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Earthquake of March 11th
Tectonic setting of the hazard
Tectonic setting of the hazard
Japan is located at the meeting point of 3 tectonic plates, The Eurasian, Pacific and Philippines. The boundary is to the East of the 4 main Japanese islands, Hokkaido, Honshu, Shikoku and Kyushu. It is a convergent DESTRUCTIVE boundary, with faults running off the boundary. In effect, Japan owes its existence to this boundary and the Islands are volcanic in origin. Japan gets 30% of the world’s earthquakes every year, and there is 90mm of movement of the Pacific Plate under the Eurasian.
There was a magnitude 7.2 earthquake on the 9th of March, 2 days before the 8.9-9.0 magnitude earthquake of the 11th.
There were also huge numbers of large sized aftershocks, as big as magnitude 6.
The reason why the Tōhoku Earthquake happened was due to the 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.
The earthquake was the biggest ever recorded to have stuck Japan, at approximately 9.0. The epicenter approximately 70 kilometres east of the Oshika Peninsula of Tōhoku and the hypocenter or FOCUS at an underwater depth of approximately 32 km (20 mi).
There were 7 foreshocks, including a magnitude 7.2 earthquake on the 9th of March, 2 days before the 8.9-9.0 magnitude earthquake of the 11th. There were also 1235 aftershocks, many at 7 of above and over eight hundred aftershocks of magnitude 4.5 MW or greater . The earthquake also followed Omori’s law, where the number & size of earthquake aftershocks declines with time from the largest event. In addition, 30% of the world’s earthquakes occur close to Japan, so Earthquakes are common, but earthquakes of this size are rare.
The upper 10m of the soil in this zone was also very vulnerable, as the waves amplified in this soil and caused liquefaction.
In this instance it was the Eastern seaboard of Japan and the Island of Honshu that were vulnerable. The Fukushima nuclear power plant also faced directly the epicentre of the Earthquake.
As a result of the high frequency of Earthquakes in this area Japan has developed a high capacity to cope with both Earthquakes and tsunami.
40% of Japan’s coastline has sea walls of up to 10m high to withstand incoming tsunami waves for example.
Japan has a hazards agency, the Japanese Meteorological Agency, which is set up for the prediction of earthquakes and tsunami. It detected the Earthquake and issued televised warnings just after the very rapid P-waves that arrived but before the more damaging S waves. This gave people a chance to get outside of buildings to safety. It also predicted the tsunami from this event just 3 minutes after the major earthquake, giving people 20 minutes to get to safety. The JMA broke this news on live television, and messages went out on Japan’s mobile network.
Buildings in Japan are also designed to cope with Earthquakes, and Japan’s high level of development means that buildings are made to be life safe and can actually move with earthquake waves and reduce damage.
Japan had its emergency crews and the army on site very quickly after the event. They have readily trained teams of people to go in and assist with events like this
Buildings are earthquake proof and people in Japan are trained YEARLY on the 1st of September in how to survive earthquakes, this is a result of the Tokyo (great Kanto) Earthquake of 1923.
Japan has a huge GDP; it was $34,000 in 2011, which allows it huge leeway ion terms of planning for Earthquakes and tsunami. 40% of Japan’s coastline has sea walls of up to 10m high to withstand incoming tsunami waves for example.
To monitor earthquakes, the Japanese Meteorological Agency operates
network of about 200 seismographs and 600 seismic intensity meters. It also
collects data from over 3,600 seismic intensity meters managed by local
governments and the National Research Institute for Earth Science and Disaster
Prevention (NIED). This information is put into the Earthquake Phenomena
Observation System (EPOS) at the headquarters in Tokyo
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.
The Tsunami and Earthquake both had devastating impacts, but the tsunami caused the most damage.
The tsunami waves that reached heights of up to 40 metres 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.
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.
This resulted in a social impact; 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.
In addition 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.
Around 4.4 million households in northeastern Japan were left without electricity and 1.5 million without water.
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.
All of Japan’s ports had to close at least temporarily during the disaster, and 10% of the fishing ports were damaged.
Interactive – how Japan had recovered one year on.
Just 6 days after the quake a motorway was repaired – this shows the incredible rapidity with which the Japanese can work with their capacity to cope. The BBC also released a series of photographs showing the same areas directly after the tsunami and one year later, the response is incredible.