"The size of the fault patch that breaksand the accumulated stressdetermine the size of the earthquake," said Carol Raymond, a physicist at JPL who studies plate tectonics.
Faults are fractures in the Earth's crust found at or near the boundaries between the Earth's plates. In recent years scientists have discovered that faults exhibit a system behaviorthey interact.
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"You can't wiggle one part of the system without the rest of it wiggling," Rundle explained.
To understand and better forecast earthquakes, scientists must understand how an earthquake along one fault affects the rest of the fault system, Donnellan said.
Rundle likens the process to phase changes. The phrase describes how a critical state is reached after a small change occurs in one part of a system: Changes form a nucleus, then grow rapidly and affect the entire system.
Examples include sticking a pot of water into a freezer, which turns water into ice. Another is found when volcanic rock is heated above what known as its Curie pointtypically between 930 and 1,300 degrees Fahrenheit (500 and 700 degrees Celsius)so that the rock loses its magnetism.
An earthquake, according to Rundle, is nothing more than a phase change from a pre-slipped state to a post-slipped state along an earthquake fault line.
"But you can't understand earthquakes through simple observationsyou miss a lot in the geology," he said. "You can only observe at the surface, and you can only observe at timescales that are short, relative to the human lifespan."
The QuakeSim suite of technologies overcome the limitations of human earthquake observations by allowing scientists to study earthquake physics at various depths in the Earth and over all timescales and space scales.
The computer models represent a virtual world that is based on what scientists know about the real world. When this virtual world is robust enough to reflect the real world, Rundle said, scientists can gain insight to the real phenomenon by asking the virtual model questions.
"How does stress get transferred? How does it build up? What are the observable patterns in smaller earthquakes that lead up to big earthquakes?" he said. "We can ask questions like these about the virtual world and once we find answers, we can go look at the real world and ask if that is what's going on there as well."
According to Rundle, this is the same process meteorologists have used over the past several decades to develop the computer models that are now the basis of their daily weather forecasts. "We are adapting the same philosophy of forecasting and predicting to the earthquake world," he said.
One of the things Rundle and his colleagues are beginning to learn from their simulations is that earthquakes tend to cluster in space and time. An earthquake on one fault section can increase or decrease earthquake activity on nearby fault sections.
"It really depends on the orientation of the neighboring faults and their position relative to the fault that has an earthquake on it," Rundle said.
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