Challenging earthquake prediction A seismologist's thoughtsMarch 3 22:14

"If Ms. Ito observes somewhere, an earthquake will occur," says seismologist Yoshihiro Ito,

who is often told by scientists around him. He is an associate professor at the Disaster Prevention Research Institute, Kyoto University, and is studying a phenomenon called "slow slip" that may lead to the prediction of the occurrence of a large earthquake.

The Great East Japan Earthquake in 2011 and the three major earthquakes that occurred in Mexico in succession from 2017 to 2018 all occurred in the area where Ms. Ito was observing slow slips.

According to current science, it is difficult to predict when and where a huge earthquake will occur. Nevertheless, Ms. Ito has expanded her field to Mexico and other countries to continue to observe slow-slips and take on the challenge of predicting huge earthquakes.

It all started with the frustration I experienced during the Great East Japan Earthquake in 3. Ms. Ito's thoughts have brought about unexpected changes in the people of Mexico who have been commuting since 2011.
(News Program Center Makoto Kanamori)

Remorse for the Great East Japan Earthquake Failure to Utilize Research for Disaster Prevention

Ms. Ito's research attracted attention after the Great East Japan Earthquake in 2011.

Two weeks after the magnitude 9.0 earthquake, Ito, who was doing research at Tohoku University at the time, recovered a pressure gauge installed on the seabed off the coast of Tohoku and analyzed the data, and discovered that surprising data had been recorded.

A small waveform that has been going on since about January 3, about a month and a half before March 11.

It is due to the slow slip quake.

What kind of phenomenon is slow slip?

Normal earthquakes cause strong shaking due to the rapid displacement of faults, causing great damage.

On the other hand, in slow slip, the fault moves slowly at a speed of about 1/1,24 to 10/1 million compared to a normal earthquake, so it does not generate strong shaking that people feel, but it is known that it occurs at the plate boundary that causes a huge earthquake.

The pressure gauge on the seabed that Ms. Ito recovered after the earthquake captured the slight vibration of the slow slip.

Where did this slow slip happen? It is a map showing the location.

The location is off the coast of Miyagi Prefecture.

The orange area is where the slow slip was occurring.
And the red area is where a huge earthquake occurred.

You can see that these two areas overlap.

It indicates that a huge earthquake occurred immediately after the slow slip.

Ms. Ito discovered this fact after seeing the devastation in the areas affected by the Great East Japan Earthquake.

I felt that if we had been able to notice the existence of slow slips in advance and issue some kind of alert, we would have been able to reduce the damage caused by the earthquake and reduce the number of casualties as much as possible.

Associate Professor
Yoshihiro Ito, Kyoto University: "At the time of the Tohoku-Pacific Ocean Earthquake (Great East Japan Earthquake), we had data that a slow slip occurred on the seabed, leading to a huge earthquake, even though it was an observation method that was not real-time. I feel very frustrated that even though I have such data, I could not connect it to the prediction of the occurrence, so I am proceeding with research activities with the hope of expanding the observation network and somehow applying the research results so that no one dies in disasters as much as possible for the next Nankai Trough."

Can we predict a Nankai Trough mega-earthquake?

Ms. Ito is now wary of a Nankai Trough mega-earthquake that is expected to occur with a probability of occurring 30% to 70% within the next 80 years. The government estimates that the death toll will be as high as 32,3000 at worst, and half of the population will be affected.

Along the Nankai Trough, various observation networks have been established by the national government and research institutes to detect phenomena such as slow slips.

Off the coast of Tohoku, there was a problem that data such as slow slips could not be found until the seabed pressure gauge was collected, but along the Nankai Trough, observation devices on the seabed are connected by submarine cables, so data can be acquired in real time.

Then, if it is found that a slow slip has occurred in the Nankai Trough, will it be possible to predict a huge earthquake in advance?

Ms. Ito said:

Associate Professor
Yoshihiro Ito, Kyoto University: "I don't think prediction is that easy. However, I think it can be said that the occurrence of slow slips increases seismic activity in the surrounding area, and as a result, the probability of occurrence of large earthquakes increases, so I hope that we can understand the slow slip itself and actively disseminate information such as prediction of surrounding phenomena associated with slow slips and prediction of the occurrence of large earthquakes with higher accuracy."

"At least we are now observing slow slips using seabed observation networks and land observation networks, and I think it is important to first proceed with such information obtained in real time in the form of some kind of warning or warning to people living in the vicinity, even if the accuracy is relatively low. 」

New discovery in Mexico: Slow slip that triggers a major earthquake

Ms. Ito believes that in order to use slow slips to predict the occurrence of large earthquakes, it is necessary to know more about slow slips.

