How is Japan shoring up its defences against tsunamis? 

A post-tsunami shot of Iwaki, Fukushima, Japan.ryuki_a_g/Wikimedia Commons

Japan's location on the ring of fire (a geologically riotous area of the world) means it has been subject to a long history of volcanism, earthquakes, and, therefore, tsunamis. Because of the frequency of these events, and its long history has to deal with them, Japan has had to find innovative and imaginative ways to cope.

Since tsunami defence is an ongoing battle for the Japanese, let's take a peek at Japan's engineering solutions for future tsunamis.

What are tsunamis?

A tsunami, or 'harbour wave', is a series of waves in a body of water created by the rapid displacement of a large amount of water very. Observed in any appreciably large body of water, such as oceans or lakes, tsunamis are often incredibly destructive forces of nature.

You will recall that waves are generally a consequence of either lunar gravitational forces (tidal waves) or the effects of the interaction wind on the surface of the water (wind-driven waves/surface waves).

However, one of the most common causes of tsunamis is the sudden subaquatic uplift of the sea floor associated with earthquakes. Tsunamis are generally caused by other large catastrophic natural events like earthquakes, volcanic eruptions, or other violent underwater (or above water) events like landslides, glacial calvings, or meteorite impacts, to name but a few.

Aerial photograph of the aftermath of the 2004 Indonesia tsunami. Source: AusAID/Wikimedia Commons

Depending on the source of the energy that creates tsunamis, they generally consist of a series of enormous waves with periods of between minutes and hours that arrive in what is called a 'wave train'. 

Coastal areas, including those inhabited by people, can be literally wiped off the map if they are unlucky enough to be in the path of an incoming tsunami. For this reason, island nations, like Japan, live in near-constant fear of the next tsunami event within range. 

Where the source event (earthquake or other) takes place far away from civilisation, tsunamis often cause more destruction and rack up higher death tolls than the original cause.

Why are tsunamis so destructive?

Tsunamis 'wave trains' tend to consist of a series of waves with extremely long wavelengths. Oftentimes, these waves are able to travel for many kilometres without a significant loss of energy – especially in open water.

Once these waves meet shallow waters they rapidly slow and become compressed, however, the back of the wave (in deeper water) is still travelling faster. This water has to go somewhere, so it goes up, building into waves of 10, 20, or even 30 metres in height.

From our perspective, where tsunami waves reach land, the destruction wrought, if the area is not inhabited, may not be a problem. However, water-hugging areas of the world have been preferred sites of habitation for our species for many millennia. When tsunamis impact these inhabited areas, the loss of human life can be, quite frankly, terrifying. 

Source: Petra Bensted/Flickr

The sheer power of tsunami waves, combined with the presence of buildings and other potential water-borne projectiles, is literally a 'recipe for disaster'. Once a tsunami wave makes landfall its energy is dissipated over a wide area, and, if great enough, for some distance inland.

At all points along their path, the waves will rip up, smash, and carry anything in their path (be it buildings, trees, cars, etc), turning them into ad hoc battering rams, further compounding the already enormous destructive potential of these events. 

This obviously makes tsunami events very, very dangerous. Your chances of survival, if ever caught in the path of this moving debris, are pathetically low – though not unheard of.

The past decade or so has seen a total of 16 tsunamis around the world – mainly around the Pacific. These events have claimed the lives of an estimated 6,000 people. 

To put that into perspective, that is roughly the death toll from all earthquakes globally for the same period. Bear in mind that earthquakes are a far more common event. 

Of course, there have been some very tragic tsunami events in living memory that were far worse than the relatively smaller events since around 2010. For example, the 2004 Indian Ocean tsunami claimed about 230,000 lives and is considered one of the worst natural disasters in history.

So, you might be wondering, given their incredible power, and often unexpected arrival, is there anything that can be done to protect against them? Or, at the very least, reduce the potential for loss of life to a minimum?

Source: Max Pixel

How is Japan protecting itself from tsunamis?

Japan's experience with these tragic events has led to the development of a strategy of countermeasure, defensive structures, and relocation of population centres over the years. With regards to the latter, Japan has made moving population centres away from coastal areas one of its priorities, where possible. They have also been working on ways to provide as much advanced warning as possible in order to facilitate timely evacuation.

This is especially true when tsunami-triggering events occur close to the coast. Under such circumstances, there may be only five to 10 minutes to facilitate an evacuation attempt. Clearly, for large population centres, this is less than ideal.

