Tohoku Earthquake and Tsunami

On 11 March 2011, the lives of many Japanese people changed as they lived the greatest magnitude earthquake experienced by Japan in its recorded history. The Tohoku earthquake and tsunami occurred with a magnitude of 9. Its epicentre was located 130 kilometres from the east of Sendai (the largest city in the Tohoku region), below the North Pacific Ocean. The shaking began at 2:46pm local time and lasted about six minutes. This caused a tsunami within 30 minutes with waves reaching 40 metres. The tsunami reached the land and flooded 561 square kilometres.

The cities of Iwate, Miyagi, and Fukushima were the most affected by the earthquake and tsunami. However, it was also felt in cities such as Tokyo, which is approximately 400 kilometres from the epicentre.

Map of Japan with the epicentre of the earthquake

What caused the Tohoku earthquake and tsunami?

The Tohoku earthquake and tsunami were caused by centuries of build-up stress that was released in the convergent tectonic plate margin between the Pacific and the Eurasian plates. This is a common cause of Earthquakes as the Pacific tectonic plate is being subducted below the Eurasian plate. It was later discovered that a slippery layer of clay at the fault had let the plates slide 50 metres. Changes in sea levels were detected in the countries of the Pacific Rim, Antarctica, and the West Coast of Brazil.

What are the environmental impacts of the Tohoku earthquake and tsunami?

The environmental impacts of the Tohoku earthquake and tsunami include contamination of groundwater (as the saltwater and pollution from the ocean infiltrate to the ground due to the tsunami), removal of silt from coastal waterways due to the force of the tsunami, and destruction of coastal ecosystems. Further indirect impacts include the environmental toll of reconstruction. The earthquake also caused some beachfronts to drop by 0.5m, generating landfalls in the coastal areas.

What are the social impacts of the Tohoku earthquake and tsunami?

The social impacts of the earthquake and tsunami include:

• 15,899 people dead.
• 2527 missing and now presumed dead.
• 6157 injured.
• 450,000 lost their homes.

The unfortunate events caused other long-term consequences:

• 50,000 people were still living in temporary homes by 2017.
• 2083 children of all ages lost their parents.

To deal with the social impacts, in 2014 Ashinaga, a non-profit organisation based in Japan, built three emotional support facilities in the affected areas, where children and families are able to support each other and work through their grief. Ashinaga has also been providing emotional and financial support.

They conducted a survey ten years after the disaster, which showed that 54.9% of widowed parents are still in disbelief about losing their spouse due to the disaster. (1) Moreover, many continued to live in fear of radiation from the nuclear power meltdowns, and didn’t allow their children to play outdoors even in areas deemed safe.

What are the economic impacts of the Tohoku earthquake and tsunami?

The economic impact of the earthquake and tsunami has been estimated to cost £159 billion, the most expensive disaster to date. The earthquake and tsunami destroyed most of the infrastructure (ports, factories, businesses, and transportation systems) in the worst affected areas and they had to implement a ten-year recovery plan.

What mitigation strategies existed before the Tohoku earthquake and tsunami?

The mitigation strategies before the Tohoku earthquake and tsunami consisted of methods such as seawalls, breakwaters, and hazard maps. The Kamaishi tsunami breakwater was the deepest breakwater in the world at 63m deep, but it could not fully protect the citizens. However, it provided a six minute delay and reduced the tsunami height by 40% in the harbour. In 2004, the government published maps that pointed out the areas flooded by past tsunamis, how to find shelter, and instructions on evacuation and methods of survival. Moreover, people often carried out evacuation drills.

Additionally, they enforced a warning system that alerted Tokyo residents of the earthquake using a siren and text message. This stopped trains and assembly lines, reducing the consequences of the earthquake.

From 1993, when a tsunami devastated Okushiri Island, the government decided to implement more urban planning to provide tsunami resilience (e.g. evacuation buildings, which are tall, vertical buildings raised above the water, for temporary refuge). However, the predicted maximum magnitude of possible earthquakes in the area was Mw 8.5. This was concluded through monitoring seismic activity around Japan, which suggested that the Pacific plate was moving at a rate of 8.5cm per year.

What new mitigation strategies were implemented after the Tohoku earthquake and tsunami?

The new mitigation strategies after the Tohoku earthquake and tsunami have focused on evacuation and easy reconstruction instead of defence. Their reliance on seawalls made some citizens feel that they were safe enough to not evacuate during the Tohoku earthquake and tsunami. However, what we have learnt is that we cannot depend on infrastructure based on defence. The newer buildings are designed to allow the waves to pass through their large doorways and windows, which minimises the possible damages and allows the citizens to flee to elevated grounds. Investment into tsunami forecasting has included research using AI to provide more opportunities for the citizens to evacuate.

Footnotes

Ashinaga. ‘Ten Years Since March 11, 2011: Remembering the Devastating Triple Disaster in Tohoku,’ 2011.