Therefore, in order to investigate the relationship between slow slips and huge earthquakes in more detail, Mexico was chosen as a new research field after the Great East Japan Earthquake.

In 2015, in collaboration with a local research group led by Professor Victor Cruz (right) of the National Autonomous University of Mexico, we launched a research project to explore the relationship between massive earthquakes and slow slips along the Pacific coast of Mexico.

Ms. Ito, who began observing Mexico by bringing observation equipment such as the yellow submarine seismometer and pressure gauge shown in the photo from Japan, obtained surprising data off the coast of Tohoku and Mexico as well.

Why did you choose Mexico in the first place? This map plots the epicenters of earthquakes of magnitude 40.7 or higher that have occurred in Mexico over the past 0 years.

There are 26 of them. It can be seen that it is concentrated especially in the Pacific coast.

In 1985, a massive earthquake with a magnitude of 8.1 occurred, killing nearly 1,2012 people, including the collapse of a high-rise building in the capital Mexico City.

In 2, tsunamis of 3 to 2 meters in height were also observed along the coast. Just like Japan, they have in common that they have been repeatedly hit by large earthquakes and tsunamis along the coast.

Ms. Ito thought that if slow slips and large earthquakes could be observed in Mexico, it could be used for earthquake research in Japan.

That prediction came true in 2017, about two years after the observation began.

This figure shows the size of the slow slip at the plate boundary by analyzing GPS data.

The slow slip, which began in the red area in June, continued for about three months.

Then, on September 6, a massive earthquake with a magnitude of 3.9 occurred in the eastern area.

The following figure shows what happened.

This time, the slow slip is enlarged in another area shown in red.

In February of the following year, a large earthquake of magnitude 2.7 was triggered on the south side.

Associate Professor
Yoshihiro Ito, Kyoto University: "When a large earthquake occurs, the slow slip is activated by the large earthquake, and the activated slow slip triggers another large earthquake. Slow slips and large earthquakes have been observed as if they were talking. In other words, in the future, by accurately investigating the slip zone of slow slip, there is a possibility that some kind of warning will be issued against the occurrence of a huge earthquake. I think it is extremely important to observe slow slips in various seismic cycles in various areas and to properly understand how large earthquakes occur in the vicinity and how they are linked, in order to predict the occurrence of Nankai Trough megaearthquakes in the future."

Professor Victor Cruz of the National Autonomous University of Mexico:
"In order to identify phenomena that predict the occurrence of large earthquakes Japan, it is necessary to continue to study slow slips. If we can grasp the process before a major earthquake occurs more clearly, we may be able to predict the occurrence of an earthquake in advance. This is a dream that seismologists around the world have had for generations."

Changes in the people of Mexico: Facing the risk of tsunami

There is a researcher who sympathizes with Ms. Ito's thoughts and is working on disaster prevention in Mexico.

I'm Assistant Professor Genta Nakano of Kyoto University.

After experiencing the Great Hanshin-Awaji Earthquake at the age of seven and studying disaster prevention at high school and university, Nakano has been focusing on regional disaster prevention and disaster prevention education as a researcher at Kyoto University, including in Kochi Prefecture, where there is a risk of tsunamis.

The practice is set in Zihuatanejo, a town on the Pacific coast about an hour by plane from the capital Mexico City.

It is a city with a simple atmosphere overlooking the beautiful sea, and resort hotels are lined up along the coast, making it a tourist destination visited by many foreign tourists.

During the interview, I met a tourist who came from the United States and Canada.

街を歩くとまず目についたのはこの看板。津波の避難ルートを示す標識で、2022年春に新たに設置されました。

Tsunami is an internationally accepted term known as "tsunami," but many residents in this area were not properly aware of the risk.

In fact, there is a record of being hit by an 100-meter tsunami in 1925, about 11 years ago.

However, many people have migrated from other regions, and most of them do not know about the tsunami 100 years ago.

Rafael, the city's disaster prevention manager, said:

Rafael Baldobino, Director
of the Disaster Prevention Bureau of Zihuatanejo City, said, "Before starting the project with Kyoto University, the residents of Zihuatanejo did not really know what a tsunami was. I got an answer like this. In addition, we were in charge of disaster prevention and assumed that the height of the tsunami would be about 1.5 meters at most, and we thought that it would be lower because of the obstruction of buildings."

If you look closely at the sign, you can see that it has an arrow written on it. Even those who come to this place for the first time can immediately know in which direction to escape.

This direction of escape is also determined by making use of scientific knowledge.

