If the quakes had struck a big city, such as Los Angeles, the toll would have been higher. The Big One is the name that scientists have given to a severe earthquake expected to strike California within the next 30 years. Scientists explain that the earth's crust, or outer shell, is made up of massive slabs of rock called plates. These plates, which can be as big as a continent or as small as a city, are constantly shifting. You can visualize the shifting of these plates by looking at what happens when Arctic ice floes meet each other.
Some floes break apart, some slide partially over the other, and some simply grind past each other.
One of the most visible is California's San Andreas Fault, where the Pacific Plate slides past the North American Plate. When two plates slip by each other, tremendous tension builds up. The tension is released in violent jerks or shock waves, which we call an earthquake. Minutes before the start of the third game of the World Series between the Oakland A's and the San Francisco Giants, the city was rocked and rattled by a magnitude 7.1 earthquake. Buildings and bridges collapsed, fires broke out, and 59 people were killed.