On March 11, 2011, a chain of devastating natural disasters struck the Pacific coast of Japan. It began with a staggering 9.0 magnitude earthquake - the largest ever recorded in Japan, and only the third largest recorded worldwide - which hit northeastern Japan at approximately 14:46 JST, followed by 7.0, 7.4 and 7.2 magnitude aftershocks later that day. [1,2] The main earthquake also generated a massive tsunami, whose waves reached heights of up to 38 m, devastating large areas of Japan and triggering tsunami warnings in over 20 countries. [1] The catastrophe was compounded by accidents at several nuclear power plants in the wake of the earthquake and tsunami, particularly the meltdown at Fukushima Daiichi, which was later assessed as a level 7 on the International Nuclear Event Scale - the worst possible rating. [3]
Studies by the USGS indicate that the 9.0 earthquake and subsequent tremors were the result of the Pacific Plate sliding beneath Japan, with the quake's epicenter located at 38.322°N and 142.369°E, just 80 miles off the coast of Sendai. [1,2,4] Even prior to the Tohoku earthquake, the Pacific Plate was continually shifting, moving west by approximately 3.5 inches per year; this led to an energy buildup, which was violently released when the Pacific Plate broke away from its overhead plate [1,4]. USGS calculates that the earthquake released roughly 1.9 × 1017 Joules of surface energy. [1] Since the quake's hypocenter was a mere depth of 15 miles below sea level, much of its energy was released at the seafloor, generating the massive tsunami. [4]
As a consequence of the Tohoku earthquake, Honshu island has moved possibly as much as 12 feet towards North America, and over 200 miles of Japan's eastern coastline have been shifted south by several feet. [5] Even more remarkably, the resulting changes to earth's moment of inertia may have altered the earth's axis by up to 25 cm, as well as infinitesimally speeding up its rotation. [1,5] The effects on Earth's geology, however, were trivial in comparison to the effects on Japan's population. Analysis by the Japan National Police Agency in April of that year reported 13,392 people dead and an additional 15,133 missing. [1] In the city of Rikuzentakata alone, 10.4% of the population - almost 2.5 thousand people - were reported missing or dead in the wake of the tsunami. [2]
The earthquake and tsunami caused accidents at several nuclear power plants in the immediate vicinity, the most critical of which was the cooling systems failures at Fukushima Daiichi Nuclear Power Plant. [1,3] While it may take years to fully understand what went wrong at Fukushima, many technical and semi-technical reports are already available to the public. [6] When the earthquake hit, the reactors automatically shut down, and the plant lost connection with its offsite power grid. Emergency on-site diesel generators kicked in and took over the process of coolant circulation, but were damaged by flooding from the tsunami that followed, as were the back-up batteries. With the coolant system failing, the high temperatures caused the coolant water to evaporate, exposing the fuel rods and putting them under risk of melting. [1,6] Seawater was injected to cool the reactors, which experts say significantly mitigated the catastrophe, but the resultant increase in vessel pressure led to hydrogen explosions and the escape of massive quantities of radioactive isotopes. [1,7] It is estimated that the radiation released by Fukushima is in the range of tens of thousands of terabecquerels, and that radiations levels could eventually exceed the 1986 Chernobyl explosion. [3]
© Ellie Kitanidis. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] O. Norio et al., "The 2011 Eastern Japan Great Earthquake Disaster: Overview and Comments," Int. J. Disaster Risk Sci. 2, 34 (2011).
[2] N. Mimura et al., "Damage from the Great East Japan Earthquake and Tsunami - a Quick Report," Mitigation and Adaptation Strategies for Global Change 16, 803 (2011).
[3] H. Tabuchi and K. Bradsher, "Japan Nuclear Disaster Put on Par with Chernobyl," New York Times, 11 Apr 11.
[4] I. Sample, "Japan Earthquake and Tsunami - What Happened and Why," The Guardian, 11 Mar 11.
[5] E. Brown, "9.0 Japan Earthquake Shifted Earth on its Axis," Los Angeles Times, 13 Mar 11.
[6] F. D'Auria et al., "The Fukushima Event: The Outline and the Technological Background," Sci. Technol. Nucl. Installations 2012, 507921 (2012).
[7] N. Onishi and M. Fackler, "In Nuclear Crisis, Crippling Mistrust," New York Times, 12 Jun 11.