SAN FRANCISCO, June 23 (Xinhua) -- The U.S. National Tsunami Warning Center downgraded the tsunami warning to a tsunami advisory Monday afternoon after an 8.0-magnitude earthquake struck in the Aleutian Islands, Alaska.
The center said tsunami waves were less than 18 cm high.
The Aleutian Islands are known to be sparsely populated, and media reports reaching here said there were no reports of casualties.
The tsunami warning was initially issued for coastal areas of Alaska from Nikolski to Attu after the quake struck 23 km southeast of Little Sitkin Island at a depth of 114 km at 12:53 p.m. Alaska Daylight Time (2053 GMT).
A tsunami advisory was issued for coastal areas from Unimak Pass to Nikolski.
The U.S. Geological Survey (USGS) said the quake was the result of oblique normal faulting at moderate depths. At the location of the quake, the Pacific plate subducts northward beneath the North America plate at a rate of about 59 mm per year.
The epicenter of the quake, likely within the subducting Pacific plate, is in a seismically active region, with 26 events of 7-magnitude or greater having occurred within 250 km since 1900. Notable events, as shown by USGS, include an 8.4-magnitude quake in 1906, 8.7-magnitude in 1965 and 7.9-magnitude in 1996.