Coming Soon: Your Local Earthquake Forecasts?

John Roach
for National Geographic News

September 17, 2004

In life, few events happen in isolation. Earthquakes are no exception. Scientists are now developing computer models that show how an earthquake in one area can increase or decrease the potential for earthquakes in adjacent areas.

University of California, Davis, computational physicist John Rundle is a member of the QuakeSim project team, a NASA-sponsored initiative to develop the computer models.

Rundle says that within a decade, these models may be able to forecast some types of earthquakes with accuracy similar to that of current forecasts for hurricane paths.

However, he noted that scientists have indications that there may be different classes of earthquakes and that quite possibly some earthquakes are inherently unpredictable, he said.

One scientist leading Rundle and his colleagues on the quest for new earthquake computer models is Andrea Donnellan. A geophysicist, Donnellan is QuakeSim's principal investigator at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

"We're currently aiming for five- to ten-year forecasts at a resolution of about 10 kilometers [6.2 miles]," she said.

A 10-kilometer resolution corresponds to a magnitude 6 earthquake. Such earthquakes are strong enough to damage poorly constructed buildings and other structures that lie within 10 kilometers from the epicenter of an earthquake.

Donnellan says the first generation suite of QuakeSim software packages, which will focus on southern California, should be complete within six months.

Earthquake Processes

The Earth's surface is divided into about a dozen thin shells of crust, commonly known as continental plates. These plates move as a result of motions in the Earth's interior.

Where these shells push against each other, stress builds up. The force grows until it overcomes the strength of rocks and dirt found in the different layers at the boundary. The result is an earthquake.

"The size of the fault patch that breaks—and the accumulated stress—determine 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 behavior—they interact.

"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 point—typically 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 observations—you 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."

Enter QuakeSim

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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