A powerful earthquake shook north-eastern Japan early yesterday, prompting tsunami warnings and jolting residents awake in the Tohoku region that was ravaged by a monster quake five years ago.
At least 12 people suffered minor injuries. There was no major damage from the temblor, which struck at 5.59am local time (4.59am in Singapore) and could be felt 240km away in Tokyo.
As tsunami warning sirens blared in Fukushima and Miyagi prefectures, many remembered the March 11, 2011 triple tragedy of an earthquake, tsunami and nuclear disaster that killed 18,500 people and displaced 174,000 residents.
Fukushima resident Masatoshi Matsumoto, 53, told The Straits Times he was most worried about the tsunami and how it would affect the nuclear situation, referring to fears of radiation leakage from nuclear reactors in Fukushima damaged in the 2011 disaster.
"I'm used to how there seems to be more earthquakes now, and it's only a matter of time before a stronger one," said the manager of a construction firm. He said yesterday's disaster response and public information measures assuaged his concerns and showed Japan has learnt its lessons. "I could very quickly return to my daily life."
With initial predictions of tsunami waves as high as 3m, public broadcaster NHK urged residents to "not be complacent and evacuate right away" and to not go home until the warnings were fully lifted due to the risk of repeated waves.
About a dozen coastal regions were hit by waves, with the peak - 1.4m - recorded in Sendai in Miyagi prefecture just after 8am. The tsunami warnings were downgraded to advisories at 9.46am, which were then called off at 12.50pm.
The quake was initially recorded at a magnitude of 7.3 and while the Japan Meteorological Agency (JMA) revised it upwards to 7.4, the United States Geological Survey corrected its reading to 6.9. The epicentre, at a depth of 25km, was off the coast of Namie in Fukushima prefecture. It temporarily halted rail and flight services, which resumed by mid-morning.
JMA's earthquake and volcano observations division director Koji Nakamura said residents should brace themselves for aftershocks of similar intensity, with the possibility of more tsunamis, over the next week.
He added that the agency was looking at yesterday's quake as an "aftershock" of the magnitude 9 quake in 2011 that triggered monster waves of more than 10m.
Two days before the 2011 quake, there was a foreshock of 7.2. Assistant Professor Wei Shengji of the Earth Observatory of Singapore said while aftershocks are to be expected, it was unlikely that yesterday's quake would foreshadow an even stronger earthquake.
"It will take hundreds of years to re-accumulate the same amount of stress on the main plate boundary."
The Tokyo Electric Power Compan, still trying to contain the nuclear fallout at its Fukushima Dai-ichi power plant, said there were "no irregularities" nor any change in radiation levels.
The system that cools spent nuclear fuel at a reactor of the Fukushima Daini plant went down after the quake, but was reactivated about 1½ hours later after it was confirmed there was no water leakage.