Japan has a long history of natural disasters.

Now, the power of science is helping to overcome them.

BOSAI: Science that Can Save Your Life.

In 2011, the Great East Japan Earthquake left more than 18,000 people dead or missing.

Most of them died as a result of the tsunami that followed the earthquake.

11 years later, the Japanese government is drawing attention to the risk of a "major tsunami" which would be even more dangerous than the Great East Japan Earthquake.

It could be caused by a "megathrust" earthquake with its epicenter in the Chishima Trench or the Japan Trench, which extend from the coast of Hokkaido to the Tohoku region.

Deaths in the disaster could exceed 190,000, more than 10 times that of the Great East Japan Earthquake, with most due to the resulting tsunami.

Living in Japan and surrounded by the sea on all sides, the risk of a tsunami is unavoidable.

What are the newly discovered risks of an earthquake in the Chishima and Japan Trenches?

There are 2 areas at high risk of this kind of a megathrust earthquake.

One is the focal zone along the Chishima Trench, where an earthquake could have a magnitude of up to 9.3.

The other is the north side of the Japan Trench, running from the south of Hokkaido to the coast of Iwate Prefecture, where an earthquake could have a magnitude of up to 9.1.

Both are expected to be megathrust earthquakes with a magnitude of 9 or more, which would exceed the Great East Japan Earthquake.

A major tsunami of up to 30 meters is also expected to occur.

When a major tsunami occurs, what will decide whether we live or die?

Dr. Makoto Tomatsu studies tsunami disaster preparedness in Hokkaido.

He believes the most important thing is to provide accurate tsunami information as quickly as possible.

Thank you for joining us today.

It's my pleasure.

What kind of research are you doing?

We've been conducting research
on tsunami evacuation.

Tomatsu recently conducted an evacuation experiment for a tsunami that could be caused by a megathrust earthquake in the Chishima Trench.

50 residents from Hokkaido's Hamanaka Town participated.

Hamanaka Town is located near the focal zone of the Chishima Trench, and is a town with a high tsunami risk.

If a major tsunami occurred, about half of the population could lose their lives.

In this experiment, participants wore GPS trackers
and moved to evacuation centers.

Location information was provided second by second,
and accurate evacuation times could be measured.

Each of these red circles is a participant.

The map shows the evacuation route from their homes to the centers, and records their evacuation time.

There were 2 evacuation centers, one on the roof of a school on flat ground, and the other at the town hall on high ground.

Then, by superimposing the evacuation data of the residents and the tsunami simulation from the Chishima Trench megathrust earthquake, the time required for a safe evacuation can be predicted.

Tomatsu focused on the time from when the earthquake occurred until the evacuation was completed.

This is what would happen if the evacuation began 15 minutes after the earthquake.

The evacuation begins.

Immediately after the evacuation begins, a tsunami with a maximum height of 20 meters arrives and engulfs the residents, who are in the process of evacuating.

This is what would happen if the evacuation began 5 minutes after the earthquake.

Residents are moving to the 2 evacuation centers.

20 minutes after the earthquake, the tsunami arrives and floods the town.

Residents who evacuated to the school can go up to the roof and escape from the tsunami.

If the residents started to evacuate 5 minutes after the earthquake occurred, they could all reach the evacuation centers.

But if they started to evacuate 15 minutes after the earthquake occurred, many would be caught in the tsunami.

Just 10 minutes could be the
difference between life and death.

This experiment asks residents to
reflect on their evacuation behavior, and shows that if they are slow to evacuate
they might be caught in the tsunami.

But if a megathrust earthquake and tsunami occur, will people be able to evacuate as quickly as in a practice drill?

Quick and accurate tsunami information is essential in the confusion of a disaster situation.

In the Great East Japan Earthquake of 2011, an inadequate observation system for earthquakes and tsunami made it impossible to accurately predict the height of the tsunami,

which contributed to a delay in evacuating residents.

At that time, the Japan Meteorological Agency issued a tsunami warning 3 minutes after the earthquake struck.

However, the predicted height of the tsunami was much smaller than what actually occurred.

