Slow-moving faults may help protect some cities against destructive quakes

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Washington, August 29 (ANI): A new research by scientists from the University of Arizona (UA) in Tucson has determined that some slow-moving faults may help protect some regions of Italy and other parts of the world against destructive earthquakes.

Until now, geologists thought when the crack between two pieces of the Earth's crust was at a very gentle slope, there was no movement along that particular fault line.

"This study is the first to show that low-angle normal faults are definitely active," said Sigrun Hreinsdottir, UA geosciences research associate.

According to Richard A. Bennett, a UA assistant professor of geosciences, "We can show that the Alto Tiberina fault beneath Perugia is steadily slipping as we speak - fortunately, for Perugia, without producing large earthquakes."

Perugia is the capital city of Italy's Umbria region.

Creeping slowly is unusual. Most faults stick, causing strain to build up, and then become unstuck with a big jerk. Big jerks are big earthquakes.

For decades, researchers have known about the Alto Tiberina and similar faults and debated whether such features in the Earth's crust were faults at all, because they didn't seem to produce earthquakes.

Hreinsdottir and Bennett have now shown that the gently sloping fault beneath Perugia is moving steadily at the rate of approximately one-tenth of an inch (2.4 mm) a year.

Perugia has not experienced a damaging earthquake in about 2,000 years, according to Hreinsdottir.

"Because the fault is actively slipping, it might not be collecting strain. To have an earthquake, you have to have strain," she said.

Other towns in the region that lie near steeply sloping faults, including L'Aquila and Assisi, have experienced large earthquakes within the last 20 years.

The UA team became interested in the Alto Tiberina fault because previous research suggested the fault might be moving.

To check on the fault, the UA team measured rock movements in and around Perugia using a technique called geodesy.

The geodesy network can tell where one antenna and its rock are relative to another antenna. Taking repeated measurements over time shows whether the rocks moved relative to one another.

The UA team analyzed data from 19 GPS stations within approximately a 30-mile (50 km) radius around Perugia.

"Having such closely spaced stations and several years of data were key for detecting the fault's tiny motions," said Hreinsdottir.

"This study is one more piece in the puzzle to understand seismic hazards in the region and can apply to other regions of the world that have low-angle normal faults," she added. (ANI)

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