Plate Tectonics- Seismicity Case Study

Japanese Earthquake & Tsunami, 2011

Key Facts

• Date: 11th March 2011
• Magnitude: 9
• Pacific Ocean
• Pacific plate subducted beneath North American Plate

Location 

A massive 9.0-magnitude earthquake struck Japan, Friday afternoon, on 11 March 2011. The quake was centred 130 kilometres to the east of the prefecture’s capital, Sendai. A tsunami was sent crashing into the country’s north-eastern coast. It was originally reported at a magnitude of 7.9, but later was upgraded to 8.9 and then to a 9.0. It lasted 6 minutes. 

Causes 

• Japan is located on the east edge of the Eurasian Plate. 
• There was a build-up in strain energy as the Pacific plate subducted under the Eurasian plate. This strain energy eventually overcame the frictional force holding the plates in place, and was released as earthquake waves.
• The tsunami is a secondary consequence of this initial movement. The Eurasian plate was down warped (dragged down) as the Pacific plate descended. When the strain energy was released this section of the Eurasian plate “popped” or bounced back upwards. This displaced the water above in the Pacific Ocean causing a Tsunami wave to ripple radially outwards. This was known as a megathrust earthquake. 
• The aftershocks occurred as the strain energy was passed along the fault, causing further quakes. 

Impact 

• Japan was largely prepared for the earthquake and many buildings remained standing afterwards, but it was not prepared for the subsequent Tsunami. A tsunami warning extended to at least 50 nations and territories, as far away as South America. 
• The tsunami waves that reached heights of up to 40 meters in Miyako and which, in the Sendai area of Honshu, travelled up to 10 km (6 mi) inland. 
• The island of Honshu was moved 2.4 m east and shifted the Earth on its axis by estimates of between 10 cm and 25 cm. 

Social: 

• Residents within a 20 km radius of the Plant were evacuated. 
• The official death toll report confirmed 15,854 deaths, 26,992 injured and 3,155 people missing across twenty prefectures. 
• Around 4.4 million households in northeastern Japan were left without electricity and 1.5 million without water. 
• All of Japan’s ports had to close at least temporarily during the disaster, and 10% of the fishing ports were damaged. 

Economic: 

• The yen fell sharply but recouped most of its decline several hours later. Tokyo stocks fell. 
• 130,000 buildings totally collapsed and another near 700,000 buildings partially damaged. 
• The earthquake and tsunami also caused extensive and severe structural damage in north-eastern Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse. 
• The economic losses are thought to be huge, given Japan’s highly developed infrastructure and level of development there was a lot to be damaged. The World Bank estimated cost was US$235 billion, making it the most expensive natural disaster in world history. 
• Estimates of insured losses from the earthquake alone ranged from US$14.5 to $34.6 billion. The Bank of Japan offered 15 trillion Yen (US$183 billion) to the banking system to normalize market conditions. 

Environmental: 

• The most worrying impact was on Japan’s famed nuclear power industry. There were several nuclear incidents but the most notable was 3 nuclear meltdowns at the Fukushima power plant. This cause contamination of the sea and land, and force the evacuation of local residents. A brave team of nuclear power plant workers battled bravely to prevent the nuclear reactors overheating completely and exploding. 

Response 

• Many people got outside during the earthquake and the response to the Earthquake was reasonably good. The warnings from the JMSA also helped save lives. Many people did not react quickly enough to the tsunami alert, and even if they did the 20 minutes or less warning was insufficient for the people to escape. 
• The JMA and government did a good job of monitoring and getting warning to people, and this probably saved many lives. 
• Over 340,000 displaced people in the region needed catering for, and issues included shortages of food, water, shelter, medicine and fuel for survivors. 
• The Japanese government responded by sending in specially trained people such as the Self-Defence Forces, a domestic response. 
• Many countries such as the UK sent search and rescue teams to help search for survivors. NGOs and other Aid agencies helped too, with the Japanese Red Cross reporting $1 billion in donations.