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Onset of a catastrophe

I was watching the news on NHK TV (Japan’s public broadcaster) on September 11, 2011 when the broadcast was abruptly interrupted by a news flash that a JMA (the Japan Meteorological Agency) magnitude 7.9 earthquake had occurred off the Tohoku coast of northern Japan (Risk Frontiers Briefing Note 217, 2011). It was night in Japan and at first there was not much to see as no reports of extensive shaking damage were shown. As JMA continued to update its estimate of the magnitude from 7.9 to 8.4 and then 8.7, I received an email from my colleague Dr Thio in California estimating the magnitude at 9.0 about 20 minutes after the event began, confirmed by JMA five minutes later. Soon the first arrivals of tsunamis at ports along the Tohoku coast began to appear on the screen, followed by dramatic images of waves and inundation never seen before on TV. The tsunami killed more than 18,000 people along Japan’s north-east coast, including Fukushima. Initially there was little mention of the Fukushima Nuclear Power Plant, operated by Tokyo Electric Power Company (TEPCO), and it took weeks before the dire condition of the five units became clear, as graphically chronicled by Australian journalist Mark Willacy (2013).

Reactors 1 to 3 at the plant suffered nuclear fuel meltdowns, while hydrogen explosions damaged the buildings housing units 1, 3 and 4 (Figure 1). The nuclear meltdowns sent plumes of radiation into the atmosphere and forced the evacuation of 160,000 people living near the plant, 31,000 of whom are still unable to return to their homes. TEPCO has said it will take 40 years to locate and remove the melted fuel from the reactor cores, although some experts believe decommissioning could take longer. The government has estimated that the total cost of dismantling the plant, decontaminating surrounding areas and compensating victims at about $US200bn. TEPCO this week announced that its preferred method of disposing of more than a million tonnes of contaminated water stored at the site is to discharge it into the Pacific ocean, which is strongly opposed by local fishermen who have spent the last eight years rebuilding their industry.

Figure 1. From top: The 15.5 metre high tsunami overtopping the tsunami sea walls on March 11, 2011; The tsunami inundating the reactors; An explosion on March 15 ruptured the reactor components of Reactor no. 2 and breached the main containment; Smoke rising from damaged Reactor No. 3 Source: TEPCO

Acquittal of TEPCO executives

On 19 September 2019, three former top executives of TEPCO were acquitted of professional negligence resulting in death and injury related to the 2011 Fukushima nuclear accident. The trial started in June 2017 after a judicial review panel comprising ordinary citizens ruled that the former executives should be indicted. Initially, prosecutors twice declined to proceed with the case, citing insufficient evidence and a slim chance of conviction. A total of 37 hearings were held for the trial, during which more than 20 witnesses, including current and former TEPCO officials as well as earthquake and tsunami experts, were questioned.

While no one is officially recorded as having died as a direct result of the meltdowns, the former executives were indicted for negligence that allegedly resulted in the deaths of 44 people, including patients who were forced to evacuate from a nearby hospital, as well as injuries suffered by 13 people as a result of the hydrogen explosions.

In concluding the two-year trial, the Tokyo District Court ruled that it was not realistic for the former executives to have predicted all possible tsunami scenarios. The defendants, who were the only people facing prosecution in relation to the nuclear disaster, had all pleaded not guilty to charges of professional negligence resulting in death, arguing that the data available to them before the disaster was unreliable, that the tsunami was unforeseeable and that the meltdowns would have occurred even if they had implemented preventive measures. Prosecutors had sought five-year prison terms for them.

The Fukushima nuclear accident, and what TEPCO knew

In planning the design of the Fukushima plant in 1967, TEPCO decided to reduce the natural 35-metre cliff at the site to just ten metres in height. The 15.5 metre high tsunami generated by the earthquake overtopped the plant’s 5.7-meter tsunami seawall (Figure 2), flooding the basements of the power plant’s turbine buildings and disabling both the main power supply and the emergency diesel generators used for cooling the reactor cores to avoid meltdown. Installation of the emergency diesel generators just ten metres higher may have prevented the meltdowns from occurring.

Figure 2. The height of the tsunami that inundated the power station buildings.

