On March 9, 2011, Japan experienced a series of earthquakes with magnitudes reaching 6-7. These were merely warnings of what was to come. A few days later, on March 11, a 9.0 magnitude earthquake on the Richter scale triggered a tsunami, turning the northeast of Japan into ruins. The major earthquake resulted in at least 18,000 people being killed or missing. Over one hundred thousand homes were swept away from the Tohoku coastline by 9-meter waves.
In their place, stone monuments have been erected, indicating that living there is not advisable. Although there are no specific reasons, plaques with messages such as “To the children of tomorrow: run to higher ground” were placed in the devastated cities. So why did Japan, known as the most seismically prepared country in the world, find itself in such a dire situation after the 2011 earthquake?
The Tohoku Earthquake
The seismic activity that caused the Tohoku Earthquake in 2011 occurred in the ocean at the boundary of two tectonic plates, near the Japan Trench, 130 km from the Sendai region. Here, tectonic plates meet, forming a subduction zone. The Pacific tectonic plate was moving under the American plate at a rate of 830mm/year.
As a result of the powerful earthquake on March 11, 2011, the northeastern part of Honshu Island shifted 2.4 meters towards South America, a movement that would normally take 30 years. Seismic forces created a vertical displacement of water masses in the ocean, generating tsunami waves that flooded and destroyed coastal areas of three prefectures – Iwate, Miyagi, and Fukushima.
Tsunami
The proximity of the earthquake’s epicenter to the coast gave residents of settlements between 10 to 30 minutes to leave their homes and reach a safe place following the tsunami warnings issued by the prefectures. Not everyone managed to do so β elderly residents of coastal towns and people with disabilities were unable to evacuate the dangerous regions and were swept away by waves up to 10 meters high.
To mitigate the risk of tsunamis, the entire coastline of the affected regions was protected by a network of seawalls. However, not all hydraulic structures fulfilled their purpose, with many being destroyed by the seismic shocks and then by the massive waves. As a result, 54 out of 174 towns on the northeastern coast were struck by the waves. The Sendai International Airport was hit by the tsunami 25 minutes after the earthquake began and was completely destroyed. Thus, despite the modern warning system, a portion of the population simply did not have enough time to take measures to save themselves from the tsunami.
Fukushima Accident
The first waves following the earthquake struck the northern coast and then rapidly spread east and south, soon reaching the Fukushima Dai-ichi Nuclear Power Plant. The plant is located in the town of Okuma, Fukushima Prefecture, and was among the 25 most powerful nuclear power plants in the world.
The earthquake on March 11 led to an emergency shutdown of all the plant’s facilities, and waves up to 15 meters high flooded all technical rooms, disabling emergency generators responsible for cooling the reactors. In three of the six reactors, overheating led to the meltdown of nuclear fuel, subsequent explosions, and the release of radioactive materials into the air and sea.
The radiation level at the site boundary immediately after the explosion reached 1015 microsieverts/hour (30 micro-roentgens/hour), which is 60 times the permissible radiation background levels. The entire population within a 30 km radius of the plant was evacuated. As a result, the disaster at the Fukushima Dai-ichi nuclear power plant was assigned a 7th (maximum) level on the International Nuclear Event Scale. This rating was previously given only to the Chernobyl nuclear disaster.
Consequences of the Tohoku Earthquake
Thus, despite the measures adopted in 1950… The seismic safety construction program and the implementation of the world’s first earthquake and tsunami warning system could not prevent the catastrophic consequences of the 2011 events for Japan:
- In 20 prefectures, the earthquake and tsunami claimed the lives of 19,000 people, with more than 6,000 injured. Approximately 2,500 coastal residents remain missing, swept away by the tsunami into the ocean;
- 1 million buildings were destroyed, leaving 460,000 Japanese citizens homeless;
- To address the Fukushima disaster, the Japanese government spent $275 billion from 2011 to 2015. Some regions of the Fukushima province remain uninhabitable to this day;
- The cleanup of radioactive contamination might take 50 years or more.
These facts remind us that humanity can never be fully prepared for earthquakes and their consequences. No matter the efforts of scientists and policymakers, nature will always be stronger.