PERRYVILLE, Alaska—A powerful earthquake which struck just off Alaska’s southern coast caused prolonged shaking and prompted tsunami warnings that sent people scrambling for shelters. Residents reported only minor damage, but officials said that could change after sunrise and people get a better look. The National Tsunami Warning Center canceled the warnings early Thursday when the biggest wave, of just over a half foot, was recorded in Old Harbor. A tsunami warning that had also been issued for Hawaii was also canceled, and officials said there was no threat to Guam, American Samoa or the Commonwealth of Northern Mariana Islands. The warning for Alaska covered nearly a 1,000-mile (1,600-kilometer) stretch from Prince William Sound to Samalga Island, Alaska, near the end of the Aleutian Islands. The U.S. Geological Survey said the quake was magnitude 8.2 and hit 56 miles (91 kilometers) east southeast of Perryville, Alaska at about 8:15 p.m. Wednesday. …