Catastrophe 100 Years Ago Provides Lessons We Should Heed Today

This September marks exactly 100 years since one of the worst natural disasters in Japan’s history, the Great Kanto Earthquake. Living in Japan, where natural disasters happen frequently, we should use this milestone as an important opportunity to learn many lessons for thinking about disaster prevention.

The Great Kanto Earthquake occurred at 11:58 a.m. on Sept. 1, 1923. Although many people believe even now that Tokyo was at the epicenter of the quake, the actual epicenter was south of Tokyo. It extended over an area 130 kilometers long, from Kanagawa Prefecture across Tokyo Bay to Chiba Prefecture’s Boso Peninsula. The quake’s magnitude, a measurement of its seismic energy, is estimated to have been 7.9. The main quake was followed by a series of large aftershocks, with a total of five magnitude 7 or greater aftershocks occurring in two days.

Cities across the affected areas were hit with tremors equivalent to 7 and upper 6 on the current Japanese seismic intensity scale. Approximately 80,000 houses were destroyed. The 50-meter-plus Ryounkaku Tower, a famous Tokyo landmark at the time, was shaken so badly that its upper eight floors collapsed.

The number of dead and missing in the Great Kanto Earthquake exceeded 100,000, which stands out even in comparison to the about 6,400 in the Great Hanshin Earthquake in 1995 and the about 22,000 in the Great East Japan Earthquake in 2011. The reason for this is that the Great Kanto Earthquake was an unprecedentedly complex disaster.

Ninety percent of the victims were killed by fire. The damage was concentrated in Tokyo and Yokohama, as it was lunchtime and many houses had cooking fires. Strong winds were blowing at the time, and the rapidly spreading flames swirled into a superheated tornado that burned to death some 38,000 people who had evacuated to a section of Tokyo’s Honjo Ward (now Sumida Ward). The fire is said to have lasted for almost two days.

The earthquake was accompanied by a tsunami. In Atami, Shizuoka Prefecture, a tsunami of up to 12 meters reached the coast and swept away about 170 homes, leaving about 100 people dead or missing. In mountainous areas, the earthquake triggered landslides and cliff collapses. At Nebukawa Station in Odawara, Kanagawa Prefecture, a hill behind the station collapsed, killing more than 130 people.

Years earlier, seismologist Akitsune Imamura had predicted the occurrence of such a catastrophic disaster and sounded the alarm. Born in Kagoshima City in southern Japan in 1870 as the third son of Akikiyo, a member of the Satsuma clan, Imamura was known for his intelligence from childhood and became interested in physics under the influence of a teacher at school. Soon after entering the Imperial University, which later became the University of Tokyo, he was involved in field research on an earthquake that happened in the Chubu region in 1891. Although he had not decided which area he would major in until then, he chose to pursue seismology research after witnessing the devastation of the disaster, which killed more than 7,000 people.

Spending a lot of time doing research on earthquake observation and analysis, he published a paper titled “A Simple Method for Mitigating Damage to Life and Property Caused by Earthquakes in Urban Areas” in 1905. The paper warned that based on the cycle of past strong earthquakes, a major earthquake was likely to strike Tokyo soon and that precautions should be taken in advance. Imamura urged paying attention to fires. If an oil lamp were to fall over in densely populated Tokyo, the resulting fire would spread far and fast. He emphasized the threat of fire by saying, “If even a small amount of wind blows, the entire city will be reduced to ashes.” He stressed the importance of strengthening the earthquake resistance of houses and using electric lights.

However, his boss at the university criticized him for the paper, saying that it was a “baseless theory.” Imamura’s intention was not only to predict earthquakes but also to sound an alarm about how to protect the lives and property of citizens, but his true intentions were not fully understood, and adequate disaster prevention measures were not taken. Eighteen years after the paper was published, the Great Kanto Earthquake occurred.

This disaster, which caused unprecedented damage, led to enhanced earthquake research in Japan. Imamura, who regretted that he had been unable to prevent such terrible losses, also invested his own money to set up observation networks in areas such as the Kii Peninsula, which faces the Pacific Ocean between Osaka and Nagoya. While serving as president of the Seismological Society of Japan, he energetically continued his research to find signs of the next big earthquake before passing away in 1948.

Are the lessons of Imamura’s efforts to strengthen disaster prevention being built upon by people of the present day?

Researchers have made progress in observation accuracy and disaster prevention technologies, such as earthquake early warning systems and tsunami prediction through an expanded seafloor observation network. However, even though researchers have developed new technologies for disaster prevention, it is not necessarily true that public awareness of disaster prevention has sufficiently increased. In a 2021 survey, the Land, Infrastructure, Transport and Tourism Ministry asked 10,000 people what they had done to prepare for natural disasters in the past two or three years. The answer given by 39.5% of respondents was “nothing.”

Honestly, I can understand the mindset of the many people who think they will not be involved in a disaster. I was working as a reporter for The Yomiuri Shimbun’s Fukushima Bureau when the Great East Japan Earthquake struck on March 11, 2011. In fact, just before the earthquake, on March 9 and 10, earthquakes of seismic intensity from 1 to 4 were also observed intermittently in Fukushima Prefecture. At the time, I myself did not imagine that a major earthquake would occur. It is not easy to prepare for a threat that may come at any time.

In July, The Yomiuri Shimbun digitally mapped the estimated seismic intensity of the Great Kanto Earthquake for Tokyo, Kanagawa, Chiba, Saitama and Shizuoka prefectures, and published the digital map online. Anyone can access it and check the seismic intensity, total number of buildings, and number of collapsed buildings at approximately 1,000 locations. They can easily check what happened 100 years ago in the vicinity of their own residence, workplace, school, hospital and so on. Hidenori Watanabe, a professor at the University of Tokyo who assisted in the creation of the digital map, said, “This map is very important because it allows people to find out by themselves what happened around them and gives them a chance to consider disaster prevention.”

Fortunately, no earthquakes that could cause extensive damage to the Tokyo metropolitan area have occurred in the past 100 years. However, there is a 70% probability that a magnitude 7 or greater earthquake directly under the area will take place within the next 30 years. In addition to collapsed buildings and fires, we face new challenges such as people having difficulty returning home or being trapped in elevators for a long time. By learning from past disasters, we need to build up our preparations for future disasters, one step at a time.

Political Pulse appears every Saturday.

Sho Funakoshi

Funakoshi is a staff writer in the Science News Department of The Yomiuri Shimbun.