The prosecution claimed that the TEPCO top executives should be held responsible because they could have predicted tsunamis of the height that inundated the Fukushima plant. They claimed that the executives were present at meetings where experts warned of massive tsunamis that could inundate the Fukushima coast. The findings were reported to TEPCO executives, according to a written statement from former TEPCO executive Kazuhiko Yamashita, who said the three executives had approved plans to carry out tsunami safety measures in March 2008. However, in July the same year, according to Yamashita, the trio shelved the plans, saying it would be difficult to convince the government and local residents of the power plant’s safety and that the move could prompt calls for halting operations, implying that the executives had recognized the necessity for such measures.

Figure 3. Stone marker indicating historical tsunami inundation limits, with road descending the slope to a narrow coastal plain. One such marker dates back to the 869 Jogan tsunami.

What was known of the hazard?

The Japanese government’s Headquarters for Earthquake Research Promotion (HERP) released its long-term evaluation in 2002 predicting that a very large tsunami could occur off Tohoku including the area off Fukushima. It was known that a very large tsunami-generating earthquake, the Jogan earthquake, had occurred in the Tohoku region on 9 July 869, about one thousand years earlier. The extent of flooding of the Sendai plain caused by the Jogan tsunami, which had been mapped using dated deposits of sand, extended at least 4 kilometres inland. Its inundated areas closely matched those of the 2011 Tohoku tsunami in Sendai, suggesting that it may have also had a magnitude of 9.0 (Minoura et al., 2001). The Tohoku coast is dotted with markers like the one shown in Figure 2 indicating inundation limits in past earthquakes and warning people not to build at lower levels, an admonition difficult for fishermen to heed.

Dr Kunuhiko Shimazaki, who was a member of HERP’s earthquake research panel in 2002 (and my host when I was a Visiting Research Fellow at Tokyo University’s Earthquake Research Institute in earlier years), told the court that the Cabinet Office pressured the panel shortly before the announcement of the HERP long-term evaluation to state that the assessment was unreliable. The headquarters reported in its introduction to the HERP long-term evaluation that there were problems with the assessment’s reliability and accuracy. In his testimony, Shimazaki pointed out that the Central Disaster Prevention Council’s decision not to adopt the long-term evaluation led to inappropriate tsunami countermeasures, and he stated that many lives would have been saved if the countermeasures based on the HERP long-term evaluation had been in place (Mainichi Newspaper, 2018a).

Failure of regulatory authority

A former safety screening division official of the Ministry of Economy, Trade and Industry’s Nuclear and Industrial Safety Agency (NISA) reported that TEPCO did not accept the agency’s request to assess the tsunami hazard after the release of the HERP report in 2002 (Mainichi Newspaper, 2018b). The official held a hearing on TEPCO the following month as to whether the report would affect safety measures at the Fukushima No. 1 plant. NISA told the utility to calculate a possible earthquake-tsunami disaster off the coast from Fukushima to Ibaraki prefectures. In response, TEPCO representatives showed reluctance, saying that the calculation would “take time and cost money” and that there was no reliable scientific basis in the assessment report. In the end, the agency accepted the utility’s decision to shelve the earthquake-tsunami estimate. In 2006, NISA again requested TEPCO to prepare its nuclear plants for massive tsunamis exceeding envisioned levels, but the company did not comply until finally conducting a calculation in 2008.

Tsunami hazard analysis ignored

Annaka et al. (2007) and Thio et al. (2007) were the first to develop probabilistic methods for tsunami hazard analysis. Dr Annaka worked at Tokyo Electric Power Services Co. (TEPSCO), a subsidiary of TEPCO, and I saw his presentation at a conference in Japan (JNES, 2010) in which he estimated that the return period of a 5.7 metre high tsunami at Fukushima was as little as a few hundred years. In 2007 and 2008, TEPSCO estimated that tsunamis up to 15.7 meters high could inundate the nuclear plant based on the HERP analysis. The TEPSCO witness told the court that he briefed TEPCO headquarters of the outcome of TEPSCO’s estimate of possible tsunami heights in March 2008. An employee at TEPCO headquarters subsequently asked the witness whether the estimated scale of possible tsunami could be lowered by changing the calculation method. He found that it could not, and eventually his prediction was not accepted as TEPCO’s estimate of the height of a possible tsunami (Mainichi Newspaper, 2018c).

