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The strongest quake felt in Tokyo in 10 years has brought back memories of the Great East Japan Earthquake and reignited concerns over the seismic risk in the world’s most populous metropolitan area.

Over the years, a government panel has compiled various scenarios for future earthquakes in Japan, including the possibility of a magnitude 7 quake directly under the capital. But the Meteorological Agency was quick to dispel speculation that Thursday’s tremor — a magnitude 5.9 earthquake that shook Tokyo late that night — could be a foreshock for a larger quake.

“At this time, we do not believe there is a connection between yesterday’s tremor and the earthquake predicted to occur under Tokyo some time in the future,” agency official Shinya Tsukada said during a news conference early Friday.

He said Thursday night’s tremor “occurred deeper under the Earth’s surface and was smaller, with a magnitude of 5.9.”

Under the southern Kanto region, one tectonic plate approaches from the south while another, deeper plate approaches from the east. The Meteorological Agency believes the earthquake on Thursday, which occurred roughly 75 kilometers below the surface, resulted from an abrasion between those two plates.

The agency warned of a 10% to 20% chance of similar tremors occurring in the coming week.

In 2013, the central government issued a report predicting that there is a 70% chance of a magnitude 7 earthquake striking the capital region in the next 30 years. In a worst-case scenario, the quake could kill up to 23,000 people, cause more than ¥95 trillion in damage and destroy 610,000 homes. But casualties could be reduced tenfold — to around 2,300 people — if preparations are made ahead of time, namely if precautions are taken to prevent fires, which are predicted to be the cause of about 70% of casualties.

People sit on stairs at Shinagawa Station after train services were suspended due to an earthquake Thursday night. | KYODO / VIA REUTERS
People sit on stairs at Shinagawa Station after train services were suspended due to an earthquake Thursday night. | KYODO / VIA REUTERS

The report was based on an analysis of eight major earthquakes over the past 220 years in southern Kanto, which is situated directly above a subduction zone and is therefore prone to periodic seismic activity.

Earthquake preparedness in Japan has been improving for generations, but it took on renewed importance in the months and years following the megaquake that struck the Tohoku region in March 2011.

The magnitude 9 quake and subsequent tsunami killed 15,899 people and had left 2,526 people unaccounted for as of March this year and forced many more to evacuate their homes. The tsunami also triggered a triple core meltdown at the Fukushima No. 1 nuclear power plant.

The Tohoku earthquake was felt strongly in the Tokyo metropolitan area, registering a strong 5 on the Japanese seismic scale, which goes up to 7. Train services were also suspended, forcing thousands to walk home or spend the night in central Tokyo.

Chief Cabinet Secretary Hirokazu Matsuno said Friday that progress is being made when it comes to increasing the number of homes and buildings in Japan that are quake resistant. The government is also working on decreasing the number of extremely high-density areas in urban centers, which are susceptible to large fires in the event of a major quake, he said.

“It’s not limited to tremors under the capital; earthquakes can strike in Japan at any time, without warning,” Matsuno said. “It’s important to check that your furniture is anchored, stockpiles have been maintained and precautions are being taken regularly to prepare for such a situation.”

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