Steven Alden, age 11, of Baltimore, Md., for his question:

WHAT CAUSES EARTHQUAKES?

According to the plate tectonics theory, the surface of the earth is made up of about 20 rigid plates that move slowly past one another. The motion of these plates squeezes and scratches rocks at the edge of the plates.

If the force becomes too great, the rocks rupture or break and shift, causing an earthquake. These ruptures are called "faults." Most faults lie beneath the surface but some are visible.

Almost all of the world's major earthquakes occur in two great belts: the circum Pacific belt and the Alphide belt. Three fourths of the quakes occur in the circum Pacific belt which rings the Pacific ocean, including the west coast of North and South America. The Alphide belt cuts across Europe and Asia from Burma to southern Europe and North Africa.