A moderate earthquake struck in Alaska's Aleutian Islands but apparently caused no significant damage, AP quoted officials as saying. The quake, with a preliminary magnitude of 5.6, was reported at 9:01 p.m. Thursday, said geophysicist Guy Urban of the Alaska Tsunami Warning Center in Palmer. No tsunami warning was issued. It was centered 40 kilometers (25 miles) east of Nikolski on Umnak Island, Urban said. The temblor follows a 5.6-magnitude quake that struck southwestern Montana on Tuesday. A series of small-to-moderate quakes have also struck California this summer.