Earthquakes Rock Our World
by Aaron Hoffmaster, age 11
Earthquakes could first be detected a long time ago in 130 AD. That’s when a Chinese astronomer invented an instrument, that is now called a seismometer, to detect them.
Even though you can’t feel them, a small earthquake happens every 30 seconds. On average, these earth tremors happen 600,000 times a year. Modern seismometers measure even the smallest earthquakes.
Earthquakes occur when two plates underground collide, and there is a build-up of stress in the Earth’s crust. This movement happens at either a subduction zone or along a fault line.
Fault lines and subduction zones are places where there are cracks in the Earth due to the shifting of rocks. This movement makes the ground shake, sometimes enough to cause a lot of damage to buildings even miles away.
Foreshocks and aftershocks can happen long before and after the actual earthquake.
[Source: Volcanoes and Earthquakes]