Scientists have learned much about the properties of rocks in the layers of the earth and the rates at which the plates move past one another. Nevertheless, this information still doesn’t tell us when and where earthquakes will occur.
Blocks of earth are moving past one another at places called faults, which range in length from a few millimeters or inches to hundreds of kilometers or miles. An earthquake occurs when two blocks of Earth suddenly slip past one another.
Even in simple lab experiments, where a block of wood is pulled by a spring across sandpaper, we can’t accurately predict when the block will move, or how far it will move even though we extend the spring at a constant rate. Think about how much more complex the earth is compared to that experiment and you’ll understand why we cannot predict earthquakes.
However, we’re learning more about earthquakes all the time. Today, scientists have enough knowledge to establish probabilities about where the next earthquake might occur for a given time period. For example, we know that certain segments of the San Andreas Fault system, such as the southern San Andreas Fault near the Salton Sea in Imperial County, Calif. has a high probability for an earthquake in the near future.
— Neal Driscoll, geologist, Geosciences Research Division