EDITORIAL | Big Postwar Earthquakes Offer Lessons on Disaster Prevention

This year, 2023, is a big year for earthquakes. It marks the 100th anniversary of the Great Kanto Earthquake of 1923. It also marks the 80th anniversary of the Tottori Earthquake of 1943, and the 75th anniversary of the Fukui Earthquake of 1948.

The period from August 15, which marks the end of the Pacific War, to Disaster Preparedness Day on September 1 is a time to consider how disaster-prone Japan was in the days before and after the war.

In the five years straddling the end of World War II, several magnitude 7-8 tremors followed in quick succession. More than 1,000 people died in each earthquake.

*Ningyocho Street, Nihonbashi in Tokyo, was badly burned in the aftermath of the Great Kanto Earthquake. September 1923 (© Sankei)*

Earthquakes to Learn From

The following five seismic events occurred in the mid-Showa period:

Tottori Earthquake in 1943 (M7.2, 1,083 dead)
Tonankai Earthquake in 1944 (M7.9, 1,223 dead or missing)
Mikawa Earthquake in 1945 (M6.8, 2,306 dead)
Nankai Earthquake in 1946 (M8.0, 1,330 dead)
Fukui Earthquake in 1948 (M7.1, 3,769 dead).

Wartime information controls and the chaos immediately after the end of the war obscured the devastation caused by these tremors. Therefore, their memory and the lessons they held concerning earthquakes were not fully conveyed.

Mention earthquakes to a Japanese, and the Great Kanto Earthquake of 1923 or the Great East Japan Earthquake of 2011 are likely to come to mind. But, in fact, quite a few large quakes occurred during the Showa period. Moreover, they hold extremely important lessons for earthquake disaster prevention in Japan today.

The Great Kanto Earthquake damaged Tokyo's Ginza 4-chome intersection in September 1923. The wreckage of automobiles and streetcars lie in ruins (© Nippon Dempo Tsushin-sha, Japan Telegraphic Communication Co., Ltd., now known as Dentsu)

Major Earthquakes of the Showa Era

In order that these lessons might not lie undiscovered, we propose that these series of mid-Showa earthquakes be collectively referred to as "Major Earthquakes of the Showa Era."

Among this group, the 1944 Tonankai Earthquake and the 1946 Nankai Earthquake both were subduction zone tremors with their epicenters in the Nankai Trough. The other three were epicentral earthquakes occurring directly under the affected area.

There is historical evidence that large, epicentral-type tremors tend to occur frequently before and after subduction zone earthquakes. We must recognize that the likelihood of the next subduction zone quake (M8-9) occurring in the Nankai Trough is growing. That means the Japanese archipelago may well be heading for a peak in seismic activity similar to the years before and after the end of WWII.

The brick remains of this building are presumed to have been built in the Meiji era. Most of the building collapsed in the Great Kanto Earthquake, but the remaining part was excavated and preserved locally. In the back left is the Yokohama Port Opening Memorial Hall in Naka Ward, Yokohama (ⓒ SANKEI by Kazuya Kamogawa)

Drawing the Right Lessons

What is important is to draw lessons that can be applied to disaster prevention from such a series of seismic activities, rather than a single massive earthquake.

For example, the earthquake preparedness measures adopted by Osaka Prefecture and Osaka City focus on countermeasures for a Nankai Trough earthquake. They include tsunami countermeasures.

However, the Uemachi fault zone is located in the center of the Osaka Plain. It belongs to the group of active faults in Japan with a high probability of generating earthquakes.

If we extrapolate from the example of the "Major Earthquakes of the Showa Era," we can assume that there will be localized, epicentral-type tremors before or after a M8 quake in the Nankai Trough. It bears noting that the same is true for many cities and regions besides Osaka.

(Read the editorial in Japanese.)

Author: Editorial Board, The Sankei Shimbun