In a universe that's constantly in motion, the Earth, and even the ground, is moving. And when the ground moves, it can sometimes cause earthquakes. An earthquake can come without any warning and can occur at any time or place. Sometimes they are very short and sometimes they seem to last forever. There are also small earthquakes that we don't even feel and others that are so large that they can ruin entire cities.

An important thing to know is that earthquakes are caused by sudden movements of the Earth's plates along fault lines. To understand what plates are, we need to look . . .

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