Julie Conlon, acre 13, of Los Gatos, California, for her question:

Why do we expect earthquakes in California?

Our spherical planet has a rather thin skin of solid rocks. However, this surface crust does not fit the big ball as neatly as we might wish. Its land areas are wrinkled and grooved and enormous basins plunge down to hold the deep waters of the oceans. What's more, the global crust is cracked and built from enormous slabs called tectonic plates. These plates rest on the denser, more plastic mantle layer below. But they do not rest very comfortably.

Where their edges brush together, they create weak zones where all sorts of restless crustal activity is likely to occur. The most restless of these regions are long curved belts where freouent earthquakes are expected. A ring of such zones surrounds the margins of the entire Pacific Ocean. One is the earthquake zone that runs along the western side of North America  all the way down through California.