SAKIGAKE管理人 In 2026, 103 years have passed since the Great Kanto Earthquake struck on September 1, 1923. Over the past century, the seismic resistance of buildings, disaster preparedness technologies, and systems for observation and information dissemination have advanced significantly. However, modern cities face risks that are different from those of 103 years ago.
Electricity, communications, railways, logistics, IT systems, and increasingly complex supply chains.
While our society has become more convenient, corporate activities have also become increasingly dependent on a wide range of infrastructure and external services. On September 1, Japan’s “Disaster Prevention Day,” the question companies should consider is not only whether they can withstand an earthquake, but also whether they can continue critical business operations even if urban functions come to a halt.
The Great Kanto Earthquake — A Massive Disaster That Claimed Approximately 105,000 Lives
At 11:58 a.m. on September 1, 1923, the Great Kanto Earthquake, with a magnitude of 7.9, struck with its epicenter in western Kanagawa Prefecture. The hypocentral depth was 23 km. Seismic intensity 6, the highest category in use at the time, was observed in Saitama, Chiba, Tokyo, Kanagawa, and Yamanashi Prefectures, while shaking equivalent to today’s seismic intensity 7 is estimated to have occurred along the Sagami Bay coast and at the southern tip of the Boso Peninsula.
The series of disasters caused by this earthquake is known as the “Great Kanto Earthquake Disaster.” Damage extended across a broad area of southern Kanto, including Tokyo and Yokohama. According to the Cabinet Office, approximately 105,000 people were killed or went missing, and around 370,000 homes were completely or partially destroyed, burned, washed away, or buried. The disaster was not caused by strong shaking alone; fires, tsunamis, landslides, liquefaction, and other hazards also occurred across the region.
Among these, fire damage was particularly severe. Because the earthquake occurred around lunchtime, fires broke out in many locations and spread across urban areas. Of the approximately 105,000 people who were killed or went missing, around 90,000 are estimated to have died as a result of fires. In Tokyo City at the time, approximately 34.7 square kilometers were burned.
The damage was not limited to buildings and human lives. Electricity, water supply, roads, railways, and other lifelines were also severely affected, dealing a major blow to urban functions. Cabinet Office reports document widespread disruption to transportation, water supply, electricity, telecommunications, bridges, and other forms of social infrastructure.
One of the key lessons that the Great Kanto Earthquake offers for modern corporate disaster preparedness is that preparing only for building collapse is not enough. If strong shaking triggers fires, infrastructure outages, and disruptions to transportation and logistics, the impact can spread even to companies that are not directly damaged. The “chain reaction of urban function failures” experienced 103 years ago remains an important issue for the modern Tokyo metropolitan area, where dependence on infrastructure is even greater.
“Urban Function Shutdown” Risks in Tokyo in 2026
The structure of cities today is very different from that of 103 years ago.
Even if an office building itself remains intact, a power outage may make equipment and IT systems unavailable. Communications failures could disrupt employee safety confirmation and contact with business partners. If railways stop operating, employees may be unable to commute or return home. If roads and logistics networks are disrupted, supplies of raw materials and products may also be affected.
Furthermore, even if a company itself suffers no direct damage, business operations may be interrupted through disruptions affecting suppliers, logistics providers, data centers, and other external partners. The Cabinet Office also emphasizes the importance of BCPs (Business Continuity Plans), noting that stagnation in corporate activities caused by large-scale disasters can affect not only individual companies, but also supply chains, regional economies, and the Japanese economy as a whole.
From “Protecting Buildings” to “Keeping Business Running”
When companies think about earthquake preparedness, seismic reinforcement and emergency stockpiles often come to mind first. However, a BCP requires companies to go further.
For example:
“What if a power outage and communications failure occur at the same time?”
“What if senior management cannot reach the office?”
“What if a major business partner is affected?”
“What if the office cannot be used for one week?”
Even under these circumstances, companies need to identify priority operations and recovery targets in advance, while also preparing alternative sites, backup systems, personnel, employee safety confirmation methods, and emergency decision-making procedures.
The Cabinet Office likewise cites securing backup systems, offices and personnel, as well as rapid employee safety confirmation, as typical elements of BCP initiatives.
In the Tokyo metropolitan area, measures for stranded commuters are also essential. The Tokyo Metropolitan Government promotes the suppression of mass simultaneous return home and highlights corporate initiatives such as emergency stockpiles and training that allow employees to remain at workplaces for a certain period.
Make September 1 a Day to “Activate” Your BCP
A BCP is not something that should simply be created once and left unchanged.Organizations, personnel, business partners, and systems evolve, and so do the actions required during a disaster. That is why companies need to conduct regular drills to confirm whether their plans can actually function in practice and continuously improve them. The Cabinet Office also promotes training as a means of improving the effectiveness of BCPs.
103 years after the Great Kanto Earthquake, September 1 should be more than a day to check expiration dates on emergency supplies.It can also be a day to ask:“If urban functions in the Tokyo metropolitan area stopped today, could our company continue its critical operations?”
Disasters themselves cannot be prevented. However, how a company responds after a disaster, how it protects its critical operations, and how quickly it can recover can be significantly influenced by the preparations made during normal times.
Shift disaster preparedness from “measures to prevent damage” to “a management strategy for sustaining business and society.”
The lessons of the Great Kanto Earthquake must be carried forward into preparations for the next disaster.
“Paint-On” Seismic Reinforcement — Aster Power Coating
In corporate BCP, it is important not only to establish systems for business continuity, but also to improve the safety of the buildings where employees work and the facilities that support business operations.
Aster Power Coating is a next-generation seismic reinforcement and strengthening coating developed by Aster Inc., a startup originating from the Institute of Industrial Science, The University of Tokyo. The coating contains special fibers and forms a highly durable reinforcing layer on buildings and concrete structures, helping to reduce the risk of exterior wall spalling, concrete deterioration, and earthquake-related damage.
It is designed for use on a wide range of structures, including elevated bridges, apartment building exteriors, schools, public facilities, concrete block walls, and historic buildings. It has been implemented in Japan and overseas as a low-cost, short-construction-period solution for seismic reinforcement and structural longevity that does not rely solely on large-scale renovation or rebuilding.
103 years after the Great Kanto Earthquake, reviewing the seismic safety of buildings and facilities alongside BCP planning and disaster drills can be another important step toward strengthening corporate disaster resilience.