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๐ŸŒ‹ Planet Earth ๐ŸŒ‹ Volcanoes and earthquakes

Earthquakes

Earthquakes are among nature's most destructive forces. On the right, a person prays to God to ease the destruction caused by the 1990 earthquake in Iran. On the left, a stream bed has changed course because rocks shifted along the San Andreas Fault in California, USA. Such a shift can cause a destructive earthquake.
Earthquakes are among nature's most destructive forces. On the right, a person prays to God to ease the destruction caused by the 1990 earthquake in Iran. On the left, a stream bed has changed course because rocks shifted along the San Andreas Fault in California, USA. Such a shift can cause a destructive earthquake.

๐Ÿ“– In short

An earthquake is a sudden shaking of the ground. It happens when big parts of the Earth's rocky crust move and break suddenly. Some earthquakes are so gentle we hardly feel them, and some are very strong and shake buildings until they fall.

๐Ÿคฉ Did you know?

  • Most earthquakes start less than 70 kilometers down.
  • The deepest known earthquakes happen about 700 kilometers down.
  • The strongest earthquake ever recorded happened in Chile in 1960, with a magnitude of 9.5.
  • Thousands of small earthquakes happen around the world every day without us feeling them.

๐Ÿ”Ž Find out more

๐ŸŒŸ Moving plates

The Earth's crust is split into huge pieces called plates that move very slowly. Sometimes they get stuck, then slip suddenly, releasing a lot of energy as waves that shake the ground.

๐Ÿ” Measuring earthquakes

Scientists measure an earthquake's strength with sensitive machines called seismographs, which draw zigzag lines that shake with the ground. They give its strength as a number: the bigger the number, the stronger the quake.

๐Ÿ’ก Earthquakes under the sea

If a strong earthquake happens under the sea, it can lift the water and make giant waves called tsunamis that race towards the coast.

๐ŸŽฏ How to protect yourself

If you feel an earthquake at home: get down on the floor, take cover under a strong table and hold on, keep away from windows and things that might fall, and don't use the lift.

๐Ÿ“ธ More pictures

Earthquakes happen when rocks break and shift, releasing energy as vibrations called seismic waves. The point inside the Earth where the rocks first break is called the focus, and the point on the surface right above it is called the epicenter.
Earthquakes happen when rocks break and shift, releasing energy as vibrations called seismic waves. The point inside the Earth where the rocks first break is called the focus, and the point on the surface right above it is called the epicenter.
Different seismic waves travel through rock in different ways. The compression wave moves by squeezing and stretching the rock. The shear wave shakes the rock back and forth and, at the surface, shakes buildings hard. The Love wave travels along the surface, moving it from side to side, and the Rayleigh wave also travels along the surface, rolling like a sea wave.
Different seismic waves travel through rock in different ways. The compression wave moves by squeezing and stretching the rock. The shear wave shakes the rock back and forth and, at the surface, shakes buildings hard. The Love wave travels along the surface, moving it from side to side, and the Rayleigh wave also travels along the surface, rolling like a sea wave.
An earthquake-resistant building has features like shear walls, a central core, cross bracing and base isolators that absorb shocks. A trench around the building lets it sway without collapsing.
An earthquake-resistant building has features like shear walls, a central core, cross bracing and base isolators that absorb shocks. A trench around the building lets it sway without collapsing.

๐Ÿงฉ Test yourself

1 What do you do if there's an earthquake and you're at home?

2 What are the giant waves caused by an undersea earthquake called?

3 Most earthquakes start less than ?? kilometers down.

4 Which picture shows โ€œEarthquakesโ€?

๐ŸŒ‹ Discover more