Earthquakes are the rumblings, shaking or rolling of the earth’s surface. It is caused when two blocks of the earth suddenly slip past one another or when two blocks break apart from each other as a result of tension caused by prolonged energy build up. The tectonic plates move around slowly and they get stuck sometimes at their edges.
The stress on the edge builds up and overcomes the friction, and this causes an earthquake. The energy waves released during an earthquake travel through the crust of the earth and cause the shaking you feel. Intense vibrations or seismic waves spread from the initial point of rupture, the focus, like ripples of water. These waves cause the shaking on the ground and they travel in all directions. The waves can be very large near the focus and may cause heavy destruction.
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Earthquakes come in many forms. While sometimes it can be felt as a shock under your feet, sometimes it may be very powerful and destructive enough to flatten an entire city. It can happen anywhere, land or sea. The masses that shift send out powerful shock waves, which are powerful enough to:
· Alter the earth’s surface, making big cracks in the ground and thrusting up cliffs.
· Cause great damage like, tsunamis, snow avalanches, volcanic eruptions and landslides.
Foreshocks, Mainshocks and Aftershocks
Sometimes an earthquake has foreshocks. These are smaller earthquakes that happen in the same place as the larger earthquake that follows. The largest main earthquake is called the mainshock. Mainshocks are always followed by aftershocks. These are smaller earthquakes that occur afterwards in the same place as the mainshock. Aftershocks can continue for weeks, months or even years after the mainshock depending on the size of the mainshock.
What Causes Earthquakes
The earth has four layers:
· The inner core
· The outer core
The crust and the top of the mantle make up a thin skin on the earth’s surface. This skin is made up of many pieces like a large puzzle covering the earth. These puzzle pieces keep moving around slowly, sliding and bumping into each other. These pieces are called tectonic plates and the plate’s edges are called the plate boundaries. The plate boundaries are made up of many faults and most of the earthquakes occur on these faults. As the plate edges are rough, they get stuck. But, the rest of the plate keeps on moving. When they have moved far enough, the edges unstick on one of the faults and this causes an earthquake.
During an earthquake, the seismic waves shake the earth as they move through it, and when they reach the earth’s surface, they shake the ground and anything on it.