There’s a whole lotta shakin’ goin’ on on our planet every day–about 55 earthquakes a day around the world. Earthquakes are caused by sudden shifts of the rock masses that form the outer shell of the Earth, called a fault. These big plates of rock are constantly moving, but in some places the movement is more rapid than in others. This creates great pressure that builds up over time and then gets released in a big burst–the shaking you feel.
Most earthquakes happen where two plates run into each other or slide past each other. The plates cover the Earth like watermelon rinds or orange peels, and most of the land you see is on top of these plates. The plates move at the same speed that your fingernails grow, and some of them stick together (like the Pacific Plate grinding northwestward over the North American Plate on the San Andreas Fault). In places where movement is constant, there are many tiny tremors, but in places where it’s not, strain can build up for hundreds of years before there’s a big earthquake.
Scientists are working hard to find ways to predict an earthquake before it happens, but so far they haven’t found anything reliable. It’s a bit like forecasting the weather–it might be sunny today, but the chance of rain is still high tomorrow. That’s why it’s important to know what to do before and during an earthquake: Make a home emergency plan; choose a meeting place for family members after a disaster; learn first aid and CPR; anchor heavy objects; and make sure everyone knows how to turn off the gas, water and electric in your home (older members of your family should have this skill). Also, be ready for aftershocks–they can be just as dangerous as the main quake.
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