Today in Geological History; March 11th – Tōhoku Earthquake & Tsunami

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article-0-0D924D9F000005DC-785_964x591.jpgI am pretty sure I have covered this event before but seeing as today marks the 5 year anniversary of one of the worst natural disasters in the past decade I thought it deserves a much more in depth look. The events of March 11th destroyed the lives of hundreds of thousands of people and claimed the lives of nearly 20,000. For me, it opened my eyes to a world of geohazards and mad me realized this was something I wanted to study and understand so such loss of life would not happen again.

There are three elements to the events of March 11th that I am going to look at here; the earthquake, the tsunami and the Fukushima power plant. Each aspect a huge disaster in on there own but interlinked as they were caused devastation for Japan. 

The Earthquake

Instrumental Intensity Image

Japan is a volcanic island which stretches along where the North American, Pacific, Eurasian and Philippine plates all collide at different points. It is a part of the Pacific Ring of Fire, the world’s most tectonically active area. Practically all of our planets largest and most destructive earthquakes occur along the ring, one of which rocked the east coast of Japan at 2.46 pm JST (5.46am UTC) on March 11th 2011.

The magnitude 9 quake struck at the shallow depth of just 32 km roughly 70 km off the Oshika Peninsular. The area was already alert to seismic activity as several large foreshocks had occurred in the run up including a Mg 7.2 on March 9th and followed by three more above a Mg 6. Of course no one knew these were precursors to something much larger…

Initial reports from JMA and USGS put the March 11th quake at a 7.9 but this had risen first to a 8.8 and then to a 9 before most of the seismic waves had even hit Tokyo 373 km away. Luckily thanks to Japans intense seismic network the countries capital had at least 80 seconds warning before they felt the strong shaking.

The megathrust earthquake occurred where the Pacific Plate subducts beneath the North America Plate. The Pacific Plate moves at a relative speed of roughly 9 mm per year but it is not a smooth decent, tension can build and release in a large snap causing an earthquake. On March 11th this happened in epic style causing over ~50 meters of displacement near the Japan Trench which caused the tsunami which swept across the Sendai planes. The earthquake was so powerful that up to 1.69 meters of co-seismic deformation has permanently altered our planet and affected the Earths tilt shaving 1.8 microseconds of the day (not that we would ever notice!)

It was the forth largest earthquake ever recorded and the largest ever to strike Japan.

The Tsunami 

The displacement on the sea bed in turn caused a huge displacement of water in the Pacific ocean its self. Across a 180 km stretch there was recorded up thrust of 6-8 meters. Above the rupture the tsunami waves would have looked like no more than ripples on the surface radiating out across the ocean. It is as the waves reach the continental shelf and the water is forced upwards that they begin to take on their characteristic ‘wall of water’ appearance.
At its maximum height (recorded at Miyako, Iwate) the waves hit 40.5 m high (133 ft). The Pacific has the most comprehensive tsunami warning systems in the world but even this gave only about 15 minutes warning from the earthquake to waves hitting the coast line. Travelling at speeds up to 500 mph the water surged up to 6 miles (10 km) inland.

Honshu earthquake tsunami travel times

It was not just Japan which felt the repercussions of the event. Tsunami waves propagated out through out the entire Pacific. 11,000 miles away the coast of Chile experienced waves in excess of 2 meters along with most of the America west coast right up through to the Aleutian Islands and as far south as Antarctica where it broke chunks off the Sulzberger Ice Shelf

An estimated 5 million tonnes of debris began washing up on shore lines across the Pacific in the months and even years after the initial Earthquake. In April 2013 a 20 ft boat ran aground in California and was later identified as belonging to the marine sciences program at Takata High School, Japan. NOAA have kept tracks and aimed to clear as much of the debris as possible to minimize risk to ships and wild life but the operation can take more than a decade.

Fukushima

The melt down at the Fukushima was the worst nuclear disaster the world has seen since Chernobyl in 1986.

The plant ran by TEPCO had 3 of its 6 units shut down for inspection when the earthquake struck. Units 1, 2 and 3 then under went automatic shutdown cutting off power. 50 minutes later the waves up to 15 meters high breached the measly 5.7 meters seawalls and flooded the basements of the turbine buildings and disabling the emergency generators. The lack of power meant the cooling systems of the 3 active reactors failed and eventually the heat caused by decay caused the containers to burst leaking radioactive material.

