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PHOENIX -- Arizona is getting bigger every year, researcher said.

Using about 50 locations equipped with GPS technology around the state, researchers have determined that the movement of tectonic plates miles below the surface of Earth is causing Arizona to grow.

University of Arizona professor Rick Bennett said Arizona is part of the Pacific-North American plate boundary zone. The zone produces the largest earthquakes in the United States, but Arizona is in a "quiet" area of it despite the growth.

"As the plates move relative to one another, the surface of the earth responds," said Bennett. "It deforms and stretches -- in the case of Arizona -- causing faulting and contributing to the development of our mountain ranges."

Bennett said that Arizona mountains are slowly separating.

While there have been earthquakes in Arizona, Bennett said the last one that would have measured stronger than 7.0 on the Richter scale happened about 100,000 years ago.

Bennett said that Arizona expands about 3,000 square feet every year, equivalent to the size of a five-bedroom house.

"The expansion is occurring somewhere between Arizona's east and west boundaries, but we have not yet identified exactly where that stretching is taking place," he said.

When asked if Arizona is pushing California out into the Pacific Ocean, Bennett said there is two ways to look at things.

"You can think of it that way, or you can think of it that California is stretching out into the ocean and pulling Arizona out with it."

Bennett hopes that the continued study of what's going on under Arizona will lead scientists to find ways to more accurately predict when and where earthquakes will happen.

Bob McClay, Reporter

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