The quick alert drew attention to how far Japan’s early-warning technology has advanced since the 2011 disaster, when delays and inaccurate readings left coastal towns with little time to escape. That quake and tsunami killed nearly 20,000 people and caused a triple meltdown at the Fukushima Daiichi nuclear plant.

In response, Japan spent more than a decade building the world ’s largest seabed earthquake-monitoring system. 

The first network, S-net, extends across the Japan Trench and uses more than 3,500 miles of cable to link 150 ocean-floor observatories.

S-net can detect offshore shaking before it reaches land. In a 2018 quake, its sensors issued alerts 20 seconds faster than land-based instruments, allowing trains to slow and emergency warnings to be broadcast.

A second system, DONET, was built along the Nankai Trough, one of Japan’s most dangerous seismic zones. It was expanded in 2013 and later joined by N-net, completed in June 2025.

Together, the networks give Japan real-time coverage of its two major subduction zones. Authorities say the system can extend tsunami warning times by up to 20 minutes and provide more accurate readings of offshore quakes.

Scientists also benefit from continuous data on how faults move under the seabed, including slow-slip events that sometimes precede major earthquakes .

Local governments are improving evacuation plans, too. In September, the central government designated 108 coastal municipalities for enhanced tsunami-mitigation work, including new evacuation routes and warning facilities.

Sendai, one of the designated cities, has deployed automated drones that broadcast evacuation orders and relay images to disaster officials when normal communications fail.

It is indisputable that Japan, one of the world’s most disaster-prone nations, now has the world’s most advanced tsunami warning system. And the rapid alerts on December 8 showed how much more time authorities can now provide when offshore quakes strike.

The disaster claimed an estimated 228,000 lives across 15 countries, with Indonesia suffering the heaviest toll. In Aceh province alone, officials estimate more than 200,000 people lost their lives. 

For many survivors, the pain of that day lingers. Baharuddin Zainun, a 70-year-old fisherman, lost his entire family. Clutching a framed poem, he shared how the tsunami reshaped his life and his community.

“This poem serves as a reminder for all of us, our community, and everyone, to never forget the memory of the tsunami. Our village was struck by the tsunami several years ago. When people read this poem, they shall be reminded about it,” Zainun told AFP. 

Recounting his loss, he added, “My children, wife, father, mother, and all of my siblings were swept away. The same tragedy was felt by others as well. Everyone affected by the tsunami shares the same experience. We feel the same feelings.” 

Marziani, a 51-year-old teacher, recalled her own grief and guilt after losing her child in the disaster. “At that time, I couldn’t stop crying. I felt guilty because I felt like I could not protect my child. Even though, when I think about it now, I realise I could not even protect myself, let alone carry my child. And that feeling of guilt lasted for months,” she shared. 

The disaster, triggered by a massive undersea earthquake, sent waves up to 40 meters (130 feet) high crashing into villages, including Akkaraipettai in Tamil Nadu state, where Lakshmi lived. On that fateful morning, Lakshmi’s father had come to her home to look after her young daughter, Yashoda. Hours later, a deafening rumble announced the arrival of the colossal waves that swept through their village.

“She would have been 22 years old now,” Lakshmi said tearfully, holding a photograph of Yashoda, a poignant reminder of the tragedy that continues to haunt her and countless others affected by the tsunami.

Pirun, who was birdwatching when the tsunami struck, recalls the eerie sound that preceded the devastating waves. He managed to alert his neighbours and reach higher ground, but his parents were not as fortunate.

Despite his initial fear of the sea, Pirun has found a way to reconcile with it. Each morning, he sets out in his red and yellow boat from Bang Wa district, selling his catch at the local market.

"The sea makes me sad and happy at the same time," Pirun told AFP. "It reminds me of loss, but it also shaped who I am today."