Facing the Greatest Threat in Japan’s History
Why the Nankai Trough Megathrust Earthquake Could Shatter the Entire Japanese Economy
In my previous article, I discussed the historical context of the Tokyo metropolitan earthquake, predicted to occur within the next 30 years. This time, I’ll focus on an even more devastating threat—the Nankai Trough megathrust earthquake (南海トラフ巨大地震).
This massive quake is expected to strike along the plate boundary stretching from Suruga Bay to the sea off Kyushu, an area that has historically brought severe damage to Japan’s Pacific coast, especially the economic core of the Kansai region. According to historical records, these earthquakes have occurred in cycles of 100 to 150 years, repeatedly causing massive destruction through shaking and tsunamis. The last major events occurred at the end of World War II in 1944 and 1946, and based on this historical cycle, the Japanese government’s Earthquake Research Committee estimates there is an 80% chance of a Nankai Trough megathrust earthquake occurring within the next 30 years.
Let’s first look at its history. The earliest recorded Nankai Trough quake is the Hakuho Earthquake of 684 (白鳳地震), with an estimated magnitude of 8.3. It caused landslides and tsunamis along what is now the coast of Kochi and Wakayama Prefectures, leading to many casualties. In 887, the Ninna Earthquake (仁和地震) shook a wide area, including Kyoto, and brought deadly tsunamis to the coastal regions. The 1096 Eicho Earthquake (永長地震) and the 1099 Kowa Earthquake (康和地震) occurred a few years apart and are believed to be segmented quakes affecting the eastern and western parts separately. This research suggests that Nankai Trough earthquakes may not always happen all at once but could unfold in stages over several years.
The Shohei Earthquake (正平地震) of 1361 and the Meiō Earthquake (明応地震) of 1498 also caused significant damage, with tsunamis reaching as far as the Boso Peninsula in the Kanto region. Because these occurred during periods of political turmoil, recovery efforts and records were insufficient, leaving many details unknown.
In the Edo period, the Keicho Earthquake (慶長地震) of 1605 caused relatively little damage from shaking, but coastal areas were devastated by tsunamis. The Hoei Earthquake (宝永地震) of 1707, with an estimated magnitude of 8.6, is one of the largest in Japanese history and is believed to have ruptured the entire Nankai Trough at once. It killed over 20,000 people and triggered landslides and tsunamis across western Japan. Forty-nine days later, Mount Fuji erupted, highlighting the possible connection between earthquakes and volcanic activity.
In 1854, the Ansei-Tokai (安政東海地震) and Ansei-Nankai Earthquakes (安政南海地震) occurred just 32 hours apart, with magnitude 8.4 each, severely affecting areas from Tokai to Shikoku. Coastal regions such as Wakayama suffered catastrophic tsunami damage.
In modern times, the Showa Tonankai Earthquake (昭和東南海地震) of 1944 and the Showa Nankai Earthquake (昭和南海地震) of 1946 struck during the chaos of wartime and postwar Japan. Due to strict information control, damage assessment took time. The combined death toll exceeded 2,500, with serious tsunami flooding in coastal areas.
These examples clearly show that the Nankai Trough megathrust earthquake occurs cyclically and repeatedly devastates western Japan, including the Kansai region. Tsunami damage, in particular, has always been extensive. The government now estimates that in the worst-case scenario, over 230,000 people could die. Unlike the Tokyo quake, this would be the first time a megathrust earthquake strikes the postwar Japanese economic system at full scale. Let’s examine the projected damage.
According to the government’s Earthquake Research Committee, if a magnitude 8–9 class earthquake occurs along the Nankai Trough in the next 30 years, up to 2.38 million buildings may be destroyed or burned, with direct economic damage reaching 169.5 trillion yen. This figure far exceeds the 16.9 trillion yen cost of the 2011 Great East Japan Earthquake. Critical infrastructure—roads, railways, ports, and power grids—would be severely crippled. Lifelines for business and tourism such as the Tokaido and Sanyo Shinkansen and expressways may be shut down for an extended period, cutting off transportation and logistics between the Tokyo area and western Japan.
Moreover, the indirect economic damage due to supply chain disruptions would be enormous. The affected areas—mainly Tokai to western Japan—account for around 60% of Japan’s manufacturing output, and about 90% of the automobile industry. Factory damage, worker displacement, and logistics collapse would halt operations across vast areas, and the resulting parts shortages would shrink production nationwide. As a result, GDP would plummet. Government estimates suggest losses of 36 to 45 trillion yen from the immediate post-quake economic decline.
If recovery stalls, bankruptcies among small and medium-sized enterprises and job losses could mount, leading to prolonged stagnation. In the worst-case scenario, if recovery is slow, total economic loss over 20 years could reach 1,410 trillion yen. This includes an estimated 1,240 trillion yen from lost production and income due to infrastructure paralysis. Such a blow could potentially downgrade Japan’s status from one of the world’s wealthiest nations to one of its poorest. It’s not economic recession or global tech shifts that pose the gravest threat to Japan, but a catastrophic earthquake.
Naturally, such a disaster would severely affect financial markets. Trust in Japanese companies could erode due to destroyed production bases and deteriorating corporate performance, triggering stock crashes, currency instability, and rising government bond yields. Higher financing costs would worsen corporate finances and raise bankruptcy risks. Massive public funds would be needed for recovery, placing a heavy burden on national finances. If Japan has to issue more bonds to cover costs, markets may question its fiscal sustainability, raising long-term interest rates and potentially destabilizing the financial system. Past quakes like the 1995 Kobe Earthquake and the 2011 tsunami temporarily chilled consumer sentiment and caused stock declines, but the scale of a Nankai Trough quake would far surpass those impacts.
How well the economy rebounds depends largely on the speed and effectiveness of recovery. According to government analysis, demand from reconstruction efforts would begin to lift production within a few months and increase significantly after the first year. The rebuilding of aging infrastructure could even enhance industrial productivity in the long term. However, this depends on securing a workforce and rebuilding livelihoods in the affected areas. Delayed search and rescue or prolonged evacuation would slow business resumption and economic recovery.
Japan plans to concentrate reconstruction investment within the first few years, aiming to regenerate affected regions in about a decade. But minimizing nationwide GDP losses during that period requires tight coordination between affected and neighboring areas. At the same time, the massive fiscal spending must be carefully managed to avoid undermining long-term growth.
Given the immense risks posed by a Nankai Trough quake, proactive disaster mitigation is critical. Seismic reinforcement, tsunami countermeasures, and robust business continuity planning (BCP) can substantially reduce damage. According to the Japan Society of Civil Engineers, strengthening infrastructure and earthquake-resistant buildings could cut long-term economic damage by 30–40%. The government’s latest revised damage estimates in 2019 show a slight reduction in projected deaths—from 320,000 to 230,000—and in economic losses from 220 trillion to 213 trillion yen, thanks to preventive efforts.
These numbers may vary based on assumptions, but the key is to prepare for the worst. The Nankai Trough megathrust earthquake could deal a historic blow to the Japanese economy, and unless individuals, businesses, and governments face the risk head-on and take action, the damage will be irreversible. For travelers, too, who increasingly visit Japan, it’s essential to be aware of this worst-case risk. If a Nankai quake occurs, western Japan—including Kyoto, Osaka, and Nara—will be effectively cut off from the Tokyo area.
This kind of scenario may not be in tourist guides, but it’s a dark tip worth knowing. For Japanese people, it’s common knowledge that “an earthquake could happen any moment.” That is why learning from history and preparing for disaster is the most essential form of resilience.