SAKIGAKE管理人 Introduction
June 28, 1948, 4:13 PM (5:13 PM under the daylight saving time system in effect at the time). The Fukui earthquake, centered in Fukui Prefecture, registered a magnitude of 7.1 and became one of the largest disasters in postwar Japan, with approximately 3,769 dead or missing and around 36,000 homes completely destroyed. With a shallow epicenter directly beneath the city of Fukui, the earthquake reduced the city to rubble in a matter of mere seconds.
This disaster is remembered as more than simply “an earthquake that caused major damage.” The Fukui earthquake was the catalyst that changed the very framework of disaster information we use on a daily basis today: “Seismic Intensity 7.” In this article, we look back at the Fukui earthquake and explain how the highest classification, “Seismic Intensity 7,” came to be — and how its lessons can be applied to corporate disaster prevention today.
What Happened That Day in Fukui
In 1948, with postwar reconstruction still only halfway complete, the city of Fukui was in the midst of rebuilding from wartime destruction. Buildings that had survived the war stood alongside simply constructed replacements, and construction continued even in areas with weak ground. Against this backdrop, the direct-hit earthquake became a “double disaster” for the city. The wooden houses densely packed across the urban area collapsed instantly under the violent shaking. Furthermore, because the timing coincided with the dinner preparation hour, fires broke out immediately after the quake, further expanding the damage. The firefighting system at the time was also far from adequate due to the lingering effects of the war, and delays in initial firefighting efforts were a contributing factor in the scale of the disaster.
Seismic measurement technology at the time was extremely limited compared to today. When the Fukui earthquake struck, the Japan Meteorological Agency’s seismic intensity observation network was still insufficiently developed, and a situation arose in which the strength of the shaking from this earthquake could not be accurately expressed using the existing seismic intensity scale (Intensity 0 to 6). The damage within the city of Fukui clearly exceeded the maximum classification at the time, “Intensity 6.” Whether measured by the rate of building collapse, the extent of ground damage, or the scale of human casualties, the situation was catastrophic in a way the existing framework simply could not contain.
Why Was “Seismic Intensity 7” Created?
In response to this experience, the Japan Meteorological Agency began reviewing its seismic intensity scale. In 1949, based on the actual damage caused by the Fukui earthquake, a new classification — “Seismic Intensity 7 (Gekishin, or ‘violent earthquake’)” — was added to the scale. Intensity 7 was established as a classification to describe shaking at a catastrophic disaster level that exceeded what Intensity 6 had previously anticipated — conditions such as “building collapse rates exceeding 30%” and “frequent landslides and ground fissures.”
The creation of Intensity 7 was not merely the addition of a new number. It was an event in which the lesson that “disasters that exceed existing assumptions can actually occur” was formally codified into the system. Up until that point, disaster prevention systems had been centered on an “experience-based” approach, anticipating damage within the range of previously observed earthquakes. The Fukui earthquake exposed the inherent limitations of that approach to society.
This Intensity 7 classification has continued to function as a critical indicator for communicating the severity of damage to society in numerous major earthquakes since — including the Great Hanshin-Awaji Earthquake (1995), the Great East Japan Earthquake (2011), and the Kumamoto Earthquake (2016).
The Evolution of Observation Technology and Modern Disaster Prevention Infrastructure
The review of the seismic intensity scale triggered by the Fukui earthquake also led to subsequent developments in earthquake observation technology. At the time, seismic intensity was determined based on human perception and visual surveys of damage; however, in 1996 there was a complete transition from sensory judgment to mechanical measurement via seismometers, known as “instrumental seismic intensity.” Today, thanks to a high-density nationwide seismic observation network, seismic intensity has evolved into a system that is calculated mechanically, objectively, and instantly.
In addition to the Japan Meteorological Agency’s seismic observation network, the High Sensitivity Seismograph Network (Hi-net) and the strong-motion seismograph networks (K-NET, KiK-net) operated by the National Research Institute for Earth Science and Disaster Resilience have been established, building a system that issues seismic intensity information and earthquake early warnings within seconds, no matter where in Japan an earthquake occurs.
Furthermore, since the 2010s, in response to observations that “damage can vary significantly even at the same Intensity 7,” discussions on further subdividing the seismic intensity scale and research into more detailed damage projections have been progressing. This pursuit of “immediacy” and “precision” can be seen as an extension of the lesson taught by the Fukui earthquake — the philosophy that, rather than recording unexpected damage after the fact, it is essential to grasp the situation accurately in real time and connect that understanding to a swift response.
Implications for Corporate Disaster Prevention
The lessons of the Fukui earthquake offer an extremely essential perspective for companies formulating disaster prevention measures and Business Continuity Plans (BCP).
First, abandon fixed assumptions and continuously update “damage projections.”
Just as Intensity 6 was expanded into Intensity 7, existing standards and “maximum projected damage” should never be treated as fixed. In corporate disaster prevention plans and evacuation drills as well, it is essential to avoid relying on a single scenario and instead to revise plans based on the latest hazard maps. Furthermore, as the fires that broke out following the Fukui earthquake demonstrate, projections must be updated to account for “secondary disasters” and “compound risks” that can follow an earthquake.
Second, recognize that unglamorous, everyday preparedness during peacetime is what determines the scale of damage in an emergency.
The case of Fukui, struck while still in the vulnerable midst of postwar reconstruction, demonstrates that the state of infrastructure and systems maintained during normal times has a major impact on the scale of damage during a disaster. Companies, too, should be wary of believing that having a disaster prevention plan (on paper) alone is sufficient, while leaving aging equipment and inadequate systems unaddressed. Down-to-earth, ongoing peacetime preparations — seismic diagnostics, measures to prevent equipment from toppling, and checks on emergency stockpiles — are what truly determine a company’s survival rate in an emergency.
Third, build a system for “rapid and objective situational awareness,” which determines the success or failure of initial response.
Behind the creation of Intensity 7 lay the stark challenge that “there was no means of accurately grasping the actual extent of the damage.” In the chaos of a disaster, infrastructure that visualizes the situation in real time is essential for corporate leaders to make sound decisions without error. Establishing an automated safety confirmation system and a system for centrally managing damage status across business locations during peacetime significantly improves the quality of a company’s initial response.
Conclusion
The Fukui earthquake left us with a new disaster prevention indicator, “Seismic Intensity 7,” at the cost of approximately 3,800 lives. It stands as a symbolic event in which society as a whole confronted the harsh reality that disasters exceeding our assumptions can actually occur, and reflected that reality in its systems.
Even now, 77 years later, this lesson has lost none of its relevance. Companies, too, must avoid the complacency of believing “our current assumptions are sufficient” and instead maintain a posture of continuously updating their disaster prevention plans and BCPs.
As professionals in corporate disaster prevention consulting and disaster risk management, SAKIGAKE JAPAN Corp. is fully committed to supporting your disaster preparedness efforts.