The prosecution stated that, although TEPCO headquarters initially considered measures to protect the Fukushima No. 1 nuclear complex from tsunami after being briefed of the outcome of TEPSCO’s tsunami estimate, those who were on the company’s board at the time postponed drawing up tsunami countermeasures, instead commissioning the Japan Society of Civil Engineers to look into the matter. Consequently, TEPCO failed to reflect the 15.7 metre prediction in its tsunami countermeasures at the power station. The Prime Minister’s Cabinet Office’s Central Disaster Prevention Council also did not adopt the long-term evaluation in developing its disaster prevention plan.

Reconciling acquittal with the conclusions of the Nuclear Accident Independent Investigation

At first it seems difficult to reconcile the acquittal with the Message from the Chairman of the Nuclear Accident Independent Investigation Commission (National Diet of Japan, 2012):

“The .. accident at the Fukushima Daiichi Nuclear Power Plant cannot be regarded as a natural disaster. It was a profoundly manmade disaster – that could and should have been foreseen and prevented. And its effects could have been mitigated by a more effective human response….What must be admitted – very painfully – is that this was a disaster “Made in Japan.” Its fundamental causes are to be found in the ingrained conventions of Japanese culture: our reflexive obedience; our reluctance to question authority; our devotion to ‘sticking with the program’; our groupism; and our insularity. [The nuclear power industry’s] regulation was entrusted to the same government bureaucracy responsible for its promotion. This… was reinforced by the collective mindset of Japanese bureaucracy, by which the first duty of any individual bureaucrat is to defend the interests of his organization. Carried to an extreme, this led bureaucrats to put organizational interests ahead of their paramount duty to protect public safety.’

Perhaps his statements that “This report singles out numerous individuals and organizations for harsh criticism, but the goal is not—and should not be—to lay blame,” and “Had other Japanese been in the shoes of those who bear responsibility for this accident, the result may well have been the same” may have contributed to the acquittal.


Annaka, T., Satake, K., Sakakiyama, T., Yanagisawa, K., and Shuto, N. (2007). Logic-tree approach for probabilistic tsunami hazard analysis and its applications to the Japanese coasts. Pure Appl. Geophys. 164, 577–592. doi: 10.1007/s00024-006-0174-3.

Japan Nuclear Energy Safety Organisation (JNES, 2010). First Kashiwazaki International Symposium on Seismic Safety of Nuclear Installations. Kashiwazaki, Japan, November 24-26, 2010.

Mainichi Newspaper (2018a). (10 May 2018). Seismologist testifies Fukushima nuclear disaster preventable.

Mainichi Newspaper (2018b). (30 January 2018). TEPCO refused in 2002 to calculate possible tsunami hitting Fukushima: ex-gov’t official.

Mainichi Newspaper (2018c). (1 March 2018). TEPCO asked subsidiary to underestimate tsunami threat at Fukushima nuke plant: worker.

Minoura K, Imamura F, Sugawara D, Kono Y, and Iwashita T (2001) The 869 Jogan tsunami deposit and recurrence interval of large-scale tsunami on the Pacific coast of northeast Japan. Journal of Natural Disaster Science 23: 83”88. Available at:

National Diet of Japan (2012). The official report of The Fukushima Nuclear Accident Independent Investigation Commission.

Risk Frontiers (2011). The Mw 9.0 Tohoku, Japan Earthquake of 11 March 2011. Briefing Note 217, March 2011.

Thio, H. K., Somerville, P. G., and Ichinose, G. (2007). Probabilistic analysis of strong ground motion and tsunami hazards in Southeast Asia. Journal of Earthquake And Tsunami, 01,119.

Willacy, Mark (2013). Fukushima. Macmillan Australia, July 1, 2013.

About the author/s
Paul Somerville
Chief Geoscientist at Risk Frontiers | Other Posts

Paul is Chief Geoscientist at Risk Frontiers. He has a PhD in Geophysics, and has 45 years experience as an engineering seismologist, including 15 years with Risk Frontiers. He has had first hand experience of damaging earthquakes in California, Japan, Taiwan and New Zealand. He works on the development of QuakeAUS and QuakeNZ.

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