It was classified a Level 7 on the International Nuclear Event Scale (INES) and its was the way the event was handled from the very beginning my TEPCO which saw the escalation in the threat. Approximately 15 PBq of caesium-137 was released along with some 500 PBq of iodine-131, luckily all the failed reactors were in concrete containment vessels, which limited the release of strontium-90, americium-241 and plutonium.

Dozens of vehicles lie abandoned and covered in overgrown bushes along what was once a stretch of road near the power plantNo deaths were caused by the events or short term radiation exposure but it is thought people in the area worst hit will have a slightly higher risk of developing certain cancers in the future. Now 5 years on there is still a 12.5 km is still in place with thousands of people still exiled from their homes. The wild has reclaimed the land making it look like a scene from an apocalyptic film.

It could be centuries before the area is truly deemed safe to live on again.

Pre-Warning; This has happened before

Japan is no stranger to tsunamis; the 1896 and 1933 Sanriku earthquakes (Mg 8.5 and 8.4 respectively) also brought deadly waves. For this reason tsunami barriers have been constructed both on and off shore, trees were planted along the coastline, vertical evacuation buildings were built to the highest standards and regular evacuation training was introduced. But none of these were built to with stand the sheer force of a tsunami of this magnitude.

In 2001 a team from Tohoku University published an article in Journal of Natural Disaster predicting such an event occurring every 800-1100 years. Within the Sendai Plain there is evidence of at least 3 major tsunami deposits all left within the past 3000 years. On July 9th 869 BC what is believed to be a magnitude 8-9 earthquake occurred off the coast of Sanriku causing a major tsunami which left deposits up to 4 km inland. So given that we knew an event like this had occurred before, why was Japan not better prepared for March 11th?

Sadly human nature does not always listen to the reason of science. It is often easier to believe ‘it won’t happen in my life time’ and then brush the threat under the carpet for future generations. The problem is it does not matter how much we study the mechanics of our planet we are still no where near being able to predict these disasters with any degree of accuracy meaning preparation is our best defence.

Aftermath

A report issued by the Japanese government in May 2015 claimed the events of March 11th 2011 caused $300 billion dollars. A confirmed 15,894 people lost their lives, 2,562 people are still unaccounted for.

5 years on the area is yet to recover. An estimated 174,000 are still displaced mainly due to the exclusion zone still heavily in place around the Fukushima plant. Soon as the initial rescue operation was completed the Tohoku Earthquake Tsunami Joint Survey Group was assembled. A team of natural scientists and engineers from 63 universities world wide set out to understand what made this tsunami so powerful and how we can protect our selves from further events. By the end of 2011 the Japanese government had passed laws to establish “tsunami-safe cities” and pledged billions of dollars to an intense 5 year clean up operation. It was clearly a bigger job than they originally thought….

Today there are still over 60,000 people living in temporary accommodation.For residents once living near the Fukushima power plant they will probably never return to there own homes. Sendai is still trying to recover from the tragic events but also now living in fear that this could occur again.

It is for this reason I choose to go in to studying geoscience. We all live at the mercy of our planet and most of us never even consider the risk the land beneath our feet poses. Prediction, preparation and knowledge can save lives and this is what I one day want to help with.

 

Figure 1; http://www.dailymail.co.uk/news/article-1365318/Japan-earthquake-tsunami-The-moment-mother-nature-engulfed-nation.html

Figure 2; http://earthquake.usgs.gov/earthquakes/shakemap/global/shake/c0001xgp/

Figure 3; http://minookatap.com/2011/08/22/japan-book-club-the-big-wave-5/

Figure 4; http://www.livescience.com/39110-japan-2011-earthquake-tsunami-facts.html

Figure 5; https://7plaguesofgod.wordpress.com/2011-tsunami-japan/

Figure6; http://vassarchronicle.com/section/politics/foreign-affairs/lack-of-regulation-fukushima-meltdown/

Figure 7; http://www.dailymail.co.uk/news/article-3263714/Destroyed-man-reclaimed-nature-Amazing-images-reveal-exclusion-zone-Fukushima-abandoned-overgrown-wilderness.html

 

 

 

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