An earthquake with a magnitude of at least 4.5 struck off the northwest coast of the Big Island in the same area where two stronger temblors struck last month. The quake, centered about 11 miles (18 kilometers) northwest of Puuanahulu, shook homes on the Big Island, Maui and Oahu on Thursday, but it did not produce a tsunami threat, according to the Pacific Tsunami Warning Center. The US Geological Survey estimated its magnitude at 5.0; the Tsunami Warning Center estimated it at 4.5. The quake knocked out electrical service to about 5,900 customers in North Kona and Kalaoa on the Big Island for a little more than an hour, Hawaii Electric Light Co. said. No other damages were reported.