“There is a 70% chance that a major earthquake will occur in the Japanese capital within the next 30 years.”
This is not an urban legend, but something the Japanese Cabinet Office announced in 2013, more than 10 years ago. As of the time of announcement, it was “the next 30 years,” so in reality, it is a story about the next 20 years. As the damage caused by the magnitude 7.6 earthquake that struck Ishikawa Prefecture on New Year’s Day is increasing, attention is also being paid to the previously predicted ‘earthquake directly under the capital’.
The basis is the cycle of eight major earthquakes analyzed since the 1700s. Between the Great Kenroku Earthquake (1703) and the Great Kanto Earthquake (1923), a total of eight major earthquakes occurred in about 220 years.
The government’s Earthquake Investigation Committee considers the 220 years from the Great Kenroku Earthquake to the Great Kanto Earthquake as a cycle and predicts the probability of a magnitude 7 earthquake occurring in the future. Assuming that eight major earthquakes occur in the meantime, simple calculations show that it occurs once every 27.5 years. Based on this, if we plug it into the future prediction formula used in seismology, we get a probability of occurrence of ‘70% within the next 30 years’.
Some experts point out that the patterns of earthquakes in the first and second half of the cycle are different. According to NHK, the first half of the year is divided into a ‘calm period’ with a relatively low frequency of earthquakes, and the second half of the year is an ‘active period’ with a high frequency of earthquakes. In fact, 7 out of 8 earthquakes were concentrated in the second half of the year.
What is noteworthy is that these eight earthquakes occurred not on the coast, but on tectonic plates directly beneath areas where many people live, causing significant damage.
If an earthquake were to occur right under the capital in modern times, in the worst case, 23,000 people could die and economic losses worth about 95 trillion yen (about 886 trillion won) could occur. This is a huge amount equivalent to 83% of Japan’s national budget for 2023.
However, this is also an estimate based on 2013, so the scale of damage to people and property is expected to be much greater now that many tower mansions over 20 stories have been built and 27,000 listed company headquarters are concentrated.
According to the Nippon Keizai Shimbun, the Japanese government established a working subcommittee of the Central Disaster Prevention Council on the 19th of last month to reassess the scale of damage from the earthquake directly hitting the capital and revise the basic disaster prevention plan. The work committee is going ahead with the disaster prevention measures that have been in place for 10 years, including eliminating densely packed wooden urban areas, and re-estimates the number of deaths. The expected scale of damage is updated and new goals and systems are established.
Earthquakes are never a single disaster. In addition to tsunamis and floods, simultaneous fires can meet low pressure and form a huge tornado and pillar of fire. A large number of people crowded together during evacuation can lead to a crowd accident, and if it overlaps with heavy snow, it can escalate into other safety issues such as isolation. NHK even described this chain of disasters as ‘hell.’
However, if the Earthquake Investigation Committee establishes preventive measures such as introducing earthquake-resistant and fire-retardant designs according to Sewon’s measures, casualties can be reduced by about 30%.
Nittere said it is important to prepare yourself at home, and suggested that to prevent fires caused by electric current, you can install a ‘seismic breaker’ that cuts off electricity when strong vibration is detected. As of 2022, the installation rate of seismic breakers in the province was only 6%, but the Tokyo Metropolitan Government set a goal of raising it to 25% by 2030.
Source: Donga
Mark Jones is a world traveler and journalist for News Rebeat. With a curious mind and a love of adventure, Mark brings a unique perspective to the latest global events and provides in-depth and thought-provoking coverage of the world at large.