On June 18, the Kinki area, the second-largest urban area, including Osaka Prefecture, after the Tokyo metropolitan area, suffered an earthquake with its focus just below the urban area. Japan is known throughout the world for being an earthquake-prone nation, and it is not unusual for any big city to be hit by a large earthquake at any time. The Yomiuri Shimbun asked three experts how this recent earthquake should be viewed and how its lessons should be applied to future disaster prevention. The following are excerpts from the interviews.
(From The Yomiuri Shimbun, June 19, 2018)
Materials other than buildings could be lethal
The percentage of houses made resistant to earthquakes was 82 percent five years ago, up from about 75 percent 15 years ago. During the recent earthquake old wooden houses collapsed, but victims were pinned under garden walls, indoor bookcases and other materials, not by the collapse of buildings themselves.
As a result of making more houses resistant to earthquakes, structural materials such as pillars are capable of withstanding even strong quakes in most buildings. Residents are told to remain indoors after a large earthquake has struck because in a large city, if you leave a building right after an earthquake, you may encounter secondary dangers presented by falling objects and large groups of people.
During this earthquake, human life was lost due to non-structural parts of buildings such as garden walls and shelves, which has made it clear that attention must also be paid to dangers other than building collapse.
Standards for concrete-block walls became stricter after the 1978 earthquake off Miyagi Prefecture. And after the Great East Japan Earthquake in 2011, measures to prevent roofs from falling have been strengthened for buildings larger than a certain size. However, there are still many dangerous structures in large cities.
During the recent earthquake, an electronic noticeboard hanging above a train station platform fell down and traffic lights on the road tilted over. These objects might have become lethal weapons, as the earthquake occurred during the morning rush hour when many people were headed to work and school. This seems to be a blind spot in traditional countermeasures.
The Tokyo metropolitan government established regulations to promote making buildings resistant to earthquakes along main roads so that emergency vehicles can drive on them. The regulations were implemented in 2011 and to some extent there has been progress in the reinforcement of buildings that could possibly hinder evacuation as well as restoration efforts. However, progress in the areas that face side streets and are congested with old wooden houses has not reached a satisfactory level.
The government has set a target to increase the percentage of buildings that are resistant to earthquakes to 95 percent by 2020 and to almost completely eliminate houses that are non-resistant to earthquakes by 2025. It's necessary to progress steadily toward these targets.
Behind the failure to make progress with reinforcement in areas congested with wooden houses lies the fact that residents are not willing to remodel or rebuild their houses because it costs a lot and they don't understand the necessity of it. But there are also some circumstances unique to these areas. The Building Standards Law states that at least two meters of the boundary of a house lot must abut a four-meter or wider road. If old wooden houses do not fulfill these requirements, they can no longer be lived in even if they are rebuilt.
If things remain as they are, with main roads lined by sturdy buildings, behind which are congested weak wooden houses, the resistance of an entire area to earthquakes will not improve. Buildings themselves should be made stronger, but the disaster prevention capability of the entire area must be improved, including efforts made by local businesses.
-- This interview was conducted by Yomiuri Shimbun Senior Writer Jun Sato.
--Yoshiaki Hisada
Professor at Kogakuin University
Graduated from the Faculty of Science and Engineering at Waseda University and completed graduate school. Doctor of Engineering. Held such positions such as a research associate at the University of Southern California and full-time lecturer and associate professor at Kogakuin University. Specializes in seismic engineering. He is 56.
Accumulate data for future generations
The entire Japanese archipelago is pushed from east and west mainly by the Pacific plate. There are many active faults along the region between Chubu and Kinki, where the archipelago bends. When earthquakes occur there, the distortions accumulated in the bedrock are released.
Flat plains where people gather, such as around Osaka, are surrounded by active faults. The movement of the faults causes the rise and fall of the land in relation to the mountains and forms such landscape as Osaka. We do not know much about the Kanto region, as it has a thick layer of sedimentary rock, but it probably also has faults that are hidden underground.
The recent earthquake occurred at an intersection between the Arima-Takatsuki fault zone that runs from east to west and the Ikoma fault zone that runs south to north. Just like the intersection between the Futagawa and Hinagu fault zones that was responsible for the Kumamoto Earthquake, it likely has a complex underground structure. Because of this, ideas such as "it has an activity cycle of several thousand years" and "it's only been a few centuries since it was last active" may not readily apply.
When you look at the whole of Japan on average, the pace at which earthquakes occur is surprisingly constant, but if you look at each region individually, they each have their own periods of activity. For the 40 years prior to the Nankai Earthquake of 1946, western Japan experienced many earthquakes of magnitude 6 or stronger. After the Great Kanto Earthquake of 1923, there were fewer earthquakes of magnitude 6 or over in the Kanto region compared to before.