For this reason, among others, Japan has a highly developed public information campaign that informs as many citizens as possible of an oncoming tsunami, whenever possible. 

To this end, international warning systems have been developed and deployed to attempt to detect tsunami-triggering events to try to help out too. Such systems, whether domestic or international, are also usually coupled or supplemented with radio and television broadcasts and loudspeaker networks to warn the public.

But, such measures are not always practical or, indeed, possible. In fact, prediction of natural disasters, like tsunamis, is notoriously closer to an art form than a true science – at least for now. 

For this reason, one of the last lines of defence against tsunamis is to build physical barriers – like Japan's Fudai Seawall. More often than not, this is the only viable solution. However, recent events like Fukushima, have shown that such physical defences are not always foolproof. 

Sea wall in Okinawa, Japan. Source: Andrea Vanni/Flickr

So, are there any other ways we can defend against tsunami events beyond either getting out of the way or trying to physically absorb the blow? 

Engineering solutions

One of the most interesting strategies Japan has employed to help stave off the worst a tsunami has to offer is through something called 'earthquake engineering'. Through the development and installation of enormous building shock absorbers, sliding walls, and Teflon foundation pads, these structures are able to help Japanese buildings withstand the immense stresses and strains imposed on them during violent events like earthquakes. 

While primarily designed to help buildings survive tremors, these measures can also help buildings, at least a little, to bear some of the brunts of an incoming tsunami without critical structural failure. 

Another part of Japan's engineering solutions revolves around the construction of massive sea walls – sometimes up to about 12 metres tall. Such enormous structures are designed to help protect highly populated areas. 

Other engineering solutions include the design and construction of monstrous floodgates that are intended to channel, tamper, or redirect incoming tsunami waves away from critical infrastructure and population centres. These can be absolutely huge, up to 15.5 metres tall. 

Flood gates on the Sumida River, Tokyo. Source: David McKelvey/Flickr

Japan has also tested vertical structures, essentially tall platforms for people to stand on above the tsunami maximum height.

Nuclear facilities, in particular, have in recent years tended to be sited far from the coast and been designed to enter a 'safe mode' as soon as an earthquake is detected. 

 

Resistance, it appears, might be futile

When it comes to tsunami defence, Japan appears to have fully taken on board the advice of the 'Borg' from Star Trek. Believe it or not, researchers have found, using a wave tank, that allowing the water through without obstruction may appear to be the best course of action. 

"Instead of trying to obstruct the wave, you allow the wave to pass through the structure while causing minimum damage. Large doorways and windows offer a clear path to go through," says Tiziana Rossetto, a reader in earthquake engineering at University College London.

This almost counterintuitive strategy suggests that it might be better to make cleaning up the damage post-tsunami as painless as possible, rather than spend the kitchen sink on shoring up physical defences. Buildings are easier to replace, after all than lives. 

Source: Alessandro Rizzo/iStock

Especially when these measures are combined with those that allow occupants to flee to higher ground.

Japan's traditional tendency to build in timber also assists where building design cannot be altered.

"Internal doorways are aligned rather than staggered. If you have staggered doors, the wave gets 'locked' into the house," says Rossetto.

Research has also found that houses on piles could also be an answer, but this is not always practicable.

Japan has also drawn inspiration from other tsunami impacted areas – such as Hawaii or traditional 'Maya' houses. Here the traditionally built buildings tend to leave the ground floor clear, perhaps as a parking area. This effectively produces a building on stilts with the bonus of improving the building's ability to survive tsunami events (or at least keep the occupiers slightly out of the way).

Stilted homes seem to help too. Source: tian yake/Flickr

As with most tsunami-prone areas, Japan has developed a mixed strategy that primarily relies on evacuation rather than defence. As seismic detection and preemptive warnings improve, death tolls can, and likely will be, reduced over time.

Other than that, Japan is focussing more on ways to allow infrastructure damage to be repaired rapidly. This is especially the case if the building design accommodates strategic designs to either limit or allow easy repair. With regards to defensive structures, such as sea walls, Japan's experience in this area has shown that they are ineffective at best. But, they do offer a much-needed psychological boost to the local populace.

For this reason, they are likely to remain a critical component of tsunami countermeasures for some time to come. 

Given the need for improvement in detection systems and ineffectiveness of defensive structures, Japan, among other affected nations, places more emphasis, rightly or wrongly, on getting people out of the way and letting nature run its course.

After all, a building can be rebuilt. Lives cannot.