Japan earthquake 2011 Case Study

What?

An earthquake measuring 9.0 on the Richter Scale struck off Japan’s north-east coast, about 250 miles (400km) from Tokyo at a depth of 20 miles.

When?

The magnitude 9.0 earthquake happened at 2:46 pm (local time) on Friday, March 11, 2011.

Where?

The earthquake occurred 250 miles off the North East Coast of Japan’s main island Honshu.

Japan 2011 Earthquake map

Why?

Japan is located on the eastern edge of the Eurasian Plate. The Pacific Plate, which is an oceanic plate, subducts (sinks under) the Eurasian Plate, which is a continental plate, forming a subduction zone to the east of Japan. This type of plate margin is known as a destructive plate margin. The process of subduction is not smooth. Friction causes the Pacific Plate to stick. Pressure builds and is released as an earthquake.

Friction has built up over time, and when released, this caused a massive ‘megathrust’ earthquake.

The amount of energy released in this single earthquake was equivalent to 600 million times the energy of the Hiroshima nuclear bomb.

Scientists drilled into the subduction zone soon after the earthquake and discovered a thin, slippery clay layer lining the fault. The researchers think that this clay layer allowed the two plates to slide an incredible distance, some 164 feet (50 meters), facilitating the enormous earthquake and tsunami.

2011 Japan Earthquake Map

So What?

The earthquake occurred at a relatively shallow depth at 20 miles below the surface of the Pacific Ocean. This, combined with the high magnitude, caused a tsunami (find out more about how a tsunami is formed on the BBC website).

Areas affected by the 2011 Japanese earthquake.

The tsunami struck the northeastern coast of Honshu.

What were the short-term effects of the 2011 Japan earthquake?

Impacts on people

Death and injury – Some 15,894 people died, and 6,152 people were injured. 130,927 people were displaced, and 2,562 remain missing.

Nuclear crisis – A 9m high wave flooded the generators of the Fukushima nuclear power plant and destroyed electrical wiring. People lost energy immediately.

Flood defence disaster – In the past Japan has spent billions of dollars building anti-tsunami defences. The tsunami washed over the 12-metre walls, rendering them totally ineffective.

Damage – 332,395 buildings, 2,126 roads, 56 bridges and 26 railways were destroyed or damaged. 300 hospitals were damaged, and 11 were destroyed.

Blackouts – Over 4.4 million households were left without electricity in North-East, Japan.

Impacts on the environment

Fore and aftershocks – over 800 earthquakes of magnitude 4.5 or more were recorded following the main earthquake.

Tsunami –  waves up to 40 m in high devastated entire coastal areas and resulted in the loss of thousands of lives. This caused a lot of damage and pollution up to 6 miles inland.

Landfall – some coastal areas experienced land subsidence as the earthquake dropped the beachfront in some places by more than 50 cm.

What were the long-term effects of the 2011 Japan earthquake?

Impacts on people

Economy – The earthquake was the most expensive natural disaster in history with an economic cost of US$235 billion.

Tsunami – The tsunami warnings in coastal areas were only followed by 58% who headed for higher ground. The wave hit 49% of those not following the warning.

Nuclear power – Seven reactors at the Fukushima nuclear power station experienced a meltdown. Levels of radiation were over eight times the normal levels.

Transport – Japan’s transport network suffered huge disruptions.  Rural areas remained isolated for a long time because the tsunami destroyed major roads and local trains and busses. Sections of the Tohoku Expressway were damaged. Railway lines were damaged, and some trains were derailed. 

Aftermath – The ‘Japan move forward committee’ thought that young adults and teenagers could help rebuild parts of Japan devastated by the earthquake.

Impacts on the environment

Land movement – due to tectonic shift, the quake moved parts of North East Japan 2.4 m closer to North America.

Coastal changes – The tsunami was able to travel further inland due to a 250 mile stretch of coastline dropping by 0.6 m.

Plate shifts – It has been estimated by geologists that the Pacific plate has slipped westwards by between 20 and 40 m.

Seabed shift – The seabed near the epicentre shifted by 24 m and the seabed off the coast of the Miyagi province has moved by 3 m.

Earth axis moves – The earthquake moved the earth’s axis by between 10 and 25 cm, shortening the day by 1.8 microseconds.

Liquefaction occurred in many of the parts of Tokyo built on reclaimed land. 1,046 buildings were damaged

Why do people live in high-risk areas in Japan?

There are several reasons why people live in areas of Japan at risk of tectonic hazards:

• They have lived there all their lives, are close to family and friends and have an attachment to the area.
• The north-east has fertile farmland and rich fishing waters.
• There are good services, schools and hospitals.
• 75% of Japan is mountainous and flat land is mainly found in coastal areas, which puts pressure on living space.
• They are confident about their safety due to the protective measures that have been taken, such as the construction of tsunami walls.

Japan’s worst previous earthquake was of 8.3 magnitude and killed 143,000 people in Kanto in 1923. A magnitude 7.2 quake in Kobe killed 6,400 people in 1995.