Zihuatanejo has mountains on the opposite side of the sea, so the residents thought that if they wanted to escape to a higher place, they should head towards the mountains.

However, when we conducted a tsunami inundation simulation, we found that it was not always correct to escape towards the mountains.

The mountain is located at the top (north) of the map, but simulations show that flooding begins about 13 minutes after the earthquake strikes, and that the upper (north) mountains flood earlier.

Up to 7 meters in height is predicted.

It became clear that in order to have time before flooding, it was better to flee to the right (east) of the map instead of heading for the mountains.

In addition to horizontal evacuation, we are also working to encourage owners to use tall, sturdy buildings such as hotels as tsunami evacuation buildings so that safety can be ensured immediately.

However, there are issues such as crime prevention, and we plan to continue discussions between Zihuatanejo City and the owner.

Changes in the Mexican People "Awareness of Disaster Prevention" that has begun to take root

Among the initiatives that Ms. Ito and Ms. Nakano have been promoting in Mexico, disaster prevention education is the one that the local people praise the most.

On this day, Ms. Ito and Ms. Nakano came to Lázaro Cárdenas Junior High School.

Students formed a "Disaster Prevention Committee" to learn about disaster prevention, created a risk map with local risks, and took courses to learn how to use first aid and fire extinguishers.

In addition, disaster prevention education has been conducted at 18 schools from kindergarten to high school, and more than 1,<> children have learned about disaster prevention so far.

Luis Alberto, 14:
"Through the training, I learned that I can reduce the risk of earthquakes and fires, which gave me confidence and allowed me to walk around the city with peace of mind. When a disaster strikes, I want to take care of myself and protect everyone who is with me."

In some cases, we have actually achieved results.

This is an example of a voluntary disaster prevention organization called CERT, which was created by calling on local residents.

In 2018, a fire burned 100 houses, and residents were among the first to extinguish the fire and provide evacuation guidance before the fire trucks arrived.

Some residents did not evacuate immediately in an attempt to carry out their belongings, but by persuading them to evacuate, we were able to reduce the number of casualties to zero.

Ms. Ito's series of initiatives was a research program jointly conducted by the Japan Science and Technology Agency (JST) and the Japan International Cooperation Agency (JICA), and 2022 was the final year of the research period.

Then, on November 2022, 11, World Tsunami Day, a seminar was held in Zihuatanejo City to report the results of the project.

More than 5 people, including residents and government disaster prevention officials, gathered.

Rafael, who is in charge of disaster prevention in Zihuatanejo City, gave the following presentation on the change in awareness among residents.

Rafael Baldobino, Director of the Zihuatanejo Disaster Management Department: "In the past, disaster prevention was a one-way way of communicating the risks of earthquakes and tsunamis by experts and government agencies,
but the change to a participatory approach has brought about a big change for residents. The first change is the idea of "self-help," in which you protect your own life. They began to stockpile food and drinking water. The second is mutual assistance. We began to help each other in the local community and protect the community by ourselves. This kind of learning will not be forgotten across generations, and I think it will be effective in the event of a tsunami that may occur 2 years from now."

Associate Professor
Yoshihiro Ito, Kyoto University: "It has been a total of seven years since I started working on Mexico from scratch. In Zihuatanejo City, the awareness of disaster prevention has taken root very much. Unprecedented efforts are being made in school education. It is very moving that seismologists and sociologists have collaborated to achieve such results. I think we need to think seriously about how seismologists should respond and what kind of information they should provide. We want to produce better data and results so that we can lead to disaster prevention as much as possible."

A Q&A session was held at the end of the seminar. During the lively exchange of opinions, there was a scene where a woman from a neighboring city called for "work on this in your own community."

The thoughts of Ms. Ito and other researchers are gradually but steadily bringing about changes for the people of Mexico.

In the heart of the city of Zihuatanejo, there is a time capsule that was buried in 2017 with this project.

Messages to be buried were widely solicited from citizens, and Mr. Nakano and others also included messages.

It is scheduled to open in 50, 2067 years later, and Mr. Nakano said, "I am over 80 years old, but if I am healthy, I would like to open it."

How will the people of Wrinklitanejo of the future feel when they open the time capsule?

I hope that this project will be a great force in overcoming future disasters.

On the other hand, how well are each of us, Japan who are seen by the people of Mexico as an "advanced disaster prevention area," able to do disaster prevention?

It was an interview in Mexico that gave me the opportunity to think again.

Makoto
Kanamori, Director
of the News Program Center (Social Program Department) Joined Tottori
Broadcasting Station and Morioka Broadcasting Station in 2006 and was in charge of news programs such as NHK specials and
Close-up Gendai.