30 minutes after the first report, the Japan Meteorological Agency updated the predicted height, but by this time a tsunami exceeding 15 meters was already approaching the coast.

Why was the tsunami warning, which is so important for the evacuation of residents, underestimated?

Tsunami warnings are based on simulation results that have been carried out in advance and stored in a database.

When an earthquake occurs, the simulation with the most similar epicenter position and scale is retrieved.

The selected simulation results are then announced as an alert.

In the 2011 Great East Japan Earthquake, the seismographs were shaken by stronger than expected tremors, and the magnitude of the earthquake was entered incorrectly, leading to major errors.

If the size of the tsunami had been accurately predicted, and promptly conveyed to residents, the number of casualties could have been reduced.

More than 10 years have passed since the Great East Japan Earthquake, and tsunami observation technology in Japan has advanced significantly.

What are the latest developments in tsunami observation?

Dr. Shin Aoi is conducting research on the real time observation of earthquakes and tsunami all over Japan, to inform disaster preparedness.

What was the system for observing
the 2011 earthquake and tsunami?

There were about 1,500 seismographs on land,
making careful observations.

But offshore there were only 40 seismographs
and 30 tsunami gauges, so observations at sea were insufficient.

The Great Hanshin-Awaji Earthquake of 1995 led to the development of an earthquake and tsunami observation network centered on land.

This was a near-field inland earthquake, so the resulting focus was on the installation of seismographs on land.

However, the epicenter of the Great East Japan Earthquake of 2011 was off the Pacific coast.

The system for observing undersea earthquakes and tsunami was inadequate, and contributed to the underestimation of the tsunami warning and the loss of many lives.

At that time, there was a device that could accurately measure the height of a tsunami.

The cable type water pressure gauge.

When a tsunami occurs and the water level rises, the weight of the water increases and the water pressure on the device increases.

The height of the tsunami is measured using these changes in pressure.

This kind of water pressure gauge was installed on the seabed 70 kilometers off the coast of Kamaishi.

A tsunami exceeding 5 meters was measured 15 minutes after the earthquake occurred.

It could have predicted that this tsunami would exceed 15 meters if it reached the coast.

Was it difficult to use water pressure gauge
observation data for tsunami warnings?

At that time, this observation data
was not used for tsunami warnings.

Offshore tsunami observations have
since been shown to be very effective.

It made us realize the importance
of offshore observations.

Japan's tsunami observation technology is evolving based on lessons learned from the Great East Japan Earthquake.

A special observatory has been developed by adding new functions to the cable type water pressure gauge.

A device about 2 meters long containing seismometers and pressure gauges can be installed on the seafloor.

150 of these ocean-bottom observatories have now been installed in a system known as S-net.

Its undersea optical cables span a total length of 5,500 kilometers, extending from the coast of Hokkaido to the Boso Peninsula.

Observation data from these observatories can be obtained 24 hours a day in real time, and sent to relevant organizations.

It is now being used for the Earthquake Early Warning or EEW and tsunami warning systems.

This is the observation data from the earthquake that occurred off the coast of Sanriku in 2016.

The S-net observation data is at the top, and the land observation data is at the bottom.

S-net detected the earthquake 22 seconds earlier than the land observation.

Observation nearer the epicenter of the earthquake increases the speed of detection and leads to more accurate tsunami prediction.

What are the benefits of detecting
an earthquake 22 seconds earlier?

We can prevent major accidents
by issuing earthquake warnings sooner and stopping Shinkansen trains
as soon as possible.

The risk of a major tsunami is not limited to eastern Japan.

In the worst case scenario, 320,000 might lose their lives in a Nankai Trough Megathrust Earthquake.

Aoi and his team are currently constructing the Nankai Trough Seafloor Observation Network for Earthquakes and Tsunamis, or N-net, which they aim to complete in 2025, as the observation system in this area is not yet sufficient.

I was surprised to learn that the earthquake early warning and tsunami information we see in times of emergency is updated daily based on sophisticated observations.

An earthquake and tsunami can strike at any time.

That's why it's important to be aware of the latest disaster prevention information.

And if there is a tsunami warning, remember to evacuate to higher ground as soon as possible.