The quake late Thursday was the strongest tremor since the March 11 jumbo and did some damage, but it appeared to have spared the area's nuclear power plants. The Fukushima Dai-ichi complex — where workers have been frantically trying to cool overheated reactors since they lost cooling systems last month — reported no new abnormalities. Other facilities switched to diesel generators after the 7.1-magnitude quake knocked out power to much of the area.

Many people in the area have lived without water and electricity for nearly a month, and the latest tremor sunk more homes into blackness: In total, around 3.6 million households — about 60 percent of residents in the area — were dark Friday, said Souta Nozu, a spokesman for Tohoku-Electric Power Co., which serves northern Japan.

Matsuko Ito, who has been living in a shelter in Natori since the tsunami, said there's no getting used to the terror of being awoken by shaking.

"I was almost as scared as much as last time," said the 64-year-old while smoking a cigarette outside.

She said she started screaming when the quake struck around 11:30 p.m.

"Something has changed," she said. "The world feels strange now. Even the way the clouds move isn't right."

Thursday's quake initiated a tsunami warning of its own, but it was later canceled. Two people were killed, fire department spokesman Junichi Sawada reported Friday. A 79-year-old man died of shock and a woman in her 60s was killed when power was cut to her oxygen tank. More than 130 people were injured, according to the national police agency.