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Tohoku-oki tsunami of 11 March 2011 | One year on

Figure 1. Flooding of the Sendai Plain: Before and after the 11 March 2011 tsunami (hover to view after tsunami) © Mr Ikeuchi.

Figure 2. Tsunami-damaged building, Yuriage, Sendai Plain.

Sunday 11 March 2012 marked the first anniversary of the magnitude 9.0 Great Tohoku earthquake and devastating tsunami that struck the east coast of Japan (Figures 1 and 2).

The impact of the tsunami was catastrophic; 15 847 people died and 3 306 are still missing, almost certainly dead. Ninety per cent of those killed in the event were drowned when tsunami waves up to 40 m high over ran the coast.

The damage was catastrophic with 129 000 houses destroyed or washed away.

One year on the clearance of debris and reconstruction continues, but there remains 23 million tons of debris; much of which was washed out to sea and is now travelling inexorably across the Pacific to make landfall on Hawaii and the west coast of the Americas that will continue for many years (see Tsunami debris heading towards USA .

The total cost of the tsunami is still uncertain but estimated to be between £130–200 billion.

At this time the Director and staff of BGS send to the people of Japan their sympathies for their personal losses on the anniversary of this catastrophic event and their best wishes for the future.

Research around eastern Honshu

BGS scientists have been researching the impact of the tsunami (Goto et al. 2011) and have now visited the devastated area of eastern Honshu three times since the Great Tohoku earthquake to study Tsunami sediments.

Most recently, between 11 and 25 February 2012, Professor Dave Tappin and Hannah Evans returned to Japan to attend an international symposium on the tsunami; convened by IOC-UNESCO. They revisited some of the devastated areas to review the reconstruction and to continue their scientific research in the Sendai area on the tsunami impact.

The symposium was the first international and multidisciplinary meeting on the tsunami to be convened in Japan. It offered high level perspectives from decision makers and scientists on the tsunami, tsunami warning systems, tsunami preparedness and event experiences; it also considered what lessons have been learned from the tsunami and their policy implications.

There will undoubtedly be an international focus on the tsunami following its first anniversary; reviewing the catastrophe and the recovery and reconstruction. Dave Tappin and Hannah give their personal views on the tsunami and its context, together with a brief review on the results of their visit including comments on the progress made in recovery and on the plans being made to address future tsunami events.

Dave Tappin writes:

Fig 3. Panel Meeting at the IOC-UNESCO Symposium, February 2012.

Figure 4. Locations of some recent major tsunami. © Hannah Evans.

Figure 5. Minamisanriku in May 2011. Major clearing of debris taking place.

Figure 6. Crossing the field are lines of footprints made by searchers looking for bodies after the tsunami but before flood waters receded.

Figure 7. A survivor (right) talking with one of the survey team.

Figure 8. A pile of tsunami damaged cars awaiting crushing.

Figure 9. Onagawa, destroyed by the tsunami, with snow falling. © Hannah Evans

Figure 10. Severely damaged tsunami defences.

Figure 11. Tsunami defences repaired and land cleared.

Figure 12. Repaired defences and the tetrapods that will form part of the new defences.

Figure 13. Piles of fir tree logs cleared from the coastal forest destroyed in the tsunami. © Hannah Evans

Fig 14. The road bridge at Yuriagi, where people stayed in their cars rather than getting out and climbing onto the bridge, that as can be seen survived.

Figure 15. This is what to do! © Patrick Corcoran

My comments here lead on from a question I was asked as a panel member at the IOC-UNESCO meeting in Japan in the session on strengthening international cooperation in tsunami mitigation and research (Figure 3).

Specifically, I was asked how we can best enable research that underpins the development of warning systems and facilitate equal development of preparedness.

A tricky question because of the uncertainty in knowing when and where the next tsunami will strike as well as the likelihood that the next event will be at an entirely unforeseen location and possibly from an unusual source.

Tsunami background

I have been researching tsunamis now since 1998 when, as a marine geologist, I worked on an event in Papua New Guinea that killed over 2000 people.

This tsunami was subsequently demonstrated to be sourced from a submarine landslide.

In 2004 when a catastrophic tsunami struck the Indian Ocean I worked for the first time on an earthquake tsunami.

I give lots of public lectures on tsunamis and a common question is 'Do we live in the Age of Tsunamis'?

When Japan was devastated by the tsunami last March, this certainly seemed to be the case. A perception supported at the IOC-UNESCO meeting in Japan when a senior tsunami scientist, working in the field for over 40 years, commented that for almost 30 of those nothing of note had happened and during this time he had to fight for funds to support his research programme.

The past decade has been astonishing, with two major events and numerous smaller, yet still locally damaging tsunamis, taking place all over the world (Figure 4).

Catastrophic tsunami events

The Indian Ocean tsunami of 2004 was a wake-up call as it was unexpected at that location.

Afterward, there was a reappraisal of where large magnitude earthquakes, of magnitude 9 or greater, might occur. However, in Japan this was overlooked and estimation of the largest magnitude earthquakes was based on the local geological environment.

Notwithstanding, in the context of the Indian Ocean event where over 220 000 people died, the warning and evacuation procedures in Japan resulted in far less loss of life.

There has been much criticism of the underestimation of the tsunami wave height, but in the context of the Indian Ocean casualties, in Japan their warning and evacuation probably saved 200 000 lives.

Knowing the unknowns

Based on this longer term perspective of most recent tsunami events there are several aspects of the Japan tsunami that come to mind. Firstly, in spite of our advanced understanding of fundamental earth processes, natural events such as tsunamis, when they strike are still unexpected and unpredictable, and this includes their magnitude.

We increasingly know where they may occur but never when.

