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Aftermath of northern California's Loma Prieta earthquake in 1989. (Photo: U.S. Geological Survey)

PHOENIX -- Hundreds of earthquakes occur in Arizona each year and most go unfelt.

Mike Conway with the Arizona Geological Survey said faults in Arizona are capable of producing a 7.5 magnitude quake, but a quake that large in the state is unlikely.

"It would not be surprising to see something in the neighborhood of a 6.5 to 7.0," he said. "A 7.5 is a very large earthquake.

The Valley is only a couple of hundred miles away from the gold standard of faults: the San Andreas in California. Arizona is also surrounded by Utah, New Mexico and Mexico, which Conway said are all prime for large earthquakes.

"A 6.5 to 7.0 earthquake could cost significant damage if it occurred near the major metro areas," said Conway. "Phoenix probably wouldn't see a large quake based on what we know about fault rupture beneath the Valley, at least the ones that we're aware of.

"There are dozens of young and active faults in Arizona that probably haven't been identified yet."

Arizona's largest quakes happened in the early 1900s, when Flagstaff had a series of intense earthquakes around 6.0.

The 6.9 Loma Prieta earthquake that struck the San Francisco Bay Area in 1989 lasted 10-15 seconds, killed 63 people and caused $6 billion in damage.

Jim Cross, Reporter

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