Jan. 23 (UPI) -- A powerful magnitude 7.9 earthquake shook the Gulf of Alaska early Tuesday, leading to a short-lived tsunami watch for the West Coast, from Washington to California.
The quake struck at 4:31 a.m. EST about 330 miles off the Alaskan coast, southeast of Kodiak Island -- the result of a strike slip faulting within the shallow lithosphere of the Pacific plate, the United States Geological Survey said.
The USGS initially measured the quake at a magnitude of 8.2, but later changed the power to 7.9, with aftershocks peaking at 5.6.
An advisory remains in effect for a part of the Alaskan coast -- but watches for Washington, Oregon, California, British Columbia and Hawaii were deactivated.
The National Weather Service previously warned Alaskans via text message to "go to high ground or move inland."
"Tsunami warnings mean that a tsunami with significant inundation is possible or is already occurring. Tsunamis are a series of waves dangerous many hours after initial arrival time," the Anchorage Office of Emergency Management said earlier.
The earliest wave reached near Kodiak, Alaska, two hours after the quake, with warning sirens sounding over the town and local police department. Police said shortly afterward that no waves had hit land.
Tsunami forecasts projected waves reaching Washington's coasts early Tuesday morning. A wave of only six inches was reported in Alaska.
In San Francisco, the department of emergency management warned residents within three blocks of the Pacific coast or within 5 blocks of the San Francisco Bay to "prepare to evacuate."
There were no reports of injuries or damage.