To fund research that underpins tsunami mitigation and warning therefore requires what a famous US politician termed 'knowing the unknowns' and acting on these; Einstein also had a similar view.

This terminology may seem rather confusing, but when rephrased as follows it makes more sense:

What do we know?'

What are the unsolved problems?

What have we failed to consider?

To move forward in developing improved mitigation strategies we need to appreciate what we do not, rather than what we do, know.

Reconstruction in Japan after the tsunami

During my first visit to Japan in May 2011 there had been significant clearing of debris (Figure 5), but many areas were cordoned off as relief activities were still going on especially the search for bodies (Figure 6).

We often met with survivors who told of their experiences (Figure 7). In June when I next visited, the clearance operation was still ongoing and the country looked like a giant recycling plant with great piles of debris everywhere (Figure 8).

During my latest visit my first impression was that this is what it must have been like in March last year.

I think we forget that after the tsunami struck it was bitterly cold and snowy, people who had lost their homes suffered terribly (Figure 9).

At the symposium, many of the talks were focused on planning the reconstruction, building safe havens above sea level, resettlement above flood level, improving warning systems and better evacuation strategies. During our fieldwork we saw how the reconstruction was proceeding (Figures 10 to 13).

Recognising the magnitude of the danger

With regard to the failures in evacuating people, one term that was repeated constantly during the meeting was 'normalcy'. This refers to the condition where although people probably recognised there was a danger, they didn't recognise the actual magnitude of and threat from the tsunami.

In one instance people leaving the danger zone in cars waited in an orderly queue as the tsunami wave swamped them.

Getting out of their cars to walk a few yards to a nearby bridge would have saved their lives (Figure 14).

There is little reconstruction inland as of yet, but much work has been carried out on the coast, reinforcing the protective levees or tsunami walls (Figures 10–13).

There is a great deal of discussion still going on about whether to retreat from flooded areas or build higher defences.

Generally, it has been agreed that the recurrence interval of the 2011 tsunami is long, thus construction of 10–15 m levees is unnecessary, so the older 10 m high levees will be rebuilt. In some areas on low lying land there will be rebuilding on artificial mounds, but whether this will be for housing was unclear.

In the more mountainous northern areas the alternatives are resettlement on higher ground or improved vertical evacuation strategies with better training to overcome the normalcy syndrome.

Japan is very well organised society and one message came through very clearly — 'in any future event, act on your own instincts without telling' (Figure 15).

With regard to building reconstruction there has been research on the impact of the tsunami waves and how buildings can be constructed to withstand these.

In conclusion

After every new tsunami event lessons are learned and from these we develop new understandings of the hazard.

I have no doubt the Japan tsunami, just like that of 2004, will improve our knowledge base and lead to new mitigation strategies that will help save lives in the future.

Because Japan was so well prepared, with such amazing technology available to measure the event, I anticipate that the science base for tsunami hazard will improve significantly.

Hannah Evans writes:

Figure 16. Pine forest destroyed by the tsunami.

Figure 17. Cleared land areas with only the house foundations remaining.

Figure 18. Volunteers on the beach sorting tsunami debris.

Figure 19. Temporary housing. © Patrick Corcoran

Figure 20. Delegates at the IOC-UNESCO Symposium. © Patrick Corcoran

We spent four days in the field validating the interpretations we had made from time-series satellite imagery from before and after the tsunami, using digital data capture.

In our field area the low lying Sendai Plain was protected by both soft and hard engineering structures.

In the Sendai region our surveys show that the power of the tsunami was concentrated in the areas immediately landward of the destroyed hard defences (see Figure 10).

The coastal pine forests were extensively damaged and selected areas of beach were eroded (Figure 16).

Great progress

In the months since my last visit to Japan astonishing progress has been made in the clean-up operations.

The devastated towns of Minamisanriku and Onagowa, which were once covered in all manner of debris, are now largely bare with only the foundations of destroyed houses remaining (Figure 17).

Debris has been sorted into huge piles for recycling and local volunteer teams have scoured the area removing personal possessions left scattered over the ground (Figure 18).

Sea defences have been largely rebuilt in some areas around the Sendai Plain, including sea walls over 7 m high (Figures 11 and 12). Temporary housing has been built and many families rehomed (Figure 19).

Rebuilding

In terms of rebuilding, there is ongoing debate about where to allow redevelopment of residential areas.

Many locals whose livelihood depends upon the low-lying coastal zone for farming or access to the sea for fishing wish to return to the original site of their settlements whilst others appreciate the safety afforded by higher ground.

Tsunami Warning Systems: Policy Perspectives

Many delegates at the IOC-UNESCO Symposium had travelled from all over the world, with representatives from the USA, Caribbean, UK and Indonesia as well as many colleagues from Japan (Figure 20).

The importance of the symposium was defined by the attendance of the Crown Prince of Japan for the first morning session.

The meeting started with a minutes silence for the lost lives. Our thoughts went out to the families of the victims of the tsunami, those who had lost their homes and who are still working to rebuild their lives.

The huge turnout revealed the extent of research that is ongoing into the Japan tsunami. Scientists, policy makers, government officials and broadcasting media combined to share their experiences and results of their research in order to develop plans to address future events.

References

Goto, K, Chagué-Goff, C, Fujino, S, Goff, J, Jaffe, B, Nishimura, Y, Richmond, B, Sugawara, D, Szczuciński, W, Tappin, D R, Witter, R C, and Yulianto, E.  2011.  New insights of tsunami hazard from the 2011 Tohoku-oki event.   Marine Geology. Vol. 290, no. 1–4, p. 46–50.

Photos © David Tappin – BGS, unless otherwise stated in hover text.

Contact

Contact Dave Tappin for further information