Japan steps up earthquake, tsunami defenses amid quake swarm – DW – 07/09/2025

DW

09-07-2025

Authorities have evacuated dozens of people from remote islands in southern Japan that have been shaken by over 1,700 tremors in recent weeks.
The Japanese government on July 1 approved significant upgrades to the national plan to safeguard the public in the event of a major earthquake off southern Japan and to respond in the event that disaster does strike.
The move comes amid an unprecedented swarm of quakes hitting the Tokara Islands.
Dozens of residents of the remote island chain, half-way between Japan's most southerly main island of Kyushu and Okinawa Prefecture, have been evacuated to the mainland after enduring more than 1,700 tremors since June 21.
The islands were hit by 60 quakes on Monday alone, according to the Japan Meteorological Agency, with Akusekijima island shaken by multiple tremors of magnitude 5.
Experts say earthquake swarms have been recorded in the area before, but never of such magnitude or for such an extended period of time.
Authorities have instructed residents who have chosen to remain on the islands to be prepared for further tremors, although they have gone to great lengths to emphasize that the ongoing seismic activity in the Tokara islands is not a precursor to the much-feared Nankai Trough earthquake.
They agree, however, that disaster is unavoidable and edging closer.
Japan is one of the world's most seismically active countries.
The archipelago, home to around 125 million people, sits on top of four major tectonic plates along the western edge of the Pacific "Ring of Fire."
The nation typically experiences around 1,500 jolts every year and accounts for about 18% of the world's earthquakes of magnitude 6 or greater.
In March, the Japanese government released an updated report on the threat posed by a quake in the Nankai Trough, a 900-kilometer fault that runs parallel to the coast off southern Japan, from Kyushu in the west to Tokyo at its far eastern end.
The study now puts the likelihood of a magnitude-9 quake on the fault at 80% in the next 30 years.
In 2014, a similar report estimated a potential death toll of 332,000 and the destruction of 2.5 million buildings, primarily due to a resulting tsunami impacting coastal communities.
But the revised report now lowered the number of potential fatalities to 298,000, the vast majority of them victims of tsunami waves, while 2.35 million buildings would be destroyed.
In response, the government's Central Disaster Management Council has drawn up new plans, aiming to cut the projected death toll by 80% within the next decade.
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Takeshi Sagiya, a professor at Nagoya University's Research Center for Seismology, Vulcanology and Disaster Mitigation, says the 80% target is commendable but probably not achievable in the event of a magnitude-9 disaster.
"The government's priority is to reduce loss of life, but while we learned a lot from the Tohoku earthquake of 2011, we also realized that it is impossible to protect everyone and everything," he told DW.
Taller and more robust sea walls have been constructed in some areas, with hundreds of tsunami refuge towers built in communities identified as most at risk in the event of an earthquake-triggered tsunami. One of the newest is in Kuroshio town in Kochi Prefecture, where experts suggest a tsunami of up to 34 meters tall could come ashore in a worst-case scenario.
"The infrastructure is important, but probably more important is to educate local people on what to do when an earthquake happens, how they can evacuate quickly and which routes they should take," Sagiya said.
"People need to better understand the hazards because the estimates say that the first tsunami could hit the shore just five minutes after a quake," he said.
In 2011 in Tohoku, in contrast, it was around 30 minutes before the first waves struck the coast, with the tsunami blamed for virtually all the around 20,000 dead.
Sagiya said it is "clearly impractical" to attempt to build 30-meter seawalls around the entire coastline of southern Japan and that, inevitably, the coastal cities of Nagoya and Osaka will be impacted by tsunami.
"And when there is widespread destruction in the cities, who is going to be available to provide help in the coastal communities that have been hit?" he asked.
The other hard lessons that Japan learned in 2011 involved the nuclear power plant at Fukushima, said Kazuto Suzuki, a professor of science and technology policy at Tokyo University and leader of the 10-year investigation into the disaster.
"The reason the Fukushima Daiichi reactors failed was due to the diesel generators that were the backup power supply being placed in basements that were flooded," he told DW.
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Similarly, the fire engines that were needed to pump water onto the three reactors that experienced meltdowns were all parked in one place that was overwhelmed by waves, rendering them inoperable.
"Lessons were learned in 2011 and there are new regulations in place about emergency generators, fire engines and other safety measures," he said. "But there are a lot of unknowns when it comes to an earthquake in the Nankai Trough and it is important that there are constant efforts to improve safety, to keep looking and looking to try to identify weaknesses and then to solve them."
And while there are a number of nuclear facilities on Japan's southern coast that would feel the impact of a tremor in the Nankai Trough, Suzuki says the one he is most concerned about is the Sendai plant on the coast of Kagoshima Prefecture.
"It is not directly facing the trough, but I believe it is the most vulnerable and there is the possibility that it might fail," he said.