Lisa Thornton, age 9, of Two Mountains, Quebec, Canada, for her question:

HOW ARE EARTHQUAKES MADE?

Earthquakes are made by the earth, which is a round ball as big as the whole world. We live on the outside crust, which is made of rocky and crumbly minerals. This outside layer is just a few miles thick, and under it there are other layers of different materials. The center is made of hot, heavy metals. Earthquakes happen in the top crusty layer, just under our feet.

They happen because the earth's crust does not fit very well. It is rather loose and broken up into huge chunks. Some of the chunks tend to slither around the globe, often in different directions. Sometimes two edges rub together and pull apart with a jerk. This is what makes an earthquake happen. The great slabs of moving crust shiver and shake, up and down and sideways‑‑and so does the ground under our feet.