Tohoku Earthquake: a Horrible Disaster in Japan

Japan is an island nation with a population that has a deep connection to the environment that surrounds and nourishes them. This environment has shaped the people of Japan in many ways. Japans history as been one that has been riddled with shows of the force of nature. The March 11th 2011 Tohoku earthquake has been the worst natural disaster in Japan and arguably one of the worlds most devastating natural disasters. This disaster was not just an earthquake, but also a tsunami set off by the earthquake and a nuclear meltdown set off by the tsunami. These three events combined make this the single worst event in Japanese history since WWII. To better understand the effect of the earthquake, one must have a basic knowledge of plate tectonics, the logarithmic scale used to rate earthquakes and how tsunamis work.        

To talk about the impact of this natural disaster is to talk about the geography of Japan and the tectonic plates it sits upon. Japan is classified as a volcanic archipelago, with three main mountainous arcs. The largest of these arcs is Japan proper, which includes the four main islands, Hokkaido, Honshu, Shikoku, Kyushu, and many other smaller islands (Trewatha Pg. 3). The Kuril arc and the Ryukyu arc are made up of many small volcanic islands. The Kuril arc is located above the northern end of Japan proper, and the Ryukyu arc is located on the southern end of Japan proper (Trewatha Pg. 4).

The tectonic activity that is experienced in Japan can be explained by the interactions between the Eurasian, Amurian, Okhost, Pacific, and Philippine Sea plates (Taira Pg. 110). These plates are sections of the earths lithosphere, a solid layer of rock that constitutes the outer layer of the earth. This layer includes the crust and parts of the upper mantle. The lithosphere is broken up into a few large plates, and many more smaller plates. These plates sit on top of the asthenosphere, a viscous and mechanically weak layer that makes up the upper mantle. Convection currents in the asthenosphere move the tectonic plates causing them to bump into each other. The interaction of plates at their boundaries cause three types of movements. Deep under the oceans, plates can pull apart. This movement, called divergence, causes lava to rise up and create new rock at the plate boundaries. Plates can converge, where they come together. At a continental-continental boundary, formation of mountains occur. At an oceanic-oceanic boundary, deep ocean trenches are formed. At an oceanic-continental boundary, volcanic arcs can be created. Subduction zones are created at convergent boundaries, these are zones of major activity that creates the most powerful earthquakes. The final movement is when two plates slide past each other, called transformation. This movement creates friction that releases stored energy in the plates, causing earthquakes. A strike-slip fault is one where two plates move laterally against each other in opposite directions. The Great Japan Earthquake was caused by the subduction of the Pacific plate beneath the Okhotsk plate (The Geological Society).        

Earthquakes are rated by a complicated logarithmic equation called the Richter scale. The old Richter scale measured ground movements but since 1970, scientists use an updated scale that measures shaking based on a complicated formula that is designed to be able to be used to compare most earthquakes (Coontz). Since this new scale is logarithmic, every increase in magnitude is more powerful than the previous one by a factor of 10. A magnitude 4 earthquake shakes 10 times harder than a magnitude 3 earthquake, and an earthquake that is magnitude 4 shakes 100 times harder than one that is magnitude 2. Comparing the amount of energy two earthquakes release involve a similar process. Subtract the magnitudes, add 50%, then use the result as a power of 10, this process works because the energy of an earthquake scales with 3/2 of magnitude (Coontz).

For comparison, the March 11th Tohoku (M9.1) earthquake was 79.432 times bigger and 707.945 times stronger than the January 17th Kobe earthquake (M7.2). The Kobe earthquake, also known as the Great Hanshin Earthquake, was deadly in its own respect, killing more than 6,000 and making more then 45,000 people homeless (Sue). The Tohoku earthquake was substantially larger than other magnitude 7+ earthquakes in the Japan Trench subduction zone. The largest one at magnitude 7.8 occurred about 260 km north of the Tohoku epicenter, and caused 3 deaths and almost 700 injuries in December of 1994 (USGS). The United States Geological Survey puts the 2011 Tohoku earthquake at number 4 of the largest earthquakes in the world (USGS). Relatively speaking, the 2011 Tohoku earthquake is not that far away from the most powerful earthquake ever recorded. The May 22nd, 1960 Valdivia earthquake in Bio-Bio, Chile registered as a magnitude 9.5, making it only 2.511 times bigger and 3.981 times stronger than the Tohoku earthquake (USGS).        

The 2011 Tohoku earthquake may not be the most powerful recorded earthquake but it had very disastrous effects. The magnitude 9.1 earthquake took place 72 km east of Tohoku at a depth of 24 km below the surface (The Geological Society). The hypocenter of an earthquake is the point in the earths crust where the earthquake originated from, and the epicenter is the point directly above the hypocenter on top of the earths crust. The closer the hypocenter and epicenter, the more disastrous the quake. The Tohoku earthquake's relatively shallow depth of 24 km was a factor in its strength. Another factor that added to its strength was a layer of slippery clay lining the fault, this layer of clay allowed the plates to slide around 50 meters past each other (Oskin). The resulting magnitude 9.1 caused 15,718 deaths with 4,086 missing totaling 19,867 (Batten Pg. 23). Reportedly, 121,806 buildings were destroyed, 278,575 were half destroyed, and 726,176 were partially destroyed, with over 470,000 people being evacuated from their homes (Reconstruction Agency). Massive damage was caused by the earthquake, but the cause of the majority of the damage was the resulting tsunami.        

A tsunami is a gigantic wave that differs from normal breaking waves. A tsunami is caused by the displacement of a large volume of water out in the ocean. The cause of the displacement can range from earthquakes to volcanic eruptions. Normal ocean waves are caused either by the wind or by the tides, which are subsequently caused by the gravity of the moon and the sun. Tsunamis also have longer wavelengths and are much more massive than breaking waves. To call a tsunami a mere wave does not do it justice. Early measurements recorded the 2011 tsunami to be 37.9 meters, coming in just shy of the highest ever recorded tsunami which was recorded at 38.2 meters in 1896 (Normile). After further inspections, the Tohoku tsunami was calculated to be 38.9 meters at its highest, which would make it the tallest tsunami ever recorded in Japan (Miller Pg. 255). A tsunami of this size could easily swallow a 12 story building. Footage taken of the tsunami reveals boats and buildings being tossed around like toys by the monstrous tsunami. Buildings are easily swept away in the strong currents.The third factor that made the 2011 Tohoku earthquake so devastating was a nuclear meltdown caused by the tsunami. In the first three days   the total economic cost of this disaster is estimated to be $360 billion USD (Reid). Adjusted for inflation, this is $404 billion USD as of November of 2018 (US Inflation Calculator). To put this into perspective, the Great Hanshin earthquake cost has been estimated to be $114 billion USD, which was three times more than the recorded cost of any other historical natural disaster in the world (Horwich Pg. 522). This amounts to $190 billion adjusted for inflation (US Inflation Calculator).        

Japan is often thought of as a world leader in disaster preparedness. Decades of being hit with the raw forces of nature has led the Japanese people to develop better buildings in preparation for the next disaster. whatever the extent of the death and destruction, it would be much worse if not for Japan's hard-earned culture of preparedness says Emily Rauhala of Time magazine about the 2011 Tohoku earthquake and tsunami.

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