By Yereth Rosen
ANCHORAGE (Reuters) - A large 7.0 magnitude earthquake struck early on Friday in waters 57 miles off the remote Alaska island of Adak, a former U.S. Navy station that is now a commercial fishing and maritime-service center, according to the U.S. Geological Survey.
There were no initial reports of damage, and the West Coast and Alaska Tsunami Warning Center said there was no tsunami watch, warning or advisory in effect.
"At this point, we've seen no ocean-surface disturbance," said Bill Knight, a scientist at the tsunami warning center in Palmer, Alaska. While no tsunami was expected, he said scientists were still monitoring the area for any earthquake-induced waves.
The earthquake, which struck at 8:25 a.m. Alaska Daylight Time, was strongly felt in Adak, about 1,300 miles southwest of Anchorage, said City Manager Layton Lockett.
"It was kind of hard to miss," Lockett said. "The strangest thing about this one was its length in time. I think people actually had time to get out of bed to see what was going on."
A magnitude 7 earthquake is likely to produce shaking that lasts 20 to 30 seconds, although it could last longer depending on local tectonics, Knight said.
A public radio station in Unalaska/Dutch Harbor, KUCB, interviewed a woman in Adak who said she timed the temblor at 40 seconds. The earthquake was followed by about 10 aftershocks of magnitude 3.5 or higher, Knight said.
Most structures in Adak can withstand earthquakes and other forces of nature, and any damage would likely be limited to water pipes and similar facilities that have yet to be fully examined, Lockett said.
"Generally, the buildings are built really strong. We do live on a volcano," he said of the town, which state records indicate has 321 residents.
There are two volcanoes on Adak Island, along with remnants of a third volcano, according to the Alaska Volcano Observatory.
The quake was also felt in Atka, a tiny Aleutian Island Native Aleut village 65 miles northeast of the quake's center, where Knight said callers reported "strong shaking" but no damage.
(Additional reporting by Bill Rigby in Seattle; Editing by Cynthia Johnston, Bernadette Baum and Andrew Hay)