As is often pointed out, it is thought that before the next earthquake happens in the Nankai Trough, western Japan will once again see the number of earthquakes with a certain intensity growing.
However, we can't say that the recent increase in the number of earthquakes means a Nankai Trough earthquake will occur soon. If the number of quakes falls after the next Nankai Trough earthquake occurs, that is when we will first know that this is the case. Even judging from the way in which earthquakes are occurring at the moment, we don't have sufficient knowledge to say, "The number of earthquakes is increasing because there is about to be a Nankai Trough earthquake."
After the Great Hanshin Earthquake of 1995, an observation network of things like seismographs and GPS was put into place and the amount of data has rapidly increased. In preparation for the next Nankai Trough earthquake, we can record what kinds of changes occur, meaning we may be able to predict the next big earthquake in the future. If we don't store up our experience, we can't predict the events of the future based on it. Properly amassing data will be of much use to future generations.
Earthquakes on the scale of the recent one in Osaka could happen at any time and at any place within Japan. Even in places like Hokkaido and Shikoku, which seem relatively quiet, I want people to take proper precautions, such as fastening down furniture, and understand that "next time it could be us."
--This interview was conducted by Yomiuri Shimbun Senior Writer Hiroshi Masumitsu.
--Yoshimitsu Okada
Administration officer for the Association for the Development of Earthquake Prediction
Specializes in seismology. Held the position of chairman of the board at the National Research Institute for Earth Science and Disaster Resilience until 2015. Author of "Nihon no Jishin Chizu" (Japan Earthquake Map) and other books. He is 73.
Always be prepared for the 'worst case scenario'
I want the people affected by the recent earthquake to be vigilant about another quake. At the time of the 2016 Kumamoto Earthquake, a larger "main quake" of magnitude 7 occurred two days after the first quake. Traditionally we have referred to these earthquakes as "aftershocks," but this word has connotations of "a smaller earthquake," so the Japan Meteorological Agency stopped using the word after the Kumamoto Earthquake. We need to abandon the preconception that the first earthquake will always be the biggest.
There was an earthquake registering a lower 5 on the Japanese seismic intensity scale in Gunma Prefecture on June 17. It's not unusual for quakes to strike anywhere within Japan. When it comes to any disaster, not just earthquakes, people tend to think, "It'll never happen to me." However, in reality, large earthquakes still occur in areas with a low possibility of earthquakes striking. Furthermore, we can't predict most risks like earthquakes and volcanic eruptions. As we can't predict these events, how to respond when they happen is ever more important.
What's special about the recent quake is that it occurred in a densely populated area during the morning rush hour. Even if the magnitude of an earthquake is not particularly large, casualties will increase depending on the location of the hypocenter and the time that it occurs. When people are crushed by collapsing walls, transport networks fall into disarray and it becomes difficult to provide care at medical institutions, there is still a lot of damage and suffering even when the earthquake isn't large in size.
First, to protect yourself and your family, you should have an action plan in your head for the worst-case scenario. In case you get trapped in a train, you should always carry water with you. If it's winter, you should have portable heat packs at the ready.
If an earthquake strikes when children are headed to school, like the recent one, this will put elementary school students in danger. Other risks like crime also exist. It may be necessary for children to carry cell phones so that they can contact their parents should the worst happen. Through these preparations, people can gain some "resilience" that will make them better able to respond to a disaster.
In addition, rail and other transport companies should actively broadcast information throughout the station and train cars about when service will be restored and what kind of assistance is offered to vulnerable people such as the sick and elderly. I'd also like businesses and schools to quickly issue directions that employees don't have to come to companies or that schools are closed. In the case of schools, the Board of Education often decides to close all schools simultaneously, but what if this operation was handed over to head teachers to decide autonomously?
Disasters also tend to become hotbeds of false information. This trend has been especially prevalent in recent years with the development of platforms like Twitter. During the recent earthquake, false information like "there is a crack in the stadium roof" proliferated. Extreme information that people hastily latch on to should be doubted for its validity. I want people to check such information using newspapers and TV.
-- This interview was conducted by Yomiuri Shimbun Senior Writer Fumihiko Abe.
--Hirotada Hirose
Professor Emeritus at Tokyo Woman's Christian University
Director of the Research Center for Safety & Security, and has served as the chairman of the Society for Risk Analysis Japan. Books authored include "Hito wa Naze Nigeokureru no ka?" (Why don't people escape in time?) and "Kyodaisaigai no Seiki o Ikinuku" (Surviving the century of big disasters). He is 75.
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