Quake knocks out power to Japanese nuclear plants

>>> good evening. i'm ann curry in tonight for brian williams as today a major aftershock, a 7.1, the strongest yet, and not far from last month's 9.0 quake and tsunami struck off the coast of japan , and after the shaking, again, the fear of another tsunami and worries about whether the nuclear plant was further damaged. if you're wondering just how much japan can take, you're not alone. lee is in tokyo. good evening.

>> reporter: this certainly was a powerful quake, and it hit along the same stretch of battered coastline hit so hard from the earthquake and tsunami last month. there weren't a lot of people left to evacuate, and so many places, the damage there had been done, but there were a lot of people questioning what happened at the stricken power plant that some fear is already hanging on by a thread. it struck nearly four weeks to the day since last month's massive quake. a grim reminder japan is hardly out of the woods yet.

>> people near the coast should immediately evacuate to higher ground .

>> the magnitude 7.1 centered 41 miles off the coast of sendai trigger said more fears around japan , but they were canceled about an hour late r. still, the quake was hardly generous. it injured dozens, cut off power to millions, and ignited fires. rattling the nerves of those already near the breaking point. and experts warn there could be more.

>> on average, we would expect to see an aftershock sequence to a magnitude nine for a decade or two.

>> at the power plant , experts quick to reassure the public the quake had not interrupted the power flow around the reactors to keep them cool and there was no release of radiation. but with the structures already so heavily damaged, any aftershock is risky.

>> it was a very worrisome thing because if they had a catastrophic failure with all of the radioactive water in the containment, they would be starting to run out of options.

>> adding to the worries, it knocked out external power to two other nuclear plants along the coast, but emergency back-up generators have taken over. still, for the tens of thousands of weary residents looking for a break, the ground just doesn't seem willing to give it.

>> now, ann, just to give you an idea of scale here, the aftershock was larger in terms of magnitude than the earthquake that struck kobe, japan , in 1995 . it left more than 5,000 people dead. but in terms of the energy, it was 700 times less the amount of energy as the quake that struck hire last month.

>> lee, thank you so much.