Many buildings and bridges collapsed. Large crack in the ground.
- 9.0 and up – Entire city destroyed and large scale damage.
Epicenters and Hypocenters
The place where the earthquake started, below the surface of the earth, is called hypocrisy. The place just above this surface is called the epicenter. The earthquake will be strongest at this point on the surface.
Can Scientists Predict Earthquakes?
Unfortunately, scientists cannot predict earthquakes. The best they can do now is point out where the fault lines are so we know where an earthquake is likely.
Interesting Facts about Earthquakes
The largest earthquake ever recorded in the world occurred in Chile in 1960. It measured 9.6 on the Richter scale. The largest in the United States was magnitude 9.2 in Alaska in 1964.
They can cause huge waves in the ocean known as tsunamis.
The movement of tectonic plates has formed large mountain ranges such as the Himalayas and the Andes.
Earthquakes can happen in any weather.
Alaska is the most seismically active state and suffers more earthquakes than California.